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Agmatine has been shown to enhance glomerular filtration rate (GFR) and to exert nephroprotective effects. | 1 | Biochemistry |
Resin acid refers to mixtures of several related carboxylic acids, primarily abietic acid, found in tree resins. Nearly all resin acids have the same basic skeleton: three fused rings having the empirical formula CHCOOH. Resin acids are tacky, yellowish gums that are water-insoluble. They are used to produce soaps for diverse applications, but their use is being displaced increasingly by synthetic acids such as 2-ethylhexanoic acid or petroleum-derived naphthenic acids. | 1 | Biochemistry |
Methanol is a fuel for heat engines and fuel cells. Due to its high octane rating it can be used directly as a fuel in flex-fuel cars (including hybrid and plug-in hybrid vehicles) using existing internal combustion engines (ICE). Methanol can also be burned in some other kinds of engine or to provide heat as other liquid fuels are used. Fuel cells, can use methanol either directly in Direct Methanol Fuel Cells (DMFC) or indirectly (after conversion into hydrogen by reforming) in a Reformed Methanol Fuel Cell (RMFC). | 2 | Environmental Chemistry |
In Japan, modafinil is Schedule I psychotropic drug. This means that it is considered to have a high potential for abuse and dependence, and is therefore subject to strict regulations. The use of Schedule I drugs in Japan is generally prohibited, except under certain circumstances, such as for medical purposes. It can only be prescribed by a doctor. It cannot be imported or exported without a permit.
It cannot be used while driving or operating machinery. Cephalon licensed Alfresa Corporation to produce, and Mitsubishi Tanabe Pharma to sell modafinil products under the trade name Modiodal in Japan. There have been arrests of people who imported modafinil for personal use. | 4 | Stereochemistry |
There are no general solutions to the general dynamic equation (GDE); common methods used to solve the general dynamic equation include:
* Moment method
* Modal/sectional method, and
* Quadrature method of moments/Taylor-series expansion method of moments, and
* Monte Carlo method. | 7 | Physical Chemistry |
The PubChem links gives access to more information on the compounds, including other names, ids, toxicity and safety. | 0 | Organic Chemistry |
Uricotelism is the excretion of excess nitrogen in the form of uric acid. Uricotelic animals include insects, birds and most reptiles. Though requiring more metabolic energy to make than urea, uric acid's low toxicity and low solubility in water allow it to be concentrated into a small volume of pasty white suspension in feces, compared to the liquid urine of mammals. Notably however, great apes and humans, while ureotelic, are also uricotelic to a small extent, with uric acid potentially causing problems such as kidney stones and gout, but also functioning as a blood antioxidant. | 1 | Biochemistry |
Urinary VMA is elevated in patients with tumors that secrete catecholamines.
These urinalysis tests are used to diagnose an adrenal gland tumor called pheochromocytoma, a tumor of catecholamine-secreting chromaffin cells. These tests may also be used to diagnose neuroblastomas, and to monitor treatment of these conditions.
Norepinephrine is metabolised into normetanephrine and VMA. Norepinephrine is one of the hormones produced by the adrenal glands, which are found on top of the kidneys. These hormones are released into the blood during times of physical or emotional stress, which are factors that may skew the results of the test. | 1 | Biochemistry |
The bacteriophages used for cloning are the λ phage and M13 phage. There is an upper limit on the amount of DNA that can be packed into a phage (a maximum of 53 kb), therefore to allow foreign DNA to be inserted into phage DNA, phage cloning vectors may need to have some non-essential genes deleted, for example the genes for lysogeny since using phage λ as a cloning vector involves only the lytic cycle. There are two kinds of λ phage vectors - insertion vector and replacement vector. Insertion vectors contain a unique cleavage site whereby foreign DNA with size of 5–11 kb may be inserted. In replacement vectors, the cleavage sites flank a region containing genes not essential for the lytic cycle, and this region may be deleted and replaced by the DNA insert in the cloning process, and a larger sized DNA of 8–24 kb may be inserted.
There is also a lower size limit for DNA that can be packed into a phage, and vector DNA that is too small cannot be properly packaged into the phage. This property can be used for selection - vector without insert may be too small, therefore only vectors with insert may be selected for propagation. | 1 | Biochemistry |
In 2018, the Iowa Department of Natural Resources found microcystins at levels of 0.3 µg/L, or micrograms per liter (ppb), in the raw water supplies of 15 out of 26 public water systems tested. | 2 | Environmental Chemistry |
Another type of topographic contrast, extinction contrast, is slightly more complex. While the two above variants are explicable in simple terms based on geometrical theory (basically, the Bragg law) or kinematical theory of X-ray diffraction, extinction contrast can be understood based on dynamical theory.
Qualitatively, extinction contrast arises e.g. when the thickness of a sample, compared to the respective extinction length (Bragg case) or Pendelloesung length (Laue case), changes across the image. In this case, diffracted beams from areas of different thickness, having suffered different degrees of extinction, are recorded within the same image, giving rise to contrast. Topographists have systematically investigated this effect by studying wedge-shaped samples, of linearly varying thickness, allowing to directly record in one image the dependence of diffracted intensity on sample thickness as predicted by dynamical theory.
In addition to mere thickness changes, extinction contrast also arises when parts of a crystal are diffracting with different strengths, or when the crystal contains deformed (strained) regions.
The governing quantity for an overall theory of extinction contrast in deformed crystals is called the effective misorientation
where is the displacement vector field, and and are the directions of the incident and diffracted beam, respectively.
In this way, different kinds of disturbances are "translated" into equivalent misorientation values, and contrast formation can be understood analogously to orientation contrast.
For instance, a compressively strained material requires larger Bragg angles for diffraction at unchanged wavelength. To compensate for this and to reach diffraction conditions, the sample needs to be rotated, similarly as in the case of lattice tilts.
A simplified and more "transparent" formula taking into account the combined effect of tilts and strains onto contrast is the following: | 3 | Analytical Chemistry |
Salicylaldoxime is an organic compound described by the formula CHCH=NOH-2-OH. It is the oxime of salicylaldehyde. This crystalline, colorless solid is a chelator and sometimes used in the analysis of samples containing transition metal ions, with which it often forms brightly coloured coordination complexes. | 3 | Analytical Chemistry |
The pathway bears resemblance to CAM; both act to concentrate around RuBisCO, thereby increasing its efficiency. CAM concentrates it temporally, providing during the day, and not at night, when respiration is the dominant reaction. plants, in contrast, concentrate spatially, with a RuBisCO reaction centre in a "bundle sheath cell" being inundated with . Due to the inactivity required by the CAM mechanism, carbon fixation has a greater efficiency in terms of PGA synthesis.
There are some /CAM intermediate species, such as Peperomia camptotricha, Portulaca oleracea, and Portulaca grandiflora. It was previously thought that the two pathways of photosynthesis in such plants could occur in the same leaves but not in the same cells, and that the two pathways could not couple but only occur side by side. It is now known, however, that in at least some species such as Portulaca oleracea, C and CAM photosynthesis are fully integrated within the same cells, and that CAM-generated metabolites are incorporated directly into the C cycle. | 5 | Photochemistry |
Baldwin's rules in organic chemistry are a series of guidelines outlining the relative favorabilities of ring closure reactions in alicyclic compounds. They were first proposed by Jack Baldwin in 1976.
Baldwin's rules discuss the relative rates of ring closures of these various types. These terms are not meant to describe the absolute probability that a reaction will or will not take place, rather they are used in a relative sense. A reaction that is disfavoured (slow) does not have a rate that is able to compete effectively with an alternative reaction that is favoured (fast). However, the disfavoured product may be observed, if no alternate reactions are more favoured.
The rules classify ring closures in three ways:
*the number of atoms in the newly formed ring
*into exo and endo ring closures, depending whether the bond broken during the ring closure is inside (endo) or outside (exo) the ring that is being formed
*into tet, trig and dig geometry of the atom being attacked, depending on whether this electrophilic carbon is tetrahedral (sp hybridised), trigonal (sp hybridised) or diagonal (sp hybridised).
Thus, a ring closure reaction could be classified as, for example, a 5-exo-trig.
Baldwin discovered that orbital overlap requirements for the formation of bonds favour only certain combinations of ring size and the exo/endo/dig/trig/tet parameters. Interactive 3D models of several of these transition states can be seen [http://www.chemtube3d.com/Baldwin'sRule-Classes.html here] (javascript required).
There are sometimes exceptions to Baldwins rules. For example, cations often disobey Baldwins rules, as do reactions in which a third-row atom is included in the ring. An expanded and revised version of the rules is available:
The rules apply when the nucleophile can attack the bond in question in an ideal angle. These angles are 180° (Walden inversion) for exo-tet reactions, 109° (Bürgi–Dunitz angle) for exo-trig reaction and 120° for endo-dig reactions. Angles for nucleophilic attack on alkynes were reviewed and redefined recently. The "acute angle" of attack postulated by Baldwin was replaced with a trajectory similar to the Bürgi–Dunitz angle. | 4 | Stereochemistry |
In crystallography, a fractional coordinate system is used in order to better reflect the symmetry of the underlying lattice of a crystal pattern (or any other periodic pattern in space). In a fractional coordinate system the basis vectors of the coordinate system are chosen to be lattice vectors and the basis is then termed a crystallographic basis (or lattice basis).
In a lattice basis, any lattice vector can be represented as,
There are an infinite number of lattice bases for a crystal pattern. However, these can be chosen in such a way that the simplest description of the pattern can be obtained. These bases are used in the International Tables of Crystallography Volume A and are termed conventional bases. A lattice basis is called primitive if the basis vectors are lattice vectors and all lattice vectors can be expressed as,
However, the conventional basis for a crystal pattern is not always chosen to be primitive. Instead, it is chosen so the number of orthogonal basis vectors is maximized. This results in some of the coefficients of the equations above being fractional. A lattice in which the conventional basis is primitive is called a primitive lattice, while a lattice with a non-primitive conventional basis is called a centered lattice.
The choice of an origin and a basis implies the choice of a unit cell which can further be used to describe a crystal pattern. The unit cell is defined as the parallelotope (i.e., generalization of a parallelogram (2D) or parallelepiped (3D) in higher dimensions) in which the coordinates of all points are such that, .
Furthermore, points outside of the unit cell can be transformed inside of the unit cell through standardization, the addition or subtraction of integers to the coordinates of points to ensure . In a fractional coordinate system, the lengths of the basis vectors and the angles between them are called the lattice parameters (lattice constants) of the lattice. In two- and three-dimensions, these correspond to the lengths and angles between the edges of the unit cell.
The fractional coordinates of a point in space in terms of the lattice basis vectors is defined as, | 3 | Analytical Chemistry |
An electron microprobe (EMP), also known as an electron probe microanalyzer (EPMA) or electron micro probe analyzer (EMPA), is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials. It works similarly to a scanning electron microscope: the sample is bombarded with an electron beam, emitting x-rays at wavelengths characteristic to the elements being analyzed. This enables the abundances of elements present within small sample volumes (typically 10-30 cubic micrometers or less) to be determined, when a conventional accelerating voltage of 15-20 kV is used. The concentrations of elements from lithium to plutonium may be measured at levels as low as 100 parts per million (ppm), material dependent, although with care, levels below 10 ppm are possible. The ability to quantify lithium by EPMA became a reality in 2008. | 3 | Analytical Chemistry |
The IL 1-butyl-3-methylimidazolium chloride has been investigated for the recovery of uranium and other metals from spent nuclear fuel and other sources. | 7 | Physical Chemistry |
Substitution of all 20 hydrogens by fluorine atoms yields the relatively unstable perfluorododecahedrane CF, which was obtained in milligram quantities. Trace amounts of the analogous perchlorododecahedrane CCl were obtained, among other partially chlorinated derivatives, by reacting dissolved in liquid chlorine under pressure at about 140 °C and under intense light for five days. Complete replacement by heavier halogens seems increasingly difficult due to their larger size. Half or more of the hydrogen atoms can be substituted by hydroxyl groups to yield polyols, but the extreme compound C(OH) remained elusive as of 2006. Amino-dodecahedranes comparable to amantadine have been prepared, but were more toxic and with weaker antiviral effects.
Annulated dodecahedrane structures have been proposed. | 0 | Organic Chemistry |
Ferrous metallurgy is the metallurgy of iron and its alloys. The earliest surviving prehistoric iron artifacts, from the 4th millennium BC in Egypt, were made from meteoritic iron-nickel. It is not known when or where the smelting of iron from ores began, but by the end of the 2nd millennium BC iron was being produced from iron ores in the region from Greece to India, and sub-Saharan Africa. The use of wrought iron (worked iron) was known by the 1st millennium BC, and its spread defined the Iron Age. During the medieval period, smiths in Europe found a way of producing wrought iron from cast iron, in this context known as pig iron, using finery forges. All these processes required charcoal as fuel.
By the 4th century BC southern India had started exporting wootz steel, with a carbon content between pig iron and wrought iron, to ancient China, Africa, the Middle East, and Europe. Archaeological evidence of cast iron appears in 5th-century BC China. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. During the Industrial Revolution, new methods of producing bar iron by substituting coke for charcoal emerged, and these were later applied to produce steel, ushering in a new era of greatly increased use of iron and steel that some contemporaries described as a new "Iron Age".
In the late 1850s Henry Bessemer invented a new steelmaking process which involved blowing air through molten pig-iron to burn off carbon, and so producing mild steel. This and other 19th-century and later steel-making processes have displaced wrought iron. Today, wrought iron is no longer produced on a commercial scale, having been displaced by the functionally equivalent mild or low-carbon steel. | 8 | Metallurgy |
Because of the greater electronegativity of oxygen than nitrogen, the carbonyl (C=O) is a stronger dipole than the N–C dipole. The presence of a C=O dipole and, to a lesser extent a N–C dipole, allows amides to act as H-bond acceptors. In primary and secondary amides, the presence of N–H dipoles allows amides to function as H-bond donors as well. Thus amides can participate in hydrogen bonding with water and other protic solvents; the oxygen atom can accept hydrogen bonds from water and the N–H hydrogen atoms can donate H-bonds. As a result of interactions such as these, the water solubility of amides is greater than that of corresponding hydrocarbons. These hydrogen bonds also have an important role in the secondary structure of proteins.
The solubilities of amides and esters are roughly comparable. Typically amides are less soluble than comparable amines and carboxylic acids since these compounds can both donate and accept hydrogen bonds. Tertiary amides, with the important exception of N,N-dimethylformamide, exhibit low solubility in water. | 0 | Organic Chemistry |
Organometallic compounds are distinguished by the prefix "organo-" (e.g., organopalladium compounds), and include all compounds which contain a bond between a metal atom and a carbon atom of an organyl group. In addition to the traditional metals (alkali metals, alkali earth metals, transition metals, and post transition metals), lanthanides, actinides, semimetals, and the elements boron, silicon, arsenic, and selenium are considered to form organometallic compounds. Examples of organometallic compounds include Gilman reagents, which contain lithium and copper, and Grignard reagents, which contain magnesium. Boron-containing organometallic compounds are often the result of hydroboration and carboboration reactions. Tetracarbonyl nickel and ferrocene are examples of organometallic compounds containing transition metals. Other examples of organometallic compounds include organolithium compounds such as n-butyllithium (n-BuLi), organozinc compounds such as diethylzinc (EtZn), organotin compounds such as tributyltin hydride (BuSnH), organoborane compounds such as triethylborane (EtB), and organoaluminium compounds such as trimethylaluminium (MeAl).
A naturally occurring organometallic complex is methylcobalamin (a form of Vitamin B), which contains a cobalt-methyl bond. This complex, along with other biologically relevant complexes are often discussed within the subfield of bioorganometallic chemistry. | 0 | Organic Chemistry |
Proline isomerization of certain prolines in RNA polymerase II is key in the process of recruiting and placing processing factors during transcription. PPIases target RNA polymerase II by interacting with the Rpb1 carboxy terminal domain, or CTD. Proline isomerization is then used as part of the mechanism of the CTD to recruit co-factors required for co-transcriptional RNA processing, regulating RNA polymerase II activity. Nrd1 is a protein that is responsible for many of the transcriptional activities of RNAP II, specifically through the Nrd1- dependent termination pathway. This pathway requires the parvulin Ess1, or Pin1 depending on the organism, to isomerize the pSer5-Pro6 bond in the CTD. Without the cis conformation of the pSer5-Pro6 bond, created by Ess1/Pin1, Nrd1 cannot bind to RNAP II. Any variation from this process leads to a decrease in Nrd1 binding affinity, lowering the ability of RNAP II to process and degrade noncoding RNAs. | 4 | Stereochemistry |
Metal formyl complexes are often prepared by the reaction of metal carbonyls with hydride reagents:
:[Re(CO)] + H → (CO)ReCHO
The CO ligand is the electrophile and the hydride (provided typically from a borohydride) is the nucleophile.
Some metal formyls are produced by reaction of metal carbonyl anions with reagents that donate the equivalent of a formyl cation, such a mixed formate anhydrides.
Metal formyls participate in many reactions, many of which are motivated by interest in Fischer-Tropsch chemistry. O-alkylation gives carbenoid complexes. The formyl ligand also functions as a base, allowing the formation of M-CH=O-M' linkages. Decarbonylation leads to de-insertion of the carbonyl, yielding hydride complexes. | 0 | Organic Chemistry |
As 1,3dipoles, nitrones perform [[1,3-dipolar cycloaddition|[3+2] cycloaddition]]s. For example, a dipolarophilic alkene combines to form isoxazolidine:
Other ring-closing reactions are known, including formal [3+3] and [5+2] cycloadditions. | 0 | Organic Chemistry |
Pollutants can be deleted from groundwater by perstraction. Different techniques have been patented. The oldest one has published in 1990 and the youngest one in 1998. In the 2000s has been done few patent applications but no granted patents.
Organic compounds through a membrane has been concentrated from groundwater. The concentration factor is from 1 000 to 10 000 bringing 0.1 ppb concentrations to between 0.1 and 1.0 ppm. Besides the concentration of a contaminant has been analyzed in real-time. The membrane is polymer like polysulphane. The hole diameter is 300 µm and thickness is 30 µm. | 3 | Analytical Chemistry |
Carbomethoxymethylenetriphenylphosphorane reacts with aldehydes to give a two carbon atom extension. The carbomethoxymethylene group replaces the oxygen of the aldehyde to give a trans- double bond. | 0 | Organic Chemistry |
Uranium deposits are usually sourced from radioactive granites, where certain minerals such as monazite are leached during hydrothermal activity or during circulation of groundwater. The uranium is brought into solution by acidic conditions and is deposited when this acidity is neutralised. Generally this occurs in certain carbon-bearing sediments, within an unconformity in sedimentary strata. The majority of the world's nuclear power is sourced from uranium in such deposits.
Uranium is also found in nearly all coal at several parts per million, and in all granites. Radon is a common problem during mining of uranium as it is a radioactive gas.
Uranium is also found associated with certain igneous rocks, such as granite and porphyry. The Olympic Dam deposit in Australia is an example of this type of uranium deposit. It contains 70% of Australia's share of 40% of the known global low-cost recoverable uranium inventory. | 9 | Geochemistry |
Hot blast was the single most important advance in fuel efficiency of the blast furnace and was one of the most important technologies developed during the Industrial Revolution. Hot blast was patented by James Beaumont Neilson at Wilsontown Ironworks in Scotland in 1828. Within a few years of the introduction, hot blast was developed to the point where fuel consumption was cut by one-third using coke or two-thirds using coal, while furnace capacity was also significantly increased. Within a few decades, the practice was to have a "stove" as large as the furnace next to it into which the waste gas (containing CO) from the furnace was directed and burnt. The resultant heat was used to preheat the air blown into the furnace.
Hot blast enabled the use of raw anthracite coal, which was difficult to light, in the blast furnace. Anthracite was first tried successfully by George Crane at Ynyscedwyn Ironworks in south Wales in 1837. It was taken up in America by the Lehigh Crane Iron Company at Catasauqua, Pennsylvania, in 1839. Anthracite use declined when very high capacity blast furnaces requiring coke were built in the 1870s. | 8 | Metallurgy |
Since ethanol boils at a much lower temperature than water, simple distillation can separate ethanol from water by applying heat to the mixture. Historically, a copper vessel was used for this purpose, since copper removes undesirable sulfur-based compounds from the alcohol. However, many modern stills are made of stainless steel pipes with copper linings to prevent erosion of the entire vessel and lower copper levels in the waste product (which in large distilleries is processed to become animal feed). Copper is the preferred material for stills because it yields an overall better-tasting spirit. The taste is improved by the chemical reaction between the copper in the still and the sulfur compounds created by the yeast during fermentation. These unwanted and flavor-changing sulfur compounds are chemically removed from the final product resulting in a smoother, better-tasting drink. All copper stills will require repairs about every eight years due to the precipitation of copper-sulfur compounds. The beverage industry was the first to implement a modern distillation apparatus and led the way in developing equipment standards which are now widely accepted in the chemical industry.
There is also an increasing usage of the distillation of gin under glass and PTFE, and even at reduced pressures, to facilitate a fresher product. This is irrelevant to alcohol quality because the process starts with triple distilled grain alcohol, and the distillation is used solely to harvest botanical flavors such as limonene and other terpene like compounds. The ethyl alcohol is relatively unchanged.
The simplest standard distillation apparatus is commonly known as a pot still, consisting of a single heated chamber and a vessel to collect purified alcohol. A pot still incorporates only one condensation, whereas other types of distillation equipment have multiple stages which result in higher purification of the more volatile component (alcohol). Pot still distillation gives an incomplete separation, but this can be desirable for the flavor of some distilled beverages.
If a purer distillate is desired, a reflux still is the most common solution. Reflux stills incorporate a fractionating column, commonly created by filling copper vessels with glass beads to maximize available surface area. As alcohol boils, condenses, and reboils through the column, the effective number of distillations greatly increases. Vodka and gin and other neutral grain spirits are distilled by this method, then diluted to concentrations appropriate for human consumption.
Alcoholic products from home distilleries are common throughout the world but are sometimes in violation of local statutes. The product of illegal stills in the United States is commonly referred to as moonshine and in Ireland, poitín. However, poitín, although made illegal in 1661, has been legal for export in Ireland since 1997. Note that the term moonshine itself is often misused as many believe it to be a specific kind of high-proof alcohol that was distilled from corn, but the term can refer to any illicitly distilled alcohol. | 3 | Analytical Chemistry |
The first passive sampling devices were developed in the 1970s to determine concentrations of contaminants in the air. In 1980 this technology was first adapted for the monitoring of organic contaminants in water. The initial type of passive sampler developed for aquatic monitoring purposes was the semipermeable membrane device (SMPD). SPMD samplers are most effective at absorbing hydrophobic pollutants with an octanol-water partition coefficient (Kow) ranging from 4-8. As the global emission of bioconcentratable persistent organic pollutants (POPs) was shown to result in adverse ecological effects, industry developed a wide range of increasing water-soluble, polar hydrophilic organic compounds (HpOCs) to replace them. These compounds generally have lower bioconcentration factors. However, there is evidence that large fluxes of these HpOCs into aquatic environments may be responsible for a number of adverse effects to aquatic organisms, such as altered behavior, neurotoxicity, endocrine disruption, and impaired reproduction. In the late 1990s research was underway to develop a new passive sampler in order to monitor HpOCs with a log Kow value of less than 3. In 1999 the POCIS sampler was under development at the University of Missouri-Columbia. It gathered more support in the early 2000s as concern increased regarding the effects of pharmaceutical and personal care products in surface waters.
The United States Geological Survey (USGS) has been heavily involved in the development of passive samplers and has articles in their database regarding the development of POCIS as early as 2000. The USGS Columbia Environmental Research Center (CERC) is a self-proclaimed international leader in the field of passive sampling. There have been recent efforts by the USGS to connect people who have an interest in passive sampling. An international workshop and symposium on passive sampling was held by the USGS in 2013 to connect developers, policy makers and end users in order to discuss ways of monitoring environmental pollution. | 3 | Analytical Chemistry |
Humans have between 10 and 20 million olfactory receptor neurons (ORNs). In vertebrates, ORNs are bipolar neurons with dendrites facing the external surface of the cribriform plate with axons that pass through the cribriform foramina with terminal end at olfactory bulbs. The ORNs are located in the olfactory epithelium in the nasal cavity. The cell bodies of the ORNs are distributed among all three of the stratified layers of the olfactory epithelium.
Many tiny hair-like non-motile cilia protrude from the olfactory receptor cell's dendrites. The dendrites extend to the olfactory epithelial surface and each ends in a dendritic knob from which around 20 to 35 cilia protrude. The cilia have a length of up to 100 micrometres and with the cilia from other dendrites form a meshwork in the olfactory mucus. The surface of the cilia is covered with olfactory receptors, a type of G protein-coupled receptor. Each olfactory receptor cell expresses only one type of olfactory receptor (OR), but many separate olfactory receptor cells express ORs which bind the same set of odors. The axons of olfactory receptor cells which express the same OR converge to form glomeruli in the olfactory bulb. | 1 | Biochemistry |
The vast majority of important organic molecules contain heteroatoms, which polarize carbon skeletons by virtue of their electronegativity. Therefore, in standard organic reactions, the majority of new bonds are formed between atoms of opposite polarity. This can be considered to be the "normal" mode of reactivity.
One consequence of this natural polarization of molecules is that 1,3- and 1,5- heteroatom substituted carbon skeletons are extremely easy to synthesize (Aldol reaction, Claisen condensation, Michael reaction, Claisen rearrangement, Diels-Alder reaction), whereas 1,2-, 1,4-, and 1,6- heteroatom substitution patterns are more difficult to access via "normal" reactivity. It is therefore important to understand and develop methods to induce umpolung in organic reactions. | 0 | Organic Chemistry |
Catalytic engineered systems are designed to pass air from the atmosphere, either passively or actively, through catalytic systems which leverage energy from the sun, an artificial light, or heat to oxidize methane. These catalysts include thermocatalysts, photocatalysts, and radicals produced artificially through photolysis (using light to break apart a molecule). | 2 | Environmental Chemistry |
This book describes how an official, the Bergmeister, is in charge of mining. He marks out the land into areas called meers when a vein is discovered. The rest of the book covers the laws of mining. There is a section on how the mine can be divided into shares. The roles of various other officials in regulating mines and taxing the production are stated. The shifts of the miners are fixed. The chief trades in the mine are listed and are regulated by both the Bergmeister and their foremen. | 8 | Metallurgy |
Non-stop decay (NSD) is a cellular pathway that identifies and degrades aberrant mRNA transcripts that do not contain a proper stop codon. Stop codons are signals in messenger RNA that signal for synthesis of proteins to end. Aberrant transcripts are identified during translation when the ribosome translates into the poly A tail at the 3' end of mRNA. A non-stop transcript can occur when point mutations damage the normal stop codon. Moreover, some transcriptional events are more likely to preserve gene expression on a lower scale in particular states.
The NSD pathway discharges ribosomes that have stalled at the 3' end of mRNA and directs the mRNA to the exosome complex in eukaryotes or RNase R in bacteria. Once directed to their appropriate sites, the transcripts are then degraded. The NSD mechanism requires the interaction of RNA exosome with the Ski complex, a multi-protein structure that includes the Ski2p helicase and (notably) Ski7p. The combination of these proteins and subsequent complex formation activates the degradation of aberrant mRNAs. Ski7p is thought to bind the ribosome stalled at the 3’ end of the mRNA poly(A) tail and recruit the exosome to degrade the aberrant mRNA. However in mammalian cells, Ski7p is not found, and even the presence of the NSD mechanism itself has remained relatively unclear. The short splicing isoform of HBS1L (HBS1LV3) was found to be the long-sought after human homologue of Ski7p, linking the exosome and SKI complexes. Recently, it has been reported that NSD also occurs in mammalian cells, albeit through a slightly different system. In mammals, due to the absence of Ski7, the GTPase Hbs1, as well as its binding partner Dom34, were identified as potential regulators of decay. Together, Hbs1/Dom34 are capable of binding to the 3’ end of an mis-regulated mRNA, facilitating the dissociation of malfunctioning or inactive ribosomes in order to restart the process of translation. In addition, once the Hbs1/Dom34 complex has dissociated and recycled a ribosome, it has also been shown to recruit the exosome/Ski complex. | 1 | Biochemistry |
To diketone 23, sodium acetylide(Alkynylation) was added (bringing in carbon atoms 22 and 23) to give alkyne 24. This compound was reduced to the allyl alcohol 25 using the Lindlar catalyst and lithium aluminium hydride removed the remaining amide group in 26. An allylic rearrangement to alcohol 27 (isostrychnine) was brought about by hydrogen bromide in acetic acid followed by hydrolysis with sulfuric acid. In the final step to (−)-strychnine 28 treatment of 27 with ethanolic potassium hydroxide caused rearrangement of the C12-13 double bond and ring closure in a conjugate addition by the hydroxyl anion. | 0 | Organic Chemistry |
The best explanation of the phenomenon of optical molasses is based on the principle of polarization gradient cooling. Counterpropagating beams of circularly polarized light cause a standing wave, where the light polarization is linear but the direction rotates along the direction of the beams at a very fast rate. Atoms moving in the spatially varying linear polarisation have a higher probability density of being in a state that is more susceptible to absorption of light from the beam coming head-on, rather than the beam from behind. This results in a velocity dependent damping force that is able to reduce the velocity of a cloud of atoms to near the recoil limit., is set by the energy of the photon emitted in the decay from the J’ to J state, where the J state is the ground state angular momentum and the J’ state is the excited state angular momentum. This temperature is given by though practically the limit is a few times this value because of the extreme sensitivity to external magnetic fields in this cooling scheme. Atoms typically reach temperatures on the order of , as compared to the doppler limit . | 7 | Physical Chemistry |
In 1928, Frederick Griffith, encountered a virulence property in pneumococcus bacteria, which was killing lab rats. According to Mendel, prevalent at that time, gene transfer could occur only from parent to daughter cells only. Griffith advanced another theory, stating that gene transfer occurring in member of same generation is known as horizontal gene transfer (HGT). This phenomenon is now referred to as genetic transformation.
Griffiths experiment addressed the pneumococcus bacteria, which had two different strains, one virulent and smooth and one avirulent and rough. The smooth strain had glistering appearance owing to the presence of a type of specific polysaccharide – a polymer of glucose and glucuronic acid capsule. Due to this polysaccharide layer of bacteria, a hosts immune system cannot recognize the bacteria and it kills the host. The other, avirulent, rough strain lacks this polysaccharide capsule and has a dull, rough appearance.
Presence or absence of capsule in the strain, is known to be genetically determined. Smooth and rough strains occur in several different type such as S-I, S-II, S-III, etc. and R-I, R-II, R-III, etc. respectively. All this subtypes of S and R bacteria differ with each other in antigen type they produce. | 1 | Biochemistry |
An alternative form of the Arruda–Boyce model, using the first five terms of the inverse Langevin function, is
where is a material constant. The quantity can also be interpreted as a measure of the limiting network stretch.
If is the stretch at which the polymer chain network becomes locked, we can express the Arruda–Boyce strain energy density as
We may alternatively express the Arruda–Boyce model in the form
where and
If the rubber is compressible, a dependence on can be introduced into the strain energy density; being the deformation gradient. Several possibilities exist, among which the Kaliske–Rothert extension has been found to be reasonably accurate. With that extension, the Arruda-Boyce strain energy density function can be expressed as
where is a material constant and . For consistency with linear elasticity, we must have where is the bulk modulus. | 7 | Physical Chemistry |
When the ovarian follicles have reached a certain degree of development, induction of final oocyte maturation is performed, generally by an injection of human chorionic gonadotropin (hCG). Commonly, this is known as the "trigger shot." hCG acts as an analogue of luteinising hormone, and ovulation would occur between 38 and 40 hours after a single HCG injection, but the egg retrieval is performed at a time usually between 34 and 36 hours after hCG injection, that is, just prior to when the follicles would rupture. This avails for scheduling the egg retrieval procedure at a time where the eggs are fully mature. HCG injection confers a risk of ovarian hyperstimulation syndrome. Using a GnRH agonist instead of hCG eliminates most of the risk of ovarian hyperstimulation syndrome, but with a reduced delivery rate if the embryos are transferred fresh. For this reason, many centers will freeze all oocytes or embryos following agonist trigger. | 1 | Biochemistry |
Like other members of the microbial rhodopsin family, archaerhodopsins are expressed in specialised, protein-rich domains of the cell surface membrane, commonly called the claret membrane. In addition to ether lipids, the claret membrane contains bacterioruberin, (a 50-carbon carotenoid pigment) which is thought to protect against photobleaching. Atomic force microscope images of the claret membranes of several archaerhodopsins, show that the proteins are trimeric and are arranged in a hexagonal lattice. Bacterioruberin has also been implicated in oligomerisation and may facilitate protein-protein interactions in the native membrane. | 5 | Photochemistry |
Bacterial recombination undergoes various different processes. The processes include: transformation, transduction, conjugation and homologous recombination. Homologous recombination relies on cDNA transferring genetic material. Complementary DNA sequences transport genetic material in the identical homologous chromosomes. The paternal and maternal paired chromosomes will align in order for the DNA sequences to undergo the process of crossing over. Transformation involves the uptake of exogenous DNA from the encircling environment. DNA fragments from a degraded bacterium will transfer into the surrounding, competent bacterium resulting in an exchange of DNA from the recipient. Transduction is associated with viral-mediated vectors transferring DNA material from one bacterium to another within the genome. Bacterial DNA is placed into the bacteriophage genome via bacterial transduction. In bacterial conjugation, DNA is transferred via cell-to-cell communication. Cell-to-cell communication may involve plasmids that allow for the transfer of DNA into another neighboring cell. The neighboring cells absorb the F-plasmid (fertility plasmid: inherited material that is present in the chromosome). The recipient and donor cell come into contact during a F-plasmid transfer. The cells undergo horizontal gene transfer in which the genetic material is transferred.
Mechanisms for double-stranded breaks
The RecBCD pathway in homologous recombination repairs the double-strand breaks in DNA that has degraded in bacteria. Base pairs attached to the DNA strands go through an exchange at a Holliday junction. In the second step of bacterial recombination, branch migration. involves the base pairs of the homologous DNA strands to continuously be interchanged at a Holliday junction. This results in the formation of two DNA duplexes. The RecBCD pathway undergoes helicase activity by unzipping the DNA duplex and stops when the nucleotide sequence reaches 5′-GCTGGTGG-3′. This nucleotide sequence is known as the Chi site. RecBCD enzymes will change after the nucleotide sequence reaches the Chi site. The RecF pathway repairs the degradation of the DNA strands. | 1 | Biochemistry |
Ractopamine has been banned in Taiwan since 2006. In the summer of 2007, two US shipments including ractopamine-laced pork were rejected by Taiwans health authorities, while the Taiwan government had been considering lifting the ban on such imports. This resulted in mass protests in the capital city, Taipei, by swine farmers insisting that the ban remain in place. Health Minister Hou Sheng-mou (侯勝茂) declared no lifting of the ban would occur unless related laws were amended. Although the use of ractopamine in livestock is still banned and enforced on the domestic industry, and the government has maintained a "zero tolerance" policy on pork imports that contain it, Taiwans legislature amended the food safety act in August 2012 to allow the import of beef products containing up to a maximum residue level of 10 parts per billion of the additive. The remaining restrictions have been an obstacle to the two nations signing a free-trade agreement, and the Office of the United States Trade Representative (USTR)'s 2018 Trade Policy Agenda and 2017 Annual Report assert that these remaining restrictions "...are not based upon science..." and highlights their removal as among the main priorities for the US in its trade with Taiwan. However, Taiwan plans to ease the import restrictions on US pork commencing January 1, 2021 | 4 | Stereochemistry |
Some varying factors in splat quenching are the drop size and velocity of the metal in ensuring the complete solidification of the metal. In cases where the volume of the drop is too large or the velocity is too slow, the metal will not solidify past equilibrium causing it to remelt. Therefore, experiments are carried out to determine the precise volume and velocity of the droplet that will ensure complete solidification of a certain metal.
Intrinsic and extrinsic factors influencing the glass-forming ability of metallic alloys were analyzed and classified. | 8 | Metallurgy |
In physics, terahertz time-domain spectroscopy (THz-TDS) is a spectroscopic technique in which the properties of matter are probed with short pulses of terahertz radiation. The generation and detection scheme is sensitive to the sample's effect on both the amplitude and the phase of the terahertz radiation. | 7 | Physical Chemistry |
Since its reduction potential is similar to that of oxygen and can be reduced by components of the electron transport chain, large doses of methylene blue are sometimes used as an antidote to potassium cyanide poisoning, a method first successfully tested in 1933 by Dr. Matilda Moldenhauer Brooks in San Francisco, although first demonstrated by Bo Sahlin of Lund University, in 1926. | 3 | Analytical Chemistry |
The assay is separated into three main parts:
preparation of the Diluted Albumin (BSA) Standards,
preparation of the bicinchoninic acid (BCA) working reagent,
and quantification of proteins (using either test tube or microplate procedure). | 1 | Biochemistry |
Premelting (also surface melting) refers to a quasi-liquid film that can occur on the surface of a solid even below melting point (). The thickness of the film is temperature () dependent. This effect is common for all crystalline materials.
Premelting shows its effects in frost heave, and, taking grain boundary interfaces into account, maybe even in the movement of glaciers.
Considering a solid-vapour interface, complete and incomplete premelting can be distinguished. During a temperature rise from below to above , in the case of complete premelting, the solid melts homogeneously from the outside to the inside; in the case of incomplete premelting, the liquid film stays very thin during the beginning of the melting process, but droplets start to form on the interface. In either case, the solid always melts from the outside inwards, never from the inside. | 7 | Physical Chemistry |
Diethanolamides are common ingredients used in cosmetics to act as a foaming agents or as emulsifiers. Chemically, they are amides formed from diethanolamine and carboxylic acids, typically fatty acids.
Examples include:
* Cocamide diethanolamine
* Lauramide diethanolamine
* Oleamide diethanolamine | 0 | Organic Chemistry |
A crystal model is a teaching aid used for understanding concepts in crystallography and the morphology of crystals. Models are ideal to learn recognizing symmetry elements in crystals. | 3 | Analytical Chemistry |
Marine macrophytes (i.e., macroalgae and seagrass) are highly productive and extend over large areas in coastal waters but their production of DOC has not received much attention. Macrophytes release DOC during growth with a conservative estimate (excluding release from decaying tissues) suggesting that macroalgae release between 1-39% of their gross primary production, while seagrasses release less than 5% as DOC of their gross primary production. The released DOC has been shown to be rich in carbohydrates, with rates depending on temperature and light availability. Globally the macrophyte communities have been suggested to produce ~160 Tg C yr of DOC, which is approximately half the annual global river DOC input (250 Tg C yr). | 2 | Environmental Chemistry |
Like all metals, gold is insoluble in a water. Gold does however exhibit the distinctive properties that in the presence of cyanide ions, it dissolves in the presence of oxygen (or air). This transformation was reported in 1783 by Carl Wilhelm Scheele, but it was not until the late 19th century, that the reactions were exploited commercially. The expansion of gold mining in the Rand of South Africa began to slow down in the 1880s, as the new deposits being found tended to be pyritic ore. The gold was difficult to extract from such ores.
In 1887, John Stewart MacArthur, working in collaboration with brothers Dr Robert and Dr William Forrest for the Tennant Company in Glasgow, Scotland, developed the MacArthur-Forrest Process for the extraction of gold ores. By suspending the crushed ore in a cyanide solution, up to 96 percent gold was extracted.
The process was first used on a large scale at the Witwatersrand in 1890, leading to a boom of investment as larger gold mines were opened up. In 1896, Bodländer confirmed that oxygen was necessary for the process, something that had been doubted by MacArthur, and discovered that hydrogen peroxide was formed as an intermediate.
The method known as heap leaching was first proposed in 1969 by the United States Bureau of Mines, and was in use by the 1970s. | 8 | Metallurgy |
The information available about the people of the Copper Age has not substantially increased along with the number of archaeological sites. Several ideas have been proffered, one of the most followed is that the metal itself did not bring abrupt transformation into the people's life, or even more that early copper does not produce anything useful at all, meaning with this that with the copper, they produced mainly jewellery and, overall, weapons that obviously were not within reach of the majority of the population but only to privileged individuals. In other words, the real importance of the metal is not utilitarian but social. This is a suitable explanation about the rising of Great Cultures of Metal such as Vinča culture (Ex-Yugoslavia) Tiszapolgar and Unetice culture (Central Europe), Remedello and Rinaldone (Italy), Montagne Noire (France), El Argar and Targas (Spain), etc.
As the period moved forward, especially around the 3rd millennium, new and complex realities would appear strongly linked to the metal, like the impressive fortified villages of Los Millares (Spain), Vila Nova de Sao Pedro (Portugal) or the more modest cairn next to Copa Hill in the United Kingdom destinated to control the centres of extraction, or the equally and generalized cultural phenomenons of Megalithism, Rock Art, Bell Beakers Vessels that are known from Scandinavia to the South of Spain and from Scotland to Turkey. | 8 | Metallurgy |
Calculating rates of VO and/or VCO requires knowledge of the flow rates into and out of the chamber, plus fractional concentrations of the gas mixtures into and out of the animal chamber. In general, metabolic rates are calculated from steady-state conditions (i.e., animal's metabolic rate is assumed to be constant). To know the rates of oxygen consumed, one needs to know the location of the flow meter relative to the animal chamber (if positioned before the chamber, the flow meter is "upstream," if positioned after the chamber, the flow meter is "downstream"), and whether or not reactive gases are present (e.g., CO, water, methane, see inert gas).
For an open system with upstream flow meter, water (e.g., anhydrous calcium sulfate) and CO removed prior to the oxygen analyzer, a suitable equation is
For an open system with downstream flow meter, water and CO removed prior to the oxygen analyzer, a suitable equation is
where
*FR is the volumetric flow rate adjusted to STP (see Standard conditions for temperature and pressure)
*FO is the fractional amount of oxygen present in the incurrent air stream (the baseline or reference), and
*FO is the fractional amount of oxygen present in the excurrent air stream (what the animal has consumed relative to baseline per unit time).
For example, values for BMR of a 20 g mouse (Mus musculus) might be FR = 200 mL/min, and readings of fractional concentration of O from an oxygen analyzer are FO = 0.2095, FO = 0.2072. The calculated rate of oxygen consumption is 0.58 mL/min or 35 mL/hour. Assuming an enthalpy of combustion for O of 20.1 joules per milliliter, we would then calculate the heat production (and therefore metabolism) for the mouse as 703.5 J/h. | 1 | Biochemistry |
Succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC) is a heterobifunctional amine-to-sulfhydryl crosslinker, which contains two reactive groups at opposite ends: N-hydroxysuccinimide-ester and maleimide, reactive with amines and thiols respectively. SMCC is often used in bioconjugation to link proteins with other functional entities (fluorescent dyes, tracers, nanoparticles, cytotoxic agents). For example, a targeted anticancer agent – trastuzumab emtansine (antibody-drug conjugate containing an antibody trastuzumab chemically linked to a highly potent drug DM-1) – is prepared using SMCC reagent. | 1 | Biochemistry |
Mars Guy Fontana graduated with a Bachelor of Science followed by a Master of Science and then awarded a Doctor of Philosophy in the field of metallurgical engineering from the University of Michigan. He was known as a researcher/engineer who added to the field of knowledge in the fairly specialized area of corrosion and its various applications in engineering – corrosion engineering. As well as writing numerous papers he wrote the textbook Corrosion Engineering which was first published in 1967 ; there have been a number of updated editions since then. This book has been used as the primary textbook and recommended reading for at least one highly ranked University masters degree course. In his lifetime he wrote many papers in various scientific and engineering journals/periodicals. He also authored Corrosion: A Compilation.
In the late 1940s, he was given the chair in the Corrosion Center at Ohio State University. At the time it was the largest university corrosion research department in the United States. He combined the disciplines of engineering design, Material Science and Corrosion so they could be viewed together.
His contribution at the university was of such significance that he has a building named after him - the Fontana Laboratories. He also has a professorship named after him. | 8 | Metallurgy |
The simple cubic Bravais lattice, with cubic primitive cell of side , has for its reciprocal a simple cubic lattice with a cubic primitive cell of side (or in the crystallographer's definition). The cubic lattice is therefore said to be self-dual, having the same symmetry in reciprocal space as in real space. | 3 | Analytical Chemistry |
Transformations are often seen to follow a characteristic s-shaped, or sigmoidal, profile where the transformation rates are low at the beginning and the end of the transformation but rapid in between.
The initial slow rate can be attributed to the time required for a significant number of nuclei of the new phase to form and begin growing. During the intermediate period the transformation is rapid as the nuclei grow into particles and consume the old phase while nuclei continue to form in the remaining parent phase.
Once the transformation approaches completion, there remains little untransformed material for further nucleation, and the production of new particles begins to slow. Additionally, the previously formed particles begin to touch one another, forming a boundary where growth stops. | 3 | Analytical Chemistry |
The Geochemical Journal is a peer-reviewed open-access scientific journal covering all aspects of geochemistry and cosmochemistry. It is published by the Geochemical Society of Japan and the editor-in-chief is Katsuhiko Suzuki. | 9 | Geochemistry |
Pancratistatin is thought to have potential as a basis for the development of new pharmaceuticals, particularly in the field of cancer treatment. | 0 | Organic Chemistry |
Silicon microcantilevers are used for both contact AFM and nc-AFM. Silicon microcantilevers are produced from etching small (~100×10×1 μm) rectangular, triangular, or V-shaped cantilevers from silicon nitride. Originally they were produced without integrated tips and metal tips had to be evaporated on, later a method was found to integrate the tips into the cantilever fabrication process.
nc-AFM cantilevers tend to have a higher stiffness, ~40 N/m, and resonant frequency, ~200 kHz, than contact AFM cantilevers (with stiffnesses ~0.2 N/m and resonant frequencies ~15 kHz). The reason for the higher stiffness is stop the probe snapping to contact with the surface due to Van der Waals forces.
Silicon microcantilever tips can be coated for specific purposes, such as a ferromagnetic coatings for use as a magnetic force microscope. By doping the silicon, the sensor can be made conductive to allow simultaneous scanning tunneling microscopy (STM) and nc-AFM operation. | 6 | Supramolecular Chemistry |
An assay (analysis) is never an isolated process, as it must be accompanied with pre- and post-analytic procedures. Both the communication order (the request to perform an assay plus related information) and the handling of the specimen itself (the collecting, documenting, transporting, and processing done before beginning the assay) are pre-analytic steps. Similarly, after the assay is completed the results must be documented, verified and communicated—the post-analytic steps. As with any multi-step information handling and transmission system, the variation and errors in reporting final results entail not only those intrinsic to the assay itself but also those occurring in the pre-analytic and post-analytic procedures.
While the analytic steps of the assay itself get much attention, it is those that get less attention of the chain of users—the pre-analytic and post-analytic procedures—that typically accumulate the most errors; e.g., pre-analytic steps in medical laboratory assays may contribute 32–75% of all lab errors.
Assays can be very diverse, but generally involve the following general steps:
# Sample processing and manipulation in order to selectively present the target in a discernible or measurable form to a discrimination/identification/detection system. It might involve a simple centrifugal separation or washing or filtration or capture by some form of selective binding or it may even involve modifying the target e.g. epitope retrieval in immunological assays or cutting down the target into pieces e.g. in Mass Spectrometry. Generally there are multiple separate steps done before an assay and are called preanalytic processing. But some of the manipulations may be inseparable part of the assay itself and will not thus be considered pre-analytic.
# Target-specific discrimination/identification principle: to discriminate from background (noise) of similar components and specifically identify a particular target component ("analyte") in a biological material by its specific attributes. (e.g. in a PCR assay a specific oligonucleotide primer identifies the target by base pairing based on the specific nucleotide sequence unique to the target).
# Signal (or target) amplification system: The presence and quantity of that analyte is converted into a detectable signal generally involving some method of signal amplification, so that it can be easily discriminated from noise and measured - e.g. in a PCR assay among a mixture of DNA sequences only the specific target is amplified into millions of copies by a DNA polymerase enzyme so that it can be discerned as a more prominent component compared to any other potential components. Sometimes the concentration of the analyte is too large and in that case the assay may involve sample dilution or some sort of signal diminution system which is a negative amplification.
# Signal detection (and interpretation) system: A system of deciphering the amplified signal into an interpretable output that can be quantitative or qualitative. It can be visual or manual very crude methods or can be very sophisticated electronic digital or analog detectors.
#Signal enhancement and noise filtering may be done at any or all of the steps above. Since the more downstream a step/process during an assay, the higher the chance of carrying over noise from the previous process and amplifying it, multiple steps in a sophisticated assay might involve various means of signal-specific sharpening/enhancement arrangements and noise reduction or filtering arrangements. These may simply be in the form of a narrow band-pass optical filter, or a blocking reagent in a binding reaction that prevents nonspecific binding or a quenching reagent in a fluorescence detection system that prevents "autofluorescence" of background objects. | 1 | Biochemistry |
Many coordination complexes catalyze electrochemical reactions, but only heterogeneous catalysts are of commercial value. | 7 | Physical Chemistry |
Since late 2000s, propanephosphonic acid anhydride, sold commercially under various names such as "T3P", has become a useful reagent for amide bond formation in commercial applications. It converts the oxygen of the carboxylic acid into a leaving group, whose peptide-coupling byproducts are water-soluble and can be easily washed away. In a performance comparison between propanephosphonic acid anhydride and other peptide coupling reagents for the preparation of a nonapeptide drug, it was found that this reagent was superior to other reagents with regards to yield and low epimerization. | 1 | Biochemistry |
NMR spectroscopy has been utilized for the analysis of biological samples since the 1980s, and can be used as an effective technique for the identification and quantification of both known and unknown metabolites. For details on the principles of this technique, see NMR spectroscopy. In pharmacometabolomics analyses, NMR is advantageous because minimal sample preparation is required. Isolated patient samples typically include blood or urine due to their minimally-invasive acquisition, however, other fluid types and solid tissue samples have also been studied with this approach. Due to the minimal preparation of samples before analysis, samples can be potentially fully recovered following NMR analysis (If samples are kept refrigerated to avoid degradation). This permits samples to be repeatedly analysed with extremely high levels of reproducibility, as well as maintaining precious patient samples for an alternative analysis. The high reproducibility and precision of NMR, coupled with relatively fast processing time (greater than 100 samples per day), makes this process a relatively high-throughput form of sample analysis. One disadvantage of this technique is the relatively poor metabolite detection sensitivity compared to MS-based analysis, leading to a requirement for greater initial sample volume. Furthermore, the initial instrument costs are extremely high, for both NMR and MS equipment. | 1 | Biochemistry |
Although MRM has been used extensively in metabolomics and proteomics, its high sensitivity and linear response over a wide dynamic range make it especially suited for glycan biomarker research and discovery. MRM is performed on a triple quadrupole (QqQ) instrument, which is set to detect a predetermined precursor ion in the first quadrupole, a fragmented in the collision quadrupole, and a predetermined fragment ion in the third quadrupole. It is a non-scanning technique, wherein each transition is detected individually and the detection of multiple transitions occurs concurrently in duty cycles. This technique is being used to characterize the immune glycome.
Table 1: Advantages and disadvantages of mass spectrometry in glycan analysis | 0 | Organic Chemistry |
As with other cycloaddition reactions of a 1,3-dipole with a π-system, 1,3-dipolar cycloaddition using an azomethine ylide is a six-electron process. According to the Woodward–Hoffmann rules, this addition is suprafacial with respect to both the dipole and dipolarophile. The reaction is generally viewed as concerted, in which the two carbon-carbon bonds are being formed at the same time, but asynchronously. However, depending on the nature of the dipole and dipolarophile, diradical or zwitterionic intermediates are possible. The endo product is generally favored, as in the isoelectronic Diels–Alder reaction. In these reactions, the azomethine ylide is typically the HOMO, and the electron-deficient dipolarophile the LUMO, although cycloaddition reactions with unactivated π-systems are known to occur, especially when the cyclization is intramolecular. For a discussion of frontier molecular orbital theory of 1,3-dipolar cycloadditions, see 1,3-dipolar cycloaddition#Frontier molecular orbital theory.
1,3-Dipolar cycloaddition reactions of azomethine ylides commonly use alkenes or alkynes as dipolarophiles, to form pyrrolidines or pyrrolines, respectively. A reaction of an azomethine ylide with an alkene is shown above, and results in a pyrrolidine. This kind of reactions can be used to synthesis Ullazine. While dipolarophiles are typically α,β-unsaturated carbonyl compounds, there have been many recent advances in developing new types of dipolarophiles.
When the dipole and dipolarophile are part of the same molecule, an intramolecular cyclization reaction can lead to a polycyclic product of considerable complexity. If the dipolarophile is tethered to a carbon of the dipole, a fused bicycle is formed. If it is tethered to the nitrogen, a bridged structure results. The intramolecular nature of the reaction can also be useful in that regioselectivity is often constrained. Another advantage to intramolecular reactions is that the dipolarophile need not be electron-deficient—many examples of cyclization reactions with electron-rich, alkyl-substituted dipolarophiles have been reported, including the synthesis of martinellic acid shown below. | 0 | Organic Chemistry |
Reverse cholesterol transport is a multi-step process resulting in the net movement of cholesterol from peripheral tissues back to the liver first via entering the lymphatic system, then the bloodstream.
Cholesterol from non-hepatic peripheral tissues is transferred to HDL by the ABCA1 (ATP-binding cassette transporter). Apolipoprotein A1 (ApoA-1), the major protein component of HDL, acts as an acceptor, and the phospholipid component of HDL acts as a sink for the mobilised cholesterol.
The cholesterol is converted to cholesteryl esters by the enzyme LCAT (lecithin-cholesterol acyltransferase).
The cholesteryl esters can be transferred, with the help of CETP (cholesterylester transfer protein) in exchange for triglycerides, to other lipoproteins (such as LDL and VLDL), and these lipoproteins can be taken up by secreting unesterified cholesterol into the bile or by converting cholesterol to bile acids.
Adiponectin induces ABCA1-mediated reverse cholesterol transport from macrophages by activation of PPAR-γ and LXRα/β.
Uptake of HDL is mediated by hepatic lipase, a special form of lipoprotein lipase found only in the liver. Hepatic lipase activity is increased by androgens and decreased by estrogens, which may account for higher concentrations of HDL in women.
Discoidal (Nascent) HDL:
Initially, HDL is discoidal in shape because it lacks esterified cholesterol but as it keeps accumulating free cholesterol in it, the enzyme LCAT keeps esterifying the free cholesterol.
When the HDL molecule is cholesterol rich, its shape is changed into more spherical and it becomes less dense (HDL 2). This is carried to the liver to release all the esterified cholesterol into the liver. | 1 | Biochemistry |
A similar phenomenon occurs in many other systems. Another example is vibrational modes in a liquid. Each molecule of the liquid has vibrational modes, and the vibrational frequency is influenced by the positions of nearby molecules. However, if the nearby molecules reorient and move around fast enough, the vibration will essentially occur at an averaged frequency, and therefore have a smaller linewidth. For example, simulations suggest that the OH stretch vibration linewidth in liquid water is 30% smaller than it would be without this motional narrowing effect. | 7 | Physical Chemistry |
Pairs of octahedra can be fused in a way that preserves the octahedral coordination geometry by replacing terminal ligands with bridging ligands. Two motifs for fusing octahedra are common: edge-sharing and face-sharing. Edge- and face-shared bioctahedra have the formulas [ML(μ-L)] and ML(μ-L), respectively. Polymeric versions of the same linking pattern give the stoichiometries [ML(μ-L)] and [M(μ-L)], respectively.
The sharing of an edge or a face of an octahedron gives a structure called bioctahedral. Many metal pentahalide and pentaalkoxide compounds exist in solution and the solid with bioctahedral structures. One example is niobium pentachloride. Metal tetrahalides often exist as polymers with edge-sharing octahedra. Zirconium tetrachloride is an example. Compounds with face-sharing octahedral chains include MoBr, RuBr, and TlBr. | 4 | Stereochemistry |
Above the theoretical shear strength of the material, a type of defect-less flow can still occur, shearing the material. Dislocation motion through glide (any temperature) or dislocation creep (at high temperatures) is a typical mechanism found at high stresses in deformation maps. | 8 | Metallurgy |
The Wien effect is the experimentally-observed increase in ionic mobility or conductivity of electrolytes at very high gradient of electrical potential. A theoretical explanation has been proposed by Lars Onsager.
A related phenomenon is known as the Second Wien Effect or the dissociation field effect, and it involves increased dissociation constants of weak acids at high electrical gradients. The dissociation of weak chemical bases is unaffected.
The effects are important at very high electrical fields (10 – 10 V/m), like those observed in electrical double layers at interfaces or at the surfaces of electrodes in electrochemistry.
More generally, the electric field effect (directly, through space rather than through chemical bonds) on chemical behaviour of systems (e.g., on reaction rates) is known as the field effect or the direct effect.
The terms are named after Max Wien. | 7 | Physical Chemistry |
When the mud layer is exposed at the tidal fringe, mudflats result affording a unique ecotone that affords numerous shorebird species a safe feeding and resting habitat. Because the muds function much like quicksand, heavier mammalian predators not only cannot gain traction for pursuit, but would actually become trapped in the sinking muds. The muds are also an important substrate for primary marsh productivity including eelgrass, cordgrass and pickleweed. Furthermore, they are home to a large variety of molluscs and estuarine arthropods. Richardson Bay, for example, exposes one third of its areal extent as mudflat at low tide, which hosts a productive eelgrass expanse and also a large shorebird community.
Mammals such as the Harbor seal may use mudflats to haul out of estuary waters; however, larger mammals such as humpback whales may become accidentally stranded at low tides. Note that normally humpback whales do not frequent estuaries containing mudflats, but at least one errant whale, publicized by the media as Humphrey the humpback whale, became stuck on a mudflat in San Francisco Bay at Sierra Point in Brisbane, California. | 2 | Environmental Chemistry |
ζ-Carotene (zeta-carotene) is a carotenoid. It is different from α-carotene and β-carotene because it is acyclic. ζ-Carotene is similar in structure to lycopene, but has an additional 4 hydrogen atoms. ζ-carotene can be used as an intermediate in forming β-carotene. A dehydrogenation reaction converts ζ-carotene into lycopene, which then can be transformed into β-carotene through the action of lycopene beta-cyclase. ζ-Carotene is a natural product found in Lonicera japonica and Rhodospirillum rubrum. | 1 | Biochemistry |
In hydrohalogenation, an alkene reacts with a dry hydrogen halide (HX) electrophile like hydrogen chloride () or hydrogen bromide () to form a mono-haloalkane. The double bond of the alkene is replaced by two new bonds, one with the halogen and one with the hydrogen atom of the hydrohalic acid. Markovnikov's rule states that under normal conditions, hydrogen is attached to the unsaturated carbon with the most hydrogen substituents. The rule is violated when neighboring functional groups polarize the multiple bond, or in certain additions of hydrogen bromide (addition in the presence of peroxides and the Wohl-Ziegler reaction) which occur by a free-radical mechanism.
Alkenes also react with halogens (X) to form haloalkanes with two neighboring halogen atoms in a halogen addition reaction. Alkynes react similarly, forming the tetrahalo compounds. This is sometimes known as "decolorizing" the halogen, since the reagent X is colored and the product is usually colorless and odorless. | 0 | Organic Chemistry |
A common example is NMR. In this process, the nuclear spin of an atom starts rotating, with the frequency of rotation proportional to the external magnetic field that the atom experiences. However, in an inhomogeneous medium, the magnetic field often varies from point to point (depending, for example, on the magnetic susceptibility of nearby atoms), so the frequency of nuclear spin rotation is different in different places. Therefore, when detecting the resonant rotation frequency, there is a linewidth (i.e., finite range of different frequencies) due to the variation in that resonant frequency from point to point. (This is called "inhomogeneous broadening".)
However, if the atoms are diffusing around the system, they will experience a higher magnetic field than average sometimes, and a lower magnetic field than average other times. Therefore, (in accordance with the central limit theorem), the time-averaged magnetic field experienced by an atom has less variation than the instantaneous magnetic field does. As a consequence, when detecting the resonant rotation frequency, the linewidth is smaller (narrower) than it would be if the atoms were stationary. This is the motional narrowing effect. | 7 | Physical Chemistry |
Armodafinil (trade name Nuvigil) is the enantiopure compound of the eugeroic modafinil (Provigil). It consists of only the (R)-(−)-enantiomer of the racemic modafinil. Armodafinil is produced by the pharmaceutical company Cephalon Inc. and was approved by the U.S. Food and Drug Administration (FDA) in June 2007. In 2016, the FDA granted Mylan rights for the first generic version of Cephalon's Nuvigil to be marketed in the U.S.
Because armodafinil has a longer half-life than modafinil does, it may be more effective at improving wakefulness in patients with excessive daytime sleepiness. | 4 | Stereochemistry |
Vacuum induction melting (VIM) utilizes electric currents to melt metal within a vacuum. The first prototype was developed in 1920. Induction heating induces eddy currents within conductors. Eddy currents create heating effects to melt the metal. Vacuum induction melting has been used in both the aerospace and nuclear industries. | 8 | Metallurgy |
Interannual variability on metabolic rates can be driven by extensive changes in the catchment or by directional and cyclical climate change and climate disturbances, such as the events associated with the El Niño Southern Oscillation (ENSO). Those changes in the catchment, air temperature, and precipitation between years affect metabolic rates by altering nutrient and organic matter inputs to the lake, light attenuation, mixing dynamics, and by direct temperature-dependence of metabolic processes.
The increase in precipitation increases external loading of organic matter, nutrients and sediments in lakes. Moreover, increased discharge events promoted by increased rainfall can also alter mixing dynamics and cause physical flushing of organisms. While lower precipitation associated with high evaporation rates also affects limnological conditions by reducing the water level and thereby increasing the concentration of nutrients and chlorophyll, as well as changing the thermal stability of aquatic environments. During warmer years, a stronger water column stability limits the inputs of nutrients and organic matter to the photic zone. In contrast, during colder years, a less stable water column enhances resuspension of the sediments and the inputs of nutrients and organic matter from deeper waters. This lowers light availability, while enhances nutrient and organic matter availability. Thus, the effects of differences in precipitation and temperature between years in metabolic rates will depend on the intensity and duration of these changes, and also in which factors are limiting GPP and ER in each water body.
In lakes with nutrients and organic matter limitation of GPP and ER, wetter years can enhance GPP and ER rates, due to higher inputs of nutrients and organic matter from the landscape. This will depend if the terrestrial inputs will be promptly available for the primary producers and heterotrophic communities or if it is going to enter the lake through deeper waters, in which metabolic processes are very low or non-existent. In this case, the inputs will only be available in the next water column mixing event. Thus, increases in metabolic rates due to rainfall depend also on the stratification and mixing dynamics, hydrology, and morphometry of the lake. On the other hand, drier years can also have enhanced GPP and ER rates if it is accompanied by lower water levels, which would lead to higher nutrients and organic matter concentrations. A lower water level is associated with a less stable water column and higher proximity with the sediments, thus increased inputs of nutrients and organic matter from deeper waters. Also, a reduction in water level through water evaporation leads to a concentration effect. In turn, during warmer years the water column is more stable, and the depth of the mixing layer is shallower, thus reducing internal inputs of nutrients and organic matter to the mixed layer. Metabolic rates, in this scenario, will be lower in the upper mixed layer. In lakes with a photic zone extending deeper than the mixed layer, metabolic rates will be higher in intermediated depths, coinciding with the deep chlorophyll maxima.
In lakes with primary production limited mostly by light availability, increases in rainfall could lead to lower light availability, associated with increased dissolved organic matter and total suspended matter. Consequently, increased rainfall would be associated with lower levels of GPP, which would reduce respiration rates associated with autochthonous production, leading to a decoupling of GPP and ER rates. In addition, increased allochthonous organic matter availability during wet years can lead to higher ER, and consequently leading the metabolic balance to be negative (NEP <0).
Changes in annual precipitation can also affect the spatial variability in metabolic rates within lakes. Williamson and collaborators, for example, found that, in a hyper-eutrophic reservoir in North America, the relative spatial variability in GPP and ER rates were higher in a dry year compared to a wet one. These suggest higher relevance of internal processes, such as internal loading, nutrient uptake, sedimentation, and resuspension, to metabolic rates during dry years. | 1 | Biochemistry |
The first ORF of L1 encodes a 500-amino acid, 40-kDa protein that lacks homology with any protein of known function. In vertebrates, it contains a conserved C-terminus domain and a highly variable coiled-coil N-terminus that mediates the formation of ORF1 trimeric complexes. ORF1 trimers have RNA-binding and nucleic acid chaperone activity that are necessary for retrotransposition. | 1 | Biochemistry |
The G3P is converted to 1,3-bisphosphoglycerate in the presence of enzyme glyceraldehyde-3-phosphate dehydrogenase (an oxido-reductase).
The aldehyde groups of the triose sugars are oxidised, and inorganic phosphate is added to them, forming 1,3-bisphosphoglycerate.
The hydrogen is used to reduce two molecules of NAD, a hydrogen carrier, to give NADH + H for each triose.
Hydrogen atom balance and charge balance are both maintained because the phosphate (P) group actually exists in the form of a hydrogen phosphate anion (HPO), which dissociates to contribute the extra H ion and gives a net charge of -3 on both sides. | 1 | Biochemistry |
A variety of defense mechanisms can lead to ecological escape from predators. Plants use chemical defenses in the form of secondary metabolites or allelochemicals. These allelochemicals inhibit the growth, behavior, and health of herbivores, allowing plants to escape. An example of a plant allelochemical are alkaloids that can inhibit protein synthesis in herbivores. Other forms of plant defense include mechanical defenses such as thigmonasty movements which have the plant leaves close in response to tactile stimulation. Indirect mechanisms plant include shedding of plant leaves so less leaves are available which deters herbivores, growth in locations in that are difficult to reach, and even mimicry. For organisms other than plants, examples of defense mechanisms allowing for escape include camouflage, aposematism, heightened senses and physical capabilities, and even defensive behaviors such as feigning death. An example of an organism using one of these defense mechanisms is the granular poison frog which defends itself through aposematism. It is important to understand that in order for escape and radiate coevolution to occur, it is necessary that the developed defense is novel rather than previously established.
Induced defense stemming from adaptive phenotypic plasticity may help a plant defend itself against multiple enemies. Phenotypic plasticity occurs when an organism undergoes an environmental change forcing a change altering its behavior, physiology, etc. These induced defenses allow for an organism to escape. | 1 | Biochemistry |
There are 2 regular complex apeirogons, sharing the vertices of the trihexagonal tiling. Regular complex apeirogons have vertices and edges, where edges can contain 2 or more vertices. Regular apeirogons p{q}r are constrained by: 1/p + 2/q + 1/r = 1. Edges have p vertices arranged like a regular polygon, and vertex figures are r-gonal.
The first is made of triangular edges, two around every vertex, second has hexagonal edges, two around every vertex. | 3 | Analytical Chemistry |
Secreted frizzled-related protein 1, also known as SFRP1, is a protein which in humans is encoded by the SFRP1 gene. | 1 | Biochemistry |
Normative mineralogy is a calculation of the composition of a rock sample that estimates the idealised mineralogy of a rock based on a quantitative chemical analysis according to the principles of geochemistry.
Normative mineral calculations can be achieved via either the CIPW Norm or the Barth-Niggli Norm (also known as the Cation Norm).
Normative calculations are used to produce an idealised mineralogy of a crystallized melt. First, a rock is chemically analysed to determine the elemental constituents. Results of the chemical analysis traditionally are expressed as oxides (e.g., weight percent Mg is expressed as weight percent MgO). The normative mineralogy of the rock then is calculated, based upon assumptions about the order of mineral formation and known phase relationships of rocks and minerals, and using simplified mineral formulas. The calculated mineralogy can be used to assess concepts such as silica saturation of melts.
Because the normative calculation is essentially a computation, it can be achieved via computer programs. | 9 | Geochemistry |
In laboratory settings, ELISA and immunodiffusion assays are most commonly used to detect levels of Anti-Ro/SSA antibodies in patient sera.
Antibodies specific to Ro52 are difficult to detect via laboratory testing. Their low detectability may be attributed to several factors: the antibodies are precipitin negative, lack antinuclear antibody (ANA) specific fluorescence staining patterns, and have a low signature in ELISA assays. Furthermore, Ro52 can be masked by Anti-Ro60 antibodies in lab tests that simultaneously assess the two antibodies. | 1 | Biochemistry |
Thermodynamic cycles may be used to model real devices and systems, typically by making a series of assumptions. simplifying assumptions are often necessary to reduce the problem to a more manageable form. For example, as shown in the figure, devices such a gas turbine or jet engine can be modeled as a Brayton cycle. The actual device is made up of a series of stages, each of which is itself modeled as an idealized thermodynamic process. Although each stage which acts on the working fluid is a complex real device, they may be modelled as idealized processes which approximate their real behavior. If energy is added by means other than combustion, then a further assumption is that the exhaust gases would be passed from the exhaust to a heat exchanger that would sink the waste heat to the environment and the working gas would be reused at the inlet stage.
The difference between an idealized cycle and actual performance may be significant. For example, the following images illustrate the differences in work output predicted by an ideal Stirling cycle and the actual performance of a Stirling engine:
As the net work output for a cycle is represented by the interior of the cycle, there is a significant difference between the predicted work output of the ideal cycle and the actual work output shown by a real engine. It may also be observed that the real individual processes diverge from their idealized counterparts; e.g., isochoric expansion (process 1-2) occurs with some actual volume change. | 7 | Physical Chemistry |
Filiform corrosion may be considered as a type of crevice corrosion and is sometimes seen on metals coated with an organic coating (paint). Filiform corrosion is unusual in that it does not weaken or destroy the integrity of the metal but only affects the surface appearance. | 8 | Metallurgy |
Currently there are no existing compounds that can mimic the peptide bond of proline to other amino acids while maintaining only a cis or trans configuration because most mimics found will eventually change from one isomer to another. This makes research on the direct effect of each of the isomers on biological mechanisms more difficult. Also, the actual isomerization of proline is a slow process, meaning that any studying of the effects of the different isomers of proline takes a large amount of time to complete. | 4 | Stereochemistry |
Gay-Lussacs law usually refers to Joseph-Louis Gay-Lussacs law of combining volumes of gases, discovered in 1808 and published in 1809. However, it sometimes refers to the proportionality of the volume of a gas to its absolute temperature at constant pressure. The latter law was published by Gay-Lussac in 1802, but in the article in which he described his work, he cited earlier unpublished work from the 1780s by Jacques Charles. Consequently, the volume-temperature proportionality is usually known as Charles's Law. | 7 | Physical Chemistry |
A symmetry of a Euclidean graph is an isometry of the underlying Euclidean space whose restriction to the graph is an automorphism; the symmetry group of the Euclidean graph is the group of its symmetries. A Euclidean graph in three-dimensional Euclidean space is periodic if there exist three linearly independent translations whose restrictions to the net are symmetries of the net. Often (and always, if one is dealing with a crystal net), the periodic net has finitely many orbits, and is thus uniformly discrete in that there exists a minimum distance between any two vertices.
The result is a three-dimensional periodic graph as a geometric object.
The resulting crystal net will induce a lattice of vectors so that given three vectors that generate the lattice, those three vectors will bound a unit cell, i.e. a parallelepiped which, placed anywhere in space, will enclose a fragment of the net that repeats in the directions of the three axes. | 3 | Analytical Chemistry |
In physical organic chemistry, a free-energy relationship or Gibbs energy relation relates the logarithm of a reaction rate constant or equilibrium constant for one series of chemical reactions with the logarithm of the rate or equilibrium constant for a related series of reactions. Free energy relationships establish the extent at which bond formation and breakage happen in the transition state of a reaction, and in combination with kinetic isotope experiments a reaction mechanism can be determined. Free energy relationships are often used to calculate equilibrium constants since they are experimentally difficult to determine.
The most common form of free-energy relationships are linear free-energy relationships (LFER). The Brønsted catalysis equation describes the relationship between the ionization constant of a series of catalysts and the reaction rate constant for a reaction on which the catalyst operates. The Hammett equation predicts the equilibrium constant or reaction rate of a reaction from a substituent constant and a reaction type constant. The Edwards equation relates the nucleophilic power to polarisability and basicity. The Marcus equation is an example of a quadratic free-energy relationship (QFER).
IUPAC has suggested that this name should be replaced by linear Gibbs energy relation, but at present there is little sign of acceptance of this change.
The area of physical organic chemistry which deals with such relations is commonly referred to as linear free-energy relationships. | 7 | Physical Chemistry |
The yeast Saccharomyces cerevisiae is a simple single-celled eukaryote with both a diploid and haploid mode of existence. The mating of yeast only occurs between haploids, which can be either the a or α (alpha) mating type and thus display simple sexual differentiation. Mating type is determined by a single locus, MAT, which in turn governs the sexual behaviour of both haploid and diploid cells. Through a form of genetic recombination, haploid yeast can switch mating type as often as every cell cycle. | 1 | Biochemistry |
By modifying the amino acid sequence of sunflower trypsin inhibitor, more specifically, sunflower trypsin inhibitor-1 (SFTI-1), researchers have been able to develop synthetic serine protease inhibitors that have specificity and improved inhibitory activity towards certain serine proteases that are found in the human body, such as tissue kallikreins and human matriptase-1. For instance, researchers from the Institute of Child Health and the Department of Chemistry of the University College London, have created two SFTI-1 analogs (I10G and I10H) by substituting residue 10 of SFTI-1 (isoleucine, I) with glycine (G) and histidine (H), respectively. Out of the two analogs, SFTI-I10H was found to be the more potent KLK5 inhibitor. Another group of researchers from the previously mentioned institute and department of the University College London, conducted further research on the development of synthetic kallikrein inhibitors by modifying the amino acid sequence of SFTI-I10H. Out of the six SFTI-I10H variants that were constructed by modifying SFTI-I10H, the first and second variant (K5R_I10H and I10H_F12W) demonstrated improved KLK5 inhibition and the sixth variant (K5R_I10H_F12W) showed dual-inhibition of KLK5 and KLK7, improved KLK5 inhibition potency, and specificity for KLK5 and KLK14. The first variant (K5R_I10H) was made by replacing residue 5 of SFTI-I10H (lysine, K) with arginine (R), and in order to get the second variant (I10H_F12W) residue 12 (phenylalanine, F) was replaced with tryptophan (W). Lastly, the sixth variant (K5R_I10H_F12W) was developed by combining the amino acid substitutions of the first and second variants.
Moreover, researchers from the Clemens-Schöpf Institute of Organic Chemistry and Biochemistry and Helmholtz-Institute for Pharmaceutical Research Saarland, developed potent synthetic human matriptase-1 inhibitors based on a different SFTI-1 variant, SDMI-1. SFTI-1 derived matriptase inhibitor-1 (SDMI-1) was previously developed by replacing residue 10 of SFTI-1 (isoleucine, I) with arginine (R) and residue 12 (phenylalanine, F) with histidine (H). Further modifications of SDMI-1 resulted in synthetic matriptase-1 inhibitors with improved inhibitory activity, matriptase binding, and inhibition potency. The SDMI-1 variant that resulted in enhanced inhibitory activity was developed by replacing residue 1 of SDMI-1 (glycine, G) with lysine (K) and by keeping it as a monocyclic structure. The SDMI-1 variant that resulted in improved matriptase binding was created by using the same amino acid substitutions of the previously mentioned SDMI-1 variant and by attaching a bulky fluorescein moiety to the side chain of lysine. Lastly, the SDMI-1 variant that had enhanced inhibition potency was developed by applying the same amino acid substitutions of the previous variants, cleaving the proline-aspartic acid sequence found at the C-terminus (PD-OH), and by making it a bicyclic compound via tail-to-side-chain cyclization. | 1 | Biochemistry |
"Upper bainite" forms around 400–550 °C in sheaves. These sheaves contain several laths of ferrite that are approximately parallel to each other and which exhibit a Kurdjumov-Sachs relationship with the surrounding austenite, though this relationship degrades as the transformation temperature is lowered. The ferrite in these sheaves has a carbon concentration below 0.03%, resulting in carbon-rich austenite around the laths.
The amount of cementite that forms between the laths is based on the carbon content of the steel. For a low carbon steel, typically discontinuous "stringers" or small particles of cementite will be present between laths. For steel with a higher carbon content, the stringers become continuous along the length of the adjacent laths. | 8 | Metallurgy |
Galanin-like peptide (GALP) is a neuropeptide present in humans and other mammals. It is a 60-amino acid polypeptide produced in the arcuate nucleus of the hypothalamus and the posterior pituitary gland. It is involved in the regulation of appetite and may also have other roles such as in inflammation, sex behavior, and stress.
Findings additionally suggest that GALP could play a function in energy metabolism due to its ability to maintain continual activation of the sympathetic nervous system (SNS) via thermogenesis, which refers to the production of heat within living organisms. In addition, the administration of GALP directly into the brain leads to a reduction in the secretion of thyroid-stimulating hormone (TSH), which indicates the involvement of GALP in the neuroendocrine regulation of the hypothalamic-pituitary-thyroid (HPT) axis, and further adding to the evidence of the role of GALP in energy homeostasis. | 1 | Biochemistry |
If the natural log is taken on both sides of the disequilibrium ratio and both sides is multiplied by RT, one obtains:
However, is the standard free energy, so that is the free energy of the reaction.
This shows that the free energy of a reaction is just an alternative way of expressing the disequilibrium ratio and as such gives a more intuitive interpretation of free energy. That is if the free energy for a reaction is less than zero then it indicates that and hence , i.e the net reaction rate is from left to right. | 7 | Physical Chemistry |
in chemistry, sulfoxidation refers to two distinct reactions.
In one meaning, sulfoxidation refers to the reaction of alkanes with a mixture of sulfur dioxide and oxygen. This reaction is employed industrially to produce alkyl sulfonic acids, which are used as surfactants. The reaction requires UV-radiation.
The reaction favors secondary positions in accord with its free-radical mechanism. Mixtures are produced. Semiconductor-sensitized variants have been reported.
Sulfoxidation can also refer to the oxidation of a thioether to a sulfoxide.
A typical source of "O" is hydrogen peroxide. | 5 | Photochemistry |
Base excess is defined as the amount of strong acid that must be added to each liter of fully oxygenated blood to return the pH to 7.40 at a temperature of 37°C and a pCO of . A base deficit (i.e., a negative base excess) can be correspondingly defined by the amount of strong base that must be added.
A further distinction can be made between actual and standard base excess: actual base excess is that present in the blood, while standard base excess is the value when the hemoglobin is at 5 g/dl. The latter gives a better view of the base excess of the entire extracellular fluid.
Base excess (or deficit) is one of several values typically reported with arterial blood gas analysis that is derived from other measured data.
The term and concept of base excess were first introduced by Poul Astrup and Ole Siggaard-Andersen in 1958. | 1 | Biochemistry |
In addition to the Nobel Prize, his awards and distinctions include Sloan Fellow (1969); Fellow of American Academy of Arts and Sciences (1975); Fellow Am. Phys. Soc. (1976); Guggenheim Fellow (1977); Member National Academy of Sciences (1979); Member International Academy of Science, Munich, Member Academia Sinica (1980); E.O. Lawrence Award (1981); Miller Professor, Berkeley (1981); Fairchild Distinguished Scholar (1983); Harrison Howe Award (1983); Peter Debye Award (1986); National Medal of Science (1986); Golden Plate Award of the American Academy of Achievement (1987) and Faraday Lectureship Prize (1992). Yuan Tseh Lee was awarded the Othmer Gold Medal in 2008 in recognition of his outstanding contributions to progress in chemistry and science. His post-doctoral supervisor and fellow Nobel Laureate Dudley Herschbach congratulated Lee. In 2019 Yuan T. Lee was also awarded the Fray International Sustainability Award by FLOGEN Star Outreach at SIPS 2019. | 7 | Physical Chemistry |
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