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Copper N-Heterocyclic Carbene: A Catalyst for Aerobic Oxidation or Reduction Reactions.
Zhan, Le-Wu; Han, Lei; Xing, Ping; Jiang, Biao
Copper N-heterocyclic carbene complexes can be readily used as catalysts for both aerobic oxidation of alcohols to aldehydes and reduction of imines to amines. Our methodology is universal for aromatic substrates and shows versatile tolerance to potential cascade reactions. A one-pot tandem synthetic strategy could afford useful imines and secondary amines via an oxidation-reduction strategy. PMID:26633757
Development of Safe and Scalable Continuous-Flow Methods for Palladium-Catalyzed Aerobic Oxidation Reactions.
Ye, Xuan; Johnson, Martin D; Diao, Tianning; Yates, Matthew H; Stahl, Shannon S
The synthetic scope and utility of Pd-catalyzed aerobic oxidation reactions has advanced significantly over the past decade, and these reactions have potential to address important green-chemistry challenges in the pharmaceutical industry. This potential has been unrealized, however, because safety concerns and process constraints hinder large-scale applications of this chemistry. These limitations are addressed by the development of a continuous-flow tube reactor, which has been demonstrated on several scales in the aerobic oxidation of alcohols. Use of a dilute oxygen gas source (8% O(2) in N(2)) ensures that the oxygen/organic mixture never enters the explosive regime, and efficient gas-liquid mixing in the reactor minimizes decomposition of the homogeneous catalyst into inactive Pd metal. These results provide the basis for large-scale implementation of palladium-catalyzed (and other) aerobic oxidation reactions for pharmaceutical synthesis. PMID:20694169
Aerobic oxidation reactions catalyzed by vanadium complexes of bis(phenolate) ligands.
Zhang, Guoqi; Scott, Brian L; Wu, Ruilian; Silks, L A Pete; Hanson, Susan K
Vanadium(V) complexes of the tridentate bis(phenolate)pyridine ligand H(2)BPP (H(2)BPP = 2,6-(HOC(6)H(2)-2,4-(t)Bu(2))(2)NC(5)H(3)) and the bis(phenolate)amine ligand H(2)BPA (H(2)BPA = N,N-bis(2-hydroxy-4,5-dimethylbenzyl)propylamine) have been synthesized and characterized. The ability of the complexes to mediate the oxidative C-C bond cleavage of pinacol was tested. Reaction of the complex (BPP)V(V)(O)(O(i)Pr) (4) with pinacol afforded the monomeric vanadium(IV) product (BPP)V(IV)(O)(HO(i)Pr) (6) and acetone. Vanadium(IV) complex 6 was oxidized rapidly by air at room temperature in the presence of NEt(3), yielding the vanadium(V) cis-dioxo complex [(BPP)V(V)(O)(2)]HNEt(3). Complex (BPA)V(V)(O)(O(i)Pr) (5) reacted with pinacol at room temperature, to afford acetone and the vanadium(IV) dimer [(BPA)V(IV)(O)(HO(i)Pr)](2). Complexes 4 and 5 were evaluated as catalysts for the aerobic oxidation of 4-methoxybenzyl alcohol and arylglycerol β-aryl ether lignin model compounds. Although both 4 and 5 catalyzed the aerobic oxidation of 4-methoxybenzyl alcohol, complex 4 was found to be a more active and robust catalyst for oxidation of the lignin model compounds. The catalytic activities and selectivities of the bis(phenolate) complexes are compared to previously reported catalysts. PMID:22708725
Catalytic Fehling's Reaction: An Efficient Aerobic Oxidation of Aldehyde Catalyzed by Copper in Water.
Liu, Mingxin; Li, Chao-Jun
The first example of homogeneous copper-catalyzed aerobic oxidation of aldehydes is reported. This method utilizes atmospheric oxygen as the sole oxidant, proceeds under extremely mild aqueous conditions, and covers a wide range of various functionalized aldehydes. Chromatography is generally not necessary for product purification. PMID:27505714
Continuous Flow Aerobic Alcohol Oxidation Reactions Using a Heterogeneous Ru(OH)x/Al2O3 Catalyst
Ru(OH)x/Al2O3 is among the more versatile catalysts for aerobic alcohol oxidation and dehydrogenation of nitrogen heterocycles. Here, we describe the translation of batch reactions to a continuous-flow method that enables high steady-state conversion and single-pass yields in the oxidation of benzylic alcohols and dehydrogenation of indoline. A dilute source of O2 (8% in N2) was used to ensure that the reaction mixture, which employs toluene as the solvent, is nonflammable throughout the process. A packed bed reactor was operated isothermally in an up-flow orientation, allowing good liquid–solid contact. Deactivation of the catalyst during the reaction was modeled empirically, and this model was used to achieve high conversion and yield during extended operation in the aerobic oxidation of 2-thiophene methanol (99+% continuous yield over 72 h). PMID:25620869
Mechanistic studies on a Cu-catalyzed aerobic oxidative coupling reaction with N-phenyl tetrahydroisoquinoline: structure of intermediates and the role of methanol as a solvent.
Boess, Esther; Sureshkumar, Devarajulu; Sud, Abhishek; Wirtz, Cornelia; Farès, Christophe; Klussmann, Martin
The mechanism of an aerobic copper-catalyzed oxidative coupling reaction with N-phenyl tetrahydroisoquinoline was investigated. The oxidized species formed from the reaction of the amine with the copper catalyst were analyzed by NMR-spectroscopy. An iminium dichlorocuprate was found to be the reactive intermediate and could be structurally characterized by X-ray crystallography. The effect of methanol to effectively stabilize the iminium ion was investigated and shown to be beneficial in an oxidative allylation reaction. PMID:21561084
Mechanistic study of copper-catalyzed aerobic oxidative coupling of arylboronic esters and methanol: insights into an organometallic oxidase reaction.
King, Amanda E; Brunold, Thomas C; Stahl, Shannon S
Copper-catalyzed aerobic oxidative coupling of arylboronic acid derivatives and heteroatom nucleophiles is a highly useful method for the formation of aryl-heteroatom bonds. Mechanistic studies reveal that this reaction proceeds via an "oxidase"-style mechanism. Kinetic and spectroscopic studies establish that transmetalation of the aryl group from boron to Cu(II) is the turnover-limiting step and reoxidation of the reduced catalyst by O(2) is rapid. Further mechanistic analysis implicates the involvement of an aryl-copper(III) intermediate that undergoes facile C-O bond formation. PMID:19309072
The synthesis of a bifunctional copper metal organic framework and its application in the aerobic oxidation/Knoevenagel condensation sequential reaction.
Miao, Zongcheng; Luan, Yi; Qi, Chao; Ramella, Daniele
A novel one-pot aerobic oxidation/Knoevenagel condensation reaction system was developed employing a Cu(ii)/amine bifunctional, basic metal-organic framework (MOF) as the catalyst. The sequential aerobic alcohol oxidation/Knoevenagel condensation reaction was efficiently promoted by the Cu3TATAT MOF catalyst in the absence of basic additives. The benzylidenemalononitrile product was produced in high yield and selectivity from an inexpensive benzyl alcohol starting material under an oxygen atmosphere. The role of the basic functionality was studied to demonstrate its role in the aerobic oxidation and Knoevenagel condensation reactions. The reaction progress was monitored in order to identify the reaction intermediate and follow the accumulation of the desired product. Lastly, results showed that the yield was not significantly compromised by the reuse of a batch of catalyst, even after more than five cycles. PMID:27523776
Reaction progress kinetic analysis of a copper-catalyzed aerobic oxidative coupling reaction with N-phenyl tetrahydroisoquinoline.
Scott, Martin; Sud, Abhishek; Boess, Esther; Klussmann, Martin
The results from a kinetic investigation of a Cu-catalyzed oxidative coupling reaction between N-phenyl tetrahydroisoquinoline and a silyl enol ether using elemental oxygen as oxidant are presented. By using reaction progress kinetic analysis as an evaluation method for the obtained data, we discovered information regarding the reaction order of the substrates and catalysts. Based on this information and some additional experiments, a refined model for the initial oxidative activation of the amine substrate and the activation of the nucleophile by the catalyst was developed. The mechanistic information also helped to understand why silyl nucleophiles have previously failed in a related Cu-catalyzed reaction using tert-butyl hydroperoxide as oxidant and how to overcome this limitation. PMID:25203932
Metallic Sn spheres and SnO2@C core-shells by anaerobic and aerobic catalytic ethanol and CO oxidation reactions over SnO2 nanoparticles
Kim, Won Joo; Lee, Sung Woo; Sohn, Youngku
SnO2 has been studied intensely for applications to sensors, Li-ion batteries and solar cells. Despite this, comparatively little attention has been paid to the changes in morphology and crystal phase that occur on the metal oxide surface during chemical reactions. This paper reports anaerobic and aerobic ethanol and CO oxidation reactions over SnO2 nanoparticles (NPs), as well as the subsequent changes in the nature of the NPs. Uniform SnO2@C core-shells (10 nm) were formed by an aerobic ethanol oxidation reaction over SnO2 NPs. On the other hand, metallic Sn spheres were produced by an anaerobic ethanol oxidation reaction at 450 °C, which is significantly lower than that (1200 °C) used in industrial Sn production. Anaerobic and aerobic CO oxidation reactions were also examined. The novelty of the methods for the production of metallic Sn and SnO2@C core-shells including other anaerobic and aerobic reactions will contribute significantly to Sn and SnO2-based applications. PMID:26300041
Methane oxidation in a crude oil contaminated aquifer: Delineation of aerobic reactions at the plume fringes
Amos, R.T.; Bekins, B.A.; Delin, G.N.; Cozzarelli, I.M.; Blowes, D.W.; Kirshtein, J.D.
High resolution direct-push profiling over short vertical distances was used to investigate CH4 attenuation in a petroleum contaminated aquifer near Bemidji, Minnesota. The contaminant plume was delineated using dissolved gases, redox sensitive components, major ions, carbon isotope ratios in CH4 and CO2, and the presence of methanotrophic bacteria. Sharp redox gradients were observed near the water table. Shifts in ??13CCH4 from an average of - 57.6??? (?? 1.7???) in the methanogenic zone to - 39.6??? (?? 8.7???) at 105 m downgradient, strongly suggest CH4 attenuation through microbially mediated degradation. In the downgradient zone the aerobic/anaerobic transition is up to 0.5 m below the water table suggesting that transport of O2 across the water table is leading to aerobic degradation of CH4 at this interface. Dissolved N2 concentrations that exceeded those expected for water in equilibrium with the atmosphere indicated bubble entrapment followed by preferential stripping of O2 through aerobic degradation of CH4 or other hydrocarbons. Multivariate and cluster analysis were used to distinguish between areas of significant bubble entrapment and areas where other processes such as the infiltration of O 2 rich recharge water were important O2 transport mechanisms. ?? 2011 Elsevier B.V. All rights reserved.
Cu(II)-catalyzed esterification reaction via aerobic oxidative cleavage of C(CO)-C(alkyl) bonds.
Ma, Ran; He, Liang-Nian; Liu, An-Hua; Song, Qing-Wen
A novel Cu(II)-catalyzed aerobic oxidative esterification of simple ketones for the synthesis of esters has been developed with wide functional group tolerance. This process is assumed to go through a tandem sequence consisting of α-oxygenation/esterification/nucleophilic addition/C-C bond cleavage and carbon dioxide is released as the only byproduct. PMID:26698150
Controlling the catalytic aerobic oxidation of phenols.
Esguerra, Kenneth Virgel N; Fall, Yacoub; Petitjean, Laurène; Lumb, Jean-Philip
The oxidation of phenols is the subject of extensive investigation, but there are few catalytic aerobic examples that are chemo- and regioselective. Here we describe conditions for the ortho-oxygenation or oxidative coupling of phenols under copper (Cu)-catalyzed aerobic conditions that give rise to ortho-quinones, biphenols or benzoxepines. We demonstrate that each product class can be accessed selectively by the appropriate choice of Cu(I) salt, amine ligand, desiccant and reaction temperature. In addition, we evaluate the effects of substituents on the phenol and demonstrate their influence on selectivity between ortho-oxygenation and oxidative coupling pathways. These results create an important precedent of catalyst control in the catalytic aerobic oxidation of phenols and set the stage for future development of catalytic systems and mechanistic investigations. PMID:24784319
Copper-catalyzed aerobic oxidation of hydroxamic acids leads to a mild and versatile acylnitroso ene reaction.
Frazier, Charles P; Engelking, Jarred R; Read de Alaniz, Javier
A mild formation of transient acylnitroso intermediates using a copper chloride catalyst and 1 atm of air as the terminal oxidant is described. The mild reaction conditions enable the inter- and intramolecular acylnitroso ene reaction with a wide range of functionalized alkene partners, as well as the first asymmetric variant. Notably, this transformation provides a practical and operationally simple method for effecting allylic amidation using an environmentally benign oxidant and a readily abundant transition metal. PMID:21678942
Aerobic Alcohol Oxidation Using a Copper(I)/TEMPO Catalyst System: A Green, Catalytic Oxidation Reaction for the Undergraduate Organic Chemistry Laboratory
ERIC Educational Resources Information Center
Hill, Nicholas J.; Hoover, Jessica M.; Stahl, Shannon S.
Modern undergraduate organic chemistry textbooks provide detailed discussion of stoichiometric Cr- and Mn-based reagents for the oxidation of alcohols, yet the use of such oxidants in instructional and research laboratories, as well as industrial chemistry, is increasingly avoided. This work describes a laboratory exercise that uses ambient air as…
Surface Structure of Aerobically Oxidized Diamond Nanocrystals
We investigate the aerobic oxidation of high-pressure, high-temperature nanodiamonds (5–50 nm dimensions) using a combination of carbon and oxygen K-edge X-ray absorption, wavelength-dependent X-ray photoelectron, and vibrational spectroscopies. Oxidation at 575 °C for 2 h eliminates graphitic carbon contamination (>98%) and produces nanocrystals with hydroxyl functionalized surfaces as well as a minor component (<5%) of carboxylic anhydrides. The low graphitic carbon content and the high crystallinity of HPHT are evident from Raman spectra acquired using visible wavelength excitation (λexcit = 633 nm) as well as carbon K-edge X-ray absorption spectra where the signature of a core–hole exciton is observed. Both spectroscopic features are similar to those of chemical vapor deposited (CVD) diamond but differ significantly from the spectra of detonation nanodiamond. The importance of these findings to the functionalization of nanodiamond surfaces for biological labeling applications is discussed. PMID:25436035
The development of copper-catalyzed aerobic oxidative coupling of H-tetrazoles with boronic acids and an insight into the reaction mechanism.
Liu, Chao-You; Li, Yu; Ding, Jin-Ying; Dong, De-Wen; Han, Fu-She
The development of a highly efficient and practical protocol for the direct C-N coupling of H-tetrazole and boronic acid was presented. A careful and patient optimization of a variety of reaction parameters revealed that this conventionally challenge reaction could indeed proceed efficiently in a very simple system, that is, just by stirring the tetrazoles and boronic acids under oxygen in the presence of different Cu(I) or Cu(II) salts with only 5 mol % loading in DMSO at 100 °C. Most significantly, the reaction could proceed very smoothly in a regiospecific manner to afford the 2,5-disubstituted tetrazoles in high to excellent yields. A mechanistic study revealed that both tetrazole and DMSO are crucial for the generation of catalytically active copper species in the reaction process in addition to their role as reactant and solvent, respectively. It is demonstrated that in the reaction cycle, the Cu(I) catalyst could be oxidized to Cu(II) by oxygen to form a [CuT2D] complex (T = tetrazole anion; D = DMSO) through an oxidative copper amination reaction. The Cu(II) complex thus formed was confirmed to be the real catalytically active copper species. Namely, the Cu(II) complex disproportionates to aryl Cu(III) and Cu(I) in the presence of boronic acid. Facile elimination of the Cu(III) species delivers the C-N-coupled product. The results presented herein not only provide a reliable and efficient protocol for the synthesis of 2,5-disubstituted tetrazoles, but most importantly, the mechanistic results would have broad implications for the de novo design and development of new methods for Cu-catalyzed coupling reactions. PMID:24449340
Cu/Nitroxyl Catalyzed Aerobic Oxidation of Primary Amines into Nitriles at Room Temperature.
Kim, Jinho; Stahl, Shannon S
An efficient catalytic method has been developed for aerobic oxidation of primary amines to the corresponding nitriles. The reactions proceed at room temperature and employ a catalyst consisting of (4,4'- (t) Bu2bpy)CuI/ABNO (ABNO = 9-azabicyclo[3.3.1]nonan-3-one N-oxyl). The reactions exhibit excellent functional group compatibility and substrate scope, and are effective with benzylic, allylic and aliphatic amines. Preliminary mechanistic studies suggest that aerobic oxidation of the Cu catalyst is the turnover-limiting step of the reaction. PMID:24015373
Mechanism of copper(I)/TEMPO-catalyzed aerobic alcohol oxidation.
Hoover, Jessica M; Ryland, Bradford L; Stahl, Shannon S
Homogeneous Cu/TEMPO catalyst systems (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) have emerged as some of the most versatile and practical catalysts for aerobic alcohol oxidation. Recently, we disclosed a (bpy)Cu(I)/TEMPO/NMI catalyst system (NMI = N-methylimidazole) that exhibits fast rates and high selectivities, even with unactivated aliphatic alcohols. Here, we present a mechanistic investigation of this catalyst system, in which we compare the reactivity of benzylic and aliphatic alcohols. This work includes analysis of catalytic rates by gas-uptake and in situ IR kinetic methods and characterization of the catalyst speciation during the reaction by EPR and UV-visible spectroscopic methods. The data support a two-stage catalytic mechanism consisting of (1) "catalyst oxidation" in which Cu(I) and TEMPO-H are oxidized by O(2) via a binuclear Cu(2)O(2) intermediate and (2) "substrate oxidation" mediated by Cu(II) and the nitroxyl radical of TEMPO via a Cu(II)-alkoxide intermediate. Catalytic rate laws, kinetic isotope effects, and spectroscopic data show that reactions of benzylic and aliphatic alcohols have different turnover-limiting steps. Catalyst oxidation by O(2) is turnover limiting with benzylic alcohols, while numerous steps contribute to the turnover rate in the oxidation of aliphatic alcohols. PMID:23317450
Surface Structure of Aerobically Oxidized Diamond Nanocrystals
Wolcott, Abraham; Schiros, Theanne; Trusheim, Matthew E.; Chen, Edward H.; Nordlund, Dennis; Diaz, Rosa E.; Gaaton, Ophir; Englund, Dirk; Owen, Jonathan S.
Here we investigate the aerobic oxidation of high-pressure, high-temperature nanodiamonds (5–50 nm dimensions) using a combination of carbon and oxygen K-edge X-ray absorption, wavelength-dependent X-ray photoelectron, and vibrational spectroscopies. Oxidation at 575 °C for 2 h eliminates graphitic carbon contamination (>98%) and produces nanocrystals with hydroxyl functionalized surfaces as well as a minor component (<5%) of carboxylic anhydrides. The low graphitic carbon content and the high crystallinity of HPHT are evident from Raman spectra acquired using visible wavelength excitation (λexcit = 633 nm) as well as carbon K-edge X-ray absorption spectra where the signature of a core–hole exciton is observed.more » Both spectroscopic features are similar to those of chemical vapor deposited (CVD) diamond but differ significantly from the spectra of detonation nanodiamond. Lastly, we discuss the importance of these findings to the functionalization of nanodiamond surfaces for biological labeling applications.« less
Surface Structure of Aerobically Oxidized Diamond Nanocrystals
Wolcott, Abraham; Schiros, Theanne; Trusheim, Matthew E.; Chen, Edward H.; Nordlund, Dennis; Diaz, Rosa E.; Gaaton, Ophir; Englund, Dirk; Owen, Jonathan S.
Here we investigate the aerobic oxidation of high-pressure, high-temperature nanodiamonds (5–50 nm dimensions) using a combination of carbon and oxygen K-edge X-ray absorption, wavelength-dependent X-ray photoelectron, and vibrational spectroscopies. Oxidation at 575 °C for 2 h eliminates graphitic carbon contamination (>98%) and produces nanocrystals with hydroxyl functionalized surfaces as well as a minor component (<5%) of carboxylic anhydrides. The low graphitic carbon content and the high crystallinity of HPHT are evident from Raman spectra acquired using visible wavelength excitation (λexcit = 633 nm) as well as carbon K-edge X-ray absorption spectra where the signature of a core–hole exciton is observed. Both spectroscopic features are similar to those of chemical vapor deposited (CVD) diamond but differ significantly from the spectra of detonation nanodiamond. Lastly, we discuss the importance of these findings to the functionalization of nanodiamond surfaces for biological labeling applications.
Copper-catalyzed aerobic oxidative C-H functionalizations: trends and mechanistic insights.
Wendlandt, Alison E; Suess, Alison M; Stahl, Shannon S
The selective oxidation of C-H bonds and the use of O(2) as a stoichiometric oxidant represent two prominent challenges in organic chemistry. Copper(II) is a versatile oxidant, capable of promoting a wide range of oxidative coupling reactions initiated by single-electron transfer (SET) from electron-rich organic molecules. Many of these reactions can be rendered catalytic in Cu by employing molecular oxygen as a stoichiometric oxidant to regenerate the active copper(II) catalyst. Meanwhile, numerous other recently reported Cu-catalyzed C-H oxidation reactions feature substrates that are electron-deficient or appear unlikely to undergo single-electron transfer to copper(II). In some of these cases, evidence has been obtained for the involvement of organocopper(III) intermediates in the reaction mechanism. Organometallic C-H oxidation reactions of this type represent important new opportunities for the field of Cu-catalyzed aerobic oxidations. PMID:22034061
Mechanism of Copper(I)/TEMPO-Catalyzed Aerobic Alcohol Oxidation
Hoover, Jessica M.; Ryland, Bradford L.; Stahl, Shannon S.
Homogeneous Cu/TEMPO catalyst systems (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) have emerged as some of the most versatile and practical catalysts for aerobic alcohol oxidation. Recently, we disclosed a (bpy)CuI/TEMPO/NMI catalyst system (NMI = N-methylimidazole) that exhibits fast rates and high selectivities, even with unactivated aliphatic alcohols. Here, we present a mechanistic investigation of this catalyst system, in which we compare the reactivity of benzylic and aliphatic alcohols. This work includes analysis of catalytic rates by gas-uptake and in situ IR kinetic methods and characterization of the catalyst speciation during the reaction by EPR and UV–visible spectroscopic methods. The data support a two-stage catalytic mechanism consisting of (1) "catalyst oxidation" in which CuI and TEMPO–H are oxidized by O2 via a binuclear Cu2O2 intermediate and (2) "substrate oxidation" mediated by CuII and the nitroxyl radical of TEMPO via a CuII-alkoxide intermediate. Catalytic rate laws, kinetic isotope effects, and spectroscopic data show that reactions of benzylic and aliphatic alcohols have different turnover-limiting steps. Catalyst oxidation by O2 is turnover limiting with benzylic alcohols, while numerous steps contribute to the turnover rate in the oxidation of aliphatic alcohols. PMID:23317450
Bioinspired aerobic oxidation of secondary amines and nitrogen heterocycles with a bifunctional quinone catalyst.
Wendlandt, Alison E; Stahl, Shannon S
Copper amine oxidases are a family of enzymes with quinone cofactors that oxidize primary amines to aldehydes. The native mechanism proceeds via an iminoquinone intermediate that promotes high selectivity for reactions with primary amines, thereby constraining the scope of potential biomimetic synthetic applications. Here we report a novel bioinspired quinone catalyst system consisting of 1,10-phenanthroline-5,6-dione/ZnI2 that bypasses these constraints via an abiological pathway involving a hemiaminal intermediate. Efficient aerobic dehydrogenation of non-native secondary amine substrates, including pharmaceutically relevant nitrogen heterocycles, is demonstrated. The ZnI2 cocatalyst activates the quinone toward amine oxidation and provides a source of iodide, which plays an important redox-mediator role to promote aerobic catalytic turnover. These findings provide a valuable foundation for broader development of aerobic oxidation reactions employing quinone-based catalysts. PMID:24328193
Bioinspired Aerobic Oxidation of Secondary Amines and Nitrogen Heterocycles with a Bifunctional Quinone Catalyst
Wendlandt, Alison E.; Stahl, Shannon S.
Copper amine oxidases are a family of enzymes with quinone cofactors that oxidize primary amines to aldehydes. The native mechanism proceeds via an iminoquinone intermediate that promotes high selectivity for reactions with primary amines, thereby constraining the scope of potential biomimetic synthetic applications. Here, we report a novel bioinspired quinone catalyst system, consisting of 1,10-phenanthroline-5,6-dione/ZnI2, that bypasses these constraints via an abiological pathway involving a hemiaminal intermediate. Efficient aerobic dehydrogenation of non-native secondary amine substrates, including pharmaceutically relevant nitrogen heterocycles, is demonstrated. The ZnI2 cocatalyst activates the quinone toward amine oxidation and provides a source of iodide, which plays an important redox-mediator role to promote aerobic catalytic turnover. These findings provide a valuable foundation for broader development of aerobic oxidation reactions employing quinone-based catalysts. PMID:24328193
Copper-catalyzed aerobic oxidative coupling: From ketone and diamine to pyrazine
Wu, Kun; Huang, Zhiliang; Qi, Xiaotian; Li, Yingzi; Zhang, Guanghui; Liu, Chao; Yi, Hong; Meng, Lingkui; Bunel, Emilio E.; Miller, Jeffrey T.; Pao, Chih-Wen; Lee, Jyh-Fu; Lan, Yu; Lei, Aiwen
Copper-catalyzed aerobic oxidative C–H/N–H coupling between simple ketones and diamines was developed toward the synthesis of a variety of pyrazines. Various substituted ketones were compatible for this transformation. Preliminary mechanistic investigations indicated that radical species were involved. X-ray absorption fine structure experiments elucidated that the Cu(II) species 5 coordinated by two N atoms at a distance of 2.04 Å and two O atoms at a shorter distance of 1.98 Å was a reactive one for this aerobic oxidative coupling reaction. Density functional theory calculations suggested that the intramolecular coupling of cationic radicals was favorable in this transformation. PMID:26601302
Practical Aerobic Oxidations of Alcohols and Amines with Homogeneous Cu/TEMPO and Related Catalyst Systems
Ryland, Bradford L.; Stahl, Shannon S.
Alcohol and amine oxidations are common reactions in laboratory and industrial synthesis of organic molecules. Aerobic oxidation methods have long been sought for these transformations, but few practical methods exist that offer advantages over traditional oxidation methods. Recently developed homogeneous Cu/TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidinyl-N-oxyl) and related catalyst systems appear to fill this void. The reactions exhibit high levels of chemoselectivity and broad functional-group tolerance, and they often operate efficiently at room temperature with ambient air as the oxidant. These advances, together with their historical context and recent applications, are highlighted in this minireview. PMID:25044821
Practical Synthesis of Amides via Copper/ABNO-Catalyzed Aerobic Oxidative Coupling of Alcohols and Amines.
Zultanski, Susan L; Zhao, Jingyi; Stahl, Shannon S
A modular Cu/ABNO catalyst system has been identified that enables efficient aerobic oxidative coupling of alcohols and amines to amides. All four permutations of benzylic/aliphatic alcohols and primary/secondary amines are viable in this reaction, enabling broad access to secondary and tertiary amides. The reactions exhibit excellent functional group compatibility and are complete within 30 min-3 h at rt. All components of the catalyst system are commercially available. PMID:27171973
Highly practical copper(I)/TEMPO catalyst system for chemoselective aerobic oxidation of primary alcohols.
Hoover, Jessica M; Stahl, Shannon S
Aerobic oxidation reactions have been the focus of considerable attention, but their use in mainstream organic chemistry has been constrained by limitations in their synthetic scope and by practical factors, such as the use of pure O(2) as the oxidant or complex catalyst synthesis. Here, we report a new (bpy)Cu(I)/TEMPO catalyst system that enables efficient and selective aerobic oxidation of a broad range of primary alcohols, including allylic, benzylic, and aliphatic derivatives, to the corresponding aldehydes using readily available reagents, at room temperature with ambient air as the oxidant. The catalyst system is compatible with a wide range of functional groups and the high selectivity for 1° alcohols enables selective oxidation of diols that lack protecting groups. PMID:21861488
Aerobic sulfur-oxidizing bacteria: Environmental selection and diversification
NASA Technical Reports Server (NTRS)
Caldwell, D.
Sulfur-oxidizing bacteria oxidize reduced inorganic compounds to sulfuric acid. Lithotrophic sulfur oxidizer use the energy obtained from oxidation for microbial growth. Heterotrophic sulfur oxidizers obtain energy from the oxidation of organic compounds. In sulfur-oxidizing mixotrophs energy are derived either from the oxidation of inorganic or organic compounds. Sulfur-oxidizing bacteria are usually located within the sulfide/oxygen interfaces of springs, sediments, soil microenvironments, and the hypolimnion. Colonization of the interface is necessary since sulfide auto-oxidizes and because both oxygen and sulfide are needed for growth. The environmental stresses associated with the colonization of these interfaces resulted in the evolution of morphologically diverse and unique aerobic sulfur oxidizers.
Mechanism of Copper/Azodicarboxylate-Catalyzed Aerobic Alcohol Oxidation: Evidence for Uncooperative Catalysis.
McCann, Scott D; Stahl, Shannon S
Cooperative catalysis between Cu(II) and redox-active organic cocatalysts is a key feature of important chemical and enzymatic aerobic oxidation reactions, such as alcohol oxidation mediated by Cu/TEMPO and galactose oxidase. Nearly 20 years ago, Markó and co-workers reported that azodicarboxylates, such as di-tert-butyl azodicarboxylate (DBAD), are effective redox-active cocatalysts in Cu-catalyzed aerobic alcohol oxidation reactions [Markó, I. E., et al. Science 1996, 274, 2044], but the nature of the cooperativity between Cu and azodicarboxylates is not well understood. Here, we report a mechanistic study of Cu/DBAD-catalyzed aerobic alcohol oxidation. In situ infrared spectroscopic studies reveal a burst of product formation prior to steady-state catalysis, and gas-uptake measurements show that no O2 is consumed during the burst. Kinetic studies reveal that the anaerobic burst and steady-state turnover have different rate laws. The steady-state rate does not depend on [O2] or [DBAD]. These results, together with other EPR and in situ IR spectroscopic and kinetic isotope effect studies, reveal that the steady-state mechanism consists of two interdependent catalytic cycles that operate in sequence: a fast Cu(II)/DBAD pathway, in which DBAD serves as the oxidant, and a slow Cu(II)-only pathway, in which Cu(II) is the oxidant. This study provides significant insight into the redox cooperativity, or lack thereof, between Cu and redox-active organic cocatalysts in aerobic oxidation reactions. PMID:26694091
The Aerobic Oxidation of Bromide to Dibromine Catalyzed by Homogeneous Oxidation Catalysts and Initiated by Nitrate in Acetic Acid
Partenheimer, Walt; Fulton, John L.; Sorensen, Christina M.; Pham, Van Thai; Chen, Yongsheng
A small amount of nitrate, ~0.002 molal, initiates the Co/Mn catalyzed aerobic oxidation of bromide compounds (HBr,NaBr,LiBr) to dibromine in acetic acid at room temperature. At temperatures 40oC or less , the reaction is autocatalytic. Co(II) and Mn(II) themselves and mixed with ionic bromide are known homogeneous oxidation catalysts. The reaction was discovered serendipitously when a Co/Br and Co/Mn/Br catalyst solution was prepared for the aerobic oxidation of methyaromatic compounds and the Co acetate contained a small amount of impurity i.e. nitrate. The reaction was characterized by IR, UV-VIS, MALDI and EXAFS spectroscopies and the coordination chemistry is described. The reaction is inhibited by water and its rate changed by pH. The change in these variables, as well as others, are identical to those observed during homogeneous, aerobic oxidation of akylaromatics. A mechanism is proposed. Accidental addition of a small amount of nitrate compound into a Co/Mn/Br/acetic acid mixture in a large, commercial feedtank is potentially dangerous.
Revealing the halide effect on the kinetics of the aerobic oxidation of Cu(I) to Cu(II)
Deng, Yi; Zhang, Guanghui; Qi, Xiaotian; Liu, Chao; Miller, Jeffrey T.; Kropf, A. Jeremy; Bunel, Emilio E.; Lan, Yu; Lei, Aiwen
In situ infrared (IR) and X-ray absorption near-edge structure (XANES) spectroscopic investigations reveal that different halide ligands have distinct effects on the aerobic oxidation of Cu(I) to Cu(II) in the presence of TMEDA (tetramethylethylenediamine). The iodide ligand gives the lowest rate and thus leads to the lowest catalytic reaction rate of aerobic oxidation of hydroquinone to benzoquinone. Further DFT calculations suggest that oxidation of CuI–TMEDA involves a side-on transition state, while oxidation of CuCl–TMEDA involves an end-on transition state which has a lower activation energy.
Aerobic Denitrifying Bacteria That Produce Low Levels of Nitrous Oxide
Takaya, Naoki; Catalan-Sakairi, Maria Antonina B.; Sakaguchi, Yasushi; Kato, Isao; Zhou, Zhemin; Shoun, Hirofumi
Most denitrifiers produce nitrous oxide (N2O) instead of dinitrogen (N2) under aerobic conditions. We isolated and characterized novel aerobic denitrifiers that produce low levels of N2O under aerobic conditions. We monitored the denitrification activities of two of the isolates, strains TR2 and K50, in batch and continuous cultures. Both strains reduced nitrate (NO3−) to N2 at rates of 0.9 and 0.03 μmol min−1 unit of optical density at 540 nm−1 at dissolved oxygen (O2) (DO) concentrations of 39 and 38 μmol liter−1, respectively. At the same DO level, the typical denitrifier Pseudomonas stutzeri and the previously described aerobic denitrifier Paracoccus denitrificans did not produce N2 but evolved more than 10-fold more N2O than strains TR2 and K50 evolved. The isolates denitrified NO3− with concomitant consumption of O2. These results indicated that strains TR2 and K50 are aerobic denitrifiers. These two isolates were taxonomically placed in the β subclass of the class Proteobacteria and were identified as P. stutzeri TR2 and Pseudomonas sp. strain K50. These strains should be useful for future investigations of the mechanisms of denitrifying bacteria that regulate N2O emission, the single-stage process for nitrogen removal, and microbial N2O emission into the ecosystem. PMID:12788710
Heterogeneous Rhodium-Catalyzed Aerobic Oxidative Dehydrogenative Cross-Coupling: Nonsymmetrical Biaryl Amines.
Matsumoto, Kenji; Yoshida, Masahiro; Shindo, Mitsuru
The first heterogeneously catalyzed oxidative dehydrogenative cross-coupling of aryl amines is reported herein. 2-Naphthylamine analogues were reacted with various electron-rich arenes using a heterogeneous Rh/C catalyst under mild aerobic conditions, thus affording nonsymmetrical biaryl amines in excellent yields with high selectivities. This reaction provides a mild, operationally simple, and efficient approach for the synthesis of biaryls which are important to pharmaceutical and materials chemistry. PMID:26996772
Iron/ABNO-Catalyzed Aerobic Oxidation of Alcohols to Aldehydes and Ketones under Ambient Atmosphere.
Wang, Lianyue; Shang, SenSen; Li, Guosong; Ren, Lanhui; Lv, Ying; Gao, Shuang
We report a new Fe(NO3)3·9H2O/9-azabicyclo[3.3.1]nonan-N-oxyl catalyst system that enables efficient aerobic oxidation of a broad range of primary and secondary alcohols to the corresponding aldehydes and ketones at room temperature with ambient air as the oxidant. The catalyst system exhibits excellent activity and selectivity for primary aliphatic alcohol oxidation. This procedure can also be scaled up. Kinetic analysis demonstrates that C-H bond cleavage is the rate-determining step and that cationic species are involved in the reaction. PMID:26859251
Copper/TEMPO-Catalyzed Aerobic Alcohol Oxidation: Mechanistic Assessment of Different Catalyst Systems.
Hoover, Jessica M; Ryland, Bradford L; Stahl, Shannon S
Combinations of homogeneous Cu salts and TEMPO have emerged as practical and efficient catalysts for the aerobic oxidation of alcohols. Several closely related catalyst systems have been reported, which differ in the identity of the solvent, the presence of 2,2'-bipyridine as a ligand, the identity of basic additives, and the oxidation state of the Cu source. These changes have a significant influence on the reaction rates, yields, and substrate scope. In this report, we probe the mechanistic basis for differences among four different Cu/TEMPO catalyst systems and elucidate the features that contribute to efficient oxidation of aliphatic alcohols. PMID:24558634
Copper/TEMPO-Catalyzed Aerobic Alcohol Oxidation: Mechanistic Assessment of Different Catalyst Systems
Hoover, Jessica M.; Ryland, Bradford L.; Stahl, Shannon S.
Combinations of homogeneous Cu salts and TEMPO have emerged as practical and efficient catalysts for the aerobic oxidation of alcohols. Several closely related catalyst systems have been reported, which differ in the identity of the solvent, the presence of 2,2′-bipyridine as a ligand, the identity of basic additives, and the oxidation state of the Cu source. These changes have a significant influence on the reaction rates, yields, and substrate scope. In this report, we probe the mechanistic basis for differences among four different Cu/TEMPO catalyst systems and elucidate the features that contribute to efficient oxidation of aliphatic alcohols. PMID:24558634
Respirometric characterization of aerobic sulfide, thiosulfate and elemental sulfur oxidation by S-oxidizing biomass.
Mora, Mabel; López, Luis R; Lafuente, Javier; Pérez, Julio; Kleerebezem, Robbert; van Loosdrecht, Mark C M; Gamisans, Xavier; Gabriel, David
Respirometry was used to reveal the mechanisms involved in aerobic biological sulfide oxidation and to characterize the kinetics and stoichiometry of a microbial culture obtained from a desulfurizing biotrickling filter. Physical-chemical processes such as stripping and chemical oxidation of hydrogen sulfide were characterized since they contributed significantly to the conversions observed in respirometric tests. Mass transfer coefficient for hydrogen sulfide and the kinetic parameters for chemical oxidation of sulfide with oxygen were estimated. The stoichiometry of the process was determined and the different steps in the sulfide oxidation process were identified. The conversion scheme proposed includes intermediate production of elemental sulfur and thiosulfate and the subsequent oxidation of both compounds to sulfate. A kinetic model describing each of the reactions observed during sulfide oxidation was calibrated and validated. The product selectivity was found to be independent of the dissolved oxygen to hydrogen sulfide concentration ratio in the medium at sulfide concentrations ranging from 3 to 30 mg S L(-1). Sulfide was preferentially consumed (SOURmax = 49.2 mg DO g(-1) VSS min(-1)) and oxidized to elemental sulfur at dissolved oxygen concentrations above 0.8 mg DO L(-1). Substrate inhibition of sulfide oxidation was observed (K(i,S(2-))= 42.4 mg S L(-1)). Intracellular sulfur accumulation also affected negatively the sulfide oxidation rate. The maximum fraction of elemental sulfur accumulated inside cells was estimated (25.6% w/w) and a shrinking particle equation was included in the kinetic model to describe elemental sulfur oxidation. The microbial diversity obtained through pyrosequencing analysis revealed that Thiothrix sp. was the main species present in the culture (>95%). PMID:26704759
Aerobic Methane Oxidation in Alaskan Lakes Along a Latitudinal Transect
NASA Astrophysics Data System (ADS)
Martinez-Cruz, K. C.; Sepulveda-Jauregui, A.; Walter Anthony, K. M.; Anthony, P.; Thalasso, F.
Karla Martinez-Cruz* **, Armando Sepulveda-Jauregui*, Katey M. Walter Anthony*, Peter Anthony*, and Frederic Thalasso**. * Water and Environmental Research Center, Institute of Northern Engineering, University of Alaska Fairbanks, Fairbanks, Alaska. ** Biotechnology and Bioengineering Department, Cinvestav, Mexico city, D. F., Mexico. Methane (CH4) is the third most important greenhouse gas in the atmosphere, after carbon dioxide and water vapor. Boreal lakes play an important role in the current global warming by contributing as much as 6% of global atmospheric CH4 sources annually. On the other hand, aerobic methane oxidation (methanotrophy) in lake water is a fundamental process in global methane cycling that reduces the amount of CH4 emissions to the atmosphere. Several environmental factors affect aerobic methane oxidation in the water column both directly and indirectly, including concentration of CH4 and O2, temperature and carbon budgets of lakes. We analyzed the potential of aerobic methane oxidation (PMO) rates in incubations of water collected from 30 Alaskan lakes along a north-south transect during winter and summer 2011. Our findings showed an effect of CH4 and O2 concentrations, temperature and yedoma thawing permafrost on PMO activity in the lake water. The highest PMO rates were observed in summer by lakes situated on thawing yedoma permafrost, most of them located in the interior of Alaska. We also estimated that 60-80% of all CH4 produced in Alaskan lakes could be taken up by methanotrophs in the lake water column, showing the significant influence of aerobic methane oxidation of boreal lakes to the global CH4 budget.
Aerobic Oxidation of an Osmium(III) N-Hydroxyguanidine Complex To Give Nitric Oxide.
Xiang, Jing; Wang, Qian; Yiu, Shek-Man; Man, Wai-Lun; Kwong, Hoi-Ki; Lau, Tai-Chu
The aerobic oxidation of the N-hydroxyguanidinum moiety of N-hydroxyarginine to NO is a key step in the biosynthesis of NO by the enzyme nitric oxide synthase (NOS). So far, there is no chemical system that can efficiently carry out similar aerobic oxidation to give NO. We report here the synthesis and X-ray crystal structure of an osmium(III) N-hydroxyguanidine complex, mer-[Os(III){NH═C(NH2)(NHOH)}(L)(CN)3](-) (OsGOH, HL = 2-(2-hydroxyphenyl)benzoxazole), which to the best of our knowledge is the first example of a transition metal N-hydroxyguanidine complex. More significantly, this complex readily undergoes aerobic oxidation at ambient conditions to generate NO. The oxidation is pH-dependent; at pH 6.8, fac-[Os(NO)(L)(CN)3](-) is formed in which the NO produced is bound to the osmium center. On the other hand, at pH 12, aerobic oxidation of OsGOH results in the formation of the ureato complex [Os(III)(NHCONH2)(L)(CN)3](2-) and free NO. Mechanisms for this aerobic oxidation at different pH values are proposed. PMID:27135258
Enantioselective oxidative boron Heck reactions.
Lee, A-L
This review highlights the use of the oxidative boron Heck reaction in enantioselective Heck-type couplings. The enantioselective oxidative boron Heck reaction overcomes several limitations of the traditional Pd(0)-catalysed Heck coupling and has subsequently allowed for intermolecular couplings of challenging systems such as cyclic enones, acyclic alkenes, and even site selectively on remote alkenes. PMID:26529247
Oxovanadium complex-catalyzed aerobic oxidation of propargylic alcohols.
Maeda, Yasunari; Kakiuchi, Nobuyuki; Matsumura, Satoshi; Nishimura, Takahiro; Kawamura, Takashi; Uemura, Sakae
A catalytic system consisting of vanadium oxyacetylacetonate [VO(acac)(2)] and 3 A molecular sieves (MS3A) in acetonitrile works effectively for the aerobic oxidation of propargylic alcohols [R(1)CH(OH)Ctbd1;CR(2)] to the corresponding carbonyl compounds under an atmospheric pressure of molecular oxygen. Although the reactivity of alpha-acetylenic alkanols (R(1) = alkyl) is lower compared to that of the alcohols of R(1) = aryl, alkenyl, and alkynyl, the use of VO(hfac)(2) as a catalyst and the addition of hexafluoroacetylacetone improve the product yield in these cases. A catalytic cycle involving a vanadium(V) alcoholate species and beta-hydrogen elimination from it has been proposed for this oxidation. PMID:12227802
Ruthenium(salen)-catalyzed aerobic oxidative desymmetrization of meso-diols and its kinetics.
Shimizu, Hideki; Onitsuka, Satoaki; Egami, Hiromichi; Katsuki, Tsutomu
Chiral (nitrosyl)ruthenium(salen) complexes were found to be efficient catalysts for aerobic oxidative desymmetrization of meso-diols under photoirradiation to give optically active lactols. The scope of the applicability of this reaction ranges widely from acyclic diols to mono-cyclic diols, although fine ligand-tuning of the ruthenium(salen) complexes was required to attain high enantioselectivity (up to 93% ee). In particular, the nature of the apical ligand was found to affect not only enantioselectivity but also kinetics of the desymmetrization reaction. Spectroscopic analysis of the oxidation disclosed that irradiation of visible light is indispensable not only for dissociation of the nitrosyl ligand but also for single electron transfer from the alcohol-bound ruthenium ion to dioxygen. PMID:15826178
Toxic effects of butyl elastomers on aerobic methane oxidation
NASA Astrophysics Data System (ADS)
Niemann, Helge; Steinle, Lea I.; Blees, Jan H.; Krause, Stefan; Bussmann, Ingeborg; Lehmann, Moritz F.; Treude, Tina
Large quantities of the potent greenhouse gas methane are liberated into the water column of marine and lacustrine environments where it may be consumed by aerobic methane oxidising bacteria before reaching the atmosphere.The reliable quantification of aerobic methane oxidation (MOx) rates is consequently of paramount importance for estimating methane budgets and to understand the controls on water column methane cycling. A widely used set of methods for measuring MOx rates is based on the incubation of water samples during which the consumption of methane is monitored, for instance with radio-tracer assays. Typically, incubation vessels are sealed with butyl rubber stoppers because these elastomers are essentially impermeable for gases at the relevant time scales. We tested the effect of different stopper materials (unmodified- and halogenated butyl rubber) on MOx activity in environmental samples and in cultures of methane oxidising bacteria. MOx rates in samples sealed with unmodified butyl rubber were > 75% lower compared to parallel incubations with halogenated butyl rubber seals, suggesting inhibiting/toxic effects associated with the use of unmodified butyl elastomers. To further explore the cause of these effects, we analysed aqueous extracts of the different stoppers. Halogenated butyl rubber stoppers appeared to bleed off comparably little amounts of organics. In stark contrast, extracts of unmodified butyl rubber were contaminated with various organic compounds including potential bactericides such as benzyltoluenes, phenylalkanes and benzuothiazoles. We also found tetramethylthiourea, a scavenger of active oxygen species, which may inhibit the MOx pathway.
Microsensor Measurements of Sulfate Reduction and Sulfide Oxidation in Compact Microbial Communities of Aerobic Biofilms
Kühl, Michael; Jørgensen, Bo Barker
The microzonation of O2 respiration, H2S oxidation, and SO42- reduction in aerobic trickling-filter biofilms was studied by measuring concentration profiles at high spatial resolution (25 to 100 μm) with microsensors for O2, S2-, and pH. Specific reaction rates were calculated from measured concentration profiles by using a simple one-dimensional diffusion reaction model. The importance of electron acceptor and electron donor availability for the microzonation of respiratory processes and their reaction rates was investigated. Oxygen respiration was found in the upper 0.2 to 0.4 mm of the biofilm, whereas sulfate reduction occurred in deeper, anoxic parts of the biofilm. Sulfate reduction accounted for up to 50% of the total mineralization of organic carbon in the biofilms. All H2S produced from sulfate reduction was reoxidized by O2 in a narrow reaction zone, and no H2S escaped to the overlying water. Turnover times of H2S and O2 in the reaction zone were only a few seconds owing to rapid bacterial H2S oxidation. Anaerobic H2S oxidation with NO3- could be induced by addition of nitrate to the medium. Total sulfate reduction rates increased when the availability of SO42- or organic substrate increased as a result of deepening of the sulfate reduction zone or an increase in the sulfate reduction intensity, respectively. PMID:16348687
Aqueous Oxidative Heck Reaction as a Protein-Labeling Strategy
Ourailidou, Maria Eleni; van der Meer, Jan-Ytzen; Baas, Bert-Jan; Jeronimus-Stratingh, Margot; Gottumukkala, Aditya L; Poelarends, Gerrit J; Minnaard, Adriaan J; Dekker, Frank J
An increasing number of chemical reactions are being employed for bio-orthogonal ligation of detection labels to protein-bound functional groups. Several of these strategies, however, are limited in their application to pure proteins and are ineffective in complex biological samples such as cell lysates. Here we present the palladium-catalyzed oxidative Heck reaction as a new and robust bio-orthogonal strategy for linking functionalized arylboronic acids to protein-bound alkenes in high yields and with excellent chemoselectivity even in the presence of complex protein mixtures from living cells. Advantageously, this reaction proceeds under aerobic conditions, whereas most other metal-catalyzed reactions require inert atmosphere. PMID:24376051
Silver(I) as a widely applicable, homogeneous catalyst for aerobic oxidation of aldehydes toward carboxylic acids in water—"silver mirror": From stoichiometric to catalytic
Liu, Mingxin; Wang, Haining; Zeng, Huiying; Li, Chao-Jun
The first example of a homogeneous silver(I)-catalyzed aerobic oxidation of aldehydes in water is reported. More than 50 examples of different aliphatic and aromatic aldehydes, including natural products, were tested, and all of them successfully underwent aerobic oxidation to give the corresponding carboxylic acids in extremely high yields. The reaction conditions are very mild and greener, requiring only a very low silver(I) catalyst loading, using atmospheric oxygen as the oxidant and water as the solvent, and allowing gram-scale oxidation with only 2 mg of our catalyst. Chromatography is completely unnecessary for purification in most cases. PMID:26601150
Identification of key nitrous oxide production pathways in aerobic partial nitrifying granules.
Ishii, Satoshi; Song, Yanjun; Rathnayake, Lashitha; Tumendelger, Azzaya; Satoh, Hisashi; Toyoda, Sakae; Yoshida, Naohiro; Okabe, Satoshi
The identification of the key nitrous oxide (N2O) production pathways is important to establish a strategy to mitigate N2O emission. In this study, we combined real-time gas-monitoring analysis, (15)N stable isotope analysis, denitrification functional gene transcriptome analysis and microscale N2O concentration measurements to identify the main N2O producers in a partial nitrification (PN) aerobic granule reactor, which was fed with ammonium and acetate. Our results suggest that heterotrophic denitrification was the main contributor to N2O production in our PN aerobic granule reactor. The heterotrophic denitrifiers were probably related to Rhodocyclales bacteria, although different types of bacteria were active in the initial and latter stages of the PN reaction cycles, most likely in response to the presence of acetate. Hydroxylamine oxidation and nitrifier denitrification occurred, but their contribution to N2O emission was relatively small (20-30%) compared with heterotrophic denitrification. Our approach can be useful to quantitatively examine the relative contributions of the three pathways (hydroxylamine oxidation, nitrifier denitrification and heterotrophic denitrification) to N2O emission in mixed microbial populations. PMID:24650173
Osmium(ii) complexes for light-driven aerobic oxidation of amines to imines.
Li, Yong-Hui; Liu, Xiao-Le; Yu, Zhen-Tao; Li, Zhao-Sheng; Yan, Shi-Cheng; Chen, Guang-Hui; Zou, Zhi-Gang
Herein, we describe the synthesis and characterization of three Os(ii) complexes (i.e., [Os(fptz)2(PPhMe2)2] (1, fptzH = 3-trifluoromethyl-5-pyridyl-1,2,4-triazole), [Os(fptz)2(CO)(L1)] (2, L1 = PPh3; 3, L1 = pyridine)) that have been successfully utilized as good photocatalysts to promote aerobic oxidative coupling of amines to imines with molecular oxygen in air as a green oxidant. Complex 1 is the most effective catalyst for the oxidative coupling of benzylamine with molecular O2 (air) as the oxidant because of the complex's strong absorption of visible light and long-lived triplet state. The application of a low catalyst loading (0.06 mol%) of complex 1 to the oxidative coupling of a wide range of amines affords the corresponding imines efficiently and selectively in most cases. The reaction mechanism was investigated via relevant control and quenching experiments. The results indicated that the reaction occurs via an active (1)O2-involved pathway. The (1)O2-generating ability of complex 1 as a photosensitizer was evaluated using 9,10-dimethylanthracene (DMA) as a chemical trap for (1)O2. PMID:27431765
TEMPO-catalyzed aerobic oxidation of alcohols to aldehydes and ketones in ionic liquid [bmim][PF6].
Ansari, Imtiaz A; Gree, Rene
[reaction: see text]. A simple and mild TEMPO-CuCl catalyzed aerobic oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones in ionic liquid [bmim][PF6] with no trace of overoxidation to carboxylic acids has been developed. The product can be isolated by a simple extraction with organic solvent, and the ionic liquid can be recycled or reused. PMID:11975615
Copper(I)/ABNO-catalyzed aerobic alcohol oxidation: alleviating steric and electronic constraints of Cu/TEMPO catalyst systems.
Steves, Janelle E; Stahl, Shannon S
Cu/TEMPO catalyst systems promote efficient aerobic oxidation of sterically unhindered primary alcohols and electronically activated substrates, but they show reduced reactivity with aliphatic and secondary alcohols. Here, we report a catalyst system, consisting of ((MeO)bpy)Cu(I)(OTf) and ABNO ((MeO)bpy = 4,4'-dimethoxy-2,2'-bipyridine; ABNO = 9-azabicyclo[3.3.1]nonane N-oxyl), that mediates aerobic oxidation of all classes of alcohols, including primary and secondary allylic, benzylic, and aliphatic alcohols with nearly equal efficiency. The catalyst exhibits broad functional group compatibility, and most reactions are complete within 1 h at room temperature using ambient air as the source of oxidant. PMID:24128057
Environmental control on aerobic methane oxidation in coastal waters
NASA Astrophysics Data System (ADS)
Steinle, Lea; Maltby, Johanna; Engbersen, Nadine; Zopfi, Jakob; Bange, Hermann; Elvert, Marcus; Hinrichs, Kai-Uwe; Kock, Annette; Lehmann, Moritz; Treude, Tina; Niemann, Helge
Large quantities of methane are produced in anoxic sediments of continental margins and may be liberated to the overlying water column, where some of it is consumed by aerobic methane oxidizing bacteria (MOB). Aerobic methane oxidation (MOx) in the water column is consequently the final sink for methane before its release to the atmosphere, where it acts as a potent greenhouse gas. In the context of the ocean's contribution to atmospheric methane, coastal seas are particularly important accounting >75% of global methane emission from marine systems. Coastal oceans are highly dynamic, in particular with regard to the variability of methane and oxygen concentrations as well as temperature and salinity, all of which are potential key environmental factors controlling MOx. To determine important environmental controls on the activity of MOBs in coastal seas, we conducted a two-year time-series study with measurements of physicochemical water column parameters, MOx activity and the composition of the MOB community in a coastal inlet in the Baltic Sea (Boknis Eck Time Series Station, Eckernförde Bay - E-Bay). In addition, we investigated the influence of temperature and oxygen on MOx during controlled laboratory experiments. In E-Bay, hypoxia developed in bottom waters towards the end of the stratification period. Constant methane liberation from sediments resulted in bottom water methane accumulations and supersaturation (with respect to the atmospheric equilibrium) in surface waters. Here, we will discuss the factors impacting MOx the most, which were (i) perturbations of the water column (ii) temperature and (iii) oxygen concentration. (i) Perturbations of the water column caused by storm events or seasonal mixing led to a decrease in MOx, probably caused by replacement of stagnant water with a high standing stock of MOB by 'new' waters with a lower abundance of methanotrophs. b) An increase in temperature generally led to higher MOx rates. c) Even though methane was
KIO3-Catalyzed Aerobic Cross-Coupling Reactions of Enaminones and Thiophenols: Synthesis of Polyfunctionalized Alkenes by Metal-Free C-H Sulfenylation.
Wan, Jie-Ping; Zhong, Shanshan; Xie, Lili; Cao, Xiaoji; Liu, Yunyun; Wei, Li
The synthesis of polyfunctionalized aminothioalkenes has been realized via the direct C-H sulfenylation of enaminones and analogous enamines. These cross-coupling reactions have been achieved by simple KIO3 catalysis under aerobic conditions without employing any transition metal catalyst or additional oxidant. The employment of bio-based green solvent ethyl lactate as the reaction medium constitutes another sustainable feature of the present work. PMID:26811952
Supercritical carbon dioxide, a new medium for aerobic alcohol oxidations catalysed by copper-TEMPO.
Herbert, Matthew; Montilla, Francisco; Galindo, Agustín
The copper catalysed aerobic oxidation of selected alcohol substrates in supercritical carbon dioxide (scCO(2)), employing a range of simple copper(II) catalyst compounds, is here described. The copper acetate complex of polydimethylsiloxane (PDMS) functionalised pyridine (1), compound 2, has previously been synthesised and characterised by us and its solubility in scCO(2) demonstrated. Due to this solubility we anticipated that the selective aerobic oxidation of alcohols to aldehydes could be homogeneously catalysed by this compound in scCO(2) in combination with the co-catalyst 2,2,6,6-tetramethylpiperidin-1-yloxy free radical (TEMPO). Our initial results showed that complete oxidation of 4-nitrobenzyl alcohol was achieved within 4 h of reaction. However, the activities of analogous copper derivatives containing simpler pyridine substituents, [Cu(AcO)(2)(py)](2) and [Cu(AcO)(2)(4VP)](2) (4VP = 4-vinylpyridine), were shown to be similar, in spite of their negligible solubility in scCO(2). When we repeated the reactions in highly non-polar hexane rather than scCO(2) similar observations were made. In both cases, as 2 is soluble and the pyridine analogues are not, a much higher reaction rate was anticipated for 2 as it is the only compound capable of homogeneous catalysis. However, in some cases slightly better activities were observed for [Cu(AcO)(2)(py)](2) rather than for the PDMS functionalised analogue, 2. Thus, despite poor catalyst solubility typically being very inhibitory in this type of catalytic process, in this system solubilisation of the catalyst is not necessary. In continuation the activity of silica supported copper complexes was therefore investigated. Employing such catalysts the 4-nitrobenzyl and benzyl alcohol substrates were completely oxidised to the corresponding aldehydes in scCO(2), this time employing lower catalyst loadings. Other types of alcohol substrate showed more limited conversions however. To conclude, alcohol oxidation in the non
High-Potential Electrocatalytic O2 Reduction with Nitroxyl/NOx Mediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis
Efficient reduction of O2 to water is a central challenge in energy conversion and many aerobic oxidation reactions. Here, we show that the electrochemical oxygen reduction reaction (ORR) can be achieved at high potentials by using soluble organic nitroxyl and nitrogen oxide (NOx) mediators. When used alone, neither organic nitroxyls, such as 2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl (TEMPO), nor NOx species, such as sodium nitrite, are effective ORR mediators. The combination of nitroxyl/NOx species, however, mediates sustained O2 reduction with overpotentials as low as 300 mV in acetonitrile containing trifluoroacetic acid. Mechanistic analysis of the coupled redox reactions supports a process in which the nitrogen oxide catalyst drives aerobic oxidation of a nitroxyl mediator to an oxoammonium species, which then is reduced back to the nitroxyl at the cathode. The electrolysis potential is dictated by the oxoammonium/nitroxyl reduction potential. The overpotentials accessible with this ORR system are significantly lower than widely studied molecular metal-macrocycle ORR catalysts and benefit from the mechanism-based specificity for four-electron reduction of oxygen to water mediated by NOx species, together with kinetically efficient reduction of oxidized NOx species by TEMPO and other organic nitroxyls. PMID:27162977
Reduced graphene oxide supported Au nanoparticles as an efficient catalyst for aerobic oxidation of benzyl alcohol
NASA Astrophysics Data System (ADS)
Yu, Xianqin; Huo, Yujia; Yang, Jing; Chang, Sujie; Ma, Yunsheng; Huang, Weixin
Various Au/C catalysts were prepared by Au nanoparticels supported on different carbonaceous supports including reduced graphene oxide (RGO), activated carbon (AC) and graphite (GC) using sol-immobilization method. Au/RGO shows a much higher activity than Au/AC and Au/GC in the liquid phase aerobic oxidation of benzyl alcohol. The superior catalytic performance of Au/RGO may be related to the presence of surface O-containing functional groups and moderate graphite character of RGO supports.
Self-assembled dicopper(II) diethanolaminate cores for mild aerobic and peroxidative oxidation of alcohols.
Figiel, Paweł J; Kirillov, Alexander M; Guedes da Silva, M Fátima C; Lasri, Jamal; Pombeiro, Armando J L
The new dicopper(ii) complexes [Cu(2)(μ-Hmdea)(2)(NCS)(2)] (1) and [Cu(2)(μ-Hedea)(2)(N(3))(2)]·(H(2)O)(0.25) (2) with the {Cu(2)(μ-O)(2)} diethanolaminate cores have been easily generated by aqueous medium self-assembly reactions of copper(ii) nitrate with N-methyl- or N-ethyldiethanolamine (H(2)mdea or H(2)edea, respectively), in the presence of sodium thiocyanate (for 1) or sodium azide (for 2) as ancillary ligands sources. They have been isolated as air-stable crystalline solids and fully characterized by IR and UV-vis spectroscopies, ESI-MS(+), elemental and single-crystal X-ray diffraction analyses. The latter complex also features a fourfold linkage of neighbouring dimeric units via strong intermolecular O-HO hydrogen bonds, giving rise to the formation of tetracopper aggregates. The catalytic activity of compounds 1 and 2 has been studied for the mild (50-80 °C) and selective oxidations of alcohols, namely for (i) the aerobic aqueous medium oxidation of benzyl alcohols to benzaldehydes, mediated by TEMPO radical, and for (ii) the solvent-free oxidation of secondary alcohols to ketones by t-BuOOH under microwave (MW) irradiation. Complex 2 shows the highest efficiency in both oxidation systems, resulting in up to 99% molar yields (based on the alcohol substrate) of products. In addition, remarkably high values of TON (1020) and TOF (4080 h(-1)) have been achieved in the MW-assisted peroxidative oxidation of 1-phenylethanol to acetophenone (model reaction). Attractive green features of these catalytic systems include the operation in aqueous or solvent-free reaction medium, under mild conditions and with high yields and selectivities, using Cu catalyst precursors that are readily available by self-assembly in water of simple chemicals. PMID:20844801
Mechanistic insight into aerobic alcohol oxidation using NOx-nitroxide catalysis based on catalyst structure-activity relationships.
Shibuya, Masatoshi; Nagasawa, Shota; Osada, Yuji; Iwabuchi, Yoshiharu
The mechanism of an NOx-assisted, nitroxide(nitroxyl radical)-catalyzed aerobic oxidation of alcohols was investigated using a set of sterically and electronically modified nitroxides (i.e., TEMPO, AZADO (1), 5-F-AZADO (2), 5,7-DiF-AZADO (3), 5-MeO-AZADO (4), 5,7-DiMeO-AZADO (5), oxa-AZADO (6), TsN-AZADO (7), and DiAZADO (8)). The motivation for the present study stemmed from our previous observation that the introduction of an F atom at a remote position from the nitroxyl radical moiety on the azaadamantane nucleus effectively enhanced the catalytic activity under typical NOx-mediated aerobic-oxidation conditions. The kinetic profiles of the azaadamantane-N-oxyl-[AZADO (1)-, 5-F-AZADO (2)-, and 5,7-DiF-AZADO (3)]-catalyzed aerobic oxidations were closely investigated, revealing that AZADO (1) showed a high initial reaction rate compared to 5-F-AZADO (2) and 5,7-DiF-AZADO (3); however, AZADO-catalyzed oxidation exhibited a marked slowdown, resulting in ∼90% conversion, whereas 5-F-AZADO-catalyzed oxidation smoothly reached completion without a marked slowdown. The reasons for the marked slowdown and the role of the fluoro group are discussed. Oxa-AZADO (6), TsN-AZADO (7), and DiAZADO (8) were designed and synthesized to confirm their comparable catalytic efficiency to that of 5-F-AZADO (2), providing supporting evidence for the electronic effect on the catalytic efficiency of the heteroatoms under NOx-assisted aerobic-oxidation conditions. PMID:25286356
Unexpected copper-catalyzed aerobic oxidative cleavage of C(sp3)-C(sp3) bond of glycol ethers.
Liu, Zhong-Quan; Zhao, Lixing; Shang, Xiaojie; Cui, Zili
An unexpected Cu-catalyzed oxidative cleavage of the C(sp(3))-C(sp(3)) bond in glycol ethers by using air or molecular oxygen as the terminal stoichiometric oxidant is demonstrated. As a result, the corresponding α-acyloxy ethers and formates of 1,2-ethanediol are formed by direct coupling of carboxylic acids and aldehydes with glycol ethers under the reaction conditions. This method represents the first example of Cu-catalyzed aerobic cleavage of saturated C-C bond in ethers. PMID:22668348
Environmental Controls on Aerobic Methane Oxidation in Coastal Waters
NASA Astrophysics Data System (ADS)
Steinle, L.; Maltby, J.; Engbersen, N.; Zopfi, J.; Bange, H. W.; Elvert, M.; Hinrichs, K. U.; Kock, A.; Lehmann, M. F.; Treude, T.; Niemann, H.
Large quantities of the greenhouse gas CH4 are produced in anoxic sediments of continental margins and may be liberated to the overlying water column, and later into the atmosphere. Indeed, coastal seas account for more than 75% of global oceanic CH4 emissions. Yet, aerobic CH4 oxidizing bacteria (MOB) consume an important part of CH4 in the water column, thus mitigating CH4 release to the atmosphere. Coastal oceans are highly dynamic systems, in particular with regard to the variability of temperature, salinity and oxygen concentrations, all of which are potential key environmental factors controlling MOx. To determine the most important controlling factors, we conducted a two-year time-series study with measurements of CH4, MOx, the composition of the MOB community, and physicochemical water column parameters in a coastal inlet in the Baltic Sea (Eckernförde(E-) Bay, Boknis Eck Time Series Station). In addition, we investigated the influence of temperature and oxygen on MOx during controlled laboratory experiments. In E-Bay, seasonal stratification leads to hypoxia in bottom waters towards the end of the stratification period. Methane is produced year-round in the sediments, resulting in accumulation of methane in bottom waters, and supersaturation (with respect to the atmospheric equilibrium) in surface waters. Here, we will discuss the factors impacting MOx the most, which were a) perturbations of the water column caused by storm events, currents or seasonal mixing, b) temperature and c) oxygen concentration. a) Perturbations of the water column led to a sharp decrease in MOx within hours, probably caused by replacement of 'old' water with a high standing stock of MOB by 'new' waters with a lower abundance of MOB. b) An increase in temperature generally led to higher MOx rates. c) Even though CH4 was abundant at all depths, MOx was highest in bottom waters (1-5 nM/d), which usually contain the lowest O2 concentrations. Lab-based experiments with adjusted O2
Formation of Amides from Imines via Cyanide-Mediated Metal-Free Aerobic Oxidation.
Seo, Hong-Ahn; Cho, Yeon-Ho; Lee, Ye-Sol; Cheon, Cheol-Hong
A new protocol for the direct formation of amides from imines derived from aromatic aldehydes via metal-free aerobic oxidation in the presence of cyanide is described. This protocol was applicable to various aldimines, and the desired amides were obtained in moderate to good yields. Mechanistic studies suggested that this aerobic oxidative amidation might proceed via the addition of cyanide to imines followed by proton transfer from carbon to nitrogen in the original imines, leading to carbanions of α-amino nitriles, which undergo subsequent oxidation with molecular oxygen in air to provide the desired amide compounds. PMID:26580330
Acute aerobic exercise and information processing: energizing motor processes during a choice reaction time task.
Audiffren, Michel; Tomporowski, Phillip D; Zagrodnik, James
The immediate and short-term after effects of a bout of aerobic exercise on young adults' information processing were investigated. Seventeen participants performed an auditory two-choice reaction time (RT) task before, during, and after 40 min of ergometer cycling. In a separate session, the same sequence of testing was completed while seated on an ergometer without pedalling. Results indicate that exercise (1) improves the speed of reactions by energizing motor outputs; (2) interacts with the arousing effect of a loud auditory signal suggesting a direct link between arousal and activation; (3) gradually reduces RT and peaks between 15 and 20 min; (4) effects on RT disappear very quickly after exercise cessation; and (5) effects on motor processes cannot be explained by increases in body temperature caused by exercise. Taken together, these results support a selective influence of acute aerobic exercise on motor adjustment stage. PMID:18930445
Large-scale synthesis of ultrathin tungsten oxide nanowire networks: an efficient catalyst for aerobic oxidation of toluene to benzaldehyde under visible light.
Bai, Hua; Yi, Wencai; Liu, Jingyao; Lv, Qing; Zhang, Qing; Ma, Qiang; Yang, Haifeng; Xi, Guangcheng
As a very important chemical raw material, the selective formation of benzaldehyde from toluene at preparative or industrial levels requires the use of highly corrosive chlorine and high reaction temperatures, which severely corrodes equipment, pollutes the environment, and consumes a lot of energy. Herein, we report a robust and highly active catalyst for the benzaldehyde evolution reaction that is constructed by the surfactant-free growth of oxygen vacancy-rich W18O49 ultrathin nanowire networks. Under atmospheric pressure and visible-light irradiation, the new catalyst can selectively (92% selectivity) catalyze the aerobic oxidation of toluene to benzaldehyde with yields of above 95%. PMID:27357748
Analysis of Reaction Times and Aerobic Capacities of Soccer Players According to Their Playing Positions
ERIC Educational Resources Information Center
Taskin, Cengiz; Karakoc, Onder; Taskin, Mine; Dural, Murat
70 soccer players in Gaziantep amateur league voluntarily participated in this study, (average of their ages 19,17±1,34years, average of their heights 181,28±5,06 cm, average of their body weights 76,75±4,43 kg and average of their sports experiences 3,78±0,95 years) to analyze visual and auditory reaction times and aerobic capacities of amateur…
Solvent-free aerobic oxidation of hydrocarbons and alcohols with Pd@N-doped carbon from glucose.
Zhang, Pengfei; Gong, Yutong; Li, Haoran; Chen, Zhirong; Wang, Yong
The development of efficient systems for selective aerobic oxidation of hydrocarbons and alcohols to produce more functional compounds (aldehydes, ketones, acids or esters) with atmospheric air or molecular oxygen is a grand challenge for the chemical industry. Here we report the synthesis of palladium nanoparticles supported on novel nanoporous nitrogen-doped carbon, and their impressive performance in the controlled oxidation of hydrocarbons and alcohols with air. In terms of catalytic activity, these catalysts afford much higher turnover frequencies (up to 863 turnovers per hour for hydrocarbon oxidation and up to ~210,000 turnovers per hour for alcohol oxidation) than most reported palladium catalysts under the same reaction conditions. This work provides great potential for the application of ambient air and recyclable palladium catalysts in fine-chemical production with high activity. PMID:23481401
Trimetallic Au/Pt/Rh Nanoparticles as Highly Active Catalysts for Aerobic Glucose Oxidation
NASA Astrophysics Data System (ADS)
Zhang, Haijun; Cao, Yingnan; Lu, Lilin; Cheng, Zhong; Zhang, Shaowei
This paper reports the findings of an investigation of the correlations between the catalytic activity for aerobic glucose oxidation and the composition of Au/Pt/Rh trimetallic nanoparticles (TNPs) with average diameters of less than 2.0 nm prepared by rapid injection of NaBH4. The prepared TNPs were characterized by UV-Vis, TEM, and HR-TEM. The catalytic activity of the alloy-structured TNPs for aerobic glucose oxidation is several times higher than that of Au monometallic nanoparticles with nearly the same particle size. The catalytic activities of the TNP catalysts were dependent not only on the composition, but also on the electronic structure. The high catalytic activities of the Au/Pt/Rh TNPs can be ascribed to the formed negative-charged Au atoms due to electron donation of Rh neighboring atoms acting as catalytically active sites for aerobic glucose oxidation.
High-Potential Electrocatalytic O2 Reduction with Nitroxyl / NOx Mediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis
Gerken, James B.; Stahl, Shannon S.
Efficient reduction of O2 to water is a central challenge in energy conversion and aerobic oxidation catalysis. In the present study, we investigate the electrochemical reduction of O2 with soluble organic nitroxyl and nitrogen oxide (NOx) mediators. When used alone, neither organic nitroxyls, such as TEMPO (2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl), nor NOx species, such as sodium nitrite, are effective mediators of electrochemical O2 reduction. The combination of nitroxyl/NOx species, however, mediates sustained O2 reduction at electrochemical potentials of 0.19–0.33 V (vs. Fc/Fc+) in acetonitrile containing trifluoroacetic acid. Mechanistic analysis of the coupled redox reactions supports a process in which the nitrogen oxide catalyst drives aerobic oxidation of a nitroxyl mediator to an oxoammonium species, which then is reduced back to the nitroxyl at the cathode. The electrolysis potential is dictated by the oxoammonium/nitroxyl reduction potential. The high potentials observed with this ORR system benefit from the mechanism-based specificity for four-electron reduction of oxygen to water mediated by NOx species, together with kinetically efficient reduction of oxidized NOx species by TEMPO and other organic nitroxyls. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.
Cu-Catalyzed Consecutive Hydroxylation and Aerobic Oxidative Cycloetherification under Microwave Conditions: Entry to 2-Arylbenzofuran-3-carboxylic Acids.
Xu, Tianlong; Zhang, Ensheng; Wang, Dejian; Wang, Yan; Zou, Yong
A convenient one-pot synthesis of 2-arylbenzofuran-3-carboxylic acids from (E)-2-(2-bromophenyl)-3-phenylacrylic acids via Cu-catalyzed consecutive hydroxylation and aerobic oxidative cycloetherification under microwave conditions has been developed. This protocol employed the reagent combination of Cu(OAc)2, 1,10-phen, and KOH in DMSO/H2O (1:1), all of which are cost-effective, readily available, and easily removable from the reaction mixture. Utilizing this synthetic protocol, various 2-arylbenzofuran-3-carboxylic acids as well as the natural product moracin M have been synthesized in satisfactory yields under mild conditions. PMID:25836742
Molecular characterization of a microbial consortium involved in methane oxidation coupled to denitrification under micro-aerobic conditions
Liu, Jingjing; Sun, Faqian; Wang, Liang; Ju, Xi; Wu, Weixiang; Chen, Yingxu
Methane can be used as an alternative carbon source in biological denitrification because it is nontoxic, widely available and relatively inexpensive. A microbial consortium involved in methane oxidation coupled to denitrification (MOD) was enriched with nitrite and nitrate as electron acceptors under micro-aerobic conditions. The 16S rRNA gene combined with pmoA phylogeny of methanotrophs and nirK phylogeny of denitrifiers were analysed to reveal the dominant microbial populations and functional microorganisms. Real-time quantitative polymerase chain reaction results showed high numbers of methanotrophs and denitrifiers in the enriched consortium. The 16S rRNA gene clone library revealed that Methylococcaceae and Methylophilaceae were the dominant populations in the MOD ecosystem. Phylogenetic analyses of pmoA gene clone libraries indicated that all methanotrophs belonged to Methylococcaceae, a type I methanotroph employing the ribulose monophosphate pathway for methane oxidation. Methylotrophic denitrifiers of the Methylophilaceae that can utilize organic intermediates (i.e. formaldehyde, citrate and acetate) released from the methanotrophs played a vital role in aerobic denitrification. This study is the first report to confirm micro-aerobic denitrification and to make phylogenetic and functional assignments for some members of the microbial assemblages involved in MOD. PMID:24245852
Copper(II)-catalyzed room temperature aerobic oxidation of hydroxamic acids and hydrazides to acyl-nitroso and azo intermediates, and their Diels-Alder trapping.
Chaiyaveij, Duangduan; Cleary, Leah; Batsanov, Andrei S; Marder, Todd B; Shea, Kenneth J; Whiting, Andrew
CuCl(2), in the presence of a 2-ethyl-2-oxazoline ligand, is an effective catalyst for the room temperature, aerobic oxidation of hydroxamic acids and hydrazides, to acyl-nitroso and azo dienophiles respectively, which are efficiently trapped in situ via both inter- and intramolecular hetero-Diels-Alder reactions with dienes. Both inter- and intramolecular variants of the Diels-Alder reaction are suitable under the reaction conditions using a variety of solvents. Under the same conditions, an acyl hydrazide was also oxidized to give an acyl-azo dienophile which was trapped intramolecularly by a diene. PMID:21644530
Highly Dispersed Gold Nanoparticles Supported on SBA-15 for Vapor Phase Aerobic Oxidation of Benzyl Alcohol.
Kumar, Ashish; Sreedhar, Bojja; Chary, Komandur V R
Gold nanoparticles supported on SBA-15 are prepared by homogenous deposition-precipitation method (HDP) using urea as the precipitating agent. The structural features of the synthesized catalysts were characterized by various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption (BET), pore size distribution (PSD), CO chemisorption and X-ray photoelectron spectroscopy (XPS). The catalytic activity and stability of the Au/SBA-15 catalysts are investigated during the vapor phase aerobic oxidation of benzyl alcohol. The BJH pore size distribution results of SBA-15 support and Au/SBA-15 catalysts reveals that the formation of mesoporous structure in all the samples. TEM results suggest that Au nanoparticles are highly dispersed over SBA-15 and long range order of hexagonal mesopores of SBA-15 is well retained even after the deposition of Au metallic nanoparticles. XPS study reveals the formation of Au (0) after chemical reduction by NaBH4. The particle size measured from CO-chemisorption and TEM analysis are well correlated with the TOF values of the reaction. Au/SBA-1 5 catalysts are found to show higher activity compare to Au/TiO2 and Au/MgO catalysts during the vapor phase oxidation of benzyl alcohol. The catalytic functionality are well substantiated with particle size measured from TEM. The crystallite size of Au in both fresh and spent catalysts were measured from X-ray diffraction. PMID:26353720
Aerobic composting of waste activated sludge: Kinetic analysis for microbiological reaction and oxygen consumption
Yamada, Y.; Kawase, Y. . E-mail: email@example.com
In order to examine the optimal design and operating parameters, kinetics for microbiological reaction and oxygen consumption in composting of waste activated sludge were quantitatively examined. A series of experiments was conducted to discuss the optimal operating parameters for aerobic composting of waste activated sludge obtained from Kawagoe City Wastewater Treatment Plant (Saitama, Japan) using 4 and 20 L laboratory scale bioreactors. Aeration rate, compositions of compost mixture and height of compost pile were investigated as main design and operating parameters. The optimal aerobic composting of waste activated sludge was found at the aeration rate of 2.0 L/min/kg (initial composting mixture dry weight). A compost pile up to 0.5 m could be operated effectively. A simple model for composting of waste activated sludge in a composting reactor was developed by assuming that a solid phase of compost mixture is well mixed and the kinetics for microbiological reaction is represented by a Monod-type equation. The model predictions could fit the experimental data for decomposition of waste activated sludge with an average deviation of 2.14%. Oxygen consumption during composting was also examined using a simplified model in which the oxygen consumption was represented by a Monod-type equation and the axial distribution of oxygen concentration in the composting pile was described by a plug-flow model. The predictions could satisfactorily simulate the experiment results for the average maximum oxygen consumption rate during aerobic composting with an average deviation of 7.4%.
Aerobic bacterial pyrite oxidation and acid rock drainage during the Great Oxidation Event.
Konhauser, Kurt O; Lalonde, Stefan V; Planavsky, Noah J; Pecoits, Ernesto; Lyons, Timothy W; Mojzsis, Stephen J; Rouxel, Olivier J; Barley, Mark E; Rosìere, Carlos; Fralick, Phillip W; Kump, Lee R; Bekker, Andrey
The enrichment of redox-sensitive trace metals in ancient marine sedimentary rocks has been used to determine the timing of the oxidation of the Earth's land surface. Chromium (Cr) is among the emerging proxies for tracking the effects of atmospheric oxygenation on continental weathering; this is because its supply to the oceans is dominated by terrestrial processes that can be recorded in the Cr isotope composition of Precambrian iron formations. However, the factors controlling past and present seawater Cr isotope composition are poorly understood. Here we provide an independent and complementary record of marine Cr supply, in the form of Cr concentrations and authigenic enrichment in iron-rich sedimentary rocks. Our data suggest that Cr was largely immobile on land until around 2.48 Gyr ago, but within the 160 Myr that followed--and synchronous with independent evidence for oxygenation associated with the Great Oxidation Event (see, for example, refs 4-6)--marked excursions in Cr content and Cr/Ti ratios indicate that Cr was solubilized at a scale unrivalled in history. As Cr isotope fractionations at that time were muted, Cr must have been mobilized predominantly in reduced, Cr(III), form. We demonstrate that only the oxidation of an abundant and previously stable crustal pyrite reservoir by aerobic-respiring, chemolithoautotrophic bacteria could have generated the degree of acidity required to solubilize Cr(III) from ultramafic source rocks and residual soils. This profound shift in weathering regimes beginning at 2.48 Gyr ago constitutes the earliest known geochemical evidence for acidophilic aerobes and the resulting acid rock drainage, and accounts for independent evidence of an increased supply of dissolved sulphate and sulphide-hosted trace elements to the oceans around that time. Our model adds to amassing evidence that the Archaean-Palaeoproterozoic boundary was marked by a substantial shift in terrestrial geochemistry and biology. PMID:22012395
Light-Dependent Aerobic Methane Oxidation Reduces Methane Emissions from Seasonally Stratified Lakes
Oswald, Kirsten; Milucka, Jana; Brand, Andreas; Littmann, Sten; Wehrli, Bernhard; Kuypers, Marcel M. M.; Schubert, Carsten J.
Lakes are a natural source of methane to the atmosphere and contribute significantly to total emissions compared to the oceans. Controls on methane emissions from lake surfaces, particularly biotic processes within anoxic hypolimnia, are only partially understood. Here we investigated biological methane oxidation in the water column of the seasonally stratified Lake Rotsee. A zone of methane oxidation extending from the oxic/anoxic interface into anoxic waters was identified by chemical profiling of oxygen, methane and δ13C of methane. Incubation experiments with 13C-methane yielded highest oxidation rates within the oxycline, and comparable rates were measured in anoxic waters. Despite predominantly anoxic conditions within the zone of methane oxidation, known groups of anaerobic methanotrophic archaea were conspicuously absent. Instead, aerobic gammaproteobacterial methanotrophs were identified as the active methane oxidizers. In addition, continuous oxidation and maximum rates always occurred under light conditions. These findings, along with the detection of chlorophyll a, suggest that aerobic methane oxidation is tightly coupled to light-dependent photosynthetic oxygen production both at the oxycline and in the anoxic bottom layer. It is likely that this interaction between oxygenic phototrophs and aerobic methanotrophs represents a widespread mechanism by which methane is oxidized in lake water, thus diminishing its release into the atmosphere. PMID:26193458
Large-scale synthesis of ultrathin tungsten oxide nanowire networks: an efficient catalyst for aerobic oxidation of toluene to benzaldehyde under visible light
NASA Astrophysics Data System (ADS)
Bai, Hua; Yi, Wencai; Liu, Jingyao; Lv, Qing; Zhang, Qing; Ma, Qiang; Yang, Haifeng; Xi, Guangcheng
As a very important chemical raw material, the selective formation of benzaldehyde from toluene at preparative or industrial levels requires the use of highly corrosive chlorine and high reaction temperatures, which severely corrodes equipment, pollutes the environment, and consumes a lot of energy. Herein, we report a robust and highly active catalyst for the benzaldehyde evolution reaction that is constructed by the surfactant-free growth of oxygen vacancy-rich W18O49 ultrathin nanowire networks. Under atmospheric pressure and visible-light irradiation, the new catalyst can selectively (92% selectivity) catalyze the aerobic oxidation of toluene to benzaldehyde with yields of above 95%.As a very important chemical raw material, the selective formation of benzaldehyde from toluene at preparative or industrial levels requires the use of highly corrosive chlorine and high reaction temperatures, which severely corrodes equipment, pollutes the environment, and consumes a lot of energy. Herein, we report a robust and highly active catalyst for the benzaldehyde evolution reaction that is constructed by the surfactant-free growth of oxygen vacancy-rich W18O49 ultrathin nanowire networks. Under atmospheric pressure and visible-light irradiation, the new catalyst can selectively (92% selectivity) catalyze the aerobic oxidation of toluene to benzaldehyde with yields of above 95%. Electronic supplementary information (ESI) available: Experimental procedure, XRD patterns, TEM and HRTEM images, energy-dispersive X-ray spectra, UV-vis spectra, X-ray photoelectron spectroscopy (XPS), and EDS. See DOI: 10.1039/c6nr02949c
Treatment of real industrial wastewater using the combined approach of advanced oxidation followed by aerobic oxidation.
Ramteke, Lokeshkumar P; Gogate, Parag R
Fenton oxidation and ultrasound-based pretreatment have been applied to improve the treatment of real industrial wastewater based on the use of biological oxidation. The effect of operating parameters such as Fe(2+) loading, contact time, initial pH, and hydrogen peroxide loading on the extent of chemical oxygen demand (COD) reduction and change in biochemical oxygen demand (BOD5)/COD ratio has been investigated. The optimum operating conditions established for the pretreatment were initial pH of 3.0, Fe(2+) loading of 2.0, and 2.5 g L(-1) for the US/Fenton/stirring and Fenton approach, respectively, and temperature of 25 °C with initial H2O2 loading of 1.5 g L(-1). The use of pretreatment resulted in a significant increase in the BOD5/COD ratio confirming the production of easily digestible intermediates. The effect of the type of sludge in the aerobic biodegradation was also investigated based on the use of primary activated sludge (PAS), modified activated sludge (MAS), and activated sludge (AS). Enhanced removal of the pollutants as well as higher biomass yield was observed for MAS as compared to PAS and AS. The use of US/Fenton/stirring pretreatment under the optimized conditions followed by biological oxidation using MAS resulted in maximum COD removal at 97.9 %. The required hydraulic retention time for the combined oxidation system was also significantly lower as compared to only biological oxidation operation. Kinetic studies revealed that the reduction in the COD followed a first-order kinetic model for advanced oxidation and pseudo first-order model for biodegradation. The study clearly established the utility of the combined technology for the effective treatment of real industrial wastewater. PMID:26846248
Cu-NHC-TEMPO catalyzed aerobic oxidation of primary alcohols to aldehydes.
Liu, Xiaolong; Xia, Qinqin; Zhang, Yuejiao; Chen, Congyan; Chen, Wanzhi
Imidazolium salts bearing TEMPO groups react with commercially available copper powder affording Cu-NHC complexes. The in situ generated Cu-NHC-TEMPO complexes are quite efficient catalysts for aerobic oxidation of primary alcohols into aldehydes. The catalyst is easily available, and various primary alcohols were selectively converted to aldehydes in excellent yields. PMID:23944937
Effects of Aerobic and Microaerobic Conditions on Anaerobic Ammonium-Oxidizing (Anammox) Sludge
Strous, M.; Van Gerven, E.; Kuenen, J. G.; Jetten, M.
The anaerobic ammonium oxidation (Anammox) process is a promising novel option for removing nitrogen from wastewater. In this study it was shown that the Anammox process was inhibited reversibly by the presence of oxygen. Furthermore, aerobic nitrifiers were shown not to play an important role in the Anammox process. PMID:16535633
Aerobic Oxidation in Nanomicelles of Aryl Alkynes, in Water at Room Temperature**
Handa, Sachin; Fennewald, James C.; Rainey, Shane
On the basis of the far higher solubility of oxygen gas inside the hydrocarbon core of nanomicelles, metal and peroxide free aerobic oxidation of aryl alkynes has been achieved in water at room temperature. Many examples are offered that illustrate broad functional group tolerance. The overall process is environmentally friendly, documented by the associated low E Factors. PMID:24616243
High resolution and comprehensive techniques to analyze aerobic methane oxidation in mesocosm experiments
NASA Astrophysics Data System (ADS)
Chan, E. W.; Kessler, J. D.; Redmond, M. C.; Shiller, A. M.; Arrington, E. C.; Valentine, D. L.; Colombo, F.
Many studies of microbially mediated aerobic methane oxidation in oceanic environments have examined the many different factors that control the rates of oxidation. However, there is debate on how quickly methane is oxidized once a microbial population is established and what factor(s) are limiting in these types of environments. These factors include the availability of CH4, O2, trace metals, nutrients, and the density of cell population. Limits to these factors can also control the temporal aspects of a methane oxidation event. In order to look at this process in its entirety and with higher temporal resolution, a mesocosm incubation system was developed with a Dissolved Gas Analyzer System (DGAS) coupled with a set of analytical tools to monitor aerobic methane oxidation in real time. With the addition of newer laser spectroscopy techniques (cavity ringdown spectroscopy), stable isotope fractionation caused by microbial processes can also be examined on a real time and automated basis. Cell counting, trace metal, nutrient, and DNA community analyses have also been carried out in conjunction with these mesocosm samples to provide a clear understanding of the biology in methane oxidation dynamics. This poster will detail the techniques involved to provide insights into the chemical and isotopic kinetics controlling aerobic methane oxidation. Proof of concept applications will be presented from seep sites in the Hudson Canyon and the Sleeping Dragon seep field, Mississippi Canyon 118 (MC 118). This system was used to conduct mesocosm experiments to examine methane consumption, O2 consumption, nutrient consumption, and biomass production.
A new approach to carbon-carbon bond formation: Development of aerobic Pd-catalyzed reductive coupling reactions of organometallic reagents and styrenes
Gligorich, Keith M.; Iwai, Yasumasa; Cummings, Sarah A.; Sigman, Matthew S.
Alkenes are attractive starting materials for organic synthesis and the development of new selective functionalization reactions are desired. Previously, our laboratory discovered a unique Pd-catalyzed hydroalkoxylation reaction of styrenes containing a phenol. Based upon deuterium labeling experiments, a mechanism involving an aerobic alcohol oxidation coupled to alkene functionalization was proposed. These results inspired the development of a new Pd-catalyzed reductive coupling reaction of alkenes and organometallic reagents that generates a new carbon-carbon bond. Optimization of the conditions for the coupling of both organostannanes and organoboronic esters is described and the initial scope of the transformation is presented. Additionally, several mechanistic experiments are outlined and support the rationale for the development of the reaction based upon coupling alcohol oxidation to alkene functionalization. PMID:20161306
Aerobic oxidation of starch catalyzed by isopolyoxovanadate Na4Co(H2O)6V10O28.
Chen, Xiaoli; Yan, Siqi; Wang, Hang; Hu, Zhiyun; Wang, Xiaohong; Huo, Mingxin
The partial oxidation of starch was achieved in the presence of oxygen with Na4Co(H2O)6V10O28·18H2O (abbreviated as CoV10) as catalyst. The oxidation degree of starch was determined by FT-IR, XRD and SEM measurements, which indicated that the aerobic oxidation of starch was promoted by oxidative catalyst CoV10. The application of CoV10 could give a high oxidation degree (DO) of 1.35 COOH/100 GU and 2.07 CO/100 GU with 86 wt.% yield of solid starch under mild reaction conditions (pH=6; reaction time, 8 h; temperature, 50 °C; catalyst amount, 8 mg, when 1.5 g starch was used as substrate; atmospheric pressure). Among some vanadium compounds, CoV10 exhibited 4-fold activity higher than orthovanadate due to its coordination effect of cobalt and V10O28. Meanwhile, CoV10 could be recycled for six times with only a slight decrease in activity. Thus, CoV10/O2 is one of the most efficient systems for partial oxidation of starch reported so far. PMID:25498687
Nitrous oxide production by Alcaligenes faecalis under transient and dynamic aerobic and anaerobic conditions
Otte, S.; Grobben, N.G.; Robertson, L.A.; Jetten, M.S.M.; Kuenen, J.G.
Nitrous oxide production contributes to both greenhouse effect and ozone depletion in the stratosphere. A significant part of the global N2O emission can be attributed to microbial processes, especially nitrification and denitrification, used in biological wastewater treatment systems. This study looks at the efficiency of denitrification and the enzymes involved, with the emphasis on N2O production during the transient phase from aerobic to anaerobic conditions and vice versa. The effect of repetitive changing aerobic-anaerobic conditions on N2O was also studied. Alcaligenes faecalis was used as the model denitrofing organism. 35 refs., 3 figs., 1 tab.
Nanoscaled copper metal-organic framework (MOF) based on carboxylate ligands as an efficient heterogeneous catalyst for aerobic epoxidation of olefins and oxidation of benzylic and allylic alcohols.
Qi, Yue; Luan, Yi; Yu, Jie; Peng, Xiong; Wang, Ge
Aerobic epoxidation of olefins at a mild reaction temperature has been carried out by using nanomorphology of [Cu3(BTC)2] (BTC = 1,3,5-benzenetricarboxylate) as a high-performance catalyst through a simple synthetic strategy. An aromatic carboxylate ligand was employed to furnish a heterogeneous copper catalyst and also serves as the ligand for enhanced catalytic activities in the catalytic reaction. The utilization of a copper metal-organic framework catalyst was further extended to the aerobic oxidation of aromatic alcohols. The shape and size selectivity of the catalyst in olefin epoxidation and alcohol oxidation was investigated. Furthermore, the as-synthesized copper catalyst can be easily recovered and reused several times without leaching of active species or significant loss of activity. PMID:25430789
Dissimilatory perchlorate reduction linked to aerobic methane oxidation via chlorite dismutase
NASA Astrophysics Data System (ADS)
Oremland, R. S.; Baesman, S. M.; Miller, L. G.
accumulation of chloride ions either in spent media or in slurries prepared from Searsville Lake soil, neither of these oxyanions evoked methane oxidation when added to either anaerobic mixed cultures or soils enriched in methanotrophs. This result leads us to surmise that the release of O2 during enzymatic perchlorate reduction was low, and that the oxygen produced was unavailable to the aerobic methanotrophs. This was borne out by patterns of O2 and CO2 production during experiments with lake soil, growth media, and pure cultures of dissimilatory perchlorate reducing bacteria. We observed that O2 release during incubation of D. agitata CKB with 10 mM ClO4- or ClO3- was decoupled from metabolism. More O2 was released during incubations without added acetate than with 10 mM acetate and an even greater amount of O2 was released during incubation with heat-killed cells. This suggests a chemical mechanism of O2 production during reaction with ClO4- and ClO3-. Hence, perchlorate reducing bacteria need not be present to facilitate O2 release from the surface of Mars, in support of recent interpretations of Viking LR and GEx experiments.
(E)-α,β-unsaturated amides from tertiary amines, olefins and CO via Pd/Cu-catalyzed aerobic oxidative N-dealkylation.
Shi, Renyi; Zhang, Hua; Lu, Lijun; Gan, Pei; Sha, Yuchen; Zhang, Heng; Liu, Qiang; Beller, Matthias; Lei, Aiwen
A novel Pd/Cu-catalyzed chemoselective aerobic oxidative N-dealkylation/carbonylation reaction has been developed. Tertiary amines are utilized as a "reservoir" of "active" secondary amines in this transformation, which inhibits the formation of undesired by-products and the deactivation of the catalysts. This protocol allows for an efficient and straightforward construction of synthetically useful and bioactive (E)-α,β-unsaturated amide derivatives from easily available tertiary amines, olefins and CO. PMID:25610923
Organocatalytic Aerobic Oxidation of Benzylic sp(3) C-H Bonds of Ethers and Alkylarenes Promoted by a Recyclable TEMPO Catalyst.
Zhang, Zhiguang; Gao, Yuan; Liu, Yuan; Li, Jianjun; Xie, Hexin; Li, Hao; Wang, Wei
An entirely metal-free catalyst system consisting of an easily prepared recyclable new TEMPO derived sulfonic salt catalyst, and mineral acids (NaNO2 and HCl) has been developed for selective aerobic oxidation of structurally diverse benzylic sp(3) C-H bonds of ethers and alkylarenes. The mild reaction conditions allow for the generation of synthetically and biologically valued isochromanones and xanthones from readily accessible alkyl aromatic precursors in good yields. PMID:26513695
CuBr catalyzed aerobic oxidative coupling of 2-aminopyridines with cinnamaldehydes: direct access to 3-formyl-2-phenyl-imidazo[1,2-a]pyridines.
Bharate, Jaideep B; Abbat, Sheenu; Bharatam, Prasad V; Vishwakarma, Ram A; Bharate, Sandip B
Copper bromide catalyzed aerobic oxidative coupling of 2-aminopyridines with cinnamaldehydes directly led to the formation of 3-formyl-2-phenyl-imidazo[1,2-a]pyridines. The quantum chemical calculations were performed to trace the reaction mechanism and get insights into the possible reaction pathway. 2-Aminopyridines on coupling with cinnamaldehyde generate (E)-3-phenyl-3-(pyridin-2-ylamino)acrylaldehyde IV as a key intermediate, which undergoes C-N bond formation reaction to produce 3-formyl-2-phenyl-imidazo[1,2-a]pyridines. PMID:26103156
Activated carbon for aerobic oxidation: Benign approach toward 2-benzoylbenzimidazoles and 2-benzoylbenzoxazoles synthesis
Bao, Kai; Li, Fuqing; Liu, Hanjing; Wang, Zhiwei; Shen, Qirong; Wang, Jian; Zhang, Weige
A general strategy involving a novel and highly efficient aerobic benzylic oxidation promoted by cheap, reusable activated carbon in water is developed. Application of this method has been demonstrated in the benign synthesis of bioactive 2-benzoylbenzimidazoles and 2-benzoylbenzoxazoles derivatives. Furthermore, the activated carbon catalyst could be recovered and reused at least three times without significantly losing its activity. Preliminary research suggests that the oxidation mechanism may involve intermediate hydroperoxidation and that a portion of the final carbonyl product is obtained through a secondary benzylic alcohol intermediate. Finally, theoretical calculations reveal that the oxidation yield is closely associated with the electric density at the benzylic position of the substrate. PMID:26041483
Uranium oxidation: characterization of oxides formed by reaction with water
Fuller, E.L. Jr.; Smyrl, N.R.; Condon, J.B.; Eager, M.H.
Three different uranium oxide samples have been characterized with respect to the different preparation techniques. Results show that the water reaction with uranium metal occurs cyclically forming laminar layers of oxide which spall off due to the strain at the oxide/metal interface. Single laminae are released if liquid water is present due to the prizing penetration at the reaction zone. The rate of reaction of water with uranium is directly proportional to the amount of adsorbed water on the oxide product. Rapid transport is effected through the open hydrous oxide product. Dehydration of the hydrous oxide irreversibly forms a more inert oxide which cannot be rehydrated to the degree that prevails in the original hydrous product of uranium oxidation with water. 27 figures.
P-Doped Porous Carbon as Metal Free Catalysts for Selective Aerobic Oxidation with an Unexpected Mechanism.
Patel, Mehulkumar A; Luo, Feixiang; Khoshi, M Reza; Rabie, Emann; Zhang, Qing; Flach, Carol R; Mendelsohn, Richard; Garfunkel, Eric; Szostak, Michal; He, Huixin
An extremely simple and rapid (seconds) approach is reported to directly synthesize gram quantities of P-doped graphitic porous carbon materials with controlled P bond configuration. For the first time, it is demonstrated that the P-doped carbon materials can be used as a selective metal free catalyst for aerobic oxidation reactions. The work function of P-doped carbon materials, its connectivity to the P bond configuration, and the correlation with its catalytic efficiency are studied and established. In direct contrast to N-doped graphene, the P-doped carbon materials with higher work function show high activity in catalytic aerobic oxidation. The selectivity trend for the electron donating and withdrawing properties of the functional groups attached to the aromatic ring of benzyl alcohols is also different from other metal free carbon based catalysts. A unique catalytic mechanism is demonstrated, which differs from both GO and N-doped graphene obtained by high temperature nitrification. The unique and unexpected catalytic pathway endows the P-doped materials with not only good catalytic efficiency but also recyclability. This, combined with a rapid, energy saving approach that permits fabrication on a large scale, suggests that the P-doped porous materials are promising materials for "green catalysis" due to their higher theoretical surface area, sustainability, environmental friendliness, and low cost. PMID:26751165
Palladium-catalyzed oxidative carbonylation reactions.
Wu, Xiao-Feng; Neumann, Helfried; Beller, Matthias
Palladium-catalyzed coupling reactions have become a powerful tool for advanced organic synthesis. This type of reaction is of significant value for the preparation of pharmaceuticals, agrochemicals, as well as advanced materials. Both, academic as well as industrial laboratories continuously investigate new applications of the different methodologies. Clearly, this area constitutes one of the major topics in homogeneous catalysis and organic synthesis. Among the different palladium-catalyzed coupling reactions, several carbonylations have been developed and widely used in organic syntheses and are even applied in the pharmaceutical industry on ton-scale. Furthermore, methodologies such as the carbonylative Suzuki and Sonogashira reactions allow for the preparation of interesting building blocks, which can be easily refined further on. Although carbonylative coupling reactions of aryl halides have been well established, palladium-catalyzed oxidative carbonylation reactions are also interesting. Compared with the reactions of aryl halides, oxidative carbonylation reactions offer an interesting pathway. The oxidative addition step could be potentially avoided in oxidative reactions, but only few reviews exist in this area. In this Minireview, we summarize the recent development in the oxidative carbonylation reactions. PMID:23307763
Evaluation of methyl fluoride and dimethyl ether as inhibitors of aerobic methane oxidation
Oremland, R.S.; Culbertson, C.W.
Methyl fluoride (MF) and dimethyl ether (DME) were effective inhibitors of aerobic methanotrophy in a variety of soils. MF and DME blocked consumption of CH4 as well as the oxidation of 14CH4 to 14CO2, but neither MF nor DME affected the oxidation of [14C]methanol or [14C]formate to 14CO2. Cooxidation of ethane and propane by methane-oxidizing soils was also inhibited by MF. Nitrification (ammonia oxidation) in soils was inhibited by both MF and DME. Production of N2O via nitrification was inhibited by MF; however, MF did not affect N2O production associated with denitrification. Methanogenesis was partially inhibited by MF but not by DME. Methane oxidation was ~100-fold more sensitive to MF than was methanogenesis, indicating that an optimum concentration could be employed to selectively block methanotrophy. MF inhibited methane oxidation by cell suspensions of Methylococcus capsulatus; however, DME was a much less effective inhibitor.
An insight into the mechanism of the aerobic oxidation of aldehydes catalyzed by N-heterocyclic carbenes.
Bortolini, O; Chiappe, C; Fogagnolo, M; Giovannini, P P; Massi, A; Pomelli, C S; Ragno, D
N-Heterocyclic carbene catalysis for the aerobic oxidation and esterification of aromatic aldehydes was monitored by ESI-MS (MS/MS) and the key intermediates were intercepted and characterized using the charge-tag strategy. PMID:24413829
Palladium-Catalyzed Aerobic Oxidative Dehydrogenation of Cyclohexenes to Substituted Arene Derivatives
Iosub, Andrei V.; Stahl, Shannon S.
A palladium(II) catalyst system has been identified for aerobic dehydrogenation of substituted cyclohexenes to the corresponding arene derivatives. Use of sodium anthraquinone-2-sulfonate (AMS) as a co-catalyst enhances the product yields. A wide range of functional groups are tolerated in the reactions, and the scope and limitations of the method are described. The catalytic dehydrogenation of cyclohexenes is showcased in an efficient route to a phthalimide-based TRPA1 activity modulator. PMID:25734414
Determination of reaction rates and activation energy in aerobic composting processes for yard waste.
Uma, R N; Manjula, G; Meenambal, T
The reaction rates and activation energy in aerobic composting processes for yard waste were determined using specifically designed reactors. Different mixture ratios were fixed before the commencement of the process. The C/N ratio was found to be optimum for a mixture ratio of 1:6 containing one part of coir pith to six parts of other waste which included yard waste, yeast sludge, poultry yard waste and decomposing culture (Pleurotosis). The path of stabilization of the wastes was continuously monitored by observing various parameters such as temperature, pH, Electrical Conductivity, C.O.D, VS at regular time intervals. Kinetic analysis was done to determine the reaction rates and activation energy for the optimum mixture ratio under forced aeration condition. The results of the analysis clearly indicated that the temperature dependence of the reaction rates followed the Arrhenius equation. The temperature coefficients were also determined. The degradation of the organic fraction of the yard waste could be predicted using first order reaction model. PMID:18476403
Role of ammonia-oxidizing bacteria in micropollutant removal from wastewater with aerobic granular sludge.
Margot, Jonas; Lochmatter, Samuel; Barry, D A; Holliger, Christof
Nitrifying wastewater treatment plants (WWTPs) are more efficient than non-nitrifying WWTPs to remove several micropollutants such as pharmaceuticals and pesticides. This may be related to the activity of nitrifying organisms, such as ammonia-oxidizing bacteria (AOBs), which could possibly co-metabolically oxidize micropollutants with their ammonia monooxygenase (AMO). The role of AOBs in micropollutant removal was investigated with aerobic granular sludge (AGS), a promising technology for municipal WWTPs. Two identical laboratory-scale AGS sequencing batch reactors (AGS-SBRs) were operated with or without nitrification (inhibition of AMOs) to assess their potential for micropollutant removal. Of the 36 micropollutants studied at 1 μg l(-1) in synthetic wastewater, nine were over 80% removed, but 17 were eliminated by less than 20%. Five substances (bisphenol A, naproxen, irgarol, terbutryn and iohexol) were removed better in the reactor with nitrification, probably due to co-oxidation catalysed by AMOs. However, for the removal of all other micropollutants, AOBs did not seem to play a significant role. Many compounds were better removed in aerobic condition, suggesting that aerobic heterotrophic organisms were involved in the degradation. As the AGS-SBRs did not favour the growth of such organisms, their potential for micropollutant removal appeared to be lower than that of conventional nitrifying WWTPs. PMID:26877039
High-Potential Electrocatalytic O2 Reduction with Nitroxyl/NO x Mediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis.
Gerken, James B; Stahl, Shannon S
Efficient reduction of O2 to water is a central challenge in energy conversion and many aerobic oxidation reactions. Here, we show that the electrochemical oxygen reduction reaction (ORR) can be achieved at high potentials by using soluble organic nitroxyl and nitrogen oxide (NO x ) mediators. When used alone, neither organic nitroxyls, such as 2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl (TEMPO), nor NO x species, such as sodium nitrite, are effective ORR mediators. The combination of nitroxyl/NO x species, however, mediates sustained O2 reduction with overpotentials as low as 300 mV in acetonitrile containing trifluoroacetic acid. Mechanistic analysis of the coupled redox reactions supports a process in which the nitrogen oxide catalyst drives aerobic oxidation of a nitroxyl mediator to an oxoammonium species, which then is reduced back to the nitroxyl at the cathode. The electrolysis potential is dictated by the oxoammonium/nitroxyl reduction potential. The overpotentials accessible with this ORR system are significantly lower than widely studied molecular metal-macrocycle ORR catalysts and benefit from the mechanism-based specificity for four-electron reduction of oxygen to water mediated by NO x species, together with kinetically efficient reduction of oxidized NO x species by TEMPO and other organic nitroxyls. PMID:27162977
Dissolution of Fe(III)(hydr)oxides by an Aerobic Bacterium
Maurice, P.
This project investigated the effects of an aerobic Pseudomonas mendocina bacterium on the dissolution of Fe(III)(hydr)oxides. The research is important because metals and radionuclides that adsorb to Fe(III)(hydr)oxides could potentially be remobilized by dissolving bacteria. We showed that P. mendocina is capable of dissolving Fe-bearing minerals by a variety of mechanisms, including production of siderophores, pH changes, and formation of reductants. The production of siderophores by P. mendocina was quantified under a variety of growth conditions. Finally, we demonstrated that microbial siderophores may adsorb to and enhance dissolution of clay minerals.
Aerobic and anaerobic methane oxidation in terrestrial mud volcanoes in the Northern Apennines
NASA Astrophysics Data System (ADS)
Wrede, C.; Brady, S.; Rockstroh, S.; Dreier, A.; Kokoschka, S.; Heinzelmann, S. M.; Heller, C.; Reitner, J.; Taviani, M.; Daniel, R.; Hoppert, M.
Methane oxidizing prokaryotes are ubiquitous in oxic and anoxic habitats wherever C1-compounds are present. Thus, methane saturated mud volcano fluids should be a preferred habitat of methane consuming prokaryotes, using the readily available electron donors. In order to understand the relevance of methane as a carbon and energy source in mud volcano communities, we investigate the diversity of prokaryotic organisms involved in oxidation of methane in fluid samples from the Salse di Nirano mud volcano field situated in the Northern Apennines. Cell counts were at approximately 0.7 × 106 microbial cells/ml. A fraction of the microbial biomass was identified as ANME (anaerobic methanotroph) archaea by fluorescence in situ hybridization (FISH) analysis. They are associated in densely colonized flakes, of some tens of μm in diameter, embedded in a hyaline matrix. Diversity analysis based on the 16S rDNA genes, retrieved from amplified and cloned environmental DNA, revealed a high proportion of archaea, involved in anaerobic oxidation of methane (AOM). Aerobic methane-oxidizing proteobacteria could be highly enriched from mud volcano fluids, indicating the presence of aerobic methanotrophic bacteria, which may contribute to methane oxidation, whenever oxygen is readily available. The results imply that biofilms, dominated by ANME archaea, colonize parts of the mud volcano venting system.
Oxidative hemoglobin reactions: Applications to drug metabolism.
Spolitak, Tatyana; Hollenberg, Paul F; Ballou, David P
Hb is a protein with multiple functions, acting as an O2 transport protein, and having peroxidase and oxidase activities with xenobiotics that lead to substrate radicals. However, there is a lack of evidence for intermediates involved in these reactions of Hb with redox-active compounds, including those with xenobiotics such as drugs, chemical carcinogens, and sulfides. In particular, questions exist as to what intermediates participate in reactions of either metHb or oxyHb with sulfides. The studies presented here elaborate kinetics and intermediates involved in the reactions of Hb with oxidants (H2O2 and mCPBA), and they demonstrate the formation of high valent intermediates, providing insights into mechanistic issues of sulfur and drug oxidations. Overall, we propose generalized mechanisms that include peroxidatic reactions using H2O2 generated from the autooxidation of oxyHb, with involvement of substrate radicals in reactions of Hb with oxidizable drugs such as metyrapone or 2,4-dinitrophenylhydrazine and with sulfides. We identify ferryl intermediates (with a Soret band at 407 nm) in oxidative reactions with all of the above-mentioned reactions. These spectral properties are consistent with a protonated ferryl heme, such as Cpd II or Cpd ES-like species (Spolitak et al., JIB, 2006, 100, 2034-2044). Mechanism(s) of Hb oxidative reactions are discussed. PMID:27091316
Oxidative Reactions with Nonaqueous Enzymes
Jonathan S. Dordick; Douglas Clark; Brian H Davison; Alexander Klibanov
The objective of this work is to demonstrate a proof-of-concept of enzymatic oxidative processing in nonaqueous media using alkene epoxidation and phenolic polymerization as relevant targets. This project will provide both the fundamental and applied investigations necessary to initiate the implementation of oxidative biocatalysts as commercially relevant alternatives to chemical processing in general, and to phenolic polymerizations and alkene epoxidation specifically. Thus, this work will address the Bioprocessing Solicitation Area to: (1) makes major improvements to phenolic polymerization and alkene epoxidation technologies; (2) is expected to be cost competitive with competing conventional processes; and (3) produces higher yields with less waste.
Overcoming the "oxidant problem": strategies to use O2 as the oxidant in organometallic C-H oxidation reactions catalyzed by Pd (and Cu).
Campbell, Alison N; Stahl, Shannon S
Oxidation reactions are key transformations in organic chemistry because they can increase chemical complexity and incorporate heteroatom substituents into carbon-based molecules. This principle is manifested in the conversion of petrochemical feedstocks into commodity chemicals and in the synthesis of fine chemicals, pharmaceuticals, and other complex organic molecules. The utility and function of these molecules correlate directly with the presence and specific placement of oxygen and nitrogen heteroatoms and other functional groups within the molecules. Methods for selective oxidation of C-H bonds have expanded significantly over the past decade, and their role in the synthesis of organic chemicals will continue to increase. Our group's contributions to this field are linked to our broader interest in the development and mechanistic understanding of aerobic oxidation reactions. Molecular oxygen (O(2)) is the ideal oxidant. Its low cost and lack of toxic byproducts make it a highly appealing reagent that can address key "green chemistry" priorities in industry. With strong economic and environmental incentives to use O(2), the commmodity chemicals industry often uses aerobic oxidation reactions. In contrast, O(2) is seldom used to prepare more-complex smaller-volume chemicals, a limitation that reflects, in part, the limited synthetic scope and utility of existing aerobic reactions. Pd-catalyzed reactions represent some of the most versatile methods for selective C-H oxidation, but they often require stoichiometric transition-metal or organic oxidants, such as Cu(II), Ag(I), or benzoquinone. This Account describes recent strategies that we have identified to use O(2) as the oxidant in these reactions. In Pd-catalyzed C-H oxidation reactions that form carbon-heteroatom bonds, the stoichiometric oxidant is often needed to promote difficult reductive elimination steps in the catalytic mechanism. To address this challenge, we have identified new ancillary ligands for
Ammonium-oxidizing bacteria facilitate aerobic degradation of sulfanilic acid in activated sludge.
Chen, Gang; Ginige, Maneesha P; Kaksonen, Anna H; Cheng, Ka Yu
Sulfanilic acid (SA) is a toxic sulfonated aromatic amine commonly found in anaerobically treated azo dye contaminated effluents. Aerobic acclimatization of SA-degrading mixed microbial culture could lead to co-enrichment of ammonium-oxidizing bacteria (AOB) because of the concomitant release of ammonium from SA oxidation. To what extent the co-enriched AOB would affect SA oxidation at various ammonium concentrations was unclear. Here, a series of batch kinetic experiments were conducted to evaluate the effect of AOB on aerobic SA degradation in an acclimatized activated sludge culture capable of oxidizing SA and ammonium simultaneously. To account for the effect of AOB on SA degradation, allylthiourea was used to inhibit AOB activity in the culture. The results indicated that specific SA degradation rate of the mixed culture was negatively correlated with the initial ammonium concentration (0-93 mM, R²= 0.99). The presence of AOB accelerated SA degradation by reducing the inhibitory effect of ammonium (≥ 10 mM). The Haldane substrate inhibition model was used to correlate substrate concentration (SA and ammonium) and oxygen uptake rate. This study revealed, for the first time, that AOB could facilitate SA degradation at high concentration of ammonium (≥ 10 mM) in an enriched activated sludge culture. PMID:25259503
Molecular Engineering of Trifunctional Supported Catalysts for the Aerobic Oxidation of Alcohols.
Fernandes, Antony E; Riant, Olivier; Jensen, Klavs F; Jonas, Alain M
We describe a simple and general method for the preparation and molecular engineering of supported trifunctional catalysts and their application in the representative Cu/TEMPO/NMI-catalyzed aerobic oxidation of benzyl alcohol. The methodology allows in one single step to immobilize, with precise control of surface composition, both pyta, Cu(I) , TEMPO, and NMI sites on azide-functionalized silica particles. To optimize the performance of the heterogeneous trifunctional catalysts, synergistic interactions are finely engineered through modulating the degree of freedom of the imidazole site as well as tuning the relative surface composition, leading to catalysts with an activity significantly superior to the corresponding homogeneous catalytic system. PMID:27430481
The effect of widespread early aerobic marine ecosystems on methane cycling and the Great Oxidation
NASA Astrophysics Data System (ADS)
Daines, Stuart J.; Lenton, Timothy M.
The balance of evidence suggests that oxygenic photosynthesis had evolved by 3.0-2.7 Ga, several hundred million years prior to the Great Oxidation ≈2.4 Ga. Previous work has shown that if oxygenic photosynthesis spread globally prior to the Great Oxidation, this could have supported widespread aerobic ecosystems in the surface ocean, without oxidising the atmosphere. Here we use a suite of models to explore the implications for carbon cycling and the Great Oxidation. We find that recycling of oxygen and carbon within early aerobic marine ecosystems would have restricted the balanced fluxes of methane and oxygen escaping from the ocean, lowering the atmospheric concentration of methane in the Great Oxidation transition and its aftermath. This in turn would have minimised any bi-stability of atmospheric oxygen, by weakening a stabilising feedback on oxygen from hydrogen escape to space. The result would have been a more reversible and probably episodic rise of oxygen at the Great Oxidation transition, consistent with existing geochemical evidence. The resulting drop in methane levels to ≈10 ppm is consistent with climate cooling at the time but adds to the puzzle of what kept the rest of the Proterozoic warm. A key test of the scenario of abundant methanotrophy in oxygen oases before the Great Oxidation is its predicted effects on the organic carbon isotope (δ13Corg) record. Our open ocean general circulation model predicts δC13org ≈ - 30 to -45‰ consistent with most data from 2.65 to 2.45 Ga. However, values of δC13org ≈ - 50 ‰ require an extreme scenario such as concentrated methanotroph production where shelf-slope upwelling of methane-rich water met oxic shelf water.
Effect of selected monoterpenes on methane oxidation, denitrification, and aerobic metabolism by bacteria in pure culture.
Amaral, J A; Ekins, A; Richards, S R; Knowles, R
Selected monoterpenes inhibited methane oxidation by methanotrophs (Methylosinus trichosporium OB3b, Methylobacter luteus), denitrification by environmental isolates, and aerobic metabolism by several heterotrophic pure cultures. Inhibition occurred to various extents and was transient. Complete inhibition of methane oxidation by Methylosinus trichosporium OB3b with 1.1 mM (-)-alpha-pinene lasted for more than 2 days with a culture of optical density of 0.05 before activity resumed. Inhibition was greater under conditions under which particulate methane monooxygenase was expressed. No apparent consumption or conversion of monoterpenes by methanotrophs was detected by gas chromatography, and the reason that transient inhibition occurs is not clear. Aerobic metabolism by several heterotrophs was much less sensitive than methanotrophy was; Escherichia coli (optical density, 0.01), for example, was not affected by up to 7.3 mM (-)-alpha-pinene. The degree of inhibition was monoterpene and species dependent. Denitrification by isolates from a polluted sediment was not inhibited by 3.7 mM (-)-alpha-pinene, gamma-terpinene, or beta-myrcene, whereas 50 to 100% inhibition was observed for isolates from a temperate swamp soil. The inhibitory effect of monoterpenes on methane oxidation was greatest with unsaturated, cyclic hydrocarbon forms [e.g., (-)-alpha-pinene, (S)-(-)-limonene, (R)-(+)-limonene, and gamma-terpinene]. Lower levels of inhibition occurred with oxide and alcohol derivatives [(R)-(+)-limonene oxide, alpha-pinene oxide, linalool, alpha-terpineol] and a noncyclic hydrocarbon (beta-myrcene). Isomers of pinene inhibited activity to different extents. Given their natural sources, monoterpenes may be significant factors affecting bacterial activities in nature. PMID:9464387
Geographic and seasonal variation of dissolved methane and aerobic methane oxidation in Alaskan lakes
NASA Astrophysics Data System (ADS)
Martinez-Cruz, K.; Sepulveda-Jauregui, A.; Anthony, K. Walter; Thalasso, F.
Methanotrophic bacteria play an important role oxidizing a significant fraction of methane (CH4) produced in lakes. Aerobic CH4 oxidation depends mainly on lake CH4 and oxygen (O2) concentrations, in such a manner that higher MO rates are usually found at the oxic/anoxic interface, where both molecules are present. MO also depends on temperature, and via methanogenesis, on organic carbon input to lakes, including from thawing permafrost in thermokarst (thaw)-affected lakes. Given the large variability in these environmental factors, CH4 oxidation is expected to be subject to large seasonal and geographic variations, which have been scarcely reported in the literature. In the present study, we measured CH4 oxidation rates in 30 Alaskan lakes along a north-south latitudinal transect during winter and summer with a new field laser spectroscopy method. Additionally, we measured dissolved CH4 and O2 concentrations. We found that in the winter, aerobic CH4 oxidation was mainly controlled by the dissolved O2 concentration, while in the summer it was controlled primarily by the CH4 concentration, which was scarce compared to dissolved O2. The permafrost environment of the lakes was identified as another key factor. Thermokarst (thaw) lakes formed in yedoma-type permafrost had significantly higher CH4 oxidation rates compared to other thermokarst and non-thermokarst lakes formed in non-yedoma permafrost environments. As thermokarst lakes formed in yedoma-type permafrost have been identified to receive large quantities of terrestrial organic carbon from thaw and subsidence of the surrounding landscape into the lake, confirming the strong coupling between terrestrial and aquatic habitats and its influence on CH4 cycling.
Pd/Cu-cocatalyzed aerobic oxidative carbonylative homocoupling of arylboronic acids and CO: a highly selective approach to diaryl ketones.
Ren, Long; Jiao, Ning
A highly selective Pd/Cu-cocatalyzed aerobic oxidative carbonylative homocoupling of arylboronic acids has been developed. This method employs a simple catalytic system, readily available boronic acids as the substrates, molecular oxygen as the oxidant, and 1 atm of CO/O2 , which makes this method practical for further applications. PMID:24990473
Copper(II) complexes as catalyst for the aerobic oxidation of o-phenylenediamine to 2,3-diaminophenazine
NASA Astrophysics Data System (ADS)
Khattar, Raghvi; Yadav, Anjana; Mathur, Pavan
Two new mononuclear copper(II) complexes [Cu (L) (NO3)2] (1) and [Cu (L) Br2] (2) where (L = bis(1-(pyridin-2-ylmethyl)-benzimidazol-2-ylmethyl)ether) are synthesized and characterized by single-crystal X-ray diffraction analysis, elemental analysis, UV-Visible, IR spectroscopy, EPR and cyclic voltammetry. The complexes exhibit different coordination structures; the E1/2 value of the complex (1) is found to be relatively more cathodic than that of complex (2). X-band EPR spectra at low temperature in DMF supports a tetragonally distorted complex (1) while complex (2) shows three different g values suggesting a rhombic geometry. These complexes were utilized as a catalyst for the aerobic oxidation of o-phenylenediamine to 2,3-diaminophenazine assisted by molecular oxygen. The initial rate of reaction is dependent on the concentration of Cu(II) complex as well as substrate, and was found to be higher for the nitrate bound complex, while presence of acetate anion acts as a mild inhibitor of the reaction, as it is likely to pick up protons generated during the course of reaction. The inhibition suggests that the generated protons are further required in another important catalytic step.
Production of pesticide metabolites by oxidative reactions.
Hodgson, E
The cytochrome P-450-dependent monooxygenase system catalyzes a wide variety of oxidations of pesticide chemicals and related compounds. These reactions include epoxidation and aromatic hydroxylation, aliphatic hydroxylation, O-, N- and S-dealkylation, N-oxidation, oxidative deamination, S-oxidation, P-oxidation, desulfuration and ester cleavage and may result in either detoxication or activation of the pesticide. The current status of such reactions, relative to the production, in vivo, of biologically active intermediates in pesticide metabolism is summarized. More recently we have shown that the FAD-containing monooxygenase of mammalian liver (E.C.18.104.22.168), a xenobiotic metabolizing enzyme of broad specificity formerly known as an amine oxidase, is involved in a variety of pesticide oxidations. These include sulfoxidation of organophosphorus insecticides such as phorate and disulfoton, oxidative desulfuration of phosphonate insecticides such as fonofos and oxidation at the phosphorus atom in such compounds as the cotton defoliant, folex. The relative importance of the FAD-containing monooxygenase vis-a-vis the cytochrome P-450-dependent monooxygenase system is discussed, based on in vitro studies on purified enzymes. PMID:7161848
Free radicals: how do we stand them? Anaerobic and aerobic free radical (chain) reactions involved in the use of fluorogenic probes and in biological systems.
Liochev, Stefan I
Biologically significant conclusions have been based on the use of fluorogenic and luminogenic probes for the detection of reactive species. The basic mechanisms of the processes involved have not been satisfactorily elucidated. In the present work, the mechanism of the enzyme and photosensitized oxidation of NAD(P)H by resorufin is analyzed and appears to involve both aerobic and anaerobic free radical chain reactions. There are two major fallouts of this analysis. Many of the conclusions about the participation of radicals based on the use of probes such as resorufin and Amplex red need reevaluation. It is also concluded that anaerobic free radical reactions may be biologically significant, and the possible existence of enzymatic systems to eliminate certain free radicals is discussed. PMID:24356000
Chiral tetranuclear and dinuclear copper(ii) complexes for TEMPO-mediated aerobic oxidation of alcohols: are four metal centres better than two?
Zhang, Guoqi; Proni, Gloria; Zhao, Sherry; Constable, Edwin C; Housecroft, Catherine E; Neuburger, Markus; Zampese, Jennifer A
The one-pot reaction of 3,5-di-tert-butyl-2-hydroxybenzaldehyde, (R)-2-aminoglycinol and Cu(OAc)2·2H2O in a 1 : 1 : 1 ratio in the presence of triethylamine led to the isolation of X-ray quality crystals of the chiral complex (R)- in high yield. The single crystal structure of (R)- reveals a tetranuclear copper(ii) complex that contains a {Cu4(μ-O)2(μ3-O)2N4O4} core. A reaction using (1S,2R)-2-amino-1,2-diphenylethanol as precursor under the same conditions generated the chiral complex (S,R)-; its structure was determined by single crystal X-ray crystallography and was found to contain a {Cu2(μ-O)2N2O2} core. Both (R)- and (S,R)- have been used for catalytic aerobic oxidation of benzylic alcohols in combination with the TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) radical. (R)- selectively catalyses the conversion of various aromatic primary alcohols to the corresponding aldehydes with high yields (99%) and TONs (770) in the air, while (S,R)- exhibits less promising catalytic performance under the same reaction conditions. The role of the cluster structures in (R)- and (S,R)- in controlling the reactivity towards aerobic oxidation reactions is discussed. PMID:24986135
Oxidation-reduction processes in ice swimmers after ice-cold water bath and aerobic exercise.
Sutkowy, Paweł; Woźniak, Alina; Boraczyński, Tomasz; Boraczyński, Michał; Mila-Kierzenkowska, Celestyna
The effect of an ice-cold water (ICW) bath as a recovery intervention from aerobic exercise on the oxidant-antioxidant balance in healthy ice swimmers was determined. Twenty ice swimmers aged 31.2 ± 6.3 years performed a 30-min cycloergometer exercise test at room temperature (20°C, RT), followed by recovery at RT or in a pool of ice-cold water (ICW bath, 3°C, 5 min). Blood for laboratory assays was collected from the basilic vein two times: before the exercise (baseline) and 40 min after the RT or ICW recovery. The concentrations of plasma and erythrocytic thiobarbituric acid reactive substances (plTBARS and erTBARS, respectively), serum concentrations of 8-iso-prostaglandin F2α, 4-hydroxynonenal and malondialdehyde, along with the erythrocytic activities of catalase (CAT) and superoxide dismutase (SOD), as well as the serum level of total antioxidant capacity, were assessed. No statistically significant changes were observed. However, a statistically significant negative linear correlation between the erTBARS concentration and the SOD activity was found 40 min after the combination of exercise/RT recovery (r=-0.571, P<0.01). The baseline CAT and SOD activities were also linearly correlated (r=0.469, P<0.05). Both the 5-min ICW bath and the 30-min aerobic exercise have practically no impact on the oxidant-antioxidant balance in healthy ice swimmers. PMID:25910677
Surface reactions of several sulfur-containing molecules have been studied in order to understand the mechanism by which sulfate ions are formed on atmospheric aerosols. At 25C the heterogeneous oxidation of SO2 by NO2 to sulfuric acid and sulfate ions occurred on hydrated silica...
Antibacterial Action of Nitric Oxide-Releasing Chitosan Oligosaccharides against Pseudomonas aeruginosa under Aerobic and Anaerobic Conditions
Reighard, Katelyn P.
Chitosan oligosaccharides were modified with N-diazeniumdiolates to yield biocompatible nitric oxide (NO) donor scaffolds. The minimum bactericidal concentrations and MICs of the NO donors against Pseudomonas aeruginosa were compared under aerobic and anaerobic conditions. Differential antibacterial activities were primarily the result of NO scavenging by oxygen under aerobic environments and not changes in bacterial physiology. Bacterial killing was also tested against nonmucoid and mucoid biofilms and compared to that of tobramycin. Smaller NO payloads were required to eradicate P. aeruginosa biofilms under anaerobic versus aerobic conditions. Under oxygen-free environments, the NO treatment was 10-fold more effective at killing biofilms than tobramycin. These results demonstrate the potential utility of NO-releasing chitosan oligosaccharides under both aerobic and anaerobic environments. PMID:26239983
From ketones to esters by a Cu-catalyzed highly selective C(CO)-C(alkyl) bond cleavage: aerobic oxidation and oxygenation with air.
Huang, Xiaoqiang; Li, Xinyao; Zou, Miancheng; Song, Song; Tang, Conghui; Yuan, Yizhi; Jiao, Ning
The Cu-catalyzed aerobic oxidative esterification of simple ketones via C-C bond cleavage has been developed. Varieties of common ketones, even inactive aryl long-chain alkyl ketones, are selectively converted into esters. The reaction tolerates a wide range of alcohols, including primary and secondary alcohols, chiral alcohols with retention of the configuration, electron-deficient phenols, as well as various natural alcohols. The usage of inexpensive copper catalyst, broad substrate scope, and neutral and open air conditions make this protocol very practical. (18)O labeling experiments reveal that oxygenation occurs during this transformation. Preliminary mechanism studies indicate that two novel pathways are mainly involved in this process. PMID:25251943
Potential application of aerobic denitrifying bacterium Pseudomonas aeruginosa PCN-2 in nitrogen oxides (NOx) removal from flue gas.
Zheng, Maosheng; Li, Can; Liu, Shufeng; Gui, Mengyao; Ni, Jinren
Conventional biological removal of nitrogen oxides (NOx) from flue gas has been severely restricted by the presence of oxygen. This paper presents an efficient alternative for NOx removal at varying oxygen levels using the newly isolated bacterial strain Pseudomonas aeruginosa PCN-2 which was capable of aerobic and anoxic denitrification. Interestingly, nitric oxide (NO), as the obligatory intermediate, was negligibly accumulated during nitrate and nitrite reduction. Moreover, normal nitrate reduction with decreasing NO accumulation was realized under O2 concentration ranging from 0 to 100%. Reverse transcription and real-time quantitative polymerase chain reaction (RT-qPCR) analysis revealed that high efficient NO removal was attributed to the coordinate regulation of gene expressions including napA (for periplasmic nitrate reductase), nirS (for cytochrome cd1 nitrite reductase) and cnorB (for NO reductase). Further batch experiments demonstrated the immobilized strain PCN-2 possessed high capability of removing NO and nitrogen dioxide (NO2) at O2 concentration of 0-10%. A biotrickling filter established with present strain achieved high NOx removal efficiencies of 91.94-96.74% at inlet NO concentration of 100-500ppm and O2 concentration of 0-10%, which implied promising potential applications in purifying NOx contaminated flue gas. PMID:27469045
Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters
NASA Astrophysics Data System (ADS)
Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki
Understanding of the "structure-activity" relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au3+ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size.
Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters
Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki
Understanding of the "structure-activity" relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au3+ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size. PMID:27476577
Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters.
Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki
Understanding of the "structure-activity" relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au(3+) ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size. PMID:27476577
Aerobic addition of secondary phosphine oxides to vinyl sulfides: a shortcut to 1-hydroxy-2-(organosulfanyl)ethyl(diorganyl)phosphine oxides
Malysheva, Svetlana F; Artem'ev, Alexander V; Gusarova, Nina K; Belogorlova, Nataliya A; Albanov, Alexander I; Liu, C W
Summary Secondary phosphine oxides react with vinyl sulfides (both alkyl- and aryl-substituted sulfides) under aerobic and solvent-free conditions (80 °C, air, 7–30 h) to afford 1-hydroxy-2-(organosulfanyl)ethyl(diorganyl)phosphine oxides in 70–93% yields. PMID:26664618
Metabolic reprogramming during neuronal differentiation from aerobic glycolysis to neuronal oxidative phosphorylation
Zheng, Xinde; Boyer, Leah; Jin, Mingji; Mertens, Jerome; Kim, Yongsung; Ma, Li; Ma, Li; Hamm, Michael; Gage, Fred H; Hunter, Tony
How metabolism is reprogrammed during neuronal differentiation is unknown. We found that the loss of hexokinase (HK2) and lactate dehydrogenase (LDHA) expression, together with a switch in pyruvate kinase gene splicing from PKM2 to PKM1, marks the transition from aerobic glycolysis in neural progenitor cells (NPC) to neuronal oxidative phosphorylation. The protein levels of c-MYC and N-MYC, transcriptional activators of the HK2 and LDHA genes, decrease dramatically. Constitutive expression of HK2 and LDHA during differentiation leads to neuronal cell death, indicating that the shut-off aerobic glycolysis is essential for neuronal survival. The metabolic regulators PGC-1α and ERRγ increase significantly upon neuronal differentiation to sustain the transcription of metabolic and mitochondrial genes, whose levels are unchanged compared to NPCs, revealing distinct transcriptional regulation of metabolic genes in the proliferation and post-mitotic differentiation states. Mitochondrial mass increases proportionally with neuronal mass growth, indicating an unknown mechanism linking mitochondrial biogenesis to cell size. DOI: http://dx.doi.org/10.7554/eLife.13374.001 PMID:27282387
Impact of aerobic and anaerobic exercise training on oxidative stress and antioxidant defense in athletes
Park, Song-Young; Kwak, Yi-Sub
Exercise mediates an excessive free radical production leading to oxidative stress (OS). The body has natural antioxidant systems that help decrease OS, and these systems may be enhanced with exercise training. However, only a few studies have investigated the differences in resting OS and antioxidant capacity (AOC) between aerobically trained athletes (ET), anaerobically trained athletes (RT), and untrained individuals (UT). Therefore, this study sought to investigate the resting and postexercise OS and AOC in ET, RT, and UT. Sixty healthy young males (26.6±0.8 yr) participated in this study. Subjects were divided into three groups, ET, RT, and UT by distinct training background. Resting plasma malondialdehyde (MDA) and protein carbonyls (PC) were not significantly different in ET, RT, and UT. However, MDA and PC were significantly increased following a graded exercise test (GXT) in UT but not in ET and RT. Resting total antioxidant capacity (TAC) levels and TAC were not different in ET, RT, and UT. Interestingly, TAC levels significantly decreased after the GXT in all groups. Additionally, UT showed lower post-exercise TAC levels compared to ET and RT. These results showed that ET, RT, and UT have similar OS and AOC at rest. However, both ET and RT have greater AOC against exercise mediated OS compared to UT. These findings may explain, at least in part, why both aerobic and anaerobic types of exercise training improve redox balance. However, it appears there is no specific exercise type effect in terms of redox balance. PMID:27162773
Impact of aerobic and anaerobic exercise training on oxidative stress and antioxidant defense in athletes.
Park, Song-Young; Kwak, Yi-Sub
Exercise mediates an excessive free radical production leading to oxidative stress (OS). The body has natural antioxidant systems that help decrease OS, and these systems may be enhanced with exercise training. However, only a few studies have investigated the differences in resting OS and antioxidant capacity (AOC) between aerobically trained athletes (ET), anaerobically trained athletes (RT), and untrained individuals (UT). Therefore, this study sought to investigate the resting and postexercise OS and AOC in ET, RT, and UT. Sixty healthy young males (26.6±0.8 yr) participated in this study. Subjects were divided into three groups, ET, RT, and UT by distinct training background. Resting plasma malondialdehyde (MDA) and protein carbonyls (PC) were not significantly different in ET, RT, and UT. However, MDA and PC were significantly increased following a graded exercise test (GXT) in UT but not in ET and RT. Resting total antioxidant capacity (TAC) levels and TAC were not different in ET, RT, and UT. Interestingly, TAC levels significantly decreased after the GXT in all groups. Additionally, UT showed lower post-exercise TAC levels compared to ET and RT. These results showed that ET, RT, and UT have similar OS and AOC at rest. However, both ET and RT have greater AOC against exercise mediated OS compared to UT. These findings may explain, at least in part, why both aerobic and anaerobic types of exercise training improve redox balance. However, it appears there is no specific exercise type effect in terms of redox balance. PMID:27162773
Ammonia-oxidizing archaea use the most energy-efficient aerobic pathway for CO2 fixation.
Könneke, Martin; Schubert, Daniel M; Brown, Philip C; Hügler, Michael; Standfest, Sonja; Schwander, Thomas; Schada von Borzyskowski, Lennart; Erb, Tobias J; Stahl, David A; Berg, Ivan A
Archaea of the phylum Thaumarchaeota are among the most abundant prokaryotes on Earth and are widely distributed in marine, terrestrial, and geothermal environments. All studied Thaumarchaeota couple the oxidation of ammonia at extremely low concentrations with carbon fixation. As the predominant nitrifiers in the ocean and in various soils, ammonia-oxidizing archaea contribute significantly to the global nitrogen and carbon cycles. Here we provide biochemical evidence that thaumarchaeal ammonia oxidizers assimilate inorganic carbon via a modified version of the autotrophic hydroxypropionate/hydroxybutyrate cycle of Crenarchaeota that is far more energy efficient than any other aerobic autotrophic pathway. The identified genes of this cycle were found in the genomes of all sequenced representatives of the phylum Thaumarchaeota, indicating the environmental significance of this efficient CO2-fixation pathway. Comparative phylogenetic analysis of proteins of this pathway suggests that the hydroxypropionate/hydroxybutyrate cycle emerged independently in Crenarchaeota and Thaumarchaeota, thus supporting the hypothesis of an early evolutionary separation of both archaeal phyla. We conclude that high efficiency of anabolism exemplified by this autotrophic cycle perfectly suits the lifestyle of ammonia-oxidizing archaea, which thrive at a constantly low energy supply, thus offering a biochemical explanation for their ecological success in nutrient-limited environments. PMID:24843170
Ammonia-oxidizing archaea use the most energy-efficient aerobic pathway for CO2 fixation
Könneke, Martin; Schubert, Daniel M.; Brown, Philip C.; Hügler, Michael; Standfest, Sonja; Schwander, Thomas; Schada von Borzyskowski, Lennart; Erb, Tobias J.; Stahl, David A.; Berg, Ivan A.
Archaea of the phylum Thaumarchaeota are among the most abundant prokaryotes on Earth and are widely distributed in marine, terrestrial, and geothermal environments. All studied Thaumarchaeota couple the oxidation of ammonia at extremely low concentrations with carbon fixation. As the predominant nitrifiers in the ocean and in various soils, ammonia-oxidizing archaea contribute significantly to the global nitrogen and carbon cycles. Here we provide biochemical evidence that thaumarchaeal ammonia oxidizers assimilate inorganic carbon via a modified version of the autotrophic hydroxypropionate/hydroxybutyrate cycle of Crenarchaeota that is far more energy efficient than any other aerobic autotrophic pathway. The identified genes of this cycle were found in the genomes of all sequenced representatives of the phylum Thaumarchaeota, indicating the environmental significance of this efficient CO2-fixation pathway. Comparative phylogenetic analysis of proteins of this pathway suggests that the hydroxypropionate/hydroxybutyrate cycle emerged independently in Crenarchaeota and Thaumarchaeota, thus supporting the hypothesis of an early evolutionary separation of both archaeal phyla. We conclude that high efficiency of anabolism exemplified by this autotrophic cycle perfectly suits the lifestyle of ammonia-oxidizing archaea, which thrive at a constantly low energy supply, thus offering a biochemical explanation for their ecological success in nutrient-limited environments. PMID:24843170
Biochemical and Genetic Investigation of Initial Reactions in Aerobic Degradation of the Bile Acid Cholate in Pseudomonas sp. Strain Chol1▿
Birkenmaier, Antoinette; Holert, Johannes; Erdbrink, Henrike; Moeller, Heiko M.; Friemel, Anke; Schoenenberger, René; Suter, Marc J.-F.; Klebensberger, Janosch; Philipp, Bodo
Bile acids are surface-active steroid compounds with toxic effects for bacteria. Recently, the isolation and characterization of a bacterium, Pseudomonas sp. strain Chol1, growing with bile acids as the carbon and energy source was reported. In this study, initial reactions of the aerobic degradation pathway for the bile acid cholate were investigated on the biochemical and genetic level in strain Chol1. These reactions comprised A-ring oxidation, activation with coenzyme A (CoA), and β-oxidation of the acyl side chain with the C19-steroid dihydroxyandrostadienedione as the end product. A-ring oxidizing enzyme activities leading to Δ1,4-3-ketocholyl-CoA were detected in cell extracts and confirmed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Cholate activation with CoA was demonstrated in cell extracts and confirmed with a chemically synthesized standard by LC-MS/MS. A transposon mutant with a block in oxidation of the acyl side chain accumulated a steroid compound in culture supernatants which was identified as 7α,12α-dihydroxy-3-oxopregna-1,4-diene-20-carboxylate (DHOPDC) by nuclear magnetic resonance spectroscopy. The interrupted gene was identified as encoding a putative acyl-CoA-dehydrogenase (ACAD). DHOPDC activation with CoA in cell extracts of strain Chol1 was detected by LC-MS/MS. The growth defect of the transposon mutant could be complemented by the wild-type ACAD gene located on the plasmid pBBR1MCS-5. Based on these results, the initiating reactions of the cholate degradation pathway leading from cholate to dihydroxyandrostadienedione could be reconstructed. In addition, the first bacterial gene encoding an enzyme for a specific reaction step in side chain degradation of steroid compounds was identified, and it showed a high degree of similarity to genes in other steroid-degrading bacteria. PMID:17693490
A template-free solvent-mediated synthesis of high surface area boron nitride nanosheets for aerobic oxidative desulfurization.
Wu, Peiwen; Zhu, Wenshuai; Chao, Yanhong; Zhang, Jinshui; Zhang, Pengfei; Zhu, Huiyuan; Li, Changfeng; Chen, Zhigang; Li, Huaming; Dai, Sheng
Hexagonal boron nitride nanosheets (h-BNNs) with rather high specific surface area (SSA) are important two-dimensional layer-structured materials. Here, a solvent-mediated synthesis of h-BNNs revealed a template-free lattice plane control strategy that induced high SSA nanoporous structured h-BNNs with outstanding aerobic oxidative desulfurization performance. PMID:26502800
Soluble porous coordination polymers by mechanochemistry: from metal-containing films/membranes to active catalysts for aerobic oxidation.
Zhang, Pengfei; Li, Haiying; Veith, Gabriel M; Dai, Sheng
Soluble porous coordination polymers from mechanochemical synthesis are presented through a coordination polymerization between highly contorted, rigid tetraphenol and a broad variety of transition metal ions. These polymers can be easily cast as metal-containing films or freestanding membranes. Importantly, as-made coordination polymers are highly active and stable in the aerobic oxidation of allylic C-H bonds. PMID:25389070
The effect of aerobic exercise on hepatotoxicity induced by intratracheal instillation of iron oxide nanoparticles in Wistar rats.
Vasili, Azadeh; Sharifi, Gholamreza; Faramarzi, Mohammad; Noori, Ali; Yazdanshenas, Shora
Iron oxide nanoparticles (IONPs) can cause significant health problems due to their unique physicochemical properties and environmental characteristics. They are found as ultrafine particles in ambient air. After inhalation, these particles move from the lung to phagocytosis tissues, especially the liver. The aim of present study was to investigate the effect of concurrent aerobic exercise and IONPs on liver enzymes and histological hepatic appearance. 48 rats were divided into six groups: experimental 1 (aerobic exercise), experimental 2 (nanoparticle, anesthesia), experimental 3 (aerobic exercise, nanoparticles, anesthesia), placebo 4 (distilled water, anesthesia), placebo 5 (aerobic exercise, anesthesia), and control group. In groups 2 and 3, 40 mg/kg/b.w. of IONPs was injected via intratracheal installation every other day for 14 days. Groups 1, 3, and 5 [corrected] run on treadmill for 30 minutes with the intensity of 35-40% VO2max (maximal oxygen consumption) every day. ALT was increased in group 1 but decreased in groups 2 and 3. AST was not significant in any of the groups, while ALP was reduced significantly in groups 2 and 3 (p < 0.05). Histological examination of the liver showed that, in groups 2 and 3, hepatic cells were damaged and also the congestion, inflammation, mononuclear cell infiltration, and ballooning degeneration were occurred. Tissue injuries in group 3 were less than those of group 2. These findings indicated that hepatotoxicity was caused by iron oxide nanoparticles; however, low-intensity aerobic exercise could decrease the damage somewhat. PMID:26492071
Aerobic and Anaerobic Thiosulfate Oxidation by a Cold-Adapted, Subglacial Chemoautotroph.
Harrold, Zoë R; Skidmore, Mark L; Hamilton, Trinity L; Desch, Libby; Amada, Kirina; van Gelder, Will; Glover, Kevin; Roden, Eric E; Boyd, Eric S
Geochemical data indicate that protons released during pyrite (FeS2) oxidation are important drivers of mineral weathering in oxic and anoxic zones of many aquatic environments, including those beneath glaciers. Oxidation of FeS2 under oxic, circumneutral conditions proceeds through the metastable intermediate thiosulfate (S2O3 (2-)), which represents an electron donor capable of supporting microbial metabolism. Subglacial meltwaters sampled from Robertson Glacier (RG), Canada, over a seasonal melt cycle revealed concentrations of S2O3 (2-) that were typically below the limit of detection, despite the presence of available pyrite and concentrations of the FeS2 oxidation product sulfate (SO4 (2-)) several orders of magnitude higher than those of S2O3 (2-). Here we report on the physiological and genomic characterization of the chemolithoautotrophic facultative anaerobe Thiobacillus sp. strain RG5 isolated from the subglacial environment at RG. The RG5 genome encodes genes involved with pathways for the complete oxidation of S2O3 (2-), CO2 fixation, and aerobic and anaerobic respiration with nitrite or nitrate. Growth experiments indicated that the energy required to synthesize a cell under oxygen- or nitrate-reducing conditions with S2O3 (2-) as the electron donor was lower at 5.1°C than 14.4°C, indicating that this organism is cold adapted. RG sediment-associated transcripts of soxB, which encodes a component of the S2O3 (2-)-oxidizing complex, were closely affiliated with soxB from RG5. Collectively, these results suggest an active sulfur cycle in the subglacial environment at RG mediated in part by populations closely affiliated with RG5. The consumption of S2O3 (2-) by RG5-like populations may accelerate abiotic FeS2 oxidation, thereby enhancing mineral weathering in the subglacial environment. PMID:26712544
Aerobic and Anaerobic Thiosulfate Oxidation by a Cold-Adapted, Subglacial Chemoautotroph
Harrold, Zoë R.; Skidmore, Mark L.; Hamilton, Trinity L.; Desch, Libby; Amada, Kirina; van Gelder, Will; Glover, Kevin; Roden, Eric E.
Geochemical data indicate that protons released during pyrite (FeS2) oxidation are important drivers of mineral weathering in oxic and anoxic zones of many aquatic environments, including those beneath glaciers. Oxidation of FeS2 under oxic, circumneutral conditions proceeds through the metastable intermediate thiosulfate (S2O32−), which represents an electron donor capable of supporting microbial metabolism. Subglacial meltwaters sampled from Robertson Glacier (RG), Canada, over a seasonal melt cycle revealed concentrations of S2O32− that were typically below the limit of detection, despite the presence of available pyrite and concentrations of the FeS2 oxidation product sulfate (SO42−) several orders of magnitude higher than those of S2O32−. Here we report on the physiological and genomic characterization of the chemolithoautotrophic facultative anaerobe Thiobacillus sp. strain RG5 isolated from the subglacial environment at RG. The RG5 genome encodes genes involved with pathways for the complete oxidation of S2O32−, CO2 fixation, and aerobic and anaerobic respiration with nitrite or nitrate. Growth experiments indicated that the energy required to synthesize a cell under oxygen- or nitrate-reducing conditions with S2O32− as the electron donor was lower at 5.1°C than 14.4°C, indicating that this organism is cold adapted. RG sediment-associated transcripts of soxB, which encodes a component of the S2O32−-oxidizing complex, were closely affiliated with soxB from RG5. Collectively, these results suggest an active sulfur cycle in the subglacial environment at RG mediated in part by populations closely affiliated with RG5. The consumption of S2O32− by RG5-like populations may accelerate abiotic FeS2 oxidation, thereby enhancing mineral weathering in the subglacial environment. PMID:26712544
Iron Catalysis for Room-Temperature Aerobic Oxidation of Alcohols to Carboxylic Acids.
Jiang, Xingguo; Zhang, Jiasheng; Ma, Shengming
Oxidation from alcohols to carboxylic acids, a class of essential chemicals in daily life, academic laboratories, and industry, is a fundamental reaction, usually using at least a stoichiometric amount of an expensive and toxic oxidant. Here, an efficient and practical sustainable oxidation technology of alcohols to carboxylic acids using pure O2 or even O2 in air as the oxidant has been developed: utilizing a catalytic amount each of Fe(NO3)3·9H2O/TEMPO/MCl, a series of carboxylic acids were obtained from alcohols (also aldehydes) in high yields at room temperature. A 55 g-scale reaction was demonstrated using air. As a synthetic application, the first total synthesis of a naturally occurring allene, i.e., phlomic acid, was accomplished. PMID:27304226
Oxidative stability of pork emulsion containing tomato products and pink guava pulp during refrigerated aerobic storage.
Joseph, Serlene; Chatli, Manish K; Biswas, Ashim K; Sahoo, Jhari
Lipid oxidation-induced quality problems can be minimized with the use of natural antioxidants. Antioxidant potential of tomato puree (10 %; T-1), tomato pulp (12.5 %; T-2), lyophilized tomato peel (6 %; T-3), and pink guava pulp (10 %; T-4) was evaluated in raw pork emulsion during refrigerated storage for 9 days under aerobic packaging. The lycopene and β-carotene content varied in pork emulsion as T-3 > T-1 > T-2 > T-4 and decreased (P < 0.05) during storage. The surface redness (a* value) increased (P < 0.05) with the incorporation of tomato products and pink guava pulp. Furthermore, metmyoglobin formation and lipid oxidation were lower (P < 0.05) in tomato- and guava-treated emulsions than in control. Overall, incorporation of tomato products and pink guava pulp improved the visual colour and odour scores of raw pork emulsion. These results indicated that tomato products and guava pulp can be utilized as sources of natural antioxidants in raw pork products to minimize lipid oxidation, off-odour development, and surface discolouration. PMID:26396313
Copper-catalyzed domino synthesis of quinazolinones via Ullmann-type coupling and aerobic oxidative C-H amidation.
Xu, Wei; Jin, Yibao; Liu, Hongxia; Jiang, Yuyang; Fu, Hua
An efficient copper-catalyzed approach to quinazolinone derivatives has been developed, and the protocol uses cheap and readily available substituted 2-halobenzamides and (aryl)methanamines as the starting materials as well as economical and environmentally friendly air as the oxidant. This can be the first example of constructing N-heterocycles via sequential Ullmann-type coupling under air and aerobic oxidative C-H amidation. PMID:21344914
Aerobic oxidation of lignin models using a base metal vanadium catalyst.
Hanson, Susan K; Baker, R Tom; Gordon, John C; Scott, Brian L; Thorn, David L
Dipicolinate vanadium(V) complexes oxidize lignin model complexes pinacol monomethyl ether (A), 2-phenoxyethanol (B), 1-phenyl-2-phenoxyethanol (C), and 1,2-diphenyl-2-methoxyethanol (D). With substrates having C-H bonds adjacent to the alcohol moiety (B-D), the C-H bond is broken in pyridine-d(5) solvent, yielding 2-phenoxyacetaldehyde from B, 2-phenoxyacetophenone from C, and benzoin methyl ether from D. In DMSO-d(6) solvent the reaction is slower, and both C-H and C-C bond cleavage products are observed for D. The vanadium(IV) products of these reactions have been identified and characterized. Catalytic oxidation of C and D has been demonstrated using air and (dipic)V(O)O(i)Pr. For both substrates, the C-C bond between the alcohol and ether groups is broken in the catalytic oxidation. 1-Phenyl-2-phenoxyethanol is oxidized to a mixture of phenol, formic acid, benzoic acid, and 2-methoxyacetophenone. The products of oxidation of 1,2-diphenyl-2-methoxyethanol depend on the solvent; in DMSO benzaldehyde and methanol are the major products, while benzoic acid and methyl benzoate are the major products obtained in pyridine solvent. Phenyl substituents on the model complex facilitate the oxidation, with relative rates of oxidation D > C > B. PMID:20491453
Aerobic training prevents oxidative profile and improves nitric oxide and vascular reactivity in rats with cardiometabolic alteration.
Medeiros, Renata F; Gaique, Thaiane G; Bento-Bernardes, Thais; Motta, Nádia A V; Brito, Fernanda C F; Fernandes-Santos, Caroline; Castro-Pinheiro, Camila; Oliveira, Karen J; Nóbrega, Antonio C L
Cardiovascular disease is the major cause of death worldwide; therefore it is important to understand the natural history of the pathophysiologic process and develop strategies to halt its progression. Thus this study investigated the protective effect of aerobic training on pathophysiological mechanisms involved in subclinical cardiometabolic alterations in a model with constant exposure to a prejudicial agent. Male Wistar rats were divided into a control group (C), which received drinking water, fructose group (F), which was fed 10% fructose in drinking water for 10 wk, and control training (CT) and fructose training groups (FT), in which moderate aerobic training was added in the last 8 wk of the study. Insulin, triacylglycerol, and isoprostane were higher and superoxide dismutase (SOD) was lower in the F group. There was no difference in thoracic aorta histology, but a decreased vascularization was seen in the F group, avoided by training in left ventricle. Regarding vascular function, the F group exhibited increased vasoconstrictory reactivity to phenylephrine. The F group presented impaired vasodilation to acetylcholine. Regarding endothelial nitric oxide synthase (eNOS), the F group presented a lower expression, and phosphorylated eNOS was higher in the trained groups than in their respective control groups. This same pattern was observed for nitric oxide bioavailability, antioxidant protein expression in aorta, left ventricle, and muscle (catalase, SOD, and glutathione peroxidase), serum SOD activity, and muscle mass. These results suggest that exercise training enhanced the antioxidant pathway and, as a consequence, the eNOS pathway, preventing an impairment in vascular vasodilatory capacity. PMID:27255525
Microbiology and potential applications of aerobic methane oxidation coupled to denitrification (AME-D) process: A review.
Zhu, Jing; Wang, Qian; Yuan, Mengdong; Tan, Giin-Yu Amy; Sun, Faqian; Wang, Cheng; Wu, Weixiang; Lee, Po-Heng
Aerobic methane oxidation coupled to denitrification (AME-D) is an important link between the global methane and nitrogen cycles. This mini-review updates discoveries regarding aerobic methanotrophs and denitrifiers, as a prelude to spotlight the microbial mechanism and the potential applications of AME-D. Until recently, AME-D was thought to be accomplished by a microbial consortium where denitrifying bacteria utilize carbon intermediates, which are excreted by aerobic methanotrophs, as energy and carbon sources. Potential carbon intermediates include methanol, citrate and acetate. This mini-review presents microbial thermodynamic estimations and postulates that methanol is the ideal electron donor for denitrification, and may serve as a trophic link between methanotrophic bacteria and denitrifiers. More excitingly, new discoveries have revealed that AME-D is not only confined to the conventional synergism between methanotrophic bacteria and denitrifiers. Specifically, an obligate aerobic methanotrophic bacterium, Methylomonas denitrificans FJG1, has been demonstrated to couple partial denitrification with methane oxidation, under hypoxia conditions, releasing nitrous oxide as a terminal product. This finding not only substantially advances the understanding of AME-D mechanism, but also implies an important but unknown role of aerobic methanotrophs in global climate change through their influence on both the methane and nitrogen cycles in ecosystems. Hence, further investigation on AME-D microbiology and mechanism is essential to better understand global climate issues and to develop niche biotechnological solutions. This mini-review also presents traditional microbial techniques, such as pure cultivation and stable isotope probing, and powerful microbial techniques, such as (meta-) genomics and (meta-) transcriptomics, for deciphering linked methane oxidation and denitrification. Although AME-D has immense potential for nitrogen removal from wastewater, drinking
Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review
Melone, Lucio
Summary Since the beginning of the century, N-hydroxyphthalimide and related compounds have been revealed to be efficient organocatalysts for free-radical processes and have found ample application in promoting the aerobic oxidation of a wide range of organic substrates. When combined with different co-catalysts, they are activated to the corresponding N-oxyl radical species and become able to promote radical chains, involving molecular oxygen, directly or indirectly. Most of the examples reported in the literature describe the use of these N-hydroxy derivatives in the presence of transition-metal complexes. However, eco-friendly standards, including the demand for highly selective transformations, impose the development of metal-free processes, especially for large-scale productions, as in the case of the oxygenation of hydrocarbons. For this reason, many efforts have been devoted in the past decade to the design of new protocols for the activation of N-hydroxy imides in the presence of nonmetal initiators. Herein we provide a concise overview of the most significant and successful examples in this field, with the final aim to furnish a useful instrument for all scientists actively involved in the O2-mediated selective oxidation of organic compounds and looking for environmentally safe alternatives to metal catalysis. PMID:23843925
Heterogeneous reaction of ozone with aluminum oxide
NASA Technical Reports Server (NTRS)
Keyser, L. F.
Rates and collision efficiencies for ozone decomposition on aluminum oxide surfaces were determined. Samples were characterized by BET surface area, X-ray diffraction, particle size, and chemical analysis. Collision efficiencies were found to be between 2 times 10 to the -10 power and 2 times 10 to the -9 power. This is many orders of magnitude below the value of 0.000001 to 0.00001 needed for appreciable long-term ozone loss in the stratosphere. An activation energy of 7.2 kcal/mole was found for the heterogeneous reaction between -40 C and 40 C. Effects of pore diffusion, outgassing and treatment of the aluminum oxide with several chemical species were also investigated.
Techno-economic evaluation of the application of ozone-oxidation in a full-scale aerobic digestion plant.
Chiavola, Agostina; D'Amato, Emilio; Gori, Riccardo; Lubello, Claudio; Sirini, Piero
This paper deals with the application of the ozone-oxidation in a full scale aerobic sludge digester. Ozonation was applied continuously to a fraction of the biological sludge extracted from the digestion unit; the ozonated sludge was then recirculated to the same digester. Three different ozone flow rates were tested (60,500 and 670g O3 h(-1)) and their effects evaluated in terms of variation of the total and soluble fractions of COD, nitrogen and phosphorous, of total and volatile suspended solids concentrations and Sludge Volume Index in the aerobic digestion unit. During the 7-month operation of the ozonation process, it was observed an appreciable improvement of the aerobic digestion efficiency (up to about 20% under the optimal conditions) and of the sludge settleability properties. These results determined an average reduction of about 60% in the biological sludge extracted from the plant and delivered to final disposal. A thorough economic analysis showed that this reduction allowed to achieve a significant cost saving for the plant with respect to the previous years operated without ozonation. Furthermore, it was determined the threshold disposal cost above which implementation of the ozone oxidation in the aerobic digestion units of similar WWTPs becomes economically convenient (about 60€t(-1) of sludge). PMID:23384542
Effect of electrochemical redox reaction on biochemical ammonium oxidation and chemical nitrite oxidation.
Jeon, Bo Young; Seo, Ha Na; Kang, Seung Won; Park, Doo Hyun
A modified graphite felt electrode with neutral red (NRelectrode) was shown to catalyze the chemical oxidation of nitrite to nitrate under aerobic conditions. The electrochemically oxidized NR-electrode (EO-NR-electrode) and reduced NR-electrode (ER-NR-electrode) catalyzed the oxidation of 1,094+/-39 mg/l and 382+/-45 mg/l of nitrite, respectively, for 24 h. The electrically uncharged NRelectrode (EU-NR-electrode) catalyzed the oxidation of 345+/-47 mg/l of nitrite for 24 h. The aerobic bacterial community immobilized in the EO-NR-electrode did not oxidize ammonium to nitrite; however, the aerobic bacterial community immobilized in the ER-NR-electrode bioelectrochemically oxidized 1,412+/-39 mg/l of ammonium for 48 h. Meanwhile, the aerobic bacterial community immobilized on the EU-NR-electrode biochemically oxidized 449+/-22 mg/l of ammonium for 48 h. In the continuous culture system, the aerobic bacterial community immobilized on the ER-NR-electrode bioelectrochemically oxidized a minimal 1,337+/-38 mg/l to a maximal 1,480+/-38 mg/l of ammonium to nitrate, and the community immobilized on the EU-NR-electrode biochemically oxidized a minimal 327+/-23 mg/l to a maximal 412+/-26 mg/l of ammonium to nitrate every two days. The bacterial communities cultivated in the ER-NR-electrode and EU-NR-electrode in the continuous culture system were analyzed by TGGE on the 20th and 50th days of incubation. Some ammoniumoxidizing bacteria were enriched on the ER-NR-electrode, but not on the EU-NR-electrode. PMID:20372016
Plutonium Oxidation State Distribution under Aerobic and Anaerobic Subsurface Conditions for Metal-Reducing Bacteria
NASA Astrophysics Data System (ADS)
Reed, D. T.; Swanson, J.; Khaing, H.; Deo, R.; Rittmann, B.
The fate and potential mobility of plutonium in the subsurface is receiving increased attention as the DOE looks to cleanup the many legacy nuclear waste sites and associated subsurface contamination. Plutonium is the near-surface contaminant of concern at several DOE sites and continues to be the contaminant of concern for the permanent disposal of nuclear waste. The mobility of plutonium is highly dependent on its redox distribution at its contamination source and along its potential migration pathways. This redox distribution is often controlled, especially in the near-surface where organic/inorganic contaminants often coexist, by the direct and indirect effects of microbial activity. The redox distribution of plutonium in the presence of facultative metal reducing bacteria (specifically Shewanella and Geobacter species) was established in a concurrent experimental and modeling study under aerobic and anaerobic conditions. Pu(VI), although relatively soluble under oxidizing conditions at near-neutral pH, does not persist under a wide range of the oxic and anoxic conditions investigated in microbiologically active systems. Pu(V) complexes, which exhibit high chemical toxicity towards microorganisms, are relatively stable under oxic conditions but are reduced by metal reducing bacteria under anaerobic conditions. These facultative metal-reducing bacteria led to the rapid reduction of higher valent plutonium to form Pu(III/IV) species depending on nature of the starting plutonium species and chelating agents present in solution. Redox cycling of these lower oxidation states is likely a critical step in the formation of pseudo colloids that may lead to long-range subsurface transport. The CCBATCH biogeochemical model is used to explain the redox mechanisms and final speciation of the plutonium oxidation state distributions observed. These results for microbiologically active systems are interpreted in the context of their importance in defining the overall migration
C3N4-H5PMo10V2O40: a dual-catalysis system for reductant-free aerobic oxidation of benzene to phenol
Long, Zhouyang; Zhou, Yu; Chen, Guojian; Ge, Weilin; Wang, Jun
Hydroxylation of benzene is a widely studied atom economical and environmental benign reaction for producing phenol, aiming to replace the existing three-step cumene process. Aerobic oxidation of benzene with O2 is an ideal and dream process, but benzene and O2 are so inert that current systems either require expensive noble metal catalysts or wasteful sacrificial reducing agents; otherwise, phenol yields are extremely low. Here we report a dual-catalysis non-noble metal system by simultaneously using graphitic carbon nitride (C3N4) and Keggin-type polyoxometalate H5PMo10V2O40 (PMoV2) as catalysts, showing an exceptional activity for reductant-free aerobic oxidation of benzene to phenol. The dual-catalysis mechanism results in an unusual route to create phenol, in which benzene is activated on the melem unit of C3N4 and O2 by the V-O-V structure of PMoV2. This system is simple, highly efficient and thus may lead the one-step production of phenol from benzene to a more practical pathway. PMID:24413448
Remediation of a winery wastewater combining aerobic biological oxidation and electrochemical advanced oxidation processes.
Moreira, Francisca C; Boaventura, Rui A R; Brillas, Enric; Vilar, Vítor J P
Apart from a high biodegradable fraction consisting of organic acids, sugars and alcohols, winery wastewaters exhibit a recalcitrant fraction containing high-molecular-weight compounds as polyphenols, tannins and lignins. In this context, a winery wastewater was firstly subjected to a biological oxidation to mineralize the biodegradable fraction and afterwards an electrochemical advanced oxidation process (EAOP) was applied in order to mineralize the refractory molecules or transform them into simpler ones that can be further biodegraded. The biological oxidation led to above 97% removals of dissolved organic carbon (DOC), chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD5), but was inefficient on the degradation of a bioresistant fraction corresponding to 130 mg L(-1) of DOC, 380 mg O2 L(-1) of COD and 8.2 mg caffeic acid equivalent L(-1) of total dissolved polyphenols. Various EAOPs such as anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), UVA photoelectro-Fenton (PEF) and solar PEF (SPEF) were then applied to the recalcitrant effluent fraction using a 2.2 L lab-scale flow plant containing an electrochemical cell equipped with a boron-doped diamond (BDD) anode and a carbon-PTFE air-diffusion cathode and coupled to a photoreactor with compound parabolic collectors (CPCs). The influence of initial Fe(2+) concentration and current density on the PEF process was evaluated. The relative oxidative ability of EAOPs increased in the order AO-H2O2 < EF < PEF ≤ SPEF. The SPEF process using an initial Fe(2+) concentration of 35 mg L(-1), current density of 25 mA cm(-2), pH of 2.8 and 25 °C reached removals of 86% on DOC and 68% on COD after 240 min, regarding the biologically treated effluent, along with energy consumptions of 45 kWh (kg DOC)(-1) and 5.1 kWh m(-3). After this coupled treatment, color, odor, COD, BOD5, NH4(+), NO3(-) and SO4(2-) parameters complied with the legislation targets and, in addition, a total
Selective aerobic oxidation of HMF to 2,5-diformylfuran on covalent triazine frameworks-supported Ru catalysts.
Artz, Jens; Mallmann, Sabrina; Palkovits, Regina
The selective aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran has been performed under mild conditions at 80 °C and 20 bar of synthetic air in methyl t-butyl ether. Ru clusters supported on covalent triazine frameworks (CTFs) allowed excellent selectivity and superior catalytic activity compared to other support materials such as activated carbon, γ-Al2 O3 , hydrotalcite, or MgO. CTFs with varying pore size, specific surface area, and N content could be prepared from different monomers. The structural properties of the CTF materials influence the catalytic activity of Ru/CTF significantly in the aerobic oxidation of HMF, which emphasizes the superior activity of mesoporous CTFs. Recycling of the catalysts is challenging, but promising methods to maintain high catalytic activity were developed that facilitate only minor deactivation in five consecutive recycling experiments. PMID:25586312
[Enhanced Resistance of Pea Plants to Oxidative: Stress Caused by Paraquat during Colonization by Aerobic Methylobacteria].
Agafonova, N V; Doronina, N Y; Trotsenko, Yu A
The influence of colonization of the pea (Pisum sativum L.) by aerobic methylobacteria of five different species (Methylophilus flavus Ship, Methylobacterium extorquens G10, Methylobacillus arboreus Iva, Methylopila musalis MUSA, Methylopila turkiensis Sidel) on plant resistance to paraquat-induced stresses has been studied. The normal conditions of pea colonization by methylobacteria were characterized by a decrease in the activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidases) and in the concentrations of endogenous H2O2, proline, and malonic dialdehyde, which is a product of lipid peroxidation and indicator of damage to plant cell membranes, and an increase in the activity of the photosynthetic apparatus (the content of chlorophylls a, b and carotenoids). In the presence of paraquat, the colonized plants had higher activities of antioxidant enzymes, stable photosynthetic indices, and a less intensive accumulation of the products of lipid peroxidation as compared to noncolonized plants. Thus, colonization by methylobacteria considerably increased the adaptive protection of pea plants to the paraquat-induced oxidative stress. PMID:27266250
Central release of nitric oxide mediates antinociception induced by aerobic exercise.
Galdino, G S; Duarte, I D; Perez, A C
Nitric oxide (NO) is a soluble gas that participates in important functions of the central nervous system, such as cognitive function, maintenance of synaptic plasticity for the control of sleep, appetite, body temperature, neurosecretion, and antinociception. Furthermore, during exercise large amounts of NO are released that contribute to maintaining body homeostasis. Besides NO production, physical exercise has been shown to induce antinociception. Thus, the present study aimed to investigate the central involvement of NO in exercise-induced antinociception. In both mechanical and thermal nociceptive tests, central [intrathecal (it) and intracerebroventricular (icv)] pretreatment with inhibitors of the NO/cGMP/KATP pathway (L-NOArg, ODQ, and glybenclamide) prevented the antinociceptive effect induced by aerobic exercise (AE). Furthermore, pretreatment (it, icv) with specific NO synthase inhibitors (L-NIO, aminoguanidine, and L-NPA) also prevented this effect. Supporting the hypothesis of the central involvement of NO in exercise-induced antinociception, nitrite levels in the cerebrospinal fluid increased immediately after AE. Therefore, the present study suggests that, during exercise, the NO released centrally induced antinociception. PMID:25517916
Rh- and Cu-Cocatalyzed Aerobic Oxidative Approach to Quinazolines via [4 + 2] C-H Annulation with Alkyl Azides.
Wang, Xiaoyang; Jiao, Ning
A novel and efficient rhodium- and copper-co-catalyzed C-H bond activation and annulation for the construction of bioactively important quinazolines has been developed. This [4 + 2] annulation strategy utilizing alkyl azides as the carbon-heteroatom synthons shows high efficiency in the synthesis of six-membered benzoheterocycles containing two heteroatoms. This aerobic oxidative protocol provides a useful application of simple alkyl azides in N-heterocycle synthesis with N2 and H2O as byproducts. PMID:27081916
Aerobic nitrous oxide production through N-nitrosating hybrid formation in ammonia-oxidizing archaea.
Stieglmeier, Michaela; Mooshammer, Maria; Kitzler, Barbara; Wanek, Wolfgang; Zechmeister-Boltenstern, Sophie; Richter, Andreas; Schleper, Christa
Soil emissions are largely responsible for the increase of the potent greenhouse gas nitrous oxide (N2O) in the atmosphere and are generally attributed to the activity of nitrifying and denitrifying bacteria. However, the contribution of the recently discovered ammonia-oxidizing archaea (AOA) to N2O production from soil is unclear as is the mechanism by which they produce it. Here we investigate the potential of Nitrososphaera viennensis, the first pure culture of AOA from soil, to produce N2O and compare its activity with that of a marine AOA and an ammonia-oxidizing bacterium (AOB) from soil. N. viennensis produced N2O at a maximum yield of 0.09% N2O per molecule of nitrite under oxic growth conditions. N2O production rates of 4.6±0.6 amol N2O cell(-1) h(-1) and nitrification rates of 2.6±0.5 fmol NO2(-) cell(-1) h(-1) were in the same range as those of the AOB Nitrosospira multiformis and the marine AOA Nitrosopumilus maritimus grown under comparable conditions. In contrast to AOB, however, N2O production of the two archaeal strains did not increase when the oxygen concentration was reduced, suggesting that they are not capable of denitrification. In (15)N-labeling experiments we provide evidence that both ammonium and nitrite contribute equally via hybrid N2O formation to the N2O produced by N. viennensis under all conditions tested. Our results suggest that archaea may contribute to N2O production in terrestrial ecosystems, however, they are not capable of nitrifier-denitrification and thus do not produce increasing amounts of the greenhouse gas when oxygen becomes limiting. PMID:24401864
Copper(II)-Mediated Aerobic Oxidation of Benzylimidates: Synthesis of Primary α-Ketoamides.
Kumar, Yogesh; Shaw, Mukta; Thakur, Rima; Kumar, Amit
A simple and straightforward method for the synthesis of primary α-ketoamides has been discovered. The reaction represents the first example of benzylimidates directly converting to primary α-ketoamides by using sustainable molecular oxygen as an oxidant. This reaction proceeds in the presence of copper(II) salt via cleavage of benzylic C-H and C-O bonds of the benzylimidates with liberation of alcohols as the only byproduct. A wide substrate scope, operationally mild conditions, the use of single substrates, and a reaction scaled up to grams make this strategy very attractive and practical. Furthermore, mechanistic studies illustrate that the imidate group adjacent to the benzylic position plays crucial role in facilitating this chemical process. PMID:27347744
Fan, Xingjun; Sell, David R; Zhang, Jianye; Nemet, Ina; Theves, Mathilde; Lu, Jie; Strauch, Christopher; Halushka, Marc K.; Monnier, Vincent M.
The effects of anaerobic (lens) vs aerobic (skin) environment on carbonyl and oxidant stress are compared using de novo and existing data on advanced glycation and oxidation products in human crystallins and collagen. Almost all modifications increase with age. Methylglyoxal hydroimidazolones (MG-H1), carboxymethyl-lysine (CML), and carboxyethyl-lysine (CEL) are several folds higher in lens than skin, and markedly increase upon incubation of lens crystallins with 5 mM ascorbic acid. Vice-versa, fructose-lysine, glucosepane crosslinks, glyoxal hydroimidazolones (G-H1), metal catalyzed oxidation (allysine) and H2O2 dependent modifications (2-aminoapidic acid and methionine sulfoxide) are markedly elevated in skin, but relatively suppressed in the aging lens. In both tissues ornithine is the dominant modification, implicating arginine residues as the principal target of the Maillard reaction in vivo. Diabetes (here mostly type 2 studied) increases significantly fructose-lysine and glucosepane in both tissues (P<0.001) but has surprisingly little effect on the absolute level of most other advanced glycation end products (AGEs) . However, diabetes strengthens the Spearman correlation coefficients for age-related accumulation of hydrogen peroxide mediated modifications in the lens. Overall, the data suggest oxoaldehyde stress involving methylglyoxal from either glucose or ascorbate is predominant in the aging non-cataractous lens, while aging skin collagen undergoes combined attack by non-oxidative glucose mediated modifications, as well as those from metal catalyzed oxidation and H2O2. PMID:20541005
Diversity and abundance of aerobic and anaerobic methane oxidizers at the Haakon Mosby Mud Volcano, Barents Sea.
Lösekann, Tina; Knittel, Katrin; Nadalig, Thierry; Fuchs, Bernhard; Niemann, Helge; Boetius, Antje; Amann, Rudolf
Submarine mud volcanoes are formed by expulsions of mud, fluids, and gases from deeply buried subsurface sources. They are highly reduced benthic habitats and often associated with intensive methane seepage. In this study, the microbial diversity and community structure in methane-rich sediments of the Haakon Mosby Mud Volcano (HMMV) were investigated by comparative sequence analysis of 16S rRNA genes and fluorescence in situ hybridization. In the active volcano center, which has a diameter of about 500 m, the main methane-consuming process was bacterial aerobic oxidation. In this zone, aerobic methanotrophs belonging to three bacterial clades closely affiliated with Methylobacter and Methylophaga species accounted for 56%+/-8% of total cells. In sediments below Beggiatoa mats encircling the center of the HMMV, methanotrophic archaea of the ANME-3 clade dominated the zone of anaerobic methane oxidation. ANME-3 archaea form cell aggregates mostly associated with sulfate-reducing bacteria of the Desulfobulbus (DBB) branch. These ANME-3/DBB aggregates were highly abundant and accounted for up to 94%+/-2% of total microbial biomass at 2 to 3 cm below the surface. ANME-3/DBB aggregates could be further enriched by flow cytometry to identify their phylogenetic relationships. At the outer rim of the mud volcano, the seafloor was colonized by tubeworms (Siboglinidae, formerly known as Pogonophora). Here, both aerobic and anaerobic methane oxidizers were found, however, in lower abundances. The level of microbial diversity at this site was higher than that at the central and Beggiatoa species-covered part of the HMMV. Analysis of methyl-coenzyme M-reductase alpha subunit (mcrA) genes showed a strong dominance of a novel lineage, mcrA group f, which could be assigned to ANME-3 archaea. Our results further support the hypothesis of Niemann et al. (54), that high methane availability and different fluid flow regimens at the HMMV provide distinct niches for aerobic and
N-Heterocyclic Carbene Complexes in Oxidation Reactions
NASA Astrophysics Data System (ADS)
Jurčík, Václav; Cazin, Catherine S. J.
This chapter describes applications of N-heterocyclic carbenes (NHCs) in oxidation chemistry. The strong σ-donation capabilities of the NHCs allow an efficient stabilisation of metal centres in high oxidation states, while high metal-NHC bond dissociation energies suppress their oxidative decomposition. These properties make NHCs ideal ligands for oxidation processes. The first part of this chapter is dedicated to the reactivity of NHC-metal complexes towards molecular oxygen whilst the second half highlights all oxidation reactions catalysed by such complexes. These include oxidation of alcohols and olefins, oxidative cyclisations, hydrations of alkynes and nitriles, oxidative cleavage of alkenes and the oxidation of methane.
Gold-catalyzed homogeneous oxidative cross-coupling reactions.
Zhang, Guozhu; Peng, Yu; Cui, Li; Zhang, Liming
Oxidizing gold? A gold(I)/gold(III) catalytic cycle is essential for the first oxidative cross-coupling reaction in gold catalysis. By using Selectfluor for gold(I) oxidation, this chemistry reveals the synthetic potential of incorporating gold(I)/gold(III) catalytic cycles into contemporary gold chemistry and promises a new area of gold research by merging powerful gold catalysis and oxidative metal-catalyzed cross-coupling reactions. PMID:19322869
Copper-Catalyzed Oxidative Heck Reactions between Alkyltrifluoroborates and Vinylarenes
Liwosz, Timothy W.; Chemler, Sherry R.
We report herein that potassium alkyltrifluoroborates can be utilized in oxidative Heck-type reactions with vinyl arenes. The reaction is catalyzed by a Cu(OTf)2/1,10-phenanthroline with MnO2 as the stoichiometric oxidant. In addition to the alkyl Heck, amination, esterification and dimerization reactions of alkyltrifluoroborates are demonstrated under analogous reaction conditions. Evidence for an alkyl radical intermediate is presented. PMID:23734764
QuadraPure-Supported Palladium Nanocatalysts for Microwave-Promoted Suzuki Cross-Coupling Reaction under Aerobic Condition
Loh, Poh Lee; Juan, Joon Ching; Yarmo, Mohd Ambar; Yusop, Rahimi M.
Cross-linked resin-captured palladium (XL-QPPd) was readily prepared by simple physical adsorption onto the high loading QuadraPure macroporous resin and a subsequent reduction process. To enhance the mechanical stability, entrapped palladium nanocatalysts were cross-linked with succinyl chloride. Both transmission electron microscopy images and X-ray diffraction analysis revealed that the palladium nanoparticles were well dispersed with diameters ranging in 4–10 nm. The catalyst performed good catalytic activity in microwave-promoted Suzuki cross-coupling reactions in water under aerobic condition with mild condition by using various aryl halides and phenylboronic acid. In addition, the catalyst showed an excellent recyclability without significant loss of catalytic activity. PMID:25054185
Six weeks of aerobic dance exercise improves blood oxidative stress status and increases interleukin-2 in previously sedentary women.
Leelarungrayub, Donrawee; Saidee, Kunteera; Pothongsunun, Prapas; Pratanaphon, Sainetee; YanKai, Araya; Bloomer, Richard J
This study evaluated the change in blood oxidative stress, blood interleukin-2, and physical performance following 6 weeks of moderate intensity and duration aerobic dance exercise in 24 sedentary women. Blood samples were collected at rest twice before (baseline) and after the 6-week intervention for analysis of protein hydroperoxide (PrOOH), malondialdehyde (MDA), total anti-oxidant capacity (TAC), and interleukin-2 (IL-2) levels. Maximal treadmill run time (Time(max)) and maximal oxygen consumption (VO(2max)) were also measured. All variables were statistically analyzed with a repeated measurement ANOVA and Tukey post hoc. No differences were noted in any variable during the baseline period (p > 0.05). After aerobic dance exercise, VO(2max), Time(max), TAC and IL-2 were significantly increased, whereas MDA levels were decreased significantly (p < 0.05). PrOOH did not change either between baseline measures or after exercise. It can be concluded that aerobic dance exercise at a moderate intensity and duration can improve physical fitness, decrease MDA, and increase TAC and IL-2 in previously sedentary women. PMID:21665113
Catalytic Amine Oxidation under Ambient Aerobic Conditions: Mimicry of Monoamine Oxidase B.
Murray, Alexander T; Dowley, Myles J H; Pradaux-Caggiano, Fabienne; Baldansuren, Amgalanbaatar; Fielding, Alistair J; Tuna, Floriana; Hendon, Christopher H; Walsh, Aron; Lloyd-Jones, Guy C; John, Matthew P; Carbery, David R
The flavoenzyme monoamine oxidase (MAO) regulates mammalian behavioral patterns by modulating neurotransmitters such as adrenaline and serotonin. The mechanistic basis which underpins this enzyme is far from agreed upon. Reported herein is that the combination of a synthetic flavin and alloxan generates a catalyst system which facilitates biomimetic amine oxidation. Mechanistic and electron paramagnetic (EPR) spectroscopic data supports the conclusion that the reaction proceeds through a radical manifold. This data provides the first example of a biorelevant synthetic model for monoamine oxidase B activity. PMID:26087676
Wet aerobic oxidation of lignin into aromatic aldehydes catalysed by a perovskite-type oxide: LaFe(1-x)Cu(x)O3 (x=0, 0.1, 0.2).
Zhang, Junhua; Deng, Haibo; Lin, Lu
The perovskite-type oxide catalyst LaFe(1-x)Cu(x)O(3 )(x=0, 0.1, 0.2) was prepared by the sol-gel method, and tested as a catalyst in the wet aerobic oxidation (WAO) of lignin into aromatic aldehydes. The lignin conversion and the yield of each aromatic aldehyde were significantly enhanced in the catalytic process, compared with the non-catalyzed process. Moreover, it was shown that the stability of activity and structure of LaFe(1-x)Cu(x)O(3 )(x=0, 0.1, 0.2) remained nearly unchanged after a series of successive recyclings of the catalytic reactions, indicating it was an efficient and recyclable heterogeneous catalyst for the conversion of lignin into aromatic aldehydes in the WAO process. PMID:19701121
Anaerobic vs aerobic pathways of carbonyl and oxidant stress in human lens and skin during aging and in diabetes: A comparative analysis.
Fan, Xingjun; Sell, David R; Zhang, Jianye; Nemet, Ina; Theves, Mathilde; Lu, Jie; Strauch, Christopher; Halushka, Marc K; Monnier, Vincent M
The effects of anaerobic (lens) vs aerobic (skin) environment on carbonyl and oxidant stress are compared using de novo and existing data on advanced glycation and oxidation products in human crystallins and collagen. Almost all modifications increase with age. Methylglyoxal hydroimidazolones, carboxymethyllysine, and carboxyethyllysine are severalfold higher in lens than in skin and markedly increase upon incubation of lens crystallins with 5mM ascorbic acid. In contrast, fructose-lysine, glucosepane crosslinks, glyoxal hydroimidazolones, metal-catalyzed oxidation (allysine), and H(2)O(2)-dependent modifications (2-aminoapidic acid and methionine sulfoxide) are markedly elevated in skin, but relatively suppressed in the aging lens. In both tissues ornithine is the dominant modification, implicating arginine residues as the principal target of the Maillard reaction in vivo. Diabetes (here mostly type 2 studied) increases significantly fructose-lysine and glucosepane in both tissues (P<0.001) but has surprisingly little effect on the absolute level of most other advanced glycation end products. However, diabetes strengthens the Spearman correlation coefficients for age-related accumulation of hydrogen peroxide-mediated modifications in the lens. Overall, the data suggest that oxoaldehyde stress involving methylglyoxal from either glucose or ascorbate is predominant in the aging noncataractous lens, whereas aging skin collagen undergoes combined attack by nonoxidative glucose-mediated modifications, as well as those from metal-catalyzed oxidation and H(2)O(2). PMID:20541005
Whole-Genome Transcriptional Analysis of Chemolithoautotrophic Thiosulfate Oxidation by Thiobacillus denitrificans Under Aerobic vs. Denitrifying Conditions
Beller, H R; Letain, T E; Chakicherla, A; Kane, S R; Legler, T C; Coleman, M A
Thiobacillus denitrificans is one of the few known obligate chemolithoautotrophic bacteria capable of energetically coupling thiosulfate oxidation to denitrification as well as aerobic respiration. As very little is known about the differential expression of genes associated with ke chemolithoautotrophic functions (such as sulfur-compound oxidation and CO2 fixation) under aerobic versus denitrifying conditions, we conducted whole-genome, cDNA microarray studies to explore this topic systematically. The microarrays identified 277 genes (approximately ten percent of the genome) as differentially expressed using Robust Multi-array Average statistical analysis and a 2-fold cutoff. Genes upregulated (ca. 6- to 150-fold) under aerobic conditions included a cluster of genes associated with iron acquisition (e.g., siderophore-related genes), a cluster of cytochrome cbb3 oxidase genes, cbbL and cbbS (encoding the large and small subunits of form I ribulose 1,5-bisphosphate carboxylase/oxygenase, or RubisCO), and multiple molecular chaperone genes. Genes upregulated (ca. 4- to 95-fold) under denitrifying conditions included nar, nir, and nor genes (associated respectively with nitrate reductase, nitrite reductase, and nitric oxide reductase, which catalyze successive steps of denitrification), cbbM (encoding form II RubisCO), and genes involved with sulfur-compound oxidation (including two physically separated but highly similar copies of sulfide:quinone oxidoreductase and of dsrC, associated with dissimilatory sulfite reductase). Among genes associated with denitrification, relative expression levels (i.e., degree of upregulation with nitrate) tended to decrease in the order nar > nir > nor > nos. Reverse transcription, quantitative PCR analysis was used to validate these trends.
Development and Comparison of the Substrate Scope of Pd-Catalysts for the Aerobic Oxidation of Alcohols
Schultz, Mitchell J.; Hamilton, Steven S.; Jensen, David R.; Sigman, Matthew S.
Three catalysts for aerobic oxidation of alcohols are discussed and the effectiveness of each is evaluated for allylic, benzylic, aliphatic, and functionalized alcohols. Additionally, chiral nonracemic substrates as well as chemoselective and diastereoselective oxidations are investigated. In this study, the most convenient system for the Pd-catalyzed aerobic oxidation of alcohols is Pd(OAc)2 in combination with triethylamine. This system functions effectively for the majority of alcohols tested and uses mild conditions (3 to 5 mol % of catalyst, room temperature). Pd(IiPr)(OAc)2(H2O) (1) also successfully oxidizes the majority of alcohols evaluated. This system has the advantage of significantly lowering catalyst loadings but requires higher temperatures (0.1 to 1 mol % of catalyst, 60 °C). A new catalyst is also disclosed, Pd(IiPr)(OPiv)2 (2). This catalyst operates under very mild conditions (1 mol %, room temperature, and air as the O2 source) but with a more limited substrate scope. PMID:15844968
Chiral N-salicylidene vanadyl carboxylate-catalyzed enantioselective aerobic oxidation of α-hydroxy esters and amides
Weng, Shiue-Shien; Shen, Mei-Wen; Kao, Jun-Qi; Munot, Yogesh S.; Chen, Chien-Tien
A series of chiral vanadyl carboxylates derived from N-salicylidene-l-α-amino acids and vanadyl sulfate has been developed. These configurationally well defined complexes were examined for the kinetic resolution of double- and mono-activated 2° alcohols. The best chiral templates involve the combination of l-tert-leucine and 3,5-di-t-butyl-, 3,5-diphenyl-, or 3,4-dibromo-salicylaldehyde. The resulting vanadyl(V)-methoxide complexes after recrystallization from air-saturated methanol serve as highly enantioselective catalysts for asymmetric aerobic oxidation of α-hydroxyl-esters and amides with a diverse array of α-, O-, and N-substituents at ambient temperature in toluene. The asymmetric inductions of the oxidation process are in the range of 10 to >100 in terms of selectivity factors (krel) in most instances. The previously undescribed aerobic oxidation protocol is also applicable to the kinetic resolution of C-13 taxol side chain with high selectivity factor (krel = 35). X-ray crystallographic analysis of an adduct between a given vanadyl complex and N-benzyl-mandelamide allows for probing the stereochemical origin of the nearly exclusive asymmetric control in the oxidation process. PMID:16501046
A comparative study of silver-graphene oxide nanocomposites as a recyclable catalyst for the aerobic oxidation of benzyl alcohol: Support effect
NASA Astrophysics Data System (ADS)
Zahed, Bahareh; Hosseini-Monfared, Hassan
Three different nanocomposites of silver and graphene oxide, namely silver nanoparticles (AgNPs) immobilized on reduced graphene oxide (AgNPs/rGO), partially reduced graphene oxide (AgNPs/GO) and thiolated partially reduced graphene oxide (AgNPs/GOSH), were synthesized in order to compare their properties. Characterizations were carried out by infrared and UV-Vis and Raman spectroscopy, ICP, X-ray diffraction, SEM and TEM, confirming both the targeted chemical modification and the composite formation. The nanocomposites were successfully employed in the aerobic oxidation of benzyl alcohol at atmospheric pressure. AgNPs/GOSH is stable and recyclable catalyst which showed the highest activity in the aerobic oxidation of benzyl alcohol in the presence of N-hydroxyphthalimide (NHPI) to give benzaldehyde with 58% selectivity in 24 h at 61% conversion. The favorite properties of AgNPs/GOSH are reasonably attributed to the stable and well distributed AgNPs over GOSH due to strong adhesion between AgNPs and GOSH.
Complete Genome Sequence of the Aerobic CO-Oxidizing Thermophile Thermomicrobium roseum
Wu, Dongying; Raymond, Jason; Wu, Martin; Chatterji, Sourav; Ren, Qinghu; Graham, Joel E.; Bryant, Donald A.; Robb, Frank; Colman, Albert; Tallon, Luke J.; Badger, Jonathan H.; Madupu, Ramana; Ward, Naomi L.; Eisen, Jonathan A.
In order to enrich the phylogenetic diversity represented in the available sequenced bacterial genomes and as part of an "Assembling the Tree of Life" project, we determined the genome sequence of Thermomicrobium roseum DSM 5159. T. roseum DSM 5159 is a red-pigmented, rod-shaped, Gram-negative extreme thermophile isolated from a hot spring that possesses both an atypical cell wall composition and an unusual cell membrane that is composed entirely of long-chain 1,2-diols. Its genome is composed of two circular DNA elements, one of 2,006,217 bp (referred to as the chromosome) and one of 919,596 bp (referred to as the megaplasmid). Strikingly, though few standard housekeeping genes are found on the megaplasmid, it does encode a complete system for chemotaxis including both chemosensory components and an entire flagellar apparatus. This is the first known example of a complete flagellar system being encoded on a plasmid and suggests a straightforward means for lateral transfer of flagellum-based motility. Phylogenomic analyses support the recent rRNA-based analyses that led to T. roseum being removed from the phylum Thermomicrobia and assigned to the phylum Chloroflexi. Because T. roseum is a deep-branching member of this phylum, analysis of its genome provides insights into the evolution of the Chloroflexi. In addition, even though this species is not photosynthetic, analysis of the genome provides some insight into the origins of photosynthesis in the Chloroflexi. Metabolic pathway reconstructions and experimental studies revealed new aspects of the biology of this species. For example, we present evidence that T. roseum oxidizes CO aerobically, making it the first thermophile known to do so. In addition, we propose that glycosylation of its carotenoids plays a crucial role in the adaptation of the cell membrane to this bacterium's thermophilic lifestyle. Analyses of published metagenomic sequences from two hot springs similar to the one from which this strain
Oxidation and Reduction Reactions in Organic Chemistry
ERIC Educational Resources Information Center
Shibley, Ivan A., Jr.; Amaral, Katie E.; Aurentz, David J.; McCaully, Ronald J.
A variety of approaches to the concept of oxidation and reduction appear in organic textbooks. The method proposed here is different than most published approaches. The oxidation state is calculated by totaling the number of heterogeneous atoms, [pi]-bonds, and rings. A comparison of the oxidation states of reactant and product determine what type…
Stable TEMPO and ABNO Catalyst Solutions for User-Friendly (bpy)Cu/Nitroxyl-Catalyzed Aerobic Alcohol Oxidation.
Steves, Janelle E; Stahl, Shannon S
Two solutions, one consisting of bpy/TEMPO/NMI and the other bpy/ABNO/NMI (bpy =2,2'-bipyridyl; TEMPO = 2,2,6,6-tetramethylpiperidine N-oxyl, ABNO = 9-azabicyclo[3.3.1]nonane N-oxyl; NMI = N-methylimidazole), in acetonitrile are shown to have good long-term stability (≥1 year) under air at 5 °C. The solutions may be combined in appropriate quantities with commercially available [Cu(MeCN)4]OTf to provide a convenient catalyst system for the aerobic oxidation of primary and secondary alcohols. PMID:26457658
Experimental Limiting Oxygen Concentrations for Nine Organic Solvents at Temperatures and Pressures Relevant to Aerobic Oxidations in the Pharmaceutical Industry
Applications of aerobic oxidation methods in pharmaceutical manufacturing are limited in part because mixtures of oxygen gas and organic solvents often create the potential for a flammable atmosphere. To address this issue, limiting oxygen concentration (LOC) values, which define the minimum partial pressure of oxygen that supports a combustible mixture, have been measured for nine commonly used organic solvents at elevated temperatures and pressures. The solvents include acetic acid, N-methylpyrrolidone, dimethyl sulfoxide, tert-amyl alcohol, ethyl acetate, 2-methyltetrahydrofuran, methanol, acetonitrile, and toluene. The data obtained from these studies help define safe operating conditions for the use of oxygen with organic solvents. PMID:26622165
Water oxidation reaction in natural and artificial photosynthetic systems
Yano, Junko; Yachandra, Vittal
Understanding the structure and mechanism of water oxidation catalysts is an essential component for developing artificial photosynthetic devices. In the natural water oxidation catalyst, the geometric and electronic structure of its inorganic core, the Mn{sub 4}CaO{sub 5} cluster, has been studied by spectroscopic and diffraction measurements. In inorganic systems, metal oxides seem to be good candidates for water oxidation catalysts. Understanding the reaction mechanism in both natural and oxide-based catalysts will helpin further developing efficient and robust water oxidation catalysts.
Aerobic oxidation of anthracene in the presence of manganese porphyrinates and NaBH/sub 4/ reducing agent
Lukashova, E.A.; Solov'ev, A.B.; Chugreev, A.L.; Enikolopyan, N.S.
The authors investigate the kinetics of anthracene oxidation by molecular oxygen in the presence of manganese, iron, and cobalt porphyrinate catalysts and a sodium borohydride reducing agent at room temperature in solutions of ethanol or ethanol with chloroform and benzene. Effective rate constants for the reactions are determined based on the amount of anthraquinone formed in the reaction. In all cases with the exception of cobalt tetraphenylporphyrinate the only oxidation product was anthraquinone. Its structure was verified by NMR and IR spectroscopy.
Design of Highly Selective Platinum Nanoparticle Catalysts for the Aerobic Oxidation of KA-Oil using Continuous-Flow Chemistry.
Gill, Arran M; Hinde, Christopher S; Leary, Rowan K; Potter, Matthew E; Jouve, Andrea; Wells, Peter P; Midgley, Paul A; Thomas, John M; Raja, Robert
Highly active and selective aerobic oxidation of KA-oil to cyclohexanone (precursor for adipic acid and ɛ-caprolactam) has been achieved in high yields using continuous-flow chemistry by utilizing uncapped noble-metal (Au, Pt & Pd) nanoparticle catalysts. These are prepared using a one-step in situ methodology, within three-dimensional porous molecular architectures, to afford robust heterogeneous catalysts. Detailed spectroscopic characterization of the nature of the active sites at the molecular level, coupled with aberration-corrected scanning transmission electron microscopy, reveals that the synthetic methodology and associated activation procedures play a vital role in regulating the morphology, shape and size of the metal nanoparticles. These active centers have a profound influence on the activation of molecular oxygen for selective catalytic oxidations. PMID:26833972
Iodine Oxide Thermite Reactions: Physical and Biological Effects
NASA Astrophysics Data System (ADS)
Russell, Rod; Pantoya, Michelle; Bless, Stephan; Clark, William
We investigated the potential for some thermite-like material reactions to kill bacteria spores. Iodine oxides and silver oxides react vigorously with metals like aluminum, tantalum, and neodymium. These reactions theoretically produce temperatures as high as 8000K, leading to vaporization of the reactants, producing very hot iodine and/or silver gases. We performed a series of computations and experiments to characterize these reactions under both quasi-static and ballistic impact conditions. Criteria for impact reaction were established. Measurements of temperature and pressure changes and chemical evolution will be reported. Basic combustion characterizations of these reactions, such as thermal equilibrium analysis and reaction propagation rates as well as ignition sensitivity, will be discussed. Additionally, testing protocols were developed to characterize the biocidal effects of these reactive materials on B. subtilis spores. The evidence from these tests indicates that these reactions produce heat, pressure, and highly biocidal gases.
Uranium oxidation: Characterization of oxides formed by reaction with water by infrared and sorption analyses
NASA Astrophysics Data System (ADS)
Fuller, E. L.; Smyrl, N. R.; Condon, J. B.; Eager, M. H.
Three different uranium oxide samples have been characterized with respect to the different preparation techniques. The results show that the water reaction with uranium metal occurs cyclically forming laminar layers of oxide which spall off due to the strain at the oxide/metal interface. Single laminae are released if liquid water is present due to the prizing penetration at the reaction zone. The rate of reaction of water with uranium is directly proportional to the amount of adsorbed water on the oxide product. Rapid transport is effected through the open hydrous oxide product. Dehydration of the hydrous oxide irreversibly forms a more inert oxide which cannot be rehydrated to the degree that prevails in the original hydrous product of uranium oxidation with water. Inert gas sorption analyses and diffuse reflectance infrared studies combined with electron microscopy prove valuable in defining the chemistry and morphology of the oxidic products and hydrated intermediates.
Oxidant-free dehydrogenative coupling reactions via hydrogen evolution.
He, Ke-Han; Li, Yang
Oxidant-free dehydrogenative coupling reactions: Recently, coupling reactions have followed a novel strategy for the construction of C==C, C==N, C==P, and S==S bonds by dehydrogenation without using any extra oxidant, via H2 evolution. These breakthroughs inspire a new direction in the construction of chemical bonds, towards more sustainable, highly atom-economical, and environmentally benign synthetic methods. PMID:25139249
A ground water treatment process is proposed involving two cgemical processes: adsorption and oxidation. Adsorption of an organic compound onto granulated activated carbon (GAC) containing iron conveniently results in immobilizing and concentrating contaminants from the ground w...
The pathophysiology of extracellular hemoglobin associated with enhanced oxidative reactions
Rifkind, Joseph M.; Mohanty, Joy G.; Nagababu, Enika
Hemoglobin (Hb) continuously undergoes autoxidation producing superoxide which dismutates into hydrogen peroxide (H2O2) and is a potential source for subsequent oxidative reactions. Autoxidation is most pronounced under hypoxic conditions in the microcirculation and for unstable dimers formed at reduced Hb concentrations. In the red blood cell (RBC), oxidative reactions are inhibited by an extensive antioxidant system. For extracellular Hb, whether from hemolysis of RBCs and/or the infusion of Hb-based blood substitutes, the oxidative reactions are not completely neutralized by the available antioxidant system. Un-neutralized H2O2 oxidizes ferrous and ferric Hbs to Fe(IV)-ferrylHb and OxyferrylHb, respectively. FerrylHb further reacts with H2O2 producing heme degradation products and free iron. OxyferrylHb, in addition to Fe(IV) contains a free radical that can undergo additional oxidative reactions. Fe(III)Hb produced during Hb autoxidation also readily releases heme, an additional source for oxidative stress. These oxidation products are a potential source for oxidative reactions in the plasma, but to a greater extent when the lower molecular weight Hb dimers are taken up into cells and tissues. Heme and oxyferryl have been shown to have a proinflammatory effect further increasing their potential for oxidative stress. These oxidative reactions contribute to a number of pathological situations including atherosclerosis, kidney malfunction, sickle cell disease, and malaria. The toxic effects of extracellular Hb are of particular concern with hemolytic anemia where there is an increase in hemolysis. Hemolysis is further exacerbated in various diseases and their treatments. Blood transfusions are required whenever there is an appreciable decrease in RBCs due to hemolysis or blood loss. It is, therefore, essential that the transfused blood, whether stored RBCs or the blood obtained by an Autologous Blood Recovery System from the patient, do not further increase
Metal-Organic Frameworks as Catalysts for Oxidation Reactions.
Dhakshinamoorthy, Amarajothi; Asiri, Abdullah M; Garcia, Hermenegildo
This Concept is aimed at describing the current state of the art in metal-organic frameworks (MOFs) as heterogeneous catalysts for liquid-phase oxidations, focusing on three important substrates, namely, alkenes, alkanes and alcohols. Emphases are on the nature of active sites that have been incorporated within MOFs and on future targets to be set in this area. Thus, selective alkene epoxidation with peroxides or oxygen catalyzed by constitutional metal nodes of MOFs as active sites are still to be developed. Moreover, no noble metal-free MOF has been reported to date that can act as a general catalyst for the aerobic oxidation of primary and secondary aliphatic alcohols. In contrast, in the case of alkanes, a target should be to tune the polarity of MOF internal pores to control the outcome of the autooxidation process, resulting in the selective formation of alcohol/ketone mixtures at high conversion. PMID:27113486
High temperature heterogeneous reaction kinetics and mechanisms of tungsten oxidation
NASA Astrophysics Data System (ADS)
Sabourin, Justin L.
Tungsten, which is a material used in many high temperature applications, is limited by its susceptibility to oxidation at elevated temperatures. Although tungsten has the highest melting temperature of any metal, at much lower temperatures volatile oxides are formed during oxidation with oxygen containing species. This differs from many heterogeneous oxidation reactions involving metals since most reactions form very stable oxides that have higher melting or boiling points than the pure metal (e.g., aluminum, iron). Understanding heterogeneous oxidation and vaporization processes may allow for the expansion and improvement of high temperature tungsten applications. In order to increase understanding of the oxidation processes of tungsten, there is a need to develop reaction mechanisms and kinetics for oxidation processes involving oxidizers and environmental conditions of interest. Tungsten oxidation was thoroughly studied in the past, and today there is a good phenomenological understanding of these processes. However, as the design of large scale systems increasingly relies on computer modeling there becomes a need for improved descriptions of chemical reactions. With the increase in computing power over the last several decades, and the development of quantum chemistry and physics theories, heterogeneous systems can be modeled in detail at the molecular level. Thermochemical parameters that may not be measured experimentally may now be determined theoretically, a tool that was previously unavailable to scientists and engineers. Additionally, chemical kinetic modeling software is now available for both homogeneous and heterogeneous reactions. This study takes advantage of these new theoretical tools, as well as a thermogravimetric (TG) flow reactor developed as part of this study to learn about mechanisms and kinetics of tungsten oxidation. Oxidizers of interest are oxygen (O2), carbon dioxide (CO 2), water (H2O), and other oxidizers present in combustion and
Copper-catalyzed aerobic oxidative transformation of ketone-derived N-tosyl hydrazones: an entry to alkynes.
Li, Xianwei; Liu, Xiaohang; Chen, Huoji; Wu, Wanqing; Qi, Chaorong; Jiang, Huanfeng
A novel strategy involving Cu-catalyzed oxidative transformation of ketone-derived hydrazone moiety to various synthetic valuable internal alkynes and diynes has been developed. This method features inexpensive metal catalyst, green oxidant, good functional group tolerance, high regioselectivity and readily available starting materials. Oxidative deprotonation reactions were carried out to form internal alkynes and symmetrical diynes. Cross-coupling reactions of hydrazones with halides and terminal alkynes were performed to afford functionalized alkynes and unsymmetrical conjugated diynes. A mechanism proceeding through a Cu-carbene intermediate is proposed for the CC triple bond formation. PMID:25424976
Isotopomeric characterization of nitrous oxide produced by reaction of enzymes extracted from nitrifying and denitrifying bacteria
NASA Astrophysics Data System (ADS)
Yamazaki, T.; Hozuki, T.; Arai, K.; Toyoda, S.; Koba, K.; Fujiwara, T.; Yoshida, N.
Nitrous oxide (N2O) is a potent greenhouse gas and produced in denitrification and nitrification by various microorganisms. Site preference (SP) of 15N in N2O, which is defined as the difference in the natural abundance of isotopomers 14N15NO and 15N14NO relative to 14N14NO, has been reported to be a useful tool to quantitatively distinguish N2O production pathways. To determine representative SP values for each microbial process, we firstly measured SP of N2O produced in the enzyme reaction of hydroxylamine oxidoreductase (HAO) purified from two species of ammonia oxidizing bacteria (AOB), Nitrosomonas europaea and Nitrosococcus oceani, and that of nitric oxide reductase (NOR) from Paracoccus denitrificans. The SP value for NOR reaction (-5.9 ± 2.1‰) showed nearly the same value as that reported for N2O produced by P. denitrificans in pure culture. In contrast, SP value for HAO reaction (36.3 ± 2.3‰) was a little higher than the values reported for N2O produced by AOB in aerobic pure culture. Using the SP values obtained by HAO and NOR reactions, we calculated relative contribution of the nitrite (NO2-) reduction (which is followed by NO reduction) to N2O production by N. oceani incubated under different O2 availability. Our calculations revealed that previous in vivo studies might have underestimated the SP value for the NH2OH oxidation pathway possibly due to a small contribution of NO2- reduction pathway. Further evaluation of isotopomer signatures of N2O using common enzymes of other processes related to N2O would improve the isotopomer analysis of N2O in various environments.
Isotopomeric characterization of nitrous oxide produced by reaction of enzymes extracted from nitrifying and denitrifying bacteria
NASA Astrophysics Data System (ADS)
Yamazaki, T.; Hozuki, T.; Arai, K.; Toyoda, S.; Koba, K.; Fujiwara, T.; Yoshida, N.
Nitrous oxide (N2O) is a potent greenhouse gas and produced in denitrification and nitrification in environmental nitrogen cycle by various microorganism. Site preference (SP) of 15N in N2O, which is defined as the difference in the natural abundance of isotopomers 14N15NO and 15N14NO relative to 14N14NO, has been reported to be a useful tool to quantitatively distinguish N2O production pathway. To determine representative SP value for each microbial process, we firstly measured SP of N2O produced in the enzyme reaction of hydroxylamine oxidoreductase (HAO) purified from two species of ammonia oxidizing bacteria (AOB), Nitrosomonas europaea and Nitrosococcus oceani, and that of nitric oxide reductase (NOR) from Paracoccus denitrificans, respectively. The SP value for NOR reaction (-5.9 ± 2.1‰) showed nearly the same value as that reported for N2O produced by P. denitrificans in pure culture. In contrast, SP value for HAO reaction (36.3 ± 2.3‰) was a little higher than the values reported for N2O produced by AOB in aerobic pure culture. Using the SP values obtained by HAO and NOR reactions, we calculated relative contribution of the nitrite (NO2-) reduction (which is followed by NO reduction) to N2O production by N. oceani incubated under different O2 availability. Our calculations revealed that previous in vivo studies might have underestimated the SP value for NH2OH oxidation pathway possibly due to a small contribution of NO2- reduction pathway. Further evaluation of isotopomer signatures of N2O using common enzymes of other processes related to N2O would improve the isotopomer analysis of N2O in various environments.
The Effect of Metal Oxide on Nanoparticles from Thermite Reactions
ERIC Educational Resources Information Center
Moore, Lewis Ryan
The purpose of this research was to determine how metal oxide used in a thermite reaction can impact the production of nanoparticles. The results showed the presence of nanoparticles (less than 1 micron in diameter) of at least one type produced by each metal oxide. The typical particles were metallic spheres, which ranged from 300 nanometers in…
Divergent role of nitric oxide in insulin-stimulated aortic vasorelaxation between low- and high-intrinsic aerobic capacity rats.
Crissey, Jacqueline M; Padilla, Jaume; Vieira-Potter, Victoria J; Thorne, Pamela K; Koch, Lauren G; Britton, Steven L; Thyfault, John P; Laughlin, M Harold
Low-intrinsic aerobic capacity is associated with increased risk for cardiovascular and metabolic diseases and is a strong predictor of early mortality. The effects of intrinsic aerobic capacity on the vascular response to insulin are largely unknown. We tested the hypothesis that rats selectively bred for a low capacity to run (LCR) exhibit vascular dysfunction and impaired vascular reactivity to insulin compared to high capacity running (HCR) rats. Mature female LCR (n = 21) and HCR (n = 17) rats were maintained under sedentary conditions, and in vitro thoracic aortic vascular function was assessed. LCR exhibited greater body mass (13%), body fat (35%), and subcutaneous, perigonadal, and retroperitoneal adipose tissue mass, than HCR. During an intraperitoneal glucose tolerance test, glucose area under the curve (AUC) was not different but insulin AUC was 2-fold greater in LCR than HCR. Acetylcholine and insulin-stimulated aortic vasorelaxation was significantly greater in LCR (65.2 ± 3.8%, and 32.7 ± 4.1%) than HCR (55.0 ± 3.3%, and 16.7 ± 2.8%). Inhibition of nitric oxide synthase (NOS) with L-NAME entirely abolished insulin-mediated vasorelaxation in the aorta of LCR, with no effect in HCR. LCR rats exhibited greater expression of Insulin Receptor protein, lower Endothelin Receptor-A protein, a down-regulation of transcripts for markers of immune cell infiltration (CD11C, CD4, and F4/80) and up-regulation of pro-atherogenic inflammatory genes (VCAM-1 and MCP-1) in the aorta wall. Contrary to our hypothesis, low-aerobic capacity was associated with enhanced aortic endothelial function and NO-mediated reactivity to insulin, despite increased adiposity and evidence of whole body insulin resistance. PMID:26197933
A study was conducted to identify the specific organic reaction products of natural aquatic humic materials with selected oxidants (KMnO4, HOCl, Cl02, O3 and monochloramine). Reaction products were identified by GC/MS after solvent extraction and derivatization. The two most reac...
Ultrafine MnO2 nanoparticles decorated on graphene oxide as a highly efficient and recyclable catalyst for aerobic oxidation of benzyl alcohol.
Hu, Zonggao; Zhao, Yafei; Liu, Jindun; Wang, Jingtao; Zhang, Bing; Xiang, Xu
The highly active and selective aerobic oxidation of aromatic alcohols over earth-abundant, inexpensive and recyclable catalysts is highly desirable. We fabricated herein MnO2/graphene oxide (GO) composites by a facile in-situ growth approach at room temperature and used them in selective aerobic oxidation of benzyl alcohol to benzaldehyde. TEM, XRD, FTIR, XPS and N2 adsorption/desorption analysis were employed to systematically investigate the morphology, particle size, structure and surface properties of the catalysts. The 96.8% benzyl alcohol conversion and 100% benzaldehyde selectivity over the MnO2/GO (10/100) catalyst with well dispersive ultrafine MnO2 nanoparticles (ca. 3nm) can be obtained within 3h under 383K. Simultaneously, no appreciable loss of activity and selectivity occurred after recycling use up to six times. Due to their significant low cost, excellent catalytic performance, the MnO2/GO composites have huge application prospect in organic synthesis. PMID:27544446
Chemoselective Oxidation of Benzyl, Amino, and Propargyl Alcohols to Aldehydes and Ketones under Mild Reaction Conditions
Reddy, C B Rajashekar; Reddy, Sabbasani Rajasekhara; Naidu, Shivaji
Catalytic oxidation reactions often suffer from drawbacks such as low yields and poor selectivity. Particularly, selective oxidation of alcohols becomes more difficult when a compound contains more than one oxidizable functional group. In order to deliver a methodology that addresses these issues, herein we report an efficient, aerobic, chemoselective and simplified approach to oxidize a broad range of benzyl and propargyl alcohols containing diverse functional groups to their corresponding aldehydes and ketones in excellent yields under mild reaction conditions. Optimal yields were obtained at room temperature using 1 mmol substrate, 10 mol % copper(I) iodide, 10 mol % 4-dimethylaminopyridine (DMAP), and 1 mol % 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) in acetonitrile, under an oxygen balloon. The catalytic system can be applied even when sensitive and oxidizable groups such as alkynes, amines, and phenols are present; starting materials and products containing such groups were found to be stable under the developed conditions. PMID:25969806
Chemoselective Oxidation of Benzyl, Amino, and Propargyl Alcohols to Aldehydes and Ketones under Mild Reaction Conditions.
Reddy, C B Rajashekar; Reddy, Sabbasani Rajasekhara; Naidu, Shivaji
Catalytic oxidation reactions often suffer from drawbacks such as low yields and poor selectivity. Particularly, selective oxidation of alcohols becomes more difficult when a compound contains more than one oxidizable functional group. In order to deliver a methodology that addresses these issues, herein we report an efficient, aerobic, chemoselective and simplified approach to oxidize a broad range of benzyl and propargyl alcohols containing diverse functional groups to their corresponding aldehydes and ketones in excellent yields under mild reaction conditions. Optimal yields were obtained at room temperature using 1 mmol substrate, 10 mol % copper(I) iodide, 10 mol % 4-dimethylaminopyridine (DMAP), and 1 mol % 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) in acetonitrile, under an oxygen balloon. The catalytic system can be applied even when sensitive and oxidizable groups such as alkynes, amines, and phenols are present; starting materials and products containing such groups were found to be stable under the developed conditions. PMID:25969806
Highly efficient direct aerobic oxidative esterification of cinnamyl alcohol with alkyl alcohols catalysed by gold nanoparticles incarcerated in a nanoporous polymer matrix: a tool for investigating the role of the polymer host.
Buonerba, Antonio; Noschese, Annarita; Grassi, Alfonso
The selective aerobic oxidation of cinnamyl alcohol to cinnamaldehyde, as well as direct oxidative esterification of this alcohol with primary and secondary aliphatic alcohols, were achieved with high chemoselectivity by using gold nanoparticles supported in a nanoporous semicrystalline multi-block copolymer matrix, which consisted of syndiotactic polystyrene-co-cis-1,4-polybutadiene. The cascade reaction that leads to the alkyl cinnamates occurs through two oxidation steps: the selective oxidation of cinnamyl alcohol to cinnamaldehyde, followed by oxidation of the hemiacetal that results from the base-catalysed reaction of cinnamaldehyde with an aliphatic alcohol. The rate constants for the two steps were evaluated in the temperature range 10-45 °C. The cinnamyl alcohol oxidation is faster than the oxidative esterification of cinnamaldehyde with methanol, ethanol, 2-propanol, 1-butanol, 1-hexanol or 1-octanol. The rate constants of the latter reaction are pseudo-zero order with respect to the aliphatic alcohol and decrease as the bulkiness of the alcohol is increased. The activation energy (Ea) for the two oxidation steps was calculated for esterification of cinnamyl alcohol with 1-butanol (Ea = 57.8±11.5 and 62.7±16.7 kJ mol(-1) for the first and second step, respectively). The oxidative esterification of cinnamyl alcohol with 2-phenylethanol follows pseudo-first-order kinetics with respect to 2-phenylethanol and is faster than observed for other alcohols because of fast diffusion of the aromatic alcohol in the crystalline phase of the support. The kinetic investigation allowed us to assess the role of the polymer support in the determination of both high activity and selectivity in the title reaction. PMID:24644103
Organization of the Escherichia coli aerobic enzyme complexes of oxidative phosphorylation in dynamic domains within the cytoplasmic membrane
Erhardt, Heiko; Dempwolff, Felix; Pfreundschuh, Moritz; Riehle, Marc; Schäfer, Caspar; Pohl, Thomas; Graumann, Peter; Friedrich, Thorsten
The Escherichia coli cytoplasmic membrane contains the enzyme complexes of oxidative phosphorylation (OXPHOS). Not much is known about their supramolecular organization and their dynamics within the membrane in this model organism. In mitochondria and other bacteria, it was demonstrated by nondenaturing electrophoretic methods and electron microscopy that the OXPHOS complexes are organized in so-called supercomplexes, stable assemblies with a defined number of the individual enzyme complexes. To investigate the organization of the E. coli enzyme complexes of aerobic OXPHOS in vivo, we established fluorescent protein fusions of the NADH:ubiquinone oxidoreductase, the succinate:ubiquinone oxidoreductase, the cytochrome bd-I, and the cytochrome bo3 terminal oxidases, and the FoF1 ATP-synthase. The fusions were integrated in the chromosome to prevent artifacts caused by protein overproduction. Biochemical analysis revealed that all modified complexes were fully assembled, active, and stable. The distribution of the OXPHOS complexes in living cells was determined using total internal reflection fluorescence microscopy. The dynamics within the membrane were detected by fluorescence recovery after photobleaching. All aerobic OXPHOS complexes showed an uneven distribution in large mobile patches within the E. coli cytoplasmic membrane. It is discussed whether the individual OXPHOS complexes are organized as clustered individual complexes, here called "segrazones." PMID:24729508
Thermal oxidative degradation reactions of perfluoroalkylethers
NASA Technical Reports Server (NTRS)
Paciorek, K. L.; Ito, T. I.; Kratzer, R. H.
The mechanisms operative in thermal oxidative degradation of Fomblin Z and hexafluoropropene oxide derived fluids and the effect of alloys and additives upon these processes are investigated. The nature of arrangements responsible for the inherent thermal oxidative instability of the Fomblin Z fluids is not established. It was determined that this behavior is not associated with hydrogen end groups or peroxy linkages. The degradation rate of these fluids at elevated temperatures in oxidizing atmospheres is dependent on the surface/volume ratio. Once a limiting ratio is reached, a steady rate appears to be attained. Based on elemental analysis and oxygen consumption data, CF2OCF2CF2O2, no. CF2CF2O, is one of the major arrangements present. The action of the M-50 and Ti(4 Al, 4 Mn) alloys is much more drastic in the case of Fomblin Z fluids than that observed for the hexafluoropropene derived materials. The effectiveness of antioxidation anticorrosion additives, P-3 and phospha-s-triazine, in the presence of metal alloys is very limited at 316 C; at 288 C the additives arrested almost completely the fluid degradation. The phospha-s-triazine appears to be at least twice as effective as the P-3 compound; it also protected the coupon better. The Ti(4 Al, 4 Mn) alloy degraded the fluid mainly by chain scission processes this takes place to a much lesser degree with M-50.
Thermal oxidative degradation reactions of perfluoroalklethers
NASA Technical Reports Server (NTRS)
Paciorek, K. L.; Harris, D. H.; Smythe, M. E.; Kratzer, R. H.
The objective of this contract was to investigate the mechanisms operative in thermal and thermal oxidative degradation of Fomblin Z and hexafluoropropene oxide derived fluids and the effect of alloys and additives upon these processes. The nature of arrangements responsible for the inherent thermal oxidative instability of the Fomblin Z fluids has not been established. It was determined that this behavior was not associated with hydrogen end-groups or peroxy linkages. The degradation rate of these fluids at elevated temperatures in oxidizing atmospheres was found to be dependent on the surface/volume ratio. Once a limiting ratio was reached, a steady rate appeared to be attained. Based on elemental analysis and oxygen consumption data, -CF2OCF2CF2O-, not -CF2CF2O-, is one of the major arrangements present. The action of the M-50 and Ti(4 Al, 4 Mn) alloys was found to be much more drastic in the case of Fomblin Z fluids than that observed for the hexalfuoropropane oxide derived materials. The effectiveness of antioxidation/anticorrosion additives, P-3 and phospha-s-triazine, in the presence of metal alloys was very limited at 316 C; at 288 C the additives arrested almost completely the fluid degradation. The phospha-s-triazine appeared to be at least twice as effective as the P-3 compound; it also protected the coupon better. The Ti(4 Al, 4 Mn) alloy degraded the fluid mainly by chain scission processes; this took place to a much lesser degree with M-50.
New reaction system for hydrocarbon oxidation by chloroperoxidase.
Park, Jin-Byung; Clark, Douglas S
A novel reaction system was developed to maximize the catalytic efficiency of chloroperoxidase (CPO, from Caldariomyces fumago) toward the oxidation of hydrocarbons. The reaction system consisted of an organic/aqueous emulsion comprising pure substrate and aqueous buffer supplemented with the surfactant dioctyl sulfosuccinate. The emulsion system attenuated not only the destabilizing effects of the substrate and product on the enzyme by emulsifying the compounds, but also oxidant toxicity (oxidative stress) by increasing substrate availability. As a result, CPO exhibited total turnover numbers (TTNs, defined as the amount of product produced over the catalytic lifetime of the enzyme) of ca. 20,000 mol product/mol enzyme for the oxidation of styrene, toluene, and o-, m-, p-xylenes. The TTNs are over 10-fold higher than those previously reported for the oxidation of benzylic hydrocarbons by CPO. This study represents a significant step toward the development of CPO as a practical catalyst for large-scale organic syntheses. PMID:16276530
A Bioorthogonal Reaction of N-Oxide and Boron Reagents.
Kim, Justin; Bertozzi, Carolyn R
The development of bioorthogonal reactions has classically focused on bond-forming ligation reactions. In this report, we seek to expand the functional repertoire of such transformations by introducing a new bond-cleaving reaction between N-oxide and boron reagents. The reaction features a large dynamic range of reactivity, showcasing second-order rate constants as high as 2.3×10(3) M(-1) s(-1) using diboron reaction partners. Diboron reagents display minimal cell toxicity at millimolar concentrations, penetrate cell membranes, and effectively reduce N-oxides inside mammalian cells. This new bioorthogonal process based on miniscule components is thus well-suited for activating molecules within cells under chemical control. Furthermore, we demonstrate that the metabolic diversity of nature enables the use of naturally occurring functional groups that display inherent biocompatibility alongside abiotic components for organism-specific applications. PMID:26568479
Aqueous aerobic oxidation of alkyl arenes and alcohols catalyzed by copper(II) phthalocyanine supported on three-dimensional nitrogen-doped graphene at room temperature.
Mahyari, Mojtaba; Laeini, Mohammad Sadegh; Shaabani, Ahmad
Copper(ii) tetrasulfophthalocyanine supported on three-dimensional nitrogen-doped graphene-based frameworks was synthesized and introduced as a bifunctional catalyst for selective aerobic oxidation of alkyl arenes and alcohols to the corresponding carbonyl compounds. The ease of catalyst separation, high turnover, low catalyst loading and recyclability could potentially render it applicable in industrial setting. PMID:24912023
One-pot synthesis of amides by aerobic oxidative coupling of alcohols or aldehydes with amines using supported gold and base as catalysts.
Kegnæs, Søren; Mielby, Jerrik; Mentzel, Uffe V; Jensen, Thomas; Fristrup, Peter; Riisager, Anders
Synthesis of amides by aerobic oxidative coupling of alcohols or aldehydes with amines via intermediate formation of methyl esters is highly efficient and selective when using a catalytic system comprised of supported gold nanoparticles and added base in methanol. PMID:22274843
Synthesis and reactions of the oxides of hexafluoropropylene trimers
Zapevalov, A.Ya.; Filyakova, T.I.; Peschanskii, N.V.; Kodess, M.I.; Kolenko, I.P.
By the oxidation of the hexafluoropropylene trimers with an aqueous solution of sodium hypochlorite in the presence of acetonitrile the following ..cap alpha..-oxides were obtained: 2,3-Epoxyperfluoro-3-isopropyl-4-methylpentane and 2,3-epoxyperfluoro-3-ethyl-2,4-dimethylpentane. According to the /sup 19/F NMR data, the epoxidation takes place stereoselectively with the formation of only one conformer of the ..cap alpha..-oxide in each case. The determining effect of the steric factors on the reactivity of the oxides of hexafluoropropylene trimers in reaction with nucleophiles was demonstrated.
New evidence for Cu-decorated binary-oxides mediating bacterial inactivation/mineralization in aerobic media.
Rtimi, S; Pulgarin, C; Bensimon, M; Kiwi, J
Binary oxide semiconductors TiO2-ZrO2 and Cu-decorated TiO2-ZrO2 (TiO2-ZrO2-Cu) uniform films were sputtered on polyester (PES). These films were irradiated under low intensity solar simulated light and led to bacterial inactivation in aerobic and anaerobic media as evaluated by CFU-plate counting. But bacterial mineralization was only induced by TiO2-ZrO2-Cu in aerobic media. The highly oxidative radicals generated on the films surface under light were identified by the use of appropriate scavengers. The hole generated on the TiO2-ZrO2 films is shown to be the main specie leading to bacterial inactivation. TiO2-ZrO2 and Cu-decorated TiO2-ZrO2 films release Zr and Ti <1ppb and Cu 4.6ppb/cm(2) as determined by inductively coupled plasma mass spectrometry (ICP-MS) This level is far below the citotoxicity permitted level allowed for mammalian cells suggesting that bacterial disinfection proceeds through an oligodynamic effect. By Fourier transform attenuated infrared spectroscopy (ATR-FTIR) the systematic shift of the predominating νs(CH2) vibrational-rotational peak making up most of the bacterial cell-wall content in C was monitored. Based on this evidence a mechanism suggested leading to CH bond stretching followed by cell lysis and cell death. Bacterial inactivation cycling was observed on TiO2-ZrO2-Cu showing the stability of these films leading to bacterial inactivation. PMID:27088192
Investigation of oxidative phosphorylation in continuous cultures. A non-equilibrium thermodynamic approach to energy transduction for Escherichia coli in aerobic condition
NASA Astrophysics Data System (ADS)
Ghafuri, Mohazabeh; Nosrati, Mohsen; Hosseinkhani, Saman
Adenosine triphosphate (ATP) production in living cells is very important. Different researches have shown that in terms of mathematical modeling, the domain of these investigations is essentially restricted. Recently the thermodynamic models have been suggested for calculation of the efficiency of oxidative phosphorylation process and rate of energy loss in animal cells using chemiosmotic theory and non-equilibrium thermodynamics equations. In our previous work, we developed a mathematical model for mitochondria of animal cells. In this research, according to similarities between oxidative phosphorylation process in microorganisms and animal cells, Golfar's model was developed to predict the non-equilibrium thermodynamic behavior of the oxidative phosphorylation process for bacteria in aerobic condition. With this model the rate of energy loss, P/O ratio, and efficiency of oxidative phosphorylation were calculated for Escherichia coli in aerobic condition. The results then were compared with experimental data given by other authors. The thermodynamic model had an acceptable agreement with the experimental data.
Copper-catalyzed aerobic oxidation and cleavage/formation of C-S bond: a novel synthesis of aryl methyl sulfones from aryl halides and DMSO.
Yuan, Gaoqing; Zheng, Junhua; Gao, Xiaofang; Li, Xianwei; Huang, Liangbin; Chen, Huoji; Jiang, Huanfeng
With atmospheric oxygen as the oxidant, a novel copper(I)-catalyzed synthesis of aryl methyl sulfones from aryl halides and widely available DMSO is described. The procedure tolerates aryl halides with various functional groups (such as methoxy, acetyl, chloro, fluoro and nitro groups), which could afford aryl methyl sulfones in moderate to high yields. The copper-catalyzed aerobic oxidation and the cleavage/formation of C-S bond are the key steps for this transformation. PMID:22728918
Biofilter for removal of nitrogen oxides from contaminated gases under aerobic conditions
Apel, W.A.
A biofilter is described for reducing concentrations of gaseous nitrogen oxides in a polluted gas comprises a porous organic filter bed medium disposed in a housing, the filter bed medium including a mixed culture of naturally occurring denitrifying bacteria for converting the nitrogen oxides to nitrogen gas, carbon dioxide, and water. A method is described of reducing concentrations of nitrogen oxides in polluted gas comprises conducting the polluted gas through the biofilter so that the denitrifying bacteria can degrade the nitrogen oxides. A preferred filter medium is wood compost, however composts of other organic materials are functional. Regulation of pH, moisture content, exogenous carbon sources, and temperature are described. 6 figs.
Biofilter for removal of nitrogen oxides from contaminated gases under aerobic conditions
Apel, William A.
A biofilter for reducing concentrations of gaseous nitrogen oxides in a polluted gas comprises a porous organic filter bed medium disposed in a housing, the filter bed medium including a mixed culture of naturally occurring denitrifying bacteria for converting the nitrogen oxides to nitrogen gas, carbon dioxide, and water. A method of reducing concentrations of nitrogen oxides in polluted gas comprises conducting the polluted gas through the biofilter so that the denitrifying bacteria can degrade the nitrogen oxides. A preferred filter medium is wood compost, however composts of other organic materials are functional. Regulation of pH, moisture content, exogenous carbon sources, and temperature are described.
Computational studies of polysiloxanes : oxidation potentials and decomposition reactions.
Assary, R. S.; Curtiss, L. A.; Redfern, P. C.; Zhang, Z.; Amine, K.
Silicon-containing solvents have tremendous potential for application as electrolytes for electrical energy storage devices such as lithium-ion (air) batteries and supercapacitors. Quantum chemical methods were employed to investigate trends in oxidation potentials and decomposition reactions of a series of polysiloxanes. Various electron-donating and -withdrawing substituents can be used to tune the oxidation potential in shorter chain siloxanes but not in longer ones. Decomposition reactions of siloxanes in their oxidized states were investigated and compared against their carbon analogues. These studies suggest that the Si-O group provides added stability for siloxanes over their carbon analogues. Computational studies have also been performed for various disiloxanes and siloxanes with spacer groups to understand their thermochemical stability and oxidation potentials.
Reaction of ethanol on oxidized and metallic cobalt surfaces
NASA Astrophysics Data System (ADS)
Hyman, Matthew P.; Vohs, John M.
The reaction of ethanol on metallic and oxidized cobalt surfaces was studied using temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) in order to determine the dependence of the reaction pathways on the cobalt oxidation state. The primary reaction for ethoxide species on metallic cobalt surfaces was decarbonylation producing CO, H 2 and carbon. This reaction was facile and occurred below 400 K. In contrast, CoO x surfaces which predominantly contained Co 2+ were selective for the dehydrogenation of ethoxide groups to produce acetaldehyde at 400 K. A fraction of the acetaldehyde molecules produced by this pathway were further oxidized to acetate which decomposed to produce CO 2 at 495 K. More highly oxidized Co surfaces that contained both CO 2+ and Co 3+ were active for the complete oxidation of ethanol producing CO, CO 2, and H 2O as the primary products. The insights that these results provide for understanding the mechanism of the steam reforming of ethanol on cobalt catalysts is discussed.
Chemical Characterization and Reactivity of Fuel-Oxidizer Reaction Product
NASA Technical Reports Server (NTRS)
David, Dennis D.; Dee, Louis A.; Beeson, Harold D.
Fuel-oxidizer reaction product (FORP), the product of incomplete reaction of monomethylhydrazine and nitrogen tetroxide propellants prepared under laboratory conditions and from firings of Shuttle Reaction Control System thrusters, has been characterized by chemical and thermal analysis. The composition of FORP is variable but falls within a limited range of compositions that depend on three factors: the fuel-oxidizer ratio at the time of formation; whether the composition of the post-formation atmosphere is reducing or oxidizing; and the reaction or post-reaction temperature. A typical composition contains methylhydrazinium nitrate, ammonium nitrate, methylammonium nitrate, and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. Thermal decomposition reactions of the FORP compositions used in this study were unremarkable. Neither the various compositions of FORP, the pure major components of FORP, nor mixtures of FORP with propellant system corrosion products showed any unusual thermal activity when decomposed under laboratory conditions. Off-limit thruster operations were simulated by rapid mixing of liquid monomethylhydrazine and liquid nitrogen tetroxide in a confined space. These tests demonstrated that monomethylhydrazine, methylhydrazinium nitrate, ammonium nitrate, or Inconel corrosion products can induce a mixture of monomethylhydrazine and nitrogen tetroxide to produce component-damaging energies. Damaging events required FORP or metal salts to be present at the initial mixing of monomethylhydrazine and nitrogen tetroxide.
Biochemical properties of Paracoccus denitrificans FnrP: reactions with molecular oxygen and nitric oxide.
Crack, Jason C; Hutchings, Matthew I; Thomson, Andrew J; Le Brun, Nick E
In Paracoccus denitrificans, three CRP/FNR family regulatory proteins, NarR, NnrR and FnrP, control the switch between aerobic and anaerobic (denitrification) respiration. FnrP is a [4Fe-4S] cluster-containing homologue of the archetypal O2 sensor FNR from E. coli and accordingly regulates genes encoding aerobic and anaerobic respiratory enzymes in response to O2, and also NO, availability. Here we show that FnrP undergoes O2-driven [4Fe-4S] to [2Fe-2S] cluster conversion that involves up to 2 O2 per cluster, with significant oxidation of released cluster sulfide to sulfane observed at higher O2 concentrations. The rate of the cluster reaction was found to be ~sixfold lower than that of E. coli FNR, suggesting that FnrP can remain transcriptionally active under microaerobic conditions. This is consistent with a role for FnrP in activating expression of the high O2 affinity cytochrome c oxidase under microaerobic conditions. Cluster conversion resulted in dissociation of the transcriptionally active FnrP dimer into monomers. Therefore, along with E. coli FNR, FnrP belongs to the subset of FNR proteins in which cluster type is correlated with association state. Interestingly, two key charged residues, Arg140 and Asp154, that have been shown to play key roles in the monomer-dimer equilibrium in E. coli FNR are not conserved in FnrP, indicating that different protomer interactions are important for this equilibrium. Finally, the FnrP [4Fe-4S] cluster is shown to undergo reaction with multiple NO molecules, resulting in iron nitrosyl species and dissociation into monomers. PMID:26790880
Selective aerobic alcohol oxidation method for conversion of lignin into simple aromatic compounds
Stahl, Shannon S; Rahimi, Alireza
Described is a method to oxidize lignin or lignin sub-units. The method includes oxidation of secondary benzylic alcohol in the lignin or lignin sub-unit to a corresponding ketone in the presence of unprotected primarily aliphatic alcohol in the lignin or lignin sub-unit. The optimal catalyst system consists of HNO.sub.3 in combination with another Bronsted acid, in the absence of a metal-containing catalyst, thereby yielding a selectively oxidized lignin or lignin sub-unit. The method may be carried out in the presence or absence of additional reagents including TEMPO and TEMPO derivatives.
Oxidation Protection of Porous Reaction-Bonded Silicon Nitride
NASA Technical Reports Server (NTRS)
Fox, D. S.
Oxidation kinetics of both as-fabricated and coated reaction-bonded silicon nitride (RBSN) were studied at 900 and 1000 C with thermogravimetry. Uncoated RBSN exhibited internal oxidation and parabolic kinetics. An amorphous Si-C-O coating provided the greatest degree of protection to oxygen, with a small linear weight loss observed. Linear weight gains were measured on samples with an amorphous Si-N-C coating. Chemically vapor deposited (CVD) Si3N4 coated RBSN exhibited parabolic kinetics, and the coating cracked severely. A continuous-SiC-fiber-reinforced RBSN composite was also coated with the Si-C-O material, but no substantial oxidation protection was observed.
Oxidative Half-reaction of Arabidopsis thaliana Sulfite Oxidase
Byrne, Robert S.; Hänsch, Robert; Mendel, Ralf R.; Hille, Russ
Vertebrate forms of the molybdenum-containing enzyme sulfite oxidase possess a b-type cytochrome prosthetic group that accepts reducing equivalents from the molybdenum center and passes them on to cytochrome c. The plant form of the enzyme, on the other hand, lacks a prosthetic group other than its molybdenum center and utilizes molecular oxygen as the physiological oxidant. Hydrogen peroxide is the ultimate product of the reaction. Here, we present data demonstrating that superoxide is produced essentially quantitatively both in the course of the reaction of reduced enzyme with O2 and during steady-state turnover and only subsequently decays (presumably noncatalytically) to form hydrogen peroxide. Rapid-reaction kinetic studies directly following the reoxidation of reduced enzyme demonstrate a linear dependence of the rate constant for the reaction on [O2] with a second-order rate constant of kox = 8.7 × 104 ± 0.5 × 104 m−1s−1. When the reaction is carried out in the presence of cytochrome c to follow superoxide generation, biphasic time courses are observed, indicating that a first equivalent of superoxide is generated in the oxidation of the fully reduced Mo(IV) state of the enzyme to Mo(V), followed by a slower oxidation of the Mo(V) state to Mo(VI). The physiological implications of plant sulfite oxidase as a copious generator of superoxide are discussed. PMID:19875441
Systemic oxidative-nitrosative-inflammatory stress during acute exercise in hypoxia; implications for microvascular oxygenation and aerobic capacity.
Woodside, John D S; Gutowski, Mariusz; Fall, Lewis; James, Philip E; McEneny, Jane; Young, Ian S; Ogoh, Shigehiko; Bailey, Damian M
Exercise performance in hypoxia may be limited by a critical reduction in cerebral and skeletal tissue oxygenation, although the underlying mechanisms remain unclear. We examined whether increased systemic free radical accumulation during hypoxia would be associated with elevated microvascular deoxygenation and reduced maximal aerobic capacity (V̇O2 max ). Eleven healthy men were randomly assigned single-blind to an incremental semi-recumbent cycling test to determine V̇O2 max in both normoxia (21% O2) and hypoxia (12% O2) separated by a week. Continuous-wave near-infrared spectroscopy was employed to monitor concentration changes in oxy- and deoxyhaemoglobin in the left vastus lateralis muscle and frontal cerebral cortex. Antecubital venous blood samples were obtained at rest and at V̇O2 max to determine oxidative (ascorbate radical by electron paramagnetic resonance spectroscopy), nitrosative (nitric oxide metabolites by ozone-based chemiluminescence and 3-nitrotyrosine by enzyme-linked immunosorbent assay) and inflammatory stress biomarkers (soluble intercellular/vascular cell adhesion 1 molecules by enzyme-linked immunosorbent assay). Hypoxia was associated with increased cerebral and muscle tissue deoxygenation and lower V̇O2 max (P < 0.05 versus normoxia). Despite an exercise-induced increase in oxidative-nitrosative-inflammatory stress, hypoxia per se did not have an additive effect (P > 0.05 versus normoxia). Consequently, we failed to observe correlations between any metabolic, haemodynamic and cardiorespiratory parameters (P > 0.05). Collectively, these findings suggest that altered free radical metabolism cannot explain the elevated microvascular deoxygenation and corresponding lower V̇O2 max in hypoxia. Further research is required to determine whether free radicals when present in excess do indeed contribute to the premature termination of exercise in hypoxia. PMID:25344270
Aerobic exercise training improves oxidative stress and ubiquitin proteasome system activity in heart of spontaneously hypertensive rats.
de Andrade, Luiz Henrique Soares; de Moraes, Wilson Max Almeida Monteiro; Matsuo Junior, Eduardo Hiroshi; de Orleans Carvalho de Moura, Elizabeth; Antunes, Hanna Karen Moreira; Montemor, Jairo; Antonio, Ednei Luiz; Bocalini, Danilo Sales; Serra, Andrey Jorge; Tucci, Paulo José Ferreira; Brum, Patricia Chakur; Medeiros, Alessandra
The activity of the ubiquitin proteasome system (UPS) and the level of oxidative stress contribute to the transition from compensated cardiac hypertrophy to heart failure in hypertension. Moreover, aerobic exercise training (AET) is an important therapy for the treatment of hypertension, but its effects on the UPS are not completely known. The aim of this study was to evaluate the effect of AET on UPS's activity and oxidative stress level in heart of spontaneously hypertensive rats (SHR). A total of 53 Wistar and SHR rats were randomly divided into sedentary and trained groups. The AET protocol was 5×/week in treadmill for 13 weeks. Exercise tolerance test, non-invasive blood pressure measurement, echocardiographic analyses, and left ventricle hemodynamics were performed during experimental period. The expression of ubiquitinated proteins, 4-hydroxynonenal (4-HNE), Akt, phospho-Akt(ser473), GSK3β, and phospho-GSK3β(ser9) were analyzed by western blotting. The evaluation of lipid hydroperoxide concentration was performed using the xylenol orange method, and the proteasomal chymotrypsin-like activity was measured by fluorimetric assay. Sedentary hypertensive group presented cardiac hypertrophy, unaltered expression of total Akt, phospho-Akt, total GSK3β and phospho-GSK3β, UPS hyperactivity, increased lipid hydroperoxidation as well as elevated expression of 4-HNE but normal cardiac function. In contrast, AET significantly increased exercise tolerance, decreased resting systolic blood pressure and heart rate in hypertensive animals. In addition, the AET increased phospho-Akt expression, decreased phospho-GSK3β, and did not alter the expression of total Akt, total GSK3β, and ubiquitinated proteins, however, significantly attenuated 4-HNE levels, lipid hydroperoxidation, and UPS's activity toward normotensive group levels. Our results provide evidence for the main effect of AET on attenuating cardiac ubiquitin proteasome hyperactivity and oxidative stress in SHR
Uniform distributions of glucose oxidation and oxygen extraction in gray matter of normal human brain: No evidence of regional differences of aerobic glycolysis.
Hyder, Fahmeed; Herman, Peter; Bailey, Christopher J; Møller, Arne; Globinsky, Ronen; Fulbright, Robert K; Rothman, Douglas L; Gjedde, Albert
Regionally variable rates of aerobic glycolysis in brain networks identified by resting-state functional magnetic resonance imaging (R-fMRI) imply regionally variable adenosine triphosphate (ATP) regeneration. When regional glucose utilization is not matched to oxygen delivery, affected regions have correspondingly variable rates of ATP and lactate production. We tested the extent to which aerobic glycolysis and oxidative phosphorylation power R-fMRI networks by measuring quantitative differences between the oxygen to glucose index (OGI) and the oxygen extraction fraction (OEF) as measured by positron emission tomography (PET) in normal human brain (resting awake, eyes closed). Regionally uniform and correlated OEF and OGI estimates prevailed, with network values that matched the gray matter means, regardless of size, location, and origin. The spatial agreement between oxygen delivery (OEF≈0.4) and glucose oxidation (OGI ≈ 5.3) suggests that no specific regions have preferentially high aerobic glycolysis and low oxidative phosphorylation rates, with globally optimal maximum ATP turnover rates (VATP ≈ 9.4 µmol/g/min), in good agreement with (31)P and (13)C magnetic resonance spectroscopy measurements. These results imply that the intrinsic network activity in healthy human brain powers the entire gray matter with ubiquitously high rates of glucose oxidation. Reports of departures from normal brain-wide homogeny of oxygen extraction fraction and oxygen to glucose index may be due to normalization artefacts from relative PET measurements. PMID:26755443
Method for facilitating catalyzed oxidation reactions, device for facilitating catalyzed oxidation reactions
Beuhler, Robert J.; White, Michael G.; Hrbek, Jan
A catalytic process for the oxidation of organic. Oxygen is loaded into a metal foil by heating the foil while in contact with an oxygen-containing fluid. After cooling the oxygen-activated foil to room temperature, oxygen diffuses through the foil and oxidizes reactants exposed to the other side of the foil.
Nitrite-driven nitrous oxide production under aerobic soil conditions: Kinetics and biochemical controls
Technology Transfer Automated Retrieval System (TEKTRAN)
Nitrite (NO2-) can accumulate during nitrification in soil following fertilizer application. While the role of NO2- as a substrate regulating nitrous oxide (N2O) production is recognized, kinetic data are not available that allow for estimating N2O production or soil-to-atmosphere fluxes as a functi...
Nitrite-Driven Nitrous Oxide Production Under Aerobic Soil Conditions: Kinetics and Biochemical Controls
Technology Transfer Automated Retrieval System (TEKTRAN)
Nitrite (NO2-) can accumulate during nitrification in soil following fertilizer application. While the role of NO2- as a substrate regulating nitrous oxide (N2O) production is recognized, kinetic data are not available that allow for estimating N2O production or soil-to-atmosphere fluxes as a functi...
Physical Training Status Determines Oxidative Stress and Redox Changes in Response to an Acute Aerobic Exercise.
Seifi-Skishahr, Farnaz; Damirchi, Arsalan; Farjaminezhad, Manoochehr; Babaei, Parvin
Objective. To assess the influence of different physical training status on exercise-induced oxidative stress and changes in cellular redox state. Methods. Thirty male subjects participated in this study and were assigned as well-trained (WT), moderately trained (MT), and untrained (UT) groups. The levels of cortisol, creatine kinase, plasma reduced glutathione to oxidized glutathione (GSH/GSSG), cysteine/cystine (Cys/CySS), and GSH/GSSG ratio in red blood cells (RBCs) were measured immediately and 10 and 30 min after exercise. Results. Following the exercise, plasma GSH/GSSG (p = 0.001) and Cys/CySS (p = 0.005) were significantly reduced in all groups. Reduction in plasma GSH/GSSG ratio in all groups induced a transient shift in redox balance towards a more oxidizing environment without difference between groups (p = 0.860), while RBCs GSH/GSSG showed significant reduction (p = 0.003) and elevation (p = 0.007) in UT and MT groups, respectively. The highest level of RBCs GSH/GSSG ratio was recorded in MT group, and the lowest one was recorded in the WT group. Conclusion. Long term regular exercise training with moderate intensity shifts redox balance towards more reducing environment, versus intensive exercise training leads to more oxidizing environment and consequently development of related diseases. PMID:27064342
Confined iron nanowires enhance the catalytic activity of carbon nanotubes in the aerobic oxidation of cyclohexane.
Yang, Xixian; Yu, Hao; Peng, Feng; Wang, Hongjuan
Inside job: New applications of carbon materials pave the way towards greener chemical syntheses. The encapsulation of metallic Fe within CNTs improves electron transfer between the metal and the CNTs. The resulting material offers a high catalytic activity and easy magnetic separation of catalyst in the heterogeneous selective oxidation of cyclohexane. PMID:22488987
Selective Aerobic Oxidation of 5-(Hydroxymethyl)furfural to 5-Formyl-2-furancarboxylic Acid in Water.
Ventura, Maria; Aresta, Michele; Dibenedetto, Angela
A simple, cheap, and selective catalyst based on copper/cerium oxides is described for the oxidation of 5-(hydroxymethyl)furfural (5-HMF) in water. An almost quantitative conversion (99 %) with excellent (90 %) selectivity towards the formation of 5-formyl-2-furancarboxylic acid, a platform molecule for other high value chemicals, is observed. The catalyst does not require any pretreatment or additives, such as bases, to obtain high yield and selectivity in water as solvent and using oxygen as oxidant. When a physical mixture of the oxides is used, low conversion and selectivity are observed. Air can be used instead of oxygen, but a lower conversion rate is observed if the same overall pressure is used, and the selectivity remains high. The catalyst can be recovered almost quantitatively and reused. Deactivation of the catalyst, observed in repeated runs, is due to the deposition of humins on its surface. Upon calcination the catalyst almost completely recovers its activity and selectivity, proving that the catalyst is robust. PMID:27101568
Physical Training Status Determines Oxidative Stress and Redox Changes in Response to an Acute Aerobic Exercise
Damirchi, Arsalan; Farjaminezhad, Manoochehr
Objective. To assess the influence of different physical training status on exercise-induced oxidative stress and changes in cellular redox state. Methods. Thirty male subjects participated in this study and were assigned as well-trained (WT), moderately trained (MT), and untrained (UT) groups. The levels of cortisol, creatine kinase, plasma reduced glutathione to oxidized glutathione (GSH/GSSG), cysteine/cystine (Cys/CySS), and GSH/GSSG ratio in red blood cells (RBCs) were measured immediately and 10 and 30 min after exercise. Results. Following the exercise, plasma GSH/GSSG (p = 0.001) and Cys/CySS (p = 0.005) were significantly reduced in all groups. Reduction in plasma GSH/GSSG ratio in all groups induced a transient shift in redox balance towards a more oxidizing environment without difference between groups (p = 0.860), while RBCs GSH/GSSG showed significant reduction (p = 0.003) and elevation (p = 0.007) in UT and MT groups, respectively. The highest level of RBCs GSH/GSSG ratio was recorded in MT group, and the lowest one was recorded in the WT group. Conclusion. Long term regular exercise training with moderate intensity shifts redox balance towards more reducing environment, versus intensive exercise training leads to more oxidizing environment and consequently development of related diseases. PMID:27064342
Reversibility of heme-nitric oxide reactions for use in an inhaled nitric oxide sensor
NASA Astrophysics Data System (ADS)
Parikh, Bhairavi R.; Soller, Babs R.; Rencus, Tal
Nitric Oxide is a simple gaseous compound which serves as a regulatory molecule in a number of physiological processes. Due to its biological role as a potent local vasodilator,there has been widespread interest in the therapeutic use of gaseous nitric oxide a selective pulmonary vasodilator. Our goal is the development of a sensor for the direct and continuous measurement of inhaled nitric oxide concentrations. This study evaluated the reversibility of potential sensing compounds upon reaction with nitric oxide. Previously, absorption spectroscopy was used to study the sensitivity of the Fe II, Fe III and oxygenated forms of three biologically active hemes known to rapidly react with NO: hemoglobin, myoglobin, and cytochrome-c. This study focused on the photo-reversibility of the hem's reaction with nitric oxide. Hemoglobin, myoglobin and cytochrome-c in the Fe III state reversibly reacted with nitric oxide. Hemoglobin and myoglobin in the Fe II state non-reversibly reacted with nitric oxide to form an unstable product. Cytochrome-c (FeII) does not react with nitric oxide. The oxy forms of hemoglobin and myoglobin react with nitric oxide to form their respective met forms, unreversible via photolysis. For all reversible reactions, photolysis was gradual and complete within five minutes.
Aerobic oxidative amidation of aromatic and cinnamic aldehydes with secondary amines by CuI/2-pyridonate catalytic system.
Zhu, Mingwen; Fujita, Ken-ichi; Yamaguchi, Ryohei
A simple and convenient CuI/2-pyridonate catalytic system for the oxidative amidation of aldehydes with secondary amines has been developed. With this system, a variety of useful arylamides have been synthesized in moderate to good yields in the presence of small amount of copper catalyst and the pyridonate ligand, generating only water as a coproduct. Synthesis of cinnamamides was also achieved by the reactions of cinnamaldehydes with secondary amines in moderate yields. Air was successfully employed as a green oxidant in this catalytic system, achieving a safe and atom-efficient system for the synthesis of amides. PMID:23006061
New Insights of the Fenton Reaction Using Glycerol as the Experimental Model. Effect of O2, Inhibition by Mg(2+), and Oxidation State of Fe.
Vitale, Arturo Alberto; Bernatene, Eduardo A; Vitale, Martín Gustavo; Pomilio, Alicia Beatriz
The use of iron ions as catalyst of oxidation with hydrogen peroxide, known as the Fenton reaction, is important for industry and biological systems. It has been widely studied since its discovery in the 19th century, but important aspects of the reaction as which is the oxidant, the role of oxygen, and the oxidation state of Fe still remain unclear. In this work new mechanistic insights of the oxidation of carbohydrates by the Fenton reaction using glycerol as experimental model are described. The reaction was studied by means of oxidation reduction potential (ORP) measures. The stoichiometry was measured, showing the important role of oxygen for lowering H2O2 consumption under aerobic conditions. Evidence is provided to demonstrate that in this system Fe(2+) generates a catalyst by reacting with a substrate to produce a complex, which gives rise to singlet oxygen after reacting with H2O2. This is the first time that the inhibitor effect of Mg(2+) is reported in this reaction, and its participation in the mechanism is described. A rational mechanism for the oxidation of glycerol using the Fenton reaction under these specific conditions is proposed. The role of oxygen, the participation of Fe(2+), and the inhibition by Mg(2+) are fully demonstrated experimentally. PMID:27340836
The oxidative burst reaction in mammalian cells depends on gravity
Gravity has been a constant force throughout the Earth's evolutionary history. Thus, one of the fundamental biological questions is if and how complex cellular and molecular functions of life on Earth require gravity. In this study, we investigated the influence of gravity on the oxidative burst reaction in macrophages, one of the key elements in innate immune response and cellular signaling. An important step is the production of superoxide by the NADPH oxidase, which is rapidly converted to H2O2 by spontaneous and enzymatic dismutation. The phagozytosis-mediated oxidative burst under altered gravity conditions was studied in NR8383 rat alveolar macrophages by means of a luminol assay. Ground-based experiments in "functional weightlessness" were performed using a 2 D clinostat combined with a photomultiplier (PMT clinostat). The same technical set-up was used during the 13th DLR and 51st ESA parabolic flight campaign. Furthermore, hypergravity conditions were provided by using the Multi-Sample Incubation Centrifuge (MuSIC) and the Short Arm Human Centrifuge (SAHC). The results demonstrate that release of reactive oxygen species (ROS) during the oxidative burst reaction depends greatly on gravity conditions. ROS release is 1.) reduced in microgravity, 2.) enhanced in hypergravity and 3.) responds rapidly and reversible to altered gravity within seconds. We substantiated the effect of altered gravity on oxidative burst reaction in two independent experimental systems, parabolic flights and 2D clinostat / centrifuge experiments. Furthermore, the results obtained in simulated microgravity (2D clinorotation experiments) were proven by experiments in real microgravity as in both cases a pronounced reduction in ROS was observed. Our experiments indicate that gravity-sensitive steps are located both in the initial activation pathways and in the final oxidative burst reaction itself, which could be explained by the role of cytoskeletal dynamics in the assembly and
The oxidative burst reaction in mammalian cells depends on gravity.
Adrian, Astrid; Schoppmann, Kathrin; Sromicki, Juri; Brungs, Sonja; von der Wiesche, Melanie; Hock, Bertold; Kolanus, Waldemar; Hemmersbach, Ruth; Ullrich, Oliver
Gravity has been a constant force throughout the Earth's evolutionary history. Thus, one of the fundamental biological questions is if and how complex cellular and molecular functions of life on Earth require gravity. In this study, we investigated the influence of gravity on the oxidative burst reaction in macrophages, one of the key elements in innate immune response and cellular signaling. An important step is the production of superoxide by the NADPH oxidase, which is rapidly converted to H2O2 by spontaneous and enzymatic dismutation. The phagozytosis-mediated oxidative burst under altered gravity conditions was studied in NR8383 rat alveolar macrophages by means of a luminol assay. Ground-based experiments in "functional weightlessness" were performed using a 2 D clinostat combined with a photomultiplier (PMT clinostat). The same technical set-up was used during the 13th DLR and 51st ESA parabolic flight campaign. Furthermore, hypergravity conditions were provided by using the Multi-Sample Incubation Centrifuge (MuSIC) and the Short Arm Human Centrifuge (SAHC). The results demonstrate that release of reactive oxygen species (ROS) during the oxidative burst reaction depends greatly on gravity conditions. ROS release is 1.) reduced in microgravity, 2.) enhanced in hypergravity and 3.) responds rapidly and reversible to altered gravity within seconds. We substantiated the effect of altered gravity on oxidative burst reaction in two independent experimental systems, parabolic flights and 2D clinostat / centrifuge experiments. Furthermore, the results obtained in simulated microgravity (2D clinorotation experiments) were proven by experiments in real microgravity as in both cases a pronounced reduction in ROS was observed. Our experiments indicate that gravity-sensitive steps are located both in the initial activation pathways and in the final oxidative burst reaction itself, which could be explained by the role of cytoskeletal dynamics in the assembly and function
Special role of corn flour as an ideal carbon source for aerobic denitrification with minimized nitrous oxide emission.
Zhu, Shuangyue; Zheng, Maosheng; Li, Can; Gui, Mengyao; Chen, Qian; Ni, Jinren
Much effort has been made for reducing nitrous oxide (N2O) emission in wastewater treatment processes. This paper presents an interesting way to minimize N2O in aerobic denitrification by strain Pseudomonas stutzeri PCN-1 with help of corn flour as cheaper additional carbon source. Experimental results showed that maximal N2O accumulation by strain PCN-1 was only 0.02% of removed nitrogen if corn flour was used as sole carbon source, which was significantly reduced by 52.07-99.81% comparing with others such as succinate, glucose, acetate and citrate. Sustained release of reducing sugar from starch and continuous expression of nosZ coding for N2O reductase contributed to the special role of corn flour as the ideal carbon source for strain PCN-1. Further experiments in sequencing batch reactors (SBRs) demonstrated similarly efficient nitrogen removal with much less N2O emission due to synergy of the novel strain and activated sludge, which was then confirmed by quantitative PCR analysis. PMID:25802047
Selective aerobic oxidation of 1,3-propanediol to 3-hydroxypropanoic acid using hydrotalcite supported bimetallic gold nanoparticle catalyst in water
NASA Astrophysics Data System (ADS)
Mohammad, Mujahid; Nishimura, Shun; Ebitani, Kohki
Selective oxidation of 1,3-propanediol (1,3-PD) to 3-hydroxypropanoic acid (3-HPA), an important industrial building block, was successfully achieved using hydrotalcite-supported bimetallic Au nanoparticle catalysts in water at 343 K under aerobic and base-free conditions. The highest yield of 42% with 73% selectivity towards 3-HPA was afforded by 1wt% Au0.8Pd0.2-PVP/HT catalyst.
High fat intake lowers hepatic fatty acid synthesis and raises fatty acid oxidation in aerobic muscle in Shetland ponies.
Geelen, S N; Blázquez, C; Geelen, M J; Sloet van Oldruitenborgh-Oosterbaan, M M; Beynen, A C
The metabolic effects of feeding soyabean oil instead of an isoenergetic amount of maize starch plus glucose were studied in ponies. Twelve adult Shetland ponies were given a control diet (15 g fat/kg DM) or a high-fat diet (118 g fat/kg DM) according to a parallel design. The diets were fed for 45 d. Plasma triacylglycerol (TAG) concentrations decreased by 55 % following fat supplementation. Fat feeding also reduced glycogen concentrations significantly by up to 65 % in masseter, gluteus and semitendinosus muscles (P < 0.05 and P < 0.01 and P < 0.01 respectively). The high-fat diet significantly increased the TAG content of semitendinosus muscle by 80 % (P < 0.05). Hepatic acetyl-CoA carboxylase and fatty acid synthase activities were 53 % (P < 0.01) and 56 % (P < 0.01) lower respectively in the high-fat group, but diacylglycerol acyltransferase activity was unaffected. Although carnitine palmitoyltransferase-I (CPT-I) activity in liver mitochondria was not influenced, fat supplementation did render CPT-I less sensitive to inhibition by malonyl-CoA. There was no significant effect of diet on the activity of phosphofructokinase in the different muscles. The activity of citrate synthase was raised significantly (by 25 %; P < 0.05) in the masseter muscle of fat-fed ponies, as was CPT-I activity (by 46 %; P < 0.01). We conclude that fat feeding enhances both the transport of fatty acids through the mitochondrial inner membrane and the oxidative capacity of highly-aerobic muscles. The higher oxidative ability together with the depressed rate of de novo fatty acid synthesis in liver may contribute to the dietary fat-induced decrease in plasma TAG concentrations in equines. PMID:11432762
Effect of process design and operating parameters on aerobic methane oxidation in municipal WWTPs.
Daelman, Matthijs R J; Van Eynde, Tamara; van Loosdrecht, Mark C M; Volcke, Eveline I P
Methane is a potent greenhouse gas and its emission from municipal wastewater treatment plants (WWTPs) should be prevented. One way to do this is to promote the biological conversion of dissolved methane over stripping in aeration tanks. In this study, the well-established Activated Sludge Model n°1 (ASM1) and Benchmark Simulation Model n°1 (BSM1) were extended to study the influence of process design and operating parameters on biological methane oxidation. The aeration function used in BSM 1 was upgraded to more accurately describe gas-liquid transfer of oxygen and methane in aeration tanks equipped with subsurface aeration. Dissolved methane could be effectively removed in an aeration tank at an aeration rate that is in agreement with optimal effluent quality. Subsurface bubble aeration proved to be better than surface aeration, while a CSTR configuration was superior to plug flow conditions in avoiding methane emissions. The conversion of methane in the activated sludge tank benefits from higher methane concentrations in the WWTP's influent. Finally, if an activated sludge tank is aerated with methane containing off-gas, a limited amount of methane is absorbed and converted in the mixed liquor. This knowledge helps to stimulate the methane oxidizing capacity of activated sludge in order to abate methane emissions from wastewater treatment to the atmosphere. PMID:25225767
Use of Advanced Oxidation and Aerobic Degradation for Remediation of Various Hydrocarbon Contaminates
Paul Fallgren
Western Research Institute in conjunction with Sierra West Consultants, Inc., Tetra Tech, Inc., and the U.S. Department of Energy conducted laboratory and field studies to test different approaches to enhance degradation of hydrocarbons and associated contaminants. WRI in conjunction with Sierra West Consultants, Inc., conducted a laboratory and field study for using ozone to treat a site contaminated with MTBE and other hydrocarbons. Results from this study demonstrate that a TOD test can be used to resolve the O{sub 3} dosage problem by establishing a site-specific benchmark dosage for field ozone applications. The follow-up testing of the laboratory samples provided indications that intrinsic biodegradation could be stimulated by adding oxygen. Laboratory studies also suggests that O3 dosage in the full-scale field implementation could be dialed lower than stoichiometrically designed to eliminate the formation of Cr(VI). WRI conducted a study involving a series of different ISCO oxidant applications to diesel-contaminated soil and determined the effects on enhancing biodegradation to degrade the residual hydrocarbons. Soils treated with permanganate followed by nutrients and with persulfate followed by nutrients resulted in the largest decrease in TPH. The possible intermediates and conditions formed from NOM and TPH oxidation by permanganate and activated persulfate favors microbial TPH degrading activity. A 'passive-oxidation' method using microbial fuel cell (MFC) technology was conducted by WRI in conjunction with Tetra Tech, Inc., to degrade MTBE in groundwater. These experiments have demonstrated that a working MFC (i.e., one generating power) could be established in the laboratory using contaminated site water or buffered media inoculated with site water and spiked with MTBE, benzene, or toluene. Electrochemical methods were studied by WRI with goal of utilizing low voltage and amperage electrical sources for 'geo-oxidation' of organic contaminants. The
Effects of oxidation reduction potential in the bypass micro-aerobic sludge zone on sludge reduction for a modified oxic-settling-anaerobic process.
Li, Kexun; Wang, Yi; Zhang, Zhongpin; Liu, Dongfang
Batch experiments were conducted to determine the effect of oxidation reduction potential (ORP) on sludge reduction in a bypass micro-aerobic sludge reduction system. The system was composed of a modified oxic-settling-anaerobic process with a sludge holding tank in the sludge recycle loop. The ORPs in the micro-aerobic tanks were set at approximately +350, -90, -150, -200 and -250 mV, by varying the length of aeration time for the tanks. The results show that lower ORP result in greater sludge volume reduction, and the sludge production was reduced by 60% at the lowest ORP. In addition, low ORP caused extracellular polymer substances dissociation and slightly reduced sludge activity. Comparing the sludge backflow characteristics of the micro-aerobic tank's ORP controlled at -250 mV with that of +350 mV, the average soluble chemical oxygen (SCOD), TN and TP increased by 7, 0.4 and 2 times, median particle diameter decreased by 8.5 μm and the specific oxygen uptake rate (SOUR) decreased by 0.0043 milligram O2 per gram suspended solids per minute. For the effluent, SCOD and TN and TP fluctuated around 30, 8.7 and 0.66 mg/L, respectively. Therefore, the effective assignment of ORP in the micro-aerobic tank can remarkably reduce sludge volume and does not affect final effluent quality. PMID:24845332
Reaction Mechanism and Kinetics of Enargite Oxidation at Roasting Temperatures
NASA Astrophysics Data System (ADS)
Padilla, Rafael; Aracena, Alvaro; Ruiz, Maria C.
Roasting of enargite (Cu3AsS4) in the temperature range of 648 K to 898 K (375 °C to 625 °C) in atmospheres containing variable amounts of oxygen has been studied by thermogravimetric methods. From the experimental results of weight loss/gain data and X-ray diffraction (XRD) analysis of partially reacted samples, the reaction mechanism of the enargite oxidation was determined, which occurred in three sequential stages:
Field and experimental evidence for low-O2 affinity of aerobic methane oxidizers in coastal waters
NASA Astrophysics Data System (ADS)
Steinle, Lea; Maltby, Johanna; Bange, Hermann; Kock, Annette; Lehmann, Moritz F.; Treude, Tina; Niemann, Helge
The coastal ocean accounts for more than 75 % of the global oceanic methane emissions. An important process in mitigating methane emissions from the seawater to the atmosphere is aerobic methane oxidation (MOx). Coastal oceans are highly dynamic systems, in particular with regard to the variability of temperature, salinity, and oxygen concentrations, all of which are potential key environmental factors controlling MOx. We conducted a two-year time-series study of MOx measurements in the water column of a coastal inlet in the southwestern Baltic Sea (Eckernförde Bay, Boknis Eck Time Series Station, 54°31.823 N, 10°02.764 E, 28 m water depth; www.bokniseck.de). Physicochemical parameters at this station have been monitored since 1957. Seasonal stratification during summer/autumn leads to intermittent oxygen depletion (hypoxic to anoxic) in bottom waters in the later part of the stratification period. The duration of these low-oxygen events increased since the 1970s (Lennartz et al., 2014). Furthermore, the organic-rich seafloor continuously produces methane, which leads to gas ebullition followed by accumulation of dissolved methane in bottom waters (up to 470 nM) and supersaturation (with respect to the atmospheric equilibrium) in surface waters (up to 27 nM). MOx communities were most active in bottom waters (1-5 nM/day), which usually contain the lowest oxygen concentrations (sometimes below the in situ detection limit of ~1 µM). In order to better understand the effect of low oxygen concentrations, and thus of hypoxic and suboxic events, on MOx in coastal systems, we conducted lab-based experiments, during which we adjusted oxygen concentrations to values between 0.2 - 220 µM in methane-rich (~100 nM) Eckernförde Bay waters. These samples were then incubated with trace amounts of tritium-labeled methane to assess first order rate constants of methane oxidation. Highest MOx rates were detected at oxygen concentrations of ~0.5 µM (considerably higher than at
Manganese chlorins immobilized on silica as oxidation reaction catalysts.
Castro, Kelly A D F; Pires, Sónia M G; Ribeiro, Marcos A; Simões, Mário M Q; Neves, M Graça P M S; Schreiner, Wido H; Wypych, Fernando; Cavaleiro, José A S; Nakagaki, Shirley
Synthetic strategies that comply with the principles of green chemistry represent a challenge: they will enable chemists to conduct reactions that maximize the yield of products with commercial interest while minimizing by-products formation. The search for catalysts that promote the selective oxidation of organic compounds under mild and environmentally friendly conditions constitutes one of the most important quests of organic chemistry. In this context, metalloporphyrins and analogues are excellent catalysts for oxidative transformations under mild conditions. In fact, their reduced derivatives chlorins are also able to catalyze organic compounds oxidation effectively, although they have been still little explored. In this study, we synthesized two chlorins through porphyrin cycloaddition reactions with 1.3-dipoles and prepared the corresponding manganese chlorins (MnCHL) using adequate manganese(II) salts. These MnCHL were posteriorly immobilized on silica by following the sol-gel process and the resulting solids were characterized by powder X-ray diffraction (PXRD), UVVIS spectroscopy, FTIR, XPS, and EDS. The catalytic activity of the immobilized MnCHL was investigated in the oxidation of cyclooctene, cyclohexene and cyclohexane and the results were compared with the ones obtained under homogeneous conditions. PMID:25841060
Reaction between nitric oxide and ozone in solid nitrogen
NASA Technical Reports Server (NTRS)
Lucas, D.; Pimentel, G. C.
Nitrogen dioxide, NO2, is produced when nitric oxide, NO, and ozone, O3, are suspended in a nitrogen matrix at 11-20 K. The NO2 is formed with first-order kinetics, a 12 K rate constant of (1.4 + or - 0.2) x 0.00001/sec, and an apparent activation energy of 106 + or - 10 cal/mol. Isotopic labeling, variation of concentrations, and cold shield experiments show that the growth of NO2 is due to reaction between ozone molecules and NO monomers, and that the reaction is neither infrared-induced nor does it seem to be a heavy atom tunneling process. Reaction is attributed to nearest-neighbor NO.O3 pairs probably held in a specific orientational relationship that affects the kinetic behavior. When the temperature is raised, more such reactive pairs are generated, presumably by local diffusion. Possible mechanisms are discussed.
Reaction rate oscillations during catalytic CO oxidation: A brief overview
NASA Technical Reports Server (NTRS)
Tsotsis, T. T.; Sane, R. C.
It is not the intent here to present a comprehensive review of the dynamic behavior of the catalytic oxidation of CO. This reaction is one of the most widely studied in the field of catalysis. A review paper by Engel and Ertl has examined the basic kinetic and mechanistic aspects, and a comprehensive paper by Razon and Schmitz was recently devoted to its dynamic behavior. Those interested in further study of the subject should consult these reviews and a number of general review papers on catalytic reaction dynamics. The goal is to present a brief overview of certain interesting aspects of the dynamic behavior of this reaction and to discuss a few questions and issues, which are still the subject of study and debate.
Kinetics of the reaction of nitric oxide with hydrogen
NASA Technical Reports Server (NTRS)
Flower, W. L.; Hanson, R. K.; Kruger, C. H.
Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The reaction kinetics were studied in the temperature range 2400-4500 K using a shock-tube technique. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principle result of the study was the determination of the rate constant for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k sub 1 were obtained for each test through comparisons of measured and numerically predicted NO profiles.
Characterization of DMSO Coordination to Palladium(II) in Solution and Insights into the Aerobic Oxidation Catalyst, Pd(DMSO)2(TFA)2
Diao, Tianning; White, Paul; Guzei, Ilia; Stahl, Shannon S.
Recent studies have shown that Pd(DMSO)2(TFA)2 (TFA = trifluoroacetate) is an effective catalyst for a number of different aerobic oxidation reactions. Here, we provide insights into the coordination properties of DMSO to palladium(II) in both the solid state and in solution. A crystal structure of Pd(DMSO)2(TFA)2 confirms that the solid-state structure of this species has one O-bound and one S-bound DMSO ligand, and a crystallographically characterized mono-DMSO complex, trans-Pd(DMSO)(OH2)(TFA)2, exhibits an S-bound DMSO ligand. 1H and 19F NMR spectroscopic studies show that, in EtOAc and THF-d8, Pd(DMSO)2(TFA)2 consists of an equilibrium mixture of Pd(S-DMSO)(O-DMSO)(TFA)2 and Pd(S-DMSO)2(TFA)2. The O-bound DMSO is determined to be more labile than the S-bound DMSO ligand, and both DMSO ligands are more labile in THF relative to EtOAc as the solvent. DMSO coordination to PdII is substantially less favorable when the TFA ligands are replaced with acetate. An analogous carboxylate ligand effect is observed in the coordination of PdII to the bidentate sulfoxide ligand, 1,2-bis(phenylsulfinyl)ethane. DMSO coordination to Pd(TFA)2 is shown to be incomplete in AcOH-d4 and toluene-d8, resulting in PdII/DMSO adducts with < 2:1 DMSO:PdII stoichiometry. Collectively, these results provide useful insights into the coordination properties of DMSO to PdII under catalytically relevant conditions. PMID:23092381
Maillard reaction, mitochondria and oxidative stress: potential role of antioxidants.
Edeas, M; Attaf, D; Mailfert, A-S; Nasu, M; Joubet, R
Glycation and oxidative stress are two important processes known to play a key role in complications of many disease processes. Oxidative stress, either via increasing reactive oxygen species (ROS), or by depleting the antioxidants may modulate the genesis of early glycated proteins in vivo. Maillard Reactions, occur in vivo as well as in vitro and are associated with the chronic complications of diabetes, aging and age-related diseases. Hyperglycaemia causes the autoxidation of glucose, glycation of proteins, and the activation of polyol metabolism. These changes facilitate the generation of reactive oxygen species and decrease the activity of antioxidant enzymes such as Cu,Zn-superoxide dismutase, resulting in a remarkable increase of oxidative stress. A large body of evidence indicates that mitochondria alteration is involved and plays a central role in various oxidative stress-related diseases. The damaged mitochondria produce more ROS (increase oxidative stress) and less ATP (cellular energy) than normal mitochondria. As they are damaged, they cannot burn or use glucose or lipid and cannot provide cell with ATP. Further, glucose, amino acids and lipid will not be correctly used and will accumulate outside the mitochondria; they will undergo more glycation (as observed in diabetes, obesity, HIV infection and lipodystrophia). The objective of this paper is to discuss how to stop the vicious circle established between oxidative stress, Maillard Reaction and mitochondria. The potential application of some antioxidants to reduce glycation phenomenon and to increase the antioxidant defence system by targeting mitochondria will be discussed. Food and pharmaceutical companies share the same challenge, they must act now, urgently and energetically. PMID:20031340
Carbon nanotube-supported Au-Pd alloy with cooperative effect of metal nanoparticles and organic ketone/quinone groups as a highly efficient catalyst for aerobic oxidation of amines.
Deng, Weiping; Chen, Jiashu; Kang, Jincan; Zhang, Qinghong; Wang, Ye
Functionalised carbon nanotube (CNT)-supported Au-Pd alloy nanoparticles were highly efficient catalysts for the aerobic oxidation of amines. We achieved the highest turnover frequencies (>1000 h(-1)) for the oxidative homocoupling of benzylamine and the oxidative dehydrogenation of dibenzylamine. We discovered a cooperative effect between Au-Pd nanoparticles and ketone/quinone groups on CNTs. PMID:27125360
Potential of nitrous oxide recovery from an aerobic/oxic/anoxic SBR process.
Zhao, Jianqiang; Huang, Nan; Hu, Bo; Jia, Luwei; Ge, Guanghuan
A single sequencing batch reactor (SBR) with an operating mode of anaerobic/oxic/anoxic (A/O/A) was developed to determine a simpler process to recover nitrous oxide (N2O) from synthetic wastewater containing ammonia and glucose. This SBR system was initiated in A/O mode to implement nitritation (ammonia to nitrite) and then switched to A/O/A mode. Using measurements of the dissolved N2O concentration and release rate, the total production and conversion rate of N2O were calculated to reveal the potential of producing and recovering N2O in the extended anoxic phase. Results showed that the A/O/A SBR could convert the majority of the nitrite available in the system into N2O by heterotrophic denitritation over longer anoxic periods, and a conversion rate of 77% could be achieved. As a consequence, the A/O/A SBR presents potential ability to produce and recover N2O from wastewater containing ammonia and organic carbon. PMID:26942527
Photovoltaic-driven organic electrosynthesis and efforts toward more sustainable oxidation reactions
Nguyen, Bichlien H; Perkins, Robert J; Smith, Jake A
Summary The combination of visible light, photovoltaics, and electrochemistry provides a convenient, inexpensive platform for conducting a wide variety of sustainable oxidation reactions. The approach presented in this article is compatible with both direct and indirect oxidation reactions, avoids the need for a stoichiometric oxidant, and leads to hydrogen gas as the only byproduct from the corresponding reduction reaction. PMID:25815081
Osmium(0) nanoclusters stabilized by zeolite framework; highly active catalyst in the aerobic oxidation of alcohols under mild conditions.
Zahmakiran, Mehmet; Akbayrak, Serdar; Kodaira, Tetsuya; Ozkar, Saim
Osmium(0) nanoclusters stabilized by zeolite-Y framework were reproducibly prepared by a simple two step procedure involving the incorporation of osmium(III) cations into the zeolite matrix by ion-exchange, followed by their reduction within the cavities of zeolite with sodium borohydride in aqueous solution all at room temperature. The composition and morphology of osmium(0) nanoclusters stabilized by zeolite framework, as well as the integrity and crystallinity of the host material were investigated by using ICP-OES, XRD, XPS, SEM, TEM, HRTEM, TEM/EDX, mid-IR, far-IR spectroscopies, and N(2)-adsorption/desorption technique. The results of the multiprong analysis reveal the formation of osmium(0) nanoclusters within the cavities of zeolite-Y without causing alteration in the framework lattice, formation of mesopores, or loss in the crystallinity of the host material. More importantly, far-IR studies showed that after the reduction of Os(3+) cations by sodium borohydride the Na(+) cations reoccupy their authentic cation sites restoring the integrity of zeolite-Y. The catalytic activity of osmium(0) nanoclusters stabilized by zeolite framework was tested in the aerobic oxidation of activated, unactivated and heteroatom containing alcohols to carbonyl compounds and was found to provide high activity and selectivity even under mild conditions (80 degrees C and 1 atm O(2) or air). Moreover, they were found to be stable enough to be isolated and bottled as solid material, which can be reused as active catalyst under the identical conditions of the first run. PMID:20614055
Continuous Aerobic Training in Individualized Intensity Avoids Spontaneous Physical Activity Decline and Improves MCT1 Expression in Oxidative Muscle of Swimming Rats
Scariot, Pedro P. M.; Manchado-Gobatto, Fúlvia de Barros; Torsoni, Adriana S.; dos Reis, Ivan G. M.; Beck, Wladimir R.; Gobatto, Claudio A.
Although aerobic training has been shown to affect the lactate transport of skeletal muscle, there is no information concerning the effect of continuous aerobic training on spontaneous physical activity (SPA). Because every movement in daily life (i.e., SPA) is generated by skeletal muscle, we think that it is possible that an improvement of SPA could affect the physiological properties of muscle with regard to lactate transport. The aim of this study was to evaluate the effect of 12 weeks of continuous aerobic training in individualized intensity on SPA of rats and their gene expressions of monocarboxylate transporters (MCT) 1 and 4 in soleus (oxidative) and white gastrocnemius (glycolytic) muscles. We also analyzed the effect of continuous aerobic training on aerobic and anaerobic parameters using the lactate minimum test (LMT). Sixty-day-old rats were randomly divided into three groups: a baseline group in which rats were evaluated prior to initiation of the study; a control group (Co) in which rats were kept without any treatment during 12 weeks; and a chronic exercise group (Tr) in which rats swam for 40 min/day, 5 days/week at 80% of anaerobic threshold during 12 weeks. After the experimental period, SPA of rats was measured using a gravimetric method. Rats had their expression of MCTs determined by RT-PCR analysis. In essence, aerobic training is effective in maintaining SPA, but did not prevent the decline of aerobic capacity and anaerobic performance, leading us to propose that the decline of SPA is not fully attributed to a deterioration of physical properties. Changes in SPA were concomitant with changes in MCT1 expression in the soleus muscle of trained rats, suggestive of an additional adaptive response toward increased lactate clearance. This result is in line with our observation showing a better equilibrium on lactate production-remotion during the continuous exercise (LMT). We propose an approach to combat the decline of SPA of rats in their home
Continuous Aerobic Training in Individualized Intensity Avoids Spontaneous Physical Activity Decline and Improves MCT1 Expression in Oxidative Muscle of Swimming Rats.
Scariot, Pedro P M; Manchado-Gobatto, Fúlvia de Barros; Torsoni, Adriana S; Dos Reis, Ivan G M; Beck, Wladimir R; Gobatto, Claudio A
Although aerobic training has been shown to affect the lactate transport of skeletal muscle, there is no information concerning the effect of continuous aerobic training on spontaneous physical activity (SPA). Because every movement in daily life (i.e., SPA) is generated by skeletal muscle, we think that it is possible that an improvement of SPA could affect the physiological properties of muscle with regard to lactate transport. The aim of this study was to evaluate the effect of 12 weeks of continuous aerobic training in individualized intensity on SPA of rats and their gene expressions of monocarboxylate transporters (MCT) 1 and 4 in soleus (oxidative) and white gastrocnemius (glycolytic) muscles. We also analyzed the effect of continuous aerobic training on aerobic and anaerobic parameters using the lactate minimum test (LMT). Sixty-day-old rats were randomly divided into three groups: a baseline group in which rats were evaluated prior to initiation of the study; a control group (Co) in which rats were kept without any treatment during 12 weeks; and a chronic exercise group (Tr) in which rats swam for 40 min/day, 5 days/week at 80% of anaerobic threshold during 12 weeks. After the experimental period, SPA of rats was measured using a gravimetric method. Rats had their expression of MCTs determined by RT-PCR analysis. In essence, aerobic training is effective in maintaining SPA, but did not prevent the decline of aerobic capacity and anaerobic performance, leading us to propose that the decline of SPA is not fully attributed to a deterioration of physical properties. Changes in SPA were concomitant with changes in MCT1 expression in the soleus muscle of trained rats, suggestive of an additional adaptive response toward increased lactate clearance. This result is in line with our observation showing a better equilibrium on lactate production-remotion during the continuous exercise (LMT). We propose an approach to combat the decline of SPA of rats in their home
Visible-Light-Induced Photoredox Catalysis of Dye-Sensitized Titanium Dioxide: Selective Aerobic Oxidation of Organic Sulfides.
Lang, Xianjun; Zhao, Jincai; Chen, Xiaodong
TiO2 photoredox catalysis has recently attracted much interest for use in performing challenging organic transformations under mild reaction conditions. However, the reaction scheme is hampered by the fact that TiO2 can only be excited by UV light of wavelengths λ shorter than 385 nm. One promising strategy to overcome this issue is to anchor an organic, preferably metal-free dye onto the surface of TiO2 . Importantly, we observed that the introduction of a catalytic amount of the redox mediator TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl)oxyl] ensured the stability of the anchored dye, alizarin red S, thereby resulting in the selective oxidation of organic sulfides with O2 . This result affirms the essential role of the redox mediator in enabling the organic transformations by visible-light photoredox catalysis. PMID:26969891
Formation of phenol under conditions of the reaction of oxidative carbonylation of benzene to benzoic acid
Kalinovsky, I.O.; Leshcheva, A.N.; Pogorelov, V.V.; Gelbshtein, A.I.
This paper describes conditions for the oxidation of benzene to phenol. It is shown that a reaction mixture of water, carbon monoxide, and oxygen are essential to the oxidation. The oxidation is a side reaction found to occur during the oxidative carbonylation of benzene to benzoic acid in a medium of trifluoroacetic acid.
Complete reaction mechanisms of mercury oxidation on halogenated activated carbon.
Rungnim, Chompoonut; Promarak, Vinich; Hannongbua, Supa; Kungwan, Nawee; Namuangruk, Supawadee
The reaction mechanisms of mercury (Hg) adsorption and oxidation on halogenated activated carbon (AC) have been completely studied for the first time using density functional theory (DFT) method. Two different halogenated AC models, namely X-AC and X-AC-X (X=Cl, Br, I), were adopted. The results revealed that HgX is found to be stable-state on the AC edge since its further desorption from the AC as HgX, or further oxidation to HgX2, are energetically unfavorable. Remarkably, the halide type does not significantly affect the Hg adsorption energy but it strongly affects the activation energy barrier of HgX formation, which obviously increases in the order HgI
Kinetics of the reaction of nitric oxide with hydrogen
NASA Technical Reports Server (NTRS)
Flower, W. L.; Hanson, R. K.; Kruger, C. H.
The reaction of nitric oxide with hydrogen has been studied in the temperature range 2400-4500 K using a shock-tube technique. Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principal result of the study was the determination of the rate constant k1 for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k1 were obtained for each test through comparisons of measured and numerically predicted NO profiles. The data are fit closely by the expression k1 = 1.34 times 10 to the fourteenth power exp(-49 200/RT) cu cm/mole-sec. These data appear to be the first available for this rate constant.
Surface-oxidized carbon black as a catalyst for the water oxidation and alcohol oxidation reactions.
Suryanto, Bryan H R; Zhao, Chuan
Carbon black (CB) is popularly used as a catalyst support for metal/metal oxide nanoparticles due to its large surface area, excellent conductivity and stability. Herein, we show that surface oxidized CB itself, after acidic treatment and electrochemical oxidation, exhibits significant catalytic activity for the electrochemical oxidation of water and alcohols. PMID:27097802
The effect of low-level laser therapy on oxidative stress and functional fitness in aged rats subjected to swimming: an aerobic exercise.
Guaraldo, Simone A; Serra, Andrey Jorge; Amadio, Eliane Martins; Antônio, Ednei Luis; Silva, Flávio; Portes, Leslie Andrews; Tucci, Paulo José Ferreira; Leal-Junior, Ernesto Cesar Pinto; de Carvalho, Paulo de Tarso Camillo
The aim of the present study was to determine whether low-level laser therapy (LLLT) in conjunction with aerobic training interferes with oxidative stress, thereby influencing the performance of old rats participating in swimming. Thirty Wistar rats (Norvegicus albinus) (24 aged and six young) were tested. The older animals were randomly divided into aged-control, aged-exercise, aged-LLLT, aged-LLLT/exercise, and young-control. Aerobic capacity (VO2max(0.75)) was analyzed before and after the training period. The exercise groups were trained for 6 weeks, and the LLLT was applied at 808 nm and 4 J energy. The rats were euthanized, and muscle tissue was collected to analyze the index of lipid peroxidation thiobarbituric acid reactive substances (TBARS), glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) activities. VO2 (0.75)max values in the aged-LLLT/exercise group were significantly higher from those in the baseline older group (p <0.01) and the LLLT and exercise group (p <0.05). The results indicate that the activities of CAT, SOD, and GPx were higher and statistically significant (p <0.05) in the LLLT/exercise group than those in the LLLT and exercise groups. Young animals presented lesser and statistically significant activities of antioxidant enzymes compared to the aged group. The LLLT/exercise group and the LLLT and exercise group could also mitigate the concentration of TBARS (p > 0.05). Laser therapy in conjunction with aerobic training may reduce oxidative stress, as well as increase VO2 (0.75)max, indicating that an aerobic exercise such as swimming increases speed and improves performance in aged animals treated with LLLT. PMID:26861983
A biomimetic pathway for vanadium-catalyzed aerobic oxidation of alcohols: evidence for a base-assisted dehydrogenation mechanism.
Wigington, Bethany N; Drummond, Michael L; Cundari, Thomas R; Thorn, David L; Hanson, Susan K; Scott, Susannah L
The first step in the catalytic oxidation of alcohols by molecular O(2), mediated by homogeneous vanadium(V) complexes [LV(V)(O)(OR)], is ligand exchange. The unusual mechanism of the subsequent intramolecular oxidation of benzyl alcoholate ligands in the 8-hydroxyquinolinato (HQ) complexes [(HQ)(2)V(V)(O)(OCH(2)C(6)H(4)-p-X)] involves intermolecular deprotonation. In the presence of triethylamine, complex 3 (X = H) reacts within an hour at room temperature to generate, quantitatively, [(HQ)(2)V(IV)(O)], benzaldehyde (0.5 equivalents), and benzyl alcohol (0.5 equivalents). The base plays a key role in the reaction: in its absence, less than 12% conversion was observed after 72 hours. The reaction is first order in both 3 and NEt(3), with activation parameters ΔH(≠)=(28±4) kJ mol(-1) and ΔS(≠)=(-169±4) J K(-1) mol(-1). A large kinetic isotope effect, 10.2±0.6, was observed when the benzylic hydrogen atoms were replaced by deuterium atoms. The effect of the para substituent of the benzyl alcoholate ligand on the reaction rate was investigated using a Hammett plot, which was constructed using σ(p). From the slope of the Hammett plot, ρ=+(1.34±0.18), a significant buildup of negative charge on the benzylic carbon atom in the transition state is inferred. These experimental findings, in combination with computational studies, support an unusual bimolecular pathway for the intramolecular redox reaction, in which the rate-limiting step is deprotonation at the benzylic position. This mechanism, that is, base-assisted dehydrogenation (BAD), represents a biomimetic pathway for transition-metal-mediated alcohol oxidations, differing from the previously identified hydride-transfer and radical pathways. It suggests a new way to enhance the activity and selectivity of vanadium catalysts in a wide range of redox reactions, through control of the outer coordination sphere. PMID:23080554
Laccase-Functionalized Graphene Oxide Assemblies as Efficient Nanobiocatalysts for Oxidation Reactions
Patila, Michaela; Kouloumpis, Antonios; Gournis, Dimitrios; Rudolf, Petra; Stamatis, Haralambos
Multi-layer graphene oxide-enzyme nanoassemblies were prepared through the multi-point covalent immobilization of laccase from Trametes versicolor (TvL) on functionalized graphene oxide (fGO). The catalytic properties of the fGO-TvL nanoassemblies were found to depend on the number of the graphene oxide-enzyme layers present in the nanostructure. The fGO-TvL nanoassemblies exhibit an enhanced thermal stability at 60 °C, as demonstrated by a 4.7-fold higher activity as compared to the free enzyme. The multi-layer graphene oxide-enzyme nanoassemblies can efficiently catalyze the oxidation of anthracene, as well as the decolorization of an industrial dye, pinacyanol chloride. These materials retained almost completely their decolorization activity after five reaction cycles, proving their potential as efficient nano- biocatalysts for various applications. PMID:26927109
Reactions of oxidatively activated arylamines with thiols: reaction mechanisms and biologic implications. An overview.
Eyer, P
Aromatic amines belong to a group of compounds that exert their toxic effects usually after oxidative biotransformation, primarily in the liver. In addition, aromatic amines also undergo extrahepatic activation to yield free arylaminyl radicals. The reactive intermediates are potential promutagens and procarcinogens, and responsible for target tissue toxicity. Since thiols react with these intermediates at high rates, it is of interest to know the underlying reaction mechanisms and the toxicologic implications. Phenoxyl radicals from aminophenols and aminyl radicals from phenylenediamines quickly disproportionate to quinone imines and quinone diimines. Depending on the structure, Michael addition or reduction reactions with thiols may prevail. Products of sequential oxidation/addition reactions (e.g., S-conjugates of aminophenols) are occasionally more toxic than the parent compounds because of their higher autoxidizability and their accumulation in the kidney. Even after covalent binding of quinone imines to protein SH groups, the resulting thioethers are able to autoxidize. The quinoid thioethers can then cross-link the protein by addition to neighboring nucleophiles. The reactions of nitrosoarenes with thiols yield a so-called "semimercaptal" from which various branching reactions detach, depending on substituents. Compounds with strong pi-donors, like 4-nitrosophenetol, give a resonance-stabilized N-(thiol-S-yl)-arylamine cation that may lead to bicyclic products, thioethers, and DNA adducts. Examples of toxicologic implications of the interactions of nitroso compounds with thiols are given for nitrosoimidazoles, heterocyclic nitroso compounds from protein pyrolysates, and nitrosoarenes. These data indicate that interactions of activated arylamines with thiols may not be regarded exclusively as detoxication reactions. PMID:7889834
A factorial randomized controlled trial to evaluate the effect of micronutrients supplementation and regular aerobic exercise on maternal endothelium-dependent vasodilatation and oxidative stress of the newborn
Background Many studies have suggested a relationship between metabolic abnormalities and impaired fetal growth with the development of non-transmissible chronic diseases in the adulthood. Moreover, it has been proposed that maternal factors such as endothelial function and oxidative stress are key mechanisms of both fetal metabolic alterations and subsequent development of non-transmissible chronic diseases. The objective of this project is to evaluate the effect of micronutrient supplementation and regular aerobic exercise on endothelium-dependent vasodilation maternal and stress oxidative of the newborn. Methods and design 320 pregnant women attending to usual prenatal care in Cali, Colombia will be included in a factorial randomized controlled trial. Women will be assigned to the following intervention groups: 1. Control group: usual prenatal care (PC) and placebo (maltodextrine). 2. Exercise group: PC, placebo and aerobic physical exercise. 3. Micronutrients group: PC and a micronutrients capsule consisting of zinc (30 mg), selenium (70 μg), vitamin A (400 μg), alphatocopherol (30 mg), vitamin C (200 mg), and niacin (100 mg). 4. Combined interventions Group: PC, supplementation of micronutrients, and aerobic physical exercise. Anthropometric measures will be taken at the start and at the end of the interventions. Discussion Since in previous studies has been showed that the maternal endothelial function and oxidative stress are related to oxidative stress of the newborn, this study proposes that complementation with micronutrients during pregnancy and/or regular physical exercise can be an early and innovative alternative to strengthen the prevention of chronic diseases in the population. Trial registration NCT00872365. PMID:21356082
[Inactivation of o-diphenoloxidase in the pyrocatechol oxidation reaction].
Butovich, I A; Tertykh, V A
The inactivation kinetics of o-diphenoloxidase isolated from potato tubers was studied in the process of pyrocatechol oxidation. The enzyme when saturated with the substrate is inactivated with the inactivation rate constant kin = 0.5-1.0 min-1; kin depends on the initial concentration of pyrocatechol. The ultimate yield of the enzymic reaction product increases linearly with the initial concentration of the enzyme. Introduction of ethylene-diaminosulphate, a substance which condenses with o-quinones, does not increase the operation stability of o-diphenoloxidase. The data obtained evidence for inactivation of o-diphenoloxidase either at the level of the enzyme-substrate complex or due to bimolecular reaction with the substrate. PMID:6438852
Photochemical reactions of biologically important quinoxaline n-oxides
Dvoryantseva, G.G.; Tetenchuk, K.P.; Pol'shakov, V.I.; Elina, A.S.
The authors study the photochemical reactions of quinoxidine, dioxidine, and a number of related derivatives of quinoxaline 1,4-di-N-oxides containing methyl, halomethyl, and carboxamide groups in the pyrazine ring. Thin-layer chromatography, UV spectrophotometry, and NMR/sup 1/H and /sup 13/C spectroscopy were used as the main methods for monitoring the photolysis process and establishing the structure of the products formed. The investigation established that two types of photochemical reactions are observed in the series of compounds discussed: photoisomerization with migration of a substitutent to the nitrogen atom of the heterocycle, and photorearrangement with elimination of a substituent and the formation of the corresponding lactams.
Direct Reaction of Amides with Nitric Oxide To Form Diazeniumdiolates
We report the apparently unprecedented direct reaction of nitric oxide (NO) with amides to generate ions of structure R(C=O)NH–N(O)=NO–, with examples including R = Me (1a) or 3-pyridyl (1b). The sodium salts of both released NO in pH 7.4 buffer, with 37 °C half-lives of 1–3 min. As NO-releasing drug candidates, diazeniumdiolated amides would have the advantage of generating only 1 equiv of base on hydrolyzing exhaustively to NO, in contrast to their amine counterparts, which generate 2 equiv of base. PMID:25210948
Fly Ash and Mercury Oxidation/Chlorination Reactions
Sukh Sidhu; Patanjali Varanasi
Mercury is a known pollutant that has detrimental effect on human health and environment. The anthropogenic emissions of mercury account for 10 to 30% of worldwide mercury emissions. There is a need to control/reduce anthropogenic mercury emissions. Many mercury control technologies are available but their effectiveness is dependent on the chemical form of mercury, because different chemical forms of mercury have different physical and chemical properties. Mercury leaves the boiler in its elemental form but goes through various transformations in the post-combustion zone. There is a need to understand how fly ash and flue gas composition affect speciation, partitioning, and reactions of mercury under the full range of post-combustion zone conditions. This knowledge can then be used to predict the chemical transformation of mercury (elemental, oxidized or particulate) in the post combustion zone and thus help with the control of mercury emissions from coal-burning power plants. To accomplish this goal present study was conducted using five coal fly ashes. These ashes were characterized and their catalytic activity was compared under selected reaction conditions in a fixed bed reactor. Based on the results from these fly ash experiments, three key components (carbon, iron oxide and calcium oxide) were chosen. These three components were then used to prepare model fly ashes. Silica/alumina was used as a base for these model fly ashes. One, two or three component model fly ashes were then prepared to investigate mercury transformation reactions. The third set of experiments was performed with CuO and CuCl2 catalysts to further understand the mercury oxidation process. Based on the results of these three studies the key components were predicted for different fly ash compositions under variety of flue gas conditions. A fixed bed reactor system was used to conduct this study. In all the experiments, the inlet concentration of Hg0(g) was maintained at 35 {micro}g/m3 using
Reduction of a phosphorus oxide and acid reaction set
Twarowski, A.
It has been predicted for some time that hypersonic aircraft will suffer from diminished fuel efficiency due to the slow speed of radical recombination in the nozzle of the aircraft and the consequent expulsion of high-energy fragments during high Mach number flight. The addition of small amounts of phosphine combustion products (phosphorus oxides and acids) to water vapor has been found to result in a faster relaxation rate of OH to its equilibrium density following H{sub 2}O photolysis. This article describes the systematic construction of a reaction model of 162 phosphorus reactions among 17 phosphorus-containing species. Those reactions that contribute to the reestablishment of equilibrium following the perturbation of the system by H{sub 2}O photolysis or by an increase in temperature are identified. A thermodynamic free energy function is used to quantify the rate of system relaxation back to equilibrium for a series of 36 reaction conditions covering a temperature range of 1,500 to 3,000 K, a gas density range of 5 {times} 10{sup {minus}7} to 5 {times} 10{sup {minus}5} mol/cm{sup 3} and a fuel equivalence ratio of 0.8 to 1.2.
Self-catalysed aerobic oxidization of organic linker in porous crystal for on-demand regulation of sorption behaviours
NASA Astrophysics Data System (ADS)
Liao, Pei-Qin; Zhu, Ai-Xin; Zhang, Wei-Xiong; Zhang, Jie-Peng; Chen, Xiao-Ming
Control over the structure and property of synthetic materials is crucial for practical applications. Here we report a facile, green and controllable solid-gas reaction strategy for on-demand modification of porous coordination polymer. Copper(I) and a methylene-bridged bis-triazolate ligand are combined to construct a porous crystal consisting of both enzyme-like O2-activation site and oxidizable organic substrate. Thermogravimetry, single-crystal X-ray diffraction, electron paramagnetic resonance and infrared spectroscopy showed that the methylene groups can be oxidized by O2/air even at room temperature via formation of the highly active Cu(II)-O2˙- intermediate, to form carbonyl groups with enhance rigidity and polarity, without destroying the copper(I) triazolate framework. Since the oxidation degree or reaction progress can be easily monitored by the change of sample weight, gas sorption property of the crystal can be continuously and drastically (up to 4 orders of magnitude) tuned to give very high and even invertible selectivity for CO2, CH4 and C2H6.
Direct growth of flower-like manganese oxide on reduced graphene oxide towards efficient oxygen reduction reaction.
Zhang, Jintao; Guo, Chunxian; Zhang, Lianying; Li, Chang Ming
Three-dimensional manganese oxide is directly grown on reduced graphene oxide (RGO) sheets, exhibiting comparable catalytic activity, higher selectivity and better stability towards oxygen reduction reaction than those of the commercial Pt/XC-72 catalyst. PMID:23745182
Missing aerobic-phase nitrogen: The potential for heterotrophic reduction of autotrophically generated nitrous oxide in a sequencing batch reactor wastewater treatment system.
Shiskowskii, D M; Mavinic, D S
Several biochemical pathways can induce nitrogen loss from aerated, aerobic wastewater treatment bioreactors. These pathways include "traditional" simultaneous nitrification-denitrification (SND) (i.e. autotrophic nitrification - heterotrophic denitrification), autotrophic denitrification, and anaerobic ammonia oxidation. An oxygen limitation, often expressed in terms of low dissolved oxygen (DO) concentration, is a common element of these pathways. The presented research investigated the effect of mixed liquor DO concentration and biomass slowly degradable carbon (SDC) utilization rate on the heterotrophic nitrous oxide (N2O) reduction rate, for biomass cultured in an anoxic/aerobic wastewater treatment bioreactor. Biomass oxygen and SDC availability-limitation, expressed in terms of DO concentration and SDC ultilization rate, respectively, were found to significantly impact the observed heterotrophic N2O reduction rate. The findings support the hypothesis that nitrogen lost from the mixed liquor of an aerobic bioreactor could result from simultaneous autotrophic N2O generation (i.e. autotrophic denitrification) and heterotrophic N2O reduction. The results also support the idea that autotrophic N2O generation could be occurring in a bioreactor, although N2O may not be measurable in the reactor off-gas. Therefore, this autotrophic N2O generation - heterotrophic N2O reduction mechanism provides an alternative explanation to nitrogen loss, when compared to "conventional" SND, where heterotrophic organisms are assumed to reduce autotrophically generated nitrite and nitrate to dinitrogen (N2). In addition, nitrogen loss speculatively attributed to N2 formation via anaerobic ammonia oxidation in oxygen-limited environments, again because of the absence of measurable N2O, may in fact be due to the autotrophic N2O generation - heterotrophic N2O reduction mechanism. PMID:16128383
Functionalized poly(ethylene glycol)-stabilized water-soluble palladium nanoparticles: property/activity relationship for the aerobic alcohol oxidation in water.
Feng, Bo; Hou, Zhenshan; Yang, Hanmin; Wang, Xiangrui; Hu, Yu; Li, Huan; Qiao, Yunxiang; Zhao, Xiuge; Huang, Qingfa
The preparation, characterization, and catalytic properties of water-soluble palladium nanoparticles stabilized by the functionalized-poly(ethylene glycol) as a protective ligand were demonstrated for aerobic oxidation of alcohols in aqueous phase. UV/vis spectra and X-ray photoelectron spectroscopy (XPS) proved that there was an electronic interaction between the bidentate nitrogen ligand and palladium atoms. Transmission electron microscopy and XPS analysis showed that the particle size and surface properties of the generated palladium nanoparticles can be controlled by varying the amount of protective ligand and the kinds of reducing agents. It was found that both the size and surface properties of palladium nanoparticles played very important roles in affecting catalytic performance. The stabilized metallic palladium nanoparticles were proven to be the active centers for benzyl alcohol oxidation in the present system, and the water-soluble Pd nanocatalysts can also be extended to the selective oxidation of various alcohols. PMID:20039597
Pd-catalyzed intramolecular aerobic oxidative C-H amination of 2-aryl-3-(arylamino)quinazolinones: synthesis of fluorescent indazolo[3,2-b]quinazolinones.
Yang, Weiguang; Chen, Jiuxi; Huang, Xiaobo; Ding, Jinchang; Liu, Miaochang; Wu, Huayue
A palladium-catalyzed intramolecular aerobic oxidative C-H amination of 2-aryl-3-(arylamino)quinazolinones has been developed, providing a variety of substituted indazolo[3,2-b]quinazolinone derivatives in moderate to excellent yields. Preliminary mechanistic studies suggested that a palladacycle dimer could be the key intermediate, which underwent a cascade "rollover" cyclometalation and C-H amination sequence. Furthermore, the potential utility of these products has been demonstrated as a new class of blue fluorophores for fluorescent materials. PMID:25290066
Theoretical study on the catalytic reactivity of N-hydroxyphthalimide tuned by different heterocyclic substitutions on its phenyl ring for aerobic oxidation
NASA Astrophysics Data System (ADS)
Chen, Kexian; Xie, Haiying; Jiang, Kezhi; Mao, Jianyong
The structure-reactivity relationship of new hydroxyimide organocatalysts based on the heterocyclic replacements of the phenyl ring of N-hydroxyphthalimide (NHPI) has been theoretically investigated to gain a mature understanding of this particular catalysis for aerobic oxidation. We find that the reactivity of catalysts with the common five-member aromatic rings is lower than that of NHPI. The catalyst with the recyclable structure of imidazolium ionic liquid may serve as a novel model catalyst for further improvements due to its reactivity comparable to that of NHPI. The catalytic reactivity of multi-nitroxyl catalysts is theoretically more fascinating than that of the highly efficient N,N-dihydroxypyromellitimide.
Theagalloflavic Acid, a New Pigment Derived from Hexahydroxydiphenoyl Group, and Lignan Oxidation Products Produced by Aerobic Microbial Fermentation of Green Tea.
Matsuo, Yosuke; Matsuda, Tomoko; Sugihara, Keisuke; Saito, Yoshinori; Zhang, Ying-Jun; Yang, Chong-Ren; Tanaka, Takashi
Chinese ripe pu-erh tea is produced by aerobic microbial fermentation of green tea. To clarify the microbial degradation of tea polyphenols, Japanese commercial green tea was mixed with Chinese ripe pu-erh tea, which retains microorganisms, and fermented for 5 d. Chromatographic separation yielded a novel water-soluble yellow pigment termed theagalloflavic acid. Spectroscopic and chemical evidence suggested that this pigment was produced by oxidative ring cleavage of hexahydroxydiphenoyl esters. In addition, two new oxygenated lignin metabolites, (+)-5,5'-dihydroxypinoresinol and 5-hydroxydihydrodehydrodiconiferyl alcohol, were also isolated together with known degradation products of quercetin and tea catechins. PMID:27373646
Release of substituents from phenolic compounds during oxidative coupling reactions.
Dec, Jerzy; Haider, Konrad; Bollag, Jean-Marc
Phenolic compounds originating from plant residue decomposition or microbial metabolism form humic-like polymers during oxidative coupling reactions mediated by various phenoloxidases or metal oxides. Xenobiotic phenols participating in these reactions undergo either polymerization or binding to soil organic matter. Another effect of oxidative coupling is dehalogenation, decarboxylation or demethoxylation of the substrates. To investigate these phenomena, several naturally occurring and xenobiotic phenols were incubated with various phenoloxidases (peroxidase, laccase, tyrosinase) or with birnessite (delta-MnO(2)), and monitored for chloride release, CO(2) evolution, and methanol or methane production. The release of chloride ions during polymerization and binding ranged between 0.2% and 41.4%. Using the test compounds labeled with 14C in three different locations (carboxyl group, aromatic ring, or aliphatic chain), it was demonstrated that 14CO(2) evolution was mainly associated with the release of carboxyl groups (17.8-54.8% of the initial radioactivity). Little mineralization of 14C-labeled aromatic rings or aliphatic carbons occurred in catechol, ferulic or p-coumaric acids (0.1-0.7%). Demethoxylation ranged from 0.5% to 13.9% for 2,6-dimethoxyphenol and syringic acid, respectively. Methylphenols showed no demethylation. In conclusion, dehalogenation, decarboxylation and demethoxylation of phenolic substrates appear to be controlled by a common mechanism, in which various substituents are released if they are attached to carbon atoms involved in coupling. Electron-withdrawing substituents, such as -COOH and -Cl, are more susceptible to release than electron-donating ones, such as -OCH(3) and -CH(3). The release of organic substituents during polymerization and binding of phenols may add to CO(2) production in soil. PMID:12738292
Porous platinum mesoflowers with enhanced activity for methanol oxidation reaction
Zhuang Lina; Wang Wenjin; Hong Feng; Yang Shengchun; You Hongjun; Fang Jixiang; Ding Bingjun
Porous Pt and Pt-Ag alloy mesoflowers (MFs) with about 2 {mu}m in diameter and high porosity were synthesized using Ag mesoflowers as sacrificial template by galvanic reaction. The silver content in Pt-Ag alloys can be facilely controlled by nitric acid treatment. And the pure Pt MFs can be obtained by selective removal of silver element from Pt{sub 72}Ag{sub 28} MFs electrochemically. Both Pt{sub 45}Ag{sub 55}, Pt{sub 72}Ag{sub 28} and pure Pt show a high catalytic performance in methanol oxidation reaction (MOR). Especially, pure Pt MFs exhibited a 2 to 3 times current density enhancement in MOR compared with the commercial used Pt black, which can be attributed to their porous nanostructure with 3-dimentional nature and small crystal sizes. - Graphical Abstract: The CVs of MOR on Pt (red) and Pt black (green) catalysts in 0.1 M HClO{sub 4} and 0.5 M CH{sub 3}OH for specific mass current. The insert shows the SEM images of two porous Pt MFs. Platinum mesoflowers (MFs) with about 2 {mu}m in diameter and high porosity were synthesised with Ag mesoflowers as sacrificial template by galvanic replacement. The porous Pt MFs exhibited a more than 3 times enhancement in electrocatalytic performance for methanol oxidation reaction compared the commercial used Pt black. Highlights: Black-Right-Pointing-Pointer Porous Pt and Pt-Ag mesoflowers (MFs) were synthesized using Ag MFs sacrifical template. Black-Right-Pointing-Pointer Pt MFs presents an improved catalytic activity in MOR compared with Pt black. Black-Right-Pointing-Pointer We provided a facile approach for the development of high performance Pt electrocatalysts for fuel cells.
Kinetics and dynamics of oxidation reactions involving an adsorbed CO species on bulk and supported platinum and copper-oxide
Harold, M.P.
The proposed research is an integrated experimental and modeling study of oxidation reactions involving CO as a key player -- be it a reactant, adsorbed intermediate, and/or partial oxidation product -- in the catalytic sequence and chemistry. The reaction systems of interest in the project include CO, formaldehyde, and methanol oxidation by O{sub 2} and CO oxidation by NO, on both Pt and copper oxide catalysts. These reactions are of importance in automobile exhaust catalysis. There is a paucity of rate data in the literature for these important environmental control reactions. The goal of this research is to better understand the catalytic chemistry and kinetics of oxidations reactions involving CO as an adsorbed intermediate. Successfully meeting this goal requires an integration of basic kinetic measurements, in situ catalyst surface monitoring, kinetic modeling, and nonlinear mathematical tools.
Pyrite oxidation in unsaturated aquifer sediments. Reaction stoichiometry and rate of oxidation.
Andersen, M S; Larsen, F; Postma, D
The oxidation of pyrite (FeS2) contained in unsaturated aquifer sediment was studied by sediment incubation in gas impermeable polymer laminate bags. Reaction progress was followed over a period of nearly 2 months by monitoring the gas composition within the laminate bag. The gas phase in the incubation bags became depleted in O2 and enriched in CO2 and N2 and was interpreted as due to pyrite oxidation in combination with calcite dissolution. Sediment incubation provides a new method to estimate low rates of pyrite oxidation in unsaturated zone aquifer sediments. Oxidation rates of up to 9.4 x 10(-10) mol FeS2/g x s are measured, and the rates are only weakly correlated with the sediment pyrite content. The reactivity of pyrite, including the inhibition by FeOOH layers formed on its surface, apparently has a major effect on the rate of oxidation. The code PHREEQC 2.0 was used to calculate the reaction stoichiometry and partitioning of gases between the solution and the gas phase. Pyrite oxidation with concurrent calcite dissolution was found to be consistent with the experimental data while organic carbon oxidation was not. The reaction involves changes in the total volume of the gas phase. The reaction scheme predicts the volume of O2 gas consumed to be larger than of CO2 produced. In addition the solubility of CO2 in water is about 30 times larger than of O2 causing a further decrease in total gas volume. The change in total gas volume therefore also depends on the gas/water volume ratio and the lower the ratio the more pronounced the loss of volume will be. Under field conditions the change in total volume may amount up to 20% in the absence of calcite and over 10% in the presence of calcite. Such changes in gas volume during the oxidation of pyrite are expected to result in pressure gradients causing advective transport of gaseous oxygen. PMID:11686369
Pd@Cu(II)-MOF-Catalyzed Aerobic Oxidation of Benzylic Alcohols in Air with High Conversion and Selectivity.
Chen, Gong-Jun; Wang, Jing-Si; Jin, Fa-Zheng; Liu, Ming-Yang; Zhao, Chao-Wei; Li, Yan-An; Dong, Yu-Bin
A new 3D porous Cu(II)-MOF (1) was synthesized based on a ditopic pyridyl substituted diketonate ligand and Cu(OAc)2 in solution, and it features a 3D NbO motif which is determined by the X-ray crystallography. Furthermore, the Pd NPs-loaded hybrid material Pd@Cu(II)-MOF (2) was prepared based on 1 via solution impregnation, and its structure was confirmed by HRTEM, SEM, XRPD, gas adsorption-desorption, and ICP measurement. 2 exhibits excellent catalytic activity (conversion, 93% to >99%) and selectivity (>99% to benzaldehydes) for various benzyl alcohol substrates (benzyl alcohol and its derivatives with electron-withdrawing and electron-donating groups) oxidation reactions in air. In addition, 2 is a typical heterogeneous catalyst, which was confirmed by hot solution leaching experiment, and it can be recycled at least six times without significant loss of its catalytic activity and selectivity. PMID:26959340
The Campylobacter jejuni MarR-like transcriptional regulators RrpA and RrpB both influence bacterial responses to oxidative and aerobic stresses
Gundogdu, Ozan; da Silva, Daiani T.; Mohammad, Banaz; Elmi, Abdi; Mills, Dominic C.; Wren, Brendan W.; Dorrell, Nick
The ability of the human intestinal pathogen Campylobacter jejuni to respond to oxidative stress is central to bacterial survival both in vivo during infection and in the environment. Re-annotation of the C. jejuni NCTC11168 genome revealed the presence of two MarR-type transcriptional regulators Cj1546 and Cj1556, originally annotated as hypothetical proteins, which we have designated RrpA and RrpB (regulator of response to peroxide) respectively. Previously we demonstrated a role for RrpB in both oxidative and aerobic (O2) stress and that RrpB was a DNA binding protein with auto-regulatory activity, typical of MarR-type transcriptional regulators. In this study, we show that RrpA is also a DNA binding protein and that a rrpA mutant in strain 11168H exhibits increased sensitivity to hydrogen peroxide oxidative stress. Mutation of either rrpA or rrpB reduces catalase (KatA) expression. However, a rrpAB double mutant exhibits higher levels of resistance to hydrogen peroxide oxidative stress, with levels of KatA expression similar to the wild-type strain. Mutation of either rrpA or rrpB also results in a reduction in the level of katA expression, but this reduction was not observed in the rrpAB double mutant. Neither the rrpA nor rrpB mutant exhibits any significant difference in sensitivity to either cumene hydroperoxide or menadione oxidative stresses, but both mutants exhibit a reduced ability to survive aerobic (O2) stress, enhanced biofilm formation and reduced virulence in the Galleria mellonella infection model. The rrpAB double mutant exhibits wild-type levels of biofilm formation and wild-type levels of virulence in the G mellonella infection model. Together these data indicate a role for both RrpA and RrpB in the C. jejuni peroxide oxidative and aerobic (O2) stress responses, enhancing bacterial survival in vivo and in the environment. PMID:26257713
Oxidation of humic substances supports denitrification reactions in agricultural soils.
NASA Astrophysics Data System (ADS)
van Trump, J. I.; Coates, J. D.
, nitrite, Fe(II), and humic-born hydroquinones. All data were analyzed with respect to dilution factors obtained through analysis of a conservative bromide tracer present in electron donor medium. Addition of oxidized HS, reduced HS, and acetate all resulted in significant loss of nitrate from the columns. Significant nitrite accumulation was not observed. Of all the electron donor treatments, reduced HS, enriched for hydroquinone-containing functional moieties, supported the greatest degree of denitrification. The participation of excess hydroquinones in denitrification accounted for approximately 104% of the difference in nitrate reduction between reduced and oxidized HS treatments. This electron balance allowed for assignment of respiratory activity due to hydroquinone oxidation, rather than degradation of humic substances or associated electron-donating compounds. These results suggest that denitrification reactions catalyzed by microbial oxidation of reduced HS may be prevalent in agricultural soils. Likewise, these results demonstrate for the first time that respiratory behavior due to hydroquinone oxidation, as well as impact upon local geochemistry, can be analyzed in complex flow-through model systems.
Oxidation Numbers, Oxidants, and Redox Reactions: Variants of the Electrophilic Bromination of Alkenes and Variants of the Application of Oxone
ERIC Educational Resources Information Center
Eissen, Marco; Strudthoff, Merle; Backhaus, Solveig; Eismann, Carolin; Oetken, Gesa; Kaling, Soren; Lenoir, Dieter
Oxidation-state and donor-acceptor concepts are important areas in the chemical education. Student worksheets containing problems that emphasize oxidation numbers, redox reactions of organic compounds, and stoichiometric reaction equations are presented. All of the examples are incorporated under one unifying topic: the production of vicinal…
Segregation of biomass in cyclic anaerobic/aerobic granular sludge allows the enrichment of anaerobic ammonium oxidizing bacteria at low temperatures.
Winkler, Mari K H; Kleerebezem, Robbert; Kuenen, J Gijs; Yang, Jingjing; van Loosdrecht, Mark C M
A cyclic anaerobic/aerobic bubble column reactor was run for 420 days to study the competition for nitrite between nitrite oxidizing bacteria (NOB) and anaerobic ammonium oxidizing bacteria (Anammox) at low temperatures. An anaerobic feeding period with nitrite and ammonium in the influent followed by an aerated period was applied resulting in a biomass specific conversion rate of 0.18 ± 0.02 [gN(2) - N · gVSS(-1)· day(-1)] when the dissolved oxygen concentration was maintained at 1.0 mgO(2) · L(-1). An increase in white granules was observed in the reactor which were mainly located at the top of the settled sludge bed, whereas red granules were located at the bottom. FISH, activity tests, and qPCR techniques revealed that red biomass was dominated by Anammox bacteria and white granules by NOB. Granules from the top of the sludge bed were smaller and therefore had a higher aerobic volume fraction, a lower density, and consequently a slower settling rate. Sludge was manually removed from the top of the settled sludge bed to selectively remove NOB which resulted in an increased overall biomass specific N-conversion rate of 0.32 ± 0.02 [gN(2) - N · gVSS(-1) · day(-1)]. Biomass segregation in granular sludge reactors gives an extra opportunity to select for specific microbial groups by applying a different SRT for different microbial groups. PMID:21744798
Efficient and General Aerobic Oxidative Cross-Coupling of THIQs with Organozinc Reagents Catalyzed by CuCl2: Proof of a Radical Intermediate.
Wang, Tongtong; Schrempp, Michael; Berndhäuser, Andreas; Schiemann, Olav; Menche, Dirk
A general new method for the highly concise synthesis of C-1-alkylated tetrahydroisoquinolines (THIQ) is reported. The CuCl2-catalyzed procedure is based on a coupling of nonfunctionalized THIQs with organozinc reagents under aerobic conditions. It proceeds in high yields and is broadly applicable to a wide range of substrates. It relies on a regioselective sp(3) C-H bond activation allowing for an sp(3)-sp(3) bond union under mild reaction conditions in a rapid and effective manner. Mechanistically it involves an iminium ion intermediate that is formed via an organic radical involving a single-electron-transfer process. For the first time for this type of reaction a radical intermediate has been proven by EPR spectroscopy. PMID:26252357
Total Synthesis of Clavosolide A via Tandem Allylic Oxidation/Oxa-Conjugate Addition Reaction
Baker, Joseph B.; Kim, Hyoungsu; Hong, Jiyong
The tandem allylic oxidation/oxa-conjugate addition reaction promoted by the gem-disubstituent effect in conjunction with the NHC-mediated oxidative esterification was explored for the facile synthesis of clavosolide A. PMID:26236051
Kinetics and Mechanism of Iodide Oxidation by Iron(III): A Clock Reaction Approach
ERIC Educational Resources Information Center
Bauer, Jurica; Tomisic, Vladislav; Vrkljan, Petar B. A.
A simple method for studying the kinetics of a chemical reaction is described and the significance of reaction orders in deducing reaction mechanisms is demonstrated. In this student laboratory experiment, oxidation of iodide by iron(III) ions in an acidic medium is transformed into a clock reaction. By means of the initial rates method, it is…
The reaction of hydrogen peroxide with nitrogen dioxide and nitric oxide.
NASA Technical Reports Server (NTRS)
Gray, D.; Lissi, E.; Heicklen, J.
The reactions were studied with the aid of a mass spectrometer. A pinhole bleed system provided continuous sampling of the gas mixture in the cell during the reaction. It was found that the homogeneous reactions of nitric oxide and nitrogen dioxide with hydrogen peroxide are too slow to be of any significance in the upper atmosphere. However, the heterogeneous reactions may be important in the conversion of nitric oxide to nitrogen dioxide in the case of polluted urban atmospheres.
Aerobic Anoxygenic Phototrophic Bacteria
Yurkov, Vladimir V.; Beatty, J. Thomas
The aerobic anoxygenic phototrophic bacteria are a relatively recently discovered bacterial group. Although taxonomically and phylogenetically heterogeneous, these bacteria share the following distinguishing features: the presence of bacteriochlorophyll a incorporated into reaction center and light-harvesting complexes, low levels of the photosynthetic unit in cells, an abundance of carotenoids, a strong inhibition by light of bacteriochlorophyll synthesis, and the inability to grow photosynthetically under anaerobic conditions. Aerobic anoxygenic phototrophic bacteria are classified in two marine (Erythrobacter and Roseobacter) and six freshwater (Acidiphilium, Erythromicrobium, Erythromonas, Porphyrobacter, Roseococcus, and Sandaracinobacter) genera, which phylogenetically belong to the α-1, α-3, and α-4 subclasses of the class Proteobacteria. Despite this phylogenetic information, the evolution and ancestry of their photosynthetic properties are unclear. We discuss several current proposals for the evolutionary origin of aerobic phototrophic bacteria. The closest phylogenetic relatives of aerobic phototrophic bacteria include facultatively anaerobic purple nonsulfur phototrophic bacteria. Since these two bacterial groups share many properties, yet have significant differences, we compare and contrast their physiology, with an emphasis on morphology and photosynthetic and other metabolic processes. PMID:9729607
Batch- and Continuous-Flow Aerobic Oxidation of 14-Hydroxy Opioids to 1,3-Oxazolidines-A Concise Synthesis of Noroxymorphone.
Gutmann, Bernhard; Weigl, Ulrich; Cox, D Phillip; Kappe, C Oliver
14-Hydroxymorphinone is converted to noroxymorphone, the immediate precursor of important opioid antagonists, such as naltrexone and naloxone, in a three-step reaction sequence. The initial oxidation of the N-methyl group in 14-hydroxymorphinone with in situ generated colloidal palladium(0) as the catalyst and molecular oxygen as the terminal oxidant constitutes the key transformation in this new route. This oxidation results in the formation of an unexpected oxazolidine ring structure. Subsequent hydrolysis of the oxazolidine under reduced pressure followed by hydrogenation in a packed-bed flow reactor using palladium(0) as the catalyst provides noroxymorphone in high purity and good overall yield. To overcome challenges associated with gas-liquid reactions with molecular oxygen, the key oxidation reaction was translated to a continuous-flow process. PMID:27172347
5-Carboxamido-5-formamido-2-iminohydantoin, in Addition to 8-oxo-7,8-Dihydroguanine, Is the Major Product of the Iron-Fenton or X-ray Radiation-Induced Oxidation of Guanine under Aerobic Reducing Conditions in Nucleoside and DNA Contexts
Exogenously and endogenously produced reactive oxygen species attack the base and sugar moieties of DNA showing a preference for reaction at 2′-deoxyguanosine (dG) sites. In the present work, dG was oxidized by HO• via the Fe(II)-Fenton reaction or by X-ray radiolysis of water. The oxidized lesions observed include the 2′-deoxynucleosides of 8-oxo-7,8-dihydroguanine (dOG), spiroiminodihydantoin (dSp), 5-guanidinohydantoin (dGh), oxazolone (dZ), 5-carboxamido-5-formamido-2-iminohydantoin (d2Ih), 5′,8-cyclo-2′-deoxyguanosine (cyclo-dG), and the free base guanine (Gua). Reactions conducted with ascorbate or N-acetylcysteine as a reductant under aerobic conditions identified d2Ih as the major lesion formed. Studies were conducted to identify the role of O2 and the reductant in product formation. From these studies, mechanisms are proposed to support d2Ih as a major oxidation product detected under aerobic conditions in the presence of the reductant. These nucleoside observations were then validated in oxidations of oligodeoxynucleotide and λ-DNA contexts that demonstrated high yields of d2Ih in tandem with dOG, dSp, and dGh. These results identify dG oxidation to d2Ih to occur in high yields leading to a hypothesis that d2Ih could be found from in cells stressed with HO•. Further, the distorted ring structure of d2Ih likely causes this lesion to be highly mutagenic. PMID:26092110
Aerobic Production and Utilization of Lactate Satisfy Increased Energy Demands Upon Neuronal Activation in Hippocampal Slices and Provide Neuroprotection Against Oxidative Stress
Schurr, Avital; Gozal, Evelyne
Ever since it was shown for the first time that lactate can support neuronal function in vitro as a sole oxidative energy substrate, investigators in the field of neuroenergetics have been debating the role, if any, of this glycolytic product in cerebral energy metabolism. Our experiments employed the rat hippocampal slice preparation with electrophysiological and biochemical methodologies. The data generated by these experiments (a) support the hypothesis that lactate, not pyruvate, is the end-product of cerebral aerobic glycolysis; (b) indicate that lactate plays a major and crucial role in affording neural tissue to respond adequately to glutamate excitation and to recover unscathed post-excitation; (c) suggest that neural tissue activation is accompanied by aerobic lactate and NADH production, the latter being produced when the former is converted to pyruvate by mitochondrial lactate dehydrogenase (mLDH); (d) imply that NADH can be utilized as an endogenous scavenger of reactive oxygen species (ROS) to provide neuroprotection against ROS-induced neuronal damage. PMID:22275901
Activation Energy of Tantalum-Tungsten Oxide Thermite Reaction
Cervantes, O; Kuntz, J; Gash, A; Munir, Z
The activation energy of a high melting temperature sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the High Pressure Spark Plasma Sintering (HPSPS) technique to 300 and 400 C to produce pellets with dimensions of 5 mm diameter by 1.5 mm height. A custom built ignition setup was developed to measure ignition temperatures at high heating rates (500-2000 C {center_dot} min{sup -1}). Such heating rates were required in order to ignite the thermite composite. Unlike the 400 C samples, results show that the samples consolidated to 300 C undergo an abrupt change in temperature response prior to ignition. This change in temperature response has been attributed to the crystallization of the amorphous WO{sub 3} in the SG derived Ta-WO{sub 3} thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO{sub 3} thermite ranged from approximately 465-670 C. The activation energy of the SG derived Ta-WO{sup 3} thermite composite consolidated to 300 and 400 C were determined to be 37.787 {+-} 1.58 kJ {center_dot} mol{sup -1} and 57.381 {+-} 2.26 kJ {center_dot} mol{sup -1}, respectively.
Activation energy of tantalum-tungsten oxide thermite reactions
Cervantes, Octavio G.; Munir, Zuhair A.; Kuntz, Joshua D.; Gash, Alexander E.
The activation energy of a sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the high-pressure spark plasma sintering (HPSPS) technique at 300 and 400 C. The ignition temperatures were investigated under high heating rates (500-2000 C min{sup -1}). Such heating rates were required in order to ignite the thermite composite. Samples consolidated at 300 C exhibit an abrupt change in temperature response prior to the main ignition temperature. This change in temperature response is attributed to the crystallization of the amorphous WO{sub 3} in the SG derived Ta-WO{sub 3} thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO{sub 3} thermite ranged from approximately 465 to 670 C. The activation energies of the SG derived Ta-WO{sub 3} thermite composite consolidated at 300 and 400 C were determined to be 38{+-} 2 kJ mol{sup -1} and 57 {+-} 2 kJ mol{sup -1}, respectively. (author)
40 CFR 721.10574 - Alkylcarboxy polyester acrylate reaction products with mixed metal oxides (generic).
Code of Federal Regulations, 2013 CFR
... reaction products with mixed metal oxides (generic). (a) Chemical substance and significant new uses... reaction products with mixed metal oxides (generic). 721.10574 Section 721.10574 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) TOXIC SUBSTANCES CONTROL ACT SIGNIFICANT NEW USES OF...
40 CFR 721.10574 - Alkylcarboxy polyester acrylate reaction products with mixed metal oxides (generic).
Code of Federal Regulations, 2014 CFR
... reaction products with mixed metal oxides (generic). (a) Chemical substance and significant new uses... reaction products with mixed metal oxides (generic). 721.10574 Section 721.10574 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) TOXIC SUBSTANCES CONTROL ACT SIGNIFICANT NEW USES OF...
Surface Reactions of Uranium Oxide Powder, Thin Films and Single Crystals
Idriss, H.
The review deals with surface reactions of the complex uranium oxide systems with relevance to catalysis and the environment. After a brief introduction on the properties of uranium oxides, the focus of the review is on surface science studies of defined structures of uranium oxides which are entirely on UO{sub 2} because of the lack of available model on other uranium oxide systems. Powder work is also included as it has given considerable information related to the dynamics between the many phases of uranium oxides. Many chemical reactions are mapped and these include water dissociative adsorption and reaction, CO oxidation and reductive coupling, as well as the reaction of oxygen containing organic compounds such as alcohols, aldehydes, ketones and carboxylic acids in addition to a few examples of sulfur and nitrogen containing compounds.
Surface reactions of uranium oxide powder, thin films and single crystals
NASA Astrophysics Data System (ADS)
Idriss, H.
The review deals with surface reactions of the complex uranium oxide systems with relevance to catalysis and the environment. After a brief introduction on the properties of uranium oxides, the focus of the review is on surface science studies of defined structures of uranium oxides which are entirely on UO 2 because of the lack of available model on other uranium oxide systems. Powder work is also included as it has given considerable information related to the dynamics between the many phases of uranium oxides. Many chemical reactions are mapped and these include water dissociative adsorption and reaction, CO oxidation and reductive coupling, as well as the reaction of oxygen containing organic compounds such as alcohols, aldehydes, ketones and carboxylic acids in addition to a few examples of sulfur and nitrogen containing compounds.
Development of Nitric Oxide Oxidation Catalysts for the Fast SCR Reaction
Mark Crocker
This study was undertaken in order to assess the potential for oxidizing NO to NO{sub 2} in flue gas environments, with the aim of promoting the so-called fast SCR reaction. In principle this can result in improved SCR kinetics and reduced SCR catalyst volumes. Prior to commencing experimental work, a literature study was undertaken to identify candidate catalysts for screening. Selection criteria comprised (1) proven (or likely) activity for NO oxidation, (2) low activity for SO2 oxidation (where data were available), and (3) inexpensive component materials. Catalysts identified included supported base metal oxides, supported and unsupported mixed metal oxides, and metal ion exchanged ZSM-5 (Fe, Co, Cu). For comparison purposes, several low loaded Pt catalysts (0.5 wt% Pt) were also included in the study. Screening experiments were conducted using a synthetic feed gas representative of flue gas from coal-fired utility boilers: [NO] = 250 ppm, [SO{sub 2}] = 0 or 2800 ppm, [H{sub 2}O] = 7%, [CO{sub 2}] = 12%, [O{sub 2}] = 3.5%, balance = N{sub 2}; T = 275-375 C. Studies conducted in the absence of SO{sub 2} revealed a number of supported and unsupported metal oxides to be extremely active for NO oxidation to NO{sub 2}. These included known catalysts (Co{sub 3}O{sub 4}/SiO{sub 2}, FeMnO{sub 3}, Cr{sub 2}O{sub 3}/TiO{sub 2}), as well as a new one identified in this work, CrFeO{sub x}/SiO{sub 2}. However, in the presence of SO{sub 2}, all the catalysts tested were found to be severely deactivated with respect to NO oxidation. Of these, Co{sub 3}O{sub 4}/SiO{sub 2}, Pt/ZSM-5 and Pt/CeO{sub 2} showed the highest activity for NO oxidation in the presence of SO{sub 2} (based on peak NO conversions to NO{sub 2}), although in no cases did the NO conversion exceed 7%. Reactor studies indicate there are two components to SO{sub 2}-induced deactivation of Co{sub 3}O{sub 4}/SiO{sub 2}, corresponding to an irreversible deactivation due to sulfation of the surface of the Co{sub 3
Thermodynamics and Kinetics of Sulfide Oxidation by Oxygen: A Look at Inorganically Controlled Reactions and Biologically Mediated Processes in the Environment
Luther, George W.; Findlay, Alyssa J.; MacDonald, Daniel J.; Owings, Shannon M.; Hanson, Thomas E.; Beinart, Roxanne A.; Girguis, Peter R.
The thermodynamics for the first electron transfer step for sulfide and oxygen indicates that the reaction is unfavorable as unstable superoxide and bisulfide radical ions would need to be produced. However, a two-electron transfer is favorable as stable S(0) and peroxide would be formed, but the partially filled orbitals in oxygen that accept electrons prevent rapid kinetics. Abiotic sulfide oxidation kinetics improve when reduced iron and/or manganese are oxidized by oxygen to form oxidized metals which in turn oxidize sulfide. Biological sulfur oxidation relies on enzymes that have evolved to overcome these kinetic constraints to affect rapid sulfide oxidation. Here we review the available thermodynamic and kinetic data for H2S and HS• as well as O2, reactive oxygen species, nitrate, nitrite, and NOx species. We also present new kinetic data for abiotic sulfide oxidation with oxygen in trace metal clean solutions that constrain abiotic rates of sulfide oxidation in metal free solution and agree with the kinetic and thermodynamic calculations. Moreover, we present experimental data that give insight on rates of chemolithotrophic and photolithotrophic sulfide oxidation in the environment. We demonstrate that both anaerobic photolithotrophic and aerobic chemolithotrophic sulfide oxidation rates are three or more orders of magnitude higher than abiotic rates suggesting that in most environments biotic sulfide oxidation rates will far exceed abiotic rates due to the thermodynamic and kinetic constraints discussed in the first section of the paper. Such data reshape our thinking about the biotic and abiotic contributions to sulfide oxidation in the environment. PMID:21833317
The report describes an airborne measurements program in the downwind urban plume of Boston. The variables measured included ozone, nitric oxide, oxides of nitrogen, nitric acid, peroxyacetylnitrate, carbon monoxide, nonmethane hydrocarbon, freon-11, C1-C5 hydrocarbons, condensat...
Green synthesis of Pd/CuO nanoparticles by Theobroma cacao L. seeds extract and their catalytic performance for the reduction of 4-nitrophenol and phosphine-free Heck coupling reaction under aerobic conditions.
Nasrollahzadeh, Mahmoud; Sajadi, S Mohammad; Rostami-Vartooni, Akbar; Bagherzadeh, Mojtaba
We report the green synthesis of palladium/CuO nanoparticles (Pd/CuO NPs) using Theobroma cacao L. seeds extract and their catalytic activity for the reduction of 4-nitrophenol and Heck coupling reaction under aerobic conditions. The catalyst was characterized using the powder XRD, TEM, EDS, UV-vis and FT-IR. This method has the advantages of high yields, elimination of surfactant, ligand and homogeneous catalysts, simple methodology and easy work up. The catalyst can be recovered from the reaction mixture and reused several times without any significant loss of catalytic activity. PMID:25721860
Palladium and gold nanotubes as oxygen reduction reaction and alcohol oxidation reaction catalysts in base.
Alia, Shaun M; Duong, Kathlynne; Liu, Toby; Jensen, Kurt; Yan, Yushan
Palladium (PdNTs) and gold nanotubes (AuNTs) were synthesized by the galvanic displacement of silver nanowires. PdNTs and AuNTs have wall thicknesses of 6 nm, outer diameters of 60 nm, and lengths of 5-10 and 5-20 μm, respectively. Rotating disk electrode experiments showed that the PdNTs and AuNTs have higher area normalized activities for the oxygen reduction reaction (ORR) than conventional nanoparticle catalysts. The PdNTs produced an ORR area activity that was 3.4, 2.2, and 3.7 times greater than that on carbon-supported palladium nanoparticles (Pd/C), bulk polycrystalline palladium, and carbon-supported platinum nanoparticles (Pt/C), respectively. The AuNTs produced an ORR area activity that was 2.3, 9.0, and 2.0 times greater than that on carbon-supported gold nanoparticles (Au/C), bulk polycrystalline gold, and Pt/C, respectively. The PdNTs also had lower onset potentials than Pd/C and Pt/C for the oxidation of methanol (0.236 V), ethanol (0.215 V), and ethylene glycol (0.251 V). In comparison to Pt/C, the PdNTs and AuNTs further demonstrated improved alcohol tolerance during the ORR. PMID:24757078
Conditional knockout of Mn-SOD targeted to type IIB skeletal muscle fibers increases oxidative stress and is sufficient to alter aerobic exercise capacity
Lustgarten, Michael S.; Jang, Youngmok C.; Liu, Yuhong; Muller, Florian L.; Qi, Wenbo; Steinhelper, Mark; Brooks, Susan V.; Larkin, Lisa; Shimizu, Takahiko; Shirasawa, Takuji; McManus, Linda M.; Bhattacharya, Arunabh; Richardson, Arlan
In vitro studies of isolated skeletal muscle have shown that oxidative stress is limiting with respect to contractile function. Mitochondria are a potential source of muscle function-limiting oxidants. To test the hypothesis that skeletal muscle-specific mitochondrial oxidative stress is sufficient to limit muscle function, we bred mice expressing Cre recombinase driven by the promoter for the inhibitory subunit of troponin (TnIFast-iCre) with mice containing a floxed Sod2 (Sod2fl/fl) allele. Mn-SOD activity was reduced by 82% in glycolytic (mainly type II) muscle fiber homogenates from young TnIFastCreSod2fl/fl mice. Furthermore, Mn-SOD content was reduced by 70% only in type IIB muscle fibers. Aconitase activity was decreased by 56%, which suggests an increase in mitochondrial matrix superoxide. Mitochondrial superoxide release was elevated more than twofold by mitochondria isolated from glycolytic skeletal muscle in TnIFastCreSod2fl/fl mice. In contrast, the rate of mitochondrial H2O2 production was reduced by 33%, and only during respiration with complex II substrate. F2-isoprostanes were increased by 36% in tibialis anterior muscles isolated from TnIFastCreSod2fl/fl mice. Elevated glycolytic muscle-specific mitochondrial oxidative stress and damage in TnIFastCreSod2fl/fl mice were associated with a decreased ability of the extensor digitorum longus and gastrocnemius muscles to produce contractile force as a function of time, whereas force production by the soleus muscle was unaffected. TnIFastCreSod2fl/fl mice ran 55% less distance on a treadmill than wild-type mice. Collectively, these data suggest that elevated mitochondrial oxidative stress and damage in glycolytic muscle fibers are sufficient to reduce contractile muscle function and aerobic exercise capacity. PMID:19776389
Method and reaction pathway for selectively oxidizing organic compounds
Camaioni, Donald M.; Lilga, Michael A.
A method of selectively oxidizing an organic compound in a single vessel comprises: a) combining an organic compound, an acid solution in which the organic compound is soluble, a compound containing two oxygen atoms bonded to one another, and a metal ion reducing agent capable of reducing one of such oxygen atoms, and thereby forming a mixture; b) reducing the compound containing the two oxygen atoms by reducing one of such oxygen atoms with the metal ion reducing agent to, 1) oxidize the metal ion reducing agent to a higher valence state, and 2) produce an oxygen containing intermediate capable of oxidizing the organic compound; c) reacting the oxygen containing intermediate with the organic compound to oxidize the organic compound into an oxidized organic intermediate, the oxidized organic intermediate having an oxidized carbon atom; d) reacting the oxidized organic intermediate with the acid counter ion and higher valence state metal ion to bond the acid counter ion to the oxidized carbon atom and thereby produce a quantity of an ester incorporating the organic intermediate and acid counter ion; and e) reacting the oxidized organic intermediate with the higher valence state metal ion and water to produce a quantity of alcohol which is less than the quantity of ester, the acid counter ion incorporated in the ester rendering the carbon atom bonded to the counter ion less reactive with the oxygen containing intermediate in the mixture than is the alcohol with the oxygen containing intermediate.
Au@Cu(II)-MOF: Highly Efficient Bifunctional Heterogeneous Catalyst for Successive Oxidation-Condensation Reactions.
Wang, Jing-Si; Jin, Fa-Zheng; Ma, Hui-Chao; Li, Xiao-Bo; Liu, Ming-Yang; Kan, Jing-Lan; Chen, Gong-Jun; Dong, Yu-Bin
A new composite Au@Cu(II)-MOF catalyst has been synthesized via solution impregnation and full characterized by HRTEM, SEM-EDS, XRD, gas adsorption-desorption, XPS, and ICP analysis. It has been shown here that the Cu(II)-framework can be a useful platform to stabilize and support gold nanoparticles (Au NPs). The obtained Au@Cu(II)-MOF exhibits a bifunctional catalytic behavior and is able to promote selective aerobic benzyl alcohol oxidation-Knoevenagel condensation in a stepwise way. PMID:27322613
High-temperature oxidation behavior of reaction-formed silicon carbide ceramics
NASA Technical Reports Server (NTRS)
Ogbuji, Linus U. J. T.; Singh, M.
The oxidation behavior of reaction-formed silicon carbide (RFSC) ceramics was investigated in the temperature range of 1100 to 1400 C. The oxidation weight change was recorded by TGA; the oxidized materials were examined by light and electron microscopy, and the oxidation product by x-ray diffraction analysis (XRD). The materials exhibited initial weight loss, followed by passive weight gain (with enhanced parabolic rates, k(sub p)), and ending with a negative (logarithmic) deviation from the parabolic law. The weight loss arose from the oxidation of residual carbon, and the enhanced k(sub p) values from internal oxidation and the oxidation of residual silicon, while the logarithmic kinetics is thought to have resulted from crystallization of the oxide. The presence of a small amount of MoSi, in the RFSC material caused a further increase in the oxidation rate. The only solid oxidation product for all temperatures studied was silica.
Thermochemistry and reaction paths in the oxidation reaction of benzoyl radical: C6H5C•(═O).
Sebbar, Nadia; Bozzelli, Joseph W; Bockhorn, Henning
Alkyl substituted aromatics are present in fuels and in the environment because they are major intermediates in the oxidation or combustion of gasoline, jet, and other engine fuels. The major reaction pathways for oxidation of this class of molecules is through loss of a benzyl hydrogen atom on the alkyl group via abstraction reactions. One of the major intermediates in the combustion and atmospheric oxidation of the benzyl radicals is benzaldehyde, which rapidly loses the weakly bound aldehydic hydrogen to form a resonance stabilized benzoyl radical (C6H5C(•)═O). A detailed study of the thermochemistry of intermediates and the oxidation reaction paths of the benzoyl radical with dioxygen is presented in this study. Structures and enthalpies of formation for important stable species, intermediate radicals, and transition state structures resulting from the benzoyl radical +O2 association reaction are reported along with reaction paths and barriers. Enthalpies, ΔfH298(0), are calculated using ab initio (G3MP2B3) and density functional (DFT at B3LYP/6-311G(d,p)) calculations, group additivity (GA), and literature data. Bond energies on the benzoyl and benzoyl-peroxy systems are also reported and compared to hydrocarbon systems. The reaction of benzoyl with O2 has a number of low energy reaction channels that are not currently considered in either atmospheric chemistry or combustion models. The reaction paths include exothermic, chain branching reactions to a number of unsaturated oxygenated hydrocarbon intermediates along with formation of CO2. The initial reaction of the C6H5C(•)═O radical with O2 forms a chemically activated benzoyl peroxy radical with 37 kcal mol(-1) internal energy; this is significantly more energy than the 21 kcal mol(-1) involved in the benzyl or allyl + O2 systems. This deeper well results in a number of chemical activation reaction paths, leading to highly exothermic reactions to phenoxy radical + CO2 products. PMID:21942384
Layered double hydroxide supported gold nanoclusters by glutathione-capped Au nanoclusters precursor method for highly efficient aerobic oxidation of alcohols
NASA Astrophysics Data System (ADS)
Li, Lun; Dou, Liguang; Zhang, Hui
M3Al-layered double hydroxide (LDH, M = Mg, Ni, Co) supported Au nanoclusters (AuNCs) catalysts have been prepared for the first time by using water-soluble glutathione-capped Au nanoclusters as precursor. Detailed characterizations show that the ultrafine Au nanoclusters (ca. 1.5 +/- 0.6 nm) were well dispersed on the surface of LDH with a loading of Au below ~0.23 wt% upon synergetic interaction between AuNCs and M3Al-LDH. AuNCs/Mg3Al-LDH-0.23 exhibits much higher catalytic performance for the oxidation of 1-phenylethanol in toluene than Au/Mg3Al-LDH(DP) by the conventional deposition precipitation method and can be applied for a wide range of alcohols without basic additives. This catalyst can also be reused without loss of activity or selectivity. The AuNCs/M(= Ni, Co)3Al-LDH catalysts present even higher alcohol oxidation activity than AuNCs/Mg3Al-LDH. Particularly, AuNCs/Ni3Al-LDH-0.22 exhibits the highest activity (46 500 h-1) for the aerobic oxidation of 1-phenylethanol under solvent-free conditions attributed to its strongest Au-support synergy. The excellent activity and stability of AuNCs/M3Al-LDH catalysts render these materials promising candidates for green base-free selective oxidation of alcohols by molecular oxygen.M3Al-layered double hydroxide (LDH, M = Mg, Ni, Co) supported Au nanoclusters (AuNCs) catalysts have been prepared for the first time by using water-soluble glutathione-capped Au nanoclusters as precursor. Detailed characterizations show that the ultrafine Au nanoclusters (ca. 1.5 +/- 0.6 nm) were well dispersed on the surface of LDH with a loading of Au below ~0.23 wt% upon synergetic interaction between AuNCs and M3Al-LDH. AuNCs/Mg3Al-LDH-0.23 exhibits much higher catalytic performance for the oxidation of 1-phenylethanol in toluene than Au/Mg3Al-LDH(DP) by the conventional deposition precipitation method and can be applied for a wide range of alcohols without basic additives. This catalyst can also be reused without loss of activity
North Pond: a natural observatory for sub-seafloor oxidant supply and metabolic reactions
NASA Astrophysics Data System (ADS)
Ziebis, Wiebke; Ferdelman, Timothy; McManus, James; Muratli, Jesse; Picard, Aude; Schmidt-Schierhorn, Friederike; Stephan, Sebastian; Villinger, Heinrich; Edwards, Katrina J.
Evidence of upward transport of oxidants from basaltic aquifers to deeply buried sediments has raised questions on microbial respiration and energy cycling within the deep biosphere. Sediment ponds that occur over a vast area of sea floor on the flank of the Mid-Atlantic Ridge maybe ideal observatories to study the role of unsuspected sources of oxidants for sub-seafloor microbial life. The western flank of the Mid-Atlantic Ridge, at 22°45'N is characterized by depressions filled with sediment and surrounded by high relief topography of 7 Ma old basement. The largest depressions are 5 km to 20 km wide and sediment thickness varies but can reach 400 m (Langseth et al. 1992). They are believed to overly recharge zones for the venting of fluids that takes place locally through unsedimented young ocean crust. If we consider the sediments as boundaries overlying the hydrologically active crustal environment, then using profiles of bioactive compounds measured through the sediment layer with the goal to extract information on transport and reactions is an obvious approach to understanding the implications of subsurface transport of oxidants on metabolic activity. Recently obtained deep oxygen profiles obtained during a site survey expedition in February/March of 2009 onboard RV Maria S. Merian to North Pond, one of the larger (70 square km) and best studied sediment ponds, provided proof of this principal. North Pond is the site of the proposed IODP Expedition "677 Mid-Atlantic Microbiology". Investigations included heat-flow, single-channel seismic and bathymetry surveys, as well as gravity coring. Oxygen measurements and pore water sampling (25 cm depth intervals) were performed directly on intact sediment cores, which were subsequently sampled for microbiological analyses, as well as for incubation experiments to test for autotrophic and heterotrophic microbial activity. The entire sediment column down to > 8 m sediment depth contained oxygen. In the central part of
Sporicidal effects of iodine-oxide thermite reaction products
NASA Astrophysics Data System (ADS)
Russell, Rod; Bless, Stephan; Blinkova, Alexandra; Chen, Tiffany
Iodine pentoxide-aluminum thermite reactions have been driven by impacts at 1000 m/s on steel plates 3 mm or thicker. This reaction releases iodine gas that is known to be a sporicide. To test the impact reactions for sporicidal effects, reactions took place in closed chambers containing dried Bacillus subtilis spores. The reduction in colony-forming units was dependent on the exposure time; long exposure times resulted in a 105 decrease in germination rate. This was shown to be due to the gas exposure rather than the heat or turbulence. Sporicidal effectiveness was increased by adding neodymium and saran resin.
Aerobic Exercise Training Prevents the Onset of Endothelial Dysfunction via Increased Nitric Oxide Bioavailability and Reduced Reactive Oxygen Species in an Experimental Model of Menopause
Braga, Viviane A. V. N.; Couto, Gisele K.; Lazzarin, Mariana C.; Rossoni, Luciana V.; Medeiros, Alessandra
Objective Previous studies have shown that estrogen deficiency, arising in postmenopause, promotes endothelial dysfunction. This study evaluated the effects of aerobic exercise training on endothelial dependent vasodilation of aorta in ovariectomized rats, specifically investigating the role of nitric oxide (NO) and reactive oxygen species (ROS). Methods Female Wistar rats ovariectomized (OVX – n=20) or with intact ovary (SHAM – n=20) remained sedentary (OVX and SHAM) or performed aerobic exercise training on a treadmill 5 times a week for a period of 8 weeks (OVX-TRA and SHAM-TRA). In the thoracic aorta the endothelium-dependent and –independent vasodilation was assessed by acetylcholine (ACh) and sodium nitroprusside (SNP), respectively. Certain aortic rings were incubated with L-NAME to assess the NO modulation on the ACh-induced vasodilation. The fluorescence to dihydroethidium in aortic slices and plasma nitrite/nitrate concentrations were measured to evaluate ROS and NO bioavailability, respectively. Results ACh-induced vasodilation was reduced in OVX rats as compared SHAM (Rmax: SHAM: 86±3.3 vs. OVX: 57±3.0%, p<0.01). Training prevented this response in OVX-TRA (Rmax: OVX-TRA: 88±2.0%, p<0.01), while did not change it in SHAM-TRA (Rmax: SHAM-TRA: 80±2.2%, p<0.01). The L-NAME incubation abolished the differences in ACh-induced relaxation among groups. SNP-induced vasodilation was not different among groups. OVX reduced nitrite/nitrate plasma concentrations and increased ROS in aortic slices, training as effective to restore these parameters to the SHAM levels. Conclusions Exercise training, even in estrogen deficiency conditions, is able to improve endothelial dependent vasodilation in rat aorta via enhanced NO bioavailability and reduced ROS levels. PMID:25923465
Fundamental kinetics and mechanistic pathways for oxidation reactions in supercritical water
NASA Technical Reports Server (NTRS)
Webley, Paul A.; Tester, Jefferson W.
Oxidation of the products of human metabolism in supercritical water has been shown to be an efficient way to accomplish the on-board water/waste recycling in future long-term space flights. Studies of the oxidation kinetics of methane to carbon dioxide in supercritical water are presented in this paper in order to enhance the fundamental understanding of the oxidation of human waste compounds in supercritical water. It is concluded that, although the elementary reaction models remain the best hope for simulating oxidation in supercritical water, several modifications to existing mechanisms need to be made to account for the role of water in the reaction mechanism.
Influence of Alumina Reaction Tube Impurities on the Oxidation of Chemically-Vapor-Deposited Silicon Carbide
NASA Technical Reports Server (NTRS)
Opila, Elizabeth
Pure coupons of chemically vapor deposited (CVD) SiC were oxidized for 100 h in dry flowing oxygen at 1300 C. The oxidation kinetics were monitored using thermogravimetry (TGA). The experiments were first performed using high-purity alumina reaction tubes. The experiments were then repeated using fused quartz reaction tubes. Differences in oxidation kinetics, scale composition, and scale morphology were observed. These differences were attributed to impurities in the alumina tubes. Investigators interested in high-temperature oxidation of silica formers should be aware that high-purity alumina can have significant effects on experiment results.
Azo dye removal in a membrane-free up-flow biocatalyzed electrolysis reactor coupled with an aerobic bio-contact oxidation reactor.
Cui, Dan; Guo, Yu-Qi; Cheng, Hao-Yi; Liang, Bin; Kong, Fan-Ying; Lee, Hyung-Sool; Wang, Ai-Jie
Azo dyes that consist of a large quantity of dye wastewater are toxic and persistent to biodegradation, while they should be removed before being discharged to water body. In this study, Alizarin Yellow R (AYR) as a model azo dye was decolorized in a combined bio-system of membrane-free, continuous up-flow bio-catalyzed electrolysis reactor (UBER) and subsequent aerobic bio-contact oxidation reactor (ABOR). With the supply of external power source 0.5 V in the UBER, AYR decolorization efficiency increased up to 94.8±1.5%. Products formation efficiencies of p-phenylenediamine (PPD) and 5-aminosalicylic acid (5-ASA) were above 90% and 60%, respectively. Electron recovery efficiency based on AYR removal in cathode zone was nearly 100% at HRTs longer than 6 h. Relatively high concentration of AYR accumulated at higher AYR loading rates (>780 gm(-3) d(-1)) likely inhibited acetate oxidation of anode-respiring bacteria on the anode, which decreased current density in the UBER; optimal AYR loading rate for the UBER was 680 gm(-3) d(-1) (HRT 2.5 h). The subsequent ABOR further improved effluent quality. Overall the Chroma decreased from 320 times to 80 times in the combined bio-system to meet the textile wastewater discharge standard II in China. PMID:23009797
Influence of a reaction medium on the oxidation of aromatic nitrogen-containing compounds by peroxyacids
NASA Astrophysics Data System (ADS)
Dutka, V. S.; Matsyuk, N. V.; Dutka, Yu. V.
The influence of different solvents on the oxidation reaction rate of pyridine (Py), quinoline (QN), acridine (AN), α-oxyquinoline (OQN) and α-picolinic acid (APA) by peroxydecanoic acid (PDA) was studied. It was found that the oxidation rate grows in the series Py < QN < AN, and the rate of the oxidation reaction of compounds containing a substituent in the α position from a reactive center is significantly lower than for unsubstituted analogues. The effective energies of activation of the oxidation reaction were found. It was shown that in the first stage, the reaction mechanism includes the rapid formation of an intermediate complex nitrogen-containing compound, peroxyacid, which forms products upon decomposing in the second stage. A kinetic equation that describes the studied process is offered. The constants of equilibrium of the intermediate complex formation ( K eq) and its decomposition constant ( k 2) in acetone and benzene were calculated. It was shown that the nature of the solvent influences the numerical values of both K p and k 2. It was established that introduction of acetic acid (which is able to form compounds with Py) into the reaction medium slows the rate of the oxidation process drastically. Correlation equations linking the polarity, polarizability, electrophilicity, and basicity of solvents with the constant of the PDA oxidation reaction rate for Py were found. It was concluded that the basicity and polarity of the solvent have a decisive influence on the oxidation reaction rate, while the polarizability and electrophilicity of the reaction medium do not influence the oxidation reaction rate.
Thermal oxidative degradation reactions of linear perfluoroalky lethers
NASA Technical Reports Server (NTRS)
Jones, W. R., Jr.; Paciorek, K. J. L.; Ito, T. I.; Kratzer, R. H.
Thermal and thermal oxidative stability studies were performed on linear perfluoro alkyl ether fluids. The effect on degradation by metal catalysts and degradation inhibitors are reported. The liner perfluoro alkylethers are inherently unstable at 316 C in an oxidizing atmosphere. The metal catalysts greatly increased the rate of degradation in oxidizing atmospheres. In the presence of these metals in an oxidizing atmosphere, the degradation inhibitors were highly effective in arresting degradation at 288 C. However, the inhibitors had only limited effectiveness at 316 C. The metals promote degradation by chain scission. Based on elemental analysis and oxygen consumption data, the linear perfluoro alkylether fluids have a structural arrangement based on difluoroformyl and tetrafluoroethylene oxide units, with the former predominating.
Comparative temporal analysis of multiwalled carbon nanotube oxidation reactions: Evaluating chemical modifications on true nanotube surface
NASA Astrophysics Data System (ADS)
Pacheco, Flávia G.; Cotta, Alexandre A. C.; Gorgulho, Honória F.; Santos, Adelina P.; Macedo, Waldemar A. A.; Furtado, Clascídia A.
The influence of extensive purification on oxidized multiwalled carbon nanotube surface composition was studied through the characterization and differentiation of the actual surface submitted to three oxidation methods: microwave-assisted acid oxidation, hydrogen peroxide reflux, and Fenton reaction. The oxidized samples were purified by a multi-step procedure including the sequential use of basic reflux and dispersion in dimethylformamide (DMF). The results showed a significant increase in the amount of oxidation debris with hydrogen peroxide and Fenton reaction times longer than 8 h and strong surface characteristic modification. With regard to sample purification, basic reflux led to a reduction in oxygenated group concentration of only 10% in the samples treated by acid oxidation. On the other hand, the subsequent use of DMF led to a further decrease in concentration of 39%, proving to be a more efficient method for the removal of oxidation debris.
Efficient synthesis of biazoles by aerobic oxidative homocoupling of azoles catalyzed by a copper(I)/2-pyridonate catalytic system.
Zhu, Mingwen; Fujita, Ken-ichi; Yamaguchi, Ryohei
A highly efficient and convenient CuCl/2-pyridonate catalytic system for oxidative homocoupling of azoles affording a biazole product has been developed. With this system, a variety of biazoles have been effectively synthesized in good to excellent yields in the presence of a very small amount of copper catalyst (1.0 mol%). It was feasible to employ air as a green oxidant. PMID:22076830
Enhancement of Bacterial Transport in Aerobic and Anaerobic Environments: Assessing the Effect of Metal Oxide Chemical Heterogeneities
T.C. Onstott
The goal of our research was to understand the fundamental processes that control microbial transport in physically and chemically heterogeneous aquifers and from this enhanced understanding determine the requirements for successful, field-scale delivery of microorganisms to metal contaminated subsurface sites. Our specific research goals were to determine; (1) the circumstances under which the preferential adsorption of bacteria to Fe, Mn, and Al oxyhydroxides influences field-scale bacterial transport, (2) the extent to which the adhesion properties of bacterial cells affect field-scale bacterial transport, (3) whether microbial Fe(III) reduction can enhance field-scale transport of Fe reducing bacteria (IRB) and other microorganisms and (4) the effect of field-scale physical and chemical heterogeneity on all three processes. Some of the spin-offs from this basic research that can improve biostimulation and bioaugmentation remediation efforts at contaminated DOE sites have included; (1) new bacterial tracking tools for viable bacteria; (2) an integrated protocol which combines subsurface characterization, laboratory-scale experimentation, and scale-up techniques to accurately predict field-scale bacterial transport; and (3) innovative and inexpensive field equipment and methods that can be employed to enhance Fe(III) reduction and microbial transport and to target microbial deposition under both aerobic and anaerobic conditions.
Sporicidal Effects of Iodine-oxide Thermite Reaction Products
NASA Astrophysics Data System (ADS)
Russell, Rod; Bless, Stephan; Blinkova, Alexandra; Chen, Tiffany; InstituteAdvanced Tehnology Collaboration; Dept of Molecular Genetics; Microbiology-UT Austin Collaboration; Chemistry; Biochemistry-UT Austin Collaboration
Iodine pentoxide-aluminum thermite reactions have been driven by impacts at 1000 m/s on steel plates 3 mm or thicker. The activation energy of this material reaction is 197 J/g. The reactivity is increased by reducing grain size. This reaction releases iodine gas that is known to be a sporicide. In order to test the impact reactions for sporicidal effects, reactions took place in closed chambers containing dried Bacillus subtilis spores. The reduction in colony-forming units was dependent on the exposure time; long exposure times resulted in a 105 decrease in germination rate. This was shown to be due to the gas exposure and not the heat or turbulence. Sporicidal effectiveness was increased by adding neodymium and saran resin. The sporicidal effect is very dependent on exposure time, ranging from about 90% kill for times on the order of a second to 99.99% for one-hour times.
Enhanced performance of denitrifying sulfide removal process under micro-aerobic condition.
Chen, Chuan; Ren, Nanqi; Wang, Aijie; Liu, Lihong; Lee, Duu-Jong
The denitrifying sulfide removal (DSR) process with bio-granules comprising both heterotrophic and autotrophic denitrifiers can simultaneously convert nitrate, sulfide and acetate into di-nitrogen gas, elementary sulfur and carbon dioxide, respectively, at high loading rates. This study determines the reaction rate of sulfide oxidized into sulfur, as well as the reduction of nitrate to nitrite, would be enhanced under a micro-aerobic condition. The presence of limited oxygen mitigated the inhibition effects of sulfide on denitrifier activities, and enhanced the performance of DSR granules. The advantages and disadvantages of applying the micro-aerobic condition to the DSR process are discussed. PMID:20233637
The Energetics of Aerobic versus Anaerobic Respiration.
ERIC Educational Resources Information Center
Champion, Timothy D.; Schwenz, Richard W.
Background information, laboratory procedures, and a discussion of the results of an experiment designed to investigate the difference in energy gained from the aerobic and anaerobic oxidation of glucose are presented. Sample experimental and calculated data are included. (CW)
Diffusion - Reaction: The Oxidation of Silicides in Electronics and Elsewhere
NASA Astrophysics Data System (ADS)
D'Heurle, F. M.
The present article is a review of the up-to-date state of knowledge about the oxidation of silicide in film and "bulk" forms. The oxidation of silicides is analyzed with due respect to thermodynamics but the emphasis is placed on the kinetics of the process. A distinction is made between what occurs with silicide thin films used as conductors in the electronic industry, where the silicides are always in presence of excess silicon, and in the oxidation of "bulk" silicide structural parts where this condition is not encountered. Use is made of a graphical approach that was originally used to illustrate the oxidation of Si itself. The kinetic analysis provides at least a qualitative explanation of the conditions that must be met in the electronic industry to maintain the integrity of silicide layers in oxidizing atmospheres, and of the conditions that cause the occurrence of the "pest" phenomenon in structural parts. Although attention is directed mostly to silicides, it is clear that the approach and the model used are valid for other refractory compounds, so that allusions are made also to aluminides and beryllides, etc. Marker experiments to probe the motion of atoms in the silicides during oxidation are analyzed. It is suggested that the relation between electron concentrations and oxidation rates is related to the decomposition of oxygen molecules.
The use of ionic liquids in various synthetic transformations is gaining significance due to the enhanced reaction rates, potential for recycling and compatibility with various organic compounds and organometallic catalysts. Palladium-catalyzed oxidation of styrene and other alk...
Carbon-coated magnetic palladium: applications in partial oxidation of alcohols and coupling reactions.
Magnetic carbon supported Pd catalyst has been synthesized via in situ generation of nanoferrites and incorporation of carbon from renewable cellulose via calcination; catalyst can be used for oxidation of alcohols, amination reaction and arylation of aryl halides (cross coupli...
Bulk Gold-Catalyzed Reactions of Isocyanides, Amines, and Amine N-Oxides
Klobukowski, Erik; Angelici, Robert; Woo, Keith L.
Bulk gold powder (5–50 μm particles) catalyzes the reactions of isocyanides with amines and amine N-oxides to produce ureas. The reaction of n-butyl isocyanide (nBu–N≡C) with di-n-propylamine and N-methylmorpholine N-oxide in acetonitrile, which was studied in the greatest detail, produced 3-butyl-1,1-dipropylurea (O═C(NHnBu)(NnPr2)) in 99% yield at 60 °C within 2 h. Sterically and electronically different isocyanides, amines, and amine N-oxides react successfully under these conditions. Detailed studies support a two-step mechanism that involves a gold-catalyzed reaction of adsorbed isocyanide with the amine N-oxide to form an isocyanate (RN═C═O), which rapidly reacts with the amine to give the urea product. These investigations show that bulk gold, despite its reputation for poor catalytic activity, is capable of catalyzing these reactions.
Process of forming catalytic surfaces for wet oxidation reactions
NASA Technical Reports Server (NTRS)
Jagow, R. B. (Inventor)
A wet oxidation process was developed for oxidizing waste materials, comprising dissolved ruthenium salt in a reactant feed stream containing the waste materials. The feed stream is introduced into a reactor, and the reactor contents are then raised to an elevated temperature to effect deposition of a catalytic surface of ruthenium black on the interior walls of the reactor. The feed stream is then maintained in the reactor for a period of time sufficient to effect at least partial oxidation of the waste materials.
Reaction mechanism for methanol oxidation on Au(1 1 1): A density functional theory study
NASA Astrophysics Data System (ADS)
Liu, Shuping; Jin, Peng; Zhang, Donghui; Hao, Ce; Yang, Xueming
The microscopic reaction mechanism for methanol oxidation on Au(1 1 1) surface has been thoroughly investigated by means of density functional theory (DFT) computations. The adsorption geometries and energies were obtained for all the adsorbates, including the reactants, the products, and various possible intermediates on the metal. According to different oxygen conditions, we propose two possible reaction pathways for methanol oxidation on Au(1 1 1): (1) HCHO esterification: the intermediate formaldehyde and methoxy couple to yield methyl formate at low oxygen coverage or without the presence of oxygen atoms; (2) HCHO oxidation: the formaldehyde is oxidized to form formate at high oxygen coverage, which further dissociates to give CO2. Our study emphasizes the critical role of oxygen coverage during the methanol oxidation reaction, and can perfectly explain the difference in product distributions observed in previous experiments.
A kinetics study of the atmospheric pressure CVD reaction of silane and nitrous oxide
Chapple-Sokol, J.D.; Giunta, C.J.; Gordon, R.G. . Dept. of Chemistry)
A mechanistic study of oxide deposition from silane and nitrous oxide between 495{sup 0}C and 690{sup 0}C was performed in a laminar flow, cool wall reactor. Results indicate the existence of two distinct chemical pathways. At high nitrous oxide concentrations, the deposition reaction is dominated by radical chain chemistry initiated by the decomposition of N/sub 2/O. At lower N/sub 2/O concentrations, the decomposition of silane to form silylene (SiH/sub 2/) initiates the deposition. Studies of the reaction of disilane and nitrous oxide confirmed the role of SiH/sub 2/ in the deposition. Reactions involving SiH/sub 2/ are used to explain the observed growth of sub-stoichiometric oxides under low N/sub 2/O conditions.
Bench-scale study of the effect of phosphate on an aerobic iron oxidation plant for mine water treatment.
Tischler, Judith S; Wiacek, Claudia; Janneck, Eberhard; Schlömann, Michael
At the opencast pit Nochten acidic iron- and sulfate-rich mine waters are treated biotechnologically in a mine-water treatment plant by microbial iron oxidation. Due to the low phosphate concentration in such waters the treatment plant was simulated in bench-scale to investigate the influence of addition of potassium dihydrogen phosphate on chemical and biological parameters of the mine-water treatment. As a result of the phosphate addition the number of cells increased, which resulted in an increase of the iron oxidation rate in the reactor with phosphate addition by a factor of 1.7 compared to a reference approach without phosphate addition. Terminal restriction fragment length polymorphism (T-RFLP) analysis during the cultivation revealed a shift of the microbial community depending on the phosphate addition. While almost exclusively iron-oxidizing bacteria related to "Ferrovum" sp. were detected with phosphate addition, the microbial community was more diverse without phosphate addition. In the latter case, iron-oxidizing bacteria ("Ferrovum" sp., Acidithiobacillus spp.) as well as non-iron-oxidizing bacteria (Acidiphilium sp.) were identified. PMID:24139104
Fast and Efficient Oxidative Cycloreversion Reaction of a π-Extended Photochromic Terarylene.
Calupitan, Jan Patrick; Nakashima, Takuya; Hashimoto, Yuichiro; Kawai, Tsuyoshi
We report herein a dramatic improvement in the kinetics and efficiency of an oxidative cycloreversion reaction of photochromic dithiazolylthiazoles. The cycloreversion reaction of a colored isomer of dithiazolylthiazole proceeds not only by photo-irradiation, but also through chemical oxidation with a net efficiency far exceeding 100 % owing to a chain reaction mechanism. By introducing aromatic groups on the reactive carbon atoms at the ends of a photoreactive 6π system in a dithiazolylthiazole, the net bleaching reaction rates were increased by up to 1300-fold, and turnover rates increased by two orders of magnitude. Based on a combination of classical kinetic analyses and DFT calculations, we attribute this improvement to acceleration of the rate-determining step to produce the active species in the chain-reaction oxidative cycloreversion. PMID:27380748
Oxides reactions with a high-chrome sesquioxide refractory
Rawers, James C.; Collins, W. Keith; Peck, M.
In slagging coal-gasifier systems, the combination of oxides present as impurities in coal and combustion temperatures that can exceed 1650 degrees C restrict the use of liner materials in the coal combustion chambers to refractories. In this study, the slag-refractory interactions of a new high chrome sesquioxide refractory was characterized. High-temperature cup tests showed that the molten oxides infused into the refractory and that the sesquioxide refractory reacts with the oxides in a manner similar to spinel phase refractories. Studies of the coal slag's individual oxide components showed CaO reacts with the chrome refractory to form a low melting Ca(CrO2)2. FeO reacts with the sesquioxide to form a interface layer of (Cr,Fe)3O4 spinel phase. Results of this study now make it possible to design studies for improving corrosion resistance to increase refractory life.
Hydrogenophaga carboriunda sp. nov., a tertiary butyl alcohol-oxidizing, psychrotolerant aerobe derived from granular-activated carbon (GAC).
Reinauer, Kimberly M; Popovic, Jovan; Weber, Christopher D; Millerick, Kayleigh A; Kwon, Man Jae; Wei, Na; Zhang, Yang; Finneran, Kevin T
A Gram-negative, rod-shaped bacterium was isolated from a mixed culture that degraded tert-butyl alcohol (TBA) in a granular-activated carbon (GAC) sample from a Biological-GAC reactor. Strain YZ2(T) was assigned to the Betaproteobacteria within the family Comamonadaceae based on 16S rRNA gene similarities. The nearest phylogenetic relative (95.0 % similarity) with a valid name was Hydrogenophaga taeniospiralis. The DNA G+C content was 66.4 mol%. DNA:DNA hybridization indicated that the level of relatedness to members of the genus Hydrogenophaga ranged from 1.1 to 10.8 %. The dominant cellular fatty acids were: 18:1 w7c (75 %), 16:0 (4.9 %), 17:0 (3.85 %), 18:0 (2.93 %), 11 methyl 18:1 w7c (2.69 %), Summed Feature 2 (2.27 %), and 18:0 3OH (1.35 %). The primary substrate used was TBA, which is a fuel oxygenate and groundwater contaminant. YZ2(T) was non-motile, without apparent flagella. It is a psychrotolerant, facultative aerobe that grew between pH 6.5 and 9.5, and 4 and 30 °C. The culture grew on and mineralized TBA at 4 °C, which is the first report of psychrotolerant TBA degradation. Hydrogen was used as an alternative electron donor. The culture also grew well in defined freshwater medium with ethanol, butanol, hydroxy isobutyric acid, acetate, pyruvate, citrate, lactate, isopropanol, and benzoic acid as electron donors. Nitrate was reduced with hydrogen as the sole electron donor. On the basis of morphological, physiological, and chemotaxonomic data, a new species, Hydrogenophaga carboriunda is proposed, with YZ2(T) as the type strain. PMID:24343174
Redox reactions involving soil minerals and materials are important processes in environmental chemistry, but unfortunately they only have been characterized in the solution phase. he lack of a suitable method has prevented investigations of the mineral surface component of redox...
New Insights into the Diels-Alder Reaction of Graphene Oxide.
Brisebois, Patrick P; Kuss, Christian; Schougaard, Steen B; Izquierdo, Ricardo; Siaj, Mohamed
Graphene oxide is regarded as a major precursor for graphene-based materials. The development of graphene oxide based derivatives with new functionalities requires a thorough understanding of its chemical reactivity, especially for canonical synthetic methods such as the Diels-Alder cycloaddition. The Diels-Alder reaction has been successfully extended with graphene oxide as a source of diene by using maleic anhydride as a dienophile, thereby outlining the presence of the cis diene present in the graphene oxide framework. This reaction provides fundamental information for understanding the exact structure and chemical nature of graphene oxide. On the basis of high-resolution (13) C-SS NMR spectra, we show evidence for the formation of new sp(3) carbon centers covalently bonded to graphene oxide following hydrolysis of the reaction product. DFT calculations are also used to show that the presence of a cis dihydroxyl and C vacancy on the surface of graphene oxide are promoting the reaction with significant negative reaction enthalpies. PMID:26953926
Heterogeneous photochemical reactions of a propylene-nitrogen dioxide-metal oxide-dry air system
NASA Astrophysics Data System (ADS)
Takeuchi, Koji; Ibusuki, Takashi
Photochemical reactions of a C 3H 6-NO 2-air system in the presence of metal oxide were investigated. The metal oxides showing strong photooxidation activity were found to be n-type semiconductor oxides with the energy band gap around 3 eV. Formation of cyano-compounds (HCN and CH 3CN) was also observed and the activity can be explained in terms of the adsorptivity of NO onto metal oxides. Coalfired fly ash as a model of mixed metal oxides was also examined and their photocatalytic action was discussed.
Conversion Reaction-Based Oxide Nanomaterials for Lithium Ion Battery Anodes.
Yu, Seung-Ho; Lee, Soo Hong; Lee, Dong Jun; Sung, Yung-Eun; Hyeon, Taeghwan
Developing high-energy-density electrodes for lithium ion batteries (LIBs) is of primary importance to meet the challenges in electronics and automobile industries in the near future. Conversion reaction-based transition metal oxides are attractive candidates for LIB anodes because of their high theoretical capacities. This review summarizes recent advances on the development of nanostructured transition metal oxides for use in lithium ion battery anodes based on conversion reactions. The oxide materials covered in this review include oxides of iron, manganese, cobalt, copper, nickel, molybdenum, zinc, ruthenium, chromium, and tungsten, and mixed metal oxides. Various kinds of nanostructured materials including nanowires, nanosheets, hollow structures, porous structures, and oxide/carbon nanocomposites are discussed in terms of their LIB anode applications. PMID:26627913
The aerobic respiratory chain of the acidophilic archaeon Ferroplasma acidiphilum: A membrane-bound complex oxidizing ferrous iron.
Castelle, Cindy J; Roger, Magali; Bauzan, Marielle; Brugna, Myriam; Lignon, Sabrina; Nimtz, Manfred; Golyshina, Olga V; Giudici-Orticoni, Marie-Thérèse; Guiral, Marianne
The extremely acidophilic archaeon Ferroplasma acidiphilum is found in iron-rich biomining environments and is an important micro-organism in naturally occurring microbial communities in acid mine drainage. F. acidiphilum is an iron oxidizer that belongs to the order Thermoplasmatales (Euryarchaeota), which harbors the most extremely acidophilic micro-organisms known so far. At present, little is known about the nature or the structural and functional organization of the proteins in F. acidiphilum that impact the iron biogeochemical cycle. We combine here biochemical and biophysical techniques such as enzyme purification, activity measurements, proteomics and spectroscopy to characterize the iron oxidation pathway(s) in F. acidiphilum. We isolated two respiratory membrane protein complexes: a 850 kDa complex containing an aa3-type cytochrome oxidase and a blue copper protein, which directly oxidizes ferrous iron and reduces molecular oxygen, and a 150 kDa cytochrome ba complex likely composed of a di-heme cytochrome and a Rieske protein. We tentatively propose that both of these complexes are involved in iron oxidation respiratory chains, functioning in the so-called uphill and downhill electron flow pathways, consistent with autotrophic life. The cytochrome ba complex could possibly play a role in regenerating reducing equivalents by a reverse ('uphill') electron flow. This study constitutes the first detailed biochemical investigation of the metalloproteins that are potentially directly involved in iron-mediated energy conservation in a member of the acidophilic archaea of the genus Ferroplasma. PMID:25896560
Ceramic oxide reactions with V2O5 and SO3
NASA Technical Reports Server (NTRS)
Jones, R. L.; Williams, C. E.
Ceramic oxides are not inert in combustion environments, but can react with, inter alia, SO3, and Na2SO4 to yield low melting mixed sulfate eutectics, and with vanadium compounds to produce vanadates. Assuming ceramic degradation to become severe only when molten phases are generated in the surface salt (as found for metallic hot corrosion), the reactivity of ceramic oxides can be quantified by determining the SO3 partial pressure necessary for molten mixed sulfate formation with Na2SO3. Vanadium pentoxide is an acidic oxide that reacts with Na2O, SO3, and the different ceramic oxides in a series of Lux-Flood type of acid-base displacement reactions. To elucidate the various possible vanadium compound-ceramic oxide interactions, a study was made of the reactions of a matrix involving, on the one axis, ceramix oxides of increasing acidity, and on the other axis, vanadium compounds of increasing acidity. Resistance to vanadium compound reaction increased as the oxide acidity increased. Oxides more acidic than ZrO2 displaced V2O5. Examination of Y2O3- and CeO2-stabilized ZrO2 sintered ceramics which were degraded in 700 C NaVO3 has shown good agreement with the reactions predicted above, except that the CeO2-ZrO2 ceramic appears to be inexplicably degraded by NaVO3.
Mechanistic examination of aerobic Pt oxidation: insertion of molecular oxygen into Pt-H bonds through a radical chain mechanism.
Keith, Jason M; Ye, Yixin; Wei, Haochuan; Buck, Matthew R
DFT calculations were performed in an effort to evaluate the mechanism of O2 insertion into the Pt-H bond of Tp(Me2)Pt(IV)Me2H catalyzed by AIBN or light. Results are consistent with a radical chain mechanism involving H˙ loss to form a Pt(III)˙ species followed by addition of O2 to form Pt(III)OO˙. Subsequent radical propagation involving this Pt(III)OO˙ species and an additional equivalent of the Pt(IV) starting material result in the formation of the observed Pt(IV)OOH and regeneration of the Pt(III)˙. In addition examination of the reaction between AIBN and the Pt(IV) hydroperoxo product demonstrates that radical initiation reactions involving the product occur with a lower barrier than with the initial starting material supporting the idea of autoacceleration in this reaction. Other possible mechanisms were examined in an effort to understand the limited reactivity reported in the absence of light or radical initiators. TDDFT calculations were performed in an effort to understand the reported parallel photo-induced reaction. These calculations found the reactant to be transparent in the relevant light range. An experimental UV-Vis spectrum was obtained and is in agreement with the calculations. PMID:27364984
Impact-Driven Thermite Reactions with Iodine Pentoxide and Silver Oxide
NASA Astrophysics Data System (ADS)
Russell, R.; Bless, S.; Pantoya, M.
Thermite reactions using aluminum (Al) fuel and either iodine pentoxide (I2O5) or silver oxide (Ag2O) were initiated by high-velocity impact or thermal initiation and examined for their flame propagation behavior. In the impact-ignition experiments, the Al-Ag2O reaction produced more energy than the Al-I2O5 reaction; in the thermal-ignition experiments, the I2O5 reaction produced higher flame propagation rates (1,305 m/s compared with 531 m/s). The energy released from impact-initiated reactions is significantly enhanced by reducing the size of the oxide particles. Results suggest that the reaction propagation mechanisms may be the same, even though ignition is spurred by two different stimuli (mechanically induced compaction versus thermal).
Mutagenicity screening of reaction products from the enzyme-catalyzed oxidation of phenolic pollutants
Massey, I.J.; Aitken, M.D.; Ball, L.M.; Heck, P.E. . Dept. of Environmental Sciences and Engineering)
Phenol-oxidizing enzymes such as peroxidases, laccases, and mushroom polyphenol oxidase are capable of catalyzing the oxidation of a wide range of phenolic pollutants. Although the use of these enzymes in waste-treatment applications has been proposed by a number of investigators, little information exists on the toxicological characteristics of the oxidation products. The enzymes chloroperoxidase, horseradish peroxidase, lignin peroxidase, and mushroom polyphenol oxidase were used in this study to catalyze the oxidation of phenol, several mono-substituted phenols, and pentachlorophenol. Seventeen reaction mixtures representing selected combinations of enzyme and parent phenol were subjected to mutagenicity screening using the Ames Salmonella typhimurium plate incorporation assay; five selected mixtures were also incubated with the S9 microsomal preparation to detect the possible presence of promutagens. The majority of reaction mixtures tested were not directly mutagenic, and none of those tested with S9 gave a positive response. Such lack of mutagenicity of enzymatic oxidation products provides encouragement for establishing the feasibility of enzyme-catalyzed oxidation as a waste-treatment process. The only positive responses were obtained with reaction products from the lignin peroxidase-catalyzed oxidation of 2-nitrophenol and 4-nitrophenol. Clear positive responses were observed when strain TA100 was incubated with 2-nitrophenol reaction-product mixtures, and when strain TA98 was incubated with the 4-nitrophenol reaction mixture. Additionally, 2,4-dinitrophenol was identified as a reaction product from 4-nitrophenol, and preliminary evidence indicates that both 2,4- and 2,6-dinitrophenol are produced from the oxidation of 2-nitrophenol. Possible mechanism by which these nitration reactions occur are discussed.
Determination of carbon by the oxidation reduction reaction with chromium
NASA Technical Reports Server (NTRS)
Mashkovich, L.; Kuteynikov, A. F.
Free carbon was determined in silicon and boron carbides in ash, oxides, and other materials by oxidation to carbon dioxide with a mixture of K2Cr2O7 + H2SO4. The determination was made from the amount of CR(6) consumed, by adding excess Mohr's salt and titrating with a standard solution of KMnO4. The amount of Cr(6) self reduced was determined in a blank test. Optimum oxidation and conditions were achieved when the volumes of 5% k2Cr2Oz and H2SO4 were equal. The mixture was boiled for 1-2 hours using a reflex condenser. The volume should not be reduced, in order to avoid an increase in the sulfuric acid concentration. The relative error was 4-7% for 0.005-0.04 g C and less than or equal to 3.5% for 0.1 g C.
Theoretical analysis of hydrogen oxidation reaction in solid oxide fuel cell anode based on species territory adsorption model
NASA Astrophysics Data System (ADS)
Nagasawa, Tsuyoshi; Hanamura, Katsunori
A modified reaction model of hydrogen oxidation around a triple phase boundary (TPB) is proposed for solid oxide fuel cells (SOFCs) with a Ni/oxide ion conductor cermet anode containing proton conductor particles in order to describe the mechanism of anode overpotential reduction. In this model, three kinds of TPBs consisting of nickel metal, oxide ion conductors, proton conductors, and gas phases were considered. It was assumed that the chemical species could be adsorbed within a finite narrow area on each material around the TPB. The reaction rate in the anode was controlled by the surface reaction between the adsorbed hydrogen and adsorbed oxygen; all other reactions took place under chemical equilibrium. Based on the reaction model, analytical expressions of current density with oxygen activity and anode overpotential with current density could be obtained. The latter could combine the anode overpotential at low- and high-current-density regions, which were conventionally expressed independently. The analytical results were in good agreement with the experimental results for both the conventional anode and the new anode incorporating a proton conductor. Especially, the anode overpotential reduction could be explained by the additional supply of adsorbed hydrogen from the proton conductor to the TPB.
Fluorine-Doped and Partially Oxidized Tantalum Carbides as Nonprecious Metal Electrocatalysts for Methanol Oxidation Reaction in Acidic Media.
Yue, Xin; He, Chunyong; Zhong, Chengyong; Chen, Yuanping; Jiang, San Ping; Shen, Pei Kang
A nonprecious metal electrocatalyst based on fluorine-doped tantalum carbide with an oxidative surface on graphitized carbon (TaCx FyOz/(g)C) is developed by using a simple one-pot in situ ion exchange and adsorption method, and the TaCxFyOz/(g)C shows superior performance and durability for methanol oxidation reaction and extreme tolerance to CO poisoning in acidic media. PMID:26779940
Synthesis of multisubstituted pyrroles from doubly activated cyclopropanes using an iron-mediated oxidation domino reaction.
Zhang, Zhiguo; Zhang, Wei; Li, Junlong; Liu, Qingfeng; Liu, Tongxin; Zhang, Guisheng
An alternative route has been developed for the construction of multisubstituted pyrrole derivatives from readily available, doubly activated cyclopropanes and anilines using an iron-mediated oxidation domino reaction (i.e., sequential ring-opening, cyclization, and dehydrogenation reactions). This reaction uses readily available reactants and is tolerant of a broad range of substrates, with the desired products being formed in good to excellent yields. PMID:25330125
Irrelevance of Carbon Monoxide Poisoning in the Methanol Oxidation Reaction on a PtRu Electrocatalyst.
Chen, De-Jun; Tong, YuYe J
Based on detailed in situ attenuated total-reflection-surface-enhanced IR reflection absorption spectroscopy (ATR-SEIRAS) studies of the methanol oxidation reaction (MOR) on Ru/Pt thin film and commercial Johnson-Matthey PtRu/C, a revised MOR enhancement mechanism is proposed in which CO on Pt sites is irrelevant but instead Pt-Ru boundary sites catalyze the oxygen insertion reaction that leads to the formation of formate and enhances the direct reaction pathway. PMID:26148459
Method for catalyzing oxidation/reduction reactions of simple molecules
Bicker, D.; Bonaventura, J.
A method for oxidizing carbon monoxide to carbon dioxide is described comprising: (1) contacting, together, carbon monoxide, a nitrogen-containing chelating agent and water; wherein the chelating agent is at least one member selected from the group consisting of methmeoglobin bound to a support, ferric hemoglobin bound to a support, iron-containing porphyrins bound to a support, and sperm whale myoglobin bound to a support, wherein the support is glass, a natural fiber, a synthetic fiber, a gel, charcoal, carbon ceramic material, a metal oxide, a synthetic polymer, a zeolite, a silica compound of an alumina compound; and (2) obtaining carbon dioxide.
Graphitic-Carbon Layers on Oxides: Toward Stable Heterogeneous Catalysts for Biomass Conversion Reactions.
Xiong, Haifeng; Schwartz, Thomas J; Andersen, Nalin I; Dumesic, James A; Datye, Abhaya K
Conversion of biomass-derived molecules involves catalytic reactions under harsh conditions in the liquid phase (e.g., temperatures of 250 °C and possibly under either acidic or basic conditions). Conventional oxide-supported catalysts undergo pore structure collapse and surface area reduction leading to deactivation under these conditions. Here we demonstrate an approach to deposit graphitic carbon to protect the oxide surface. The heterogeneous catalysts supported on the graphitic carbon/oxide composite exhibit excellent stability (even under acidic conditions) for biomass conversion reactions. PMID:25973732
In situ observation of surface species on iridium oxide nanoparticles during the oxygen evolution reaction.
Sanchez Casalongue, Hernan G; Ng, May Ling; Kaya, Sarp; Friebel, Daniel; Ogasawara, Hirohito; Nilsson, Anders
An iridium oxide nanoparticle electrocatalyst under oxygen evolution reaction conditions was probed in situ by ambient-pressure X-ray photoelectron spectroscopy. Under OER conditions, iridium undergoes a change in oxidation state from Ir(IV) to Ir(V) that takes place predominantly at the surface of the catalyst. The chemical change in iridium is coupled to a decrease in surface hydroxide, providing experimental evidence which strongly suggests that the oxygen evolution reaction on iridium oxide occurs through an OOH-mediated deprotonation mechanism. PMID:24889896
This study accounts for the observations that the metabolism of benzene is dominated by the formation of phenol. As demonstrated here, the pathway leading to S-phenylmercapturic acid is necessarily minor on account of the low efficiency of benzene oxide capture by glutathione at ...
The reactions of imidogen with nitric oxide and molecular oxygen
Miller, J.A.; Melius, C.F.
Using potential energy surface information from BAC-MP4 calculations and statistical-dynamical methods, we have calculated the branching fraction for the NH + NO reaction, NH + NO {r arrow} N{sub 2} + H (1) NH + NO {r arrow} N{sub 2}O + H (2). We find that reaction (2) dominates over the entire temperature range considered, 300 K < T < 3500 K, with f=k{sub 1}/(k{sub 1} + K{sub 2}) varying from about 0.07 at room temperature to about 0.20 at 3500 K. In addition, we have calculated rate coefficients for the two-channel process, NH + O{sub 2} {r arrow} HNO + O (3) NH + O{sub 2} {r arrow} NO + OH (4). In this case we find that reaction (4) dominates at low temperature, reaction (3) at high temperature. All these results are discussed in terms of the experimental results available and compared with previous theoretical investigations where appropriate. 21 refs., 4 figs., 3 tabs.
The reactions of imidogen with nitric oxide and molecular oxygen
Miller, J.A.; Melius, C.F.
Using potential energy surface information from BAC-MP4 calculations and statistical-dynamical methods, we have calculated the branching fraction for the NH + NO reaction, NH + NO {r_arrow} N{sub 2} + H (1) NH + NO {r_arrow} N{sub 2}O + H (2). We find that reaction (2) dominates over the entire temperature range considered, 300 K < T < 3500 K, with f=k{sub 1}/(k{sub 1} + K{sub 2}) varying from about 0.07 at room temperature to about 0.20 at 3500 K. In addition, we have calculated rate coefficients for the two-channel process, NH + O{sub 2} {r_arrow} HNO + O (3) NH + O{sub 2} {r_arrow} NO + OH (4). In this case we find that reaction (4) dominates at low temperature, reaction (3) at high temperature. All these results are discussed in terms of the experimental results available and compared with previous theoretical investigations where appropriate. 21 refs., 4 figs., 3 tabs.
Iron oxide mineral-water interface reactions studied by AFM
Hawley, M.E.; Rogers, P.S.Z.
Natural iron mineral surfaces have been examined in air by atomic force (AFM) and scanning tunneling (STM) microscopies. A number of different surface features were found to be characteristic of the native surface. Even surfaces freshly exposed by crushing larger crystals were found to have a pebbly surface texture caused by the presence of thin coatings of what might be surface precipitates. This finding is interpreted as evidence for previous exposure to water, probably through an extensive network of microfractures. Surface reactions on the goethite crystals were studied by AFM at size resolutions ranging from microns to atomic resolution before, during, and after reaction with distilled water and 0.lN HCl. Immediate and extensive surface reconfiguration occurred on contact with water. In one case, after equilibration with water for 3 days, surface reprecipitation, etching and pitting were observed. Atomic resolution images taken under water were found to be disordered. The result of surface reaction was generally to increase the surface area substantially through the extension of surface platelet arrays, present prior to reaction. This work is being done in support of the site characterization project at Yucca Mountain.
Tailoring the composition of ultrathin, ternary alloy PtRuFe nanowires for the methanol oxidation reaction and formic acid oxidation reaction
Scofield, Megan E.; Koenigsmann, Christopher; Wang, Lei; Liu, Haiqing; Wong, Stanislaus S.
In the search for alternatives to conventional Pt electrocatalysts, we have synthesized ultrathin, ternary PtRuFe nanowires (NW), possessing different chemical compositions in order to probe their CO tolerance as well as electrochemical activity as a function of composition for both (i) the methanol oxidation reaction (MOR) and (ii) the formic acid oxidation reaction (FAOR). As-prepared 'multifunctional' ternary NW catalysts exhibited both higher MOR and FAOR activity as compared with binary Pt₇Ru₃ NW, monometallic Pt NW, and commercial catalyst control samples. In terms of synthetic novelty, we utilized a sustainably mild, ambient wet-synthesis method never previously applied to the fabrication of crystalline, pure ternary systems in order to fabricate ultrathin, homogeneous alloy PtRuFe NWs with a range of controlled compositions. Thus, these NWs were subsequently characterized using a suite of techniques including XRD, TEM, SAED, and EDAX in order to verify not only the incorporation of Ru and Fe into the Pt lattice but also their chemical homogeneity, morphology, as well as physical structure and integrity. Lastly, these NWs were electrochemically tested in order to deduce the appropriateness of conventional explanations such as (i) the bi-functional mechanism as well as (ii) the ligand effect to account for our MOR and FAOR reaction data. Specifically, methanol oxidation appears to be predominantly influenced by the Ru content, whereas formic acid oxidation is primarily impacted by the corresponding Fe content within the ternary metal alloy catalyst itself.
Tailoring the composition of ultrathin, ternary alloy PtRuFe nanowires for the methanol oxidation reaction and formic acid oxidation reaction
Scofield, Megan E.; Koenigsmann, Christopher; Wang, Lei; Liu, Haiqing; Wong, Stanislaus S.
In the search for alternatives to conventional Pt electrocatalysts, we have synthesized ultrathin, ternary PtRuFe nanowires (NW), possessing different chemical compositions in order to probe their CO tolerance as well as electrochemical activity as a function of composition for both (i) the methanol oxidation reaction (MOR) and (ii) the formic acid oxidation reaction (FAOR). As-prepared 'multifunctional' ternary NW catalysts exhibited both higher MOR and FAOR activity as compared with binary Pt₇Ru₃ NW, monometallic Pt NW, and commercial catalyst control samples. In terms of synthetic novelty, we utilized a sustainably mild, ambient wet-synthesis method never previously applied to the fabrication ofmore » crystalline, pure ternary systems in order to fabricate ultrathin, homogeneous alloy PtRuFe NWs with a range of controlled compositions. Thus, these NWs were subsequently characterized using a suite of techniques including XRD, TEM, SAED, and EDAX in order to verify not only the incorporation of Ru and Fe into the Pt lattice but also their chemical homogeneity, morphology, as well as physical structure and integrity. Lastly, these NWs were electrochemically tested in order to deduce the appropriateness of conventional explanations such as (i) the bi-functional mechanism as well as (ii) the ligand effect to account for our MOR and FAOR reaction data. Specifically, methanol oxidation appears to be predominantly influenced by the Ru content, whereas formic acid oxidation is primarily impacted by the corresponding Fe content within the ternary metal alloy catalyst itself.« less
Evaluation of Salivary Nitric Oxide Levels in Smokers, Tobacco Chewers and Patients with Oral Lichenoid Reactions
Jose, Joy Idiculla; Sivapathasundharam, B.; Sabarinath, B.
Introduction Nitric oxide (NO), a free radical, acts as a signalling molecule affecting numerous physiological and pathological processes. Role of nitric oxide as a mediator in tobacco related habits and the resultant oral lichenoid reactions was assessed. Aim The aim of the study is to evaluate and compare the salivary nitric oxide levels in normal patients with that of smokers, tobacco chewers and patients with oral lichenoid reactions. Materials and Methods One hundred and twenty patients were enrolled in the study which included 30 healthy patients without any chronic inflammatory lesion and habit as controls (group I), 30 smokers without the habit of tobacco/betel nut chewing and any oral lesion (group II), 30 tobacco chewers without the habit of smoking and any oral lesion (group III) and 30 histologically confirmed cases of oral lichenoid reaction with the habit of tobacco usage (group IV). Saliva from these patients was collected and the nitrite concentration was assessed. Results Our results concluded that there was highly significant increase in the nitric oxide levels in smokers, tobacco chewers and patients with oral lichenoid reactions compared to that of controls. Also, there was a significant increase in nitric oxide levels in patients with smoking associated oral lichenoid reactions in comparison with smokers and in patients with lichenoid reactions associated with tobacco chewing in comparison with tobacco chewers. Conclusion Estimation of salivary nitric oxide levels is a simple, non-invasive procedure and could be analysed to suggest the role of nitric oxide in the pathogenesis of these lesions. The increased activity of the enzyme may indicate that nitric oxide has a pathophysiological role in these lesions. PMID:26894179
The true nature of the Di-iron(III) gamma-Keggin structure in water: catalytic aerobic oxidation and chemistry of an unsymmetrical trimer.
Botar, Bogdan; Geletii, Yurii V; Kögerler, Paul; Musaev, Djamaladdin G; Morokuma, Keiji; Weinstock, Ira A; Hill, Craig L
The complex [gamma(1,2)-SiW(10){Fe(OH(2))}(2)O(38)](6)(-) (1) has been reported to catalyze the much sought reductant-free selective O(2)-based epoxidation of alkenes (Nishiyama, Y.; Nakagawa, Y.; Mizuno, N. Angew. Chem. Int. Ed. 2001, 40, 3639-3641) in chlorocarbon-acetonitrile solution. The challenge of reproducing catalysis by 1 led us to examine this chemistry in detail. In H(2)O, a desirable solvent for catalysis, 1, does not exist in the proposed organic-medium form in which the two iron atoms are in the binding pocket defined by the equatorial oxygens and, importantly, by two oxygens bound to the central Si heteroatom. Instead, 1 in H(2)O initially forms an unusual trimer [{Fe(2)(OH)(3)(H(2)O)(2)}(3)(gamma-SiW(10)O(36))(3)](15)(-) (2). The X-ray structure of 2 shows that the Fe-O(Si) bonds are cleaved and new bonds (mu-hydroxo bridges) form between these Fe centers and those of the neighboring [gamma(1,2)-SiW(10)Fe(2)] units. Structural, physical, and computational evidence indicate that if the bonds between the d-electron center, M (Fe in the case of 1 and 2), and the terminal ligands on M are stronger than the M-O(x)() bonds, then the out-of-pocket form is more stable and is the one observed. Significantly, 2 in H(2)O forms an intermediate that catalyzes the effective aerobic oxidation of sulfur compounds (mercaptoethanol is oxidized to the corresponding disulfide by O(2) at ambient pressure and temperature). All experimental findings are consistent with dissociation of a gamma-SiW(10) Keggin unit from the trimer, 2, to form the catalytically active species. PMID:16925446
Implications of sterically constrained n-butane oxidation reactions on the reaction mechanism and selectivity to 1-butanol
NASA Astrophysics Data System (ADS)
Dix, Sean T.; Gómez-Gualdrón, Diego A.; Getman, Rachel B.
Density functional theory (DFT) is used to analyze the reaction network in n-butane oxidation to 1-butanol over a Ag/Pd alloy catalyst under steric constraints, and the implications on the ability to produce 1-butanol selectively using MOF-encapsulated catalysts are discussed. MOFs are porous crystalline solids comprised of metal nodes linked by organic molecules. Recently, they have been successfully grown around metal nanoparticle catalysts. The resulting porous networks have been shown to promote regioselective chemistry, i.e., hydrogenation of trans-1,3-hexadiene to 3-hexene, presumably by forcing the linear alkene to stand "upright" on the catalyst surface and allowing only the terminal C-H bonds to be activated. In this work, we extend this concept to alkane oxidation. Our goal is to determine if a MOF-encapsulated catalyst could be used to selectively produce 1-butanol. Reaction energies and activation barriers are presented for more than 40 reactions in the pathway for n-butane oxidation. We find that C-H bond activation proceeds through an oxygen-assisted pathway and that butanal and 1-butanol are some of the possible products.
Effects of high-intensity interval versus continuous moderate-intensity aerobic exercise on apoptosis, oxidative stress and metabolism of the infarcted myocardium in a rat model.
Lu, Kai; Wang, Li; Wang, Changying; Yang, Yuan; Hu, Dayi; Ding, Rongjing
The optimal aerobic exercise training (AET) protocol for patients following myocardial infarction (MI) has remained under debate. The present study therefore aimed to compare the effects of continuous moderate-intensity training (CMT) and high-intensity interval training (HIT) on cardiac functional recovery, and to investigate the potential associated mechanisms in a post-MI rat model. Female Sprague Dawley rats (8-10 weeks old) undergoing MI or sham surgery were subsequently submitted to CMT or HIT, or kept sedentary for eight weeks. Prior to and following AET, echocardiographic parameters and exercise capacity of the rats were measured. Western blotting was used to evaluate the levels of apoptosis and associated signaling pathway protein expression. The concentrations of biomarkers of oxidative stress were also determined by ELISA assay. Messenger (m)RNA levels and activity of the key enzymes for glycolysis and fatty acid oxidation, as well as the rate of adenosine triphosphate (ATP) synthesis, were also measured. Compared with the MI group, exercise capacity and cardiac function were significantly improved following AET, particularly following HIT. Left ventricular ejection fraction and fraction shortening were further improved in the MI-HIT group in comparison to that of the MI-CMT group. The two forms of AET almost equally attenuated apoptosis of the post-infarction myocardium. CMT and HIT also alleviated oxidative stress by decreasing the concentration of malondialdehyde and increasing the concentration of superoxide dismutase and glutathione peroxidase (GPx). In particular, HIT induced a greater increase in the concentration of GPx than that of CMT. AET, and HIT in particular, significantly increased the levels of mRNA and the maximal activity of phosphofructokinase-1 and carnitine palmitoyl transferase-1, as well as the maximal ratio of ATP synthesis. In addition, compared with the MI group, the expression of signaling proteins PI3K, Akt, p38mapk and AMPK
Theoretical study of reactions of HO{sub 2} in low-temperature oxidation of benzene
Altarawneh, Mohammednoor; Dlugogorski, Bogdan Z.; Kennedy, Eric M.; Mackie, John C.
We have generated a set of thermodynamic and kinetic parameters for the reactions involving HO{sub 2} in the very early stages of benzene oxidation at low temperatures using density functional theory (DFT). In particular, we report the rate constants for the reactions of HO{sub 2} with benzene and phenyl. The calculated reaction rate constant for the abstraction of H-C{sub 6}H{sub 5} by HO{sub 2} is found to be in good agreement with the limited experimental values. HO{sub 2} addition to benzene is found to be more important than direct abstraction. We show that the reactions of HO{sub 2} with the phenyl radical generate the propagating radical OH in a highly exoergic reaction. The results presented herein should be useful in modeling the oxidation of aromatic compounds at low temperatures. (author)
Rare Branched Fatty Acids Characterize the Lipid Composition of the Intra-Aerobic Methane Oxidizer "Candidatus Methylomirabilis oxyfera"
Zhu, Baoli; Rijpstra, W. Irene C.; Jetten, Mike S. M.; Ettwig, Katharina F.; Sinninghe Damsté, Jaap S.
The recently described bacterium "Candidatus Methylomirabilis oxyfera" couples the oxidation of the important greenhouse gas methane to the reduction of nitrite. The ecological significance of "Ca. Methylomirabilis oxyfera" is still underexplored, as our ability to identify the presence of this bacterium is thus far limited to DNA-based techniques. Here, we investigated the lipid composition of "Ca. Methylomirabilis oxyfera" to identify new, gene-independent biomarkers for the environmental detection of this bacterium. Multiple "Ca. Methylomirabilis oxyfera" enrichment cultures were investigated. In all cultures, the lipid profile was dominated up to 46% by the fatty acid (FA) 10-methylhexadecanoic acid (10MeC16:0). Furthermore, a unique FA was identified that has not been reported elsewhere: the monounsaturated 10-methylhexadecenoic acid with a double bond at the Δ7 position (10MeC16:1Δ7), which comprised up to 10% of the total FA profile. We propose that the typical branched fatty acids 10MeC16:0 and 10MeC16:1Δ7 are key and characteristic components of the lipid profile of "Ca. Methylomirabilis oxyfera." The successful detection of these fatty acids in a peatland from which one of the enrichment cultures originated supports the potential of these unique lipids as biomarkers for the process of nitrite-dependent methane oxidation in the environment. PMID:23042164
Proteomic analysis reveals perturbed energy metabolism and elevated oxidative stress in hearts of rats with inborn low aerobic capacity
Burniston, Jatin G.; Kenyani, Jenna; Wastling, Jonathan M.; Burant, Charles F.; Qi, Nathan R.; Koch, Lauren G.; Britton, Steven L.
Selection on running capacity has created rat phenotypes of high capacity runners (HCR) that have enhanced cardiac function and low capacity runners (LCR) that exhibit risk factors of metabolic syndrome. We analysed hearts of HCR and LCR from generation 22 of selection using DIGE and identified proteins from MS database searches. The running capacity of HCR was 6-fold greater than LCR. DIGE resolved 957 spots and proteins were unambiguously identified in 369 spots. Protein expression profiling detected 67 statistically significant (P<0.05; false discovery rate <10 %, calculated using q-values) differences between HCR and LCR. Hearts of HCR rats exhibited robust increases in the abundance of each enzyme of the beta-oxidation pathway. In contrast, LCR hearts were characterised by the modulation of enzymes associated with ketone body or amino acid metabolism. LCR also exhibited enhanced expression of antioxidant enzymes such as catalase and greater phosphorylation of alpha B-crystallin at serine 59, which is a common point of convergence in cardiac stress signalling. Thus proteomic analysis revealed selection on low running capacity is associated with perturbations in cardiac energy metabolism and provided the first evidence that the LCR cardiac proteome is exposed to greater oxidative stress. PMID:21751351
Reaction network and kinetics for the catalytic oxidation of toluene over V sub 2 O sub 5
Zhu, J.; Andersson, L.T. )
The oxidation of three methyl-diphenylmethane isomers and of bibenzyl, benzyl alcohol, and benzaldehyde, which are intermediates in the catalytic oxidation of toluene over V{sub 2}O{sub 5}, has been studied to elucidate the reaction network and relative importance of various reactions. Selectivity dependences reveal that the network is composed mainly of three parallel reaction routes: (1) side-chain oxidation with consecutive reactions, (2) oxidative coupling with both parallel and consecutive reactions, and (3) carbon oxide formation. Coupling products are not negligible, with an initial selectivity of 29% (400{degree}C). Anthraquinone is produced mainly from o-methyl-diphenylmethane conditions and catalyst used. Selectivity dependences suggested product lumping and a simplified network. Kinetic analysis of this reaction network indicates that higher temperatures favor route 2 over route 1. The same initial intermediates for route 1 of side-chain oxidation and for route 2 of oxidative coupling are suggested.
Concurrent Formation of Carbon-Carbon Bonds and Functionalized Graphene by Oxidative Carbon-Hydrogen Coupling Reaction.
Morioku, Kumika; Morimoto, Naoki; Takeuchi, Yasuo; Nishina, Yuta
Oxidative C-H coupling reactions were conducted using graphene oxide (GO) as an oxidant. GO showed high selectivity compared with commonly used oxidants such as (diacetoxyiodo) benzene and 2,3-dichloro-5,6-dicyano-p-benzoquinone. A mechanistic study revealed that radical species contributed to the reaction. After the oxidative coupling reaction, GO was reduced to form a material that shows electron conductivity and high specific capacitance. Therefore, this system could concurrently achieve two important reactions: C-C bond formation via C-H transformation and production of functionalized graphene. PMID:27181191
Concurrent Formation of Carbon–Carbon Bonds and Functionalized Graphene by Oxidative Carbon-Hydrogen Coupling Reaction
NASA Astrophysics Data System (ADS)
Morioku, Kumika; Morimoto, Naoki; Takeuchi, Yasuo; Nishina, Yuta
Oxidative C–H coupling reactions were conducted using graphene oxide (GO) as an oxidant. GO showed high selectivity compared with commonly used oxidants such as (diacetoxyiodo) benzene and 2,3-dichloro-5,6-dicyano-p-benzoquinone. A mechanistic study revealed that radical species contributed to the reaction. After the oxidative coupling reaction, GO was reduced to form a material that shows electron conductivity and high specific capacitance. Therefore, this system could concurrently achieve two important reactions: C–C bond formation via C–H transformation and production of functionalized graphene.
Concurrent Formation of Carbon–Carbon Bonds and Functionalized Graphene by Oxidative Carbon-Hydrogen Coupling Reaction
Morioku, Kumika; Morimoto, Naoki; Takeuchi, Yasuo; Nishina, Yuta
Oxidative C–H coupling reactions were conducted using graphene oxide (GO) as an oxidant. GO showed high selectivity compared with commonly used oxidants such as (diacetoxyiodo) benzene and 2,3-dichloro-5,6-dicyano-p-benzoquinone. A mechanistic study revealed that radical species contributed to the reaction. After the oxidative coupling reaction, GO was reduced to form a material that shows electron conductivity and high specific capacitance. Therefore, this system could concurrently achieve two important reactions: C–C bond formation via C–H transformation and production of functionalized graphene. PMID:27181191
Metabolic alkene labeling and in vitro detection of histone acylation via the aqueous oxidative Heck reaction
Ourailidou, Maria E.; Dockerty, Paul; Witte, Martin; Poelarends, Gerrit J.; Dekker, Frank J.
The detection of protein lysine acylations remains a challenge due to a lack of specific antibodies for acylations with various chain lengths. This problem can be addressed by metabolic labeling techniques using carboxylates with reactive functionalities. Subsequent chemoselective reactions with a complementary moiety connected to a detection tag enable the visualization and quantification of the protein lysine acylome. In this study, we present EDTA-Pd(II) as a novel catalyst for the oxidative Heck reaction on protein-bound alkenes, which allows employment of fully aqueous reaction conditions. We used this reaction to monitor histone lysine acylation in vitro after metabolic incorporation of olefinic carboxylates as chemical reporters. PMID:25672493
The general mathematical model of CO oxidation reaction over Pd-zeolite catalyst
NASA Astrophysics Data System (ADS)
Kurkina, E. S.; Tolstunova, E. D.
A new distributed mathematical model of reaction of CO oxidation over Pd-zeolite catalyst is presented. The model takes into account passing of the reactant flow through the catalyst layer, diffusion in pores of zeolite matrix, reaction on the surface of embedded Pd clusters, heat effect of the reaction, heat and mass transfer across the catalyst layer. Reaction on the Pd clusters is described by the new point model suggested herein. The model admits the existence of regular, chaotic and mixed-mode oscillations at the values of the parameters close to the experimental conditions.
Evaluation of reaction mechanism of coal-metal oxide interactions in chemical-looping combustion
Siriwardane, Ranjani; Richards, George; Poston, James; Tian, Hanjing; Miller, Duane; Simonyi, Thomas
The knowledge of reaction mechanism is very important in designing reactors for chemical-looping combustion (CLC) of coal. Recent CLC studies have considered the more technically difficult problem of reactions between abundant solid fuels (i.e. coal and waste streams) and solid metal oxides. A definitive reaction mechanism has not been reported for CLC reaction of solid fuels. It has often been assumed that the solid/solid reaction is slow and therefore requires that reactions be conducted at temperatures high enough to gasify the solid fuel, or decompose the metal oxide. In contrast, data presented in this paper demonstrates that solid/solid reactions can be completed at much lower temperatures, with rates that are technically useful as long as adequate fuel/metal oxide contact is achieved. Density functional theory (DFT) simulations as well as experimental techniques such as thermo-gravimetric analysis (TGA), flow reactor studies, in situ X-ray photo electron spectroscopy (XPS), in situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to evaluate how the proximal interaction between solid phases proceeds. The data indicate that carbon induces the Cu-O bond breaking process to initiate the combustion of carbon at temperatures significantly lower than the spontaneous decomposition temperature of CuO, and the type of reducing medium in the vicinity of the metal oxide influences the temperature at which the oxygen release from the metal oxide takes place. Surface melting of Cu and wetting of carbon may contribute to the solid-solid contacts necessary for the reaction. (author)
Photocatalytic activity of layered perovskite-like oxides in practically valuable chemical reactions
NASA Astrophysics Data System (ADS)
Rodionov, I. A.; Zvereva, I. A.
The photocatalytic properties of layered perovskite-like oxides corresponding to the Ruddlesen–Popper, Dion–Jacobson and Aurivillius phases are considered. Of the photocatalytic reactions, the focus is on the reactions of water splitting, hydrogen evolution from aqueous solutions of organic substances and degradation of model organic pollutants. Possibilities to conduct these reactions under UV and visible light in the presence of layered perovskite-like oxides and composite photocatalysts based on them are shown. The specific surface area, band gap energy, particle morphology, cation and anion doping and surface modification are considered as factors that affect the photocatalytic activity. Special attention is paid to the possibilities to enhance the photocatalytic activity by intercalation, ion exchange and exfoliation, which are inherent in this class of compounds. Conclusions are made about the prospects for the use of layered perovskite-like oxides in photocatalysis. The bibliography includes 253 references.
Oxidation reaction of high molecular weight carboxylic acids in supercritical water.
Jin, Fangming; Moriya, Takehiko; Enomoto, Heiji
Stearic acid, being a model compound of high molecular weight carboxylic acids, was oxidized in a batch reactor by changing the oxygen supply with an insufficient oxygen supply at a constant reaction time at 420 degrees C. On the basis of the intermediate products identified by GC/MS, NMR, and HPLC analyses and the free-radical reaction mechanism, the oxidation pathways of high molecular weight carboxylic acids in supercritical water are discussed. The reaction of carboxylic acids in supercritical water proceeds with the consecutive oxidation of higher molecular weight carboxylic acids to lower molecular weight carboxylic acids through several major pathways. The attack of the hydroxyl radical occurs not only at the carbons in alpha-, beta-, gamma-positions to a --COOH group but also at the carbons ((omega-1)-carbon and/or omega-carbon) far in the alkyl chain from a --COOH group, which may lead to the formation of dicarboxylic acids. PMID:12901673
Powerful fluoroalkoxy molybdenum(V) reagent for selective oxidative arene coupling reaction.
Schubert, Moritz; Leppin, Jana; Wehming, Kathrin; Schollmeyer, Dieter; Heinze, Katja; Waldvogel, Siegfried R
We introduce the novel fluoroalkoxy molybdenum(V) reagent 1 which has superior reactivity and selectivity in comparison to MoCl5 or the MoCl5 /TiCl4 reagent mixture in the oxidative coupling reactions of aryls. Common side reactions, such as chlorination and/or oligomer formation, are drastically diminished creating a powerful and useful reagent for oxidative coupling. Theoretical treatment of the reagent interaction with 1,2-dimethoxybenzene-type substrates indicates an inner-sphere electron transfer followed by a radical cationic reaction pathway for the oxidative-coupling process. EPR spectroscopic and electrochemical studies, X-ray analyses, computational investigations, and the experimental scope provide a highly consistent picture. The substitution of chlorido ligands by hexafluoroisopropoxido moieties seems to boost both the reactivity and selectivity of the metal center which might be applied to other reagents as well. PMID:24478061
Treatment of gaseous alpha-pinene by a combined system containing photo oxidation and aerobic biotrickling filtration.
Cheng, Zhuo-Wei; Zhang, Li-Li; Chen, Jian-Meng; Yu, Jian-Ming; Gao, Zeng-Liang; Jiang, Yi-Feng
Biofiltration of hydrophobic and/or recalcitrant volatile pollutants is intrinsically limited. In the present study, a combined ultraviolet-biotrickling filter (UV-BTF) was developed to improve the removal of these compounds, and a single BTF as the control was operated under the same conditions. The experimental results showed that the UV-BTF provided higher removal efficiencies than the single BTF at an inlet concentration range of 600-1500 mg m(-3) under shorter residence times. The maximum elimination capacities (ECs) obtained were 94.2 mg m(-3)h(-1) and 44 mg m(-3)h(-1) in the combined UV-BTF and single BTF, respectively. The mass ratio of carbon dioxide produced to α-pinene removed in the UV-BTF was approximately 2.74, which was much higher than that of the single BTF (1.99). Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis indicated that there was more complicated microbial community in the UV-BTF than that in the single BTF. In addition, we investigated the effect of starvation or stagnation on re-acclimation and removal performance from an engineering standpoint. The results showed that the combined UV-BTF could deal with fluctuating conditions or periods without any flow (air or liquid) supply much better than the single BTF. PMID:21803492
Heterobifunctional PEG Ligands for Bioconjugation Reactions on Iron Oxide Nanoparticles
Bloemen, Maarten; Van Stappen, Thomas; Willot, Pieter; Lammertyn, Jeroen; Koeckelberghs, Guy; Geukens, Nick; Gils, Ann; Verbiest, Thierry
Ever since iron oxide nanoparticles have been recognized as promising scaffolds for biomedical applications, their surface functionalization has become even more important. We report the synthesis of a novel polyethylene glycol-based ligand that combines multiple advantageous properties for these applications. The ligand is covalently bound to the surface via a siloxane group, while its polyethylene glycol backbone significantly improves the colloidal stability of the particle in complex environments. End-capping the molecule with a carboxylic acid introduces a variety of coupling chemistry possibilities. In this study an antibody targeting plasminogen activator inhibitor-1 was coupled to the surface and its presence and binding activity was assessed by enzyme-linked immunosorbent assay and surface plasmon resonance experiments. The results indicate that the ligand has high potential towards biomedical applications where colloidal stability and advanced functionality is crucial. PMID:25275378
Rubrivivax gelatinosus acsF (previously orf358) codes for a conserved, putative binuclear-iron-cluster-containing protein involved in aerobic oxidative cyclization of Mg-protoporphyrin IX monomethylester.
Pinta, Violaine; Picaud, Martine; Reiss-Husson, Françoise; Astier, Chantal
This study describes the characterization of orf358, an open reading frame of previously unidentified function, in the purple bacterium Rubrivivax gelatinosus. A strain in which orf358 was disrupted exhibited a phenotype similar to the wild type under photosynthesis or low-aeration respiratory growth conditions. In contrast, under highly aerated respiratory growth conditions, the wild type still produced bacteriochlorophyll a (Bchl a), while the disrupted strain accumulated a compound that had the same absorption and fluorescence emission spectra as Mg-protoporphyrin but was less polar, suggesting that it was Mg-protoporphyrin monomethylester (MgPMe). These data indicated a blockage in Bchl a synthesis at the oxidative cyclization stage and implied the coexistence of two different mechanisms for MgPMe cyclization in R. gelatinosus, an anaerobic mechanism active under photosynthesis or low oxygenation and an aerobic mechanism active under high-oxygenation growth conditions. Based on these results as well as on sequence analysis indicating the presence of conserved putative binuclear-iron-cluster binding motifs, the designation of orf358 as acsF (for aerobic cyclization system Fe-containing subunit) is proposed. Several homologs of AcsF were found in a wide range of photosynthetic organisms, including Chlamydonomas reinhardtii Crd1 and Pharbitis nil PNZIP, suggesting that this aerobic oxidative cyclization mechanism is conserved from bacteria to plants. PMID:11790744
Rubrivivax gelatinosus acsF (Previously orf358) Codes for a Conserved, Putative Binuclear-Iron-Cluster-Containing Protein Involved in Aerobic Oxidative Cyclization of Mg-Protoporphyrin IX Monomethylester
Pinta, Violaine; Picaud, Martine; Reiss-Husson, Françoise; Astier, Chantal
This study describes the characterization of orf358, an open reading frame of previously unidentified function, in the purple bacterium Rubrivivax gelatinosus. A strain in which orf358 was disrupted exhibited a phenotype similar to the wild type under photosynthesis or low-aeration respiratory growth conditions. In contrast, under highly aerated respiratory growth conditions, the wild type still produced bacteriochlorophyll a (Bchl a), while the disrupted strain accumulated a compound that had the same absorption and fluorescence emission spectra as Mg-protoporphyrin but was less polar, suggesting that it was Mg-protoporphyrin monomethylester (MgPMe). These data indicated a blockage in Bchl a synthesis at the oxidative cyclization stage and implied the coexistence of two different mechanisms for MgPMe cyclization in R. gelatinosus, an anaerobic mechanism active under photosynthesis or low oxygenation and an aerobic mechanism active under high-oxygenation growth conditions. Based on these results as well as on sequence analysis indicating the presence of conserved putative binuclear-iron-cluster binding motifs, the designation of orf358 as acsF (for aerobic cyclization system Fe-containing subunit) is proposed. Several homologs of AcsF were found in a wide range of photosynthetic organisms, including Chlamydonomas reinhardtii Crd1 and Pharbitis nil PNZIP, suggesting that this aerobic oxidative cyclization mechanism is conserved from bacteria to plants. PMID:11790744
Process for the oxidation of materials in water at supercritical temperatures utilizing reaction rate enhancers
Swallow, K.C.; Killilea, W.R.; Hong, G.T.; Bourhis, A.L.
A method is described for substantially completely oxidizing combustible materials in which an aqueous stream bearing the combustible materials is reacted in the presence of an oxidant comprising diatomic oxygen and at a temperature greater than the critical temperature of water and at a pressure greater than about 25 bar, within a reactor for a period of less than about 5 minutes to produce a reaction product stream, wherein the reaction is initiated in the presence of a rate enhancer comprising at least one oxidizing agent in addition to said oxidant selected from the group consisting of ozone, hydrogen peroxide, salts containing persulfate, salts containing permanganate, nitric acid, salts containing nitrate, oxyacids of chlorine and their corresponding salts, hypochlorous acid, salts containing hypochlorite, chlorous acid, salts containing chlorite, chloric acid, salts containing chlorate, perchloric acid, and salts containing perchlorate.
Surface-catalyzed air oxidation reactions of hydrazines: Tubular reactor studies
NASA Technical Reports Server (NTRS)
Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.
The surface-catalyzed air oxidation reactions of hydrazine, monomethylhydrazine, unsymmetrical dimethylhydrazine, symmetrical dimethylhydrazine, trimethylhydrazine and tetramethylhydrazine were investigated in a metal-powder packed turbular flow reactor at 55 plus or minus 3 C. Hydrazine was completely reacted on all surfaces studied. The major products of monomethylhydrazine (MMH) oxidation were methanol, methane and methyldiazene. The di-, tri- and tetra-methyl hydrazines were essentially unreactive under these conditions. The relative catalytic reactivities toward MMH are: Fe greater than Al2O3 greater than Ti greater than Zn greater than 316 SS greater than Cr greater than Ni greater than Al greater than 304L SS. A kinetic scheme and mechanism involving adsorption, oxidative dehydrogenation and reductive elimination reactions on a metal oxide surface are proposed.
Interfacial Cu+ promoted surface reactivity: Carbon monoxide oxidation reaction over polycrystalline copper-titania catalysts
NASA Astrophysics Data System (ADS)
Senanayake, Sanjaya D.; Pappoe, Naa Adokaley; Nguyen-Phan, Thuy-Duong; Luo, Si; Li, Yuanyuan; Xu, Wenqian; Liu, Zongyuan; Mudiyanselage, Kumudu; Johnston-Peck, Aaron C.; Frenkel, Anatoly I.; Heckler, Ilana; Stacchiola, Dario; Rodriguez, José A.
We have studied the catalytic carbon monoxide (CO) oxidation (CO + 0.5O2 → CO2) reaction using a powder catalyst composed of both copper (5 wt.% loading) and titania (CuOx-TiO2). Our study was focused on revealing the role of Cu, and the interaction between Cu and TiO2, by systematic comparison between two nanocatalysts, CuOx-TiO2 and pure CuOx. We interrogated these catalysts under in situ conditions using X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to probe the structure and electronic properties of the catalyst at all stages of the reaction and simultaneously probe the surface states or intermediates of this reaction. With the aid of several ex situ characterization techniques including transmission electron microscopy (TEM), the local catalyst morphology and structure were also studied. Our results show that a CuOx-TiO2 system is more active than bulk CuOx for the CO oxidation reaction due to its lower onset temperature and better stability at higher temperatures. Our results also suggest that surface Cu+ species observed in the CuOx-TiO2 interface are likely to be a key player in the CO oxidation mechanism, while implicating that the stabilization of this species is probably associated with the oxide-oxide interface. Both in situ DRIFTS and XAFS measurements reveal that there is likely to be a Cu(Ti)-O mixed oxide at this interface. We discuss the nature of this Cu(Ti)-O interface and interpret its role on the CO oxidation reaction.
Optimization of operation conditions for the mitigation of nitrous oxide (N2O) emissions from aerobic nitrifying granular sludge system.
Liu, Rui-Ting; Wang, Xin-Hua; Zhang, Yan; Wang, Ming-Yu; Gao, Ming-Ming; Wang, Shu-Guang
The optimization of operation parameters is a key consideration to minimize nitrous oxide (N2O) emissions in biological nitrogen removal processes. So far, different parameters have only been investigated individually, making it difficult to compare their specific effects and combined influences. In this study, we applied the Plackett-Burman (PB) multifactorial experimental design and response surface methodology (RSM) analysis to find the optimized condition for the mitigation of N2O release in a nitrifying granular sludge system. Seven parameters (temperature, pH, feeding strategy, C/N ratio, aeration rate, Cu(2+) concentration, and aeration mode) were tested in parallel. Five of them (other than chemical oxygen demand/nitrogen (C/N) ratio and Cu(2+) concentration) were selected as influential factors. Since the type of feeding strategies and aeration modes cannot be quantified, continuous feed strategy and anoxic/oxic aeration mode were applied for the following study. Influences of temperature, pH, and aeration rate on N2O emissions were tested with RSM analysis to further investigate the mutual interactions among the parameters and to identify the optimal values that would minimize N2O release. Results showed the minimum emission value could be obtained under the temperature of 22.3 °C, pH of 7.1 and aeration rate of 0.20 m(3)/h. Predicted results were then verified by subsequent validation experiments. The estimated N2O emission value of each design by RSM was also observed in good relationships with experimental result. PMID:26841778
Endothelial cell-derived nitric oxide enhances aerobic glycolysis in astrocytes via HIF-1α-mediated target gene activation.
Brix, Britta; Mesters, Jeroen R; Pellerin, Luc; Jöhren, Olaf
Astrocytes exhibit a prominent glycolytic activity, but whether such a metabolic profile is influenced by intercellular communication is unknown. Treatment of primary cultures of mouse cortical astrocytes with the nitric oxide (NO) donor DetaNONOate induced a time-dependent enhancement in the expression of genes encoding various glycolytic enzymes as well as transporters for glucose and lactate. Such an effect was shown to be dependent on the hypoxia-inducible factor HIF-1α, which is stabilized and translocated to the nucleus to exert its transcriptional regulation. NO action was dependent on both the PI3K/Akt/mTOR and MEK signaling pathways and required the activation of COX, but was independent of the soluble guanylate cyclase pathway. Furthermore, as a consequence of NO treatment, an enhanced lactate production and release by astrocytes was evidenced, which was prevented by downregulating HIF-1α. Several brain cell types represent possible sources of NO. It was found that endothelial cells, which express the endothelial NO synthase (eNOS) isoform, constitutively produced the largest amount of NO in culture. When astrocytes were cocultured with primary cultures of brain vascular endothelial cells, stabilization of HIF-1α and an enhancement in glucose transporter-1, hexokinase-2, and monocarboxylate transporter-4 expression as well as increased lactate production was found in astrocytes. This effect was inhibited by the NOS inhibitor l-NAME and was not seen when astrocytes were cocultured with primary cultures of cortical neurons. Our findings suggest that endothelial cell-derived NO participates to the maintenance of a high glycolytic activity in astrocytes mediated by astrocytic HIF-1α activation. PMID:22787058
Morphological impact on the reaction kinetics of size-selected cobalt oxide nanoparticles
Bartling, Stephan Meiwes-Broer, Karl-Heinz; Barke, Ingo; Pohl, Marga-Martina
Apart from large surface areas, low activation energies are essential for efficient reactions, particularly in heterogeneous catalysis. Here, we show that not only the size of nanoparticles but also their detailed morphology can crucially affect reaction kinetics, as demonstrated for mass-selected, soft-landed, and oxidized cobalt clusters in a 6 nm to 18 nm size range. The method of reflection high-energy electron diffraction is extended to the quantitative determination of particle activation energies which is applied for repeated oxidation and reduction cycles at the same particles. We find unexpectedly small activation barriers for the reduction reaction of the largest particles studied, despite generally increasing barriers for growing sizes. We attribute these observations to the interplay of reaction-specific material transport with a size-dependent inner particle morphology.
Teaching Aerobic Fitness Concepts.
ERIC Educational Resources Information Center
Sander, Allan N.; Ratliffe, Tom
Discusses how to teach aerobic fitness concepts to elementary students. Some of the K-2 activities include location, size, and purpose of the heart and lungs; the exercise pulse; respiration rate; and activities to measure aerobic endurance. Some of the 3-6 activities include: definition of aerobic endurance; heart disease risk factors;…
Inhibition of nitric oxide and prostaglandins, but not endothelial-derived hyperpolarizing factors, reduces blood flow and aerobic energy turnover in the exercising human leg.
Mortensen, Stefan P; González-Alonso, José; Damsgaard, Rasmus; Saltin, Bengt; Hellsten, Ylva
Prostaglandins, nitric oxide (NO) and endothelial-derived hyperpolarizing factors (EDHFs) are substances that have been proposed to be involved in the regulation of skeletal muscle blood flow during physical activity. We measured haemodynamics, plasma ATP at rest and during one-legged knee-extensor exercise (19 +/- 1 W) in nine healthy subjects with and without intra-arterial infusion of indomethacin (Indo; 621 +/- 17 microg min(-1)), Indo + N(G)-monomethyl-L-arginine (L-NMMA; 12.4 +/- 0.3 mg min(-1)) (double blockade) and Indo + L-NMMA + tetraethylammonium chloride (TEA; 12.4 +/- 0.3 mg min(-1)) (triple blockade). Double and triple blockade lowered leg blood flow (LBF) at rest (P<0.05), while it remained unchanged with Indo. During exercise, LBF and vascular conductance were 2.54 +/- 0.10 l min(-1) and 25 +/- 1 mmHg, respectively, in control and they were lower with double (33 +/- 3 and 36 +/- 4%, respectively) and triple (26 +/- 4 and 28 +/- 3%, respectively) blockade (P<0.05), while there was no difference with Indo. The lower LBF and vascular conductance with double and triple blockade occurred in parallel with a lower O(2) delivery, cardiac output, heart rate and plasma [noradrenaline] (P<0.05), while blood pressure remained unchanged and O(2) extraction and femoral venous plasma [ATP] increased. Despite the increased O(2) extraction, leg was 13 and 17% (triple and double blockade, respectively) lower than control in parallel to a lower femoral venous temperature and lactate release (P<0.05). These results suggest that NO and prostaglandins play important roles in skeletal muscle blood flow regulation during moderate intensity exercise and that EDHFs do not compensate for the impaired formation of NO and prostaglandins. Moreover, inhibition of NO and prostaglandin formation is associated with a lower aerobic energy turnover and increased concentration of vasoactive ATP in plasma. PMID:17347273
Bimolecular Coupling Reactions through Oxidatively Generated Aromatic Cations: Scope and Stereocontrol
Cui, Yubo; Villafane, Louis A.; Clausen, Dane J.
Chromenes, isochromenes, and benzoxathioles react with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to form stable aromatic cations that react with a range of nucleophiles. These oxidative fragment coupling reactions provide rapid access to structurally diverse heterocycles. Conducting the reactions in the presence of a chiral Brønsted acid results in the formation of an asymmetric ion pair that can provide enantiomerically enriched products in a rare example of a stereoselective process resulting from the generation of a chiral electrophile through oxidative carbon–hydrogen bond cleavage. PMID:23913987
Optical modulation spectroscopy: a study of the self-reaction of benzophenone oxide
Girard, M.; Griller, D.
The bimolecular self-reaction of benzophenone oxide was investigated by optical modulation spectroscopy and by product studies. The transient decayed to give benzophenone and oxygen and the rate constants for its disappearance, 2k, are described by the expression log (2k) = (9.1 +/- 0.2) - (1.8 +/- 0.3)/theta where theta = 2.30RT kcal mol/sup -1/. The significance of these parameters is discussed in terms of the orientational requirements for self-reaction. Benzophenone oxide was found to react with octanal with a rate constant 2.0 x 10/sup 4/ M/sup -1/ s/sup -1/.
Reaction Mechanism for m-Xylene Oxidation in the Claus Process by Sulfur Dioxide.
Sinha, Sourab; Raj, Abhijeet; Al Shoaibi, Ahmed S; Chung, Suk Ho
In the Claus process, the presence of aromatic contaminants such benzene, toluene, and xylenes (BTX), in the H2S feed stream has a detrimental effect on catalytic reactors, where BTX form soot particles and clog and deactivate the catalysts. Among BTX, xylenes are proven to be most damaging contaminant for catalysts. BTX oxidation in the Claus furnace, before they enter catalyst beds, provides a solution to this problem. A reaction kinetics study on m-xylene oxidation by SO2, an oxidant present in Claus furnace, is presented. The density functional theory is used to study the formation of m-xylene radicals (3-methylbenzyl, 2,6-dimethylphenyl, 2,4-dimethylphenyl, and 3,5-dimethylphenyl) through H-abstraction and their oxidation by SO2. The mechanism begins with SO2 addition on the radicals through an O-atom rather than the S-atom with the release of 180.0-183.1 kJ/mol of reaction energies. This exothermic reaction involves energy barriers in the range 3.9-5.2 kJ/mol for several m-xylene radicals. Thereafter, O-S bond scission takes place to release SO, and the O-atom remaining on aromatics leads to CO formation. Among four m-xylene radicals, the resonantly stabilized 3-methylbenzyl exhibited the lowest SO2 addition and SO elimination rates. The reaction rate constants are provided to facilitate Claus process simulations to find conditions suitable for BTX oxidation. PMID:26334187
Aerobic Linear Allylic C-H Amination: Overcoming Benzoquinone Inhibition.
Pattillo, Christopher C; Strambeanu, Iulia I; Calleja, Pilar; Vermeulen, Nicolaas A; Mizuno, Tomokazu; White, M Christina
An efficient aerobic linear allylic C-H amination reaction is reported under palladium(II)/bis-sulfoxide/Brønsted base catalysis. The reaction operates under preparative, operationally simple conditions (1 equiv of olefin, 1 atm O2 or air) with reduced Pd(II)/bis-sulfoxide catalyst loadings while providing higher turnovers and product yields than systems employing stoichiometric benzoquinone (BQ) as the terminal oxidant. Pd(II)/BQ π-acidic interactions have been invoked in various catalytic processes and are often considered beneficial in promoting reductive functionalizations. When such electrophilic activation for functionalization is not needed, however, BQ at high concentrations may compete with crucial ligand (bis-sulfoxide) binding and inhibit catalysis. Kinetic studies reveal an inverse relationship between the reaction rate and the concentration of BQ, suggesting that BQ is acting as a ligand for Pd(II) which results in an inhibitory effect on catalysis. PMID:26730458
Organo-Iodine(III)-Catalyzed Oxidative Phenol-Arene and Phenol-Phenol Cross-Coupling Reaction.
Morimoto, Koji; Sakamoto, Kazuma; Ohshika, Takao; Dohi, Toshifumi; Kita, Yasuyuki
The direct oxidative coupling reaction has been an attractive tool for environmentally benign chemistry. Reported herein is that the hypervalent iodine catalyzed oxidative metal-free cross-coupling reaction of phenols can be achieved using Oxone as a terminal oxidant in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP). This method features a high efficiency and regioselectivity, as well as functional-group tolerance under very mild reaction conditions without using metal catalysts. PMID:26879796
Electrophilic activation of hydrogen peroxide: selective oxidation reactions in perfluorinated alcohol solvents.
Neimann, K; Neumann, R
[reaction; see text] The catalytic electrophilic activation of hydrogen peroxide with transition metal compounds toward reaction with nucleophiles is a matter of very significant research and practical interest. We have now found that use of perfluorinated alcoholic solvents such as 1,1, 1,3,3,3-hexafluoro-2-propanol in the absence of catalysts allowed electrophilic activation of hydrogen peroxide toward epoxidation of alkenes and the Baeyer-Villiger oxidation of ketones. PMID:10964384
Enantiomerically pure bithiophene diphosphine oxides as catalysts for direct double aldol reactions.
Genoni, Andrea; Benaglia, Maurizio; Rossi, Sergio; Celentano, Giuseppe
The direct aldol reaction between aryl methyl ketones with aromatic aldehydes in the presence of tetrachlorosilane and a catalytic amount of a chiral bithiophene diphosphine oxide was studied; the product of double aldol addition was isolated as diacetate in good diastereoselectivity (up to 95:5) and enantioselectivities up to 91%. The reaction with heteroaromatic aldehydes was also investigated leading to the corresponding 1,3 diols, in some cases with excellent stereoselectivities. PMID:23744602
Kinetic and photochemical data for atmospheric chemistry reactions of the nitrogen oxides
NASA Technical Reports Server (NTRS)
Hampson, R. F., Jr.
Data sheets for thermal and photochemical reactions of importance in the atmospheric chemistry of the nitrogen oxides are presented. For each reaction the available experimental data are summarized and critically evaluated, and a preferred value of the rate coefficient is given. The selection of the preferred value is discussed and an estimate of its accuracy is given. For the photochemical process, the data are summarized, and preferred for the photoabsorption cross section and primary quantum yields are given.
Proton Coupled Electron Transfer Reactions at the Surface of Metal Oxide Nanomaterials
NASA Astrophysics Data System (ADS)
Braten, Miles N.
Nanostructured metal oxide materials are found in many products and processes in our society today, but they play a particularly important role in the conversion and storage of energy. The materials are used as catalysts and redox active supports in devices such as dye sensitized solar cells, solid oxide fuel cells, and flow batteries, where they transfer and store electrons and charge balancing cations. Oftentimes electron transfer is modulated by the cations and when the cation is a proton, these redox reactions are known as proton coupled electron transfer (PCET) reactions. The work described in this dissertation focuses on understanding the PCET reactivity of nanocrystalline metal oxide materials. Chapter 1 introduces the concept of PCET and provides background information on the zinc oxide (ZnO) nanocrystals (NCs) which the majority of the research is focused on. Chapter 2 examines the chemistry that occurs during the photoreduction of ZnO NCs. Chapter 3 describes experiments probing how ZnO NC capping ligand concentration and NC size modulate PCET reaction rates. Chapter 4 describes experiments that compare the PCET reactivity of ZnO NCs with different numbers of electrons and protons stored on them. Chapter 5 describes attempts to observe the electrochemical reduction of ZnO NCs attached to gold electrodes. Finally, Chapter 6 contains attempts to identify a nanostructured metal oxide alkane oxidation catalyst for use in fuel cell.
Efficient processing of reaction-sintered silicon carbide by anodically oxidation-assisted polishing
NASA Astrophysics Data System (ADS)
Tu, Qunzhang; Shen, Xinmin; Zhou, Jianzhao; He, Xiaohui; Yamamura, Kazuya
Reaction-sintered silicon carbide (RS-SiC) is a promising optical material for the space telescope systems. Anodically oxidation-assisted polishing is a method to machine RS-SiC. The electrolyte used in this study is a mixture of hydrogen peroxide (H2O2) and hydrochloric acid (HCl), and the oxidation potential has two modes: constant potential and high-frequency-square-wave potential. Oxide morphologies are compared by scanning electron microscope/energy dispersive x-ray spectroscopy and scanning white-light interferometer. The results indicate that anodic oxidation under constant potential can not only obtain a relatively smooth surface but also be propitious to obtain high material removal rate. The oxidation depth in anodic oxidation under constant potential is calculated by comparing surface morphologies before and after hydrofluoric acid etching. The theoretical oxidation rate is 5.3 nm/s based on the linear Deal-Grove model. Polishing of the oxidized RS-SiC is conducted to validate the machinability of the oxide layer. The obtained surface roughness root-mean-square is around 4.5 nm. Thus, anodically oxidation-assisted polishing can be considered as an efficient method, which can fill the performance gap between the rough figuring and fine finishing of RS-SiC. It can improve the machining quality of RS-SiC parts and promote the application of RS-SiC products.
Pd/C-catalyzed aerobic oxidative esterification of alcohols and aldehydes: a highly efficient microwave-assisted green protocol.
Caporaso, Marina; Cravotto, Giancarlo; Georgakopoulos, Spyros; Heropoulos, George; Martina, Katia; Tagliapietra, Silvia
We herein describe an environmentally friendly microwave-assisted oxidative esterification of alcohols and aldehydes in the presence of molecular oxygen and a heterogeneous catalysis (Pd/C, 5 mol %). This efficient and ligandless conversion procedure does not require the addition of an organic hydrogen acceptor. The reaction rate is strongly enhanced by mild dielectric heating. Furthermore, it is a versatile green procedure which generally enables the isolation of esters to be carried out by simple filtration in almost quantitative yields. PMID:24991300
Pd/C-catalyzed aerobic oxidative esterification of alcohols and aldehydes: a highly efficient microwave-assisted green protocol
Caporaso, Marina; Georgakopoulos, Spyros; Heropoulos, George; Martina, Katia; Tagliapietra, Silvia
Summary We herein describe an environmentally friendly microwave-assisted oxidative esterification of alcohols and aldehydes in the presence of molecular oxygen and a heterogeneous catalysis (Pd/C, 5 mol %). This efficient and ligandless conversion procedure does not require the addition of an organic hydrogen acceptor. The reaction rate is strongly enhanced by mild dielectric heating. Furthermore, it is a versatile green procedure which generally enables the isolation of esters to be carried out by simple filtration in almost quantitative yields. PMID:24991300
Nonenzymatic Reactions above Phospholipid Surfaces of Biological Membranes: Reactivity of Phospholipids and Their Oxidation Derivatives
Solís-Calero, Christian; Ortega-Castro, Joaquín; Frau, Juan; Muñoz, Francisco
Phospholipids play multiple and essential roles in cells, as components of biological membranes. Although phospholipid bilayers provide the supporting matrix and surface for many enzymatic reactions, their inherent reactivity and possible catalytic role have not been highlighted. As other biomolecules, phospholipids are frequent targets of nonenzymatic modifications by reactive substances including oxidants and glycating agents which conduct to the formation of advanced lipoxidation end products (ALEs) and advanced glycation end products (AGEs). There are some theoretical studies about the mechanisms of reactions related to these processes on phosphatidylethanolamine surfaces, which hypothesize that cell membrane phospholipids surface environment could enhance some reactions through a catalyst effect. On the other hand, the phospholipid bilayers are susceptible to oxidative damage by oxidant agents as reactive oxygen species (ROS). Molecular dynamics simulations performed on phospholipid bilayers models, which include modified phospholipids by these reactions and subsequent reactions that conduct to formation of ALEs and AGEs, have revealed changes in the molecular interactions and biophysical properties of these bilayers as consequence of these reactions. Then, more studies are desirable which could correlate the biophysics of modified phospholipids with metabolism in processes such as aging and diseases such as diabetes, atherosclerosis, and Alzheimer's disease. PMID:25977746
H2 oxidation versus organic substrate oxidation in non-heme iron mediated reactions with H2O2.
Hassanpour, Azin; Acuña-Parés, Ferran; Luis, Josep M; Cusso, Olaf; Morales de la Rosa, Silvia; Campos-Martín, José Miguel; Fierro, Jose L G; Costas, Miquel; Lloret-Fillol, Julio; Mas-Ballesté, Rubén
Herein we show that species generated upon reaction of α-[Fe(CF3SO3)2(BPMCN)] (BPMCN = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane) with H2O2 (putatively [Fe(V)(O)(OH)(BPMCN)]) is able to efficiently oxidize H2 to H2O even in the presence of organic substrates, while species formed in the presence of acetic acid (putatively [Fe(V)(O)(OAc)(BPMCN)]) prefer organic substrate oxidation over H2 activation. Mechanistic implications have been analysed with the aid of computational methods. PMID:26311021
Wastewater treatment from biodiesel production via a coupled photo-Fenton-aerobic sequential batch reactor (SBR) system.
Ramírez, Ximena María Vargas; Mejía, Gina Maria Hincapié; López, Kelly Viviana Patiño; Vásquez, Gloria Restrepo; Sepúlveda, Juan Miguel Marín
A coupled system of the photo-Fenton advanced oxidation technique and an aerobic sequential batch reactor (SBR) was used to treat wastewater from biodiesel production using either palm or castor oil. The photo-Fenton reaction and biological process were evaluated individually and were effective at treating the wastewater; nevertheless, each process required longer degradation times for the wastewater pollutants compared with the coupled system. The proposed coupled photo-Fenton/aerobic SBR system obtained a 90% reduction of the chemical oxygen demand (COD) in half of the time required for the biological system individually. PMID:22766873
Variability in aerobic methane oxidation over the past 1.2 Myrs recorded in microbial biomarker signatures from Congo fan sediments
NASA Astrophysics Data System (ADS)
Talbot, Helen M.; Handley, Luke; Spencer-Jones, Charlotte L.; Dinga, Bienvenu Jean; Schefuß, Enno; Mann, Paul J.; Poulsen, John R.; Spencer, Robert G. M.; Wabakanghanzi, Jose N.; Wagner, Thomas
Methane (CH4) is a strong greenhouse gas known to have perturbed global climate in the past, especially when released in large quantities over short time periods from continental or marine sources. It is therefore crucial to understand and, if possible, quantify the individual and combined response of these variable methane sources to natural climate variability. However, past changes in the stability of greenhouse gas reservoirs remain uncertain and poorly constrained by geological evidence. Here, we present a record from the Congo fan of a highly specific bacteriohopanepolyol (BHP) biomarker for aerobic methane oxidation (AMO), 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol), that identifies discrete periods of increased AMO as far back as 1.2 Ma. Fluctuations in the concentration of aminopentol, and other 35-aminoBHPs, follow a pattern that correlates with late Quaternary glacial-interglacial climate cycles, with highest concentrations during warm periods. We discuss possible sources of aminopentol, and the methane consumed by the precursor methanotrophs, within the context of the Congo River setting, including supply of methane oxidation markers from terrestrial watersheds and/or marine sources (gas hydrate and/or deep subsurface gas reservoir). Compound-specific carbon isotope values of -30‰ to -40‰ for BHPs in ODP 1075 and strong similarities between the BHP signature of the core and surface sediments from the Congo estuary and floodplain wetlands from the interior of the Congo River Basin, support a methanotrophic and likely terrigenous origin of the 35-aminoBHPs found in the fan sediments. This new evidence supports a causal connection between marine sediment BHP records of tropical deep sea fans and wetland settings in the feeding river catchments, and thus tropical continental hydrology. Further research is needed to better constrain the different sources and pathways of methane emission. However, this study identifies the large potential
Exceptionally Active and Stable Spinel Nickel Manganese Oxide Electrocatalysts for Urea Oxidation Reaction.
Periyasamy, Sivakumar; Subramanian, Palaniappan; Levi, Elena; Aurbach, Doron; Gedanken, Aharon; Schechter, Alex
Spinel nickel manganese oxides, widely used materials in the lithium ion battery high voltage cathode, were studied in urea oxidation catalysis. NiMn2O4, Ni1.5Mn1.5O4, and MnNi2O4 were synthesized by a simple template-free hydrothermal route followed by a thermal treatment in air at 800 °C. Rietveld analysis performed on nonstoichiometric nickel manganese oxide-Ni1.5Mn1.5O4 revealed the presence of three mixed phases: two spinel phases with different lattice parameters and NiO unlike the other two spinels NiMn2O4 and MnNi2O4. The electroactivity of nickel manganese oxide materials toward the oxidation of urea in alkaline solution is evaluated using cyclic voltammetric measurements. Ni1.5Mn1.5O4 exhibits excellent redox characteristics and lower charge transfer resistances in comparison with other compositions of nickel manganese oxides and nickel oxide prepared under similar conditions.The Ni1.5Mn1.5O4modified electrode oxidizes urea at 0.29 V versus Ag/AgCl with a corresponding current density of 6.9 mA cm(-2). At a low catalyst loading of 50 μg cm(-2), the urea oxidation current density of Ni1.5Mn1.5O4 in alkaline solution is 7 times higher than that of nickel oxide and 4 times higher than that of NiMn2O4 and MnNi2O4, respectively. PMID:27123873
40 CFR 721.10375 - Hydroxypropyl methacrylate, reaction products with propylene oxide and ethylene oxide, copolymer...
Code of Federal Regulations, 2014 CFR
... reporting. (1) The chemical substance identified generically as hydroxypropyl methacrylate, reaction... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Hydroxypropyl methacrylate, reaction... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific...
40 CFR 721.10375 - Hydroxypropyl methacrylate, reaction products with propylene oxide and ethylene oxide, copolymer...
Code of Federal Regulations, 2012 CFR
... reporting. (1) The chemical substance identified generically as hydroxypropyl methacrylate, reaction... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Hydroxypropyl methacrylate, reaction... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific...
40 CFR 721.10375 - Hydroxypropyl methacrylate, reaction products with propylene oxide and ethylene oxide, copolymer...
Code of Federal Regulations, 2013 CFR
... reporting. (1) The chemical substance identified generically as hydroxypropyl methacrylate, reaction... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Hydroxypropyl methacrylate, reaction... CONTROL ACT SIGNIFICANT NEW USES OF CHEMICAL SUBSTANCES Significant New Uses for Specific...
Chemiluminescence spectra of the reaction products of gallium, indium and thallium vapors with nitrous oxide
Eliseev, M.V.; Koryazhkin, V.A.; Mal'tsev, A.A.; Popov, A.D.
The search for active media for chemical lasers generating in the visible range has led to numerous investigations of the chemiluminescence of oxidation reactions of metals in the gas phase. In the present work, the chemiluminescence spectra of flames of gallium, indium, and thallium vapors in nitrous oxide in an argon flux are investigated. The chemiluminescence intensity was studied as a function of the total pressure in the reactor, the rate of admission of the nitrous oxide, the rate of admission of argon and the cell temperature. The oxide molecules formed are in vibrational levels of the electronic ground state that are close to the dissociational limit. As a result of collisions with argon atoms, the oxide molecule passes to the excited electronic state. The thermal effects of the above reaction and the equal dissociational energies of the oxide molecules are sufficient for excitation of the vibrational levels 10 and 2 of the excited electronic states of the GaO and InO molecules, respectively. Atomic chemiluminescence is evidently a consequence of collision of metal oxide molecules with metal atoms in the electronic ground states.
Literature information applicable to the reaction of uranium oxides with chlorine to prepare uranium tetrachloride
Haas, P.A.
The reaction of uranium oxides and chlorine to prepare anhydrous uranium tetrachloride (UCl{sub 4}) are important to more economical preparation of uranium metal. The most practical reactions require carbon or carbon monoxide (CO) to give CO or carbon dioxide (CO{sub 2}) as waste gases. The chemistry of U-O-Cl compounds is very complex with valances of 3, 4, 5, and 6 and with stable oxychlorides. Literature was reviewed to collect thermochemical data, phase equilibrium information, and results of experimental studies. Calculations using thermodynamic data can identify the probable reactions, but the results are uncertain. All the U-O-Cl compounds have large free energies of formation and the calculations give uncertain small differences of large numbers. The phase diagram for UCl{sub 4}-UO{sub 2} shows a reaction to form uranium oxychloride (UOCl{sub 2}) that has a good solubility in molten UCl{sub 4}. This appears more favorable to good rates of reaction than reaction of solids and gases. There is limited information on U-O-Cl salt properties. Information on the preparation of titanium, zirconium, silicon, and thorium tetrachlorides (TiCl{sub 4}, ZrCl{sub 4}, SiCl{sub 4}, ThCl{sub 4}) by reaction of oxides with chlorine (Cl{sub 2}) and carbon has application to the preparation of UCl{sub 4}.
The reactions of O(ID) and OH with CH3OH, oxidation of the HCO radial, and the photochemical oxidation of formaldehyde. [photochemical reactions in stratosphere
NASA Technical Reports Server (NTRS)
Osif, T. L.
An experimental, laboratory study of the various photochemical reactions that can occur in the mesosphere and stratosphere is presented. N2O was photolyzed at 2139 A in the presence of CH3OH and CO. The O(id) produced in the photolysis reacted with CH3OH to produce OH radicals, and thus the reactions of both O(id) and OH were able to be studied. Also considered was the oxidation of the HCO radical. Mixtures of Cl2, O2, H2CO, and sometimes N2 or He were irradiated at 3660 A at several temperatures to photodecompose the Cl2. The photochemical oxidation of formaldehyde was studied as follows: formaldehyde in the presence of N2 and/or O2 (usually dry air) was photolyzed with a medium pressure Hg lamp used in conjunction with various filters which transmit different relative amounts of Hg lines from 2894 A to 3660 A. Results are presented and discussed, along with a description of experimental procedures and apparatus, and chemical reaction kinetics.
Oxidative degradation of nalidixic acid by nano-magnetite via Fe2+/O2-mediated reactions.
Ardo, Sandy G; Nélieu, Sylvie; Ona-Nguema, Georges; Delarue, Ghislaine; Brest, Jessica; Pironin, Elsa; Morin, Guillaume
Organic pollution has become a critical issue worldwide due to the increasing input and persistence of organic compounds in the environment. Iron minerals are potentially able to degrade efficiently organic pollutants sorbed to their surfaces via oxidative or reductive transformation processes. Here, we explored the oxidative capacity of nano-magnetite (Fe3O4) having ∼ 12 nm particle size, to promote heterogeneous Fenton-like reactions for the removal of nalidixic acid (NAL), a recalcitrant quinolone antibacterial agent. Results show that NAL was adsorbed at the surface of magnetite and was efficiently degraded under oxic conditions. Nearly 60% of this organic contaminant was eliminated after 30 min exposure to air bubbling in solution in the presence of an excess of nano-magnetite. X-ray diffraction (XRD) and Fe K-edge X-ray absorption spectroscopy (XANES and EXAFS) showed a partial oxidation of magnetite to maghemite during the reaction, and four byproducts of NAL were identified by liquid chromatography-mass spectroscopy (UHPLC-MS/MS). We also provide evidence that hydroxyl radicals (HO(•)) were involved in the oxidative degradation of NAL, as indicated by the quenching of the degradation reaction in the presence of ethanol. This study points out the promising potentialities of mixed valence iron oxides for the treatment of soils and wastewater contaminated by organic pollutants. PMID:25756496
Rapid Covalent Modification of Silicon Oxide Surfaces through Microwave-Assisted Reactions with Alcohols.
Lee, Austin W H; Gates, Byron D
We demonstrate the method of a rapid covalent modification of silicon oxide surfaces with alcohol-containing compounds with assistance by microwave reactions. Alcohol-containing compounds are prevalent reagents in the laboratory, which are also relatively easy to handle because of their stability against exposure to atmospheric moisture. The condensation of these alcohols with the surfaces of silicon oxides is often hindered by slow reaction kinetics. Microwave radiation effectively accelerates this condensation reaction by heating the substrates and/or solvents. A variety of substrates were modified in this demonstration, such as silicon oxide films of various thicknesses, glass substrates such as microscope slides (soda lime), and quartz. The monolayers prepared through this strategy demonstrated the successful formation of covalent surface modifications of silicon oxides with water contact angles of up to 110° and typical hysteresis values of 2° or less. An evaluation of the hydrolytic stability of these monolayers demonstrated their excellent stability under acidic conditions. The techniques introduced in this article were successfully applied to tune the surface chemistry of silicon oxides to achieve hydrophobic, oleophobic, and/or charged surfaces. PMID:27396288
Iron(III) Fluorinated Porphyrins: Greener Chemistry from Synthesis to Oxidative Catalysis Reactions.
Rebelo, Susana L H; Silva, André M N; Medforth, Craig J; Freire, Cristina
Iron(III) fluorinated porphyrins play a central role in the biomimetics of heme enzymes and enable cleaner routes to the oxidation of organic compounds. The present work reports significant improvements in the eco-compatibility of the synthesis of 5,10,15,20-tetrakis-pentafluorophenylporphyrin (H₂TPFPP) and the corresponding iron complex [Fe(TPFPP)Cl], and the use of [Fe(TPFPP)Cl] as an oxidation catalyst in green conditions. The preparations of H₂TPFPP and [Fe(TPFPP)Cl] typically use toxic solvents and can be made significantly greener and simpler using microwave heating and optimization of the reaction conditions. In the optimized procedure it was possible to eliminate nitrobenzene from the porphyrin synthesis and replace DMF by acetonitrile in the metalation reaction, concomitant with a significant reduction of reaction time and simplification of the purification procedure. The Fe(III)porphyrin is then tested as catalyst in the selective oxidation of aromatics at room temperature using a green oxidant (hydrogen peroxide) and green solvent (ethanol). Efficient epoxidation of indene and selective oxidation of 3,5-dimethylphenol and naphthalene to the corresponding quinones is observed. PMID:27077840
Methanol oxidation and hydrogen reactions on NiZr in acid solution
NASA Astrophysics Data System (ADS)
Hays, C. C.; Manoharan, R.; Goodenough, J. B.
The electrochemical properties of a Ni 50Zr 50 (at.%) alloy have been investigated by cyclic voltammetry and steady-state polarization measurements. The alloy forms a passivating oxyhydroxide film that makes it electrochemically stable in an acid solution. The oxyhydroxide film is shown to be an electrocatalyst for the methanol oxidation reaction (MOR). The reaction proceeds at surface O 2- ions neighboring a Ni 3+ ion of a thicker passivating film; electron transfer from the surface to the electrode occurs diffusively by the nickel atoms of the film. A reaction pathway is presented that accounts for the observation of an optimum thickness for the passivating film. The NiZr alloy was also found to catalyze both hydrogen-oxidation and proton-reduction reactions (HOR and PRR) if it has a thinner surface oxyhydroxide film. The alloy appears to form mixed NiZrH and NiZrH 3- x hydrides on cycling negative of the normal hydrogen potential. The activity of the hydrogen-oxidation reaction on a hydride surface was found to increase in the presence of streaming hydrogen gas and also with increasing negative initial potential. Although the hydride is unstable in acid, it may be an attractive candidate for use as a rechargeable negative electrode in an alkaline metal/air or nickel-metal hydride secondary battery.
Recovery after aerobic exercise is manipulated by tempo change in a rhythmic sound pattern, as indicated by autonomic reaction on heart functioning
Wallert, John; Madison, Guy
Physical prowess is associated with rapid recovery from exhaustion. Here we examined whether recovery from aerobic exercise could be manipulated with a rhythmic sound pattern that either decreased or increased in tempo. Six men and six women exercised repeatedly for six minutes on a cycle ergometer at 60 percent of their individual maximal oxygen consumption, and then relaxed for six minutes while listening to one of two sound pattern conditions, which seemed to infinitely either decrease or increase in tempo, during which heart and breathing activity was measured. Participants exhibited more high-frequent heart rate variability when listening to decreasing tempo than when listening to increasing tempo, accompanied by a non-significant trend towards lower heart rate. The results show that neuropsychological entrainment to a sound pattern may directly affect the autonomic nervous system, which in turn may facilitate physiological recovery after exercise. Applications using rhythmic entrainment to aid physical recovery are discussed. PMID:25285076
Oxidation and dechlorination of chlorophenols in dilute aqueous suspensions of manganese oxides: Reaction products
Ukrainczyk, L.; McBride, M.B. . Dept.of Soil, Crop, and Atmospheric Sciences)
Some monomeric and dimeric oxidation products of para- and/or ortho-chlorinated phenols in dilute (1 mmol/L phenol), acidified, aqueous suspensions of manganese oxide (Na-buserite) were identified by MS, Fourier-transform IR spectroscopy and UV/visible spectroscopy. The para-chlorinated phenols (4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 4-chloro-2-methylphenol) gave corresponding p-benzoquionones (benzoquinone, 2-chlorobenzoquinone, 2,6-dichlorobenzoquinone, 2-methylbenzoquinone) as the detectable water-soluble oxidation products. Dimeric products were present in the extracts obtained by washing the oxide with methylene chloride. Michael addition of phenolate to quinone seems to be the predominant mode of coupling. Chlorinated phenols without chlorine in the para-position (2-chlorophenol, 2,6-dichlorophenol) were more difficult to oxidize and afforded diphenoquinones as the only detectable water-soluble products. For all studied phenols, with the exception of 2,4,6-trichlorophenol, the amount of water-soluble products accounts only for a small fraction of oxidized phenol. The quinone and diphenoquinone products readily couple with phenols into humus like materials.
Chemical reaction at ferromagnet/oxide interface and its influence on anomalous Hall effect
Liu, Yi-Wei; Teng, Jiao E-mail: email@example.com; Zhang, Jing-Yan; Liu, Yang; Chen, Xi; Li, Xu-Jing; Feng, Chun; Wang, Hai-Cheng; Li, Ming-Hua; Yu, Guang-Hua E-mail: email@example.com; Wu, Zheng-Long
Chemical reactions at the ferromagnet/oxide interface in [Pt/Fe]{sub 3}/MgO and [Pt/Fe]{sub 3}/SiO{sub 2} multilayers before and after annealing were investigated by X-ray photoelectron spectroscopy. The results show that Fe atoms at the Fe/MgO interface were completely oxidized in the as-grown state and significantly deoxidized after vacuum annealing. However, only some of the Fe atoms at the Fe/SiO{sub 2} interface were oxidized and rarely deoxidized after annealing. The anomalous Hall effect was modified by this interfacial chemical reaction. The saturation anomalous Hall resistance (R{sub xy}) was greatly increased in the [Pt/Fe]{sub 3}/MgO multilayers after annealing and was 350% higher than that in the as-deposited film, while R{sub xy} of the [Pt/Fe]{sub 3}/SiO{sub 2} multilayer only increased 10% after annealing.
Review of photochemical reaction constants of organic micropollutants required for UV advanced oxidation processes in water.
Wols, B A; Hofman-Caris, C H M
Emerging organic contaminants (pharmaceutical compounds, personal care products, pesticides, hormones, surfactants, fire retardants, fuel additives etc.) are increasingly found in water sources and therefore need to be controlled by water treatment technology. UV advanced oxidation technologies are often used as an effective barrier against organic contaminants. The combined operation of direct photolysis and reaction with hydroxyl radicals ensures good results for a wide range of contaminants. In this review, an overview is provided of the photochemical reaction parameters (quantum yield, molar absorption, OH radical reaction rate constant) of more than 100 organic micropollutants. These parameters allow for a prediction of organic contaminant removal by UV advanced oxidation systems. An example of contaminant degradation is elaborated for a simplified UV/H(2)O(2) system. PMID:22483836
Peroxygenase-Catalyzed Oxyfunctionalization Reactions Promoted by the Complete Oxidation of Methanol.
Ni, Yan; Fernández-Fueyo, Elena; Gomez Baraibar, Alvaro; Ullrich, René; Hofrichter, Martin; Yanase, Hideshi; Alcalde, Miguel; van Berkel, Willem J H; Hollmann, Frank
Peroxygenases catalyze a broad range of (stereo)selective oxyfunctionalization reactions. However, to access their full catalytic potential, peroxygenases need a balanced provision of hydrogen peroxide to achieve high catalytic activity while minimizing oxidative inactivation. Herein, we report an enzymatic cascade process that employs methanol as a sacrificial electron donor for the reductive activation of molecular oxygen. Full oxidation of methanol is achieved, generating three equivalents of hydrogen peroxide that can be used completely for the stereoselective hydroxylation of ethylbenzene as a model reaction. Overall we propose and demonstrate an atom-efficient and easily applicable alternative to established hydrogen peroxide generation methods, which enables the efficient use of peroxygenases for oxyfunctionalization reactions. PMID:26607550
Aerobic Microbial Respiration In Oceanic Oxygen Minimum Zones
Kalvelage, Tim; Lavik, Gaute; Jensen, Marlene M.; Revsbech, Niels Peter; Löscher, Carolin; Schunck, Harald; Desai, Dhwani K.; Hauss, Helena; Kiko, Rainer; Holtappels, Moritz; LaRoche, Julie; Schmitz, Ruth A.; Graco, Michelle I.; Kuypers, Marcel M. M.
Oxygen minimum zones are major sites of fixed nitrogen loss in the ocean. Recent studies have highlighted the importance of anaerobic ammonium oxidation, anammox, in pelagic nitrogen removal. Sources of ammonium for the anammox reaction, however, remain controversial, as heterotrophic denitrification and alternative anaerobic pathways of organic matter remineralization cannot account for the ammonium requirements of reported anammox rates. Here, we explore the significance of microaerobic respiration as a source of ammonium during organic matter degradation in the oxygen-deficient waters off Namibia and Peru. Experiments with additions of double-labelled oxygen revealed high aerobic activity in the upper OMZs, likely controlled by surface organic matter export. Consistently observed oxygen consumption in samples retrieved throughout the lower OMZs hints at efficient exploitation of vertically and laterally advected, oxygenated waters in this zone by aerobic microorganisms. In accordance, metagenomic and metatranscriptomic analyses identified genes encoding for aerobic terminal oxidases and demonstrated their expression by diverse microbial communities, even in virtually anoxic waters. Our results suggest that microaerobic respiration is a major mode of organic matter remineralization and source of ammonium (~45-100%) in the upper oxygen minimum zones, and reconcile hitherto observed mismatches between ammonium producing and consuming processes therein. PMID:26192623
Predicting gold-mediated catalytic oxidative-coupling reactions from single crystal studies.
Xu, Bingjun; Madix, Robert J; Friend, Cynthia M
Though metallic gold is chemically inert under ambient conditions, its surface is extremely reactive and selective for many key oxidative chemical transformations when activated by atomic oxygen. A molecular-level understanding of the mechanism of these processes could allow researchers to design "green" catalytic processes mediated by gold-based materials. This Account focuses on the mechanistic framework for oxidative-coupling reactions established by fundamental studies on oxygen-activated Au(111) and the application of these principles to steady-state catalytic conditions. We also discuss the importance of the paradigms discovered both for predicting new oxidative-coupling reactions and for understanding existing literature. The mechanistic framework for the oxidative coupling of alcohols on gold surfaces predicts that new oxidative-coupling reactions should occur between amines and aldehydes and amines and alcohols as well as through alcohol carbonylation. Adsorbed atomic oxygen on the gold surface facilitates the activation of the substrates, and nucleophilic attack and β-H elimination are the two fundamental reactions that propagate the versatile chemistry that ensues. In the self-coupling of primary alcohols, adsorbed atomic oxygen first activates the O-H bond in the hydroxyl group at ∼150 K, which forms the corresponding adsorbed alkoxy groups. The rate-limiting step of the self-coupling reaction is the β-H elimination reaction of alkoxy groups to form the corresponding aldehydes and occurs with an activation barrier of approximately 12 kcal/mol. The remaining alkoxy groups nucleophilically attack the electron-deficient aldehyde carbonyl carbon to yield the adsorbed "hemiacetal". This intermediate undergoes facile β-H elimination to produce the final coupling products, esters with twice the number of carbon atoms as the starting alcohols. This mechanistic insight suggests that cross-coupling occurs between alcohols and aldehydes, based on the logic
Chlorine activation indoors and outdoors via surface-mediated reactions of nitrogen oxides with hydrogen chloride
Raff, Jonathan D.; Njegic, Bosiljka; Chang, Wayne L.; Gordon, Mark S.; Dabdub, Donald; Gerber, R. Benny; Finlayson-Pitts, Barbara J.
Gaseous HCl generated from a variety of sources is ubiquitous in both outdoor and indoor air. Oxides of nitrogen (NOy) are also globally distributed, because NO formed in combustion processes is oxidized to NO2, HNO3, N2O5 and a variety of other nitrogen oxides during transport. Deposition of HCl and NOy onto surfaces is commonly regarded as providing permanent removal mechanisms. However, we show here a new surface-mediated coupling of nitrogen oxide and halogen activation cycles in which uptake of gaseous NO2 or N2O5 on solid substrates generates adsorbed intermediates that react with HCl to generate gaseous nitrosyl chloride (ClNO) and nitryl chloride (ClNO2), respectively. These are potentially harmful gases that photolyze to form highly reactive chlorine atoms. The reactions are shown both experimentally and theoretically to be enhanced by water, a surprising result given the availability of competing hydrolysis reaction pathways. Airshed modeling incorporating HCl generated from sea salt shows that in coastal urban regions, this heterogeneous chemistry increases surface-level ozone, a criteria air pollutant, greenhouse gas and source of atmospheric oxidants. In addition, it may contribute to recently measured high levels of ClNO2 in the polluted coastal marine boundary layer. This work also suggests the potential for chlorine atom chemistry to occur indoors where significant concentrations of oxides of nitrogen and HCl coexist. PMID:19620710
Chemical oxidation of anthracite with hydrogen peroxide via the Fenton reaction
Heard, I.; Senftle, F.E.
Solutions of 30% H2O2 ranging from pH = 0 to pH = 11.5 have been used to oxidize anthracite at room temperature. The inorganic impurities, primarily pyrite, catalysed the oxidation and reduction of H2O2 (the Fenton reaction) to form the hydroxyl radical; the oxidation of the organic matter was minimal and was observed only in strong acidic solutions (pH < 1.5). After acid demineralization, samples of the same anthracite underwent a significant enhancement of oxidation in both acid and alkaline solutions (pH = 0.4-11.5). As all the iron had been removed from the surface and the reactions were completed in a much shorter time, the oxidation mechanism must have been of a different nature than that for the untreated anthracite. A qualitative model based on the catalytic decomposition of H2O2 by activated carbon sites in the coal surface is used to explain the oxidation of the demineralized anthracite. ?? 1984.
Mathematical modeling of an exothermic leaching reaction system: pressure oxidation of wide size arsenopyrite participates
NASA Astrophysics Data System (ADS)
Papangelakis, V. G.; Berk, D.; Demopoulos, G. P.
In the design of processes involving exothermic reactions, as is the case of several sulfide leaching systems, it is desirable to utilize the energy liberated by the reaction to drive the reactor toward autogenous operation. For optimal reactor design, models which couple leaching kinetics and heat effects are needed. In this paper, the principles of modeling exothermic leaching reactions are outlined. The system investigated is the high-temperature (160 °C to 200 °C) pressure (O2) oxidation of arsenopyrite (FeAsS). The reaction system is characterized by three consecutive reactions: (1) heterogeneous dissolution of arsenopyrite particles, (2) homogeneous oxidation of iron(II) to iron(III), and (3) precipitation of scorodite (FeAsO4-2H2O). The overall kinetics is controlled by the arsenopyrite surface reaction. There was good agreement between laboratory-scale batch tests and model predictions. The model was expanded to simulate the performance of large-scale batch and single-stage continuous stirred tank reactor (CSTR) for the same rate-limiting regime. Emphasis is given to the identification of steady-state temperatures for autogenous processing. The effects of operating variables, such as feed temperature, slurry density, and retention time, on reactor operation and yield of leaching products are discussed.
Aqueous Phase Photo-Oxidation of Succinic Acid: Changes in Hygroscopic Properties and Reaction Products
NASA Astrophysics Data System (ADS)
Hudson, P. K.; Ninokawa, A.; Hofstra, J.; de Lijser, P.
Atmospheric aerosol particles have been identified as important factors in understanding climate change. The extent to which aerosols affect climate is determined, in part, by hygroscopic properties which can change as a result of atmospheric processing. Dicarboxylic acids, components of atmospheric aerosol, have a wide range of hygroscopic properties and can undergo oxidation and photolysis reactions in the atmosphere. In this study, the hygroscopic properties of succinic acid aerosol, a non-hygroscopic four carbon dicarboxylic acid, were measured with a humidified tandem differential mobility analyzer (HTDMA) and compared to reaction products resulting from the aqueous phase photo-oxidation reaction of hydrogen peroxide and succinic acid. Reaction products were determined and quantified using gas chromatography-flame ionization detection (GC-FID) and GC-mass spectrometry (GC-MS) as a function of hydrogen peroxide:succinic acid concentration ratio and photolysis time. Although reaction products include larger non-hygroscopic dicarboxylic acids (e.g. adipic acid) and smaller hygroscopic dicarboxylic acids (e.g. malonic and oxalic acids), comparison of hygroscopic growth curves to Zdanovskii-Stokes-Robinson (ZSR) predictions suggests that the hygroscopic properties of many of the product mixtures are largely independent of the hygroscopicity of the individual components. This study provides a framework for future investigations to fully understand and predict the role of chemical reactions in altering atmospheric conditions that affect climate.
Water-gas Shift Reaction on oxide/Cu(111): Rational Catalyst Screening from Density Functional Theory
Liu, P.
Developing improved catalysts based on a fundamental understanding of reaction mechanism has become one of the grand challenges in catalysis. A theoretical understanding and screening the metal-oxide composite catalysts for the water-gas shift (WGS) reaction is presented here. Density functional theory was employed to identify the key step for the WGS reaction on the Au, Cu-oxide catalysts, where the calculated reaction energy for water dissociation correlates well with the experimental measured WGS activity. Accordingly, the calculated reaction energy for water dissociation was used as the scaling descriptor to screen the inverse model catalysts, oxide/Cu(111), for the better WGS activity. Our calculations predict that the WGS activity increases in a sequence: Cu(111), ZnO/Cu(111) < TiO{sub 2}/Cu(111), ZrO{sub 2}/Cu(111) < MoO{sub 3}/Cu(111). Our results imply that the high performances of Au, Cu-oxide nanocatalysts in the WGS reaction rely heavily on the direct participation of both oxide and metal sites. The degree that the oxide is reduced by Cu plays an important role in determining the WGS activity of oxide/Cu catalysts. The reducible oxide can be transformed from the fully oxidized form to the reduced form due to the interaction with Cu and, therefore, the transfer of electron density from Cu, which helps in releasing the bottleneck water dissociation and, therefore, facilitating the WGS reaction on copper.
Water-gas shift reaction on oxide/Cu(111): Rational catalyst screening from density functional theory
NASA Astrophysics Data System (ADS)
Liu, Ping
Developing improved catalysts based on a fundamental understanding of reaction mechanism has become one of the grand challenges in catalysis. A theoretical understanding and screening the metal-oxide composite catalysts for the water-gas shift (WGS) reaction is presented here. Density functional theory was employed to identify the key step for the WGS reaction on the Au, Cu-oxide catalysts, where the calculated reaction energy for water dissociation correlates well with the experimental measured WGS activity. Accordingly, the calculated reaction energy for water dissociation was used as the scaling descriptor to screen the inverse model catalysts, oxide/Cu(111), for the better WGS activity. Our calculations predict that the WGS activity increases in a sequence: Cu(111), ZnO/Cu(111) < TiO2/Cu(111), ZrO2/Cu(111) < MoO3/Cu(111). Our results imply that the high performances of Au, Cu-oxide nanocatalysts in the WGS reaction rely heavily on the direct participation of both oxide and metal sites. The degree that the oxide is reduced by Cu plays an important role in determining the WGS activity of oxide/Cu catalysts. The reducible oxide can be transformed from the fully oxidized form to the reduced form due to the interaction with Cu and, therefore, the transfer of electron density from Cu, which helps in releasing the bottleneck water dissociation and, therefore, facilitating the WGS reaction on copper.
Kinetic study of the hydrogen oxidation reaction on sub-stoichiometric titanium oxide-supported platinum electrocatalyst in acid solution
NASA Astrophysics Data System (ADS)
Babić, B.; Gulicovski, J.; Gajić-Krstajić, Lj.; Elezović, N.; Radmilović, V. R.; Krstajić, N. V.; Vračar, Lj. M.
The kinetics and mechanism of the hydrogen oxidation reaction were studied in 0.5 mol dm -3 HClO 4 solution on an electrode based on titanium oxide with Magneli phase structure-supported platinum electrocatalyst applied on rotation Au disk electrode. Pt catalyst was prepared by impregnation method from 2-propanol solution of Pt(NH 3) 2(NO 2) 2 and sub-stoichiometric titanium oxide powder. Sub-stiochiometric titanium oxide support was characterized by X-ray diffraction and BET techniques. The synthesized catalyst was analyzed by TEM technique. Based on Tafel-Heyrovsky-Volmer mechanism the corresponding kinetic equations were derived to describe the hydrogen oxidation current-potential behavior on RDE over the entire potential region. The polarization RDE curves were fitted with derived polarization equations according to proposed model. The fitting shows that the HOR on Pt proceeds most likely via the Tafel-Volmer (TV) pathway in the lower potential region, while the Heyrovsky-Volmer (HV) pathway is operative in the higher potential region. It is pointed out that Tafel equation that has been frequently used for the kinetics analysis in the HOR, can not reproduce the polarization curves measured with high mass-transport rates. Polarization measurements on RDE revealed that the Pt catalyst deposited on titanium suboxide support showed equal specific activity for the HOR compared to conventional carbon-supported Pt fuel cell catalyst.
Bio-inspired immobilization of metal oxides on monolithic microreactor for continuous Knoevenagel reaction.
Song, Wentong; Shi, Da; Tao, Shengyang; Li, Zhaoliang; Wang, Yuchao; Yu, Yongxian; Qiu, Jieshan; Ji, Min; Wang, Xinkui
A facile method is reported to construct monolithic microreactor with high catalytic performance for Knoevenagel reaction. The microreactor is based on hierarchically porous silica (HPS) which has interconnected macro- and mesopores. Then the HPS is surface modified by pyrogallol (PG) polymer. Al(NO3)3 and Mg(NO3)2 are loaded on the surface of HPS through coordination with -OH groups of PG. After thermal treatment, Al(NO3)3 and Mg(NO3)2 are converted Al2O3 and MgO. The as-synthesized catalytic microreactor shows a high and stable performance in Knoevenagel reaction. The microreactor possess large surface area and interconnected pore structures which are beneficial for reactions. Moreover, this economic, facile and eco-friendly surface modification method can be used in loading more metal oxides for more reactions. PMID:27459172
Stable stoichiometry of gas-phase cerium oxide cluster ions and their reactions with CO.
Nagata, Toshiaki; Miyajima, Ken; Mafuné, Fumitaka
Cerium oxide cluster ions, Ce(n)O(2n+x)(+) (n = 2-9, x = -1 to +2), were prepared in the gas phase by laser ablation of a cerium oxide rod in the presence of oxygen diluted in He as the carrier gas. The stable stoichiometry of the cluster ions was investigated using a mass spectrometer in combination with a newly developed post heating device. The oxygen-rich clusters, Ce(n)O(2n+x)(+) (x = 1, 2), were found to release oxygen molecules, and Ce(n)O(2n+x)(+) (x = -1, 0) were exclusively formed by post heating treatment at 573 K. The Ce(n)O(2n-1)(+) and Ce(n)O(2n)(+) clusters were found to be thermally stable, and the oxygen-rich clusters consisted of robust Ce(n)O(2n-1)(+) and Ce(n)O(2n)(+) and weakly bound oxygen atoms. Evaluation of the reactivity of Ce(n)O(2n+x)(+) with CO molecules demonstrated that Ce(n)O(2n)(+) oxidized CO to form Ce(n)O(2n-1)(+) and CO2, and the rate constants of the reaction were in the range of 10(-12)-10(-16) cm(3) s(-1). The CO oxidation reaction was distinct for n = 5, which occurred in parallel with the CO attachment reaction. PMID:25651032
Oxidation of flavonoids by hypochlorous acid: reaction kinetics and antioxidant activity studies.
Krych-Madej, Justyna; Stawowska, Katarzyna; Gebicka, Lidia
Flavonoids, plant polyphenols, ubiquitous components of human diet, are excellent antioxidants. Hypochlorous acid (HOCl), produced by activated neutrophils, is highly reactive chlorinating and oxidizing species. It has been reported earlier that flavonoids are chlorinated by HOCl. Here we show that flavonoids from flavonol subclass are also oxidized by HOCl, but only if the latter is in a large molar excess (≥ 10). The kinetics of this reaction was studied by stopped-flow spectrophotometry, at different pH. We found that flavonols were oxidized by HOCl with the rate constants of the order of 10(4)-10(5) M(-1) s(-1) at pH 7.5. Antioxidant activity of HOCl-modified flavonoids was measured by 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) method. Slightly higher antioxidant activity, compared to parent compounds, was observed for flavonols after their reaction with equimolar or moderate excess of HOCl whereas flavonols treated with high molar excess of HOCl exhibited decrease in antioxidant activity. The mechanism of flavonoid reaction with HOCl at physiological pH is proposed, and biological consequences of this reaction are discussed. PMID:27225705
Supercritical water oxidation of Quinazoline: Effects of conversion parameters and reaction mechanism.
Gong, Yanmeng; Guo, Yang; Wang, Shuzhong; Song, Wenhan
The supercritical water oxidation reaction of quinazoline and a set of related reaction products were investigated in batch reactors by varying the temperature (T, 400-600 °C), time (t, 0-400 s), water density (ρ, 70.79-166.28 kg m(-3)) and oxidation coefficient (OC, 0-4.0). The TOC removal efficiency (CRE) increased significantly as the OC increased, whereas this effect was very limited at high OC (>2.0). Lack of oxygen resulted in low CRE and TN removal efficiency (NRE), also cause coke-formation, and giving high yield of NH3 and nitrogenous organic intermediates. Prolonging reaction time did not provide an appreciable improvement on CRE but remarkably increased NRE at temperature higher than 500 °C. Pyrimidines and pyridines as the nitrogenous intermediates were largely found in GC-MS spectrum. Polymerization among benzene, phenyl radical and benzyl radical played important roles in the formation of PAHs, such as naphthalene, biphenyl, phenanthrene. These collective results showed how the yield of intermediate products responded to changes in the process variables, which permitted the development of a potential reaction network for supercritical water oxidation of quinazoline. PMID:27179598
Water oxidation by a cytochrome p450: mechanism and function of the reaction.
Prasad, Brinda; Mah, Derrick J; Lewis, Andrew R; Plettner, Erika
P450(cam) (CYP101A1) is a bacterial monooxygenase that is known to catalyze the oxidation of camphor, the first committed step in camphor degradation, with simultaneous reduction of oxygen (O2). We report that P450(cam) catalysis is controlled by oxygen levels: at high O2 concentration, P450(cam) catalyzes the known oxidation reaction, whereas at low O2 concentration the enzyme catalyzes the reduction of camphor to borneol. We confirmed, using (17)O and (2)H NMR, that the hydrogen atom added to camphor comes from water, which is oxidized to hydrogen peroxide (H2O2). This is the first time a cytochrome P450 has been observed to catalyze oxidation of water to H2O2, a difficult reaction to catalyze due to its high barrier. The reduction of camphor and simultaneous oxidation of water are likely catalyzed by the iron-oxo intermediate of P450(cam) , and we present a plausible mechanism that accounts for the 1:1 borneol:H2O2 stoichiometry we observed. This reaction has an adaptive value to bacteria that express this camphor catabolism pathway, which requires O2, for two reasons: 1) the borneol and H2O2 mixture generated is toxic to other bacteria and 2) borneol down-regulates the expression of P450(cam) and its electron transfer partners. Since the reaction described here only occurs under low O2 conditions, the down-regulation only occurs when O2 is scarce. PMID:23634216
Oxidation of triclosan by ferrate: reaction kinetics, products identification and toxicity evaluation.
Yang, Bin; Ying, Guang-Guo; Zhao, Jian-Liang; Zhang, Li-Juan; Fang, Yi-Xiang; Nghiem, Long Duc
The oxidation of triclosan by commercial grade aqueous ferrate (Fe(VI)) was investigated and the reaction kinetics as a function of pH (7.0-10.0) were experimentally determined. Intermediate products of the oxidation process were characterized using both GC-MS and RRLC-MS/MS techniques. Changes in toxicity during the oxidation process of triclosan using Fe(VI) were investigated using Pseudokirchneriella subcapitata growth inhibition tests. The results show that triclosan reacted rapidly with Fe(VI), with the apparent second-order rate constant, k(app), being 754.7 M(-1) s(-1) at pH 7. At a stoichiometric ratio of 10:1 (Fe(VI):triclosan), complete removal of triclosan was achieved. Species-specific rate constants, k, were determined for reaction of Fe(VI) with both the protonated and deprotonated triclosan species. The value of k determined for neutral triclosan was 6.7(±1.9)×10(2) M(-1) s(-1), while that measured for anionic triclosan was 7.6(±0.6)×10(3) M(-1) s(-1). The proposed mechanism for the oxidation of triclosan by the Fe(VI) involves the scission of ether bond and phenoxy radical addition reaction. Coupling reaction may also occur during Fe(VI) degradation of triclosan. Overall, the degradation processes of triclosan resulted in a significant decrease in algal toxicity. The toxicity tests showed that Fe(VI) itself dosed in the reaction did not inhibit green algae growth. PMID:21093982
Development of new palladium(0)-catalyzed reactions based on novel oxidative addition mode.
Tsukamoto, Hirokazu
We have developed palladium(0)/monophosphine-catalyzed trans-selective arylative, alkenylative, alkylative, and alkynylative cyclization reactions of alkyne-aldehydes and -ketones with organoboron reagents. These reactions afford six-membered allylic alcohols with endo tri- or tetra-substituted olefin groups and/or five-membered counterparts with exo olefin groups. The ratios of these products are dramatically affected by alkyne substituents as well as the phosphine ligand. The remarkable trans selectivity of the process results from the novel reaction mechanism involving 'anti-Wacker'-type oxidative addition. Although the cyclization reactions are influenced by the length of the tether between the alkyne and carbonyl group, they can be applied to a multi-component synthesis of biologically important indenes bearing three substituent groups at 1, 2, 3-positions from available o-ethynylbenzaldehyde derivatives. A two-component coupling reaction in methanol provides 1H-indenols, while a three-component reaction involving secondary aliphatic amines as the third component in DMF affords 1H-indenamines. This method allows combinatorial preparation of unsymmetrically substituted 1H-indenes that cannot be prepared via previous synthetic routes. The same catalytic system can also transform allene-carbonyl compounds into 3-cyclohexenols and -cyclopentenols with alkyl, aryl, alkenyl, alkynyl, and boryl groups at C-3. Microwave irradiation efficiently increases not only the reaction rate but also the product yield by suppressing formation of hydroarylation byproducts. Cyclization of optically active 1,3-disubstituted allene-aldehyde reveals that the reaction proceeds through not carbopalladation but 'anti-Wacker'-type oxidative addition. PMID:18758139
Aerobic granulation and nitrogen removal with the effluent of internal circulation reactor in start-up of a pilot-scale sequencing batch reactor.
Wei, Dong; Si, Wei; Zhang, Yongfang; Qiao, Zhuangming; Yao, Zhenxing; Zhao, Wei; Zhao, Jie; Chen, Guodong; Wei, Qin; Du, Bin
Aerobic granular sludge was successfully cultivated with the effluent of internal circulation (IC) reactor in a pilot-scale sequencing batch reactor (SBR) using activated sludge as seeding sludge. N removal was investigated in the start-up of aerobic granulation process. Initially, the phenomenon of partial nitrification was observed and nitrite accumulation rates (NO(2) (-)-N/NO (x) (-) -N) were between 84.6 and 99.1 %. It was potentially caused by ammonium oxidizing bacteria (AOB) in the seeding activated sludge, high external environmental temperature (~32 °C) and free ammonia (FA) concentration. After 50 days' running, the aerobic granules-based bioreactor demonstrated perfect performance in simultaneous removal of organic matter and ammonia nitrogen, and average removal efficiencies were maintained above 93 and 96 %, respectively. The maximum nitrogen removal efficiency of 83.1 % was achieved after the formation of aerobic granules. The average diameter of mature aerobic granular sludge mostly ranged from 0.5 to 1.0 mm. Furthermore, one typical cyclic test indicated that pH and DO profiles could be used as effective parameters for biological reactions occurring in the aerobic/anoxic process. The obtained results could provide further information on the cultivation of aerobic granular sludge with practical wastewater, especially with regard to nitrogen-rich industrial wastewater. PMID:22562444
Understanding the role of gold nanoparticles in enhancing the catalytic activity of manganese oxides in water oxidation reactions.
Kuo, Chung-Hao; Li, Weikun; Pahalagedara, Lakshitha; El-Sawy, Abdelhamid M; Kriz, David; Genz, Nina; Guild, Curtis; Ressler, Thorsten; Suib, Steven L; He, Jie
The Earth-abundant and inexpensive manganese oxides (MnOx) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnOx catalysts are still much lower than that of nanostructured IrO2 and RuO2 catalysts. Herein, we demonstrate that doping MnOx polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnOx/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn(3+) species, a small amount of AuNPs (<5%) in α-MnO2/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α-MnO2. PMID:25284796
A metal-free aerobic oxidation of nitrotoluenes catalyzed by N,N',N″-trihydroxyisocyanuric acid (THICA) and a novel approach to the catalyst.
Wang, Kai; Zhou, Zhiming; Song, Jinhong; Bi, Lixue; Shen, Ning; Wu, Yukai; Chen, Fuxue; Wen, Hongliang
A metal-free catalytic system with N,N',N″-trihydroxyisocyanuric acid (THICA) as the catalyst for the oxidation of nitrotoluenes is introduced, and a novel Pd-free approach for the synthesis of THICA was developed. In a solution of acetic acid, THICA and concentrated nitric acid, nitrotoluenes especially polynitrotoluenes such as 2,4,6-trinitrotoluene (TNT), were converted into the desired carboxylic acids under 0.2 MPa of O(2) at 100°C with yields up to 99%. THICA was synthesized from N-hydroxyphtalimide through a four-step synthesis in a total yield of 46%. A possible mechanism of this catalytic process was proposed where NO(2) and nitric acid first induced a radical of THICA, which then abstracts a hydrogen atom from the methyl on the aromatic ring to form a benzyl radical. This radical then initiates subsequent reactions. The production of the benzyl radical was supported by ESR measurements. PMID:20869170
Formation of carriers in Ti-oxide thin films by substitution reactions
Liu, Y. S.; Lin, Y. H.; Wei, Y. S.; Liu, C. Y.
Conductive Ti-oxide thin films are produced using a reactive sputtering and post-annealing process. The lowest resistivity of Ti-oxide thin films (2.30 x 10{sup -2}{Omega}-cm) can be achieved after annealing for 1 h at 400 deg. C in ambient O{sub 2}. Additionally, the Hall measurement results indicate that the carrier concentration increases during the initial 1-h annealing process before decreasing during subsequent annealing. By curve fitting the O{sub ls} core-level peaks in the x ray photoelectron spectroscopy (XPS) spectrum of the annealed Ti-oxide thin films, we found that the oxygen (O) vacancy concentration monotonically increases with annealing time, which differs from the behavior of the carrier concentration regarding annealing time. This means that the O-vacancy mechanism alone cannot explain the formation of carriers in Ti-oxide thin films. By curve-fitting core-level Ti peaks in the XPS spectrum of annealed Ti-oxide thin films, a Ti{sup 3+}-to-Ti{sup 4+} substitution reaction in the TiO{sub 2} phase of the Ti-oxide thin film after annealing plays the dominant role in the formation of conduction carriers. Instead of the O-vacancy mechanism, the Ti{sup 3+}-to-Ti{sup 4+} substitution mechanism can explain the concentration of carriers in Ti-oxide thin films following annealing.
Oxidation of LDL by myeloperoxidase and reactive nitrogen species: reaction pathways and antioxidant protection.
Carr, A C; McCall, M R; Frei, B
Oxidative modification of low density lipoprotein (LDL) appears to play an important role in atherogenesis. Although the precise mechanisms of LDL oxidation in vivo are unknown, several lines of evidence implicate myeloperoxidase and reactive nitrogen species, in addition to ceruloplasmin and 15-lipoxygenase. Myeloperoxidase generates a number of reactive species, including hypochlorous acid, chloramines, tyrosyl radicals, and nitrogen dioxide. These reactive species oxidize the protein, lipid, and antioxidant components of LDL. Modification of apolipoprotein B results in enhanced uptake of LDL by macrophages with subsequent formation of lipid-laden foam cells. Nitric oxide synthases produce nitric oxide and, under certain conditions, superoxide radicals. Numerous other sources of superoxide radicals have been identified in the arterial wall, including NAD(P)H oxidases and xanthine oxidase. Nitric oxide and superoxide readily combine to form peroxynitrite, a reactive nitrogen species capable of modifying LDL. In this review, we examine the reaction pathways involved in LDL oxidation by myeloperoxidase and reactive nitrogen species and the potential protective effects of the antioxidant vitamins C and E. PMID:10894808
Oxidative Degradation of Nadic-End-Capped Polyimides. 2; Evidence for Reactions Occurring at High Temperatures
NASA Technical Reports Server (NTRS)
Meador, Mary Ann B.; Johnston, J. Christopher; Cavano, Paul J.; Frimer, Aryeh A.
The oxidative degradation of PMR (for polymerization of monomeric reactants) polyimides at elevated temperatures was followed by cross-polarized magic angle spinning (Cp-MAS) NMR. C-13 labeling of selected sites in the polymers allowed for direct observation of the transformations arising from oxidation processes. As opposed to model compound studies, the reactions were followed directly in the polymer. The labeling experiments confirm the previously reported oxidation of the methylene carbon to ketone in the methylenedianiline portion of the polymer chain. They also show the formation of two other oxidized species, acid and ester, from this same carbon. In addition, the technique provides the first evidence of the kind of degradation reactions that are occurring in the nadic end caps. Several PMR formulations containing moieties determined to be present after oxidation, as suggested by the labeling study, were synthesized. Weight loss, FTIR, and natural abundance NMR of these derivatives were followed during aging. In this way, weight loss could be related to the observed transformations.
Rate Equations and Kinetic Parameters of the Reactions Involved in Pyrite Oxidation by Thiobacillus ferrooxidans.
Lizama, H M; Suzuki, I
Rate equations and kinetic parameters were obtained for various reactions involved in the bacterial oxidation of pyrite. The rate constants were 3.5 muM Fe per min per FeS(2) percent pulp density for the spontaneous pyrite dissolution, 10 muM Fe per min per mM Fe for the indirect leaching with Fe, 90 muM O(2) per min per mg of wet cells per ml for the Thiobacillus ferrooxidans oxidation of washed pyrite, and 250 muM O(2) per min per mg of wet cells per ml for the T. ferrooxidans oxidation of unwashed pyrite. The K(m) values for pyrite concentration were similar and were 1.9, 2.5, and 2.75% pulp density for indirect leaching, washed pyrite oxidation by T. ferrooxidans, and unwashed pyrite oxidation by T. ferrooxidans, respectively. The last reaction was competitively inhibited by increasing concentrations of cells, with a K(i) value of 0.13 mg of wet cells per ml. T. ferrooxidans cells also increased the rate of Fe production from Fe plus pyrite. PMID:16348054
Direct determination of the activation energy for the reaction of nitric oxide with ozone
Borders, R.A.
The activation energy for the reaction of nitric oxide with ozone has been directly measured as a function of temperature. The instrument constructed for this study consisted of two flow tubes that are connected together at each end, where the reaction zone temperature of each flow tube was controlled independently. The reaction of nitric oxide and ozone was pseudo-first order ((NO)/(O/sub 3/) greater than or equal to 250) and studied by following the reduction of the chemiluminescence of one of the products (NO/sup *//sub 2/(/sup 2/B/sub 1,2/)) of the reaction. The chemiluminescence was measured using a microcomputer-controlled photon counter designed for these studies. The activation energy has been found to vary with temperature. The activation energy varies from 2390 +/- 10 calories at 216 K to 2970 +/- 60 calories at 333 K. The variation over the complete temperature range studied (204-353 K) is large enough (650 calories) that the errors associated with the method cannot account for all of the variation. There are other pathways for this reaction other than ground state reactants going to ground state products, and their contribution to the activation energy (approx.500 calories) has been found to be sufficient to account for the observed variation with temperature when added to the variation predicted by either transition state (180 calories) or collision (150 calories) theory.
Plasmon-enhanced reverse water gas shift reaction over oxide supported Au catalysts
Upadhye, AA; Ro, I; Zeng, X; Kim, HJ; Tejedor, I; Anderson, MA; Dumesic, JA; Huber, GW
We show that localized surface plasmon resonance (LSPR) can enhance the catalytic activities of different oxide-supported Au catalysts for the reverse water gas shift (RWGS) reaction. Oxide-supported Au catalysts showed 30 to 1300% higher activity for RWGS under visible light compared to dark conditions. Au/TiO2 catalyst prepared by the deposition-precipitation (DP) method with 3.5 nm average Au particle size showed the highest activity for the RWGS reaction. Visible light is converted into chemical energy for this reaction with up to a 5% overall efficiency. A shift in the apparent activation energy (from 47 kJ mol(-1) in dark to 35 kJ mol(-1) in light) and apparent reaction order with respect to CO2 (from 0.5 in dark to 1.0 in light) occurs due to the LSPR. Our kinetic results indicate that the LSPR increases the rate of either the hydroxyl hydrogenation or carboxyl decomposition more than any other steps in the reaction network.
Development of Ag dendrites-reduced graphene oxide composite catalysts via galvanic replacement reaction
NASA Astrophysics Data System (ADS)
Fu, Li; Sokiransky, Mika Matsunaka; Wang, James; Lai, Guosong; Yu, Aimin
Silver dendrites/reduced graphene oxide (AgD/RGO) composites were synthesized via a facile galvanic replacement method. The successful formation of Ag dendrites and the graphene oxide reduction were proved by a series of characterization techniques. The possible formation mechanism of Ag dendrites during the galvanic replacement reaction was discussed. The catalytic activity of the as-synthesized AgD/RGO composite was evaluated by its performance on the chemical reduction of an organic dye methylene blue. The AgD/RGO composite showed a much higher catalytic performance and stability than that of Ag dendrites.
Aerobic exercise and not a diet supplemented with jussara açaí (Euterpe edulis Martius) alters hepatic oxidative and inflammatory biomarkers in ApoE-deficient mice.
de Castro, Cynthia Aparecida; Natali, Antonio José; Cardoso, Luciana Marques; Ferreira-Machado, Alessandra Barbosa; Novello, Alexandre Azevedo; da Silva, Karina Ana; Tafuri, Natalia Filard; da Matta, Sergio Luis Pinto; Pedrosa, Maria Lucia; Peluzio, Maria do Carmo Gouveia
The pulp of jussara açaí (Euterpe edulis Martius) fruit is rich in anthocyanins that exert antioxidant and anti-inflammatory effects similar to those exerted by aerobic exercise. In the present study, we investigated the effects of jussara açaí fruit pulp consumption, either alone or in combination with aerobic exercise, on the hepatic oxidative and inflammatory status of ApoE-deficient (ApoE - / - ) mice. Male mice were divided into four groups (control (C), control plus açaí, exercise plus açaí (EXA) and exercise (EX)) and fed the AIN-93M diet or the AIN-93M diet formulated to contain 2 % freeze-dried açaí pulp. Mice in the EX and EXA groups were subjected to a progressive running programme (5 d/week, 60 min/d, 16 m/min) for 12 weeks. Mice that were made to exercise exhibited reduced (40·85 %; P< 0·05) hepatic superoxide dismutase activity when compared with the C mice, independent of the açaí diet. Mice in the EX group exhibited a lower (42 %; P< 0·05) mRNA expression of monocyte chemotactic protein-1 in the liver compared with the C mice. Mice in the EXA and EX groups had lower percentages of hepatic lipid droplets (70 % and 56 %, respectively; P< 0·05) when compared with the C mice. Mice in the EX group had smaller (58 %; P< 0·05) area of lesions in the aorta when compared with the C mice. Serum lipid profile was not affected (P>0·05). In conclusion, aerobic exercise training rather than açaí fruit pulp consumption or a combination of both enhances the hepatic oxidative and inflammatory status of ApoE - / - mice. PMID:24787366
Human 2-Oxoglutarate Dehydrogenase Complex E1 Component Forms a Thiamin-derived Radical by Aerobic Oxidation of the Enamine Intermediate*
Nemeria, Natalia S.; Ambrus, Attila; Patel, Hetalben; Gerfen, Gary; Adam-Vizi, Vera; Tretter, Laszlo; Zhou, Jieyu; Wang, Junjie; Jordan, Frank
Herein are reported unique properties of the human 2-oxoglutarate dehydrogenase multienzyme complex (OGDHc), a rate-limiting enzyme in the Krebs (citric acid) cycle. (a) Functionally competent 2-oxoglutarate dehydrogenase (E1o-h) and dihydrolipoyl succinyltransferase components have been expressed according to kinetic and spectroscopic evidence. (b) A stable free radical, consistent with the C2-(C2α-hydroxy)-γ-carboxypropylidene thiamin diphosphate (ThDP) cation radical was detected by electron spin resonance upon reaction of the E1o-h with 2-oxoglutarate (OG) by itself or when assembled from individual components into OGDHc. (c) An unusual stability of the E1o-h-bound C2-(2α-hydroxy)-γ-carboxypropylidene thiamin diphosphate (the "ThDP-enamine"/C2α-carbanion, the first postdecarboxylation intermediate) was observed, probably stabilized by the 5-carboxyl group of OG, not reported before. (d) The reaction of OG with the E1o-h gave rise to superoxide anion and hydrogen peroxide (reactive oxygen species (ROS)). (e) The relatively stable enzyme-bound enamine is the likely substrate for oxidation by O2, leading to the superoxide anion radical (in d) and the radical (in b). (f) The specific activity assessed for ROS formation compared with the NADH (overall complex) activity, as well as the fraction of radical intermediate occupying active centers of E1o-h are consistent with each other and indicate that radical/ROS formation is an "off-pathway" side reaction comprising less than 1% of the "on-pathway" reactivity. However, the nearly ubiquitous presence of OGDHc in human tissues, including the brain, makes these findings of considerable importance in human metabolism and perhaps disease. PMID:25210035
Human 2-oxoglutarate dehydrogenase complex E1 component forms a thiamin-derived radical by aerobic oxidation of the enamine intermediate.
Nemeria, Natalia S; Ambrus, Attila; Patel, Hetalben; Gerfen, Gary; Adam-Vizi, Vera; Tretter, Laszlo; Zhou, Jieyu; Wang, Junjie; Jordan, Frank
Herein are reported unique properties of the human 2-oxoglutarate dehydrogenase multienzyme complex (OGDHc), a rate-limiting enzyme in the Krebs (citric acid) cycle. (a) Functionally competent 2-oxoglutarate dehydrogenase (E1o-h) and dihydrolipoyl succinyltransferase components have been expressed according to kinetic and spectroscopic evidence. (b) A stable free radical, consistent with the C2-(C2α-hydroxy)-γ-carboxypropylidene thiamin diphosphate (ThDP) cation radical was detected by electron spin resonance upon reaction of the E1o-h with 2-oxoglutarate (OG) by itself or when assembled from individual components into OGDHc. (c) An unusual stability of the E1o-h-bound C2-(2α-hydroxy)-γ-carboxypropylidene thiamin diphosphate (the "ThDP-enamine"/C2α-carbanion, the first postdecarboxylation intermediate) was observed, probably stabilized by the 5-carboxyl group of OG, not reported before. (d) The reaction of OG with the E1o-h gave rise to superoxide anion and hydrogen peroxide (reactive oxygen species (ROS)). (e) The relatively stable enzyme-bound enamine is the likely substrate for oxidation by O2, leading to the superoxide anion radical (in d) and the radical (in b). (f) The specific activity assessed for ROS formation compared with the NADH (overall complex) activity, as well as the fraction of radical intermediate occupying active centers of E1o-h are consistent with each other and indicate that radical/ROS formation is an "off-pathway" side reaction comprising less than 1% of the "on-pathway" reactivity. However, the nearly ubiquitous presence of OGDHc in human tissues, including the brain, makes these findings of considerable importance in human metabolism and perhaps disease. PMID:25210035
Ion dynamics in the pseudocapacitive reaction of hydrous ruthenium oxide. Effect of the temperature pre-treatment
NASA Astrophysics Data System (ADS)
Sopčić, Suzana; Mandić, Zoran; Inzelt, György; Roković, Marijana Kraljić; Meštrović, Ernest
Pseudocapacitive redox reaction of hydrous ruthenium oxide was investigated by the combined electrochemical and quartz crystal nanobalance measurements on gold support in H2SO4 and Na2SO4 solutions. The results show that the pseudocapacitance arises from at least two different Faradaic reactions with significant influence of double layer capacitance. All three processes simultaneously take place during charging/discharging reaction, but their contribution vary depending on the electrolyte used, the temperature pre-treatment and on the potential range. One Faradaic reaction releases protons during oxidation reaction resulting in the electrode mass decrease, while another Faradaic reaction results in the chemical binding of water leading to the mass gain during the oxidation reaction. The former reaction is favoured in acidic electrolyte and at lower anodic potentials, and the latter reaction proceeds predominantly in neutral media and at higher anodic potentials. The influence of annealing temperatures on the characteristics of the redox reaction of hydrous ruthenium oxide, as well as on its capacitance, was confirmed. It was demonstrated that specific capacitances of hydrous ruthenium oxide could achieve values as high as 1500 F g-1, provided that conditions of good electronic conductivity among RuO2 particles, as well as good electrical contact between gold and RuO2, are met.
Reactions of calcium orthosilicate and barium zirconate with oxides and sulfates of various elements
NASA Technical Reports Server (NTRS)
Zaplatynsky, I.
Calcium orthosilicate and barium zirconate were evaluated as the insulation layer of thermal barrier coatings for air cooled gas turbine components. Their reactions with various oxides and sulfates were studied at 1100 C and 1300 C for times ranging up to 400 and 200 hours, respectively. These oxides and sulfates represent potential impurities or additives in gas turbine fuels and in turbine combustion air, as well as elements of potential bond coat alloys. The phase compositions of the reaction products were determined by X-ray diffraction analysis. BaZrO3 and 2CaO-SiO2 both reacted with P2O5, V2O5, Cr2O3, Al2O3, and SiO2. In addition, 2CaO-SiO2 reacted with Na2O, BaO, MgO, and CoO and BaZrO3 reacted with Fe2O3.
Copper-catalyzed tandem phosphination-decarboxylation-oxidation of alkynyl acids with H-phosphine oxides: a facile synthesis of β-ketophosphine oxides.
Zhang, Pengbo; Zhang, Liangliang; Gao, Yuzhen; Xu, Jian; Fang, Hua; Tang, Guo; Zhao, Yufen
The general method for the tandem phosphination-decarboxylation-oxidation of alkynyl acids under aerobic conditions has been developed. In the presence of CuSO4·5H2O and TBHP, the reactions provide a novel access to β-ketophosphine oxides in good to excellent yields. This transformation allows the direct formation of a P-C bond and the construction of a keto group in one reaction. PMID:25855268
Oxidation of elemental mercury by chlorine: Gas phase, Surface,and Photo-induced reaction pathways
Yan, Nai-Qiang; Liu, Shou-Heng; Chang, Shih-Ger
Accurate oxidation rate constants of mercury gas are needed for determining its dispersion and lifetime in the atmosphere. They would also help in developing a technology for the control of mercury emissions from coal-fired power plants. However, it is difficult to establish the accurate rate constants primarily due to the fact that mercury easily adsorbs on solid surface and its reactions can be catalyzed by the surface. We have demonstrated a procedure that allows the determination of gas phase, surface-induced, and photo-induced contributions in the kinetic study of the oxidation of mercury by chlorine gas. The kinetics was studied using reactors with various surface to volume ratios. The effect of the surface and the photo irradiation on the reaction was taken into consideration. The pressure dependent study revealed that the gas phase oxidation was a three-body collision process. The third order rate constant was determined to be 7.5({+-}0.2) x 10{sup -39} mL{sup 2} molecules{sup -2}s{sup -1} with N{sub 2} as the third body at 297 {+-} 1 K. The surface induced reaction on quartz window was second order and the rate constant was 2.7 x 10{sup -17} mL{sup 2} molecules{sup -1} cm{sup -2} sec. Meanwhile, the 253.7 nm photon employed for mercury detection was found to accelerate the reaction. The utilization efficiency of 253.7 nm photon for Hg{sup 0} oxidation was 6.7 x 10{sup -4} molecules photon{sup -1} under the conditions employed in this study.
Selenium-catalyzed oxidations with aqueous hydrogen peroxide. 2. Baeyer-Villiger reactions in homogeneous solution.
ten Brink, G J; Vis, J M; Arends, I W; Sheldon, R A
Several diselenides were tested for catalytic activity in Baeyer-Villiger reactions with 60% aqueous hydrogen peroxide. Bis[3,5-bis(trifluoromethyl)phenyl] diselenide forms the corresponding 3,5-bis(trifluoromethyl)benzene seleninic acid in situ, which is a highly reactive and selective catalyst for the oxidation of carbonyl compounds in 1,1,1,3,3,3-hexafluoro-2-propanol, 2,2,2-trifluoroethanol, or dichloromethane. PMID:11281784
Oxidation of butane to butanol coupled to electrochemical redox reaction of NAD+/NADH.
Kang, Hye Sun; Na, Byung Kwan; Park, Doo Hyun
A crude cell extract from a butane-utilizing bacterium, Alcaligenes sp., catalyzed the oxidation of butane to butanol coupled to NADH. A graphite electrode modified with Neutral Red (NR-electrode) catalyzed the reduction of NAD(+) to NADH. About 4.9 mM butanol was produced from 50% n-butane/O(2) mixture through the combined reactions of the crude enzyme and the NR-electrode in 250 ml reactor for 3 h. PMID:17549436
Proteins and protein complexes involved in the biochemical reactions of anaerobic ammonium-oxidizing bacteria.
de Almeida, Naomi M; Maalcke, Wouter J; Keltjens, Jan T; Jetten, Mike S M; Kartal, Boran
It has been less than two decades since anammox (anaerobic ammonium oxidation) coupled to nitrite reduction has been discovered. Already, this process has been recognized as an important sink for fixed nitrogen in the natural environment and has been implemented as a cost-effective ammonium removal technology. Still, little is known about the molecular mechanism of this remarkable reaction. In this mini review, we present an insight into how ammonium and nitrite are combined to form dinitrogen gas. PMID:21265793
Quantum Diffusion-Controlled Chemistry: Reactions of Atomic Hydrogen with Nitric Oxide in Solid Parahydrogen.
Ruzi, Mahmut; Anderson, David T
Our group has been working to develop parahydrogen (pH2) matrix isolation spectroscopy as a method to study low-temperature condensed-phase reactions of atomic hydrogen with various reaction partners. Guided by the well-defined studies of cold atom chemistry in rare-gas solids, the special properties of quantum hosts such as solid pH2 afford new opportunities to study the analogous chemical reactions under quantum diffusion conditions in hopes of discovering new types of chemical reaction mechanisms. In this study, we present Fourier transform infrared spectroscopic studies of the 193 nm photoinduced chemistry of nitric oxide (NO) isolated in solid pH2 over the 1.8 to 4.3 K temperature range. Upon short-term in situ irradiation the NO readily undergoes photolysis to yield HNO, NOH, NH, NH3, H2O, and H atoms. We map the postphotolysis reactions of mobile H atoms with NO and document first-order growth in HNO and NOH reaction products for up to 5 h after photolysis. We perform three experiments at 4.3 K and one at 1.8 K to permit the temperature dependence of the reaction kinetics to be quantified. We observe Arrhenius-type behavior with a pre-exponential factor of A = 0.036(2) min(-1) and Ea = 2.39(1) cm(-1). This is in sharp contrast to previous H atom reactions we have studied in solid pH2 that display definitively non-Arrhenius behavior. The contrasting temperature dependence measured for the H + NO reaction is likely related to the details of H atom quantum diffusion in solid pH2 and deserves further study. PMID:26317154
Activity and stability of the oxygen evolution reaction on electrodeposited Ru and its thermal oxides
NASA Astrophysics Data System (ADS)
Kim, Jin Yeong; Choi, Jihui; Kim, Ho Young; Hwang, Eunkyoung; Kim, Hyoung-Juhn; Ahn, Sang Hyun; Kim, Soo-Kil
The activity and stability of Ru metal and its thermal oxide films for the oxygen evolution reaction (OER) were investigated. The metallic Ru films were prepared by electrodeposition on a Ti substrate and then thermally oxidized at various temperatures under atmospheric conditions. During long-term operation of the OER with cyclic voltammetry (CV) in H2SO4 electrolyte, changes in the properties of the Ru and its thermal oxides were monitored in terms of their morphology, crystal structure, and electronic structure. In the initial stages of the OER, all of the Ru thermal oxide films underwent an activation process that was related to the continuous removal of low-activity Ru oxides from the surface. With further cycling, the OER activity decreased. The rate of decrease was different for each Ru film and was related to the annealing temperatures. Monitoring of material properties indicates that the amount of stable anhydrous RuO2 is important for OER stability because it prevents both the severe dissolution of metallic Ru beneath the oxide surface and the formation of a less active hydrous RuO2 at the surface.
Adsorption and Reaction of Methanethiol on Thin-Film Cerium Oxide
Mullins, David R; McDonald, Tom S
The adsorption and reaction of methanethiol, CH{sub 3}SH, have been studied on cerium oxide thin films that were vapor deposited on Ru(0 0 0 1). The behavior of the CH{sub 3}SH was examined as a function of the Ce oxidation state. CH{sub 3}SH weakly interacts with fully oxidized CeO{sub 2}(1 1 1) forming both chemisorbed CH{sub 3}SH and CH{sub 3}S + OH. OH forms through the reaction of the sulfhydrol H with the surface O. These species recombine and desorb near 180 K leaving the surface virtually clean. When the ceria is ca. 50% reduced, the chemisorbed CH{sub 3}SH desorbs near 150 K while the CH{sub 3}S + OH are stable to 400 K. These species react above 450 K to produce predominantly CH{sub 4} and CH{sub 3}SH. A small amount of CH{sub 2}O and water are also formed through reaction with the O in the ceria. Atomic S is left on the surface. S 2p, C 1s and O 1s soft X-ray photoelectron spectroscopy were used to identify the nature of the chemisorbed species and the adsorption site of the CH{sub 3}S or S.
Adsorption and reaction of methanethiol on thin-film cerium oxide
NASA Astrophysics Data System (ADS)
Mullins, D. R.; McDonald, T. S.
The adsorption and reaction of methanethiol, CH 3SH, have been studied on cerium oxide thin films that were vapor deposited on Ru(0 0 0 1). The behavior of the CH 3SH was examined as a function of the Ce oxidation state. CH 3SH weakly interacts with fully oxidized CeO 2(1 1 1) forming both chemisorbed CH 3SH and CH 3S + OH. OH forms through the reaction of the sulfhydrol H with the surface O. These species recombine and desorb near 180 K leaving the surface virtually clean. When the ceria is ca. 50% reduced, the chemisorbed CH 3SH desorbs near 150 K while the CH 3S + OH are stable to 400 K. These species react above 450 K to produce predominantly CH 4 and CH 3SH. A small amount of CH 2O and water are also formed through reaction with the O in the ceria. Atomic S is left on the surface. S 2p, C 1s and O 1s soft X-ray photoelectron spectroscopy were used to identify the nature of the chemisorbed species and the adsorption site of the CH 3S or S.
Stable platinum nanoclusters on genomic DNA–graphene oxide with a high oxygen reduction reaction activity
Tiwari, Jitendra N.; Nath, Krishna; Kumar, Susheel; Tiwari, Rajanish N.; Kemp, K. Christian; Le, Nhien H.; Youn, Duck Hyun; Lee, Jae Sung; Kim, Kwang S.
Nanosize platinum clusters with small diameters of 2–4 nm are known to be excellent catalysts for the oxygen reduction reaction. The inherent catalytic activity of smaller platinum clusters has not yet been reported due to a lack of preparation methods to control their size (<2 nm). Here we report the synthesis of platinum clusters (diameter ≤1.4 nm) deposited on genomic double-stranded DNA–graphene oxide composites, and their high-performance electrocatalysis of the oxygen reduction reaction. The electrochemical behaviour, characterized by oxygen reduction reaction onset potential, half-wave potential, specific activity, mass activity, accelerated durability test (10,000 cycles) and cyclic voltammetry stability (10,000 cycles) is attributed to the strong interaction between the nanosize platinum clusters and the DNA–graphene oxide composite, which induces modulation in the electronic structure of the platinum clusters. Furthermore, we show that the platinum cluster/DNA–graphene oxide composite possesses notable environmental durability and stability, vital for high-performance fuel cells and batteries. PMID:23900456
Biotransformations Utilizing β-Oxidation Cycle Reactions in the Synthesis of Natural Compounds and Medicines
Œwizdor, Alina; Panek, Anna; Milecka-Tronina, Natalia; Kołek, Teresa
β-Oxidation cycle reactions, which are key stages in the metabolism of fatty acids in eucaryotic cells and in processes with a significant role in the degradation of acids used by microbes as a carbon source, have also found application in biotransformations. One of the major advantages of biotransformations based on the β-oxidation cycle is the possibility to transform a substrate in a series of reactions catalyzed by a number of enzymes. It allows the use of sterols as a substrate base in the production of natural steroid compounds and their analogues. This route also leads to biologically active compounds of therapeutic significance. Transformations of natural substrates via β-oxidation are the core part of the synthetic routes of natural flavors used as food additives. Stereoselectivity of the enzymes catalyzing the stages of dehydrogenation and addition of a water molecule to the double bond also finds application in the synthesis of chiral biologically active compounds, including medicines. Recent advances in genetic, metabolic engineering, methods for the enhancement of bioprocess productivity and the selectivity of target reactions are also described. PMID:23443116
Biotransformations utilizing β-oxidation cycle reactions in the synthesis of natural compounds and medicines.
Swizdor, Alina; Panek, Anna; Milecka-Tronina, Natalia; Kołek, Teresa
β-Oxidation cycle reactions, which are key stages in the metabolism of fatty acids in eucaryotic cells and in processes with a significant role in the degradation of acids used by microbes as a carbon source, have also found application in biotransformations. One of the major advantages of biotransformations based on the β-oxidation cycle is the possibility to transform a substrate in a series of reactions catalyzed by a number of enzymes. It allows the use of sterols as a substrate base in the production of natural steroid compounds and their analogues. This route also leads to biologically active compounds of therapeutic significance. Transformations of natural substrates via β-oxidation are the core part of the synthetic routes of natural flavors used as food additives. Stereoselectivity of the enzymes catalyzing the stages of dehydrogenation and addition of a water molecule to the double bond also finds application in the synthesis of chiral biologically active compounds, including medicines. Recent advances in genetic, metabolic engineering, methods for the enhancement of bioprocess productivity and the selectivity of target reactions are also described. PMID:23443116
Investigation of the Transformation of a Modified Iron Oxide Structure During Redox Reaction
NASA Astrophysics Data System (ADS)
Anh, Luu Thi Lan; Trung, Nguyen Ngoc; Tho, Van Dinh Son
Iron oxides can be used for the storage of hydrogen based on their redox reaction. Iron oxides were synthesized by the sol-gel method was a structure transformation of maghemite γ-Fe2O3 into hematite α-Fe2O3 during calcinations process could be observed. The addition of a Mo6+ cation by the preparation method results in the substitution of Mo6+ into the Fe2O3 structure and formation of Fe2(MoO4)3. There was a formation of two crystalline phases Fe2O3 and ZrO2 separately incase of the addition of Zr4+cation into Fe2O3.During redox reaction, the structure of Fe2O3 was converted into Fe and regenerated Fe3O4. There was a transformation of Fe2 (MoO4)3 into Fe2Mo3O8 phases after reduction. However ZrO2 was did not change its structure during redox reaction. The Zr-Fe2O3 very easy to be reduced into Fe and convenience formed hydrogen in the oxidation.
Oxidative cyclization reaction of 2-aryl-substituted cinnamates to form phenanthrene carboxylates by using MoCl5.
Wehming, Kathrin; Schubert, Moritz; Schnakenburg, Gregor; Waldvogel, Siegfried R
The oxidative cyclization reaction of 2-aryl cinnamates and derivatives thereof can be easily performed with MoCl5 as the oxidant. This powerful reagent allows oxidative coupling reactions for which other reagents fail. The best results are obtained when the 2-phenyl substituent of the cinnamate is equipped with two methoxy groups. Even iodo moieties in the bay region of phenanthrene are tolerated under the reaction conditions. If naphthalene moieties are involved, a rearrangement of the skeleton occurs, providing an elegant route to highly functionalized angular arenes. The cyclization is demonstrated for 15 example substrates with isolated yields of up to 99 % for the phenanthrene derivative. The broad scope of the reaction underlines the usefulness of MoCl5 and MoCl5 /TiCl4 in the oxidative coupling reaction. PMID:25043751
Effect of temperature towards lipid oxidation and non-enzymatic browning reactions in krill oil upon storage.
Lu, F S H; Bruheim, I; Haugsgjerd, B O; Jacobsen, C
The main objective of this study was to investigate the effect of temperature towards lipid oxidation and non-enzymatic browning reactions in krill oil upon storage. Krill oil was incubated at two different temperatures (20 and 40 °C) for 28 or 42 days. The oxidative stability of krill oil was assessed by peroxide value and anisidine value, measurement of lipid derived volatiles, lipid classes and antioxidants. The non-enzymatic browning reactions were assessed through the measurement of pyrroles, free amino acids content and Strecker-derived volatiles. The increase of incubation temperature firstly increased the lipid oxidation in krill oil and subsequently the non-enzymatic browning reactions. The occurrence of these reactions was most likely due to the reaction between α-dicarbonyl or carbonyl compounds with amino acids or ammonia. In addition to tocopherol and astaxanthin esters, the formation of pyrroles might help to protect the krill oil against lipid oxidation. PMID:24679797
Nitric oxide is consumed, rather than conserved, by reaction with oxyhemoglobin under physiological conditions
NASA Astrophysics Data System (ADS)
Joshi, Mahesh S.; Ferguson, T. Bruce, Jr.; Han, Tae H.; Hyduke, Daniel R.; Liao, James C.; Rassaf, Tienush; Bryan, Nathan; Feelisch, Martin; Lancaster, Jack R., Jr.
Although irreversible reaction of NO with the oxyheme of hemoglobin (producing nitrate and methemoglobin) is extremely rapid, it has been proposed that, under normoxic conditions, NO binds preferentially to the minority deoxyheme to subsequently form S-nitrosohemoglobin (SNOHb). Thus, the primary reaction would be conservation, rather than consumption, of nitrogen oxide. Data supporting this conclusion were generated by using addition of a small volume of a concentrated aqueous solution of NO to a normoxic hemoglobin solution. Under these conditions, however, extremely rapid reactions can occur before mixing. We have thus compared bolus NO addition to NO generated homogeneously throughout solution by using NO donors, a more physiologically relevant condition. With bolus addition, multiple hemoglobin species are formed (as judged by visible spectroscopy) as well as both nitrite and nitrate. With donor, only nitrate and methemoglobin are formed, stoichiometric with the amount of NO liberated from the donor. Studies with increasing hemoglobin concentrations reveal that the nitrite-forming reaction (which may be NO autoxidation under these conditions) competes with reaction with hemoglobin. SNOHb formation is detectable with either bolus or donor; however, the amounts formed are much smaller than the amount of NO added (less than 1%). We conclude that the reaction of NO with hemoglobin under normoxic conditions results in consumption, rather than conservation, of NO.
Synthesis and structure characterization of chromium oxide prepared by solid thermal decomposition reaction.
Li, Li; Yan, Zi F; Lu, Gao Q; Zhu, Zhong H
Mesoporous chromium oxide (Cr2O3) nanocrystals were first synthesized by the thermal decomposition reaction of Cr(NO3)3.9H2O using citric acid monohydrate (CA) as the mesoporous template agent. The texture and chemistry of chromium oxide nanocrystals were characterized by N2 adsorption-desorption isotherms, FTIR, X-ray diffraction (XRD), UV-vis, and thermoanalytical methods. It was shown that the hydrate water and CA are the crucial factors in influencing the formation of mesoporous Cr2O3 nanocrystals in the mixture system. The decomposition of CA results in the formation of a mesoporous structure with wormlike pores. The hydrate water of the mixture provides surface hydroxyls that act as binders, making the nanocrystals aggregate. The pore structures and phases of chromium oxide are affected by the ratio of precursor-to-CA, thermal temperature, and time. PMID:16471518
Adsorption and Reaction of Methanol on Thin-film Cerium Oxide
Mullins,D.; Robbins, M.; Zhou, J.
Formaldehyde adsorption and reaction have been studied on cerium oxide thin films that were vapor deposited on Ru(0 0 0 1). The formaldehyde behavior was examined as a function of temperature, exposure and Ce oxidation state. Formaldehyde chemisorbs on fully oxidized CeO{sub 2} as dioxymethylene, CH{sub 2}O{sub 2}. The dioxymethylene decomposes and desorbs as formaldehyde between 200 K and 400 K. No other products are formed. On reduced ceria, formaldehyde also adsorbs as dioxymethylene. In addition to the formaldehyde desorption between 200 K and 400 K, a more strongly bound form of dioxymethylene is formed that produces formaldehyde at 440 K. Above 400 K, some of the dioxymethylene reacts to form formate and methoxy on the surface. These species decompose to produce H{sub 2}, CO and CH{sub 2}O above 500 K.
Adsorption and Reaction of Formaldehyde on Thin-film Cerium Oxide
Zhou,J.; Mullins, D.
Formaldehyde adsorption and reaction have been studied on cerium oxide thin films that were vapor deposited on Ru(0 0 0 1). The formaldehyde behavior was examined as a function of temperature, exposure and Ce oxidation state. Formaldehyde chemisorbs on fully oxidized CeO{sub 2} as dioxymethylene, CH{sub 2}O{sub 2}. The dioxymethylene decomposes and desorbs as formaldehyde between 200 K and 400 K. No other products are formed. On reduced ceria, formaldehyde also adsorbs as dioxymethylene. In addition to the formaldehyde desorption between 200 K and 400 K, a more strongly bound form of dioxymethylene is formed that produces formaldehyde at 440 K. Above 400 K, some of the dioxymethylene reacts to form formate and methoxy on the surface. These species decompose to produce H{sub 2}, CO and CH{sub 2}O above 500 K.
Iron Oxides from Volcanic Soils as Potential Catalysts in the Water Gas Shift Reaction
Pizarro, C.; Escudey, M.; Moya, S.A.; Fabris, J.D.
This study was focused on changes of the iron oxide mineralogy with temperature of two Chilean soils (Andisol and Ultisol) derived from volcanic materials and their use as iron-based catalysts in the water gas shift reaction (WGSR). Ultisol materials produced about twice as much hydrogen than did those from Andisol upon WGSR, but in both cases hydrogen yielding increased as the heating temperature of the soil materials increased from 124 deg. C to 500 deg. C. The room temperature Moessbauer spectra showed an increase of the relative proportion of the magnetically ordered components as temperature increased. Higher heating temperature produced a negative effect on the catalytic activity, whereas the organic matter destruction led to a positive effect, due to an increasing exposition of the iron oxide surfaces; heating the soil sample at 600 deg. C induced changes on the iron oxide mineralogy with a significant decrease of the catalytic activity.
Iron Oxides from Volcanic Soils as Potential Catalysts in the Water Gas Shift Reaction
NASA Astrophysics Data System (ADS)
Pizarro, C.; Escudey, M.; Moya, S. A.; Fabris, J. D.
This study was focused on changes of the iron oxide mineralogy with temperature of two Chilean soils (Andisol and Ultisol) derived from volcanic materials and their use as iron-based catalysts in the water gas shift reaction (WGSR). Ultisol materials produced about twice as much hydrogen than did those from Andisol upon WGSR, but in both cases hydrogen yielding increased as the heating temperature of the soil materials increased from 124°C to 500°C. The room temperature Mössbauer spectra showed an increase of the relative proportion of the magnetically ordered components as temperature increased. Higher heating temperature produced a negative effect on the catalytic activity, whereas the organic matter destruction led to a positive effect, due to an increasing exposition of the iron oxide surfaces; heating the soil sample at 600 °C induced changes on the iron oxide mineralogy with a significant decrease of the catalytic activity.
Construction materials for reaction unit in the liquid-phase synthesis of propylene oxide
Zaritskii, V.I.D.
The main components of the reaction medium in equipment for the synthesis of propylene oxide by liquid-phase oxidation of gaseous propylene with peracetic acid are propylene, peracetic acid, ethyl acetate, acetic acid, propylene oxide, carbon dioxide, oxygen, methane, and propylene glycol acetates. The operating conditions of the equipment and content of the main components of the medium are shown. Results are given for the investigation of the corrosion behavior of 12Kh18N10T, 10Kh17N13M2T, 08Kh22N6T, and 08Kh21N6M2T steels, AD0 and AD1 aluminum, and VT1-0 titanium. VSt3 carbon steel was tested for comparison.
Management of aerobic vaginitis.
Tempera, Gianna; Furneri, Pio Maria
Aerobic vaginitis is a new nonclassifiable pathology that is neither specific vaginitis nor bacterial vaginosis. The diversity of this microbiological peculiarity could also explain several therapeutic failures when patients were treated for infections identified as bacterial vaginosis. The diagnosis 'aerobic vaginitis' is essentially based on microscopic examinations using a phase-contrast microscope (at ×400 magnification). The therapeutic choice for 'aerobic vaginitis' should take into consideration an antibiotic characterized by an intrinsic activity against the majority of bacteria of fecal origin, bactericidal effect and poor/absent interference with the vaginal microbiota. Regarding the therapy for aerobic vaginitis when antimicrobial agents are prescribed, not only the antimicrobial spectrum but also the presumed ecological disturbance on the anaerobic and aerobic vaginal and rectal microbiota should be taken into a consideration. Because of their very low impact on the vaginal microbiota, kanamycin or quinolones are to be considered a good choice for therapy. PMID:21051843
Insight into the Mechanism of Graphene Oxide Degradation via the Photo-Fenton Reaction.
Bai, Hao; Jiang, Wentao; Kotchey, Gregg P; Saidi, Wissam A; Bythell, Benjamin J; Jarvis, Jacqueline M; Marshall, Alan G; Robinson, Renã A S; Star, Alexander
Graphene represents an attractive two-dimensional carbon-based nanomaterial that holds great promise for applications such as electronics, batteries, sensors, and composite materials. Recent work has demonstrated that carbon-based nanomaterials are degradable/biodegradable, but little work has been expended to identify products formed during the degradation process. As these products may have toxicological implications that could leach into the environment or the human body, insight into the mechanism and structural elucidation remain important as carbon-based nanomaterials become commercialized. We provide insight into a potential mechanism of graphene oxide degradation via the photo-Fenton reaction. We have determined that after 1 day of treatment intermediate oxidation products (with MW 150-1000 Da) were generated. Upon longer reaction times (i.e., days 2 and 3), these products were no longer present in high abundance, and the system was dominated by graphene quantum dots (GQDs). On the basis of FTIR, MS, and NMR data, potential structures for these oxidation products, which consist of oxidized polycyclic aromatic hydrocarbons, are proposed. PMID:24860637
Insight into the Mechanism of Graphene Oxide Degradation via the Photo-Fenton Reaction
Graphene represents an attractive two-dimensional carbon-based nanomaterial that holds great promise for applications such as electronics, batteries, sensors, and composite materials. Recent work has demonstrated that carbon-based nanomaterials are degradable/biodegradable, but little work has been expended to identify products formed during the degradation process. As these products may have toxicological implications that could leach into the environment or the human body, insight into the mechanism and structural elucidation remain important as carbon-based nanomaterials become commercialized. We provide insight into a potential mechanism of graphene oxide degradation via the photo-Fenton reaction. We have determined that after 1 day of treatment intermediate oxidation products (with MW 150–1000 Da) were generated. Upon longer reaction times (i.e., days 2 and 3), these products were no longer present in high abundance, and the system was dominated by graphene quantum dots (GQDs). On the basis of FTIR, MS, and NMR data, potential structures for these oxidation products, which consist of oxidized polycyclic aromatic hydrocarbons, are proposed. PMID:24860637
Redox reactions in mammalian spermatogenesis and the potential targets of reactive oxygen species under oxidative stress
Fujii, Junichi; Imai, Hirotaka
Reduction-oxidation (Redox) reactions are ubiquitous mechanisms for vital activities in all organisms, and they play pivotal roles in the regulation of spermatogenesis as well. Here we focus on 3 redox-involved processes that have drawn much recent attention: the regulation of signal transduction by reactive oxygen species (ROS) such as hydrogen peroxide, oxidative protein folding in the endoplasmic reticulum (ER), and sulfoxidation of protamines during sperm chromatin condensation. The first 2 of these processes are emerging topics in cell biology and are applicable to most living cells, which includes spermatogenic cells. The roles of ROS in signal transduction have been elucidated in the last 2 decades and have received broad attention, most notably from the viewpoint of the proper control of mitotic signals. Redox processes in the ER are important because this is the organelle where secretory and membrane proteins are synthesized and proceed toward their functional structure, so that malfunction of the ER affects not only the involved cells but also the accepting cells of the secreted proteins in multicellular organisms. Sulfoxidation is the third of these processes, and the sulfoxidation of chromatin is a unique process in sperm maturation. During recent sulfoxidase research, GPX4 has emerged as a promising enzyme that plays essential roles in the production of fertile sperm, but the involvement of other redox proteins is also becoming evident. Because the molecules involved in the redox reactions are prone to oxidation, they can be sensitive to oxidative damage, which makes them potential targets for antioxidant therapy. PMID:26413390
Multiscale Informatics for Low-Temperature Propane Oxidation: Further Complexities in Studies of Complex Reactions.
Burke, Michael P; Goldsmith, C Franklin; Klippenstein, Stephen J; Welz, Oliver; Huang, Haifeng; Antonov, Ivan O; Savee, John D; Osborn, David L; Zádor, Judit; Taatjes, Craig A; Sheps, Leonid
The present paper describes further development of the multiscale informatics approach to kinetic model formulation of Burke et al. (Burke, M. P.; Klippenstein, S. J.; Harding, L. B. Proc. Combust. Inst. 2013, 34, 547-555) that directly incorporates elementary kinetic theories as a means to provide reliable, physics-based extrapolation of kinetic models to unexplored conditions. Here, we extend and generalize the multiscale informatics strategy to treat systems of considerable complexity-involving multiwell reactions, potentially missing reactions, nonstatistical product branching ratios, and non-Boltzmann (i.e., nonthermal) reactant distributions. The methodology is demonstrated here for a subsystem of low-temperature propane oxidation, as a representative system for low-temperature fuel oxidation. A multiscale model is assembled and informed by a wide variety of targets that include ab initio calculations of molecular properties, rate constant measurements of isolated reactions, and complex systems measurements. Active model parameters are chosen to accommodate both "parametric" and "structural" uncertainties. Theoretical parameters (e.g., barrier heights) are included as active model parameters to account for parametric uncertainties in the theoretical treatment; experimental parameters (e.g., initial temperatures) are included to account for parametric uncertainties in the physical models of the experiments. RMG software is used to assess potential structural uncertainties due to missing reactions. Additionally, branching ratios among product channels are included as active model parameters to account for structural uncertainties related to difficulties in modeling sequences of multiple chemically activated steps. The approach is demonstrated here for interpreting time-resolved measurements of OH, HO2, n-propyl, i-propyl, propene, oxetane, and methyloxirane from photolysis-initiated low-temperature oxidation of propane at pressures from 4 to 60 Torr and
Sub-micrometer sized yttrium oxide fibers prepared through hydrothermal reaction
Li, Nan; Yanagisawa, Kazumichi
Research highlights: {yields} Y{sub 2}O{sub 3} fibers were synthesized by hydrothermal reaction followed by calcination. {yields} Y(OH){sub x}Cl{sub 3-x}.yH{sub 2}O was received from hydrothermal reaction. {yields} Y{sub 2}O{sub 3} fibers showed outstanding high-temperature stability. -- Abstract: Yttrium oxide fibers have been synthesized via hydrothermal reaction and subsequent thermal treatment using yttrium chloride as precursor. The products before and after the thermal treatment were characterized by powder X-ray diffractions (XRD), scanning electron microscopy (SEM), ion-chromatograph analysis, and thermogravimetry and differential thermal analysis (TG-DTA). The fiber diameter ranged from 100 to 300 nm, while the length was up to tens of microns. It was found that the chemical composition and morphology of the products were closely related to the pH value of reaction solution, and fibrous products could be obtained at pH 9.5-10.25. These oxide fibers exhibited outstanding high-temperature stability, which maintained their morphology at temperature up to 1400 {sup o}C.
Citric Acid-Modified Fenton's Reaction for the Oxidation of Chlorinated Ethylenes in Soil Solution Systems
Seol, Yongkoo; Javandel, Iraj
Fenton's reagent, a solution of hydrogen peroxide and ferrous iron catalyst, is used for an in-situ chemical oxidation of organic contaminants. Sulfuric acid is commonly used to create an acidic condition needed for catalytic oxidation. Fenton's reaction often involves pressure buildup and precipitation of reaction products, which can cause safety hazards and diminish efficiency. We selected citric acid, a food-grade substance, as an acidifying agent to evaluate its efficiencies for organic contaminant removal in Fenton's reaction, and examined the impacts of using citric acid on the unwanted reaction products. A series of batch and column experiments were performed with varying H{sub 2}O{sub 2} concentrations to decompose selected chlorinated ethylenes. Either dissolved iron from soil or iron sulfate salt was added to provide the iron catalyst in the batch tests. Batch experiments revealed that both citric and sulfuric acid systems achieved over 90% contaminant removal rates, and the presence of iron catalyst was essential for effective decontamination. Batch tests with citric acid showed no signs of pressure accumulation and solid precipitations, however the results suggested that an excessive usage of H{sub 2}O{sub 2} relative to iron catalysts (Fe{sup 2+}/H{sub 2}O{sub 2} < 1/330) would result in lowering the efficiency of contaminant removal by iron chelations in the citric acid system. Column tests confirmed that citric acid could provide suitable acidic conditions to achieve higher than 55% contaminant removal rates.
Heterogeneous oxidation reactions relevant to tropospheric aerosol chemistry studied by sum frequency generation
NASA Astrophysics Data System (ADS)
Stokes, Grace; Buchbinder, Avram; Gibbs-Davis, Julianne; Scheidt, Karl; Geiger, Franz
Unsaturated organic molecules (terpenes) that commonly form molecular films on tropospheric aerosols can be oxidized by ozone, influencing the microphysics of cloud formation and thus the earth's climate. Using a laboratory approach that combines organic synthesis with surface spectroscopy, we track the ozone oxidation reactions of tropospherically relevant terpenes bound to glass surfaces that serve as mimics for mineral dust. Specifically, vibrational broadband sum frequency generation (SFG) is used to study a number of tailor-made terpene-modified glass surfaces and to track their interactions with ozone in real time. Exposure of these surfaces to ppm levels of ozone at 1 atm and 300 K yield initial reaction probabilities that are significantly higher than corresponding gas phase reactions. SFG spectra help elucidate the molecular orientations of the surface-bound terpenes and the accessibility of reactive C=C bonds. Our work shows the successful use of SFG spectroscopy to determine heterogeneous atmospheric reaction probabilities and bridges the gap between atmospheric aerosol science and surface spectroscopy.
Macromolecular crowding conditions enhance glycation and oxidation of whey proteins in ultrasound-induced Maillard reaction.
Perusko, Marija; Al-Hanish, Ayah; Cirkovic Velickovic, Tanja; Stanic-Vucinic, Dragana
High intensity ultrasound (HIUS) can promote Maillard reaction (MR). Macromolecular crowding conditions accelerate reactions and stabilise protein structure. The aim of this study was to investigate if combined application of ultrasound and macromolecular crowding can improve efficiency of MR. The presence of crowding agent (polyethylene glycol) significantly increased ultrasound-induced whey protein (WP) glycation by arabinose. An increase in glycation efficiency results only in slight change of WP structure. Macromolecular crowding intensifies oxidative modifications of WP, as well as formation of amyloid-like structures by enhancement of MR. Solubility at different pH, thermal stability and antioxidative capacity of glycated WP were increased, especially in the presence of crowding agent, compared to sonicated nonglycated proteins. The application of HIUS under crowding conditions can be a new approach for enhancement of reactions in general, enabling short processing time and mild conditions, while preserving protein structure and minimising protein aggregation. PMID:25660883
Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides
NASA Technical Reports Server (NTRS)
Collins, J.; Rosner, D. E.; Castillo, J.
A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.
Solid-State Thermal Reaction of a Molecular Material and Solventless Synthesis of Iron Oxide
NASA Astrophysics Data System (ADS)
Roy, Debasis; Roy, Madhusudan; Zubko, Maciej; Kusz, Joachim; Bhattacharjee, Ashis
Solid-state thermal decomposition reaction of a molecular material {As}({C}6{H}5)4[{Fe}^{II}{Fe}^{III} ({C}2{O}4)3]}n has been studied using non-isothermal thermogravimetry (TG) in an inert atmosphere. By analyzing the TG data collected at multiple heating rates in 300 K-1300 K range, the kinetic parameters (activation energy, most probable reaction mechanism function and frequency factor) are determined using different multi-heating rate analysis programs. Activation energy and the frequency factor are found to be strongly dependent on the extent of decomposition. The decomposed material has been characterized to be hematite using physical techniques (FT-IR and powder XRD). Particle morphology has been checked by TEM. A solid-state reaction pathway leading the molecular precursor to hematite has been proposed illustrating an example of solventless synthesis of iron oxides utilizing thermal decomposition as a technique using innocuous materials.
Kinetics of phyllosemiquinone oxidation in the Photosystem I reaction centre of Acaryochloris marina.
Santabarbara, Stefano; Bailleul, Benjamin; Redding, Kevin; Barber, James; Rappaport, Fabrice; Telfer, Alison
Light-induced electron transfer reactions in the chlorophyll a/d-binding Photosystem I reaction centre of Acaryochloris marina were investigated in whole cells by pump-probe optical spectroscopy with a temporal resolution of ~5ns at room temperature. It is shown that phyllosemiquinone, the secondary electron transfer acceptor anion, is oxidised with bi-phasic kinetics characterised by lifetimes of 88±6ns and 345±10ns. These lifetimes, particularly the former, are significantly slower than those reported for chlorophyll a-binding Photosystem I, which typically range in the 5-30ns and 200-300ns intervals. The possible mechanism of electron transfer reactions in the chlorophyll a/d-binding Photosystem I and the slower oxidation kinetics of the secondary acceptors are discussed. PMID:22037394
Effect of atmospheric oxidative plasma treatments on polypropylenic fibers surface: Characterization and reaction mechanisms
NASA Astrophysics Data System (ADS)
Nisticò, Roberto; Magnacca, Giuliana; Faga, Maria Giulia; Gautier, Giovanna; D'Angelo, Domenico; Ciancio, Emanuele; Lamberti, Roberta; Martorana, Selanna
Atmospheric pressure plasma-dielectric barrier discharge (APP-DBD, open chamber configuration) was used to functionalize polypropylene (PP) fibers surface in order to generate oxidized-reactive groups such as hydroperoxides, alcohols and carbonyl species (i.e. ketones and others). Such a species increased the surface polarity, without causing material degradation. Three different types of plasma mixture (He, He/O2, He/O2/H2O) under three different values of applied power (750, 1050, 1400 W) were investigated. The formed plasma species (O2+, O single atom and OH radical) and their distribution were monitored via optical emission spectrometry (OES) measurements, and the plasma effects on PP surface species formation were followed by X-ray photoemission spectroscopy (XPS). Results allowed to better understand the reaction pathways between plasma phase and PP fibers. In fact, two reaction mechanisms were proposed, the first one concerning the plasma phase reactions and the second one involving material surface modifications.
Enhanced methanol electro-oxidation reaction on Pt-CoOx/MWCNTs hybrid electro-catalyst
NASA Astrophysics Data System (ADS)
Nouralishahi, Amideddin; Rashidi, Ali Morad; Mortazavi, Yadollah; Khodadadi, Abbas Ali; Choolaei, Mohammadmehdi
The electro-catalytic behavior of Pt-CoOx/MWCNTs in methanol electro-oxidation reaction (MOR) is investigated and compared to that of Pt/MWCNTs. The electro-catalysts were synthesized by an impregnation method using NaBH4 as the reducing agent. The morphological and physical characteristics of samples are examined by XRD, TEM, ICP and EDS techniques. In the presence of CoOx, Pt nanoparticles were highly distributed on the support with an average particle size of 2 nm, an obvious decrease from 5.1 nm for Pt/MWCNTs. Cyclic voltammetry, CO-stripping, Chronoamperometry, and electrochemical impedance spectroscopy (EIS) measurements are used to study the electrochemical behavior of the electro-catalysts. The results revealed a considerable enhancement in the oxidation kinetics of COads on Pt active sites by the participation of CoOx. Compared to Pt/MWCNTs, Pt-CoOx/MWCNTs sample has a larger electrochemical active surface area (ECSA) and higher electro-catalytic activity and stability toward methanol electro-oxidation. According to the results of cyclic voltammetry, the forward anodic peak current density enhances more than 89% at the optimum atomic ratio of Pt:Co = 2:1. Furthermore, inclusion of cobalt oxide species causes the onset potential of methanol electro-oxidation reaction to shift 84 mV to negative values compared to that on Pt/MWCNTs. Based on EIS data, dehydrogenation of methanol is the rate-determining step of MOR on both Pt/MWCNTs and Pt-CoOx/MWCNTs, at small overpotentials. However, at higher overpotentials, the oxidation of adsorbed oxygen-containing groups controls the total rate of MOR process.
Effects of aminosalicylates and immunosuppressive agents on nitric oxide-dependent N-nitrosation reactions.
Grisham, M B; Miles, A M
Recent studies have demonstrated that nitric oxide (NO) rapidly and spontaneously decomposes in oxygenated solutions to generate potent N-nitrosating agents. These electrophilic substances have been shown to mediate mutagenesis and carcinogenesis via the formation of aliphatic and aromatic nitrosamines. We have also demonstrated that extravasated neutrophils and macrophages produce significant amounts of N-nitrosating agents derived exclusively from NO. During the course of these studies, we found that certain antioxidants, including 5-aminosalicylic acid (5-ASA), inhibited the leukocyte-mediated N-nitrosation reaction. Because 5-ASA and other anti-inflammatory and immunosuppressive drugs are used to treat inflammatory bowel disease, we wondered if any of these other compounds might also modulate N-nitrosation reactions in vitro. Therefore, the objectives of this study were to assess the ability of aminosalicylates and certain immunosuppressive agents to inhibit NO-dependent N-nitrosation of a model aromatic amine (2,3-diaminonaphthalene) and to determine whether this inhibitory activity correlated with their oxidation potential. We found that the concentrations necessary to inhibit the N-nitrosation reaction by 50% (IC50) were 25, 50 and 100 microM for 5-ASA, olsalazine (dimeric 5-ASA) and sulfasalazine, respectively. In contrast, sulfapyridine, 4-ASA, N-acetyl-5-ASA, 6-mercaptopurine, azathioprine, and methotrexate were either much less effective or inactive at inhibiting the N-nitrosation reaction. Although 5-ASA was able to fully scavenge the stable free radical 1,1-diphenyl-2-picrylhydrazyl, neither olsalazine nor sulfasalazine was found to be effective at scavenging this weak oxidant. We did find that olsalazine possessed an oxidation potential substantially less than that of sulfasalazine, suggesting that it may, in fact, scavenge more potent oxidizing agents such as the N-nitrosating agent. We conclude that 5-ASA and olsalazine inhibit NO-dependent N
[Spectral Study on Coordination Reaction Between metMyoglobin and Nitric Oxide].
Tang, Qian; Zhang, Yue; Cao, Hong-yu; Shi, Shan-shan; Zheng, Xue-fang
As we all known, the instantaneous reaction between protein and ligands are very important to adjust the normal playing of biological function. And nitric oxide interactions with iron are the most important biological reactions in which NO participates. Unlike carbon monoxide or oxygen, NO can also bind reversibly to ferric iron. In this paper, UV-Vis absorption and CD spectra were used to study coordination reaction process between horse heart metMb and NO, to demonstrate the coordination reaction mechanism and to explore the influencing factors of metMb with NO. The experimental results showed that metMb could react with NO, and obtained three new peaks at 420 nm, 534 and 568 nm, respectively, which implied metMb and NO have reacted and generated a new complex-nitrosylmetmyoglobin (metMbNO). Then as time went on, NO concentration decreased in the solution, and the Fe-N bond fractured under the attack of H2O, then NO leaves slowly from metMbNO, and met-Mb was regenerated. In this experiment, we also found that external conditions such as buffer medium, ionic strength, pH, temperature, etc, had an important influence on the coordination reaction between metMb and NO. It was favorable for the coordination reaction, when the 0.01 mol x L(-1) phosphate buffer. solution is near neutral condition, the temperature is 280 K, the coordination reaction could reach equilibrium at a fastest speed. In addition, the CD date show that NO only reacts with Fe atom in the center of heme and has less effect on the secondary structuers of protein. The research of metMb and NO played an important role to further study the function of NO. Especially the establish of equilibrium reaction mechanism between NO and heme protein has an important research value on maintaining the balance of NO in vivo and keeping the normal function in the body's cells. PMID:26717761
Natural DNA-modified graphene/Pd nanoparticles as highly active catalyst for formic acid electro-oxidation and for the Suzuki reaction.
Qu, Konggang; Wu, Li; Ren, Jinsong; Qu, Xiaogang
Natural DNA has been considered as a building block for developing novel functional materials. It is abundant, renewable, and biodegradable and has a well-defined structure and conformation with many unique features, which are difficult to find in other polymers. Herein, calf thymus DNA modified graphene/Pd nanoparticle (DNA-G-Pd) hybrid materials are constructed for the first time using DNA as a mediator, and the prepared DNA-G-Pd hybrid shows high catalytic activity for fuel cell formic acid electro-oxidation and for organic Suzuki reaction. The main advantages of using DNA are not only because the aromatic nucleobases in DNA can interact through π-π stacking with graphene basal surface but also because they can chelate Pd via dative bonding in such defined sites along the DNA lattice. Our results indicate that isolated, homogeneous, and ultrafine spherical Pd nanoparticles are densely in situ decorated on DNA-modified graphene surfaces with high stability and dispersibility. The prepared DNA-G-Pd hybrid has much greater activity and durability for formic acid electro-oxidation than the commercial Pd/C catalyst and polyvinylpyrrolidone-mediated graphene/Pd nanoparticle (PVP-G-Pd) hybrid used for direct formic acid fuel cells (DFAFCs). Besides, the DNA-G-Pd hybrid can also be an efficient and recyclable catalyst for the organic Suzuki reaction in aqueous solution under aerobic conditions without any preactivation. Since DNA can chelate various transition metal cations, this proof-of-concept protocol provides the possibility for the tailored design of other novel catalytic materials based on graphene with full exploitation of their properties. PMID:22973944
Theoretical study on the reaction mechanism and thermodynamics of tin oxidation by oxygen species and chlorine species
NASA Astrophysics Data System (ADS)
Li, Lai-Cai; Deng, Ping; Zhu, Yuan-Qiang; Zha, Dong; Tian, An-Min; Xu, Ming-Hou; Wong, Ning-Bew
In this work ab initio molecular orbital methods were employed to study the coal combustion reaction mechanisms of tin oxidized by different oxidants, including HOCl, HCl, ClO, ClO2, NO3, CO2, and O2. Eleven reaction pathways were identified. The results show that Sn can react with HCl, ClOO, CO2, O2, and NO3 to form SnO and SnCl. SnO can be oxidized into SnCl by HOCl and HCl. SnCl can be further oxidized into a soluble compound, SnCl2.
Dehydrogenative Coupling Reactions with Oxidized Guanidino-Functionalized Aromatic Compounds: Novel Options for σ-Bond Activation.
Wild, Ute; Federle, Stefanie; Wagner, Arne; Kaifer, Elisabeth; Himmel, Hans-Jörg
We present a new option for metal-free σ-bond activation, making use of oxidized, guanidino-functionalized aromatic compounds (GFAs). We demonstrate this new option by the homocoupling reactions of thiols and phosphines. The kinetics and the reaction pathway were studied by a number of experiments (including heterocoupling of thiols and phosphines), supported by quantum-chemical computations. Reaction of the oxidized GFA with p-dihydrobenzoquinone to give p-benzoquinone shows that typical proton-coupled electron-transfer reactions are also possible. PMID:27430589
Optically active P5-deltacyclenes: selective oxidation, ligand properties, and a diastereoselective rearrangement reaction.
Keller, I C; Bauer, W; Heinemann, F W; Höhn, C; Rohwer, L; Zenneck, U
Cage-chiral tetra-tert-butyl-P5-deltacyclene is accessible as a pair of highly enriched enantiomers and . The only secondary phosphorus atom P1 of the cage can be selectively oxidized by reaction with t-BuOOH. The P1-oxo species and , allow the direct determination of their ee values. Oxidation occurs with the complete retention of the optical activity of the compounds. The chiroptical properties of and are strongly dominated by their cage chirality, the oxygen atom does not contribute significantly. Elemental sulfur and selenium oxidize P5 with high preference to yield P5-thio- and P5-seleno-P5-deltacyclenes and of the intact cages again. Longer reaction time and more than stoichiometric amounts of selenium, leads to tri-seleno-P5-tetracycloundecane , a partially opened oxidized rearrangement product. The ligand properties of racemic were determined. Diphosphetane phosphorus atom P2 of is the active donor center to bind a Cr(CO)5 fragment, but a tautomerization of takes place if [(benzene)RuCl2]2 is added. A hydrogen atom migrates from P1 to the oxygen atom to form a phosphinous acid ligand. The lone pair of P1 is regenerated and acts as the active ligand function of the cage in this case. As for , the base n-BuLi induces an efficient cage rearrangement reaction of , where P1 and the neighboring carbon atom C4 containing its t-Bu substituent change places. C4 moves to its new position without breaking the bond with P5, this way forming the novel P1-oxo-P5-norsnoutene cage in a highly diastereoselective process. PMID:27055252
Reaction of uranium oxides with chlorine and carbon or carbon monoxide to prepare uranium chlorides
Haas, P.A.; Lee, D.D.; Mailen, J.C.
The preferred preparation concept of uranium metal for feed to an AVLIS uranium enrichment process requires preparation of uranium tetrachloride (UCI{sub 4}) by reacting uranium oxides (UO{sub 2}/UO{sub 3}) and chlorine (Cl{sub 2}) in a molten chloride salt medium. UO{sub 2} is a very stable metal oxide; thus, the chemical conversion requires both a chlorinating agent and a reducing agent that gives an oxide product which is much more stable than the corresponding chloride. Experimental studies in a quartz reactor of 4-cm ID have demonstrated the practically of some chemical flow sheets. Experimentation has illustrated a sequence of results concerning the chemical flow sheets. Tests with a graphite block at 850{degrees}C demonstrated rapid reactions of Cl{sub 2} and evolution of carbon dioxide (CO{sub 2}) as a product. Use of carbon monoxide (CO) as the reducing agent also gave rapid reactions of Cl{sub 2} and formation of CO{sub 2} at lower temperatures, but the reduction reactions were slower than the chlorinations. Carbon powder in the molten salt melt gave higher rates of reduction and better steady state utilization of Cl{sub 2}. Addition of UO{sub 2} feed while chlorination was in progress greatly improved the operation by avoiding the plugging effects from high UO{sub 2} concentrations and the poor Cl{sub 2} utilizations from low UO{sub 2} concentrations. An UO{sub 3} feed gave undesirable effects while a feed of UO{sub 2}-C spheres was excellent. The UO{sub 2}-C spheres also gave good rates of reaction as a fixed bed without any molten chloride salt. Results with a larger reactor and a bottom condenser for volatilized uranium show collection of condensed uranium chlorides as a loose powder and chlorine utilizations of 95--98% at high feed rates. 14 refs., 7 figs., 14 tabs.
Reaction mechanism of WGS and PROX reactions catalyzed by Pt/oxide catalysts revealed by an FeO(111)/Pt(111) inverse model catalyst.
Xu, Lingshun; Wu, Zongfang; Jin, Yuekang; Ma, Yunsheng; Huang, Weixin
We have employed XPS and TDS to study the adsorption and surface reactions of H2O, CO and HCOOH on an FeO(111)/Pt(111) inverse model catalyst. The FeO(111)-Pt(111) interface of the FeO(111)/Pt(111) inverse model catalyst exposes coordination-unsaturated Fe(II) cations (Fe(II)CUS) and the Fe(II)CUS cations are capable of modifying the reactivity of neighbouring Pt sites. Water facilely dissociates on the Fe(II)CUS cations at the FeO(111)-Pt(111) interface to form hydroxyls that react to form both water and H2 upon heating. Hydroxyls on the Fe(II)CUS cations can react with CO(a) on the neighbouring Pt(111) sites to produce CO2 at low temperatures. Hydroxyls act as the co-catalyst in the CO oxidation by hydroxyls to CO2 (PROX reaction), while they act as one of the reactants in the CO oxidation by hydroxyls to CO2 and H2 (WGS reaction), and the recombinative reaction of hydroxyls to produce H2 is the rate-limiting step in the WGS reaction. A comparison of reaction behaviors between the interfacial CO(a) + OH reaction and the formate decomposition reaction suggest that formate is the likely surface intermediate of the CO(a) + OH reaction. These results provide some solid experimental evidence for the associative reaction mechanism of WGS and PROX reactions catalyzed by Pt/oxide catalysts. PMID:23576093
Oxygen radical-mediated oxidation reactions of an alanine peptide motif - density functional theory and transition state theory study
Background Oxygen-base (O-base) oxidation in protein backbone is important in the protein backbone fragmentation due to the attack from reactive oxygen species (ROS). In this study, an alanine peptide was used model system to investigate this O-base oxidation by employing density functional theory (DFT) calculations combining with continuum solvent model. Detailed reaction steps were analyzed along with their reaction rate constants. Results Most of the O-base oxidation reactions for this alanine peptide are exothermic except for the bond-breakage of the Cα-N bond to form hydroperoxy alanine radical. Among the reactions investigated in this study, the activated energy of OH α-H abstraction is the lowest one, while the generation of alkylperoxy peptide radical must overcome the highest energy barrier. The aqueous situation facilitates the oxidation reactions to generate hydroxyl alanine peptide derivatives except for the fragmentations of alkoxyl alanine peptide radical. The Cα-Cβ bond of the alkoxyl alanine peptide radical is more labile than the peptide bond. Conclusion the rate-determining step of oxidation in protein backbone is the generation of hydroperoxy peptide radical via the reaction of alkylperoxy peptide radical with HO2. The stabilities of alkylperoxy peptide radical and complex of alkylperoxy peptide radical with HO2 are crucial in this O-base oxidation reaction. PMID:22524792
Design Insights for Tuning the Electrocatalytic Activity of Perovskite Oxides for the Oxygen Evolution Reaction
Malkhandi, S; Trinh, P; Manohar, AK; Manivannan, A; Balasubramanian, M; Prakash, GKS; Narayanan, SR
Rechargeable metal-air batteries and water electrolyzers based on aqueous alkaline electrolytes hold the potential to be sustainable solutions to address the challenge of storing large amounts of electrical energy generated from solar and wind resources. For these batteries and electrolyzers to be economically viable, it is essential to have efficient, durable, and inexpensive electrocatalysts for the oxygen evolution reaction. In this article, we describe new insights for predicting and tuning the activity of inexpensive transition metal oxides for designing efficient and inexpensive electrocatalysts. We have focused on understanding the factors determining the electrocatalytic activity for oxygen evolution in a strong alkaline medium. To this end, we have conducted a systematic investigation of nanophase calcium-doped lanthanum cobalt manganese oxide, an example of a mixed metal oxide that can be tuned for its electrocatalytic activity by varying the transition metal composition. Using X-ray absorption spectroscopy (XANES), X-ray photoelectron spectroscopy (XPS), electrochemical polarization experiments, and analysis of mechanisms, we have identified the key determinants of electrocatalytic activity. We have found that the Tafel slopes are determined by the oxidation states and the bond energy of the surface intermediates of Mn-OH and Co-OH bonds while the catalytic activity increased with the average d-electron occupancy of the sigma* orbital of the M-OH bond. We anticipate that such understanding will be very useful in predicting the behavior of other transition metal oxide catalysts.
Metastable structures and isotope exchange reactions in polyoxometalate ions provide a molecular view of oxide dissolution.
Rustad, James R; Casey, William H
Reactions involving minerals and glasses in water are slow and difficult to probe spectroscopically but are fundamental to the performance of oxide materials in green technologies such as automotive thermoelectric power generation, CO2 capture and storage and water-oxidation catalysis; these must be made from geochemically common elements and operate in hydrous environments. Polyoxometalate ions (POMs) have structures similar to condensed oxide phases and can be used as molecular models of the oxide/water interface. Oxygen atoms in POM exchange isotopes at different rates, but, at present, there is no basis for predicting how the coordination environment and metal substitution influences rates and mechanisms. Here we identify low-energy metastable configurations that form from the breaking of weak bonds between metals and underlying highly coordinated oxygen atoms, followed by facile hydroxide, hydronium or water addition. The mediation of oxygen exchange by these stuffed structures suggests a new view of the relationship between structure and reactivity at the oxide/solution interface. PMID:22231599
Aerobic palladium(II)-catalyzed dehydrogenative heck reaction in the synthesis of pyrenyl fluorophores. a photophysical study of β-pyrenyl acrylates in solution and in the solid state.
Piotrowicz, Michał; Zakrzewski, Janusz; Métivier, Rémi; Brosseau, Arnaud; Makal, Anna; Woźniak, Krzysztof
An aerobic dehydrogenative Heck reaction of pyrene (1a) and 2,7-di-tert-butylpyrene (1b) with ethyl acrylate is reported. The reaction is catalyzed by a Pd(OAc)2/4,5-diazafluoren-9-one (DAF) system and takes place in acetic or pivalic acid as solvents at 110-130 °C. The reaction of 1a afforded a 6:1 mixture of C-1- and C-4-alkenylated pyrenes (2a and 3a, respectively) in 71% yield. In the case of 1b, only a C-4-substituted product (3b) was formed in 46% yield. Compounds 2a and 3a,b exhibited fluorescence in solution and in the solid state. In chloroform and THF solution the fluorescence maxima were in the range of 440-465 nm, and quantum yields decreased in the order 2a > 3a> 3b. In the solid state, 3a,b showed blue-green fluorescence (ΦF = 0.26 and 0.14, respectively), whereas 2a emitted yellow-green fluorescence) (ΦF = 0.35). Besides blue-emitting monomers, the presence of green-emitting aggregated species (preformed dimers) in the crystals of 3a,b and red-emitting dynamic excimers in the crystals of 2a has been demonstrated. Single-crystal X-ray diffraction analyses of 2a and 3b confirmed π-stacking of pyrenyl moieties in the crystals of the former and the absence of stacking in the crystals of the latter compound. PMID:25642784
Study of the Reaction Stages and Kinetics of the Europium Oxide Carbochlorination
NASA Astrophysics Data System (ADS)
Pomiro, Federico J.; Fouga, Gastón G.; Gaviría, Juan P.; Bohé, Ana E.
The europium oxide (Eu2O3(s)) chlorination reaction with sucrose carbon was studied by thermogravimetry between room temperature and 1223 K (950 °C). The nonisothermal thermogravimetry showed that the reaction consists of three stages, and their stoichiometries were studied. The product of the first stage was europium oxychloride, and it showed independence of the reaction kinetics with the carbon content. Subsequently, in the second stage, the EuOCl(s) was carbochlorinated with formation of EuCl3(l) and its evaporation is observed in the third stage. The analysis by Fourier transform infrared spectroscopy of gaseous species showed that the reaction at second stage occurs with the formation of CO2(g) and CO(g). Both reactants and products were analyzed by X-ray diffraction, scanning electron microscopy and wavelength-dispersive X-ray fluorescence spectroscopy. The influence of carbon content, total flow rate, sample initial mass, chlorine partial pressure, and temperature were evaluated. The second stage kinetics was analyzed, which showed an anomalous behavior caused by generation of chlorine radicals during interaction of Cl2(g) and carbon. It was found that the reaction rate at 933 K (660 °C) was proportional to a potential function of the chlorine partial pressure whose exponent is 0.56. The conversion curves were analyzed with the Avrami-Erofeev model and it was obtained an activation energy of 154 ± 5 kJ mol-1.
Limonene ozonolysis in the presence of nitric oxide: Gas-phase reaction products and yields
NASA Astrophysics Data System (ADS)
Ham, Jason E.; Harrison, Joel C.; Jackson, Stephen R.; Wells, J. R.
The reaction products from limonene ozonolysis were investigated using the new carbonyl derivatization agent, O-tert-butylhydroxylamine hydrochloride (TBOX). With ozone (O3) as the limiting reagent, five carbonyl compounds were detected. The yields of the carbonyl compounds are discussed with and without the presence of a hydroxyl radical (OHrad) scavenger, giving insight into the influence secondary OH radicals have on limonene ozonolysis products. The observed reaction product yields for limonaketone (LimaKet), 7-hydroxyl-6-oxo-3-(prop-1-en-2-yl)heptanal (7H6O), and 2-acetyl-5-oxohexanal (2A5O) were unchanged suggesting OHrad generated by the limonene + O3 reaction does not contribute to their formation. The molar yields of 3-isopropenyl-6-oxo-heptanal (IPOH) and 3-acetyl-6-oxoheptanal (3A6O) decreased by 68% and >95%; respectively, when OHrad was removed. This suggests that OHrad radicals significantly impact the formation of these products. Nitric oxide (NO) did not significantly affect the molar yields of limonaketone or IPOH. However, NO (20 ppb) considerably decreased the molar reaction product yields of 7H6O (62%), 2A5O (63%), and 3A6O (47%), suggesting NO reacted with peroxyl intermediates, generated during limonene ozonolysis, to form other carbonyls (not detected) or organic nitrates. These studies give insight into the transformation of limonene and its reaction products that can lead to indoor exposures.
Limonene ozonolysis in the presence of nitric oxide: Gas-phase reaction products and yields
Ham, Jason E.; Harrison, Joel C.; Jackson, Stephen R.; Wells, J.R.
The reaction products from limonene ozonolysis were investigated using the new carbonyl derivatization agent, O-tert-butylhydroxylamine hydrochloride (TBOX). With ozone (O3) as the limiting reagent, five carbonyl compounds were detected. The yields of the carbonyl compounds are discussed with and without the presence of a hydroxyl radical (OH•) scavenger, giving insight into the influence secondary OH radicals have on limonene ozonolysis products. The observed reaction product yields for limonaketone (LimaKet), 7-hydroxyl-6-oxo-3-(prop-1-en-2-yl)heptanal (7H6O), and 2-acetyl-5-oxohexanal (2A5O) were unchanged suggesting OH• generated by the limonene + O3 reaction does not contribute to their formation. The molar yields of 3-isopropenyl-6-oxo-heptanal (IPOH) and 3-acetyl-6-oxoheptanal (3A6O) decreased by 68% and >95%; respectively, when OH• was removed. This suggests that OH• radicals significantly impact the formation of these products. Nitric oxide (NO) did not significantly affect the molar yields of limonaketone or IPOH. However, NO (20 ppb) considerably decreased the molar reaction product yields of 7H6O (62%), 2A5O (63%), and 3A6O (47%), suggesting NO reacted with peroxyl intermediates, generated during limonene ozonolysis, to form other carbonyls (not detected) or organic nitrates. These studies give insight into the transformation of limonene and its reaction products that can lead to indoor exposures. PMID:27346977
Reactions of Propylene Oxide on Supported Silver Catalysts: Insights into Pathways Limiting Epoxidation Selectivity
Kulkarni, Apoorva; Bedolla-Pantoja, Marco; Singh, Suyash; Lobo, Raul F.; Mavrikakis, Manos; Barteau, Mark A.
The reactions of propylene oxide (PO) on silver catalysts were studied to understand the network of parallel and sequential reactions that may limit the selectivity of propylene epoxidation by these catalysts. The products of the anaerobic reaction of PO on Ag/a-Al2O3 were propanal, acetone and allyl alcohol for PO conversions below 2–3%. As the conversion of PO was increased either by increasing the temperature or the contact time, acrolein was formed at the expense of propanal, indicating that acrolein is a secondary reaction product in PO decomposition. With addition of oxygen to the feedstream the conversion of PO increased moderately. In contrast to the experiments in absence of oxygen, CO2 was a significant product while the selectivity to propanal decreased as soon as oxygen was introduced in the system. Allyl alcohol disappeared completely from the product stream in the presence of oxygen, reacting to form acrolein and CO2. The product distribution may be explained by a network of reactions involving two types of oxametallacycles formed by ring opening of PO: one with the oxygen bonded to C1 (OMC1, linear) and the other with oxygen bonded to C2 (OMC2, branched). OMC1 reacts to form PO, propanal, and allyl alcohol.
A thermodynamically consistent surface reaction mechanism for CO oxidation on Pt
Mhadeshwar, A.B.; Vlachos, D.G.
The thermodynamic inconsistency of catalytic combustion reaction mechanisms has been a long-standing, fundamental, and practical problem. Here, we develop a thermodynamically consistent catalytic reaction mechanism for CO oxidation on Pt. First, we propose a modification of the bond index of the unity bond index-quadratic exponential potential (UBI-QEP) semiempirical framework for calculation of the activation energy of the Langmuir-Hinshelwood-type bimolecular surface reaction between co-adsorbed CO{sup *} and O{sup *}. Thermodynamic consistency is then ensured in the reaction mechanism by combining the semiempirical UBI-QEP theory, statistical mechanics, and constraint-based optimization against experimental data. Atmospheric pressure ignition and ultrahigh vacuum molecular beam experiments are selected as targets for optimization. The optimized mechanism is validated against redundant experiments, including temperature-programmed desorption, temperature-programmed reaction, and molecular beam experiments. Our microkinetic model is able to capture multiple types of data while being thermodynamically consistent over a wide range of conditions.
A novel mechanism for the oxidation reaction of VO2+ on a graphite electrode in acidic solutions
NASA Astrophysics Data System (ADS)
Wang, Wenjun; Fan, Xinzhuang; Liu, Jianguo; Yan, Chuanwei; Zeng, Chaoliu
With the consideration of optimizing the performance of the all-vanadium redox flow battery (VRB), the oxidation reaction mechanism of VO2+ on a rotating graphite disk electrode has been investigated by potentiodynamic polarization in sulfuric acid solutions with various pH and vanadium concentrations. Furthermore, the reaction orders of VO2+ and H+ for the oxidation reaction of VO2+ have been calculated from the polarization results and compared with the theoretical results according to the possible reaction mechanisms available in the literature. However, a new oxidation reaction mechanism has been proposed to describe the oxidation of VO2+ at last, and the theoretic reaction orders of VO2+ and H+ based on the new mechanism are consistent with the experimental results when the electrochemical reaction is the rate-limited process. Moreover, a corresponding kinetic equation has been established for the oxidation reaction of VO2+ on a spectroscopically pure graphite electrode, and can be well used to predict the polarization behavior in V (IV) acidic solutions.
Immunological reaction and oxidative stress after light or heavy polypropylene mesh implantation in inguinal hernioplasty
Donati, Marcello; Brancato, Giovanna; Grosso, Giuseppe; Li Volti, Giovanni; La Camera, Giuseppina; Cardì, Francesco; Basile, Francesco; Donati, Angelo
Abstract The relationship between mesh weight and host tissue reaction has, so far, not been fully investigated. Lightweight meshes (LWM) are thought to give less inflammatory response compared with heavyweight meshes (HWM). The present study is a randomized, controlled, double-blind clinical trial performed in 61 patients who underwent an elective inguinal hernioplasty. The primary outcome of the study was to investigate the relationship between total amount of prosthetic material (polypropylene), immunological reaction, and oxidative stress. The study was double-blinded. Sixty-one patients were recruited for the study and randomly assigned to 2 groups (groups A and B). Levels of inflammation markers (interleukin-6 [IL-6] and tumor necrosis factor-α [TNF-α]) and oxidative stress markers (reduced glutathione [GSH] and lipid hydroperoxides [LOOH]) were determined preoperatively and after undergoing inguinal hernioplasty (after 6, 72, and 288 hours), respectively, with LWM and HWM. There was no significant difference in IL-6 levels between HWM and LWM (P = 0.3, 0.7, 0.8 after 6, 72, and 288 hours, respectively). A statistically significant difference was found after 72 hours for TNF-α (P = 0.01), for GSH after 6 hours (P < 0.01), and after 6 and 72 hours for LOOH (P = 0.05, 0.01, respectively). Oxidative stress occurred at earlier time points and was pore accentuated HWM versus LWM and prodromal to TNF-α increase. Also, in randomized clinical trial, the use of LWM gives advantages in terms of less inflammatory response when compared with HWM. Moreover, there is a significant higher oxidative stress after implantation of HWM. The intensity of oxidative stress seems to be strongly related to the amount of implanted polypropylene. (Trial registration number: NCT01090284). PMID:27310955
Pt NPs immobilized on core-shell magnetite microparticles: novel and highly efficient catalysts for the selective aerobic oxidation of ethanol and glycerol in water.
Long, Yu; Liang, Kun; Niu, Jianrui; Yuan, Bing; Ma, Jiantai
Three core-shell structures were prepared with pyrrole, glucose, and tetraethyl orthosilicate (TEOS), respectively, encasing magnetic Fe3O4 microparticles, through three different "green" approaches without any toxic solvents. Pt nanoparticles (NPs) were immobilized onto these supports with NaBH4 as the reducing agent. The as-prepared catalysts were characterized thoroughly by TEM, VSM, XRD, FT-IR, ICP, and XPS. As expected, the shells remarkably affected the distribution of Pt NPs and catalytic activity. Pt NPs dispersed evenly on the surface of Fe3O4@PPy and Fe3O4@C, which were much better than Fe3O4@SiO2. Most attractively, the prepared catalysts exhibited better kinetics, higher activity and stability than Pt/Fe3O4 and Pt/C for selective oxidation of ethanol to acetic acid and glycerol to glyceric acid with molecular oxygen in water. Among them, the catalyst with a shell of polypyrrole (PPy) showed the best catalytic property, affording yields of 88% and 55%, respectively. Moreover, it could be recovered facilely from the reaction mixture and recycled four times without any significant loss in activity. PMID:25854708
Mechanisms and reaction pathways for simultaneous oxidation of NOx and SO₂ by ozone determined by in situ IR measurements.
Sun, Chenglang; Zhao, Nan; Zhuang, Zhuokai; Wang, Haiqiang; Liu, Yue; Weng, Xiaole; Wu, Zhongbiao
Ozone (O3) oxidation combined with wet scrubbing is a promising method for the simultaneous removal of SO2 and NOx in flue gas. In this study, the O3 oxidation processes of NO and SO2, as well as their coexistence, were investigated using an in situ IR spectrometer. Experimental results showed that the O3 concentration and the reaction temperature played critical roles in the O3 oxidation process of NO. Around 80°C, when inlet molar ratio of O3/NO was less than 1, NO was mainly oxidized to NO2, while when the ratio was greater than 1, NO would be further oxidized to NO3, N2O5, and HNO3. NO3 was the key intermediate product for the formation of N2O5 and HNO3. However, the subsequent reactions of NO3 were temperature dependence. With the increase of reaction temperature above 100°C, the concentration of NO2 increased whereas the concentrations of N2O5 and HNO3 decreased. The oxidation of SO2 by O3 was negligible and SO2 had little influence on the oxidation of NO in the simultaneous oxidation of NO and SO2. Finally, based on the in situ IR results, the oxidation mechanism is discussed and the reaction pathways are proposed. PMID:24801895
Reaction pathway and oxidation mechanisms of dibutyl phthalate by persulfate activated with zero-valent iron.
Li, Huanxuan; Wan, Jinquan; Ma, Yongwen; Wang, Yan
This study investigated reaction pathway and oxidation mechanisms of dibutyl phthalate (DBP) by persulfate (PS) activated with zero-valent iron (ZVI). The DBP degradation was studied at three pH values (acidic, neutral and basic) in the presence of different organic scavengers. Using a chemical probe method, both sulfate radical (SO4(-)) and hydroxyl radical (·OH) were found to be primary oxidants at pH3.0 and pH7.0, respectively while ·OH was the major specie to oxidize DBP at pH11.0. A similar result was found in an experiment of Electron Spin Resonance spin-trapping where in addition to OH, superoxide radical (O2(-)) was detected at pH11.0. The transformation of degradation products including dimethyl phthalate (DMP), diethyl phthalate (DEP), phthalic anhydride, and acetophenone exhibited diverse variation during the reaction processes. The phthalic anhydride concentration appeared to be maximum at all pHs. Another eleven intermediate products were also found at pH3.0 by GC-MS and HPLC analysis, and their degradation mechanisms and pathways were proposed. It was suggested that dealkylation, hydroxylation, decarboxylation and hydrogen extraction were the dominant degradation mechanisms of DBP at pH3.0. PMID:27125682