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Chiral resolution, or enantiomeric resolution, is a process in stereochemistry for the separation of racemic mixture into their enantiomers. It is an important tool in the production of optically active compounds, including drugs. Another term with the same meaning is optical resolution.
The use of chiral resolution to obtain enantiomerically pure compounds has the disadvantage of necessarily discarding at least half of the starting racemic mixture. Asymmetric synthesis of one of the enantiomers is one means of avoiding this waste. | 4 | Stereochemistry |
Micelles are composed of surfactant, or detergent, monomers with a hydrophobic moiety, or tail, on one end, and a hydrophilic moiety, or head group, on the other. The polar head group may be anionic, cationic, zwitterionic, or non-ionic. When the concentration of a surfactant in solution reaches its critical micelle concentration (CMC), it forms micelles which are aggregates of the monomers. The CMC is different for each surfactant, as is the number of monomers which make up the micelle, termed the aggregation number (AN). Table 1 lists some common detergents used to form micelles along with their CMC and AN where available.
Many of the characteristics of micelles differ from those of bulk solvents. For example, the micelles are, by nature, spatially heterogeneous with a hydrocarbon, nearly anhydrous core and a highly solvated, polar head group. They have a high surface-to-volume ratio due to their small size and generally spherical shape. Their surrounding environment (pH, ionic strength, buffer ion, presence of a co-solvent, and temperature) has an influence on their size, shape, critical micelle concentration, aggregation number and other properties.
Another important property of micelles is the Kraft point, the temperature at which the solubility of the surfactant is equal to its CMC. For HPLC applications involving micelles, it is best to choose a surfactant with a low Kraft point and CMC. A high CMC would require a high concentration of surfactant which would increase the viscosity of the mobile phase, an undesirable condition. Additionally, a Kraft point should be well below room temperature to avoid having to apply heat to the mobile phase. To avoid potential interference with absorption detectors, a surfactant should also have a small molar absorptivity at the chosen wavelength of analysis. Light scattering should not be a concern due to the small size, a few nanometers, of the micelle.
The effect of organic additives on micellar properties is another important consideration. A small amount of organic solvent is often added to the mobile phase to help improve efficiency and to improve separations of compounds. Care needs to be taken when determining how much organic to add. Too high a concentration of the organic may cause the micelle to disperse, as it relies on hydrophobic effects for its formation. The maximum concentration of organic depends on the organic solvent itself, and on the micelle. This information is generally not known precisely, but a generally accepted practice is to keep the volume percentage of organic below 15–20%. | 3 | Analytical Chemistry |
The current production method is based on the first scalable synthesis developed by Gilead Sciences starting from naturally occurring quinic acid or shikimic acid. Due to lower yields and the extra steps required (because of the additional dehydration), the quinic acid route was dropped in favour of the one based on shikimic acid, which received further improvements by Hoffmann-La Roche.
The current industrial synthesis is summarised below: | 0 | Organic Chemistry |
After a hiatus, Norşuntepe was again occupied during the Early Bronze Age. During this period, the site was surrounded by a mudbrick city wall built on a stone foundation. There is evidence for copper production and some sort of palace or large, central building appears at the site in the final phases. In terms of material culture and architecture, there are clear parallels with Transcaucasia, and the Kura–Araxes culture. The latest Early Bronze Age phase in Norşuntepe ends in fire. | 8 | Metallurgy |
The most abundant chlorin is the photosynthetic pigment chlorophyll. Chlorophylls have a fifth, ketone-containing ring unlike the chlorins. Diverse chlorophylls exists, such as chlorophyll a, chlorophyll b, chlorophyll d, chlorophyll e, chlorophyll f, and chlorophyll g. Chlorophylls usually feature magnesium as a central metal atom, replacing the two NH centers in the parent. | 1 | Biochemistry |
In alkanes, optimum overlap of atomic orbitals is achieved at 109.5°. The most common cyclic compounds have five or six carbons in their ring. Adolf von Baeyer received a Nobel Prize in 1905 for the discovery of the Baeyer strain theory, which was an explanation of the relative stabilities of cyclic molecules in 1885.
Angle strain occurs when bond angles deviate from the ideal bond angles to achieve maximum bond strength in a specific chemical conformation. Angle strain typically affects cyclic molecules, which lack the flexibility of acyclic molecules.
Angle strain destabilizes a molecule, as manifested in higher reactivity and elevated heat of combustion. Maximum bond strength results from effective overlap of atomic orbitals in a chemical bond. A quantitative measure for angle strain is strain energy. Angle strain and torsional strain combine to create ring strain that affects cyclic molecules.
Normalized energies that allow comparison of ring strains are obtained by measuring per methylene group (CH) of the molar heat of combustion in the cycloalkanes.
: per CH − 658.6 kJ = strain per CH
The value 658.6 kJ per mole is obtained from an unstrained long-chain alkane.
Cycloalkanes generally have less ring strain than cycloalkenes, which is seen when comparing cyclopropane and cyclopropene. | 7 | Physical Chemistry |
Coatings act as a barrier between the metal substrate and the surrounding environment, hindering the ingress of hydrogen atoms. These coatings can be applied through various techniques such as electroplating, chemical conversion coatings, or organic coatings. The choice of coating depends on factors such as the type of metal, the operating environment, and the specific requirements of the application.
Electroplating is a commonly used method to deposit a protective layer onto the metal surface. This process involves immersing the metal substrate into an electrolyte solution containing metal ions. By applying an electric current, the metal ions are reduced and form a metallic coating on the substrate. Electroplating can provide an excellent protective layer that enhances corrosion resistance and reduces the susceptibility to hydrogen embrittlement.
Chemical conversion coatings are another effective method for surface protection. These coatings are typically formed through chemical reactions between the metal substrate and a chemical solution. The conversion coating chemically reacts with the metal surface, resulting in a thin, tightly adhering protective layer. Examples of conversion coatings include chromate, phosphate, and oxide coatings. These coatings not only provide a barrier against hydrogen diffusion but also enhance the corrosion resistance of the metal.
Organic coatings, such as paints or polymer coatings, offer additional protection against hydrogen embrittlement. These coatings form a physical barrier between the metal surface and the environment. They provide excellent adhesion, flexibility, and resistance to environmental factors. Organic coatings can be applied through various methods, including spray coating, dip coating, or powder coating. They can be formulated with additives to further enhance their resistance to hydrogen ingress.
Thermally sprayed coatings offer several advantages in the context of hydrogen embrittlement prevention. The coating materials used in this process are often composed of materials with excellent resistance to hydrogen diffusion, such as ceramics or cermet alloys. These materials have a low permeability to hydrogen, creating a robust barrier against hydrogen ingress into the metal substrate. | 7 | Physical Chemistry |
The high electronegativity of fluorine (4.0 for fluorine vs. 2.5 for carbon) gives the carbon–fluorine bond a significant polarity or dipole moment. The electron density is concentrated around the fluorine, leaving the carbon relatively electron poor. This introduces ionic character to the bond through partial charges (C—F). The partial charges on the fluorine and carbon are attractive, contributing to the unusual bond strength of the carbon–fluorine bond. The bond is labeled as "the strongest in organic chemistry," because fluorine forms the strongest single bond to carbon. Carbon–fluorine bonds can have a bond dissociation energy (BDE) of up to 130 kcal/mol. The BDE (strength of the bond) of C–F is higher than other carbon–halogen and carbon–hydrogen bonds. For example, the BDEs of the C–X bond within a CH–X molecule is 115, 104.9, 83.7, 72.1, and 57.6 kcal/mol for X = fluorine, hydrogen, chlorine, bromine, and iodine, respectively. | 0 | Organic Chemistry |
The dissociation constant is commonly used to describe the affinity between a ligand (such as a drug) and a protein ; i.e., how tightly a ligand binds to a particular protein. Ligand–protein affinities are influenced by non-covalent intermolecular interactions between the two molecules such as hydrogen bonding, electrostatic interactions, hydrophobic and van der Waals forces. Affinities can also be affected by high concentrations of other macromolecules, which causes macromolecular crowding.
The formation of a ligand–protein complex can be described by a two-state process
the corresponding dissociation constant is defined
where , and represent molar concentrations of the protein, ligand, and protein–ligand complex, respectively.
The dissociation constant has molar units (M) and corresponds to the ligand concentration at which half of the proteins are occupied at equilibrium, i.e., the concentration of ligand at which the concentration of protein with ligand bound equals the concentration of protein with no ligand bound . The smaller the dissociation constant, the more tightly bound the ligand is, or the higher the affinity between ligand and protein. For example, a ligand with a nanomolar (nM) dissociation constant binds more tightly to a particular protein than a ligand with a micromolar (μM) dissociation constant.
Sub-picomolar dissociation constants as a result of non-covalent binding interactions between two molecules are rare. Nevertheless, there are some important exceptions. Biotin and avidin bind with a dissociation constant of roughly 10 M = 1 fM = 0.000001 nM.
Ribonuclease inhibitor proteins may also bind to ribonuclease with a similar 10 M affinity.
The dissociation constant for a particular ligand–protein interaction can change with solution conditions (e.g., temperature, pH and salt concentration). The effect of different solution conditions is to effectively modify the strength of any intermolecular interactions holding a particular ligand–protein complex together.
Drugs can produce harmful side effects through interactions with proteins for which they were not meant to or designed to interact. Therefore, much pharmaceutical research is aimed at designing drugs that bind to only their target proteins (negative design) with high affinity (typically 0.1–10 nM) or at improving the affinity between a particular drug and its in vivo protein target (positive design). | 7 | Physical Chemistry |
Compounds with disphenoidal (see-saw) geometry have two types of ligands: axial and equatorial. The axial pair lie along a common bond axis so that are related by a bond angle of 180°. The equatorial pair of ligands is situated in a plane orthogonal to the axis of the axial pair. Typically the bond distance to the axial ligands is longer than to the equatorial ligands. The ideal angle between the axial ligands and the equatorial ligands is 90°; whereas the ideal angle between the two equatorial ligands themselves is 120°.
Disphenoidal molecules, like trigonal bipyramidal ones, are subject to Berry pseudorotation in which the axial ligands move to equatorial positions and vice versa. This exchange of positions results in similar time-averaged environments for the two types of ligands. Thus, the F NMR spectrum of SF (like that of PF) consists of single resonance near room temperature. The four atoms in motion act as a lever about the central atom; for example, the four fluorine atoms of sulfur tetrafluoride rotate around the sulfur atom. | 4 | Stereochemistry |
Sulfonyl fluorides have the general formula RSOF. They can be produced by treating sulfonic acids with sulfur tetrafluoride:
Perfluorooctanesulfonyl derivatives, such as PFOS, are produced from their sulfonyl fluoride, which are produced by electrofluorination
In the molecular biology, sulfonyl fluorides are used to label proteins. They specifically react with serine, threonine, tyrosine, lysine, cysteine, and histidine residues. The fluorides are more resistant than the corresponding chlorides and are therefore better suited to this task.
Some sulfonyl fluorides can also be used as deoxyfluorinating reagents, such as 2-pyridinesulfonyl fluoride (PyFluor) and N-tosyl-4-chlorobenzenesulfonimidoyl fluoride (SulfoxFluor). | 0 | Organic Chemistry |
Despite flucloxacillin being insensitive to beta-lactamases, some organisms have developed resistance to it and other narrow-spectrum β-lactam antibiotics including methicillin. Such organisms include methicillin-resistant Staphylococcus aureus, which has developed resistance to flucloxacillin and other penicillins by having an altered penicillin-binding protein. | 4 | Stereochemistry |
A B2 intermetallic compound has equal numbers of atoms of two metals such as aluminium and iron, arranged as two interpenetrating simple cubic lattices of the component metals. | 8 | Metallurgy |
Léon-Albert Arnaud (15 February 1853 – 27 March 1915) was a French chemist born in Paris.
From 1872 he worked as an assistant in the laboratory of Michel Eugène Chevreul (1786–1889) at the Muséum national dhistoire naturelle. In 1883 he succeeded François Stanislas Cloez (1817–1883) as aide-naturaliste', and from 1890 to 1915 was chair of applied organic chemistry at the museum.
Arnaud was the first scientist to describe the chemical make-up of tariric acid, an extraction from the glucoside of the "tariri plant" found in Guatemala. He is also credited with isolating tanghinine, taken from Tanghinia venenifera; (family Apocynaceae), and in 1883 discovered a new alkaloid called cinchonamine. | 0 | Organic Chemistry |
The track of the first competition is a gold surface, equipped with grooves to define race lanes in order to avoid losing vehicles. It is about 100 nanometres long, and includes two bends. It is located in a small enclosure cooled to -269°C under a primary vacuum of 10 mbar and is observed simultaneously by four scanning tunneling microscopes (STM) miniaturized for this event and operating on the same surface. Each microscope is responsible for driving a single vehicle (a single nanocar).
During this competition, the nanocars should move as far as possible on the gold track during the 36 hours race. Speeds of 5 nanometers per hour were expected. | 6 | Supramolecular Chemistry |
Photoautotrophs are organisms that can utilize light energy from sunlight and elements (such as carbon) from inorganic compounds to produce organic materials needed to sustain their own metabolism (i.e. autotrophy). This biological activity is known as photosynthesis, and examples of such photosynthetic organisms include plants, algae and cyanobacteria.
Eukaryotic photoautotrophs absorb photon energy through the photopigment chlorophyll (a porphyrin derivative) in their endosymbiont chloroplasts, which splits water and carbon dioxide to synthesize carbohydrates that can be metabolized later to produce adenosine triphosphate (ATP). Prokaryotic photoautotrophs use both chlorophylls and bacteriochlorophylls (which split hydrogen sulfide instead of water) present in free-floating cytoplasmic thylakoids to produce carbohydrates, or, in rare cases, use membrane-bound retinal derivatives such as bacteriorhodopsin proton pumps which captures light to directly produce ATP. The vast majority of known photoautotrophs perform photosynthesis that split water molecules to produce oxygen as a byproduct, while a small minority (such as haloarchaea and sulfur-reducing bacteria) perform anoxygenic photosynthesis. | 5 | Photochemistry |
These thermocouples are well-suited for measuring extremely high temperatures. Typical uses are hydrogen and inert atmospheres, as well as vacuum furnaces. They are not used in oxidizing environments at high temperatures because of embrittlement. A typical range is 0 to 2315 °C, which can be extended to 2760 °C in inert atmosphere and to 3000 °C for brief measurements.
Pure tungsten at high temperatures undergoes recrystallization and becomes brittle. Therefore, types C and D are preferred over type G in some applications.
In presence of water vapor at high temperature, tungsten reacts to form tungsten(VI) oxide, which volatilizes away, and hydrogen. Hydrogen then reacts with tungsten oxide, after which water is formed again. Such a "water cycle" can lead to erosion of the thermocouple and eventual failure. In high temperature vacuum applications, it is therefore desirable to avoid the presence of traces of water.
An alternative to tungsten/rhenium is tungsten/molybdenum, but the voltage–temperature response is weaker and has minimum at around 1000 K.
The thermocouple temperature is limited also by other materials used. For example beryllium oxide, a popular material for high temperature applications, tends to gain conductivity with temperature; a particular configuration of sensor had the insulation resistance dropping from a megaohm at 1000 K to 200 ohms at 2200 K. At high temperatures, the materials undergo chemical reaction. At 2700 K beryllium oxide slightly reacts with tungsten, tungsten-rhenium alloy, and tantalum; at 2600 K molybdenum reacts with BeO, tungsten does not react. BeO begins melting at about 2820 K, magnesium oxide at about 3020 K. | 8 | Metallurgy |
Fluorescence spectroscopy is used in, among others, biochemical, medical, and chemical research fields for analyzing organic compounds. There has also been a report of its use in differentiating malignant skin tumors from benign.
Atomic Fluorescence Spectroscopy (AFS) techniques are useful in other kinds of analysis/measurement of a compound present in air or water, or other media, such as CVAFS which is used for heavy metals detection, such as mercury.
Fluorescence can also be used to redirect photons, see fluorescent solar collector.
Additionally, Fluorescence spectroscopy can be adapted to the microscopic level using microfluorimetry
In analytical chemistry, fluorescence detectors are used with HPLC.
In the field of water research, fluorescence spectroscopy can be used to monitor water quality by detecting organic pollutants. Recent advances in computer science and machine learning have even enabled detection of bacterial contamination of water | 7 | Physical Chemistry |
Fermentation of sugar to ethanol and can also be done by Zymomonas mobilis, however the path is slightly different since formation of pyruvate does not happen by glycolysis but instead by the Entner–Doudoroff pathway.
Other microorganisms can produce ethanol from sugars by fermentation but often only as a side product. Examples are
* Heterolactic acid fermentation in which Leuconostoc bacteria produce lactate + ethanol +
* Mixed acid fermentation where Escherichia produce ethanol mixed with lactate, acetate, succinate, formate, , and H
* 2,3-butanediol fermentation by Enterobacter producing ethanol, butanediol, lactate, formate, , and H | 1 | Biochemistry |
Diaryl-strained-cyclooctynes including dibenzylcyclooctyne (DIBO) have also been used to react with 1,3-nitrones in strain-promoted alkyne-nitrone cycloadditions (SPANC) to yield N-alkylated isoxazolines.
Because this reaction is metal-free and proceeds with fast kinetics (k2 as fast as 60 1/Ms, faster than both the CuAAC or the SPAAC) SPANC can be used for live cell labeling. Moreover, substitution on both the carbon and nitrogen atoms of the nitrone dipole, and acyclic and endocyclic nitrones are all tolerated. This large allowance provides a lot of flexibility for nitrone handle or probe incorporation.
However, the isoxazoline product is not as stable as the triazole product of the CuAAC and the SpAAC, and can undergo rearrangements at biological conditions. Regardless, this reaction is still very useful as it has notably fast reaction kinetics.
The applications of this reaction include labeling proteins containing serine as the first residue: the serine is oxidized to aldehyde with NaIO and then converted to nitrone with p-methoxybenzenethiol, N-methylhydroxylamine and p-ansidine, and finally incubated with cyclooctyne to give a click product. The SPANC also allows for multiplex labeling. | 0 | Organic Chemistry |
Dissimilatory metal-reducing microorganisms are a group of microorganisms (both bacteria and archaea) that can perform anaerobic respiration utilizing a metal as terminal electron acceptor rather than molecular oxygen (O), which is the terminal electron acceptor reduced to water (HO) in aerobic respiration. The most common metals used for this end are iron [Fe(III)] and manganese [Mn(IV)], which are reduced to Fe(II) and Mn(II) respectively, and most microorganisms that reduce Fe(III) can reduce Mn(IV) as well. But other metals and metalloids are also used as terminal electron acceptors, such as vanadium [V(V)], chromium [Cr(VI)], molybdenum [Mo(VI)], cobalt [Co(III)], palladium [Pd(II)], gold [Au(III)], and mercury [Hg(II)]. | 1 | Biochemistry |
Thioketenes are electrophilic. They add amines to give thioamides:
With peroxyacids, they produce thioketene-S-oxides:
Thioketenes bind to metal carbonyls giving adducts. | 0 | Organic Chemistry |
Take samples from the chamber and let them dry in the room air. An initial assessment is made before any corrosion products are removed. When the tested parts are cleaned, the evaluation criteria must be taken into account.
Possible characteristics for evaluation: appearance after the test, appearance after removal of the corrosion products, number and size of imperfections, time to first corrosion, loss of mass.
The results are described in a test report. | 8 | Metallurgy |
A cubane-type cluster is an arrangement of atoms in a molecular structure that forms a cube. In the idealized case, the eight vertices are symmetry equivalent and the species has O symmetry. Such a structure is illustrated by the hydrocarbon cubane. With chemical formula , cubane has carbon atoms at the corners of a cube and covalent bonds forming the edges. Most cubanes have more complicated structures, usually with nonequivalent vertices. They may be simple covalent compounds or macromolecular or supramolecular cluster compounds. | 4 | Stereochemistry |
L-isoaspartyl methyltransferase repairs isoaspartate and D-aspartate residues by sticking a methyl group onto the side chain carboxyl group in the residue, creating an ester. The ester rapidly and spontaneously turns into the succinimide (red), and randomly turns back into normal aspartic acid (black) or isoaspartate again (green) for another attempt. | 1 | Biochemistry |
A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, by retrotransposon mobile genetic elements to proliferate within the host genome, and by eukaryotic cells to extend the telomeres at the ends of their linear chromosomes. Contrary to a widely held belief, the process does not violate the flows of genetic information as described by the classical central dogma, as transfers of information from RNA to DNA are explicitly held possible.
Retroviral RT has three sequential biochemical activities: RNA-dependent DNA polymerase activity, ribonuclease H (RNase H), and DNA-dependent DNA polymerase activity. Collectively, these activities enable the enzyme to convert single-stranded RNA into double-stranded cDNA. In retroviruses and retrotransposons, this cDNA can then integrate into the host genome, from which new RNA copies can be made via host-cell transcription. The same sequence of reactions is widely used in the laboratory to convert RNA to DNA for use in molecular cloning, RNA sequencing, polymerase chain reaction (PCR), or genome analysis. | 1 | Biochemistry |
Levonorgestrel is a weak agonist of the androgen receptor (AR), the main biological target of the androgen sex hormone testosterone. It is a weakly androgenic progestin and in women may cause androgenic biochemical changes and side effects such as decreased sex hormone-binding globulin (SHBG) levels, decreased cholesterol levels, weight gain, and acne.
In combination with a potent estrogen like ethinylestradiol however, all contraceptives containing androgenic progestins are negligibly androgenic in practice and in fact can be used to treat androgen-dependent conditions like acne and hirsutism in women. This is because ethinylestradiol causes a marked increase in SHBG levels and thereby decreases levels of free and hence bioactive testosterone, acting as a functional antiandrogen. Nonetheless, contraceptives containing progestins that are less androgenic increase SHBG levels to a greater extent and may be more effective for such indications. Levonorgestrel is currently the most androgenic progestin that is used in contraceptives, and contraceptives containing levonorgestrel may be less effective for androgen-dependent conditions relative to those containing other progestins that are less androgenic. | 4 | Stereochemistry |
The thermodynamic formalism allows that a system may have contact with several other systems at once, which may or may not also have mutual contact, the contacts having respectively different permeabilities. If these systems are all jointly isolated from the rest of the world those of them that are in contact then reach respective contact equilibria with one another.
If several systems are free of adiabatic walls between each other, but are jointly isolated from the rest of the world, then they reach a state of multiple contact equilibrium, and they have a common temperature, a total internal energy, and a total entropy. Amongst intensive variables, this is a unique property of temperature. It holds even in the presence of long-range forces. (That is, there is no "force" that can maintain temperature discrepancies.) For example, in a system in thermodynamic equilibrium in a vertical gravitational field, the pressure on the top wall is less than that on the bottom wall, but the temperature is the same everywhere.
A thermodynamic operation may occur as an event restricted to the walls that are within the surroundings, directly affecting neither the walls of contact of the system of interest with its surroundings, nor its interior, and occurring within a definitely limited time. For example, an immovable adiabatic wall may be placed or removed within the surroundings. Consequent upon such an operation restricted to the surroundings, the system may be for a time driven away from its own initial internal state of thermodynamic equilibrium. Then, according to the second law of thermodynamics, the whole undergoes changes and eventually reaches a new and final equilibrium with the surroundings. Following Planck, this consequent train of events is called a natural thermodynamic process. It is allowed in equilibrium thermodynamics just because the initial and final states are of thermodynamic equilibrium, even though during the process there is transient departure from thermodynamic equilibrium, when neither the system nor its surroundings are in well defined states of internal equilibrium. A natural process proceeds at a finite rate for the main part of its course. It is thereby radically different from a fictive quasi-static process that proceeds infinitely slowly throughout its course, and is fictively reversible. Classical thermodynamics allows that even though a process may take a very long time to settle to thermodynamic equilibrium, if the main part of its course is at a finite rate, then it is considered to be natural, and to be subject to the second law of thermodynamics, and thereby irreversible. Engineered machines and artificial devices and manipulations are permitted within the surroundings. The allowance of such operations and devices in the surroundings but not in the system is the reason why Kelvin in one of his statements of the second law of thermodynamics spoke of "inanimate" agency; a system in thermodynamic equilibrium is inanimate.
Otherwise, a thermodynamic operation may directly affect a wall of the system.
It is often convenient to suppose that some of the surrounding subsystems are so much larger than the system that the process can affect the intensive variables only of the surrounding subsystems, and they are then called reservoirs for relevant intensive variables. | 7 | Physical Chemistry |
Backscattering is the principle behind radar systems. In weather radar, backscattering is proportional to the 6th power of the diameter of the target multiplied by its inherent reflective properties, provided the wavelength is larger than the particle diameter (Rayleigh scattering). Water is almost 4 times more reflective than ice but droplets are much smaller than snow flakes or hail stones. So the backscattering is dependent on a mix of these two factors. The strongest backscatter comes from hail and large graupel (solid ice) due to their sizes, but non-Rayleigh (Mie scattering) effects can confuse interpretation. Another strong return is from melting snow or wet sleet, as they combine size and water reflectivity. They often show up as much higher rates of precipitation than actually occurring in what is called a brightband. Rain is a moderate backscatter, being stronger with large drops (such as from a thunderstorm) and much weaker with small droplets (such as mist or drizzle). Snow has rather weak backscatter. Dual polarization weather radars measure backscatter at horizontal and vertical polarizations to infer shape information from the ratio of the vertical and horizontal signals. | 7 | Physical Chemistry |
Esomeprazole can be used as a parasiticide. Gokmen et al., 2016 screen for efficacy against Trichomonas vaginalis isolates from horses. They found esomeprazole to be effective as a veterinary antiparasitic. | 4 | Stereochemistry |
Tamiflu is a carbocyclic mimic of the cell-surface carbohydrate sialic acid. Tamiflu is an enzyme inhibitor that blocks the action of influenza virus neuraminidases (sialidases). | 1 | Biochemistry |
AMTEC requires energy input at modest elevated temperatures and thus is easily adapted to any heat source, including radioisotope, concentrated solar power, external combustion, or a nuclear reactor. A solar thermal power conversion system based on an AMTEC could have advantages over other technologies for some applications including (thermal energy storage with phase-change material) and power conversion in a compact unit. The overall system could achieve as high as 14 W/kg with present collector technology and future AMTEC conversion efficiencies. The energy storage system has the potential to batteries, and the temperatures at which the system operates allows long life and reduced radiator size (heat-reject temperature of 600 K).
NASA investigated AMTEC conversion as a next-generation radioisotope power source for deep-space applications, but the technology was not selected for the next-generation systems.
While space power systems are of intrinsic interest, terrestrial applications could offer large-scale applications for AMTEC systems. At the 25% efficiency projected for the device and projected costs of 350 USD/kW, AMTEC could prove useful for a very wide variety of distributed generation applications including self-powered fans for high-efficiency furnaces and water heaters and recreational vehicle power supplies. | 7 | Physical Chemistry |
The marine biological pump depends on a number of key pools, components and processes that influence its functioning. There are four main pools of carbon in the ocean.
* Dissolved inorganic carbon (DIC) is the largest pool. It constitutes around 38,000 Pg C and includes dissolved carbon dioxide (CO), bicarbonate (), carbonate (), and carbonic acid (). The equilibrium between carbonic acid and carbonate determines the pH of the seawater. Carbon dioxide dissolves easily in water and its solubility is inversely related to temperature. Dissolved CO is taken up in the process of photosynthesis, and can reduce the partial pressure of CO in the seawater, favouring drawdown from the atmosphere. The reverse process respiration, releases CO back into the water, can increase partial pressure of CO in the seawater, favouring release back to the atmosphere. The formation of calcium carbonate by organisms such as coccolithophores has the effect of releasing CO into the water.
* Dissolved organic carbon (DOC) is the next largest pool at around 662 Pg C. DOC can be classified according to its reactivity as refractory, semi-labile or labile. The labile pool constitutes around 0.2 Pg C, is bioavailable, and has a high production rate (~ 15−25 Pg C y). The refractory component is the biggest pool (~642 Pg C ± 32; but has a very low turnover rate (0.043 Pg C y). The turnover time for refractory DOC is thought to be greater than 1000 years.
* Particulate organic carbon (POC) constitutes around 2.3 Pg C, and is relatively small compared with DIC and DOC. Though small in size, this pool is highly dynamic, having the highest turnover rate of any organic carbon pool on the planet. Driven by primary production, it produces around 50 Pg C y globally. It can be separated into living (e.g. phytoplankton, zooplankton, bacteria) and non-living (e.g. detritus) material. Of these, the phytoplankton carbon is particularly important, because of its role in marine primary production, and also because it serves as the food resource for all the larger organisms in the pelagic ecosystem.
* Particulate inorganic carbon (PIC) is the smallest of the pools at around 0.03 Pg C. It is present in the form of calcium carbonate (CaCO) in particulate form, and impacts the carbonate system and pH of the seawater. Estimates for PIC production are in the region of 0.8–1.4 Pg C y, with at least 65% of it being dissolved in the upper water column, the rest contributing to deep sediments. Coccolithophores and foraminifera are estimated to be the dominant sources of PIC in the open ocean. The PIC pool is of particular importance due to its role in the ocean carbonate system, and in facilitating the export of carbon to the deep ocean through the carbonate pump, whereby PIC is exported out of the photic zone and deposited in the bottom sediments. | 9 | Geochemistry |
Ostwalds law of dilution, which gives the dissociation constant of a weak electrolyte as a function of concentration, can be written in terms of molar conductivity. Thus, the pK values of acids can be calculated by measuring the molar conductivity and extrapolating to zero concentration. Namely, pK = p() at the zero-concentration limit, where K is the dissociation constant from Ostwalds law. | 7 | Physical Chemistry |
Sucrose esters or sucrose fatty acid esters are a group of non-naturally occurring surfactants chemically synthesized from the esterification of sucrose and fatty acids (or glycerides). This group of substances is remarkable for the wide range of hydrophilic-lipophilic balance (HLB) that it covers. The polar sucrose moiety serves as a hydrophilic end of the molecule, while the long fatty acid chain serves as a lipophilic end of the molecule. Due to this amphipathic property, sucrose esters act as emulsifiers; i.e., they have the ability to bind both water and oil simultaneously. Depending on the HLB value, some can be used as water-in-oil emulsifiers, and some as oil-in-water emulsifiers. Sucrose esters are used in cosmetics, food preservatives, food additives, and other products. A class of sucrose esters with highly substituted hydroxyl groups, olestra, is also used as a fat replacer in food. | 0 | Organic Chemistry |
A typical Danheiser benzannulation reaction is run with a 0.4-2.0 M solution of the cyclobutenone in toluene heated at 80-160 °C with a slight excess of the cyclobutenone. Upon addition of the alkyne a [2+2] cycloaddition occurs. The crude annulation product is treated with 10% potassium hydroxide in methanol to saponify the ester side product formed from the reaction of the phenolic product with excess vinylketene (Scheme 6).
For the second generation reaction starting with the diazoketone, the reaction is performed by irradiation of a 0.7 M solution of the ketone with 1.0-1.2 equivalents of acetylene. A low-pressure mercury-vapor lamp at 254 nm in a photochemical reactor is used for 5–8 hours until all the diazoketone has been consumed as determined by TLC analysis. Dichloromethane, chloroform, and 1,2-dichloroethane, are all appropriate solvents for the annulation reaction. | 0 | Organic Chemistry |
Bhushan began his education in his native India, completing his undergraduate degree and his master's from the University of Jodhpur. He received his Ph.D. in chemistry (working on structure elucidation of natural products isolated from certain desert plants) in 1978 at the University of Jodhpur. Bhushan joined as lecturer at the University of Roorkee (now Indian Institute of Technology Roorkee, India) in 1979 and was later selected for the position of full professor of chemistry in 1996 and served there till retirement in 2018. | 3 | Analytical Chemistry |
Archaeometallurgical scientific knowledge and technological development originated in numerous centers of Africa; the centers of origin were located in West Africa, Central Africa, and East Africa; consequently, as these origin centers are located within inner Africa, these archaeometallurgical developments are thus native African technologies. Iron metallurgical development occurred 2631 BCE – 2458 BCE at Lejja, in Nigeria, 2136 BCE – 1921 BCE at Obui, in Central Africa Republic, 1895 BCE – 1370 BCE at Tchire Ouma 147, in Niger, and 1297 BCE – 1051 BCE at Dekpassanware, in Togo.
Though there is some uncertainty, some archaeologists believe that iron metallurgy was developed independently in sub-Saharan Africa (possibly in West Africa).
Inhabitants of Termit, in eastern Niger, smelted iron around 1500 BC.
In the region of the Aïr Mountains in Niger there are also signs of independent copper smelting between 2500 and 1500 BC. The process was not in a developed state, indicating smelting was not foreign. It became mature about 1500 BC.
Archaeological sites containing iron smelting furnaces and slag have also been excavated at sites in the Nsukka region of southeast Nigeria in what is now Igboland: dating to 2000 BC at the site of Lejja (Eze-Uzomaka 2009) and to 750 BC and at the site of Opi (Holl 2009). The site of Gbabiri (in the Central African Republic) has yielded evidence of iron metallurgy, from a reduction furnace and blacksmith workshop; with earliest dates of 896–773 BC and 907–796 BC respectively. Similarly, smelting in bloomery-type furnaces appear in the Nok culture of central Nigeria by about 550 BC and possibly a few centuries earlier.
There is also evidence that carbon steel was made in Western Tanzania by the ancestors of the Haya people as early as 2,300 to 2,000 years ago (about 300 BC or soon after) by a complex process of "pre-heating" allowing temperatures inside a furnace to reach 1300 to 1400 °C.
Iron and copper working spread southward through the continent, reaching the Cape around AD 200. The widespread use of iron revolutionized the Bantu-speaking farming communities who adopted it, driving out and absorbing the rock tool using hunter-gatherer societies they encountered as they expanded to farm wider areas of savanna. The technologically superior Bantu-speakers spread across southern Africa and became wealthy and powerful, producing iron for tools and weapons in large, industrial quantities.
The earliest records of bloomery-type furnaces in East Africa are discoveries of smelted iron and carbon in Nubia that date back between the 7th and 6th centuries BC, particularly in Meroe where there are known to have been ancient bloomeries that produced metal tools for the Nubians and Kushites and produced surplus for their economy. | 8 | Metallurgy |
Analysis of metabolic networks of proteins hearkens back to the 1940s, but it was not until the late 1990s and early 2000s that computational data-driven genomic analyses to predict functional context and networks of genetic associations appeared in earnest. Since then, the interactomes of many model organisms are considered to have been well characterized, notably the Saccharomyces cerevisiae Interactome and the Drosophila interactome.
High throughput experimental approaches for discovering protein–protein interactions typically perform a version of the two-hybrid screening approach or tandem affinity purification followed by mass spectrometry. Information from experiments and literature curation are compiled into databases of protein interactions, such as DIP, and BioGRID. A more recent effort, HINT-KB, attempts to amalgamate most of the current PPI databases, but filtering systematically erroneous interactions as well as trying to correct for inherent sociological sampling biases in literature curated datasets.
Smaller human interactome networks have been described in the specific context of important drivers of many different disorders, including neurodegenerative disorders, autism and other psychiatric disorders, and cancer. Cancer gene networks have been particularly well studied, due in part to large genome initiatives such as The Cancer Genome Atlas (TCGA). A large portion of the mutational landscape including intra-tumoural heterogeneity has been mapped for most common types of cancers (for example, breast cancer has been well studied), and many studies have also investigated the difference between active driver genes and passive passenger mutations in the context of cancer interaction networks.
The first attempts at large-scale integrative human interactome mapping occurred around 2005. Stetzl et al. used a protein matrix of 4500 baits and 5600 preys in a yeast two hybrid system to piece together the interactome, and Rual et al. performed a similar yeast-two hybrid study verified with co-affinity purification and correlation with other biological attributes, revealing more than 300 connections to 100 disease-associated proteins. Since those pioneering efforts, hundreds of similar studies have been conducted. Compiled databases such as UniHI provide platform for single entry. Futschik et al. performed a meta analysis of eight interactome maps and found that of 57 000 interacting proteins in total, there was a small (albeit statistically significant) overlap between the different databases, indicating considerable selection and detection biases.
In 2010, around 130 000 binary interactions in the interactome were described in the most popular databases, but many were verified with only one source. With the rapid development of high throughput methods, datasets still suffer from high rates of false positives and low coverage of the interactome. Tyagi et al. described a novel framework for incorporating structural complexes and binding interfaces for verification. This was part of much larger efforts for PPI verification; interaction networks are typically validated further by using a combination of coexpression profiles, protein structural information, Gene ontology terms, topological considerations, and colocalization before being considered “high-confidence”.
A recent resource paper (November 2014) attempts to provide a more comprehensive proteome level map of the human interactome. It found vast uncharted territory in the human interactome, and used diverse methods to build a new interactome map correcting for curation bias, including probing all pairwise combinations of 13 000 protein products for interaction using Yeast two hybrid and co-affinity purification, in a massive coordinated effort across research labs in Canada and the United States. However, this still represents confirmation of but a fraction of expected interactions – around 30 000 of high confidence. Despite the coordinated efforts of many, the human interactome is still very much a work in progress. | 1 | Biochemistry |
Early evolution is defined as beginning with the origin of life and ending with the last universal common ancestor (LUCA). According to the iron–sulfur world theory it covers a coevolution of cellular organization (cellularization), the genetic machinery and enzymatization of the metabolism. | 1 | Biochemistry |
The washability analysis is widely known in bulk material analysis, where the specific density is the physical property describing the liberation and the separation results, which is then in the form of the partition curve. The partition curve is defined as the curve which gives as a function of a physical property or characteristic, the proportions in which different elemental classes of raw feed having the same property are split into separate products. It is thus per its definition not limited to, but predominantly applied in analysis of liberation and process efficiency of density separation processes. For sensor-based ore sorting, the partition (also called Tromp) curves for chromite, iron ore and coal are known and can thus be applied for process modelling. | 3 | Analytical Chemistry |
Other equations now exist that refine the original Hammett equation: the Swain–Lupton equation, the Taft equation, the Grunwald–Winstein equation, and the Yukawa–Tsuno equation. An equation that addresses stereochemistry in aliphatic systems has also been developed. | 7 | Physical Chemistry |
Using ethenolysis, higher molecular weight internal alkenes can be converted to more valuable terminal alkenes. The Shell higher olefin process (SHOP process) uses ethenolysis on an industrial scale. The SHOP α-olefin mixtures are separated by distillation, the higher molecular weight fractions are isomerized by alkaline alumina catalysts in the liquid phase. The resulting internal olefins are reacted with ethylene to regenerate α-olefins. The large excess of ethylene moves the reaction equilibrium to the terminal α-olefins. Catalysts are often prepared from Rhenium(VII) oxide () supported on alumina.
In one application, neohexene, a precursor to perfumes, is prepared by ethenolysis of diisobutene:
α,ω-Dienes, i.e., diolefins of the formula , are prepared industrially by ethenolysis of cyclic alkenes. For example, 1,5-hexadiene, a useful crosslinking agent and synthetic intermediate, is produced from 1,5-cyclooctadiene:
The catalyst is derived from rhenium(VII) oxide supported on alumina. 1,9-Decadiene, a related species, is produced similarly from cyclooctene.
In an application directed at using renewable feedstocks, methyl oleate, derived from natural seed oils, can be converted to 1-decene and methyl 9-decenoate: | 0 | Organic Chemistry |
Continuous network models of GRNs are an extension of the Boolean networks described above. Nodes still represent genes and connections between them regulatory influences on gene expression. Genes in biological systems display a continuous range of activity levels and it has been argued that using a continuous representation captures several properties of gene regulatory networks not present in the Boolean model. Formally most of these approaches are similar to an artificial neural network, as inputs to a node are summed up and the result serves as input to a sigmoid function, e.g., but proteins do often control gene expression in a synergistic, i.e. non-linear, way. However, there is now a continuous network model that allows grouping of inputs to a node thus realizing another level of regulation. This model is formally closer to a higher order recurrent neural network. The same model has also been used to mimic the evolution of cellular differentiation and even multicellular morphogenesis. | 1 | Biochemistry |
Methods of nuclear spectroscopy use properties of a nucleus to probe a materials properties, especially the materials local structure. Common methods include nuclear magnetic resonance spectroscopy (NMR), Mössbauer spectroscopy (MBS), and perturbed angular correlation (PAC). | 3 | Analytical Chemistry |
Some of the benefits of BNAs include ideal for the detection of short RNA and DNA targets; increase the thermal stability of duplexes; capable of single nucleotide discrimination; increases the thermal stability of triplexes; resistance to exo- and endonucleases resulting in a high stability for in vivo and in vitro applications; increased target specificity; facilitate Tm normalization; strand invasion enables detection of "hard to access" samples; compatible with standard enzymatic processes. | 1 | Biochemistry |
In particle physics, the Klein–Nishina formula gives the differential cross section (i.e. the "likelihood" and angular distribution) of photons scattered from a single free electron, calculated in the lowest order of quantum electrodynamics. It was first derived in 1928 by Oskar Klein and Yoshio Nishina, constituting one of the first successful applications of the Dirac equation. The formula describes both the Thomson scattering of low energy photons (e.g. visible light) and the Compton scattering of high energy photons (e.g. x-rays and gamma-rays), showing that the total cross section and expected deflection angle decrease with increasing photon energy. | 7 | Physical Chemistry |
In gravimetric method, the weight change of the adsorbent sample in the gravity field due to adsorption from the gas phase is recorded. Various types of sensitive microbalance have been developed for this purpose. A continuous-flow gravimetric technique coupled with wavelet rectification allows for higher precision, especially in the near-critical region.
Major advantages of gravimetric method include sensitivity, accuracy, and the possibility of checking the state of activation of an adsorbent sample. However, consideration must be given to buoyancy correction in gravimetric measurement. A counterpart is used for this purpose. The solid sample is placed in a sample holder on one arm of the microbalance while the counterpart is loaded on the other arm. Care must be taken to keep the volume of the sample and the counterpart as close as possible to reduce the buoyancy effect. The system is vacuumed and the balance is zeroed before starting experiments. Buoyancy is measured by introducing helium and pressurizing up to the highest pressure of the experiment. It is assumed that helium does not adsorb and any weight change (ΔW) is due to buoyancy. Knowing the density of helium (), one can determine the difference in volume (ΔV) between the sample and the counterpart:
The measured weight can be corrected for the buoyancy effect at a specified temperature and pressure:
is the weight reading before correction. | 7 | Physical Chemistry |
Aqueous solutions of methanol can decompose into CO hydrogen gas, and water. Although this process is thermodynamically favored, the activation barrier is extremely high, so in practice this reaction is not typically observed. However, electrocatalysts can speed up this reaction greatly, making methanol a possible route to hydrogen storage for fuel cells. Electrocatalysts such as gold, platinum, and various carbon-based materials have been shown to effectively catalyze this process. An electrocatalyst of platinum and rhodium on carbon backed tin-dioxide nanoparticles can break carbon bonds at room temperature with only carbon dioxide as a by-product, so that ethanol can be oxidized into the necessary hydrogen ions and electrons required to create electricity. | 7 | Physical Chemistry |
An evaporative light scattering detector (ELSD) is a destructive chromatography detector, used in conjunction with high-performance liquid chromatography (HPLC), ultra high-performance liquid chromatography (UHPLC), purification liquid chromatography such as flash or preparative chromatography (using a splitter), countercurrent or centrifugal partition chromatography and supercritical fluid chromatography (SFC). It is commonly used for analysis of compounds that do not absorb UV-VIS radiation significantly, such as sugars, antiviral drugs, antibiotics, fatty acids, lipids, oils, phospholipids, polymers, surfactants, terpenoids and triglycerides.
ELSDs works by nebulizing the column's effluents into a fine aerosol mist, which then passes through a heated drift tube, where the solvent evaporates. Thus, it can be easily used in gradient method of LC and SFC. The remaining non-volatile analyte particles are carried further by a carrier gas to a light scattering cell, where a beam of light illuminates them and they scatter it. The scattered light proceeds to a photodiode which converts it to a signal, which is proportional to the mass of the analyte particles. This is why it is considered as a sort of "universal detector" as it is able to detect all compound which are less volatile than the mobile phase, i.e. non volatile and semi-volatile compounds.
ELSD is related to the charged aerosol detector (CAD), in which the aerosol is charged. Like the CAD, it falls under the category of destructive detectors. | 3 | Analytical Chemistry |
The first consumer commercial application was a shape-memory coupling for piping, e.g. oil pipe lines, for industrial applications, water pipes and similar types of piping for consumer/commercial applications. | 8 | Metallurgy |
EDC is a water-soluble carbodiimide reagent used for a wide range of purposes. Apart from uses similar to those of DCC and DIC, it is also used for various biochemical purposes as a crosslinker or chemical probe. | 0 | Organic Chemistry |
Unlike alkyl halide refrigerants that contain bromine or chlorine, R-410A (which contains only fluorine) does not contribute to ozone depletion and is therefore becoming more widely used as ozone-depleting refrigerants like R-22 are phased out. However, like methane, its global warming potential (GWP) is appreciably worse than CO for the time it persists. Because R410A is a 50% combination of CHF (HFC-32) and 50% CHFCF (HFC-125), it is not easy to express their combined effects in a single global warming potential (GWP), However, HFC-32 has a 4.9 year lifetime and a 100-year GWP of 675 and HFC-125 has a 29-year lifetime and a 100-year GWP of 3500. The combination has a GWP of 2088, higher than that of R-22 (100-year GWP=1810), and an atmospheric lifetime of nearly 30 years compared with the 12-year lifetime of R-22.
Since R-410A allows for higher SEER ratings than an R-22 system by reducing power consumption, the overall impact on global warming of R-410A systems can, in some cases, be lower than that of R-22 systems due to reduced greenhouse gas emissions from power plants. This assumes that the atmospheric leakage will be sufficiently managed. Under the assumption that preventing ozone depletion is more important in the short term than GWP reduction, R-410A is preferable to R-22. | 2 | Environmental Chemistry |
Glycan-Protein interactions represent a class of biomolecular interactions that occur between free or protein-bound glycans and their cognate binding partners. Intramolecular glycan-protein (protein-glycan) interactions occur between glycans and proteins that they are covalently attached to. Together with protein-protein interactions, they form a mechanistic basis for many essential cell processes, especially for cell-cell interactions and host-cell interactions. For instance, SARS-CoV-2, the causative agent of COVID-19, employs its extensively glycosylated spike (S) protein to bind to the ACE2 receptor, allowing it to enter host cells. The spike protein is a trimeric structure, with each subunit containing 22 N-glycosylation sites, making it an attractive target for vaccine search.
Glycosylation, i.e., the addition of glycans (a generic name for monosaccharides and oligosaccharides) to a protein, is one of the major post-translational modification of proteins contributing to the enormous biological complexity of life. Indeed, three different hexoses could theoretically produce from 1056 to 27,648 unique trisaccharides in contrast to only 6 peptides or oligonucleotides formed from 3 amino acids or 3 nucleotides respectively. In contrast to template-driven protein biosynthesis, the "language" of glycosylation is still unknown, making glycobiology a hot topic of current research given their prevalence in living organisms.
The study of glycan-protein interactions provides insight into the mechanisms of cell-signaling and allows to create better-diagnosing tools for many diseases, including cancer. Indeed, there are no known types of cancer that do not involve erratic patterns of protein glycosylation. | 1 | Biochemistry |
The number of peaks produced by a single element varies from 1 to more than 20. Tables of binding energies that identify the shell and spin-orbit of each peak produced by a given element are included with modern XPS instruments, and can be found in various handbooks and websites. Because these experimentally determined energies are characteristic of specific elements, they can be directly used to identify experimentally measured peaks of a material with unknown elemental composition.
Before beginning the process of peak identification, the analyst must determine if the binding energies of the unprocessed survey spectrum (0-1400 eV) have or have not been shifted due to a positive or negative surface charge. This is most often done by looking for two peaks that are due to the presence of carbon and oxygen. | 7 | Physical Chemistry |
The Polenske value (also known as the Polenske number) is a value determined when examining fat. It is an indicator of how much volatile fatty acid can be extracted from fat through saponification. It is equal to the number of milliliters of 0.1 normal alkali solution necessary for the neutralization of the water-insoluble volatile fatty acids distilled and filtered from 5 grams of a given saponified fat. (The hydroxide solution used in such a titration is typically made from sodium hydroxide, potassium hydroxide, or barium hydroxide.)
It is measure of the steam volatile and water insoluble fatty acids, chiefly caprylic, capric and lauric acids, present in oil and fat. The value is named for the chemist who developed it, Eduard Polenske.
The Reichert value and Kirschner value are related numbers based on similar tests. | 0 | Organic Chemistry |
Deformation mechanisms are commonly characterized as brittle, ductile, and brittle-ductile. The driving mechanism responsible is an interplay between internal (e.g. composition, grain size and lattice-preferred orientation) and external (e.g. temperature and fluid pressure) factors. These mechanisms produce a range of micro-structures studied in rocks to constrain the conditions, rheology, dynamics, and motions of tectonic events. More than one mechanism may be active under a given set of conditions and some mechanisms can develop independently. Detailed microstructure analysis can be used to define the conditions and timing under which individual deformation mechanisms dominate for some materials. Common deformation mechanisms processes include:
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(recovery) | 8 | Metallurgy |
Phosgene is a planar molecule as predicted by VSEPR theory. The C=O distance is 1.18 Å, the C−Cl distance is 1.74 Å and the Cl−C−Cl angle is 111.8°. Phosgene is a carbon oxohalide and it can be considered one of the simplest acyl chlorides, being formally derived from carbonic acid. | 0 | Organic Chemistry |
This section is not concerned with sculpture in bronze, but rather with the many artistic applications of the metal in connection with architecture, or with objects for ecclesiastical and domestic use. Why bronze was preferred in Italy, iron in Spain and Germany and brass in the Low Countries cannot be satisfactorily determined; national temperamente is impressed on the choice of metals and also on the methods of working them. Centres of artistic energy shift from one place to another owing to wars, conquests or migrations. | 8 | Metallurgy |
USP26 is a peptidase enzyme. The USP26 gene is an X-linked gene exclusively expressed in the testis and it codes for the ubiquitin-specific protease 26. The USP26 gene is found at Xq26.2 on the X-chromosome as a single exon. The enzyme that this gene encodes comprises 913 amino acid residues and it is 104 kilodalton in size, which is transcribed from a sequence of 2794 nucleotide base-pairs on the X-chromosome. The USP26 enzyme is a deubiquitinating enzyme that places a very significant role in the regulation of protein turnover during spermatogenesis. It is a testis-specific enzyme that is solely express in spermatogonia and can prevent the degradation of ubiquitinated USP26 substrates.
Recent research has suggested that defects in USP26 may be involved in some cases of male infertility, specifically Sertoli cell-only syndrome, and an absence of sperm in the ejaculate (azoospermia). | 1 | Biochemistry |
Photo-reflectance is a highly sensitive measurement technique and provides unmatched capability for characterizing the material and electronic properties of thin films. Photo-reflectance has been particularly important in basic research on semiconductors due to its ability to precisely determine semiconductor bandstructures (even at room temperature). As an optical technique, photo-reflectance would appear suited to industrial applications because it is non-contact, and because it has good spatial resolution. However, the need for spectroscopic information limits measurement speed, and consequently the adoption of spectroscopic photo-reflectance in industrial applications such as process control of microelectronics manufacturing.
Nevertheless, where spectroscopic information is not required, photo-reflectance techniques have been implemented in semiconductor manufacturing process control. For example, in the late 1980s, Therma-Wave, Inc. introduced the "Therma-Probe" photo-modulated reflectance system to the market for semiconductor process control equipment. The original Therma-Probe focused an intensity modulated pump laser beam onto a spot on a silicon sample, modulating the sample reflectance. The reflectance changes were detected by a coincident laser probe beam of 633 nanometer wavelength. At this wavelength no electro-reflectance signal is present, since it is far removed from any interband transitions in silicon. Rather, the mechanisms responsible for the Therma-Probe signal are thermo-modulation and the Drude free carrier effect. The Therma-Probe was used primarily for monitoring of the ion implantation process in silicon semiconductor manufacturing. Measurement systems such as the Therma-Probe are particularly desirable in process control of microelectronics manufacturing because they provide the ability to quickly verify the correct execution of process steps, without contacting the wafer or removing the wafer from the clean room. Generally a number of measurements will be made on certain areas of the wafer and compared with expected values. As long as the measured values are within a certain range, the wafers are passed for continued processing. (This is known as statistical process control.) Other photo-modulated reflectance systems marketed for process control of implant processes are the "TWIN" metrology system marketed by [http://www.pvatepla.com/en/home PVA TePla AG], and the "PMR-3000" marketed by [https://www.semilab.hu/ Semilab Co. Ltd] (originally Boxer-Cross, Inc.).
However, by the mid 2000s, new manufacturing processes were requiring new process control capabilities, for example the need for control of new "diffusion-less" annealing processes and advanced strained silicon processes. To address these new process control requirements, in 2007, [https://xcalipr.com Xitronix Corporation] introduced a photo-reflectance system to the semiconductor process control market. Like the Therma-Probe, the Xitronix metrology system utilized a fixed wavelength probe beam generated by a laser. However, the probe beam of the Xitronix system had a wavelength of approximately 375 nanometers, near the first major interband transition in silicon. At this wavelength the electro-modulation signal is dominant, which enabled the Xitronix system to precisely measure active doping concentration in diffusion-less annealing processes. This probe beam wavelength also provided excellent sensitivity to strain in strained silicon processes. More recently, the use of laser photo-reflectance technology for precision measurement of carrier diffusion lengths, recombination lifetimes, and mobilities has been demonstrated. | 7 | Physical Chemistry |
Indo-1 is a popular calcium indicator similar to Fura-2. In contrast to Fura-2, Indo-1 has a dual emissions peak. The main emission peak in calcium-free solution is 475 nm while in the presence of calcium the emission is shifted to 400 nm. It is widely used in flow cytometry.
The penta potassium salt is commercially available and preferred to the free acid because of its higher solubility in water. While Indo-1 is not cell permeable the penta acetoxymethyl ester Indo-1 AM enters the cell where it is cleaved by intracellular esterases to Indo-1.
The synthesis and properties of Indo-1 were presented in 1985 by the group of Roger Y Tsien. | 1 | Biochemistry |
Deprotonation of carbene precursor salts with strong bases has proved a reliable route to almost all stable carbenes:
Imidazol-2-ylidenes and dihydroimidazol-2-ylidenes, such IMes, have been prepared by the deprotonation of the respective imidazolium and dihydroimidazolium salts. The acyclic carbenes and the tetrahydropyrimidinyl based carbenes were prepared by deprotonation using strong homogeneous bases.
Several bases and reaction conditions have been employed with varying success. The degree of success has been principally dependent on the nature of the precursor being deprotonated. The major drawback with this method of preparation is the problem of isolation of the free carbene from the metals ions used in their preparation. | 0 | Organic Chemistry |
The purest copper is obtained by an electrolytic process, undertaken using a slab of impure copper as the anode and a thin sheet of pure copper as the cathode. The electrolyte is an acidic solution of copper sulphate. By passing electricity through the cell, copper is dissolved from the anode and deposited on the cathode. However impurities either remain in solution or collect as an insoluble sludge. This process only became possible following the invention of the dynamo; it was first used in South Wales in 1869. | 8 | Metallurgy |
The use of cloning for military purposes has also been explored in several fictional works. In Doctor Who, an alien race of armour-clad, warlike beings called Sontarans was introduced in the 1973 serial "The Time Warrior". Sontarans are depicted as squat, bald creatures who have been genetically engineered for combat. Their weak spot is a "probic vent", a small socket at the back of their neck which is associated with the cloning process. The concept of cloned soldiers being bred for combat was revisited in "The Doctors Daughter" (2008), when the Doctors DNA is used to create a female warrior called Jenny.
The 1977 film Star Wars was set against the backdrop of a historical conflict called the Clone Wars. The events of this war were not fully explored until the prequel films Attack of the Clones (2002) and Revenge of the Sith (2005), which depict a space war waged by a massive army of heavily armoured clone troopers that leads to the foundation of the Galactic Empire. Cloned soldiers are "manufactured" on an industrial scale, genetically conditioned for obedience and combat effectiveness. It is also revealed that the popular character Boba Fett originated as a clone of Jango Fett, a mercenary who served as the genetic template for the clone troopers. | 1 | Biochemistry |
Ipaktschi is known for the use of ethereal solutions of lithium perchlorate as a medium for organic reactions and organometallic chemistry. | 0 | Organic Chemistry |
Carbohydrate–protein interactions are the intermolecular and intramolecular interactions between protein and carbohydrate moieties. These interactions form the basis of specific recognition of carbohydrates by lectins. Carbohydrates are important biopolymers and have a variety of functions. Often carbohydrates serve a function as a recognition element. That is, they are specifically recognized by other biomolecules. Proteins which bind carbohydrate structures are known as lectins. Compared to the study of protein–protein and protein–DNA interaction, it is relatively recent that scientists get to know the protein–carbohydrate binding.
Many of these interactions involved carbohydrates found at the cell surface, as part of a membrane glycoprotein or glycolipid. These interactions can play a role in cellular adhesion and other cellular recognition events. Intramolecular carbohydrate–protein interactions refer to interactions between glycan and polypeptide moieties in glycoproteins or the glycosylated proteins. | 0 | Organic Chemistry |
The vast majority of organisms encode their genes in long strands of DNA (deoxyribonucleic acid). DNA consists of a chain made from four types of nucleotide subunits, each composed of: a five-carbon sugar (2-deoxyribose), a phosphate group, and one of the four bases adenine, cytosine, guanine, and thymine.
Two chains of DNA twist around each other to form a DNA double helix with the phosphate-sugar backbone spiraling around the outside, and the bases pointing inwards with adenine base pairing to thymine and guanine to cytosine. The specificity of base pairing occurs because adenine and thymine align to form two hydrogen bonds, whereas cytosine and guanine form three hydrogen bonds. The two strands in a double helix must, therefore, be complementary, with their sequence of bases matching such that the adenines of one strand are paired with the thymines of the other strand, and so on.
Due to the chemical composition of the pentose residues of the bases, DNA strands have directionality. One end of a DNA polymer contains an exposed hydroxyl group on the deoxyribose; this is known as the 3 end of the molecule. The other end contains an exposed phosphate group; this is the 5 end. The two strands of a double-helix run in opposite directions. Nucleic acid synthesis, including DNA replication and transcription occurs in the 5→3 direction, because new nucleotides are added via a dehydration reaction that uses the exposed 3' hydroxyl as a nucleophile.
The expression of genes encoded in DNA begins by transcribing the gene into RNA, a second type of nucleic acid that is very similar to DNA, but whose monomers contain the sugar ribose rather than deoxyribose. RNA also contains the base uracil in place of thymine. RNA molecules are less stable than DNA and are typically single-stranded. Genes that encode proteins are composed of a series of three-nucleotide sequences called codons, which serve as the "words" in the genetic "language". The genetic code specifies the correspondence during protein translation between codons and amino acids. The genetic code is nearly the same for all known organisms. | 1 | Biochemistry |
The slippery sequence for a +1 frameshift signal does not have the same motif, and instead appears to function by pausing the ribosome at a sequence encoding a rare amino acid. Ribosomes do not translate proteins at a steady rate, regardless of the sequence. Certain codons take longer to translate, because there are not equal amounts of tRNA of that particular codon in the cytosol. Due to this lag, there exist in small sections of codons sequences that control the rate of ribosomal frameshifting. Specifically, the ribosome must pause to wait for the arrival of a rare tRNA, and this increases the kinetic favorability of the ribosome and its associated tRNA slipping into the new frame. In this model, the change in reading frame is caused by a single tRNA slip rather than two. | 1 | Biochemistry |
As the anode materials used are generally more costly than iron, using this method to protect ferrous metal structures may not appear to be particularly cost effective. However, consideration should also be given to the costs incurred to repair a corroded hull or to replace a steel pipeline or tank because their structural integrity has been compromised by corrosion.
However, there is a limit to the cost effectiveness of a galvanic system. On larger structures, such as long pipelines, so many anodes may be needed that it would be more cost-effective to install impressed current cathodic protection. | 7 | Physical Chemistry |
An inhibitor is usually a material added in a small quantity to a particular environment that reduces the rate of corrosion. They may be classified a number of ways but are usually 1) Oxidizing; 2) Scavenging; 3) Vapor-phase inhibitors; Sometimes they are called Volatile corrosion inhibitor 4) Adsorption inhibitors; 5) Hydrogen-evolution retarder. Another way to classify them is chemically. As there is more concern for the environment and people are more keen to use Renewable resources, there is ongoing research to modify these materials so they may be used as corrosion inhibitors. | 8 | Metallurgy |
The outbreak of hostilities in eastern Ukraine in 2014 complicated the activities of the enterprise. As a result, the plant ended 2014 with a net loss of UAH 4,871.533 million. In the first nine months of 2015, the plant produced 426 thousand tons of pig iron and 1.664 million tons of grade K coal concentrate, but losses continued to increase.
In June 2016, the leadership of the unrecognized DPR introduced external management at the plant, by which time its communications and a significant part of the equipment had become unusable due to repeated shutdowns and long downtime.
Also in June 2016, on the basis of the Donetsk Electrometallurgical Plant (DEMP), the state enterprise Yuzovsky Metallurgical Plant was opened. The YuMZ industrial complex is located on the same territory as the Donetsk Metallurgical Plant, which, in turn, is located in three districts of the DPR capital at once - Voroshilovsky, Budenovsky, Leninsk.
It was Re-launched on October 5, 2017.
In 2018 YuMZ began to supply products to Turkey, Iran and Syria.
Since May 1, 2019, blast-furnace production has been stopped. The company does not manufacture products. During the heating period of 2019–2020, only the factory CHPP-PVS and related power plants worked, in order to supply heat to part of the above three districts of the city of Donetsk.
From March to August 2020, the plant suspended work due to a shortage of raw materials. As of November 2020, the YuMZ complex, separated from the main part of the plant, continues to produce steel, specializing in the production of continuously cast square billets. The workforce consists of 858 people.
At the DMZ, there are energy workshops that provide transit and supply to factory consumers and sub-consumers of drinking and industrial water, electricity, natural gas, steam and hot water. | 8 | Metallurgy |
In July 2007, officials of the People's Republic of China seized US-produced pork for containing ractopamine residues. Further shipments of Canadian ractopamine-fed pork were seized in September 2007.
In June 2019, customs inspectors in China detected ractopamine in a shipment of Canadian pork products destined for Chinese consumption. The Chinese government thereupon suspended not only pork, but also beef imports from Canada. Canadian Agriculture Minister Marie-Claude Bibeau stated that the CRFPCP certificate was a forgery and called in the RCMP, while Canadian Public Safety Minister Ralph Goodale stressed that the federal government would vigorously defend Canadian meat producers. It was also revealed that the Canadian Cattlemen's Association said in a statement that "We are fully confident in our meat production systems in Canada and the safeguards we have in place." Meanwhile, holes were found in the CRFPCP programme because the meat packer at the centre of the controversy was a chilled butcher shop only.<what> It was disclosed on 3 July that the Chinese authorities had discovered 188 falsified CRFPCP certificates. | 4 | Stereochemistry |
To derive Darkens second equation the gradient in Gibbs chemical potential is analyzed. The gradient in potential energy, denoted by F, is the force which causes atoms to diffuse. To begin, the flux J is equated to the product of the differential of the gradient and the mobility B, which is defined as the diffusing atoms velocity per unit of applied force. In addition, N is the Avogadro constant, and C' is the concentration of diffusing component two. This yields
which can be equated to the expression for Fick's first law:
so that the expression can be written as
After some rearrangement of variables the expression can be written for D, the diffusivity of component two:
Assuming that atomic volume is constant, so C = C + C,
Using a definition activity, , where R is the gas constant, and T is the temperature, to rewrite the equation in terms of activity gives
The above equation can be rewritten in terms of the activity coefficient γ, which is defined in terms of activity by the equation . This yields
The same equation can also be written for the diffusivity of component one, , and combining the equations for D and D gives the final equation: | 7 | Physical Chemistry |
Polyoxins are a group of nucleoside antibiotics composed of heterocyclic moieties containing nitrogen. An example is Polyoxin B.
Polyoxins work by inhibiting the biosynthesis of chitin. | 1 | Biochemistry |
Bacterial endospores of the highly UV-resistant Bacillus subtilis strain MW01 were exposed to low Earth orbit and simulated Martian surface conditions for 559 days. It was clearly shown that solar extraterrestrial UV radiation (λ ≥110 nm) as well as the Martian UV spectrum (λ ≥200 nm) was the most deleterious factor applied; in some samples only a few spore survivors were recovered from B. subtilis MW01 spores exposed in monolayers. However, if shielded from solar irradiation, about 8% of MW01 spores survived, and 100% survived in simulated Martian conditions, compared to the laboratory controls.
Halococcus dombrowskii (ADAPT II) and a naturally UV-adapted phototrophic community (ADAPT III) were two other targets of the experiment. For ADAPT-II, no counting from the space station has been published, but preliminary ground experiments have established some tolerance levels. The results for ADAPT-III has been published. Many dyes (chlorophyll and carotenoids) used by the microbials are bleached by the UV rays, and quite a few species used in the dark control groups died. Chroococcidiopsis was the one to survive every group. Chlorella, Gloeocapsa, and Geminicoccus roseus were able to survide a lower UV level. | 1 | Biochemistry |
In a general sense, transition metal-based catalysis can be viewed as template reactions: Reactants coordinate to adjacent sites on the metal ion and, owing to their adjacency, the two reactants interconnect (insert or couple) either directly or via the action of another reagent. In the area of homogeneous catalysis, the cyclo-oligomerization of acetylene to cyclooctatetraene at a nickel(II) centre reflects the templating effect of the nickel, where it is supposed that four acetylene molecules occupy four sites around the metal and react simultaneously to give the product. This simplistic mechanistic hypotheses was influential in the development of these catalytic reactions. For example, if a competing ligand such as triphenylphosphine were added to occupy one coordination site, then only three molecules of acetylene could bind, and these come together to form benzene (see Reppe chemistry). | 7 | Physical Chemistry |
QPNC-PAGE, or Quantitative Preparative Native Continuous Polyacrylamide Gel Electrophoresis, is a bioanalytical, one-dimensional, high-resolution and high-precision electrophoresis technique applied in biochemistry and bioinorganic chemistry to separate proteins quantitatively by isoelectric point and by continuous elution from a gel column.
This standardized variant of native gel electrophoresis and subset of preparative polyacrylamide gel electrophoresis is used by biologists to resolve macromolecules in solution with high recovery, for example, into active or native metalloproteins in biological samples or properly and improperly folded metal cofactor-containing proteins or protein isoforms in complex protein mixtures. | 3 | Analytical Chemistry |
The formation of humic substances in nature is one of the least understood aspects of humus chemistry and one of the most intriguing. There are three main theories to explain it: the lignin theory of Waksman (1932), the polyphenol theory, and the sugar-amine condensation theory of Maillard (1911). Those theories are insufficient to account for observations in soil research.
Humic substances are formed by the microbial degradation of dead plant matter, such as lignin, cellulose and charcoal. Humic substances in the lab are very resistant to further biodegradation. The structure, elemental composition and content of functional groups of a given sample depend on the water or soil source and the specific conditions of extraction. Nevertheless, the average properties of lab produced humic substances from different sources are remarkably similar. | 9 | Geochemistry |
There are four categories of restriction modification systems: type I, type II, type III and type IV, all with restriction enzyme activity and a methylase activity (except for type IV that has no methylase activity). They were named in the order of discovery, although the type II system is the most common.
Type I systems are the most complex, consisting of three polypeptides: R (restriction), M (modification), and S (specificity). The resulting complex can both cleave and methylate DNA. Both reactions require ATP, and cleavage often occurs a considerable distance from the recognition site. The S subunit determines the specificity of both restriction and methylation. Cleavage occurs at variable distances from the recognition sequence, so discrete bands are not easily visualized by gel electrophoresis.
Type II systems are the simplest and the most prevalent. Instead of working as a complex, the methyltransferase and endonuclease are encoded as two separate proteins and act independently (there is no specificity protein). Both proteins recognize the same recognition site, and therefore compete for activity. The methyltransferase acts as a monomer, methylating the duplex one strand at a time. The endonuclease acts as a homodimer, which facilitates the cleavage of both strands. Cleavage occurs at a defined position close to or within the recognition sequence, thus producing discrete fragments during gel electrophoresis. For this reason, Type II systems are used in labs for DNA analysis and gene cloning.
Type III systems have R (res) and M (mod) proteins that form a complex of modification and cleavage. The M protein, however, can methylate on its own. Methylation also only occurs on one strand of the DNA unlike most other known mechanisms. The heterodimer formed by the R and M proteins competes with itself by modifying and restricting the same reaction. This results in incomplete digestion.
Type IV systems are not true RM systems because they only contain a restriction enzyme and not a methylase. Unlike the other types, type IV restriction enzymes recognize and cut only modified DNA. | 1 | Biochemistry |
Much of the SIMIBI class of GTPases is activated by dimerization. Named after the signal recognition particle (SRP), MinD, and BioD, the class is involved in protein localization, chromosome partitioning, and membrane transport. Several members of this class, including MinD and Get3, has shifted in substrate specificity to become ATPases. | 1 | Biochemistry |
To measure the partial molar property of a binary solution, one begins with the pure component denoted as and, keeping the temperature and pressure constant during the entire process, add small quantities of component ; measuring after each addition. After sampling the compositions of interest one can fit a curve to the experimental data. This function will be .
Differentiating with respect to will give .
is then obtained from the relation: | 7 | Physical Chemistry |
Approximately 95% of hydroxylamine is used in the synthesis of cyclohexanone oxime, a precursor to Nylon 6. The treatment of this oxime with acid induces the Beckmann rearrangement to give caprolactam (3). The latter can then undergo a ring-opening polymerization to yield Nylon 6. | 0 | Organic Chemistry |
A colour-indicator titration, for example using test method ASTM D974, can be carried out to indicate relative changes that occur in an oil sample during its use under oxidising conditions. A sample is dissolved in a solvent mixture of Toluene/ Propan-2-ol with 0.5% deionised water. A methyl orange indicator is added and the solution is titrated using alcoholic potassium hydroxide. The end point is indicated by a colour change from orange to green. | 3 | Analytical Chemistry |
In soils, it is assumed that larger amounts of phenols are released from decomposing plant litter rather than from throughfall in any natural plant community. Decomposition of dead plant material causes complex organic compounds to be slowly oxidized lignin-like humus or to break down into simpler forms (sugars and amino sugars, aliphatic and phenolic organic acids), which are further transformed into microbial biomass (microbial humus) or are reorganized, and further oxidized, into humic assemblages (fulvic and humic acids), which bind to clay minerals and metal hydroxides. There has been a long debate about the ability of plants to uptake humic substances from their root systems and to metabolize them. There is now a consensus about how humus plays a hormonal role rather than simply a nutritional role in plant physiology.
In the soil, soluble phenols face four different fates. They might be degraded and mineralized as a carbon source by heterotrophic microorganisms; they can be transformed into insoluble and recalcitrant humic substances by polymerization and condensation reactions (with the contribution of soil organisms); they might adsorb to clay minerals or form chelates with aluminium or iron ions; or they might remain in dissolved form, leached by percolating water, and finally leave the ecosystem as part of dissolved organic carbon (DOC).
Leaching is the process by which cations such as iron (Fe) and aluminum (Al), as well as organic matter, are removed from the litterfall and transported downward into the soil below. This process is known as podzolization and is particularly intense in boreal and cool temperate forests that are mainly constituted by coniferous pines, whose litterfall is rich in phenolic compounds and fulvic acid. | 0 | Organic Chemistry |
The division between prokaryotes and eukaryotes is usually considered the most important distinction or difference among organisms. The distinction is that eukaryotic cells have a "true" nucleus containing their DNA, whereas prokaryotic cells do not have a nucleus.
Both eukaryotes and prokaryotes contain large RNA/protein structures called ribosomes, which produce protein, but the ribosomes of prokaryotes are smaller than those of eukaryotes. Mitochondria and chloroplasts, two organelles found in many eukaryotic cells, contain ribosomes similar in size and makeup to those found in prokaryotes. This is one of many pieces of evidence that mitochondria and chloroplasts are descended from free-living bacteria. The endosymbiotic theory holds that early eukaryotic cells took in primitive prokaryotic cells by phagocytosis and adapted themselves to incorporate their structures, leading to the mitochondria and chloroplasts.
The genome in a prokaryote is held within a DNA/protein complex in the cytosol called the nucleoid, which lacks a nuclear envelope. The complex contains a single, cyclic, double-stranded molecule of stable chromosomal DNA, in contrast to the multiple linear, compact, highly organized chromosomes found in eukaryotic cells. In addition, many important genes of prokaryotes are stored in separate circular DNA structures called plasmids. Like Eukaryotes, prokaryotes may partially duplicate genetic material, and can have a haploid chromosomal composition that is partially replicated, a condition known as merodiploidy.
Prokaryotes lack mitochondria and chloroplasts. Instead, processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic cell membrane. However, prokaryotes do possess some internal structures, such as prokaryotic cytoskeletons. It has been suggested that the bacterial phylum Planctomycetota has a membrane around the nucleoid and contains other membrane-bound cellular structures. However, further investigation revealed that Planctomycetota cells are not compartmentalized or nucleated and, like other bacterial membrane systems, are interconnected.
Prokaryotic cells are usually much smaller than eukaryotic cells. Therefore, prokaryotes have a larger surface-area-to-volume ratio, giving them a higher metabolic rate, a higher growth rate, and as a consequence, a shorter generation time than eukaryotes.
There is increasing evidence that the roots of the eukaryotes are to be found in (or at least next to) the archaean asgard group, perhaps Heimdallarchaeota (an idea which is a modern version of the 1984 eocyte hypothesis, eocytes being an old synonym for Thermoproteota, a taxon to be found nearby the then-unknown Asgard group). For example, histones which usually package DNA in eukaryotic nuclei, have also been found in several archaean groups, giving evidence for homology. This idea might clarify the mysterious predecessor of eukaryotic cells (eucytes) which engulfed an alphaproteobacterium forming the first eucyte (LECA, last eukaryotic common ancestor) according to endosymbiotic theory. There might have been some additional support by viruses, called viral eukaryogenesis.
The non-bacterial group comprising archaea and eukaryota was called Neomura by Thomas Cavalier-Smith in 2002.
However, in a cladistic view, eukaryota are archaea in the same sense as birds are dinosaurs because they evolved from the maniraptora dinosaur group. In contrast, archaea without eukaryota appear to be a paraphyletic group, just like dinosaurs without birds. | 1 | Biochemistry |
In general, acidity of donor sites correlates well with the strength of the donor. For example, it is a common strategy to add electron-withdrawing aryl substituents on a thiourea catalyst, which can increase its acidity and thus the strength of its hydrogen bonding. However, it is still unclear how donor strength correlates with desired reactivity. Importantly, more acidic catalysts are not necessarily more effective. For instance, ureas are less acidic than thioureas by roughly 6 pKa units, but it is not generally true that ureas are significantly worse are catalyzing reactions.
Furthermore, the effect of varying substituents on the catalyst is rarely well understood. Small substituent changes can completely change reactivity or selectivity. An example of this was in the optimization studies of a bifunctional Strecker reaction catalyst, one of the first well-studied thiourea catalysts. Specifically, varying the X substituent on the salicylaldimine substituent, it was found that typical electron-withdrawing or electron-donating substituents had little effect on the rate, but ester substituents such as acetate or pivaloate seemed to cause noticeable rate acceleration. This observation is difficult to rationalize given that the X group is far from the reactive center during the course of the reaction and electronics do not seem to be the cause. In general, despite the relative ease of electronic tuning with organic catalysts, chemists have not yet reached a useful understanding of these modifications. | 0 | Organic Chemistry |
LncRNA has evolved rather recently from those of other species but still maintains some functionality. With regards to this specific form, researchers believe that it can serve as a diagnostic and predictive biomarker for cancers where its normal expression is altered. Much work is still required to fully understand the function and regulatory mechanisms of BC200 RNA but new approaches may seek to develop probes for human BC200 RNA that will assist in developing novel pharmaceuticals. As RNA polymerase III is responsible for transcribing BC200 RNA, it can also serve as a potential target for addressing disease where the expression of it is elevated. | 1 | Biochemistry |
A large fraction of human tumor mutations are effectively patient-specific. Therefore, neoantigens may also be based on individual tumor genomes. Deep-sequencing technologies can identify mutations within the protein-coding part of the genome (the exome) and predict potential neoantigens. In mice models, for all novel protein sequences, potential MHC-binding peptides were predicted. The resulting set of potential neoantigens was used to assess T cell reactivity. Exome–based analyses were exploited in a clinical setting, to assess reactivity in patients treated by either tumor-infiltrating lymphocyte (TIL) cell therapy or checkpoint blockade. Neoantigen identification was successful for multiple experimental model systems and human malignancies.
The false-negative rate of cancer exome sequencing is low—i.e.: the majority of neoantigens occur within exonic sequence with sufficient coverage. However, the vast majority of mutations within expressed genes do not produce neoantigens that are recognized by autologous T cells.
As of 2015 mass spectrometry resolution is insufficient to exclude many false positives from the pool of peptides that may be presented by MHC molecules. Instead, algorithms are used to identify the most likely candidates. These algorithms consider factors such as the likelihood of proteasomal processing, transport into the endoplasmic reticulum, affinity for the relevant MHC class I alleles and gene expression or protein translation levels.
The majority of human neoantigens identified in unbiased screens display a high predicted MHC binding affinity. Minor histocompatibility antigens, a conceptually similar antigen class are also correctly identified by MHC binding algorithms. Another potential filter examines whether the mutation is expected to improve MHC binding. The nature of the central TCR-exposed residues of MHC-bound peptides is associated with peptide immunogenicity. | 1 | Biochemistry |
The nomenclature for SNPs include several variations for an individual SNP, while lacking a common consensus.
The rs### standard is that which has been adopted by dbSNP and uses the prefix "rs", for "reference SNP", followed by a unique and arbitrary number. SNPs are frequently referred to by their dbSNP rs number, as in the examples above.
The Human Genome Variation Society (HGVS) uses a standard which conveys more information about the SNP. Examples are:
* c.76A>T: "c." for coding region, followed by a number for the position of the nucleotide, followed by a one-letter abbreviation for the nucleotide (A, C, G, T or U), followed by a greater than sign (">") to indicate substitution, followed by the abbreviation of the nucleotide which replaces the former
* p.Ser123Arg: "p." for protein, followed by a three-letter abbreviation for the amino acid, followed by a number for the position of the amino acid, followed by the abbreviation of the amino acid which replaces the former. | 1 | Biochemistry |
A surface core level shift (SCS) is a kind of core-level shift that often emerges in X-ray photoelectron spectroscopy spectra of surface atoms.
Because surface atoms have different chemical environments from bulk atoms, small shifts of binding energies are observed by X-ray photoelectron spectroscopy. SCS is ascribed mainly to the lower coordination numbers of surface atoms than bulk atoms. Reduced coordination leads to narrower valence bandwidth. Such narrowing of the bandwidth increases the density of states, and if more than half of the valence band is filled, the band center is lower than bulk and the binding energy increases. In contrast, if less than half of the valence band is filled, the band center is higher than bulk, and the binding energy decreases.
Because the binding energy in X-ray photoelectron spectroscopy is affected by the final state and other chemical environments, this simple explanation cannot always be applied to the interpretation of X-ray photoelectron spectra. In spite of such complexity, the SCS gives important information about the chemical nature of surface atoms. | 7 | Physical Chemistry |
The EDF1 gene encodes a protein that acts as a transcriptional coactivator by interconnecting the general transcription factor TATA element-binding protein (TBP) and gene-specific activators.
TFIID and human mediator coactivator (THRAP3) complexes (mediator complex, plus THRAP3 protein) assemble cooperatively on promoter DNA, from which they become part of the RNAPII holoenzyme. | 1 | Biochemistry |
Naturally occurring moissanite is found in only minute quantities in certain types of meteorite, corundum deposits, and kimberlite. Virtually all the silicon carbide sold in the world, including moissanite jewels, is synthetic.
Natural moissanite was first found in 1893 as a small component of the Canyon Diablo meteorite in Arizona by Ferdinand Henri Moissan, after whom the material was named in 1905. Moissan's discovery of naturally occurring SiC was initially disputed because his sample may have been contaminated by silicon carbide saw blades that were already on the market at that time.
While rare on Earth, silicon carbide is remarkably common in space. It is a common form of stardust found around carbon-rich stars, and examples of this stardust have been found in pristine condition in primitive (unaltered) meteorites. The silicon carbide found in space and in meteorites is almost exclusively the beta-polymorph. Analysis of SiC grains found in the Murchison meteorite, a carbonaceous chondrite meteorite, has revealed anomalous isotopic ratios of carbon and silicon, indicating that these grains originated outside the solar system. | 8 | Metallurgy |
Design equations are equations relating the space time to the fractional conversion and other properties of the reactor. Different design equations have been derived for different types of the reactor and depending on the reactor the equation more or less resemble that describing the average residence time. Often design equations are used to minimize the reactor volume or volumetric flow rate required to operate a reactor. | 9 | Geochemistry |
In vehicles, a ducted fan is a method of propulsion in which a fan, propeller or rotor is surrounded by an aerodynamic duct or shroud which enhances its performance to create aerodynamic thrust or lift to transport the vehicle. | 7 | Physical Chemistry |
When resistance is first suspected or confirmed, the efficacy of alternatives is likely to be the first consideration. If there is resistance to a single group of herbicides, then the use of herbicides from other groups may provide a simple and effective solution, at least in the short term. For example, many triazine-resistant weeds have been readily controlled by the use of alternative herbicides such as dicamba or glyphosate. | 2 | Environmental Chemistry |
VOCs are also found in hospital and health care environments. In these settings, these chemicals are widely used for cleaning, disinfection, and hygiene of the different areas. Thus, health professionals such as nurses, doctors, sanitation staff, etc., may present with adverse health effects such as asthma; however, further evaluation is required to determine the exact levels and determinants that influence the exposure to these compounds.
Studies have shown that the concentration levels of different VOCs such as halogenated and aromatic hydrocarbons differ substantially between areas of the same hospital. However, one of these studies reported that ethanol, isopropanol, ether, and acetone were the main compounds in the interior of the site. Following the same line, in a study conducted in the United States, it was established that nursing assistants are the most exposed to compounds such as ethanol, while medical equipment preparers are most exposed to 2-propanol.
In relation to exposure to VOCs by cleaning and hygiene personnel, a study conducted in 4 hospitals in the United States established that sterilization and disinfection workers are linked to exposures to d-limonene and 2-propanol, while those responsible for cleaning with chlorine-containing products are more likely to have higher levels of exposure to α-pinene and chloroform. Those who perform floor and other surface cleaning tasks (e.g., floor waxing) and who use quaternary ammonium, alcohol, and chlorine-based products are associated with a higher VOC exposure than the two previous groups, that is, they are particularly linked to exposure to acetone, chloroform, α-pinene, 2-propanol or d-limonene.
Other healthcare environments such as nursing and age care homes have been rarely a subject of study, even though the elderly and vulnerable populations may spend considerable time in these indoor settings where they might be exposed to VOCs, derived from the common use of cleaning agents, sprays and fresheners. In a study conducted in France, a team of researchers developed an online questionnaire for different social and age care facilities, asking about cleaning practices, products used, and the frequency of these activities. As a result, more than 200 chemicals were identified, of which 41 are known to have adverse health effects, 37 of them being VOCs. The health effects include skin sensitization, reproductive and organ-specific toxicity, carcinogenicity, mutagenicity, and endocrine-disrupting properties. Furthermore, in another study carried out in the same European country, it was found that there is a significant association between breathlessness in the elderly population and elevated exposure to VOCs such as toluene and o-xylene, unlike the remainder of the population. | 0 | Organic Chemistry |
There are many ways in which humans may limit the viability of a potential biosignature. The resolution of a telescope becomes important when vetting certain false-positive mechanisms, and many current telescopes do not have the capabilities to observe at the resolution needed to investigate some of these. In addition, probes and telescopes are worked on by huge collaborations of scientists with varying interests. As a result, new probes and telescopes carry a variety of instruments that are a compromise to everyone's unique inputs. For a different type of scientist to detect something unrelated to biosignatures, a sacrifice may have to be made in the capability of an instrument to search for biosignatures. | 2 | Environmental Chemistry |
The barcoded DNA fragments are amplified using PCR to create a library of DNA fragments with identical barcodes. All the fragments derived from a given DNA molecule are tagged with the same barcode. This step increases the quantity of DNA for sequencing and reduces the chances of losing unique DNA fragments during sequencing. Droplets (or GEM) are later collected in a tube, and the emulsion is broken, releasing the amplified, barcoded DNA sequences.
Standard Illumina next-generation sequencing technology can be used to sequence libraries. During sequencing, the barcodes are read along with the DNA sequences, allowing researchers and scientists to group together DNA fragments that originate from the same DNA molecule. Even though each DNA fragment is typically not fully sequenced, the information from many overlapping fragments in the same genomic region can be combined to reconstruct the long stretches of the genome. Therefore, a genome can be easily assembled from scratch without any prior reference. | 1 | Biochemistry |
Applications involving dendrimers in general take advantage of either stuffing cargo into the interior of the dendrimer (sometimes referred to as the "dendritic box"), or attaching cargo onto the dendrimer surface. PAMAM dendrimer applications have generally focused on surface modification, taking advantage of both electrostatic and covalent methods for binding cargo. Currently, major areas of study using PAMAM dendrimers and their functionalized derivatives involve drug delivery and gene delivery. | 6 | Supramolecular Chemistry |
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