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SBO is built in collaboration by the [http://www.ebi.ac.uk/compneur Computational Neurobiology Group] (Nicolas Le Novère, EMBL-EBI, United-Kingdom) and the SBMLTeam (Michael Hucka, Caltech, USA). | 1 | Biochemistry |
David G. Cory is a Professor of Chemistry at the University of Waterloo where he holds the Canada Excellence Research Chair in Quantum Information Processing. He works at the Institute for Quantum Computing, and is also associated with the Waterloo Institute for Nanotechnology. | 7 | Physical Chemistry |
Thomas Anderson (2 July 1819 – 2 November 1874) was a 19th-century Scottish chemist. In 1853 his work on alkaloids led him to discover the correct formula/composition for codeine. In 1868 he discovered pyridine and related organic compounds such as picoline through studies on the distillation of bone oil and other animal matter.
As well as his work on organic chemistry, Anderson made important contributions to agricultural chemistry, writing over 130 reports on soils, fertilisers and plant diseases. He kept abreast of all areas of science, and was able to advise his colleague Joseph Lister on Pasteur's germ theory and the use of carbolic acid as an antiseptic. | 0 | Organic Chemistry |
:This type of reactor contains two banks of heat exchangers which remove heat; the remainder of which is removed by the products and recycled in the system. The formation of heavy waxes should be avoided, since they condense on the catalyst and form agglomerations. This leads to fluidization. Hence, risers are operated over 297 °C (570 K). | 0 | Organic Chemistry |
The statistical analysis of the large quantity of data generated from sequencing approaches is a challenge. Even by only sequencing the exomes of individuals, a large quantity of data and sequence information is generated which requires a significant amount of data analysis. Challenges associated with the analysis of this data include changes in programs used to align and assemble sequence reads. Various sequencing technologies also have different error rates and generate various read-lengths which can pose challenges in comparing results from different sequencing platforms.
False positive and false negative findings are associated with genomic resequencing approaches and are critical issues. A few strategies have been developed to improve the quality of exome data such as:
* Comparing the genetic variants identified between sequencing and array-based genotyping
* Comparing the coding SNPs to a whole genome sequenced individual with the disorder
* Comparing the coding SNPs with Sanger sequencing of HapMap individuals
Rare recessive disorders may not have single nucleotide polymorphisms (SNPs) in public databases such as dbSNP. More common recessive phenotypes would be more likely to have disease-causing variants reported in dbSNP. For example, the most common cystic fibrosis variant has an allele frequency of about 3% in most populations. Screening out such variants might erroneously exclude such genes from consideration. Genes for recessive disorders are usually easier to identify than dominant disorders because the genes are less likely to have more than one rare nonsynonymous variant. The system that screens common genetic variants relies on dbSNP which may not have accurate information about the variation of alleles. Using lists of common variation from a study exome or genome-wide sequenced individual would be more reliable. A challenge in this approach is that as the number of exomes sequenced increases, dbSNP will also increase in the number of uncommon variants. It will be necessary to develop thresholds to define the common variants that are unlikely to be associated with a disease phenotype.
Genetic heterogeneity and population ethnicity are also major limitations as they may increase the number of false positive and false negative findings which will make the identification of candidate genes more difficult. Of course, it is possible to reduce the stringency of the thresholds in the presence of heterogeneity and ethnicity, however this will reduce the power to detect variants as well. Using a genotype-first approach to identify candidate genes might also offer a solution to overcome these limitations.
Unlike common variant analysis, the analysis of rare variants in whole-exome sequencing studies evaluates variant sets rather than single variants. Functional annotations predict the effect or function of rare variants and help prioritize rare functional variants. Incorporating these annotations can effectively boost the power of genetic association of rare variants analysis of whole genome sequencing studies. Some methods and tools have been developed to perform functionally-informed rare variant association analysis by incorporating functional annotations to empower analysis in whole exome sequencing studies. | 1 | Biochemistry |
Immediately after his Ph.D, in 1980, René Roy joined the National Research Council (NRC) in Ottawa where he worked as researcher in the Institute for Biological Sciences. Then, in 1985, he began his career as professor in the department of chemistry of the University of Ottawa where he served until December 2002. In parallel, he held the positions of Associate Director of the Ottawa-Carleton Chemistry Institute from 1993 to 1996, Director from 1996 to 1999, and again Associate Director in 2000. From 2002 to 2004, he was chairman of the American Chemical Society (ACS) Division of Carbohydrate Chemistry and, in 2005, head of the ACS awards committee.
In 2008, he returned to Montreal to teach organic chemistry at the Université du Québec à Montréal. There, he also founded the PharmaQAM biopharmaceutical research center which gathers some 50 professors and 17 institutions with common interests in the molecular aspects of medicinal chemistry and drug discovery working on new bioactive molecules, their mechanism of action and the way they are vectorized in vivo. He served as director of PharmaQAM until December 2017.
During his career, René Roy has co-developed meningitis vaccines, for humans and animals, that led to commercial success. One of them, targeting the Haemophilus influenzae b (HIB) bacteria, has been designed jointly with the Cuban researcher Vincente Verez Bencomo to prevent lethal meningitis and pneumonia in developing countries. It is the first human semi-synthetic glycoconjugate vaccine approved and remains the only one. In use since 2004, more than 34 million doses have been distributed to children in several countries including Vietnam, Syria, Brazil, Venezuela and Angola, eradicating the infectious disease in Cuba.
Rene Roy is a cofounder of Glycovax Pharma, a biotech company operating in Montreal, developing glycochemistry-based treatments against cancer and other disease with unmet medical needs. | 0 | Organic Chemistry |
In hydroesterification, alkenes and alkynes insert into the bond of carboxylic acids. Vinyl acetate is produced industrially by the addition of acetic acid to acetylene in the presence of zinc acetate catalysts: Presently, zinc acetate is used as the catalyst:
Vinyl acetate can also be produced by palladium-catalyzed reaction of ethylene, acetic acid, and oxygen:
Silicotungstic acid is used to manufacture ethyl acetate by the alkylation of acetic acid by ethylene: | 0 | Organic Chemistry |
In organic chemistry, hydroxamic acids are a class of organic compounds having a general formula bearing the functional group , where R and R' are typically organyl groups (e.g., alkyl or aryl) or hydrogen. They are amides () wherein the nitrogen atom has a hydroxyl () substituent. They are often used as metal chelators.
Common example of hydroxamic acid is aceto-N-methylhydroxamic acid (). Some uncommon examples of hydroxamic acids are formo-N-chlorohydroxamic acid () and chloroformo-N-methylhydroxamic acid (). | 0 | Organic Chemistry |
Polysulfides are a class of chemical compounds derived from anionic chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. The inorganic polysulfides have the general formula . These anions are the conjugate bases of polysulfanes . Organic polysulfides generally have the formulae , where R is an alkyl or aryl group. | 8 | Metallurgy |
Temperature measurement (also known as thermometry) describes the process of measuring a current temperature for immediate or later evaluation. Datasets consisting of repeated standardized measurements can be used to assess temperature trends. | 7 | Physical Chemistry |
The Curiosity rover encountered rocks of special interest on the surface of Aeolis Palus near Aeolis Mons ("Mount Sharp") in Gale Crater. In the autumn of 2012, rocks studied, on the way from Bradbury Landing to Glenelg Intrigue, included "Coronation" rock (August 19, 2012), "Jake Matijevic" rock (September 19, 2012), "Bathurst Inlet" rock (September 30, 2012). | 9 | Geochemistry |
The c-ANCA antigen is specifically proteinase 3 (PR3). p-ANCA antigens include myeloperoxidase (MPO) and bacterial permeability increasing factor Bactericidal/permeability-increasing protein (BPI). Other antigens exist for c-ANCA (atypical), however many are as yet unknown. Classical p-ANCA occurs with antibodies directed to MPO. p-ANCA without nuclear extension occurs with antibodies to BPI, cathepsin G, elastase, lactoferrin and lysozyme. GS-ANA are antibodies directed to granulocyte specific nuclear antigens. Atypical ANCA are thought to be antigens similar to that of the p-ANCAs, however may occur due to differences in neutrophil processing.
Other less common antigens include HMG1 (p-ANCA pattern), HMG2 (p-ANCA pattern), alpha enolase (p and c-ANCA pattern), catalase (p and c-ANCA pattern), beta glucuronidase (p-ANCA pattern), azurocidin (p and c-ANCA pattern), actin (p and a-ANCA) and h-lamp-2 (c-ANCA). | 1 | Biochemistry |
Frequent geometries considered involve the interaction between two identical spheres of radius R where the effective radius becomes
In the case of interaction between a sphere of radius R and a planar surface, one has
The above two relations can be obtained as special cases of the expression for R given further above. For the situation of perpendicularly crossing cylinders as used in the surface forces apparatus, one has
where R and R are the curvature radii of the two cylinders involved. | 7 | Physical Chemistry |
In chemistry, the common-ion effect refers to the decrease in solubility of an ionic precipitate by the addition to the solution of a soluble compound with an ion in common with the precipitate. This behaviour is a consequence of Le Chatelier's principle for the equilibrium reaction of the ionic association/dissociation. The effect is commonly seen as an effect on the solubility of salts and other weak electrolytes. Adding an additional amount of one of the ions of the salt generally leads to increased precipitation of the salt, which reduces the concentration of both ions of the salt until the solubility equilibrium is reached. The effect is based on the fact that both the original salt and the other added chemical have one ion in common with each other. | 7 | Physical Chemistry |
An analyte, component (in clinical chemistry), titrand (in titrations), or chemical species is a substance or chemical constituent that is of interest in an analytical procedure. The purest substances are referred to as analytes, such as 24 karat gold, NaCl, water, etc. In reality, no substance has been found to be 100% pure in its quality, so a substance that is found to be most pure (for some metals, 99% after electrolysis) is called an analyte. | 3 | Analytical Chemistry |
Polyethylene may be considered either as -[CH-CH-]- with a repeat unit of -[CH-CH]-, or as [-CH-]-, with a repeat unit of -[CH]-. Chemists tend to consider the repeat unit as -[CH-CH]- since this polymer is made from the monomer ethylene (CH=CH).
More complex repeat units can occur in vinyl polymers -[CH-CHR]-, if one hydrogen in the ethylene repeat unit is substituted by a larger fragment R. Polypropylene -[CH-CH(CH)]- has the repeat unit -[CH-CH(CH)]. Polystyrene has a chain where the substituent R is a phenyl group (CH), corresponding to a benzene ring minus one hydrogen: -[CH-CH(CH)]-, so the repeat unit is -[CH-CH(CH)]-. | 7 | Physical Chemistry |
Tamm et al. have shown that survivin inhibits both Bax and Fas-induced apoptotic pathways. The experiment involved transfecting HEK 293 cells with a Bax-encoding plasmid, which resulted in an increase in apoptosis (~7 fold) as measured by DAPI staining. They then contransfected the 293 cells with Bax-encoding plasmid and survivin-encoding plasmids. They observed that cells transfected along with the survivin showed a significant decrease in apoptosis (~3 fold). A similar result also showed for cells transfected with the Fas-overexpressing plasmid. Immunoblots were performed and confirmed that survivin does not inhibit by mechanism of preventing Bax or Fas protein from being made into fully functional proteins. Therefore, survivin should be acting somewhere downstream of the Bax or Fas signaling pathway to inhibit apoptosis through these pathways. | 1 | Biochemistry |
Of some interest in organic synthesis, electropositive metals react with many organic halides in a metal-halogen exchange:
The resulting organometallic compound is susceptible to hydrolysis:
Heavily studied examples are found in organolithium chemistry and organomagnesium chemistry. Some illustrative cases follow.
Lithium-halogen exchange is essentially irrelevant to remediation, but the method is useful for fine chemical synthesis. Sodium metal has been used for dehalogenation process.
Removal of halogen atom from arene-halides in the presence of Grignard agent and water for the formation of new compound is known as Grignard degradation. Dehalogenation using Grignard reagents is a two steps hydrodehalogenation process. The reaction begins with the formation of alkyl/arene-magnesium-halogen compound, followed by addition of proton source to form dehalogenated product. Egorov and his co-workers have reported dehalogenation of benzyl halides using atomic magnesium in 3P state at 600 °C. Toluene and bi-benzyls were produced as the product of the reaction. Morrison and his co-workers also reported dehalogenation of organic halides by flash vacuum pyrolysis using magnesium. | 0 | Organic Chemistry |
To deal with decreased ATP production through the electron transport chain, fish must activate anaerobic means of energy production (see anaerobic metabolism) while suppressing metabolic demands. The ability to decrease energy demand by metabolic suppression is essential to ensure hypoxic survival due to the limited efficiency of anaerobic ATP production. | 9 | Geochemistry |
In the spinodal region of the phase diagram, the free energy can be lowered by allowing the components to separate, thus increasing the relative concentration of a component material in a particular region of the material. The concentration will continue to increase until the material reaches the stable part of the phase diagram. Very large regions of material will change their concentration slowly due to the amount of material that must be moved. Very small regions will shrink away due to the energy cost of maintaining an interface between two dissimilar component materials.
To initiate a homogeneous quench a control parameter, such as temperature, is abruptly and globally changed. For a binary mixture of -type and -type materials, the Landau free-energy
is a good approximation of the free energy near the critical point and is often used to study homogeneous quenches. The mixture concentration is the density difference of the mixture components, the control parameters which determine the stability of the mixture are and , and the interfacial energy cost is determined by .
Diffusive motion often dominates at the length-scale of spinodal decomposition. The equation of motion for a diffusive system is
where is the diffusive mobility, is some random noise such that , and the chemical potential is derived from the Landau free-energy:
We see that if , small fluctuations around have a negative effective diffusive mobility and will grow rather than shrink. To understand the growth dynamics, we disregard the fluctuating currents due to , linearize the equation of motion around and perform a Fourier transform into -space. This leads to
which has an exponential growth solution:
Since the growth rate is exponential, the fastest growing angular wavenumber
will quickly dominate the morphology. We now see that spinodal decomposition results in domains of the characteristic length scale called the spinodal length:
The growth rate of the fastest-growing angular wave number is
where is known as the spinodal time.
The spinodal length and spinodal time can be used to nondimensionalize the equation of motion, resulting in universal scaling for spinodal decomposition. | 7 | Physical Chemistry |
Because oxygen and argon leak through packaging material at different rates, comparing the ratios inside a package can determine if and how quickly air from outside has leaked in. | 3 | Analytical Chemistry |
In Egypt around 2000 BC, the juice of Ammi majus was rubbed on patches of vitiligo after which patients were encouraged to lie in the sun. In the 13th century, vitiligo was treated with a tincture of honey and the powdered seeds of a plant called "aatrillal", which was abundant in the Nile Valley. The plant has since been identified as A. majus, which contains significant amounts of both bergapten and methoxsalen, two psoralen derivatives well known for their photosensitizing effects.
In the 1890s Niels Ryberg Finsen of Copenhagen developed a bulky phototherapy machine to treat skin diseases using UV light. In 1900, the French electrical engineer Gustave Trouvé miniaturized Finsen's machine with a series of portable light radiators to heal skin diseases such as lupus and epithelioma. Such machines have only been available in a chemically synthesized form since the 1970s.
In the 1940s, Abdel Monem El Mofty from Cairo University Medical School used crystalline methoxsalen (8-methoxypsoralen, also called xanthotoxin) followed by sunlight exposure to treat vitiligo. This began the development of modern PUVA therapy for the treatment of vitiligo, psoriasis, and other diseases of the skin. | 5 | Photochemistry |
The development of the Isa Process tank house technology at CRL eliminated the whole process and cost of producing the starter sheets by using stainless-steel permanent cathodes. It also included substantial automation of the process of inserting the permanent cathodes into the electrolytic cells and their subsequent removal and stripping of the sheets of deposited cathode copper. The labour force required to operate a refinery using the IsaKidd technology has been estimated at 60–70% less of that required for refineries using starter sheets.
MIM Holdings began marketing the Isa Process technology in 1980, as a result of demand from other refinery operators.
Falconbridge subsequently independently developed a similar process to improve operations at its Kidd Creek copper refinery, near Timmins, Ontario. The initial development of permanent cathodes was for internal use, but marketing of the Kidd Process was initiated in 1992 after requests from other refinery operators.
The two technologies were brought together as the IsaKidd Technology in 2006, when Xstrata bought Falconbridge.
The IsaKidd Technology now dominates global copper refining. It has been licensed to 102 users and Xstrata Technology, which markets the technology, reports on its website a total installed capacity of some 12 million tonnes per year (“t/y”) of copper production, as of October 2011. This is about 60% of the estimated 2011 global refined copper production of 19.7 million tonnes.
The development of the IsaKidd technology allowed increased productivity, reduced operating costs and the production of consistent, high-quality cathode copper. | 8 | Metallurgy |
Core-electron binding energy (CEBE) shifts correlate linearly with the Hammett substituent constants (σ) in substituted benzene derivatives.
Consider para-disubstituted benzene p-F-CH-Z, where Z is a substituent such as NH, NO, etc. The fluorine atom is para with respect to the substituent Z in the benzene ring. The image on the right shows four distinguished ring carbon atoms, C1(ipso), C2(ortho), C3(meta), C4(para) in p-F-CH-Z molecule. The carbon with Z is defined as C1(ipso) and fluorinated carbon as C4(para). This definition is followed even for Z = H. The left-hand side of () is called CEBE shift or ΔCEBE, and is defined as the difference between the CEBE of the fluorinated carbon atom in p-F-CH-Z and that of the fluorinated carbon in the reference molecule FCH.
The right-hand side of Eq. is a product of a parameter κ and a Hammett substituent constant at the para position, σp. The parameter is defined by eq. :
where and are the Hammett reaction constants for the reaction of the neutral molecule and core ionized molecule, respectively. ΔCEBEs of ring carbons in p-F-CH-Z were calculated with density functional theory to see how they correlate with Hammett σ-constants. Linear plots were obtained when the calculated CEBE shifts at the ortho, meta and para carbon were plotted against Hammett σ, σ and σ constants respectively.
* value calculated ≈ 1.
Hence the approximate agreement in numerical value and in sign between the CEBE shifts and their corresponding Hammett σ constant. | 7 | Physical Chemistry |
Heterolytic bond cleavage is a process where the electron pair that comprised a bond moves to one of the atoms that was formerly joined by a bond. The bond breaks, forming a negatively charged species (an anion) and a positively charged species (a cation). The anion is the species that retains the electrons from the bond while the cation is stripped of the electrons from the bond. The anion usually forms on the most electronegative atom, in this example atom A. This is because the most electronegative atom will naturally attract electrons towards itself more strongly, leading to its negative charge. | 0 | Organic Chemistry |
Swansea University has had a long established history of development and innovation in mass spectrometry and chromatography. | 3 | Analytical Chemistry |
In the secondary structure of proteins, hydrogen bonds form between the backbone oxygens and amide hydrogens. When the spacing of the amino acid residues participating in a hydrogen bond occurs regularly between positions i and , an alpha helix is formed. When the spacing is less, between positions i and , then a 3 helix is formed. When two strands are joined by hydrogen bonds involving alternating residues on each participating strand, a beta sheet is formed. Hydrogen bonds also play a part in forming the tertiary structure of protein through interaction of R-groups. (See also protein folding).
Bifurcated H-bond systems are common in alpha-helical transmembrane proteins between the backbone amide of residue i as the H-bond acceptor and two H-bond donors from residue : the backbone amide and a side-chain hydroxyl or thiol . The energy preference of the bifurcated H-bond hydroxyl or thiol system is -3.4 kcal/mol or -2.6 kcal/mol, respectively. This type of bifurcated H-bond provides an intrahelical H-bonding partner for polar side-chains, such as serine, threonine, and cysteine within the hydrophobic membrane environments.
The role of hydrogen bonds in protein folding has also been linked to osmolyte-induced protein stabilization. Protective osmolytes, such as trehalose and sorbitol, shift the protein folding equilibrium toward the folded state, in a concentration dependent manner. While the prevalent explanation for osmolyte action relies on excluded volume effects that are entropic in nature, circular dichroism (CD) experiments have shown osmolyte to act through an enthalpic effect. The molecular mechanism for their role in protein stabilization is still not well established, though several mechanisms have been proposed. Computer molecular dynamics simulations suggest that osmolytes stabilize proteins by modifying the hydrogen bonds in the protein hydration layer.
Several studies have shown that hydrogen bonds play an important role for the stability between subunits in multimeric proteins. For example, a study of sorbitol dehydrogenase displayed an important hydrogen bonding network which stabilizes the tetrameric quaternary structure within the mammalian sorbitol dehydrogenase protein family.
A protein backbone hydrogen bond incompletely shielded from water attack is a dehydron. Dehydrons promote the removal of water through proteins or ligand binding. The exogenous dehydration enhances the electrostatic interaction between the amide and carbonyl groups by de-shielding their partial charges. Furthermore, the dehydration stabilizes the hydrogen bond by destabilizing the nonbonded state consisting of dehydrated isolated charges.
Wool, being a protein fibre, is held together by hydrogen bonds, causing wool to recoil when stretched. However, washing at high temperatures can permanently break the hydrogen bonds and a garment may permanently lose its shape. | 6 | Supramolecular Chemistry |
Presently known "super" states of matter are superconductors, superfluid liquids and gases, and supersolids. Egor Babaev predicted that if hydrogen and deuterium have liquid metallic states, they might have quantum ordered states that cannot be classified as superconducting or superfluid in the usual sense. Instead, they might represent two possible novel types of quantum fluids: superconducting superfluids and metallic superfluids. Such fluids were predicted to have highly unusual reactions to external magnetic fields and rotations, which might provide a means for experimental verification of Babaev's predictions. It has also been suggested that, under the influence of a magnetic field, hydrogen might exhibit phase transitions from superconductivity to superfluidity and vice versa. | 7 | Physical Chemistry |
A glycosidic bond or glycosidic linkage is a type of ether bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.
A glycosidic bond is formed between the hemiacetal or hemiketal group of a saccharide (or a molecule derived from a saccharide) and the hydroxyl group of some compound such as an alcohol. A substance containing a glycosidic bond is a glycoside.
The term glycoside is now extended to also cover compounds with bonds formed between hemiacetal (or hemiketal) groups of sugars and several chemical groups other than hydroxyls, such as -SR (thioglycosides), -SeR (selenoglycosides), -NRR (N-glycosides), or even -CRRR (C-glycosides).
Particularly in naturally occurring glycosides, the compound ROH from which the carbohydrate residue has been removed is often termed the aglycone, and the carbohydrate residue itself is sometimes referred to as the glycone. | 0 | Organic Chemistry |
Another proposal is that the dual-molecule system we see today, where a nucleotide-based molecule is needed to synthesize protein, and a peptide-based (protein) molecule is needed to make nucleic acid polymers, represents the original form of life. This theory is called RNA-peptide coevolution, or the Peptide-RNA world, and offers a possible explanation for the rapid evolution of high-quality replication in RNA (since proteins are catalysts), with the disadvantage of having to postulate the coincident formation of two complex molecules, an enzyme (from peptides) and a RNA (from nucleotides). In this Peptide-RNA World scenario, RNA would have contained the instructions for life, while peptides (simple protein enzymes) would have accelerated key chemical reactions to carry out those instructions. The study leaves open the question of exactly how those primitive systems managed to replicate themselves — something neither the RNA World hypothesis nor the Peptide-RNA World theory can yet explain, unless polymerases (enzymes that rapidly assemble the RNA molecule) played a role.
A research project completed in March 2015 by the Sutherland group found that a network of reactions beginning with hydrogen cyanide and hydrogen sulfide, in streams of water irradiated by UV light, could produce the chemical components of proteins and lipids, alongside those of RNA. The researchers used the term "cyanosulfidic" to describe this network of reactions. In November 2017, a team at the Scripps Research Institute identified reactions involving the compound diamidophosphate which could have linked the chemical components into short peptide and lipid chains as well as short RNA-like chains of nucleotides. | 9 | Geochemistry |
In organic chemistry, Möbius aromaticity is a special type of aromaticity believed to exist in a number of organic molecules. In terms of molecular orbital theory these compounds have in common a monocyclic array of molecular orbitals in which there is an odd number of out-of-phase overlaps, the opposite pattern compared to the aromatic character to Hückel systems. The nodal plane of the orbitals, viewed as a ribbon, is a Möbius strip, rather than a cylinder, hence the name. The pattern of orbital energies is given by a rotated Frost circle (with the edge of the polygon on the bottom instead of a vertex), so systems with 4n electrons are aromatic, while those with 4n + 2 electrons are anti-aromatic/non-aromatic. Due to incrementally twisted nature of the orbitals of a Möbius aromatic system, stable Möbius aromatic molecules need to contain at least 8 electrons, although 4 electron Möbius aromatic transition states are well known in the context of the Dewar-Zimmerman framework for pericyclic reactions. Möbius molecular systems were considered in 1964 by Edgar Heilbronner by application of the Hückel method, but the first such isolable compound was not synthesized until 2003 by the group of Rainer Herges. However, the fleeting trans-CH cation, one conformation of which is shown on the right, was proposed to be a Möbius aromatic reactive intermediate in 1998 based on computational and experimental evidence. | 7 | Physical Chemistry |
Slayton A. Evans Jr. (May 17, 1943 – March 24, 2001) was an American chemist and professor at the University of North Carolina, Chapel Hill. He was a leading researcher into organophosphorus chemistry. His research led to a greater understanding of the functions of organophosphate compounds and innovations in methods to produce chemical compounds for pharmaceutical drugs. | 4 | Stereochemistry |
The process in which amylase breaks down starch for sugar consumption is not consistent with all organisms that use amylase to breakdown stored starch. There are different amylase pathways that are involved in starch degradation. The occurrence of starch degradation into sugar by the enzyme amylase was most commonly known to take place in the Chloroplast, but that has been proven wrong. One example is the spinach plant, in which the chloroplast contains both alpha and beta amylase (They are different versions of amylase involved in the breakdown of starch and they differ in their substrate specificity). In spinach leaves, the extrachloroplastic region contains the highest level of amylase degradation of starch. The difference between chloroplast and extrachloroplastic starch degradation is in the amylase pathway they prefer; either beta or alpha amylase. For spinach leaves, Alpha-amylase is preferred but for plants/organisms like wheat, barley, peas, etc. the Beta-amylase is preferred. | 0 | Organic Chemistry |
Metal carbonyls are often characterized by C NMR spectroscopy. To improve the sensitivity of this technique, complexes are often enriched with CO. Typical chemical shift range for terminally bound ligands is 150 to 220 ppm. Bridging ligands resonate between 230 and 280 ppm. The C signals shift toward higher fields with an increasing atomic number of the central metal.
NMR spectroscopy can be used for experimental determination of the fluxionality.
The activation energy of ligand exchange processes can be determined by the temperature dependence of the line broadening. | 0 | Organic Chemistry |
The reason that Pseudomonas aeruginosa produces rhamnolipids is the subject of much speculation. They have been shown to have several properties, and investigations in a rhlA mutant that does not make HAAs nor rhamnolipids have attributed many functions to rhamnolipids which may in fact be due to HAAs. These functions fall broadly into five categories, described below. | 0 | Organic Chemistry |
Once transported, the translated protein is 396 residues in length, with an N-terminus located at amino acids 1-25, a C-terminus at 155-396 (note that the spectrin homology located at 228-380 within the C-terminal), and a putative coiled coil domain at amino acids 26-154. Additionally, the protein has binding sites for endophilin 3 and dynamin 2 at amino acids 89-100 and 195-214, respectively. While Arc mRNA is subject to degradation by NMD, the translated protein contains a PEST sequence at amino acids 351-392, indicating proteasome-dependent degradation. The translated protein can be visualized with an immunoblot as a band at 55 kDa. The ARC protein can form virus-like capsids that package mRNA and can traffic between cells.
Synaptically localized Arc protein interacts with dynamin and endophilin, proteins involved in clathrin-mediated endocytosis, and facilitates the removal of AMPA receptors from the plasma membrane. Consistent with this, increased Arc levels reduce AMPA currents, while Arc KOs display increases in surface AMPA expression. | 1 | Biochemistry |
Studies have shown that Zn, Pb, Cd, Sn and In can embrittle steel at temperature below each embrittler’s melting point.
*Cadmium can embrittle titanium at temperatures below its melting point.
*Hg can embrittle zinc at temperatures below its melting point.
*Hg can embrittle copper at temperatures below its melting point. | 8 | Metallurgy |
HTK (branded as Custodiol® by Essential Pharmaceuticals LLC), has been presented by industry to surgeons as an alternative solution that exceeds other cardioplegias in myocardial protection during cardiac surgery. This claim relies on the single-dose administration of HTK compared with other multidose cardioplegias (MDC), sparing time in the adjustment of equipment during cardioplegia re-administration, allowing greater time to operate and thus a decreased CPB duration. Other benefits include a lower concentration of sodium, calcium, and potassium compared with other cardioplegias with cardiac arrest arising from the deprivation of sodium. Finally, histidine is thought to aid buffering, mannitol and tryptophan to improve membrane stability, and ketoglutarate to help ATP production during reperfusion.
A 2021 meta-analysis demonstrated no statistical advantage of HTK over blood or other crystalloid cardioplegias during adult cardiac surgery. The only practical advantage of HTK, therefore, is the single-dose administration compared to multi-dose requirements of blood and other crystalloid cardioplegia. | 1 | Biochemistry |
Non-pathogenic species of the gram-positive Corynebacterium are used for the commercial production of various amino acids. The C. glutamicum species is widely used for producing glutamate and lysine, components of human food, animal feed and pharmaceutical products.
Expression of functionally active human epidermal growth factor has been done in C. glutamicum, thus demonstrating a potential for industrial-scale production of human proteins. Expressed proteins can be targeted for secretion through either the general, secretory pathway (Sec) or the twin-arginine translocation pathway (Tat).
Unlike gram-negative bacteria, the gram-positive Corynebacterium lack lipopolysaccharides that function as antigenic endotoxins in humans. | 1 | Biochemistry |
When two lipid bilayers approach each other, they experience weak van der Waals attractive forces and much stronger repulsive forces due to hydration repulsion. These forces are normally dominant over the hydrophobic attractive forces between the membranes. Studies done on membrane bilayers using Surface forces apparatus (SFA) indicate that membrane fusion can instantaneously occur when two bilayers are still at a finite distance from each other without them having to overcome the short-range repulsive force barrier. This is attributed to the molecular rearrangements that occur resulting in the bypassing of these forces by the membranes. During fusion, the hydrophobic tails of a small patch of lipids on the cell membrane are exposed to the aqueous phase surrounding them. This results in very strong hydrophobic attractions (which dominate the repulsive force) between the exposed groups leading to membrane fusion. The attractive van der Waals forces play a negligible role in membrane fusion. Thus, fusion is a result of the hydrophobic attractions between internal hydrocarbon chain groups that are exposed to the normally inaccessible aqueous environment. Fusion is observed to start at points on the membranes where the membrane stresses are either the weakest or the strongest. | 6 | Supramolecular Chemistry |
Lichen associations may be examples of mutualism or commensalism, but the lichen relationship can be considered parasitic under circumstances where the photosynthetic partner can exist in nature independently of the fungal partner, but not vice versa. Photobiont cells are routinely destroyed in the course of nutrient exchange. The association continues because reproduction of the photobiont cells matches the rate at which they are destroyed. The fungus surrounds the algal cells, often enclosing them within complex fungal tissues unique to lichen associations. In many species the fungus penetrates the algal cell wall, forming penetration pegs (haustoria) similar to those produced by pathogenic fungi that feed on a host. Cyanobacteria in laboratory settings can grow faster when they are alone rather than when they are part of a lichen. | 2 | Environmental Chemistry |
Jun 1943. Further report on the use of aged chromate baths to specification DTD 911, Bath iii (30 minute hot chromate bath). Petch M K. RAE MR7147(A). Met/RTN/22
Feb 1944. Variations in corrosion properties over magnesium alloy sheet. Jones E R W Petch M K. RAE MR6858. Met/RTN/21, also in J. Inst. Metals, Nov. I946
Feb 1944. Protection of magnesium alloy sheet to specification DTD 118 by a modified form of the I.G. acid dip (bath iv of specification.DTD 911). Petch M K. RAE MR7588. Met/RTN/23
Mar 1944. Protection of magnesium alloys against corrosion by electrolytic chromate films. Petch M K. RAE MR3726(D). Met/RTN/17
Nov 1944. The protection of magnesium alloy components against corrosion by sprayed coatings of "Thickal" Latex. Petch M K. RAE MR7290. Met/RTN/22
1949. Some Observations on the Behaviour of Platinum/Platinum-Rhodium Thermocouples at High Temperatures. M K McQuillan. Journal of Scientific Instruments, Volume 26, Number 10
1956. Titanium - Metallurgy of the Rarer Metals – 4. by McQuillan MK.; Publisher: London, Butterworths, 1956.
1956. Titanium. McQuillan, A. D.; McQuillan, M. K.; Castle, J. G.Physics Today, vol. 9, issue 10, p. 24. Publication Date: 00/1956
1956. Titanium. Alan Dennis McQuillan; Marion Katharine McQuillan. Publisher: New York : Academic Press ; London : Butterworths Scientific Publications, 1956.
1957. Titanium. Alan D MacQuillan; Marion Katharine Macquillan. Publisher: London Butterworth [1957]
1958. Titan. Alan Denis McQuillan; Marion Katharine McQuillan; Sergej Georgievič Glazunov; Leonid Pavlovič Lužnikov.Language: Russian . Publisher: Moskva : Gosudarstvennoe Naučno-Tehničeskoe Izdatel'stvo Literatury po Černoj i Cvetnoj Metallurgii, 1958.
1978. McQuillan, Marion. Graduate Engineers in Production. Cranfield Inst of Tech, 1978.
1979. Graduate myth. Production Engineer (Volume: 58 , Issue: 4 , April 1979 ) | 8 | Metallurgy |
The most environmentally relevant species of these nanoparticles are silver chloride within marine ecosystems and organic thiols within terrestrial ecosystems. Once Ag enters the environment, it is oxidized to Ag. Of the potential species formed in seawater, such as AgS and AgCO, AgCl is the most thermodynamically favored due to its stability, solubility, and the abundance of Cl in seawater. Research has shown that partially oxidized nanoparticles may be more toxic than those that are freshly prepared.
It was also found that Ag dissolutes more in solution when the pH is low and bleaching has occurred. This effect, coupled with ocean acidification and increasing coral reef bleaching events, leads to a compounding effect of Ag accumulation in the global marine ecosystem. These free formed Ag ions can accumulate and block the regulation of Na and Cl ion exchange within the gills of fish, leading to blood acidosis which is fatal if left unchecked. Additionally, fish can accumulate Ag through their diet. Phytoplankton, which form the base level of aquatic food chains, can absorb and collect silver from their surroundings.
As fish eat phytoplankton, the silver accumulates within their circulatory system, which has been shown to negatively impact embryonic fish, causing spinal cord deformities and cardiac arrhythmia. The other class of organisms heavily affected by silver nanoparticles is bivalves. Filter feeding bivalves accumulate nanoparticles to concentrations 10,000 times greater than was added to seawater, and Ag ions are proven to be extremely toxic to them.
The base of complex food webs consists of microbes, and these organisms are most heavily impacted by nanoparticles. These effects cascade into the problems that have now reached an observable scale. As global temperatures rise and oceanic pH drops, some species, such as oysters, will be even more susceptible to the negative impacts of nanoparticles as they are stressed. | 2 | Environmental Chemistry |
Bottromycin is a macrocyclic peptide with antibiotic activity. It was first discovered in 1957 as a natural product isolated from Streptomyces bottropensis. It has been shown to inhibit methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE) among other Gram-positive bacteria and mycoplasma. Bottromycin is structurally distinct from both vancomycin, a glycopeptide antibiotic, and methicillin, a beta-lactam antibiotic.
Bottromycin binds to the A site of the ribosome and blocks the binding of aminoacyl-tRNA, therefore inhibiting bacterial protein synthesis. Although bottromycin exhibits antibacterial activity in vitro, it has not yet been developed as a clinical antibiotic, potentially due to its poor stability in blood plasma. To increase its stability in vivo, some bottromycin derivatives have been explored.
The structure of bottromycin contains a macrocyclic amidine as well as a thiazole ring. The absolute stereochemistry at several chiral centers has been determined as of 2009. In 2012, a three-dimensional solution structure of bottromycin was published. The solution structure revealed that several methyl groups are on the same face of the structure.
Bottromycin falls within the ribosomally synthesized and post-translationally modified peptide class of natural product. | 0 | Organic Chemistry |
Electron-deficient olefins, such as enones and acryl derivatives can be epoxidized using nucleophilic oxygen compounds such as peroxides. The reaction is a two-step mechanism. First the oxygen performs a nucleophilic conjugate addition to give a stabilized carbanion. This carbanion then attacks the same oxygen atom, displacing a leaving group from it, to close the epoxide ring.. | 0 | Organic Chemistry |
Examples of amphiphilic compounds are the salts of fatty acids, phospholipids. Many simple amphiphiles are used as detergents. A mixture of soap and water is an everyday example of a lyotropic liquid crystal.
Biological structures such as fibrous proteins showings relatively long and well-defined hydrophobic and hydrophilic ‘‘blocks’’ of aminoacids can also show lyotropic liquid crystalline behaviour. | 7 | Physical Chemistry |
The four fundamental classes of forces and interaction in protein adsorption are: 1) ionic or electrostatic interaction, 2) hydrogen bonding, 3) hydrophobic interaction (largely entropically driven), and 4) interactions of charge-transfer or particle electron donor/acceptor type. | 1 | Biochemistry |
Salbutamol's low toxicity makes it safe for other animals and thus is the medication of choice for treating acute airway obstruction in most species. It is usually used to treat bronchospasm or coughs in cats and dogs and used as a bronchodilator in horses with recurrent airway obstruction; it can also be used in emergencies to treat asthmatic cats.
Toxic effects require an extremely high dose, and most overdoses are due to dogs chewing on and puncturing an inhaler or nebulizer vial. | 4 | Stereochemistry |
To carry out metal cation titrations using EDTA, it is almost always necessary to use a complexometric indicator to determine when the end point has been reached. Common indicators are organic dyes such as Fast Sulphon Black, Eriochrome Black T, Eriochrome Red B, Patton Reeder, or Murexide. Color change shows that the indicator has been displaced (usually by EDTA) from the metal cations in solution when the end point has been reached. Thus, the free indicator (rather than the metal complex) serves as the endpoint indicator. | 3 | Analytical Chemistry |
If the two free ends of an ideal chain are pulled apart by some sort of device, then the device experiences a force exerted by the polymer. As the ideal chain is stretched, its energy remains constant, and its time-average, or internal energy, also remains constant, which means that this force necessarily stems from a purely entropic effect.
This entropic force is very similar to the pressure experienced by the walls of a box containing an ideal gas. The internal energy of an ideal gas depends only on its temperature, and not on the volume of its containing box, so it is not an energy effect that tends to increase the volume of the box like gas pressure does. This implies that the pressure of an ideal gas has a purely entropic origin.
What is the microscopic origin of such an entropic force or pressure? The most general answer is that the effect of thermal fluctuations tends to bring a thermodynamic system toward a macroscopic state that corresponds to a maximum in the number of microscopic states (or micro-states) that are compatible with this macroscopic state. In other words, thermal fluctuations tend to bring a system toward its macroscopic state of maximum entropy.
What does this mean in the case of the ideal chain? First, for our ideal chain, a microscopic state is characterized by the superposition of the states of each individual monomer (with i varying from 1 to N). In its solvent, the ideal chain is constantly subject to shocks from moving solvent molecules, and each of these shocks sends the system from its current microscopic state to another, very similar microscopic state. For an ideal polymer, as will be shown below, there are more microscopic states compatible with a short end-to-end distance than there are microscopic states compatible with a large end-to-end distance. Thus, for an ideal chain, maximizing its entropy means reducing the distance between its two free ends. Consequently, a force that tends to collapse the chain is exerted by the ideal chain between its two free ends.
In this section, the mean of this force will be derived. The generality of the expression obtained at the thermodynamic limit will then be discussed. | 7 | Physical Chemistry |
The release of neurotransmitter is accomplished by the fusion of neurotransmitter vesicles to the presynaptic membrane. Although the details of this mechanism are still being studied there is a consensus on some details of the process. Synaptic vesicle fusion with the presynaptic membrane is known to require a local increase of calcium from as few as a single, closely associated calcium channels and the formation of highly stable SNARE complexes. One prevailing model of synaptic vesicle fusion is that SNARE complex formation is catalyzed by the proteins of the active zone such as Munc18, Munc13, and RIM. The formation of this complex is thought to "prime" the vesicle to be ready for vesicle fusion and release of neurotransmitter (see below: releasable pool). After the vesicle is primed then complexin binds to the SNARE complex this is called "superprimed". The vesicles that are superprimed are within the readily releasable pool (see below) and are ready to be rapidly released. The arrival of an action potential opens voltage gated calcium channels near the SNARE/complexin complex. Calcium then binds to change the conformation of synaptotagmin. This change in conformation of allows synaptotagmin to then dislodge complexin, bind to the SNARE complex, and bind to the target membrane. When synaptotagmin binds to both the SNARE complex and the membrane this induces a mechanical force on the membrane so that it causes the vesicle membrane and presynaptic membrane to fuse. This fusion opens a membrane pore that releases the neurotransmitter. The pore increases in size until the entire vesicle membrane is indistinguishable from the presynaptic membrane. | 1 | Biochemistry |
Large-scale oceanic circulation has a direct impact on opal deposition. The Pacific (characterized by nutrient poor surface waters, and deep nutrient rich waters) and Atlantic Ocean circulations favor the production/preservation of silica and carbonate respectively. For instance, Si/N and Si/P ratios increase from the Atlantic to the Pacific and Southern Ocean, favoring opal versus carbonate producers. Consequently, the modern configuration of large-scale oceanic circulation resulted in the localization of major opal burial zones in the Equatorial Pacific, in the eastern boundary current upwelling systems, and by far the most important, the Southern Ocean. | 1 | Biochemistry |
Zelinsky created a large scientific school and its scientists made fundamental contributions to various fields of chemistry. Among his students werw Academicians of the Academy of Sciences of the USSR A. A. Balandin, L. F. Vereshchagin, B. A. Kazansky, K. A. Kocheshkov, S. S. Nametkin, A. N. Nesmeyanov; Corresponding Members of the Academy of Sciences of the USSR N. A. Izgaryshev, K. P. Lavrovsky, Yu. G. Mamedaliev, B. M. Mikhailov, A. V. Rakovsky, V. V. Chelintsev, N. I. Shuikin; professors V. V. Longinov, A. E. Uspensky, L. A. Chugaev, N. A. Shilov, V. A. Nekrasova-Popova and others.
N. D. Zelinsky - one of the organizers of the All-Union Chemical Society named after D. I. Mendeleev; since 1941 he was its honorary member. Since 1921 - an honorary member of the Moscow Society of Naturalists, since 1935 he was its president. | 0 | Organic Chemistry |
Propionyl-CoA has can have many adverse and toxic affects on different species, including bacterium. For example, inhibition of pyruvate dehydrogenase by an accumulation of propionyl-CoA in Rhodobacter sphaeroides can prove deadly. Furthermore, as with E. coli, an influx of propionyl-CoA in Myobacterial species can result in toxicity if not dealt with immediately. This toxicity is caused by a pathway involving the lipids that form the bacterial cell wall. Using esterification of long-chain fatty acids, excess propionyl-CoA can be sequestered and stored in the lipid, triacylglycerol (TAG), leading to regulation of elevated propionyl-CoA levels. Such a process of methyl branching of the fatty acids causes them to act as sinks for accumulating propion | 1 | Biochemistry |
Yuan Chengye (; 1924–2018) was a Chinese organic chemist.
Yuan was born in Shangyu, Zhejiang province in 1924. He graduated from National College of Pharmacy (now China Pharmaceutical University) in 1948 and received Degree for Candidate for D.Sc from All-Union Research Institute of Pharmaceutical Chemistry, Moscow in 1955. He worked at the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences after returning to China. He led a research team for nuclear fuel extractants since 1958. In 1997, he was elected an academician of the Chinese Academy of Sciences. He died on 9 January 2018. | 0 | Organic Chemistry |
PCBs have low water solubility, so they adhere tightly to soil and cannot be easily accessed by bacteria. Especially, if the contaminations site has been exposed to PCBs for long period, PCBs can be integrated into soil or sediment matrices, then further decrease their bioavailability. Some surfactants can help solubilize but cannot increase the rate of PCBs degrading. However, if PCBs are linked to surfactants tightly too, then this process cannot promote the absorption of PCBs and even lower it. Also, many surfactants have been proven to be toxic to cells and the high cost of surfactants is another issues. | 1 | Biochemistry |
The inversion of ammonia was first detected by microwave spectroscopy in 1934.
In one study the inversion in an aziridine was slowed by a factor of 50 by placing the nitrogen atom in the vicinity of a phenolic alcohol group compared to the oxidized hydroquinone.
The system interconverts by oxidation by oxygen and reduction by sodium dithionite. | 4 | Stereochemistry |
Organic esters, ketones, and aldehydes with an α-hydrogen ( bond adjacent to the carbonyl group) often form enols. The reaction involves migration of a proton () from carbon to oxygen:
In the case of ketones, the conversion is called a keto-enol tautomerism, although this name is often more generally applied to all such tautomerizations. Usually the equilibrium constant is so small that the enol is undetectable spectroscopically.
In some compounds with two (or more) carbonyls, the enol form becomes dominant. The behavior of 2,4-pentanedione illustrates this effect:
Enols are derivatives of vinyl alcohol, with a connectivity. Deprotonation of organic carbonyls gives the enolate anion, which are a strong nucleophile. A classic example for favoring the keto form can be seen in the equilibrium between vinyl alcohol and acetaldehyde (K = [enol]/[keto] ≈ 3). In 1,3-diketones, such as acetylacetone (2,4-pentanedione), the enol form is favored.
The acid-catalyzed conversion of an enol to the keto form proceeds by proton transfer from O to carbon. The process does not occur intramolecularly, but requires participation of solvent or other mediators. | 0 | Organic Chemistry |
PDE3 enzymes are involved in regulation of cardiac and vascular smooth muscle contractility. Molecules that inhibit PDE3 were originally investigated for the treatment of heart failure, but, because of unwanted arrhythmic side-effects, they are not studied for that indication any longer. Nonetheless, the PDE3 inhibitor milrinone is approved for use in heart failure in intravenous form.
Both PDE3A and PDE3B are expressed in vascular smooth muscle cells and are likely to modulate contraction. Their expression in vascular smooth muscle is altered under specific conditions such as elevated cAMP and hypoxia. | 1 | Biochemistry |
DNA ends refer to the properties of the ends of linear DNA molecules, which in molecular biology are described as "sticky" or "blunt" based on the shape of the complementary strands at the terminus. In sticky ends, one strand is longer than the other (typically by at least a few nucleotides), such that the longer strand has bases which are left unpaired. In blunt ends, both strands are of equal length – i.e. they end at the same base position, leaving no unpaired bases on either strand.
The concept is used in molecular biology, in cloning, or when subcloning insert DNA into vector DNA. Such ends may be generated by restriction enzymes that break the molecule's phosphodiester backbone at specific locations, which themselves belong to a larger class of enzymes called exonucleases and endonucleases. A restriction enzyme that cuts the backbones of both strands at non-adjacent locations leaves a staggered cut, generating two overlapping sticky ends, while an enzyme that makes a straight cut (at locations directly across from each other on both strands) generates two blunt ends. | 1 | Biochemistry |
An Alfvén resonator or Ionosphere Alfvén resonator is a spectral resonance structure found within geomagnetic fields in the frequency range of 0.1–10 Hz. First reported in 1989, they are ionospheric short-period geomagnetic variations primarily seen as nighttime phenomena and rarely observed during the day. The nighttime preference is due to lower electrical conductivity in the ionospheric dynamo region, which enables the feedback instability. | 7 | Physical Chemistry |
Carboxylation is a standard conversion in organic chemistry. Specifically carbonation (i.e. carboxylation) of Grignard reagents and organolithium compounds is a classic way to convert organic halides into carboxylic acids.
Sodium salicylate, precursor to aspirin, is commercially prepared by treating sodium phenolate (the sodium salt of phenol) with carbon dioxide at high pressure (100 atm) and high temperature (390 K) – a method known as the Kolbe-Schmitt reaction. Acidification of the resulting salicylate salt gives salicylic acid.
Many detailed procedures are described in the journal Organic Syntheses.
Carboxylation catalysts include N-Heterocyclic carbenes and catalysts based on silver. | 0 | Organic Chemistry |
A proton-pumping, ubiquinone-using NADH dehydrogenase complex, homologous to complex I, is found in the chloroplast genomes of most land plants under the name ndh. This complex is inherited from the original symbiosis from cyanobacteria, but has been lost in most eukaryotic algae, some gymnosperms (Pinus and gnetophytes), and some very young lineages of angiosperms. The purpose of this complex is originally cryptic as chloroplasts do not participate in respiration, but now it is known that ndh serves to maintain photosynthesis in stressful situations. This makes it at least partially dispensable in favorable conditions. It is evident that angiosperm lineages without ndh do not last long from their young ages, but how gymnosperms survive on land without ndh for so long is unknown. | 1 | Biochemistry |
The term depletion gilding usually refers to the production of a layer of gold. However, it can also be used to produce a layer that is an alloy of gold and silver, sometimes referred to as electrum. Certain chemicals, such as oxalic acid, attack copper but do not affect either silver or gold. Using such a chemical, it is possible to remove only the copper in an alloy, leaving both silver and the gold behind. Thus, if the original object is composed of copper, silver, and gold, it can be given a gold surface by removing both silver and copper, or an electrum surface by removing only the copper.
Likewise, with an appropriate chemical, a layer of nearly pure silver can be produced on an object made of copper and silver. For instance, sterling silver can be depleted—depletion silvering—to produce a fine silver surface, perhaps as preamble to application of gold, as in the Keum-boo technique.
However, in the majority of cases depletion gilding is in fact used to produce a gold finish, rather than one of electrum or silver. | 8 | Metallurgy |
In an isotropic and linear medium, this polarization field P is proportional and parallel to the electric field E:
where χ is the electric susceptibility of the medium. The relation between D and E is thus:
where
is the dielectric constant of the medium. The value 1+χ is called the relative permittivity of the medium, and is related to the refractive index n, for non-magnetic media, by | 3 | Analytical Chemistry |
*Volcanic eruptions release large amounts of sulphuric acid, hydrogen sulfide and hydrochloric acid into the atmosphere. These gases represent aerosols and eventually return to earth as acid rain, having a number of adverse effects on the environment and human life.
*Aerosols interact with the Earth's energy budget in two ways, directly and indirectly.
::E.g., a direct effect is that aerosols scatter and absorb incoming solar radiation. This will mainly lead to a cooling of the surface (solar radiation is scattered back to space) but may also contribute to a warming of the surface (caused by the absorption of incoming solar energy). This will be an additional element to the greenhouse effect and therefore contributing to the global climate change.
::The indirect effects refer to the aerosol interfering with formations that interact directly with radiation. For example, they are able to modify the size of the cloud particles in the lower atmosphere, thereby changing the way clouds reflect and absorb light and therefore modifying the Earth's energy budget.
:There is evidence to suggest that anthropogenic aerosols actually offset the effects of greenhouse gases in some areas, which is why the Northern Hemisphere shows slower surface warming than the Southern Hemisphere, although that just means that the Northern Hemisphere will absorb the heat later through ocean currents bringing warmer waters from the South. On a global scale however, aerosol cooling decreases greenhouse-gases-induced heating without offsetting it completely.
*When aerosols absorb pollutants, it facilitates the deposition of pollutants to the surface of the earth as well as to bodies of water. This has the potential to be damaging to both the environment and human health.
*Aerosols in the 20 μm range show a particularly long persistence time in air conditioned rooms due to their "jet rider" behaviour (move with air jets, gravitationally fall out in slowly moving air); as this aerosol size is most effectively adsorbed in the human nose, the primordial infection site in COVID-19, such aerosols may contribute to the pandemic.
*Aerosol particles with an effective diameter smaller than 10 μm can enter the bronchi, while the ones with an effective diameter smaller than 2.5 μm can enter as far as the gas exchange region in the lungs, which can be hazardous to human health. | 7 | Physical Chemistry |
Proteins can be engineered to improve the chance of successful protein crystallization by using techniques like Surface Entropy Reduction or engineering in crystal contacts. Frequently, problematic cysteine residues can be replaced by alanine to avoid disulfide-mediated aggregation, and residues such as lysine, glutamate, and glutamine can be changed to alanine to reduce intrinsic protein flexibility, which can hinder crystallization.. | 3 | Analytical Chemistry |
The first genes discovered in a mutagenesis screen for mutants unable to produce rhamnolipids were rhlA and rhlB. They are arranged in an operon, adjacent to rhlRI, a master regulator of quorum sensing in Pseudomonas aeruginosa. The proteins encoded by rhlA and rhlB; RhlA and RhlB respectively, are expected to form a complex because of the operonic nature of the genes which encode these two proteins and because both proteins are necessary for production of rhamnolipids. Furthermore, it was supposed that the role of RhlA was to stabilise RhlB in the cell membrane and thus the RhlAB complex was labelled as the enzyme Rhamnosyltransferase 1 and is frequently cited as such although there is no biochemical evidence for this and RhlA has been shown to be monomeric in solution. RhlA was subsequently shown to be involved in the production of the precursor to RHLs, HAAs. RhlB adds a rhamnose group to the HAA precursor to form mono-rhamnolipid. Therefore, the products of the rhlAB operon, RhlA and RhlB, catalyse the formation of HAAs and mono-rhamnolipids respectively.
RhlA is an α, β hydrolase (analysis by Fugue structural prediction programme). This fold is a common structural motif in fatty acid synthetic proteins and RhlA shows homology to transacylases. It has been shown using enzyme assays that the substrate for RhlA is hydroxyacyl-ACP rather than hydroxyacyl-CoA suggesting that it catalyses the formation of HAAs directly from the type II fatty acid synthase pathway (FASII). Furthermore, RhlA preferentially interacts with hydroxyacyl-ACP with an acyl chain length of ten carbon residues. The hydroxyacyl-ACP substrate of RhlA is the product of FabG, a protein which encodes the NADPH-dependent β-keto-acyl-ACP reductase required for fatty acid synthesis. It is a member of the FASII cycle along with FabI and FabA, which synthesise the precursors utilised by FabG.
Another gene necessary for synthesis of di-rhamnolipids, rhlC, has also been identified. RhlC catalyses the addition of the second rhamnose moiety to mono-rhamnolipids forming di-rhamnolipids, hence is often labelled rhamnosyltransferase 2. Like rhlA and rhlB, rhlC is thought to be an ancestral gene controlled by the same quorum sensing system as rhlA and rhlB. The rhamnose moiety for mono- and di-rhamnolipids is derived from AlgC activity and the RmlABCD pathway, encoded on the rmlBCAD operon. AlgC produces sugar precursors directly for alginate and lipopolysaccharide (LPS) as well as rhamnolipids. In rhamnose synthesis, AlgC produces glucose-1-phosphate (G1P) which is converted to dTDP-D-glucose by RmlA followed by conversion to dTDP-6-deoxy-D-4-hexulose and then dTDP-6-deoxy-L-lyxo-4-hexulose by RmlB and RmlC respectively. Finally, dTDP-6-deoxy-L-lyxo-4-hexulose is converted to dTDP-L-rhamnose by RmlD. The rhamnose can then be used in the synthesis of rhamnolipids by RhlB and RhlC.
The complete pathway of biosynthesis of rhamnolipids has not been confirmed. In summary, mono- and di- rhamnolipids are produced by sequential rhamnosyltransferase reactions catalysed by RhlB and RhlC respectively. The substrate for RhlB is the fatty acid moiety of the detergent, produced by RhlA. | 0 | Organic Chemistry |
In carbohydrate chemistry, a pair of anomers () is a pair of near-identical stereoisomers or diastereomers that differ at only the anomeric carbon, the carbon that bears the aldehyde or ketone functional group in the sugar's open-chain form. However, in order for anomers to exist, the sugar must be in its cyclic form, since in open-chain form, the anomeric carbon is planar and thus achiral. More formally stated, then, an anomer is an epimer at the hemiacetal/hemiketal carbon in a cyclic saccharide. Anomerization is the process of conversion of one anomer to the other. As is typical for stereoisomeric compounds, different anomers have different physical properties, melting points and specific rotations. | 4 | Stereochemistry |
Rosocyanine and rubrocurcumin are two red colored materials, which are formed by the reaction between curcumin and borates. | 3 | Analytical Chemistry |
Photoinhibition occurs in all organisms capable of oxygenic photosynthesis, from vascular plants to cyanobacteria. In both plants and cyanobacteria, blue light causes photoinhibition more efficiently than other wavelengths of visible light, and all wavelengths of ultraviolet light are more efficient than wavelengths of visible light. Photoinhibition is a series of reactions that inhibit different activities of PSII, but there is no consensus on what these steps are. The activity of the oxygen-evolving complex of PSII is often found to be lost before the rest of the reaction centre loses activity. However, inhibition of PSII membranes under anaerobic conditions leads primarily to inhibition of electron transfer on the acceptor side of PSII. Ultraviolet light causes inhibition of the oxygen-evolving complex before the rest of PSII becomes inhibited. Photosystem I (PSI) is less susceptible to light-induced damage than PSII, but slow inhibition of this photosystem has been observed. Photoinhibition of PSI occurs in chilling-sensitive plants and the reaction depends on electron flow from PSII to PSI. | 5 | Photochemistry |
Both the oral and intravenous preparations of flucloxacillin are inexpensive and are available as the sodium salt flucloxacillin sodium, in capsules (250 or 500 mg), oral suspensions (125 mg/5 ml or 250 mg/5 ml), and injections (powder for reconstitution, 250, 500, 1000 and 2000 mg per vial).
Flucloxacillin is not commonly used in the United States or Canada as of 2011. In several other countries however, it is supplied under a variety of trade names including Floxapen, Flopen, Flubex, Flupen, Phylopen, and Staphylex. | 4 | Stereochemistry |
Choline is an essential nutrient. The cholines are a family of water-soluble quaternary ammonium compounds. Choline is the parent compound of the cholines class, consisting of ethanolamine having three methyl substituents attached to the amino function. Healthy humans fed artificially composed diets that are deficient in choline develop fatty liver, liver damage, and muscle damage. Choline was not initially classified as essential because the human body can produce choline in small amounts through phosphatidylcholine metabolism. | 9 | Geochemistry |
For many years, the mechanism by which RNA polymerase moves along the DNA strand during abortive initiation remained elusive. It had been observed that RNA polymerase did not escape from the promoter during transcription initiation, so it was unknown how the enzyme could read the DNA strand to transcribe it without moving downstream. Within the last decade, studies have revealed that abortive initiation involves DNA scrunching, in which RNA polymerase remains stationary while it unwinds and pulls downstream DNA into the transcription complex to pass the nucleotides through the polymerase active site, thereby transcribing the DNA without moving. This causes the unwound DNA to accumulate within the enzyme, hence the name DNA "scrunching". In abortive initiation, RNA polymerase re-winds and ejects the downstream portion of the unwound DNA, releasing the RNA, and reverting to the RNA polymerase-promoter open complex; in contrast, in productive initiation, RNA polymerase re-winds and ejects the upstream portion of the unwound DNA, breaking RNA polymerase-promoter interactions, escaping the promoter, and forming a transcription elongation complex.
A 2006 paper that demonstrated the involvement of DNA scrunching in initial transcription proposed the idea that the stress incurred during DNA scrunching provides the driving force for both abortive initiation and productive initiation. A companion paper published the same year confirmed that detectable DNA scrunching occurs in 80% of transcription cycles, and is actually estimated to be 100%, given the limitation of the ability to detect rapid scrunching (20% of scrunches have a duration of less than 1 second).
A 2016 paper showed that DNA scrunching also occurs before RNA synthesis during transcription start site selection. | 1 | Biochemistry |
In the cytoplasm, ferrous iron is found in a soluble, chelatable state which constitutes the labile iron pool (~0.001 mM). In this pool, iron is thought to be bound to low-mass compounds such as peptides, carboxylates and phosphates, although some might be in a free, hydrated form (aqua ions). Alternatively, iron ions might be bound to specialized proteins known as metallochaperones. Specifically, poly-r(C)-binding proteins PCBP1 and PCBP2 appear to mediate transfer of free iron to ferritin (for storage) and non-heme iron enzymes (for use in catalysis). The labile iron pool is potentially toxic due to iron's ability to generate reactive oxygen species. Iron from this pool can be taken up by mitochondria via mitoferrin to synthesize Fe-S clusters and heme groups. | 1 | Biochemistry |
Formula: or
* Density: 0.180 kg/m at STP (0 °C, 101325 Pa).
* Atomic weight: 2.0141017926 Da.
* Mean abundance in ocean water (from VSMOW) 155.76 ± 0.1 atoms of deuterium per million atoms of all isotopes of hydrogen (about 1 atom of in 6420); that is, about 0.015% of all atoms of hydrogen (any isotope)
Data at approximately 18 K for H (triple point):
* Density:
** Liquid: 162.4 kg/m
** Gas: 0.452 kg/m
* Viscosity: 12.6 μPa·s at 300 K (gas phase)
* Specific heat capacity at constant pressure c:
** Solid: 2950 J/(kg·K)
** Gas: 5200 J/(kg·K) | 9 | Geochemistry |
Hyperchromicity is the increase of absorbance (optical density) of a material. The most famous example is the hyperchromicity of DNA that occurs when the DNA duplex is denatured. The UV absorption is increased when the two single DNA strands are being separated, either by heat or by addition of denaturant or by increasing the pH level. The opposite, a decrease of absorbance is called hypochromicity. | 7 | Physical Chemistry |
Similar to foraminifera shells, the isotopic composition of coral skeletons is used to reconstruct past temperature, CO concentrations, and pH. Vital effects arise from algal symbionts and biological responses to changes in conditions such as pH. Again, culture experiments are used to quantify vital effects and calibrate the use of coral isotopic composition as a proxy. | 9 | Geochemistry |
The fundamental series is a set of spectral lines in a set caused by transition between d and f orbitals in atoms.
Originally the series was discovered in the infrared by Fowler and independently by Arno Bergmann. This resulted in the name Bergmann series used for such a set of lines in a spectrum. However the name was changed as Bergmann also discovered other series of lines. And other discoverers also established other such series. They became known as the fundamental series. Bergmann observed lithium at 5347 cm, sodium at 5416 cm potassium at 6592 cm. Bergmann observed that the lines in the series in the caesium spectrum were double. His discovery was announced in Contributions to the Knowledge of the Infra-Red Emission Spectra of the Alkalies, Jena 1907. Carl Runge called this series the "new series". He predicted that the lines of potassium and rubidium would be in pairs. He expressed the frequencies of the series lines by a formula and predicted a connection of the series limit to the other known series. In 1909 W. M. Hicks produced approximate formulas for the various series and noticed that this series had a simpler formula than the others and thus called it the "fundamental series" and used the letter F.
The formula that more resembled the hydrogen spectrum calculations was because of a smaller quantum defect. There is no physical basis to call this fundamental. The fundamental series was described as badly-named. It is the last spectroscopic series to have a special designation. The next series involving transitions between F and G subshells is known as the FG series.
Frequencies of the lines in the series are given by this formula:
R is the Rydberg constant, is the series limit, represented by 3D, and is represented by mF. A shortened formula is then given by with values of m being integers from 4 upwards. The two numbers separated by the "−" are called terms, that represent the energy level of an atom.
The limit of the fundamental series is the same as the 3D level.
The terms can have different designations, mF for single line systems, mΦ for doublets and mf for triplets.
Lines in the fundamental series are split into compound doublets, due to the D and F subshells having different spin possibilities. The splitting of the D subshell is very small and that of the F subshell even less so, so the fine structure in the fundamental series is harder to resolve than that in the sharp or diffuse series. | 7 | Physical Chemistry |
Artificial transactivation of a gene is achieved by inserting it into the genome at the appropriate area as transactivator gene adjoined to special promoter regions of DNA. The transactivator gene expresses a transcription factor that binds to specific promoter region of DNA. By binding to the promoter region of a gene, the transcription factor causes that gene to be expressed. The expression of one transactivator gene can activate multiple genes, as long as they have the same, specific promoter region attached. Because the expression of the transactivator gene can be controlled, transactivation can be used to turn genes on and off. If this specific promoter region is also attached to a reporter gene, we can measure when the transactivator is being expressed. | 1 | Biochemistry |
Paper chromatography is one method for testing the purity of compounds and identifying substances. Paper chromatography is a useful technique because it is relatively quick and requires only small quantities of material. Separations in paper chromatography involve the principle of partition. In paper chromatography, substances are distributed between a stationary phase and a mobile phase. The stationary phase is the water trapped between the cellulose fibers of the paper. The mobile phase is a developing solution that travels up the stationary phase, carrying the samples with it. Components of the sample will separate readily according to how strongly they adsorb onto the stationary phase versus how readily they dissolve in the mobile phase.
When a colored chemical sample is placed on a filter paper, the colors separate from the sample by placing one end of the paper in a solvent. The solvent diffuses up the paper, dissolving the various molecules in the sample according to the polarities of the molecules and the solvent. If the sample contains more than one color, that means it must have more than one kind of molecule. Because of the different chemical structures of each kind of molecule, the chances are very high that each molecule will have at least a slightly different polarity, giving each molecule a different solubility in the solvent. The unequal solubility causes the various color molecules to leave solution at different places as the solvent continues to move up the paper. The more soluble a molecule is, the higher it will migrate up the paper. If a chemical is very non-polar it will not dissolve at all in a very polar solvent. This is the same for a very polar chemical and a very non-polar solvent.
It is very important to note that when using water (a very polar substance) as a solvent, the more polar the color, the higher it will rise on the papers. | 3 | Analytical Chemistry |
Electron-withdrawing groups are the opposite effect of electron-donating groups (EDGs). Both describe functional groups, however, electron-withdrawing groups pull electron density away from a molecule, whereas EDGs push electron density onto a substituent. | 7 | Physical Chemistry |
Suspension Peroxide Oxidation Combined Acidity and Sulfur (SPOCAS) method is a suite of tests used to determine the net acidity via the measurement of: Titratable Peroxide Acidity (TPA) (as a measure of PSA); Titratable Actual Acidity (TAA); Excess Acid Neutralising Capacity (ANC); and Residual Acid Soluble Sulfur (S) or Net Acid-Soluble Sulfur (S) (as measures of retained acidity).
As SPOCAS is effectively a self-contained ABA test, it is very useful and popular. However, the use of peroxide digestion for TPA may overestimate PSA where organic matter is present (see discussion on S). Therefore, it is recommended to measure S for at least one sample per batch of samples to determine if there is a substantial discrepancy between PSA measured via S and TPA. Additionally, note that S does not reliably measure the concentration of jarosite or schwertmannite (the typical sources of retained acidity); and S typically only accounts for 50-60% of jarosite. Consequently, S should be doubled to obtain a more accurate measure of Retained Acidity where jarosite is likely the principal source of Retained Acidity (which is the usual case). This calculation may or may not be performed by commercial labs before they present the ABA results to the client.
Retained Acidity is a very recalcitrant pool of acidity in that it is slow to release and not easily neutralised. Therefore, soils with high amounts of Retained Acidity may require special management considerations to mitigate gradual acidification over tens to hundreds of years. | 9 | Geochemistry |
TCF4 proteins act as transcription factors which will bind to the immunoglobulin enhancer mu-E5/kappa-E2 motif. TCF4 activates transcription by binding to the E-box (5’-CANNTG-3’) found usually on SSTR2-INR, or somatostatin receptor 2 initiator element. TCF4 is primarily involved in neurological development of the fetus during pregnancy by initiating neural differentiation by binding to DNA. It is found in the central nervous system, somites, and gonadal ridge during early development. Later in development it will be found in the thyroid, thymus, and kidneys while in adulthood TCF4 it is found in lymphocytes, muscles, mature neurons, and gastrointestinal system. | 1 | Biochemistry |
The mass fraction is the fraction of one substance with mass to the mass of the total mixture , defined as:
The SI unit is kg/kg. However, the deprecated parts-per notation is often used to describe small mass fractions. | 3 | Analytical Chemistry |
Vitamin A deficiency (VAD) caused night blindness is a reversible difficulty for the eyes to adjust to dim light. It is common in young children who have a diet inadequate in retinol and beta-carotene. A process called dark adaptation typically causes an increase in photopigment amounts in response to low levels of illumination. This increases light sensitivity by up to 100,000 times compared to normal daylight conditions. Significant improvement in night vision takes place within ten minutes, but the process can take up to two hours to reach maximal effect. People expecting to work in a dark environment wore red-tinted goggles or were in a red light environment to not reverse the adaptation because red light does not deplete rhodopsin versus what occurs with yellow or green light. | 1 | Biochemistry |
Reinforced lipids are lipid molecules in which some of the fatty acids contain deuterium instead of hydrogen. They can be used for the protection of living cells by slowing the chain reaction due to isotope effect on lipid peroxidation. The lipid bilayer of the cell and organelle membranes contain polyunsaturated fatty acids (PUFA) are key components of cell and organelle membranes. Any process that either increases oxidation of PUFAs or hinders their ability to be replaced can lead to serious disease. Correspondingly, use of reinforced lipids that stop the chain reaction of lipid peroxidation has preventive and therapeutic potential. | 1 | Biochemistry |
Common chemical shift ranges for nuclei within carbohydrate residues are:
*Typical H NMR chemical shifts of carbohydrate ring protons are 3–6 ppm (4.5–5.5 ppm for anomeric protons).
*Typical C NMR chemical shifts of carbohydrate ring carbons are 60–110 ppm
In the case of simple mono- and oligosaccharide molecules, all proton signals are typically separated from one another (usually at 500 MHz or better NMR instruments) and can be assigned using 1D NMR spectrum only. However, bigger molecules exhibit significant proton signal overlap, especially in the non-anomeric region (3-4 ppm). Carbon-13 NMR overcomes this disadvantage by larger range of chemical shifts and special techniques allowing to block carbon-proton spin coupling, thus making all carbon signals high and narrow singlets distinguishable from each other.
The typical ranges of specific carbohydrate carbon chemical shifts in the unsubstituted monosaccharides are:
*Anomeric carbons: 90-100 ppm
*Sugar ring carbons bearing a hydroxy function: 68-77
*Open-form sugar carbons bearing a hydroxy function: 71-75
*Sugar ring carbons bearing an amino function: 50-56
*Exocyclic hydroxymethyl groups: 60-64
*Exocyclic carboxy groups: 172-176
*Desoxygenated sugar ring carbons: 31-40
*A carbon at pyranose ring closure: 71-73 (α-anomers), 74-76 (β-anomers)
*A carbon at furanose ring closure: 80-83 (α-anomers), 83-86 (β-anomers) | 0 | Organic Chemistry |
In the pharmaceutical industry, shikimic acid from the Chinese star anise (Illicium verum) is used as a base material for production of oseltamivir (Tamiflu). Although shikimic acid is present in most autotrophic organisms, it is a biosynthetic intermediate and in general found in very low concentrations. The low isolation yield of shikimic acid from the Chinese star anise is blamed for the 2005 shortage of oseltamivir. Shikimic acid can also be extracted from the seeds of the sweetgum (Liquidambar styraciflua) fruit, which is abundant in North America, in yields of around 1.5%. For example, of sweetgum seeds is needed for fourteen packages of Tamiflu. By comparison, star anise has been reported to yield 3% to 7% shikimic acid. Biosynthetic pathways in E. coli have recently been enhanced to allow the organism to accumulate enough material to be used commercially. A 2010 study released by the University of Maine showed that shikimic acid can also be readily harvested from the needles of several species of pine tree.
Protecting groups are more commonly used in small-scale laboratory work and initial development than in industrial production processes because their use adds additional steps and material costs to the process. However, the availability of a cheap chiral building block can overcome these additional costs, for example, shikimic acid for oseltamivir.
Aminoshikimic acid is also an alternative to shikimic acid as a starting material for the synthesis of oseltamivir. | 1 | Biochemistry |
The overall reaction catalyzed by ETF-QO is as follows:
ETF-QO(red) + ubiquinone ↔ ETF-QO(ox) + ubiquinol
Enzymatic activity is usually assayed spectrophotometrically by reaction with octanoyl-CoA as the electron donor and ubiquinone-1 as the electron acceptor. The enzyme can also be assayed via disproportionation of ETF semiquinone. Both reactions are below:
Octanoyl-CoA + Q ↔ QH + Oct-2-enoyl-CoA
2 ETF ↔ ETF + ETF | 1 | Biochemistry |
Ethyl bromoacetate is the chemical compound with the formula . It is the ethyl ester of bromoacetic acid and is prepared in two steps from acetic acid. It is a lachrymator and has a fruity, pungent odor. It is also a highly toxic alkylating agent and may be fatal if inhaled. | 0 | Organic Chemistry |
Coordination cages are three-dimensional ordered structures in solution that act as hosts in host–guest chemistry. They are self-assembled in solution from organometallic precursors, and often rely solely on noncovalent interactions rather than covalent bonds. Coordinate bonds are useful in such supramolecular self-assembly because of their versatile geometries. However, there is controversy over calling coordinate bonds noncovalent, as they are typically strong bonds and have covalent character. The combination of a coordination cage and a guest is a type of inclusion compound. Coordination complexes can be used as "nano-laboratories" for synthesis, and to isolate interesting intermediates. The inclusion complexes of a guest inside a coordination cage show intriguing chemistry as well; often, the properties of the cage will change depending on the guest. Coordination complexes are molecular moieties, so they are distinct from clathrates and metal-organic frameworks. | 6 | Supramolecular Chemistry |
The fineness of a precious metal object (coin, bar, jewelry, etc.) represents the weight of fine metal therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hardness and durability of coins and jewelry, alter colors, decrease the cost per weight, or avoid the cost of high-purity refinement. For example, copper is added to the precious metal silver to make a more durable alloy for use in coins, housewares and jewelry. Coin silver, which was used for making silver coins in the past, contains 90% silver and 10% copper, by mass. Sterling silver contains 92.5% silver and 7.5% of other metals, usually copper, by mass.
Various ways of expressing fineness have been used and two remain in common use: millesimal fineness expressed in units of parts per 1,000 and karats or carats used only for gold. Karats measure the parts per 24, so that 18 karat = = 75% and 24 karat gold is considered 100% gold. | 8 | Metallurgy |
Paired-end tags (PET) (sometimes "Paired-End diTags", or simply "ditags") are the short sequences at the 5’ and 3 ends of a DNA fragment which are unique enough that they (theoretically) exist together only once in a genome, therefore making the sequence of the DNA in between them available upon search (if full-genome sequence data is available) or upon further sequencing (since tag sites are unique enough to serve as primer annealing sites). Paired-end tags (PET) exist in PET libraries with the intervening DNA absent, that is, a PET "represents" a larger fragment of genomic or cDNA by consisting of a short 5 linker sequence, a short 5 sequence tag, a short 3 sequence tag, and a short 3' linker sequence. It was shown conceptually that 13 base pairs are sufficient to map tags uniquely. However, longer sequences are more practical for mapping reads uniquely. The endonucleases (discussed below) used to produce PETs give longer tags (18/20 base pairs and 25/27 base pairs) but sequences of 50–100 base pairs would be optimal for both mapping and cost efficiency. After extracting the PETs from many DNA fragments, they are linked (concatenated) together for efficient sequencing. On average, 20–30 tags could be sequenced with the Sanger method, which has a longer read length. Since the tag sequences are short, individual PETs are well suited for next-generation sequencing that has short read lengths and higher throughput. The main advantages of PET sequencing are its reduced cost by sequencing only short fragments, detection of structural variants in the genome, and increased specificity when aligning back to the genome compared to single tags, which involves only one end of the DNA fragment. | 1 | Biochemistry |
Mass spectrometry methods are generally used for analysis of environmental contaminant monitoring, particularly in aquatic environments (though they can be applied in non-aquatic environments, such as with screening pesticides on plant matter), paired with chromatography for separation. For target screening, this means using gas chromatography–mass spectrometry (GC-MS) or liquid chromatography–mass spectrometry (LC-MS) methods "that use single reaction monitoring (SIM) or selected reaction monitoring (SRM) modes." However, for suspect and non-target screening, these methods are inadequate due to recording only a limited number of compounds and insufficient useful information can be determined about unknown compounds, particularly given the dearth of LC-MS comparison libraries. For those non-targeted screening approaches, high-resolution mass spectrometry and high mass accuracy chromatography techniques are required. Combinations of quadrupole, time-of-flight, ion trap, and orbitrap mass spectrometry analyzers have emerged, along with high-performance liquid chromatography (and ultra-high-performance liquid chromatography), to more rapidly and effectively tackle suspect and non-target screening. | 3 | Analytical Chemistry |
A Metabolic Panel (MP) is a routine group of blood tests commonly used for health screenings, disease detection, and monitoring vital signs of hospitalized patients with specific medical conditions. MP panel analyzes common analytes in the blood to assess the functions of the kidneys and liver, as well as electrolyte and acid-base balances. There are two types of MPs - Basic Metabolic Panel (BMP) or Comprehensive Metabolic Panel (CMP). | 1 | Biochemistry |
Single-Molecule electrochemistry is an electrochemical technique used to study the faradaic response of redox molecules in electrochemical environments. The ability to study singular molecules gives rise to the potential of developing ultra-sensitive sensors which are necessary in SEE. From the work of Bard and Fan, this technique has had large advances with the use of redox cycling. Redox cycling amplifies a charge transfer by reducing and oxidizing a molecule multiple times as it diffuses between electrodes. Specifically in this technique, an insulated nano-electrode tip is placed near a substrate electrode to form an ultra-small electrochemical chamber. Molecules will become trapped in this chamber where the redox cycling and charge amplification will occur, allowing for detection of single molecules. From this technique, the necessary tool of charge amplification of redox reactions helped improve SEE measurements. It has helped increase detection limits, which need to be high for SEE. | 7 | Physical Chemistry |
For electrolyte solution in a channel with a macro- or micro-scaled radius, surface charges at the wall attract counterions and repel co-ions due to electrostatic force. Therefore, an electrical double layer exists between the wall of channel and the solution. The dimension of the electrical double layer is determined by the Debye length in this system, which is typically much smaller than the channel radius. Most of the solution in the channel is electrically neutral due to the shielding effect of the electrical double layer.
In a nanochannel, however, the solution is charged when the dimension of channel radius is smaller than the Debye length. Therefore, it is possible to manipulate the flow of ions inside the nanochannel by introducing surface charges on the wall or by applying an external electrical potential.
Ionic concentration of solution has an important effect on the ion transport. Because a higher concentration leads to a shorter Debye length for the electrical double layer at the channel wall. Its rectifying effect decreases with increasing ionic concentration. On the other hand, ion rectification can be improved by having a dilute solution. | 7 | Physical Chemistry |
In 1989, Alan Mackay suggested that if chemical synthesis could be used to make L-protein and D-protein enantiomers, it would enable the use of racemic mixtures to crystallize proteins in centrosymmetric space groups. He stated that, because in the X-ray diffraction data obtained from a centrosymmetric crystal the off-diagonal phases would cancel giving phases that differ by 180 degrees, this would facilitate solving the phase problem in protein structure determination through X-ray crystallography.
In 1993, Laura Zawadzke and Jeremy Berg first used the small (45 amino acids) protein rubredoxin to synthesize it in racemic form. This was done since the structural determination would potentially be easier and more robust by using diffraction data from a centrosymmetric crystal, which requires growth from a racemic mixture. By having a centre of symmetry formed by the racemic protein pairs, the steps of phasing diffraction in data analysis would be further simplified. As mentioned above, in 1995 Stephanie Wukovitz and Todd Yeates had developed a mathematical theory to explain why protein molecules tend to crystallize more frequently in certain space groups than in others; they predicted that the most favored protein space group would be P1<bar>, and predicted that globular proteins would crystallize more easily as racemates, from a racemic protein mixture. | 3 | Analytical Chemistry |
6-Phosphogluconolactone is an intermediate in the pentose phosphate pathway (PPP).
In the PPP pathway, it is produced from glucose-6-phosphate by glucose-6-phosphate dehydrogenase. It is then converted to 6-Phosphogluconic acid by 6-phosphogluconolactonase. | 1 | Biochemistry |
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