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The molecule is tetrahedral with C symmetry. The S-O distance is 140.5 pm, S-F is 153.0 pm. As predicted by VSEPR, the O-S-O angle is more open than the F-S-F angle, 124° and 97°, respectively.
One synthesis begins with the preparation of potassium fluorosulfite:
:SO + KF → KSOF
This salt is then chlorinated to give sulfuryl chloride fluoride:
:KSOF + Cl → SOClF + KCl
Further heating at 180 °C of potassium fluorosulfite with the sulfuryl chloride fluoride gives the desired product:
:SOClF + KSOF → SOF + KCl + SO
Heating metal fluorosulfonate salts also gives this molecule:
:Ba(OSOF) → BaSO + SOF
It can be prepared by direct reaction of fluorine with sulfur dioxide:
:SO + F → SOF
On a laboratory scale, sulfuryl fluoride has been conveniently prepared from 1,1'-sulfonyldiimidazole, in the presence of potassium fluoride and acid.
Sulfuryl fluoride is unreactive toward molten sodium metal. Similarly it is slow to hydrolyze, but eventually converts to sulfur trioxide.
Sulfuryl fluoride gas is a precursor to fluorosulfates and sulfamoyl fluorides:
:SOF + ROH + base → ROSOF + HbaseF | 2 | Environmental Chemistry |
Neurotrophins are a family of proteins that induce the survival, development, and function of neurons.
They belong to a class of growth factors, secreted proteins that can signal particular cells to survive, differentiate, or grow. Growth factors such as neurotrophins that promote the survival of neurons are known as neurotrophic factors. Neurotrophic factors are secreted by target tissue and act by preventing the associated neuron from initiating programmed cell death – allowing the neurons to survive. Neurotrophins also induce differentiation of progenitor cells, to form neurons.
Although the vast majority of neurons in the mammalian brain are formed prenatally, parts of the adult brain (for example, the hippocampus) retain the ability to grow new neurons from neural stem cells, a process known as neurogenesis. Neurotrophins are chemicals that help to stimulate and control neurogenesis. | 1 | Biochemistry |
Supramolecular electronics is the experimental field of supramolecular chemistry that bridges the gap between molecular electronics and bulk plastics in the construction of electronic circuitry at the nanoscale. In supramolecular electronics, assemblies of pi-conjugated systems on the 5 to 100 nanometer scale are prepared by molecular self-assembly with the aim to fit these structures between electrodes. With single molecules as researched in molecular electronics at the 5 nanometer scale this would be impractical. Nanofibers can be prepared from polymers such as polyaniline and polyacetylene. Chiral oligo(p-phenylenevinylene)s self-assemble in a controlled fashion into (helical) wires. An example of actively researched compounds in this field are certain coronenes. | 6 | Supramolecular Chemistry |
In the case of oxide copper ore, a heap leaching pad will dissolve a dilute copper sulfate solution in a weak sulfuric acid solution. This pregnant leach solution (PLS) is pumped to an extraction mixer settler where it is mixed with the organic phase (a kerosene hosted extractant). The copper transfers to the organic phase, and the aqueous phase (now called raffinate) is pumped back to the heap to recover more copper.
In a high-chloride environment typical of Chilean copper mines, a wash stage will rinse any residual pregnant solution entrained in the organic with clean water.
The copper is then stripped from organic phase in the strip stage into a strong sulfuric acid solution suitable for electrowinning. This strong acid solution is called barren electrolyte when it enters the cell, and strong electrolyte when it is copper bearing after reacting in the cell. | 3 | Analytical Chemistry |
The DNA sense strand looks like the messenger RNA (mRNA) transcript, and can therefore be used to read the expected codon sequence that will ultimately be used during translation (protein synthesis) to build an amino acid sequence and then a protein. For example, the sequence "ATG" within a DNA sense strand corresponds to an "AUG" codon in the mRNA, which codes for the amino acid methionine. However, the DNA sense strand itself is not used as the template for the mRNA; it is the DNA antisense strand that serves as the source for the protein code, because, with bases complementary to the DNA sense strand, it is used as a template for the mRNA. Since transcription results in an RNA product complementary to the DNA template strand, the mRNA is complementary to the DNA antisense strand.
Hence, a base triplet 3′-TAC-5′ in the DNA antisense strand (complementary to the 5′-ATG-3′ of the DNA sense strand) is used as the template which results in a 5′-AUG-3′ base triplet in the mRNA. The DNA sense strand will have the triplet ATG, which looks similar to the mRNA triplet AUG but will not be used to make methionine because it will not be directly used to make mRNA. The DNA sense strand is called a "sense" strand not because it will be used to make protein (it won't be), but because it has a sequence that corresponds directly to the RNA codon sequence. By this logic, the RNA transcript itself is sometimes described as "sense". | 1 | Biochemistry |
Cosmids are predominantly plasmids with a bacterial oriV, an antibiotic selection marker and a cloning site, but they carry one, or more recently two, cos sites derived from bacteriophage lambda. Depending on the particular aim of the experiment, broad host range cosmids, shuttle cosmids or mammalian cosmids (linked to SV40 oriV and mammalian selection markers) are available. The loading capacity of cosmids varies depending on the size of the vector itself but usually lies around 40–45 kb. The cloning procedure involves the generation of two vector arms which are then joined to the foreign DNA. Selection against wild type cosmid DNA is simply done via size exclusion. Cosmids, therefore, always form colonies and not plaques. Also the clone density is much lower with around 10 – 10 CFU per µg of ligated DNA.
After the construction of recombinant lambda or cosmid libraries the total DNA is transferred into an appropriate E. coli host via a technique called in vitro packaging. The necessary packaging extracts are derived from E. coli cI857 lysogens (red- gam- Sam and Dam (head assembly) and Eam (tail assembly) respectively). These extracts will recognize and package the recombinant molecules in vitro, generating either mature phage particles (lambda-based vectors) or recombinant plasmids contained in phage shells (cosmids). These differences are reflected in the different infection frequencies seen in favour of lambda-replacement vectors. This compensates for their slightly lower loading capacity. Phage libraries are also stored and screened more easily than cosmid libraries.
Target DNA: the genomic DNA to be cloned has to be cut into the appropriate size range of restriction fragments. This is usually done by partial restriction followed by either size fractionation or dephosphorylation (using calf-intestine phosphatase) to avoid chromosome scrambling, i.e. the ligation of physically unlinked fragments. | 1 | Biochemistry |
Under 1.59 GPa pressure at 25 °C, methane converts to a cubic solid. The molecules are rotationally disordered. But over 5.25 GPa the molecules become locked into position and cannot spin. Other hydrocarbons under high pressure have hardly been studied. | 9 | Geochemistry |
Many C–H activation reactions, particularly those involving late transition metals, require carboxylate or carbonate bases. The need for this reaction component often suggests the occurrence of a CMD pathway. However, in order to be classified as CMD, the transition state does not need to involve the carboxylate as a ligand on the metal. Common sources of carboxylate include pivalate, acetate, and benzoate. | 0 | Organic Chemistry |
The reciprocal lattice to a BCC lattice is the FCC lattice, with a cube side of .
It can be proven that only the Bravais lattices which have 90 degrees between (cubic, tetragonal, orthorhombic) have primitive translation vectors for the reciprocal lattice, , parallel to their real-space vectors. | 3 | Analytical Chemistry |
Mass analyzed threshold ionization (MATI) was developed with idea of collecting the mass of the ions in a ZEKE experiment.
MATI offered a mass resolution advantage to ZEKE. Because MATI also exploits vibrational autoionization of near-threshold Rydberg states, it also can offer a comparable resolution with the laser bandwidth. This information can be indispensable in understanding a variety of systems. | 7 | Physical Chemistry |
Conventional dielectrometry is carried out typically in a parallel plate configuration of the dielectric sensor (capacitance probe) and has the capability of monitoring the resin cure throughout the entire cycle, from the liquid to the rubber to the solid state. It is capable of monitoring phase separation in complex resin blends curing also within a fibrous perform. The same attributes belong to the more recent development of the dielectric technique, namely microdielectrometry.
Several versions of dielectric sensors are available commercially. The most suitable format for use in cure monitoring applications are the flat interdigital capacitive structures bearing a sensing grid on their surface. Depending on their design (specifically those on durable substrates) they have some reusability, while flexible substrate sensors can be used also in the bulk of the resin systems as embedded sensors. | 7 | Physical Chemistry |
FLiNaK salt was researched heavily during the late 1950s by Oak Ridge National Laboratory as potential candidate for a coolant in the molten salt reactor because of its low melting point, its high heat capacity, and its chemical stability at high temperatures. Ultimately, its sister salt, FLiBe, was chosen as the solvent salt for the molten salt reactor due to a more desirable nuclear cross section. FLiNaK still gathers interest as an intermediate coolant for a high-temperature molten salt reactor where it could transfer heat without being in the presence of the fuel. | 7 | Physical Chemistry |
Littrow expansion and its counterpart Littrow compression are optical effects associated with slitless imaging spectrographs. These effects are named after austrian physicist Otto von Littrow.
In a slitless imaging spectrograph, light is focused with a conventional optical system, which includes a transmission or reflection grating as in a conventional spectrograph. This disperses the light, according to wavelength, in one direction; but no slit is interposed into the beam. For pointlike objects (such as distant stars) this results in a spectrum on the focal plane of the instrument for each imaged object. For distributed objects with emission-line spectra (such as the Sun in extreme ultraviolet), it results in an image of the object at each wavelength of interest, overlapping on the focal plane, as in a spectroheliograph. | 7 | Physical Chemistry |
Clinical and translational data suggest that sensitive tumor types, with adequate parameters and functional apoptosis pathways, might not need high doses of mTOR inhibitors to trigger apoptosis. In most cases, cancer cells might only be partially sensitive to mTOR inhibitors due to redundant signal transduction or lack of functional apoptosis signaling pathways. In situations like this, high doses of mTOR inhibitors might be required. In a recent study of patients with Renal cell carcinoma, resistance to Temsirolimus was associated with low levels of p-AKT and p-S6K1, that play the key role in mTOR activation. These data strongly suggests number of tumors with an activated PI3K/AKT/mTOR signaling pathway that does not respond to mTOR inhibitors. For future studies, it is recommended to exclude patients with low or negative p-AKT levels from trials with mTOR inhibitors.
Current data is insufficient to predict sensitivity of tumors to rapamycin. However, the existing data allows us to characterize tumors that might not respond to rapalogs. | 1 | Biochemistry |
In terms of its coordination properties, phenanthroline is similar to 2,2'-bipyridine (bipy) with the advantage that the two nitrogen donors are preorganized for chelation. Phenanthroline is a stronger base than bipy. According to one ligand ranking scale, phen is a weaker donor than bipy.
Several homoleptic complexes are known of the type [M(phen)]. Particularly well studied is [Fe(phen)], called "ferroin." It can be used for the photometric determination of Fe(II). It is used as a redox indicator with standard potential +1.06 V. The reduced ferrous form has a deep red colour and the oxidised form is light-blue. The pink complex [Ni(phen)] has been resolved into its Δ and Λ isomers. The complex [Ru(phen)] is bioactive.
Copper(I) forms [Cu(phen)], which is luminescent. | 3 | Analytical Chemistry |
A single material may have several distinct solid states capable of forming separate phases. Water is a well-known example of such a material. For example, water ice is ordinarily found in the hexagonal form ice I, but can also exist as the cubic ice I, the rhombohedral ice II, and many other forms. Polymorphism is the ability of a solid to exist in more than one crystal form. For pure chemical elements, polymorphism is known as allotropy. For example, diamond, graphite, and fullerenes are different allotropes of carbon. | 7 | Physical Chemistry |
Several theories describe the equilibrium segregation activity in materials. The adsorption theories for the solid-solid interface and the solid-vacuum surface are direct analogues of theories well known in the field of gas adsorption on the free surfaces of solids. | 7 | Physical Chemistry |
Boyles law is often used as part of an explanation on how the breathing system works in the human body. This commonly involves explaining how the lung volume may be increased or decreased and thereby cause a relatively lower or higher air pressure within them (in keeping with Boyles law). This forms a pressure difference between the air inside the lungs and the environmental air pressure, which in turn precipitates either inhalation or exhalation as air moves from high to low pressure. | 7 | Physical Chemistry |
The CD family of co-receptors are a well-studied group of extracellular receptors found in immunological cells. The CD receptor family typically act as co-receptors, illustrated by the classic example of CD4 acting as a co-receptor to the T cell receptor (TCR) to bind major histocompatibility complex II (MHC-II). This binding is particularly well-studied in T-cells where it serves to activate T-cells that are in their resting (or dormant) phase and to cause active cycling T-cells to undergo programmed cell death. Boehme et al. demonstrated this interesting dual outcome by blocking the binding of CD4 to MHC-II which prevented the programmed cell death reaction that active T-cells typically display.
The CD4 receptor is composed of four concatamerized Ig-like domains and is anchored to the cell membrane by a single transmembrane domain. CD family receptors are typically monomers or dimers, though they are all primarily extracellular proteins. The CD4 receptor in particular interacts with murine MHC-II following the "ball-on-stick" model, where the Phe-43 ball fits into the conserved hydrophobic α2 and β2 domain residues. During binding with MHC-II, CD4 maintains independent structure and does not form any bonds with the TCR receptor.
The members of the CD family of co-receptors have a wide range of function. As well as being involved in forming a complex with MHC-II with TCR to control T-cell fate, the CD4 receptor is infamously the primary receptor that HIV envelope glycoprotein GP120 binds to. In comparison, CD28 acts as a ‘co-coreceptor’ (costimulatory receptor) for the MHC-II binding with TCR and CD4. CD28 increases the IL-2 secretion from the T-cells if it is involved in the initial activation; however, CD28 blockage has no effect on programmed cell death after the T-cell has been activated. | 1 | Biochemistry |
The non-stoichiometric cycles with CeO can be describes with the following reactions:
::Reduction reaction: CeO → CeO + δ/2 O
::Oxidation reaction: CeO + δ HO → CeO + δ H
The reduction occurs when CeO, or ceria, is exposed to a inert atmosphere at around 1500 °C to 1600 °C, and hydrogen release occurs at 800 °C during hydrolysis when it is subjected to an atmosphere containing water vapor. One advantage of ceria over iron oxide lies in its higher melting point, which allows it to sustain higher temperature during reduction cycle. In addition, cerias ionic conductivity allows oxygen atoms to diffuse through its structure several orders of magnitude faster than Fe ions can diffuse through iron oxide. Consequently, the redox reactions of ceria can occur at occur at a larger length scale, making it an ideal candidate for thermochemical reactor testing. Ceria-based thermochemical reactor has been created and tested as early as 2010, and viability of cycling was corroborated under realistic solar concentrating conditions. One disadvantage that limits cerias application is its relatively lower oxygen storage capability. | 7 | Physical Chemistry |
In early 2004, Novartis Pharmaceuticals have disclosed the detail of a 60g-scale synthesis of (+)-discodermolide. This synthesis utilized the Smith gram-scale approach and the Paterson first-generation endgame. This synthesis allows (+)-discodermolide to be evaluated as an in vivo chemotherapeutic agent for adult patients presenting with advanced solid malignancies in Phase I clinical trials. The Novartis synthesis of (+)-discodermolide has an overall yield of 0.65% with a longest linear sequence of 26 steps and 33 total steps. | 0 | Organic Chemistry |
*2.C.1 The TonB-ExbB-ExbD/TolA-TolQ-TolR (TonB) Family of Auxiliary Proteins for Energization of Outer Membrane Receptor (OMR)-mediated Active Transport | 1 | Biochemistry |
The physical presence of introns promotes cellular resistance to starvation via intron enhanced repression of ribosomal protein genes of nutrient-sensing pathways. | 1 | Biochemistry |
closo- is formed by the face-sharing condensation of two icosahedra. The m + n + o + p − q rule demands 23 SEPs; 18 BH units provide 18 pairs and 3 shared boron atoms provide pairs; the negative charge provides one half pair. | 7 | Physical Chemistry |
Zeise made several scientific discoveries. His discovery of mercaptans (thiols) in 1832 and thioethers in 1833, was once a weighty support for the influential (now obsolete) "Radical Theory" which Berzelius and Liebig developed, provoking important chemical studies. His discovery and work on xanthates, led to the widespread use of xanthate salts in synthetic chemistry.
In 1830, Zeise attempted to react platinum chloride with ethanol, leading to a series of platinum-based organometallic compounds. One of these compounds, originally referred to by Zeise himself as “sal kalicoplatinicus inflammabilis”, was subsequently named after him according to the tradition of the day – it is still called Zeises salt. Zeises claim that the newly discovered salt contained ethylene was received with distrust by Justus von Liebig, whose understandable attacks on Zeise were quite unjustified. The complex indeed contains ethylene. Attempts to establish the correct structure and composition of Zeises salt drove much basic research during the second half of the 19th century and led to a greater sophistication in organometallic chemistry. The structure of Zeises salt was definitively resolved only with the advent of X-ray crystallography and the nature of its platinum to ethylene bond was not understood until the development of the Dewar–Chatt–Duncanson model in the 1950s.
Shortly before he died, Zeise published his attempts to purify the pigment carotene from carrot juice while in the Polytechnic Institute; finding it to be soluble in carbon disulfide and correctly identifying it as a hydrocarbon. | 0 | Organic Chemistry |
Vancomycin is usually given intravenously, as an infusion, and can cause tissue necrosis and phlebitis at the injection site if given too rapidly. Pain at site of injection is indeed a common adverse event. One of the side-effects is red man syndrome, an idiosyncratic reaction to bolus caused by histamine release. Some other side-effects of vancomycin are nephrotoxicity including kidney failure and interstitial nephritis, blood disorders including neutropenia, and deafness, which is reversible once therapy has stopped. Over 90% of the dose is excreted in the urine, therefore there is a risk of accumulation in patients with renal impairment, so therapeutic drug monitoring (TDM) is recommended.
Oral preparations of vancomycin are available, however they are not absorbed from the lumen of the gut, so are of no use in treating systemic infections. The oral preparations are formulated for the treatment of infections within the gastrointestinal tract, Clostridium difficile, for example. | 0 | Organic Chemistry |
Early studies on donor-acceptor complexes focused on the solvatochromism exhibited by iodine, which often results from I forming adducts with electron donors such as amines and ethers. Dihalogens X (X = Cl, Br, I) and interhalogens XY(X = I; Y = Cl, Br) are Lewis acid species capable of forming a variety of products when reacted with donor species. Among these species (including oxidation or protonated products), CT adducts D·XY have been largely investigated. The CT interaction has been quantified and is the basis of many schemes for parameterizing donor and acceptor properties, such as those devised by Gutmann, Childs, Beckett, and the ECW model.
Many organic species featuring chalcogen or pnictogen donor atoms form CT salts. The nature of the resulting adducts can be investigated both in solution and in the solid state.
In solution, the intensity of charge-transfer bands in the UV-Vis absorbance spectrum is strongly dependent upon the degree (equilibrium constant) of this association reaction. Methods have been developed to determine the equilibrium constant for these complexes in solution by measuring the intensity of absorption bands as a function of the concentration of donor and acceptor components in solution. The Benesi-Hildebrand method, named for its developers, was first described for the association of iodine dissolved in aromatic hydrocarbons.
In the solid state a valuable parameter is the elongation of the X–X or X–Y bond length, resulting from the antibonding nature of the σ* LUMO. The elongation can be evaluated by means of structural determinations (XRD) and FT-Raman spectroscopy.
A well-known example is the complex formed by iodine when combined with starch, which exhibits an intense purple charge-transfer band. This has widespread use as a rough screen for counterfeit currency. Unlike most paper, the paper used in US currency is not sized with starch. Thus, formation of this purple color on application of an iodine solution indicates a counterfeit. | 7 | Physical Chemistry |
In chemical kinetics, an Arrhenius plot displays the logarithm of a reaction rate constant, ordinate axis) plotted against reciprocal of the temperature abscissa). Arrhenius plots are often used to analyze the effect of temperature on the rates of chemical reactions. For a single rate-limited thermally activated process, an Arrhenius plot gives a straight line, from which the activation energy and the pre-exponential factor can both be determined.
The Arrhenius equation can be given in the form:
where:
* = rate constant
* = pre-exponential factor
* = (molar) activation energy
* = gas constant, (, where is the Avogadro constant).
* = activation energy (for a single reaction event)
* = Boltzmann constant
* = absolute temperature
The only difference between the two forms of the expression is the quantity used for the activation energy: the former would have the unit joule/mole, which is common in chemistry, while the latter would have the unit joule and would be for one molecular reaction event, which is common in physics. The different units are accounted for in using either the gas constant or the Boltzmann constant .
Taking the natural logarithm of the former equation gives:
When plotted in the manner described above, the value of the y-intercept (at ) will correspond to , and the slope of the line will be equal to . The values of y-intercept and slope can be determined from the experimental points using simple linear regression with a spreadsheet.
The pre-exponential factor, , is an empirical constant of proportionality which has been estimated by various theories which take into account factors such as the frequency of collision between reacting particles, their relative orientation, and the entropy of activation.
The expression represents the fraction of the molecules present in a gas which have energies equal to or in excess of activation energy at a particular temperature. In almost all practical cases, , so that this fraction is very small and increases rapidly with In consequence, the reaction rate constant increases rapidly with temperature , as shown in the direct plot of against . (Mathematically, at very high temperatures so that , would level off and approach as a limit, but this case does not occur under practical conditions.) | 7 | Physical Chemistry |
Droplet countercurrent chromatography (DCCC) was introduced in 1970 by Tanimura, Pisano, Ito, and Bowman. DCCC uses only gravity to move the mobile phase through the stationary phase which is held in long vertical tubes connected in series. In the descending mode, droplets of the denser mobile phase and sample are allowed to fall through the columns of the lighter stationary phase using only gravity. If a less-dense mobile phase is used it will rise through the stationary phase; this is called ascending mode. The eluent from one column is transferred to another; the more columns that are used, the more theoretical plates can be achieved. DCCC enjoyed some success with natural product separations but was largely eclipsed by the rapid development of high-speed countercurrent chromatography. The main limitation of DCCC is that flow rates are low, and poor mixing is achieved for most binary solvent systems. | 3 | Analytical Chemistry |
Class I AMGs encode for metabolism pathways in the cell and are found in KEGG. In particular, these genes are found in photosynthesis and carbon metabolism. psbA is almost a ubiquitous photosynthetic AMG for the photosystem Il reaction center D1 found in Synechococcus and Prochlorococcus cyanophages. Photosynthetic machinery for other reaction centers and electron transport are also found in many viruses infecting phototrophs. Phages encode for nearly all genes involved in carbon metabolism. In particular, viruses redirect host metabolism to increase dNTP biosynthesis for viral genome replication. glgA can induce starvation by converting glucose-6-phosphate to glycogen, forcing the host to compensate by deriving ribulose-5-phosphate from glyceraldehyde-3-phosphate and fructose-6-phosphate. | 1 | Biochemistry |
Favipiravir is sold under the brand names , Avifavir, Avipiravir, Areplivir, FabiFlu, Favipira, Reeqonus, and Qifenda. | 4 | Stereochemistry |
Eslicarbazepine acetate (ESL), sold under the brand names Aptiom and Zebinix among others, is an anticonvulsant medication approved for use in Europe and the United States as monotherapy or as additional therapy for partial-onset seizures epilepsy.
Similarly to oxcarbazepine, ESL behaves as a prodrug to (S)-(+)-licarbazepine. As such, their mechanisms of action are identical. | 4 | Stereochemistry |
Outer sphere ET is the basis of the biological function of the iron-sulfur proteins. The Fe centers are typically further coordinated by cysteinyl ligands. The [FeS] electron-transfer proteins ([FeS] ferredoxins) may be further subdivided into low-potential (bacterial-type) and high-potential (HiPIP) ferredoxins. Low- and high-potential ferredoxins are related by the following redox scheme:
Because of the small structural differences between the individual redox states, ET is rapid between these clusters. | 7 | Physical Chemistry |
An antibody titer is a measurement of how much antibody an organism has produced that recognizes a particular epitope. It is conventionally expressed as the inverse of the greatest dilution level that still gives a positive result on some test. ELISA is a common means of determining antibody titers. For example, the indirect Coombs test detects the presence of anti-Rh antibodies in a pregnant womans blood serum. A patient might be reported to have an "indirect Coombs titer" of 16. This means that the patients serum gives a positive indirect Coombs test at any dilution down to 1/16 (1 part serum to 15 parts diluent). At greater dilutions the indirect Coombs test is negative. If a few weeks later the same patient had an indirect Coombs titer of 32 (1/32 dilution which is 1 part serum to 31 parts diluent), this would mean that she was making more anti-Rh antibody, since it took a greater dilution to abolish the positive test.
Many traditional serological tests such as hemagglutination or complement fixation employ this principle. Such tests can typically be read visually, which makes them fast, cost-effective, and able to be deployed in a wide variety of laboratory environments. The interpretation of any serological titer result is guided by reference values that are specific to the antigen or antibody in question, so a titer of 1:32 may be below the cut-off for one test but above for another. | 1 | Biochemistry |
The usual process of electrorefining copper consists of placing a copper anode (about 99.5–99.7% pure copper) in sulfuric acid (HSO) bath of copper electrolyte, together with a cathode, and passing a current between the anode and cathode through an external circuit. At the applied electropotential, copper and less noble elements dissolve in the electrolyte, while elements more noble than copper, such as gold (Au) and silver (Ag), do not. Under the influence of the applied electrical potential, copper ions migrate from the anode and deposit on the cathode, forming cathode copper.
The current IsaKidd technology represents the merger of the copper refining technologies developed by the two different organisations. The initial Isa Process development in the late 1970s, with its reusable stainless-steel cathode starter sheets, represented an advance on the previous technology of single-use starter sheets of pure copper, the production of which was a labour-intensive process.
The production of the single-use starter sheets involved laying down a sheet of copper by electrolysis on each side of a “mother plate”. Generating the sheet took a day, and thousands of sheets could be needed every day. Originally, the copper starter sheets were separated from the mother plate manually, but over time the process was automated. In addition, limitations associated with the use of copper starter sheets meant that it was difficult to meet the purity specifications of some new copper applications that were, in the 1970s and 1980s, demanding higher quality copper. | 8 | Metallurgy |
CRISPR-associated transposons or CASTs are mobile genetic elements (MGEs) that have evolved to make use of minimal CRISPR systems for RNA-guided transposition of their DNA. Unlike traditional CRISPR systems that contain interference mechanisms to degrade targeted DNA, CASTs lack proteins and/or protein domains responsible for DNA cleavage. Specialized transposon machinery, similar to that of the well characterized Tn7 transposon, complexes with the CRISPR RNA (crRNA) and associated Cas proteins for transposition. CAST systems have been characterized in a wide range of bacteria and make use of variable CRISPR configurations including Type I-F, Type I-B, Type I-C, Type I-D, Type I-E, Type IV, and Type V-K. MGEs remain an important part of genetic exchange by horizontal gene transfer and CASTs have been implicated in the exchange of antibiotic resistance and antiviral defense mechanisms, as well as genes involved in central carbon metabolism. These systems show promise for genetic engineering due to their programmability, PAM flexibility, and ability to insert directly into the host genome without double strand breaks requiring activation of host repair mechanisms. They also lack Cas1 and Cas2 proteins and so rely on other more complete CRISPR systems for spacer acquisition in trans. | 1 | Biochemistry |
The first known IPN was a combination of phenol-formaldehyde resin with vulcanized natural rubber made by Jonas Aylsworth in 1914. However, this was before Staudinger's hypothesis on macromolecules and thus the terms "polymer" or "IPN" were not yet used. The first usage of the term "interpenetrating polymer networks" was first introduced by J.R. Millar in 1960 while discussing networks of sulfonated and unsulfonated styrene–divinylbenzene copolymers. | 7 | Physical Chemistry |
Systems that admit a treatment with the system size expansion may be described by a probability distribution , giving the probability of observing the system in state at time . may be, for example, a vector with elements corresponding to the number of molecules of different chemical species in a system. In a system of size (intuitively interpreted as the volume), we will adopt the following nomenclature: is a vector of macroscopic copy numbers, is a vector of concentrations, and is a vector of deterministic concentrations, as they would appear according to the rate equation in an infinite system. and are thus quantities subject to stochastic effects.
A master equation describes the time evolution of this probability. Henceforth, a system of chemical reactions will be discussed to provide a concrete example, although the nomenclature of "species" and "reactions" is generalisable. A system involving species and reactions can be described with the master equation:
Here, is the system size, is an operator which will be addressed later, is the stoichiometric matrix for the system (in which element gives the stoichiometric coefficient for species in reaction ), and is the rate of reaction given a state and system size .
is a step operator, removing from the th element of its argument. For example, . This formalism will be useful later.
The above equation can be interpreted as follows. The initial sum on the RHS is over all reactions. For each reaction , the brackets immediately following the sum give two terms. The term with the simple coefficient −1 gives the probability flux away from a given state due to reaction changing the state. The term preceded by the product of step operators gives the probability flux due to reaction changing a different state into state . The product of step operators constructs this state . | 7 | Physical Chemistry |
Polyadenylation is the addition of a poly(A) tail to an RNA transcript, typically a messenger RNA (mRNA). The poly(A) tail consists of multiple adenosine monophosphates; in other words, it is a stretch of RNA that has only adenine bases. In eukaryotes, polyadenylation is part of the process that produces mature mRNA for translation. In many bacteria, the poly(A) tail promotes degradation of the mRNA. It, therefore, forms part of the larger process of gene expression.
The process of polyadenylation begins as the transcription of a gene terminates. The 3′-most segment of the newly made pre-mRNA is first cleaved off by a set of proteins; these proteins then synthesize the poly(A) tail at the RNA's 3′ end. In some genes these proteins add a poly(A) tail at one of several possible sites. Therefore, polyadenylation can produce more than one transcript from a single gene (alternative polyadenylation), similar to alternative splicing.
The poly(A) tail is important for the nuclear export, translation and stability of mRNA. The tail is shortened over time, and, when it is short enough, the mRNA is enzymatically degraded. However, in a few cell types, mRNAs with short poly(A) tails are stored for later activation by re-polyadenylation in the cytosol. In contrast, when polyadenylation occurs in bacteria, it promotes RNA degradation. This is also sometimes the case for eukaryotic non-coding RNAs.
mRNA molecules in both prokaryotes and eukaryotes have polyadenylated 3′-ends, with the prokaryotic poly(A) tails generally shorter and fewer mRNA molecules polyadenylated. | 1 | Biochemistry |
Nucleophilic epoxidation is the formation of epoxides from electron-deficient double bonds through the action of nucleophilic oxidants. Nucleophilic epoxidation methods represent a viable alternative to electrophilic methods, many of which do not epoxidize electron-poor double bonds efficiently.
Although the most commonly used asymmetric epoxidation methods (the Sharpless-Katsuki, and Jacobsen epoxidations) rely on the catalytic reactivity of electrophilic oxidants, nucleophilic oxygen sources substituted with a suitable leaving group can also act as epoxidation reagents. The classic example, the Weitz-Scheffer reaction employs hydrogen peroxide under basic conditions (Z = OH below). Other notable examples have employed hypochlorites (Z = Cl) and chiral peroxides (Z = OR*).
Asymmetric versions of the above reaction have taken advantage of a number of strategies for achieving asymmetric induction. The highest yielding and most enantioselective methods include:
* Use of stoichiometric chiral oxidant
* Use of stoichiometric metal peroxides substituted with chiral ligands
* Use of stoichiometric chiral base
* Use of polypeptides
Although the mechanisms of each of these reactions differ somewhat, in each case the chiral catalyst or reagent must be involved in the [https://en.wiktionary.org/wiki/enantio- enantio] determining conjugate addition step. Cis-epoxides are difficult to access using nucleophilic epoxidation methods. Nearly all nucleophilic epoxidations of cis olefins afford trans epoxides. | 0 | Organic Chemistry |
In some cases, the adsorbed molecule is chemically bonded to the surface/material, providing a strong adhesion and limiting desorption. If this is the case, desorption requires a chemical reaction which cleaves the chemical bonds. One way to accomplish this is to apply a voltage to the surface, resulting in either reduction or oxidation of the adsorbed molecule (depending on the bias and the adsorbed molecules).
In a typical example of reductive desorption, a self-assembled monolayers of alkyl thiols on a gold surface can be removed by applying a negative bias to the surface resulting in reduction of the sulfur head-group. The chemical reaction for this process would be:
where R is an alkyl chain (e.g. CH), S is the sulfur atom of the thiol group, Au is a gold surface atom and e is an electron supplied by an external voltage source.
Another application for reductive/oxidative desorption is to clean active carbon material through electrochemical regeneration. | 7 | Physical Chemistry |
Tetrafluoromethane is a potent greenhouse gas that contributes to the greenhouse effect. It is very stable, has an atmospheric lifetime of 50,000 years, and a high greenhouse warming potential 6,500 times that of CO.
Tetrafluoromethane is the most abundant perfluorocarbon in the atmosphere, where it is designated as PFC-14. Its atmospheric concentration is growing. As of 2019, the man-made gases CFC-11 and CFC-12 continue to contribute a stronger radiative forcing than PFC-14.
Although structurally similar to chlorofluorocarbons (CFCs), tetrafluoromethane does not deplete the ozone layer because the carbon–fluorine bond is much stronger than that between carbon and chlorine.
Main industrial emissions of tetrafluoromethane besides hexafluoroethane are produced during production of aluminium using Hall-Héroult process. CF also is produced as product of the breakdown of more complex compounds such as halocarbons. | 2 | Environmental Chemistry |
eIF2 activity is regulated by a mechanism involving both guanine nucleotide exchange and phosphorylation. Phosphorylation takes place at the α-subunit, which is a target for a number of serine kinases that phosphorylate serine 51. Those kinases act as a result of stress such as amino acid deprivation (GCN2), ER stress (PERK), the presence of dsRNA (PKR) heme deficiency (HRI), or interferon. Once phosphorylated, eIF2 shows increased affinity for eIF2B, its GEF. However, eIF2B is able to exchange GDP for GTP only if eIF2 is in its unphosphorylated state. Phosphorylated eIF2, however, due to its stronger binding, acts as an inhibitor of its own GEF (eIF2B). Since the cellular concentration of eIF2B is much lower than that of eIF2, even a small amount of phosphorylated eIF2 can completely abolish eIF2B activity by sequestration. Without the GEF, eIF2 can no longer be returned to its active (GTP-bound) state. As a consequence, translation comes to a halt since initiation is no longer possible without any available ternary complex. Furthermore, low concentration of ternary complex allows the expression of GCN4 (starved condition), which, in turn, results in increased activation of amino acid synthesis genes | 1 | Biochemistry |
In the estimation of human exposures to environmental chemicals, the following systemic errors have been known to occur:
* an ever increasing number of chemicals registered for use and difficulty of regulatory agencies to keep track. Many producers use the term confidential business information to withhold information, so exposure data are per se unavailable even though under TSCA, the US EPA may as of 2016, review and determine if a company´s claim is valid.
* assessments are difficult to be kept up-to-date;
* underestimates of exposure occur because of inadequate assumptions about human behaviors and co-exposures ;
* evolving or insufficient models of toxicokinetics | 2 | Environmental Chemistry |
This approach relies on observation and experimental data. It is specifically tailored to the geometrical shape of the vortex tube and the details of its flow and is designed to match the particular observables of the complex vortex tube flow, namely turbulence, acoustic phenomena, pressure fields, air velocities and many others. The earlier published models of the vortex tube are phenomenological. They are:
# Radial pressure difference: centrifugal compression and air expansion
# Radial transfer of angular momentum
# Radial acoustic streaming of energy
# Radial heat pumping
More on these models can be found in recent review articles on vortex tubes.
The phenomenological models were developed at an earlier time when the turbine equation of Euler was not thoroughly analyzed; in the engineering literature, this equation is studied mostly to show the work output of a turbine; while temperature analysis is not performed since turbine cooling has more limited application unlike power generation, which is the main application of turbines. Phenomenological studies of the vortex tube in the past have been useful in presenting empirical data. However, due to the complexity of the vortex flow this empirical approach was able to show only aspects of the effect but was unable to explain its operating principle. Dedicated to empirical details, for a long time the empirical studies made the vortex tube effect appear enigmatic and its explanation – a matter of debate. | 7 | Physical Chemistry |
The dbEST is a division of Genbank established in 1992. As for GenBank, data in dbEST is directly submitted by laboratories worldwide and is not curated. | 1 | Biochemistry |
Termination finishes of nickel, gold or palladium have been shown to eliminate whisker formation in controlled trials. | 8 | Metallurgy |
RAFT is one of the most versatile and convenient techniques in this context. The most common RAFT-processes are carried out in the presence of thiocarbonylthio compounds that act as radical buffers.
While in ATRP and NMP reversible deactivation of propagating radical-radical reactions takes place and the dormant structures are a halo-compound in ATRP and the alkoxyamine in NMP, both being a sink for radicals and source at the same time and described by the corresponding equilibria. RAFT on the contrary, is controlled by chain-transfer reactions that are in a deactivation-activation equilibrium. Since no radicals are generated or destroyed an external source of radicals is necessary for initiation and maintenance of the propagation reaction.
;Initiation step of a RAFT polymerization
;Reversible chain transfer
;Reinitiation step
;Chain equilibration step
;Termination step | 7 | Physical Chemistry |
* Davis, Frederick Rowe. "Pesticides and the perils of synecdoche in the history of science and environmental history." History of Science 57.4 (2019): 469–492.
* Davis, Frederick Rowe. Banned: a history of pesticides and the science of toxicology (Yale UP, 2014).
* Matthews, Graham A. A history of pesticides (CABI, 2018). | 2 | Environmental Chemistry |
The setup for projection topography (also called "traverse" topography") is essentially identical to section topography, the difference being that both sample and film are now scanned laterally (synchronously) with respect to the narrow incident beam. A projection topograph therefore corresponds to the superposition of many adjacent section topographs, able to investigate not just a restricted portion, but the entire volume of a crystal.
The technique is rather simple and has been in routine use at "Lang cameras" in many research laboratories. | 3 | Analytical Chemistry |
Okano’s group expanded on their success by using different modifiers to enhance hydrophobicity through the attachment of butyl methacrylate (BMA), a hydrophobic comonomer. For simplification the resultant polymer has been labeled as IBc (isopropylacrylamide butyl methacrylate copolymer). The polymers were synthesized using radical telomerization with varying BMA content. Where pure PNIPAAm was unable to resolve hydrophobic steroids at any temperature, IBc-grafted silica stationary phases were able to resolve steroid peaks with increasingly retarded retention times in correlation to both increased BMA content and increased temperature. They went on to develop a method to separate phenylthiohydantoin(PTH)-amino acids using their IBc stationary phase with a stronger emphasis of implementing environmentally friendly conditions using a purely aqueous phase in HPLC. Another group separated catechins using PNIPAAm. | 3 | Analytical Chemistry |
In analytical chemistry, quantitative analysis is the determination of the absolute or relative abundance (often expressed as a concentration) of one, several or all particular substance(s) present in a sample. | 3 | Analytical Chemistry |
Photoluminescence (abbreviated as PL) is light emission from any form of matter after the absorption of photons (electromagnetic radiation). It is one of many forms of luminescence (light emission) and is initiated by photoexcitation (i.e. photons that excite electrons to a higher energy level in an atom), hence the prefix photo-. Following excitation, various relaxation processes typically occur in which other photons are re-radiated. Time periods between absorption and emission may vary: ranging from short femtosecond-regime for emission involving free-carrier plasma in inorganic semiconductors up to milliseconds for phosphoresence processes in molecular systems; and under special circumstances delay of emission may even span to minutes or hours.
Observation of photoluminescence at a certain energy can be viewed as an indication that an electron populated an excited state associated with this transition energy.
While this is generally true in atoms and similar systems, correlations and other more complex phenomena also act as sources for photoluminescence in many-body systems such as semiconductors. A theoretical approach to handle this is given by the semiconductor luminescence equations. | 7 | Physical Chemistry |
When anaerobic pathways are turned on, glycogen stores are depleted and accumulation of acidic waste products occurs. This is known as a Pasteur effect. A challenge hypoxia-tolerant fish face is how to produce ATP anaerobically without creating a significant Pasteur effect. Along with a reduction in metabolism, some fish have adapted traits to avoid accumulation of lactate. For example, the crucian carp, a highly hypoxia-tolerant fish, has evolved to survive months of anoxic waters. A key adaptation is the ability to convert lactate to ethanol in the muscle and excrete it out of their gills. Although this process is energetically costly is it crucial to their survival in hypoxic waters. | 9 | Geochemistry |
The locally remove strategy begins with covering the entire surface with a SAM. Then individual SAM molecules are removed from locations where the deposition of nanostructures is not desired. The result is the same as in the locally attract strategy, the difference being in the way this is achieved. The major techniques that use this strategy are:
* Scanning tunneling microscope
:The scanning tunneling microscope can remove SAM molecules in many different ways. The first is to remove them mechanically by dragging the tip across the substrate surface. This is not the most desired technique as these tips are expensive and dragging them causes a lot of wear and reduction of the tip quality. The second way is to degrade or desorb the SAM molecules by shooting them with an electron beam. The scanning tunneling microscope can also remove SAMs by field desorption and field enhanced surface diffusion.
* Atomic force microscope
:The most common use of this technique is to remove the SAM molecules in a process called shaving, where the atomic force microscope tip is dragged along the surface mechanically removing the molecules. An atomic force microscope can also remove SAM molecules by local oxidation nanolithography.
* Ultraviolet irradiation
:In this process, UV light is projected onto the surface with a SAM through a pattern of apertures in a chromium film. This leads to photo oxidation of the SAM molecules. These can then be washed away in a polar solvent. This process has 100 nm resolutions and requires exposure time of 15–20 minutes. | 6 | Supramolecular Chemistry |
Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp hybridized carbon atom. Although this sp center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds are still observed for such compounds. This formal discontinuity is apparently bridged by p-orbital overlap, maintaining a contiguous cycle of π electrons that is responsible for this preserved chemical stability.
The concept of homoaromaticity was pioneered by Saul Winstein in 1959, prompted by his studies of the “tris-homocyclopropenyl” cation. Since the publication of Winsteins paper, much research has been devoted to understanding and classifying these molecules, which represent an additional class of aromatic molecules included under the continuously broadening definition of aromaticity. To date, homoaromatic compounds are known to exist as cationic and anionic species, and some studies support the existence of neutral homoaromatic molecules, though these are less common. The homotropylium' cation (CH) is perhaps the best studied example of a homoaromatic compound. | 7 | Physical Chemistry |
The defining property of a crystal is its inherent symmetry. Performing certain symmetry operations on the crystal lattice leaves it unchanged. All crystals have translational symmetry in three directions, but some have other symmetry elements as well. For example, rotating the crystal 180° about a certain axis may result in an atomic configuration that is identical to the original configuration; the crystal has twofold rotational symmetry about this axis. In addition to rotational symmetry, a crystal may have symmetry in the form of mirror planes, and also the so-called compound symmetries, which are a combination of translation and rotation or mirror symmetries. A full classification of a crystal is achieved when all inherent symmetries of the crystal are identified. | 3 | Analytical Chemistry |
Advances in understanding genes and inheritance continued throughout the 20th century. Deoxyribonucleic acid (DNA) was shown to be the molecular repository of genetic information by experiments in the 1940s to 1950s. The structure of DNA was studied by Rosalind Franklin and Maurice Wilkins using X-ray crystallography, which led James D. Watson and Francis Crick to publish a model of the double-stranded DNA molecule whose paired nucleotide bases indicated a compelling hypothesis for the mechanism of genetic replication.
In the early 1950s the prevailing view was that the genes in a chromosome acted like discrete entities arranged like beads on a string. The experiments of Benzer using mutants defective in the rII region of bacteriophage T4 (1955–1959) showed that individual genes have a simple linear structure and are likely to be equivalent to a linear section of DNA.
Collectively, this body of research established the central dogma of molecular biology, which states that proteins are translated from RNA, which is transcribed from DNA. This dogma has since been shown to have exceptions, such as reverse transcription in retroviruses. The modern study of genetics at the level of DNA is known as molecular genetics.
In 1972, Walter Fiers and his team were the first to determine the sequence of a gene: that of Bacteriophage MS2 coat protein. The subsequent development of chain-termination DNA sequencing in 1977 by Frederick Sanger improved the efficiency of sequencing and turned it into a routine laboratory tool. An automated version of the Sanger method was used in early phases of the Human Genome Project. | 1 | Biochemistry |
Carbon compounds can be distinguished as either organic or inorganic, and dissolved or particulate, depending on their composition. Organic carbon forms the backbone of key component of organic compounds such as – proteins, lipids, carbohydrates, and nucleic acids. Inorganic carbon is found primarily in simple compounds such as carbon dioxide, carbonic acid, bicarbonate, and carbonate (CO, HCO, HCO, CO respectively).
Marine carbon is further separated into particulate and dissolved phases. These pools are operationally defined by physical separation – dissolved carbon passes through a 0.2 μm filter, and particulate carbon does not. | 9 | Geochemistry |
Two families of naturally occurring products feature the diazo group: kinamycin and lomaiviticin. These molecules are DNA-intercalators, with diazo functionality as their "warheads". Loss of N, induced reductively, generates a DNA-cleaving fluorenyl radical. | 0 | Organic Chemistry |
The cyano group usually cannot be introduced by nucleophilic substitution of haloarenes, but such compounds can be easily prepared from diazonium salts. Illustrative is the preparation of benzonitrile using the reagent cuprous cyanide:
This reaction is a special type of Sandmeyer reaction. | 0 | Organic Chemistry |
Apoptosis, the process of programmed cell death, involves complex signaling pathways and cascades of molecular events. This process is needed for proper development during embryonic and fetal growth where there is destruction and reconstruction of cellular structures. In adult organisms, apoptosis is needed to maintain differentiated tissue by striking the balance between proliferation and cell death. It is known that intracellular proteases called caspases degrade the cellular contents of the cell by proteolysis upon activation of the death pathway.
Mammalian cells have two main pathways that lead to apoptosis.
1. Extrinsic pathway: Initiated by extrinsic ligands binding to death receptors on the surface of the cell. An example of this is the binding of tumour necrosis factor-alpha (TNF-alpha) to TNF-alpha receptor. An example of a TNF receptor is Fas (CD95), which recruits activator caspases like caspase-8 upon binding TNF at the cell surface. The activation of the initiator caspases then initiates a downstream cascade of events that results in the induction of effector caspases that function in apoptosis.
2. Intrinsic pathway: This pathway is initiated by intracellular or environmental stimuli. It is focused on detecting the improper functioning of the mitochondria in the cell and, as a result, activates signaling pathways to commit suicide. The membrane permeability of the mitochondria increases and particular proteins are released into the cytoplasm that facilitates the activation of initiator caspases. The particular protein released from the mitochondria is cytochrome c. Cytochrome c then binds to Apaf-1 in the cytosol and results in the activation of initiator caspase-9. The activation of the initiator caspases then initiates a downstream cascade of events that results in the induction of effector caspases that function in apoptosis.
One family of proteins called IAPs plays a role in regulating cell death by inhibiting the process. IAPs like survivin, inhibit apoptosis by physically binding to and inhibiting proper caspase function. The function of IAPs is evolutionarily conserved as Drosophila homologues of IAPs have been shown to be essential for cell survival.
IAPs have been implicated in studies to have a regulatory effect on cell division. Yeast cells with knock-outs of certain IAP genes did not show problems associated with cell death, but showed defects in mitosis characterized by improper chromosome segregation or failed cytokinesis.
Deletion of particular IAPs does not seem to have a profound effect on the cell-death pathway as there is a redundancy of function by the many IAPs that exist in a cell. They have been implicated, however, to play a role in maintaining an anti-apoptotic environment intracellularly. Changing the expression of particular IAPs has shown an increase in spontaneous cell death induction or increased sensitivity to death stimuli. | 1 | Biochemistry |
Galvanism influenced metaphysical thought in the domain of abiogenesis, the underlying process of the generation of living forms. In 1836, Andrew Crosse recorded what he referred to as "the perfect insect, standing erect on a few bristles which formed its tail," as having appeared during an experiment wherein he used electricity to produce mineral crystals. While Crosse himself never claimed to have generated the insects, even in private, the scientific world at the time viewed the connection between life and electricity to be sufficiently clear that he received threats against his life for this "blasphemy." | 7 | Physical Chemistry |
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecules characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecules composition. This enables systematic prediction of chemical reactions and behavior of chemical compounds and the design of chemical synthesis. The reactivity of a functional group can be modified by other functional groups nearby. Functional group interconversion can be used in retrosynthetic analysis to plan organic synthesis.
A functional group is a group of atoms in a molecule with distinctive chemical properties, regardless of the other atoms in the molecule. The atoms in a functional group are linked to each other and to the rest of the molecule by covalent bonds. For repeating units of polymers, functional groups attach to their nonpolar core of carbon atoms and thus add chemical character to carbon chains. Functional groups can also be charged, e.g. in carboxylate salts (), which turns the molecule into a polyatomic ion or a complex ion. Functional groups binding to a central atom in a coordination complex are called ligands. Complexation and solvation are also caused by specific interactions of functional groups. In the common rule of thumb "like dissolves like", it is the shared or mutually well-interacting functional groups which give rise to solubility. For example, sugar dissolves in water because both share the hydroxyl functional group () and hydroxyls interact strongly with each other. Plus, when functional groups are more electronegative than atoms they attach to, the functional groups will become polar, and the otherwise nonpolar molecules containing these functional groups become polar and so become soluble in some aqueous environment.
Combining the names of functional groups with the names of the parent alkanes generates what is termed a systematic nomenclature for naming organic compounds. In traditional nomenclature, the first carbon atom after the carbon that attaches to the functional group is called the alpha carbon; the second, beta carbon, the third, gamma carbon, etc. If there is another functional group at a carbon, it may be named with the Greek letter, e.g., the gamma-amine in gamma-aminobutyric acid is on the third carbon of the carbon chain attached to the carboxylic acid group. IUPAC conventions call for numeric labeling of the position, e.g. 4-aminobutanoic acid. In traditional names various qualifiers are used to label isomers, for example, isopropanol (IUPAC name: propan-2-ol) is an isomer of n-propanol (propan-1-ol). The term moiety has some overlap with the term "functional group". However, a moiety is an entire "half" of a molecule, which can be not only a single functional group, but also a larger unit consisting of multiple functional groups. For example, an "aryl moiety" may be any group containing an aromatic ring, regardless of how many functional groups the said aryl has. | 0 | Organic Chemistry |
Since there is no single experimental feature which identifies a material as a spin liquid, several experiments have to be conducted to gain information on different properties which characterize a spin liquid. | 7 | Physical Chemistry |
An especially notable irregular maximum density is that of water, which reaches a density peak at . This has important ramifications in Earth's ecosystem. | 7 | Physical Chemistry |
The pharmaceuticals pass sewage treatment plants. They like estrogen conjugates may cause problems. Drugs of the research were common, present in the aquatic environment and inability to be adequately removed by sewage treatment plants. There were seven different drugs in the research. Dibutyl sebacate and oleic acid formed liquid cores in capsules because they do not diffuse away from capsules and have affinity for drugs. Capsule external diameters were 740 µm and 680 µm and internal diameters were 570 µm and 500 µm. Agitation was 300 rpm. Equilibrium times were 30, 50 and 90 minutes.
Since dibutyl sebacate and oleic acid were different affinity for drugs, they were used concurrently. Four drugs were extracted effectively for 40–50 minutes (at least 50% removed). Extraction rates did not change significantly above 150 rpm. Membrane thickness did not affect the result significantly. On the contrary the capsule size was remarkable for mass transfer. | 3 | Analytical Chemistry |
Larive received her Bachelor of Science from South Dakota State University in 1980, and her Master of Science degree from Purdue University in 1982. In 1992, she was awarded a Ph.D. in chemistry from the University of California, Riverside after working under the direction of Dallas L. Rabenstein. | 3 | Analytical Chemistry |
Following sonoporation-mediated membrane permeabilization, cells can automatically repair the membrane openings through a phenomenon called "reparable sonoporation." The membrane resealing process has been shown to be calcium-dependent. This property may suggest that the membrane repair process involves a cell's active repair mechanism in response to the cellular influx of calcium. | 1 | Biochemistry |
A method commonly used to protect a structural metal is to attach a metal which is more anodic than the metal to be protected. This forces the structural metal to be cathodic, thus spared corrosion. It is called "sacrificial" because the anode dissolves and has to be replaced periodically.
Zinc bars are attached to various locations on steel ship hulls to render the ship hull cathodic. The zinc bars are replaced periodically. Other metals, such as magnesium, would work very well but zinc is the least expensive useful metal.
To protect pipelines, an ingot of buried or exposed magnesium (or zinc) is buried beside the pipeline and is connected electrically to the pipe above ground. The pipeline is forced to be a cathode and is protected from being oxidized and rusting. The magnesium anode is sacrificed. At intervals new ingots are buried to replace those dissolved. | 7 | Physical Chemistry |
The degree distribution describes the number of proteins that have a certain number of connections. Most protein interaction networks show a scale-free (power law) degree distribution where the connectivity distribution P(k) ~ k with k being the degree. This relationship can also be seen as a straight line on a log-log plot since, the above equation is equal to log(P(k)) ~ —y•log(k). One characteristic of such distributions is that there are many proteins with few interactions and few proteins that have many interactions, the latter being called "hubs". | 1 | Biochemistry |
Galvanic corrosion (also called bimetallic corrosion) is an electrochemical process in which one metal (more active one) corrodes preferentially when it is in electrical contact with another dissimilar metal, in the presence of an electrolyte. A similar galvanic reaction is exploited in primary cells to generate a useful electrical voltage to power portable devices – a classic example being a cell with zinc and copper electrodes. Galvanic corrosion is also exploited when a sacrificial metal is used in cathodic protection. Galvanic corrosion happens when there are an active metal and a more noble metal in contact in the presence of electrolyte. | 8 | Metallurgy |
This approach uses protein sequence data and the chemical and physical interactions of the encoded amino acids to predict the 3-D structures of proteins with no homology to solved protein structures. One highly successful method for ab initio modeling is the Rosetta program, which divides the protein into short segments and arranges short polypeptide chain into a low-energy local conformation. Rosetta is available for commercial use and for non-commercial use through its public program, Robetta. | 1 | Biochemistry |
Eutectoid steel can in principle be transformed completely into pearlite; hypoeutectoid steels can also be completely pearlitic if transformed at a temperature below the normal eutectoid. Pearlite can be hard and strong but is not particularly tough. It can be wear-resistant because of a strong lamellar network of ferrite and cementite. Examples of applications include cutting tools, high strength wires, knives, chisels, and nails. | 8 | Metallurgy |
In 1896 Zeeman learned that his laboratory had one of Henry Augustus Rowlands highest resolving Rowland grating, an imaging spectrographic mirror. Zeeman had read James Clerk Maxwells article in Encyclopædia Britannica describing Michael Faraday's failed attempts to influence light with magnetism. Zeeman wondered if the new spectrographic techniques could succeed where early efforts had not.
When illuminated by a slit shaped source, the grating produces a long array of slit images corresponding to different wavelengths. Zeeman placed a piece of asbestos soaked in salt water into a Bunsen burner flame at the source of the grating: he could easily see two lines for sodium light emission. Energizing a 10 kilogauss magnet around the flame he observed a slight broadening of the sodium images.
When Zeeman switched to cadmium at the source he observed the images split when the magnet was energized. These splitting could be analyzed with Hendrik Lorentz's then new electron theory. In retrospect we now know that the magnetic effects on sodium require quantum mechanical treatment. Zeeman and Lorentz were awarded the 1902 Nobel prize; in his acceptance speech Zeeman explained his apparatus and showed slides of the spectrographic images. | 7 | Physical Chemistry |
The types of spectroscopy are distinguished by the type of radiative energy involved in the interaction. In many applications, the spectrum is determined by measuring changes in the intensity or frequency of this energy. The types of radiative energy studied include:
* Electromagnetic radiation was the first source of energy used for spectroscopic studies. Techniques that employ electromagnetic radiation are typically classified by the wavelength region of the spectrum and include microwave, terahertz, infrared, near-infrared, ultraviolet-visible, x-ray, and gamma spectroscopy.
* Particles, because of their de Broglie waves, can also be a source of radiative energy. Both electron and neutron spectroscopy are commonly used. For a particle, its kinetic energy determines its wavelength.
* Acoustic spectroscopy involves radiated pressure waves.
* Dynamic mechanical analysis can be employed to impart radiating energy, similar to acoustic waves, to solid materials. | 7 | Physical Chemistry |
A DNA-binding dye binds to all double-stranded (ds) DNA in PCR, increasing the fluorescence quantum yield of the dye. An increase in DNA product during PCR therefore leads to an increase in fluorescence intensity measured at each cycle. However, dsDNA dyes such as SYBR Green will bind to all dsDNA PCR products, including nonspecific PCR products (such as primer dimer). This can potentially interfere with, or prevent, accurate monitoring of the intended target sequence.
In real-time PCR with dsDNA dyes the reaction is prepared as usual, with the addition of fluorescent dsDNA dye. Then the reaction is run in a real-time PCR instrument, and after each cycle, the intensity of fluorescence is measured with a detector; the dye only fluoresces when bound to the dsDNA (i.e., the PCR product).
This method has the advantage of only needing a pair of primers to carry out the amplification, which keeps costs down; multiple target sequences can be monitored in a tube by using different types of dyes. | 1 | Biochemistry |
The swelling and bioadhesion of hydrogels can be controlled based on the fluid environment they are introduced to in the body. These properties make them excellent for use as controlled drug delivery devices. Where the hydrogel adheres in the body will be determined by its chemistry and reactions with the surrounding tissues. If introduced by mouth, the hydrogel could adhere to anywhere in the gastrointestinal tract including the mouth, the stomach, the small intestine, or the colon. Adhesion in a specifically targeted region will cause for a localized drug delivery and an increased concentration of the drug taken up by the tissues. | 7 | Physical Chemistry |
Sedoheptulose-bisphosphatase (also sedoheptulose-1,7-bisphosphatase or SBPase, EC number 3.1.3.37; systematic name sedoheptulose-1,7-bisphosphate 1-phosphohydrolase) is an enzyme that catalyzes the removal of a phosphate group from sedoheptulose 1,7-bisphosphate to produce sedoheptulose 7-phosphate. SBPase is an example of a phosphatase, or, more generally, a hydrolase. This enzyme participates in the Calvin cycle. | 5 | Photochemistry |
Removal of the hydrogen atoms as protons turns a phosphoric acid into a phosphate anion. Partial removal yields various hydrogen phosphate anions. | 0 | Organic Chemistry |
Oxygen is one of the reagents consumed during cyanidation, accepting the electrons from the gold, and a deficiency in dissolved oxygen slows leaching rate. Air or pure oxygen gas can be purged through the pulp to maximize the dissolved oxygen concentration. Intimate oxygen-pulp contactors are used to increase the partial pressure of the oxygen in contact with the solution, thus raising the dissolved oxygen concentration much higher than the saturation level at atmospheric pressure. Oxygen can also be added by dosing the pulp with hydrogen peroxide solution. | 8 | Metallurgy |
A common simplification to (14) is the harmonic approximation, in which the probability density function is modeled as a Gaussian. Under this approximation, static displacive disorder is ignored and it is assumed that atomic displacements are determined entirely by motion (alternative models in which the Gaussian approximation is invalid have been considered elsewhere).
From equations (7) and (14), the Debye–Waller factor contributes to the observed intensity of a diffraction experiment. And based on (16), we see that our anisotropic displacement factor is responsible for determining . Additionally, (15) shows that may be directly related to the probability density function for a nuclear displacement from the mean position. As a result, its possible to conduct a scattering experiment on a crystal, fit the resulting spectrum for the various atomic values, and derive each atoms tendency for nuclear displacement from . | 7 | Physical Chemistry |
Single-molecule analysis<br />
Since minimal DNA sample required, time-consuming and costly amplification step is avoided to streamline sample preparation process.
Large DNA molecule templates (~500 kb) vs. Short DNA molecule templates (< 1kb)
While most next generation sequencing technologies aim of massive amounts of smalls sequence reads, these small sequence reads make de novo sequencing efforts and genome repeat regions difficult to comprehend. Optical sequencing uses large DNA molecule templates (~500 kb) for sequencing and these offer several advantages over small templates:
#These large DNA templates can be "DNA barcoded" to determine their genomic localization with confidence. Therefore, any sequence reads that are taken from the large template can be mapped onto the genome with a high degree of confidence. More importantly, sequence reads from high repeat regions can placed with a greater degree of confidence whereas the short reads suffer from mapping uncertainty in high repeat regions. Special algorithms and software such as optical mapping and nanocoding have been developed to align single-molecule barcodes with a reference genome.
#Multiple sequence reads from the same large template molecule. These multiple sequence reads reduce the complexity of de novo assembly, disambiguate genomic rearrangement regions, and "intrinsically free from any assembly errors."
#Molecular barcoding of large DNA molecular templates with sequence acquisition provides broad and specific genomic analyses | 1 | Biochemistry |
Stainless steel forms a passivation layer of chromium(III) oxide. Similar passivation behavior occurs with magnesium, titanium, zinc, zinc oxides, aluminium, polyaniline, and other electroactive conductive polymers.
Special "weathering steel" alloys such as Cor-Ten rust at a much slower rate than normal, because the rust adheres to the surface of the metal in a protective layer. Designs using this material must include measures that avoid worst-case exposures since the material still continues to rust slowly even under near-ideal conditions. | 8 | Metallurgy |
The leukotriene (LT) receptors are G protein-coupled receptors that bind and are activated by the leukotrienes. They include the following proteins:
* Leukotriene B4 receptors (BLTRs) – bind to and are activated by LTB4:
** BLT (Leukotriene B receptor 1) –
** BLT (Leukotriene B receptor 2) –
* Cysteinyl leukotriene receptors (CysLTRs) – bind to and are activated by LTC4, LTD4, and LTE4:
** CysLT (Cysteinyl leukotriene receptor 1) –
** CysLT (Cysteinyl leukotriene receptor 2) –
The recently elucidated CysLT, represented by GPR99/OXGR1, may constitute a third CysLTR. | 1 | Biochemistry |
Anodizing can be carried out in phosphoric acid, usually as a surface preparation for adhesives. This is described in standard ASTM D3933. | 8 | Metallurgy |
Spectrum analyzers are widely used to measure the frequency response, noise and distortion characteristics of all kinds of radio-frequency (RF) circuitry, by comparing the input and output spectra. For example, in RF mixers, spectrum analyzer is used to find the levels of third order inter-modulation products and conversion loss. In RF oscillators, spectrum analyzer is used to find the levels of different harmonics.
In telecommunications, spectrum analyzers are used to determine occupied bandwidth and track interference sources. For example, cell planners use this equipment to determine interference sources in the GSM frequency bands and UMTS frequency bands.
In EMC testing, a spectrum analyzer is used for basic precompliance testing; however, it can not be used for full testing and certification. Instead, an EMI receiver is used.
A spectrum analyzer is used to determine whether a wireless transmitter is working according to defined standards for purity of emissions. Output signals at frequencies other than the intended communications frequency appear as vertical lines (pips) on the display. A spectrum analyzer is also used to determine, by direct observation, the bandwidth of a digital or analog signal.
A spectrum analyzer interface is a device that connects to a wireless receiver or a personal computer to allow visual detection and analysis of electromagnetic signals over a defined band of frequencies. This is called panoramic reception and it is used to determine the frequencies of sources of interference to wireless networking equipment, such as Wi-Fi and wireless routers.
Spectrum analyzers can also be used to assess RF shielding. RF shielding is of particular importance for the siting of a magnetic resonance imaging machine since stray RF fields would result in artifacts in an MR image. | 7 | Physical Chemistry |
Definitive mechanistic studies of rhodium-catalyzed cyclopropanation are lacking. However, the mechanism has been rationalized based on product distribution and stereoselectivity. Attack of the diazo compound on the metal center generates a zwitterionic metal alkyl complex, which expels nitrogen gas to afford a metal carbene intermediate. Concerted addition of the metal carbene to the olefin (without direct coordination of the olefin to the metal) generates the observed cyclopropane product. The configuration of the olefin is retained throughout the process; however, metal carbenes with heterotopic faces may generate a mixture of diastereomers, as shown at the right of Eq. (2).
The configuration of the product is determined by the trajectory of approach of the olefin to the metal carbene. In reactions of monosubstituted metal carbenes with terminal olefins, the olefin likely approaches "end-on" (with the carbon-carbon double bond of the olefin nearly parallel to the metal-carbon double bond of the carbene) with the olefin R group pointed away from the substituent of the carbene. A second transition state model has been proposed for reactions of vinyl-substituted carbenes. In this model, the olefin approaches "side-on" (with the carbon-carbon double bond of the olefin perpendicular to the metal-carbon double bond of the carbene) with the olefin R group far from the vinyl group. | 0 | Organic Chemistry |
In the sintering of ceramic materials, abnormal grain growth is often viewed as an undesirable phenomenon because rapidly growing grains may lower the hardness of the bulk material through Hall-Petch-type effects. However, the controlled introduction of dopants to bring about controlled AGG may be used to impart fibre-toughening in ceramic materials. Additionally, AGG is undesirable in piezoelectric ceramics, as it may degrade the piezoelectric effect. | 3 | Analytical Chemistry |
The seipin gene BSCL2 was originally identified in mammals and the fruit fly, and later extended to fungi and plants. The human seipin gene is located on chromosome 11q13, with protein coding on the Crick strand.
There are three validated coding transcripts in GenBank. The primary transcript originally described, contained 11 exons with protein coding beginning on exon 2 and ending in exon 11 (transcript variant 2), resulting in a 398 amino acid protein with two strongly predicted transmembrane domains (TMDs), coded in exons 2 and 7 (isoform 2).
However, a longer transcript (variant 1) is generated with an alternative first exon containing a translational start site that results in an additional 64 amino acids at the N-terminal extension, 462 amino acids in total (isoform 1).
A third coding transcript (variant 3) splices out exon 7 and produces a shortened and altered carboxy terminus in exon 10, generating a protein of 287 amino acids (isoform 3). Celias encephalopathy is associated with a mutation in BSCL2' that leads to increased alternative splicing of the pre-mRNA to an mRNA that lacks the seventh exon, corresponding to the second transmembrane domain of the protein product. | 1 | Biochemistry |
The Casein kinase 1 family () of protein kinases are serine/threonine-selective enzymes that function as regulators of signal transduction pathways in most eukaryotic cell types. CK1 isoforms are involved in Wnt signaling, circadian rhythms, nucleo-cytoplasmic shuttling of transcription factors, DNA repair, and DNA transcription. | 1 | Biochemistry |
Environmental Toxicology and Chemistry is a monthly peer-reviewed scientific journal covering environmental toxicology and environmental chemistry. It was established in 1982 and is published by Wiley-Blackwell in conjunction with the Society of Environmental Toxicology and Chemistry. The founding editor-in-chief was C.H. Ward (Rice University), and the current one is G.A. Burton, Jr. (University of Michigan). According to the Journal Citation Reports, the journal has a 2021 impact factor of 4.218, ranking it 117th out of 279 journals in the category Environmental sciences and 29th out of 94 in the category Toxicology. | 2 | Environmental Chemistry |
As they require the conjunction of specific environmental conditions to form, particular mineral deposit types tend to occupy specific geodynamic niches, therefore, this page has been organised by metal commodity. It is also possible to organise theories the other way, namely according to geological criteria of formation. Often ores of the same metal can be formed by multiple processes, and this is described here under each metal or metal complex. | 9 | Geochemistry |
Time-translation symmetry or temporal translation symmetry (TTS) is a mathematical transformation in physics that moves the times of events through a common interval. Time-translation symmetry is the law that the laws of physics are unchanged (i.e. invariant) under such a transformation. Time-translation symmetry is a rigorous way to formulate the idea that the laws of physics are the same throughout history. Time-translation symmetry is closely connected, via Noether's theorem, to conservation of energy. In mathematics, the set of all time translations on a given system form a Lie group.
There are many symmetries in nature besides time translation, such as spatial translation or rotational symmetries. These symmetries can be broken and explain diverse phenomena such as crystals, superconductivity, and the Higgs mechanism. However, it was thought until very recently that time-translation symmetry could not be broken. Time crystals, a state of matter first observed in 2017, break time-translation symmetry. | 7 | Physical Chemistry |
Molybdenum is an essential trace dietary element. Four mammalian Mo-dependent enzymes are known, all of them harboring a pterin-based molybdenum cofactor (Moco) in their active site: sulfite oxidase, xanthine oxidoreductase, aldehyde oxidase, and mitochondrial mitochondrial amidoxime reductase. People severely deficient in molybdenum have poorly functioning sulfite oxidase and are prone to toxic reactions to sulfites in foods. The human body contains about 0.07 mg of molybdenum per kilogram of body weight, with higher concentrations in the liver and kidneys and lower in the vertebrae. Molybdenum is also present within human tooth enamel and may help prevent its decay.
Acute toxicity has not been seen in humans, and the toxicity depends strongly on the chemical state. Studies on rats show a median lethal dose (LD) as low as 180 mg/kg for some Mo compounds. Although human toxicity data is unavailable, animal studies have shown that chronic ingestion of more than 10 mg/day of molybdenum can cause diarrhea, growth retardation, infertility, low birth weight, and gout; it can also affect the lungs, kidneys, and liver. Sodium tungstate is a competitive inhibitor of molybdenum. Dietary tungsten reduces the concentration of molybdenum in tissues.
Low soil concentration of molybdenum in a geographical band from northern China to Iran results in a general dietary molybdenum deficiency, and is associated with increased rates of esophageal cancer. Compared to the United States, which has a greater supply of molybdenum in the soil, people living in those areas have about 16 times greater risk for esophageal squamous cell carcinoma.
Molybdenum deficiency has also been reported as a consequence of non-molybdenum supplemented total parenteral nutrition (complete intravenous feeding) for long periods of time. It results in high blood levels of sulfite and urate, in much the same way as molybdenum cofactor deficiency. Since pure molybdenum deficiency from this cause occurs primarily in adults, the neurological consequences are not as marked as in cases of congenital cofactor deficiency.
A congenital molybdenum cofactor deficiency disease, seen in infants, is an inability to synthesize molybdenum cofactor, the heterocyclic molecule discussed above that binds molybdenum at the active site in all known human enzymes that use molybdenum. The resulting deficiency results in high levels of sulfite and urate, and neurological damage. | 1 | Biochemistry |
* 1.B.1 General bacterial porin family
* 1.B.2 Chlamydial porin (CP) family
* 1.B.3 Sugar porin (SP) family
* 1.B.4 Brucella-Rhizobium porin (BRP) family
* 1.B.5 Pseudomonas OprP porin (POP) family
* 1.B.6 OmpA-OmpF porin (OOP) family
* 1.B.7 Rhodobacter PorCa porin (RPP) family
* 1.B.8 Mitochondrial and plastid porin (MPP) family
* 1.B.9 FadL outer membrane protein (FadL) family
* 1.B.10 Nucleoside-specific channel-forming outer membrane porin (Tsx) family
* 1.B.11 Outer membrane fimbrial usher porin (FUP) family
* 1.B.12 Autotransporter-1 (AT-1) family
* 1.B.13 Alginate export porin (AEP) family
* 1.B.14 Outer membrane receptor (OMR) family
* 1.B.15 Raffinose porin (RafY) family
* 1.B.16 Short chain amide and urea porin (SAP) family
* 1.B.17 Outer membrane factor (OMF) family
* 1.B.18 Outer membrane auxiliary (OMA) protein family
* 1.B.19 Glucose-selective OprB porin (OprB) family
* 1.B.20 Two-partner secretion (TPS) family
* 1.B.21 OmpG porin (OmpG) family
* 1.B.22 Outer bacterial membrane secretin (secretin) family
* 1.B.23 Cyanobacterial porin (CBP) family
* 1.B.24 Mycobacterial porin
* 1.B.25 Outer membrane porin (Opr) family
* 1.B.26 Cyclodextrin porin (CDP) family
* 1.B.31 Campylobacter jejuni major outer membrane porin (MomP) family
* 1.B.32 Fusobacterial outer membrane porin (FomP) family
* 1.B.33 Outer membrane protein insertion porin (Bam complex) (OmpIP) family
* 1.B.34 Corynebacterial porins
* 1.B.35 Oligogalacturonate-specific porin (KdgM) family
* 1.B.39 Bacterial porin, OmpW (OmpW) family
* 1.B.42 Outer membrane lipopolysaccharide export porin (LPS-EP) family
* 1.B.43 Coxiella porin P1 (CPP1) family
* 1.B.44 Probable protein translocating porphyromonas gingivalis porin (PorT) family
* 1.B.49 Anaplasma P44 (A-P44) porin family
* 1.B.48 Curli-like transporters
* 1.B.54 Intimin/Invasin (Int/Inv) or Autotransporter-3 family
* 1.B.55 Poly-acetyl-D-glucosamine porin (PgaA) family
* 1.B.57 Legionella major-outer membrane protein (LM-OMP) family
* 1.B.60 Omp50 porin (Omp50 Porin) family
* 1.B.61 Delta-proteobacterial porin (Delta-porin) family
* 1.B.62 Putative bacterial porin (PBP) family
* 1.B.66 Putative beta-barrel porin-2 (BBP2) family
* 1.B.67 Putative beta barrel porin-4 (BBP4) family
* 1.B.68 Putative beta barrel porin-5 (BBP5) superfamily
* 1.B.70 Outer membrane channel (OMC) family
* 1.B.71 Proteobacterial/verrucomicrobial porin (PVP) family
* 1.B.72 Protochlamydial outer membrane porin (PomS/T) family
* 1.B.73 Capsule biogenesis/assembly (CBA) family
* 1.B.78 DUF3374 electron transport-associated porin (ETPorin) family | 1 | Biochemistry |
The dominant application of metal carbenes involves none of the above classes of compounds, but rather heterogeneous catalysts used for alkene metathesis for the synthesis of higher alkenes. A variety of related reactions are used to interconvert light alkenes, e.g. butenes, propylene, and ethylene. Carbene complexes are invoked as intermediates in the Fischer–Tropsch route to hydrocarbons.
A variety of homogeneous carbene catalysts, especially the Grubbs' ruthenium and Schrock molybdenum-imido catalysts have been used for olefin metathesis in laboratory-scale synthesis of natural products and materials science. | 0 | Organic Chemistry |
While lists of noble metals can differ, they tend to cluster around the six platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, platinum) plus gold.
In addition to this terms function as a compound noun, there are circumstances where noble is used as an adjective for the noun metal'. A galvanic series is a hierarchy of metals (or other electrically conductive materials, including composites and semimetals) that runs from noble to active, and allows one to predict how materials will interact in the environment used to generate the series. In this sense of the word, graphite is more noble than silver and the relative nobility of many materials is highly dependent upon context, as for aluminium and stainless steel in conditions of varying pH.
The term noble metal can be traced back to at least the late 14th century and has slightly different meanings in different fields of study and application.
Prior to Mendeleev's publication in 1869 of the first (eventually) widely accepted periodic table, Odling published a table in 1864, in which the "noble metals" rhodium, ruthenium, palladium; and platinum, iridium, and osmium were grouped together, and adjacent to silver and gold. | 8 | Metallurgy |
Cellulose is synthesized by cellulose synthase or Rosette terminal complexes which reside on a cells membrane. As cellulose fibrils are synthesized and grow extracellularly they push up against neighboring cells. Since the neighboring cell can not move easily the Rosette complex is instead pushed around the cell through the fluid phospholipid membrane. Eventually this results in the cell becoming wrapped in a microfibril layer. This layer becomes the cell wall. The organization of microfibrils forming the primary cell wall is rather disorganized. However, another mechanism is used in secondary cell walls leading to its organization. Essentially, lanes on the secondary cell wall are built with microtubules. These lanes force microfibrils to remain in a certain area while they wrap. During this process microtubules can spontaneously depolymerize and repolymerize in a different orientation. This leads to a different direction in which the cell continues getting wrapped.
Fibrillin microfibrils are found in connective tissues, which mainly makes up fibrillin-1 and provides elasticity. During the assembly, mirofibrils exhibit a repeating stringed-beads arrangement produced by the cross-linking of molecules forming a striated pattern with a given periodicity when viewed stained under an electron microscope. In the formation of elastic fiber, fibrillin microfibrils guides the deposit of tropoelastin and remains in the outer layer of mature elastin fibers. The microfibril is also associated in cell communication. Formation of fibrillin microfibrils in the pericellular region affects the activity of a growth factor called TGFβ. | 1 | Biochemistry |
Transcription factors are proteins that bind to specific DNA sequences in order to regulate the expression of a given gene. There are approximately 1,400 transcription factors in the human genome and they constitute about 6% of all human protein coding genes. The power of transcription factors resides in their ability to activate and/or repress wide repertoires of downstream target genes. The fact that these transcription factors work in a combinatorial fashion means that only a small subset of an organism's genome encodes transcription factors.
Transcription factors function through a wide variety of mechanisms. In one mechanism, CpG methylation influences binding of most transcription factors to DNA—in some cases negatively and in others positively. In addition, often they are at the end of a signal transduction pathway that functions to change something about the factor, like its subcellular localization or its activity. Post-translational modifications to transcription factors located in the cytosol can cause them to translocate to the nucleus where they can interact with their corresponding enhancers. Other transcription factors are already in the nucleus, and are modified to enable the interaction with partner transcription factors. Some post-translational modifications known to regulate the functional state of transcription factors are phosphorylation, acetylation, SUMOylation and ubiquitylation.
Transcription factors can be divided in two main categories: activators and repressors. While activators can interact directly or indirectly with the core machinery of transcription through enhancer binding, repressors predominantly recruit co-repressor complexes leading to transcriptional repression by chromatin condensation of enhancer regions. It may also happen that a repressor may function by allosteric competition against a determined activator to repress gene expression: overlapping DNA-binding motifs for both activators and repressors induce a physical competition to occupy the site of binding. If the repressor has a higher affinity for its motif than the activator, transcription would be effectively blocked in the presence of the repressor.
Tight regulatory control is achieved by the highly dynamic nature of transcription factors. Again, many different mechanisms exist to control whether a transcription factor is active. These mechanisms include control over protein localization or control over whether the protein can bind DNA. An example of this is the protein HSF1, which remains bound to Hsp70 in the cytosol and is only translocated into the nucleus upon cellular stress such as heat shock. Thus the genes under the control of this transcription factor will remain untranscribed unless the cell is subjected to stress. | 1 | Biochemistry |
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