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Side effects seen more often with levomilnacipran than with placebo in clinical trials included nausea, dizziness, sweating, constipation, insomnia, increased heart rate and blood pressure, urinary hesitancy, erectile dysfunction and delayed ejaculation in males, vomiting, tachycardia, and palpitations. | 4 | Stereochemistry |
Ertl and his wife Barbara have two children and several grandchildren. His hobbies include playing the piano and also playing with his cats when he is not doing experiments. He identifies as Christian. | 7 | Physical Chemistry |
All consideration of nuclear electrons ended with James Chadwicks discovery of the neutron in 1932. An atom of gold now was seen as containing 118 neutrons rather than 118 nuclear electrons, and its positive nuclear charge now was realized to come entirely from a content of 79 protons. Since Moseley had previously shown that the atomic number Z of an element equals this positive charge, it was now clear that Z' is identical to the number of protons of its nuclei. | 3 | Analytical Chemistry |
The study of the fate of persistent organic chemicals in the environment has revealed a large reservoir of enzymatic reactions with a large potential in preparative organic synthesis, which has already been exploited for a number of oxygenases on pilot and even on industrial scale. Novel catalysts can be obtained from metagenomic libraries and DNA sequence based approaches. Our increasing capabilities in adapting the catalysts to specific reactions and process requirements by rational and random mutagenesis broadens the scope for application in the fine chemical industry, but also in the field of biodegradation. In many cases, these catalysts need to be exploited in whole cell bioconversions or in fermentations, calling for system-wide approaches to understanding strain physiology and metabolism and rational approaches to the engineering of whole cells as they are increasingly put forward in the area of systems biotechnology and synthetic biology. | 2 | Environmental Chemistry |
He was born at Vizille and trained at the Ecole des Arts et Métiers at Aix. From 1874 until about 1880, he worked as a chemist at the new factory of the Cotton Powder Company at Uplees, Faversham, Kent, England. While there, he and the factory manager, George Trench, took out patents for Tonite (a new high explosive) (1874), and an improved dynamite detonator (1878).
In 1880, Faure patented a method of coating lead plates with a paste of lead oxides, sulphuric acid and water, which was then cured by gentle warming in a humid atmosphere. The curing process caused the paste to change to a mixture of lead sulphates which adhered to the lead plate. During charging the cured paste was converted into electrochemically active material (the "active mass") and gave a substantial increase in capacity compared with Planté's battery. This was a significant breakthrough that led to the industrial manufacture of lead-acid batteries, as now used for starting motor cars.
Towards the end of his life Faure was granted further patents, among them ones for the manufacture of aluminium alloys and improvements to hot air engines and motor vehicle steering mechanisms. | 7 | Physical Chemistry |
Carbene C−H insertion in organic chemistry concerns the insertion reaction of a carbene into a carbon–hydrogen bond. This organic reaction is of some importance in the synthesis of new organic compounds.
Simple carbenes such as the methylene and dichlorocarbene are not regioselective towards insertion. When the carbene is stabilized by a metal the selectivity increases. The compound dirhodium tetraacetate is found to be especially effective. In a typical reaction ethyl diazoacetate (a well-known carbene precursor) and dirhodium tetraacetate react with hexane; the insertion into a C−H bond occurs 1% on one of the methyl groups, 63% on the alpha-methylene unit and 33% on the beta-methylene unit.
The first such reaction was reported in 1981, and the general reaction mechanism proposed by Doyle in 1993. the metal that stabilizes the carbene, dissociates at the same time but not to the same degree as carbon–carbon bond formation and hydrogen atom migration. The reaction is distinct from a metal catalyzed C−H activation reaction (sensu stricto) in which the metal actually inserts itself between carbon and hydrogen to form a species with a metal–carbon bond. It does, however, serve as a premier example of a metal-catalyzed C–H functionalization reaction, which some authors also refer to as C–H activation (sensu lato).
The metal employed as a catalyst in this reaction historically was copper until superseded by rhodium. Other metals stabilize the carbene too much (e.g. molybdenum as in Fischer carbenes) or result in carbenes too reactive (e.g. gold, silver). Many dirhodium carboxylates and carboxamidates exist, including chiral ones. An effective chiral dirhodium catalyst is Rh(MPPIM) with MPPIM (Methyl PhenylPropyl IMidazolidinecarboxylato) asymmetric ligand.
Most successful reactions are intramolecular within geometrically rigid systems, as pioneered by Wenkert (1982) and Taber (1982). | 0 | Organic Chemistry |
Calcineurin is linked to receptors for several brain chemicals including glutamate, dopamine and GABA. An experiment with genetically-altered mice that could not produce calcineurin showed similar symptoms as in humans with schizophrenia: impairment in working memory, attention deficits, aberrant social behavior, and several other abnormalities characteristic of schizophrenia. | 1 | Biochemistry |
Aratashen (, also Romanized as Arratashen; also, Artashen; until 1978 Zeyva Hayi – meaning "Armenian Zeyva", Zeyva, Bol’shaya Zeyva and Nerkin-Zeyva) is a town in the Armavir Province of Armenia. It is located on the Ararat Plain. | 8 | Metallurgy |
The extracellular polysaccharide colanic acid is produced by species of the family Enterobacteriaceae. In Escherichia coli strain K12 the colanic acid cluster comprises 19 genes. The wzx gene encodes a protein with multiple transmembrane segments that may function in export of the colanic acid repeat unit from the cytoplasm into the periplasm in a process analogous to O-unit export. The colanic acid gene clusters may be involved in the export of polysaccharide from the cell. | 1 | Biochemistry |
Amines can be classified according to the nature and number of substituents on nitrogen. Aliphatic amines contain only H and alkyl substituents. Aromatic amines have the nitrogen atom connected to an aromatic ring.
Amines, alkyl and aryl alike, are organized into three subcategories based on the number of carbon atoms adjacent to the nitrogen (how many hydrogen atoms of the ammonia molecule are replaced by hydrocarbon groups):
*Primary (1°) amines—Primary amines arise when one of three hydrogen atoms in ammonia is replaced by an alkyl or aromatic group. Important primary alkyl amines include methylamine, most amino acids, and the buffering agent tris, while primary aromatic amines include aniline.
*Secondary (2°) amines—Secondary amines have two organic substituents (alkyl, aryl or both) bound to the nitrogen together with one hydrogen. Important representatives include dimethylamine, while an example of an aromatic amine would be diphenylamine.
*Tertiary (3°) amines—In tertiary amines, nitrogen has three organic substituents. Examples include trimethylamine, which has a distinctively fishy smell, and EDTA.
A fourth subcategory is determined by the connectivity of the substituents attached to the nitrogen:
*Cyclic amines—Cyclic amines are either secondary or tertiary amines. Examples of cyclic amines include the 3-membered ring aziridine and the six-membered ring piperidine. N-methylpiperidine and N-phenylpiperidine are examples of cyclic tertiary amines.
It is also possible to have four organic substituents on the nitrogen. These species are not amines but are quaternary ammonium cations and have a charged nitrogen center. Quaternary ammonium salts exist with many kinds of anions. | 0 | Organic Chemistry |
Transient kinetic isotope effects (or fractionation) occur when the reaction leading to isotope fractionation does not follow pure first-order kinetics and therefore isotopic effects cannot be described with the classical equilibrium fractionation equations or with steady-state kinetic fractionation equations (also known as the Rayleigh equation). In these instances, the general equations for biochemical isotope kinetics (GEBIK) and the general equations for biochemical isotope fractionation (GEBIF) can be used.
The GEBIK and GEBIF equations are the most generalized approach to describe isotopic effects in any chemical, catalytic reaction and biochemical reactions because they can describe isotopic effects in equilibrium reactions, kinetic chemical reactions and kinetic biochemical reactions. In the latter two cases, they can describe both stationary and non-stationary fractionation (i.e., variable and inverse fractionation). In general, isotopic effects depend on the number of reactants and on the number of combinations resulting from the number of substitutions in all reactants and products. Describing with accuracy isotopic effects, however, depends also on the specific rate law used to describe the chemical or biochemical reaction that produces isotopic effects. Normally, regardless of whether a reaction is purely chemical or whether it involves some enzyme of biological nature, the equations used to describe isotopic effects base on first-order kinetics. This approach systematically leads to isotopic effects that can be described by means of the Rayleigh equation. In this case, isotopic effects will always be expressed as a constant, hence will not be able to describe isotopic effects in reactions where fractionation and enrichment are variable or inverse during the course of a reaction. Most chemical reactions do not follow first-order kinetics; neither biochemical reactions can normally be described with first-order kinetics. To properly describe isotopic effects in chemical or biochemical reactions, different approaches must be employed such as the use of Michaelis–Menten reaction order (for chemical reactions) or coupled Michaelis–Menten and Monod reaction orders (for biochemical reactions). However, conversely to Michaelis–Menten kinetics, GEBIK and GEBIF equations are solved under the hypothesis of non-steady state. This characteristic allows GEBIK and GEBIF to capture transient isotopic effects. | 7 | Physical Chemistry |
Calculation of rate constants of the processes of generation and relaxation of electronically and vibrationally excited particles are of significant importance. It is used, for example, in the computer simulation of processes in plasma chemistry or microelectronics. First-principle based models should be used for such calculation. It can be done with the help of computer simulation software. | 7 | Physical Chemistry |
The two classes of carbenes are singlet and triplet carbenes. Triplet carbenes are diradicals with two unpaired electrons, typically form from reactions that break two σ bonds (α elimination and some extrusion reactions), and do not rehybridize the carbene atom. Singlet carbenes have a single lone pair, typically form from diazo decompositions, and adopt an sp orbital structure. Bond angles (as determined by EPR) are 125–140° for triplet methylene and 102° for singlet methylene.
Most carbenes have a nonlinear triplet ground state. For simple hydrocarbons, triplet carbenes are usually only 8 kcal/mol (33 kJ/mol) more stable than singlet carbenes, comparable to nitrogen inversion. The stabilization is in part attributed to Hund's rule of maximum multiplicity. However, strategies to stabilize triplet carbenes at room temperature are elusive. 9-Fluorenylidene has been shown to be a rapidly equilibrating mixture of singlet and triplet states with an approximately 1.1 kcal/mol (4.6 kJ/mol) energy difference, although extensive electron delocalization into the rings complicates any conclusions drawn from diaryl carbenes. Simulations suggest that electropositive heteroatoms can thermodynamically stabilize triplet carbenes, such as in silyl and silyloxy carbenes, especially carbenes.
Lewis-basic nitrogen, oxygen, sulphur, or halide substituents bonded to the divalent carbon can delocalize an electron pair into an empty p orbital to stabilize the singlet state. This phenomenon underlies persistent carbenes' remarkable stability. | 0 | Organic Chemistry |
Swedish law required bars of iron to have the forges mark stamped into it for quality control reasons. In Britain, the iron was known by these marks', and the quality of each brand was well-known to the buyers in London, Sheffield, Birmingham and elsewhere. It was divided into two grades:
* First oregrounds came from Österby (double bullet), Leufsta (now Lövsta - hoop L), and Åkerby (PL crown). Later Gimo joined them.
* Second oregrounds came from the other forges, including Forsmark, Harg, Vattholma, and Ullfors.
Its special property was its purity. The manganese content of the Dannemora ore caused impurities, which would otherwise have remained in the iron, to react preferentially with the manganese and to be carried off into the slag. This level of purity meant that the iron was particularly suitable for conversion to steel by being re-carburized, using the cementation process. This made it particularly suitable for making steel, oregrounds iron was an indispensable raw material for metal manufactures, particularly the Sheffield cutlery industry. Substantial quantities were also (until about 1808) bought for use by the British Navy.
This and other uses absorbed substantially the whole output of the industry. The trade in oregrounds iron was controlled from the 1730s to the 1850s by a cartel of merchants, of whom the longest enduring members were the Sykes family of Hull. Other participants were resident in (or controlling imports through) London and Bristol. These merchants advanced money to Swedish exporting houses, which in turn advanced it to the ironmasters, thus buying up the output of the forges several years in advance. | 8 | Metallurgy |
Sources:
The choice of the dividing surface, strictly speaking, is arbitrary, however, it is very desirable to take into account the type of external potential . Otherwise, these expressions are at odds with the generally accepted concepts and common sense.
First, must lie close to the transition layer (i.e., the region where the number density varies), otherwise it would mean the attribution of the bulk properties of one of the phase to the surface.
Second. In the case of weak adsorption, for example, when the potential is close to the stepwise, it is logical to choose close to . (In some cases, choosing , where is particle radius, excluding the "dead" volume.)
In the case of pronounced adsorption it is advisable to choose close to the right border of the transition region. In this case all particles from the transition layer will be attributed to the solid, and is always positive. Trying to put in this case will lead to a strong shift of to the solid body domain, which is clearly unphysical.
Conversely, if (fluid on the left), it is advisable to choose lying on the left side of the transition layer. In this case the surface particles once again refer to the solid and is back positive.
Thus, except in the case of static membrane, we can always avoid the "negative adsorption" for one-component systems. | 7 | Physical Chemistry |
The nomenclature used for organosulfur compounds is often non-systematic. Sometimes persulfides are called hydrodisulfides to further avoid confusion with disulfides with the grouping R-S-S-R, by emphasizing the presence of an H at one end of a disulfide bond. | 0 | Organic Chemistry |
Multiple solar cells in an integrated group, all oriented in one plane, constitute a solar photovoltaic panel or module. Photovoltaic modules often have a sheet of glass on the sun-facing side, allowing light to pass while protecting the semiconductor wafers. Solar cells are usually connected in series creating additive voltage. Connecting cells in parallel yields a higher current.
However, problems in paralleled cells such as shadow effects can shut down the weaker (less illuminated) parallel string (a number of series connected cells) causing substantial power loss and possible damage because of the reverse bias applied to the shadowed cells by their illuminated partners.
Although modules can be interconnected to create an array with the desired peak DC voltage and loading current capacity, which can be done with or without using independent MPPTs (maximum power point trackers) or, specific to each module, with or without module level power electronic (MLPE) units such as microinverters or DC-DC optimizers. Shunt diodes can reduce shadowing power loss in arrays with series/parallel connected cells.
By 2020, the United States cost per watt for a utility scale system had declined to $0.94. | 7 | Physical Chemistry |
The reciprocal to a simple hexagonal Bravais lattice with lattice constants and is another simple hexagonal lattice with lattice constants and rotated through 90° about the c axis with respect to the direct lattice. The simple hexagonal lattice is therefore said to be self-dual, having the same symmetry in reciprocal space as in real space. Primitive translation vectors for this simple hexagonal Bravais lattice vectors are | 3 | Analytical Chemistry |
PetroSA, another South African company, operates a refinery with a 36,000 barrels a day plant that completed semi-commercial demonstration in 2011, paving the way to begin commercial preparation. The technology can be used to convert natural gas, biomass or coal into synthetic fuels. | 0 | Organic Chemistry |
Photochromic molecules can belong to various classes: triarylmethanes, stilbenes, azastilbenes, nitrones, fulgides, spiropyrans, naphthopyrans, spiro-oxazines, quinones and others. | 5 | Photochemistry |
Propionyl chloride is industrially produced by chlorination of propionic acid with phosgene:
:CHCHCOH + COCl → CHCHCOCl + HCl + CO | 0 | Organic Chemistry |
In a 1998 analysis of the E. coli genome, a large number of genes with unknown function were designated names beginning with the letter y, followed by sequentially generated letters without a mnemonic meaning (e.g., ydiO and ydbK). Since being designated, some y-genes have been confirmed to have a function, and assigned a synonym (alternative) name in recognition of this. However, as y-genes are not always re-named after being further characterised, this designation is not a reliable indicator of a gene's significance. | 1 | Biochemistry |
The light-harvesting complex (or antenna complex; LH or LHC) is an array of protein and chlorophyll molecules embedded in the thylakoid membrane of plants and cyanobacteria, which transfer light energy to one chlorophyll a molecule at the reaction center of a photosystem.
The antenna pigments are predominantly chlorophyll b, xanthophylls, and carotenes. Chlorophyll a is known as the core pigment. Their absorption spectra are non-overlapping and broaden the range of light that can be absorbed in photosynthesis. The carotenoids have another role as an antioxidant to prevent photo-oxidative damage of chlorophyll molecules. Each antenna complex has between 250 and 400 pigment molecules and the energy they absorb is shuttled by resonance energy transfer to a specialized chlorophyll-protein complex known as the reaction center of each photosystem. The reaction center initiates a complex series of chemical reactions that capture energy in the form of chemical bonds.
For photosystem II, when either of the two chlorophyll a molecules at the reaction center absorb energy, an electron is excited and transferred to an electron acceptor molecule, pheophytin, leaving the chlorophyll a in an oxidized state. The oxidised chlorophyll a replaces the electrons by photolysis that involves the oxidation of water molecules to oxygen, protons and electrons.
The N-terminus of the chlorophyll a-b binding protein extends into the stroma where it is involved with adhesion of granal membranes and photo-regulated by reversible phosphorylation of its threonine residues. Both these processes are believed to mediate the distribution of excitation energy between photosystems I and II.
This family also includes the photosystem II protein PsbS, which plays a role in energy-dependent quenching that increases thermal dissipation of excess absorbed light energy in the photosystem. | 5 | Photochemistry |
* Nigeria: Assistant Police Commissioner stated that pepper sprays are illegal for civilians to possess.
* South Africa: Pepper sprays are legal to own by civilians for self defense. | 1 | Biochemistry |
Signaling pathways are often inactivated by enzymes that reverse the activation state and/or induce the degradation of signaling components. Scaffolds have been proposed to protect activated signaling molecules from inactivation and/or degradation. Mathematical modeling has shown that kinases in a cascade without scaffolds have a higher probability of being dephosphorylated by phosphatases before they are even able to phosphorylate downstream targets. Furthermore, scaffolds have been shown to insulate kinases from substrate- and ATP-competitive inhibitors. | 1 | Biochemistry |
GC–MS can analyze the particles from a human body in order to help link a criminal to a crime. The analysis of fire debris using GC–MS is well established, and there is even an established American Society for Testing and Materials (ASTM) standard for fire debris analysis. GCMS/MS is especially useful here as samples often contain very complex matrices and results, used in court, need to be highly accurate. | 3 | Analytical Chemistry |
One efficiency-focused research topic is improving the efficiency of photorespiration. Around 25% of the time RuBisCO incorrectly collects oxygen molecules instead of , creating and ammonia that disrupt the photosynthesis process. Plants remove these byproducts via photorespiration, requiring energy and nutrients that would otherwise increase photosynthetic output. In C3 plants photorespiration can consume 20-50% of photosynthetic energy. | 5 | Photochemistry |
Molecular biomarkers have been defined as biomarkers that can be discovered using basic and acceptable platforms such as genomics and proteomics. Many genomic and proteomics techniques are available for biomarker discovery and a few techniques that are recently being used can be found on that page. Apart from genomics and proteomics platforms biomarker assay techniques, metabolomics, lipidomics, glycomics, and secretomics are the most commonly used as techniques in identification of biomarkers. | 1 | Biochemistry |
The effect was theoretically predicted in 1979, in a mathematical description of hyper Raman scattering optical activity. Within this theoretical model, upon setting the initial and final frequencies of light to the same value, the mathematics describe the hyper Rayleigh scattering optical activity. The theory was well in advance of its time, and the effect remained elusive for 40 years. Its author David L. Andrews referred to it as the "impossible theory". However, in January 2019, an experimental demonstration was reported by Ventsislav K. Valev and his team. The team investigated the hyper Rayleigh scattering (at the second harmonic generation frequency) from chiral nanohelices made of silver. Valev and his team observed that the intensity of the hyper Rayleigh scattering light depended on the direction of circularly polarized light and that this dependence reversed with the chirality of the nanohelices. Valev's work unambiguously established that the effect is physically possible, opening the way for nonlinear chiroptical investigations of a variety of chiral light-scattering materials; including molecules, plasmonic metal nanoparticles and semiconductor nanoparticles. | 4 | Stereochemistry |
In chemistry, a water cluster is a discrete hydrogen bonded assembly or cluster of molecules of water. Many such clusters have been predicted by theoretical models (in silico), and some have been detected experimentally in various contexts such as ice, bulk liquid water, in the gas phase, in dilute mixtures with non-polar solvents, and as water of hydration in crystal lattices. The simplest example is the water dimer (HO).
Water clusters have been proposed as an explanation for some anomalous properties of liquid water, such as its unusual variation of density with temperature. Water clusters are also implicated in the stabilization of certain supramolecular structures. They are expected to play a role also in the hydration of molecules and ions dissolved in water. | 7 | Physical Chemistry |
In molecular biology and genetics, a blot is a method of transferring large biomolecules (proteins, DNA or RNA) onto a carrier, such as a membrane composed of nitrocellulose, polyvinylidene fluoride or nylon. In many instances, this is done after a gel electrophoresis, transferring the molecules from the gel onto the blotting membrane, and other times adding the samples directly onto the membrane. After the blotting, the transferred molecules are then visualized by colorant staining (for example, silver staining of proteins), autoradiographic visualization of radiolabelled molecules (performed before the blot), or specific labelling of some proteins or nucleic acids. The latter is done with antibodies or hybridization probes that bind only to some molecules of the blot and have an enzyme joined to them. After proper washing, this enzymatic activity (and so, the molecules found in the blot) is visualized by incubation with a proper reagent, rendering either a colored deposit on the blot or a chemiluminescent reaction which is registered by photographic film. | 1 | Biochemistry |
Imines are common in nature. The pyridoxal phosphate-dependent enzymes (PLP enzymes) catalyze myriad reactions involving aldimines (or Schiff bases). Cyclic imines are also substrates for many imine reductase enzymes. | 0 | Organic Chemistry |
Many protein-containing solutions have the highest absorption at 280 nm in the spectrophotometer, the UV range. This requires spectrophotometers capable of measuring in the UV range, which many cannot. Additionally, the absorption maxima at 280 nm requires that proteins contain aromatic amino acids such as tyrosine (Y), phenylalanine (F) and/or tryptophan (W). Not all proteins contain these amino acids, a fact which will skew the concentration measurements. If nucleic acids are present in the sample, they would also absorb light at 280 nm, skewing the results further. By using the Bradford protein assay, one can avoid all of these complications by simply mixing the protein samples with the Coomassie brilliant blue G-250 dye (Bradford reagent) and measuring their absorbances at 595 nm, which is in the visible range and may be accurately measured by the use of a mobile smartphone camera.
The procedure for Bradford protein assay is very easy and simple to follow. It is done in one step where the Bradford reagent is added to a test tube along with the sample. After mixing well, the mixture almost immediately changes to a blue color. When the dye binds to the proteins through a process that takes about 2 minutes, a change in the absorption maximum of the dye from 465 nm to 595 nm in acidic solutions occurs. This dye creates strong noncovalent bonds with the proteins, via electrostatic interactions with the amino and carboxyl groups, as well as Van Der Waals interactions. Only the molecules that bind to the proteins in solution exhibit this change in absorption, which eliminates the concern that unbound molecules of the dye might contribute to the experimentally obtained absorption reading. This process is more beneficial since it is less pricey than other methods, easy to use, and has high sensitivity of the dye for protein.
After 5 minutes of incubation, the absorbance can be read at 595 nm using a spectrophotometer or a mobile smartphone camera (RGBradford method).
This assay is one of the fastest assays performed on proteins. The total time it takes to set up and complete the assay is under 30 minutes. The entire experiment is done at room temperature.
The Bradford protein assay can measure protein quantities as little as 1 to 20 μg. It is an extremely sensitive technique.
The dye reagent is a stable ready to use product prepared in phosphoric acid. It can remain at room temperature for up to 2 weeks before it starts to degrade.
Protein samples usually contain salts, solvents, buffers, preservatives, reducing agents and metal chelating agents. These molecules are frequently used for solubilizing and stabilizing proteins. Other protein assay like BCA and Lowry are ineffective because molecules like reducing agents interfere with the assay. Using Bradford can be advantageous against these molecules because they are compatible to each other and will not interfere.
The linear graph acquired from the assay (absorbance versus protein concentration in μg/mL) can be easily extrapolated to determine the concentration of proteins by using the slope of the line.
It is a sensitive technique. It is also very simple: measuring the OD at 595 nm after 5 minutes of incubation. This method can also make use of a Vis spectrophotometer or a mobile smartphone camera (RGBradford method). | 3 | Analytical Chemistry |
1,8-Bis(dimethylamino)naphthalene is an organic compound with the formula CH(NMe) (Me = methyl). It is classified as a peri-naphthalene, i.e. a 1,8-disubstituted derivative of naphthalene. Owing to its unusual structure, it exhibits exceptional basicity. It is often referred by the trade name Proton Sponge, a trademark of Sigma-Aldrich. | 0 | Organic Chemistry |
YcaO is a protein found in bacteria which is involved in the synthesis of thiazole/oxazole modified microcin antibiotics, such as bottromycin. YcaO performs ATP dependent cyclodehydration to form the oxazole and thiazole moieties of the microcin.
The YcaO name origin is from a gene naming rubric that was established from the bacterium Escherichia coli. If a gene has an unknown function, it was given a four-letter name starting with the letter Y and the next three letters are given based on the genomic location.
Methyl coenzyme M reductase (MCR) or Coenzyme-B sulfoethylthiotransferase is a protein known in thioamidation (a posttranslational modification). A Ycao enzyme dependent on ATP is needed for MCR thioamidation as well as a sulfide source. YcaO enzymes are needed to catalyze the ATP-dependent backbone cyclodehydration of polar amino acids such as Cysteine, Serine, and Threonine to the correct thiazoline and (methyl) oxazoline Heterocycle. The side chains of these amino acids can act as Nucleophiles. The Thiol group in cysteine and the hydroxyl group of serine and threonine are strong nucleophiles. | 1 | Biochemistry |
In the [Mn(HO)] metal complex, manganese has an oxidation state of +2, thus it is a d ion. HO is a weak field ligand (spectrum shown below), and according to the Tanabe–Sugano diagram for d ions, the ground state is A. Note that there is no sextet spin multiplicity in any excited state, hence the transitions from this ground state are expected to be spin-forbidden and the band intensities should be low. From the spectra, only very low intensity bands are observed (low molar absorptivity (ε) values on y-axis). | 7 | Physical Chemistry |
The most commonly observed health effects in people exposed to extremely high levels of PCBs are skin conditions, such as chloracne and rashes, but these were known to be symptoms of acute systemic poisoning dating back to 1922. Studies in workers exposed to PCBs have shown changes in blood and urine that may indicate liver damage. In Japan in 1968, 280 kg of PCB-contaminated rice bran oil was used as chicken feed, resulting in a mass poisoning, known as Yushō disease, in over 1800 people. Common symptoms included dermal and ocular lesions, irregular menstrual cycles and lowered immune responses. Other symptoms included fatigue, headaches, coughs, and unusual skin sores. Additionally, in children, there were reports of poor cognitive development. Women exposed to PCBs before or during pregnancy can give birth to children with lowered cognitive ability, immune compromise, and motor control problems.
There is evidence that crash dieters that have been exposed to PCBs have an elevated risk of health complications. Stored PCBs in the adipose tissue become mobilized into the blood when individuals begin to crash diet.
PCBs have shown toxic and mutagenic effects by interfering with hormones in the body. PCBs, depending on the specific congener, have been shown to both inhibit and imitate estradiol, the main sex hormone in females. Imitation of the estrogen compound can feed estrogen-dependent breast cancer cells, and possibly cause other cancers, such as uterine or cervical. Inhibition of estradiol can lead to serious developmental problems for both males and females, including sexual, skeletal, and mental development issues. In a cross-sectional study, PCBs were found to be negatively associated with testosterone levels in adolescent boys.
High PCB levels in adults have been shown to result in reduced levels of the thyroid hormone triiodothyronine, which affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. It also resulted in reduced immunity and increased thyroid disorders. | 2 | Environmental Chemistry |
Imines are widely used as intermediates in the synthesis of heterocycles.
*Aromatic imines react with an enol ether to a quinoline in the Povarov reaction.
*Imines react, thermally, with ketenes in [2+2] cycloadditions to form β-lactams in the Staudinger synthesis. Several variants have been described.
*Imine react with dienes in the Imine Diels-Alder reaction to a tetrahydropyridine.
*tosylimines react with α,β-unsaturated carbonyl compound to give allylic amines in the Aza-Baylis–Hillman reaction. | 0 | Organic Chemistry |
Lactate dehydrogenase catalyzes the interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD. It converts pyruvate, the final product of glycolysis, to lactate when oxygen is absent or in short supply, and it performs the reverse reaction during the Cori cycle in the liver. At high concentrations of lactate, the enzyme exhibits feedback inhibition, and the rate of conversion of pyruvate to lactate is decreased. It also catalyzes the dehydrogenation of 2-hydroxybutyrate, but this is a much poorer substrate than lactate. | 1 | Biochemistry |
Besides the experimental study, it is important to have a good thermodynamic model to describe and predict liquid-liquid equilibrium conditions in engineering and design. To obtain global and reliable parameters for thermodynamic models usually, phase equilibrium data is suitable for this purpose. As there are polymer, electrolyte and water in polymer/salt systems, all different types of interactions should be taken into account. Up to now, several models have been used such as NRTL, Chen-NRTL, Wilson, UNIQUAC, NRTL-NRF and UNIFAC-NRF. It has been shown that, in all cases, the mentioned models were successful in reproducing tie-line data of polymer/salt aqueous two-phase systems. In most of the previous works, excess Gibbs functions have been used for modeling. | 3 | Analytical Chemistry |
The nines scale is also used in other contexts, such as describing the purity of gases. The purity of a gas is an indication of the ratio of it to other gases in its mixture, as measured by volume. Thus, a high purity refers to a low amount of other gases, or impurities. Gases of higher purity are in many contexts considered to be of better quality and are usually more expensive.
The purity of a gas is generally expressed as a grade prefixed with the letter N (rather than postfixed), indicating the "number of nines" in the percentage or decimal fraction. For example, a N2.0 gas is 99% (two nines) pure and 1% impurities by volume; a N6.0 gas is 99.9999% (six nines) pure, with 1 part per million (1 ppm or 1 vpm, volume per million) impurities.
Intermediate values indicate the digit following the last nine. For example, N4.6 estimates a purity level of 99.996% (four nines followed by a six). An alternative representation uses the common logarithm: for example, a gas which is 99.97% pure would be described as N3.5, since log(0.03%) = −3.523. | 8 | Metallurgy |
In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers. The name is composed of Greek elements oligo-, "a few" and -mer, "parts". An adjective form is oligomeric.
The oligomer concept is contrasted to that of a polymer, which is usually understood to have a large number of units, possibly thousands or millions. However, there is no sharp distinction between these two concepts. One proposed criterion is whether the molecule's properties vary significantly with the removal of one or a few of the units.
An oligomer with a specific number of units is referred to by the Greek prefix denoting that number, with the ending -mer: thus dimer, trimer, tetramer, pentamer, and hexamer refer to molecules with two, three, four, five, and six units, respectively. The units of an oligomer may be arranged in a linear chain (as in melam, a dimer of melamine); a closed ring (as in 1,3,5-trioxane, a cyclic trimer of formaldehyde); or a more complex structure (as in tellurium tetrabromide, a tetramer of with a cube-like core). If the units are identical, one has a homo-oligomer; otherwise one may use hetero-oligomer. An example of a homo-oligomeric protein is collagen, which is composed of three identical protein chains.
Some biologically important oligomers are macromolecules like proteins or nucleic acids; for instance, hemoglobin is a protein tetramer. An oligomer of amino acids is called an oligopeptide or just a peptide. An oligosaccharide is an oligomer of monosaccharides (simple sugars). An oligonucleotide is a short single-stranded fragment of nucleic acid such as DNA or RNA, or similar fragments of analogs of nucleic acids such as peptide nucleic acid or Morpholinos.
The units of an oligomer may be connected by covalent bonds, which may result from bond rearrangement or condensation reactions, or by weaker forces such as hydrogen bonds.
The term multimer () is used in biochemistry for oligomers of proteins that are not covalently bound. The major capsid protein VP1 that comprises the shell of the polio virus is a self-assembling multimer of 72 pentamers held together by local electric charges.
Many oils are oligomeric, such as liquid paraffin. Plasticizers are oligomeric esters widely used to soften thermoplastics such as PVC. They may be made from monomers by linking them together, or by separation from the higher fractions of crude oil. Polybutene is an oligomeric oil used to make putty.
Oligomerization is a chemical process that converts monomers to macromolecular complexes through a finite degree of polymerization. Telomerization is an oligomerization carried out under conditions that result in chain transfer, limiting the size of the oligomers. (This concept is not to be confused with the formation of a telomere, a region of highly repetitive DNA at the end of a chromosome.) | 7 | Physical Chemistry |
Cross disproportionation occurs when two different alkyl radicals disproportionate to form two new products. Different products can be formed depending on which alkyl radical acts as a donor and which acts as an acceptor. The efficiency of primary and secondary alkyl radicals as donors depends on the steric effects and configuration of the radical acceptors. | 0 | Organic Chemistry |
In chemistry, sparging, also known as gas flushing in metallurgy, is a technique in which a gas is bubbled through a liquid in order to remove other dissolved gas(es) and/or dissolved volatile liquid(s) from that liquid. It is a method of degassing. According to Henry's law, the concentration of each gas in a liquid is proportional to the partial pressure of that gas (in the gaseous state) in contact with the liquid. Sparging introduces a gas that has little or no partial pressure of the gas(es) to be removed, and increases the area of the gas-liquid interface, which encourages some of the dissolved gas(es) to diffuse into the sparging gas before the sparging gas escapes from the liquid. Many sparging processes, such as solvent removal, use air as the sparging gas. To remove oxygen, or for sensitive solutions or reactive molten metals, a chemically inert gas such as nitrogen, argon, or helium is used. | 8 | Metallurgy |
The structural and compositional versatility of clay minerals gives them interesting biological properties. Due to disc-shaped and charged surfaces, clay interacts with a range of drugs, protein, polymers, DNA, or other macromolecules. Some of the applications of clays include drug delivery, tissue engineering, and bioprinting. | 9 | Geochemistry |
The cluster cation has the Keggin structure with a tetrahedral Al atom in the centre of the cluster coordinated to 4 oxygen atoms. The formula can be expressed as . This ion is generally called the ion. A analogue is known an unusual ionic compound with an cation and a Keggin polyoxoanion has been characterised. | 7 | Physical Chemistry |
Ehrlich and Raven's paper was highly influential on a generation of biologists and contributed to the explosion of research on plant-insect interactions and chemical ecology. The theory of escape and radiate coevolution purports to explain why we see such vast biological diversity on earth. After the organism escapes, it then radiates into multiple species, and spreads geographically. Evidence of escape and radiate coevolution can be seen through the starburst effect in plant and herbivore clades. When analyzing clades of predator-prey associations, although it varies, the starburst effect is a good indicator that escape and radiate coevolution may be occurring. Eventually this cycle must come to an end because adaptations that entail costs (such as allocation of resources, or vulnerability to other predators) at some point outweigh their benefits.
Escape and radiate coevolution may support parallel cladogenesis, wherein plant and herbivore phylogenies might match with ancestral insects exploiting ancestral plants. This is significant because it allows researchers to hypothesize about the relationships between ancestral organisms. Unfortunately, there have not yet been any known examples specifically involving escape and radiate coevolution being used for hypothesizing ancestral relationships.
Many times the organism that has "escaped" continuously undergoes selective pressure because the predator it has escaped from evolves to create another adaptation in response, causing the process to continue. These "offensive" traits developed by predators range widely. For example, herbivores can develop an adaptation that allows for improved detoxification which allow to overcome plant defenses, thus causing escape and radiate coevolution to continue. Often the term "evolutionary arms race" is used to illustrate the idea that continuous evolution is needed to maintain the same relative fitness while the two species are coevolving. This idea also ties in with the Red Queen hypothesis. Counter adaptations among two organisms through escape and radiate coevolution is a major driving force behind diversity.
Escape and radiate coevolution produces much more biological variation than other evolutionary mechanisms. For instance, cospeciation is important for diversity amongst species that share a symbiotic relationship, however this does not create nearly as much diversity in comparison to reciprocal evolutionary change due to natural selection.
Evidence of rapid diversification following a novel adaptation is shown through the evolution of resin and latex canal tubes in 16 different lineages of plants. Plants with resin or latex canals can easily defend themselves against insect herbivores. When lineages of canal bearing plants are compared to the lineages of canal free plants, it is apparent that canal bearing plants are far more diverse, supporting escape and radiate coevolution. | 1 | Biochemistry |
Isocyanide dichlorides participate in Friedel-Crafts-like reactions, leading, after hydrolysis, to benzamides:
:RN=CCl + ArH → RN=C(Cl)Ar + HCl
:RN=C(Cl)Ar + HO → R(H)NC(O)Ar + HCl | 0 | Organic Chemistry |
Soils represent a short to long-term carbon storage medium, and contain more carbon than all terrestrial vegetation and the atmosphere combined. Plant litter and other biomass including charcoal accumulates as organic matter in soils, and is degraded by chemical weathering and biological degradation. More recalcitrant organic carbon polymers such as cellulose, hemi-cellulose, lignin, aliphatic compounds, waxes and terpenoids are collectively retained as humus.
Organic matter tends to accumulate in litter and soils of colder regions such as the boreal forests of North America and the Taiga of Russia. Leaf litter and humus are rapidly oxidized and poorly retained in sub-tropical and tropical climate conditions due to high temperatures and extensive leaching by rainfall. Areas where shifting cultivation or slash and burn agriculture are practiced are generally only fertile for two to three years before they are abandoned. These tropical jungles are similar to coral reefs in that they are highly efficient at conserving and circulating necessary nutrients, which explains their lushness in a nutrient desert.
Grasslands contribute to soil organic matter, stored mainly in their extensive fibrous root mats. Due in part to the climatic conditions of these regions (e.g. cooler temperatures and semi-arid to arid conditions), these soils can accumulate significant quantities of organic matter. This can vary based on rainfall, the length of the winter season, and the frequency of naturally occurring lightning-induced grass-fires. While these fires release carbon dioxide, they improve the quality of the grasslands overall, in turn increasing the amount of carbon retained in the humic material. They also deposit carbon directly to the soil in the form of biochar that does not significantly degrade back to carbon dioxide.
Wetlands are a natural carbon sink, however climate change can cause these biomes to turn into a carbon source. The high temperature and low water resulted from climate change causes the wetland to transform into a carbon source. This can be seen in peatbogs which are a type of wetland. They undergoes slow anaerobic decomposition below the surface. This process is slow enough that in many cases the bog grows rapidly and fixes more carbon from the atmosphere than is released. Over time, the peat grows deeper. Peat bogs hold approximately one-quarter of the carbon stored in land plants and soils. | 5 | Photochemistry |
Reaction with acids or fluorides such as tetra-n-butylammonium fluoride removes the silyl group when protection is no longer needed. Larger substituents increase resistance to hydrolysis, but also make introduction of the silyl group more difficult.
In acidic media, the relative resistance is:
:TMS (1) < TES (64) < TBS (20 000) < TIPS (700,000) < TBDPS (5,000,000)
In basic media, the relative resistance is:
:TMS (1) < TES (10-100) < TBS~TBDPS (20 000) < TIPS (100,000) | 0 | Organic Chemistry |
PSI accepts electrons from plastocyanin and transfers them either to NADPH (noncyclic electron transport) or back to cytochrome bf (cyclic electron transport):
plastocyanin → P700 → P700 → FNR → NADPH
bf ← phylloquinone
PSI, like PSII, is a complex, highly organized transmembrane structure that contains antenna chlorophylls, a reaction center (P700), phylloquinone, and a number of iron-sulfur proteins that serve as intermediate redox carriers.
The light-harvesting system of PSI uses multiple copies of the same transmembrane proteins used by PSII. The energy of absorbed light (in the form of delocalized, high-energy electrons) is funneled into the reaction center, where it excites special chlorophyll molecules (P700, with maximum light absorption at 700 nm) to a higher energy level. The process occurs with astonishingly high efficiency.
Electrons are removed from excited chlorophyll molecules and transferred through a series of intermediate carriers to ferredoxin, a water-soluble electron carrier. As in PSII, this is a solid-state process that operates with 100% efficiency.
There are two different pathways of electron transport in PSI. In noncyclic electron transport, ferredoxin carries the electron to the enzyme ferredoxin reductase (FNR) that reduces to NADPH. In cyclic electron transport, electrons from ferredoxin are transferred (via plastoquinol) to a proton pump, cytochrome bf. They are then returned (via plastocyanin) to P700. NADPH and ATP are used to synthesize organic molecules from . The ratio of NADPH to ATP production can be adjusted by adjusting the balance between cyclic and noncyclic electron transport.
It is noteworthy that PSI closely resembles photosynthetic structures found in green sulfur bacteria, just as PSII resembles structures found in purple bacteria. | 5 | Photochemistry |
Salts of carboxylic acids are named following the usual cation-then-anion conventions used for ionic compounds in both IUPAC and common nomenclature systems. The name of the carboxylate anion () is derived from that of the parent acid by replacing the "–oic acid" ending with "–oate" or "carboxylate." For example, , the sodium salt of benzoic acid (), is called sodium benzoate. Where an acid has both a systematic and a common name (like , for example, which is known as both acetic acid and as ethanoic acid), its salts can be named from either parent name. Thus, can be named as potassium acetate or as potassium ethanoate. The prefix form, is "carboxylato-". | 0 | Organic Chemistry |
In part 1a of the schematic the oligonucleotide probe, labeled on its left end (asterisk), is shown on the top line. It is fully complementary to its target DNA (here taken from the human β-hemoglobin gene), as shown on the next line. Part of the probe includes the Recognition site for the restriction enzyme Dde I (underlined).
In part 1b, the restriction enzyme has cleaved the probe and its target (Dde I leaves three bases unpaired at each end). The labeled end of the probe is now just 8 bases in length, and is easily separated by Gel electrophoresis from the uncut probe, which was 40 bases long.
In part 2, the same probe is shown hybridized to a target DNA which includes a single base mutation (here the mutation responsible for Sickle Cell Anemia, or SCA). The mismatched hybrid no longer acts as a recognition site for the restriction enzyme, and the probe remains at its original length. | 1 | Biochemistry |
This spot test may be performed by wetting the thallus with K followed immediately by C. The initial application of K breaks down (via hydrolysis) ester bonds in depsides and depsidones. If a phenolic hydroxyl group is released that is meta to another hydroxyl, then a red to orange colour is produced as C is applied. Alectoronic acid and physodic acid produce this colour, while a violet colour results when picrolichenic acid is present. The CK test is a less commonly used variation that reverses the order of the application of chemicals. It is used in special cases when testing for orange colour produced by barbatic acid or diffractaic acid, such as is present in Cladonia floerkeana. Lugol's iodine is another reagent that may be useful in identifying certain species.
Hypogymnia tubulosa is a lichen that is KC+ (orange-pink) because of the depsidone physodic acid; Cetrelia olivetorum is KC+ (pink-red) due to the depsidone alectoronic acid. | 3 | Analytical Chemistry |
Metal ions are essential to virtually all biological systems and hence studying their concentrations with effective probes is highly advantageous. Since metal ions are key to the causes of cancer, diabetes, and other diseases, monitoring them with probes that can provide insight into their concentrations with spatial and temporal resolution is of great interest to the scientific community. There are many applications that one can envision for small molecule sensors. It has been shown that one can use them to differentiate effectively between acceptable and harmful concentrations of mercury in fish. Further, since some types of neurons uptake zinc during their operation, these probes can be used as a way to track activity in the brain and could serve as an effective alternative to functional MRI. One can also track and quantify the growth of a cell, such as a fibroblast, that uptakes metal ions as it constructs itself. Numerous other biological processes can be tracked using small molecule sensors as many change metal concentrations as they occur, which can then be monitored. Still, the sensor must be tailored for its specific environment and sensing requirements. Depending on the application, the metal sensor should be selective for a certain type of metal, and especially needs to be able to bind its target metal with greater affinity than metals that naturally exist at high concentrations within the cell . Further, they should provide a response with a strong modulation in fluorescent spectrum and hence provide a high signal-to-noise ratio. Finally, it is essential that a sensor is not toxic to the biological system in which it is used. | 5 | Photochemistry |
Restriction enzymes recognize a specific sequence of nucleotides and produce a double-stranded cut in the DNA. The recognition sequences can also be classified by the number of bases in its recognition site, usually between 4 and 8 bases, and the number of bases in the sequence will determine how often the site will appear by chance in any given genome, e.g., a 4-base pair sequence would theoretically occur once every 4^4 or 256bp, 6 bases, 4^6 or 4,096bp, and 8 bases would be 4^8 or 65,536bp. Many of them are palindromic, meaning the base sequence reads the same backwards and forwards. In theory, there are two types of palindromic sequences that can be possible in DNA. The mirror-like palindrome is similar to those found in ordinary text, in which a sequence reads the same forward and backward on a single strand of DNA, as in GTAATG. The inverted repeat palindrome is also a sequence that reads the same forward and backward, but the forward and backward sequences are found in complementary DNA strands (i.e., of double-stranded DNA), as in GTATAC (GTATAC being complementary to CATATG). Inverted repeat palindromes are more common and have greater biological importance than mirror-like palindromes.
EcoRI digestion produces "sticky" ends,
whereas SmaI restriction enzyme cleavage produces "blunt" ends:
Recognition sequences in DNA differ for each restriction enzyme, producing differences in the length, sequence and strand orientation (5 end or 3 end) of a sticky-end "overhang" of an enzyme restriction.
Different restriction enzymes that recognize the same sequence are known as neoschizomers. These often cleave in different locales of the sequence. Different enzymes that recognize and cleave in the same location are known as isoschizomers. | 1 | Biochemistry |
Above approximately 900 °C a typical low-carbon steel is composed entirely of austenite, a high-temperature phase of iron that has a cubic close-packed crystal structure. On cooling, it tends to transform into a mixture of phases, ferrite and cementite, depending on the exact chemical composition. A steel of eutectoid composition will under equilibrium conditions transform into pearlite – an interleaved mixture of ferrite and cementite (FeC). In addition to the thermodynamic considerations indicated by the phase diagram, the phase transformations in steel are heavily influenced by the chemical kinetics. This is because the diffusion of iron atoms becomes difficult below about 600 °C under typical processing conditions. As a consequence, a complex array of microstructures occurs when the atomic mobility is limited. This leads to the complexity of steel microstructures which are strongly influenced by the cooling rate. This can be illustrated by a continuous cooling transformation (CCT) diagram which plots the time required to form a phase when a sample is cooled at a specific rate thus showing regions in time-temperature space from which the expected phase fractions can be deduced for a given thermal cycle.
If the steel is cooled slowly or isothermally transformed at elevated temperatures, the microstructure obtained will be closer to equilibrium, containing for example of allotriomorphic ferrite, cementite and pearlite. However, the transformation from austenite to pearlite is a time-dependent reconstructive reaction which requires the large scale movement of the iron and carbon atoms. While the interstitial carbon diffuses readily even at moderate temperatures the self-diffusion of iron becomes extremely slow at temperatures below 600 °C until, for all practical purposes, it stops. As a consequence, a rapidly cooled steel may reach a temperature where pearlite can no longer form despite the reaction being incomplete and the remaining austenite being thermodynamically unstable.
Austenite that is cooled sufficiently rapidly to avoid higher temperature transformations, can form martensite, without any diffusion of either iron or carbon, by the deformation of the austenite's face-centred crystal structure into a distorted body-centred tetragonal or body-centred cubic structure. This non-equilibrium phase can only form at low temperatures, where the driving force for the reaction is sufficient to overcome the considerable lattice strain imposed by the transformation. The transformation is essentially time-independent with the phase fraction depending only the degree of cooling below the critical martensite start temperature. Further, it occurs without the diffusion of either substitutional or interstitial atoms and so martensite inherits the composition of the parent austenite.
Bainite occupies a region between these two process in a temperature range where iron self-diffusion is limited but there is insufficient driving force to form martensite. The bainite, like martensite, grows without diffusion but some of the carbon then partitions into any residual austenite, or precipitates as cementite. A further distinction is often made between so-called lower-bainite, which forms at temperatures closer to the martensite start temperature, and upper-bainite which forms at higher temperatures. This distinction arises from the diffusion rates of carbon at the temperature at which the bainite is forming. If the temperature is high then the carbon will diffuse rapidly away from the newly formed ferrite and form carbides in the carbon-enriched residual austenite between the ferritic plates leaving them carbide-free. At low temperatures the carbon will diffuse more sluggishly and may precipitate before it can leave the bainitic ferrite. There is some controversy over the specifics of bainite's transformation mechanism; both theories are represented below. | 8 | Metallurgy |
The strongly correlated quantum spin liquid (SCQSL) is a specific realization of a possible quantum spin liquid (QSL) representing a new type of strongly correlated electrical insulator (SCI) that possesses properties of heavy fermion metals with one exception: it resists the flow of electric charge. At low temperatures T the specific heat of this type of insulator is proportional to T, with n less or equal 1 rather than n=3, as it should be in the case of a conventional insulator whose heat capacity is proportional to T. When a magnetic field B is applied to SCI the specific heat depends strongly on B, contrary to conventional insulators. There are a few candidates of SCI; the most promising among them is Herbertsmithite, a mineral with chemical structure ZnCu(OH)Cl. | 7 | Physical Chemistry |
Dallol is a unique, terrestrial hydrothermal system around a cinder cone volcano in the Danakil Depression, northeast of the Erta Ale Range in Ethiopia. It is known for its unearthly colors and mineral patterns, and the very acidic fluids that discharge from its hydrothermal springs. | 9 | Geochemistry |
In recent years, there has been increasing recognition that methylmercury affects fish and wildlife health, both in acutely polluted ecosystems and ecosystems with modest methylmercury levels. Two reviews document numerous studies of diminished reproductive success of fish, fish-eating birds, and mammals due to methylmercury contamination in aquatic ecosystems. | 0 | Organic Chemistry |
* Plant cuticle/surface
* Plant cell walls
* Antimicrobial chemicals (for example: polyphenols, sesquiterpene lactones, saponins)
* Antimicrobial peptides
* Enzyme inhibitors
* Detoxifying enzymes that break down pathogen-derived toxins
* Receptors that perceive pathogen presence and activate inducible plant defences | 1 | Biochemistry |
Here, the aglycone is a flavonoid. Examples of this large group of glycosides include:
*Hesperidin (aglycone: hesperetin, glycone: rutinose)
*Naringin (aglycone: naringenin, glycone: rutinose)
*Rutin (aglycone: quercetin, glycone: rutinose)
*Quercitrin (aglycone: quercetin, glycone: rhamnose)
Among the important effects of flavonoids are their antioxidant effect. They are also known to decrease capillary fragility. | 0 | Organic Chemistry |
Sodium trifluoromethanesulfinate (CFSONa) is the sodium salt of trifluoromethanesulfinic acid. Together with t-butyl hydroperoxide, an oxidant, this compound was found to be a suitable reagent for introducing trifluoromethyl groups onto electron-rich aromatic compounds by Langlois; this reagent is also known as the Langlois reagent. This reaction operates via a free radical mechanism.
This reagent is also able to trifluoromethylate electron-deficient aromatic compounds under biphasic conditions. Zinc difluoromethanesulfinate, a related polymeric coordination complex, is able to introduce difluoromethyl groups (CHF-) onto aromatic compounds under similar biphasic conditions as well.
With the use of DMSO as an oxidant, it provides an environmentally friendly way for the synthesis of β-trifluoromethyl alcohols from alkenes. | 0 | Organic Chemistry |
Carbocations are formed in two major alkene addition reactions. In an HX addition reaction, the pi bond of an alkene acts as a nucleophile and bonds with the proton of an HX molecule, where the X is a halogen atom. This forms a carbocation intermediate, and the X then bonds to the positive carbon that is available, as in the following two-step reaction.
Similarly, in an addition reaction, the pi bond of an alkene acts as a nucleophile and bonds with the proton of an molecule. This forms a carbocation intermediate (and an atom); the oxygen atom of then bonds with the positive carbon of the intermediate. The oxygen finally deprotonates to form a final alcohol product, as follows. | 7 | Physical Chemistry |
Tautomerization is pervasive in organic chemistry. It is typically associated with polar molecules and ions containing functional groups that are at least weakly acidic. Most common tautomers exist in pairs, which means that the hydrogen is located at one of two positions, and even more specifically the most common form involves a hydrogen changing places with a double bond: . Common tautomeric pairs include:
* ketone – enol: , see keto–enol tautomerism
* enamine – imine:
**cyanamide – carbodiimide
**guanidine – guanidine – guanidine: With a central carbon surrounded by three nitrogens, a guanidine group allows this transform in three possible orientations
* amide – imidic acid: (e.g., the latter is encountered during nitrile hydrolysis reactions)
**lactam – lactim, a cyclic form of amide-imidic acid tautomerism in 2-pyridone and derived structures such as the nucleobases guanine, thymine, and cytosine
* imine – imine, e.g., during pyridoxal phosphate catalyzed enzymatic reactions
*nitro – aci-nitro (nitronic acid):
* nitroso – oxime:
* ketene – ynol, which involves a triple bond:
* amino acid – ammonium carboxylate, which applies to the building blocks of the proteins. This shifts the proton more than two atoms away, producing a zwitterion rather than shifting a double bond:
*phosphite – phosphonate: between trivalent and pentavalent phosphorus. | 4 | Stereochemistry |
Glyoxylate and dicarboxylate metabolism describes a variety of reactions involving glyoxylate or dicarboxylates. Glyoxylate is the conjugate base of glyoxylic acid, and within a buffered environment of known pH such as the cell cytoplasm these terms can be used almost interchangeably, as the gain or loss of a hydrogen ion is all that distinguishes them, and this can occur in the aqueous environment at any time. Likewise dicarboxylates are the conjugate bases of dicarboxylic acids, a general class of organic compounds containing two carboxylic acid groups, such as oxalic acid or succinic acid.
A compact graphical description of major biochemical reactions involved can be found at KEGG This provides information on the relevant enzymes and details the relationship with several other metabolic processes: glycine, serine, and threonine metabolism which provides hydroxypyruvate and glyoxylate, purine metabolism which provides glyoxylate, pyruvate metabolism which provides (S)-malate and formate, carbon fixation which consumes 3-phospho-D-glycerate and provides D-ribulose 1,5-P2, ascorbate and aldarate metabolism which shares tartronate-semialdehyde, nitrogen metabolism which shares formate, pyruvate metabolism and the citrate cycle which share oxaloacetate, and vitamin B metabolism which consumes glycolaldehyde.
The glyoxylate cycle describes an important subset of these reactions involved in biosynthesis of carbohydrates from fatty acids or two-carbon precursors which enter the system as acetyl-coenzyme A. Its crucial enzymes are isocitrate lyase and malate synthase. However, alternate pathways have been proposed in organisms lacking isocitrate lyase. | 1 | Biochemistry |
Lithium plasma concentrations are known to be increased with concurrent use of diuretics—especially loop diuretics (such as furosemide) and thiazides—and non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen. Lithium concentrations can also be increased with concurrent use of ACE inhibitors such as captopril, enalapril, and lisinopril.
Lithium is primarily cleared from the body through glomerular filtration, but some is then reabsorbed together with sodium through the proximal tubule. Its levels are therefore sensitive to water and electrolyte balance. Diuretics act by lowering water and sodium levels; this causes more reabsorption of lithium in the proximal tubules so that the removal of lithium from the body is less, leading to increased blood levels of lithium. ACE inhibitors have also been shown in a retrospective case-control study to increase lithium concentrations. This is likely due to constriction of the afferent arteriole of the glomerulus, resulting in decreased glomerular filtration rate and clearance. Another possible mechanism is that ACE inhibitors can lead to a decrease in sodium and water. This will increase lithium reabsorption and its concentrations in the body.
There are also drugs that can increase the clearance of lithium from the body, which can result in decreased lithium levels in the blood. These drugs include theophylline, caffeine, and acetazolamide. Additionally, increasing dietary sodium intake may also reduce lithium levels by prompting the kidneys to excrete more lithium.
Lithium is known to be a potential precipitant of serotonin syndrome in people concurrently on serotonergic medications such as antidepressants, buspirone and certain opioids such as pethidine (meperidine), tramadol, oxycodone, fentanyl and others. Lithium co-treatment is also a risk factor for neuroleptic malignant syndrome in people on antipsychotics and other antidopaminergic medications.
High doses of haloperidol, fluphenazine, or flupenthixol may be hazardous when used with lithium; irreversible toxic encephalopathy has been reported.
Indeed, these and other antipsychotics have been associated with increased risk of lithium neurotoxicity, even with low therapeutic lithium doses.
Classical psychedelics such as psilocybin and LSD may cause seizures if taken while using lithium, although further research is needed. | 1 | Biochemistry |
Methane has a limited atmospheric lifetime, about 10 years, due to substantial methane sinks. The primary methane sink is atmospheric oxidation, from hydroxyl radicals (~90% of the total sink) and chlorine radicals (0-5% of the total sink). The rest is consumed by methanotrophs and other methane-oxidizing bacteria and archaea in soils (~5%). | 2 | Environmental Chemistry |
An α,β-unsaturated acid is a type of α,β-unsaturated carbonyl compound that consists of an alkene conjugated to a carboxylic acid. The simplest example is acrylic acid (CH=CHCOH). These compounds are prone to polymerization, giving rise to the large area of polyacrylate plastics. Acrylate polymers are derived from but do not contain the acrylate group. The carboxyl group of acrylic acid can react with ammonia to form acrylamide, or with an alcohol to form an acrylate ester. Acrylamide and methyl acrylate are commercially important examples of α,β-unsaturated amides and α,β-unsaturated esters, respectively. They also polymerize readily. Acrylic acid, its esters, and its amide derivatives feature the acryloyl group.
α,β-Unsaturated dicarbonyls are also common. The parent compounds are maleic acid and the isomeric fumaric acid. Maleic acid forms esters, an imide, and an anhydride, i.e. diethyl maleate, maleimide, and maleic anhydride. Fumaric acid, as fumarate, is an intermediate in the Krebs citric acid cycle, which is of great importance in bioenergy. | 0 | Organic Chemistry |
Scientists Miquel Vila-Perello´, Matthew R. Pratt, Frej Tulin, and Tom W. Muir wanted to create an efficient synthesis as the original had required an enzymatic solution and had a low yield. So, they started with L-glutamic acid with protecting groups on both the carboxylic acid (tert-butyl), and Boc on the amine. This synthesis will not undergo detail as the classic, but below is the full synthesis. To find the actual steps, look to the reference.
So, once they had synthesized L-photo-methionine, the yield was 32%, much higher (by six times) the original synthesis. It was used then (with a protection group Fmoc on the amine) which that product underwent more synthetic steps to study if an amino-acid cross linker and a post-translational modification (PTM) could be introduced to the same protein site specifically to capture a covalent interaction of the amino-acid is dependent on the PTM. PTM's regulate protein-protein interactions that have characteristics that are transient and substoichiometric; making these difficult to detect by standard methods. So, in order to see if it would work, the MH2 domain of Smad2 was used because this signaling protein is known to form stable homo-trimers once they come into contact with receptor-phosphorylated serine residues. Expression protein ligation (known as EPL) was used to synthesize to form Smad2-MH2-CSpSM-photo-Met (1). The product was studied with the cross-linker (photo-Met) against a control protein: HA-MH2-CSpSMpS (this lacks photo-methionine, 2) using SDS-PAGE and western blotting using anti-HA antibody. 1 had generated two major cross-linked species that have molecular weight consistent with a dimer and trimer of Smad2-SH2. Without that cross-linker, the dimer and trimer were barely detected in the non-irradiated 1, and in 2 before and after UV irradiation. Proving that l-photo-methionine can be used with EPL and could be used to determine a transient MH2-MH2 interaction that was dependent on a PTM. | 5 | Photochemistry |
From alpha iron undergoes a phase transition from body-centered cubic (BCC) to the face-centered cubic (FCC) configuration of gamma iron, also called austenite. This is similarly soft and ductile but can dissolve considerably more carbon (as much as 2.03% by mass at ). This gamma form of iron is present in the most commonly used type of stainless steel for making hospital and food-service equipment. | 8 | Metallurgy |
At high temperatures in air, it decomposes or burns to produce poisonous phosgene. This was a common problem when carbon tetrachloride was used as a fire extinguisher: there have been deaths due to its conversion to phosgene reported.
Carbon tetrachloride is a suspected human carcinogen based on sufficient evidence of carcinogenicity from studies in experimental animals. The World Health Organization reports carbon tetrachloride can induce hepatocellular carcinomas (hepatomas) in mice and rats. The doses inducing hepatic tumours are higher than those inducing cell toxicity. The International Agency for Research on Cancer (IARC) classified this compound in Group 2B, "possibly carcinogenic to humans". Carbon tetrachloride is one of the most potent hepatotoxins (toxic to the liver), so much so that it is widely used in scientific research to evaluate hepatoprotective agents. Exposure to high concentrations of carbon tetrachloride (including vapor) can affect the central nervous system and degenerate the liver and kidneys, and prolonged exposure may lead to coma or death. Chronic exposure to carbon tetrachloride can cause liver and kidney damage and could result in cancer.
Consumption of alcohol increases the toxic effects of carbon tetrachloride and may cause more severe organ damage, such as acute renal failure, in heavy drinkers. The doses that can cause mild toxicity to non-drinkers can be fatal to drinkers.
The effects of carbon tetrachloride on human health and the environment have been assessed under REACH in 2012 in the context of the substance evaluation by France.
In 2008, a study of common cleaning products found the presence of carbon tetrachloride in "very high concentrations" (up to 101 mg/m) as a result of manufacturers' mixing of surfactants or soap with sodium hypochlorite (bleach).
Carbon tetrachloride is also both ozone-depleting and a greenhouse gas. However, since 1992 its atmospheric concentrations have been in decline for the reasons described above (see atmospheric concentration graphs in the gallery). CCl has an atmospheric lifetime of 85 years. | 2 | Environmental Chemistry |
One type of ion beam source is the duoplasmatron. Ion beams can be used for sputtering or ion beam etching and for ion beam analysis.
Ion beam application, etching, or sputtering, is a technique conceptually similar to sandblasting, but using individual atoms in an ion beam to ablate a target. Reactive ion etching is an important extension that uses chemical reactivity to enhance the physical sputtering effect.
In a typical use in semiconductor manufacturing, a mask can selectively expose a layer of photoresist on a substrate made of a semiconductor material such as a silicon dioxide or gallium arsenide wafer. The wafer is developed, and for a positive photoresist, the exposed portions are removed in a chemical process. The result is a pattern left on the surface areas of the wafer that had been masked from exposure. The wafer is then placed in a vacuum chamber, and exposed to the ion beam. The impact of the ions erodes the target, abrading away the areas not covered by the photoresist.
Focused ion beam (FIB) instruments have numerous applications for characterization of thin-film devices. Using a focused, high-brightness ion beam in a scanned raster pattern, material is removed (sputtered) in precise rectilinear patterns revealing a two-dimensional, or stratigraphic profile of a solid material. The most common application is to verify the integrity of the gate oxide layer in a CMOS transistor. A single excavation site exposes a cross section for analysis using a scanning electron microscope. Dual excavations on either side of a thin lamella bridge are utilized for preparing transmission electron microscope samples.
Another common use of FIB instruments is for design verification and/or failure analysis of semiconductor devices. Design verification combines selective material removal with gas-assisted material deposition of conductive, dielectric, or insulating materials. Engineering prototype devices may be modified using the ion beam in combination with gas-assisted material deposition in order to rewire an integrated circuit's conductive pathways. The techniques are effectively used to verify the correlation between the CAD design and the actual functional prototype circuit, thereby avoiding the creation of a new mask for the purpose of testing design changes.
Materials science use sputtering for extending surface analytical techniques such as secondary ion mass spectrometry or electron spectroscopy (XPS, AES) so that they can depth profile them. | 7 | Physical Chemistry |
The Bilbao Crystallographic Server also hosts the [https://web.archive.org/web/20111205170131/http://158.227.21.14/incstrdb/ B-IncStrDB: Bilbao Incommensurate Crystal Structures Database], a database for incommensurately modulated and composite structures. | 3 | Analytical Chemistry |
Compartmentalization was important in the origin of life. Membranes form enclosed compartments that are separate from the external environment, thus providing the cell with functionally specialized aqueous spaces. As the lipid bilayer of membranes is impermeable to most hydrophilic molecules (dissolved by water), modern cells have membrane transport-systems that achieve nutrient uptake as well as the export of waste. Prior to the development of these molecular assemblies, protocells likely employed vesicle dynamics that are relevant to cellular functions, such as membrane trafficking and self-reproduction, using amphiphilic molecules. On the primitive Earth, numerous chemical reactions of organic compounds produced the ingredients of life. Of these substances, amphiphilic molecules might be the first player in the evolution from molecular assembly to cellular life. Vesicle dynamics could progress towards protocells with the development of self-replication coupled with early metabolism. It is possible that protocells might have had a primitive metabolic system (Wood-Ljungdahl pathway) at alkaline hydrothermal vents or other geological environments like impact crater lakes from meteorites, which are known to be composed of elements found in the Wood-Ljungdahl pathway.
Another conceptual model of a protocell relates to the term "chemoton" (short for chemical automaton) which refers to the fundamental unit of life introduced by Hungarian theoretical biologist Tibor Gánti. It is the oldest known computational abstract of a protocell. Gánti conceived the basic idea in 1952 and formulated the concept in 1971 in his book The Principles of Life (originally written in Hungarian, and translated to English only in 2003). He surmised the chemoton as the original ancestor of all organisms, or the last universal common ancestor.
The basic assumption of the chemoton model is that life should fundamentally and essentially have three properties: metabolism, self-replication, and a bilipid membrane. The metabolic and replication functions together form an autocatalytic subsystem necessary for the basic functions of life, and a membrane encloses this subsystem to separate it from the surrounding environment. Therefore, any system having such properties may be regarded as alive, and will contain self sustaining cellular information that is subject to natural selection. Some consider this model a significant contribution to origin of life as it provides a philosophy of evolutionary units. | 9 | Geochemistry |
Fungi can be used for many of the same processes as bacteria. For industrial applications, yeasts combine the bacterial advantages of being a single-celled organism that is easy to manipulate and grow with the advanced protein modifications found in eukaryotes. They can be used to produce large complex molecules for use in food, pharmaceuticals, hormones, and steroids. Yeast is important for wine production and as of 2016 two genetically modified yeasts involved in the fermentation of wine have been commercialized in the United States and Canada. One has increased malolactic fermentation efficiency, while the other prevents the production of dangerous ethyl carbamate compounds during fermentation. There have also been advances in the production of biofuel from genetically modified fungi.
Fungi, being the most common pathogens of insects, make attractive biopesticides. Unlike bacteria and viruses they have the advantage of infecting the insects by contact alone, although they are out competed in efficiency by chemical pesticides. Genetic engineering can improve virulence, usually by adding more virulent proteins, increasing infection rate or enhancing spore persistence. Many of the disease carrying vectors are susceptible to entomopathogenic fungi. An attractive target for biological control are mosquitos, vectors for a range of deadly diseases, including malaria, yellow fever and dengue fever. Mosquitos can evolve quickly so it becomes a balancing act of killing them before the Plasmodium they carry becomes the infectious disease, but not so fast that they become resistant to the fungi. By genetically engineering fungi like Metarhizium anisopliae and Beauveria bassiana to delay the development of mosquito infectiousness the selection pressure to evolve resistance is reduced. Another strategy is to add proteins to the fungi that block transmission of malaria or remove the Plasmodium altogether.
Agaricus bisporus the common white button mushroom, has been gene edited to resist browning, giving it a longer shelf life. The process used CRISPR to knock out a gene that encodes polyphenol oxidase. As it didn't introduce any foreign DNA into the organism it was not deemed to be regulated under existing GMO frameworks and as such is the first CRISPR-edited organism to be approved for release. This has intensified debates as to whether gene-edited organisms should be considered genetically modified organisms and how they should be regulated. | 1 | Biochemistry |
The structure of active centers in Ziegler–Natta catalysts is well established only for metallocene catalysts. An idealized and simplified metallocene complex CpZrCl represents a typical precatalyst. It is unreactive toward alkenes. The dihalide reacts with MAO and is transformed into a metallocenium ion CpCH, which is ion-paired to some derivative(s) of MAO. A polymer molecule grows by numerous insertion reactions of C=C bonds of 1-alkene molecules into the Zr–C bond in the ion:
Many thousands of alkene insertion reactions occur at each active center resulting in the formation of long polymer chains attached to the center. The Cossee–Arlman mechanism describes the growth of stereospecific polymers. This mechanism states that the polymer grows through alkene coordination at a vacant site at the titanium atom, which is followed by insertion of the C=C bond into the Ti−C bond at the active center. | 7 | Physical Chemistry |
When material is heated enough, it begins to break down into smaller compounds, including flammable or even explosive gas, typically hydrocarbons. This is called pyrolysis, and does not require oxygen. If oxygen is also provided, then the hydrocarbons can combust, starting a fire.
If material undergoing pyrolysis is later given sufficient oxygen, the hydrocarbons will ignite, and therefore, combustion takes place. | 7 | Physical Chemistry |
The general structure is RR′C(X)C(=O)R where R is an alkyl or aryl residue and X any one of the halogens.
The preferred conformation of a halo ketone is that of a cisoid with the halogen and carbonyl sharing the same plane as the steric hindrance with the carbonyl alkyl group is generally larger. | 0 | Organic Chemistry |
Trifluoroperacetic acid is one of the strongest reagents used for Baeyer–Villiger oxidations, as a consequence of its high acidity relative to similar peracids and peroxides. This reaction converts ketones to either straight-chain esters or lactones, and is named for Adolf von Baeyer and Victor Villiger, who first reported it 1899. The reaction is believed to proceed via a Criegee intermediate and demonstrates good regioselectivity and chemoselectivity for the position of oxygen atom insertion, along with retention of stereochemistry at the adjacent position, as can be seen in the following example. The disodium phosphate () is added as a pH buffer to prevent the highly acidic trifluoroacetic acid byproduct from causing hydrolysis or transesterification of the ester product. | 0 | Organic Chemistry |
Only the unbound fraction of the drug undergoes metabolism in the liver and other tissues. As the drug dissociates from the protein, more and more drug undergoes metabolism. Changes in the levels of free drug change the volume of distribution because free drug may distribute into the tissues leading to a decrease in plasma concentration profile. For the drugs which rapidly undergo metabolism, clearance is dependent on the hepatic blood flow. For drugs which slowly undergo metabolism, changes in the unbound fraction of the drug directly change the clearance of the drug.
The most commonly used methods for measuring drug concentration levels in the plasma measure bound as well as unbound fractions of the drug.
The fraction unbound can be altered by a number of variables, such as the concentration of drug in the body, the amount and quality of plasma protein, and other drugs that bind to plasma proteins. Higher drug concentrations would lead to a higher fraction unbound, because the plasma protein would be saturated with drug and any excess drug would be unbound. If the amount of plasma protein is decreased (such as in catabolism, malnutrition, liver disease, renal disease), there would also be a higher fraction unbound. Additionally, the quality of the plasma protein may affect how many drug-binding sites there are on the protein. | 1 | Biochemistry |
The composition of the solar system is similar to that of many other stars, and aside from small anomalies it can be assumed to have formed from a solar nebula that had a uniform composition, and the composition of the Suns photosphere is similar to that of the rest of the Solar System. The composition of the photosphere is determined by fitting the absorption lines in its spectrum to models of the Suns atmosphere. By far the largest two elements by fraction of total mass are hydrogen (74.9%) and helium (23.8%), with all the remaining elements contributing just 1.3%. There is a general trend of exponential decrease in abundance with increasing atomic number, although elements with even atomic number are more common than their odd-numbered neighbors (the Oddo–Harkins rule). Compared to the overall trend, lithium, boron and beryllium are depleted and iron is anomalously enriched.
The pattern of elemental abundance is mainly due to two factors. The hydrogen, helium, and some of the lithium were formed in about 20 minutes after the Big Bang, while the rest were created in the interiors of stars. | 9 | Geochemistry |
Electrodeionization was developed in the early 1950s to eliminate or minimize the concentration polarization phenomenon present in electrolysis systems of the time. A patent on the technology was filed in 1953, and subsequent publications popularized the technology.
The technology was limited in application because of the low tolerance of total dissolved solids, hardness and organics. During the 1970s and 1980s, reverse osmosis became a preferred technology to ion exchange resin for high TDS waters. As RO gained popularity, EDI emerged as a suitable polishing technology. Packaged RO and EDI systems began to displace chemically regenerated ion exchange systems.
In 1986 and 1989, several companies developed new EDI devices. The initial devices were large, costly, and often unreliable. However, in the 1990s, smaller and less costly modular designs were introduced. Nonetheless, these designs and their contemporary descendants still face limitations such as cost and limited operational envelope. | 7 | Physical Chemistry |
The acid converts deoxyribose to a molecule that binds with diphenylamine to form a blue substance. The reagent does not interact with RNA, so can be used to distinguish DNA from RNA. | 3 | Analytical Chemistry |
Statistical mechanics, also known as statistical thermodynamics, emerged with the development of atomic and molecular theories in the late 19th century and early 20th century, and supplemented classical thermodynamics with an interpretation of the microscopic interactions between individual particles or quantum-mechanical states. This field relates the microscopic properties of individual atoms and molecules to the macroscopic, bulk properties of materials that can be observed on the human scale, thereby explaining classical thermodynamics as a natural result of statistics, classical mechanics, and quantum theory at the microscopic level. | 7 | Physical Chemistry |
In organophosphorus chemistry, phosphoramidates (sometimes also called amidophosphates) are a class of phosphorus compounds structurally related to phosphates (or organophosphates) via the substitution of an group for an amine group (). They are derivatives of phosphoramidic acids, which possess the structure or .
A phosphorodiamidate is a phosphate that has two of its hydroxyl () groups substituted by amine () groups to give a species with the general formula . The substitution of all three OH groups gives the phosphoric triamides (), which are commonly referred to as phosphoramides. | 0 | Organic Chemistry |
A liquid rheostat or water rheostat or salt water rheostat is a type of variable resistor.
This may be used as a dummy load or as a starting resistor for large slip ring motors.
In the simplest form it consists of a tank containing brine or other electrolyte solution, in which electrodes are submerged to create an electrical load. The electrodes may be raised or lowered into the liquid to respectively increase or decrease the electrical resistance of the load. To stabilize the load, the mixture must not be allowed to boil.
Modern designs use stainless steel electrodes, and sodium carbonate, or other salts, and do not use the container as one electrode. In some designs the electrodes are fixed and the liquid is raised and lowered by an external cylinder or pump. Motor start systems used for frequent and rapid starts and re-starts, thus a high heat load to the rheostats, may include water circulation to external heat exchangers. In such cases anti-freeze and anti-corrosion additives must be carefully chosen to not change the resistance or support the growth of algae or bacteria.
The salt water rheostat operates at unity power factor and presents a resistance with negligible series inductance compared to a wire wound equivalent, and was widely used by generator assemblers, until 20 years ago, as a matter of course. They are still sometimes constructed on-site for the commissioning of large diesel generators in remote places, where discarded oil drums and scaffold tubes may form an improvised tank and electrodes. | 7 | Physical Chemistry |
*Significant improvement of resolution in data collection
*Reduced or eliminated radiation damage in crystals | 3 | Analytical Chemistry |
In these thermocouples (chromel–gold/iron alloy), the negative wire is gold with a small fraction (0.03–0.15 atom percent) of iron. The impure gold wire gives the thermocouple a high sensitivity at low temperatures (compared to other thermocouples at that temperature), whereas the chromel wire maintains the sensitivity near room temperature. It can be used for cryogenic applications (1.2–300 K and even up to 600 K). Both the sensitivity and the temperature range depend on the iron concentration. The sensitivity is typically around 15 μV/K at low temperatures, and the lowest usable temperature varies between 1.2 and 4.2 K. | 8 | Metallurgy |
It had long been thought that the sigma factor obligatorily leaves the core enzyme once it has initiated transcription, allowing it to link to another core enzyme and initiate transcription at another site. Thus, the sigma factor would cycle from one core to another.
However, fluorescence resonance energy transfer was used to show that the sigma factor does not obligatorily leave the core. Instead, it changes its binding with the core during initiation and elongation. Therefore, the sigma factor cycles between a strongly bound state during initiation and a weakly bound state during elongation. | 1 | Biochemistry |
Apoptotic cells degrade their DNA in a characteristic nucleosome ladder pattern. This generates DNA fragments that can be ligated and amplified during the DamID procedure (van Steensel laboratory, unpublished observations). The influence of these nucleosomal fragments on the binding profile of a protein is not known. | 1 | Biochemistry |
For composite lattices, (crystals which have more than one vector in their basis) each single lattice point represents multiple atoms. We can break apart each Wigner–Seitz cell into subcells by further Voronoi decomposition according to the closest atom, instead of the closest lattice point. For example, the diamond crystal structure contains a two atom basis. In diamond, carbon atoms have tetrahedral sp bonding, but since tetrahedra do not tile space, the voronoi decomposition of the diamond crystal structure is actually the triakis truncated tetrahedral honeycomb. Another example is applying Voronoi decomposition to the atoms in the A15 phases, which forms the polyhedral approximation of the Weaire–Phelan structure. | 3 | Analytical Chemistry |
A mode of vibration is characterized by a modal frequency and a mode shape. It is numbered according to the number of half waves in the vibration. For example, if a vibrating beam with both ends pinned displayed a mode shape of half of a sine wave (one peak on the vibrating beam) it would be vibrating in mode 1. If it had a full sine wave (one peak and one trough) it would be vibrating in mode 2.
In a system with two or more dimensions, such as the pictured disk, each dimension is given a mode number. Using polar coordinates, we have a radial coordinate and an angular coordinate. If one measured from the center outward along the radial coordinate one would encounter a full wave, so the mode number in the radial direction is 2. The other direction is trickier, because only half of the disk is considered due to the anti-symmetric (also called skew-symmetry) nature of a disk's vibration in the angular direction. Thus, measuring 180° along the angular direction you would encounter a half wave, so the mode number in the angular direction is 1. So the mode number of the system is 2–1 or 1–2, depending on which coordinate is considered the "first" and which is considered the "second" coordinate (so it is important to always indicate which mode number matches with each coordinate direction).
In linear systems each mode is entirely independent of all other modes. In general all modes have different frequencies (with lower modes having lower frequencies) and different mode shapes. | 7 | Physical Chemistry |
Dendrimer drug delivery has also shown major promise as a potential solution for many traditionally difficult drug delivery problems. In the case of drug delivery to the brain, dendrimers are able to take advantage of the EPR effect and blood-brain barrier (BBB) impairment to cross the BBB effectively in vivo. For example, hydroxyl-terminated PAMAM dendrimers possess an intrinsic targeting ability to inflamed macrophages in the brain, verified using fluorescently labeled neutral generation dendrimers in a rabbit model of cerebral palsy. This intrinsic targeting has enabled drug delivery in a variety of conditions, ranging from cerebral palsy and other neuroinflammatory disorders to traumatic brain injury and hypothermic circulatory arrest, across a variety of animal models ranging from mice and rabbits to canines. Dendrimer uptake into the brain correlates with severity of inflammation and BBB impairment and it is believed that the BBB impairment is the key driving factor allowing dendrimer penetration. Localization is heavily skewed towards activated microglia. Dendrimer-conjugated N-acetyl cysteine has shown efficacy in vivo as an anti-inflammatory at more than 1000-fold lower dose than free drug on a drug basis, reversing the phenotype of cerebral palsy, Rett syndrome, macular degeneration and other inflammatory diseases. | 6 | Supramolecular Chemistry |
Closely related is mmCIF, macromolecular CIF, which is intended as an successor to the Protein Data Bank (PDB) format. It is now the default format used by the Protein Data Bank.
Also closely related is Crystallographic Information Framework, a broader system of exchange protocols based on data dictionaries and relational rules expressible in different machine-readable manifestations, including, but not restricted to, Crystallographic Information File and XML. | 3 | Analytical Chemistry |
The Parkes process is a pyrometallurgical industrial process for removing silver from lead during the production of bullion. It is an example of liquid–liquid extraction.
The process takes advantage of two liquid-state properties of zinc. The first is that zinc is immiscible with lead, and the other is that silver is 3000 times more soluble in zinc than it is in lead. When zinc is added to liquid lead that contains silver as a contaminant, the silver preferentially migrates into the zinc. Because the zinc is immiscible in the lead it remains in a separate layer and is easily removed. The zinc-silver solution is then heated until the zinc vaporizes, leaving nearly pure silver. If gold is present in the liquid lead, it can also be removed and isolated by the same process.
The process was patented by Alexander Parkes in 1850. Parkes received two additional patents in 1852.
The Parkes process was not adopted in the United States, due to the low native production of lead. The problems were overcome during the 1880s and by 1923 only when the Parkes process was used. | 8 | Metallurgy |
To measure the polarization of an electron beam, a Mott detector is required. In order to maximize the spin-orbit coupling, it is necessary that the electrons arrive near to the nuclei of the target. To achieve this condition, a system of electron optics is usually present, in order to accelerate the beam up to keV or to MeV energies. Since standard electron detectors count electrons being insensitive to their spin, after the scattering with the target any information about the original polarization of the beam is lost. Nevertheless, by measuring the difference in the counts of the two detectors, the asymmetry can be evaluated and, if the Sherman function is known from previous calibration, the polarization can be calculated by inverting the last formula.
In order to characterize completely the in-plane polarization, setups are available, with four channeltrons, two devoted to the left-right measure and two devoted to the up-right measure. | 7 | Physical Chemistry |
The major difference between RNA and DNA is the presence of a hydroxyl group at the 2-position of the ribose sugar in RNA (illustration, right). This group makes the molecule less stable because, when not constrained in a double helix, the 2 hydroxyl can chemically attack the adjacent phosphodiester bond to cleave the phosphodiester backbone. The hydroxyl group also forces the ribose into the C3-endo sugar conformation unlike the C2-endo conformation of the deoxyribose sugar in DNA. This forces an RNA double helix to change from a B-DNA structure to one more closely resembling A-DNA.
RNA also uses a different set of bases than DNA—adenine, guanine, cytosine and uracil, instead of adenine, guanine, cytosine and thymine. Chemically, uracil is similar to thymine, differing only by a methyl group, and its production requires less energy. In terms of base pairing, this has no effect. Adenine readily binds uracil or thymine. Uracil is, however, one product of damage to cytosine that makes RNA particularly susceptible to mutations that can replace a GC base pair with a GU (wobble) or AU base pair.
RNA is thought to have preceded DNA, because of their ordering in the biosynthetic pathways. The deoxyribonucleotides used to make DNA are made from ribonucleotides, the building blocks of RNA, by removing the 2'-hydroxyl group. As a consequence, a cell must have the ability to make RNA before it can make DNA. | 9 | Geochemistry |
In physics, the Toda oscillator is a special kind of nonlinear oscillator. It represents a chain of particles with exponential potential interaction between neighbors. These concepts are named after Morikazu Toda. The Toda oscillator is used as a simple model to understand the phenomenon of self-pulsation, which is a quasi-periodic pulsation of the output intensity of a solid-state laser in the transient regime. | 7 | Physical Chemistry |
Photosensitizers that are readily incorporated into the external tissues can increase the rate at which reactive oxygen species are generated upon exposure to UV light (such as UV-containing sunlight). Some photosensitizing agents, such as St. John's Wort, appear to increase the incidence of inflammatory skin conditions in animals and have been observed to slightly reduce the minimum tanning dose in humans.
Some examples of photosensitizing medications (both investigatory and approved for human use) are:
* St. John's Wort
* 9-me-bc
* Doxepin
* Amoxapine
* Ethinyl estradiol | 5 | Photochemistry |
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