text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
The principles involved can be understood by considering the most efficient way of packing together equal-sized spheres and stacking close-packed atomic planes in three dimensions. For example, if plane A lies beneath plane B, there are two possible ways of placing an additional atom on top of layer B. If an additional layer were placed directly over plane A, this would give rise to the following series:
:...ABABABAB...
This arrangement of atoms in a crystal structure is known as hexagonal close packing (hcp).
If, however, all three planes are staggered relative to each other and it is not until the fourth layer is positioned directly over plane A that the sequence is repeated, then the following sequence arises:
:...ABCABCABC...
This type of structural arrangement is known as cubic close packing (ccp).
The unit cell of a ccp arrangement of atoms is the face-centered cubic (fcc) unit cell. This is not immediately obvious as the closely packed layers are parallel to the {111} planes of the fcc unit cell. There are four different orientations of the close-packed layers. | 3 | Analytical Chemistry |
IBX is notable for oxidizing vicinal diols (or glycols) to diketones without cleavage of the carbon-carbon bond, but oxidative cleavage of glycols to two aldehydes or ketones can occur when modified conditions are used (elevated temperatures or trifluoroacetic acid solvent).
The reaction mechanism for this glycol cleavage is based on initial formation of an adduct between 10-I-4 IBX and DMSO to a 12-I-5 intermediate 3 in which DMSO acts as a leaving group for incoming alcohol 4 to intermediate 5. One equivalent of water is split off forming 12-I-5 spirobicyclic periodinane 6 setting the stage for fragmentation to 7. With hydroxyl alpha protons present, oxidation to the acyloin competes. Trifluoroacetic acid is found to facilitate the overall reaction. | 0 | Organic Chemistry |
The furanose ring is a cyclic hemiacetal of an aldopentose or a cyclic hemiketal of a ketohexose.
A furanose ring structure consists of four carbon and one oxygen atom with the anomeric carbon to the right of the oxygen. The highest numbered chiral carbon (typically to the left of the oxygen in a Haworth projection) determines whether or not the structure has a -configuration or -configuration. In an -configuration furanose, the substituent on the highest numbered chiral carbon is pointed downwards out of the plane, and in a -configuration furanose, the highest numbered chiral carbon is facing upwards.
The furanose ring will have either alpha or beta configuration, depending on which direction the anomeric hydroxy group is pointing. In a -configuration furanose, alpha configuration has the hydroxy pointing down, and beta has the hydroxy pointing up. It is the opposite in an -configuration furanose. Typically, the anomeric carbon undergoes mutarotation in solution, and the result is an equilibrium mixture of α and β configurations. | 0 | Organic Chemistry |
Another family of carbonyl-based PPGs exists that is structurally like the phenacyl motif, but which reacts through a separate mechanism. As the name suggests, these PPGs react through abstraction of the carbonyl's γ-hydrogen. The compound is then able to undergo a photoenolization, which is mechanistically like a keto-enol tautomerization. From the enol form, the compound can finally undergo a ground-state transformation that releases the substrate. The quantum yield of this mechanism directly corresponds to the ability of the protected substrate to be a good leaving group. For good leaving groups, the rate-determining step is either hydrogen abstraction or isomerization; however, if the substrate is a poor leaving group, release is the rate-determining step. | 5 | Photochemistry |
Ortho esters can be prepared by the Pinner reaction, in which nitriles react with alcohols in the presence of one equivalent of hydrogen chloride. The reaction proceeds by formation of imido ester hydrochloride:
:RCN + R′OH + HCl → [RC(OR′)=NH]Cl
Upon standing in the presence of excess alcohol, this intermediate converts to the ortho ester:
:[RC(OR′)=NH]Cl + 2R′OH → RC(OR′) + NHCl
The reaction requires anhydrous conditions.
Although a less common method, ortho esters were first produced by reaction of 1,1,1-trichloroalkanes with sodium alkoxide:
:RCCl + 3NaOR′ → RC(OR′) + 3NaCl | 0 | Organic Chemistry |
Illustrative of their alkylating activity are reactions with potassium iodide in acetone, chloroacetone reacts faster than 1-chloropropane by a factor of 36,000. Halo ketones react with phosphites in the Perkow reaction.
The halo group can be removed in reductive dehalogenation of halo ketones. α-Halo ketones can also be converted to alkenes by treatment with hydrazine.
Due to the presence of two electron withdrawing groups (carbonyl and halide), the α-hydrogen is acidic. This property is exploited in the Favorskii rearrangement, where base abstracts first an acidic α-hydrogen and the resulting carbanion then displaces the halogen.
In crossed aldol reactions between halo ketones and aldehydes, the initial reaction product is a halohydrin which can subsequently form an oxirane in the presence of base.
α-Halo ketones can react with amines to form an α-halo imine, which can be converted back to the parent halo ketone by hydrolysis, so that halo imines may be used as masked versions of halo ketones. This allows some chemical transformations to be achieved that are not possible with the parent halo ketones directly. | 0 | Organic Chemistry |
Plasmid preparation can be divided into five main categories based on the scale of the preparation: minipreparation, midipreparation, maxipreparation, megapreparation, and gigapreparation. The choice of which method to use will depend on the amount of plasmid DNA required, as well as the specific application for which it will be used.
Kits are available from varying manufacturers to purify plasmid DNA, which are named by size of bacterial culture and corresponding plasmid yield. In increasing order they are: miniprep, midiprep, maxiprep, megaprep, and gigaprep. The plasmid DNA yield will vary depending on the plasmid copy number, type and size, the bacterial strain, the growth conditions, and the kit. | 1 | Biochemistry |
The term is used in pathology, for example in calcareous conjunctivitis, and when referring to calcareous metastasis or calcareous deposits, which may both be removed surgically. | 9 | Geochemistry |
Sphingosine is synthesized from palmitoyl CoA and serine in a condensation required to yield dihydrosphingosine.
Dehydrosphingosine is then reduced by NADPH to dihydrosphingosine (sphinganine), acylated to dihydroceramide finally oxidized by FAD to ceramide. Sphingosine is then solely formed via degradation of sphingolipid in the lysosome. | 1 | Biochemistry |
Several methods are being pursued for controlling gene expression spatially, temporally and in different degrees. One method is by using operon inducer/repressor system which provides temporal control of gene expression. To control gene expression spatially inkjet printers are under development for printing ligands on gel culture. Other popular method involves use of light to control gene expression in spatiotemporal fashion. Since light can also be controlled easily in space, time and degree, several methods of controlling gene expression at DNA and RNA level have been developed and are under study. For example, RNA interference can be controlled using light and also patterning of gene expression has been performed in cell monolayer and in zebrafish embryos using caged morpholino or peptide nucleic acid demonstrating the control of gene expression spatiotemporally. Recently light based control has been shown at DNA level using transgene based system or caged triplex forming oligos | 1 | Biochemistry |
Back-of-house testing is more restrictive. The substances tested do not come directly from event participants. Instead, they may come from samples confiscated by police or event security or samples that are disposed of via drug amnesty bins. The results may not be available to event attendees. | 3 | Analytical Chemistry |
K2.3 contains 6 transmembrane domains, a pore-forming region, and intracellular N- and C- termini and is readily blocked by apamin. The gene for K2.3, KCNN3, is located on chromosome 1q21. | 1 | Biochemistry |
There is a half-life describing any exponential-decay process. For example:
*As noted above, in radioactive decay the half-life is the length of time after which there is a 50% chance that an atom will have undergone nuclear decay. It varies depending on the atom type and isotope, and is usually determined experimentally. See List of nuclides.
*The current flowing through an RC circuit or RL circuit decays with a half-life of or , respectively. For this example the term half time tends to be used rather than "half-life", but they mean the same thing.
*In a chemical reaction, the half-life of a species is the time it takes for the concentration of that substance to fall to half of its initial value. In a first-order reaction the half-life of the reactant is , where (also denoted as ) is the reaction rate constant. | 7 | Physical Chemistry |
Many reactions in organic chemistry can occur in either an intramolecular or intermolecular senses. Some reactions are by definition intramolecular or are only practiced intramolecularly, e.g.,
* Dieckmann condensation of diesters is the intramolecular version of aldol condensation.
* Madelung synthesis of indoles
* Smiles rearrangement
* Hydroacylation is almost invariably practiced intramolecularly to produce ketones.
:RCHO + CH=CHR → RC(O)CHCHR
* Nazarov cyclization reaction for the synthesis of cyclopentenones
*The Wurtz reaction, involving reductive coupling of alkyl halides, essentially is only useful when conducted intramolecularly. Its utility is illustrated with the synthesis of strained rings:
Some transformations that are enabled or enhanced intramolecularly. For example, the acyloin condensation of diesters almost uniquely produces 10-membered carbocycles, which are difficult to construct otherwise. Another example is the 2+2 cycloaddition of norbornadiene to give quadricyclane. | 0 | Organic Chemistry |
In accordance with the terms of IOP purchase, Fulmer's capital investment in new facilities was expected to be financed from profit and Fulmer would make a modest annual contribution to IOP funds.
However, Fulmer's recent expansion and its large investment in capital equipment required increasing bank borrowing. Considerable management effort and other resources had been taken up with the transfer of facilities between Fulmer, Chessington, Ashtead, Redhill and Slough and there had been a damaging fire at Ashtead.
It was clear that alternative sources of finance were needed. A management buyout was explored and found to be not feasible. Preparations were made for a stock exchange flotation but, in the late 1980s Fulmer sustained large losses and plans to float were postponed.
The balance of Fulmer's activities had changed. Academic research was now a minor part of its work. Most of its income came from testing, consultancy and small scale manufacture. The IOP were becoming concerned that their ownership of Fulmer as a commercial organization might be judged incompatible with their charitable status as a learned society. They were also concerned that Fulmer was making losses and had a growing overdraft. The IOP Council finally decided to sell Fulmer. | 8 | Metallurgy |
Although Jaffes name is synonymous with clinical creatinine testing, his paper only described the principle behind what would later become the enduring method. It was Otto Folin (1867–1934), a Harvard biochemist, who adapted Jaffes research—abandoning the standard Neubauer reaction of the time—and published several papers using the Jaffe reaction to analyze creatinine levels in both blood and urine. Folin began using the picric acid procedure in 1901 and included it in his 1916 Lab Manual of Biological Chemistry. During his career, Folin modified and improved several quantitative colorimetric procedures, the first of which was for creatinine. He took advantage of technology available at the time, using a Duboscq colorimeter for measurement precision, and is credited for introducing colorimetry into modern biochemical analysis.
Folin's research did not focus on creatinine as a renal function indicator. Since the precursors of creatinine are synthesized in the liver, at this point in history, creatinine was considered indicative of liver function. It was not until 1926 that Poul Kristian Brandt Rehberg suggested creatinine was a significant marker for renal function. | 1 | Biochemistry |
The defensive spray of skunks consists mainly of low-molecular-weight thiols and derivatives with a foul odor, which protects the skunk from predators. Owls are able to prey on skunks, as they lack a sense of smell. | 0 | Organic Chemistry |
When a heat ray arrives at a body they may interact in three different ways:
# The body may absorb the heat
# The body may reflect the heat
# The heat may transmit through the body
Absorption and reflection are typically modeled as surface phenomena that occur within a fraction of a micrometer of the surface. For example, a highly polished piece of steel will be highly reflective, regardless of the material under the surface. Transmission on the other hand is a volumetric phenomena that is dependent on the properties of the entire thickness of the body. A glass window for instance must be translucent through its entire thickness for radiation to get through.
The term absorption is used to describe the change of heat into other forms of energy when it contacts particle or body. Only material particles can absorb heat rays, not elements of surfaces. For a given frequency of radiation, all mediums have a coefficient of absorption, that represents how much heat will be absorbed per unit distance through a medium. | 7 | Physical Chemistry |
In Sisyphus cooling, the two hyperfine ground states of experience equal and opposite AC Stark shifts from the near-resonant counter-propagating beams. The beams also effect a polarization gradient, alternating between linear and circular polarizations. The potential energy maxima of one coincide with pure circular polarization, which optically pumps atoms to the other , which experiences its minima in the same location. Over time, the atoms expend their kinetic energy traversing the potential energy landscape and transferring the potential energy difference between the crests and troughs of the AC-Stark-shifted ground state levels to emitted photons.
In contrast, gray molasses only has one sinusoidally light-shifted ground state; optical pumping at the peaks of this potential energy landscape takes atoms to the dark state, which can selectively evolve to the bright state and re-enter the cycle with sufficient momentum. Sisyphus cooling is difficult to implement when the excited state manifold is poorly-resolved (i.e. whose hyperfine spacing is comparable to or less than the constituent linewidths); in these atomic species, the Raman-type gray molasses is preferable. | 7 | Physical Chemistry |
Analogous to sulfamic acid (HNSO) and as is the case generally for amino acids, HOSA exists in the solid state as a zwitterion: HNOSO. It resembles an ammonia molecule coordinate covalently bonded to a sulfate group. | 0 | Organic Chemistry |
Resazurin can be used as one of a series of rapid tests to determine the quality of a milk sample. In this test, resazurin is added as a violet redox dye which turns mauvish-pink due to conversion to resorufin and then to colourless dihydroresorufin. This happens due to lowering of the oxidation-reduction potential in the milk sample caused by presence of bacteria which utilize available oxygen present in the milk for aerobic respiration. The rate of the colour change is used as an index for the number of bacteria present in the milk sample. | 3 | Analytical Chemistry |
Fulgurites have been classified by Pasek et al. (2012) into five types related to the type of sediment in which the fulgurite formed, as follows:
* Type I – sand fulgurites with tubaceous structure; their central axial void may be collapsed
* Type II – soil fulgurites; these are glass-rich, and form in a wide range of sediment compositions, including clay-rich soils, silt-rich soils, gravel-rich soils, and loessoid; these may be tubaceous, branching, vesicular, irregular/slaggy, or may display a combination of these structures, and can produce exogenic fulgurites (droplet fulgurites)
* Type III – caliche or calcic sediment fulgurites, having thick, often surficially glazed granular walls with calcium-rich vitreous groundmass with little or no lechatelierite glass; their shapes are variable, with multiple narrow central channels common, and can span the entire range of morphological and structural variation for fulguritic objects
* Type IV – rock fulgurites, which are either crusts on minimally altered rocks, networks of tunneling within rocks, vesicular outgassed rocks (often glazed by a silicide-rich and/or metal oxide crust), or completely vitrified and dense rock material and masses of these forms with little sedimentary groundmass
* Type V – [droplet] fulgurites (exogenic fulgurites), which show evidence of ejection (e.g. spheroidal, filamentous, or aerodynamic), related by composition to Type II and Type IV fulgurites
* phytofulgurite – a proposed class of objects resulting from partial to total alteration of biomass (e.g. grasses, lichens, moss, wood) by lightning. Pasek et al. (2012) described fulgurites as "natural glasses formed by cloud-to-ground lightning." Pasek et al. excluded phytofulgurites from their classification scheme because they are not glasses, so classifying them as a subset of fulgurites is debatable. | 9 | Geochemistry |
The receptor has a broad tissue distribution but is especially abundant in the cerebellum. Most of the InsP3Rs are found integrated into the endoplasmic reticulum. | 1 | Biochemistry |
* Wide range of genomic applications and scientific questions, including de novo genome assembly, haplotype phasing, structural variant analysis, and transcriptome and epigenetic analysis.
* Accuracy and scalability.
* Method requires small quantities of input DNA, which can be beneficial for small samples or single cell studies.
* More cost effective per sample in comparison with long-read technologies such as Oxford Nanopore sequencing.
* Libraries produced by linked-read can be processed using Illumina short read sequencing, increasing accessibility. | 1 | Biochemistry |
Kode FSL constructs consist of three components; a functional moiety (F), a spacer (S) and a lipid (L).
Function groups on FSL constructs that can be used to create kodecytes include saccharides (including ABO blood group-related determinants, sialic acids, hyaluronin polysaccharides), fluorophores, biotin, and a range of peptides.
Although kodecytes are created by modifying natural cells, they are different from natural cells. For example, FSL constructs, influenced by the composition of the lipid tail, are laterally mobile in the membrane and some FSL constructs may also cluster due to the characteristics of the functional group (F). As FSL constructs are anchored in the membrane via a lipid tail (L) it is believed they do not participate in signal transduction, but may be designed to act as agonists or antagonists of the initial binding event. FSL constructs will not actively pass through the plasma membrane but may enter the cell via membrane invagination and endocytosis.
The "koding" of cells is stable (subject to the rate of turnover of the membrane components). FSL constructs will remain in the membrane of inactive cells (e.g. red blood cells) for the life of the cell provided it is stored in lipid free media. In the peripheral circulation FSL constructs are observed to be lost from red cell kodecytes at a rate of about 1% per hour. The initial "koding" dose and the minimum level required for detection determine how long the presence of "kodecytes" in the circulation can be monitored. For red blood "kodecytes" reliable monitoring of the presence of the "kodecytes" for up to 3 days post intravenous administration has been demonstrated in small mammals.
The spacer (S) of a FSL construct has been selected so as to have negligible cross-reactivity with serum antibodies so kodecytes can be used with undiluted serum. By increasing the length of the FSL spacer from 1.9 to 7.2 nm it has been shown sensitivity can improve two-fold in red cell agglutination based kodecyte assays. However, increasing the size of the spacer further from 7.2 to 11.5 nm did not result in any further enhancement. | 1 | Biochemistry |
With the development of bioconjugation technology, there are plenty of options to covalently ligating an artificial metal cofactor onto a protein: i) cysteine residue based chemistry like: Cys-meleimide, Cys-α-haloketone, Cys-benzylhalide chemistry and disulfide formation, ii) post-translational bioorthogonal modification based on Amber suppression (e.g., Click chemistry) and iii) enzyme active site modification (e.g., covalent bond formation between lipase and lipase inhibitor).
The video shows an example using reaction between cysteine residue and α-haloketone to introduce a phenanthroline ligand into an adipocyte lipid binding protein. In this context, the ArM can selectively hydrolyze certain racemic esters. | 0 | Organic Chemistry |
The Dallol area lies up to below sea level, and has been repeatedly flooded in the past when waters from the Red Sea have flowed into the depression. The last separation from the Red Sea was about 30,000 years ago.
The discovery of the volcano by the first European settlers certainly dates from the first colonization and expeditions in the region, in the 17th or 18th century. But the hostility of the depression, the unbearable heat which reigns there, and the dangers of the site (acid basins, toxic fumes), did not favour the exploration of the zones close to the crater. On the contrary, the Erta Ale was much more accessible, especially because the part of the rift where it is located (called the Erta Ale Range), is significantly higher. The last eruption of this phreato-magmatic volcano dates back to 2011. | 9 | Geochemistry |
Members of the MAPK family can be found in every eukaryotic organism examined so far. In particular, both classical and atypical MAP kinases can be traced back to the root of the radiation of major eukaryotic groups. Terrestrial plants contain four groups of classical MAPKs (MAPK-A, MAPK-B, MAPK-C and MAPK-D) that are involved in response to myriads of abiotic stresses. However, none of these groups can be directly equated to the clusters of classical MAPKs found in opisthokonts (fungi and animals). In the latter, the major subgroups of classical MAPKs form the ERK/Fus3-like branch (that is further sub-divided in metazoans into ERK1/2 and ERK5 subgroups), and the p38/Hog1-like kinases (that has also split into the p38 and the JNK subgroups in multicellular animals). In addition, there are several MAPKs in both fungi and animals, whose origins are less clear, either due to high divergence (e.g. NLK), or due to possibly being an early offshoot to the entire MAPK family (ERK3, ERK4, ERK7). In vertebrates, due to the twin whole genome duplications after the cephalochordate/vertebrate split, there are several paralogs in every group. Thus ERK1 and ERK2 both correspond to the Drosophila kinase rolled, JNK1, JNK2 and JNK3 are all orthologous to the gene basket in Drosophila. Although among the p38 group, p38 alpha and beta are clearly paralogous pairs, and so are p38 gamma and delta in vertebrates, the timing of the base split is less clear, given that many metazoans already possess multiple p38 homologs (there are three p38-type kinases in Drosophila, Mpk2(p38a), p38b and p38c). The single ERK5 protein appears to fill a very specialized role (essential for vascular development in vertebrates) wherever it is present. This lineage has been deleted in protostomes, together with its upstream pathway components (MEKK2/3, MKK5), although they are clearly present in cnidarians, sponges and even in certain unicellular organisms (e.g. the choanoflagellate Monosiga brevicollis) closely related to the origins of multicellular animals.
The split between classical and some atypical MAP kinases happened quite early. This is suggested not just by the high divergence between extant genes, but also recent discoveries of atypical MAPKs in primitive, basal eukaryotes. The genome sequencing of Giardia lamblia revealed the presence of two MAPK genes, one of them similar to the already-well-known mammalian MAPKs (ERKs, p38s, etc.), the other one showing similarities to the mammalian ERK7 protein. The situation is similar in the multicellular amoeba Dictyostelium discoideum, where the ddERK1 protein appears to be a classical MAPK, while ddERK2 more closely resembles our ERK7 and ERK3/4 proteins. Atypical MAPKs can also be found in higher plants, although they are poorly known. Similar to the situation in mammals, most aspects of atypical MAPKs are uncharacterized due to the lack of research focus on this area. | 1 | Biochemistry |
Tumor necrosis factor receptor 2 (TNFR2), also known as tumor necrosis factor receptor superfamily member 1B (TNFRSF1B) and CD120b, is one of two membrane receptors that binds tumor necrosis factor-alpha (TNFα). Like its counterpart, tumor necrosis factor receptor 1 (TNFR1), the extracellular region of TNFR2 consists of four cysteine-rich domains which allow for binding to TNFα. TNFR1 and TNFR2 possess different functions when bound to TNFα due to differences in their intracellular structures, such as TNFR2 lacking a death domain (DD). | 1 | Biochemistry |
Levofloxacin and later generation fluoroquinolones are collectively referred to as "respiratory quinolones" to distinguish them from earlier fluoroquinolones which exhibited modest activity toward the important respiratory pathogen Streptococcus pneumoniae.
The drug exhibits enhanced activity against the important respiratory pathogen Streptococcus pneumoniae relative to earlier fluoroquinolone derivatives like ciprofloxacin. For this reason, it is considered a "respiratory fluoroquinolone" along with more recently developed fluoroquinolones such as moxifloxacin and gemifloxacin. It is less active than ciprofloxacin against Gram-negative bacteria, especially Pseudomonas aeruginosa, and lacks the anti-methicillin-resistant Staphylococcus aureus (MRSA) activity of moxifloxacin and gemifloxacin. Levofloxacin has shown moderate activity against anaerobes, and is about twice as potent as ofloxacin against Mycobacterium tuberculosis and other mycobacteria, including Mycobacterium avium complex.
Its spectrum of activity includes most strains of bacterial pathogens responsible for respiratory, urinary tract, gastrointestinal, and abdominal infections, including Gram negative (Escherichia coli, Haemophilus influenzae, Klebsiella pneumoniae, Legionella pneumophila, Moraxella catarrhalis, Proteus mirabilis, and Pseudomonas aeruginosa), Gram positive (methicillin-sensitive but not methicillin-resistant Staphylococcus aureus, Streptococcus pneumoniae, Staphylococcus epidermidis, Enterococcus faecalis, and Streptococcus pyogenes), and atypical bacterial pathogens (Chlamydophila pneumoniae and Mycoplasma pneumoniae). Compared to earlier antibiotics of the fluoroquinoline class such as ciprofloxacin, levofloxacin exhibits greater activity towards Gram-positive bacteria but lesser activity toward Gram-negative bacteria, especially Pseudomonas aeruginosa. | 4 | Stereochemistry |
For pure elements or compounds, e.g. pure copper, pure water, etc. the liquidus and solidus are at the same temperature, and the term melting point may be used.
There are also some mixtures which melt at a particular temperature, known as congruent melting. One example is eutectic mixture. In a eutectic system, there is particular mixing ratio where the solidus and liquidus temperatures coincide at a point known as the invariant point. At the invariant point, the mixture undergoes a eutectic reaction where both solids melt at the same temperature. | 7 | Physical Chemistry |
Artists and metalworkers often deliberately add patinas as a part of the original design and decoration of art and furniture, or to simulate antiquity in newly made objects. The process is often called distressing.
A wide range of chemicals, both household and commercial, can give a variety of patinas. They are often used by artists as surface embellishments either for color, texture, or both. Patination composition varies with the reacted elements and these will determine the color of the patina. For copper alloys, such as bronze, exposure to chlorides leads to green, while sulfur compounds (such as "liver of sulfur") tend to brown. The basic palette for patinas on copper alloys includes chemicals like ammonium sulfide (blue-black), liver of sulfur (brown-black), cupric nitrate (blue-green), and ferric nitrate (yellow-brown). For artworks, patination is often deliberately accelerated by applying chemicals with heat. Colors range from matte sandstone yellow to deep blues, greens, whites, reds, and various blacks. Some patina colors are achieved by the mixing of colors from the reaction with the metal surface with pigments added to the chemicals. Sometimes the surface is enhanced by waxing, oiling, or other types of lacquers or clear-coats. More simply, the French sculptor Auguste Rodin used to instruct assistants at his studio to urinate over bronzes stored in the outside yard. A patina can be produced on copper by the application of vinegar (acetic acid). This patina is water-soluble and will not last on the outside of a building like a "true" patina. It is usually used as pigment.
Patina is also found on slip rings and commutators. This type of patina is formed by corrosion, what elements the air might hold, residue from the wear of the carbon brush, and moisture; thus, the patina needs special conditions to work as intended.
Patinas can also be found in woks or other metal baking dishes. The process of applying patinas to cookware is known as seasoning. The patina on a wok is a dark coating of oils that have been polymerized onto it to prevent food from sticking. Scrubbing or using soap on a wok or other dishware could damage the patina and possibly allow rust.
Knife collectors that own carbon steel blades sometimes force a patina onto the blade to help protect it and give it a more personalized look. This can be done using various chemicals and substances such as muriatic acid, apple cider vinegar, or mustard. It can also be done by sticking the blade into any acidic vegetable or fruit such as an orange or an apple. | 8 | Metallurgy |
Mixtures of complex acids can be resolved by thermometric titration with standard NaOH in aqueous solution. In a mixture of nitric, acetic and phosphoric acids used in the fabrication of semi-conductors, three endpoints could be predicted on the basis of the dissociation constants of the acids:
The key to determine the amount of each acid present in the mixture is the ability to obtain an accurate value for the amount of phosphoric acid present, as revealed by titration of the third proton of HPO.
Figure 10 illustrates a titration plot of this mixture, showing 3 sharp endpoints. | 3 | Analytical Chemistry |
Thiourea is a planar molecule. The C=S bond distance is 1.71 Å. The C-N distances average 1.33 Å. The weakening of the C-S bond by C-N pi-bonding is indicated by the short C=S bond in thiobenzophenone, which is 1.63 Å.
Thiourea occurs in two tautomeric forms, of which the thione form predominates in aqueous solutions. The equilibrium constant has been calculated as K is . The thiol form, which is also known as an isothiourea, can be encountered in substituted compounds such as isothiouronium salts. | 0 | Organic Chemistry |
The ICP-AES is composed of two parts: the ICP and the optical spectrometer. The ICP torch consists of 3 concentric quartz glass tubes. The output or "work" coil of the radio frequency (RF) generator surrounds part of this quartz torch. Argon gas is typically used to create the plasma.
The ICPs have two operation modes, called capacitive (E) mode with low plasma density and inductive (H) mode with high plasma density, and E to H heating mode transition occurs with external inputs. The torch is operated in the H mode.
When the torch is turned on, an intense electromagnetic field is created within the coil by the high power radio frequency signal flowing in the coil. This RF signal is created by the RF generator which is, effectively, a high power radio transmitter driving the "work coil" the same way a typical radio transmitter drives a transmitting antenna. Typical instruments run at either 27 or 40 MHz. The argon gas flowing through the torch is ignited with a Tesla unit that creates a brief discharge arc through the argon flow to initiate the ionization process. Once the plasma is "ignited", the Tesla unit is turned off.
The argon gas is ionized in the intense electromagnetic field and flows in a particular rotationally symmetrical pattern towards the magnetic field of the RF coil. A stable, high temperature plasma of about 7000 K is then generated as the result of the inelastic collisions created between the neutral argon atoms and the charged particles.
A peristaltic pump delivers an aqueous or organic sample into an analytical nebulizer where it is changed into mist and introduced directly inside the plasma flame. The sample immediately collides with the electrons and charged ions in the plasma and is itself broken down into charged ions. The various molecules break up into their respective atoms which then lose electrons and recombine repeatedly in the plasma, giving off radiation at the characteristic wavelengths of the elements involved.
In some designs, a shear gas, typically nitrogen or dry compressed air is used to cut the plasma at a specific spot. One or two transfer lenses are then used to focus the emitted light on a diffraction grating where it is separated into its component wavelengths in the optical spectrometer. In other designs, the plasma impinges directly upon an optical interface which consists of an orifice from which a constant flow of argon emerges, deflecting the plasma and providing cooling while allowing the emitted light from the plasma to enter the optical chamber. Still other designs use optical fibers to convey some of the light to separate optical chambers.
Within the optical chamber(s), after the light is separated into its different wavelengths (colours), the light intensity is measured with a photomultiplier tube or tubes physically positioned to "view" the specific wavelength(s) for each element line involved, or, in more modern units, the separated colors fall upon an array of semiconductor photodetectors such as charge coupled devices (CCDs). In units using these detector arrays, the intensities of all wavelengths (within the system's range) can be measured simultaneously, allowing the instrument to analyze for every element to which the unit is sensitive all at once. Thus, samples can be analyzed very quickly.
The intensity of each line is then compared to previously measured intensities of known concentrations of the elements, and their concentrations are then computed by interpolation along the calibration lines (use of a calibration curve).
In addition, special software generally corrects for interferences caused by the presence of different elements within a given sample matrix. | 3 | Analytical Chemistry |
As voltage is applied, the anions (and negatively charged sample molecules) migrate toward the positive electrode (anode) in the lower chamber, the leading ion is Cl ( high mobility and high concentration); glycinate is the trailing ion (low mobility and low concentration). SDS-protein particles do not migrate freely at the border between the Cl of the gel buffer and the Gly of the cathode buffer. Friedrich Kohlrausch found that Ohm's law also applies to dissolved electrolytes. Because of the voltage drop between the Cl and Glycine-buffers, proteins are compressed (stacked) into micrometer thin layers. The boundary moves through a pore gradient and the protein stack gradually disperses due to a frictional resistance increase of the gel matrix. Stacking and unstacking occurs continuously in the gradient gel, for every protein at a different position. For a complete protein unstacking the polyacrylamide-gel concentration must exceed 16% T. The two-gel system of "Laemmli" is a simple gradient gel. The pH discontinuity of the buffers is of no significance for the separation quality, and a "stacking-gel" with a different pH is not needed. | 1 | Biochemistry |
Another classic but elusive family of targets are silylenes, analogues of carbenes. It was proposed that dechlorination of dimethyldichlorosilane generates dimethylsilylene:
:SiCl(CH) + 2 K → Si(CH) + 2 KCl
This inference is supported by conducting the dechlorination in the presence of trimethylsilane, the trapped product being pentamethyldisilane:
:Si(CH) + HSi(CH) → (CH)Si(H)-Si(CH)
Not that the trapping agent does not react with dimethyldichlorosilane or potassium metal. | 3 | Analytical Chemistry |
Chaotropicity describes the entropic disordering of lipid bilayers and other biomacromolecules which is caused by substances dissolved in water. According to the original usage and work carried out on cellular stress mechanisms and responses, chaotropic substances do not necessarily disorder the structure of water.
The chaotropic activities of solutes in the aqueous phase (e.g. ethanol, butanol, urea, MgCl, and phenol) have been quantified using an agar-gelation assay. Whereas chaotropicity was first applied to studies of ions, it is equally applicable to alcohols, aromatics, ion mixtures, and other solutes. Furthermore, hydrophobic substances known to stress cellular systems (including benzene and toluene) can chaotropically disorder macromolecules and induce a chaotrope-stress response in microbial cells, even though they partition into the hydrophobic domains of macromolecular systems. | 1 | Biochemistry |
RNA therapeutics are a new class of medications based on ribonucleic acid (RNA). Research has been working on clinical use since the 1990s, with significant success in cancer therapy in the early 2010s. In 2020 and 2021, mRNA vaccines have been developed globally for use in combating the coronavirus disease (COVID-19 pandemic). The Pfizer–BioNTech COVID-19 vaccine was the first mRNA vaccine approved by a medicines regulator, followed by the Moderna COVID-19 vaccine, and others.
The main types of RNA therapeutics are those based on messenger RNA (mRNA), antisense RNA (asRNA), RNA interference (RNAi), and RNA aptamers. Of the four types, mRNA-based therapy is the only type which is based on triggering synthesis of proteins within cells, making it particularly useful in vaccine development. Antisense RNA is complementary to coding mRNA and is used to trigger mRNA inactivation to prevent the mRNA from being used in protein translation. RNAi-based systems use a similar mechanism, and involve the use of both small interfering RNA (siRNA) and micro RNA (miRNA) to prevent mRNA translation and/or degrade mRNA. However, RNA aptamers are short, single stranded RNA molecules produced by directed evolution to bind to a variety of biomolecular targets with high affinity thereby affecting their normal in vivo activity.
RNA is synthesized from template DNA by RNA polymerase with messenger RNA (mRNA) serving as the intermediary biomolecule between DNA expression and protein translation. Because of its unique properties (such as its typically single-stranded nature and its 2' OH group) and its ability to adopt many different secondary/tertiary structures, both coding and noncoding RNAs have attracted attention in medicine. Research has begun to explore RNAs potential to be used for therapeutic benefit, and unique challenges have occurred during drug discovery and implementation of RNA therapeutics. | 1 | Biochemistry |
In some settings, when the titrated system is a redox system whose equilibrium is influenced by the removal of the metal ions, a redox indicator can function as a complexometric indicator. | 3 | Analytical Chemistry |
The Beckett skimmer has some similarities to the downdraft skimmer but introduced a foam nozzle to produce the flow of air bubbles. The name Beckett comes from the patented foam nozzle developed and sold by the Beckett Corporation (United States), although similar foam nozzle designs are sold by other companies outside the United States (e.g. Sicce (Italy)). Instead of using the plastic media that is found in downdraft skimmer designs, the Beckett skimmer uses design concepts from previous generations of skimmers, specifically the downdraft skimmer and the venturi skimmer (the Beckett 1408 Foam Nozzle is a modified 4 port venturi) to produce a hybrid that is capable of using powerful pressure rated water pumps and quickly processing large amounts of aquarium water in a short period of time. Commercial Beckett skimmers come in single Beckett, dual Beckett, and quad Beckett designs. Well engineered Beckett skimmers are quiet and reliable. Due to the advances in pump technologies and introduction of DC pumps, the concerns of powerful pumps taking up additional space, introducing additional noise, and using more electricity have all been alleviated. Unlike the Downdraft and Spray Induction skimmers, Beckett skimmer designs are produced by a number of companies in the United States and elsewhere and are not known to be restricted by patents. | 3 | Analytical Chemistry |
DBT has been shown to physically interact with PER in vitro and in vivo, and to create a stable complex with PER throughout the circadian cycle. PER that has been phosphorylated by DBT is recognized by the Slimb protein. Slimb is a component of the Skp1/Cullin/F-box protein (SCF) ubiquitin ligase complex, which marks proteins for proteosomal degradation in a phosphorylation-dependent manner. Enhanced PER degradation in the cytoplasm is predicted to delay nuclear translocation of both PER and TIM, and to thus affect the period of circadian rhythms.
The mutation dbtS, associated with a proline to serine substitution at residue 47 [P47S], shortens period length by about 6 h. dbtL contains an amino acid substitution of isoleucine for methionine at residue 80 (M80I) and lengthens period to 29 h. A third mutation, dbtAR, is associated with a change from histidine 126 to tyrosine and causes arrhythmia. PER protein in this mutant is hypophosphorylated. Each of these mutations maps to the kinase domain of DBT gene. The short- and long-period alleles of DBT enhance or attenuate, respectively, PER degradation in the nucleus, further demonstrating the importance of timely PER degradation as a critical determinant in establishing 24-h rhythmicity. In addition to influencing protein degradation, DBT affects the timing of nuclear accumulation of PER. The short-period mutant dbtS delays PER nuclear accumulation, which is independent of PER protein stability, and arrhythmic alleles of dbt cause nuclear accumulation of PER in clock-containing cells of larval and adult Drosophila.
Both mammalian CK1δ and CK1ε contain closely related 123-amino-acid carboxy-terminal domains that can auto-regulate kinase activity. CK1δ and CK1ε are 53% identical. These domains are not related to the carboxy-terminal domain of double-time, suggesting a split in the evolution of the mammalian and fly homologs.
A similar function for casein kinase 2 has been reported in Arabidopsis thaliana, Drosophila, and Neurospora. | 1 | Biochemistry |
One viral epitranscriptome modification that has been identified is the 5-methylcytidine (mC). HIV-1 and MLV transcriptomes contain elevated levels of these residues by approximately 14-30 fold when compared to a cell’s normal levels. NSUN2 is the complex that codes the cytidine methyltransferases credited with mC formation in cells and amplification in viral epitranscriptomes. The NSUN2 affects the translational aspect of the mRNA in the viral cells, boosting the expression of the viral genome. It has also been found that the mC alters the splicing pattern and locations in the viral transcriptome. This affected the HIV-1 transcript in both early and late infection. | 1 | Biochemistry |
NBS is commercially available. It can also be synthesized in the laboratory. To do so, sodium hydroxide and bromine are added to an ice-water solution of succinimide. The NBS product precipitates and can be collected by filtration.
Crude NBS gives better yield in the Wohl–Ziegler reaction. In other cases, impure NBS (slightly yellow in color) may give unreliable results. It can be purified by recrystallization from 90 to 95 °C water (10 g of NBS for 100 mL of water). | 0 | Organic Chemistry |
In contrast to solid electrolyte systems under high temperatures (usually higher than 200 °C), EPOC has rarely been reported in low-temperature aqueous systems (particularly at room temperature). Only a few examples have been demonstrated for the EPOC in an aqueous electrolyte solution at ambient temperature: H oxidation at Pt catalyst surface in alkaline solutions, hydrocarbon isomerization reaction occurring at the nanoparticulate Pt catalyst, hydrazine oxidation operating at the Ni alloy catalyst in alkaline media, and reduction at the Pd-based gas diffusion electrode. Even though the perturbation of the local work function and tuning of surface binding strengths of intermediate species were suggested as the origin for the EPOC effects in the liquid electrolyte systems as similar to the EPOC examples of high-temperature solid electrolyte systems, thorough theoretical studies supported by clear experimental evidence have not been addressed. Very recently, it was additionally hypothesized for the cases of the hydrazine oxidation and the CO reduction that the mechanistic origin of the EPOC phenomena observed in these cases can be contributed to structurally non-disparate transition states and/or surface bound intermediate species for the corresponding bifurcated faradaic and non-faradaic reactions. | 7 | Physical Chemistry |
Ampicillin is well-absorbed from the GI tract (though food reduces its absorption), and reaches peak concentrations in one to two hours. The bioavailability is around 62% for parenteral routes. Unlike other penicillins, which usually bind 60–90% to plasma proteins, ampicillin binds to only 15–20%.
Ampicillin is distributed through most tissues, though it is concentrated in the liver and kidneys. It can also be found in the cerebrospinal fluid when the meninges become inflamed (such as, for example, meningitis). Some ampicillin is metabolized by hydrolyzing the beta-lactam ring to penicilloic acid, though most of it is excreted unchanged. In the kidneys, it is filtered out mostly by tubular secretion; some also undergoes glomerular filtration, and the rest is excreted in the feces and bile.
Hetacillin and pivampicillin are ampicillin esters that have been developed to increase bioavailability. | 4 | Stereochemistry |
The ubiquitin-proteasome system (UPS) figures prominently in protein degradation. The 26S proteasome consists of a catalytic subunit (the 20S core particle), and a regulatory subunit (the 19S cap). Poly-ubiquitin chains tag proteins for degradation by the proteasome, which causes hydrolysis of tagged proteins into smaller peptides.
Physiologically, PI31 attacks 20S catalytic domain of 26S Proteasome that results in decreased proteasome activity. (ADP-ribosyl)transferase Tankyrase (TNKS) causes ADP-ribosylation of PI31 which in turn increases the proteasome activity. Inhibition of TNKs further shows the reduced 26S Proteasome assembly. Therefore, ADP-ribosylation promotes 26S Proteasome activity in both Drosophila and human cells. | 1 | Biochemistry |
The Class IIA HDACs includes HDAC4, HDAC5, HDAC7 and HDAC9. HDACs 4 and 5 have been found to most closely resemble each other while HDAC7 maintains a resemblance to both of them. There have been three discovered variants of HDAC9 including HDAC9a, HDAC9b and HDAC9c/HDRP, while more have been suspected. The variants of HDAC9 have been found to have similarities to the rest of the Class IIA HDACs. For HDAC9, the splicing variants can be seen as a way of creating a "fine-tuned mechanism" for differentiation expression levels in the cell. Different cell types may take advantage and utilize different isoforms of the HDAC9 enzyme allowing for different forms of regulation. HDACs 4, 5 and 7 have their catalytic domains located in the C-terminus along with an NLS region while HDAC9 has its catalytic domain located in the N-terminus. However, the HDAC9 variant HDAC9c/HDRP lacks a catalytic domain but has a 50% similarity to the N-terminus of HDACs 4 and 5.
For HDACs 4, 5 and 7, conserved binding domains have been discovered that bind for C-terminal binding protein (CtBP), myocyte enhancer factor 2 (MEF2) and 14-3-3. All three HDACs work to repress the myogenic transcription factor MEF2 which an essential role in muscle differentiation as a DNA binding transcription factor. Binding of HDACs to MEF2 inhibits muscle differentiation, which can be reversed by action of Ca/calmodulin-dependent kinase (CaMK) which works to dissociate the HDAC/MEF2 complex by phosphorylating the HDAC portion. They have been seen to be involved in cellular hypertrophy in muscle control differentiation as well as cellular hypertrophy in muscle and cartilage tissues. HDACs 5 and 7 have been shown to work in opposition to HDAC4 during muscle differentiation regulation so as to keep a proper level of expression. There has been evidence that these HDACs also interact with HDAC3 as a co-recruitment factor to the SMRT/N-CoR factors in the nucleus. Absence of the HDAC3 enzyme has shown to lead to inactivity which makes researchers believe that HDACs 4, 5 and 7 help the incorporation of DNA-binding recruiters for the HDAC3-containing HDAC complexes located in the nucleus. When HDAC4 is knocked out in mice, they suffer from a pronounced chondrocyte hypertrophy and die due to extreme ossification. HDAC7 has been shown to suppress Nur77-dependent apoptosis. This interaction leads to a role in clonal expansion of T cells. HDAC9 KO mice are shown to suffer from cardiac hypertrophy which is exacerbated in mice that are double KO for HDACs 9 and 5. | 0 | Organic Chemistry |
Magnesium ions (Mg) in cellular biology are usually in almost all senses opposite to Ca ions, because they are bivalent too, but have greater electronegativity and thus exert greater pull on water molecules, preventing passage through the channel (even though the magnesium itself is smaller). Thus, Mg ions block Ca channels such as (NMDA channels) and have been shown to affect gap junction channels forming electrical synapses. | 1 | Biochemistry |
2-Iodoxybenzoic acid (IBX) is an organic compound used in organic synthesis as an oxidizing agent. This periodinane is especially suited to oxidize alcohols to aldehydes. IBX is prepared from 2-iodobenzoic acid, potassium bromate, and sulfuric acid. Frigerio and co-workers have also demonstrated, in 1999 that potassium bromate may be replaced by commercially available Oxone. One of the main drawbacks of IBX is its limited solubility; IBX is insoluble in many common organic solvents. In the past, it was believed that IBX was shock sensitive, but it was later proposed that samples of IBX were shock sensitive due to the residual potassium bromate left from its preparation. Commercial IBX is stabilized by carboxylic acids such as benzoic acid and isophthalic acid. | 0 | Organic Chemistry |
Radiative equilibrium is the condition where the total thermal radiation leaving an object is equal to the total thermal radiation entering it. It is one of the several requirements for thermodynamic equilibrium, but it can occur in the absence of thermodynamic equilibrium. There are various types of radiative equilibrium, which is itself a kind of dynamic equilibrium. | 7 | Physical Chemistry |
It creates volatile compounds when mixed with glucose and amino acids at 90 °C.
It is a cofactor in tyrosine oxidation. | 1 | Biochemistry |
William Otto Frohring (July 1, 1893 – September 13, 1959) was an American biochemical researcher, inventor and business executive. He was a co-developer of "simulated milk adapted" (SMA), the first infant formula to be distributed in the United States and one of the most widely consumed infant formulas in the world.
Frohring held 15 patents, and led research in dairy products, and the refinement, synthesis and manufacture of vitamin products. | 7 | Physical Chemistry |
As an endorheic basin, the Caspian Sea basin has no natural connection with the ocean. Since the medieval period, traders reached the Caspian via a number of portages that connected the Volga and its tributaries with the Don River (which flows into the Sea of Azov) and various rivers that flow into the Baltic Sea. Primitive canals connecting the Volga Basin with the Baltic were constructed as early as the early 18th century. Since then, a number of canal projects have been completed.
The two modern canal systems that connect the Volga Basin, and hence the Caspian Sea, with the ocean are the Volga–Baltic Waterway and the Volga–Don Canal.
The proposed Pechora–Kama Canal was a project that was widely discussed between the 1930s and 1980s. Shipping was a secondary consideration. Its main goal was to redirect some of the water of the Pechora River (which flows into the Arctic Ocean) via the Kama River into the Volga. The goals were both irrigation and the stabilization of the water level in the Caspian, which was thought to be falling dangerously fast at the time. During 1971, some peaceful nuclear construction experiments were carried out in the region by the U.S.S.R.
In June 2007, in order to boost his oil-rich countrys access to markets, Kazakhstans President Nursultan Nazarbayev proposed a link between the Caspian Sea and the Black Sea. It is hoped that the "Eurasia Canal" (Manych Ship Canal) would transform landlocked Kazakhstan and other Central Asian countries into maritime states, enabling them to significantly increase trade volume. Although the canal would traverse Russian territory, it would benefit Kazakhstan through its Caspian Sea ports. The most likely route for the canal, the officials at the Committee on Water Resources at Kazakhstan's Agriculture Ministry say, would follow the Kuma–Manych Depression, where currently a chain of rivers and lakes is already connected by an irrigation canal (the Kuma–Manych Canal). Upgrading the Volga–Don Canal would be another option. | 2 | Environmental Chemistry |
*[http://www.ciml.univ-mrs.fr/software/cocas/index.html] CoCAS: a free Analysis software for Agilent ChIP-on-Chip experiments
*[http://www.bioconductor.org/packages/2.4/bioc/html/rMAT.html] rMAT: R implementation from MAT program to normalize and analyze tiling arrays and ChIP-chip data. | 1 | Biochemistry |
Exclusion chromatography.
Fractionation Range of Globular Proteins and Dextrans (Da).
Ion-exchange chromatography. | 1 | Biochemistry |
If an atom, A, is double-bonded to another atom, then atom A should be treated as though it is "connected to the same atom twice". An atom that is double-bonded has a higher priority than an atom that is single bonded. When dealing with double bonded priority groups, one is allowed to visit the same atom twice as one creates an arc.
When B is replaced with a list of attached atoms, A itself, but not its "phantom", is excluded in accordance with the general principle of not doubling back along a bond that has just been followed. A triple bond is handled the same way except that A and B are each connected to two phantom atoms of the other. | 4 | Stereochemistry |
Pollution from metals is very common, as they are used in many industrial processes such as electroplating, textiles, paint and leather. The wastewater from these industries is often used for agricultural purposes, so besides the immediate damage to the ecosystem it is spilled into, the metals can enter creatures and humans far away through the food chain. Mycoremediation is one of the cheapest, most effective and environmental-friendly solutions to this problem.
Many fungi are hyperaccumulators, therefore they are able to concentrate toxins in their fruiting bodies for later removal. This is usually true for populations that have been exposed to contaminants for a long time, and have developed a high tolerance. Hyperaccumulation occurs via biosorption on the cellular surface, where the metals enter the mycelium passively with very little intracellular uptake.
A variety of fungi, such as Pleurotus, Aspergillus, Trichoderma has proven to be effective in the removal of lead, cadmium, nickel, chromium, mercury, arsenic, copper, boron, iron and zinc in marine environments, wastewater and on land.
Not all the individuals of a species are effective in the same way in the accumulation of toxins. The single individuals are usually selected from an older polluted environment, such as sludge or wastewater, where they had time to adapt to the circumstances, and the selection is carried on in the laboratory. A dilution of the water can drastically improve the ability of biosorption of the fungi.
The capacity of certain fungi to extract metals from the ground also can be useful for bioindicator purposes, and can be a problem when the mushroom is of an edible variety. For example, the shaggy ink cap (Coprinus comatus), a common edible mushroom found in the Northern Hemisphere, can be a very good bioindicator of mercury. However, as the shaggy ink cap accumulates mercury in its body, it can be toxic to the consumer.
The capacity of metals uptake of mushroom has also been used to recover precious metals from medium. For example, VTT Technical Research Centre of Finland reported an 80% recovery of gold from electronic waste using mycofiltration techniques. | 2 | Environmental Chemistry |
Sharpless married Jan Dueser in 1965 and they have three children. He was blinded in one eye during a lab accident in 1970 where an NMR tube exploded, shortly after he arrived at MIT as an assistant professor. After this accident, Sharpless stresses "theres simply never an adequate excuse for not wearing safety glasses in the laboratory at all times'." | 4 | Stereochemistry |
Phycobilisomes are protein complexes (up to 600 polypeptides) anchored to thylakoid membranes. They are made of stacks of chromophorylated proteins, the phycobiliproteins, and their associated linker polypeptides. Each phycobilisome consists of a core made of allophycocyanin, from which several outwardly oriented rods made of stacked disks of phycocyanin and (if present) phycoerythrin(s) or phycoerythrocyanin. The spectral property of phycobiliproteins are mainly dictated by their prosthetic groups, which are linear tetrapyrroles known as phycobilins including phycocyanobilin, phycoerythrobilin, phycourobilin and phycobiliviolin. The spectral properties of a given phycobilin are influenced by its protein environment. | 5 | Photochemistry |
Light sources emitting in the UV spectral region are widely used in techniques involving photo-chemical processes, e.g., curing of inks, adhesives, varnishes and coatings, photolithography, UV induced growth of dielectrics, UV induced surface modification, and cleaning or material deposition. Incoherent sources of UV radiation have some advantages over laser sources because of their lower cost, a huge area of irradiation, and ease of use, especially when large-scale industrial processes are envisaged.
Mercury lamps (λ = 253.7 nm) are widely spread UV sources, but their production, use, and disposal of old lamps pose a threat to human health and environmental pollution. Comparing with commonly used mercury lamps, excimer lamps have a number of advantages. A specific feature of an excimer molecule is the absence of a strong bond in the ground electronic state. Thanks to this, high-intensity UV radiation can be extracted from a plasma without significant self-absorption. This makes possible to convert efficiently energy deposited to the active medium into UV radiation.
Excimer lamps are referred to cold sources of UV radiation since the radiating surface of excimer lamps remains at relatively low temperatures in contrast with traditional UV lamps like a mercury one. Because the medium does not need to be heated, excimer lamps reach their peak output almost immediately after they are turned on.
Rare gas and rare gas-halide excimer lamps generally radiate in the ultraviolet (UV) and vacuum-ultraviolet (VUV) spectral regions (see table). Their unique narrow-band emission characteristics, high quantum efficiency, and high-energy photons make them suitable for applications such as absorption spectroscopy, UV curing, UV coating, disinfection, ozone generation, destruction of gaseous organic waste, photo-etching and photo-deposition and more other applications.
Light sources emitting photons in the energy range of 3.5–10 eV find applications in many fields due to the ability of high-energy photons to cleave most chemical bonds and kill microbes destroying nucleic acids and disrupting their DNA. Examples of excimer lamp applications include purification and disinfection of drinking water, pool water, air, sewage purification, decontamination of industrial waste, photochemical synthesis and degradation of organic compounds in flue gases and water, photopolymerization of organic coatings and paints, and photo-enhanced chemical vapor deposition. In all cases UV photons excite species or cleave chemical bonds, resulting in the formation of radicals or other chemical reagents, which initiate a required reaction.
An excimer lamp has selective action. UV radiation of a given wavelength can selectively excite species or generate required radicals. Such lamps can be useful for photophysical and photochemical processing such as UV curing of paints, varnishes, and adhesives, cleansing and modifying surface properties, polymerization of lacquers and paints, and photo-degradation of a variety of pollutants. Photo-etching of polymers is possible using different wavelengths: 172 nm by xenon excimer, 222 nm by krypton chloride, and 308 nm by xenon chloride. Excimer UV sources can be used for microstructuring large-area polymer surfaces. XeCl-excimer lamps (308 nm) are especially suitable to get tan.
Fluorescence spectroscopy is one of the most common methods for detecting biomolecules. Biomolecules can be labeled with fluoroprobe, which then is excited by a short pulse of UV light, leading to re-emission in the visible spectral region. Detecting this re-emitted light, one can judge the density of labeled molecules. Lanthanide complexes are commonly used as fluoroprobes. Due to their long lifetime, they play an important role in Förster resonance energy transfer (FRET) analysis.
At present, excimer lamps are coming into use in ecology, photochemistry, photobiology, medicine, criminalistics, petrochemistry, physics, microelectronics, different engineering tasks, wide-ranging technologies, science, various branches of industry including the food industry, and many others. | 5 | Photochemistry |
Presence of un-phosphorylated pRb drives cell cycle exit and maintains senescence. At the end of mitosis, PP1 dephosphorylates hyper-phosphorylated pRb directly to its un-phosphorylated state. Furthermore, when cycling C2C12 myoblast cells differentiated (by being placed into a differentiation medium), only un-phosphorylated pRb was present. Additionally, these cells had a markedly decreased growth rate and concentration of DNA replication factors (suggesting G0 arrest).
This function of un-phosphorylated pRb gives rise to a hypothesis for the lack of cell cycle control in cancerous cells: Deregulation of Cyclin D - Cdk 4/6 phosphorylates un-phosphorylated pRb in senescent cells to mono-phosphorylated pRb, causing them to enter G1. The mechanism of the switch for Cyclin E activation is not known, but one hypothesis is that it is a metabolic sensor. Mono-phosphorylated pRb induces an increase in metabolism, so the accumulation of mono-phosphorylated pRb in previously G0 cells then causes hyper-phosphorylation and mitotic entry. Since any un-phosphorylated pRb is immediately phosphorylated, the cell is then unable to exit the cell cycle, resulting in continuous division.
DNA damage to G0 cells activates Cyclin D - Cdk 4/6, resulting in mono-phosphorylation of un-phosphorylated pRb. Then, active mono-phosphorylated pRb causes repression of E2F-targeted genes specifically. Therefore, mono-phosphorylated pRb is thought to play an active role in DNA damage response, so that E2F gene repression occurs until the damage is fixed and the cell can pass the restriction point. As a side note, the discovery that damages causes Cyclin D - Cdk 4/6 activation even in G0 cells should be kept in mind when patients are treated with both DNA damaging chemotherapy and Cyclin D - Cdk 4/6 inhibitors. | 1 | Biochemistry |
Transient expression, more frequently referred to "transient gene expression", is the temporary expression of genes that are expressed for a short time after nucleic acid, most frequently plasmid DNA encoding an expression cassette, has been introduced into eukaryotic cells with a chemical delivery agent like calcium phosphate (CaPi) or polyethyleneimine (PEI). However, unlike "stable expression," the foreign DNA does not fuse with the host cell DNA, resulting in the inevitable loss of the vector after several cell replication cycles. The majority of transient gene expressions are done with cultivated animal cells. The technique is also used in plant cells; however, the transfer of nucleic acids into these cells requires different methods than those with animal cells. In both plants and animals, transient expression should result in a time-limited use of transferred nucleic acids, since any long-term expression would be called "stable expression."
Methodology varies depending on the organism to transform. While plants can be transformed with a construct introduced into Agrobacterium tumefaciens via agroinfiltration or floral dip, most animal cells would require a viral vector. In humans, the field of transient transformation advanced rapidly during the 2020–2021 COVID-19 pandemic with major COVID-19 vaccines using either direct mRNA transfer into human or adenovirus vectors, with the RNA being expressed in the host human to produce spike proteins that induce an immune response. | 1 | Biochemistry |
* Jim Wittke's class notes at Northern Arizona University
* John Fournelle's class notes at the University of Wisconsin–Madison
* John Donovan's class notes at the University of Oregon | 3 | Analytical Chemistry |
Aziridine is an organic compound consisting of the three-membered heterocycle . It is a colorless, toxic, volatile liquid that is of significant practical interest. Aziridine was discovered in 1888 by the chemist Siegmund Gabriel. Its derivatives, also referred to as aziridines, are of broader interest in medicinal chemistry. | 0 | Organic Chemistry |
Lawessons reagent has a four membered ring of alternating sulfur and phosphorus atoms. The central phosphorus/sulfur four-membered ring dissociates to form two reactive dithiophosphine ylides (R-PS). Much of the chemistry of Lawessonss reagent is in fact the chemistry of this reactive intermediate.
In general, the more electron rich a carbonyl is, the faster the carbonyl group will be converted into the corresponding thiocarbonyl by Lawesson's reagent. | 0 | Organic Chemistry |
Diel Vertical Migration (DVM) is a well-studied phenomenon, widespread in the temperate and tropical oceans, and previously understood to be the most significant contributor to the active export of carbon as a result of zooplankton migration. The most common form is the nocturnal DVM, a night-time ascent to the upper pelagic and a daytime descent to deeper waters. A relatively unique variation of this form is the twilight DVM, where the ascent happens during dusk and the descent around midnight (i.e., midnight sinking).
While DVM occurs on a daily basis, overwintering diapause (hibernation) occurs on an annual time-scale and enables zooplankton species, particularly Calanus spp., to adapt to seasonal variation in primary productivity in specific ocean basins. Individuals enter diapause and migrate deeper in the water column to overwinter below the thermocline. During diapause they survive on stored lipid reserves that are generated at the end of their time at the surface when nutrients are widely available. The seasonal end of diapause must be closely timed with the beginning of the spring phytoplankton bloom to enable acquisition of food to permit proper egg development and hatching. If the timing is disrupted, eggs that are hatched during diapause will have limited growth time and a lower likelihood of surviving overwintering, as thus is an example of match-mismatch hypothesis. Calanus spp. in ocean basins with shorter growth seasons will be increasingly sensitive to the timing of the spring bloom, such as polar regions.
In the Arctic and Antarctic environments, the productive season is typically short and certain copepods species vertically migrate during overwintering diapause. During the productive seasons of spring and summer, younger developmental stages of these copepods usually thrive in food-rich, warmer, near-surface waters, and they rapidly develop and grow. During late summer and fall, grazing pressure, nutrient limitation, and annual variations of irradiance combine to limit the pelagic primary production. Consequently, the food supply fades toward fall, and overwintering diapause initiates. These copepods migrate to deeper waters with accumulated lipid reserves for overwintering. The overwintering diapause stages remain in deeper waters with limited physical and physiological activity and ascend back to the near-surface waters and complete the life cycle at the onset of the following productive season. | 9 | Geochemistry |
Germacranolides are a group of natural chemical compounds classified as sesquiterpene lactones. They are found in a variety of plant sources. | 0 | Organic Chemistry |
In SARS-CoV-2 (COVID-19) infected Caco-2 cells, the phosphorylase activity of CK2 is increased resulting in phosphorylation of several cytoskeletal proteins. These infected cells also display CK2-containing filopodia protrusions associated with budding viral particles. Hence the protrusions may assist the virus in infecting adjacent cells. In these same cells, the CK2 inhibitor silmitasertib displayed potent antiviral activity. Senhwa Biosciences and the US National Institutes of Health have announced that they will evaluate the efficacy of silmitasertib in treating COVID-19 infections. | 1 | Biochemistry |
In the context of climate change and in particular mitigation, a sink is defined as "Any process, activity or mechanism which removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere".
In the case of non- greenhouse gases, sinks need not store the gas. Instead they can break it down into substances that have a reduced effect on global warming. For example, nitrous oxide can be reduced to harmless N.
Related terms are "carbon pool, reservoir, sequestration, source and uptake". The same publication defines carbon pool as "a reservoir in the Earth system where elements, such as carbon [...], reside in various chemical forms for a period of time."
Both carbon pools and carbon sinks are important concepts in understanding the carbon cycle, but they refer to slightly different things. A carbon pool can be thought of as the overarching term, and carbon sink is then a particular type of carbon pool: A carbon pool is all the places where carbon can be (for example the atmosphere, oceans, soil, plants, and fossil fuels). A carbon sink, on the other hand, is a type of carbon pool that has the capability to take up more carbon from the atmosphere than it releases. | 5 | Photochemistry |
One potential application of ARS involves the rapid and nondestructive identification of drug tablet verification. Currently, there are no unfailing methods to eliminate contaminated or mislabeled products, a process which sometimes results in millions of pills having to be recalled. More studies need to be completed to determine if ARS could be used as a process analytical technique in industry to prevent problems with pills before they are shipped. ARS may also be useful for quantifying the active ingredient in pharmaceutical ointments and gels. | 7 | Physical Chemistry |
Many governments impose strict regulations regarding the maximum chemical oxygen demand allowed in waste water before they can be returned to the environment. For example, in Switzerland, a maximum oxygen demand between 200 and 1000 mg/L must be reached before waste water or industrial water can be returned to the environment [https://web.archive.org/web/20040310122559/http://www.csem.ch/corporate/Report2002/pdf/p56.pdf]. | 9 | Geochemistry |
The karat (US spelling, symbol k or Kt) or carat (UK spelling, symbol c or Ct) is a fractional measure of purity for gold alloys, in parts fine per 24 parts whole. The karat system is a standard adopted by US federal law. | 8 | Metallurgy |
High-throughput analyses of ESTs often encounter similar data management challenges. A first challenge is that tissue provenance of EST libraries is described in plain English in dbEST. This makes it difficult to write programs that can unambiguously determine that two EST libraries were sequenced from the same tissue. Similarly, disease conditions for the tissue are not annotated in a computationally friendly manner. For instance, cancer origin of a library is often mixed with the tissue name (e.g., the tissue name "glioblastoma" indicates that the EST library was sequenced from brain tissue and the disease condition is cancer). With the notable exception of cancer, the disease condition is often not recorded in dbEST entries. The TissueInfo project was started in 2000 to help with these challenges. The project provides curated data (updated daily) to disambiguate tissue origin and disease state (cancer/non cancer), offers a tissue ontology that links tissues and organs by "is part of" relationships (i.e., formalizes knowledge that hypothalamus is part of brain, and that brain is part of the central nervous system) and distributes open-source software for linking transcript annotations from sequenced genomes to tissue expression profiles calculated with data in dbEST. | 1 | Biochemistry |
A disadvantage to MIKES is that observations are made later in the ion flight path when compared to other methods. Also, a smaller number of ions will typically decompose. This will in turn cause the sensitivity to be lower than other kinetic energy spectroscopy methods. | 7 | Physical Chemistry |
Proteins perform several functions in living organisms, including catalytic reactions and transport of molecules or ions within the cells, the organs or the whole body. The understanding of the processes in human organisms, which are mainly driven by biochemical reactions and protein-protein interactions, depends to a great extent on the ability to isolate active proteins in biological samples for more detailed examination of chemical structure and physiological function. This essential information can imply an important indication of a patient's state of health.
As about 30–40% of all known proteins contain one or more metal ion cofactors (e.g., ceruloplasmin, ferritin, amyloid-beta precursor protein, matrix metalloproteinase, or metallochaperones), especially native and denatured metalloproteins have to be isolated, identified and quantified after liquid biopsy. Many of these cofactors (e.g., iron, copper, or zinc) play a key role in vital enzymatic catalytic processes or stabilize globular protein molecules. Therefore, the high-precision gel electrophoresis and comparable separation techniques are highly relevant as initial step of protein and trace metal speciation analysis, subsequently, followed by modern mass spectrometric and magnetic resonance methods for quantifying and identifying the soluble proteins of interest. | 3 | Analytical Chemistry |
Each cell typically contains several hundred of a special class of enhancers that stretch over many kilobases long DNA sequences, called "super-enhancers". These enhancers contain a large number of binding sites for sequence-specific, inducible transcription factors, and regulate expression of genes involved in cell differentiation. During inflammation, the transcription factor NF-κB facilitates remodeling of chromatin in a manner that selectively redistributes cofactors from high-occupancy enhancers, thereby repressing genes involved in maintaining cellular identify whose expression they enhance; at the same time, this F-κB-driven remodeling and redistribution activates other enhancers that guide changes in cellular function through inflammation. As a result, inflammation reprograms cells, altering their interactions with the rest of tissue and with the immune system. In cancer, proteins that control NF-κB activity are dysregulated, permitting malignant cells to decrease their dependence on interactions with local tissue, and hindering their surveillance by the immune system. | 1 | Biochemistry |
The intense coloring of the molecule is generated by the absorption of specific wavelengths of light by the pi bonds. These bonds are ordinarily excited by light in the orange region of the spectrum, causing the molecule to appear blue. When the molecule interacts with protons from an acid the bonds become harder to excite and thus absorb green light which has a shorter wavelength. This is what causes the molecule to appear red in the presence of an acid. | 3 | Analytical Chemistry |
The word "benzene" derives from "gum benzoin" (benzoin resin), an aromatic resin known since ancient times in Southeast Asia, and later to European pharmacists and perfumers in the 16th century via trade routes. An acidic material was derived from benzoin by sublimation, and named "flowers of benzoin", or benzoic acid. The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene. Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen. In 1833, Eilhard Mitscherlich produced it by distilling benzoic acid (from gum benzoin) and lime. He gave the compound the name benzin. In 1836, the French chemist Auguste Laurent named the substance "phène"; this word has become the root of the English word "phenol", which is hydroxylated benzene, and "phenyl", the radical formed by abstraction of a hydrogen atom from benzene.
In 1845, Charles Blachford Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar. Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method. Gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. In 1855, Hofmann was the first to apply the word "aromatic" to designate this family relationship, after a characteristic property of many of its members. In 1997, benzene was detected in deep space. | 2 | Environmental Chemistry |
If the plasma is optically thin, the bremsstrahlung radiation leaves the plasma, carrying part of the internal plasma energy. This effect is known as the bremsstrahlung cooling. It is a type of radiative cooling. The energy carried away by bremsstrahlung is called bremsstrahlung losses and represents a type of radiative losses. One generally uses the term bremsstrahlung losses in the context when the plasma cooling is undesired, as e.g. in fusion plasmas. | 7 | Physical Chemistry |
Measurements (performed using a soy bean SCS) indicate an optimal temperature of 37 °C and an optimal pH of 7.0-8.0. | 1 | Biochemistry |
The Sleeping Beauty transposon system (SBTS) is the first successful non-viral vector for incorporation of a gene cassette into a vertebrate genome. Up until the development of this system, the major problems with non-viral gene therapy have been the intracellular breakdown of the transgene due to it being recognized as Prokaryotes and the inefficient delivery of the transgene into organ systems. The SBTS revolutionized these issues by combining the advantages of viruses and naked DNA. It consists of a transposon containing the cassette of genes to be expressed, as well as its own transposase enzyme. By transposing the cassette directly into the genome of the organism from the plasmid, sustained expression of the transgene can be attained. This can be further refined by enhancing the transposon sequences and the transposase enzymes used. SB100X is a hyperactive mammalian transposase which is roughly 100x more efficient than the typical first-generation transposase. Incorporation of this enzyme into the cassette results in even more sustained transgene expression (over one year). Additionally, transgenesis frequencies can be as high as 45% when using pronuclear injection into mouse zygotes.
The mechanism of the SBTS is similar to the Tn5 transposon system, however the enzyme and gene sequences are eukaryotic in nature as opposed to prokaryotic. The systems tranposase can act in trans as well as in cis, allowing a diverse collection of transposon structures. The transposon itself is flanked by inverted repeat sequences, which are each repeated twice in a direct fashion, designated IR/DR sequences. The internal region consists of the gene or sequence to be transposed, and could also contain the transposase gene. Alternatively, the transposase can be encoded on a separate plasmid or injected in its protein form. Yet another approach is to incorporate both the transposon and the transposase genes into a viral vector, which can target a cell or tissue of choice. The transposase protein is extremely specific in the sequences that it binds, and is able to discern its IR/DR sequences from a similar sequence by three base pairs. Once the enzyme is bound to both ends of the transposon, the IR/DR sequences are brought together and held by the transposase in a Synaptic Complex Formation (SCF). The formation of the SCF is a checkpoint ensuring proper cleavage. HMGB1 is a non-histone protein from the host which is associated with eukaryotic chromatin. It enhances the preferential binding of the transposase to the IR/DR sequences and is likely essential for SCF complex formation/stability. Transposase cleaves the DNA at the target sites, generating 3 overhangs. The enzyme then targets TA dinucleotides in the host genome as target sites for integration. The same enzymatic catalytic site which cleaved the DNA is responsible for integrating the DNA into the genome, duplicating the region of the genome in the process. Although transposase is specific for TA dinucleotides, the high frequency of these pairs in the genome indicates that the transposon undergoes fairly random integration. | 1 | Biochemistry |
GBE is encoded by the GBE1 gene.
Through Southern blot analysis of DNA derived from human/rodent somatic cell hybrids, GBE1 has been identified as an autosomal gene located on the short arm of chromosome 3 at position 12.3. The human GBE gene was also isolated by a function complementation of the Saccharomyces cerevisiae GBE deficiency. From the isolated cDNA, the length of the gene was found to be approximately 3 kb. Additionally, the coding sequence was found to comprise 2,106 base pairs and encode a 702-amino acid long GBE. The molecular mass of human GBE was calculated to be 80,438 Da. | 1 | Biochemistry |
Henry Clifton Sorby, in 1858, was the first to document microscopic melt inclusions in crystals. The study of melt inclusions has been driven more recently by the development of sophisticated chemical analysis techniques. Scientists from the former Soviet Union lead the study of melt inclusions in the decades after World War II, and developed methods for heating melt inclusions under a microscope, so changes could be directly observed. A.T. Anderson explored analysis of melt inclusions from basaltic magmas from Kilauea Volcano in Hawaii to determine initial volatile concentrations of magma at depth. | 9 | Geochemistry |
Applications:
* The rotary filter is most suitable for continuous operation on large quantities of slurry.
* If the slurry contains considerable amount of solids, that is, in the range of 15-30%.
* Examples of pharmaceutical applications include the collection of calcium carbonate, magnesium carbonate and starch.
* The separation of the mycelia from the fermentation liquor in the manufacture of antibiotics.
* block and instant yeast production. | 3 | Analytical Chemistry |
Many isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosinolates. A prominent natural isothiocyanate is allyl isothiocyanate, also known as mustard oils.
Cruciferous vegetables, such as bok choy, broccoli, cabbage, cauliflower, kale, and others, are rich sources of glucosinolate precursors of isothiocyanates. | 0 | Organic Chemistry |
Oncometabolism is the field of study that focuses on the metabolic changes that occur in cells that make up the tumor microenvironment (TME) and accompany oncogenesis and tumor progression toward a neoplastic state.
Cells with increased growth and survivability differ from non-tumorigenic cells in terms of metabolism. The Warburg Effect, which describes how cancer cells change their metabolism to become more oncogenic in order to proliferate and eventually invade other tissues in a process known as metastasis.
The chemical reactions associated with oncometabolism are triggered by the alteration of oncogenes, which are genes that have the potential to cause cancer. These genes can be functional and active during physiological conditions, producing normal amounts of metabolites. Their upregulation as a result of DNA damage can result in an overabundance of these metabolites, and lead to tumorigenesis. These metabolites are known as oncometabolites, and can act as biomarkers. | 1 | Biochemistry |
In a delay line detector the electrons are accelerated to 500 eV between the back of the last MCP and a grid. They then fly for 5 mm and are dispersed over an area of 2 mm. A grid follows. Each element has a diameter of 1 mm and consists of an electrostatic lens focusing arriving electrons through a 30 µm hole of a grounded sheet of aluminium. Behind that, a cylinder of the same size follows. The electron cloud induces a 300 ps negative pulse when entering the cylinder and a positive when leaving. After that another sheet, a second cylinder follows, and a last sheet follows. Effectively the cylinders are fused into the center-conductor of a stripline. The sheets minimize cross talk between the layers and adjacent lines in the same layer, which would lead to signal dispersion and ringing. These striplines meander across the anode to connect all cylinders, to offer each cylinder 50 Ω impedance, and to generate a position dependent delay. Because the turns in the stripline adversely affect the signal quality their number is limited and for higher resolutions multiple independent striplines are needed. At both ends the meanders are connected to detector electronics. These electronics convert the measured delays into X- (first layer) and Y-coordinates (second layer). Sometimes a hexagonal grid and 3 coordinates are used. This redundancy reduces the dead space-time by reducing the maximum travel distance and thus the maximum delay, allowing for faster measurements. The microchannel plate detector must not operate over around 60 degree Celsius, otherwise it will degrade rapidly, bakeout without voltage has no influence. | 7 | Physical Chemistry |
Cathepsin zymography is a technique for quantifying enzymatic activity of the cathepsin family of cysteine proteases. It is based on SDS-PAGE whereby samples tested for cathepsin activity are loaded into a polyacrylamide gel and then separated by molecular weight. Gelatin is embedded in the gel itself, providing a substrate for the enzymes to hydrolyze.
While the proform of cathepsins are generally stable, once activated, proteases such as cathepsin K are vulnerable to inactivation in neutral pH environments. This loss of activity complicates detection of these enzymes. Zymography, through its high sensitivity and multiplex nature allows for the simultaneous distinction between multiple cathepsins. Very small amounts of enzymatic activity can be elucidated and is capable of resolving a femtomole of cathepsin K activity. | 1 | Biochemistry |
The People's Republic of China defines a VOC as those compounds that have "originated from automobiles, industrial production and civilian use, burning of all types of fuels, storage and transportation of oils, fitment finish, coating for furniture and machines, cooking oil fume and fine particles (PM 2.5)", and similar sources. The Three-Year Action Plan for Winning the Blue Sky Defence War released by the State Council in July 2018 creates an action plan to reduce 2015 VOC emissions 10% by 2020. | 0 | Organic Chemistry |
Consider two probability distributions and . Usually, represents the data, the observations, or a measured probability distribution. Distribution represents instead a theory, a model, a description or an approximation of . The Kullback–Leibler divergence is then interpreted as the average difference of the number of bits required for encoding samples of using a code optimized for rather than one optimized for . Note that the roles of and can be reversed in some situations where that is easier to compute, such as with the expectation–maximization algorithm (EM) and evidence lower bound (ELBO) computations. | 7 | Physical Chemistry |
The heat death paradox, also known as thermodynamic paradox, Clausius paradox, and Kelvins paradox, is a reductio ad absurdum argument that uses thermodynamics to show the impossibility of an infinitely old universe. It was formulated in February 1862 by Lord Kelvin and expanded upon by Hermann von Helmholtz and William John Macquorn Rankine. | 7 | Physical Chemistry |
Geologists often refer to the temperature range in which oil forms as an "oil window". Below the minimum temperature oil remains trapped in the form of kerogen. Above the maximum temperature the oil is converted to natural gas through the process of thermal cracking. Sometimes, oil formed at extreme depths may migrate and become trapped at a much shallower level. The Athabasca oil sands are one example of this. | 7 | Physical Chemistry |
Thionyl chloride is mainly used in the industrial production of organochlorine compounds, which are often intermediates in pharmaceuticals and agrichemicals. It usually is preferred over other reagents, such as phosphorus pentachloride, as its by-products (HCl and ) are gaseous, which simplifies purification of the product.
Many of the products of thionyl chloride are themselves highly reactive and as such it is involved in a wide range of reactions. | 0 | Organic Chemistry |
To observe one-to-one binding between a single host (H) and guest (G) using UV/Vis absorbance, the Benesi–Hildebrand method can be employed. The basis behind this method is that the acquired absorbance should be a mixture of the host, guest, and the host–guest complex.
With the assumption that the initial concentration of the guest (G) is much larger than the initial concentration of the host (H), then the absorbance from H should be negligible.
The absorbance can be collected before and following the formation of the HG complex. This change in absorbance (ΔA) is what is experimentally acquired, with A being the initial absorbance before the interaction of HG and A being the absorbance taken at any point of the reaction.
Using the Beer–Lambert law, the equation can be rewritten with the absorption coefficients and concentrations of each component.
Due to the previous assumption that , one can expect that [G] = [G]. Δε represents the change in value between ε and ε.
A binding isotherm can be described as "the theoretical change in the concentration of one component as a function of the concentration of another component at constant temperature." This can be described by the following equation:
By substituting the binding isotherm equation into the previous equation, the equilibrium constant K can now be correlated to the change in absorbance due to the formation of the HG complex.
Further modifications results in an equation where a double reciprocal plot can be made with 1/ΔA as a function of 1/[G]. Δε can be derived from the intercept while K can be calculated from the slope. | 7 | Physical Chemistry |
In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl () compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds. | 0 | Organic Chemistry |
Enalapril is used to treat hypertension, symptomatic heart failure, and asymptomatic left ventricular dysfunction. ACE-inhibitors (including enalapril) have demonstrated ability to reduce the progression and worsening of existing chronic kidney disease in the presence of proteinuria/microalbuminuria (protein in the urine, a biomarker for chronic kidney disease). This renal protective effect is not seen in the absence of proteinuria/microalbuminuria, including in diabetic populations. The benefit has been particularly demonstrated in patients with hypertension and/or diabetes, and is likely to be seen in other populations (although further studies and subgroup analyses of existing studies are needed) It is widely used in chronic kidney failure. Furthermore, enalapril is an emerging treatment for psychogenic polydipsia. A double-blind, placebo-controlled trial showed that when used for this purpose, enalapril led to decreased water consumption (determined by urine output and osmolality) in 60% of patients. | 4 | Stereochemistry |
Conjugation increases the allylic strain because it forces substituents into a configuration that causes their atoms to be in closer proximity, increasing the strength of repulsive Van der Waals forces. This situation occurs most noticeably when carboxylic acid or ketone is involved as a substituent of the allylic group. Resonance effect on the carboxylic group shifts the CO double bond to a hydroxy group. The carboxylic group will thus function as a hydroxyl group that will cause a large allylic strain to form and cancel the stabilization effects of the extended conjugation. This is very common in enolization reactions and can be viewed in the figure below under "Acidic Conditions."
In situations where the molecule can either be in a conjugated system or avoid allylic strain, it has been shown that the molecule's major form will be the one that avoids strain. This has been found via the cyclization in the figure below. Under treatment of perchloric acid, molecule A cyclizes into the conjugated system show in molecule B. However, the molecule will rearrange (due to allylic strain) into molecule C, causing molecule C to be the major species. Thus, the magnitude of destabilization via the allylic strain outweighs the stabilization caused by the conjugated system. | 4 | Stereochemistry |
The third class of PTPs contains three cell cycle regulators, CDC25A, CDC25B and CDC25C, which dephosphorylate CDKs at their N-terminal, a reaction required to drive progression of the cell cycle. They are themselves regulated by phosphorylation and are degraded in response to DNA damage to prevent chromosomal abnormalities. | 1 | Biochemistry |
The term glycosynthase refers to a class of proteins that have been engineered to catalyze the formation of a glycosidic bond. Glycosynthase are derived from glycosidase enzymes, which catalyze the hydrolysis of glycosidic bonds. They were traditionally formed from retaining glycosidase by mutating the active site nucleophilic amino acid (usually an aspartate or glutamate) to a small non-nucleophilic amino acid (usually alanine or glycine). More modern approaches use directed evolution to screen for amino acid substitutions that enhance glycosynthase activity. | 0 | Organic Chemistry |
Subsets and Splits