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Adhesion G protein-coupled receptors (adhesion GPCRs) are a class of 33 human protein receptors with a broad distribution in embryonic and larval cells, cells of the reproductive tract, neurons, leukocytes, and a variety of tumours. Adhesion GPCRs are found throughout metazoans and are also found in single-celled colony forming choanoflagellates such as Monosiga brevicollis and unicellular organisms such as Filasterea. The defining feature of adhesion GPCRs that distinguishes them from other GPCRs is their hybrid molecular structure. The extracellular region of adhesion GPCRs can be exceptionally long and contain a variety of structural domains that are known for the ability to facilitate cell and matrix interactions. Their extracellular region contains the membrane proximal GAIN (GPCR-Autoproteolsis INducing) domain. Crystallographic and experimental data has shown this structurally conserved domain to mediate autocatalytic processing at a GPCR-proteolytic site (GPS) proximal to the first transmembrane helix. Autocatalytic processing gives rise to an extracellular (α) and a membrane-spanning (β) subunit, which are associated non-covalently, resulting in expression of a heterodimeric receptor at the cell surface.
Ligand profiles and in vitro studies have indicated a role for adhesion GPCRs in cell adhesion and migration. Work utilizing genetic models confined this concept by demonstrating that the primary function of adhesion GPCRs may relate to the proper positioning of cells in a variety of organ systems. Moreover, growing evidence implies a role of adhesion GPCRs in tumour cell metastasis. Formal G protein-coupled signalling has been demonstrated for a number for adhesion GPCRs, however, the orphan receptor status of many of the receptors still hampers full characterisation of potential signal transduction pathways. In 2011, the [http://www.adhesiongpcr.org/ adhesion GPCR consortium] was established to facilitate research of the physiological and pathological functions of adhesion GPCRs. | 1 | Biochemistry |
Firstly, mRNA template needs to be isolated for the creation of cDNA libraries. Since mRNA only contains exons, the integrity of the isolated mRNA should be considered so that the protein encoded can still be produced. Isolated mRNA should range from 500 bp to 8 kb. Several methods exist for purifying RNA such as trizol extraction and column purification. Column purification can be done using oligomeric dT nucleotide coated resins, and features of mRNA such as having a poly-A tail can be exploited where only mRNA sequences containing said feature will bind. The desired mRNA bound to the column is then eluted. | 1 | Biochemistry |
[https://nadp.slh.wisc.edu/pubs/brochures/ Brochures]
[https://nadp.slh.wisc.edu/pubs/Annual-Data-Summaries/ Annual Data Summaries]
[https://nadp.slh.wisc.edu/quality-assurance/#QAreports Quality Assurance Reports]
[https://nadp.slh.wisc.edu/committees/clad/ CLAD Science Committee Reports]
[https://nadp.slh.wisc.edu/committees/tdep/ TDep Science Committee Reports]
[https://nadp.slh.wisc.edu/committees/amsc/ AMSC Study Plan]
[https://nadp.slh.wisc.edu/committees/meld/ MELD Science Committee Reports] | 2 | Environmental Chemistry |
From the perspective of solid state physics, Brillouin scattering is an interaction between an electromagnetic wave and one of the three above-mentioned crystalline lattice waves (e.g. electrostriction and magnetostriction). The scattering is inelastic i.e. the photon may lose energy (Stokes process) and in the process create one of the three quasiparticle types (phonon, polariton, magnon) or it may gain energy (anti-Stokes process) by absorbing one of those quasiparticle types. Such a shift in photon energy, corresponding to a Brillouin shift in frequency, is equal to the energy of the released or absorbed quasiparticle. Thus, Brillouin scattering can be used to measure the energies, wavelengths and frequencies of various atomic chain oscillation types (quasiparticles). To measure a Brillouin shift a commonly employed device called the Brillouin spectrometer is used, the design of which is derived from a Fabry–Pérot interferometer. Alternatively, high-speed photodiodes, such as those recovered from inexpensive 25-gigabit Ethernet optical transceivers, may be used in combination with a software-defined radio or RF spectrum analyzer. | 7 | Physical Chemistry |
*Bayley, J. (1990) "The Production of Brass in Antiquity with Particular Reference to Roman Britain" in Craddock, P.T. (ed.) 2000 Years of Zinc and Brass London: British Museum
*Craddock, P.T. and Eckstein, K (2003) "Production of Brass in Antiquity by Direct Reduction" in Craddock, P.T. and Lang, J. (eds) Mining and Metal Production Through the Ages London: British Museum
*Day, J. (1990) "Brass and Zinc in Europe from the Middle Ages until the 19th century" in Craddock, P.T. (ed.) 2000 Years of Zinc and Brass London: British Museum
*Day, J (1991) "Copper, Zinc and Brass Production" in Day, J and Tylecote, R.F (eds) The Industrial Revolution in Metals London: The Institute of Metals
*Rehren, T. and Martinon Torres, M. (2008) "Naturam ars imitate: European brassmaking between craft and science" in Martinon-Torres, M and Rehren, T. (eds) Archaeology, History and Science Integrating Approaches to Ancient Material: Left Coast Press | 8 | Metallurgy |
Silyl enol ethers are generally prepared by reacting an enolizable carbonyl compound with a silyl electrophile and a base, or just reacting an enolate with a silyl electrophile. Since silyl electrophiles are hard and silicon-oxygen bonds are very strong, the oxygen (of the carbonyl compound or enolate) acts as the nucleophile to form a Si-O single bond.
The most commonly used silyl electrophile is trimethylsilyl chloride. To increase the rate of reaction, trimethylsilyl triflate may also be used in the place of trimethylsilyl chloride as a more electrophilic substrate.
When using an unsymmetrical enolizable carbonyl compound as a substrate, the choice of reaction conditions can help control whether the kinetic or thermodynamic silyl enol ether is preferentially formed. For instance, when using lithium diisopropylamide (LDA), a strong and sterically hindered base, at low temperature (e.g., -78°C), the kinetic silyl enol ether (with a less substituted double bond) preferentially forms due to sterics. When using triethylamine, a weak base, the thermodynamic silyl enol ether (with a more substituted double bond) is preferred.
Alternatively, a rather exotic way of generating silyl enol ethers is via the Brook rearrangement of appropriate substrates. | 0 | Organic Chemistry |
Deficiency of glycogenin-1 is detected in the sequence of the glycogenin-1 gene, GYG1, which revealed a non-sense mutation in one allele and a missense mutation, Thr83Met, in the other. The missense mutation resulted in inactivation of the autoglycosylation of glycogenin-1, which is necessary for the priming of glycogen synthesis in muscle.
Autoglycosylation of glycogenin-1 occurs at Tyr195 by a gulose-1-O-tyrosine linkage. An induced missense mutation of this residue results in inactivated autoglycosylation. However, missense mutation affecting some other residues of glycogenin-1 has also been shown to eliminate autoglycosilation. | 1 | Biochemistry |
These groups have a strong electron-withdrawing inductive effect (-I) either by virtue of their positive charge or because of the powerfully electronegativity of the halogens. There is no resonance effect because there are no orbitals or electron pairs which can overlap with those of the ring. The inductive effect acts like that for the carboxylate anion but in the opposite direction (i.e. it produces small positive charges on the ortho and para positions but not on the meta position and it destabilises the Wheland intermediate.) Hence these groups are deactivating and meta directing: | 0 | Organic Chemistry |
While surface energy is conventionally defined as the work required to build a unit of area of a given surface, when it comes to its measurement by the sessile drop technique, the surface energy is not quite as well defined. The values obtained through the sessile drop technique depend not only on the solid sample in question, but equally on the properties of the probe liquid being used, as well as the particular theory relating the parameters mathematically to one another.
There are numerous such theories developed by various researchers. These methods differ in several regards, such as derivation and convention, but most importantly they differ in the number of components or parameters which they are equipped to analyze. The simpler methods containing fewer components simplify the system by lumping surface energy into one number, while more rigorous methods with more components are derived to distinguish between various components of the surface energy. Again, the total surface energy of solids and liquids depends on different types of molecular interactions, such as dispersive (van der Waals), polar, and acid/base interactions, and is considered to be the sum of these independent components. Some theories account for more of these phenomena than do other theories. These distinctions are to be considered when deciding which method is appropriate for the experiment at hand. The following are a few commonly used such theories. | 7 | Physical Chemistry |
The most important benefit of CAM to the plant is the ability to leave most leaf stomata closed during the day. Plants employing CAM are most common in arid environments, where water is scarce. Being able to keep stomata closed during the hottest and driest part of the day reduces the loss of water through evapotranspiration, allowing such plants to grow in environments that would otherwise be far too dry. Plants using only carbon fixation, for example, lose 97% of the water they take up through the roots to transpiration - a high cost avoided by plants able to employ CAM. | 5 | Photochemistry |
Ladles can be "lip pour" design, "teapot spout" design, "lip-axis design" or "bottom pour" design:
*For lip pour design the ladle is tilted and the molten metal pours out of the ladle like water from a pitcher.
*The teapot spout design, like a teapot, takes liquid from the base of the ladle and pours it out via a lip-pour spout. Any impurities in the molten metal will form on the top of the metal so by taking the metal from the base of the ladle, the impurities are not poured into the mould. The same idea is behind the bottom pour process.
*Lip-axis ladles have the pivot point of the vessel as close to the tip of the pouring spout as can be practicable. Therefore as the ladle is rotated the actual pouring point has very little movement. Lip-axis pouring is often used on molten metal pouring systems where there is a need to automate the process as much as possible and the operator controls the pouring operation at a remote distance.
*For bottom pour ladles, a stopper rod is inserted into a tapping hole in the bottom of the ladle. To pour metal the stopper is raised vertically to allow the metal to flow out the bottom of the ladle. To stop pouring the stopper rod is inserted back into the drain hole. Large ladles in the steelmaking industry may use slide gates below the taphole.
Ladles can be either open-topped or covered. Covered ladles have a (sometimes removable) dome-shaped lid to contain radiant heat; they lose heat slower than open-topped ladles. Small ladles do not commonly have covers, although a ceramic blanket may be used instead (where available).
Medium and large ladles which are suspended from a crane have a bail which holds the ladle on shafts, called trunnions. To tilt the ladle a gearbox is used and this is typically a worm gear. The gear mechanism may be hand operated with a large wheel or may be operated by an electric motor or pneumatic motor. Powered rotation allows the ladle operator to be moved to a safe distance and control the rotation of the ladle via a pendant or radio remote control. Powered rotation also allows the ladle to have a number of rotation speeds which may be beneficial to the overall casting process. Powered rotation obviously also reduces the effort required by the ladle operator and allows high volumes of molten metal to be transferred and poured for long periods without operator fatigue. Where the ladle is fitted with a manually operated gearbox, the type of gearbox most commonly used is the worm and wheel design because in most practical circumstances, and when correctly maintained it can be considered as "self-locking" and does not need an internal friction brake to regulate the tilting speed of the ladle. Other types of gear system can also be used but they have to be fitted with an additional braking system that can hold the ladle if the operator takes his hand off the hand-wheel.
Lip-axis ladles may also use hydraulic rams to tilt the ladle. The largest ladles are un-geared and are typically poured using a special, two-winch crane, where the main winch carries the ladle while the second winch engages a lug at the bottom of the ladle. Raising the second winch then rotates the ladle on its trunnions.
Ladles are often designed for special purposes such as adding alloys to the molten metal. Ladles may also have porous plugs inserted into the base, so inert gases can be bubbled through the ladle to enhance alloying or metallic treatment practices. | 8 | Metallurgy |
Tholins occur on the dwarf planet Pluto and are responsible for red colors as well as the blue tint of the atmosphere of Pluto. The reddish-brown cap of the north pole of Charon, the largest of five moons of Pluto, is thought to be composed of tholins, produced from methane, nitrogen and related gases released from the atmosphere of Pluto and transferred over about distance to the orbiting moon. | 9 | Geochemistry |
Benson group-increment theory (BGIT), group-increment theory, or Benson group additivity uses the experimentally calculated heat of formation for individual groups of atoms to calculate the entire heat of formation for a molecule under investigation. This can be a quick and convenient way to determine theoretical heats of formation without conducting tedious experiments. The technique was developed by professor Sidney William Benson of the University of Southern California. It is further described in Heat of formation group additivity.
Heats of formations are intimately related to bond-dissociation energies and thus are important in understanding chemical structure and reactivity. Furthermore, although the theory is old, it still is practically useful as one of the best group-contribution methods aside from computational methods such as molecular mechanics. However, the BGIT has its limitations, and thus cannot always predict the precise heat of formation. | 7 | Physical Chemistry |
The myokine oncostatin M has been shown to inhibit the proliferation of breast cancer cells, IL-6, IL-15, epinephrine and norepinephrine for the recruitment of NK cells and replacement of old neutrophils into new and more functional ones and limit induced inflammation by Macrophages M1 and increase in Macrophages M2 (anti-inflammatory). | 1 | Biochemistry |
Derived from ribose, a pentose, pentosidine forms fluorescent cross-links between the arginine and lysine residues in collagen. It is formed in a reaction of the amino acids with the Maillard reaction products of ribose.
Although it is present only in trace concentrations among tissue proteins, it is useful for assessing cumulative damage to
proteins—advanced glycation endproducts—by non-enzymatic browning reactions with carbohydrates. | 1 | Biochemistry |
Changing the volume of the system changes the partial pressures of the products and reactants and can affect the equilibrium concentrations. With a pressure increase due to a decrease in volume, the side of the equilibrium with fewer moles is more favorable and with a pressure decrease due to an increase in volume, the side with more moles is more favorable. There is no effect on a reaction where the number of moles of gas is the same on each side of the chemical equation.
Considering the reaction of nitrogen gas with hydrogen gas to form ammonia:
: ⇌ ΔH = −92kJ mol
Note the number of moles of gas on the left-hand side and the number of moles of gas on the right-hand side. When the volume of the system is changed, the partial pressures of the gases change. If we were to decrease pressure by increasing volume, the equilibrium of the above reaction will shift to the left, because the reactant side has a greater number of moles than does the product side. The system tries to counteract the decrease in partial pressure of gas molecules by shifting to the side that exerts greater pressure. Similarly, if we were to increase pressure by decreasing volume, the equilibrium shifts to the right, counteracting the pressure increase by shifting to the side with fewer moles of gas that exert less pressure. If the volume is increased because there are more moles of gas on the reactant side, this change is more significant in the denominator of the equilibrium constant expression, causing a shift in equilibrium.
would be as follow:
If we double the pressure of the above situation, by halving the volume of both sides then would now be as follow: | 7 | Physical Chemistry |
In a quantum-mechanical description of matter, the electrons confined to a material (such as those in individual atoms, molecules or crystals) are limited to a discrete set of energy values. The ground state of such a material system is such that the most energetic electron has its minimal energy. In photoluminescence, energy is transferred from light incident on the material and absorbed to electrons. The light is absorbed in minimal "quanta" or "packets" of energy of the electromagnetic radiation called photons. The amount of energy carried by a photon is proportional to its frequency. The electron is then in an excited state of higher energy. Such states are not stable and with time the material system will return to its ground state and the electron will lose its energy. Luminescence is the process whereby light is emitted when the electron drops to a lower energy level.
Often when a photon is absorbed, the system is excited in the corresponding excited state, then it relaxes in an intermediate lower energy state, with a "non-radiative relaxation" (a relaxation that doesn't involve the emission of a photon, but e.g. involves the emission of vibrational energy) and then there is the emission of a photon with a lower energy than the absorbed one, because of the relaxation from the intermediate, lower energy state to the "ground state". Usually the strongest luminescence of the material is from the lower levels to the ground state. This process is called fluorescence. For instance, in semiconductors, most of the light emitted is at the frequency corresponding to the bandgap energy, i.e. from the bottom of the conduction band to the top of the valence band. In such systems, more light absorbed by the material, results in more electrons decaying non-radiatively to the lower states, and more luminescence in the emission wavelength. | 7 | Physical Chemistry |
Aso and Tagami were the first to report the polymerization of o-phthalaldehyde in 1967 using the cationic living polymerization technique. This technique, which was initially thought to require the usage of a strong Brönsted acid to initiate polymerization in addition to a strong nucleophile to depress polymerization and endcap the polymer chain was proven successful in a number of polymerization processes reported earlier. Interestingly, the authors were able to produce this polymer without using an initiator nor a terminator and determined the polymer's structure to be cyclic. In fact, they worked at liquid nitrogen temperature and relied on Boron trifluoride etherate catalyst which was sufficient to produce a polymer stable enough at room temperature for a few days. | 7 | Physical Chemistry |
Dimetcote is commonly used for steel corrosion resistance. It is generally reliable under humid or corrosive conditions. Because of this, Dimetcote is widely used in ships, power generation facilities, and marine, oil, and offshore structures. | 8 | Metallurgy |
Natural antisense short interfering RNA (natsiRNA) is a type of siRNA. They are endogenous RNA regulators which are between 21 and 24 nucleotides in length, and are generated from complementary mRNA transcripts which are further processed into siRNA.
natsiRNA has been implicated in several developmental and response mechanisms in plants, such as pathogen resistance, salt tolerance and cell wall biosynthesis. natsiRNA has also been shown to alter gene expression in plants responding to environmental stressors. | 1 | Biochemistry |
Nitinol is exceedingly difficult to make, due to the exceptionally tight compositional control required, and the tremendous reactivity of titanium. Every atom of titanium that combines with oxygen or carbon is an atom that is robbed from the NiTi lattice, thus shifting the composition and making the transformation temperature lower.
There are two primary melting methods used today. Vacuum arc remelting (VAR) is done by striking an electrical arc between the raw material and a water-cooled copper strike plate. Melting is done in a high vacuum, and the mold itself is water-cooled copper. Vacuum induction melting (VIM) is done by using alternating magnetic fields to heat the raw materials in a crucible (generally carbon). This is also done in a high vacuum. While both methods have advantages, it has been demonstrated that an industrial state-of-the-art VIM melted material has smaller inclusions than an industrial state-of-the-art VAR one, leading to a higher fatigue resistance. Other research report that VAR employing extreme high-purity raw materials may lead to a reduced number of inclusions and thus to an improved fatigue behavior. Other methods are also used on a boutique scale, including plasma arc melting, induction skull melting, and e-beam melting. Physical vapour deposition is also used on a laboratory scale.
Heat treating nitinol is delicate and critical. It is a knowledge intensive process to fine-tune the transformation temperatures. Aging time and temperature controls the precipitation of various Ni-rich phases, and thus controls how much nickel resides in the NiTi lattice; by depleting the matrix of nickel, aging increases the transformation temperature. The combination of heat treatment and cold working is essential in controlling the properties of nitinol products. | 8 | Metallurgy |
The chirality of a molecule is based on the molecular symmetry of its conformations. A conformation of a molecule is chiral if and only if it belongs to the C, D, T, O, I point groups (the chiral point groups). However, whether the molecule itself is considered to be chiral depends on whether its chiral conformations are persistent isomers that could be isolated as separated enantiomers, at least in principle, or the enantiomeric conformers rapidly interconvert at a given temperature and timescale through low-energy conformational changes (rendering the molecule achiral). For example, despite having chiral gauche conformers that belong to the C point group, butane is considered achiral at room temperature because rotation about the central C–C bond rapidly interconverts the enantiomers (3.4 kcal/mol barrier). Similarly, cis-1,2-dichlorocyclohexane consists of chair conformers that are nonidentical mirror images, but the two can interconvert via the cyclohexane chair flip (~10 kcal/mol barrier). As another example, amines with three distinct substituents (RRRN:) are also regarded as achiral molecules because their enantiomeric pyramidal conformers rapidly invert and interconvert through a planar transition state (~6 kcal/mol barrier).
However, if the temperature in question is low enough, the process that interconverts the enantiomeric chiral conformations becomes slow compared to a given timescale. The molecule would then be considered to be chiral at that temperature. The relevant timescale is, to some degree, arbitrarily defined: 1000 seconds is sometimes employed, as this is regarded as the lower limit for the amount of time required for chemical or chromatographic separation of enantiomers in a practical sense. Molecules that are chiral at room temperature due to restricted rotation about a single bond (barrier to rotation ≥ ca. 23 kcal/mol) are said to exhibit atropisomerism.
A chiral compound can contain no improper axis of rotation (S), which includes planes of symmetry and inversion center. Chiral molecules are always dissymmetric (lacking S) but not always asymmetric (lacking all symmetry elements except the trivial identity). Asymmetric molecules are always chiral.
The following table shows some examples of chiral and achiral molecules, with the Schoenflies notation of the point group of the molecule. In the achiral molecules, X and Y (with no subscript) represent achiral groups, whereas X and X or Y and Y represent enantiomers. Note that there is no meaning to the orientation of an S axis, which is just an inversion. Any orientation will do, so long as it passes through the center of inversion. Also note that higher symmetries of chiral and achiral molecules also exist, and symmetries that do not include those in the table, such as the chiral C or the achiral S.
An example of a molecule that does not have a mirror plane or an inversion and yet would be considered achiral is 1,1-difluoro-2,2-dichlorocyclohexane (or 1,1-difluoro-3,3-dichlorocyclohexane). This may exist in many conformers (conformational isomers), but none of them has a mirror plane. In order to have a mirror plane, the cyclohexane ring would have to be flat, widening the bond angles and giving the conformation a very high energy. This compound would not be considered chiral because the chiral conformers interconvert easily.
An achiral molecule having chiral conformations could theoretically form a mixture of right-handed and left-handed crystals, as often happens with racemic mixtures of chiral molecules (see Chiral resolution#Spontaneous resolution and related specialized techniques), or as when achiral liquid silicon dioxide is cooled to the point of becoming chiral quartz. | 4 | Stereochemistry |
Canonical bases may have either a carbonyl or an amine group on the carbons surrounding the nitrogen atom furthest away from the glycosidic bond, which allows them to base pair (Watson-Crick base pairing) via hydrogen bonds (amine with ketone, purine with pyrimidine). Adenine and 2-aminoadenine have one/two amine group(s), whereas thymine has two carbonyl groups, and cytosine and guanine are mixed amine and carbonyl (inverted in respect to each other).
The precise reason why there are only four nucleotides is debated, but there are several unused possibilities.
Furthermore, adenine is not the most stable choice for base pairing: in Cyanophage S-2L, diaminopurine (DAP) is used instead of adenine. Diaminopurine basepairs perfectly with thymine as it is identical to adenine but has an amine group at position 2 forming 3 intramolecular hydrogen bonds, eliminating the major difference between the two types of basepairs (weak A-T vs strong C-G). This improved stability affects protein-binding interactions that rely on those differences.
Other combination include:
* Isoguanine and isocytosine, which have their amine and ketone inverted compared to standard guanine and cytosine. They are not used probably as tautomers are problematic for base pairing, but isoC and isoG can be amplified correctly with PCR even in the presence of the 4 canonical bases.
* Diaminopyrimidine and xanthine, which bind like 2-aminoadenine and thymine but with inverted structures. This pair is not used as xanthine is a deamination product.
However, correct DNA structure can form even when the bases are not paired via hydrogen bonding; that is, the bases pair thanks to hydrophobicity, as studies have shown with DNA isosteres (analogues with same number of atoms) such as the thymine analogue 2,4-difluorotoluene (F) or the adenine analogue 4-methylbenzimidazole (Z). An alternative hydrophobic pair could be isoquinoline and pyrrolo[2,3-b]pyridine
Other noteworthy basepairs:
* Several fluorescent bases have also been made, such as the 2-amino-6-(2-thienyl)purine and pyrrole-2-carbaldehyde base pair.
* Metal-coordinated bases, such as pairing between a pyridine-2,6-dicarboxylate (tridentate ligand) and a pyridine (monodentate ligand) through square planar coordination to a central copper ion.
* Universal bases may pair indiscriminately with any other base, but, in general, lower the melting temperature of the sequence considerably; examples include 2'-deoxyinosine (hypoxanthine deoxynucleotide) derivatives, nitroazole analogues, and hydrophobic aromatic non-hydrogen-bonding bases (strong stacking effects). These are used as proof of concept and, in general, are not utilized in degenerate primers (which are a mixture of primers).
* The numbers of possible base pairs is doubled when xDNA is considered. xDNA contains expanded bases, in which a benzene ring has been added, which may pair with canonical bases, resulting in four additional possible base-pairs (xA-T, xT-A, xC-G, xG-C) with eight bases (or 16 bases if the unused arrangements are used). Another form of benzene added bases is yDNA, in which the base is widened by the benzene. | 1 | Biochemistry |
Volcanic gases were collected and analysed as long ago as 1790 by Scipione Breislak in Italy. The composition of volcanic gases is dependent on the movement of magma within the volcano. Therefore, sudden changes in gas composition often presage a change in volcanic activity. Accordingly, a large part of hazard monitoring of volcanoes involves regular measurement of gaseous emissions. For example, an increase in the CO content of gases at Stromboli has been ascribed to injection of fresh volatile-rich magma at depth within the system.
Volcanic gases can be sensed (measured in-situ) or sampled for further analysis. Volcanic gas sensing can be:
* within the gas by means of electrochemical sensors and flow-through infrared-spectroscopic gas cells
* outside the gas by ground-based or airborne remote spectroscopy e.g., Correlation spectroscopy (COSPEC), Differential Optical Absorption Spectroscopy (DOAS), or Fourier Transform Infrared Spectroscopy (FTIR).
Sulphur dioxide (SO) absorbs strongly in the ultraviolet wavelengths and has low background concentrations in the atmosphere. These characteristics make sulphur dioxide a good target for volcanic gas monitoring. It can be detected by satellite-based instruments, which allow for global monitoring, and by ground-based instruments such as DOAS. DOAS arrays are placed near some well-monitored volcanoes and used to estimate the flux of SO emitted. The Multi-Component Gas Analyzer System (Multi-GAS) is also used to remotely measure CO, SO and HS. The fluxes of other gases are usually estimated by measuring the ratios of different gases within the volcanic plume, e.g. by FTIR, electrochemical sensors at the volcano crater rim, or direct sampling, and multiplying the ratio of the gas of interest to SO by the SO flux.
Direct sampling of volcanic gas sampling is often done by a method involving an evacuated flask with caustic solution, first used by Robert W. Bunsen (1811-1899) and later refined by the German chemist Werner F. Giggenbach (1937-1997), dubbed Giggenbach-bottle. Other methods include collection in evacuated empty containers, in flow-through glass tubes, in gas wash bottles (cryogenic scrubbers), on impregnated filter packs and on solid adsorbent tubes.
Analytical techniques for gas samples comprise gas chromatography with thermal conductivity detection (TCD), flame ionization detection (FID) and mass spectrometry (GC-MS) for gases, and various wet chemical techniques for dissolved species (e.g., acidimetric titration for dissolved CO, and ion chromatography for sulfate, chloride, fluoride). The trace metal, trace organic and isotopic composition is usually determined by different mass spectrometric methods. | 2 | Environmental Chemistry |
For many years, the origin of residual supercoiling in eukaryotic genomes remained unclear. This topological puzzle was referred to by some as the "linking number paradox". However, when experimentally determined structures of the nucleosome displayed an over-twisted left-handed wrap of DNA around the histone octamer, this paradox was considered to be solved by the scientific community. | 4 | Stereochemistry |
piRNAs represent the largest class of small non-coding RNA molecules expressed in animal cells, deriving from a large variety of sources, including repetitive DNA and transposons. However, the biogenesis of piRNAs is also the least well understood. piRNAs appear to act both at the post-transcriptional and chromatin levels. They are distinct from miRNA due to at least an increase in terms of size and complexity. Repeat associated small interfering RNA (rasiRNAs) are considered to be a subspecies of piRNA. | 1 | Biochemistry |
In chemistry, a stepwise reaction (also called an overall reaction, complex reaction, and multistep reaction, among others) is a chemical reaction with one or more reaction intermediates, which by definition involves at least two consecutive elementary reactions.
In a stepwise reaction, not all bonds are broken and formed at the same time. Hence, intermediates appear in the reaction pathway going from the reactants to the products. A stepwise reaction distinguishes itself from an elementary reaction in which the transformation is assumed to occur in a single step and to pass through a single transition state.
In contrast to elementary reactions which follow the law of mass action, the rate law of stepwise reactions is obtained by combining the rate laws of the multiple elementary steps, and can become rather complex. Moreover, when speaking about catalytic reactions, the diffusion may also limit the reaction. In general, however, there is one very slow step, which is the rate-determining step, i.e. the reaction doesn't proceed any faster than the rate-determining step proceeds.
Organic reactions, especially when involving catalysis, are often stepwise. For example, a typical enol reaction consists of at least these elementary steps:
#Deprotonation next to (α to) the carbonyl:
#Attack of enolate:
R is an electron acceptor, for example, the carbon of a carbonyl (C=O). A very strong base, usually an alkoxide, is needed for the first step.
Reaction intermediates may be trapped in a trapping reaction. This proves the stepwise nature of the reaction and the structure of the intermediate. For example, superacids were used to prove the existence of carbocations. | 7 | Physical Chemistry |
The genetic code is the set of rules used by living cells to translate information encoded within genetic material (DNA or RNA sequences of nucleotide triplets, or codons) into proteins. Translation is accomplished by the ribosome, which links proteinogenic amino acids in an order specified by messenger RNA (mRNA), using transfer RNA (tRNA) molecules to carry amino acids and to read the mRNA three nucleotides at a time. The genetic code is highly similar among all organisms and can be expressed in a simple table with 64 entries.
The codons specify which amino acid will be added next during protein biosynthesis. With some exceptions, a three-nucleotide codon in a nucleic acid sequence specifies a single amino acid. The vast majority of genes are encoded with a single scheme (see the RNA codon table). That scheme is often referred to as the canonical or standard genetic code, or simply the genetic code, though variant codes (such as in mitochondria) exist. | 1 | Biochemistry |
Transferrins are glycoproteins found in vertebrates which bind and consequently mediate the transport of iron (Fe) through blood plasma. They are produced in the liver and contain binding sites for two Fe ions. Human transferrin is encoded by the TF gene and produced as a 76 kDa glycoprotein.
Transferrin glycoproteins bind iron tightly, but reversibly. Although iron bound to transferrin is less than 0.1% (4 mg) of total body iron, it forms the most vital iron pool with the highest rate of turnover (25 mg/24 h). Transferrin has a molecular weight of around 80 kDa and contains two specific high-affinity Fe(III) binding sites. The affinity of transferrin for Fe(III) is extremely high (association constant is 10 M at pH 7.4) but decreases progressively with decreasing pH below neutrality. Transferrins are not limited to only binding to iron but also to different metal ions. These glycoproteins are located in various bodily fluids of vertebrates. Some invertebrates have proteins that act like transferrin found in the hemolymph.
When not bound to iron, transferrin is known as "apotransferrin" (see also apoprotein). | 1 | Biochemistry |
Before a 2007 report by Alber and coworkers, crotonyl-coA carboxylases and reductases (CCRs) were known for reducing crotonyl-coA to butyryl-coA. A report by Alber and coworkers concluded that a specific CCR homolog was able to reduce crotonyl-coA to (2S)-ethyl malonyl-coA which was a favorable reaction. The specific CCR homolog came from the bacterium Rhodobacter sphaeroides. | 1 | Biochemistry |
DNA computing is a form of parallel computing in that it takes advantage of the many different molecules of DNA to try many different possibilities at once. For certain specialized problems, DNA computers are faster and smaller than any other computer built so far. Furthermore, particular mathematical computations have been demonstrated to work on a DNA computer.
DNA computing does not provide any new capabilities from the standpoint of computability theory, the study of which problems are computationally solvable using different models of computation.
For example,
if the space required for the solution of a problem grows exponentially with the size of the problem (EXPSPACE problems) on von Neumann machines, it still grows exponentially with the size of the problem on DNA machines.
For very large EXPSPACE problems, the amount of DNA required is too large to be practical. | 1 | Biochemistry |
Rust is a general name for a complex of oxides and hydroxides of iron, which occur when iron or some alloys that contain iron are exposed to oxygen and moisture for a long period of time. Over time, the oxygen combines with the metal, forming new compounds collectively called rust, in a process called rusting. Rusting is an oxidation reaction specifically occurring with iron. Other metals also corrode via similar oxidation, but such corrosion is not called rusting.
The main catalyst for the rusting process is water. Iron or steel structures might appear to be solid, but water molecules can penetrate the microscopic pits and cracks in any exposed metal. The hydrogen atoms present in water molecules can combine with other elements to form acids, which will eventually cause more metal to be exposed. If chloride ions are present, as is the case with saltwater, the corrosion is likely to occur more quickly. Meanwhile, the oxygen atoms combine with metallic atoms to form the destructive oxide compound. These iron compounds are brittle and crumbly and replace strong metallic iron, reducing the strength of the object. | 8 | Metallurgy |
Sea foam also acts as a mode of transport for both organisms and nutrients within the marine environment and, at times, into the intertidal or terrestrial environments. Wave action can deposit foam into intertidal areas where it can remain when the tide recedes, bringing nutrients to the intertidal zone. Additionally, sea foam can become airborne in windy conditions, transporting materials between marine and terrestrial environments. The ability of sea foam to transport materials is also thought to benefit macroalgal organisms, as macroalgae propagules can be carried to different microenvironments, thus influencing the tidal landscape and contributing to new possible ecological interactions. As sea foam is a wet environment, it is conducive habitat to algal spores where propagules can attach to the substrate and avoid risk of dissemination. When sea foam contains fungi, it can also aid in the decomposition of plant and animal remains in coastal ecosystems. | 9 | Geochemistry |
Reisler grew up in Israel. She studied at the Hebrew University of Jerusalem, earning her undergraduate degree in 1964. She moved to the Weizmann Institute of Science for her graduate studies, completing her PhD in physical chemistry 1972. Reisler worked as a postdoctoral fellow with John Doering at Johns Hopkins University. Here she studied the inelastic scattering of ions. | 7 | Physical Chemistry |
Carbon nucleophiles such as Grignard reagents, convert acyl chlorides to ketones, which in turn are susceptible to the attack by second equivalent to yield the tertiary alcohol. The reaction of acyl halides with certain organocadmium reagents stops at the ketone stage. The reaction with Gilman reagents also afford ketones, reflecting the low nucleophilicity of these lithium diorganocopper compounds. | 0 | Organic Chemistry |
Water vapor is the most important greenhouse gas overall, being responsible for 41–67% of the greenhouse effect, but its global concentrations are not directly affected by human activity. While local water vapor concentrations can be affected by developments such as irrigation, it has little impact on the global scale due to its short residence time of about nine days. Indirectly, an increase in global temperatures cause will also increase water vapor concentrations and thus their warming effect, in a process known as water vapor feedback. It occurs because Clausius–Clapeyron relation establishes that more water vapor will be present per unit volume at elevated temperatures. Thus, local atmospheric concentration of water vapor varies from less than 0.01% in extremely cold regions and up to 3% by mass in saturated air at about 32 °C. | 2 | Environmental Chemistry |
Soil texture influences the soil chemistry pertaining to the soil's ability to maintain its structure, the restriction of water flow and the contents of the particles in the soil. Soil texture considers all particle types and a soil texture triangle is a chart that can be used to calculate the percentages of each particle type adding up to total 100% for the soil profile. These soil separates differ not only in their sizes but also in their bearing on some of the important factors affecting plant growth such as soil aeration, work ability, movement and availability of water and nutrients. | 9 | Geochemistry |
Expendable mold casting is a generic classification that includes sand, plastic, shell, plaster, and investment (lost-wax technique) moldings. This method of mold casting involves the use of temporary, non-reusable molds. | 8 | Metallurgy |
-Enzymes are environmentally benign, being completely degraded in the environment.
-Most enzymes typically function under mild or biological conditions, which minimizes problems of undesired side-reactions such as decomposition, isomerization, racemization and rearrangement, which often plague traditional methodology.
-Enzymes selected for chemoenzymatic synthesis can be immobilized on a solid support. These immobilized enzymes demonstrate improved stability and re-usability.
-Through the development of protein engineering, specifically site-directed mutagenesis and directed evolution, enzymes can be modified to enable non-natural reactivity. Modifications may also allow for a broader substrate range, enhance reaction rate or catalyst turnover.
-Enzymes exhibit extreme selectivity towards their substrates. Typically enzymes display three major types of selectivity:
*Chemoselectivity: Since the purpose of an enzyme is to act on a single type of functional group, other sensitive functionalities, which would normally react to a certain extent under chemical catalysis, survive. As a result, biocatalytic reactions tend to be "cleaner" and laborious purification of product(s) from impurities emerging through side-reactions can largely be omitted.
*Regioselectivity and diastereoselectivity: Due to their complex three-dimensional structure, enzymes may distinguish between functional groups which are chemically situated in different regions of the substrate molecule.
*Enantioselectivity: Since almost all enzymes are made from L-amino acids, enzymes are chiral catalysts. As a consequence, any type of chirality present in the substrate molecule is "recognized" upon the formation of the enzyme-substrate complex. Thus a prochiral substrate may be transformed into an optically active product and both enantiomers of a racemic substrate may react at different rates.
These reasons, and especially the latter, are the major reasons why synthetic chemists have become interested in biocatalysis. This interest in turn is mainly due to the need to synthesize enantiopure compounds as chiral building blocks for Pharmaceutical drugs and agrochemicals. | 0 | Organic Chemistry |
This silicon α-effect was first observed in the late 1960s by researchers at Bayer AG as an increase in reactivity at the silicon atom for hydrolysis and was used for cross-linking of α-silane-terminated prepolymers. For a long time after that, people attributed this reactivity as silicon α-effect. However, the real mechanism beneath it had been debated for many years after this discovery. Generally, this effect has been rationalized as an intramolecular donor-acceptor interaction between the lone pair of the organofunctional group (such as NR, OC(O)R, N(H)COOMe) and the silicon atom. However, this hypothesis has been proved incorrect by Mitzel and coworkers and more experiments are needed to interpret this effect. | 7 | Physical Chemistry |
The study of agrominerals is termed agrogeology, and agrogeologists are concerned with issues such as the replenishment of soil fertility in areas where agrominerals have been depleted by unsustainable farming methods. With current farming practice, the system is expected to have high crop production with low soil quality. Over time with this type of practice, ground nutrients have been depleted which has led to an increase in chemical fertilizer usage. Chemical fertilizers have been shown to have runoff and it can contaminate groundwaters and are not economically feasible for third world countries. One of the major sources for chemical fertilizers is potash ore. The other concern with the potash ore is the supply is finite and is running out, hence the increase in pricing. Potash is one of the major sources for potassium and phosphorus and one of the original agrominerals. Finding alternative sources for these agrominerals was a concept that was created to focus on soil remediation, to increase productivity in a low-cost manner.
At first agrominerals were used to help recreate soil conditions for exotic plants. These were simple practices that occur on a much smaller scale. These include using perlite to enhance the aeration of the soil, using pumice to control evaporation while one can use vermiculites and zeolites to store moisture. This soil modification was the start of the agromineral concept and has evolved into looking for alternative sources to obtain the three major nutrient elements. Remineralization has been the term created for implementing rock powders into soils as a source of nutrients. This process has been implemented into bigger operations and has found great success in places like Brazil, Germany, Norway, South Africa, Sri Lanka, and Uganda. | 9 | Geochemistry |
In the mid 19th century, investigators proposed several possible structures for benzene which were consistent with its empirical formula, CH, which had been determined by combustion analysis. The first, which was proposed by Kekulé in 1865, later proved to be closest to the true structure of benzene. This structure inspired several others to draw structures that were consistent with benzenes empirical formula; for example, Ladenburg proposed prismane, Dewar proposed Dewar benzene, and Koerner and Claus proposed Claus benzene. Some of these structures would be synthesized in the following years. Prismane, like the other proposed structures for benzene, is still often cited in the literature, because it is part of the historical struggle toward understanding the mesomeric structures and resonance of benzene. Some computational chemists still research the differences between the possible isomers of CH. | 4 | Stereochemistry |
Electrical steel is one material that uses decarburization in its production. To prevent the atmospheric gases from reacting with the metal itself, electrical steel is annealed in an atmosphere of nitrogen, hydrogen, and water vapor, where oxidation of the iron is specifically prevented by the proportions of hydrogen and water vapor so that the only reacting substance is carbon being oxidized into carbon monoxide (CO). | 8 | Metallurgy |
The Fineman-Ross method can be biased towards points at low or high monomer concentration, so Kelen and Tüdős introduced an arbitrary constant,
where and are the highest and lowest values of from the Fineman-Ross method. The data can be plotted in a linear form
where and . Plotting against yields a straight line that gives when and when . This distributes the data more symmetrically and can yield better results. | 7 | Physical Chemistry |
Everhardus Ariëns 1963 was honored at the second International Congress of Pharmacology in Prague with the Purkinje Medal. In 1970 he became member of the Royal Netherlands Academy of Arts and Sciences. He also received the Dr. Saal van Zwanenberg Award (1972), the Medal of the Norwegian Poulsson Pharmacological Society (1973), the Scheele Award (1974), the Schmiedeberg Medal (1980) and the Smissman Award of the American Chemical Society (1985).
Everhardus Ariëns was awarded honorary doctorates from universities Universidade Luterana do Brasil, University of Kiel, University of Paris-Sud and Università degli Studi di Camerino. Another honorary doctorate was awarded in March 2002 at the Ohio State University. | 4 | Stereochemistry |
Secondary metabolites are compounds made in the stationary phase; penicillin, for instance, prevents the growth of bacteria which could compete with Penicillium molds for resources. Some bacteria, such as Lactobacillus species, are able to produce bacteriocins which prevent the growth of bacterial competitors as well. These compounds are of obvious value to humans wishing to prevent the growth of bacteria, either as antibiotics or as antiseptics (such as gramicidin S). Fungicides, such as griseofulvin are also produced as secondary metabolites. Typically secondary metabolites are not produced in the presence of glucose or other carbon sources which would encourage growth, and like primary metabolites are released into the surrounding medium without rupture of the cell membrane.
In the early days of the biotechnology industry, most biopharmaceutical products were made in E. coli; by 2004 more biopharmaceuticals were manufactured in eukaryotic cells, such as CHO cells, than in microbes, but used similar bioreactor systems. Insect cell culture systems came into use in the 2000s as well. | 1 | Biochemistry |
In primary aluminium production, aluminium carbides (AlC) originates from the reduction of alumina where carbon anodes and cathodes are in contact with the mix. Later in the process, any carbon tools in contact with the liquid aluminium can react and create carbides. | 8 | Metallurgy |
The diverse genome-wide repeats are derived from transposable elements, which are now understood to "jump" about different genomic locations, without transferring their original copies. Subsequent shuttling of the same sequences over numerous generations ensures their multiplicity throughout the genome. The limited recombination of the sequences between two distinct sequence elements known as conservative site-specific recombination (CSSR) results in inversions of the DNA segment, based on the arrangement of the recombination recognition sequences on the donor DNA and recipient DNA. Again, the orientation of two of the recombining sites within the donor DNA molecule relative to the asymmetry of the intervening DNA cleavage sequences, known as the crossover region, is pivotal to the formation of either inverted repeats or direct repeats. Thus, recombination occurring at a pair of inverted sites will invert the DNA sequence between the two sites. Very stable chromosomes have been observed with comparatively fewer numbers of inverted repeats than direct repeats, suggesting a relationship between chromosome stability and the number of repeats. | 1 | Biochemistry |
Natural compounds refer to those that are produced by plants or animals. Many of these are still extracted from natural sources because they would be more expensive to produce artificially. Examples include most sugars, some alkaloids and terpenoids, certain nutrients such as vitamin B, and, in general, those natural products with large or stereoisometrically complicated molecules present in reasonable concentrations in living organisms.
Further compounds of prime importance in biochemistry are antigens, carbohydrates, enzymes, hormones, lipids and fatty acids, neurotransmitters, nucleic acids, proteins, peptides and amino acids, lectins, vitamins, and fats and oils. | 0 | Organic Chemistry |
Methyl cyanoformate is the organic compound with the formula CHOC(O)CN. It is used as a reagent in organic synthesis as a source of the methoxycarbonyl group, in which context it is also known as Manders reagent. When a lithium enolate is generated in diethyl ether or methyl t-butyl ether, treatment with Manders reagent will selectively afford the C-acylation product. Thus, for enolate acylation reactions in which C- vs. O-selectivity is a concern, methyl cyanoformate is often used in place of more common acylation reagent like methyl chloroformate.
Methyl cyanoformate is also an ingredient in Zyklon A. It has lachrymatory effects. | 0 | Organic Chemistry |
The first mention of any research or study of the gold halides dates back to the early-to-mid-19th century, and there are three primary researchers associated with the extensive investigation of this particular area of chemistry: Thomsen, Schottländer, and Krüss. | 3 | Analytical Chemistry |
The electrical double layer (EDL) is the result of the variation of electric potential near a surface, and has a significant influence on the behaviour of colloids and other surfaces in contact with solutions or solid-state fast ion conductors.
The primary difference between a double layer on an electrode and one on an interface is the mechanism of surface charge formation. With an electrode, it is possible to regulate the surface charge by applying an external electric potential. This application, however, is impossible in colloidal and porous double layers, because for colloidal particles, one does not have access to the interior of the particle to apply a potential difference.
EDLs are analogous to the double layer in plasma. | 7 | Physical Chemistry |
Aziridine is produced industrially from aminoethanol via two related routes. The Nippon Shokubai process requires an oxide catalyst and high temperatures to effect the dehydration. In the Wenker synthesis, the aminoethanol is converted to the sulfate ester, which undergoes base-induced sulfate elimination. Older methods entailed amination of 1,2-dichloroethane and cyclization of 2-chloroethylamine.
Aziridine forms a wide variety of polymeric derivatives, known as polyethylenimines (PEI). These and related species are useful crosslinking agents and precursors for coatings. | 0 | Organic Chemistry |
George Ellery Hale was the first to notice the Zeeman effect in the solar spectra, indicating the existence of strong magnetic fields in sunspots. Such fields can be quite high, on the order of 0.1 tesla or higher. Today, the Zeeman effect is used to produce magnetograms showing the variation of magnetic field on the Sun. | 7 | Physical Chemistry |
Squalene is biosynthesised by coupling two molecules of farnesyl pyrophosphate. The condensation requires NADPH and the enzyme squalene synthase. | 1 | Biochemistry |
Virilization or masculinization is the biological development of adult male characteristics in young males or females. Most of the changes of virilization are produced by androgens.
Virilization is a medical term commonly used in three medical and biology of sex contexts: prenatal biological sexual differentiation, the postnatal changes of typical chromosomal male (46, XY) puberty, and excessive androgen effects in typical chromosomal females (46, XX). It is also the intended result of androgen replacement therapy in males with delayed puberty and low testosterone. | 1 | Biochemistry |
Many waters in both the UK and Europe are capable of supporting Type 1 pitting but no problems will be experienced unless a pit is initiated in the wall of the tube. When a copper tube is initially filled with a hard water salts deposit on the wall and the copper slowly reacts with the water producing a thin protective layer of mixed corrosion products and hardness scale. If any pitting of the tube is to occur then this film must be locally disrupted. There are three mechanisms that allow the disruption of the protective deposits. The most well known, although now the least common, is the presence of carbon films on the bore. Stagnation and flux residues are the most common initiation mechanisms that have led to Type 1 pitting failures in the last ten years. | 8 | Metallurgy |
In fractional order reactions, the order is a non-integer, which often indicates a chemical chain reaction or other complex reaction mechanism. For example, the pyrolysis of acetaldehyde () into methane and carbon monoxide proceeds with an order of 1.5 with respect to acetaldehyde: The decomposition of phosgene () to carbon monoxide and chlorine has order 1 with respect to phosgene itself and order 0.5 with respect to chlorine:
The order of a chain reaction can be rationalized using the steady state approximation for the concentration of reactive intermediates such as free radicals. For the pyrolysis of acetaldehyde, the Rice-Herzfeld mechanism is
;Initiation :
;Propagation :
;Termination :
where • denotes a free radical. To simplify the theory, the reactions of the to form a second are ignored.
In the steady state, the rates of formation and destruction of methyl radicals are equal, so that
so that the concentration of methyl radical satisfies
The reaction rate equals the rate of the propagation steps which form the main reaction products and CO:
in agreement with the experimental order of 3/2. | 7 | Physical Chemistry |
A tertiary carbocation will maximize the rate of reaction for an SN1 reaction by producing a stable carbocation. This happens because the rate determining step of a SN1 reaction is the formation of the carbocation. The rate of the reaction is therefore reliant on the stability of the carbocation because it means that the transition state has a lower energy level which makes the activation energy lower. Tertiary carbons are similarly preferred in E1 for the same reasons as it has a carbocation intermediate. E1 and E2 reactions follow Zaitsev's rule which states that the most substituted product in an elimination reactions is going to be the major product because it will be favored for its stability. This leads to tertiary carbons being preferred for their stability in elimination reactions. In general, SN2 reactions do not occur with tertiary carbons because of the steric hindrance produced by the substituted groups. However, recent research has shown there are exceptions to this rule; for the first time, a bimolecular nucleophilic substitution, aka SN2 reaction, can happen to a tertiary carbon. | 0 | Organic Chemistry |
In general, EPIC-seq analysis results showed a significant correlation between the inspected biological effect and the developed score. For the classification tasks Area Under the ROC (receiver operating characteristic curve) Curve (AUC) scores were over 90% with a sufficient significance interval. Also, for these tasks, cfDNA levels did not change the performance unfavourably even when the levels were below 1%. So, the method shows a good robustness against cfDNA levels as well. Finally, EPIC-seq did not show any significant changes under different pre-analytical factors, which proves that the method is robust under different circumstances that can be caused by the instruments and tools used before the analysis. | 1 | Biochemistry |
AFM-IR has been used to study hydrated Nafion membranes used as separators in fuel cells. The measurements revealed the distribution of free and ionically bound water on the Nafion surface. | 3 | Analytical Chemistry |
M30 Apoptosense® ELISA is an enzyme-linked immunosorbent assay developed for the detection of soluble caspase-cleaved keratin 18 (ccK18, K18-Asp396, formerly cytokeratin 18, ccCK18 or CK18-Asp396). | 1 | Biochemistry |
Trifluoroiodomethane is a reagent in aromatic coupling reactions. It has also been used with enones, for example with chalcone, a reaction catalysed by diethyl zinc and Wilkinson's catalyst: | 0 | Organic Chemistry |
Garson won a Royal Society postdoctoral fellowship after her PhD, undertaking research in Rome, Italy from 1977 to 1978. She continued her research at New Hall at Cambridge on a college research fellowship from 1978 to 1981. She worked as a medicinal chemist from 1981 to 1983 at Smith Kline and French Research Ltd in Welwyn, England,.
Garson won a Queen Elizabeth II Research Fellowship from James Cook University (1983–1986), based in the Townsville region to research the bioactive organic chemicals in marine organisms. In Townsville, she undertook dive training to study on the Great Barrier Reef. Garson then took a teaching/research position as the first female academic in chemistry at the University of Wollongong, before moving to the University of Queensland as a lecturer in 1990. She was promoted to Senior Lecturer in 1992 and Reader in 1998. She researches and publishes on the structure, biosynthesis and function of natural products, especially those from marine invertebrates and other microorganisms. She also researches the chemistry of South East Asian medicinal plants.
Garson was promoted to Professor in the School of Chemistry and Molecular Biosciences in 2006, and has served as Deputy Head of the School from 2005 to 2009. Since 2021, she is an Emeritus Professor of Chemistry at the university. | 0 | Organic Chemistry |
*The Ki Database is a public domain database of published binding affinities (Ki) of drugs and chemical compounds for receptors, neurotransmitter transporters, ion channels, and enzymes.
*BindingDB is a public domain database of measured binding affinities, focusing chiefly on the interactions of protein considered to be drug-targets with small, drug-like molecules | 7 | Physical Chemistry |
Laser diffraction analysis has been used to measure particle-size objects in situations such as:
* observing distribution of soil texture and sediments such as clay and mud, with an emphasis on silt and the sizes of bigger samples of clay.
* determining in situ measurements of particles in estuaries. Particles in estuaries are important as they allow for natural or pollutant chemical species to move around with ease. The size, density, and stability of particles in estuaries are important for their transportation. Laser diffraction analysis is used here to compare particle size distributions to support this claim as well as find cycles of change in estuaries that occur because of different particles.
* soil and its stability when wet. The stability of soil aggregation (clumps held together by moist clay) and clay dispersion (clay separating in moist soil), the two different states of soil in the Cerrado savanna region, were compared with laser diffraction analysis to determine if plowing had an effect on the two. Measurements were made before plowing and after plowing for different intervals of time. Clay dispersion turned out to not be affected by plowing while soil aggregation did.
* erythrocyte deformability under shear. Due to a special phenomenon called tank treading, the membrane of the erythrocyte (red blood cell, RBC) rotates relative to the shear force and the cells cytoplasm causing RBCs to orient themselves. Oriented and stretched red blood cells have a diffraction pattern representing the apparent particle size in each direction, making it possible to measure the erythrocyte deformability and the orientability of the cells. In an ektacytometer' erythrocyte deformability can be measured under changing osmotic stress or oxygen tension and is used in the diagnosis and follow up of congenital hemolytic anemias. | 7 | Physical Chemistry |
The earliest and most diverse finds of metal artifacts are from West Mexico stretching in a belt along the Pacific coast from Guerrero to Nayarit. This indicates that this region was a regional nucleus of metallurgy, from which elements of technique, form and style could have diffused throughout Mesoamerica. | 8 | Metallurgy |
Purine degradation takes place mainly in the liver of humans and requires an assortment of enzymes to degrade purines to uric acid. First, the nucleotide will lose its phosphate through 5'-nucleotidase. The nucleoside, adenosine, is then deaminated and hydrolyzed to form hypoxanthine via adenosine deaminase and nucleosidase respectively. Hypoxanthine is then oxidized to form xanthine and then uric acid through the action of xanthine oxidase. The other purine nucleoside, guanosine, is cleaved to form guanine. Guanine is then deaminated via guanine deaminase to form xanthine which is then converted to uric acid. Oxygen is the final electron acceptor in the degradation of both purines. Uric acid is then excreted from the body in different forms depending on the animal.
Free purine and pyrimidine bases that are released into the cell are typically transported intercellularly across membranes and salvaged to create more nucleotides via nucleotide salvage.
For example, adenine + PRPP --> AMP + PPi. This reaction requires the enzyme adenine phosphoribosyltransferase. Free guanine is salvaged in the same way except it requires hypoxanthine-guanine phosphoribosyltransferase.
Defects in purine catabolism can result in a variety of diseases including gout, which stems from an accumulation of uric acid crystals in various joints, and adenosine deaminase deficiency, which causes immunodeficiency. | 1 | Biochemistry |
In 1838, Justus von Liebig proposed that an acid is a hydrogen-containing compound whose hydrogen can be replaced by a metal. This redefinition was based on his extensive work on the chemical composition of organic acids, finishing the doctrinal shift from oxygen-based acids to hydrogen-based acids started by Davy. Liebig's definition, while completely empirical, remained in use for almost 50 years until the adoption of the Arrhenius definition. | 7 | Physical Chemistry |
Metallacarboxylic acids mainly arise by the attack of hydroxide on electrophilic metal carbonyl complexes. An illustrative synthesis is the reaction of a cationic iron carbonyl with a stoichiometric amount of base:
:[(CH)(CO)FeCO]BF + NaOH → [(CH)(CO)FeCOH + NaBF
When applied to simple metal carbonyls, this kind of conversion is sometimes called the Hieber base reaction. Decarboxylation of the resulting anion gives the anionic hydride complex. This conversion is illustrated by the synthesis of [[Iron tetracarbonyl hydride|[HFe(CO)]]] from iron pentacarbonyl.
:Fe(CO) + NaOH → NaFe(CO)COH
:NaFe(CO)COH → NaHFe(CO) + CO | 0 | Organic Chemistry |
In chemistry, the term "contamination" usually describes a single constituent, but in specialized fields the term can also mean chemical mixtures, even up to the level of cellular materials. All chemicals contain some level of impurity. Contamination may be recognized or not and may become an issue if the impure chemical causes additional chemical reactions when mixed with other chemicals or mixtures. Chemical reactions resulting from the presence of an impurity may at times be beneficial, in which case the label "contaminant" may be replaced with "reactant" or "catalyst." (This may be true even in physical chemistry, where, for example, the introduction of an impurity in an intrinsic semiconductor positively increases conductivity.) If the additional reactions are detrimental, other terms are often applied such as "toxin", "poison", or pollutant, depending on the type of molecule involved. Chemical decontamination of substance can be achieved through decomposition, neutralization, and physical processes, though a clear understanding of the underlying chemistry is required. Contamination of pharmaceutics and therapeutics is notoriously dangerous and creates both perceptual and technical challenges. | 9 | Geochemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), Valine (Val, V) | 1 | Biochemistry |
It is free to become a member of BOGS. To join the mailing list for BOGS, an email is sent to the BOGS webmaster at [email protected]. | 9 | Geochemistry |
"Southwestern blot mapping" is a time-efficient way of identifying DNA-binding proteins and specific sites on the genomic DNA that they interact with.
# First, proteins are prepared with a mixture that exposes them to the denaturing sodium dodecyl sulfate (SDS) agent. This exposure not only converts the proteins from a folded conformation to an unfolded conformation but also establishes uniform charge among them as well contributing to the ease of separation on a size basis using polyacrylamide gel (PAGE).
# Second, in contrast to the previous step, proteins on the resulting gel are to be renatured by removal of SDS. This serves to bring the proteins back to the form that ideally maximizes interactions later on in the procedure.
# Third, blotting takes place onto nitrocellulose membranes using methods for and properties of diffusion.
# Fourth, shifting to probe creation, particular restriction enzymes are chosen and used on the region of DNA under study to produce fragments of appropriate but different sizes.
# Fifth, the fragments are radioactively labeled and given appropriate time for binding to previously prepared blots. Once this time has elapsed, the blots are washed to remove any DNA that was not able to bind.
# Finally, the specifically-bound DNA is eluted from each individual protein-DNA complex and analyzed by another application of polyacrylamide gel electrophoresis. | 1 | Biochemistry |
Karl Schwarzschild in 1906 considered a system in which convection and radiation both operated but radiation was so much more efficient than convection that convection could be, as an approximation, neglected, and radiation could be considered predominant. This applies when the temperature is very high, as for example in a star, but not in a planet's atmosphere.
Subrahmanyan Chandrasekhar (1950, page 290) writes of a model of a stellar atmosphere in which "there are no mechanisms, other than radiation, for transporting heat within the atmosphere ... [and] there are no sources of heat in the surrounding" This is hardly different from Schwarzschild's 1906 approximate concept, but is more precisely stated. | 7 | Physical Chemistry |
Lateral manipulation means moving an adsorbate on the surface by making a temporary chemical or physical bond between the STM tip and the adsorbate. A typical lateral manipulation sequence begins by positioning the tip close to the adsorbate, bringing the tip close to the surface by increasing the tunneling current setpoint, moving the tip along a desired route and finally retracting the tip to normal scanning height. Lateral manipulation is typically applied to strongly bound adsorbates, such as metal adatoms on metal surfaces. The probability that the surface adsorbate moves the same distance traveled by the tip is strongly dependent on the tip conditions.
Depending on the tip apex and the surface/adsorbate system, the lateral motion can occur by pushing, pulling or sliding of the adsorbate. These modes result in distinct tunneling current signals during the lateral motion. For example, periodic steps in the tunneling current indicate that the adsorbate is “jumping” between adsorption sites while following the tip: this means the tip pushes or pulls the adsorbate. | 7 | Physical Chemistry |
Electro sinter forging (ESF) is an industrial single electromagnetic pulse sintering technique to rapidly produce a wide range of small components in metals, alloys, intermetallics, semiconductors, and composites. ESF was invented by Alessandro Fais, an Italian metallurgical engineer and scientist.
ESF is obtained by inserting loose, binder-less powders into the automatic dosing system, or manually inserted in the mold. The automatic procedure applies a pre-pressure onto the powders to ensure electrical contact; hence, it superimposes an intense electromagnetic pulse with a mechanical pulse. The two pulses last 30 to 100 ms. After a brief holding time, the sintered component is extracted by the lower plunger and pushed out by the extractor to leave room for the next sintering. Each sintering round lasts less than one second, and is carried out entirely in air (even with pyrophoric materials). | 8 | Metallurgy |
Primary and secondary antibodies are two groups of antibodies that are classified based on whether they bind to antigens or proteins directly or target another (primary) antibody that, in turn, is bound to an antigen or protein. | 1 | Biochemistry |
The Orbiting Carbon Observatory-3 (OCO-3) is a NASA-JPL instrument designed to measure carbon dioxide in Earths atmosphere. The instrument is mounted on the Japanese Experiment Module-Exposed Facility on board the International Space Station (ISS). OCO-3 was scheduled to be transported to space by a SpaceX Dragon from a Falcon 9 rocket on 30 April 2019, but the launch was delayed to 3 May, due to problems with the space stations electrical power system. This launch was further delayed to 4 May due to electrical issues aboard Of Course I Still Love You (OCISLY), the barge used to recover the Falcon 9’s first stage. OCO-3 was launched as part of CRS-17 on 4 May 2019 at 06:48 UTC. The nominal mission lifetime is ten years.
OCO-3 was assembled using spare materials from the Orbiting Carbon Observatory-2 satellite. Because the OCO-3 instrument is similar to the OCO-2 instrument, it is expected to have similar performance with its measurements used to quantify to 1 ppm precision or better at 3 Hz. | 2 | Environmental Chemistry |
The Treatment and management of soils and water in acid sulfate soil landscapes provides an overview of acid sulfate soil management strategies – including a discussion on groundwater management (which is not covered in the Queensland technical manual). | 9 | Geochemistry |
The high pressure pump pushes water through the membrane. Typical pressures for brackish water range from 1.6 to 2.6 MPa (225 to 376 psi). In the case of seawater, they range from 5.5 to 8 MPa (800 to 1,180 psi). This requires substantial energy. Where energy recovery is used, part of the high pressure pump's work is done by the energy recovery device, reducing energy inputs. | 3 | Analytical Chemistry |
Most biological macromolecules contain few or no halogen atoms. But when molecules do contain halogens, halogen bonds are often essential to understanding molecular conformation. Computational studies suggest that known halogenated nucleobases form halogen bonds with oxygen, nitrogen, or sulfur in vitro. Interestingly, oxygen atoms typically do not attract halogens with their lone pairs, but rather the π electrons in the carbonyl or amide group.
Halogen bonding can be significant in drug design as well. For example, inhibitor IDD 594 binds to human aldose reductase through a bromine halogen bond, as shown in the figure. The molecules fail to bind to each other if similar aldehyde reductase replaces the enzyme, or chlorine replaces the drug halogen, because the variant geometries inhibit the halogen bond. | 6 | Supramolecular Chemistry |
Hemiaminals form from the reaction of an amine and a ketone or aldehyde. The hemiaminal is sometimes isolable, but often they spontaneously dehydrate to give imines. | 0 | Organic Chemistry |
The lack of drugs and unavailability of experimental treatment in the most affected regions of the West African Ebola virus outbreak spurred some controversy. The fact that the drug was first given to Americans and a European and not to Africans, according to the Los Angeles Times, "provoked outrage, feeding into African perceptions of Western insensitivity and arrogance, with a deep sense of mistrust and betrayal still lingering over the exploitation and abuses of the colonial era". Salim S. Abdool Karim, the director of an AIDS research center in South Africa, placed the issue in the context of the history of exploitation and abuses. Responding to a question on how people might have reacted if ZMapp and other drugs had first been used on Africans, he said "It would have been the front-page screaming headline: Africans used as guinea pigs for American drug companys medicine.
In early August, the World Health Organization called for convening a panel of medical authorities "to consider whether experimental drugs should be more widely released." In a statement, Peter Piot (co-discoverer of the Ebola virus); Jeremy Farrar, the director of the Wellcome Trust; and David Heymann of the Chatham House Center on Global Health Security, called for the release of experimental drugs for affected African nations.
At an August 6, 2014 press conference, Barack Obama, the President of the United States, was questioned regarding whether the cocktail should be fast-tracked for approval or be made available to sick patients outside of the United States. He responded, "I think weve got to let the science guide us. I dont think all the information's in on whether this drug is helpful." | 1 | Biochemistry |
Pheophorbide or phaeophorbide is a product of chlorophyll breakdown and a derivative of pheophytin where both the central magnesium has been removed and the phytol tail has been hydrolyzed. It is used as a photosensitizer in photodynamic therapy.
Pheophorbide may be generated by digestion of ingested plant matter. Both worm (Caenorhabditis elegans) and mouse mitochondria are able to use the molecule in a form of ad hoc photoheterotrophy. | 1 | Biochemistry |
Liquid, submerged and solid state fermentation are age-old techniques used for the preservation and manufacturing of foods. During the second half of the twentieth century, liquid state fermentation developed on an industrial scale to manufacture vital metabolites such as antibiotics.
Economic changes and growing environmental awareness generate new perspectives for solid state fermentation. SSF adds value to insoluble agricultural byproducts thanks to its higher energy efficiency and reduced water consumption.
The renewal of SSF is now possible thanks to engineering firms, mainly from Asia, that have developed a new generation of equipment. Fujiwara makes vessels able to transform substrate areas up to for the production of soy sauce or sake. Other companies use solid state fermentation for enzyme complexes. In France Lyven has manufactured Pectinases and Hemicellulases on beet pulp and wheat bran since 1980. The company (now part of Soufflet Group) is now involved in a global R&D programme focusing on SSF technology. | 1 | Biochemistry |
Due to the range of genes that Pol II transcribes, this is the polymerase that experiences the most regulation by a range of factors at each stage of transcription. It is also one of the most complex in terms of polymerase cofactors involved.
Initiation is regulated by many mechanisms. These can be separated into two main categories:
#Protein interference.
#Regulation by phosphorylation. | 1 | Biochemistry |
For typical ionic solids, the cations are smaller than the anions, and each cation is surrounded by coordinated anions which form a polyhedron. The sum of the ionic radii determines the cation-anion distance, while the cation-anion radius ratio (or ) determines the coordination number (C.N.) of the cation, as well as the shape of the coordinated polyhedron of anions.
For the coordination numbers and corresponding polyhedra in the table below, Pauling mathematically derived the minimum radius ratio for which the cation is in contact with the given number of anions (considering the ions as rigid spheres). If the cation is smaller, it will not be in contact with the anions which results in instability leading to a lower coordination number.
The three diagrams at right correspond to octahedral coordination with a coordination number of six: four anions in the plane of the diagrams, and two (not shown) above and below this plane. The central diagram shows the minimal radius ratio. The cation and any two anions form a right triangle, with , or . Then . Similar geometrical proofs yield the minimum radius ratios for the highly symmetrical cases C.N. = 3, 4 and 8.
For C.N. = 6 and a radius ratio greater than the minimum, the crystal is more stable since the cation is still in contact with six anions, but the anions are further from each other so that their mutual repulsion is reduced. An octahedron may then form with a radius ratio greater than or equal to 0.414, but as the ratio rises above 0.732, a cubic geometry becomes more stable. This explains why in NaCl with a radius ratio of 0.55 has octahedral coordination, whereas in CsCl with a radius ratio of 0.93 has cubic coordination.
If the radius ratio is less than the minimum, two anions will tend to depart and the remaining four will rearrange into a tetrahedral geometry where they are all in contact with the cation.
The radius ratio rules are a first approximation which have some success in predicting coordination numbers, but many exceptions do exist. In a set of over 5000 oxides, only 66% of coordination environments agree with Pauling's first rule. Oxides formed with alkali or alkali-earth metal cations that contain multiple cation coordinations are common deviations from this rule. | 4 | Stereochemistry |
Many beam HREM images of extremely thin samples are only directly interpretable in terms of a projected crystal structure if they have been recorded under special conditions, i.e. the so-called Scherzer defocus. In that case the positions of the atom columns appear as black blobs in the image (when the spherical aberration coefficient of the objective lens is positive - as always the case for uncorrected TEMs). Difficulties for interpretation of HREM images arise for other defocus values because the transfer properties of the objective lens alter the image contrast as function of the defocus. Hence atom columns which appear at one defocus value as dark blobs can turn into white blobs at a different defocus and vice versa. In addition to the objective lens defocus (which can easily be changed by the TEM operator), the thickness of the crystal under investigation has also a significant influence on the image contrast. These two factors often mix and yield HREM images which cannot be straightforwardly interpreted as a projected structure. If the structure is unknown, so that image simulation techniques cannot be applied beforehand, image interpretation is even more complicated. Nowadays two approaches are available to overcome this problem: one method is the exit-wave function reconstruction method, which requires several HREM images from the same area at different defocus and the other method is crystallographic image processing (CIP) which processes only a single HREM image. Exit-wave function reconstruction provides an amplitude and phase image of the (effective) projected crystal potential over the whole field of view. The thereby reconstructed crystal potential is corrected for aberration and delocalisation and also not affected by possible transfer gaps since several images with different defocus are processed. CIP on the other side considers only one image and applies corrections on the averaged image amplitudes and phases. The result of the latter is a pseudo-potential map of one projected unit cell. The result can be further improved by crystal tilt compensation and search for the most likely projected symmetry. In conclusion one can say that the exit-wave function reconstruction method has most advantages for determining the (aperiodic) atomic structure of defects and small clusters and CIP is the method of choice if the periodic structure is in focus of the investigation or when defocus series of HREM images cannot be obtained, e.g. due to beam damage of the sample. However, a recent study on the catalyst related material Cs[NbWO] shows the advantages when both methods are linked in one study. | 3 | Analytical Chemistry |
Studies have shown that diversity among nonsynonymous substitutions is significantly lower than among synonymous substitutions. This is due to the fact that nonsynonymous substitutions are subject to much higher selective pressures than synonymous mutations. Motoo Kimura (1968) determined that calculated mutation rates were impossibly high, unless most of the mutations that occurred were either neutral or "nearly neutral". He determined that if this were true, genetic drift would be a more powerful factor in molecular evolution than natural selection. The "nearly neutral" theory proposes that molecular evolution acting on nonsynonymous substitutions is driven by mutation, genetic drift, and very weak natural selection, and that it is extremely sensitive to population size. In order to determine whether natural selection is taking place at a certain loci, the McDonald–Kreitman test can be performed. The test consists of comparing ratios of synonymous and nonsynonymous genes between closely related species to the ratio of synonymous to nonsynonymous polymorphisms within species. If the ratios are the same, then Neutral theory of molecular evolution is true for that loci, and evolution is proceeding primarily through genetic drift. If there are more nonsynonymous substitutions between species than within a species, positive natural selection is occurring on beneficial alleles and natural selection is taking place. Nonsynonymous substitutions have been found to be more common in loci involving pathogen resistance, reproductive loci involving sperm competition or egg-sperm interactions, and genes that have replicated and gained new functions, indicating that positive selection is taking place. | 1 | Biochemistry |
As hormones are defined functionally, not structurally, they may have diverse chemical structures. Hormones occur in multicellular organisms (plants, animals, fungi, brown algae, and red algae). These compounds occur also in unicellular organisms, and may act as signaling molecules however there is no agreement that these molecules can be called hormones. | 1 | Biochemistry |
The flux of the entire pathway is regulated by the rate-determining steps. These are the slowest steps in a network of reactions. The rate-limiting step occurs near the beginning of the pathway and is regulated by feedback inhibition, which ultimately controls the overall rate of the pathway. The metabolic pathway in the cell is regulated by covalent or non-covalent modifications. A covalent modification involves an addition or removal of a chemical bond, whereas a non-covalent modification (also known as allosteric regulation) is the binding of the regulator to the enzyme via hydrogen bonds, electrostatic interactions, and Van Der Waals forces.
The rate of turnover in a metabolic pathway, also known as the metabolic flux, is regulated based on the stoichiometric reaction model, the utilization rate of metabolites, and the translocation pace of molecules across the lipid bilayer. The regulation methods are based on experiments involving 13C-labeling, which is then analyzed by Nuclear Magnetic Resonance (NMR) or gas chromatography-mass spectrometry (GC-MS)-derived mass compositions. The aforementioned techniques synthesize a statistical interpretation of mass distribution in proteinogenic amino acids to the catalytic activities of enzymes in a cell. | 1 | Biochemistry |
* Anomeric effect
* Carbohydrate
* Carbohydrate conformation
* Disaccharide
* Glycosidic bond
* Monosaccharide
* Polysaccharide | 0 | Organic Chemistry |
Molecular recognition events mediated through orbital interactions are critical in a number of biological processes such as enzyme catalysis. Stabilizing interactions between proteins and carbohydrates in glycosylated proteins also exemplify the role of stereoelectronic effects in biomolecules. | 4 | Stereochemistry |
DXZ4 is a variable number tandemly repeated DNA sequence. In humans it is composed of 3kb monomers containing a highly conserved CTCF binding site. CTCF is a transcription factor protein and the main insulator responsible for partitioning of chromatin domains in the vertebrate genome.
In addition to being enriched in CpG-islands, DXZ4 transcribes long non-coding RNAs (lncRNAs) and small RNAs of unknown function. Repeat copy number of DXZ4 is highly polymorphic in human populations (varying between 50 and 100 copies). DXZ4 is one of many large tandem repeat loci defined as macrosatellites. Several macrosatellites have been described in humans and share similar features, such as high GC content, large repeat monomers, and high variability for repeat copy number within populations. DXZ4 plays an important role in the unique structural conformation of the inactive X chromosome (Xi) in female somatic cells by acting as a hinge point between two large “super domains”.
In addition to acting as the primary division between domains, DXZ4 forms long-range interactions with a number of other repeat rich regions along the inactive X chromosome. Knockout of the DXZ4 locus revealed loss of this structural conformation on the Xi with chromosome wide silencing being maintained. | 1 | Biochemistry |
Metal carbon dioxide complexes are coordination complexes that contain carbon dioxide ligands. Aside from the fundamental interest in the coordination chemistry of simple molecules, studies in this field are motivated by the possibility that transition metals might catalyze useful transformations of CO. This research is relevant both to organic synthesis and to the production of "solar fuels" that would avoid the use of petroleum-based fuels. | 0 | Organic Chemistry |
Opioid food peptides include:
* Casomorphin (from milk)
* Gluten exorphin (from gluten)
* Gliadorphin/gluteomorphin (from gluten)
* Rubiscolin (from spinach)
* Soymorphin-5 (from soy)
* Oryzatensin (from rice) | 1 | Biochemistry |
Smolková-Keulemansová suffered from dysentery, jaundice, typhus and tuberculosis after liberation. She could not give an address to anyone she knew in Prague, so the International Red Cross did not allow her to return to her country of origin. To receive medical treatment, she was selected to go to Sweden for a six-month recovery stay with 6,000 other prisoners. | 3 | Analytical Chemistry |
The material was described in NACA-TN-259 of August 1927, as "a new corrosion resistant aluminium product which is markedly superior to the present strong alloys. Its use should result in greatly increased life of a structural part. Alclad is a heat-treated aluminium, copper, manganese, magnesium alloy that has the corrosion resistance of pure metal at the surface and the strength of the strong alloy underneath. Of particular importance is the thorough character of the union between the alloy and the pure aluminium. Preliminary results of salt spray tests (24 weeks of exposure) show changes in tensile strength and elongation of Alclad 17ST, when any occurred, to be so small as to be well within the limits of experimental error." In applications involving aircraft construction, Alclad has proven to have increased resistance to corrosion at the expense of increased weight when compared to sheet aluminium.
As pure aluminium possesses a relatively greater resistance to corrosion over the majority of aluminium alloys, it was soon recognised that a thin coating of pure aluminium over the exterior surface of those alloys would take advantage of the superior qualities of both materials. Thus, a key advantage of Alclad over most aluminium alloys is its high corrosion resistance. However, considerable care must be taken while working on an Alclad-covered exterior surface, such as while cleaning the skin of an aircraft, to avoid scarring the surface to expose the vulnerable alloy underneath and prematurely age those elements.
Due to its relatively shiny natural finish, it is often considered to be cosmetically pleasing when used for external elements, particularly during restoration efforts. It has been observed that some fabrication techniques, such as welding, are not suitable when used in conjunction with Alclad. Mild cleaners with a neutral pH value and finer abrasives are recommended for cleaning and polishing Alclad surfaces. It is common for waterproof wax and other inhibitive coverings to be applied to further reduce corrosion. In the twenty-first century, research and evaluation was underway into new coatings and application techniques. | 8 | Metallurgy |
In general, on the typical laboratory scale, the direct reaction of a haloalkane with sodium hydrosulfide is inefficient owing to the competing formation of sulfides. Instead, alkyl halides are converted to thiols via an S-alkylation of thiourea. This multistep, one-pot process proceeds via the intermediacy of the isothiouronium salt, which is hydrolyzed in a separate step:
: CHCHBr + SC(NH) → [CHCHSC(NH)]Br
: [CHCHSC(NH)]Br + NaOH → CHCHSH + OC(NH) + NaBr
The thiourea route works well with primary halides, especially activated ones. Secondary and tertiary thiols are less easily prepared. Secondary thiols can be prepared from the ketone via the corresponding dithioketals. A related two-step process involves alkylation of thiosulfate to give the thiosulfonate ("Bunte salt"), followed by hydrolysis. The method is illustrated by one synthesis of thioglycolic acid:
:ClCHCOH + NaSO → Na[OSCHCOH] + NaCl
:Na[OSCHCOH] + HO → HSCHCOH + NaHSO
Organolithium compounds and Grignard reagents react with sulfur to give the thiolates, which are readily hydrolyzed:
:RLi + S → RSLi
:RSLi + HCl → RSH + LiCl
Phenols can be converted to the thiophenols via rearrangement of their O-aryl dialkylthiocarbamates.
Thiols are prepared by reductive dealkylation of sulfides, especially benzyl derivatives and thioacetals.
Thiophenols are produced by S-arylation or the replacement of diazonium leaving group with sulfhydryl anion (SH):
: + SH → ArSH + N | 0 | Organic Chemistry |
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