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Suspect screening is useful when looking for one or more suspected compounds with known structures in a sample, but reference standards are unavailable or dont exist. In this case, user-built databases containing information such as mass accuracy, retention time, isotopic patterns, and other structure information for the suspected compounds are consulted, filtered, and compared against the results of high-resolution mass spectrometry analyses using SRM or full scans. The structure of the suspected compounds are then elucidated based on that information, ideally confirmed with authentic reference standards. Compared to targeted screening, the initial work performed in suspect screening is largely qualitative, with more quantitative work to potentially follow in a more targeted approach. Aside from being able to analyze for more compounds, an additional benefit of this approach is that retrospective analysis, even years later, is enabled without reanalyzing the sample. A downside to the suspect approach is the complexity involved, including not only with data analysis (e.g., using in silico' fragmentation software) but also carefully developing suspect screening lists and choosing databases. | 3 | Analytical Chemistry |
The most common optical system uses spherical collimators and thus contains optical aberrations that curve the field where the slit images come to focus, so that slits are sometimes curved instead of simply straight, to approximate the curvature of the image. This allows taller slits to be used, gathering more light, while still achieving high spectral resolution. Some designs take another approach and use toroidal collimating mirrors to correct the curvature instead, allowing higher straight slits without sacrificing resolution. | 7 | Physical Chemistry |
Pancratistatin (PST) is a natural compound initially extracted from spider lily, a Hawaiian native plant of the family Amaryllidaceae (AMD). | 0 | Organic Chemistry |
The most studied mesoionic carbenes are based on imidazole and are referred to as imidazolin-4-ylidenes. These complexes were first reported by Crabtree in 2001. The formation of imidazolin-4-ylidenes (MIC) instead of imidazolin-2-ylidenes (NHC) is typically a matter of blocking the C2 position. Most imidazolin-4-ylidenes are trisubstituted in the N1, C2, and N3 positions or tetrasubstituted. Electron-withdrawing groups in the N3 and C5 positions stabilize the carbenes more than electron-donating groups. Free carbenes as well as numerous transition metal complexes have been synthesized. | 0 | Organic Chemistry |
All enzymes work within a range of temperature specific to the organism. Increases in temperature generally lead to increases in reaction rates. There is a limit to the increase because higher temperatures lead to a sharp decrease in reaction rates. This is due to the denaturating (alteration) of protein structure resulting from the breakdown of the weak ionic and hydrogen bonding that stabilize the three-dimensional structure of the enzyme active site. The "optimum" temperature for human enzymes is usually between 35 and 40 °C. The average temperature for humans is 37 °C. Human enzymes start to denature quickly at temperatures above 40 °C. Enzymes from thermophilic archaea found in the hot springs are stable up to 100 °C. However, the idea of an "optimum" rate of an enzyme reaction is misleading, as the rate observed at any temperature is the product of two rates, the reaction rate and the denaturation rate. If you were to use an assay measuring activity for one second, it would give high activity at high temperatures, however if you were to use an assay measuring product formation over an hour, it would give you low activity at these temperatures. | 1 | Biochemistry |
Unlike ground state oxygen, singlet oxygen participates in Diels–Alder [4+2]- and [2+2]-cycloaddition reactions and formal concerted ene reactions. It oxidizes thioethers to sulfoxides. Organometallic complexes are often degraded by singlet oxygen. With some substrates 1,2-dioxetanes are formed; cyclic dienes such as 1,3-cyclohexadiene form [4+2] cycloaddition adducts.
The [4+2]-cycloaddition between singlet oxygen and furans is widely used in organic synthesis.
In singlet oxygen reactions with alkenic allyl groups, e.g., citronella, shown, by abstraction of the allylic proton, in an ene-like reaction, yielding the allyl hydroperoxide, R–O–OH (R = alkyl), which can then be reduced to the corresponding allylic alcohol.
In reactions with water trioxidane, an unusual molecule with three consecutive linked oxygen atoms, is formed. | 7 | Physical Chemistry |
Several factors complicate simple correlation of obsidian hydration band thickness with absolute age. Temperature is known to speed up the hydration process. Thus, artifacts exposed to higher temperatures, for example by being at lower elevation, seem to hydrate faster. As well, obsidian chemistry, including the intrinsic water content, seems to affect the rate of hydration. Once an archeologist can control for the geochemical signature of the obsidian (e.g., the "source") and temperature (usually approximated using an "effective hydration temperature" or EHT coefficient), he or she may be able to date the artifact using the obsidian hydration technique. Water vapor pressure may also affect the rate of obsidian hydration.
The reliability of the method based on Friedmans empirical age equation (x²=kt, where x is the thickness of the hydration rim, k is the diffusion coefficient, and t' is the time) is questioned from several grounds regarding temperature dependence, square root of time and determination of diffusion rate per sample and per site, as part of some successful attempts on the procedure and applications. The SIMS-SS age calculation procedure is separated into two major steps. The first step concerns the calculation of a 3rd order fitting polynomial of the SIMS profile (eq. 1). The second stage regards the determination of the saturation layer, i.e. its depth and concentration. The whole computing processing is embedded in stand-alone software created in Matlab (version 7.0.1) software package with a graphical user interface and executable under Windows XP. Thus, the SIMS-SS age equation in years before present is given in eq. 2:
<br>
Eq. 1 Fitting polynomial of the SIMS profile
<br>
Eq. 2 The SIMS-SS age equation in years before present
Where, Ci is the intrinsic concentration of water, Cs is the saturation concentration, dC/dx is the diffusion coefficient for depth x=0, k is derived from a family of Crank's theoretical diffusion curves, and is an effective diffusion coefficient (eq. 3) which relates the inverse gradient of the fit polynomial to well dated samples:
:D = aD + b/ (10D) = 8.051eD+0.999/(1022D), Eq. 3'
where Ds = (1/(dC/dx))10 assuming a constant flux and taken as unity. The eq. (2) and assumption of unity is a matter of further investigation.
Several commercial companies and university laboratories provide obsidian hydration services. | 9 | Geochemistry |
NMOR is a component of tobacco products. As of 2014, detectable levels of NMOR are present in tobacco products in the United States and China. The presence of NMOR and other n-nitrosoamines is not limited to cigarettes, but is found in smokeless tobacco products (snuff tobacco, Snus, etc.) as well. Volatile nitrosamines, including NMOR, are detectable in the urine of tobacco smokers. | 0 | Organic Chemistry |
Phenylmercuric borate and acetate were used for disinfecting mucous membranes at an effective concentration of 0.07% in aqueous solutions. Due to toxicological and ecotoxicological reasons phenylmercury salts are no longer in use. However, some surgeons use mercurochrome despite toxicological objections. Mercurochrome is still available to purchase in Australia to use on minor wounds. Dental amalgam used in fillings inhibits bacterial reproduction.
Organic mercury compounds have been used as topical disinfectants (thimerosal, nitromersol, and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Mercury was used in the treatment of syphilis. Calomel was commonly used in infant teething powders in the 1930s and 1940s. Mercurials are also used agriculturally as insecticides and fungicides. | 1 | Biochemistry |
Lugols solution is commonly available in different potencies of (nominal) 1%, 2%, 5% or 10%. Iodine concentrations greater than 2.2% are subject to US regulations. If the US regulations are taken literally, their 2.2% maximum iodine concentration limits a Lugols solution to maximum (nominal) 0.87%.
The most commonly used (nominal) 5% solution consists of 5% (wt/v) iodine () and 10% (wt/v) potassium iodide (KI) mixed in distilled water and has a total iodine content of 126.4 mg/mL. The (nominal) 5% solution thus has a total iodine content of 6.32 mg per drop of 0.05 mL; the (nominal) 2% solution has 2.53 mg total iodine content per drop.
Potassium iodide renders the elementary iodine soluble in water through the formation of the triiodide () ion. It is not to be confused with tincture of iodine solutions, which consist of elemental iodine, and iodide salts dissolved in water and alcohol. Lugol's solution contains no alcohol.
Other names for Lugol's solution are (iodine-potassium iodide); Markodine, Strong solution (Systemic); and Aqueous Iodine Solution BP. | 3 | Analytical Chemistry |
This enzyme is a part of a family of enzymes called glycoside hydrolase family 31 (GH31). This is due to the digestive mechanism of the enzyme. GH31 enzymes undergo what is known as the Koshland double displacement mechanism in which a glycosylation and deglycosylation step occurs, resulting in the retention of the overall configuration of the anomeric center. | 1 | Biochemistry |
Karen Jane Faulds is a Scottish academic and Professor of Analytical Chemistry at the University of Strathclyde. She develops surface-enhanced Raman spectroscopy (SERS) for bioanalysis, and has won several awards for her research, including the Coblentz Society Craver Award. | 3 | Analytical Chemistry |
Control of the process of gene transcription affects patterns of gene expression and, thereby, allows a cell to adapt to a changing environment, perform specialized roles within an organism, and maintain basic metabolic processes necessary for survival. Therefore, it is hardly surprising that the activity of RNAP is long, complex, and highly regulated. In Escherichia coli bacteria, more than 100 transcription factors have been identified, which modify the activity of RNAP.
RNAP can initiate transcription at specific DNA sequences known as promoters. It then produces an RNA chain, which is complementary to the template DNA strand. The process of adding nucleotides to the RNA strand is known as elongation; in eukaryotes, RNAP can build chains as long as 2.4 million nucleotides (the full length of the dystrophin gene). RNAP will preferentially release its RNA transcript at specific DNA sequences encoded at the end of genes, which are known as terminators.
Products of RNAP include:
* Messenger RNA (mRNA)—template for the synthesis of proteins by ribosomes.
* Non-coding RNA or "RNA genes"—a broad class of genes that encode RNA that is not translated into protein. The most prominent examples of RNA genes are transfer RNA (tRNA) and ribosomal RNA (rRNA), both of which are involved in the process of translation. However, since the late 1990s, many new RNA genes have been found, and thus RNA genes may play a much more significant role than previously thought.
** Transfer RNA (tRNA)—transfers specific amino acids to growing polypeptide chains at the ribosomal site of protein synthesis during translation
** Ribosomal RNA (rRNA)—a component of ribosomes
** Micro RNA—regulates gene activity
** Catalytic RNA (Ribozyme)—enzymatically active RNA molecules
RNAP accomplishes de novo synthesis. It is able to do this because specific interactions with the initiating nucleotide hold RNAP rigidly in place, facilitating chemical attack on the incoming nucleotide. Such specific interactions explain why RNAP prefers to start transcripts with ATP (followed by GTP, UTP, and then CTP). In contrast to DNA polymerase, RNAP includes helicase activity, therefore no separate enzyme is needed to unwind DNA. | 1 | Biochemistry |
G proteins were discovered in 1980 when Alfred G. Gilman and Martin Rodbell investigated stimulation of cells by adrenaline. They found that when adrenaline binds to a receptor, the receptor does not stimulate enzymes (inside the cell) directly. Instead, the receptor stimulates a G protein, which then stimulates an enzyme. An example is adenylate cyclase, which produces the second messenger cyclic AMP. For this discovery, they won the 1994 Nobel Prize in Physiology or Medicine.
Nobel prizes have been awarded for many aspects of signaling by G proteins and GPCRs. These include receptor antagonists, neurotransmitters, neurotransmitter reuptake, G protein-coupled receptors, G proteins, second messengers, the enzymes that trigger protein phosphorylation in response to cAMP, and consequent metabolic processes such as glycogenolysis.
Prominent examples include (in chronological order of awarding):
* The 1947 Nobel Prize in Physiology or Medicine to Carl Cori, Gerty Cori and Bernardo Houssay, for their discovery of how glycogen is broken down to glucose and resynthesized in the body, for use as a store and source of energy. Glycogenolysis is stimulated by numerous hormones and neurotransmitters including adrenaline.
* The 1970 Nobel Prize in Physiology or Medicine to Julius Axelrod, Bernard Katz and Ulf von Euler for their work on the release and reuptake of neurotransmitters.
* The 1971 Nobel Prize in Physiology or Medicine to Earl Sutherland for discovering the key role of adenylate cyclase, which produces the second messenger cyclic AMP.
* The 1988 Nobel Prize in Physiology or Medicine to George H. Hitchings, Sir James Black and Gertrude Elion "for their discoveries of important principles for drug treatment" targeting GPCRs.
* The 1992 Nobel Prize in Physiology or Medicine to Edwin G. Krebs and Edmond H. Fischer for describing how reversible phosphorylation works as a switch to activate proteins, and to regulate various cellular processes including glycogenolysis.
* The 1994 Nobel Prize in Physiology or Medicine to Alfred G. Gilman and Martin Rodbell for their discovery of "G-proteins and the role of these proteins in signal transduction in cells".
* The 2000 Nobel Prize in Physiology or Medicine to Eric Kandel, Arvid Carlsson and Paul Greengard, for research on neurotransmitters such as dopamine, which act via GPCRs.
* The 2004 Nobel Prize in Physiology or Medicine to Richard Axel and Linda B. Buck for their work on G protein-coupled olfactory receptors.
* The 2012 Nobel Prize in Chemistry to Brian Kobilka and Robert Lefkowitz for their work on GPCR function. | 1 | Biochemistry |
However, this system of calculation gives only the mass of pure gold contained in an alloy. The term 18-karat gold means that the alloys mass consists of 75% of gold and 25% of other metals. The quantity of gold by volume' in a less-than-24-karat gold alloy differs according to the alloys used. For example, knowing that standard 18-karat yellow gold consists of 75% gold, 12.5% silver and the remaining 12.5% of copper (all by mass), the volume of pure gold in this alloy will be 60% since gold is much denser than the other metals used: 19.32 g/cm for gold, 10.49 g/cm for silver and 8.96 g/cm for copper. | 8 | Metallurgy |
The first version of SMPDB was released on January 1, 2010. This release contained more than 350 image-mapped pathways for small molecule pathways. The viewer interface was limited to scroll-bar image navigation with 3-step (small, medium, large) zooming. The pathways in this first version were limited to 1) human metabolic pathways; 2) human metabolic disease pathways; and 3) human metabolite signaling pathways. The second version of SMPDB was released in 2014. This version contained more than 620 small molecule pathways. The viewer interface was enhanced to include a Google-Map-like interface with click-n-drag image navigation and unlimited, interactive zooming. The pathways in this second version were expanded to include: 1) general human metabolic pathways; 2) human metabolic disease pathways; 3) human metabolite signaling pathways; 4) drug action pathways and 5) drug metabolism pathways. | 1 | Biochemistry |
In January 2017, the US Food and Drug Administration approved an over-the-counter preparation. Levocetirizine had previously received authorization by the FDA as a prescription drug in 2007, having already been brought to market throughout much of Europe. In India, a prescription-only drug containing levocetirizine hydrochloride and montelukast is sold as Crohist MK. | 4 | Stereochemistry |
ATSDR is starting a new registry for people with amyotrophic lateral sclerosis (also known as ALS or Lou Gehrig's Disease). President George W. Bush signed the ALS Registry Act, which provided for establishment of the registry, on October 8, 2008. It is hoped that the registry will provide information on the prevalence of ALS and lead to a better understanding of factors that may be associated with the disease. The agency began registering people for the registry on October 20, 2010. | 1 | Biochemistry |
A recent study from laboratory of Günther Rupprechter shows that operando spectroscopy can also be used to investigate the performance of VOC sensing semiconductor nanomaterials. To demonstrate this, operando spectroscopy was applied to directly investigate the room temperature detection of methanol by metal oxide semiconductor composites (mainly Anatase titanium dioxide nanoparticles with reduced graphene oxide) in gas sensors. Operando-DRIFTS along with resistance measurements, were employed to examine methanol interactions with the sensors. Moreover, mass spectroscopy (MS) with resistance measurements revealed surface electrochemical reactions. Overall, operando spectroscopy findings showed that the nanocomposite sensor's mechanism involves a combination of reversible physisorption and irreversible chemisorption of methanol, sensor modification over time, and electron/oxygen depletion and restoration, resulting in the formation of carbon dioxide and water. | 7 | Physical Chemistry |
The longitudinal invariant of a particle trapped in a magnetic mirror,
where the integral is between the two turning points, is also an adiabatic invariant. This guarantees, for example, that a particle in the magnetosphere moving around the Earth always returns to the same line of force. The adiabatic condition is violated in transit-time magnetic pumping, where the length of a magnetic mirror is oscillated at the bounce frequency, resulting in net heating. | 7 | Physical Chemistry |
The Enders SAMP/RAMP hydrazone alkylation begins with the synthesis of the hydrazone from a N,N-dialkylhydrazine and a ketone or aldehyde
The hydrazone is then deprotonated on the α-carbon position by a strong base, such as lithium diisopropylamide (LDA), leading to the formation of a resonance stabilized anion - an azaenolate. This anion is a very good nucleophile and readily attacks electrophiles, such as alkyl halides, to generate alkylated hydrazones with simultaneous creation of a new chiral center at the α-carbon.
The stereochemistry of this reaction is discussed in detail in next section. | 0 | Organic Chemistry |
In a broad academic audience, the concept of the evolution of the genetic code from the original and ambiguous genetic code to a well-defined ("frozen") code with the repertoire of 20 (+2) canonical amino acids is widely accepted.
However, there are different opinions, concepts, approaches and ideas, which is the best way to change it experimentally. Even models are proposed that predict "entry points" for synthetic amino acid invasion of the genetic code.
Since 2001, 40 non-natural amino acids have been added into proteins by creating a unique codon (recoding) and a corresponding transfer-RNA:aminoacyl – tRNA-synthetase pair to encode it with diverse physicochemical and biological properties in order to be used as a tool to exploring protein structure and function or to create novel or enhanced proteins.
H. Murakami and M. Sisido extended some codons to have four and five bases. Steven A. Benner constructed a functional 65th (in vivo) codon.
In 2015 N. Budisa, D. Söll and co-workers reported the full substitution of all 20,899 tryptophan residues (UGG codons) with unnatural thienopyrrole-alanine in the genetic code of the bacterium Escherichia coli.
In 2016 the first stable semisynthetic organism was created. It was a (single cell) bacterium with two synthetic bases (called X and Y). The bases survived cell division.
In 2017, researchers in South Korea reported that they had engineered a mouse with an extended genetic code that can produce proteins with unnatural amino acids.
In May 2019, researchers reported the creation of a new "Syn61" strain of the bacterium Escherichia coli. This strain has a fully synthetic genome that is refactored (all overlaps expanded), recoded (removing the use of three out of 64 codons completely), and further modified to remove the now unnecessary tRNAs and release factors. It is fully viable and grows 1.6× slower than its wild-type counterpart "MDS42". | 1 | Biochemistry |
Many drugs are hindered when providing treatment when crossing the blood-brain barrier yielding poor uptake into areas of the brain. Transferrin glycoproteins are able to bypass the blood-brain barrier via receptor-mediated transport for specific transferrin receptors found in the brain capillary endothelial cells. Due to this functionality, it is theorized that nanoparticles acting as drug carriers bound to transferrin glycoproteins can penetrate the blood-brain barrier allowing these substances to reach the diseased cells in the brain. Advances with transferrin conjugated nanoparticles can lead to non-invasive drug distribution in the brain with potential therapeutic consequences of central nervous system (CNS) targeted diseases (e.g. Alzheimers or Parkinsons disease). | 1 | Biochemistry |
Calmodulin plays an important role in excitation contraction (EC) coupling and the initiation of the cross-bridge cycling in smooth muscle, ultimately causing smooth muscle contraction. In order to activate contraction of smooth muscle, the head of the myosin light chain must be phosphorylated. This phosphorylation is done by myosin light chain (MLC) kinase. This MLC kinase is activated by a calmodulin when it is bound by calcium, thus making smooth muscle contraction dependent on the presence of calcium, through the binding of calmodulin and activation of MLC kinase.
Another way that calmodulin affects muscle contraction is by controlling the movement of Ca across both the cell and sarcoplasmic reticulum membranes. The Ca channels, such as the ryanodine receptor of the sarcoplasmic reticulum, can be inhibited by calmodulin bound to calcium, thus affecting the overall levels of calcium in the cell. Calcium pumps take calcium out of the cytoplasm or store it in the endoplasmic reticulum and this control helps regulate many downstream processes.
This is a very important function of calmodulin because it indirectly plays a role in every physiological process that is affected by smooth muscle contraction such as digestion and contraction of arteries (which helps distribute blood and regulate blood pressure). | 1 | Biochemistry |
The use of photoredox catalysis to generate reactive heteroatom-centered radicals was first explored in the 1990s. [Ru(bipy)] was found to catalyze the fragmentation of tosylphenylselenide to phenylselenolate anion and tosyl radical and that a radical chain propagation mechanism allowed the addition of tosyl radical and phenylseleno- radical across the double bond of electron rich alkyl vinyl ethers. Since phenylselenolate anion is readily oxidized to diphenyldiselenide, the low quantities of diphenyldiselenide observed was taken as an indication that photoredox-catalyzed fragmentation of tosylphenylselenide was only important as an initiation step, and that most of the reactivity was due to a radical chain process.
Heteroaromatic additions to olefins include multicomponent oxy- and aminotrifluoromethylation reactions. These reactions use Umemotos reagent, a sulfonium salt that serves as an electrophilic source of the trifluoromethyl group and that is precedented to react via a single-electron transfer pathway. Thus, single-electron reduction of Umemotos reagent releases trifluoromethyl radical, which adds to the reactive olefin. Subsequently, single-electron oxidation of the alkyl radical generated by this addition produces a cation which can be trapped by water, an alcohol, or a nitrile. In order to achieve high levels of regioselectivity, this reactivity has been explored mainly for styrenes, which are biased towards formation of the benzylic radical intermediate.
Hydrotrifluoromethylation of styrenes and aliphatic alkenes can be effected with a mesityl acridinium organic photoredox catalyst and Langlois' reagent as the source of CF radical. In this reaction, it was found that trifluoroethanol and substoichiometric amounts of an aromatic thiol, such as methyl thiosalicylate, employed in tandem served as the best source of hydrogen radical to complete the catalytic cycle.
Intramolecular hydroetherifications and hydroaminations proceed with anti-Markovnikov selectivity. One mechanism invokes the single-electron oxidation of the olefin, trapping the radical cation by a pendant hydroxyl or amine functional group, and quenching the resulting alkyl radical by H-atom transfer from a highly labile donor species. Extensions of this reactivity to intermolecular systems have resulted in i) a new synthetic route to complex tetrahydrofurans by a "polar-radical-crossover cycloaddition" (PRCC reaction) of an allylic alcohol with an olefin, and ii) the anti-Markovnikov addition of carboxylic acids to olefins. | 5 | Photochemistry |
Steatocrit or acid steatocrit is a simple, rapid gravimetric method to determine steatorrhea. The test is simple, rapid, inexpensive, and reliable. It is a qualitative test that can be used when other methods are impractical.
__TOC__ | 1 | Biochemistry |
The styrene-maleic acid (SMA) alternating copolymer displays amphiphilicity depending on pH, allowing it to change conformations in different environments. Some conformations that SMA can take are random coil formation, compact globular formation, micelles, and nanodiscs. SMA has been used as a dispersing agent for dyes and inks, as drug delivery vehicles, and for membrane solubilization. | 7 | Physical Chemistry |
In biochemistry and molecular biology, saline-sodium citrate (SSC) buffer is used as a hybridization buffer, to control stringency for washing steps in protocols for Southern blotting, in situ hybridization, DNA Microarray or Northern blotting. 20X SSC may be used to prevent drying of agarose gels during a vacuum transfer.
A 20X stock solution consists of 3 M sodium chloride and 300 mM trisodium citrate (adjusted to pH 7.0 with HCl). | 1 | Biochemistry |
Otto studied chemistry at the University of Groningen and in 1994, he received his Master's degree, focusing on physical organic chemistry and biochemistry, with the distinction cum laude. In 1998, he obtained his PhD, again with the distinction cum laude, from his supervisor Prof. Jan B.F.N. Engberts for his thesis entitled Catalysis of Diels-Alder reactions in water.
After his subsequent research in both the United States (in 1998, with Prof. Steven L. Regen) at Lehigh University and in the United Kingdom (first with Prof. Jeremy K.M. Sanders and then, from 2001 onwards, as a Royal Society University Research Fellow, both at the University of Cambridge), he was appointed assistant professor at the University of Groningen in 2009. In 2011, he was promoted to associate professor and in 2016, to full professor. From 2014 to 2019, he coordinated the master's degree programme in chemistry.
Alongside his work at the university, Otto is also one of the six principal investigators of the Dutch national gravity programme for functional molecular systems (FMS; €26 million, over 10 years, 2013–2023). The ambition of this programme is to gain control over molecular self-assembly. With this technology, nanomotors could be made, for example, or biomaterials to repair damaged bodily tissues.
Otto was the lead applicant and chair of the European Cooperation in Science & Technology (COST) Action CM1304 (Emergence and Evolution of Complex Chemical Systems), which united more than 95 European research groups. He is the chair of the Gordon Research Conference on Systems Chemistry 2020 and is editor-in-chief of the Journal of Systems Chemistry.
Otto is a member of the Royal Dutch Chemical Society (KNCV), fellow of the Royal Society of Chemistry and member of the American Chemical Society. He is member of the steering committee of the Origins Center. The Origins Center is a Dutch research platform for scientists who are involved in the key questions of the Dutch Research Agenda on the origin, evolution and future of life on Earth and in the universe. Otto is active on several fronts in both the Netherlands and abroad. Otto was elected a member of the Royal Netherlands Academy of Arts and Sciences in 2020. | 0 | Organic Chemistry |
Further research with double layers on ruthenium dioxide films in 1971 by Sergio Trasatti and Giovanni Buzzanca demonstrated that the electrochemical behavior of these electrodes at low voltages with specific adsorbed ions was like that of capacitors. The specific adsorption of the ions in this region of potential could also involve a partial charge transfer between the ion and the electrode. It was the first step towards understanding pseudocapacitance. | 7 | Physical Chemistry |
Ketosis induced by a ketogenic diet should not be pursued by people with pancreatitis because of the high dietary fat content. Ketosis is also contraindicated in pyruvate carboxylase deficiency, porphyria, and other rare genetic disorders of fat metabolism. | 1 | Biochemistry |
Endogenous sources of specific DNA damage include pathways like hydrolysis, oxidation, alkylation, mismatch of DNA bases, depurination, depyrimidination, double-strand breaks (DSS), and cytosine deamination. DNA lesions can also naturally occur from the release of specific compounds such as reactive oxygen species (ROS), reactive nitrogen species (RNS), reactive carbonyl species (RCS), lipid peroxidation products, adducts, and alkylating agents through metabolic processes. ROS is one of the major endogenous sources of DNA damage and the most studied oxidative DNA adduct is 8-oxo-dG. Other adducts known to form are etheno-, propano-, and malondialdehyde-derived DNA adducts. The aldehydes formed from lipid peroxidation also pose another threat to DNA. Proteins such as "damage-up" proteins (DDPs) can promote endogenous DNA lesions by either increasing the amount of reactive oxygen by transmembrane transporters, losing chromosomes by replisome binding, and stalling replication by transcription factors. For RNA lesions specifically, the most abundant types of endogenous damage include oxidation, alkylation, and chlorination. Phagocytic cells produce radical species that include hypochlorous acid (HOCl), nitric oxide (NO•), and peroxynitrite (ONOO−) to fight infections, and many cell types use nitric oxide as a signaling molecule. However, these radical species can also cause the pathways that form RNA lesions. | 1 | Biochemistry |
GEOTRACES is an international research programme that aims to improve an understanding of biogeochemical cycles in the oceans.
The concept of cycle describes the pathway by which a chemical element moves through the three major compartments of Earth (such as continents, atmosphere, and ocean). Because these cycles are directly related to climate dynamics and are heavily impacted by global change, it is essential to quantify them.
GEOTRACES focuses on the oceanic part of the cycles, with the ambition to map the distribution of trace elements and isotopes in the ocean and to understand the processes controlling this distribution. Some of these trace elements are directly linked to climate via, for example, their role as essential nutrients for life; others allow quantification of ocean processes (origin and dynamics of matter, age of water masses, etc.); some of them are pollutants (for example, lead or mercury). Modelling based on the data collected will thus achieve substantial progress in understanding the current and past of the ocean and improve projections of the ocean’s response to global change.
GEOTRACES is organised internationally under the auspices of the [http://www.scor-int.org/ Scientific Committee for Oceanic Research] (of the International Council for Science). Its management is overseen by a Scientific Steering Committee (SSC), with representatives of 15 nations from across the globe, and the programme involves active participation of more than 30 nations.
The GEOTRACES SSC was initially led by co-chairs, Prof. Robert F. Anderson of the Lamont–Doherty Earth Observatory (Columbia University) and Prof. Gideon M. Henderson from University of Oxford. Current co-chairs are Dr. Maeve Lohan of the University of Southampton and Dr. Karen Casciotti from Stanford University. | 9 | Geochemistry |
The europium anomaly is the phenomenon whereby the europium (Eu) concentration in a mineral is either enriched or depleted relative to some standard, commonly a chondrite or mid-ocean ridge basalt (MORB). In geochemistry a europium anomaly is said to be "positive" if the Eu concentration in the mineral is enriched relative to the other rare-earth elements (REEs), and is said to be "negative" if Eu is depleted relative to the other REEs.
While all lanthanides form relatively large trivalent (3+) ions, Eu and cerium (Ce) have additional valences, europium forms 2+ ions, and Ce forms 4+ ions, leading to chemical reaction differences in how these ions can partition versus the 3+ REEs. In the case of Eu, its reduced divalent (2+) cations are similar in size and carry the same charge as Ca, an ion found in plagioclase and other minerals. While Eu is an incompatible element in its trivalent form (Eu) in an oxidizing magma, it is preferentially incorporated into plagioclase in its divalent form (Eu) in a reducing magma, where it substitutes for calcium (Ca).
Enrichment or depletion is generally attributed to europiums tendency to be incorporated into plagioclase preferentially over other minerals. If a magma crystallizes stable plagioclase, most of the Eu will be incorporated into this mineral, causing a higher than expected concentration of Eu in the mineral versus other REE in that mineral (a positive anomaly). The rest of the magma will then be relatively depleted in Eu with a concentration of Eu lower than expected versus the concentrations of other REEs in that magma. If the Eu-depleted magma is then separated from its plagioclase crystals and subsequently solidifies, its chemical composition will display a negative Eu anomaly (because the Eu is locked up in the plagioclase left in the magma chamber). Conversely, if a magma accumulates' plagioclase crystals before solidification, its rock composition will display a relatively positive Eu anomaly.
A well-known example of the Eu anomaly is seen on the Moon. REE analyses of the Moons light-colored lunar highlands show a large positive Eu anomaly due to the plagioclase-rich anorthosite comprising the highlands. The darker lunar mare, consisting mainly of basalt, shows a large negative Eu anomaly. This has led geologists to speculate as to the genetic relationship between the lunar highlands and mare. It is possible that much of the Moons Eu was incorporated into the earlier, plagioclase-rich highlands, leaving the later basaltic mare strongly depleted in Eu. | 9 | Geochemistry |
Reactions involving palladium(II) acetate and phosphine ligands proceed by a third mechanism, the anionic pathway. Base mediates the oxidation of a phosphine ligand by palladium(II) to a phosphine oxide. Oxidative addition then generates the anionic palladium complex IX. Loss of halide leads to neutral complex X, which undergoes steps analogous to the neutral pathway to regenerate anionic complex IX. A similar anionic pathway is also likely operative in reactions of bulky palladium tri(tert-butyl)phosphine complexes. | 0 | Organic Chemistry |
Biological sequestration of carbon causes enrichment of carbon-12, so that substances that originate from living organisms have a higher carbon-12 content. Due to the kinetic isotope effect, chemical reactions can happen faster with lighter isotopes, so that photosynthesis fixes lighter carbon-12 faster than carbon-13. Also lighter isotopes diffuse across a biological membrane faster. Enrichment in carbon 13 is measured by delta C(o/oo) = [(C/C)sample/(C/C)standard - 1] * 1000.
The common standard for carbon is Cretaceous Peedee formation belemnite. | 9 | Geochemistry |
Cytochrome C has also been widely studied as an enzyme with peroxidase-like activity. Cytochrome C was conjugated to charged polymer to test its peroxidase-like activity. Inspired from natural examples of enzyme encapsulation in protein-based cage structures (Example: Carboxysomes, Ferritin and Encapsulin), Cytochrome C was encapsulated in a 9 nm small self-assembling DNA binding protein from nutrient starved cells (Dps) protein cage using chimeric self-assembly approach. Authors observed unique catalytic activity behavior upon encapsulating enzyme inside a protein-cage, which was different from enzyme in solution. This was attributed to local microenvironment provided by Dps nanocage's interior cavity which is different than bulk. | 1 | Biochemistry |
The elements can be divided into several categories:
The condensation temperatures are the temperatures at which 50% of the element will be in the form of a solid (rock) under a pressure of 10 bar. However, slightly different groups and temperature ranges are used sometimes. Refractory material are also often divided into refractory lithophile elements and refractory siderophile elements. | 9 | Geochemistry |
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to float on a water surface without becoming even partly submerged.
At liquid–air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion).
There are two primary mechanisms in play. One is an inward force on the surface molecules causing the liquid to contract. Second is a tangential force parallel to the surface of the liquid. This tangential force is generally referred to as the surface tension. The net effect is the liquid behaves as if its surface were covered with a stretched elastic membrane. But this analogy must not be taken too far as the tension in an elastic membrane is dependent on the amount of deformation of the membrane while surface tension is an inherent property of the liquid–air or liquid–vapour interface.
Because of the relatively high attraction of water molecules to each other through a web of hydrogen bonds, water has a higher surface tension (72.8 millinewtons (mN) per meter at 20 °C) than most other liquids. Surface tension is an important factor in the phenomenon of capillarity.
Surface tension has the dimension of force per unit length, or of energy per unit area. The two are equivalent, but when referring to energy per unit of area, it is common to use the term surface energy, which is a more general term in the sense that it applies also to solids.
In materials science, surface tension is used for either surface stress or surface energy. | 6 | Supramolecular Chemistry |
Like other crown ethers, 12-crown-4 complexes with alkali metal cations. The cavity diameter of 1.2-1.5 Å gives it a high selectivity towards the lithium cation (ionic diameter 1.36 Å)
Its point group is S. The dipole moment of 12-crown-4 varies with solvent and temperature. At 25 °C, the dipole moment of 12-crown-4 was determined as 2.33 ± 0.03 D in cyclohexane and 2.46 ± 0.01 D in benzene. | 6 | Supramolecular Chemistry |
Take a system in a certain super (i.e. Gibbs) state. By performing a Metropolis Monte Carlo walk it is possible to sample the landscape of states that the system moves between, using the equation
where ΔU = U(State) − U(State) is the difference in potential energy, β = 1/kT (T is the temperature in kelvins, while k is the Boltzmann constant), and is the Metropolis function.
The resulting states are then sampled according to the Boltzmann distribution of the super state at temperature T.
Alternatively, if the system is dynamically simulated in the canonical ensemble (also called the NVT ensemble), the resulting states along the simulated trajectory are likewise distributed.
Averaging along the trajectory (in either formulation) is denoted by angle brackets
Suppose that two super states of interest, A and B, are given. We assume that they have a common configuration space, i.e., they share all of their micro states, but the energies associated to these (and hence the probabilities) differ because of a change in some parameter (such as the strength of a certain interaction).
The basic question to be addressed is, then, how can the Helmholtz free energy change (ΔF = F − F) on moving between the two super states be calculated from sampling in both ensembles? The kinetic energy part in the free energy is equal between states so can be ignored. Also the Gibbs free energy corresponds to the NpT ensemble. | 7 | Physical Chemistry |
Biocurious planned to tweak the biobrick containing six genes, including luciferin-regenerating enzyme and luciferase from fireflies. During initial development, they would use Agrobacterium to test the transfer of the genetic circuit. When producing the final product, they intended to instead use a gene gun to avoid issues related to regulation of GM plants. Over the course of the project, several plants were mentioned as being recipients, including Arabidopsis thaliana, Nicotiana tabacum, and roses. Issues surrounding the production included the difficulty of moving the six component genes of the metabolic pathway, increasing the dim light produced by the plant following insertion, and preventing the pathway from being silenced. | 1 | Biochemistry |
Nucleophilic abstraction is a type of an organometallic reaction which can be defined as a nucleophilic attack on a ligand which causes part or all of the original ligand to be removed from the metal along with the nucleophile. | 0 | Organic Chemistry |
Under the free electron model, the electrons in a metal can be considered to form a uniform Fermi gas. The number density of conduction electrons in metals ranges between approximately 10 and 10 electrons per m, which is also the typical density of atoms in ordinary solid matter. This number density produces a Fermi energy of the order:
where m is the electron rest mass. This Fermi energy corresponds to a Fermi temperature of the order of 10 kelvins, much higher than the temperature of the Suns surface. Any metal will boil before reaching this temperature under atmospheric pressure. Thus for any practical purpose, a metal can be considered as a Fermi gas at zero temperature as a first approximation (normal temperatures are small compared to T'). | 7 | Physical Chemistry |
When the cost of producing slaves became too high to justify slave labourers for the many mines throughout the empire around the second century, a system of indentured servitude was introduced for convicts. In 369 AD, a law was reinstated due to the closure of many deep mines; the emperor Hadrian had previously given the control of mines to private employers, so that workers were hired rather than working out of force. Through the institution of this system profits increased (Shepard 1993). In the case of Noricum, there is archaeological evidence of freemen labour in the metal trade and extraction through graffiti on mine walls. In this province, many men were given Roman citizenship for their efforts contributing to the procurement of metal for the empire. Both privately owned and government run mines were in operation simultaneously (Shepard 1993). | 8 | Metallurgy |
The coupling of proton translocation and electron transport in Complex I is currently proposed as being indirect (long range conformational changes) as opposed to direct (redox intermediates in the hydrogen pumps as in heme groups of Complexes III and IV). The architecture of the hydrophobic region of complex I shows multiple proton transporters that are mechanically interlinked. The three central components believed to contribute to this long-range conformational change event are the pH-coupled N2 iron-sulfur cluster, the quinone reduction, and the transmembrane helix subunits of the membrane arm. Transduction of conformational changes to drive the transmembrane transporters linked by a connecting rod during the reduction of ubiquinone can account for two or three of the four protons pumped per NADH oxidized. The remaining proton must be pumped by direct coupling at the ubiquinone-binding site. It is proposed that direct and indirect coupling mechanisms account for the pumping of the four protons.
The N2 cluster's proximity to a nearby cysteine residue results in a conformational change upon reduction in the nearby helices, leading to small but important changes in the overall protein conformation. Further electron paramagnetic resonance studies of the electron transfer have demonstrated that most of the energy that is released during the subsequent CoQ reduction is on the final ubiquinol formation step from semiquinone, providing evidence for the "single stroke" H translocation mechanism (i.e. all four protons move across the membrane at the same time). Alternative theories suggest a "two stroke mechanism" where each reduction step (semiquinone and ubiquinol) results in a stroke of two protons entering the intermembrane space.
The resulting ubiquinol localized to the membrane domain interacts with negatively charged residues in the membrane arm, stabilizing conformational changes. An antiporter mechanism (Na/H swap) has been proposed using evidence of conserved Asp residues in the membrane arm. The presence of Lys, Glu, and His residues enable for proton gating (a protonation followed by deprotonation event across the membrane) driven by the pK of the residues. | 1 | Biochemistry |
When a force is applied on a spring, and the length of the spring changes by a differential amount dx, the work done is
For linear elastic springs, the displacement x is proportional to the force applied
where K is the spring constant and has the unit of N/m. The displacement x is measured from the undisturbed position of the spring (that is, when ). Substituting the two equations
where x and x are the initial and the final displacement of the spring respectively, measured from the undisturbed position of the spring. | 7 | Physical Chemistry |
Transforming growth factor beta-1-induced transcript 1 plays a role in a number of cell functions. Originally, TGFB1I1 was isolated as a senescence-inducing gene from mouse osteoblastic cells through treatment with transforming growth factor beta-1 and hydrogen peroxide. During this, TGFB1I1 was also being independently discovered by numerous other groups and was characterized as a focal adhesion protein, an androgen and glucocorticoid receptor co-activator, a negative regulator of muscle differentiation, and major player in the recovery of arterial media. | 1 | Biochemistry |
Blue carbon is defined by the IPCC as: "Biologically driven carbon fluxes and storage in marine systems that are amenable to management."
Another definition states: "Blue carbon refers to organic carbon that is captured and stored by the oceans and coastal ecosystems, particularly by vegetated coastal ecosystems: seagrass meadows, tidal marshes, and mangrove forests."
Coastal blue carbon focuses on "rooted vegetation in the coastal zone, such as tidal marshes, mangroves and seagrasses". Seagrass, salt marshes and mangroves are sometimes referred to as "blue forests" in contrast to land-based "green forests".
Deep blue carbon is located in the high seas beyond national jurisdictions. It includes carbon contained in "continental shelf waters, deep-sea waters and the sea floor beneath them" and makes up 90% of all ocean carbon. Deep blue carbon is generally seen as "less amenable to management" and challenging due to lack of data "relating to the permanence of their carbon stores". | 9 | Geochemistry |
Reasons cited for indoor tanning include improving appearance, acquiring a pre-holiday tan, feeling good and treating a skin condition. Tanners often cite feelings of well-being; exposure to tanning beds is reported to "increase serum beta-endorphin levels by 44%". Beta-endorphin is associated with feelings of relaxation and euphoria, including "runner's high".
Improving appearance is the most-cited reason. Studies show that tanned skin has semiotic power, signifying health, beauty, youth and the ability to seduce. Women, in particular, say not only that they prefer their appearance with tanned skin, but that they receive the same message from friends and family, especially from other women. They believe tanned skin makes them look thinner and more toned, and that it covers or heals skin blemishes such as acne. Other reasons include acquiring a base tan for further sunbathing; that a uniform tan is easier to achieve in a tanning unit than in the sun, and a desire to avoid tan lines. Proponents of indoor tanning say that tanning beds deliver more consistent, predictable exposure than the sun, but studies show that indoor tanners do suffer burns. In two surveys in the US in 1998 and 2004, 58% of indoor tanners said they had been burned during sessions. | 5 | Photochemistry |
Plasmonic nanoparticles can be individually analyzed through optoelectrochemical imaging (in which electrochemical processes are measured by optical means). When electrochemistry is performed on a nanoparticle, the refractive index of its environment will change resulting in a shift of the localized surface plasmon resonance. The spectral difference can be measured through characterization techniques such as darkfield microscopy to monitor electrochemical reactions at the surface of plasmonic nanoparticles.
Plasmonics-based electrochemical current microscopy (PECM) measures the contrast that appears from the interference of localized surface plasmon scattered light and reflected light that, like above, is sensitive to changes in the refractive index. This can be used to quantify the electrocatalytic reactions occurring at Pt nanoparticles. Since nanoparticles are inherently heterogenous (which affects catalytic activity), SEE methods can provide more information than traditional methods that measure the average of an ensemble of nanoparticles. | 7 | Physical Chemistry |
Tagging technology and instrument development occurred at the University of Toronto and DVS Sciences, Inc. CyTOF (cytometry by time of flight) was initially commercialized by DVS Sciences in 2009. In 2014, Fluidigm acquired DVS Sciences to become a reference company in single cell technology. In 2022 Fluidigm received a capitol infusion and changed its name to Standard BioTools. The CyTOF, CyTOF2, Helios (CyTOF3) and CyTOF XT(4th generation) have been commercialized up to now. Fluidigm sells a variety of commonly used metal-antibody conjugates, and an antibody conjugation kit. | 3 | Analytical Chemistry |
The process of extracting and reducing gold from pyrite in gold ores using chlorine gas was initially introduced by Karl Friedrich Plattner around 1848. | 8 | Metallurgy |
Bauxite ore is a mixture of hydrated aluminium oxides and compounds of other elements such as iron. The aluminium compounds in the bauxite may be present as gibbsite (Al(OH)), böhmite (γ-AlO(OH)) or diaspore (α-AlO(OH)); the different forms of the aluminium component and the impurities dictate the extraction conditions. Aluminium oxides and hydroxides are amphoteric, meaning that they are both acidic and basic. The solubility of Al(III) in water is very low but increases substantially at either high or low pH. In the Bayer process, bauxite ore is heated in a pressure vessel along with a sodium hydroxide solution (caustic soda) at a temperature of 150 to 200 °C. At these temperatures, the aluminium is dissolved as sodium aluminate (primarily [Al(OH)]) in an extraction process. After separation of the residue by filtering, gibbsite is precipitated when the liquid is cooled and then seeded with fine-grained aluminium hydroxide crystals from previous extractions. The precipitation may take several days without addition of seed crystals.
The extraction process (digestion) converts the aluminium oxide in the ore to soluble sodium aluminate, NaAlO, according to the chemical equation:
:AlO + 2 NaOH → 2 NaAlO + HO
This treatment also dissolves silica, forming sodium silicate :
:2 NaOH + SiO → NaSiO + HO
The other components of Bauxite, however, do not dissolve. Sometimes lime is added at this stage to precipitate the silica as calcium silicate. The solution is clarified by filtering off the solid impurities, commonly with a rotary sand trap and with the aid of a flocculant such as starch, to remove the fine particles. The undissolved waste after the aluminium compounds are extracted, bauxite tailings, contains iron oxides, silica, calcia, titania and some unreacted alumina. The original process was that the alkaline solution was cooled and treated by bubbling carbon dioxide through it, a method by which aluminium hydroxide precipitates:
:2 NaAlO + 3 HO + CO → 2 Al(OH) + NaCO
But later, this gave way to seeding the supersaturated solution with high-purity aluminium hydroxide (Al(OH)) crystal, which eliminated the need for cooling the liquid and was more economically feasible:
:2 HO + NaAlO → Al(OH) + NaOH
Some of the aluminium hydroxide produced is used in the manufacture of water treatment chemicals such as aluminium sulfate, PAC (Polyaluminium chloride) or sodium aluminate; a significant amount is also used as a filler in rubber and plastics as a fire retardant. Some 90% of the gibbsite produced is converted into aluminium oxide, AlO, by heating in rotary kilns or fluid flash calciners to a temperature of about 1470 K.
:2 Al(OH) → AlO + 3 HO
The left-over, spent sodium aluminate solution is then recycled. Apart from improving the economy of the process, recycling accumulates gallium and vanadium impurities in the liquors, so that they can be extracted profitably.
Organic impurities that accumulate during the precipitation of gibbsite may cause various problems, for example high levels of undesirable materials in the gibbsite, discoloration of the liquor and of the gibbsite, losses of the caustic material, and increased viscosity and density of the working fluid.
For bauxites having more than 10% silica, the Bayer process becomes uneconomic because of the formation of insoluble sodium aluminium silicate, which reduces yield, so another process must be chosen.
1.9-3.6 tons of bauxite (corresponding to about 90% of the alumina content of the bauxite) is required to produce 1 ton of aluminium oxide. This is due to a majority of the aluminium in the ore being dissolved in the process. Energy consumption is between 7 GJ/tonne to 21 GJ/tonne (depending on process), of which most is thermal energy. Over 90% (95-96%) of the aluminium oxide produced is used in the Hall–Héroult process to produce aluminium. | 8 | Metallurgy |
Many of the more popular terms used in discussing the compensation effect are specific to their field or phenomena. In these contexts, the unambiguous terms are preferred. The misapplication of and frequent crosstalk between fields on this matter has, however, often led to the use of inappropriate terms and a confusing picture. For the purposes of this entry different terms may refer to what may seem to be the same effect, but that either a term is being used as a shorthand (isokinetic and isoequilibrium relationships are different, yet are often grouped together synecdochically as isokinetic relationships for the sake of brevity) or is the correct term in context. This section should aid in resolving any uncertainties. (see Criticism section for more on the variety of terms)
compensation effect/rule : umbrella term for the observed linear relationship between: (i) the logarithm of the preexponential factors and the activation energies, (ii) enthalpies and entropies of activation, or (iii) between the enthalpy and entropy changes of a series of similar reactions.
enthalpy-entropy compensation : the linear relationship between either the enthalpies and entropies of activation or the enthalpy and entropy changes of a series of similar reactions.
isoequilibrium relation (IER), isoequilibrium effect : On a Van 't Hoff plot, there exists a common intersection point describing the thermodynamics of the reactions. At the isoequilibrium temperature , all the reactions in the series should have the same equilibrium constant ()
isokinetic relation (IKR), isokinetic effect : On an Arrhenius plot, there exists a common intersection point describing the kinetics of the reactions. At the isokinetic temperature , all the reactions in the series should have the same rate constant ()
isoequilibrium temperature : used for thermodynamic LFERs; refers to in the equations where it possesses dimensions of temperature
isokinetic temperature : used for kinetic LFERs; refers to in the equations where it possesses dimensions of temperature
kinetic compensation : an increase in the preexponential factors tends to compensate for the increase in activation energy:
Meyer-Neldel rule (MNR) : primarily used in materials science and condensed matter physics; the MNR is often stated as the plot of the logarithm of the preexponential factor against activation energy is linear:
where is the preexponential factor, is the activation energy, σ is the conductivity, and is Boltzmann's constant, and is temperature. | 7 | Physical Chemistry |
In electrochemistry, and more generally in solution chemistry, a Pourbaix diagram, also known as a potential/pH diagram, E–pH diagram or a pE/pH diagram, is a plot of possible thermodynamically stable phases (i.e., at chemical equilibrium) of an aqueous electrochemical system. Boundaries (50 %/50 %) between the predominant chemical species (aqueous ions in solution, or solid phases) are represented by lines. As such a Pourbaix diagram can be read much like a standard phase diagram with a different set of axes. Similarly to phase diagrams, they do not allow for reaction rate or kinetic effects. Beside potential and pH, the equilibrium concentrations are also dependent upon, e.g., temperature, pressure, and concentration. Pourbaix diagrams are commonly given at room temperature, atmospheric pressure, and molar concentrations of 10 and changing any of these parameters will yield a different diagram.
The diagrams are named after Marcel Pourbaix (1904–1998), the Russian-born Belgian chemist who invented them. | 7 | Physical Chemistry |
A molecule that allows the genetic material to be realized as a protein was first hypothesized by François Jacob and Jacques Monod. Severo Ochoa won a Nobel Prize in Physiology or Medicine in 1959 for developing a process for synthesizing RNA in vitro with polynucleotide phosphorylase, which was useful for cracking the genetic code. RNA synthesis by RNA polymerase was established in vitro by several laboratories by 1965; however, the RNA synthesized by these enzymes had properties that suggested the existence of an additional factor needed to terminate transcription correctly.
Roger D. Kornberg won the 2006 Nobel Prize in Chemistry "for his studies of the molecular basis of eukaryotic transcription". | 1 | Biochemistry |
Many systems of interest have a total density of states with the power-law form:
for some values of , , . The results of preceding sections generalize to dimensions, giving a power law with:
* for non-relativistic particles in a -dimensional box,
* for non-relativistic particles in a -dimensional harmonic potential well,
* for hyper-relativistic particles in a -dimensional box.
For such a power-law density of states, the grand potential integral evaluates exactly to:
where is the complete Fermi–Dirac integral (related to the polylogarithm). From this grand potential and its derivatives, all thermodynamic quantities of interest can be recovered. | 7 | Physical Chemistry |
The kinetic theory of gases entails that due to the microscopic reversibility of the gas particles' detailed dynamics, the system must obey the principle of detailed balance. Specifically, the fluctuation-dissipation theorem applies to the Brownian motion (or diffusion) and the drag force, which leads to the Einstein–Smoluchowski equation:where
* is the diffusion coefficient;
* is the "mobility", or the ratio of the particle's terminal drift velocity to an applied force, ;
* is the Boltzmann constant;
* is the absolute temperature.
Note that the mobility can be calculated based on the viscosity of the gas; Therefore, the Einstein–Smoluchowski equation also provides a relation between the mass diffusivity and the viscosity of the gas. | 7 | Physical Chemistry |
Another FCS based approach to studying molecular interactions uses fluorescence resonance energy transfer (FRET) instead of fluorescence, and is called FRET-FCS. With FRET, there are two types of probes, as with FCCS; however, there is only one channel and light is only detected when the two probes are very close—close enough to ensure an interaction. The FRET signal is weaker than with fluorescence, but has the advantage that there is only signal during a reaction (aside from autofluorescence). | 7 | Physical Chemistry |
Due to its density, tetrafluoromethane can displace air, creating an asphyxiation hazard in inadequately ventilated areas. Otherwise, it is normally harmless due to its stability. | 2 | Environmental Chemistry |
In the carbylamine reaction (also known as the Hofmann isocyanide synthesis) alkali base reacts with chloroform to produce dichlorocarbene. The carbene then converts primary amines to isocyanides. Illustrative is the synthesis of tert-butyl isocyanide from tert-butylamine in the presence of catalytic amount of the phase transfer catalyst benzyltriethylammonium chloride.
As it is only effective for primary amines this reaction can be used as a chemical test for their presence. | 0 | Organic Chemistry |
Nucleotides can undergo enzyme-catalyzed intramolecular cyclization in order to produce several important biological molecules. These cyclizations typically proceed through an oxocarbenium intermediate. An example of this reaction can be seen in the cyclization cyclic ADP ribose, which is an important molecule for intracellular calcium signaling. | 0 | Organic Chemistry |
One of the potent applications of siRNAs is the ability to distinguish the target versus non-target sequence with a single-nucleotide difference. This approach has been considered as therapeutically crucial for the silencing dominant gain-of-function (GOF) disorders,where mutant allele causing disease is differed from wt-allele by a single nucleotide (nt). These types of siRNAs with the capability to distinguish a single-nt difference, are termed as, allele-specific siRNAs.
ASP-RNAi is an innovative category of RNAi with the objective of suppressing the dominant mutant allele while sparing expression of the corresponding normal allele with the specificity of single-nucleotide differences between the two. ASP-siRNAs are potentially a novel and better remedial alternative for the treatment of autosomal dominant genetic disorders especially in cases where wild-type allele expression is crucial for organism survival such as Huntington disease (HD),DYT1 dystonia (Gonzalez-Alegre et al. 2003, 2005), Alzheimers disease (Sierant et al. 2011), Parkinsons disease (PD) (Takahashi et al. 2015), amyloid lateral sclerosis (ALS) (Schwarz et al. 2006), and Machado–Joseph disease (Alves et al. 2008). Their therapeutic potential has also been assessed for various skin disorders like epidermolysis bullosa simplex (Atkinson et al. 2011), epidermolytic palmoplantar keratoderma (EPPK) (Lyu et al. 2016), and lattice corneal dystrophy type I (LCDI) (Courtney et al. 2014). | 1 | Biochemistry |
For many polymers, the change between the initial lamellar thickness at T is roughly the same as at T and can thus be modeled by the Gibbs–Thomson equation fairly well. However, since it implies that the lamellar thickness over the given supercooling range (T–T) is unchanged, and many homogeneous nucleation of polymers implies a change of thickness at the growth front, Hoffman and Weeks pursued a more accurate representation. In this regard, the Hoffman-Weeks plot was created and can be modeled through the equation
where β is representative of a thickening factor given by L = L β and Tand T are the crystallization and melting temperatures, respectively.
Applying this experimentally for a constant β allows for the determination of the equilibrium melting temperature, T° at the intersection of Tand T. | 7 | Physical Chemistry |
The Goldich dissolution series follows the same pattern of the Bowen's reaction series, with the minerals that are first to crystallize also the first the undergo chemical weathering. The Bowen’s reaction series dictates that during fractional crystallization, olivine and Ca-plagioclase feldspars are the first to crystalize out of a melt, after which follows pyroxene, amphibole, biotite, Na-plagioglase, orthoclase feldspar, muscovite, and finally, quartz. This order is controlled by the temperature of the melt and its composition. Because earlier crystallizing minerals are more stable at higher temperatures and pressures, these weather the fastest under surface conditions. | 9 | Geochemistry |
A variety of alternative heteroatom oxidation reagents are known, including peroxides (often employed with a transition metal catalyst) and oxaziridines. These reagents do not suffer from the over-oxidation problems and decomposition issues associated with dioxiranes; however, their substrate scope tends to be more limited. Nucleophilic decomposition of dioxiranes to singlet oxygen is a unique problem associated with dioxirane heteroatom oxidations. Although chiral dioxiranes do not provide the same levels of enantioselectivity as other protocols, such as Kagan's sulfoxidation system, complexation to a chiral transition metal complex followed by oxidation affords optically active sulfoxides with good enantioselectivity.
Oxidation of arenes and cumulenes leads initially to epoxides. These substrates are resistant to many epoxidation reagents, including oxaziridines, hydrogen peroxide, and manganese oxo compounds. Organometallic oxidants also react sluggishly with these compounds, with the exception of methyltrioxorhenium. Peracids also react with arenes and cumulenes, but cannot be employed with substrates containing acid-sensitive functionality.
The direct oxidative functionalization of C-H bonds is an ongoing problem in oxidation chemistry. Among metal-free systems, dioxiranes are the best oxidants for the conversion of C-H bonds to alcohols or carbonyls. However, some catalytic transition-metal systems, such as White's palladium-sulfoxide system, are able to oxidize C-H bonds selectively. | 0 | Organic Chemistry |
The technique is commonly used for analyzing the chemical composition of metals, alloys, ceramics, and glasses. It is particularly useful for assessing the composition of individual particles or grains and chemical changes on the scale of a few micrometres to millimeters. The electron microprobe is widely used for research, quality control, and failure analysis. | 3 | Analytical Chemistry |
* The Zelinsky Institute of Organic Chemistry of Russian Academy of Sciences is named after him since 1953;
* In 1961, a postage stamp was issued in honor of N. D. Zelinsky in the USSR;
* One of the Moscow streets is named after him, as well as streets in the cities of Voskresensk (Moscow region), Tiraspol, Chisinau, Tyumen, Yaroslavl, Veliky Novgorod, Orsk, Karaganda, Daugavpils, Alma-Ata and Mariupol;
* On the occasion of the 150th anniversary of the birth of the scientist, the State Unitary Enterprise “Marka Pridnestrovya” issued a series of stamps and envelopes;
* The large chemical auditorium of the Faculty of Chemistry of Moscow State University is named after Zelinsky;
* The crater Zelinskiy on the Moon is named in his honor (since 1970);
* On June 2, 2014, the name of Nikolai Dmitrievich Zelinsky was given to an enterprise producing personal and collective protective equipment - JSC Elektrostal Chemical and Mechanical Plant;
* May 19, 2016 in St. Petersburg on the building of the Research Institute of Metrology. D. I. Mendeleev (Moskovsky Prospekt, 19) a commemorative plaque was installed (sculptor-artist V. A. Sivakov) with the text: “Here, in 1915, the outstanding scientist Nikolai Dmitrievich Zelinsky invented a coal gas mask” | 0 | Organic Chemistry |
In bacteria, the promoter contains two short sequence elements approximately 10 (Pribnow Box) and 35 nucleotides upstream from the transcription start site.
* The sequence at -10 (the -10 element) has the consensus sequence TATAAT.
* The sequence at -35 (the -35 element) has the consensus sequence TTGACA.
* The above consensus sequences, while conserved on average, are not found intact in most promoters. On average, only 3 to 4 of the 6 base pairs in each consensus sequence are found in any given promoter. Few natural promoters have been identified to date that possess intact consensus sequences at both the -10 and -35; artificial promoters with complete conservation of the -10 and -35 elements have been found to transcribe at lower frequencies than those with a few mismatches with the consensus.
* The optimal spacing between the -35 and -10 sequences is 17 bp.
* Some promoters contain one or more upstream promoter element (UP element) subsites (consensus sequence 5-AAAAAARNR-3 when centered in the -42 region; consensus sequence 5-AWWWWWTTTTT-3 when centered in the -52 region; W = A or T; R = A or G; N = any base).
The above promoter sequences are recognized only by RNA polymerase holoenzyme containing sigma-70. RNA polymerase holoenzymes containing other sigma factors recognize different core promoter sequences.
upstream downstream
5-XXXXXXXPPPPPPXXXXXXPPPPPPXXXXGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGXXXX-3
-35 -10 Gene to be transcribed | 1 | Biochemistry |
Unlike in vivo MRS which is intensively used in clinical settings, fMRS is used primarily as a research tool, both in a clinical context, for example, to study metabolite dynamics in patients with epilepsy, migraine and dyslexia, and to study healthy brains.
fMRS can be used to study metabolism dynamics also in other parts of the body, for example, in muscles and heart; however, brain studies have been far more popular.
The main goals of fMRS studies are to contribute to the understanding of energy metabolism in the brain, and to test and improve data acquisition and quantification techniques to ensure and enhance validity and reliability of fMRS studies. | 7 | Physical Chemistry |
Because of its antimicrobial activity, it is used to treat ich in fish. However, it usually is illegal to use in fish intended for human consumption. | 3 | Analytical Chemistry |
Localized electronic effects are a combination of inductive and field effects. Due to the similarity in these effects, it is difficult to separate their contributions to the electronic structure of a molecule. There is, however, a large body of literature devoted to developing an understanding of the relative significance of induction and field effects by analyzing related compounds in an attempt to quantify each effect based on the present substituents and molecular geometry. For example, the three compounds to the right, all octanes, differ only in the number of linkers between the electron withdrawing group X and an acidic functional group, which are approximately the same spatial distance apart in each compound. It is known that an electron-withdrawing substituent will decrease the pKa of a given proton (i.e. increase the acidity) inductively. If induction was the dominant effect in these compounds, acidity should increase linearly with the number of available inductive pathways (linkers). However, the experimental data shows that effect on acidity in related octanes and cubanes is very similar, and therefore the dominant effect must be through space.
In the cis-11,12-dichloro-9,10-dihydro-9,10-ethano-2-anthroic acid syn and anti isomers seen below and to the left, the chlorines provide a field effect. The concentration of negative charge on each chlorine has a through space effect which can be seen in the relative pKa values. When the chlorines are pointed over the carboxylic acid group, the pKa is higher because loss of a proton is less favorable due to the increase in negative charge in the area. Loss of a proton results in a negative charge which is less stable if there is already an inherent concentration of electrons. This can be attributed to a field effect because in the same compound with the chlorines pointed away from the acidic group the pKa is lower, and if the effect were inductive the conformational position would not matter. | 7 | Physical Chemistry |
When Bacillus subtilis is not under stress conditions, it is negatively regulated by the anti-sigma factor, Rsbw. RsbW is an anti-sigma factor that regulates another anti-sigma factor, sigma B. RsbW binds to sigma B and prevents it from forming an RNA polymerase holoenzyme. However, in stressed conditions, the unphosphorylated form of the protein, RsbV, competes with Sigma B for binding to RsbW. RsbV binds to RsbW, allowing sigma B to bind to the core RNA polymerase, resulting in the expression of stress response. | 1 | Biochemistry |
A patented cultivar of yeast (Saccharomyces cerevisiae CNCM I-3060) marketed as Sel-Plex® has been approved for use in animal fodder:
* U.S. Food and Drug Administration approval for use as a supplement to feed for chickens, turkeys, swine, goats, sheep, horses, dogs, bison, and beef and dairy cows.
* Organic Materials Review Institute approval for use as a feed supplement for all animal species.
* As of 2006, the European Food Safety Authority's Scientific Panel on Additives and Products or Substances used in Animal Feed allows the use of Sel-Plex® in animal fodder for poultry, swine, and bovines, as the selenium is not significantly bio-accumulated by the human consumer. Only a small amount should be used when blending animal feeds, 10x the authorized maximum selenium intake causes a drop in production. Appropriate measures to minimize inhalation exposure to the product should be taken. | 1 | Biochemistry |
Pol III has three classes of initiation, which start with different factors recognizing different control elements but all converging on TFIIIB (similar to TFIIB-TBP; consists of TBP/TRF, a TFIIB-related factor, and a B″ unit) recruiting the Pol III preinitiation complex. The overall architecture resembles that of Pol II. Only TFIIIB needs to remain attached during elongation. | 1 | Biochemistry |
The mechanism by which conservative transposition occurs is called the "cut-and-paste" method, which involves five main steps:
# The transposase enzyme is bound to the inverted repeated sequences flanking the ends of the transposon Inverted repeats define the ends of transposons and provide recognition sites for transposase to bind.
# The formation of the transposition complex In this step the DNA bends and folds into a pre-excision synaptic complex so the two transposases enzymes can interact.
# The interaction of these transposases activates the complex; transposase makes double stranded breaks in the DNA and the transposon is fully excised.
# The transposase enzymes locate, recognize and bind to the target site within the target DNA.
# Transposase creates a double stranded break in the DNA and integrates the transposon into the target site.
Both the excision and insertion of the transposon leaves single or double stranded gaps in the DNA, which are repaired by host enzymes such as DNA polymerase. | 1 | Biochemistry |
Aggressive mimicry through the use of chemicals is used among a wide variety of animals. It functions to either lure the deceived organism to the deceiver or it allows for the organism to accept the presence of a parasite. The chemical mimicry used by parasites allows for the deceived organism to accept the presence of the deceiver while they benefit from either taking up food supplies or directly preying on the host species from within their nest. | 1 | Biochemistry |
Although many of Photaki's important contributions were related to peptide synthesis, her scientific work touched on a large number of topics within organic synthesis. In total she published around 50 papers in international English- or German-language chemical journals. | 0 | Organic Chemistry |
Diazirines are often used as photoreactive crosslinking reagents, as the reactive carbenes they form upon irradiation with UV light can insert into C-H, N-H, and O-H bonds. This results in proximity dependent labeling of other species with the diazirine containing compound.
Diazirines are often preferred to other photoreactive crosslinking reagents due to their smaller size, longer irradiation wavelength, short period of irradiation required, and stability in the presence of various nucleophiles, and in both acidic and basic conditions. Benzophenones, which form reactive triplet carbonyl species upon irradiation, often require long periods of irradiation which can result in non-specific labeling, and moreover are often inert to various polar solvents. Aryl azides require a low wavelength of irradiation, which can damage the biological macromolecules under investigation. | 5 | Photochemistry |
The Zintl-Klemm-Busmann concept describes how in an anionic cluster, the atoms arrange in typical geometries found for the element to the right of it on the periodic table. So “the anionic lattice is isometric with elemental lattices having the same number of valence electrons.” In this formulation, the average charge on each atom of the cluster can be calculated by:
where n is number of anion atoms and VEC is the valence electron concentration per anion atom, then:
The number of bonds per anion predicts structure based on isoelectronic neighbor. This rule is also referred to as the 8 - N rule and can also be written as:
Not all phases follow the Zintl-Klemm-Busmann concept, particularly when there is a high content of either the electronegative or electropositive element. There are still other examples where this does not apply. | 7 | Physical Chemistry |
In order for proper gene expression to occur, transcription must stop at specific sites. Two termination mechanisms are well known:
*Intrinsic termination (also called Rho-independent termination): Specific DNA nucleotide sequences signal the RNA polymerase to stop. The sequence is commonly a palindromic sequence that causes the strand to loop which stalls the RNA polymerase. Generally, this type of termination follows the same standard procedure. A pause will occur due to a polyuridine sequence that allows the formation of a hairpin loop. This hairpin loop will aid in forming a trapped complex, which will ultimately cause the dissociation of RNA polymerase from the template DNA strand and halt transcription.
*Rho-dependent termination: ρ factor (rho factor) is a terminator protein that attaches to the RNA strand and follows behind the polymerase during elongation. Once the polymerase nears the end of the gene it is transcribing, it encounters a series of G nucleotides which causes it to stall. This stalling allows the rho factor to catch up to the RNA polymerase. The rho protein then pulls the RNA transcript from the DNA template and the newly synthesized mRNA is released, ending transcription. Rho factor is a protein complex that also displays helicase activities (is able to unwind the nucleic acid strands). It will bind to the DNA in cytosine rich regions and when RNA polymerase encounters it, a trapped complex will form causing the dissociation of all molecules involved and end transcription.
The termination of DNA transcription in bacteria may be stopped by certain mechanisms wherein the RNA polymerase will ignore the terminator sequence until the next one is reached. This phenomenon is known as antitermination and is utilized by certain bacteriophages. | 1 | Biochemistry |
Many transition-metal compounds violate this rule due to the formation of complex ions, a scenario not part of the equilibria that are involved in simple precipitation of salts from ionic solution. For example, copper(I) chloride is insoluble in water, but it dissolves when chloride ions are added, such as when hydrochloric acid is added. This is due to the formation of soluble CuCl complex ions. | 7 | Physical Chemistry |
It is an aggressive electrophile and readily hydrolyzes to the strong acid triflic acid. It is very harmful to skin and eyes. | 0 | Organic Chemistry |
Mycoestrogens are commonly found in stored grain. They can come from fungi growing on the grain as it grows, or after harvest during storage. Mycoestrogens can be found in silage. Some estimates state that 25% of global cereal production and 20% of global plant production may be at some point contaminated by mycotoxins of which mycoestrogens, especially those from fusarium strains, may make up a significant portion. Among mycoestrogens that contaminate plants are ZEN and its phase I metabolites. The limit for ZEN in unprocessed cereals, milling products, and cereal foodstuffs is 20-400 μg/kg (depending on the product in question). | 1 | Biochemistry |
René Roy (born November 4, 1952) is a Canadian organic chemist from Quebec, specializing in glycobiology and carbohydrate chemistry. He is professor emeritus, Department of chemistry, at the Université du Québec à Montréal (UQAM) and associate professor at the Institut National de la Recherche Scientifique (INRS) – Institut Armand-Frappier (IAF). He is the founder and former director of PharmaQAM, a biopharmaceutical research center based at UQAM, focusing on the discovery of new bioactive molecules, their mechanism of action and the vectorization of drugs.
He is a pioneer in the development of synthetic glycoconjugate vaccines both for human and veterinary health, having co-developed the first and sole marketed semi-synthetic vaccine for human use, preventing bacterial meningitis and pneumonia in developing countries. | 0 | Organic Chemistry |
Located within the thylakoid membrane and the inner mitochondrial membrane, ATP synthase consists of two regions F and F. F causes rotation of F and is made of c-ring and subunits a, two b, F6. F is made of α, β, γ, and δ subunits. F has a water-soluble part that can hydrolyze ATP. F on the other hand has mainly hydrophobic regions. F F creates a pathway for protons movement across the membrane. | 5 | Photochemistry |
The hypersalinity and high alkalinity (pH=10 or equivalent to 4 milligrams of NaOH per liter of water) of the lake means that no fish are native to the lake. An attempt by the California Department of Fish and Game to stock the lake failed.
The whole food chain of the lake is based on the high population of single-celled planktonic algae present in the photic zone of the lake. These algae reproduce rapidly during winter and early spring after winter runoff brings nutrients to the surface layer of water. By March the lake is "as green as pea soup" with photosynthesizing algae.
The lake is famous for the Mono Lake brine shrimp, Artemia monica, a tiny species of brine shrimp, no bigger than a thumbnail, that are endemic to the lake. During the warmer summer months, an estimated 4–6 trillion brine shrimp inhabit the lake. Brine shrimp have no food value for humans, but are a staple for birds of the region. The brine shrimp feed on microscopic algae.
Alkali flies, Ephydra hians, live along the shores of the lake and walk underwater, encased in small air bubbles, for grazing and to lay eggs. These flies are an important source of food for migratory and nesting birds.
Eight nematode species were found living in the littoral sediment:
* Auanema spec., which is outstanding for its extreme arsenic resistance (survives concentrations 500 times higher than humans), having 3 sexes, and being viviparous.
* Pellioditis spec.
* Mononchoides americanus
* Diplogaster rivalis
* species of the family Mermithidae
* Prismatolaimus dolichurus
* 2 species of the order Monhysterida | 2 | Environmental Chemistry |
Self-assembled monolayers (SAM) of organic molecules are molecular assemblies formed spontaneously on surfaces by adsorption and are organized into more or less large ordered domains. In some cases molecules that form the monolayer do not interact strongly with the substrate. This is the case for instance of the two-dimensional supramolecular networks of e.g. perylenetetracarboxylic dianhydride (PTCDA) on gold or of e.g. porphyrins on highly oriented pyrolitic graphite (HOPG). In other cases the molecules possess a head group that has a strong affinity to the substrate and anchors the molecule to it. Such a SAM consisting of a head group, tail and functional end group is depicted in Figure 1. Common head groups include thiols, silanes, phosphonates, etc.
SAMs are created by the chemisorption of "head groups" onto a substrate from either the vapor or liquid phase followed by a slow organization of "tail groups". Initially, at small molecular density on the surface, adsorbate molecules form either a disordered mass of molecules or form an ordered two-dimensional "lying down phase", and at higher molecular coverage, over a period of minutes to hours, begin to form three-dimensional crystalline or semicrystalline structures on the substrate surface. The "head groups" assemble together on the substrate, while the tail groups assemble far from the substrate. Areas of close-packed molecules nucleate and grow until the surface of the substrate is covered in a single monolayer.
Adsorbate molecules adsorb readily because they lower the surface free-energy of the substrate and are stable due to the strong chemisorption of the "head groups." These bonds create monolayers that are more stable than the physisorbed bonds of Langmuir–Blodgett films. A trichlorosilane based "head group", for example in a FDTS molecule, reacts with a hydroxyl group on a substrate, and forms very stable, covalent bond [R-Si-O-substrate] with an energy of 452 kJ/mol. Thiol-metal bonds are on the order of 100 kJ/mol, making them fairly stable in a variety of temperatures, solvents, and potentials. The monolayer packs tightly due to van der Waals interactions, thereby reducing its own free energy. The adsorption can be described by the Langmuir adsorption isotherm if lateral interactions are neglected. If they cannot be neglected, the adsorption is better described by the Frumkin isotherm. | 6 | Supramolecular Chemistry |
This form factor does not include a display and these devices are designed to enable a new class of geographically-distributed spectrum monitoring and analysis applications. The key attribute is the ability to connect the analyzer to a network and monitor such devices across a network. While many spectrum analyzers have an Ethernet port for control, they typically lack efficient data transfer mechanisms and are too bulky or expensive to be deployed in such a distributed manner. Key applications for such devices include RF intrusion detection systems for secure facilities where wireless signaling is prohibited. As well cellular operators are using such analyzers to remotely monitor interference in licensed spectral bands. The distributed nature of such devices enable geo-location of transmitters, spectrum monitoring for dynamic spectrum access and many other such applications.
Key attributes of such devices include:
* Network-efficient data transfer
* Low power consumption
* The ability to synchronize data captures across a network of analyzers
* Low cost to enable mass deployment. | 7 | Physical Chemistry |
* Kai genes – Found in the Synechococcus elongatus, these genes are essential components of the cyanobacterium clock, the leading example of bacterial circadian rhythms. Kai proteins regulate genome wide gene expression. The oscillation of phosphorylation and dephosphorylation of KaiC acts as the pacemaker of the circadian clock. | 1 | Biochemistry |
When homebrewing grew in popularity during the economic depression that followed the Finnish banking crisis of the early 1990s, yeast strains known as "turbo yeast" ("turbohiiva", "pikahiiva") were introduced to the market. These yeast strains enable a very rapid fermentation to full cask strength, in some cases in as little as three days (compared to several weeks required by traditional wine yeast strains). Such a short production time naturally does not allow the yeast to become lees. The introduction of turbo yeast reinforced the public's view of kilju as an easy method of procuring cheap alcohol. | 1 | Biochemistry |
In animal experiments diphenylamine was rapidly and completely absorbed after ingestion by mouth. It underwent metabolism to sulfonyl and glucuronyl conjugates and was rapidly excreted mainly via urine. Acute oral and dermal toxicity were low. Diphenylamine can cause severe irritation to the eyes. It was not a skin irritant, and it has not been technically feasible to test acute toxicity study by inhalation. Diphenylamine targets the red blood cell system and can cause abnormal erythropoiesis in the spleen, and thus congestion of the spleen, and haemosiderosis. Changes in liver and kidneys were found upon longer exposure. At clear toxic doses of parent animals reproductive effects were limited to reduced implantation sites in F1 females associated with reduced rat litter size, implicating a possible mutagenic or teratogenic effect. No effect on development could be attributed. The U.S. CDC's NIOSH lists the following symptoms of poisoning: irritation eyes, skin, mucous membrane; eczema; tachycardia, hypertension; cough, sneezing; methemoglobinemia; increased blood pressure and heart rate; proteinuria, hematuria (blood in the urine), bladder injury; in animals: teratogenic effects.
The short-term NOAEL of 9.6 – 10 mg/kg bw/day was derived from 90-day rat, 90-day dog and 1-year dog studies and the long-term NOAEL was 7.5 mg/kg bw/day.
The Acceptable Daily Intake of diphenylamine was 0.075 mg/kg bw/day based on the 2-year rat study, applying a safety factor of 100; the Acceptable Operator Exposure Level was 0.1 mg/kg bw/day.
In a study of diphenylamine metabolism in harvested and dipped apples at different time intervals it was observed that radiolabelled residues of diphenylamine penetrate from the surface into the pulp, which after 40 weeks contained 32% of the residue. Diphenylamine was always the major residue, but 3 metabolites were found in good amounts in the apple samples, whose identification experts considered insufficient.(Kim-Kang, H. 1993. Metabolism of 14C-diphenylamine in stored apples—nature of the residue in plants. Report RPT00124. Study XBL 91071. XenoBiotic Laboratories, Inc., USA, unpublished) cited in There is a data gap on presence or formation of nitrosamines in apple metabolism or during processing. The carcinogen 4-Aminobiphenyl can accompany diphenylamine as an impurity.
Diphenylamine has low acute and short-term toxicity to birds, but is very toxic to aquatic organisms. Risk to biological methods of sewage treatment was assessed as low.
The impurity in commercial diphenylamine which induces polycystic kidney disease in rats was identified in 1981. Laboratory studies with highly purified diphenylamine indicated that the impurity can be formed by heating diphenylamine. | 3 | Analytical Chemistry |
Mesoscopic heat engines are nanoscale devices that may serve the goal of processing heat fluxes and perform useful work at small scales. Potential applications include e.g. electric cooling devices. In such mesoscopic heat engines, work per cycle of operation fluctuates due to thermal noise. There is exact equality that relates average of exponents of work performed by any heat engine and the heat transfer from the hotter heat bath. This relation transforms the Carnots inequality into exact equality. This relation is also a Carnot cycle equality | 7 | Physical Chemistry |
Phillips began his career doing postdoctoral research at the University of Texas at Austin and the Academy of Sciences of the USSR. He was appointed a lecturer in chemistry at the University of Southampton, rising to the status of Reader then becoming Wolfson Professor of Natural Philosophy, at the Royal Institution. In 1981, Phillips became a founding member of the World Cultural Council. In 1989 he moved to Imperial College, London as professor of physical chemistry and held a number of senior posts there.
In 1987 he gave the Royal Institution Christmas Lectures on television. He was appointed Officer of the Order of the British Empire (OBE) in 1999 and Commander of the Order of the British Empire (CBE) in the 2012 New Year Honours for services to chemistry. In May 2011 he was the guest on Desert Island Discs and in June 2012 was Michael Berkeley's guest on Private Passions. | 5 | Photochemistry |
In order to increase the specificity of aptamers selected by a given SELEX procedure, a negative selection, or counter selection, step can be added prior to or immediately following target incubation. To eliminate sequences with affinity for target immobilization matrix components from the pool, negative selection can be used where the library is incubated with target immobilization matrix components and unbound sequences are retained. Negative selection can also be used to eliminate sequences that bind target-like molecules or cells by incubating the oligonucleotide library with small molecule target analogs, undesired cell types, or non-target proteins and retaining the unbound sequences. | 1 | Biochemistry |
A Latimer diagram of a chemical element is a summary of the standard electrode potential data of that element. This type of diagram is named after Wendell Mitchell Latimer, an American chemist. | 7 | Physical Chemistry |
Cellular biomarkers allow cells to be isolated, sorted, quantified and characterized by their morphology and physiology. Cellular biomarkers are used in both clinical and laboratory settings, and can discriminate between a large sample of cells based on their antigens. An example of a cellular biomarker sorting technique is Fluorescent-activated cell sorting. | 1 | Biochemistry |
P1 artificial chromosomes (PACs) have features of both P1 vectors and Bacterial Artificial Chromosomes (BACs). Similar to P1 vectors, they contain a plasmid and a lytic replicon as described above. Unlike P1 vectors, they do not need to be packaged into bacteriophage particles for transduction. Instead they are introduced into E. coli as circular DNA molecules through electroporation just as BACs are. Also similar to BACs, these are relatively harder to prepare due to a single origin of replication. | 1 | Biochemistry |
The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a number of ranges recommended by the ISO standard ISO 21348:
Several solid-state and vacuum devices have been explored for use in different parts of the UV spectrum. Many approaches seek to adapt visible light-sensing devices, but these can suffer from unwanted response to visible light and various instabilities. Ultraviolet can be detected by suitable photodiodes and photocathodes, which can be tailored to be sensitive to different parts of the UV spectrum. Sensitive UV photomultipliers are available. Spectrometers and radiometers are made for measurement of UV radiation. Silicon detectors are used across the spectrum.
Vacuum UV, or VUV, wavelengths (shorter than 200 nm) are strongly absorbed by molecular oxygen in the air, though the longer wavelengths around 150–200 nm can propagate through nitrogen. Scientific instruments can, therefore, use this spectral range by operating in an oxygen-free atmosphere (commonly pure nitrogen), without the need for costly vacuum chambers. Significant examples include 193-nm photolithography equipment (for semiconductor manufacturing) and circular dichroism spectrometers.
Technology for VUV instrumentation was largely driven by solar astronomy for many decades. While optics can be used to remove unwanted visible light that contaminates the VUV, in general; detectors can be limited by their response to non-VUV radiation, and the development of solar-blind devices has been an important area of research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes.
Extreme UV (EUV or sometimes XUV) is characterized by a transition in the physics of interaction with matter. Wavelengths longer than about 30 nm interact mainly with the outer valence electrons of atoms, while wavelengths shorter than that interact mainly with inner-shell electrons and nuclei. The long end of the EUV spectrum is set by a prominent He spectral line at 30.4 nm. EUV is strongly absorbed by most known materials, but synthesizing multilayer optics that reflect up to about 50% of EUV radiation at normal incidence is possible. This technology was pioneered by the NIXT and MSSTA sounding rockets in the 1990s, and it has been used to make telescopes for solar imaging. See also the Extreme Ultraviolet Explorer satellite.
Some sources use the distinction of "hard UV" and "soft UV". For instance, in the case of astrophysics, the boundary may be at the Lyman limit (wavelength 91.2 nm), with "hard UV" being more energetic; the same terms may also be used in other fields, such as cosmetology, optoelectronic, etc. The numerical values of the boundary between hard/soft, even within similar scientific fields, do not necessarily coincide; for example, one applied-physics publication used a boundary of 190 nm between hard and soft UV regions. | 5 | Photochemistry |
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