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Heterogeneous catalysts are easily removed from a reaction mixture by filtration. Although some amount of metal catalyst typically remains in the product from leaching, these amounts tend to be lower than those remaining after workup of a homogenous metal-catalyzed cross-coupling. | 0 | Organic Chemistry |
With a relatively low global warming potential (GWP) index of 124 and favorable thermophysical properties, 1,1-difluoroethane has been proposed as an environmentally friendly alternative to R134a. Despite its flammability, R152a also presents operating pressures and volumetric cooling capacity (VCC) similar to R134a so it can be used in large chillers or in more particular applications like heat pipe finned heat exchangers.
Furthermore, 1,1-difluoroethane is also commonly used in gas dusters and numerous other retail aerosol products, particularly those subject to stringent volatile organic compound (VOC) requirements.
The molecular weight of difluoroethane is 66, making it a useful and convenient tool for detecting vacuum leaks in Gas chromatography–mass spectrometry (GC-MS) systems. The cheap and freely available gas has a molecular weight and fragmentation pattern (base peak 51 m/z in typical EI-MS, major peak at 65 m/z) distinct from anything in air. If mass peaks corresponding to 1,1-difluoroethane are observed immediately after spraying a suspect leak point, leaks may be identified. | 2 | Environmental Chemistry |
Monika Suchanek, Anna Radzikowska and Christoph Thiele carried out an experiment in which they had successfully managed to label proteins from the cells of a monkey's kidney (COS7).
These cells were grown in a high-glucose medium, from which a sample of 3 cm² was removed to proceed with the western blotting. At about 70% of confluence, the initial medium was replaced by another one lacking the amino acids methionine, leucine, isoleucine and valine, as well as phenol red.
Afterwards, photo-amino acids were added to a final concentration of 4 mM of photo-leucine and photo-isoleucine, 1.7 mM of photo-methionine, and cultivated for 22 hours. Once the time was over, cells were washed using PBS and UV-irradiated using a 200-W high pressure mercury lamp with a glass filter that removed wavelengths under 310 nm during 1 to 3 minutes. This did not affect to the viability of the cell (which only was altered after 10 minutes of irradiation). Cell was driven to lysis and subsequent western blotting to analyse the isolated cross-linked complexes.
MacKinnon A. L. et al. used photo-leucine to label proteins in a crude membrane fraction, which allowed them to identify the central part of a translocation channel within the membrane that is the target of the cyclodepsipeptide inhibitor. | 5 | Photochemistry |
Oxygen depletion can result from a number of natural factors, but is most often a concern as a consequence of pollution and eutrophication in which plant nutrients enter a river, lake, or ocean, and phytoplankton blooms are encouraged. While phytoplankton, through photosynthesis, will raise DO saturation during daylight hours, the dense population of a bloom reduces DO saturation during the night by respiration. When phytoplankton cells die, they sink towards the bottom and are decomposed by bacteria, a process that further reduces DO in the water column. If oxygen depletion progresses to hypoxia, fish kills can occur and invertebrates like worms and clams on the bottom may be killed as well.
Hypoxia may also occur in the absence of pollutants. In estuaries, for example, because freshwater flowing from a river into the sea is less dense than salt water, stratification in the water column can result. Vertical mixing between the water bodies is therefore reduced, restricting the supply of oxygen from the surface waters to the more saline bottom waters. The oxygen concentration in the bottom layer may then become low enough for hypoxia to occur. Areas particularly prone to this include shallow waters of semi-enclosed water bodies such as the Waddenzee or the Gulf of Mexico, where land run-off is substantial. In these areas a so-called "dead zone" can be created. Low dissolved oxygen conditions are often seasonal, as is the case in Hood Canal and areas of Puget Sound, in Washington State. The World Resources Institute has identified 375 hypoxic coastal zones around the world, concentrated in coastal areas in Western Europe, the Eastern and Southern coasts of the US, and East Asia, particularly in Japan.
Hypoxia may also be the explanation for periodic phenomena such as the Mobile Bay jubilee, where aquatic life suddenly rushes to the shallows, perhaps trying to escape oxygen-depleted water. Recent widespread shellfish kills near the coasts of Oregon and Washington are also blamed on cyclic dead zone ecology. | 9 | Geochemistry |
Metal acyl complexes participate in several commercial processes, including:
*hydroformylation
*acetic acid synthesis
*Eastman acetic anhydride process
*Ethylene-carbon monoxide copolymerization
A reaction involving metal acyl complexes of occasional value in organic synthesis is the Tsuji–Wilkinson decarbonylation reaction of aldehydes. | 0 | Organic Chemistry |
Hydrogen bonds are generally denoted by dotted or dashed lines. In other contexts, dashed lines may also represent partially formed or broken bonds in a transition state. | 0 | Organic Chemistry |
Zinc is present in almost 3,000 human proteins, and thus is essential for nearly all cellular functions. Zn is also a key constituent of enzymes involved in cell regulation. Consistent with its ubiquitous presence, total cellular Zn concentrations are typically very high (~200 μM), while the concentrations of free Zn ions in the cytoplasms of cells can be as low as a few hundred picomolar, maintained within a narrow range to avoid deficiency and toxicity. One feature of Zn that makes it so critical in cellular biology is its flexibility in coordination to different numbers and types of ligands. Zn can coordinate with anywhere between three and six N-, O- and S-containing ligands (such as histidine, glutamic acid, aspartic acid and cysteine), resulting in a large number of possible coordination chemistries. Zn tends to bind to metal sites of proteins with relatively high affinities compared to other metal ions which, aside from its important functions in enzymatic reactions, partly explains its ubiquitous presence in cellular enzymes. | 9 | Geochemistry |
Indel (insertion-deletion) is a molecular biology term for an insertion or deletion of bases in the genome of an organism. Indels ≥ 50 bases in length are classified as structural variants.
In coding regions of the genome, unless the length of an indel is a multiple of 3, it will produce a frameshift mutation. For example, a common microindel which results in a frameshift causes Bloom syndrome in the Jewish or Japanese population. Indels can be contrasted with a point mutation. An indel inserts or deletes nucleotides from a sequence, while a point mutation is a form of substitution that replaces one of the nucleotides without changing the overall number in the DNA. Indels can also be contrasted with Tandem Base Mutations (TBM), which may result from fundamentally different mechanisms. A TBM is defined as a substitution at adjacent nucleotides (primarily substitutions at two adjacent nucleotides, but substitutions at three adjacent nucleotides have been observed).
Indels, being either insertions, or deletions, can be used as genetic markers in natural populations, especially in phylogenetic studies. It has been shown that genomic regions with multiple indels can also be used for species-identification procedures.
An indel change of a single base pair in the coding part of an mRNA results in a frameshift during mRNA translation that could lead to an inappropriate (premature) stop codon in a different frame. Indels that are not multiples of 3 are particularly uncommon in coding regions but relatively common in non-coding regions. There are approximately 192-280 frameshifting indels in each person. Indels are likely to represent between 16% and 25% of all sequence polymorphisms in humans. In most known genomes, including humans, indel frequency tends to be markedly lower than that of single nucleotide polymorphisms (SNP), except near highly repetitive regions, including homopolymers and microsatellites.
The term "indel" has been co-opted in recent years by genome scientists for use in the sense described above. This is a change from its original use and meaning, which arose from systematics. In systematics, researchers could find differences between sequences, such as from two different species. But it was impossible to infer if one species lost the sequence or the other species gained it. For example, species A has a run of 4 G nucleotides at a locus and species B has 5 G's at the same locus. If the mode of selection is unknown, one can not tell if species A lost one G (a "deletion" event") or species B gained one G (an "insertion" event). When one cannot infer the phylogenetic direction of the sequence change, the sequence change event is referred to as an "indel".
Using passenger-immunoglobulin mouse models, a study found that the most prevalent indel events are the activation-induced cytidine deaminase (AID)-dependent ±1-base pair (bp) indels, which can lead to deleterious outcomes, whereas longer in-frame indels were rare outcomes. | 1 | Biochemistry |
Postprandial somnolence (colloquially known as food coma, after-dinner dip, or "the itis") is a normal state of drowsiness or lassitude following a meal. Postprandial somnolence has two components: a general state of low energy related to activation of the parasympathetic nervous system in response to mass in the gastrointestinal tract, and a specific state of sleepiness. While there are numerous theories surrounding this behavior, such as decreased blood flow to the brain, neurohormonal modulation of sleep through digestive coupled signaling, or vagal stimulation, very few have been explicitly tested. To date, human studies have loosely examined the behavioral characteristics of postprandial sleep, demonstrating potential shifts in EEG spectra and self-reported sleepiness. To date, the only clear animal models for examining the genetic and neuronal basis for this behavior are the fruit fly, the mouse, and the nematode Caenorhabditis elegans. | 1 | Biochemistry |
The photoreceptor cells involved in vertebrate vision are the rods, the cones, and the photosensitive ganglion cells (ipRGCs). These cells contain a chromophore (11-cis-retinal, the aldehyde of vitamin A1 and light-absorbing portion) that is bound to a cell membrane protein, opsin. Rods are responsible for vision under low light intensity and contrast detections. Because they all have the same response across frequencies, no color information can be deduced from the rods only, as in low light conditions for example. Cones, on the other hand, are of different kinds with different frequency response, such that color can be perceived through comparison of the outputs of different kinds of cones. Each cone type responds best to certain wavelengths, or colors, of light because each type has a slightly different opsin. The three types of cones are L-cones, M-cones and S-cones that respond optimally to long wavelengths (reddish color), medium wavelengths (greenish color), and short wavelengths (bluish color) respectively. Humans have trichromatic photopic vision consisting of three opponent process channels that enable color vision.
Rod photoreceptors are the most common cell type in the retina and develop quite late. Most cells become postmitotic before birth, but differentiation occurs after birth. In the first week after birth, cells mature and the eye becomes fully functional at the time of opening. The visual pigment rhodopsin (rho) is the first known sign of differentiation in rods. | 1 | Biochemistry |
Some of the best-known examples of quorum sensing come from studies of bacteria. Bacteria use quorum sensing to regulate certain phenotype expressions, which in turn, coordinate their behavio rs. Some common phenotypes include biofilm formation, virulence factor expression, and motility. Certain bacteria are able to use quorum sensing to regulate bioluminescence, nitrogen fixation and sporulation.
The quorum-sensing function is based on the local density of the bacterial population in the immediate environment. It can occur within a single bacterial species, as well as between diverse species. Both gram-positive and gram-negative bacteria use quorum sensing, but there are some major differences in their mechanisms. | 1 | Biochemistry |
Plastocyanin is a copper-containing protein that mediates electron-transfer. It is found in a variety of plants, where it participates in photosynthesis. The protein is a prototype of the blue copper proteins, a family of intensely blue-colored metalloproteins. Specifically, it falls into the group of small type I blue copper proteins called "cupredoxins". | 5 | Photochemistry |
3-Phosphoglyceric acid (3PG, 3-PGA, or PGA) is the conjugate acid of 3-phosphoglycerate or glycerate 3-phosphate (GP or G3P). This glycerate is a biochemically significant metabolic intermediate in both glycolysis and the Calvin-Benson cycle. The anion is often termed as PGA when referring to the Calvin-Benson cycle. In the Calvin-Benson cycle, 3-phosphoglycerate is typically the product of the spontaneous scission of an unstable 6-carbon intermediate formed upon CO fixation. Thus, two equivalents of 3-phosphoglycerate are produced for each molecule of CO that is fixed. In glycolysis, 3-phosphoglycerate is an intermediate following the dephosphorylation (reduction) of 1,3-bisphosphoglycerate. | 5 | Photochemistry |
Geometrically chiral polytopes are relatively exotic compared to the more ordinary regular polytopes. It is not possible for a geometrically chiral polytope to be convex, and many geometrically chiral polytopes of note are skew. | 4 | Stereochemistry |
Carbon nanotubes and graphene-based materials can be used as electrocatalysts. The carbon surfaces of graphene and carbon nanotubes are well suited to the adsorption of many chemical species, which can promote certain electrocatalytic reactions. In addition, their conductivity means they are good electrode materials. Carbon nanotubes have a very high surface area, maximizing surface sites at which electrochemical transformations can occur. Graphene can also serve as a platform for constructing composites with other kinds of nanomaterials such as single atom catalysts. Because of their conductivity, carbon-based materials can potentially replace metal electrodes to perform metal-free electrocatalysis. | 7 | Physical Chemistry |
Cynthia Larive is an American scientist and academic administrator serving as the chancellor of University of California, Santa Cruz. Larives research focuses on nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry. She was previously a professor of chemistry and provost and executive vice chancellor at the University of California, Riverside. She is a fellow of AAAS, IUPAC and ACS, associate editor for the ACS journal Analytical Chemistry' and editor of the Analytical Sciences Digital Library. | 3 | Analytical Chemistry |
Atomicity is the total number of atoms present in a molecule of an element. For example, each molecule of oxygen (O) is composed of two oxygen atoms. Therefore, the atomicity of oxygen is 2.
In older contexts, atomicity is sometimes equivalent to valency. Some authors also use the term to refer to the maximum number of valencies observed for an element. | 7 | Physical Chemistry |
The cut-and-paste transposition mechanism of class II TEs does not involve an RNA intermediate. The transpositions are catalyzed by several transposase enzymes. Some transposases non-specifically bind to any target site in DNA, whereas others bind to specific target sequences. The transposase makes a staggered cut at the target site producing sticky ends, cuts out the DNA transposon and ligates it into the target site. A DNA polymerase fills in the resulting gaps from the sticky ends and DNA ligase closes the sugar-phosphate backbone. This results in target site duplication and the insertion sites of DNA transposons may be identified by short direct repeats (a staggered cut in the target DNA filled by DNA polymerase) followed by inverted repeats (which are important for the TE excision by transposase).
Cut-and-paste TEs may be duplicated if their transposition takes place during S phase of the cell cycle, when a donor site has already been replicated but a target site has not yet been replicated. Such duplications at the target site can result in gene duplication, which plays an important role in genomic evolution.
Not all DNA transposons transpose through the cut-and-paste mechanism. In some cases, a replicative transposition is observed in which a transposon replicates itself to a new target site (e.g. helitron).
Class II TEs comprise less than 2% of the human genome, making the rest Class I. | 1 | Biochemistry |
Graphitic corrosion is selective leaching of iron, from grey cast iron, where iron is removed and graphite grains remain intact. Affected surfaces develop a layer of graphite, rust, and metallurgical impurities that may inhibit further leaching. The effect can be substantially reduced by alloying the cast iron with nickel. | 8 | Metallurgy |
In case of resistance to thyroid hormone, the magnitude of TTSI depends on which nucleotide in the THRB gene is mutated, but also on the genotype of coactivators. A systematic investigation in mice demonstrated a strong association of TT4RI to the genotypes of THRB and the steroid receptor coactivator (SRC-1) gene. | 1 | Biochemistry |
HIRs require long exposure to relatively high light levels. The degree of response will depend on the level of light. They are characterised by the fact that they do not follow the law of reciprocity and depend on the rate of photons hitting the leaf surface, as opposed to the total light levels. This means that neither long exposure to dim levels of light nor very bright flashes of light are enough to trigger these responses. HIR does not show red and far red photoreversibility and does not obey the law of reciprocity. | 5 | Photochemistry |
Combining the laws of Charles, Boyle and Gay-Lussac gives the combined gas law, which takes the same functional form as the ideal gas law says that the number of moles is unspecified, and the ratio of to is simply taken as a constant:
where is the pressure of the gas, is the volume of the gas, is the absolute temperature of the gas, and is a constant. When comparing the same substance under two different sets of conditions, the law can be written as | 7 | Physical Chemistry |
Orthopoxviruses and some other nucleocytoplasmic large DNA viruses synthesize RNA using a virally encoded multi-subunit RNAP. They are most similar to eukaryotic RNAPs, with some subunits minified or removed. Exactly which RNAP they are most similar to is a topic of debate. Most other viruses that synthesize RNA use unrelated mechanics.
Many viruses use a single-subunit DNA-dependent RNAP (ssRNAP) that is structurally and mechanistically related to the single-subunit RNAP of eukaryotic chloroplasts (RpoT) and mitochondria (POLRMT) and, more distantly, to DNA polymerases and reverse transcriptases. Perhaps the most widely studied such single-subunit RNAP is bacteriophage T7 RNA polymerase. ssRNAPs cannot proofread.
B. subtilis prophage SPβ uses YonO, a homolog of the β+β′ subunits of msRNAPs to form a monomeric (both barrels on the same chain) RNAP distinct from the usual "right hand" ssRNAP. It probably diverged very long ago from the canonical five-unit msRNAP, before the time of the last universal common ancestor.
Other viruses use an RNA-dependent RNAP (an RNAP that employs RNA as a template instead of DNA). This occurs in negative strand RNA viruses and dsRNA viruses, both of which exist for a portion of their life cycle as double-stranded RNA. However, some positive strand RNA viruses, such as poliovirus, also contain RNA-dependent RNAP. | 1 | Biochemistry |
Flutamide has been studied in the treatment of bulimia nervosa in women.
Flutamide was found to be effective in the treatment of obsessive–compulsive disorder (OCD) in men with comorbid Tourette's syndrome in one small randomized controlled trial. Conversely, it was ineffective in patients with OCD in another study. More research is necessary to determine whether flutamide is effective in the treatment of OCD. | 4 | Stereochemistry |
The compressor has operating boundaries at the flow extremes for a particular speed which are caused by different phenomena. The steepness of the high flow part of a constant speed line is due to the effects of compressibility. The position of the other end of the line is located by blade or passage flow separation. There is a well-defined, low-flow boundary marked on the map as a stall or surge line, at which blade stall occurs due to positive incidence separation. Not marked as such on maps for turbochargers and gas turbine engines is a more gradually approached, high-flow boundary at which passages choke when the gas velocity reaches the speed of sound. This boundary is identified for industrial compressors as overload, choke, sonic or stonewall. The approach to this flow limit is indicated by the speed lines becoming more vertical.
Other areas of the map are regions where fluctuating vane stalling may interact with blade structural modes leading to failure, ie rotating stall causing metal fatigue. | 7 | Physical Chemistry |
In a homogeneous crystalline structure, because of the uniform lattice structure of the metal ions, there is hardly any momentum transfer between the conduction electrons and the metal ions. However, this symmetry does not exist at the grain boundaries and material interfaces, and so here momentum is transferred much more vigorously. Since the metal ions in these regions are bonded more weakly than in a regular crystal lattice, once the electron wind has reached a certain strength, atoms become separated from the grain boundaries and are transported in the direction of the current. This direction is also influenced by the grain boundary itself, because atoms tend to move along grain boundaries.
Diffusion processes caused by electromigration can be divided into grain boundary diffusion, bulk diffusion and surface diffusion. In general, grain boundary diffusion is the major electromigration process in aluminum wires, whereas surface diffusion is dominant in copper interconnects. | 7 | Physical Chemistry |
William Christopher Zeise (15 October 1789 – 12 November 1847) was a Danish organic chemist. He is best known for synthesising one of the first organometallic compounds, named Zeise's salt in his honour. He also performed pioneering studies in organosulfur chemistry, discovering the xanthates in 1823. | 0 | Organic Chemistry |
Particularly when two-photon absorption is utilized, high-powered lasers may be required that can be bulky, difficult to cool, and pose safety concerns. Existing optical drives utilize continuous wave diode lasers operating at 780 nm, 658 nm, or 405 nm. 3D optical storage drives may require solid-state lasers or pulsed lasers, and several examples use wavelengths easily available by these technologies, such as 532 nm (green). These larger lasers can be difficult to integrate into the read/write head of the optical drive. | 5 | Photochemistry |
Inverted cucurbiturils or iCB[x] are CB analogues with one glycoluril repeating unit inverted. In this unit the methine protons actually point into the cavity and this makes the cavity less spacious. Inverted cucurbiturils form as a side-product in CB-forming reactions, with yields between 2 and 0.4%. Isolation of this type of CB compound is possible because it is more difficult to form inclusion compounds that ordinarily form with regular CBs. Inverted cucurbiturils are believed to be the kinetically controlled reaction products because the heating of iCB[6] in acidic medium results in a mixture of CB[5], CB[6] and CB[7] in a 24:13:1 ratio.
A cucurbituril cut in half along the equator is called a hemicucurbituril. | 6 | Supramolecular Chemistry |
Knowledge of volatility is often useful in the separation of components from a mixture. When a mixture of condensed substances contains multiple substances with different levels of volatility, its temperature and pressure can be manipulated such that the more volatile components change to a vapor while the less volatile substances remain in the liquid or solid phase. The newly formed vapor can then be discarded or condensed into a separate container. When the vapors are collected, this process is known as distillation.
The process of petroleum refinement utilizes a technique known as fractional distillation, which allows several chemicals of varying volatility to be separated in a single step. Crude oil entering a refinery is composed of many useful chemicals that need to be separated. The crude oil flows into a distillation tower and is heated up, which allows the more volatile components such as butane and kerosene to vaporize. These vapors move up the tower and eventually come in contact with cold surfaces, which causes them to condense and be collected. The most volatile chemical condense at the top of the column while the least volatile chemicals to vaporize condense in the lowest portion. On the right is a picture illustrating the design of a distillation tower.
The difference in volatility between water and ethanol has traditionally been used in the refinement of drinking alcohol. In order to increase the concentration of ethanol in the product, alcohol makers would heat the initial alcohol mixture to a temperature where most of the ethanol vaporizes while most of the water remains liquid. The ethanol vapor is then collected and condensed in a separate container, resulting in a much more concentrated product. | 7 | Physical Chemistry |
*The cytochrome P450 isozymes play important roles in metabolism and steroidogenesis.
*The multiple forms of phosphodiesterase also play major roles in various biological processes. Although more than one form of these enzymes have been found in individual cells, these isoforms of the enzyme are unequally distributed in the various cells of an organism. From the clinical standpoint they have been found to be selectively activated and inhibited, an observation which has led to their use in therapy. | 1 | Biochemistry |
* Au/MCr2O4 (M = Co, Mn, Fe) catalysts in the oxidations of CO, C2, and C3 hydrocarbons (Reaction Kinetics, Mechanisms and Catalysis, 2012, v105, pp69–78).
* Oxidation of CO and propane on Pt-Au/Al2O3 catalysts (Polish Journal of Chemistry, 2008, v82, pp1991-1997).
* Oxidative Dehydrogenation of Isobutane on VOx/oxide Support Catalysts: Effect of the Potassium Additive (Polish Journal of Chemistry, 2007, v81, pp1345-1354).
* RNano-Au/oxide support catalysts in oxidation reactions: Provenance of active oxygen species (Catalysis today, 2006, v112, Issues 1–4, pp3-7).
* Effect of additives on the physicochemical and catalytic properties of oxide catalysts in selective oxidation reactions (Topics in catalysis, 2002, v21, pp35–46).
* 8 Catalysis (Royal Society of Chemistry Annual Reports Section "C" (Physical Chemistry), 2000, v96, pp297-334).
* Thirty years in selective oxidation on oxides: what have we learned? (Topics in Catalysis, 2000, v11, pp23–42).
* Active centres on vanadia-based catalysts for selective oxidation of hydrocarbons (Applied Catalysis A: General, 1997, v157, Issues 1–2, pp409-420). | 7 | Physical Chemistry |
The atomic ratio is a measure of the ratio of atoms of one kind (i) to another kind (j). A closely related concept is the atomic percent (or at.%), which gives the percentage of one kind of atom relative to the total number of atoms. The molecular equivalents of these concepts are the molar fraction, or molar percent. | 7 | Physical Chemistry |
The Woodward–Hoffmann rules can be stated succinctly as a single sentence: A ground-state pericyclic process is brought about by addition of thermal energy (i.e., heating the system, symbolized by Δ). In contrast, an excited-state pericyclic process takes place if a reactant is promoted to an electronically excited state by activation with ultraviolet light (i.e., irradiating the system, symbolized by hν). It is important to recognize, however, that the operative mechanism of a formally pericyclic reaction taking place under photochemical irradiation is generally not as simple or clearcut as this dichotomy suggests. Several modes of electronic excitation are usually possible, and electronically excited molecules may undergo intersystem crossing, radiationless decay, or relax to an unfavorable equilibrium geometry before the excited-state pericyclic process can take place. Thus, many apparent pericyclic reactions that take place under irradiation are actually thought to be stepwise processes involving diradical intermediates. Nevertheless, it is frequently observed that the pericyclic selection rules become reversed when switching from thermal to photochemical activation. This can be rationalized by considering the correlation of the first electronic excited states of the reactants and products. Although more of a useful heuristic than a rule, a corresponding generalized selection principle for photochemical pericyclic reactions can be stated: Pericyclic reactions involving an odd number of electrons are also known. With respect to application of the generalized pericyclic selection rule, these systems can generally be treated as though one more electron were involved.
In the language of aromatic transition state theory, the Woodward–Hoffmann rules can be restated as follows: A pericyclic transition state involving (4n + 2) electrons with Hückel topology or 4n electrons with Möbius topology is aromatic and allowed, while a pericyclic transition state involving 4n-electrons with Hückel topology or (4n + 2)-electrons with Möbius topology is antiaromatic and forbidden. | 7 | Physical Chemistry |
There are three types of reactions that clinopyroxene is involved in and can be used for thermobarometry.
Univariant reactions or displaced equilibria reactions either create or destroy phases within the magma. Each phase will eventually crystalize as a unique mineral. Based on the temperature and pressure conditions, different proportions of these phases will emerge in the final rock. An example reaction is jadeite and quartz reacting to make analbite. Jadeite is a type of pyroxene, so this reaction is used for clinopyroxene barometry.
This particular reaction involves a large change in volume between the reactants and the products, so the reaction is very sensitive to pressure changes.
Exchange Reactions occur when there are minerals with similar structures, and ions switch places with each other within that structure. This is a common method to calculate the temperature because most exchange reactions have a high enthalpy. One example reaction is an exchange of Fe and Mg within garnet and clinopyroxene. That causes pyrope and hedenbergite (pyroxene) to change into almandine and diopside (pyroxene).
Solvus Equilibria reactions occur when two phases dissolve into each other based on the temperature, so it is usually useful for geothermometry. One such reaction is when clinopyroxene and orthopyroxene dissolve into each other. This changes the distribution of calcium and magnesium throughout the mineral. | 9 | Geochemistry |
If a dopant is added to the material (example: Nd in BaTiO) the impurity will tend to stick to the grain boundaries. As the grain boundary tries to move (as atoms jump from the convex to concave surface) the change in concentration of the dopant at the grain boundary will impose a drag on the boundary. The original concentration of solute around the grain boundary will be asymmetrical in most cases. As the grain boundary tries to move, the concentration on the side opposite of motion will have a higher concentration and therefore have a higher chemical potential. This increased chemical potential will act as a backforce to the original chemical potential gradient that is the reason for grain boundary movement. This decrease in net chemical potential will decrease the grain boundary velocity and therefore grain growth. | 8 | Metallurgy |
Isotopic tracers are used to examine processes in natural systems, especially terrestrial and aquatic environments. In soil science N tracers are used extensively to study nitrogen cycling, whereas C and C, stable and radioisotopes of carbon respectively, are used for studying turnover of organic compounds and fixation of by autotrophs. For example, Marsh et al. (2005) used dual labeled (N- and C) urea to demonstrate utilization of the compound by ammonia oxidizers as both an energy source (ammonia oxidation) and carbon source (chemoautotrophic carbon fixation). Deuterated water is also used for tracing the fate and ages of water in a tree or in an ecosystem. | 7 | Physical Chemistry |
Many of the advantages of cell-free protein array technology address the limitations of cell-based expression system used in traditional methods of protein microarray production. | 1 | Biochemistry |
Foldamers are classified into three different categories: peptidomimetic foldamers, nucleotidomimetic foldamers, and abiotic foldamers. Peptidomimetic foldamers are synthetic molecules that mimic the structure of proteins, while nucleotidomimetic foldamers are based on the interactions in nucleic acids. Abiotic foldamers are stabilized by aromatic and charge-transfer interactions which are not generally found in nature. The three designs described below deviate from Moore's strict definition of a foldamer, which excludes helical foldamers. | 6 | Supramolecular Chemistry |
Since the deep sea cores became available in the 1960s, paleoclimatic indices of planktonic foraminifera from marine sediments have been used for paleoclimatic reconstruction. Among the early pioneers to apply foraminifera latitudinal abundances, Ericson and Wollin (1968) succeeded in establishing the Pleistocene glacial and interglacial cycles based on the ratios of cold and warm water species in tropical sediments. Similar work was extended to subantarctic region by Kennett (1970), who, based on subpolar cold and warm water planktonic foraminferal species, reconstructed paleoclimatic changes in the Pleistocene, consistent in trends with those established in the tropical region.
When drilling cores, which recovered longer sediment columns than piston cores, came along, paleoclimatic reconstruction investigations were pushed back further in geological times. A climatic curve in the Oligocene was constructed in the Gulf of Mexico by using warm water indicators (Turborotalia pseudoampliapertura, Globoquadrina tripartita, Dentoglobigerina globularis, Dentoglobigerina baroemoenensis, “Globigerina” ciperoensis and Globigerinoides groups, and Cassigerinella chipolensis) and cold water indicators (Catapsydrax spp., Globorotaloides spp., Subbotina angiporoides group, Globigerina s. str., and the tenuitellids). A more extensive geographic coverage was investigated by Spezzaferri in 1995, who analyzed samples from drilling cores in the Atlantic, Indian and South Pacific Oceans and identified and grouped foraminifera into warmer, cooler, warm-temperate and cool-temperate indices. A paleoclimatic curve in the Oligocene and Miocene transition period was established and the curve was supported by the isotope data.
A more sophisticated approach to reconstruct paleoclimate involves using factor analysis. Thompson (1981) was able to relate six foraminiferal assemblages from core top samples to present water masses in the western North Pacific. A transfer function was generated to link the assemblages to sea surface temperatures. A paleotemperature curve for the past 150,000 years was reconstructed by applying this transfer function to old sediments in the cores.
Similar technique has been applied to the Eocene and Oligocene sediments and the forams have been categorized in surface, intermediate and deep water-mass groups. Thus water-mass stratification, in addition to paleotemperature fluctuation has been reconstructed. | 9 | Geochemistry |
In 1889, Ludwig Mond discovered that the combustion of coal with air and steam produced ammonia along with an extra gas, which was named the Mond gas. He discovered this while looking for a process to form ammonium sulfate, which was useful in agriculture. The process involved reacting low-quality coal with superheated steam, which produced the Mond gas. The gas was then passed through dilute sulfuric acid spray, which ultimately removed the ammonia, forming ammonium sulfate.
Mond modified the gasification process by restricting the air supply and filling the air with steam, providing a low working temperature. This temperature was below ammonia's point of dissociation, maximizing the amount of ammonia that could be produced from the nitrogen, a product from superheating coal. | 7 | Physical Chemistry |
In geochemistry, paleoclimatology, and paleoceanography δC (pronounced "delta c thirteen") is an isotopic signature, a measure of the ratio of the two stable isotopes of carbon—C and C—reported in parts per thousand (per mil, ‰). The measure is also widely used in archaeology for the reconstruction of past diets, particularly to see if marine foods or certain types of plants were consumed.
The definition is, in per mille:
where the standard is an established reference material.
δC varies in time as a function of productivity, the signature of the inorganic source, organic carbon burial, and vegetation type. Biological processes preferentially take up the lower mass isotope through kinetic fractionation. However some abiotic processes do the same. For example, methane from hydrothermal vents can be depleted by up to 50%. | 9 | Geochemistry |
Frank B. Mallory (March 17, 1933 - November 7, 2017) was a professor of organic chemistry at Bryn Mawr College. He was on faculty at Bryn Mawr for 54 years, the longest-serving faculty member in the schools history. His work focused on photochemistry, NMR spectroscopy, and solid-state chemistry. The Mallory reaction is an organic name reaction he discovered while a graduate student. Mallorys professional honors include a John Simon Guggenheim Memorial Foundation fellowship and a Sloan Research Fellowship. | 5 | Photochemistry |
De la Pirotechnia is considered to be one of the first printed books on metallurgy to have been published in Europe. It was written in Italian and first published in Venice in 1540. The author was Vannoccio Biringuccio, a citizen of Siena, Italy, who died before it was published. Further editions were published in 1550, 1558, 1559, and 1678, with a (sloppy) French translation by Jacques Vincent being published in 1556, 1572, and 1627. Parts were translated into Latin (by Georgius Agricola), English (Richard Eden; Peter Whitehorn) and Spanish (Bernardo Perez de Vargas) at various times in the 1550s and 1560s, generally without acknowledgement.
The second book on metallurgy, De re metallica, was written in Latin by Georgius Agricola, and published in 1556.
Mining was typically left to professionals, craftsmen and experts who were not eager to share their knowledge. Much experiential knowledge had been accumulated over the course of time. This knowledge was consecutively handed down orally within a small group of technicians and mining overseers. In the Middle Ages these people held the same leading role as the master builders of the great cathedrals, or perhaps also alchemists. It was a small, cosmopolitan elite within which existing knowledge was passed on and further developed but not shared with the outside world. Only a few writers from that time wrote anything about mining itself. Partly, that was because this knowledge was very difficult to access. Most writers also found it simply not worth the effort to write about it. Only after the middle ages did this perception begin to change. With the improved transport and the invention of the printing press knowledge spread much more easily and faster than before. In 1500, the first printed book dedicated to mining engineering, called the Nutzlich Bergbuchleyn (The Useful Little Mining Book") by Ulrich Rulein von Calw, was published. Both De la pirotechnia and De re metallica were translated into English in the 20th century. The translation of Pirotechnia was by Cyril Stanley Smith, a senior chemist on the Manhattan Project, and Martha Teach Gnudi. Both books were illustrated with extensive, beautiful woodcuts.
The majority of the work is devoted to the more technical aspects of metalworking (such as the mining, assaying and smelting of ores), but Biringuccio also provides insights into the humanistic philosophy of the Italian Renaissance. Alchemy is also discussed. | 8 | Metallurgy |
In bacteria, the initiation of translation occurs when IF-3, along with the 30S ribosomal subunit, bind to the Shine–Dalgarno (SD) sequence of the 5′ UTR. This then recruits many other proteins, such as the 50S ribosomal subunit, which allows for translation to begin. Each of these steps regulates the initiation of translation.
Initiation in Archaea is less understood. SD sequences are much rarer, and the initiation factors have more in common with eukaryotic ones. There is no homolog of bacterial IF3. Some mRNAs are leaderless.
In both domains, genes without Shine–Dalgarno sequences are also translated in a less understood manner. A requirement seems to be a lack of secondary structure near the initiation codon. | 1 | Biochemistry |
A thermal reservoir, also thermal energy reservoir or thermal bath, is a thermodynamic system with a heat capacity so large that the temperature of the reservoir changes relatively little when a significant amount of heat is added or extracted. As a conceptual simplification, it effectively functions as an infinite pool of thermal energy at a given, constant temperature. Since it can act as an inertial source and sink of heat, it is often also referred to as a heat reservoir or heat bath.
Lakes, oceans and rivers often serve as thermal reservoirs in geophysical processes, such as the weather. In atmospheric science, large air masses in the atmosphere often function as thermal reservoirs.
Since the temperature of a thermal reservoir does not change during the heat transfer, the change of entropy in the reservoir is
The microcanonical partition sum of a heat bath of temperature has the property
where is the Boltzmann constant. It thus changes by the same factor when a given amount of energy is added. The exponential factor in this expression can be identified with the reciprocal of the Boltzmann factor.
For an engineering application, see geothermal heat pump. | 7 | Physical Chemistry |
A gaur that died of natural causes had some skin cells frozen and added to the San Diego Frozen Zoo. Eight years later, DNA from these cells was inserted into a domestic-cow egg to create an embryo (trans-species cloning), which was then implanted in a domestic cow (Bos taurus). On 8 January 2001, the gaur, named Noah, was born in Sioux Center, Iowa. Noah was initially healthy, but the next day, he came down with clostridial enteritis, and died of dysentery within 48 hours of birth. This is not uncommon in uncloned animals, and the researchers did not think it was due to the cloning. | 1 | Biochemistry |
RNAi intersects with a number of other pathways; as of 2010 it was not surprising that on occasion, nonspecific effects are triggered by the experimental introduction of an siRNA. When a mammalian cell encounters a double-stranded RNA such as an siRNA, it may mistake it as a viral by-product and mount an immune response. Furthermore, because structurally related microRNAs modulate gene expression largely via incomplete complementarity base pair interactions with a target mRNA, the introduction of an siRNA may cause unintended off-targeting. Chemical modifications of siRNA may alter the thermodynamic properties that also result in a loss of single nucleotide specificity. | 1 | Biochemistry |
NBS, in the presence of a strong base, such as DBU, reacts with primary amides to produce a carbamate via the Hofmann rearrangement. | 0 | Organic Chemistry |
Cerium is a rare-earth element (lanthanide) characterized by two different redox states: III and IV. Contrary to other lanthanide elements, which are only trivalent (with the notable exception of Eu), Ce can be oxidized by atmospheric oxygen (O) to Ce under alkaline conditions.
The cerium anomaly relates to the decrease in solubility, which accompanies the oxidation of Ce(III) to Ce(IV). Under reducing conditions, Ce is relatively soluble, while under oxidizing conditions CeO precipitates. Sediments deposited under oxic or anoxic conditions can preserve on the long term the geochemical signature of Ce or Ce upon reserve that no early diagenetic transformation altered it. | 9 | Geochemistry |
If one tries to predict the probability of collision with a classical model that treats the electron and atom as hard spheres, one finds that the probability of collision should be independent of the incident electron energy. However, Ramsauer and Townsend, independently observed that for slow-moving electrons in argon, krypton, or xenon, the probability of collision between the electrons and gas atoms obtains a minimum value for electrons with a certain amount of kinetic energy (about 1 electron volts for xenon gas).
No good explanation for the phenomenon existed until the introduction of quantum mechanics, which explains that the effect results from the wave-like properties of the electron. A simple model of the collision that makes use of wave theory can predict the existence of the Ramsauer–Townsend minimum. Niels Bohr presented a simple model for the phenomenon that considers the atom as a finite square potential well.
Predicting from theory the kinetic energy that will produce a Ramsauer–Townsend minimum is quite complicated since the problem involves understanding the wave nature of particles. However, the problem has been extensively investigated both experimentally and theoretically and is well understood. | 7 | Physical Chemistry |
The popularity and success of the Joback method mainly originates from the single group list for all properties. This allows one to get all eleven supported properties from a single analysis of the molecular structure.
The Joback method additionally uses a very simple and easy to assign group scheme, which makes the method usable for people with only basic chemical knowledge. | 7 | Physical Chemistry |
Alternative U-to-C mRNA editing was first reported in WT1 (Wilms Tumor-1) transcripts, and non-classic G-A mRNA changes were first observed in HNRNPK (heterogeneous nuclear ribonucleoprotein K) transcripts in both malignant and normal colorectal samples. The latter changes were also later seen alongside non-classic U-to-C alterations in brain cell TPH2 (tryptophan hydroxylase 2) transcripts. Although the reverse amination might be the simplest explanation for U-to-C changes, transamination and transglycosylation mechanisms have been proposed for plant U-to-C editing events in mitochondrial transcripts. A recent study reported novel G-to-A mRNA changes in WT1 transcripts at two hotspots, proposing the APOBEC3A (apolipoprotein B mRNA editing enzyme, catalytic polypeptide 3A) as the enzyme implicated in this class of alternative mRNA editing. It was also shown that alternative mRNA changes were associated with canonical WT1 splicing variants, indicating their functional significance. | 1 | Biochemistry |
A disaccharide (also called a double sugar or biose) is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three common examples are sucrose, lactose, and maltose.
Disaccharides are one of the four chemical groupings of carbohydrates (monosaccharides, disaccharides, oligosaccharides, and polysaccharides). The most common types of disaccharides—sucrose, lactose, and maltose—have 12 carbon atoms, with the general formula CHO. The differences in these disaccharides are due to atomic arrangements within the molecule.
The joining of monosaccharides into a double sugar happens by a condensation reaction, which involves the elimination of a water molecule from the functional groups only. Breaking apart a double sugar into its two monosaccharides is accomplished by hydrolysis with the help of a type of enzyme called a disaccharidase. As building the larger sugar ejects a water molecule, breaking it down consumes a water molecule. These reactions are vital in metabolism. Each disaccharide is broken down with the help of a corresponding disaccharidase (sucrase, lactase, and maltase). | 0 | Organic Chemistry |
As stated previously, Darken's first equation allows the calculation of the marker velocity in respect to a binary system where the two components have different diffusion coefficients. For this equation to be applicable, the analyzed system must have a constant concentration and can be modeled by the Boltzmann–Matano solution.
For the derivation, a hypothetical case is considered where two homogeneous binary alloy rods of two different compositions are in contact. The sides are protected, so that all of the diffusion occurs parallel to the length of the rod. In establishing the coordinate axes to evaluate the derivation, Darken sets the x-axis to be fixed at the far ends of the rods, and the origin at the initial position of the interface between the two rods. In addition this choice of a coordinate system allows the derivation to be simplified, whereas Smigelskas and Kirkendall's coordinate system was considered to be the non-optimal choice for this particular calculation as can be seen in the following section. At the initial planar interface between the rods, it is considered that there are infinitely small inert markers placed in a plane which is perpendicular to the length of the rods. Here, inert markers are defined to be a group of particles that are of a different elemental make-up from either of the diffusing components and move in the same fashion. For this derivation, the inert markers are assumed to be following the motion of the crystal lattice. The motion relative to the marker is associated with diffusion, , while the motion of the markers is associated with advection, . Fick’s first law, the previous equation stated for diffusion, describes the entirety of the system for only small distances from the origin, since at large distances advection needs to be accounted for. This results in the total rate of transport for the system being influenced by both factors, diffusion and advection. | 7 | Physical Chemistry |
Generic versions of esomeprazole magnesium are available worldwide. It is available over-the-counter under the brand name Nexium in the United States and the UK. | 4 | Stereochemistry |
Size-exclusion chromatography, also known as molecular sieve chromatography, is a chromatographic method in which molecules in solution are separated by their size, and in some cases molecular weight. It is usually applied to large molecules or macromolecular complexes such as proteins and industrial polymers. Typically, when an aqueous solution is used to transport the sample through the column, the technique is known as gel-filtration chromatography, versus the name gel permeation chromatography, which is used when an organic solvent is used as a mobile phase. The chromatography column is packed with fine, porous beads which are commonly composed of dextran, agarose, or polyacrylamide polymers. The pore sizes of these beads are used to estimate the dimensions of macromolecules. SEC is a widely used polymer characterization method because of its ability to provide good molar mass distribution (Mw) results for polymers.
Size exclusion chromatography (SEC) is fundamentally different from all other chromatographic techniques in that separation is based on a simple procedure of classifying molecule sizes rather than any type of interaction. | 1 | Biochemistry |
As MDCs contain low electrical conductivity in the desalination chamber and additional energy is not applied to the system, electron conductive-resins are applied to improve conductivity, decrease internal resistance and increase the desalination process of brackish waters. Brackish waters are low in salinity with a high amount of total dissolved solids, which results in difficulties in maintaining strong electrical currents due to increased internal resistance in the cell. MDCs also experience problems with the saturation of ions in the anode chamber which can be combatted by utilizing a microbial capacitive desalination cell (MCDC). MCDCs are analogous to MDCs with the exception of modification to the cation membrane by the addition of activate carbon cloth, permitting the free exchange of protons across both chambers of the cell and increasing the efficiency of desalination. | 7 | Physical Chemistry |
PT has been shown to affect the innate immune response. It inhibits the early recruitment of neutrophils and macrophages, and interferes with early chemokine production and neutrophil chemotaxis. Chemokines are signalling molecules produced by infected cells and attract neutrophils and macrophages. Neutrophil chemotaxis is thought to be disrupted by inhibiting G-protein-coupled chemokine receptors by the ADP-ribosylation of G proteins.
Because of the disrupted signalling pathways, synthesis of chemokines will be affected. This will prevent the infected cell from producing them and thereby inhibiting recruitment of neutrophils. Under normal circumstances, alveolar macrophages and other lung cells produce a variety of chemokines. PT has been found to inhibit the early transcription of keratinocyte-derived chemokine, macrophage inflammatory protein 2 and LPS-induced CXC chemokine. Eventually, PT causes lymphocytosis, one of the systemic manifestations of whooping cough.
PT, a decisive virulence determinant of B. pertussis, is able to cross the blood–brain barrier by increasing its permeability. As a result, PT can cause severe neurological complications; however, recently it has been found that the medicinal usage of Pertussis toxin can promote the development of regulatory T cells and prevent central nervous system autoimmune disease, such as multiple sclerosis. | 1 | Biochemistry |
The process is more environmentally friendly than traditional extraction methods. For the company this can translate into profit, since the necessary limiting of sulfur dioxide emissions during smelting is expensive. Less landscape damage occurs, since the bacteria involved grow naturally, and the mine and surrounding area can be left relatively untouched. As the bacteria breed in the conditions of the mine, they are easily cultivated and recycled.
Toxic chemicals are sometimes produced in the process. Sulfuric acid and H ions that have been formed can leak into the ground and surface water turning it acidic, causing environmental damage. Heavy ions such as iron, zinc, and arsenic leak during acid mine drainage. When the pH of this solution rises, as a result of dilution by fresh water, these ions precipitate, forming "Yellow Boy" pollution. For these reasons, a setup of bioleaching must be carefully planned, since the process can lead to a biosafety failure. Unlike other methods, once started, bioheap leaching cannot be quickly stopped, because leaching would still continue with rainwater and natural bacteria. Projects like Finnish Talvivaara proved to be environmentally and economically disastrous. | 8 | Metallurgy |
Originally, the FRAP technique was intended for use as a means to characterize the mobility of individual lipid molecules within a cell membrane. While providing great utility in this role, current research leans more toward investigation of artificial lipid membranes. Supported by hydrophilic or hydrophobic substrates (to produce lipid bilayers or monolayers respectively) and incorporating membrane proteins, these biomimetic structures are potentially useful as analytical devices for determining the identity of unknown substances, understanding cellular transduction, and identifying ligand binding sites. | 1 | Biochemistry |
HACNS1 (also known as CENTG2 and located in the Human Accelerated Region 2) is a gene enhancer "that may have contributed to the evolution of the uniquely opposable human thumb, and possibly also modifications in the ankle or foot that allow humans to walk on two legs". Evidence to date shows that of the 110,000 gene enhancer sequences identified in the human genome, HACNS1 has undergone the most change during the evolution of humans following the split with the ancestors of chimpanzees. | 1 | Biochemistry |
Acinetobacter anitratus, Acinetobacter calcoaceticus, Actinomyces odontolyticus, Aeromonas hydrophila, Bacteroides distasonis, Bacteroides uniformis, and Clostridium perfringens are generally susceptible to imipenem, while Acinetobacter baumannii, some Acinetobacter spp., Bacteroides fragilis, and Enterococcus faecalis have developed resistance to imipenem to varying degrees. Not many species are resistant to imipenem except Pseudomonas aeruginosa (Oman) and Stenotrophomonas maltophilia. | 4 | Stereochemistry |
[[Diels–Alder reaction|[4+2] cycloadditions]] of a diene and an alkene have been used as DCvC reactions. These reactions are often reversible at high temperatures. In the case of furan–maleimide adducts, the retro-cycloaddition is accessible at temperatures as low as 40 °C. | 6 | Supramolecular Chemistry |
Copper is found in association with many other metals and deposit styles. Commonly, copper is either formed within sedimentary rocks, or associated with igneous rocks.
The world's major copper deposits are formed within the granitic porphyry copper style. Copper is enriched by processes during crystallisation of the granite and forms as chalcopyrite — a sulfide mineral, which is carried up with the granite.
Sometimes granites erupt to surface as volcanoes, and copper mineralisation forms during this phase when the granite and volcanic rocks cool via hydrothermal circulation.
Sedimentary copper forms within ocean basins in sedimentary rocks. Generally this forms by brine from deeply buried sediments discharging into the deep sea, and precipitating copper and often lead and zinc sulfides directly onto the sea floor. This is then buried by further sediment. This is a process similar to SEDEX zinc and lead, although some carbonate-hosted examples exist.
Often copper is associated with gold, lead, zinc, and nickel deposits. | 9 | Geochemistry |
Norşuntepe is a tell, or archaeological settlement mound, in Elazığ Province (Turkey). The site was occupied between the Chalcolithic and Iron Age and is now partially submerged by Lake Keban. It was excavated between 1968 and 1974. | 8 | Metallurgy |
ESP was first developed and published in 2003 by Dr. Collins and his colleagues in University of California, San Francisco. Their study revealed the chromosome rearrangements and CNV of MCF7 human cancer cells at a 150kb resolution, which is much more accurate compared to both CGH and spectral karyotyping at that time. In 2007, Dr. Snyder and his group improved the ESP to 3kb resolution by sequencing both pairs of 3-kb DNA fragments without BAC construction. Their approach is able to identify deletions, inversions, insertions with an average breakpoint resolution of 644bp, which close to the resolution of polymerase chain reaction (PCR). | 1 | Biochemistry |
Microscopy with UV Surface Excitation (MUSE) is a novel microscopy method that utilizes the shallow penetration of UV photons (230–300 nm) excitation. Compared to conventional microscopes, which usually require sectioning to exclude blurred signals from outside of the focal plane, MUSE's low penetration depth limits the excitation volume to a thin layer, and removes the tissue sectioning requirement. The entire signal collected is the desired light, and all photons collected contribute to the image formation. | 5 | Photochemistry |
The company's formulation plant in Waltham Abbey was alleged to be at the centre and therefore the cause of a cancer hotspot. This was highlighted by Storyline, an investigative television programme by Carlton Television, in early 1993. Reports of an unusual occurrence of cancer around the plant and subsequent legal action taken by the residents were the basis for this programme. | 2 | Environmental Chemistry |
In organic chemistry, a nitrone is a functional group consisting of an N-oxide of an imine. The general structure is , where R is not a hydrogen. Their primary application is intermediates in chemical synthesis. A nitrone is a 1,3-dipole used in cycloadditions, and a carbonyl mimic. | 0 | Organic Chemistry |
Ethnoarchaeology has been widely used in conjunction with experimental archaeology using the techniques of modern peoples as analogues to the processes of the past. The attempted use of ethnology in archaeology tries to counteract the cultural distance of the researcher from process by changing the context of experimentation. Africa has played a large role in reconstructing copper smelting and bloomery iron furnaces as there are still several places that practice a workshop production of iron. Killick has been one such archaeologist to utilize surviving iron production in Africa to gain further insight into how other furnaces from around the world may have been constructed. | 8 | Metallurgy |
The active sites in PepA and in bovine lens LAP have been found to be similar. Shown in the picture below is the proposed model for the active site of LAP-A in tomato based on the work of Strater et al. It is also known that the biochemistry of the LAPs from these three kingdoms is very similar. PepA, bovine lens LAP, and LAP-A preferentially cleave N-terminal leucine, arginine, and methionine residues. These enzymes are all metallopeptidases requiring divalent metal cations for their enzymatic activity Enzymes are active in the presence of Mn, Mg and Zn. These enzymes are also known to have high pH (pH 8) and temperature optima. At pH 8, the highest enzymatic activity is seen at 60 °C. PepA, bovine lens LAP and LAP-A are also known to form hexamers in vivo. The Gu et al. from 1999 demonstrated that six 55kDA enzymatically inactive LAP-A protomers come together to form the 353kDa bioactive LAP-A hexamer. Structures of the bovine lens LAP protomer and the biologically active hexamer have been constructed can be found through Protein Data Bank (2J9A). | 1 | Biochemistry |
Bioceramics have been proposed as a possible treatment for cancer. Two methods of treatment have been proposed: hyperthermia and radiotherapy. Hyperthermia treatment involves implanting a bioceramic material that contains a ferrite or other magnetic material. The area is then exposed to an alternating magnetic field, which causes the implant and surrounding area to heat up. Alternatively, the bioceramic materials can be doped with β-emitting materials and implanted into the cancerous area.
Other trends include engineering bioceramics for specific tasks. Ongoing research involves the chemistry, composition, and micro- and nanostructures of the materials to improve their biocompatibility. | 7 | Physical Chemistry |
With a theoretical decomposition energy of about 5 kJ/g, hydroxylamine is an explosive, and aqueous solutions above 80% can be easily detonated by detonator or strong heating under confinement. At least two factories dealing in hydroxylamine have been destroyed since 1999 with loss of life. It is known, however, that ferrous and ferric iron salts accelerate the decomposition of 50% solutions. Hydroxylamine and its derivatives are more safely handled in the form of salts.
It is an irritant to the respiratory tract, skin, eyes, and other mucous membranes. It may be absorbed through the skin, is harmful if swallowed, and is a possible mutagen. | 0 | Organic Chemistry |
Calcium carbide is used in carbide lamps. Water dripping on carbide produces acetylene gas, which burns and produces light. While these lamps gave steadier and brighter light than candles, they were dangerous in coal mines, where flammable methane gas made them a serious hazard. The presence of flammable gases in coal mines led to miner safety lamps such as the Davy lamp, in which a wire gauze reduces the risk of methane ignition. Carbide lamps were still used extensively in slate, copper, and tin mines where methane is not a serious hazard. Most miners' lamps have now been replaced by electric lamps.
Carbide lamps are still used for mining in some less wealthy countries, for example in the silver mines near Potosí, Bolivia. Carbide lamps are also still used by some cavers exploring caves and other underground areas, although they are increasingly being replaced in this use by LED lights.
Carbide lamps were also used extensively as headlamps in early automobiles, motorcycles and bicycles, but have been replaced entirely by electric lamps. | 8 | Metallurgy |
TOC is the first chemical analysis to be carried out on potential petroleum source rock in oil exploration. It is very important in detecting contaminants in drinking water, cooling water, water used in semiconductor manufacturing, and water for pharmaceutical use. Analysis may be made either as an online continuous measurement or a lab-based measurement.
TOC detection is an important measurement because of the effects it may have on the environment, human health, and manufacturing processes. TOC is a highly sensitive, non-specific measurement of all organics present in a sample. It, therefore, can be used to regulate the organic chemical discharge to the environment in a manufacturing plant. In addition, low TOC can confirm the absence of potentially harmful organic chemicals in water used to manufacture pharmaceutical products. TOC is also of interest in the field of potable water purification due to byproducts of disinfection. Inorganic carbon poses little to no threat. | 3 | Analytical Chemistry |
Phases can also be inferred by using a process called molecular replacement, where a similar molecules already-known phases are grafted onto the intensities of the molecule at hand, which are observationally determined. These phases can be obtained experimentally from a homologous molecule or if the phases are known for the same molecule but in a different crystal, by simulating the molecules packing in the crystal and obtaining theoretical phases. Generally, these techniques are less desirable since they can severely bias the solution of the structure. They are useful, however, for ligand binding studies, or between molecules with small differences and relatively rigid structures (for example derivatizing a small molecule). | 3 | Analytical Chemistry |
The CAG promoter is a strong synthetic promoter frequently used to drive high levels of gene expression in mammalian expression vectors.
CAG promoter was constructed in the lab of Dr Jun-ichi Miyazaki from the following sequences:
:(C) the cytomegalovirus (CMV) early enhancer element,
:(A) the promoter, the first exon and the first intron of chicken beta-actin gene,
:(G) the splice acceptor of the rabbit beta-globin gene
The resulting synthetic element was used in the pCAGGS expression vector. The initiation codon located at the proximal region of the second exon was disrupted by digesting with NcoI restriction enzyme and replacing the site with a HindIII linker.
Although the whole construct is commonly referred to as the "CAG promoter", it is not a promoter in a strict sense, as it includes a part of the transcribed sequence (the first exon and the first intron of chicken beta-actin gene) and enhancer elements. In addition to the CMV immediate early enhancer, the intron of the chicken beta actin gene contains an enhancer element, which is highly conserved among vertebrates. The 3' part of the promoter has high GC content and is thus refractory to PCR amplification.
Some of the CAG promoter's functions as an effective tool that increases and maintains the expression level of recombinant proteins, as well as increases the expression of transgenes under low temperature conditions. | 1 | Biochemistry |
Other factors, such as signaller arousal, receiver identity, or increased risk of predation from calling, do not have a significant effect on the frequency of alarm call production. | 1 | Biochemistry |
In chemistry, ion transport number, also called the transference number, is the fraction of the total electric current carried in an electrolyte by a given ionic species :
Differences in transport number arise from differences in electrical mobility. For example, in an aqueous solution of sodium chloride, less than half of the current is carried by the positively charged sodium ions (cations) and more than half is carried by the negatively charged chloride ions (anions) because the chloride ions are able to move faster, i.e., chloride ions have higher mobility than sodium ions. The sum of the transport numbers for all of the ions in solution always equals unity:
The concept and measurement of transport number were introduced by Johann Wilhelm Hittorf in the year 1853. Liquid junction potential can arise from ions in a solution having different ion transport numbers.
At zero concentration, the limiting ion transport numbers may be expressed in terms of the limiting molar conductivities of the cation (), anion (), and electrolyte ():
and
where and are the numbers of cations and anions respectively per formula unit of electrolyte. In practice the molar ionic conductivities are calculated from the measured ion transport numbers and the total molar conductivity. For the cation , and similarly for the anion. In solutions, where ionic complexation or associaltion are important, two different transport/transference numbers can be defined.
The practical importance of high (i.e. close to 1) transference numbers of the charge-shuttling ion (i.e. Li+ in lithium-ion batteries) is related to the fact, that in single-ion devices (such as lithium-ion batteries) electrolytes with the transfer number of the ion near 1, concentration gradients do not develop. A constant electrolyte concentration is maintained during charge-discharge cycles. In case of porous electrodes a more complete utilization of solid electroactive materials at high current densities is possible, even if the ionic conductivity of the electrolyte is reduced. | 7 | Physical Chemistry |
Lectin and antibody arrays provide high-throughput screening of many samples containing glycans. This method uses either naturally occurring lectins or artificial monoclonal antibodies, where both are immobilized on a certain chip and incubated with a fluorescent glycoprotein sample.
Glycan arrays, like that offered by the Consortium for Functional Glycomics and [http://www.zbiotech.com/ Z Biotech LLC], contain carbohydrate compounds that can be screened with lectins or antibodies to define carbohydrate specificity and identify ligands. | 0 | Organic Chemistry |
The concept of cone angle is most easily visualized with symmetrical ligands, e.g. PR. But the approach has been refined to include less symmetrical ligands of the type PRR′R″ as well as diphosphines. In such asymmetric cases, the substituent angles half angles, , are averaged and then doubled to find the total cone angle, θ'. In the case of diphosphines, the of the backbone is approximated as half the chelate bite angle, assuming a bite angle of 74°, 85°, and 90° for diphosphines with methylene, ethylene, and propylene backbones, respectively. The Manz cone angle is often easier to compute than the Tolman cone angle: | 4 | Stereochemistry |
Since FFT based analyzers are only capable of considering narrow bands, one technique is to combine swept and FFT analysis for consideration of wide and narrow spans. This technique allows for faster sweep time.
This method is made possible by first down converting the signal, then digitizing the intermediate frequency and using superheterodyne or FFT techniques to acquire the spectrum.
One benefit of digitizing the intermediate frequency is the ability to use digital filters, which have a range of advantages over analog filters such as near perfect shape factors and improved filter settling time. Also, for consideration of narrow spans, the FFT can be used to increase sweep time without distorting the displayed spectrum. | 7 | Physical Chemistry |
In physics, a Bragg plane is a plane in reciprocal space which bisects a reciprocal lattice vector, , at right angles. The Bragg plane is defined as part of the Von Laue condition for diffraction peaks in x-ray diffraction crystallography.
Considering the adjacent diagram, the arriving x-ray plane wave is defined by:
Where is the incident wave vector given by:
where is the wavelength of the incident photon. While the Bragg formulation assumes a unique choice of direct lattice planes and specular reflection of the incident X-rays, the Von Laue formula only assumes monochromatic light and that each scattering center acts as a source of secondary wavelets as described by the Huygens principle. Each scattered wave contributes to a new plane wave given by:
The condition for constructive interference in the direction is that the path difference between the photons is an integer multiple (m) of their wavelength. We know then that for constructive interference we have:
where . Multiplying the above by we formulate the condition in terms of the wave vectors, and :
Now consider that a crystal is an array of scattering centres, each at a point in the Bravais lattice. We can set one of the scattering centres as the origin of an array. Since the lattice points are displaced by the Bravais lattice vectors, , scattered waves interfere constructively when the above condition holds simultaneously for all values of which are Bravais lattice vectors, the condition then becomes:
An equivalent statement (see mathematical description of the reciprocal lattice) is to say that:
By comparing this equation with the definition of a reciprocal lattice vector, we see that constructive interference occurs if is a vector of the reciprocal lattice. We notice that and have the same magnitude, we can restate the Von Laue formulation as requiring that the tip of incident wave vector, , must lie in the plane that is a perpendicular bisector of the reciprocal lattice vector, . This reciprocal space plane is the Bragg plane. | 3 | Analytical Chemistry |
A solar cell or photovoltaic cell is a device that converts light energy into electrical energy. Fundamentally, the device needs to fulfill only two functions: photo-generation of charge carriers (electrons and holes) in a light-absorbing material, and separation of the charge carriers to a conductive contact that will transmit the electricity (simply put, carrying electrons off through a metal contact into an external circuit). This conversion is called the photoelectric effect, and the field of research related to solar cells is known as photovoltaics.
Solar cells have many applications. They have long been used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth-orbiting satellites and space probes, handheld calculators, wrist watches, remote radiotelephones and water pumping applications. More recently, they are starting to be used in assemblies of solar modules (photovoltaic arrays) connected to the electricity grid through an inverter, that is not to act as a sole supply but as an additional electricity source.
All solar cells require a light absorbing material contained within the cell structure to absorb photons and generate electrons via the photovoltaic effect. The materials used in solar cells tend to have the property of preferentially absorbing the wavelengths of solar light that reach the earth surface. Some solar cells are optimized for light absorption beyond Earth's atmosphere, as well. | 7 | Physical Chemistry |
For example, consider the same problem from the previous section of a linear chain. The matrix is the unscaled elasticity matrix:
In this specific problem there are 3 species () and 4 reaction steps (), the elasticity matrix is therefore a matrix. However, a number of entries in the matrix will be zero. For example will be zero since has no effect on . The matrix, therefore, will contain the following entries:
The parameter matrix depends on which parameters are considered. In Metabolic control analysis, a common set of parameters are the enzyme activities. For the sake of argument, we can equate the rate constants with the enzyme activity parameters. We also assume that each enzyme, , only can affect its own step and no other. The matrix is the unscaled elasticity matrix with respect to the parameters. Since there are 4 reaction steps and 4 corresponding parameters, the matrix will be a 4 by 4 matrix. Since each parameter only affects one reaction, the matrix will be a diagonal matrix:
Since there are 3 species and 4 reactions, the resulting matrix will be a 3 by 4 matrix
Each expression in the matrix describes how a given parameter influences the steady-state concentration of a given species. Note that this is the unscaled derivative. It is often the case that the derivative is scaled by the parameter and concentration to eliminate units as well as turn the measure into a relative change. | 1 | Biochemistry |
* Achille Le Bel Grand Prize of the French Chemical Society (1979)
* Pierre Desnuelle Prize from the French Academy of sciences (1996)
* Medal of the Berthelot Foundation (1996)
* Claude S. Hudson Award in Carbohydrate Chemistry from the American Chemical Society (2007)
* Elected Correspondent of the French Academy of sciences (1996)
* Honorary doctorate from the University of Lisbon (2005)
* Elected member of the French Academy of sciences (2003)
* Haworth Memorial Reading and Haworth Medal from the Royal Society of Chemistry (Great Britain, 2011).
* Associate Member of the National Academy of Pharmacy (2016).
* Chevalier of the Légion d'honneur and Commandeur of the Palmes Académiques. | 0 | Organic Chemistry |
* In the manga and anime series JoJos Bizarre Adventure, the Diamond is Unbreakable and Golden Wind' story arcs prominently feature a set of six arrows which are made out of meteoric iron sourced from the Cape York meteorite. | 8 | Metallurgy |
Hydroperoxides or peroxols are compounds of the form ROOH, where R stands for any group, typically organic, which contain the hydroperoxy functional group (). Hydroperoxide also refers to the hydroperoxide anion () and its salts, and the neutral hydroperoxyl radical (•OOH) consist of an unbond hydroperoxy group. When R is organic, the compounds are called organic hydroperoxides. Such compounds are a subset of organic peroxides, which have the formula ROOR. Organic hydroperoxides can either intentionally or unintentionally initiate explosive polymerisation in materials with unsaturated chemical bonds. | 0 | Organic Chemistry |
Short-interspersed nuclear elements are transcribed by RNA polymerase III which is known to transcribe ribosomal RNA and tRNA, two types of RNA vital to ribosomal assembly and mRNA translation. SINEs, like tRNAs and many small-nuclear RNAs possess an internal promoter and thus are transcribed differently than most protein-coding genes. In other words, short-interspersed nuclear elements have their key promoter elements within the transcribed region itself. Though transcribed by RNA polymerase III, SINEs and other genes possessing internal promoters, recruit different transcriptional machinery and factors than genes possessing upstream promoters. | 1 | Biochemistry |
There is polyadenylation in the cytosol of some animal cell types, namely in the germ line, during early embryogenesis and in post-synaptic sites of nerve cells. This lengthens the poly(A) tail of an mRNA with a shortened poly(A) tail, so that the mRNA will be translated. These shortened poly(A) tails are often less than 20 nucleotides, and are lengthened to around 80–150 nucleotides.
In the early mouse embryo, cytoplasmic polyadenylation of maternal RNAs from the egg cell allows the cell to survive and grow even though transcription does not start until the middle of the 2-cell stage (4-cell stage in human). In the brain, cytoplasmic polyadenylation is active during learning and could play a role in long-term potentiation, which is the strengthening of the signal transmission from a nerve cell to another in response to nerve impulses and is important for learning and memory formation.
Cytoplasmic polyadenylation requires the RNA-binding proteins CPSF and CPEB, and can involve other RNA-binding proteins like Pumilio. Depending on the cell type, the polymerase can be the same type of polyadenylate polymerase (PAP) that is used in the nuclear process, or the cytoplasmic polymerase GLD-2. | 1 | Biochemistry |
An indicator may be used to obtain quite precise measurements of pH by measuring absorbance quantitatively at two or more wavelengths. The principle can be illustrated by taking the indicator to be a simple acid, HA, which dissociates into H and A.
:HA H + A
The value of the acid dissociation constant, pK, must be known. The molar absorbances, ε and ε at wavelengths λ and λ must also have been determined by previous experiment. Assuming Beers law to be obeyed, the measured absorbances A and A' at the two wavelengths are simply the sum of the absorbances due to each species.
These are two equations in the two concentrations [HA] and [A]. Once solved, the pH is obtained as
If measurements are made at more than two wavelengths, the concentrations [HA] and [A] can be calculated by linear least squares. In fact, a whole spectrum may be used for this purpose. The process is illustrated for the indicator bromocresol green. The observed spectrum (green) is the sum of the spectra of HA (gold) and of A (blue), weighted for the concentration of the two species.
When a single indicator is used, this method is limited to measurements in the pH range pK ± 1, but this range can be extended by using mixtures of two or more indicators. Because indicators have intense absorption spectra, the indicator concentration is relatively low, and the indicator itself is assumed to have a negligible effect on pH. | 7 | Physical Chemistry |
Dihydroxyacetone phosphate (DHAP, also glycerone phosphate in older texts) is the anion with the formula HOCHC(O)CHOPO. This anion is involved in many metabolic pathways, including the Calvin cycle in plants and glycolysis. It is the phosphate ester of dihydroxyacetone. | 5 | Photochemistry |
The stable compound cyanamide, whose minor tautomer is carbodiimide, is an isomer of diazomethane. Less stable but still isolable isomers of diazomethane include the cyclic 3H-diazirine and isocyanoamine (isodiazomethane). In addition, the parent nitrilimine has been observed under matrix isolation conditions.
<br /> | 0 | Organic Chemistry |
The PMCA technology has been used by several groups to understand the molecular mechanism of prion replication, the nature of the infectious agent, the phenomenon of prion strains and species barrier, the effect of cellular components, to detect PrP in tissues and biological fluids and to screen for inhibitors against prion replication. Recent studies by the groups of Supattapone and Ma were able to produce prion replication in vitro by PMCA using purified PrP and recombinant PrP with the sole addition of synthetic polyanions and lipids. These studies have shown that infectious prions can be produced in the absence of any other cellular component and constitute some of the strongest evidence in favor of the prion hypothesis.
Research in 2020 concluded that protein misfolding cyclic amplification could be used to distinguish between two progressive neurodegenerative diseases, Parkinson's disease and multiple system atrophy, being the first process to give an objective diagnosis of Multiple System Atrophy instead of just a differential diagnosis. | 1 | Biochemistry |
BLOSUM scores was used to predict and understand the surface gene variants among hepatitis B virus carriers and T-cell epitopes. | 1 | Biochemistry |
Patients who suffer from obstructive sleep apnea can experience impaired cardiac repolarization, increasing the morbidity and mortality of the condition greatly. Especially at higher altitudes, patients are much more susceptible to repolarization disturbances. This can be somewhat mitigated through the use of medications such as acetazolamide, but the drugs do not provide sufficient protection. Acetazolamide and similar drugs are known to be able to improve the oxygenation and sleep apnea for patients in higher altitudes, but the benefits of the drug have been observed only when traveling at altitudes temporarily, not for people who remain at a higher altitude for a longer time. | 7 | Physical Chemistry |
Photoproteins do not display typical enzyme kinetics as seen in luciferases. Instead, when mixed with luciferin, they display luminescence proportional to the amount of the photoprotein. For example, the photoprotein aequorin produces a flash of light when luciferin and calcium are added, rather than the prolonged glow that is seen for luciferases when luciferin is added. In this respect, it may appear that photoproteins are not enzymes, when in fact they do catalyze their bioluminescence reactions. This is due to a fast catalytic step, which produces the light, and a slow regeneration step, where the oxyluciferin is freed and another molecule of luciferin is then enabled to bind to the enzyme. Because of the kinetically slow step, each aequorin molecule must "recharge" with another molecule of luciferin before it can emit light again, and this makes it appear as though it is not behaving as a typical enzyme.
Photoproteins form a stable luciferin-photoprotein complex, often until the addition of another required factor such as Ca in the case of aequorin. | 1 | Biochemistry |
In two dimensions, every figure which possesses an axis of symmetry is achiral, and it can be shown that every bounded achiral figure must have an axis of symmetry. (An axis of symmetry of a figure is a line , such that is invariant under the mapping , when is chosen to be the -axis of the coordinate system.) For that reason, a triangle is achiral if it is equilateral or isosceles, and is chiral if it is scalene.
Consider the following pattern:
This figure is chiral, as it is not identical to its mirror image:
But if one prolongs the pattern in both directions to infinity, one receives an (unbounded) achiral figure which has no axis of symmetry. Its symmetry group is a frieze group generated by a single glide reflection. | 4 | Stereochemistry |
Levorphanol (brand name Levo-Dromoran) is an opioid medication used to treat moderate to severe pain. It is the levorotatory enantiomer of the compound racemorphan. Its dextrorotatory counterpart is dextrorphan.
It was first described in Germany in 1946. The drug has been in medical use in the United States since 1953. | 4 | Stereochemistry |
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