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The simplest non-Kekulé molecules are biradicals. A biradical is an even-electron chemical compound with two free radical centres which act independently of each other. They should not be confused with the more general class of diradicals.
One of the first biradicals was synthesized by Wilhelm Schlenk in 1915 following the same methodology as Moses Gomberg's triphenylmethyl radical. The so-called Schlenk-Brauns hydrocarbons are:
Eugene Müller, with the aid of a Gouy balance, established for the first time that these compounds are paramagnetic with a triplet ground state.
Another classic biradical was synthesised by Aleksei Chichibabin in 1907. Other classical examples are the biradicals described by Yang in 1960 and by Coppinger in 1962. | 0 | Organic Chemistry |
Most simply, the greater the steric hindrance the more difficult it is for reactions to take place, and the radical form is favored by default. For example, compare the hydrogen-abstracted form of N-hydroxypiperidine to the molecule TEMPO. TEMPO, or (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl, is too sterically hindered by the additional methyl groups to react making it stable enough to be sold commercially in its radical form. N-Hydroxypiperidine, however, does not have the four methyl groups to impede the way of a reacting molecule so the structure is unstable. | 2 | Environmental Chemistry |
If one dimension is very large compared to the others, the principal strain in the direction of the longest dimension is constrained and can be assumed as constant, that means there will be effectively zero strain along it, hence yielding a plane strain condition (Figure 7.2). In this case, though all principal stresses are non-zero, the principal stress in the direction of the longest dimension can be disregarded for calculations. Thus, allowing a two dimensional analysis of stresses, e.g. a dam analyzed at a cross section loaded by the reservoir.
The corresponding strain tensor is:
and the corresponding stress tensor is:
in which the non-zero term arises from the Poisson's effect. However, this term can be temporarily removed from the stress analysis to leave only the in-plane terms, effectively reducing the analysis to two dimensions. | 8 | Metallurgy |
Dinoflagellate luciferin is a chlorophyll derivative (i. e. a tetrapyrrole) and is found in some dinoflagellates, which are often responsible for the phenomenon of nighttime glowing waves (historically this was called phosphorescence, but is a misleading term). A very similar type of luciferin is found in some types of euphausiid shrimp. | 1 | Biochemistry |
Data recording in a 3D optical storage medium requires that a change take place in the medium upon excitation. This change is generally a photochemical reaction of some sort, although other possibilities exist. Chemical reactions that have been investigated include photoisomerizations, photodecompositions and photobleaching, and polymerization initiation. Most investigated have been photochromic compounds, which include azobenzenes, spiropyrans, stilbenes, fulgides, and diarylethenes. If the photochemical change is reversible, then rewritable data storage may be achieved, at least in principle. Also, MultiLevel Recording, where data is written in "grayscale" rather than as "on" and "off" signals, is technically feasible. | 5 | Photochemistry |
The term "topochemistry" was first introduced by Kohlschütter in 1919, referring to the chemical reactions driven by the molecular alignments within the crystal. The prefix "topo" came from the Greek word "topos", which means "site". These reactions quickly draw people's attention because of their high conversion as well as solvent/catalyst-free nature. However, the early studies were usually serendipitous.
In the 1960s, Schmidts work on [2+2] photodimerization of cinnamic acids established the systematic approach to study the topochemical reactions. They proposed that only double bonds adopting coplanar and parallel orientation within a distance of 3.5-4.2 Å could react with each other in the crystal lattice. This empirical rule was later referred to as Schmidts criteria.
[2+2] cycle addition and diacetylene polymerization are among the early examples of topochemical polymerization. As shown in the figure, the formation of 1,3-diphenyl substituted cyclobutane derivatives was first studied in detail by Hasegawa and his coworkers in 1967. A series of similar monomers had also been studied by them. In 1969, the 1,4-addition polymerization of diacetylene was confirmed by Wegner and his coworkers. Restricted by the experimental condition, early researchers of topochemical polymerization usually characterized the reaction process and product with traditional chemical methods. The development of modern analysis technology such as single-crystal X-ray diffraction greatly facilitated the systematic study of topochemical polymerization and kept the popularity till these days. | 7 | Physical Chemistry |
Kristi Lynn Kiick is the Blue and Gold Distinguished Professor of Materials Science and Engineering at the University of Delaware. She studies polymers, biomaterials and hydrogels for drug delivery and regenerative medicine. She is a Fellow of the American Chemical Society, the American Institute for Medical and Biological Engineering, and of the National Academy of Inventors. She served for nearly eight years as the deputy dean of the college of engineering at the University of Delaware. | 6 | Supramolecular Chemistry |
In polymer chemistry, chain termination is any chemical reaction that ceases the formation of reactive intermediates in a chain propagation step in the course of a polymerization, effectively bringing it to a halt. | 7 | Physical Chemistry |
There has been a growing interest in the application of IC in the analysis of pharmaceutical drugs. IC is used in different aspects of product development and quality control testing. For example, IC is used to improve stabilities and solubility properties of pharmaceutical active drugs molecules as well as used to detect systems that have higher tolerance for organic solvents. IC has been used for the determination of analytes as a part of a dissolution test. For instance, calcium dissolution tests have shown that other ions present in the medium can be well resolved among themselves and also from the calcium ion. Therefore, IC has been employed in drugs in the form of tablets and capsules in order to determine the amount of drug dissolve with time. IC is also widely used for detection and quantification of excipients or inactive ingredients used in pharmaceutical formulations. Detection of sugar and sugar alcohol in such formulations through IC has been done due to these polar groups getting resolved in ion column. IC methodology also established in analysis of impurities in drug substances and products. Impurities or any components that are not part of the drug chemical entity are evaluated and they give insights about the maximum and minimum amounts of drug that should be administered in a patient per day. | 3 | Analytical Chemistry |
Without any loss of generality, we shall consider the study of the effective conductivity (which can be either dc or ac) for a system made up of spherical multicomponent inclusions with different arbitrary conductivities. Then the Bruggeman formula takes the form: | 7 | Physical Chemistry |
Methyl tert-butyl ether (MTBE), also known as tert-butyl methyl ether, is an organic compound with a structural formula (CH)COCH. MTBE is a volatile, flammable, and colorless liquid that is sparingly soluble in water. Primarily used as a fuel additive, MTBE is blended into gasoline to increase its octane rating and knock resistance, and reduce unwanted emissions. | 2 | Environmental Chemistry |
*A commercial source for the cyanide group is diethylaluminum cyanide which can be prepared from triethylaluminium and HCN. It has been used in nucleophilic addition to ketones. For an example of its use see: Kuwajima Taxol total synthesis
* Cyanide ions facilitate the coupling of dibromides. Reaction of α,α′-dibromoadipic acid with sodium cyanide in ethanol yields the cyano cyclobutane:
* Aromatic nitriles can be prepared from base hydrolysis of trichloromethyl aryl ketimines () in the Houben-Fischer synthesis
* Nitriles can be obtained from primary amines via oxidation. Common methods include the use of potassium persulfate, Trichloroisocyanuric acid, or anodic electrosynthesis.
* α-Amino acids form nitriles and carbon dioxide via various means of oxidative decarboxylation. Henry Drysdale Dakin discovered this oxidation in 1916.
* From aryl carboxylic acids (Letts nitrile synthesis) | 0 | Organic Chemistry |
All influenza A virus strains need sialic acid to connect with cells. There are different forms of sialic acids which have different affinity with influenza A virus variety. This diversity is an important fact that determines which species can be infected. When a certain influenza A virus is recognized by a sialic acid receptor the cell tends to endocytose the virus so the cell becomes infected. | 0 | Organic Chemistry |
HMB is sold as an over-the-counter dietary supplement in the free acid form, β-hydroxy β-methylbutyric acid (HMB-FA), and as a monohydrated calcium salt of the conjugate base, calcium monohydrate (HMB-Ca, CaHMB). Since only a small fraction of HMB's metabolic precursor, , is metabolized into HMB, pharmacologically active concentrations of the compound in blood plasma and muscle can only be achieved by supplementing HMB directly. A healthy adult produces approximately 0.3 grams per day, while supplemental HMB is usually taken in doses of grams per day. HMB is sold at a cost of about per month when taken in doses of 3 grams per day. HMB is also contained in several nutritional products and medical foods marketed by Abbott Laboratories (e.g., certain formulations of Ensure and Juven), and is present in insignificant quantities in certain foods, such as alfalfa, asparagus, avocados, cauliflower, grapefruit, and catfish. | 1 | Biochemistry |
Embedded in the thylakoid membranes are important protein complexes which carry out the light reactions of photosynthesis. Photosystem II and photosystem I contain light-harvesting complexes with chlorophyll and carotenoids that absorb light energy and use it to energize electrons. Molecules in the thylakoid membrane use the energized electrons to pump hydrogen ions into the thylakoid space, decreasing the pH and turning it acidic. ATP synthase is a large protein complex that harnesses the concentration gradient of the hydrogen ions in the thylakoid space to generate ATP energy as the hydrogen ions flow back out into the stroma—much like a dam turbine.
There are two types of thylakoids—granal thylakoids, which are arranged in grana, and stromal thylakoids, which are in contact with the stroma. Granal thylakoids are pancake-shaped circular disks about 300–600 nanometers in diameter. Stromal thylakoids are helicoid sheets that spiral around grana. The flat tops and bottoms of granal thylakoids contain only the relatively flat photosystem II protein complex. This allows them to stack tightly, forming grana with many layers of tightly appressed membrane, called granal membrane, increasing stability and surface area for light capture.
In contrast, photosystem I and ATP synthase are large protein complexes which jut out into the stroma. They can't fit in the appressed granal membranes, and so are found in the stromal thylakoid membrane—the edges of the granal thylakoid disks and the stromal thylakoids. These large protein complexes may act as spacers between the sheets of stromal thylakoids.
The number of thylakoids and the total thylakoid area of a chloroplast is influenced by light exposure. Shaded chloroplasts contain larger and more grana with more thylakoid membrane area than chloroplasts exposed to bright light, which have smaller and fewer grana and less thylakoid area. Thylakoid extent can change within minutes of light exposure or removal. | 5 | Photochemistry |
Since all TOC analyzers only actually measure total carbon, TOC analysis always requires some accounting for the inorganic carbon that is always present. One analysis technique involves a two-stage process commonly referred to as TOC differential method. It measures the amount of inorganic carbon (IC) evolved from an acidified aliquot of a sample and also the amount of total carbon (TC) present in the sample. TOC is calculated by subtraction of the IC value from the TC of the sample. Another method directly measures TOC in the sample by acidifying the sample to a pH value of two or less to release the CO gas by decomposition of the carbonates and vent these gases to the air by a purge step. The remaining non-purgeable organic carbon (NPOC) contained in the liquid aliquot is then oxidized releasing the CO gases. These gases are then sent to the detector for measurement. This method is also referred to as the direct TOC method. A further variant employs acidification of the sample to evolve carbon dioxide and measuring it as inorganic carbon (IC), then oxidizing and measuring the remaining non-purgeable organic carbon (NPOC). This is called TIC-NPOC analysis. TC oxidizes in a combustion chamber at 1000 degrees Celsius; if no supporting catalyst is used to allow full combustion at temperatures lower than 1000 degrees C; while the combustion chamber for IC heats only to 150 degrees Celsius. The reason for this is because inorganic is decomposed at lower temperatures than organic carbons.
Whether the analysis of TOC is by TC-IC or NPOC methods, it may be broken into three main stages:
#Acidification
#Oxidation
#Detection and Quantification | 3 | Analytical Chemistry |
Monomer 1 is consumed with reaction rate:
with the concentration of all the active chains terminating in monomer 1, summed over chain lengths. is defined similarly for monomer 2.
Likewise the rate of disappearance for monomer 2 is:
Division of both equations by followed by division of the first equation by the second yields:
The ratio of active center concentrations can be found using the steady state approximation, meaning that the concentration of each type of active center remains constant.
The rate of formation of active centers of monomer 1 () is equal to the rate of their destruction () so that
or
Substituting into the ratio of monomer consumption rates yields the Mayo–Lewis equation after rearrangement: | 7 | Physical Chemistry |
The dopamine or dopaminergic system consists of several pathways, originating from the ventral tegmentum or substantia nigra as examples. It acts on dopamine receptors.
Parkinson's disease is at least in part related to dropping out of dopaminergic cells in deep-brain nuclei, primarily the melanin-pigmented neurons in the substantia nigra but secondarily the noradrenergic neurons of the locus coeruleus. Treatments potentiating the effect of dopamine precursors have been proposed and effected, with moderate success. | 1 | Biochemistry |
cDNA libraries require care to ensure that full length clones of mRNA are captured as cDNA (which will later be inserted into vectors). Several protocols have been designed to optimise the synthesis of the 1st cDNA strand and the 2nd cDNA strand for this reason, and also to make directional cloning into the vector more likely.
gDNA fragments are generated from the extracted gDNA by using non-specific frequent cutter restriction enzymes. | 1 | Biochemistry |
The Van Deemter equation can be further expanded to:
Where:
* H is plate height
* λ is particle shape (with regard to the packing)
* d is particle diameter
* γ, ω, and R are constants
* D is the diffusion coefficient of the mobile phase
* d is the capillary diameter
* d is the film thickness
* D is the diffusion coefficient of the stationary phase.
* u is the linear velocity | 3 | Analytical Chemistry |
The proportion of an emission remaining in the atmosphere after a specified time is the "airborne fraction" (AF). The annual airborne fraction is the ratio of the atmospheric increase in a given year to that year's total emissions. The annual airborne fraction for had been stable at 0.45 for the past six decades even as the emissions have been increasing. This means that the other 0.55 of emitted is absorbed by the land and atmosphere carbon sinks within the first year of an emission. In the high-emission scenarios, the effectiveness of carbon sinks will be lower, increasing the atmospheric fraction of even though the raw amount of emissions absorbed will be higher than in the present. | 2 | Environmental Chemistry |
These names are used to refer to the moieties themselves or to radical species, and also to form the names of halides and substituents in larger molecules.
When the parent hydrocarbon is unsaturated, the suffix ("-yl", "-ylidene", or "-ylidyne") replaces "-ane" (e.g. "ethane" becomes "ethyl"); otherwise, the suffix replaces only the final "-e" (e.g. "ethyne" becomes "ethynyl").
When used to refer to moieties, multiple single bonds differ from a single multiple bond. For example, a methylene bridge (methanediyl) has two single bonds, whereas a methylene group (methylidene) has one double bond. Suffixes can be combined, as in methylidyne (triple bond) vs. methylylidene (single bond and double bond) vs. methanetriyl (three double bonds).
There are some retained names, such as methylene for methanediyl, 1,x-phenylene for phenyl-1,x-diyl (where x is 2, 3, or 4), carbyne for methylidyne, and trityl for triphenylmethyl. | 0 | Organic Chemistry |
Electrophoresis is the process of separating nucleic acid species based on their length by applying an electric field to them. As nucleic acids are negatively charged, they are pushed by an electric field through a matrix, usually an agarose gel, with the smaller molecules being pushed farther, faster. Capillary electrophoresis is a technique whereby small amounts of a nucleic acid sample can be run on a gel in a very thin tube. There is a detector in the machine that can tell when nucleic acid samples pass through a specific point in the tube, with smaller samples passing through first. This can produce an electropherogram such as the one in Figure 1, where length is related to time at which the samples pass the detector.
A marker is a sample of known size run along with the sample so that the actual size of the rest of the sample can be known by comparing their running distance/time to be relative to this marker.
RNA is a biological macromolecule made of sugars and nitrogenous bases that plays a number of crucial roles in all living cells. There are several subtypes of RNA, with the most prominent in the cell being tRNA (transfer RNA), rRNA (ribosomal RNA), and mRNA (messenger RNA). All three of these are involved in the process of translation, with the most prominent species (~85%) of cellular RNA being rRNA. As a result, this is the most immediately visible species when RNA is analyzed via electrophoresis and is thus used for determining RNA quality (see Computation, below). rRNA comes in various sizes, with those in mammals belonging to the sizes 5S, 18S, and 28S. The 28S and 5S rRNAs form the large subunit and the 18S forms the small subunit of the ribosome, the molecular machinery responsible for synthesizing proteins. | 1 | Biochemistry |
5-Fluoroorotic acid (5FOA) is a fluorinated derivative of the pyrimidine precursor orotic acid. It is used in yeast genetics to select for the absence of the URA3 gene, which encodes the enzyme for the decarboxylation of 5-fluoroorotic acid to 5-fluorouracil, a toxic metabolite. It has also been used in diatom selection. | 1 | Biochemistry |
The input data on irrigation, evaporation, and surface runoff are to be specified per season for three kinds of agricultural practices, which can be chosen at the discretion of the user:
#A: irrigated land with crops of group A
#B: irrigated land with crops of group B
#U: non-irrigated land with rainfed crops or fallow land
The groups, expressed in fractions of the total area, may consist of combinations of crops or just of a single kind of crop. For example, as the A type crops one may specify the lightly irrigated cultures, and as the B type the more heavily irrigated ones, such as sugarcane and rice. But one can also take A as rice and B as sugarcane, or perhaps trees and orchards. The A, B and/or U crops can be taken differently in different seasons, e.g. A=wheat+barley in winter and A=maize in summer while B=vegetables in winter and B=cotton in summer.<br>
Un-irrigated land can be specified in two ways: (1) as U=1−A−B and (2) as A and/or B with zero irrigation. A combination can also be made.<br>
Further, a specification must be given of the seasonal rotation of the different land uses over the total area, e.g. full rotation, no rotation at all, or incomplete rotation. This occurs with a rotation index. The rotations are taken over the seasons within the year. To obtain rotations over the years it is advisable to introduce annual input changes.<br>
When a fraction A1, B1 and/or U1 in the first season differs from fractions are A2, B2 and/or U2 in the second season, because the irrigation regimes in the seasons differ, the program will detect that a certain rotation occurs. If one wishes to avoid this, one may specify the same fractions in all seasons (A2=A1, B2=B1, U2=U1), but the crops and irrigation quantities may have to be adjusted in proportion.<br>
Cropping rotation schedules vary widely in different parts of the world. Creative combinations of area fractions, rotation indexes, irrigation quantities and annual input changes can accommodate many types of agricultural practices.
Variation of the area fractions and/or the rotational schedule gives the opportunity to simulate the effect of different agricultural practices on the water and salt balance. | 9 | Geochemistry |
Despite the high number of MAPK genes, MAPK pathways of higher plants were studied less than animal or fungal ones. Although their signaling appears very complex, the MPK3, MPK4 and MPK6 kinases of Arabidopsis thaliana are key mediators of responses to osmotic shock, oxidative stress, response to cold and involved in anti-pathogen responses. Asai et al. 2002s model of MAPK mediated immunity passes the effector recognition signal from FLS2 ⇨ MEKK1 ⇨ MKK4 or MKK5 ⇨ MPK3 and MPK6 ⇨ WRKY22 or WRKY29. However the work of Mészáros et al. 2006 and Suarez-Rodriguez et al.' 2007 give other orders for this pathway and it is possible that these are parallel pathways operating simultaneously. They are also involved in morphogenesis, since MPK4 mutants display severe dwarfism. | 1 | Biochemistry |
Sodium lauryl sulfate is a widely used in the pharmaceutical field as an ionic solubilizer and emulsifier that is suitable for applications in liquid dispersions, solutions, emulsions and micro emulsions, tablets, foams and semi-solids such as creams, lotions and gels. Additionally, SLS aids in tablet wettability, as well as lubrication during manufacturing. Brand names of pharma-grade SLS include Kolliphor SLS and Kolliphor SLS Fine. | 1 | Biochemistry |
Any compound with a log Kow of less than or equal to 3 can concentrate in a POCIS sampler. Applicable classes of contaminants measured by POCIS are pharmaceuticals, household and industrial products, hormones, herbicides, and polar pesticides (Table 1). Currently, there are two POCIS configurations that are targeted for different classes of contaminants. A general POCIS design contains a sorbent that is used to collect pesticides, natural as well as synthetic hormones, and wastewater related chemicals. The pharmaceutical POCIS configuration contains a sorbent that is designed to specifically target classes of pharmaceuticals.
::Applicable contaminants that concentrate in a POCIS device. Not to be considered a complete list. | 3 | Analytical Chemistry |
Amoxicillin is an antibiotic medication belonging to the aminopenicillin class of the penicillin family. The drug is used to treat bacterial infections such as middle ear infection, strep throat, pneumonia, skin infections, odontogenic infections, and urinary tract infections. It is taken by mouth, or less commonly by injection.
Common adverse effects include nausea and rash. It may also increase the risk of yeast infections and, when used in combination with clavulanic acid, diarrhea. It should not be used in those who are allergic to penicillin. While usable in those with kidney problems, the dose may need to be decreased. Its use in pregnancy and breastfeeding does not appear to be harmful. Amoxicillin is in the β-lactam family of antibiotics.
Amoxicillin was discovered in 1958 and came into medical use in 1972. Amoxil was approved for medical use in the United States in 1974, and in the United Kingdom in 1977. It is on the (WHO) World Health Organization's List of Essential Medicines. It is one of the most commonly prescribed antibiotics in children. Amoxicillin is available as a generic medication. In 2021, it was the 38th most commonly prescribed medication in the United States, with more than 16million prescriptions. | 4 | Stereochemistry |
The original method of protein skimming, running pressurized air through a diffuser to produce large quantities of micro bubbles, remains a viable, effective, and economic choice, although newer technologies may require lower maintenance. The air stone is most often an oblong, partially hollowed block of wood, most often of the genus Tilia. The most popular wooden air-stones for skimmers are made from limewood (Tilia europaea or European limewood) although basswood (Tilia americana or American Linden), works as well, may be cheaper and is often more readily available. The wooden blocks are drilled, tapped, fitted with an air fitting, and connected by air tubing to one or more air pumps delivering at least 1 cfm. The wooden air stone is placed at the bottom of a tall column of water. The tank water is pumped into the column, allowed to pass by the rising bubbles, and back into the tank. To get enough contact time with the bubble, these units can be many feet in height.
Air stone protein skimmers may be constructed as a DIY project from pvc pipes and fittings at low cost [http://www.angelfire.com/ok/dog1/skimmer.html] [http://www.hawkfish.org/snailman/diy8inskimmer.htm] and with varying degrees of complexity [https://web.archive.org/web/20121225063946/http://ozreef.org/diy_plans/protein_skimmers/air_stone_protein_skimmer.html].
Air stone protein skimmers require powerful air pumps which are often power hungry, loud, and hot, leading to an increase in the aquarium water temperatures. While this method has been around for many years, due to more efficient technologies emerging, many regard it as inefficient current uses in larger systems or systems with large bio-loads. | 3 | Analytical Chemistry |
CTCF binds to the consensus sequence CCGCGNGGNGGCAG (in IUPAC notation). This sequence is defined by 11 zinc finger motifs in its structure. CTCF's binding is disrupted by CpG methylation of the DNA it binds to. On the other hand, CTCF binding may set boundaries for the spreading of DNA methylation. In recent studies, CTCF binding loss is reported to increase localized CpG methylation, which reflected another epigenetic remodeling role of CTCF in human genome.
CTCF binds to an average of about 55,000 DNA sites in 19 diverse cell types (12 normal and 7 immortal) and in total 77,811 distinct binding sites across all 19 cell types.
CTCF's ability to bind to multiple sequences through the usage of various combinations of its zinc fingers earned it the status of a “multivalent protein”. More than 30,000 CTCF binding sites have been characterized. The human genome contains anywhere between 15,000 and 40,000 CTCF binding sites depending on cell type, suggesting a widespread role for CTCF in gene regulation. In addition CTCF binding sites act as nucleosome positioning anchors so that, when used to align various genomic signals, multiple flanking nucleosomes can be readily identified. On the other hand, high-resolution nucleosome mapping studies have demonstrated that the differences of CTCF binding between cell types may be attributed to the differences in nucleosome locations. Methylation loss at CTCF-binding site of some genes has been found to be related to human diseases, including male infertility. | 1 | Biochemistry |
John Alexander Reina Newlands (26 November 1837 – 29 July 1898) was a British chemist who worked concerning the periodicity of elements. | 3 | Analytical Chemistry |
*Bulk Fe. Cast iron, consisting of scrap iron of construction grade, has been used as a reactive material for permeable reactive barriers for groundwater remediation. Reactions are generally believed to occur on the Fe (oxide) surface; however, graphite inclusions have been shown can also serve as a reaction sites.
*Nanoscale Fe. In addition to using macroscale iron in PRBs, nanoparticles (1-100 nm diameter) of zerovalent iron (nZVI) are effective.
*Zn. Zinc has showed much higher reactivity toward pentachlorophenol than iron. This indicates that zinc may be used as a replacement for ZVI in dechlorinating chlorinated phenols. Chlorinated phenols are sequentially dechlorinated and thus less chlorinated phenols have been identified as a reduction product. | 2 | Environmental Chemistry |
The MIQE guidelines are split up into 9 different sections that make up the checklist. These include not only considerations for doing the qPCR itself, but also how the resulting data is collected, analyzed, and presented. An important part of the latter is including information relating to the analysis software used and also submitting the raw data to the relevant databases. | 1 | Biochemistry |
Kyriacos Costa Nicolaou (; born July 5, 1946) is a Cypriot-American chemist known for his research in the area of natural products total synthesis. He is currently Harry C. and Olga K. Wiess Professor of Chemistry at Rice University, having previously held academic positions at The Scripps Research Institute/UC San Diego and the University of Pennsylvania. | 0 | Organic Chemistry |
Tantalum–tungsten alloys are in the refractory metals group that maintain useful physical and chemical properties even at high temperatures. The tantalum–tungsten alloys are characterized by their high melting point and the tension resistance. The properties of the final alloy are a combination of properties from the two elements: tungsten, the element with the highest melting point in the periodic table, and tantalum which has high corrosion resistance.
The tantalum–tungsten alloys typically vary in their percentage of tungsten. Some common variants are:
* (Ta – 2.5% W) → also called tantaloy 63 metal. The percentage of tungsten is about 2 to 3% and includes 0.5% of niobium. This alloy has a good resistance to corrosion and performs well at high temperatures. An example application is piping in chemical industries.
* (Ta - 7.5% W) → also called tantaloy 61 metal, has between 7 and 8% tungsten. The difference from this alloy to the others is that this alloy represents a high resilience modulus while maintaining its refractory properties.
* (Ta - 10% W) → also called tantaloy 60 metal, contains 9 to 11% tungsten. This alloy is less ductile than the other alloys and exhibits less plasticity. Applications include high-temperature, high-corrosion environments such as aerospace components, furnaces, and piping in nuclear plants. | 8 | Metallurgy |
The most common way of classifying ordered columnar structures uses the phyllotactic notation, adopted from botany. It is used to describe arrangements of leaves of a plant, pine cones, or pineapples, but also planar patterns of florets in a sunflower head. While the arrangement in the former are cylindrical, the spirals in the latter are arranged on a disk. For columnar structures phyllotaxis in the context of cylindrical structures is adopted.
The phyllotactic notation describes such structures by a triplet of positive integers with . Each number , , and describes a family of spirals in the 3-dimensional packing. They count the number of spirals in each direction until the spiral repeats. This notation, however, only applies to triangular lattices and is therefore restricted to the ordered structures without internal spheres. | 3 | Analytical Chemistry |
In terms of inhibitors of intrinsic termination, much is still unknown. One of the few examples that is known is bacteriophage protein 7. This is made up of 3.4A and 4.0A cryo-EM structures of P7-NusA-TEC and P7-TEC. This bacteriophage protein 7 stops transcription termination by blocking the RNA polymerase (RNAP) RNA-exit channel and impeding RNA-hairpin formation at the intrinsic terminator. Furthermore, bacteriophage protein 7 inhibits RNAP-clamp motions. Shortening the C-terminal half-helix of the RNAP slightly decreases the inhibitory activity. These RNAP clamp motions have been targeted by some other inhibitors of bacterial RNAP. These inhibitors include myxopyronin, corallopyronin, and ripostatin. These work by inhibiting isomerization. | 1 | Biochemistry |
Aerobic glycolysis in cancer cells, also known as the “Warburg effect”, is driven by hyperactivity of lactate dehydrogenase-A (LDHA). Mollapour’s team has identified the human tumor suppressor folliculin (FLCN) as a binding partner and uncompetitive inhibitor of LDHA. Their work has provided a new paradigm for the regulation of glycolysis. Cancer cells that experience the Warburg effect show FLCN dissociation from LDHA. Mollapour’s lab has shown that treatment of these cancer cells with a decapeptide derived from the FLCN loop region caused cell death, therefore providing a new avenue for targeted therapy in these cancers. | 1 | Biochemistry |
In the sodium-glucose symporter, sodium moves down its concentration gradient to move glucose up its concentration gradient. Sodium has a greater concentration outside of the cell, and binds to the symporter, which is in its outward facing conformation. Once sodium is bound, glucose can bind from the extracellular space, causing the symporter to switch into the occluded formation (closed) before opening to the inside of the cell and releasing the two sodium ions and the one glucose molecule. Once both are released, the symporter re-orients itself to the outward facing conformation and the process starts all over again. A major example of up-regulation of the sodium-glucose symporter is seen in patients with type 2 diabetes, where there is roughly a 3-4 fold up-regulation of the sodium-glucose symporter (SGLT1). This leads to an influx of glucose into the cell and results in hyperglycemia. | 1 | Biochemistry |
The amine value is useful in helping determine the correct stoichiometry of a two component amine cure epoxy resin system.
It is the number of Nitrogens x 56.1 (Mwt of KOH) x 1000 (convert to milligrams) divided by molecular mass of the amine functional compound. So using Tetraethylenepentamine (TEPA) as an example:
Mwt = 189, number of nitrogen atoms = 5
So 5 x 1000 x 56.1/189 = 1484. So the Amine Value of TEPA = 1484 | 3 | Analytical Chemistry |
The invertebrate mitochondrial code ([https://www.ncbi.nlm.nih.gov/Taxonomy/Utils/wprintgc.cgi?chapter=tgencodes#SG5 translation table 5]) is a genetic code used by the mitochondrial genome of invertebrates. Mitochondria contain their own DNA and reproduce independently from their host cell. Variation in translation of the mitochondrial genetic code occurs when DNA codons result in non-standard amino acids has been identified in invertebrates, most notably arthropods. This variation has been helpful as a tool to improve upon the phylogenetic tree of invertebrates, like flatworms. | 1 | Biochemistry |
Gene regulatory networks are generally thought to be made up of a few highly connected nodes (hubs) and many poorly connected nodes nested within a hierarchical regulatory regime. Thus gene regulatory networks approximate a hierarchical scale free network topology. This is consistent with the view that most genes have limited pleiotropy and operate within regulatory modules. This structure is thought to evolve due to the preferential attachment of duplicated genes to more highly connected genes. Recent work has also shown that natural selection tends to favor networks with sparse connectivity.
There are primarily two ways that networks can evolve, both of which can occur simultaneously. The first is that network topology can be changed by the addition or subtraction of nodes (genes) or parts of the network (modules) may be expressed in different contexts. The Drosophila Hippo signaling pathway provides a good example. The Hippo signaling pathway controls both mitotic growth and post-mitotic cellular differentiation. Recently it was found that the network the Hippo signaling pathway operates in differs between these two functions which in turn changes the behavior of the Hippo signaling pathway. This suggests that the Hippo signaling pathway operates as a conserved regulatory module that can be used for multiple functions depending on context. Thus, changing network topology can allow a conserved module to serve multiple functions and alter the final output of the network. The second way networks can evolve is by changing the strength of interactions between nodes, such as how strongly a transcription factor may bind to a cis-regulatory element. Such variation in strength of network edges has been shown to underlie between species variation in vulva cell fate patterning of Caenorhabditis worms. | 1 | Biochemistry |
A fibrous protein forms long protein filaments, which are shaped like rods or wires. Fibrous proteins are structural or storage proteins that are typically inert and water-insoluble. A fibrous protein occurs as an aggregate due to hydrophobic side chains that protrude from the molecule.
A fibrous protein's peptide sequence often has limited residues with repeats; these can form unusual secondary structures, such as a collagen helix. The structures often feature cross-links between chains (e.g., cys-cys disulfide bonds between keratin chains).
Fibrous proteins tend not to denature as easily as globular proteins.
Miroshnikov et al. (1998) are among the researchers who have attempted to synthesize fibrous proteins. | 1 | Biochemistry |
Tripartite motif-containing 28 (TRIM28), also known as transcriptional intermediary factor 1β (TIF1β) and KAP1 (KRAB-associated protein-1), is a protein that in humans is encoded by the TRIM28 gene. | 1 | Biochemistry |
A well studied biradical is trimethylenemethane (TMM), . In 1966 Paul Dowd determined with electron spin resonance that this compound also has a triplet state. In a crystalline host the 6 hydrogen atoms in TMM are identical. | 0 | Organic Chemistry |
An S1 reaction occurs when a molecule separates into a positively charged component and a negatively charged component. This generally occurs in highly polar solvents through a process called solvolysis. The positively charged component then reacts with a nucleophile forming a new compound. S1 reactions are reactions whose rate is dependent only on haloalkane concentration.
In the first stage of this reaction (solvolysis), the C-L bond breaks and both electrons from that bond join LG (the leaving group) to form LG and RC ions. This is represented by the curved arrow pointing away from the C-LG bond and towards LG. The nucleophile Nu, being attracted to the RC, then donates a pair of electrons forming a new C-Nu bond.
Because an S1 reaction proceeds with the Substitution of a leaving group with a Nucleophile, the S designation is used. Because the initial solvolysis step in this reaction involves a single molecule dissociating from its leaving group, the initial stage of this process is considered a uni-molecular reaction. The involvement of only 1 species in the initial phase of the reaction enhances the mechanistic designation to S1. An S1 reaction has two steps. | 0 | Organic Chemistry |
R-410A replaced R-22 as the preferred refrigerant for use in residential and commercial air conditioners in Japan, Europe, and the United States.
Parts designed specifically for R-410A must be used, as R-410A operates at higher pressures than other refrigerants. R-410A systems thus require service personnel to use different tools, equipment, safety standards, and techniques. Equipment manufacturers are aware of these changes and require the certification of professionals installing R-410A systems. In addition, the AC&R Safety Coalition has been created to help educate professionals about R-410A systems. | 2 | Environmental Chemistry |
X-ray photoelectron spectroscopy (XPS) and Energy-dispersive X-ray spectroscopy (EDS/EDX) are composition characterization techniques that use x-ray excitation of electrons to discrete energy levels to quantify chemical composition. These techniques provide characterization at surface depths of 1–10 nanometers, approximately the range of oxidation in plasma and corona treatments. In addition, these processes offer the benefit of characterizing microscopic variations in surface composition.
In the context of plasma processed polymer surfaces, oxidized surfaces will obviously show a greater oxygen content. Elemental analysis allows for quantitative data to be obtained and used in the analysis of process efficiency. | 7 | Physical Chemistry |
The work of Kiwako Sakabe, Reiji Okazaki and Tsuneko Okazaki provided experimental evidence supporting the hypothesis that DNA replication is a discontinuous process. Previously, it was commonly accepted that replication was continuous in both the 3 to 5 and 5 to 3 directions. 3 and 5 are specifically numbered carbons on the deoxyribose ring in nucleic acids, and refer to the orientation or directionality of a strand. In 1967, Tsuneko Okazaki and Toru Ogawa suggested that there is no found mechanism that showed continuous replication in the 3 to 5 direction, only 5 to 3 using DNA polymerase, a replication enzyme. The team hypothesized that if discontinuous replication was used, short strands of DNA, synthesized at the replicating point, could be attached in the 5 to 3 direction to the older strand.
To distinguish the method of replication used by DNA experimentally, the team pulse-labeled newly replicated areas of Escherichia coli chromosomes, denatured, and extracted the DNA. A large number of radioactive short units meant that the replication method was likely discontinuous. The hypothesis was further supported by the discovery of polynucleotide ligase, an enzyme that links short DNA strands together.
In 1968, Reiji and Tsuneko Okazaki gathered additional evidence of nascent DNA strands. They hypothesized that if discontinuous replication, involving short DNA chains linked together by polynucleotide ligase, is the mechanism used in DNA synthesis, then "newly synthesized short DNA chains would accumulate in the cell under conditions where the function of ligase is temporarily impaired." E. coli were infected with bacteriophage T4 that produce temperature-sensitive polynucleotide ligase. The cells infected with the T4 phages accumulated a large number of short, newly synthesized DNA chains, as predicted in the hypothesis, when exposed to high temperatures. This experiment further supported the Okazakis' hypothesis of discontinuous replication and linkage by polynucleotide ligase. It disproved the notion that short chains were produced during the extraction process as well.
The Okazakis' experiments provided extensive information on the replication process of DNA and the existence of short, newly synthesized DNA chains that later became known as Okazaki fragments. | 1 | Biochemistry |
* Robert Burns Woodward: Architect and Artist in the World of Molecules; Otto Theodor Benfey, Peter J. T. Morris, Chemical Heritage Foundation, April 2001.
* Robert Burns Woodward and the Art of Organic Synthesis: To Accompany an Exhibit by the Beckman Center for the History of Chemistry (Publication / Beckman Center for the History of Chemistry); Mary E. Bowden; Chemical Heritage Foundation, March 1992
*[https://web.archive.org/web/20060516234558/http://www.ch.ic.ac.uk/video/index.rss Video podcast of Robert Burns Woodward talking about cephalosporin]
*[http://www.sigmaaldrich.com/etc/medialib/docs/Aldrich/Acta/al_acta_10_01.Par.0001.File.tmp/al_acta_10_01.pdf Robert Burns Woodward: Three Score Years and Then?] David Dolphin, Aldrichimica Acta, 1977, 10(1), 3–9.
*[http://www.patentgenius.com/inventor/WoodwardRobertBurns.html Robert Burns Woodward Patents] | 4 | Stereochemistry |
In organic chemistry, hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehydes () from alkenes (). This chemical reaction entails the net addition of a formyl group () and a hydrogen atom to a carbon-carbon double bond. This process has undergone continuous growth since its invention: production capacity reached 6.6 tons in 1995. It is important because aldehydes are easily converted into many secondary products. For example, the resultant aldehydes are hydrogenated to alcohols that are converted to detergents. Hydroformylation is also used in speciality chemicals, relevant to the organic synthesis of fragrances and pharmaceuticals. The development of hydroformylation is one of the premier achievements of 20th-century industrial chemistry.
The process entails treatment of an alkene typically with high pressures (between 10 and 100 atmospheres) of carbon monoxide and hydrogen at temperatures between 40 and 200 °C. In one variation, formaldehyde is used in place of synthesis gas. Transition metal catalysts are required. Invariably, the catalyst dissolves in the reaction medium, i.e. hydroformylation is an example of homogeneous catalysis. | 0 | Organic Chemistry |
* On a prepared mould surface as a sample, permeability can be checked with use of a mould permeability attachment to permeability meter, readings such obtained are of relative permeability, and not absolute permeability. The relative permeability reading on a mould surface is only used to gauge sample-to-sample variation.
* On standard specimen as a sample
** For sands that can be compressed, e.g.: bentonite-bonded sand, also known as green sand, a compressed or rammed sample is used to check permeability.
** For sand that cannot be compressed, e.g.: Resin-coated sands, a freely filled sample is used. To check such a sample, user may have to use an attachment to the permeability meter called a core permeability tube.
The absolute permeability number, which has no units, is determined by the rate of flow of air, under standard pressure, through a rammed cylindrical specimen. DIN standards define the specimen dimensions to be 50 mm in diameter and 50 mm tall, while the American Foundry Society defines it to be two inches in diameter and two inches tall. rammed cylindrical specimen.
formula is
PN = (VxH)/PxAxT
where
* V = volume of air in ml passing through the specimen
* H = Height of the specimen in cm
* A = Cross sectional area of specimen in cm2
* P = Pressure of air in cm of water
* T = Time in minutes
American Foundry Society has also released a chart where back pressure (P) from a rammed specimen placed on a permeability meter is correlated with a Permeability number. The Permeability number so measured is used in foundries for recording permeability value. | 8 | Metallurgy |
The skeletal formula is a method to draw structural formulas of organic compounds where lines represent the chemical bonds and the vertices represent implicit carbon atoms. This notation is sometimes jestingly called chicken wire notation. | 4 | Stereochemistry |
Though transposable elements were discovered due in large part to their deleterious effects, epigenetic research has shown that they may be, in some cases, beneficial to the host organism.(1,5) This research indicates that the distinction between those two aspects, mutualist and parasite, may be harder to accurately describe than was once thought. | 1 | Biochemistry |
An essential amino acid is an amino acid that is required by an organism but cannot be synthesized de novo by it, and therefore must be supplied in its diet. Out of the twenty standard protein-producing amino acids, nine cannot be endogenously synthesized by humans: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. | 9 | Geochemistry |
Recombinant adeno-associated virus (rAAV) based genome engineering is a genome editing platform centered on the use of recombinant AAV vectors that enables insertion, deletion or substitution of DNA sequences into the genomes of live mammalian cells. The technique builds on Mario Capecchi and Oliver Smithies' Nobel Prize–winning discovery that homologous recombination (HR), a natural hi-fidelity DNA repair mechanism, can be harnessed to perform precise genome alterations in mice. rAAV mediated genome-editing improves the efficiency of this technique to permit genome engineering in any pre-established and differentiated human cell line, which, in contrast to mouse ES cells, have low rates of HR.
The technique has been widely adopted for use in engineering human cell lines to generate isogenic human disease models. It has also been used to optimize bioproducer cell lines for the biomanufacturing of protein vaccines and therapeutics. In addition, due to the non-pathogenic nature of rAAV, it has emerged as a desirable vector for performing gene therapy in live patients. | 1 | Biochemistry |
Pittcon Editors’ Awards honoured the best new products on show at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, or Pittcon, for 20 years from 1996 having been established by Dr Gordon Wilkinson, managing editor of Analytical Instrument Industry Report (later Instrumenta). On 8 March 2015, the event returned to the Morial Convention Center in New Orleans and this was the last occasion when the awards were presented.
The independent awards, which represented the results of an informal poll of leading editors, had become an important feature of the worlds largest trade show for the laboratory equipment industry. Pittcon organisers and media center supported the scheme and provided details and photographs on the exhibitions Press and Media Information page. In 2016 the group of editors and journalists that formed the core of the judging panel reluctantly decided to discontinue the awards program citing gradually dwindling support from ever-busier media representatives. | 3 | Analytical Chemistry |
Alternative splicing is one of the most important components that show functional complexity of genome. Modified splicing has significant effect on the phenotype that is relevance to disease or drug metabolism. A change in splicing can be caused by modifying any of the components of the splicing machinery such as splice sites or splice enhancers or silencers. Modification in the alternative splicing site can lead to a different protein form which will show a different function. Humans use an estimated 100,000 different proteins or more, so some genes must be capable of coding for a lot more than just one protein. Alternative splicing occurs more frequently than was previously thought and can be hard to control; genes may produce tens of thousands of different transcripts, necessitating a new gene model for each alternative splice. | 1 | Biochemistry |
The formation of electrical double layer (EDL) has been traditionally assumed to be entirely dominated by ion adsorption and redistribution. With considering the fact that the contact electrification between solid-solid is dominated by electron transfer, it is suggested by Wang that the EDL is formed by a two-step process. In the first step, when the molecules in the solution first approach a virgin surface that has no pre-existing surface charges, it may be possible that the atoms/molecules in the solution directly interact with the atoms on the solid surface to form strong overlap of electron clouds. Electron transfer occurs first to make the “neutral” atoms on solid surface become charged, i.e., the formation of ions. In the second step, if there are ions existing in the liquid, such as H+ and OH-, the loosely distributed negative ions in the solution would be attracted to migrate toward the surface bonded ions due to electrostatic interactions, forming an EDL. Both electron transfer and ion transfer co-exist at liquid-solid interface. | 7 | Physical Chemistry |
Quasi-solid, Falsely-solid, or semisolid is the physical term for something whose state lies between a solid and a liquid. While similar to solids in some respects, such as having the ability to support their own weight and hold their shapes, a quasi-solid also shares some properties of liquids, such as conforming in shape to something applying pressure to it and the ability to flow under pressure. The words quasi-solid, semisolid, and semiliquid may be used interchangeably.
Quasi-solids and semisolids are sometimes described as amorphous because at the microscopic scale they have a disordered structure unlike crystalline solids. They should not be confused with amorphous solids as they are not solids and exhibit properties such as flow which bulk solids do not. | 7 | Physical Chemistry |
The overall reaction is
: 4 Fe – cytochrome c + 4 H + O → 4 Fe – cytochrome c + 2 HO ΔG = - 218 kJ/mol, E = +565 mV
Two electrons are passed from two cytochrome cs, through the Cu and cytochrome a sites to the cytochrome a–Cu binuclear center, reducing the metals to the Fe form and Cu. The hydroxide ligand is protonated and lost as water, creating a void between the metals that is filled by O. The oxygen is rapidly reduced, with two electrons coming from the Fe-cytochrome a, which is converted to the ferryl oxo form (Fe=O). The oxygen atom close to Cu picks up one electron from Cu, and a second electron and a proton from the hydroxyl of Tyr(244), which becomes a tyrosyl radical. The second oxygen is converted to a hydroxide ion by picking up two electrons and a proton. A third electron from another cytochrome c is passed through the first two electron carriers to the cytochrome a–Cu binuclear center, and this electron and two protons convert the tyrosyl radical back to Tyr, and the hydroxide bound to Cu to a water molecule. The fourth electron from another cytochrome c flows through Cu and cytochrome a to the cytochrome a–Cu binuclear center, reducing the Fe=O to Fe, with the oxygen atom picking up a proton simultaneously, regenerating this oxygen as a hydroxide ion coordinated in the middle of the cytochrome a–Cu center as it was at the start of this cycle. Overall, four reduced cytochrome cs are oxidized while O and four protons are reduced to two water molecules. | 1 | Biochemistry |
Angiogenin (ANG) also known as ribonuclease 5 is a small 123 amino acid protein that in humans is encoded by the ANG gene. Angiogenin is a potent stimulator of new blood vessels through the process of angiogenesis. Ang hydrolyzes cellular RNA, resulting in modulated levels of protein synthesis and interacts with DNA causing a promoter-like increase in the expression of rRNA. Ang is associated with cancer and neurological disease through angiogenesis and through activating gene expression that suppresses apoptosis. | 1 | Biochemistry |
Electrons exist in energy levels (i.e. atomic orbitals) within an atom. Atomic orbitals are quantized, meaning they exist as defined values instead of being continuous (see: atomic orbitals). Electrons may move between orbitals, but in doing so they must absorb or emit energy equal to the energy difference between their atom's specific quantized orbital energy levels. In optical spectroscopy, energy absorbed to move an electron to a higher energy level (higher orbital) and/or the energy emitted as the electron moves to a lower energy level is absorbed or emitted in the form of photons (light particles). Because each element has a unique number of electrons, an atom will absorb/release energy in a pattern unique to its elemental identity (e.g. Ca, Na, etc.) and thus will absorb/emit photons in a correspondingly unique pattern. The type of atoms present in a sample, or the amount of atoms present in a sample can be deduced from measuring these changes in light wavelength and light intensity.
Atomic spectroscopy is further divided into atomic absorption spectroscopy and atomic emission spectroscopy. In atomic absorption spectroscopy, light of a predetermined wavelength is passed through a collection of atoms. If the wavelength of the source light has energy corresponding to the energy difference between two energy levels in the atoms, a portion of the light will be absorbed. The difference between the intensity of the light emitted from the source (e.g., lamp) and the light collected by the detector yields an absorbance value. This absorbance value can then be used to determine the concentration of a given element (or atoms) within the sample. The relationship between the concentration of atoms, the distance the light travels through the collection of atoms, and the portion of the light absorbed is given by the Beer–Lambert law. In atomic emission spectroscopy, the intensity of the emitted light is directly proportional to the concentration of atoms. | 7 | Physical Chemistry |
Linked-read sequencing, a type of DNA sequencing technology, uses specialized technique that tags DNA molecules with unique barcodes before fragmenting them. Unlike traditional sequencing technology, where DNA is broken into small fragments and then sequenced individually, resulting in short read lengths that has difficulties in accurately reconstructing the original DNA sequence, the unique barcodes of linked-read sequencing allows scientists to link together DNA fragments that come from the same DNA molecule. A pivotal benefit of this technology lies in the small quantities of DNA required for large genome information output, effectively combining the advantages of long-read and short-read technologies. | 1 | Biochemistry |
Thermal transmittance is the rate of transfer of heat through matter. The thermal transmittance of a material (such as insulation or concrete) or an assembly (such as a wall or window) is expressed as a U-value. The thermal insulance of a structure is the reciprocal of its thermal transmittance. | 7 | Physical Chemistry |
The EPA has published a standards handbook for the interpretation of water quality in Ireland in which definitions of water hardness are given.
In this section, reference to original EU documentation is given, which sets out no limit for hardness. The handbook also gives no "Recommended or Mandatory Limit Values" for hardness. The handbook does indicate that above the midpoint of the ranges defined as "Moderately Hard", effects are seen increasingly: "The chief disadvantages of hard waters are that they neutralise the lathering power of soap[...] and, more important, that they can cause blockage of pipes and severely reduced boiler efficiency because of scale formation. These effects will increase as the hardness rises to and beyond 200 mg/L ." | 3 | Analytical Chemistry |
The portion of the MLSS that is actually eating the incoming food(in terms of COD & BOD) is referred to as the Mixed Liquor Volatile Suspended Solids (MLVSS). The volatile solids concentration in a sample of mixed liquor will consist mostly of microorganisms and organic matter. As a result, the volatile solids concentration of mixed liquor is approximately equal to the amount of microorganisms in the water and can be used to determine whether there are enough microorganisms present to purify the water | 3 | Analytical Chemistry |
Effective therapies to manage autism remain scarce. According to the exorphin theory of autism, an increase in the levels of exorphin is linked to symptoms of autism. Based on this concept, experiments have attempted to reduce the symptoms of autism by using large amounts of protease to break down exorphins before they are absorbed. Experiments have also attempted to enhance and utilize enzymes existing in the gut to break down exorphins in a similar fashion, since the production of exorphins within the gut is inevitable. | 1 | Biochemistry |
The derivation of Avogadro's law follows directly from the ideal gas law, i.e.
where R is the gas constant, T is the Kelvin temperature, and P is the pressure (in pascals).
Solving for V/n, we thus obtain
Compare that to
which is a constant for a fixed pressure and a fixed temperature.
An equivalent formulation of the ideal gas law can be written using Boltzmann constant k, as
where N is the number of particles in the gas, and the ratio of R over k is equal to the Avogadro constant.
In this form, for V/N is a constant, we have
If T and P are taken at standard conditions for temperature and pressure (STP), then k′ = 1/n, where n is the Loschmidt constant. | 7 | Physical Chemistry |
Like the preceding method, the most popular method for synthesizing phosphaalkynes is reliant upon the expulsion of products containing strong silicon-element bonds. Specifically, it is possible to synthesize phosphaalkynes via the elimination of hexamethyldisiloxane (HMDSO) from certain silylated phosphaalkenes with the general structure RO(SiMe)C=PSiMe. These phosphaalkenes are formed rapidly following the synthesis of the appropriate acyl bis-trimethylsilylphosphine, which undergoes a rapid [1,3]-silyl shift to produce the relevant phosphaalkene. This synthetic strategy is particularly appealing because the precursors (an acyl chloride and tris-trimethylsilylphosphine or bis-trimethylsilylphosphide) are either readily available or simple to synthesize.
This method has been utilized to produce a variety of kinetically stable phosphaalkynes, including aryl, tertiary alkyl, secondary alkyl, and even primary alkyl phosphaalkynes in good yields. | 0 | Organic Chemistry |
There is little evidence of the evolution of stomata in the fossil record, but they had appeared in land plants by the middle of the Silurian period. They may have evolved by the modification of conceptacles from plants' alga-like ancestors.
However, the evolution of stomata must have happened at the same time as the waxy cuticle was evolving – these two traits together constituted a major advantage for early terrestrial plants. | 5 | Photochemistry |
DEHPA is prepared through the reaction of phosphorus pentoxide and 2-ethylhexanol:
:4 CHOH + PO → 2 [(CHO)PO(OH)]O
:[(CHO)PO(OH)]O + CHOH → (CHO)PO(OH) + (CHO)PO(OH)
These reaction produce a mixture of mono-, di-, and trisubstituted phosphates, from which DEHPA can be isolated based on solubility. | 3 | Analytical Chemistry |
Glycomics is the study of the carbohydrate components of cells. Though not exclusive to glycoproteins, it can reveal more information about different glycoproteins and their structure. One of the purposes of this field of study is to determine which proteins are glycosylated and where in the amino acid sequence the glycosylation occurs. Historically, mass spectrometry has been used to identify the structure of glycoproteins and characterize the carbohydrate chains attached. | 0 | Organic Chemistry |
Dyes are used in many industries, like paper printing or textile. They are often recalcitrant to degradation and in some cases, like some azo dyes, carcinogenic or otherwise toxic.
The mechanism by which the fungi degrade dyes is via their lignolytic enzymes, especially laccase, therefore white rot mushrooms are the most commonly used.
Mycoremediation has proven to be a cheap and effective remediation technology for dyes such as malachite green, nigrosin and basic fuchsin with Aspergillus niger and Phanerochaete chrysosporium and Congo red, a carcinogenic dye recalcitrant to biodegradative processes, direct blue 14 (using Pleurotus). | 2 | Environmental Chemistry |
The Earth-based rectenna would likely consist of many short dipole antennas connected via diodes. Microwave broadcasts from the satellite would be received in the dipoles with about 85% efficiency. With a conventional microwave antenna, the reception efficiency is better, but its cost and complexity are also considerably greater. Rectennas would likely be several kilometers across. | 7 | Physical Chemistry |
Hypermetabolism is defined as an elevated resting energy expenditure (REE) > 110% of predicted REE. Hypermetabolism is accompanied by a variety of internal and external symptoms, most notably extreme weight loss, and can also be a symptom in itself. This state of increased metabolic activity can signal underlying issues, especially hyperthyroidism. Patients with Fatal familial insomnia can also present with hypermetabolism; however, this universally fatal disorder is exceedingly rare, with only a few known cases worldwide. The drastic impact of the hypermetabolic state on patient nutritional requirements is often understated or overlooked as well. | 1 | Biochemistry |
Sugar alcohols, a class of low molecular weight polyols, are commonly obtained by hydrogenation of sugars. They have the formula (CHOH)H, where n = 4–6.
Sugar alcohols are added to foods because of their lower caloric content than sugars; however, they are also, in general, less sweet, and are often combined with high-intensity sweeteners. They are also added to chewing gum because they are not broken down by bacteria in the mouth or metabolized to acids, and thus do not contribute to tooth decay. Maltitol, sorbitol, xylitol, erythritol, and isomalt are common sugar alcohols. | 7 | Physical Chemistry |
The compound crystallizes from a heated solution of mercuric iodide, potassium iodide, and precisely 2% water in acetone. Attempted synthesis in concentrated aqueous solution will give the pale orange monohydrate instead. | 3 | Analytical Chemistry |
Iron minerals can active for dechlorination. These minerals use . Particular minerals that can be used include green rust, magnetite, pyrite, and glauconite. The most reactive of the iron minerals are the iron sulfides and oxides. Pyrite, an iron sulfide, is able to dechlorinate carbon tetrachloride in suspension. | 2 | Environmental Chemistry |
Left to equilibration, many compositions will form a uniform single phase, but depending on the temperature and pressure even a single substance may separate into two or more distinct phases. Within each phase, the properties are uniform but between the two phases properties differ.
Water in a closed jar with an air space over it forms a two-phase system. Most of the water is in the liquid phase, where it is held by the mutual attraction of water molecules. Even at equilibrium molecules are constantly in motion and, once in a while, a molecule in the liquid phase gains enough kinetic energy to break away from the liquid phase and enter the gas phase. Likewise, every once in a while a vapor molecule collides with the liquid surface and condenses into the liquid. At equilibrium, evaporation and condensation processes exactly balance and there is no net change in the volume of either phase.
At room temperature and pressure, the water jar reaches equilibrium when the air over the water has a humidity of about 3%. This percentage increases as the temperature goes up. At 100 °C and atmospheric pressure, equilibrium is not reached until the air is 100% water. If the liquid is heated a little over 100 °C, the transition from liquid to gas will occur not only at the surface but throughout the liquid volume: the water boils. | 7 | Physical Chemistry |
Isolated chloroplasts placed under light conditions but in the absence of CO, reduce and then oxidize artificial electron acceptors, allowing the process to proceed. Oxygen (O) is released as a byproduct, but not sugar (CHO).
Chloroplasts placed under dark conditions and in the absence of CO, oxidize the artificial acceptor but do not reduce it, terminating the process, without production of oxygen or sugar. | 5 | Photochemistry |
Myogenin, is a transcriptional activator encoded by the MYOG gene.
Myogenin is a muscle-specific basic-helix-loop-helix (bHLH) transcription factor involved in the coordination of skeletal muscle development or myogenesis and repair. Myogenin is a member of the MyoD family of transcription factors, which also includes MyoD, Myf5, and MRF4.
In mice, myogenin is essential for the development of functional skeletal muscle. Myogenin is required for the proper differentiation of most myogenic precursor cells during the process of myogenesis. When the DNA coding for myogenin was knocked out of the mouse genome, severe skeletal muscle defects were observed. Mice lacking both copies of myogenin (homozygous-null) suffer from perinatal lethality due to the lack of mature secondary skeletal muscle fibers throughout the body.
In cell culture, myogenin can induce myogenesis in a variety of non-muscle cell types. | 1 | Biochemistry |
4-Hydroxyestrone (4-OHE1), also known as estra-1,3,5(10)-triene-3,4-diol-17-one, is an endogenous, naturally occurring catechol estrogen and a minor metabolite of estrone and estradiol. It is estrogenic, similarly to many other hydroxylated estrogen metabolites such as 2-hydroxyestradiol, 16α-hydroxyestrone, estriol (16α-hydroxyestradiol), and 4-hydroxyestradiol but unlike 2-hydroxyestrone. | 1 | Biochemistry |
The US Government Standard Bathroom Malodor, said to be one of the worst-smelling substances, is quoted as having this composition: (Note that this substance is a concoction) | 1 | Biochemistry |
A carboxypeptidase (EC number 3.4.16 - 3.4.18) is a protease enzyme that hydrolyzes (cleaves) a peptide bond at the carboxy-terminal (C-terminal) end of a protein or peptide. This is in contrast to an aminopeptidases, which cleave peptide bonds at the N-terminus of proteins. Humans, animals, bacteria and plants contain several types of carboxypeptidases that have diverse functions ranging from catabolism to protein maturation. At least two mechanisms have been discussed. | 1 | Biochemistry |
Normally, ice crystals grown in solution only exhibit the basal (0001) and prism faces (1010), and appear as round and flat discs. However, it appears the presence of AFPs exposes other faces. It now appears the ice surface 2021 is the preferred binding surface, at least for AFP type I. Through studies on type I AFP, ice and AFP were initially thought to interact through hydrogen bonding (Raymond and DeVries, 1977). However, when parts of the protein thought to facilitate this hydrogen bonding were mutated, the hypothesized decrease in antifreeze activity was not observed. Recent data suggest hydrophobic interactions could be the main contributor. It is difficult to discern the exact mechanism of binding because of the complex water-ice interface. Currently, attempts to uncover the precise mechanism are being made through use of molecular modelling programs (molecular dynamics or the Monte Carlo method). | 1 | Biochemistry |
The airborne visible/infrared imaging spectrometer (AVIRIS) is the second in a series of imaging spectrometer instruments developed at the Jet Propulsion Laboratory (JPL) for Earth remote sensing. This instrument uses scanning optics and four spectrometers to image a 614-pixel swath simultaneously in 224 adjacent spectral bands. | 7 | Physical Chemistry |
β-Hydroxy β-methylbutyryl-coenzyme A (HMB-CoA), also known as 3-hydroxyisovaleryl-CoA, is a metabolite of -leucine that is produced in the human body. Its immediate precursors are β-hydroxy β-methylbutyric acid (HMB) and β-methylcrotonoyl-CoA (MC-CoA). It can be metabolized into HMB, MC-CoA, and HMG-CoA in humans. | 1 | Biochemistry |
When a surface is exposed to a multi-protein solution, adsorption of certain protein molecules are favored over the others. Protein molecules approaching the surface compete for binding sites. In multi-protein system attraction between molecules can occur, whereas in single-protein solutions intermolecular repulsive interactions dominate. In addition, there is a time-dependent protein spreading, where protein molecules initially make contact with minimal binding sites on the surface. With the increase in protein's residence time on the surface, the protein may unfold for interaction with additional binding sites. This results in a time-dependent increase in the contact points between protein and surface. This further makes desorption less likely. | 1 | Biochemistry |
Viral genes and host genes that are required for viruses to replicate or enter the cell, or that play an important role in the life cycle of the virus are often targeted by antiviral therapies. RNAi has been used to target genes in several viral diseases, such as the human immunodeficiency virus (HIV) and hepatitis. In particular, siRNA was used to silence the primary HIV receptor chemokine receptor 5 (CCR5). This prevented the virus from entering the human peripheral blood lymphocytes and the primary hematopoietic stem cells. A similar technique was used to decrease the amount of the detectable virus in hepatitis B and C infected cells. In hepatitis B, siRNA silencing was used to target the surface antigen on the hepatitis B virus and led to a decrease in the number of viral components. In addition, siRNA techniques used in hepatitis C were able to lower the amount of the virus in the cell by 98%.
RNA interference has been in commercial use to control virus diseases of plants for over 20 years (see Plant disease resistance). In 1986–1990, multiple examples of "coat protein-mediated resistance" against plant viruses were published, before RNAi had been discovered. In 1993, work with tobacco etch virus first demonstrated that host organisms can target specific virus or mRNA sequences for degradation, and that this activity is the mechanism behind some examples of virus resistance in transgenic plants. The discovery of small interfering RNAs (the specificity determinant in RNA-mediated gene silencing) also utilized virus-induced post-transcriptional gene silencing in plants. By 1994, transgenic squash varieties had been generated expressing coat protein genes from three different viruses, providing squash hybrids with field-validated multiviral resistance that remain in commercial use at present. Potato lines expressing viral replicase sequences that confer resistance to potato leafroll virus were sold under the trade names NewLeaf Y and NewLeaf Plus, and were widely accepted in commercial production in 1999–2001, until McDonald's Corp. decided not to purchase GM potatoes and Monsanto decided to close their NatureMark potato business. Another frequently cited example of virus resistance mediated by gene silencing involves papaya, where the Hawaiian papaya industry was rescued by virus-resistant GM papayas produced and licensed by university researchers rather than a large corporation. These papayas also remain in use at present, although not without significant public protest, which is notably less evident in medical uses of gene silencing.
Gene silencing techniques have also been used to target other viruses, such as the human papilloma virus, the West Nile virus, and the Tulane virus. The E6 gene in tumor samples retrieved from patients with the human papilloma virus was targeted and found to cause apoptosis in the infected cells. Plasmid siRNA expression vectors used to target the West Nile virus were also able to prevent the replication of viruses in cell lines. In addition, siRNA has been found to be successful in preventing the replication of the Tulane virus, part of the virus family Caliciviridae, by targeting both its structural and non-structural genes. By targeting the NTPase gene, one dose of siRNA 4 hours pre-infection was shown to control Tulane virus replication for 48 hours post-infection, reducing the viral titer by up to 2.6 logarithms. Although the Tulane virus is species-specific and does not affect humans, it has been shown to be closely related to the human norovirus, which is the most common cause of acute gastroenteritis and food-borne disease outbreaks in the United States. Human noroviruses are notorious for being difficult to study in the laboratory, but the Tulane virus offers a model through which to study this family of viruses for the clinical goal of developing therapies that can be used to treat illnesses caused by human norovirus. | 1 | Biochemistry |
In stereochemistry, a chiral auxiliary is a stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis. The chirality present in the auxiliary can bias the stereoselectivity of one or more subsequent reactions. The auxiliary can then be typically recovered for future use.
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Most biological molecules and pharmaceutical targets exist as one of two possible enantiomers; consequently, chemical syntheses of natural products and pharmaceutical agents are frequently designed to obtain the target in enantiomerically pure form. Chiral auxiliaries are one of many strategies available to synthetic chemists to selectively produce the desired stereoisomer of a given compound.
Chiral auxiliaries were introduced by Elias James Corey in 1975 with chiral 8-phenylmenthol and by Barry Trost in 1980 with chiral mandelic acid. The menthol compound is difficult to prepare and as an alternative trans-2-phenyl-1-cyclohexanol was introduced by J. K. Whitesell in 1985. | 4 | Stereochemistry |
The partial pressures of particularly oxygen () and carbon dioxide () are important parameters in tests of arterial blood gases, but can also be measured in, for example, cerebrospinal fluid. | 7 | Physical Chemistry |
Clues to the existence of a post-mortem transcriptome existed at least since the beginning of the 21st century, but the word thanatotranscriptome (from (thanatos-, Greek for "death") seems to have been first used in the scientific literature by Javan et al. in 2015, following the introduction of the concept of the human thanatomicrobiome in 2014 at the 66th Annual Meeting of the American Academy of Forensic Sciences in Seattle, Washington.
In 2016, researchers at the University of Washington confirmed that up to 2 days (48 hours) after the death of mice and zebrafish, many genes still functioned. Changes in the quantities of mRNA in the bodies of the dead animals proved that hundreds of genes with very different functions awoke just after death. The researchers detected 548 genes that awoke after death in zebrafish and 515 in laboratory mice. Among these were genes involved in development of the organism, including genes that are normally activated only in utero or in ovo (in the egg) during fetal development.
The thanatomicrobiome is characterized by a diverse assortment of microorganisms located in internal organs (brain, heart, liver, and spleen) and blood samples collected after a human dies. It is defined as the microbial community of internal body sites, created by a successional process whereby trillions of microorganisms populate, proliferate, and/or die within the dead body, resulting in temporal modifications in the community composition over time. | 1 | Biochemistry |
An extensive open-air planting used maintain genetic diversity of wild, agricultural, or forestry species. Typically species that are either difficult or impossible to conserve in seed banks are conserved in field gene banks. Field gene banks may also be used grow and select progeny of species stored by other ex situ techniques. | 1 | Biochemistry |
Analytical quality control (AQC) refers to all those processes and procedures designed to ensure that the results of laboratory analysis are consistent, comparable, accurate and within specified limits of precision. Constituents submitted to the analytical laboratory must be accurately described to avoid faulty interpretations, approximations, or incorrect results. The qualitative and quantitative data generated from the laboratory can then be used for decision making. In the chemical sense, quantitative analysis refers to the measurement of the amount or concentration of an element or chemical compound in a matrix that differs from the element or compound. Fields such as industry, medicine, and law enforcement can make use of AQC. | 2 | Environmental Chemistry |
A layered model of homogeneous and isotropic material, can be up-scaled to a transverse isotropic medium, proposed by Backus.
Backus presented an equivalent medium theory, a heterogeneous medium can be replaced by a homogeneous one that predicts wave propagation in the actual medium. Backus showed that layering on a scale much finer than the wavelength has an impact and that a number of isotropic layers can be replaced by a homogeneous transversely isotropic medium that behaves exactly in the same manner as the actual medium under static load in the infinite wavelength limit.
If each layer is described by 5 transversely isotropic parameters , specifying the matrix
The elastic moduli for the effective medium will be
where
denotes the volume weighted average over all layers.
This includes isotropic layers, as the layer is isotropic if , and . | 3 | Analytical Chemistry |
Many ylides react in sigmatropic reactions. The Sommelet-Hauser rearrangement is an example of a [2,3]-sigmatropic reaction. The Stevens rearrangement is a [1,2]-rearrangement.
A -sigmatropic reaction has been observed in certain phosphonium ylides. | 0 | Organic Chemistry |
The term ramogen refers to a biological factor, typically a growth factor or other protein, that causes a developing biological cell or tissue to branch in a tree-like manner. Ramogenic molecules are branch promoting molecules found throughout the human body,.
Brief History
The term was first coined (from the Latin ramus = branch and the Greek genesis = creation) in an article about kidney development by Davies and Davey (Pediatr Nephrol. 1999 Aug;13(6):535-41). In the article, Davies and Davy describe the existence of "ramogens" in the kidney as glial cell line-derived neurotrophic factors, neurturin and persephin. The term has now passed into general use in the technical literature concerned with branching of biological structures.
Function
A ramogen is a biochemical signal that enables the creation of a physiological branch. The signal can be in the form of a growth factor or a hormone that makes a tube branch. One specific example would be the hormone that forms the simple tube through which the mammary glands begin to form causing the formation of a highly branched “tree” of milk ducts in females.
Types of Ramogens
Mesenchyme-derived ramogens are found throughout the body and serve as chemoattractants to branching tissues.
An example of how this works is found through a study on a bead soaked in the renal ramogen GDNF. When this ramogen was placed next to a kidney sample in culture, the nearby uteric parts branch and grow toward it.
Another example of a ramogen in use was found in the lungs. The existence of Sprouty2 in the body is demonstrated in response to the signaling of the ramogen FGF10, serving as an inhibitor of branching.
The following table is a list of Key Ramogens in Branching Organs of a mouse species.
Studies involving Ramogens
The physiological capabilities of ramogens are still being postulated in medical studies involving kidney functions on mice.
In development maturing nephrons and stroma in the body may cease to produce ramogens and may begin to secrete anti-ramogenic factors, such as Bmp2 and Tgfβ.
The pattern of branching and the rate of cell proliferation can contribute to the shape of different organs. As such, the use of the glial-cell-line neurotrophic factor (GDNF) has been found to contribute to uterine tissues.
The implication of this is that the introduction of ramogens to the body can cause cell repair through the creation of side branches introduced through ramogenic signals in the body ).
This is evidenced through studies demonstrating that uterine stalks were capable of forming new tips if provided with fresh mesenchyme or with a Matrigel artificially loaded with ramogens, such as GDNF and FGF1. The ramogens used in this study were manufactured with fresh mesenchyme. | 1 | Biochemistry |
Burks-Houck was dedicated to the establishment of the NOBCChE on the West Coast and its national endeavours. She was invited to Dakar, Senegal to represent NOBCChE as an environmental chemist and deliver a presentation titled: "Environmental Applications and Regulatory Reporting". She served as the first chair of the San Francisco Bay Area Chapter from 1984 – 1990 organizing educational and professional development events for the community. Burks-Houck was elected in 1991 as the national vice-president of NOBCChE, a position she held until elected as the first female president of the organization in 1993. Burks-Houck held this role for an unprecedented four consecutive terms before stepping down in 2001. Her involvement was credited with more than 100% increase in the number of student and professional chapters, instituting new scholarships through public and private entities, updating telephone and computer systems at the National Office, and establishing the Science Quiz Bowl and the Science Fair at the National level. Burks-Houck was also credited with building partnerships with other organizations such as the American Association for the Advancement of Science (AAAS), American Chemical Society (ACS), American Indian Science and Engineering Alliance, National Aeronautics and Space Administration (NASA), and the Society for the Advancement of Chicanos and Native Americans in Science (SACNAS).
Burks-Houck's legacy with the NOBCChE was expanded upon in 2010, after her death, through the creation of the Winifred Burks-Houck Professional Leadership Awards and Symposium to honour the contributions of African American women in science and technology. There are four categories of awards: Distinguished Lecturer, Professional Awardee, Graduate Student Awardee, and Undergraduate Awardee to recognize scientific achievements, creativity, leadership, and community service. | 0 | Organic Chemistry |
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