text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
* At high glucose levels, glycolysis takes place rapidly, thus increasing the amount of citrate produced from the citric acid cycle. This citrate is then exported to other organelles outside the mitochondria to be broken into acetyl-CoA and oxaloacetate by the enzyme ATP citrate lyase (ACL). This principal reaction is coupled with the hydrolysis of ATP.
* At low glucose levels:
** CoA is acetylated using acetate by acetyl-CoA synthetase (ACS), also coupled with ATP hydrolysis.
** Ethanol also serves as a carbon source for acetylation of CoA utilizing the enzyme alcohol dehydrogenase.
** Degradation of branched-chain ketogenic amino acids such as valine, leucine, and isoleucine occurs. These amino acids are converted to α-ketoacids by transamination and eventually to isovaleryl-CoA through oxidative decarboxylation by an α-ketoacid dehydrogenase complex. Isovaleryl-CoA undergoes dehydrogenation, carboxylation and hydration to form another CoA-derivative intermediate before it is cleaved into acetyl-CoA and acetoacetate. | 1 | Biochemistry |
Transposition is the process by which a specific genetic sequence, known as a transposon, is moved from one location of the genome to another. Simple, or conservative transposition, is a non-replicative mode of transposition. That is, in conservative transposition the transposon is completely removed from the genome and reintegrated into a new, non-homologous locus, the same genetic sequence is conserved throughout the entire process. The site in which the transposon is reintegrated into the genome is called the target site. A target site can be in the same chromosome as the transposon or within a different chromosome. Conservative transposition uses the "cut-and-paste" mechanism driven by the catalytic activity of the enzyme transposase. Transposase acts like DNA scissors; it is an enzyme that cuts through double-stranded DNA to remove the transposon, then transfers and pastes it into a target site.
A simple, or conservative, transposon refers to the specific genetic sequence that is moved via conservative transposition. These specific genetic sequences range in size, they can be hundreds to thousands of nucleotide base-pairs long. A transposon contains genetic sequences that encode for proteins that mediate its own movement, but can also carry genes for additional proteins. Transposase is encoded within the transposon DNA and used to facilitate its own movement, making this process self-sufficient within organisms. All simple transposons contain a transposase encoding region flanked by terminal inverted repeats, but the additional genes within the transposon DNA can vary. Viruses, for example, encode the essential viral transposase needed for conservative transposition as well as protective coat proteins that allow them to survive outside of cells, thus promoting the spread of mobile genetic elements. | 1 | Biochemistry |
To date there have been nine human ADK protein isoforms identified. While some of these are ubiquitous throughout the body, some are localized into specific tissues. For example, ADK7 and ADK8 are both only found in the cytosol of cells; and ADK7 is found in skeletal muscle whereas ADK8 is not. Not only do the locations of the various isoforms within the cell vary, but the binding of substrate to the enzyme and kinetics of the phosphoryl transfer are different as well. ADK1, the most abundant cytosolic ADK isozyme, has a K about a thousand times higher than the K of ADK7 and 8, indicating a much weaker binding of ADK1 to AMP. Sub-cellular localization of the ADK enzymes is done by including a targeting sequence in the protein. Each isoform also has different preference for NTP's. Some will only use ATP, whereas others will accept GTP, UTP, and CTP as the phosphoryl carrier.
Some of these isoforms prefer other NTP's entirely. There is a mitochondrial GTP:AMP phosphotransferase, also specific for the phosphorylation of AMP, that can only use GTP or ITP as the phosphoryl donor. ADK has also been identified in different bacterial species and in yeast. Two further enzymes are known to be related to the ADK family, i.e. yeast uridine monophosphokinase and slime mold UMP-CMP kinase. Some residues are conserved across these isoforms, indicating how essential they are for catalysis. One of the most conserved areas includes an Arg residue, whose modification inactivates the enzyme, together with an Asp that resides in the catalytic cleft of the enzyme and participates in a salt bridge. | 1 | Biochemistry |
Amplitude modulation was one of the original modes of operation introduced by Binnig and Quate in their seminal 1986 AFM paper, in this mode the sensor is excited just off resonance. By exciting the sensor just above its resonant frequency, it is possible to detect forces which change the resonant frequency by monitoring the amplitude of oscillation. An attractive force on the probe causes a decrease in the sensors resonant frequency, thus the driving frequency is further from resonance and the amplitude decreases, the opposite is true for a repulsive force. The microscopes control electronics can then use amplitude as the SPM reference channel, either in feedback mode, or it can be recorded directly in constant height mode.
Amplitude modulation can fail if the non-conservative forces (damping) change during the experiment, as this changes the amplitude of the resonance peak itself, which will be interpreted as a change in resonant frequency. Another potential problem with amplitude modulation is that a sudden change to a more repulsive (less attractive) force can shift the resonance past the drive frequency causing it to decrease again. In constant height mode this will just lead to an image artefact, but in feedback mode the feedback will read this as a stronger attractive force, causing positive feedback until the feedback saturates.
An advantage of amplitude modulation is that there is only one feedback loop (the topography feedback loop) compared to three in frequency modulation (the phase/frequency loop, the amplitude loop, and the topography loop), making both operation and implementation much easier. Amplitude modulation, however, is rarely used in vacuum as the Q of the sensor is usually so high that the sensor oscillates many times before the amplitude settles to its new value, thus slowing down operation. | 6 | Supramolecular Chemistry |
The physical state (solid, liquid, or gas) of a reactant is also an important factor of the rate of change. When reactants are in the same phase, as in aqueous solution, thermal motion brings them into contact. However, when they are in separate phases, the reaction is limited to the interface between the reactants. Reaction can occur only at their area of contact; in the case of a liquid and a gas, at the surface of the liquid. Vigorous shaking and stirring may be needed to bring the reaction to completion. This means that the more finely divided a solid or liquid reactant the greater its surface area per unit volume and the more contact it with the other reactant, thus the faster the reaction. To make an analogy, for example, when one starts a fire, one uses wood chips and small branches — one does not start with large logs right away. In organic chemistry, on water reactions are the exception to the rule that homogeneous reactions take place faster than heterogeneous reactions ( are those reactions in which solute and solvent not mix properly) | 7 | Physical Chemistry |
The third and dominant contribution is the dispersion or London force (fluctuating dipole–induced dipole), which arises due to the non-zero instantaneous dipole moments of all atoms and molecules. Such polarization can be induced either by a polar molecule or by the repulsion of negatively charged electron clouds in non-polar molecules. Thus, London interactions are caused by random fluctuations of electron density in an electron cloud. An atom with a large number of electrons will have a greater associated London force than an atom with fewer electrons. The dispersion (London) force is the most important component because all materials are polarizable, whereas Keesom and Debye forces require permanent dipoles. The London interaction is universal and is present in atom-atom interactions as well. For various reasons, London interactions (dispersion) have been considered relevant for interactions between macroscopic bodies in condensed systems. Hamaker developed the theory of van der Waals between macroscopic bodies in 1937 and showed that the additivity of these interactions renders them considerably more long-range. | 6 | Supramolecular Chemistry |
Chlorophyll fluorescence can measure most types of plant stress. Chlorophyll fluorescence can be used as a proxy of plant stress because environmental stresses, e.g. extremes of temperature, light and water availability, can reduce the ability of a plant to metabolise normally. This can mean an imbalance between the absorption of light energy by chlorophyll and the use of energy in photosynthesis.
* Favaretto et al. (2010) investigated adaptation to a strong light environment in pioneer and late successional species, grown under 100% and 10% light. Numerous parameters, including chlorophyll a fluorescence, were measured. A greater decline in under full sun light in the late-successional species than in the pioneer species was observed. Overall, their results show that pioneer species perform better under high-sun light than late- successional species, suggesting that pioneer plants have more potential tolerance to photo-oxidative damage.
* Neocleous and Vasilakakis (2009) investigated the response of raspberry to boron and salt stress. An chlorophyll fluorometer was used to measure , and . The leaf chlorophyll fluorescence was not significantly affected by NaCl concentration when B concentration was low. When B was increased, leaf chlorophyll fluorescence was reduced under saline conditions. It could be concluded that the combined effect of B and NaCl on raspberries induces a toxic effect in photochemical parameters.
* Lu and Zhang (1999) studied heat stress in wheat plants and found that temperature stability in the Photosystem II of water-stressed leaves correlates positively to the resistance in metabolism during photosynthesis. | 5 | Photochemistry |
Ferrocene-containing dendrimers are dendrimers that contain ferrocene substituents. Some ferrocene-containing dendrimers feature ferrocene cores and others do not. All feature with peripheral ferrocene groups. | 6 | Supramolecular Chemistry |
Electron microscopy shows that the tapetal cells that surround the developing pollen grain in the anther have a highly active secretory system containing lipophilic globules. These globules are believed to contain sporopollenin precursors. Tracer experiments have shown that phenylalanine is a major precursor, but other carbon sources also contribute. The biosynthetic pathway for phenylpropanoid is very active in tapetal cells, supporting the idea that its products are needed for sporopollenin synthesis. Chemical inhibitors of pollen development and many male sterile mutants have effects on the secretion of these globules by the tapetal cells. | 1 | Biochemistry |
2,3-Bisphosphoglycerate or 2,3-BPG (formerly named 2,3-diphosphoglycerate or 2,3-DPG) is an organophosphate formed in red blood cells during glycolysis and is the conjugate base of 2,3-bisphosphoglyceric acid. The production of 2,3-BPG is likely an important adaptive mechanism, because the production increases for several conditions in the presence of diminished peripheral tissue O availability, such as hypoxemia, chronic lung disease, anemia, and congestive heart failure, among others, which necessitate easier oxygen unloading in the peripheral tissue. High levels of 2,3-BPG shift the curve to the right (as in childhood), while low levels of 2,3-BPG cause a leftward shift, seen in states such as septic shock, and hypophosphataemia. In the absence of 2,3-BPG, hemoglobins affinity for oxygen increases. 2,3-BPG acts as a heteroallosteric effector of hemoglobin, lowering hemoglobins affinity for oxygen by binding preferentially to deoxyhemoglobin. An increased concentration of BPG in red blood cells favours formation of the T (taut or tense), low-affinity state of hemoglobin and so the oxygen-binding curve will shift to the right. | 1 | Biochemistry |
Nitrogen assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment. Organisms like plants, fungi and certain bacteria that can fix nitrogen gas (N) depend on the ability to assimilate nitrate or ammonia for their needs. Other organisms, like animals, depend entirely on organic nitrogen from their food. | 1 | Biochemistry |
The oxidative aminations of olefins are generally conducted with amides or imides; amines are thought to be protonated by the acidic medium or to bind the metal center too tightly to allow for the catalytic chemistry to occur. These nitrogen nucleophiles are found to be competent in both intermolecular and intramolecular reactions, some examples are depicted (Figure 5, A, B) | 0 | Organic Chemistry |
The first recorded observations of oscillating genes come from the marches of Alexander the Great in the fourth century B.C. At this time, one of Alexanders generals, Androsthenes, wrote that the tamarind tree would open its leaves during the day and close them at nightfall. Until 1729, the rhythms associated with oscillating genes were assumed to be "passive responses to a cyclic environment". In 1729, Jean-Jacques dOrtous de Mairan demonstrated that the rhythms of a plant opening and closing its leaves continued even when placed somewhere where sunlight could not reach it. This was one of the first indications that there was an active element to the oscillations. In 1923, Ingeborg Beling published her paper "Über das Zeitgedächtnis der Bienen" ("On the Time Memory of Bees") which extended oscillations to animals, specifically bees In 1971, Ronald Konopka and Seymour Benzer discovered that mutations of the PERIOD gene caused changes in the circadian rhythm of flies under constant conditions. They hypothesized that the mutation of the gene was affecting the basic oscillator mechanism. Paul Hardin, Jeffrey Hall, and Michael Rosbash demonstrated that relationship by discovering that within the PERIOD gene, there was a feedback mechanism that controlled the oscillation. The mid-1990s saw an outpouring of discoveries, with CLOCK, CRY, and others being added to the growing list of oscillating genes. | 1 | Biochemistry |
The term lyotropic has also been applied to the liquid crystalline phases that are formed by certain polymeric materials, particularly those consisting of rigid rod-like macromolecules, when they are mixed with appropriate solvents. Examples are suspensions of rod-like viruses such as the tobacco mosaic virus as well as synthetic macromolecules, such as LiMoSe nanowire or colloidal suspensions of non-spherical colloidal particles. Cellulose and cellulose derivatives form lyotropic liquid crystal phases as do nanocrystalline (nanocellulose) suspensions. Other examples include DNA and Kevlar, which dissolve in sulfuric acid to give a lyotropic phase. It is noted that in these cases the solvent acts to lower the melting point of the materials thereby enabling the liquid crystalline phases to be accessible. These liquid crystalline phases are closer in architecture to thermotropic liquid crystalline phases than to the conventional lyotropic phases. In contrast to the behaviour of amphiphilic molecules, the lyotropic behaviour of the rod-like molecules does not involve self-assembly. | 7 | Physical Chemistry |
The process of photosynthesis provides the main input of free energy into the biosphere, and is one of four main ways in which radiation is important for plant life.
The radiation climate within plant communities is extremely variable, in both time and space.
In the early 20th century, Frederick Blackman and Gabrielle Matthaei investigated the effects of light intensity (irradiance) and temperature on the rate of carbon assimilation.
* At constant temperature, the rate of carbon assimilation varies with irradiance, increasing as the irradiance increases, but reaching a plateau at higher irradiance.
* At low irradiance, increasing the temperature has little influence on the rate of carbon assimilation. At constant high irradiance, the rate of carbon assimilation increases as the temperature is increased.
These two experiments illustrate several important points: First, it is known that, in general, photochemical reactions are not affected by temperature. However, these experiments clearly show that temperature affects the rate of carbon assimilation, so there must be two sets of reactions in the full process of carbon assimilation. These are the light-dependent photochemical temperature-independent stage, and the light-independent, temperature-dependent stage. Second, Blackman's experiments illustrate the concept of limiting factors. Another limiting factor is the wavelength of light. Cyanobacteria, which reside several meters underwater, cannot receive the correct wavelengths required to cause photoinduced charge separation in conventional photosynthetic pigments. To combat this problem, Cyanobacteria have a light-harvesting complex called Phycobilisome. This complex is made up of a series of proteins with different pigments which surround the reaction center. | 5 | Photochemistry |
A general procedure of how to perform a loss on ignition is as follows:
# Weigh the empty crucible that the sample is to be placed in and record its weight in a lab book.
# Place the sample in the empty crucible and weigh the crucible again with the sample in it. The new weight minus the empty crucible weight is the sample's wet weight.
# Place the sample in the drying oven or blast furnace as required.
# Set the oven or furnace to the desired temperature. If the researcher wants to find the dry weight of the soil then the furnace would need to be 100 °C.
# Leave the sample in the furnace for the desired length of time. If the researcher wanted to know the sample's dry weight and is using a furnace set at 100 °C, then the researcher would usually leave the furnace on overnight.
# Open the oven but also back away from it at the same time since the hot air escaping from the furnace can burn bare skin.
# Allow the oven and sample to cool down before removing the sample from the oven.
# Weigh the crucible with the sample again. Subtract the empty crucible weight from this new weight and that is the sample's dry weight. | 3 | Analytical Chemistry |
Carbon dioxide binds to metals in only a few ways. The bonding mode depends on the electrophilicity and basicity of the metal centre. Most common is the η-CO coordination mode as illustrated by Aresta's complex, Ni(CO)(PCy), which was the first reported complex of CO This square-planar compound is a derivative of Ni(II) with a reduced CO ligand. In rare cases, CO binds to metals as a Lewis base through its oxygen centres, but such adducts are weak and mainly of theoretical interest. A variety of multinuclear complexes are also known often involving Lewis basic and Lewis acidic metals, e.g. metallacarboxylate salts (CH)Fe(CO)COK. In multinuclear cases (compounds containing more than one metal), more complicated and more varied coordination geometries are observed. One example is the unsymmetrical compound containing four rhenium centres, [(CO)ReCORe(CO)]. Carbon dioxide can also bind to ligands on a metal complex (vs just the metal), e.g. by converting hydroxy ligands to carbonato ligands. | 0 | Organic Chemistry |
The second-generation of Glycoazodyes was first reported in 2008. These Glycoazodyes use an etherel linker. An ether group bonds the sugar and the dye to an n-alkane spacer, and the spacer bonds to the dye through another ether group. Like first-generation Glycoazodyes, second-generation Glycoazodyes use glucose, galactose or lactose as the sugar group. | 0 | Organic Chemistry |
The Croatian Society of Medical Biochemists (CSMB) was founded in 1953. Until 1988, CSMB had been part of the Croatian Pharmaceutical Society and afterwards became an autonomous association. In 2012, it changed its name to the Croatian Society of Medical Biochemistry and Laboratory Medicine (CSMBLM), in line with the current trends within the profession and with the recommendations of European and global professional associations. In 2015 it had 750 members. | 1 | Biochemistry |
There are several small molecule inducers that can induce the glyoxalase pathway by either promoting GLO1 function to increase conversion of MG into D-Lactate, which are called GLO1 activators, or by directly reducing MG levels or levels of MG substrate, which are called MG scavengers. GLO1 activators include the synthetic drug candesartan or natural compounds resveratrol, fisetin, the binary combination of trans-resveratrol and hesperetin (tRES-HESP), mangiferin, allyl isothiocyanate, phenethyl isothiocyanate, sulforaphane, and bardoxolone methyl, and MG scavengers include aminoguanidine, alagebrium, and benfotiamine. There is also the small molecule pyridoxamine, which acts as both a GLO1 activator and MG scavenger.
Many inhibitors of GLO1 have been discovered since GLO1 activity tends to be promoted in cancer cells, thus GLO1 serves as a potential therapeutic target for anti-cancer drug treatment and has been the focus of many research studies regarding its regulation in tumor cells. | 1 | Biochemistry |
Due to the cohesive forces, a molecule located away from the surface is pulled equally in every direction by neighboring liquid molecules, resulting in a net force of zero. The molecules at the surface do not have the same molecules on all sides of them and therefore are pulled inward. This creates some internal pressure and forces liquid surfaces to contract to the minimum area.
There is also a tension parallel to the surface at the liquid-air interface which will resist an external force, due to the cohesive nature of water molecules.
The forces of attraction acting between molecules of the same type are called cohesive forces, while those acting between molecules of different types are called adhesive forces. The balance between the cohesion of the liquid and its adhesion to the material of the container determines the degree of wetting, the contact angle, and the shape of meniscus. When cohesion dominates (specifically, adhesion energy is less than half of cohesion energy) the wetting is low and the meniscus is convex at a vertical wall (as for mercury in a glass container). On the other hand, when adhesion dominates (when adhesion energy is more than half of cohesion energy) the wetting is high and the similar meniscus is concave (as in water in a glass).
Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the imbalance in cohesive forces of the surface layer. In the absence of other forces, drops of virtually all liquids would be approximately spherical. The spherical shape minimizes the necessary "wall tension" of the surface layer according to Laplace's law.
Another way to view surface tension is in terms of energy. A molecule in contact with a neighbor is in a lower state of energy than if it were alone. The interior molecules have as many neighbors as they can possibly have, but the boundary molecules are missing neighbors (compared to interior molecules) and therefore have higher energy. For the liquid to minimize its energy state, the number of higher energy boundary molecules must be minimized. The minimized number of boundary molecules results in a minimal surface area.
As a result of surface area minimization, a surface will assume a smooth shape. | 6 | Supramolecular Chemistry |
Conductometry is a measurement of electrolytic conductivity to monitor a progress of chemical reaction. Conductometry has notable application in analytical chemistry, where conductometric titration is a standard technique. In usual analytical chemistry practice, the term conductometry is used as a synonym of conductometric titration while the term conductimetry is used to describe non-titrative applications. Conductometry is often applied to determine the total conductance of a solution or to analyze the end point of titrations that include ions. | 3 | Analytical Chemistry |
Bacteriorhodopsin is a 27 kDa integral membrane protein usually found in two-dimensional crystalline patches known as "purple membrane", which can occupy almost 50% of the surface area of the archaeal cell. The repeating element of the hexagonal lattice is composed of three identical protein chains, each rotated by 120 degrees relative to the others. Each monomer has seven transmembrane alpha helices and an extracellular-facing, two-stranded beta sheet.
Bacteriorhodopsin is synthesized as a protein precursor, known as bacterio-opsin, which is extensively modified after translation. The modifications are:
* Covalent conjugation of a retinal molecule to residue Lys216, via a Schiff base, to create the retinylidene chromophore.
* Cleavage of the signal peptide, the first 13 amino acids at the N-terminus, and the conversion of residue Gln14 to pyroglutamate
* Removal of residue Asp262 at the C-terminus | 5 | Photochemistry |
Corriu and coworkers performed early work characterizing reactions thought to proceed through a hypervalent transition state. Measurements of the reaction rates of hydrolysis of tetravalent chlorosilanes incubated with catalytic amounts of water returned a rate that is first order in chlorosilane and second order in water. This indicated that two water molecules interacted with the silane during hydrolysis and from this a binucleophilic reaction mechanism was proposed. Corriu and coworkers then measured the rates of hydrolysis in the presence of nucleophilic catalyst HMPT, DMSO or DMF. It was shown that the rate of hydrolysis was again first order in chlorosilane, first order in catalyst and now first order in water. Appropriately, the rates of hydrolysis also exhibited a dependence on the magnitude of charge on the oxygen of the nucleophile.
Taken together this led the group to propose a reaction mechanism in which there is a pre-rate determining nucleophilic attack of the tetracoordinated silane by the nucleophile (or water) in which a hypervalent pentacoordinated silane is formed. This is followed by a nucleophilic attack of the intermediate by water in a rate determining step leading to hexacoordinated species that quickly decomposes giving the hydroxysilane.
Silane hydrolysis was further investigated by Holmes and coworkers in which tetracoordinated (Mes = mesityl) and pentacoordinated were reacted with two equivalents of water. Following twenty-four hours, almost no hydrolysis of the tetracoordinated silane was observed, while the pentacoordinated silane was completely hydrolyzed after fifteen minutes. Additionally, X-ray diffraction data collected for the tetraethylammonium salts of the fluorosilanes showed the formation of hydrogen bisilonate lattice supporting a hexacoordinated intermediate from which is quickly displaced leading to the hydroxylated product. This reaction and crystallographic data support the mechanism proposed by Corriu et al..
The apparent increased reactivity of hypervalent molecules, contrasted with tetravalent analogues, has also been observed for Grignard reactions. The Corriu group measured Grignard reaction half-times by NMR for related 18-crown-6 potassium salts of a variety of tetra- and pentacoordinated fluorosilanes in the presence of catalytic amounts of nucleophile.
Though the half reaction method is imprecise, the magnitudinal differences in reactions rates allowed for a proposed reaction scheme wherein, a pre-rate determining attack of the tetravalent silane by the nucleophile results in an equilibrium between the neutral tetracoordinated species and the anionic pentavalent compound. This is followed by nucleophilic coordination by two Grignard reagents as normally seen, forming a hexacoordinated transition state and yielding the expected product.
The mechanistic implications of this are extended to a hexacoordinated silicon species that is thought to be active as a transition state in some reactions. The reaction of allyl- or crotyl-trifluorosilanes with aldehydes and ketones only precedes with fluoride activation to give a pentacoordinated silicon. This intermediate then acts as a Lewis acid to coordinate with the carbonyl oxygen atom. The further weakening of the silicon–carbon bond as the silicon becomes hexacoordinate helps drive this reaction. | 4 | Stereochemistry |
* Electrolysis of water for hydrogen production combined with solar photovoltaics using alkaline, PEM, and SOEC electrolyzers; This basic use of solar light generated electric power to separate water into hydrogen and oxygen has proven a little bit more efficient than for example hydrogen capture by steam reforming. The alkaline production technology of hydrogen has low costs and is considered mature. This has a consequence that the yield per unit of time is significantly higher than when using PEM technology. However, PEM technology has no corrosion issues and is more efficient, whereas alkaline production technology has the disadvantage of corrosion and worse efficiency. In addition to that, PEM technology has a fast start-up and simple maintenance. Though, in bulk production the alkaline hydrogen production technology is superior.
* Heliogen claims success in the use of solar heliostats used to direct sunlight to a tower, to reach temperatures over 1000°C in the production of hydrogen. Temperatures above 2500°C can thermochemically split water into hydrogen and oxygen without the use of electricity. This can be done using the heat of nuclear power plants or by adaptive solar mirror fields to redirect the sunlight to reach high temperatures needed for these thermochemical processes. However, this way of producing hydrogen is in its infancy and it has not yet been proven that this production hydrogen is profitable and efficient, because it has to compete with other, mature technologies. | 5 | Photochemistry |
Excess post-exercise oxygen consumption (EPOC, informally called afterburn) is a measurably increased rate of oxygen intake following strenuous activity. In historical contexts the term "oxygen debt" was popularized to explain or perhaps attempt to quantify anaerobic energy expenditure, particularly as regards lactic acid/lactate metabolism; in fact, the term "oxygen debt" is still widely used to this day. However, direct and indirect calorimeter experiments have definitively disproven any association of lactate metabolism as causal to an elevated oxygen uptake.
In recovery, oxygen (EPOC) is used in the processes that restore the body to a resting state and adapt it to the exercise just performed. These include: hormone balancing, replenishment of fuel stores, cellular repair, innervation, and anabolism. Post-exercise oxygen consumption replenishes the phosphagen system. New ATP is synthesized and some of this ATP donates phosphate groups to creatine until ATP and creatine levels are back to resting state levels again. Another use of EPOC is to fuel the body’s increased metabolism from the increase in body temperature which occurs during exercise.
EPOC is accompanied by an elevated consumption of fuel. In response to exercise, fat stores are broken down and free fatty acids (FFA) are released into the blood stream. In recovery, the direct oxidation of free fatty acids as fuel and the energy consuming re-conversion of FFAs back into fat stores both take place. | 1 | Biochemistry |
Pregnant leach solution or pregnant liquor solution (PLS) is acidic metal-laden water generated from stockpile leaching and heap leaching. Pregnant leach solution is used in the solvent extraction and electrowinning (SX/EW) process.
The portion of an original liquid that remains after other components have been dissolved by a solvent is called raffinate. | 8 | Metallurgy |
Campbells mona monkeys also generate alarm calls, but in a different way than vervet monkeys. Instead of having discrete calls for each predator, Campbell monkeys have two distinct types of calls which contain different calls which consist in an acoustic continuum of affixes which change meaning. It has been suggested that this is a homology to human morphology. Similarly, the cotton-top tamarin is able to use a limited vocal range of alarm calls to distinguish between aerial and land predators. Both the Campbell monkey and the cotton-top tamarin have demonstrated abilities similar to vervet monkeys ability to distinguish likely direction of predation and appropriate responses.
That these three species use vocalizations to warn others of danger has been called by some proof of proto-language in primates. However, there is some evidence that this behavior does not refer to the predators themselves but to threat, distinguishing calls from words. | 1 | Biochemistry |
Radicals play important roles in biology. Many of these are necessary for life, such as the intracellular killing of bacteria by phagocytic cells such as granulocytes and macrophages. Radicals are involved in cell signalling processes, known as redox signaling. For example, radical attack of linoleic acid produces a series of 13-hydroxyoctadecadienoic acids and 9-hydroxyoctadecadienoic acids, which may act to regulate localized tissue inflammatory and/or healing responses, pain perception, and the proliferation of malignant cells. Radical attacks on arachidonic acid and docosahexaenoic acid produce a similar but broader array of signaling products.
Radicals may also be involved in Parkinsons disease, senile and drug-induced deafness, schizophrenia, and Alzheimers. The classic free-radical syndrome, the iron-storage disease hemochromatosis, is typically associated with a constellation of free-radical-related symptoms including movement disorder, psychosis, skin pigmentary melanin abnormalities, deafness, arthritis, and diabetes mellitus. The free-radical theory of aging proposes that radicals underlie the aging process itself. Similarly, the process of mitohormesis suggests that repeated exposure to radicals may extend life span.
Because radicals are necessary for life, the body has a number of mechanisms to minimize radical-induced damage and to repair damage that occurs, such as the enzymes superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase. In addition, antioxidants play a key role in these defense mechanisms. These are often the three vitamins, vitamin A, vitamin C and vitamin E and polyphenol antioxidants. Furthermore, there is good evidence indicating that bilirubin and uric acid can act as antioxidants to help neutralize certain radicals. Bilirubin comes from the breakdown of red blood cells' contents, while uric acid is a breakdown product of purines. Too much bilirubin, though, can lead to jaundice, which could eventually damage the central nervous system, while too much uric acid causes gout. | 2 | Environmental Chemistry |
Studies indicate creatinine can be effective at killing bacteria of many species in both the Gram positive and Gram negative as well as diverse antibiotic resistant bacterial strains. Creatinine appears not to affect growth of fungi and yeast; this can be used to isolate slower growing fungi free from the normal bacterial populations found in most environmental samples. The mechanism by which creatinine kills bacteria is not presently known. A recent report also suggests that creatinine may have immunosuppressive properties. | 1 | Biochemistry |
Ester pyrolysis in organic chemistry is a vacuum pyrolysis reaction converting esters containing a β-hydrogen atom into the corresponding carboxylic acid and the alkene. The reaction is an E elimination and operates in a syn fashion.
Examples include the synthesis of acrylic acid from ethyl acrylate at 590 °C, the synthesis of 1,4-pentadiene from 1,5-pentanediol diacetate at 575 °C or the construction of a cyclobutene framework at 700 °C | 0 | Organic Chemistry |
Adrenergic means "working on adrenaline (epinephrine) or noradrenaline (norepinephrine)" (or on their receptors). When not further qualified, it is usually used in the sense of enhancing or mimicking the effects of epinephrine and norepinephrine in the body.
*Adrenergic nervous system, a part of the autonomic nervous system that uses epinephrine or norepinephrine as its neurotransmitter
Regarding proteins:
* Adrenergic receptor, a receptor type for epinephrine and norepinephrine; subtypes include α, α, β, β, and β receptors
* Adrenergic transporter (norepinephrine transporter), a protein transporting norepinephrine from the synaptic cleft into nerve cells
Regarding pharmaceutical drugs:
* Adrenergic receptor agonist, a type of drug activating one or more subtypes of adrenergic receptors
** This includes drugs regulating blood pressure and antiasthmatic drugs.
* Adrenergic receptor antagonist, a type of drug blocking one or more subtypes of adrenergic receptors
** This mainly includes drugs lowering blood pressure.
* Adrenergic reuptake inhibitor, a type of drug blocking the norepinephrine transporter
** This includes antidepressants and drugs against ADHD. | 1 | Biochemistry |
In 1976, concern over the toxicity and persistence (chemical stability) of PCBs in the environment led the United States Congress to ban their domestic production, effective January 1, 1978, pursuant to the Toxic Substances Control Act. To implement the law, EPA banned new manufacturing of PCBs, but issued regulations that allowed for their continued use in electrical equipment for economic reasons. EPA began issuing regulations for PCB usage and disposal in 1979. The agency has issued guidance publications for safe removal and disposal of PCBs from existing equipment.
EPA defined the "maximum contaminant level goal" for public water systems as zero, but because of the limitations of water treatment technologies, a level of 0.5 parts per billion is the actual regulated level (maximum contaminant level). | 2 | Environmental Chemistry |
Tartaric acid may be most immediately recognizable to wine drinkers as the source of "wine diamonds", the small potassium bitartrate crystals that sometimes form spontaneously on the cork or bottom of the bottle. These "tartrates" are harmless, despite sometimes being mistaken for broken glass, and are prevented in many wines through cold stabilization (which is not always preferred since it can change the wine's profile). The tartrates remaining on the inside of aging barrels were at one time a major industrial source of potassium bitartrate.
Tartaric acid plays an important role chemically, lowering the pH of fermenting "must" to a level where many undesirable spoilage bacteria cannot live, and acting as a preservative after fermentation. In the mouth, tartaric acid provides some of the tartness in the wine, although citric and malic acids also play a role. | 4 | Stereochemistry |
Natural and contaminant organometallic compounds are found in the environment. Some that are remnants of human use, such as organolead and organomercury compounds, are toxicity hazards. Tetraethyllead was prepared for use as a gasoline additive but has fallen into disuse because of lead's toxicity. Its replacements are other organometallic compounds, such as ferrocene and methylcyclopentadienyl manganese tricarbonyl (MMT). The organoarsenic compound roxarsone is a controversial animal feed additive. In 2006, approximately one million kilograms of it were produced in the U.S alone. Organotin compounds were once widely used in anti-fouling paints but have since been banned due to environmental concerns. | 0 | Organic Chemistry |
In higher eukaryotes, TTF-I binds and bends the termination site at the 3' end of the transcribed region. This will force Pol I to pause. TTF-I, with the help of transcript-release factor PTRF and a T-rich region, will induce Pol I into terminating transcription and dissociating from the DNA and the new transcript. Evidence suggests that termination might be rate-limiting in cases of high rRNA production. TTF-I and PTRF will then indirectly stimulate the reinitiation of transcription by Pol I at the same rDNA gene.
In organisms such as budding yeast the process seems to be much more complicated and is still not completely elucidated. | 1 | Biochemistry |
E-AB sensors can be adapted into wearable devices that monitor health of patients in real time. E-AB sensors are capable of monitoring specific biomarkers that can aid in detection of diseases in early stages. For example, the measurement of C-reactive protein can aid in detection of heart attacks on a wearable device.
E-AB sensors offer groundbreaking possibilities for monitoring molecules within the intricate in-vivo environment, with transformative applications in clinical settings. Envisioning the integration of the E-AB sensing platform into a wearable device, comparable to continuous glucose monitors, holds promise for real-time measurements of drugs and biomarkers reflective of health and disease. Notably, exploring E-AB sensors in the interstitial skin region shows potential in this regard.
In instances where sepsis is suspected, the monitoring of infection biomarkers, such as C-reactive protein, stands out as a potentially life-saving approach, providing critical insights into disease prognosis and severity. Similarly, for individuals at high cardiac risk, the deployment of a convenient wearable device could facilitate early detection of heart attacks, considering the association of specific biomarkers like troponin with the onset of cardiac events. The exceptional capability of E-AB sensors to measure picomolar concentrations of specific proteins in real-time within complex sample matrices positions the platform as a well-suited tool for such clinical monitoring applications.
Expanding beyond disease detection, E-AB sensors hold the promise of revolutionizing drug dosing practices, particularly in the realm of precision medicine. The prevalent approach to pharmaceutical dosing, grounded in assumptions about the average individual's drug absorption and response, falls short for drugs with narrow therapeutic windows relative to patient variability. Current dosing methodologies, relying on slow and infrequent blood draws or waiting for observable side effects, entail potential risks of underdosing or overdosing. E-AB sensors, with their capability to provide real-time insights into plasma drug levels, present an avenue for significantly enhancing the safety and efficacy of pharmacological treatments through improved therapeutic drug monitoring. | 7 | Physical Chemistry |
* Identification of novel modified sites – BoMoC does not capture the modification directly but rather the mis-incorporation signature resulting from the modified base. Therefore, sites where modification status has not been previously established may be difficult to confirm the identity of the modification.
* Pre-mature termination of cDNA – Approximately, 10% of miRNA species characterized using OTTR experience prematurely terminated cDNA products. While these levels are low compared to common reverse transcriptase, some species carrying very bulky modifications may be challenging to capture with OTTR.
* Diversity in species used for benchmarking – To date, miRNA and tRNA pools have been characterized with OTTR. However, more validation, with diverse RNA and DNA species will increase the potential applications of OTTR. | 1 | Biochemistry |
Some key factors that determine overall rate include protein half-life, pH, and temperature.
Protein half-life helps determine the overall rate as this designates the first step in protein catabolism. Depending on whether this step is short or long will influence the rest of the metabolic process. One key component in determining the protein half-life is based on the N-end rule. This states that the amino acid present at the N-terminus of a protein helps determine the protein's half-life. | 1 | Biochemistry |
A recent study shows that conformational proofreading is used by human DNA repair mechanisms. The research focused on the question of how DNA-repair proteins scan the human genome for UV-induced damage during the initial step of nucleotide excision repair (NER). Detailed single-molecule measurements revealed how the human UV-damaged DNA-binding protein (UV-DDB) performs a 3D search. The authors find that "UV-DDB examines sites on DNA in discrete steps before forming long-lived, nonmotile UV-DDB dimers (DDB1-DDB2) at sites of damage. Analysis of the rates of dissociation for the transient binding molecules on both undamaged and damaged DNA show multiple dwell times over three orders of magnitude... These intermediate states are believed to represent discrete UV-DDB conformers on the trajectory to stable damage detection." The authors conclude from their detailed kinetic measurements that UV-DDB recognizes lesions using a conformational proofreading mechanism via multiple intermediates. | 1 | Biochemistry |
Negishi began dating Sumire Suzuki in his freshman year and they announced their engagement to their parents in March 1958. They had met at a choir of which they were both members at in university. They married the next year and together they had two daughters.
Negishi loved playing the piano and conducting. During the "Pacifichem" 2015 conference's closing ceremony, he conducted an orchestra. | 0 | Organic Chemistry |
Neuropeptides are released by dense core vesicles after depolarization of the cell. Compared to classical neurotransmitter signaling, neuropeptide signaling is more sensitive. Neuropeptide receptor affinity is in the nanomolar to micromolar range while neurotransmitter affinity is in the micromolar to millimolar range. Additionally, dense core vesicles contain a small amount of neuropeptide (3 - 10mM) compared to synaptic vesicles containing neurotransmitters (e.g. 100mM for acetylcholine). Evidence shows that neuropeptides are released after high-frequency firing or bursts, distinguishing dense core vesicle from synaptic vesicle release. Neuropeptides utilize volume transmission and are not reuptaken quickly, allowing diffusion across broad areas (nm to mm) to reach targets. Almost all neuropeptides bind to GPCRs, inducing second messenger cascades to modulate neural activity on long time-scales.
Expression of neuropeptides in the nervous system is diverse. Neuropeptides are often co-released with other neuropeptides and neurotransmitters, yielding a diversity of effects depending on the combination of release. For example, vasoactive intestinal peptide is typically co-released with acetylcholine. Neuropeptide release can also be specific. In Drosophila larvae, for example, eclosion hormone is expressed in just two neurons. | 1 | Biochemistry |
Gallium palladide (GaPd or PdGa) is an intermetallic combination of gallium and palladium. It has the iron monosilicide crystal structure. The compound has been suggested as an improved catalyst for hydrogenation reactions. In principle, gallium palladide can be a more selective catalyst since unlike substituted compounds, the palladium atoms are spaced out in a regular crystal structure rather than randomly. | 8 | Metallurgy |
The nomenclature of the metal carbonyls depends on the charge of the complex, the number and type of central atoms, and the number and type of ligands and their binding modes. They occur as neutral complexes, as positively-charged metal carbonyl cations or as negatively charged metal carbonylates. The carbon monoxide ligand may be bound terminally to a single metal atom or bridging to two or more metal atoms. These complexes may be homoleptic, containing only CO ligands, such as nickel tetracarbonyl (Ni(CO)), but more commonly metal carbonyls are heteroleptic and contain a mixture of ligands.
Mononuclear metal carbonyls contain only one metal atom as the central atom. Except vanadium hexacarbonyl, only metals with even atomic number, such as chromium, iron, nickel, and their homologs, build neutral mononuclear complexes. Polynuclear metal carbonyls are formed from metals with odd atomic numbers and contain a metal–metal bond. Complexes with different metals but only one type of ligand are called isoleptic.
Carbon monoxide has distinct binding modes in metal carbonyls. They differ in terms of their hapticity, denoted η, and their bridging mode. In η-CO complexes, both the carbon and oxygen are bonded to the metal. More commonly only carbon is bonded, in which case the hapticity is not mentioned.
The carbonyl ligand engages in a wide range of bonding modes in metal carbonyl dimers and clusters. In the most common bridging mode, denoted μ or simply μ, the CO ligand bridges a pair of metals. This bonding mode is observed in the commonly available metal carbonyls: Co(CO), Fe(CO), Fe(CO), and Co(CO). In certain higher nuclearity clusters, CO bridges between three or even four metals. These ligands are denoted μ-CO and μ-CO. Less common are bonding modes in which both C and O bond to the metal, such as μη. | 0 | Organic Chemistry |
In May, researchers announced the first gene therapy trial for inherited retinal disease. The first operation was carried out on a 23-year-old British male, Robert Johnson, in early 2007. | 1 | Biochemistry |
Theories of chemical structure were first developed by August Kekulé, Archibald Scott Couper, and Aleksandr Butlerov, among others, from about 1858. These theories were first to state that chemical compounds are not a random cluster of atoms and functional groups, but rather had a definite order defined by the valency of the atoms composing the molecule, giving the molecules a three dimensional structure that could be determined or solved.
Concerning chemical structure, one has to distinguish between pure connectivity of the atoms within a molecule (chemical constitution), a description of a three-dimensional arrangement (molecular configuration, includes e.g. information on chirality) and the precise determination of bond lengths, angles and torsion angles, i.e. a full representation of the (relative) atomic coordinates.
In determining structures of chemical compounds, one generally aims to obtain, first and minimally, the pattern and degree of bonding between all atoms in the molecule; when possible, one seeks the three dimensional spatial coordinates of the atoms in the molecule (or other solid). | 3 | Analytical Chemistry |
Non-viral methods present certain advantages over viral methods, with simple large scale production and low host immunogenicity being just two. Previously, low levels of transfection and expression of the gene held non-viral methods at a disadvantage; however, recent advances in vector technology have yielded molecules and techniques with transfection efficiencies similar to those of viruses. | 1 | Biochemistry |
Spectroscopic notation provides a way to specify atomic ionization states, atomic orbitals, and molecular orbitals. | 7 | Physical Chemistry |
Spinning cone columns are used in a form of low temperature vacuum steam distillation to gently extract volatile chemicals from liquid foodstuffs while minimising the effect on the taste of the product. For instance, the columns can be used to remove some of the alcohol from wine, off smells from cream, and to capture aroma compounds that would otherwise be lost in coffee processing. | 3 | Analytical Chemistry |
For many reasons known and unknown, protein adsorption varies from material to material. Two of the biggest determining factors that have been observed are surface roughness and surface free energy. In the case of exposed electrodes, it is desirable to have the adsorbed protein layer as thin as possible to increase sensitivity and performance. Noble metals are an obvious choice for achieving biocompatibility; however, when acting as electrodes, some of these noble metals will actually participate in the reaction, deteriorate, and trigger adverse effects via lost particles. The most (noble metals) are gold (Au), platinum (Pt), and iridium (Ir).
* = Surface free energy
* E = Total energy per unit cell at surface
* E = Total energy per unit cell in bulk of material
* A = Area of surface
The properties of titanium were also investigated in the study that produced the data for the above table, however, its properties are not listed here since its poor conductive properties make it unsuitable for neural implants. Insight on titaniums surface chemistry may give direction to future research. Titanium has the roughest and most hydrophilic surface of any metal described thus far (the importance of protein adsorption, its mechanisms, and the interplay of hydrophilic properties are discusses further in the hydrogels section of the page). Titanium adsorbed the thickest protein layer after the first day and still after the seventh day, but actually had its thickness reduced by the 28th day. Gold, platinum and iridiums protein layers all continued to grow up until the 28th day, but the rates slowed over time.
Two more conductive materials that have notable characteristics are tungsten and indium tin oxide. Tungsten is electrically conductive and can be manufactured down to a very fine point, and for this reason has been used in intraspinal microstimulation (ISMS) for mapping out spinal cords during terminal surgeries. Tungsten electrodes, however, can corrode and form tungstic ions in the presence of HO and/or O. Tungstic acid has been seen to be highly toxic to cat motorneurons, and for this reason, does not currently make a suitable material for chronic implants. Indium tin oxide (ITO) has been used as electrode material for in vitro studies. ITO electrodes are very precise when stimulating and recording and when placed amongst plasma proteins, develop and maintain the thinnest protein layer compared to the other materials so far mentioned. It may have potential for acute in vivo usage, but over time, it has been observed to let go of particles producing highly toxic effects. | 7 | Physical Chemistry |
The LEXO uses bio-based phase-change and advanced heat transfer materials to absorb the initial heat of the beverage and cool it to a more drinkable temperature. When the temperature begins to drop, the LEXO slowly releases the stored heat back into the drink. The LEXO can also insulate cold liquids.
The LEXO has three layers of 18/8 stainless-steel and BPA-free plastic lids. | 7 | Physical Chemistry |
Russell demonstrated that alkaline vents created an abiogenic proton motive force chemiosmotic gradient, ideal for abiogenesis. Their microscopic compartments "provide a natural means of concentrating organic molecules," composed of iron-sulfur minerals such as mackinawite, endowed these mineral cells with the catalytic properties envisaged by Günter Wächtershäuser. This movement of ions across the membrane depends on a combination of two factors:
# Diffusion force caused by concentration gradient—all particles including ions tend to diffuse from higher concentration to lower.
# Electrostatic force caused by electrical potential gradient—cations like protons H tend to diffuse down the electrical potential, anions in the opposite direction.
These two gradients taken together can be expressed as an electrochemical gradient, providing energy for abiogenic synthesis. The proton motive force can be described as the measure of the potential energy stored as a combination of proton and voltage gradients across a membrane (differences in proton concentration and electrical potential).
The surfaces of mineral particles inside deep-ocean hydrothermal vents have catalytic properties similar to those of enzymes and can create simple organic molecules, such as methanol (CHOH) and formic, acetic, and pyruvic acids out of the dissolved CO in the water, if driven by an applied voltage or by reaction with H or HS.
The research reported by Martin in 2016 supports the thesis that life arose at hydrothermal vents, that spontaneous chemistry in the Earths crust driven by rock–water interactions at disequilibrium thermodynamically underpinned lifes origin and that the founding lineages of the archaea and bacteria were H-dependent autotrophs that used CO as their terminal acceptor in energy metabolism. Martin suggests, based upon this evidence, that the LUCA "may have depended heavily on the geothermal energy of the vent to survive". Pores at deep sea hydrothermal vents are suggested to have been occupied by membrane-bound compartments which promoted biochemical reactions. Metabolic intermediates in the Krebs cycle, gluconeogenesis, amino acid bio-synthetic pathways, glycolysis, the pentose phosphate pathway, and including sugars like ribose, and lipid precursors can occur non-enzymatically at conditions relevant to deep-sea alkaline hydrothermal vents.
If the deep marine hydrothermal setting was the site for the origin of life, then abiogenesis could have happened as early as 4.0-4.2 Gya. If life evolved in the ocean at depths of more than ten meters, it would have been shielded both from impacts and the then high levels of ultraviolet radiation from the sun. The available energy in hydrothermal vents is maximized at 100–150 °C, the temperatures at which hyperthermophilic bacteria and thermoacidophilic archaea live. Arguments against a hydrothermal origin of life state that hyperthermophily was a result of convergent evolution in bacteria and archaea, and that a mesophilic environment would have been more likely. This hypothesis, suggested in 1999 by Galtier, was proposed one year before the discovery of the Lost City Hydrothermal Field, where white-smoker hydrothermal vents average ~45-90 °C. Moderate temperatures and alkaline seawater at Lost City are now the favoured hydrothermal vent setting in contrast to acidic, high temperature (~350 °C) black-smokers. | 9 | Geochemistry |
When the ribosome movement on the mRNA is not linear, the ribosome gets paused at different regions without a precise reason. The ribosome pause position will help to identify the mRNA sequence features, structure, and the transacting factor that modulates this process. The advantage of ribosomal pause sites that are located at protein domain boundaries are aiding the folding of a protein. There are times when the ribosomal pause does not cause an advantage and it needs to be restricted. In translation, elF5A inhibits ribosomal pausing for translation to function better. Ribosomal pausing can cause more non-canonical start codons without elF5A in eukaryotic cells. When there is a lack of elF5A in the eukaryotic cell, it can cause an increase in ribosomal pausing. The ribosomal pausing process can also be used by amino acids to control translation. | 1 | Biochemistry |
SOBER1 is an enzyme that catalyzes the biochemical reaction of deacetylation. The SOBER (uppressor f AvrsT-licited esistance) 1 protein is conserved in plants and it suppresses the plants ability to carry out the hypersensitive response against infection by certain pathogenic effector proteins from the YopJ family. SOBER1 belongs to the protein superfamily of α/β hydrolases and possesses a canonical serine/histidine/aspartate catalytic triad to carry out the deacetylation reaction. There have been contradicting reports about SOBER1s potential phospholipase activity, with one study claiming phospholipase A activity of the protein and another study being unable to reproduce this result. | 0 | Organic Chemistry |
Xylose, fucose, mannose, and GlcNAc phosphoserine glycans have been reported in the literature. Fucose and GlcNAc have been found only in Dictyostelium discoideum, mannose in Leishmania mexicana, and xylose in Trypanosoma cruzi. Mannose has recently been reported in a vertebrate, the mouse, Mus musculus, on the cell-surface laminin receptor alpha dystroglycan. It has been suggested this rare finding may be linked to the fact that alpha dystroglycan is highly conserved from lower vertebrates to mammals. | 0 | Organic Chemistry |
Limitations to take note when using MeDIP are typical experimental factors. This includes the quality and cross-reactivity of 5mC antibodies used in the procedure. Furthermore, DNA detection methods (i.e. array hybridization and high-throughput sequencing) typically involve well established limitations. Particularly for array-based procedures, as mentioned above, sequences being analyzed are limited to the specific array design used.
Most typical limitations to high-throughput, next generation sequencing apply. The problem of alignment accuracy to repetitive regions in the genome will result in less accurate analysis of methylation in those regions. Also, as was mentioned above, short reads (e.g. 36-50bp from an [http://www.illumina.com/pages.ilmn?ID=204 Illumina Genome Analyzer]) represent a part of a sheared fragment when aligned to the genome; therefore, the exact methylation site can fall anywhere within a window that is a function of the fragment size. In this respect, bisulfite sequencing has much higher resolution (down to a single CpG site; single nucleotide level). However, this level of resolution may not be required for most applications, as the methylation status of CpG sites within < 1000 bp has been shown to be significantly correlated. | 1 | Biochemistry |
With the development of various next-generation sequencing platforms, there has been a substantial reduction in costs, and increase in throughput of DNA sequencing. However, the majority of the sequencing technologies rely on PCR-based clonal amplification of the DNA molecule in order to bring the signal to a detectable range. Sequencing of amplified clusters, or bulk sequencing in such a propose a read length-dependent phasing problem. During each cycle, not all of the molecules within the bulk have successful incorporation of an additional nucleotide. With increased sequencing cycle, the signal of the lagging molecules will eventually overwhelm the true signal. The phasing problem is a major limitation for the read lengths of the next-generation sequencing technologies. Therefore, there is an increased interest in developing single-molecule sequencing technologies, where no amplification is required. This not only shortens the preparation time for the sequencing libraries, it also has the potential to achieve much longer read lengths, as the lagging molecules with failed extensions can be ignored or considered separately. Previously known single-molecule sequencing technologies include Nanopore sequencing (Oxford Nanopore),
SMRT sequencing (Pacific Biosciences), and Heliscope single molecule sequencing (Helicos Biosciences). | 1 | Biochemistry |
After the single-stranded viral DNA enters the cytoplasm, it serves as a template for the synthesis of a complementary DNA strand. This synthesis is initiated in the intergenic region of the DNA sequence by host RNA polymerase, which synthesizes a short RNA primer on the infecting DNA as template. The host DNA polymerase III then uses this primer to synthesize the full complementary strand of DNA, yielding a double-stranded circle, sometimes called the replicative form (RF) DNA. The complementary strand of the RF is the transcription template for phage coded proteins, especially p2 and p10, which are necessary for further DNA replication.
The p2 protein cleaves the viral strand of the RF DNA, and host DNA polymerase III synthesizes a new viral strand. The old viral strand is displaced as the new one is synthesized. When a circle is complete, the covalently linked p2 cuts the displaced viral strand at the junction between the old and newly synthesized DNA and re-ligates the two ends and liberates p2. RF replicates by this rolling circle mechanism to generate dozens of copies of the RF.
When the concentration of phage proteins has increased, new viral strands are coated by the replication/assembly protein p5 rather than by the complementary DNA strands. The p5 also inhibits translation of p2, so that progeny viral ssDNA production and packaging are in synchrony. | 1 | Biochemistry |
In 2007 Houser et al. developed the analogous parameter to distinguish whether the geometry of the coordination center is square planar or tetrahedral. The formula is:
where: and are the two greatest valence angles of coordination center; is a tetrahedral angle.
When is close to 0 the geometry is similar to square planar, while if is close to 1 then the geometry is similar to tetrahedral. However, in contrast to the parameter, this does not distinguish and angles, so structures of significantly different geometries can have similar values. To overcome this issue, in 2015 Okuniewski et al. developed parameter that adopts values similar to but better differentiates the examined structures:
where: are the two greatest valence angles of coordination center; is a tetrahedral angle.
Extreme values of and denote exactly the same geometries, however is always less or equal to so the deviation from ideal tetrahedral geometry is more visible. If for tetrahedral complex the value of parameter is low, then one should check if there are some additional interactions within coordination sphere. For example, in complexes of mercury(II), the Hg···π interactions were found this way. | 3 | Analytical Chemistry |
Ion current density is typically measured in mA/cm, and ion energy in eV. The use of eV is convenient for converting between voltage and energy, especially when dealing with singly-charged ion beams, as well as converting between energy and temperature (1 eV = 11600 K). | 7 | Physical Chemistry |
Neurofurans are 22-carbon compounds formed nonenzymatically by free radical mediated peroxidation of docosahexaenoic acid (DHA), an ω-3 essential fatty acid. The neurofurans are similar to the isofurans and are formed under similar conditions of oxidative stress, containing a substituted tetrahydrofuran ring. Measurement of the neurofurans may ultimately prove useful in diagnosis, timing, and selection of dosages in the treatment and chemoprevention of neurodegenerative disease. | 1 | Biochemistry |
Anandamide and N-arachidonoyl dopamine (NADA) have been shown to act on temperature-sensing TRPV1 channels, which are involved in thermoregulation. TRPV1 is activated by the exogenous ligand capsaicin, the active component of chili peppers, which is structurally similar to endocannabinoids. NADA activates the TRPV1 channel with The high potency makes it the putative endogenous TRPV1 agonist. Anandamide has also been found to activate TRPV1 on sensory neuron terminals, and subsequently cause vasodilation. TRPV1 may also be activated by methanandamide and arachidonyl-2'-chloroethylamide (ACEA). | 1 | Biochemistry |
Although the system for maintaining optimal salt and water balance in the body is a complex one, one of the primary ways in which the human body keeps track of loss of body water is that osmoreceptors in the hypothalamus sense a balance of sodium and water concentration in extracellular fluids. Relative loss of body water will cause sodium concentration to rise higher than normal, a condition known as hypernatremia. This ordinarily results in thirst. Conversely, an excess of body water caused by drinking will result in too little sodium in the blood (hyponatremia), a condition which is again sensed by the hypothalamus, causing a decrease in vasopressin hormone secretion from the posterior pituitary, and a consequent loss of water in the urine, which acts to restore blood sodium concentrations to normal.
Severely dehydrated persons, such as people rescued from ocean or desert survival situations, usually have very high blood sodium concentrations. These must be very carefully and slowly returned to normal, since too-rapid correction of hypernatremia may result in brain damage from cellular swelling, as water moves suddenly into cells with high osmolar content.
In humans, a high-salt intake was demonstrated to attenuate nitric oxide production. Nitric oxide (NO) contributes to vessel homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the endothelium. | 1 | Biochemistry |
Orthoesters of diarylstibinic acids are fungicides and bactericides, used in paints, plastics, and fibers. Trivalent organic antimony was used in therapy for schistosomiasis. | 1 | Biochemistry |
Enzymatic lysis, also called Lysozyme lysis, involves the use of enzymes to digest the cell wall and release the plasmid DNA. The most commonly used enzyme for this purpose is lysozyme, which breaks down the peptidoglycan in the cell wall of Gram-positive bacteria. Lysozyme is usually added to the bacterial culture, followed by heating and/or shaking the culture to release the plasmid DNA. | 1 | Biochemistry |
Perfluorohexane has extremely high global warming potential (GWP) of 9,300. This leads to a need to find low GWP alternative. Novec 649 was considered a good drop-in replacement in many applications due to its similar thermo-physical properties and having a global warming potential of 1. | 2 | Environmental Chemistry |
An interspecific semiochemical that is beneficial to both interacting organisms, the emitter and receiver, e.g. floral synomone of certain Bulbophyllum species (Orchidaceae) attracts fruit fly males (Tephritidae: Diptera) as pollinators. In this true mutualistic inter-relationship, both organisms gain benefits in their respective sexual reproduction - i.e. orchid flowers are pollinated and the Dacini fruit fly males are rewarded with a sex pheromone precursor or booster; and the floral synomones, also act as rewards to pollinators, are in the form of phenylpropanoids (e.g. methyl eugenol) and phenylbutanoids (e.g. raspberry ketone zingerone and anisyl acetone/a combination of the three phenylbutanoids. | 1 | Biochemistry |
Initially devised by Mikhail Shneider and Richard Miles at Princeton University, coherent microwave scattering has become a valuable technique in applications ranging from photoionization and electron-loss rate measurements to trace species detection, gaseous mixture and reaction characterization, molecular spectroscopy, electron propulsion device characterization, standoff measurement of electron collision frequencies for momentum transfer through the scattered phase, and standoff measurement of local vector magnetic fields through magnetically-induced depolarization. | 7 | Physical Chemistry |
Poly(pentafluorophenyl acrylate) (variously abbreviated PPFPA, PolyPFPA, PPfpA, or PolyPfpA) is a highly fluorinated polymer. It features the pentafluorophenyl ester functionality, from which its properties and applications result. It is most commonly used in post-polymerization modification to synthesize functional polyacrylamides or polyacrylates. As such, it is advantageous to poly(N-acryloyl succinimide) due to its broader solubility in organic solvents as well as its higher stability towards hydrolysis. | 7 | Physical Chemistry |
Looking at the results from four meta-analyses, one reported a statistically significant decrease in fasting plasma glucose levels (FPG) and a non-significant trend in lower hemoglobin A1C (HbA1C). A second reported the same, a third reported significant decreases for both measures, while a fourth reported no benefit for either. A review published in 2016 listed 53 randomized clinical trials that were included in one or more of six meta-analyses. It concluded that whereas there may be modest decreases in FPG and/or HbA1C that achieve statistical significance in some of these meta-analyses, few of the trials achieved decreases large enough to be expected to be relevant to clinical outcome. | 1 | Biochemistry |
*Nucleobase analogues
**Fluorouracil (5FU), which inhibits thymidylate synthase
**Floxuridine (FUDR)
**6-azauracil (6-AU)
*Nucleoside analogues
**Cytarabine (Cytosine arabinoside)
**Gemcitabine
*Nucleotide analogues | 1 | Biochemistry |
In Dubin–Johnson syndrome, impaired biliary excretion of bilirubin glucuronide is due to a mutation in the canalicular multiple drug-resistance protein 2 (MRP2). A darkly pigmented liver is due to polymerized epinephrine metabolites, not bilirubin. | 1 | Biochemistry |
Deamination is the removal of an amino group from a molecule. Enzymes that catalyse this reaction are called deaminases.
In the human body, deamination takes place primarily in the liver; however, it can also occur in the kidney. In situations of excess protein intake, deamination is used to break down amino acids for energy. The amino group is removed from the amino acid and converted to ammonia. The rest of the amino acid is made up of mostly carbon and hydrogen, and is recycled or oxidized for energy. Ammonia is toxic to the human system, and enzymes convert it to urea or uric acid by addition of carbon dioxide molecules (which is not considered a deamination process) in the urea cycle, which also takes place in the liver. Urea and uric acid can safely diffuse into the blood and then be excreted in urine. | 1 | Biochemistry |
Pin1, a parvulin, regulates mRNA stability and expression in certain eukaryotics mRNAs. These mRNAs are GM-CSF, Pth, and TGFβ and each of them have AREs, or AU-rich cis-elements. The ARE binding protein KSRP has a Pin1 binding site. Pin1 binds to this site and dephosphorylates the serine and isomerizes the peptide bond between Ser181 and Pro182. This isomerization causes the decay of Pth mRNA. KSRP, and other ARE binding proteins like AUF1, are thought to affect the other mRNAs through mechanisms similar to Pth, with the requirement of a phosphorylated serine bonded to a proline in a specific conformation. Pin1 also triggers proline isomerization of Stem-Loop Binding Protein (SLBP), allowing it to control the dissociation of SLBP from histone mRNA. This leads to Pin1 being able to affect histone mRNA decay. Pin1 affects many other genes in the form of gene silencing through the disruption of cell pathways, making it important in mRNA turnover by modulating RNA binding protein activity. | 4 | Stereochemistry |
During the last couple of years there has been developments of CSPs based on novel chiral selectors viz. chitosan derivatives, cylofructan derivatives and chiral porous materials for HPLC chiral separation. | 4 | Stereochemistry |
The idea of rigid unit modes was developed for crystalline materials to enable an understanding of the origin of displacive phase transitions in materials such as silicates, which can be described as infinite three-dimensional networks of corner-lined SiO and AlO tetrahedra. The idea was that rigid unit modes could act as the soft modes for displacive phase transitions.
The original work in silicates showed that many of the phase transitions in silicates could be understood in terms of soft modes that are RUMs.
After the original work on displacive phase transitions, the RUM model was also applied to understanding the nature of the disordered high-temperature phases of materials such as cristobalite, the dynamics and localised structural distortions in zeolites, and negative thermal expansion. | 3 | Analytical Chemistry |
2D correlation analysis is frequently used for its main advantage: increasing the spectral resolution by spreading overlapping peaks over two dimensions and as a result simplification of the interpretation of one-dimensional spectra that are otherwise visually indistinguishable from each other. Further advantages are its ease of application and the possibility to make the distinction between band shifts and band overlap. Each type of spectral event, band shifting, overlapping bands of which the intensity changes in the opposite direction, band broadening, baseline change, etc. has a particular 2D pattern. See also the figure with the original dataset on the right and the corresponding 2D spectrum in the figure below. | 7 | Physical Chemistry |
Studies of individual transcripts were being performed several decades before any transcriptomics approaches were available. Libraries of silkmoth mRNA transcripts were collected and converted to complementary DNA (cDNA) for storage using reverse transcriptase in the late 1970s. In the 1980s, low-throughput sequencing using the Sanger method was used to sequence random transcripts, producing expressed sequence tags (ESTs). The Sanger method of sequencing was predominant until the advent of high-throughput methods such as sequencing by synthesis (Solexa/Illumina). ESTs came to prominence during the 1990s as an efficient method to determine the gene content of an organism without sequencing the entire genome. Amounts of individual transcripts were quantified using Northern blotting, nylon membrane arrays, and later reverse transcriptase quantitative PCR (RT-qPCR) methods, but these methods are laborious and can only capture a tiny subsection of a transcriptome. Consequently, the manner in which a transcriptome as a whole is expressed and regulated remained unknown until higher-throughput techniques were developed. | 1 | Biochemistry |
A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation (which may arise due to mutation or alteration in the genomic loci) that can be observed. A genetic marker may be a short DNA sequence, such as a sequence surrounding a single base-pair change (single nucleotide polymorphism, SNP), or a long one, like minisatellites. | 1 | Biochemistry |
The Barton evaporation engine is a heat engine based on a cycle producing power and cooled moist air from the evaporation of water into hot dry air. | 7 | Physical Chemistry |
A xerogel is a solid formed from a gel by drying with unhindered shrinkage. Xerogels usually retain high porosity (15–50%) and enormous surface area (150–900 m/g), along with very small pore size (1–10 nm). When solvent removal occurs under supercritical conditions, the network does not shrink and a highly porous, low-density material known as an aerogel is produced. Heat treatment of a xerogel at elevated temperature produces viscous sintering (shrinkage of the xerogel due to a small amount of viscous flow) which results in a denser and more robust solid, the density and porosity achieved depend on the sintering conditions. | 7 | Physical Chemistry |
Alfred G. Gilman and Martin Rodbell received the 1994 Nobel Prize in Medicine and Physiology for the discovery of the G Protein System. | 1 | Biochemistry |
After the deprotonation, the hydrazone turns into an azaenolate with lithium cation chelating both the nitrogen and oxygen. There are two possible options for lithium chelation. One is that lithium is antiperiplanar to the C=C bond (blue colored), leading to the conformation of Z; the other one is that lithium and the C=C bond are at the same side of the C-N bond (red colored), leading to the E conformer. There are also two available orientations for the chelating nitrogen and R group, being either E or Z. This leads to four possible azaenolate intermediates (A, B, C and D) for the Enders' SAMP/RAMP hydrazone alkylation reaction.
Experiments and calculations show that one specific stereoisomer of the azaenolate is favored over the other three possible candidates. Therefore, although four isomers are possible for the azaenolate, only the one (azaenolate A) with the stereochemistry of its C=C double bonds being E and that of its C-N bond being Z stereochemistry is dominant (EZ) for both cyclic and acyclic ketones. | 0 | Organic Chemistry |
Ferroin is the chemical compound with the formula [Fe(o-phen)]SO, where o-phen is an abbreviation for 1,10-phenanthroline, a bidentate ligand. The term "ferroin" is used loosely and includes salts of other anions such as chloride. | 3 | Analytical Chemistry |
In recent years, expression vectors have been used to introduce specific genes into plants and animals to produce transgenic organisms, for example in agriculture it is used to produce transgenic plants. Expression vectors have been used to introduce a vitamin A precursor, beta-carotene, into rice plants. This product is called golden rice. This process has also been used to introduce a gene into plants that produces an insecticide, called Bacillus thuringiensis toxin or Bt toxin which reduces the need for farmers to apply insecticides since it is produced by the modified organism. In addition expression vectors are used to extend the ripeness of tomatoes by altering the plant so that it produces less of the chemical that causes the tomatoes to rot. There have been controversies over using expression vectors to modify crops due to the fact that there might be unknown health risks, possibilities of companies patenting certain genetically modified food crops, and ethical concerns. Nevertheless, this technique is still being used and heavily researched.
Transgenic animals have also been produced to study animal biochemical processes and human diseases, or used to produce pharmaceuticals and other proteins. They may also be engineered to have advantageous or useful traits. Green fluorescent protein is sometimes used as tags which results in animal that can fluoresce, and this have been exploited commercially to produce the fluorescent GloFish. | 1 | Biochemistry |
Transposons vary in their structure and manner of proliferation, both of which help to define their classification. Each class contains autonomous elements, a sub-variety distinguished by the ability to self-proliferate, and also non-autonomous elements, which lack that ability. | 1 | Biochemistry |
In the United States, 49% of the 250,000 valve replacement procedures performed annually involve a mechanical valve implant. The most widely used valve is a bileaflet disc heart valve or St. Jude valve. The mechanics involve two semicircular discs moving back and forth, with both allowing the flow of blood as well as the ability to form a seal against backflow. The valve is coated with pyrolytic carbon and secured to the surrounding tissue with a mesh of woven fabric called Dacron (du Ponts trade name for polyethylene terephthalate). The mesh allows for the bodys tissue to grow, while incorporating the valve. | 1 | Biochemistry |
A similar method was proposed in 1981 by Eksborg. This method was based on Deming regression—a method introduced by Adcock in 1878.
Bland and Altman's Lancet paper was number 29 in a list of the top 100 most-cited papers of all time with over 23,000 citations. | 3 | Analytical Chemistry |
The equilibrium temperature is neither an upper nor lower bound on actual temperatures on a planet. There are several reasons why measured temperatures deviate from predicted equilibrium temperatures. | 7 | Physical Chemistry |
The allyl ligand is commonly found in organometallic chemistry. Most commonly, allyl ligands bind to metals via all three carbon atoms, the η-binding mode. The η-allyl group is classified as an LX-type ligand in the Green LXZ ligand classification scheme, serving as a 3e donor using neutral electron counting and 4e donor using ionic electron counting. More common are complexes with allyl and other ligands. Examples include (η-allyl)Mn(CO) and CpPd(allyl). | 0 | Organic Chemistry |
The furnace comprises three distinct zones:
* Firstly, the preheating zone heats the ore to 800 °C using the hot fumes within the furnace. Ore reduction occurs only if temperatures exceed 900-1,000 °C, while the coal releases its most volatile constituents.
* Secondly, the reduction zone is situated in the middle of the furnace, where coal and iron oxides combine to produce carbon monoxide. The carbon monoxide is released from the charge, generating a gaseous layer that shields the charge against the oxidizing air circulating above. As a consequence, this excessive gas is combusted, raising the temperature of the furnace walls, which then transfer the heat back to the charge due to rotary motion. The temperature eventually increases to 800 – 1,200 °C. Subsequently, the iron oxides are gradually altered into ferronickel or metallic iron. The metal produced is in the form of metallic sponge particles that are finely dispersed in the powdery gangue.
* Reduction is complete by the end of the furnace, and there is a minimal amount of CO produced. This is due to the fact that the charge is no longer protected from oxidation by the air blown in at the base of the furnace. As a result, a violent but shallow reoxidation of the iron occurs. Some of the oxidized iron is returned to the core of the charge by rotation where it is further reduced with residual coal. The remaining material mixes with waste to create a thick slag that cannot blend with the produced metal. This extremely hot reaction melts the non-oxidized iron and nickel, which clump together forming nodules named Luppen.
Control of temperature is critical in regards to the ores physicochemical characteristics. Overly high temperatures or unsuitable granulometry lead to the creation of rings of sintered material that accumulate on the walls of the furnace. Typically, a ring of iron-poor slag, known as slag, is formed at two-thirds of the distance along the furnace. Similarly, a metal ring usually forms around ten meters from the outlet. These rings disturb the flow of materials and gas, diminishing the furnaces useful capacity, sometimes completely obstructing it. The process's revival is hindered by the formation of a ring, particularly in China. In the early 21st century, industrialists abandoned its adoption after recognizing how critical and challenging managing this parameter was.
While slag melting consumes energy, it enables us to govern the charges behavior in the furnace. Additionally, we need a minimum of 800 to 1,000 kg of slag per ton of iron to prevent Luppen from growing too big. Slag limits coal segregation as coal is much less dense than ore and would float to the surface of the mixture. It transforms into a paste that guards the metal against oxidation when heated and simplifies both Luppen' processing and furnace cleaning during maintenance shutdowns through vitrification when it gets cold. | 8 | Metallurgy |
Crampton et al. have proposed a mechanism for the ssDNA-dependent hydrolysis of dTTP by T7 DNA helicase as shown in the figure below. In their model, protein loops located on each hexameric subunit, each of which contain three lysine residues, sequentially interact with the negatively charged phosphate backbone of ssDNA. This interaction presumably causes a conformational change in the actively bound subunit, providing for the efficient release of dTDP from its dTTP binding site. In the process of dTDP release, the ssDNA is transferred to the neighboring subunit, which undergoes a similar process. Previous studies have already suggested that ssDNA is able to bind to two hexameric subunits simultaneously. | 1 | Biochemistry |
In some versions of the Schilling test, B can be given both with and without intrinsic factor at the same time, using different cobalt radioisotopes Co and Co, which have different radiation signatures, in order to differentiate the two forms of B. This is performed with the Dicopac kitset. This allows for only a single radioactive urine collection. | 1 | Biochemistry |
In physics and chemistry, motional narrowing is a phenomenon where a certain resonant frequency has a smaller linewidth than might be expected, due to motion in an inhomogeneous system. The discovery of motional narrowing has been attributed to Nicolaas Bloembergen during his thesis work in the 1940s | 7 | Physical Chemistry |
Calcareous sediments are typically deposited in shallow water closer to land, as marine organisms that precipitate calcium carbonate primarily reside within shallow water ecosystems due to an inability to precipitate calcium carbonate at depth (see carbonate compensation depth). Generally speaking, the farther from land sediments fall, the less calcareous they are, and deviations from this expectation arise if (a) the ocean floor is shallower than the CCD or (b) storms/ocean currents transport calcareous sediments away from their origin point, leading to the interbedding of calcareous sediments in alternative locations.
An additional form of calcareous marine sediment consists of calcareous ooze, which is a form of calcium carbonate sediment that consists of >30% biogenous material predominantly consisting of organisms such as coccolithophores and foraminifera. These oozes form slowly under low-energy environments, and necessitate higher seawater saturation states or a deeper CCD (see supersaturation and precipitation vs. undersaturation and dissolution). Therefore, in shallow CCD conditions (i.e., undersaturation of calcium carbonate at depth), stable, non-calcareous sediments such as siliceous ooze or pelagic red clay will prevail in marine sediment records. | 9 | Geochemistry |
Very small amount of carbon is sufficient to stabilize "ScBC". This compound has a broad composition range, namely ScBC with x ≤ 2.2 and y ≤ 0.44. ScBC has a hexagonal crystal structure with space group P6mmm (No. 199) and lattice constants a, b = 1.45501(15) nm and c = 0.84543(16) nm.
There are 19 atomic sites in the unit cell, which are assigned to one scandium site Sc, 14 boron sites B1–B14 having 100% occupancy, two boron-carbon mixed-occupancy sites B/C15 and B/C16, and two partial-occupancy boron sites B17 and B18. Atomic coordinates, site occupancies and isotropic displacement factors are listed in table VII. Although a very small amount of carbon (less than 2 wt%!) plays an important role in the phase stability, carbon does not have its own sites but shares with boron two interstitial sites B/C15 and B/C16.
There are two inequivalent B icosahedra, I1 and I2, which are constructed by the B1–B5 and B8–B12 sites, respectively. A "tube" is another characteristic structure unit of ScBC. It extends along the c-axis and consists of B13, B14, B17 and B18 sites where B13 and B14 form 6-membered rings. B17 and B18 sites also form 6-membered rings; however, their mutual distances (0.985 Å for B17 and 0.955 Å for B18) are too short for a simultaneous occupation of the neighboring sites. Therefore, boron atoms occupy 2nd neighbor site forming a triangle. The occupancies of B17 and B18 sites should be 50%, but the structure analysis suggests larger values. The crystal structure viewed along the a-axis is shown in figure 20, which suggests that the ScBC is a layered material. Two layers, respectively constructed by the icosahedra I1 and I2, alternatively stack along the c-axis. However, the ScBC crystal is not layered. For example, during arc-melting, ScBC needle crystals violently grow along the c-axis – this never happens in layered compounds. The crystal structure viewed along the c-axis is shown in figure 21a. The icosahedra I1 and I2 form a ring centered by the "tube" shown in figure 21b, which probably governs the properties of the ScBC crystal. B/C15 and B/C16 mixed-occupancy sites interconnect the rings. A structural similarity can be seen between ScBC and BeB.
Figures 22a and b present HRTEM lattice images and electron diffraction patterns taken along the [0001] and [110] crystalline directions, respectively. The HRTEM lattice image of figure 22a reproduces well the (a, b) plane of the crystal structure shown in figure 21a, with the clearly visible rings membered by icosahedra I1 and I2 and centered by the "tube". Figure 22b proves that ScBC does not have layered character but its c-axis direction is built up by the ring-like structure and tubular structures. | 3 | Analytical Chemistry |
The chemistry of stable carbenes has not been fully explored. However, Enders et al.
have performed a range of organic reactions involving a triazol-5-ylidene. These reactions are outlined below and may be considered as a model for other carbenes.
These carbenes tend to behave in a nucleophilic fashion (e and f), performing insertion reactions (b), addition reactions (c), [2+1] cycloadditions (d, g and h), [4+1] cycloadditions (a) as well as simple deprotonations. The insertion reactions (b) probably proceed via deprotonation, resulting in the generation of a nucleophile (XR) which can attack the generated salt giving the impression of a H–X insertion.
The reported stable isothiazole carbene (2b) derived from an isothiazolium perchlorate (1) was questioned. The researchers were only able to isolate 2-imino-2H-thiete (4). The intermediate 3 was proposed through a rearrangement reaction. The carbene 2b is no longer considered as stable. | 0 | Organic Chemistry |
In anti-tank warfare, spalling through mechanical stress is an intended effect of high-explosive squash head (HESH) anti-tank shells and many other munitions, which may not be powerful enough to pierce the armour of a target. The relatively soft warhead, containing or made of plastic explosive, flattens against the armour plating on tanks and other armoured fighting vehicles (AFVs) and explodes, creating a shock wave that travels through the armour as a compression wave and is reflected at the free surface as a tensile wave breaking (tensile stress/strain fracture) the metal on the inside. The resulting spall is dangerous to crew and equipment, and may result in a partial or complete disablement of a vehicle and/or its crew. Many AFVs are equipped with spall liners inside their armour for protection.
A kinetic energy penetrator, if it can defeat the armour, generally causes spalling within the target as well, which helps to destroy or disable the vehicle and its crew.
An early example of anti-tank weapon intentionally designed to cause spallation instead of penetration is the wz. 35 anti-tank rifle. | 8 | Metallurgy |
The Pedersen Process was invented by Harald Pedersen in the 1920s and used in Norway for over 40 years before shutting down due to the Pedersen Process being less economically competitive than the Bayer Process. However, it is believed a modern Pedersen process could be economically viable with "low-quality" bauxite, as even though "low-quality" bauxite has less alumina in the form of trihydrate gibbsite, it has more iron oxide which would be converted to pig iron in the smelting process instead of red mud. | 8 | Metallurgy |
JNK can directly phosphorylate Bim-EL, a splicing isoform of Bcl-2 interacting mediator of cell death (Bim), which activates Bim-EL apoptotic activity. JNK activation is required for apoptosis but c-jun, a protein in the JNK signaling pathway, is not always required. | 1 | Biochemistry |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.