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Leaching involves the use of aqueous solutions to extract metal from metal-bearing materials which are brought into contact with them. In China in the 11th and 12th centuries, this technique was used to extract copper; this was used for much of the total copper production. In the 17th century it was used for the same purposes in Germany and Spain.
The lixiviant solution conditions vary in terms of pH, oxidation-reduction potential, presence of chelating agents and temperature, to optimize the rate, extent and selectivity of dissolution of the desired metal component into the aqueous phase. By using chelating agents, one can selectively extract certain metals. These agents are typically amines of Schiff bases.
The five basic leaching reactor configurations are in-situ, heap, vat, tank and autoclave. | 8 | Metallurgy |
Benzenediazonium chloride reacts with compounds containing activated double bonds to produce phenylated products. The reaction is called the Meerwein arylation: | 0 | Organic Chemistry |
Oxaziridines with unsubstituted or acylated nitrogens are capable of nitrogen atom transfer, although this reactivity has received considerably less attention. | 0 | Organic Chemistry |
# Despite scientific advances in making microdialysis probes smaller and more efficient, the invasive nature of this technique still poses some practical and ethical limitations. For example, it has been shown that implantation of a microdialysis probe can alter tissue morphology resulting in disturbed microcirculation, rate of metabolism or integrity of physiological barriers, such as the blood–brain barrier. While acute reactions to probe insertion, such as implantation traumas, require sufficient recovery time, additional factors, such as necrosis, inflammatory responses, or wound healing processes have to be taken into consideration for long-term sampling as they may influence the experimental outcome. From a practical perspective, it has been suggested to perform microdialysis experiments within an optimal time window, usually 24–48 hours after probe insertion.
# Microdialysis has a relatively low temporal and spatial resolution compared to, for example, electrochemical biosensors. While the temporal resolution is determined by the length of the sampling intervals (usually a few minutes), the spatial resolution is determined by the dimensions of the probe. The probe size can vary between different areas of application and covers a range of a few millimeters (intracerebral application) up to a few centimeters (subcutaneous application) in length and a few hundred micrometers in diameter.
# Application of the microdialysis technique is often limited by the determination of the probe’s recovery, especially for in vivo experiments. Determination of the recovery may be time-consuming and may require additional subjects or pilot experiments. The recovery is largely dependent on the flow rate: the lower the flow rate, the higher the recovery. However, in practice the flow rate cannot be decreased too much since either the sample volume obtained for analysis will be insufficient or the temporal resolution of the experiment will be lost. It is therefore important to optimize the relationship between flow rate and the sensitivity of the analytical assay. The situation may be more complex for lipophilic compounds as they can stick to the tubing or other probe components, resulting in a low or no analyte recovery. | 1 | Biochemistry |
The complex consists of three main proteins, the RNA helicase Ski2 and the proteins Ski3 and Ski8. This tetramer contains a 370 kDa core complex, containing N-terminal arms and C-terminal arms from Ski3. The helicase core of Ski2 is positioned by both the C-terminal of Ski3 and two subunits of Ski8. | 1 | Biochemistry |
MLST has provided a more richly textured picture of bacteria within human populations and on strain variants that may be pathogenic to human, plants and animals. MLST technique was first used by Maiden et al. (1) to characterize Neisseria meningitidis using six loci. The application of MLST has clearly resolved the major meningococcal lineages known to be responsible for invasive disease around the world. To improve the level of discriminatory power between the major invasive lineages, seven loci are now being used and have been accepted by many laboratories as the method of choice for characterizing meningococcal isolates. It is a well known fact that recombinational exchanges commonly occur in N. meningitidis, leading to rapid diversification of meningococcal clones. MLST has successfully provided a reliable method for characterization of clones within other bacterial species in which the rates of clonal diversification are generally lower. | 1 | Biochemistry |
The principle how SAF Microscopy works is as follows: A fluorescent specimen does not emit fluorescence isotropically when it comes close to a surface, but approximately 70% of the fluorescence emitted is directed into the solid phase. Here, the main part enters the solid body above the critical angle. When the emitter is located just 200 nm above the surface, fluorescent light entering the solid body above the critical angle is decreased dramatically. Hence, SAF Microscopy is ideally suited to discriminate between molecules and particles at or close to surfaces and all other specimen present in the bulk. | 3 | Analytical Chemistry |
The amorphous material produced by melt spinning is considered a soft magnet. That is to say that their natural coercivity is less than 1000 Am-1, which means that the metal's magnetism is more responsive to outside influences and as a result can be easily switched on and off. This makes amorphous metals particularly useful in applications requiring the repeated magnetization and demagnetization of a material in order to function. Certain amorphous alloys also provide the ability to enhance and or channel flux created by electrical currents, making them useful for magnetic shielding and insulation.
The exact magnetic properties of each alloy depend mostly on the atomic composition of the material. For example, nickel-iron alloys with a lower amount of nickel have a high electrical resistance, while those with a higher percentage of nickel have a high magnetic permeability. | 8 | Metallurgy |
Rudd grew up in Bournemouth and attended Bournemouth School for Girls. As a child she wanted to be a physicist. Her uncle was a physicist, and Rudd joined the British Junior Astronomical Association. She was the only girl in a group of 48 boys, and said she was never allowed to look down the telescope. The male dominated environment of physics made Rudd consider a career in chemistry instead. When she was fourteen, she started to use washing machines and liquidisers to create rare sugars and sugar phosphates. She sold these chemicals through and co-founded Wessex Biochemicals. Rudd was an undergraduate chemistry student at Westfield College, then part of the University of London. After earning her degree, she joined Wessex Biochemicals which employed thirty people before being acquired by Sigma-Aldrich. She compelted her PhD in 1995 which was awarded by the Open University. | 1 | Biochemistry |
Strong Acids
* Perchloric acid HClO
* Hydriodic acid HI
* Hydrobromic acid HBr
* Hydrochloric acid HCl
* Sulfuric acid HSO
* Nitric acid HNO
* Chloric acid HClO
* Bromic acid HBrO
* Perbromic acid HBrO
* Periodic acid HIO
* Fluoroantimonic acid HSbF
* Magic acid FSOHSbF
* Carborane superacid H(CHBCl)
* Fluorosulfuric acid FSOH
* Triflic acid CFSOH
Strong Bases
* Lithium hydroxide LiOH
* Sodium hydroxide NaOH
* Potassium hydroxide KOH
* Rubidium hydroxide RbOH
* Caesium hydroxide CsOH
* Calcium hydroxide Ca(OH)
* Strontium hydroxide Sr(OH)
* Barium hydroxide Ba(OH)
* Lithium diisopropylamide (LDA) CHLiN
* Lithium diethylamide (LDEA)
* Sodium amide NaNH
* Sodium hydride NaH
* Lithium bis(trimethylsilyl)amide ((CH)Si)NLi
Salts
* Sodium chloride NaCl
* Potassium nitrate KNO
* Magnesium chloride MgCl
* Sodium acetate CHCOONa | 3 | Analytical Chemistry |
Kilju () is the Finnish word for home made alcoholic beverage typically made of sugar, yeast, and water.
The ABV is around 15–17%, and since it does not contain a sweet reserve it is completely dry. Crude fermented water may be distilled to moonshine. Kilju for consumption is clarified to avoid wine fault, it is a flax-colored liquid with no discernible taste other than that of ethanol; an alcoholic beverage used as an ethanol base for drink mixers. | 1 | Biochemistry |
Decorin is an example of a proteoglycan which functions as a myokine. Kanzleiter et al have established that this myokine is secreted during muscular contraction against resistance, and plays a role in muscle growth. They reported on July 1, 2014: "The small leucine-rich proteoglycan decorin has been described as a myokine for some time. However, its regulation and impact on skeletal muscle (had) not been investigated in detail. In (our recent) study, we report decorin to be differentially expressed and released in response to muscle contraction using different approaches. Decorin is released from contracting human myotubes, and circulating decorin levels are increased in response to acute resistance exercise in humans. Moreover, decorin expression in skeletal muscle is increased in humans and mice after chronic training. Because decorin directly binds myostatin, a potent inhibitor of muscle growth, we investigated a potential function of decorin in the regulation of skeletal muscle growth. In vivo overexpression of decorin in murine skeletal muscle promoted expression of the pro-myogenic factor Mighty, which is negatively regulated by myostatin. We also found Myod1 and follistatin to be increased in response to decorin overexpression. Moreover, muscle-specific ubiquitin ligases atrogin1 and MuRF1, which are involved in atrophic pathways, were reduced by decorin overexpression. In summary, our findings suggest that decorin secreted from myotubes in response to exercise is involved in the regulation of muscle hypertrophy and hence could play a role in exercise-related restructuring processes of skeletal muscle." | 1 | Biochemistry |
It has been suggested that one third of all disease-causing mutations impact on splicing. Common errors include:
*Mutation of a splice site resulting in loss of function of that site. Results in exposure of a premature stop codon, loss of an exon, or inclusion of an intron.
*Mutation of a splice site reducing specificity. May result in variation in the splice location, causing insertion or deletion of amino acids, or most likely, a disruption of the reading frame.
*Displacement of a splice site, leading to inclusion or exclusion of more RNA than expected, resulting in longer or shorter exons.
Although many splicing errors are safeguarded by a cellular quality control mechanism termed nonsense-mediated mRNA decay (NMD), a number of splicing-related diseases also exist, as suggested above.
Allelic differences in mRNA splicing are likely to be a common and important source of phenotypic diversity at the molecular level, in addition to their contribution to genetic disease susceptibility. Indeed, genome-wide studies in humans have identified a range of genes that are subject to allele-specific splicing.
In plants, variation for flooding stress tolerance correlated with stress-induced alternative splicing of transcripts associated with gluconeogenesis and other processes. | 1 | Biochemistry |
Like all fluoroquinolones, levofloxacin is a fluorinated quinolone carboxylic acid. It is a chiral molecule and the pure (−)-(S)-enantiomer of the racemic drug ofloxacin. This enantiomer binds more effectively to the DNA gyrase enzyme and to topoisomerase IV than its (+)-(R)-counterpart. Levofloxacin is referred to as a chiral switch: These are chiral drugs that have already been patent claimed, approved and marketed as racemates (or as mixtures of diastereomers but have since been redeveloped as pure enantiomers. Distinct functional groups on this molecules include a hydroxyl group, carbonyl group, and an aromatic ring.
The substance is used as the hemihydrate, which has the empirical formula CHFNO · HO and a molecular mass of 370.38 g/mol. Levofloxacin is a light-yellowish-white to yellow-white crystal or crystalline powder. A major issue in the synthesis of levofloxacin is identifying correct entries into the benzoxazine core in order to produce the correct chiral form. | 4 | Stereochemistry |
Keith Fagnou (June 27, 1971 – November 11, 2009) was a Canadian organic chemist and studied education and was a professor of chemistry at University of Saskatchewan and associate professor of organic chemistry at the University of Ottawa. His research focused on developing new reactions that avoid unnecessary activation of substrates and that can instead directly functionalize C–H bonds of simple molecules and introduce C–C bonds. | 0 | Organic Chemistry |
The Comins' reagent is a triflyl-donating reagent that is used to synthesize vinyl triflates from the corresponding ketone enolates or dienolates.
It was first reported in 1992 by Daniel Comins. The vinyl triflates prepared are useful as substrates in the Suzuki reaction. | 0 | Organic Chemistry |
In research, whole-genome sequencing can be used in a Genome-Wide Association Study (GWAS) – a project aiming to determine the genetic variant or variants associated with a disease or some other phenotype. | 1 | Biochemistry |
A glycosidase is an enzyme that catalyzes the breakdown of a glycosidic linkage to produce two smaller sugars. This process has important implications in the utilization of stored energy, like glycogen in animals, as well as in the breakdown of cellulose by organisms that feed on plants. In general, aspartic or glutamic acid residues in the active site of the enzyme catalyze the hydrolysis of the glycosidic bond. The mechanism of these enzymes involves an oxocarbenium ion intermediate, a general example of which is shown below. | 0 | Organic Chemistry |
Neutron Activation Analysis has a wide variety of applications including within the fields of archaeology, soil science, geology, forensics, and the semiconductor industry. Forensically, hairs subjected to a detailed forensic neutron analysis to determine whether they had sourced from the same individuals was first used in the trial of John Norman Collins.
Archaeologists use NAA in order to determine the elements that comprise certain artifacts. This technique is used because it is nondestructive and it can relate an artifact to its source by its chemical signature. This method has proven to be very successful at determining trade routes, particularly for obsidian, with the ability of NAA to distinguish between chemical compositions. In agricultural processes, the movement of fertilizers and pesticides is influenced by surface and subsurface movement as it infiltrates the water supplies. In order to track the distribution of the fertilizers and pesticides, bromide ions in various forms are used as tracers that move freely with the flow of water while having minimal interaction with the soil. Neutron activation analysis is used to measure bromide so that extraction is not necessary for analysis. NAA is used in geology to aid in researching the processes that formed the rocks through the analysis of the rare-earth elements and trace elements. It also assists in locating ore deposits and tracking certain elements. Neutron activation analysis is also used to create standards in the semiconductor industry. Semiconductors require a high level of purity, with contamination significantly reducing the quality of the semiconductor. NAA is used to detect trace impurities and establish contamination standards, because it involves limited sample handling and high sensitivity. | 3 | Analytical Chemistry |
Surface diffusion is a general process involving the motion of adatoms, molecules, and atomic clusters (adparticles) at solid material surfaces. The process can generally be thought of in terms of particles jumping between adjacent adsorption sites on a surface, as in figure 1. Just as in bulk diffusion, this motion is typically a thermally promoted process with rates increasing with increasing temperature. Many systems display diffusion behavior that deviates from the conventional model of nearest-neighbor jumps. Tunneling diffusion is a particularly interesting example of an unconventional mechanism wherein hydrogen has been shown to diffuse on clean metal surfaces via the quantum tunneling effect.
Various analytical tools may be used to elucidate surface diffusion mechanisms and rates, the most important of which are field ion microscopy and scanning tunneling microscopy. While in principle the process can occur on a variety of materials, most experiments are performed on crystalline metal surfaces. Due to experimental constraints most studies of surface diffusion are limited to well below the melting point of the substrate, and much has yet to be discovered regarding how these processes take place at higher temperatures.
Surface diffusion rates and mechanisms are affected by a variety of factors including the strength of the surface-adparticle bond, orientation of the surface lattice, attraction and repulsion between surface species and chemical potential gradients. It is an important concept in surface phase formation, epitaxial growth, heterogeneous catalysis, and other topics in surface science. As such, the principles of surface diffusion are critical for the chemical production and semiconductor industries. Real-world applications relying heavily on these phenomena include catalytic converters, integrated circuits used in electronic devices, and silver halide salts used in photographic film. | 7 | Physical Chemistry |
Sutherland and collaborators proposed a geochemical scenario to argue that cyanosulfidic synthesis was a plausible process on the early Earth. Their scenario starts following a meteorite impact leads to the production of HCN and phosphate. The meteorite fragments also supply the necessary sulfide for the reaction. As ponds and lakes containing these reagents experience wet dry cycles, ferrocyanide, sodium, and potassium salts precipitate out of solution into evaporites, concentrating and storing reactants for future chemistry. These evaporites can then be thermally altered through additional impacts or geothermal heating, producing all necessary components for the proposed syntheses. Rain and runoff create streams that transport compounds along geochemical gradients, introducing new reactants along the way which causes new syntheses to occur. The streams are also exposed to ultraviolet radiation, providing energy for the reactions. The conditions described here support an evaporative lake or terrestrial hydrothermal pond scenario for the origin of life. The proposed geochemical scenario also relies on flow chemistry concepts to introduce new reactants throughout the process to cause additional chemical reactions and syntheses to occur. | 9 | Geochemistry |
Fast protein liquid chromatography (FPLC) is a form of liquid chromatography that is often used to analyze or purify mixtures of proteins. As in other forms of chromatography, separation is possible because the different components of a mixture have different affinities for two materials, a moving fluid (the mobile phase) and a porous solid (the stationary phase). In FPLC the mobile phase is an aqueous buffer solution. The buffer flow rate is controlled by a positive-displacement pump and is normally kept constant, while the composition of the buffer can be varied by drawing fluids in different proportions from two or more external reservoirs. The stationary phase is a resin composed of beads, usually of cross-linked agarose, packed into a cylindrical glass or plastic column. FPLC resins are available in a wide range of bead sizes and surface ligands depending on the application.
FPLC was developed and marketed in Sweden by Pharmacia in 1982, and was originally called fast performance liquid chromatography to contrast it with high-performance liquid chromatography (HPLC). FPLC is generally applied only to proteins; however, because of the wide choice of resins and buffers it has broad applications. In contrast to HPLC, the buffer pressure used is relatively low, typically less than 5 bar, but the flow rate is relatively high, typically 1–5 ml/min.
FPLC can be readily scaled from analysis of milligrams of mixtures in columns with a total volume of 5 ml or less to industrial production of kilograms of purified protein in columns with volumes of many liters. When used for analysis of mixtures, the eluant is usually collected in fractions of 1–5 ml which can be further analyzed. When used for protein purification there may be only two collection containers: one for the purified product and one for waste. | 3 | Analytical Chemistry |
For example, there are three distinct compounds with the molecular formula :
The first two isomers shown of are propanols, that is, alcohols derived from propane. Both have a chain of three carbon atoms connected by single bonds, with the remaining carbon valences being filled by seven hydrogen atoms and by a hydroxyl group comprising the oxygen atom bound to a hydrogen atom. These two isomers differ on which carbon the hydroxyl is bound to: either to an extremity of the carbon chain propan-1-ol (1-propanol, n-propyl alcohol, n-propanol; I) or to the middle carbon propan-2-ol (2-propanol, isopropyl alcohol, isopropanol; II). These can be described by the condensed structural formulas and .
The third isomer of is the ether methoxyethane (ethyl-methyl-ether; III). Unlike the other two, it has the oxygen atom connected to two carbons, and all eight hydrogens bonded directly to carbons. It can be described by the condensed formula .
The alcohol "3-propanol" is not another isomer, since the difference between it and 1-propanol is not real; it is only the result of an arbitrary choice in the direction of numbering the carbons along the chain. For the same reason, "ethoxymethane" is the same molecule as methoxyethane, not another isomer.
1-Propanol and 2-propanol are examples of positional isomers, which differ by the position at which certain features, such as double bonds or functional groups, occur on a "parent" molecule (propane, in that case). | 4 | Stereochemistry |
* Protolysis mechanism of cis- and trans-β-chlorovinylmercury chlorides when acted upon by HCl and DCl
* Pd-Catalyzed amination of dibromobiphenyls in the synthesis of macrocycles comprising two biphenyl and two polyamine moieties
* The influence of the substituents in the electrofilic bimolecular reaction
* New trends in the cross-coupling and other catalytic reactions | 0 | Organic Chemistry |
Haplotype refers to a group of genetic variants inherited together on a chromosome from one parent due to their genetic linkage. Haplotype phasing (also called haplotype estimation) refers to the process of reconstructing individual haplotypes, important for determining the genetic basis of diseases. Linked-read sequencing allows consistent coverage of genes related to different diseases, helping scientists to obtain all the regions carrying mutations from targeted genes. For example, in 2018, a group of researchers used linked-read sequencing technology to sequence genetic information from a pregnant woman who was a carrier of Duchenne muscular dystrophy (DMD) mutation. Linked-read sequencing allows them to identify the maternal haplotypes and determine the presence of the mutant alleles in the foetal DNA. This non-invasive prenatal diagnosis of DMD demonstrates the clinical applicability of linked-read sequencing. | 1 | Biochemistry |
*Fluorosulfonic acid, FSOOH, is a related strong acid with a diminished tendency to evolve hydrogen fluoride.
*Bromosulfonic acid, BrSOOH, is unstable, decomposing at its melting point of 8 °C to give bromine, sulfur dioxide, and sulfuric acid.
*Iodosulfonic acid is not known to occur. | 0 | Organic Chemistry |
In biochemistry, an ultratrace element is a chemical element that normally comprises less than one microgram per gram of a given organism (i.e. less than 0.0001% by weight), but which plays a significant role in its metabolism.
Possible ultratrace elements in humans include boron, silicon, nickel, vanadium and cobalt. Other possible ultratrace elements in other organisms include bromine, cadmium, fluorine, lead, lithium, and tin. | 1 | Biochemistry |
The activity of SINEs however has genetic vestiges which do not seem to play a significant role, positive or negative, and manifest themselves in the genome as pseudogenes. SINEs however should not be mistaken as RNA pseudogenes. In general, pseudogenes are generated when processed mRNAs of protein-coding genes are reverse-transcribed and incorporated back into the genome (RNA pseudogenes are reverse transcribed RNA genes). Pseudogenes are generally functionless as they descend from processed RNAs independent of their evolutionary-context which includes introns and different regulatory elements which enable transcription and processing. These pseudogenes, though non-functional may in some cases still possess promoters, CpG islands, and other features which enable transcription; they thus can still be transcribed and may possess a role in the regulation of gene expression (like SINEs and other non-coding elements). Pseudogenes thus differ from SINEs in that they are derived from transcribed- functional RNA whereas SINEs are DNA elements which retrotranspose by co-opting RNA genes transcriptional machinery. However, there are studies which suggest that retro-transposable elements such as short-interspersed nuclear elements are not only capable of copying themselves in alternate regions in the genome but are also able to do so for random genes too. Thus SINEs can be playing a vital role in the generation of pseudogenes, which themselves are known to be involved in regulatory networks. This is perhaps another means by which SINEs have been able to influence and contribute to gene-regulation. | 1 | Biochemistry |
In microprocessors, graphics processors and other high-end chips, hotspots can occur as power densities vary significantly across a chip. These hotspots can severely limit the performance of the devices. Because of the small size of the thermal bumps and the relatively high density at which they can be placed on the active surface of the chip, these structures are ideally suited for cooling hotspots. In such a case, the distribution of the thermal bumps may not need to be even. Rather, the thermal bumps would be concentrated in the area of the hotspot while areas of lower heat density would have fewer thermal bumps per unit area. In this way, cooling from the thermal bumps is applied only where needed, thereby reducing the added power necessary to drive the cooling and reducing the general thermal overhead on the system. | 7 | Physical Chemistry |
The fundamental series lines for rubidium appear in the near infrared. The valence electron moves from the 4d level as the 3d is contained in an inner shell. They were observed by R von Lamb.
Relevant energy levels are 4p4d j=5/2 19,355.282 cm and j=3/2 19,355.623 cm, and the first f levels at 4p4f j=5/2 26,792.185 cm and j=7/2 26,792.169 cm. | 7 | Physical Chemistry |
Fermentation does not require oxygen. If oxygen is present, some species of yeast (e.g., Kluyveromyces lactis or Kluyveromyces lipolytica) will oxidize pyruvate completely to carbon dioxide and water in a process called cellular respiration, hence these species of yeast will produce ethanol only in an anaerobic environment (not cellular respiration). This phenomenon is known as the Pasteur effect.
However, many yeasts such as the commonly used bakers yeast Saccharomyces cerevisiae or fission yeast Schizosaccharomyces pombe' under certain conditions, ferment rather than respire even in the presence of oxygen. In wine making this is known as the counter-Pasteur effect. These yeasts will produce ethanol even under aerobic conditions, if they are provided with the right kind of nutrition. During batch fermentation, the rate of ethanol production per milligram of cell protein is maximal for a brief period early in this process and declines progressively as ethanol accumulates in the surrounding broth. Studies demonstrate that the removal of this accumulated ethanol does not immediately restore fermentative activity, and they provide evidence that the decline in metabolic rate is due to physiological changes (including possible ethanol damage) rather than to the presence of ethanol. Several potential causes for the decline in fermentative activity have been investigated. Viability remained at or above 90%, internal pH remained near neutrality, and the specific activities of the glycolytic and alcohologenic enzymes (measured in vitro) remained high throughout batch fermentation. None of these factors appears to be causally related to the fall in fermentative activity during batch fermentation. | 1 | Biochemistry |
The Biogeography of Deep-Water Chemosynthetic Ecosystems is a field project of the Census of Marine Life programme (CoML). The main aim of ChEss is to determine the biogeography of deep-water chemosynthetic ecosystems at a global scale and to understand the processes driving these ecosystems. ChEss addresses the main questions of CoML on diversity, abundance and distribution of marine species, focusing on deep-water reducing environments such as hydrothermal vents, cold seeps, whale falls, sunken wood and areas of low oxygen that intersect with continental margins and seamounts. | 9 | Geochemistry |
Under specific conditions and in the presence of other chemicals benzoic acid (a preservative) and ascorbic acid (Vitamin C) may interact to produce benzene. In March 2006, the official Food Standards Agency in United Kingdom conducted a survey of 150 brands of soft drinks. It found that four contained benzene levels above World Health Organization limits. The affected batches were removed from sale. Similar problems were reported by the FDA in the United States. | 2 | Environmental Chemistry |
The Tensorial Anisotropy Index A extends the Zener ratio for fully anisotropic materials and overcomes the limitation of the AU that is designed for materials exhibiting internal symmetries of elastic crystals, which is not always observed in multi-component composites. It takes into consideration all the 21 coefficients of the fully anisotropic stiffness tensor and covers the directional differences among the stiffness tensor groups.
It is composed of two major parts and , the former referring to components existing in cubic tensor and the latter in anisotropic tensor so that This first component includes the modified Zener ratio and additionally accounts for directional differences in the material, which exist in orthotropic material, for instance. The second component of this index covers the influence of stiffness coefficients that are nonzero only for non-cubic materials and remains zero otherwise.
where is the coefficient of variation for each stiffness group accounting for directional differences of material stiffness, i.e. In cubic materials each stiffness component in groups 1-3 has equal value and thus this expression reduces directly to Zener ratio for cubic materials.
The second component of this index <math>
A^A | 3 | Analytical Chemistry |
V̇O max has been measured in other animal species. During loaded swimming, mice had a V̇O max of around 140 mL/(kg·min). Thoroughbred horses had a V̇O max of around 193 mL/(kg·min) after 18 weeks of high-intensity training. Alaskan huskies running in the Iditarod Trail Sled Dog Race had V̇O max values as high as 240 mL/(kg·min). Estimated V̇O max for pronghorn antelopes was as high as 300 mL/(kg·min). | 1 | Biochemistry |
It is sometimes unclear what causes specific HABs as their occurrence in some locations appears to be entirely natural, while in others they appear to be a result of human activities. Furthermore, there are many different species of algae that can form HABs, each with different environmental requirements for optimal growth. The frequency and severity of HABs in some parts of the world have been linked to increased nutrient loading from human activities. In other areas, HABs are a predictable seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents.
The growth of marine phytoplankton (both non-toxic and toxic) is generally limited by the availability of nitrates and phosphates, which can be abundant in coastal upwelling zones as well as in agricultural run-off. The type of nitrates and phosphates available in the system are also a factor, since phytoplankton can grow at different rates depending on the relative abundance of these substances (e.g. ammonia, urea, nitrate ion).
A variety of other nutrient sources can also play an important role in affecting algal bloom formation, including iron, silica or carbon. Coastal water pollution produced by humans (including iron fertilization) and systematic increase in sea water temperature have also been suggested as possible contributing factors in HABs.
Among the causes of algal blooms are:
* Excess nutrients—phosphorus and nitrates—from fertilizers or sewage that are discharged to water bodies (also called nutrient pollution)
* climate change
* thermal pollution from power plants and factories
* low water levels in inland waterways and lakes, which reduces water flow and increases water temperatures
* invasive filter feeders—especially Zebra mussels, Dreissena polymorpha—which preferentially eat non-toxic algae, competitors to harmful algae | 3 | Analytical Chemistry |
2,4,6-Tri-tert-butylpyrimidine is the organic compound with the formula HC(BuC)NCBu where Bu = (CH)C. It is a substituted derivative of the heterocycle pyrimidine. Known also as TTBP, this compound is of interest as a base that is sufficiently bulky to not bind boron trifluoride but still able to bind protons. It is less expensive that the related bulky derivatives of pyridine such as 2,6-di-tert-butylpyridine, 2,4,6-tri-tert-butylpyridine, and 2,6-di-tert-butyl-4-methylpyridine. | 0 | Organic Chemistry |
Charge ordering can occur in compounds containing ions of mixed valence when the electrons, which are delocalised at high temperature, localize in an ordered pattern on different cation sites so that the material becomes insulating. When the pattern of localized electrons is polar, the charge ordered state is ferroelectric. Usually the ions in such a case are magnetic and so the ferroelectric state is also multiferroic. The first proposed example of a charge ordered multiferroic was LuFeO, which charge orders at 330 K with an arrangement of Fe and Fe ions. Ferrimagnetic ordering occurs below 240 K. Whether or not the charge ordering is polar has recently been questioned, however. In addition, charge ordered ferroelectricity is suggested in magnetite, FeO, below its Verwey transition, and . | 7 | Physical Chemistry |
The repressor is an allosteric protein, i.e. it can assume either one of two slightly different shapes, which are in equilibrium with each other. In one form the repressor will bind to the operator DNA with high specificity, and in the other form it has lost its specificity. According to the classical model of induction, binding of the inducer, either allolactose or IPTG, to the repressor affects the distribution of repressor between the two shapes. Thus, repressor with inducer bound is stabilized in the non-DNA-binding conformation. However, this simple model cannot be the whole story, because repressor is bound quite stably to DNA, yet it is released rapidly by addition of inducer. Therefore, it seems clear that an inducer can also bind to the repressor when the repressor is already bound to DNA. It is still not entirely known what the exact mechanism of binding is. | 1 | Biochemistry |
Thionoesters are isomeric with thioesters. In a thionoester, sulfur replaces the carbonyl oxygen in an ester. Methyl thionobenzoate is CHC(S)OCH. Such compounds are typically prepared by the reaction of the thioacyl chloride with an alcohol.
They can also be made by the reaction of Lawesson's reagent with esters or by treating pinner salts with hydrogen sulphide. An alternatively, various thionoesters may be prepared through the transesterification of an existing methyl thionoester with an alcohol under base-catalyzed conditions.
Xanthates and thioamides can be transformed to thionoesters under metal-catalyzed cross-coupling conditions. | 0 | Organic Chemistry |
In the history of food, ancient fermented food processes, such as making bread, wine, cheese, curds, idli, dosa, etc., can be dated to more than seven thousand years ago. They were developed long before humanity had any knowledge of the existence of the microorganisms involved. Some foods such as Marmite are the byproduct of the fermentation process, in this case in the production of beer. | 1 | Biochemistry |
Lanthanides can be used because their small size (ionic radius) gives them the ability to replace metal ions inside protein complex such as calcium or nickel. The optical properties of lanthanide ions such as Ln(III) originate in the special features of their electronic [Xe]4f configurations. These configurations generate many electronic levels, the number of which is given by [14!/n!(14- n)!], translating into 3003 energy levels for Eu(III) and Tb(III).
The energies of these levels are well defined due to the shielding of the 4f orbitals by the filled 5s and 5p sub-shells, and are not very sensitive to the chemical environments in which the lanthanide ions are inserted. Inner-shell 4f-4f transitions span both the visible and near-infrared ranges. They are sharp and easily recognizable. Since these transitions are parity forbidden, the lifetimes of the excited states are long, which allows the use of time resolved spectroscopy, a definitive asset for bioassays and microscopy. The only drawback of f-f transitions are their faint oscillator strengths which may in fact be turned into an advantage.
The energy absorbed by the organic receptor (ligand) is transferred onto Ln(III) excited states, and sharp emission bands originating from the metal ion are detected after rapid internal conversion to the emitting level. The phenomenon is termed sensitization of the metal centered complex (also referred to as antenna effect) and is quite complex.
The energy migration path though goes through the long-lived triplet state of the ligand. Ln(III) ions are good quenchers of triplet states so that photobleaching is substantially reduced. The three types of transitions seen for lanthanide probes are: LMCT, 4f-5d, and intraconfigurational 4f-4f. The former two usually occur at energies too high to be relevant for bio-applications. | 1 | Biochemistry |
The reversible Michaelis–Menten law, as with many enzymatic rate laws, can be decomposed into a capacity term, a thermodynamic term, and an enzyme saturation level. This is more easily seen when we write the reversible rate law as:
where is the capacity term, the thermodynamic term and
the saturation term. The separation can be even better appreciated if we look at the elasticity coefficient . According to elasticity algebra, the elasticity of a product is the sum of the sub-term elasticities, that is:
Hence the elasticity of the reversible Michaelis–Menten rate law can easily be shown to be:
Since the capacity term is a constant, the first elasticity is zero. The thermodynamic term can be easily shown to be:
where is the disequilibrium ratio and equals and the mass–action ratio
The saturation term becomes: | 7 | Physical Chemistry |
is a trigonal pyramidal molecule with C molecular symmetry. The length of the P−H bond is 1.42 Å, the H−P−H bond angles are 93.5°. The dipole moment is 0.58 D, which increases with substitution of methyl groups in the series: , 1.10 D; , 1.23 D; , 1.19 D. In contrast, the dipole moments of amines decrease with substitution, starting with ammonia, which has a dipole moment of 1.47 D. The low dipole moment and almost orthogonal bond angles lead to the conclusion that in the P−H bonds are almost entirely and phosphorus 3s orbital contributes little to the P-H bonding. For this reason, the lone pair on phosphorus is predominantly formed by the 3s orbital of phosphorus. The upfield chemical shift of it P NMR signal accords with the conclusion that the lone pair electrons occupy the 3s orbital (Fluck, 1973). This electronic structure leads to a lack of nucleophilicity in general and lack of basicity in particular (pK = –14), as well as an ability to form only weak hydrogen bonds.
The aqueous solubility of is slight: 0.22 cm of gas dissolves in 1 cm of water. Phosphine dissolves more readily in non-polar solvents than in water because of the non-polar P−H bonds. It is technically amphoteric in water, but acid and base activity is poor. Proton exchange proceeds via a phosphonium () ion in acidic solutions and via phosphanide () at high pH, with equilibrium constants K = and K = . Phosphine reacts with water only at high pressure and temperature, producing phosphoric acid and hydrogen:
Burning phosphine in the air produces phosphoric acid): | 0 | Organic Chemistry |
Classically, ILs consist of salts of unsymmetrical, flexible organic cations with symmetrical weakly coordinating anions. Both cationic and anionic components have been widely varied. | 7 | Physical Chemistry |
The Romans made full use of the brown- and ochre-coloured stone in the Weald, and many of their roads there are the means of transport for the ore, and were extensively metalled with slag from iron smelting. The sites of about 113 bloomeries have been identified as Roman, mainly in East Sussex. The Weald was in this period one of the most important iron-producing regions in Roman Britain. Excavations at a few sites have produced tiles of the Classis Britannica, suggesting that they were actually run by, or were supplying iron to this Roman fleet. Total iron production has been estimated at 750 tons per year, but under 200 tons per year after 250 AD. | 8 | Metallurgy |
Oxidation of RIS occurs rapidly under ambient conditions This is especially true for iron monosulfides, which have a higher surface area than iron disulfides.
Monosulfidic material will change from pitch black to light brown within minutes of being exposed to air (see images below). Consequently, acid sulfate soil samples should be immediately cooled to < 4°C to slow oxidation; and samples containing monosulfidic material should be immediately frozen (e.g., using a portable freezer or liquid nitrogen). The use of dry ice is recommended as the gaseous carbon dioxide should further hinder oxidation. Samples should be tested for ABA within 24 h of sampling. Otherwise, additional preservation techniques (e.g., freezing or drying at > 85°C) should be used. | 9 | Geochemistry |
He received his B.A. in chemistry and physics from Harvard in 1963, and was then a Henry fellow at the MRC Laboratory of Molecular Biology at Cambridge. In 1967, he received his Ph.D. in biophysics from Harvard, was a research fellow there as well as a junior fellow in the Society of Fellows, and joined the Harvard faculty in 1971. | 1 | Biochemistry |
:See Immobilized enzyme for more information.
There are several reasons for immobilizing an enzyme. In addition to more convenient handling of the enzyme, it provides for its facile separation from the product, thereby minimizing or eliminating protein contamination of the product. Immobilization also facilitates the efficient recovery and re-use of costly enzymes, in many applications a conditio sine qua non for economic viability, and enables their use in continuous, fixed-bed operation. A further benefit is often enhanced stability, under both storage and operational conditions, e.g. towards denaturation by heat or organic solvents or by autolysis. Enzymes are rather delicate molecules that can easily lose their unique three-dimensional structure, essential for their activity, by denaturation (unfolding). Improved enzyme performance via enhanced stability, over a broad pH and temperature range as well as tolerance towards organic solvents, coupled with repeated re-use is reflected in higher catalyst productivities (kg product/kg enzyme) which, in turn, determine the enzyme costs per kg product.
Basically, three traditional methods of enzyme immobilization can be distinguished: binding to a support(carrier), entrapment (encapsulation) and cross-linking. Support binding can be physical, ionic, or covalent in nature. However, physical bonding is generally too weak to keep the enzyme fixed to the carrier under industrial conditions of high reactant and product concentrations and high ionic strength. The support can be a synthetic resin, a biopolymer or an inorganic polymer such as (mesoporous) silica or a zeolite. Entrapment involves inclusion of an enzyme in a polymer network (gel lattice) such as an organic polymer or a silica sol-gel, or a membrane device such as a hollow fiber or a microcapsule. Entrapment requires the synthesis of the polymeric network in the presence of the enzyme. The third category involves cross-linking of enzyme aggregates or crystals, using a bifunctional reagent, to prepare carrier-free macroparticles.
The use of a carrier inevitably leads to ‘dilution of activity’, owing to the introduction of a large portion of non-catalytic ballast, ranging from 90% to >99%, which results in lower space-time yields and productivities. Moreover, immobilization of an enzyme on a carrier often leads to a substantial loss of activity, especially at high enzyme loadings. Consequently, there is an increasing interest in carrier-free immobilized enzymes, such as cross-linked enzyme crystals (CLECs) and cross-linked enzyme aggregates (CLEAs) that offer the advantages of highly concentrated enzyme activity combined with high stability and low production costs owing to the exclusion of an additional (expensive) carrier. | 4 | Stereochemistry |
Corrosion in Ballast Tanks is the deterioration process where the surface of a ballast tank progresses from microblistering, to hydroscaletric electration, and finally to cracking of the tank steel itself.
::“Effective corrosion control in segregated water ballast spaces is probably the single most important feature, next to the integrity of the initial design, in determining the ship’s effective life span and structural reliability,” said Alan Gavin, Germanischer Lloyd's Principal surveyor.
Throughout the years the merchant fleet has become increasingly aware of the importance of avoiding corrosion in ballast tanks. | 8 | Metallurgy |
In physical chemistry and materials science, texture is the distribution of crystallographic orientations of a polycrystalline sample (it is also part of the geological fabric). A sample in which these orientations are fully random is said to have no distinct texture. If the crystallographic orientations are not random, but have some preferred orientation, then the sample has a weak, moderate or strong texture. The degree is dependent on the percentage of crystals having the preferred orientation.
Texture is seen in almost all engineered materials, and can have a great influence on materials properties. The texture forms in materials during thermo-mechanical processes, for example during production processes e.g. rolling. Consequently, the rolling process is often followed by a heat treatment to reduce the amount of unwanted texture. Controlling the production process in combination with the characterization of texture and the materials microstructure help to determine the materials properties, i.e. the processing-microstructure-texture-property relationship'. Also, geologic rocks show texture due to their thermo-mechanic history of formation processes.
One extreme case is a complete lack of texture: a solid with perfectly random crystallite orientation will have isotropic properties at length scales sufficiently larger than the size of the crystallites. The opposite extreme is a perfect single crystal, which likely has anisotropic properties by geometric necessity. | 8 | Metallurgy |
The expression of HERV-K, a biologically active family of HERV, produces proteins found in placenta. Furthermore, the expression of the envelope genes of HERV-W ([https://www.genenames.org/data/hgnc_data.php?hgnc_id=13525 ERVW-1] ) and HERV-FRD ([https://www.genenames.org/data/hgnc_data.php?hgnc_id=33823 ERVFRD-1] ) produces syncytins which are important for the generation of the syncytiotrophoblast cell layer during placentogenesis by inducing cell-cell fusion. The HUGO Gene Nomenclature Committee (HGNC) approves gene symbols for transcribed human ERVs. | 1 | Biochemistry |
Keto–enol tautomerism is important in several areas of biochemistry.
The high phosphate-transfer potential of phosphoenolpyruvate results from the fact that the phosphorylated compound is "trapped" in the less thermodynamically favorable enol form, whereas after dephosphorylation it can assume the keto form.
The enzyme enolase catalyzes the dehydration of 2-phosphoglyceric acid to the enol phosphate ester. Metabolism of PEP to pyruvic acid by pyruvate kinase (PK) generates adenosine triphosphate (ATP) via substrate-level phosphorylation. | 0 | Organic Chemistry |
Polyamorphism may apply to all amorphous states, i.e. glasses, other amorphous solids, supercooled liquids, ordinary liquids or fluids. A liquid–liquid transition however, is one that occurs only in the liquid state (red line in the phase diagram, top right). In this article liquid–liquid transitions are defined as transitions between two liquids of the same chemical substance. Elsewhere the term liquid–liquid transition may also refer to the more common transitions between liquid mixtures of different chemical composition.
The stable liquid state unlike most glasses and amorphous solids, is a thermodynamically stable equilibrium state. Thus new liquid–liquid or fluid-fluid transitions in the stable liquid (or fluid) states are more easily analysed than transitions in amorphous solids where arguments are complicated by the non-equilibrium, non-ergodic nature of the amorphous state. | 7 | Physical Chemistry |
Although Agricola died in 1555, the publication was delayed until the completion of the extensive and detailed woodcuts one year after his death.
A German translation was published in 1557 and a second Latin edition appeared in 1561. A version in Spanish, though not a mere translation, was produced by Bernardo Pérez de Vargas in 1569. This was translated into French as Traité singulier de metallique in 1743.
In 1912, the first English translation of De Re Metallica was privately published in London by subscription. The translators and editors were Herbert Hoover, a mining engineer (and later President of the United States), and his wife, Lou Henry Hoover, a geologist and Latinist. The translation is notable not only for its clarity of language, but for the extensive footnotes, which detail the classical references to mining and metals, such as the Naturalis Historia of Pliny the Elder, the history of mining law in England, France, and the German states; safety in mines, including historical safety; and known minerals at the time that Agricola wrote De Re Metallica. No expense was spared for this edition: in its typography, fine paper and binding, quality of reproduced images, and vellum covers, the publisher attempted to match the extraordinarily high standards of the sixteenth-century original. As a consequence, copies of this 1912 edition are now both rare and valuable. Fortunately, the translation has been reprinted by Dover Books.
Subsequent translations into other languages, including German, owe much to the Hoover translations, as their footnotes detail their difficulties with Agricola's invention of several hundred Latin expressions to cover Medieval German mining and milling terms unknown to classical Latin. | 8 | Metallurgy |
Crudden was appointed a Natural Sciences and Engineering Research Council postdoctoral fellow at University of Illinois at Urbana–Champaign working with Scott E. Denmark in 1995. She moved to University of New Brunswick in 1996 where she started her own research group. In 2002, she was appointed a Queen's National Scholar and moved her research lab to Kingston, Ontario.
Crudden was the first to identify an enantiospecific Suzuki-Miyaura cross-coupling reaction of chiral boranes. In 2014 she designed more stable nitrogen-based self-assembled monolayer treatments for metal surfaces. The N-heterocyclic carbene self-assembled monolayers can be used in a range of applications, including biosensors. Her interests lie in hydroboration, organometallic chemistry, chiral materials and persistent carbenes. In 2010 Crudden became head of a Natural Sciences and Engineering Research Council CREATE award in chiral materials, worth $1.6 million. She became President of the Canadian Society of Chemistry.
In 2015, as Principal Investigator of a group of ten collaborators, Crudden was awarded $8.8 million from the Canada Foundation for Innovation for major infrastructure purchases. She won the Queens University Research Opportunities Fund, which she used to create inexpensive, sensitive biosensors. Her group prepares carbon-based ligands for metal surfaces, which can be used as sensing systems based on surface plasmon resonance. In 2016, she and Dr. Suning Wang held a trilateral Canada-Japan-Germany symposium at Queens looking at Elements Functions for Transformative Catalysis and Materials. Crudden is a joint Professor at the Institute of Transformative Bio-Molecules, based out of Nagoya University in Japan, where she runs a satellite lab. She is one of only four international collaborators at this Institute. She was recognised as having made the most distinguished contribution to the field of catalysis by the Chemical Institute of Canada in 2018, when they awarded her the Catalysis Award. Crudden also often comments on developments in the field of organic chemistry in various media outlets. | 0 | Organic Chemistry |
Sulfinamides are traditionally produced by the reaction of sulfinyl chlorides with primary or secondary amines. They also arise by the addition of Grignard reagents to sulfinylamines, followed by protonation:
:RMgX + RN=S=O → RS(O)(NRMgX)
:RS(O)(NRMgX) + HO → RS(O)(NRH) + "MgX(OH)"
Yet another route entails peracid-oxidation of sulfenylphthalimides, which gives sulfinylphthalimides. | 0 | Organic Chemistry |
To understand cases of real chemical reactions, the HOMO-LUMO-centered view is modified by understanding of further complex, electrophile-specific repulsive and attractive electrostatic and Van der Waals interactions that alter the altitudinal BD angle, and bias the azimuthal Flippin-Lodge angle toward one substituent or the other (see graphic above). | 7 | Physical Chemistry |
In an infrared spectrum the intensity of an absorption band is proportional to the derivative of the molecular dipole moment with respect to the normal coordinate. Likewise, the intensity of Raman bands depends on the derivative of polarizability with respect to the normal coordinate. There is also a dependence on the fourth-power of the wavelength of the laser used. | 7 | Physical Chemistry |
LEAPER is analogous to CRISPR Cas-13 in that it targets RNA before proteins are synthesized. However, LEAPER is simpler and more efficient as it only requires , rather than Cas and a guide RNA. According to the developers of LEAPER, it has the potential to be easier and more precise than any CRISPR technique.
LEAPER also eliminates health concerns and technical barriers arising from the introduction of exogenous proteins.
It has also been called more ethical as it does not change DNA and thus does not result in heritable changes, unlike methods using CRISPR Cas-9. | 1 | Biochemistry |
The green patina that forms naturally on copper and bronze, sometimes called verdigris, usually consists of varying mixtures of copper chlorides, sulfides, sulfates, and carbonates, depending upon environmental conditions such as sulfur-containing acid rain. In clean air rural environments, the patina is created by the slow chemical reaction of copper with carbon dioxide and water, producing a basic copper carbonate. In industrial and urban air environments containing sulfurous acid rain from coal-fired power plants or industrial processes, the final patina is primarily composed of sulphide or sulphate compounds.
A patina layer takes many years to develop under natural weathering. Buildings in damp coastal or marine environments will develop patina layers faster than ones in dry inland areas.
Façade cladding (copper cladding; copper wall cladding) with alloys of copper, like brass or bronze, will weather differently from "pure" copper cladding. Even a lasting gold colour is possible with copper-alloy cladding, for example Bristol Beacon in Bristol, or the Novotel at Paddington Central, London.
Antique and well-used firearms will often develop a layer of rust on the action, barrel, or other steel parts after the original finish has worn. On this subject gunsmith Mark Novak says "... This is what everybody calls patina, I call it a nice thick coat of rust..." The removal of such rust is often necessary for a firearm conservation to prevent further decay of the firearm. | 8 | Metallurgy |
Similar to the ring-formation behavior in the carbene addition reaction of C=C double bonds, diphosphene can form a P-C-P three-membered ring with dihalocarbene or . Diphosphiranes can further rearrange to 1,3-diphospha-allene via ring opening reactions by using MeLi or n-BuLi. | 0 | Organic Chemistry |
Its use as an analgesic during labor is not advised due to its long onset of action (1 hour). The ratio of the mean concentration of the drug in the fetus compared to that of the mother when it is given intramuscularly for labor pains has been estimated to be 1:94. | 4 | Stereochemistry |
The inner chloroplast membrane borders the stroma and regulates passage of materials in and out of the chloroplast. After passing through the TOC complex in the outer chloroplast membrane, polypeptides must pass through the TIC complex (translocon on the inner chloroplast membrane) which is located in the inner chloroplast membrane.
In addition to regulating the passage of materials, the inner chloroplast membrane is where fatty acids, lipids, and carotenoids are synthesized. | 5 | Photochemistry |
More generally, systems in equilibrium at temperature have probability of occupying a state with energy weighted by the corresponding Boltzmann factor:
where is the partition function. Again, it is the energy-like quantity that takes central importance.
Consequences of this include (in addition to the results for ideal gases above) the Arrhenius equation in chemical kinetics. | 7 | Physical Chemistry |
Libration (from the Latin verb librare "to balance, to sway"; cf. libra "scales") is a type of reciprocating motion in which an object with a nearly fixed orientation repeatedly rotates slightly back and forth. In physics and chemistry, a molecule (or other group of atoms) can undergo libration if it is subject to external forces or constraints that restrict its orientation.
For example, in liquid water, any given water molecule is attracted to neighboring molecules, so that it has a preferred orientation and cannot freely rotate. (Of course, over time, the neighboring molecules move around and the preferred orientation changes.) However, it can undergo librational motions, which are measureable in an infrared absorption spectrum and contribute to motional narrowing of other peaks, for instance the OH stretch.
Another example is a molecular crystal: Each molecular unit has a preferred orientation due to interactions with the nearby molecules, but they have librational modes corresponding to small rotations about this preferred orientation. | 7 | Physical Chemistry |
In 2009, a different kind of Rydberg molecule was finally created by researchers from the University of Stuttgart. There, the interaction between a Rydberg atom and a ground state atom leads to a novel bond type. Two rubidium atoms were used to create the molecule which survived for 18 microseconds.
In 2015, a trilobite Rydberg molecule was observed by researchers from the University of Oklahoma. This molecule was theorized in 2000 and is characterized by an electron density distribution that resembles the shape of a trilobite when plotted in cylindrical coordinates. These molecules have lifetimes of tens of microseconds and electric dipole moments of up to 2000 Debye.
In 2016, a butterfly Rydberg molecule was observed by a collaboration involving researchers from the Kaiserslautern University of Technology and Purdue University. A butterfly Rydberg molecule is a weak pairing of a Rydberg atom and a ground state atom that is enhanced by the presence of a shape resonance in the scattering between the Rydberg electron and the ground state atom. This new kind of atomic bond was theorized in 2002 and is characterized by an electron density distribution that resembles the shape of a butterfly. As a consequence of the unconventional binding mechanism, butterfly Rydberg molecules show peculiar properties such as multiple vibrational ground states at different bond lengths and giant dipole moments in excess of 500 debye. | 7 | Physical Chemistry |
Autoacceleration (gel effect, Trommsdorff–Norrish effect) is a dangerous reaction behavior that can occur in free-radical polymerization systems. It is due to the localized increases in viscosity of the polymerizing system that slow termination reactions. The removal of reaction obstacles therefore causes a rapid increase in the overall rate of reaction, leading to possible reaction runaway and altering the characteristics of the polymers produced. | 7 | Physical Chemistry |
From the equality of the flow parameters on two different days , measured values on one day can be corrected to those that would be measured on a standard day so,
where are measured values and 519 degR and 14.7lb/sq in are the standard day temperature and pressure.
The temperature and pressure correction factors are and , so
For speed the corrected value is
Example: An engine is running at 100% speed and 107 lb of air is entering the compressor every second, and the day conditions are 14.5 psia and 30 deg F (490 deg R).
On a standard day the airflow would be which is 105.2 lb/sec. The speed would be which is 103%. These corrected values are what would appear on the compressor map for this particular engine.
This example shows that a compressor runs aerodynamically faster on a cold day and would be slower on a hot day. Since the day conditions are those at entry to the compressor an extremely hot day is produced artificially by the ram temperature rise at high Mach numbers. The aerodynamic speed is low enough, despite the engine running at its 100% rated mechanical speed, to get into the rotating stall region on the map so an engine operating at these Mach numbers needs the appropriate features. The General Electric J93 had variable inlet guide vanes and stators. The Pratt & Whitney J58 had inter-stage bleed from the compressor and 2-position inlet guide vanes. The Tumansky R-15 had pre-compressor cooling to reduce the air temperature and avoid low corrected speeds. | 7 | Physical Chemistry |
From the industrial perspective, the dominant reactions of the diols is in the production of polyurethanes and alkyd resins. | 0 | Organic Chemistry |
Ninhydrin can be used in Kaiser test to monitor deprotection in solid phase peptide synthesis. The chain is linked via its C-terminus to the solid support, with the N-terminus extending off it. When that nitrogen is deprotected, a ninhydrin test yields blue. Amino-acid residues are attached with their N-terminus protected, so if the next residue has been successfully coupled onto the chain, the test gives a colorless or yellow result.
Ninhydrin is also used in qualitative analysis of proteins. Most of the amino acids, except proline, are hydrolyzed and react with ninhydrin. Also, certain amino acid chains are degraded. Therefore, separate analysis is required for identifying such amino acids that either react differently or do not react with ninhydrin at all. The rest of the amino acids are then quantified colorimetrically after separation by chromatography.
A solution suspected of containing the ammonium ion can be tested by ninhydrin by dotting it onto a solid support (such as silica gel); treatment with ninhydrin should result in a dramatic purple color if the solution contains this species. In the analysis of a chemical reaction by thin layer chromatography (TLC), the reagent can also be used (usually 0.2% solution in either n-butanol or in ethanol). It will detect, on the TLC plate, virtually all amines, carbamates and also, after vigorous heating, amides.
Upon reaction with ninhydrin, amino acids undergo decarboxylation. The released CO originates from the carboxyl carbon of the amino acid. This reaction has been used to release the carboxyl carbons of bone collagen from ancient bones for stable isotope analysis in order to help reconstruct the palaeodiet of cave bears. Release of the carboxyl carbon (via ninhydrin) from amino acids recovered from soil that has been treated with a labeled substrate demonstrates assimilation of that substrate into microbial protein. This approach was successfully used to reveal that some ammonium oxidizing bacteria, also called nitrifying bacteria use urea as a carbon source in soil. | 0 | Organic Chemistry |
A redox gradient is a series of reduction-oxidation (redox) reactions sorted according to redox potential. The redox ladder displays the order in which redox reactions occur based on the free energy gained from redox pairs. These redox gradients form both spatially and temporally as a result of differences in microbial processes, chemical composition of the environment, and oxidative potential. Common environments where redox gradients exist are coastal marshes, lakes, contaminant plumes, and soils.
The Earth has a global redox gradient with an oxidizing environment at the surface and increasingly reducing conditions below the surface. Redox gradients are generally understood at the macro level, but characterization of redox reactions in heterogeneous environments at the micro-scale require further research and more sophisticated measurement techniques. | 7 | Physical Chemistry |
At distances on the scale of the wavelength of a radiated electromangetic wave or smaller, Planck's law is not accurate. For objects this small and close together, the quantum tunneling of EM waves has a significant impact on the rate of radiation.
A more sophisticated framework involving electromagnetic theory must be used for smaller distances from the thermal source or surface. For example, although far-field thermal radiation at distances from surfaces of more than one wavelength is generally not coherent to any extent, near-field thermal radiation (i.e., radiation at distances of a fraction of various radiation wavelengths) may exhibit a degree of both temporal and spatial coherence.
Planck's law of thermal radiation has been challenged in recent decades by predictions and successful demonstrations of the radiative heat transfer between objects separated by nanoscale gaps that deviate significantly from the law predictions. This deviation is especially strong (up to several orders in magnitude) when the emitter and absorber support surface polariton modes that can couple through the gap separating cold and hot objects. However, to take advantage of the surface-polariton-mediated near-field radiative heat transfer, the two objects need to be separated by ultra-narrow gaps on the order of microns or even nanometers. This limitation significantly complicates practical device designs.
Another way to modify the object thermal emission spectrum is by reducing the dimensionality of the emitter itself. This approach builds upon the concept of confining electrons in quantum wells, wires and dots, and tailors thermal emission by engineering confined photon states in two- and three-dimensional potential traps, including wells, wires, and dots. Such spatial confinement concentrates photon states and enhances thermal emission at select frequencies. To achieve the required level of photon confinement, the dimensions of the radiating objects should be on the order of or below the thermal wavelength predicted by Plancks law. Most importantly, the emission spectrum of thermal wells, wires and dots deviates from Plancks law predictions not only in the near field, but also in the far field, which significantly expands the range of their applications. | 7 | Physical Chemistry |
Aggregation-induced emission (AIE) is a phenomenon that is observed with certain organic luminophores (fluorescent dyes).
The photoemission efficiencies of most organic compounds is higher in solution than in the solid state. Photoemission from some organic compounds follows the reverse pattern, being greater in the solid than in solution. The effect is attributed to the decreased flexibility in the solid. | 7 | Physical Chemistry |
Cycling probe technology (CPT) is a molecular biological technique for detecting specific DNA sequences. CPT operates under isothermal conditions. In some applications, CPT offers an alternative to PCR. However, unlike PCR, CPT does not generate multiple copies of the target DNA itself, and the amplification of the signal is linear, in contrast to the exponential amplification of the target DNA in PCR. CPT uses a sequence specific chimeric probe which hybridizes to a complementary target DNA sequence and becomes a substrate for RNase H. Cleavage occurs at the RNA internucleotide linkages and results in dissociation of the probe from the target, thereby making it available for the next probe molecule. Integrated electrokinetic systems have been developed for use in CPT. | 1 | Biochemistry |
X-ray crystallography is the primary method for determining the molecular conformations of biological macromolecules, particularly protein and nucleic acids such as DNA and RNA. The double-helical structure of DNA was deduced from crystallographic data. The first crystal structure of a macromolecule was solved in 1958, a three-dimensional model of the myoglobin molecule obtained by X-ray analysis. The Protein Data Bank (PDB) is a freely accessible repository for the structures of proteins and other biological macromolecules. Computer programs such as RasMol, Pymol or VMD can be used to visualize biological molecular structures.
Neutron crystallography is often used to help refine structures obtained by X-ray methods or to solve a specific bond; the methods are often viewed as complementary, as X-rays are sensitive to electron positions and scatter most strongly off heavy atoms, while neutrons are sensitive to nucleus positions and scatter strongly even off many light isotopes, including hydrogen and deuterium.
Electron crystallography has been used to determine some protein structures, most notably membrane proteins and viral capsids. | 3 | Analytical Chemistry |
Sphingosine (2-amino-4-trans-octadecene-1,3-diol) is an 18-carbon amino alcohol with an unsaturated hydrocarbon chain, which forms a primary part of sphingolipids, a class of cell membrane lipids that include sphingomyelin, an important phospholipid. | 1 | Biochemistry |
Partitioning in digital PCR increases sensitivity and allows for detection of rare events, especially single nucleotide variants (SNVs), by isolating or greatly diminishing the target biomarker signal from potentially competing background. These events can be organized into two classes: rare mutation detection and rare sequence detection. | 1 | Biochemistry |
The intracellular degradation of protein may be achieved in two ways—proteolysis in lysosome, or a ubiquitin-dependent process that targets unwanted proteins to proteasome. The autophagy-lysosomal pathway is normally a non-selective process, but it may become selective upon starvation whereby proteins with peptide sequence KFERQ or similar are selectively broken down. The lysosome contains a large number of proteases such as cathepsins.
The ubiquitin-mediated process is selective. Proteins marked for degradation are covalently linked to ubiquitin. Many molecules of ubiquitin may be linked in tandem to a protein destined for degradation. The polyubiquinated protein is targeted to an ATP-dependent protease complex, the proteasome. The ubiquitin is released and reused, while the targeted protein is degraded. | 1 | Biochemistry |
* Increase in the melting point, boiling point, solubility, and viscosity of many compounds can be explained by the concept of hydrogen bonding.
* Negative azeotropy of mixtures of HF and water.
* The fact that ice is less dense than liquid water is due to a crystal structure stabilized by hydrogen bonds.
* Dramatically higher boiling points of , , and HF compared to the heavier analogues , , and HCl, where hydrogen-bonding is absent.
* Viscosity of anhydrous phosphoric acid and of glycerol.
* Dimer formation in carboxylic acids and hexamer formation in hydrogen fluoride, which occur even in the gas phase, resulting in gross deviations from the ideal gas law.
* Pentamer formation of water and alcohols in apolar solvents. | 6 | Supramolecular Chemistry |
Examples of other type of method of the magnetic particle capturing device are as follows.
* Pen type capture
* Tube type capture | 1 | Biochemistry |
In 2020, the monoclonal antibody therapies bamlanivimab/etesevimab and casirivimab/imdevimab were given emergency use authorizations by the US Food and Drug Administration to reduce the number of hospitalizations, emergency room visits, and deaths. In September 2021, the Biden administration purchased billion worth of Regeneron monoclonal antibodies at $2,100 per dose to curb the shortage.
As of December 2021, in vitro neutralization tests indicate monoclonal antibody therapies (with the exception of sotrovimab and tixagevimab/cilgavimab) were not likely to be active against the Omicron variant.
Over 2021–22, two Cochrane reviews found insufficient evidence for using neutralizing monoclonal antibodies to treat COVID-19 infections. The reviews applied only to people who were unvaccinated against COVID‐19, and only to the COVID-19 variants existing during the studies, not to newer variants, such as Omicron.
In March 2024, pemivibart, a monoclonal antibody drug, received an emergency use authorization from the US FDA for use as pre-exposure prophylaxis to protect certain moderately to severely immunocompromised individuals against COVID-19. | 1 | Biochemistry |
Metaphosphoric acid () is a colorless, vitreous, deliquescent solid, density 2.2 to 2.5 g/cc, which sublimes upon heating. It is soluble in ethanol. | 0 | Organic Chemistry |
The database content can be viewed in self-contained, pre-defined pathways. The database can also dynamically generate interaction networks to visualize the results of database searches. Pathways and dynamically generated networks are displayed in GIF and SVG images and can be downloaded as XML (including the standard pathway interchange format, BioPAX). The entire database is also available for download. | 1 | Biochemistry |
The two principal methods of measuring total dissolved solids are gravimetric analysis and conductivity. Gravimetric methods are the most accurate and involve evaporating the liquid solvent and measuring the mass of residues left. This method is generally the best, although it is time-consuming. If inorganic salts comprise the great majority of TDS, conductivity-based methods are appropriate.
Conductivity of water is directly related to the concentration of dissolved ionized solids. These ions allow the water to conduct electric current. This electric current can be measured using a conventional conductivity meter or TDS meter. When correlated with laboratory TDS measurements, conductivity provides an approximate value for the TDS concentration, with around 10% accuracy.
The relationship of TDS and specific conductance of groundwater can be approximated by the following equation:
:TDS = kEC
where TDS is expressed in mg/L and EC is the electrical conductivity in microsiemens per centimeter at 25 °C. The conversion factor k varies between 0.55 and 0.8.
Some TDS meters use an electrical conductivity measurement to the ppm using the above formula. Regarding units, 1 ppm indicates 1 mg of dissolved solids per 1000 g of water. | 2 | Environmental Chemistry |
Inert anodes are non-carbon based alternatives to traditional anodes used during aluminum reduction. These anodes do not chemically react with the electrolyte, and are therefore not consumed during the reduction process. Because the anode does not contain carbon, carbon dioxide is not produced. Through a review of literature, Haradlsson et al. found that inert anodes reduced the green house gas emissions of the aluminum smelting process by approximately 2 tonnes CO2eq/ tonne Al. | 8 | Metallurgy |
Hess's law is useful in the determination of enthalpies of the following:
#Heats of formation of unstable intermediates like CO and NO.
#Heat changes in phase transitions and allotropic transitions.
#Lattice energies of ionic substances by constructing Born–Haber cycles if the electron affinity to form the anion is known, or
#Electron affinities using a Born–Haber cycle with a theoretical lattice energy. | 7 | Physical Chemistry |
Perennial plants whose leaves are shed annually are said to have deciduous leaves, while leaves that remain through winter are evergreens.
Leaves attached to stems by stalks (known as petioles) are called petiolate, and if attached directly to the stem with no petiole they are called sessile.
* Ferns have fronds.
* Conifer leaves are typically needle- or awl-shaped or scale-like, they are usually evergreen, but can sometimes be deciduous. Usually, they have a single vein.
* Flowering plant (Angiosperm) leaves: the standard form includes stipules, a petiole, and a lamina.
* Lycophytes have microphylls.
* Sheath leaves are the type found in most grasses and many other monocots.
* Other specialized leaves include those of Nepenthes, a pitcher plant.
Dicot leaves have blades with pinnate venation (where major veins diverge from one large mid-vein and have smaller connecting networks between them). Less commonly, dicot leaf blades may have palmate venation (several large veins diverging from petiole to leaf edges). Finally, some exhibit parallel venation.
Monocot leaves in temperate climates usually have narrow blades, and usually parallel venation converging at leaf tips or edges. Some also have pinnate venation. | 5 | Photochemistry |
The rate for the hydrolysis of cobalt(III) ammine halide complexes are deceptive, appearing to be associative but proceeding by an alternative pathway. The hydrolysis of [Co(NH)Cl] follows second order kinetics: the rate increases linearly with concentration of hydroxide as well as the starting complex. Based on this information, the reactions would appear to proceed via nucleophilic attack of hydroxide at cobalt. Studies show, however, that the hydroxide deprotonates one NH ligand to give the conjugate base of the starting complex, i.e., [Co(NH)(NH)Cl]. In this monovalent cation, the chloride spontaneously dissociates. This pathway is called the S1cB mechanism. | 0 | Organic Chemistry |
The potential of mean force is usually applied in the Boltzmann inversion method as a first guess for the effective pair interaction potential that ought to reproduce the correct radial distribution function in a mesoscopic simulation.
Lemkul et al. have used steered molecular dynamics simulations to calculate the potential of mean force to assess the stability of Alzheimer's amyloid protofibrils. Gosai et al. have also used umbrella sampling simulations to show that potential of mean force decreases between thrombin and its aptamer (a protein-ligand complex) under the effect of electrical fields. | 7 | Physical Chemistry |
CS is synthesized by the reaction of 2-chlorobenzaldehyde and malononitrile via the Knoevenagel condensation:
::ClCHCHO + HC(CN) → ClCHCHC(CN) + HO
The reaction is catalysed with a weak base like piperidine or pyridine. The production method has not changed since the substance was discovered by Corson and Stoughton. Other bases, solvent free methods and microwave promotion have been suggested to improve the production of the substance.
The physiological properties had been discovered already by the chemists first synthesising the compound in 1928:
"Physiological Properties. Certain of these dinitriles have the effect of sneeze and tear gases. They are harmless when wet but to handle the dry powder is disastrous." | 1 | Biochemistry |
Segura and Quiles concluded that chilling stress only induces chlororespiration when the stem is significantly cool and the roots are simultaneously warmer compared to the average Spathiphyllum wallisii in controlled conditions. Segura and Quiles notice that PS II is present in chloroplast, (which is lacking in roots), thus by chilling the stem (which contains chloroplast), PS II ETCs can then be inhibited to trigger a reduction in PQ pool and as a result, chlororespiration. | 1 | Biochemistry |
The transition state model for a six-membered oxocarbenium ring was proposed earlier in 1992 by Woods et al. The general strategy for determining the stereochemistry of a nucleophilic addition to a six-membered ring follows a similar procedure to the case of the five-membered ring. The assumption that one makes for this analysis is that the ring is in the same conformation as cyclohexene, with three carbons and the oxygen in a plane with the two other carbon atome puckered out of the plane, with one above and one below (see the figure to the right). Based on the substituients present on the ring, the lowest energy conformation is determined, keeping in mind steric and stereoelectronic effects (see the section below for a discussion of stereoelectronic effects in oxocarbenium rings). Once this conformation is established, one can consider the nucleophilic addition. The addition will proceed through the low energy chair transition state, rather than the relatively high energy twist-boat. An example of this type of reaction can be seen below. The example also highlights how the stereoelectronic effect exerted by an electronegative substituent flips the lowest energy conformation and leads to opposite selectivity. | 0 | Organic Chemistry |
FDA hydrolysis is often used to measure activity in soil and compost samples; however, it may not give an accurate reading if microbes with lower activity phases, such as esterases, cleave the fluorescein first.
It is also used in combination with propidium iodide (PI) to determine viability in eukaryotic cells. Living cells will actively convert the non-fluorescent FDA into the green fluorescent compound fluorescein, a sign of viability; while nucleus of membrane-compromised cells will fluoresce red, a sign of cell death. Currently FDA/PI staining is the standard assessment of human pancreatic islet viability with suitability for transplantation when viability score is above 70%. | 1 | Biochemistry |
Magnetofection has been tested on a broad range of cell lines, hard-to-transfect and primary cells. Several optimized and efficient magnetic nanoparticle formulations have been specifically developed for several types of applications such as DNA, siRNA, and primary neuron transfection as well as viral applications.
Magnetofection research is currently in the preclinical stage. This technique has primarily been tested in vivo using plasmid DNA in mouse, rat, and rabbit models for applications in the hippocampus, subcutaneous tumors, lungs, spinal cord, and muscle.
Some applications include:
* Delivery of GFP gene into primary neural stem cells, which are typically difficult to transfect, with 18% efficacy with a static magnetic field and 32% efficacy with an oscillating field.
* Delivery of oligodesoxynucleotides (ODN) into human umbilical vein endothelial cells with 84% efficiency.
* Delivery of siRNA to HeLa cells to knock down luciferase reporter gene.
* Delivery of adenoviral vectors to primary human peripheral blood lymphocytes. | 1 | Biochemistry |
Five states are located along about of Caspian coastline. The length of the coastline of these countries:
# Kazakhstan -
# Turkmenistan -
# Azerbaijan -
# Russia -
# Iran - | 2 | Environmental Chemistry |
Substances in the chain-melted state display properties of both a solid and a liquid. The co-author of a study regarding the chain-melted state, Andreas Hermann, stated that if the matter were hypothetically to be handled by a person, it would be like holding a wet sponge that is leaking water, while the sponge itself is actually made of water. Described more formally, the potassium metal developed two internal structures, a chain-like lattice that dissolved, and a stronger Bravais lattice that remained in a solid state. This is a type of host–guest chemistry where, in this case, the host lattice of metal atoms remains solid while some of the material binds weakly and resembles a liquid. | 7 | Physical Chemistry |
In plants, production of 5-ALA is the step on which the speed of synthesis of chlorophyll is regulated. Plants that are fed by external 5-ALA accumulate toxic amounts of chlorophyll precursor, protochlorophyllide, indicating that the synthesis of this intermediate is not suppressed anywhere downwards in the chain of reaction. Protochlorophyllide is a strong photosensitizer in plants. Controlled spraying of 5-ALA at lower doses (up to 150 mg/L) can however help protect plants from stress and encourage growth. | 1 | Biochemistry |
The rotation of plane polarized light by chiral substances was first observed by Jean-Baptiste Biot in 1812, and gained considerable importance in the sugar industry, analytical chemistry, and pharmaceuticals. Louis Pasteur deduced in 1848 that this phenomenon has a molecular basis. The term chirality itself was coined by Lord Kelvin in 1894. Different enantiomers or diastereomers of a compound were formerly called optical isomers due to their different optical properties. At one time, chirality was thought to be restricted to organic chemistry, but this misconception was overthrown by the resolution of a purely inorganic compound, a cobalt complex called hexol, by Alfred Werner in 1911.
In the early 1970s, various groups established that the human olfactory organ is capable of distinguishing chiral compounds. | 4 | Stereochemistry |
The Kubelka–Munk equation describes the remission from a sample composed of an infinite number of infinitesimal layers, each having as an absorption fraction, and as a remission fraction. | 7 | Physical Chemistry |
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