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Avoiding the use of pressure to introduce the mobile phase into the column, results in a number of important advantages. Firstly, the pressure driven flow rate across a column depends directly on the square of the particle diameter and inversely on the length of the column. This restricts the length of the column and size of the particle, particle size is seldom less than 3 micrometer and the length of the column is restricted to 25 cm. Electrically driven flow rate is independent of length of column and size. A second advantage of using electroosmosis to pass the mobile phase into the column is the plug-like flow velocity profile of EOF, which reduces the solute dispersion in the column, increasing column efficiency. | 1 | Biochemistry |
Gamma spectroscopy detectors are passive materials that are able to interact with incoming gamma rays. The most important interaction mechanisms are the photoelectric effect, the Compton effect, and pair production. Through these processes, the energy of the gamma ray is absorbed and converted into a voltage signal by detecting the energy difference before and after the interaction (or, in a scintillation counter, the emitted photons using a photomultiplier). The voltage of the signal produced is proportional to the energy of the detected gamma ray. Common detector materials include sodium iodide (NaI) scintillation counters and high-purity germanium detectors.
To accurately determine the energy of the gamma ray, it is advantageous if the photoelectric effect occurs, as it absorbs all of the energy of the incident ray. Absorbing all the energy is also possible when a series of these interaction mechanisms take place within the detector volume. With Compton interaction or pair production, a portion of the energy may escape from the detector volume, without being absorbed. The absorbed energy thus gives rise to a signal that behaves like a signal from a ray of lower energy. This leads to a spectral feature overlapping the regions of lower energy. Using larger detector volumes reduces this effect. More sophisticated methods of reducing this effect include using Compton-suppression shields and employing segmented detectors with add-back (see: clover (detector)). | 7 | Physical Chemistry |
A "Zintl Phase" was first observed in 1891 by M. Joannis, who noted an unexpected green colored solution after dissolving lead and sodium in liquid ammonia, indicating the formation of a new product. It was not until many years later, in 1930, that the stoichiometry of the new product was identified as NaPb by titrations performed by Zintl et al.; and it was not until 1970 that the structure was confirmed by crystallization with ethylenediamine (en) by Kummer.
In the intervening years and in the years since, many other reaction mixtures of metals were explored to provide a great number of examples of this type of system. There are hundreds of both compounds composed of group 14 elements and group 15 elements, plus dozens of others beyond those groups, all spanning a variety of different geometries. Corbett has contributed improvements to the crystallization of Zintl ions by demonstrating the use of chelating ligands, such as cryptands, as cation sequestering agents.
More recently, Zintl phase and ion reactivity in more complex systems, with organic ligands or transition metals, have been investigated, as well as their use in practical applications, such as for catalytic purposes or in materials science. | 7 | Physical Chemistry |
Affinity-trap polyacrylamide gel electrophoresis (PAGE) has become one of the most popular methods of protein separation. This is not only due to its separation qualities, but also because it can be used in conjunction with a variety of other analytic methods, such as mass spectrometry, and western blotting. In addition to helping isolate and purify proteins from biological samples, AT-PAGE is anticipated to be helpful in analyses of variations in the expression of particular proteins as well as in investigations of posttranslational modifications of proteins. This method utilizes a two-step approach. First, a protein sample is run through a polyacrylamide gel using electrophoresis. Then, the sample is transferred to a different polyacrylamide gel (the affinity-trap gel) where affinity probes are immobilized. The proteins that do not have affinity for the affinity probes pass through the affinity-trap gel, and proteins with affinity for the probes will be "trapped" by the immobile affinity probes. These trapped proteins are then visualized and identified using mass spectrometry after in-gel digestion. | 1 | Biochemistry |
The coenzyme NAD was first discovered by the British biochemists Arthur Harden and William John Young in 1906. They noticed that adding boiled and filtered yeast extract greatly accelerated alcoholic fermentation in unboiled yeast extracts. They called the unidentified factor responsible for this effect a coferment. Through a long and difficult purification from yeast extracts, this heat-stable factor was identified as a nucleotide sugar phosphate by Hans von Euler-Chelpin. In 1936, the German scientist Otto Heinrich Warburg showed the function of the nucleotide coenzyme in hydride transfer and identified the nicotinamide portion as the site of redox reactions.
Vitamin precursors of NAD were first identified in 1938, when Conrad Elvehjem showed that liver has an "anti-black tongue" activity in the form of nicotinamide. Then, in 1939, he provided the first strong evidence that niacin is used to synthesize NAD. In the early 1940s, Arthur Kornberg was the first to detect an enzyme in the biosynthetic pathway. In 1949, the American biochemists Morris Friedkin and Albert L. Lehninger proved that NADH linked metabolic pathways such as the citric acid cycle with the synthesis of ATP in oxidative phosphorylation. In 1958, Jack Preiss and Philip Handler discovered the intermediates and enzymes involved in the biosynthesis of NAD; salvage synthesis from nicotinic acid is termed the Preiss-Handler pathway. In 2004, Charles Brenner and co-workers uncovered the nicotinamide riboside kinase pathway to NAD.
The non-redox roles of NAD(P) were discovered later. The first to be identified was the use of NAD as the ADP-ribose donor in ADP-ribosylation reactions, observed in the early 1960s. Studies in the 1980s and 1990s revealed the activities of NAD and NADP metabolites in cell signaling – such as the action of cyclic ADP-ribose, which was discovered in 1987.
The metabolism of NAD remained an area of intense research into the 21st century, with interest heightened after the discovery of the NAD-dependent protein deacetylases called sirtuins in 2000, by Shin-ichiro Imai and coworkers in the laboratory of Leonard P. Guarente. In 2009 Imai proposed the "NAD World" hypothesis that key regulators of aging and longevity in mammals are sirtuin 1 and the primary NAD synthesizing enzyme nicotinamide phosphoribosyltransferase (NAMPT). In 2016 Imai expanded his hypothesis to "NAD World 2.0", which postulates that extracellular NAMPT from adipose tissue maintains NAD in the hypothalamus (the control center) in conjunction with myokines from skeletal muscle cells. In 2018, Napa Therapeutics was formed to develop drugs against a novel aging related target based on the research in NAD metabolism conducted in the lab of Eric Verdin. | 5 | Photochemistry |
An expression cassette is a distinct component of vector DNA consisting of a gene and regulatory sequence to be expressed by a transfected cell. In each successful transformation, the expression cassette directs the cell's machinery to make RNA and protein(s). Some expression cassettes are designed for modular cloning of protein-encoding sequences so that the same cassette can easily be altered to make different proteins.
An expression cassette is composed of one or more genes and the sequences controlling their expression. An expression cassette comprises three components: a promoter sequence, an open reading frame, and a 3' untranslated region that, in eukaryotes, usually contains a polyadenylation site.
Different expression cassettes can be transfected into different organisms including bacteria, yeast, plants, and mammalian cells as long as the correct regulatory sequences are used. | 1 | Biochemistry |
As a result of the capacity of transposon mutagenesis to incorporate genes into most areas of target chromosomes, there are a number of functions associated with the process.
* Virulence genes in viruses and bacteria can be discovered by disrupting genes and observing for a change in phenotype. This has importance in antibiotic production and disease control.
* Non-essential genes can be discovered by inducing transposon mutagenesis in an organism. The transformed genes can then be identified by performing PCR on the organism's recovered genome using an ORF-specific primer and a transposon-specific primer. Since transposons can incorporate themselves into non-coding regions of DNA, the ORF-specific primer ensures that the transposon interrupted a gene. Because the organism survived after homologous integration, the interrupted gene was clearly non-essential.
* Cancer-causing genes can be identified by genome-wide mutagenesis and screening of mutants containing tumours. Based on the mechanism and results of the mutation, cancer-causing genes can be identified as oncogenes or tumour-suppressor genes. | 1 | Biochemistry |
In molecular biology, extracellular signal-regulated kinases (ERKs) or classical MAP kinases are widely expressed protein kinase intracellular signalling molecules that are involved in functions including the regulation of meiosis, mitosis, and postmitotic functions in differentiated cells. Many different stimuli, including growth factors, cytokines, virus infection, ligands for heterotrimeric G protein-coupled receptors, transforming agents, and carcinogens, activate the ERK pathway.
The term, "extracellular signal-regulated kinases", is sometimes used as a synonym for mitogen-activated protein kinase (MAPK), but has more recently been adopted for a specific subset of the mammalian MAPK family.
In the MAPK/ERK pathway, Ras activates c-Raf, followed by mitogen-activated protein kinase kinase (abbreviated as MKK, MEK, or MAP2K) and then MAPK1/2 (below). Ras is typically activated by growth hormones through receptor tyrosine kinases and GRB2/SOS, but may also receive other signals. ERKs are known to activate many transcription factors, such as ELK1, and some downstream protein kinases.
Disruption of the ERK pathway is common in cancers, especially Ras, c-Raf, and receptors such as HER2. | 1 | Biochemistry |
Urine testing is the most common method of testing for ketones. Urine test strips utilize a nitroprusside reaction with acetoacetate to give a semi-quantitative measure based on color change of the strip. Although beta-hydroxybutyrate is the predominant circulating ketone, urine test strips only measure acetoacetate. Urinary ketones often correlate poorly with serum levels because of variability in excretion of ketones by the kidney, influence of hydration status, and renal function. | 1 | Biochemistry |
There are currently around 19 research groups at the institute. The research at MPI-Marburg broadly focuses on understanding the functioning of microorganisms at the molecular, cellular and community levels. In particular, the focus is the mechanisms of cellular and community adaptation of bacteria in response to changes in the environment. | 9 | Geochemistry |
Researchers claim experiments that successfully detected the Sokolov–Ternov effect may also detect the Unruh effect under certain conditions.
Theoretical work in 2011 suggests that accelerating detectors could be used for the direct detection of the Unruh effect with current technology.
The Unruh effect may have been observed for the first time in 2019 in the high energy channeling radiation explored by the NA63 experiment at CERN. | 7 | Physical Chemistry |
*Gene fusion
** Recurrent somatic fusions of the two genes, NGFI-A–binding protein 2 (NAB2) and STAT6, located at chromosomal region 12q13, have been identified in solitary fibrous tumors.
*Amplification
**STAT6 is amplified in a subset of dedifferentiated liposarcoma. | 1 | Biochemistry |
For low energy photons the wavelength shift becomes negligible () and the Klein–Nishina formula reduces to the classical Thomson expression:
which is symmetrical in the scattering angle, i.e. the photon is just as likely to scatter backwards as forwards. With increasing energy this symmetry is broken and the photon becomes more likely to scatter in the forward direction. | 7 | Physical Chemistry |
Grignard reagents do not typically react with organic halides, in contrast with their high reactivity with other main group halides. In the presence of metal catalysts, however, Grignard reagents participate in C-C coupling reactions. For example, nonylmagnesium bromide reacts with methyl p-chlorobenzoate to give p-nonylbenzoic acid, in the presence of Tris(acetylacetonato)iron(III) (Fe(acac)), after workup with NaOH to hydrolyze the ester, shown as follows. Without the Fe(acac), the Grignard reagent would attack the ester group over the aryl halide.
For the coupling of aryl halides with aryl Grignard reagents, nickel chloride in tetrahydrofuran (THF) is also a good catalyst. Additionally, an effective catalyst for the couplings of alkyl halides is the Gilman catalyst lithium tetrachlorocuprate (), prepared by mixing lithium chloride (LiCl) and copper(II) chloride () in THF. The Kumada-Corriu coupling gives access to [substituted] styrenes. | 0 | Organic Chemistry |
An amidate/imidate anion is formed upon deprotonation of an amide or imidic acid. Since amides and imidic acids are tautomers, they form the same anion upon deprotonation. The two names are thus synonyms describing the same anion, although arguably, imidate refers to the resonance contributor on the left, while amidate refers to the resonance contributor on the right. However, they are distinguished when they act as ligands for transition metals, with O-bound species referred to as imidates and N-bound species referred to as amidates. They can be considered aza-substituted analogues of enolates with the formula R-N=C(O)R. | 0 | Organic Chemistry |
GPCRs are involved in a wide variety of physiological processes. Some examples of their physiological roles include:
# The visual sense: The opsins use a photoisomerization reaction to translate electromagnetic radiation into cellular signals. Rhodopsin, for example, uses the conversion of 11-cis-retinal to all-trans-retinal for this purpose.
# The gustatory sense (taste): GPCRs in taste cells mediate release of gustducin in response to bitter-, umami- and sweet-tasting substances.
# The sense of smell: Receptors of the olfactory epithelium bind odorants (olfactory receptors) and pheromones (vomeronasal receptors)
# Behavioral and mood regulation: Receptors in the mammalian brain bind several different neurotransmitters, including serotonin, dopamine, histamine, GABA, and glutamate
# Regulation of immune system activity and inflammation: chemokine receptors bind ligands that mediate intercellular communication between cells of the immune system; receptors such as histamine receptors bind inflammatory mediators and engage target cell types in the inflammatory response. GPCRs are also involved in immune-modulation, e. g. regulating interleukin induction or suppressing TLR-induced immune responses from T cells.
# Autonomic nervous system transmission: Both the sympathetic and parasympathetic nervous systems are regulated by GPCR pathways, responsible for control of many automatic functions of the body such as blood pressure, heart rate, and digestive processes
# Cell density sensing: A novel GPCR role in regulating cell density sensing.
# Homeostasis modulation (e.g., water balance).
# Involved in growth and metastasis of some types of tumors.
# Used in the endocrine system for peptide and amino-acid derivative hormones that bind to GCPRs on the cell membrane of a target cell. This activates cAMP, which in turn activates several kinases, allowing for a cellular response, such as transcription. | 1 | Biochemistry |
The data is weighted and integrated and a confidence score is calculated for all protein interactions. Results of the various computational predictions can be inspected from different designated views. There are two modes of STRING: Protein-mode and [https://www.ncbi.nlm.nih.gov/COG/ COG]-mode. Predicted interactions are propagated to proteins in other organisms for which interaction has been described by inference of orthology. A web interface is available to access the data and to give a fast overview of the proteins and their interactions. A plug-in for cytoscape to use STRING data is available.
Another possibility to access data STRING is to use the application programming interface (API) by constructing a URL that contain the request. | 1 | Biochemistry |
Some viral families, such as the Bromoviridae instead opt to have multipartite genomes, genomes split between multiple viral particles. For infection to occur, the plant must be infected with all particles across the genome. For instance Brome mosaic virus has a genome split between 3 viral particles, and all 3 particles with the different RNAs are required for infection to take place. | 1 | Biochemistry |
The protection of food from photodegradation is very important. Some nutrients, for example, are affected by degradation when exposed to sunlight. In the case of beer, UV radiation causes a process that entails the degradation of hop bitter compounds to 3-methyl-2-buten-1-thiol and therefore changes the taste. As amber-colored glass has the ability to absorb UV radiation, beer bottles are often made from such glass to prevent this process. | 5 | Photochemistry |
Simple, unhindered dialkylboranes are reactive at room temperature towards most alkenes and terminal alkynes but are difficult to prepare in high purity, since they exist in equilibrium with mono- and trialkylboranes. One common way of preparing them is the reduction of dialkylhalogenoboranes with metal hydrides. An important synthetic application using such dialkylboranes, such as diethylborane, is the transmetallation of the organoboron compounds to form organozinc compounds. | 0 | Organic Chemistry |
A biochemical penetrant is a chemical that increases the ability of a poison to apply its toxic effect to a living organism.
Typically, the term penetrant when used for a biochemical agent, relates to an agrichemical that is used with a weedkiller or fungicide. The term seems to be used in relation to agrichemicals within English speaking countries rather than North American.
When mixed with a weedkiller (normally as an aqua solution) the penetrant chemical causes a plant to absorb the poison in a more effective manner and so succumb more readily. Penetrants are most often used against plants that would otherwise be able to resist the weedkiller. Often such plants have tough leaves or shiny leaves that shed water easily. | 1 | Biochemistry |
Several isotopes of both hydrogen and oxygen exist, giving rise to several known isotopologues of water. Vienna Standard Mean Ocean Water is the current international standard for water isotopes. Naturally occurring water is almost completely composed of the neutron-less hydrogen isotope protium. Only 155 ppm include deuterium ( or D), a hydrogen isotope with one neutron, and fewer than 20 parts per quintillion include tritium ( or T), which has two neutrons. Oxygen also has three stable isotopes, with present in 99.76%, in 0.04%, and in 0.2% of water molecules.
Deuterium oxide, , is also known as heavy water because of its higher density. It is used in nuclear reactors as a neutron moderator. Tritium is radioactive, decaying with a half-life of 4500 days; exists in nature only in minute quantities, being produced primarily via cosmic ray-induced nuclear reactions in the atmosphere. Water with one protium and one deuterium atom occur naturally in ordinary water in low concentrations (~0.03%) and in far lower amounts (0.000003%) and any such molecules are temporary as the atoms recombine.
The most notable physical differences between and , other than the simple difference in specific mass, involve properties that are affected by hydrogen bonding, such as freezing and boiling, and other kinetic effects. This is because the nucleus of deuterium is twice as heavy as protium, and this causes noticeable differences in bonding energies. The difference in boiling points allows the isotopologues to be separated. The self-diffusion coefficient of at 25 °C is 23% higher than the value of . Because water molecules exchange hydrogen atoms with one another, hydrogen deuterium oxide (DOH) is much more common in low-purity heavy water than pure dideuterium monoxide .
Consumption of pure isolated may affect biochemical processes—ingestion of large amounts impairs kidney and central nervous system function. Small quantities can be consumed without any ill-effects; humans are generally unaware of taste differences, but sometimes report a burning sensation or sweet flavor. Very large amounts of heavy water must be consumed for any toxicity to become apparent. Rats, however, are able to avoid heavy water by smell, and it is toxic to many animals.
Light water refers to deuterium-depleted water (DDW), water in which the deuterium content has been reduced below the standard level. | 2 | Environmental Chemistry |
Multicopy single-stranded DNA (msDNA) is a type of extrachromosomal satellite DNA that consists of a single-stranded DNA molecule covalently linked via a 2-5phosphodiester bond to an internal guanosine of an RNA molecule. The resultant DNA/RNA chimera possesses two stem-loops joined by a branch similar to the branches found in RNA splicing intermediates. The coding region for msDNA, called a "retron", also encodes a type of reverse transcriptase, which is essential for msDNA synthesis. | 1 | Biochemistry |
However, fluctuations that cause the correlations between pairs of atoms to decrease as their separation increases, causes the Bragg peaks in the structure factor of a crystal to broaden. To see how this works, we consider a one-dimensional toy model: a stack of plates with mean spacing . The derivation follows that in chapter 9 of Guinier's textbook. This model has been pioneered by and applied to a number of materials by Hosemann and collaborators over a number of years. Guinier and they termed this disorder of the second kind, and Hosemann in particular referred to this imperfect crystalline ordering as paracrystalline ordering. Disorder of the first kind is the source of the Debye–Waller factor.
To derive the model we start with the definition (in one dimension) of the
To start with we will consider, for simplicity an infinite crystal, i.e., . We will consider a finite crystal with disorder of the second-type below.
For our infinite crystal, we want to consider pairs of lattice sites. For large each plane of an infinite crystal, there are two neighbours planes away, so the above double sum becomes a single sum over pairs of neighbours either side of an atom, at positions and lattice spacings away, times . So, then
where is the probability density function for the separation of a pair of planes, lattice spacings apart. For the separation of neighbouring planes we assume for simplicity that the fluctuations around the mean neighbour spacing of a are Gaussian, i.e., that
and we also assume that the fluctuations between a plane and its neighbour, and between this neighbour and the next plane, are independent. Then is just the convolution of two s, etc. As the convolution of two Gaussians is just another Gaussian, we have that
The sum in is then just a sum of Fourier transforms of Gaussians, and so
for . The sum is just the real part of the sum and so the structure factor of the infinite but disordered crystal is
This has peaks at maxima , where . These peaks have heights
i.e., the height of successive peaks drop off as the order of the peak (and so ) squared. Unlike finite-size effects that broaden peaks but do not decrease their height, disorder lowers peak heights. Note that here we assuming that the disorder is relatively weak, so that we still have relatively well defined peaks. This is the limit , where . In this limit, near a peak we can approximate , with and obtain
which is a Lorentzian or Cauchy function, of FWHM , i.e., the FWHM increases as the square of the order of peak, and so as the square of the wave vector at the peak.
Finally, the product of the peak height and the FWHM is constant and equals , in the limit. For the first few peaks where is not large, this is just the limit. | 3 | Analytical Chemistry |
The biochemistry of methanogenesis involves the following coenzymes and cofactors: F420, coenzyme B, coenzyme M, methanofuran, and methanopterin.
The mechanism for the conversion of bond into methane involves a ternary complex of methyl coenzyme M and coenzyme B fit into a channel terminated by the axial site on nickel of the cofactor F430. One proposed mechanism invokes electron transfer from Ni(I) (to give Ni(II)), which initiates formation of . Coupling of the coenzyme M thiyl radical (RS) with HS coenzyme B releases a proton and re-reduces Ni(II) by one-electron, regenerating Ni(I). | 1 | Biochemistry |
Mehrotra was involved in policy-making bodies from early stages of his career when he sat in the Review Committee in Chemistry in 1960 and the committee made a number of recommendations on improvement of curriculum, research environment, and examination procedures of chemistry education in India. During 1963–67, he sat in the Chemical Advisory Committee of the Atomic Energy Commission of India. The Commission on Revision of Pay Scales to Teachers which he chaired in 1983 recommended that the procedure for selection of teachers should also include an assessment of the physical and mental abilities of the candidates. The commission also recommended for pay scale revision of the teaching staff ranging from over 200 to more than 300 per cent which was subsequently accepted by the Government of India and the revision was implemented in 1987 with retrospective effective from 1 January 1986.
Mehrotra served as the president of the chemistry section of the Indian Science Congress Association in 1967, he would also serve as its national president in 1979. Besides participating in the UGC ad-hoc commissions, he was also associated with the body as a convener of its chemistry panel and his association with the Council of Scientific and Industrial Research (CSIR) included the chair of the Chemical Research Committee (1975) and membership in CSIR Society and CSIR Governing Body (1963–66 and 1976–80). He served as the president of the Indian Chemical Society (1976–77) and Vigyan Parishad, Allahabad, as the vice president of the Indian National Science Academy - INSA (1977–78) and as a member of the International Union of Pure and Applied Chemistry (1977–81). He was also a member of the INSA council from 1979 to 1981. | 0 | Organic Chemistry |
Thermal radiation can be concentrated on a tiny spot via reflecting mirrors, which concentrating solar power takes advantage of. Instead of mirrors, Fresnel lenses can also be used to concentrate radiant energy. In principle, any kind of lens can be used, but only the Fresnel lens design is practical for very large lenses. Either method can be used to quickly vaporize water into steam using sunlight. For example, the sunlight reflected from mirrors heats the PS10 Solar Power Plant, and during the day it can heat water to . | 7 | Physical Chemistry |
For many decades, arsenic was used medicinally to treat syphilis. It is still used in sheep dips, rat poisons, wood preservatives, weed killers, and other pesticides. Arsenic is poisonous if it enters the human body. | 1 | Biochemistry |
The esophagus, commonly known as the foodpipe or gullet, consists of a muscular tube through which food passes from the pharynx to the stomach. The esophagus is continuous with the laryngopharynx. It passes through the posterior mediastinum in the thorax and enters the stomach through a hole in the thoracic diaphragm—the esophageal hiatus, at the level of the tenth thoracic vertebra (T10). Its length averages 25 cm, varying with an individual's height. It is divided into cervical, thoracic and abdominal parts. The pharynx joins the esophagus at the esophageal inlet which is behind the cricoid cartilage.
At rest the esophagus is closed at both ends, by the upper and lower esophageal sphincters. The opening of the upper sphincter is triggered by the swallowing reflex so that food is allowed through. The sphincter also serves to prevent back flow from the esophagus into the pharynx. The esophagus has a mucous membrane and the epithelium which has a protective function is continuously replaced due to the volume of food that passes inside the esophagus. During swallowing, food passes from the mouth through the pharynx into the esophagus. The epiglottis folds down to a more horizontal position to direct the food into the esophagus, and away from the trachea.
Once in the esophagus, the bolus travels down to the stomach via rhythmic contraction and relaxation of muscles known as peristalsis. The lower esophageal sphincter is a muscular sphincter surrounding the lower part of the esophagus. The gastroesophageal junction between the esophagus and the stomach is controlled by the lower esophageal sphincter, which remains constricted at all times other than during swallowing and vomiting to prevent the contents of the stomach from entering the esophagus. As the esophagus does not have the same protection from acid as the stomach, any failure of this sphincter can lead to heartburn. | 1 | Biochemistry |
The journal publishes original research papers that include developments in analytical techniques, studies of geological-environmental reference materials, advances in statistical analysis of geoanalytical data, as well as data compilations, contributions to the characterisation of reference materials, as well as review articles and topical commentaries. It also publishes an annual bibliographic review article of the geoanalytical literature and a biennial series of critical reviews of analytical developments. | 9 | Geochemistry |
pRb has the ability to reversibly inhibit DNA replication through transcriptional repression of DNA replication factors. pRb is able to bind to transcription factors in the E2F family and thereby inhibit their function. When pRb is chronically activated, it leads to the downregulation of the necessary DNA replication factors. Within 72–96 hours of active pRb induction in A2-4 cells, the target DNA replication factor proteins—MCMs, RPA34, DBF4, RFCp37, and RFCp140—all showed decreased levels. Along with decreased levels, there was a simultaneous and expected inhibition of DNA replication in these cells. This process, however, is reversible. Following induced knockout of pRb, cells treated with cisplatin, a DNA-damaging agent, were able to continue proliferating, without cell cycle arrest, suggesting pRb plays an important role in triggering chronic S-phase arrest in response to genotoxic stress.
One such example of E2F-regulated genes repressed by pRb are cyclin E and cyclin A. Both of these cyclins are able to bind to Cdk2 and facilitate entry into the S phase of the cell cycle. Through the repression of expression of cyclin E and cyclin A, pRb is able to inhibit the G1/S transition. | 1 | Biochemistry |
xDNA (also known as expanded DNA or benzo-homologated DNA) is a size-expanded nucleotide system synthesized from the fusion of a benzene ring and one of the four natural bases: adenine, guanine, cytosine, and thymine. This size expansion produces an 8 letter alphabet which has a larger information storage capacity than natural DNA's (often referred to as B-DNA in literature) 4 letter alphabet. As with normal base-pairing, A pairs with xT, C pairs with xG, G pairs with xC, and T pairs with xA. The double helix is thus 2.4Å wider than a natural double helix. While similar in structure to B-DNA, xDNA has unique absorption, fluorescence, and stacking properties.
Initially synthesized as an enzyme probe by Nelson J. Leonards group, benzo-homologated adenine was the first base synthesized. Later, Eric T. Kools group finished synthesizing the remaining three expanded bases, eventually followed by yDNA ("wide" DNA), another benzo-homologated nucleotide system, and naphtho-homologated xxDNA and yyDNA. xDNA is more stable when compared to regular DNA when subjected to higher temperature, and while entire strands of xDNA, yDNA, xxDNA and yyDNA exist, they are currently difficult to synthesize and maintain. Experiments with xDNA provide new insight into the behavior of natural B-DNA. The extended bases xA, xC, xG, and xT are naturally fluorescent, and single strands composed of only extended bases can recognize and bind to single strands of natural DNA, making them useful tools for studying biological systems. xDNA is most commonly formed with base pairs between a natural and expanded nucleobase, however x-nucleobases can also be paired together. Current research supports xDNA as a viable genetic encoding system in the near future. | 1 | Biochemistry |
Diazo compounds are used as precursors to carbenes, which are generated by thermolysis or photolysis, for example in the Wolff rearrangement. As such they are used in cyclopropanation for example in the reaction of ethyl diazoacetate with styrene. Certain diazo compounds can couple to form alkenes in a formal carbene dimerization reaction.
Diazo compounds are intermediates in the Bamford-Stevens reaction of tosylhydrazones to alkenes, again with a carbene intermediate:
In the Doyle-Kirmse reaction certain diazo compounds react with allyl sulfides to the homoallyl sulfide. Intramolecular reactions of diazocarbonyl compounds provide access to cyclopropanes. In the Buchner ring expansion diazo compounds react with aromatic rings with ring-expansion. | 0 | Organic Chemistry |
Surface scientists commonly use an optical goniometer/tensiometer to measure the surface tension and interfacial tension of a liquid using the pendant or sessile drop methods. A drop is produced and captured using a CCD camera. The drop profile is subsequently extracted, and sophisticated software routines then fit the theoretical Young-Laplace equation to the experimental drop profile. The surface tension can then be calculated from the fitted parameters. Unlike other methods, this technique requires only a small amount of liquid making it suitable for measuring interfacial tensions of expensive liquids. | 7 | Physical Chemistry |
Stimuli to neurons can be physical, electrical, or chemical, and can either inhibit or excite the neuron being stimulated. An inhibitory stimulus is transmitted to the dendrite of a neuron, causing hyperpolarization of the neuron. The hyperpolarization following an inhibitory stimulus causes a further decrease in voltage within the neuron below the resting potential. By hyperpolarizing a neuron, an inhibitory stimulus results in a greater negative charge that must be overcome for depolarization to occur. Excitation stimuli, on the other hand, increases the voltage in the neuron, which leads to a neuron that is easier to depolarize than the same neuron in the resting state. Regardless of it being excitatory or inhibitory, the stimulus travels down the dendrites of a neuron to the cell body for integration. | 7 | Physical Chemistry |
In the protonation of an enolate ion, the kinetic product is the enol and the thermodynamic product is a ketone or aldehyde. Carbonyl compounds and their enols interchange rapidly by proton transfers catalyzed by acids or bases, even in trace amounts, in this case mediated by the enolate or the proton source.
In the deprotonation of an unsymmetrical ketone, the kinetic product is the enolate resulting from removal of the most accessible α-H while the thermodynamic product has the more highly substituted enolate moiety. Use of low temperatures and sterically demanding bases increases the kinetic selectivity. Here, the difference in pK between the base and the enolate is so large that the reaction is essentially irreversible, so the equilibration leading to the thermodynamic product is likely a proton exchange occurring during the addition between the kinetic enolate and as-yet-unreacted ketone. An inverse addition (adding ketone to the base) with rapid mixing would minimize this. The position of the equilibrium will depend on the countercation and solvent.
If a much weaker base is used, the deprotonation will be incomplete, and there will be an equilibrium between reactants and products. Thermodynamic control is obtained, however the reaction remains incomplete unless the product enolate is trapped, as in the example below. Since H transfers are very fast, the trapping reaction being slower, the ratio of trapped products largely mirrors the deprotonation equilibrium. | 7 | Physical Chemistry |
Kiemer and Cesareni raise the following concerns with the state (circa 2007) of the field especially with the comparative interactomic: The experimental procedures associated with the field are error prone leading to "noisy results". This leads to 30% of all reported interactions being artifacts. In fact, two groups using the same techniques on the same organism found less than 30% interactions in common. However, some authors have argued that such non-reproducibility results from the extraordinary sensitivity of various methods to small experimental variation. For instance, identical conditions in Y2H assays result in very different interactions when different Y2H vectors are used.
Techniques may be biased, i.e. the technique determines which interactions are found. In fact, any method has built in biases, especially protein methods. Because every protein is different no method can capture the properties of each protein. For instance, most analytical methods that work fine with soluble proteins deal poorly with membrane proteins. This is also true for Y2H and AP/MS technologies.
Interactomes are not nearly complete with perhaps the exception of S. cerevisiae. This is not really a criticism as any scientific area is "incomplete" initially until the methodologies have been improved. Interactomics in 2015 is where genome sequencing was in the late 1990s, given that only a few interactome datasets are available (see table above).
While genomes are stable, interactomes may vary between tissues, cell types, and developmental stages. Again, this is not a criticism, but rather a description of the challenges in the field.
It is difficult to match evolutionarily related proteins in distantly related species. While homologous DNA sequences can be found relatively easily, it is much more difficult to predict homologous interactions ("interologs") because the homologs of two interacting proteins do not need to interact. For instance, even within a proteome two proteins may interact but their paralogs may not.
Each protein–protein interactome may represent only a partial sample of potential interactions, even when a supposedly definitive version is published in a scientific journal. Additional factors may have roles in protein interactions that have yet to be incorporated in interactomes. The binding strength of the various protein interactors, microenvironmental factors, sensitivity to various procedures, and the physiological state of the cell all impact protein–protein interactions, yet are usually not accounted for in interactome studies. | 1 | Biochemistry |
In hot and dry conditions, plants close their stomata to prevent water loss. Under these conditions, will decrease and oxygen gas, produced by the light reactions of photosynthesis, will increase, causing an increase of photorespiration by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and decrease in carbon fixation. Some plants have evolved mechanisms to increase the concentration in the leaves under these conditions.
Plants that use the C carbon fixation process chemically fix carbon dioxide in the cells of the mesophyll by adding it to the three-carbon molecule phosphoenolpyruvate (PEP), a reaction catalyzed by an enzyme called PEP carboxylase, creating the four-carbon organic acid oxaloacetic acid. Oxaloacetic acid or malate synthesized by this process is then translocated to specialized bundle sheath cells where the enzyme RuBisCO and other Calvin cycle enzymes are located, and where released by decarboxylation of the four-carbon acids is then fixed by RuBisCO activity to the three-carbon 3-phosphoglyceric acids. The physical separation of RuBisCO from the oxygen-generating light reactions reduces photorespiration and increases fixation and, thus, the photosynthetic capacity of the leaf. plants can produce more sugar than plants in conditions of high light and temperature. Many important crop plants are plants, including maize, sorghum, sugarcane, and millet. Plants that do not use PEP-carboxylase in carbon fixation are called C plants because the primary carboxylation reaction, catalyzed by RuBisCO, produces the three-carbon 3-phosphoglyceric acids directly in the Calvin-Benson cycle. Over 90% of plants use carbon fixation, compared to 3% that use carbon fixation; however, the evolution of in over sixty plant lineages makes it a striking example of convergent evolution. C photosynthesis, which involves carbon-concentration by selective breakdown of photorespiratory glycine, is both an evolutionary precursor to and a useful carbon-concentrating mechanism in its own right.
Xerophytes, such as cacti and most succulents, also use PEP carboxylase to capture carbon dioxide in a process called Crassulacean acid metabolism (CAM). In contrast to metabolism, which spatially separates the fixation to PEP from the Calvin cycle, CAM temporally separates these two processes. CAM plants have a different leaf anatomy from plants, and fix the at night, when their stomata are open. CAM plants store the mostly in the form of malic acid via carboxylation of phosphoenolpyruvate to oxaloacetate, which is then reduced to malate. Decarboxylation of malate during the day releases inside the leaves, thus allowing carbon fixation to 3-phosphoglycerate by RuBisCO. CAM is used by 16,000 species of plants.
Calcium-oxalate-accumulating plants, such as Amaranthus hybridus and Colobanthus quitensis, show a variation of photosynthesis where calcium oxalate crystals function as dynamic carbon pools, supplying carbon dioxide (CO) to photosynthetic cells when stomata are partially or totally closed. This process was named alarm photosynthesis. Under stress conditions (e.g., water deficit), oxalate released from calcium oxalate crystals is converted to CO by an oxalate oxidase enzyme, and the produced CO can support the Calvin cycle reactions. Reactive hydrogen peroxide (HO), the byproduct of oxalate oxidase reaction, can be neutralized by catalase. Alarm photosynthesis represents a photosynthetic variant to be added to the well-known C4 and CAM pathways. However, alarm photosynthesis, in contrast to these pathways, operates as a biochemical pump that collects carbon from the organ interior (or from the soil) and not from the atmosphere. | 5 | Photochemistry |
Berg-Barrett topography uses a narrow incident beam that is reflected from the surface of the sample under study under conditions of high asymmetry (grazing incidence, steep exit). To achieve sufficient spatial resolution, the detector (film) needs to be placed rather close to the sample surface. Berg-Barrett topography is another routine technique in many X-ray laboratories. | 3 | Analytical Chemistry |
At a given point of time, degree distribution , is the probability that a randomly chosen monomer has connected neighbours. The central idea of the random graph theory of gelation is that a cross-linked or branched polymer can be studied separately at two levels: 1) monomer reaction kinetics that predicts and 2) random graph with a given degree distribution. The advantage of such a decoupling is that the approach allows one to study the monomer kinetics with relatively simple rate equations, and then deduce the degree distribution serving as input for a random graph model. In several cases the aforementioned rate equations have a known analytical solution. | 7 | Physical Chemistry |
Pleuran is an insoluble polysaccharide (β-(1,3/1,6)-D-glucan), isolated from Pleurotus ostreatus.
Pleuran belongs to a group of glucose polymers commonly called beta-glucans demonstrating biological response modifier properties. These immunomodulating properties render the host more resistant to infections and neoplasms.
In a study published in December 2010, pleuran demonstrated to have a protective effect against exercise-induced suppression of immune cell activity (NK cells) in subjects taking 100 mg per day.
In another study published in 2011, pleuran reduced the incidence of upper respiratory tract infections and increased the number of circulating NK cells.
Pleuran is also being studied as a potential immunologic adjuvant. | 1 | Biochemistry |
A transport coefficient measures how rapidly a perturbed system returns to equilibrium.
The transport coefficients occur in transport phenomenon with transport laws
where:
: is a flux of the property
: the transport coefficient of this property
: , the gradient force which acts on the property .
Transport coefficients can be expressed via a Green–Kubo relation:
where is an observable occurring in a perturbed Hamiltonian, is an ensemble average and the dot above the A denotes the time derivative.
For times that are greater than the correlation time of the fluctuations of the observable the transport coefficient obeys a generalized Einstein relation:
In general a transport coefficient is a tensor. | 7 | Physical Chemistry |
Nutriomics is the science that studies the food and nutrition domains comprehensively to improve consumer's well-being and health.
More specifically Nutriomics approaches are used to evaluate the effects of different diets to promote health and modulate the risk of disease development. | 1 | Biochemistry |
In bacteria, the same enzyme catalyzes the synthesis of mRNA and non-coding RNA (ncRNA).
RNAP is a large molecule. The core enzyme has five subunits (~400 kDa):
; β′: The β′ subunit is the largest subunit, and is encoded by the rpoC gene. The β′ subunit contains part of the active center responsible for RNA synthesis and contains some of the determinants for non-sequence-specific interactions with DNA and nascent RNA. It is split into two subunits in Cyanobacteria and chloroplasts.
; β: The β subunit is the second-largest subunit, and is encoded by the rpoB gene. The β subunit contains the rest of the active center responsible for RNA synthesis and contains the rest of the determinants for non-sequence-specific interactions with DNA and nascent RNA.
; α (α and α): Two copies of the α subunit, being the third-largest subunit, are present in a molecule of RNAP: α and α (one and two). Each α subunit contains two domains: αNTD (N-terminal domain) and αCTD (C-terminal domain). αNTD contains determinants for assembly of RNAP. αCTD (C-terminal domain) contains determinants for interaction with promoter DNA, making non-sequence-non-specific interactions at most promoters and sequence-specific interactions at upstream-element-containing promoters, and contains determinants for interactions with regulatory factors.
; ω: The ω subunit is the smallest subunit. The ω subunit facilitates assembly of RNAP and stabilizes assembled RNAP.
In order to bind promoters, RNAP core associates with the transcription initiation factor sigma (σ) to form RNA polymerase holoenzyme. Sigma reduces the affinity of RNAP for nonspecific DNA while increasing specificity for promoters, allowing transcription to initiate at correct sites. The complete holoenzyme therefore has 6 subunits: β′βα and αωσ (~450 kDa). | 1 | Biochemistry |
Transition metal oxides are compounds composed of oxygen atoms bound to transition metals. They are commonly utilized for their catalytic activity and semiconducting properties. Transition metal oxides are also frequently used as pigments in paints and plastics, most notably titanium dioxide. Transition metal oxides have a wide variety of surface structures which affect the surface energy of these compounds and influence their chemical properties. The relative acidity and basicity of the atoms present on the surface of metal oxides are also affected by the coordination of the metal cation and oxygen anion, which alter the catalytic properties of these compounds. For this reason, structural defects in transition metal oxides greatly influence their catalytic properties. The acidic and basic sites on the surface of metal oxides are commonly characterized via infrared spectroscopy, calorimetry among other techniques. Transition metal oxides can also undergo photo-assisted adsorption and desorption that alter their electrical conductivity. One of the more researched properties of these compounds is their response to electromagnetic radiation, which makes them useful catalysts for redox reactions, isotope exchange and specialized surfaces. | 7 | Physical Chemistry |
Gestation lasts 20 to 23 days. Neonates are pink and hairless, with closed eyes and ears. Fur begins to appear by three days, and young are completely furred except for the belly by seven days. Eyes and ears open by eight days. Weaning occurs from 12 to 14 days. Young born in spring and early summer attain adult weight in 12 weeks, but undergo a fall weight loss. Young born in late summer continue growing through the fall and maintain their weight through the winter. Maximum size is reached between two and 10 months.
Typical eastern meadow vole litters consist of four to six young, with extremes of one and 11 young. On average, 2.6 young are successfully weaned per litter. Litter size is not significantly correlated with latitude, elevation, or population density. Fall, winter, and spring litters tend to be smaller than summer litters. Litter size was positively correlated with body size, and is not significantly different in primaparous and multiparous females. Primaparous females had fewer young per litter than multiparous females. Litter size was constant in summer breeding periods at different population densities. Female eastern meadow voles reach reproductive maturity earlier than males; some ovulate and become pregnant as early as three weeks old. Males are usually six to eight weeks old before mature sperm are produced. One captive female produced 17 litters in one year for a total of 83 young. One of her young produced 13 litters (totalling 78 young) before she was a year old.
Patterns of mortality apparently vary among eastern meadow vole populations. The average eastern meadow vole lifespan is less than one month because of high nestling and juvenile mortality. The average time adults are recapturable in a given habitat is about two months, suggesting the average extended lifespan (i.e. how much time adult eastern meadow voles have left) is about two months, not figuring in emigration. Mortality was 88% for the first 30 days after birth. and postnestling juveniles had the highest mortality rate (61%), followed by young adults (58%) and older age groups (53%). Nestlings were estimated to have the lowest mortality rate (50%). Estimated mean longevity ranges from two to 16 months. The maximum lifespan in the wild is 16 months, and few voles live more than two years.
Eastern meadow vole populations fluctuate annually and also tend to reach peak densities at two- to five-year
intervals, with population declines in intervening years. Breeding often ceases in January and starts again in March. Over the course of a year, eastern meadow vole populations tend to be lowest in early spring; the population increases rapidly through summer and fall.
In years of average population sizes, typical eastern meadow vole population density is about 15 to 45 eastern meadow voles per acre in old-field habitat. In peak years, their population densities may reach 150 per acre in marsh habitat (more favorable for eastern meadow voles than old fields). Peak eastern meadow vole abundance can exceed 1,482 eastern meadow voles per hectare (600/acre) in northern prairie wetlands. Eastern meadow voles in optimal habitats in Virginia (old fields with dense vegetation) reached densities of 983/ha (398/ac); populations declined to 67/ha (27/ac) at the lowest point in the cycle. Different factors influencing population density have been assigned primary importance by different authors. Reich listed the following factors as having been suggested by different authors: food quality, predation, climatic events, density-related physiological stress, and the presence of genetically determined behavioral variants among dispersing individuals.
Normal population cycles do not occur when dispersal is prevented; under normal conditions, dispersers have been shown to be behaviorally, genetically, and demographically different from residents. A threshold density of cover is thought to be needed for eastern meadow vole populations to increase. Above the threshold amount, the quantity of cover influences the amplitude and possibly the duration of the population peak. Local patches of dense cover could serve as source populations or reservoirs to colonize less favorable habitats with sparse cover.
Eastern meadow voles form extensive colonies and develop communal latrine areas. They are socially aggressive and agonistic; females dominate males and males fight amongst themselves. | 2 | Environmental Chemistry |
Molten polymers are non-Newtonian fluids with high viscosities, and the interaction between their thermal and mechanical degradation can be complex. At low temperatures, the polymer-melt is more viscous and more prone to mechanical degradation via shear stress. At higher temperatures, the viscosity is reduced, but thermal degradation is increased. Friction at points of high sheer can also cause localised heating, leading to additional thermal degradation.
Mechanical degradation can be reduced by the addition of lubricants, also referred to as processing aids or flow aids. These can reduce friction against the processing machinery but also between polymer chains, resulting in a decrease in melt-viscosity. Common agents are high-molecular-weight waxes (paraffin wax, wax esters, etc.) or metal stearates (i.e.zinc stearate). | 7 | Physical Chemistry |
Xing received Chinese traditional private education in his childhood. In 1933, he graduated from Fu Jen Catholic University with a diploma in Chemistry. Xing did his postgraduate work at University of Illinois at Urbana–Champaign under Roger Adamss guidance and obtained a doctorate degree in 1936. Later he went to University of Munich, conducting research on bufotoxins at Wielands laboratory. | 0 | Organic Chemistry |
The partition system of the plasmid R388 has been found within the stb operon. This operon is composed of three genes, stbA, stbB and stbC.
* StbA protein is a DNA-binding protein (identical to [https://www.uniprot.org/uniprot/P11904 ParM]) and is strictly required for the stability and intracellular positioning of plasmid R388 in E. coli. StbA binds a cis-acting sequence, the stbDRs.
The StbA-stbDRs complex may be used to pair plasmid the host chromosome, using indirectly the bacterial partitioning system.
* StbB protein has a Walker-type ATPase motif, it favors for conjugation but is not required for plasmid stability over generations.
* StbC is an orphan protein of unknown function. StbC doesn't seem to be implicated in either partitioning or conjugation.
StbA and StbB have opposite but connected effect related to conjugation.
This system has been proposed to be the type IV partition system. It is thought to be a derivative of the type I partition system, given the similar operon organization.
This system represents the first evidence for a mechanistic interplay between plasmid segregation and conjugation processes. | 1 | Biochemistry |
A nanofactory is a proposed system in which nanomachines (resembling molecular assemblers, or industrial robot arms) would combine reactive molecules via mechanosynthesis to build larger atomically precise parts. These, in turn, would be assembled by positioning mechanisms of assorted sizes to build macroscopic (visible) but still atomically-precise products.
A typical nanofactory would fit in a desktop box, in the vision of K. Eric Drexler published in Nanosystems: Molecular Machinery, Manufacturing and Computation (1992), a notable work of "exploratory engineering". During the 1990s, others have extended the nanofactory concept, including an analysis of nanofactory convergent assembly by Ralph Merkle, a systems design of a replicating nanofactory architecture by J. Storrs Hall, Forrest Bishops "Universal Assembler", the patented exponential assembly process by Zyvex, and a top-level systems design for a primitive nanofactory by Chris Phoenix (director of research at the Center for Responsible Nanotechnology). All of these nanofactory designs (and more) are summarized in Chapter 4 of Kinematic Self-Replicating Machines' (2004) by Robert Freitas and Ralph Merkle. The Nanofactory Collaboration, founded by Freitas and Merkle in 2000, is a focused, ongoing effort involving 23 researchers from 10 organizations and 4 countries that is developing a practical research agenda specifically aimed at positionally-controlled diamond mechanosynthesis and diamondoid nanofactory development.
In 2005, an animated short film of the nanofactory concept was produced by John Burch, in collaboration with Drexler. Such visions have been the subject of much debate, on several intellectual levels. No one has discovered an insurmountable problem with the underlying theories and no one has proved that the theories can be translated into practice. However, the debate continues, with some of it being summarized in the molecular nanotechnology article.
If nanofactories could be built, severe disruption to the world economy would be one of many possible negative impacts, though it could be argued that this disruption would have little negative effect, if everyone had such nanofactories. Great benefits also would be anticipated. Various works of science fiction have explored these and similar concepts. The potential for such devices was part of the mandate of a major UK study led by mechanical engineering professor Dame Ann Dowling. | 6 | Supramolecular Chemistry |
Isoaspartic acid (isoaspartate, isoaspartyl, β-aspartate) is an aspartic acid residue isomeric to the typical α peptide linkage. It is a β-amino acid, with the side chain carboxyl moved to the backbone. Such a change is caused by a chemical reaction in which the nitrogen atom on the N+1 following peptide bond (in black at top right of Figure 1) nucleophilically attacks the γ-carbon of the side chain of an asparagine or aspartic acid residue, forming a succinimide intermediate (in red). Hydrolysis of the intermediate results in two products, either aspartic acid (in black at left) or isoaspartic acid, which is a β-amino acid (in green at bottom right). The reaction also results in the deamidation of the asparagine residue. Racemization may occur leading to the formation of D-aminoacids. | 1 | Biochemistry |
Simmons was born on May 3, 1931. He attended Massachusetts Institute of Technology (MIT) in 1949. He became a metallurgist at the Allegheny Ludlum Steel corporation in Pittsburgh. He then worked for other steel companies before returning to become the chief executive of Allegheny, taking it public and then leading a management buyout. Having become wealthy, he then created a variety of endowments at MIT.
Simmons was also chairman of the Pittsburgh Symphony Orchestra between 1989 and 1997. He returned as chairman in 2003 until his retirement in 2015. | 8 | Metallurgy |
Usually for acyclic systems trans isomers are more stable than cis isomers. This difference is attributed to the unfavorable steric interaction of the substituents in the cis isomer. Therefore, trans isomers have a less-exothermic heat of combustion, indicating higher thermochemical stability. In the Benson heat of formation group additivity dataset, cis isomers suffer a 1.10 kcal/mol stability penalty. Exceptions to this rule exist, such as 1,2-difluoroethylene, 1,2-difluorodiazene (FN=NF), and several other halogen- and oxygen-substituted ethylenes. In these cases, the cis isomer is more stable than the trans isomer. This phenomenon is called the cis effect. | 4 | Stereochemistry |
In physics and chemistry, effusion is the process in which a gas escapes from a container through a hole of diameter considerably smaller than the mean free path of the molecules. Such a hole is often described as a pinhole and the escape of the gas is due to the pressure difference between the container and the exterior. Under these conditions, essentially all molecules which arrive at the hole continue and pass through the hole, since collisions between molecules in the region of the hole are negligible. Conversely, when the diameter is larger than the mean free path of the gas, flow obeys the Sampson flow law.
In medical terminology, an effusion refers to accumulation of fluid in an anatomic space, usually without loculation. Specific examples include subdural, mastoid, pericardial and pleural effusions. | 7 | Physical Chemistry |
Validations can be broken into three stages: validating the raw data collected (data validation), the interpretation of the data into the atomic model (model-to-data validation), and finally validation on the model itself. While the first two steps are specific to the technique used, validating the arrangement of atoms in the final model is not. | 1 | Biochemistry |
* A commercial, high purity (non-recycled) polymer sample with known molecular mass distribution can be obtained or synthesized according to standard procedures.
* Common properties such as elastic modulus, tan δ, crystallinity, viscosity, density should be characterized.
* Anchor points, physical or chemical (chain entanglement, crystallinity or vulcanization), must be decided.
If crosslinking with slight vulcanization is desired, standardized methods for each polymer must be taken into account. In the case of PCO, for example, it is a polymer without shape-shape-memory effect because it does not present a clear "plateau", but the addition of a minimum amount of peroxide (~1%) provides PCO with all the requirements to present this effect.
# A permanent stress-free shape with known dimensions is prepared by conventional methods.
# The system is programmed, i.e. it is heated up to T and at that temperature the shape is modified by applying pressure or stress. Then the material is cooled and finally the pressure or stress is removed.
# After heating the sample again to T, the stresses are released and the permanent shape is recovered.
Some polymers fatigue first, so each system can be evaluated with a simple experiment that consists of programming the system 10 or 20 times in a row and measuring the recovery in % and time. | 7 | Physical Chemistry |
The measurement is generally conducted using a three-electrode setup (see the drawing):
# working electrode,
# counter electrode,
# reference electrode (standard hydrogen electrode or an equivalent).
In case of non-zero net current on the electrode, it is essential to minimize the ohmic IR-drop in the electrolyte, e.g., by positioning the reference electrode near the surface of the working electrode (e.g., see Luggin capillary), or by using a supporting electrolyte of sufficiently high conductivity. The potential measurements are performed with the positive terminal of the electrometer connected to the working electrode and the negative terminal to the reference electrode. | 7 | Physical Chemistry |
DDM was introduced in 2008 and it was applied for characterizing the dynamics of colloidal particles in Brownian motion. More recently it has been successfully applied also to the study of aggregation processes of colloidal nanoparticles, of bacterial motions, of the dynamics of anisotropic colloids and of motile cilia. | 7 | Physical Chemistry |
Lanthanide probes have been used to detect conformational changes in proteins. Recently the Shaker potassium ion channel, a voltage-gated channel involved in nerve impulses was measured using this technique. Some scientist also have used lanthanide based luminescence resonance energy transfer (LRET) which is very similar to FRET to study conformational changes in RNA polymerase upon binding to DNA and transcription initiation in prokaryotes. LRET was also used to study the interaction of the proteins dystrophin and actin in muscle cells. Dystrophin is present in the inner muscle cell membrane and is believed to stabilize muscle fibers by binding to actin filaments. Specifically labelled dystrophin with Tb labelled monoclonal antibodies labeled were used. | 1 | Biochemistry |
Coelenterazine is widely found in marine organisms including:
*radiolarians
*ctenophores
*cnidarians such as Aequorea victoria, Obelia geniculata and Renilla reniformis
*squid such as Watasenia scintillans and Vampyroteuthis infernalis
*shrimp such as Systellaspis debilis and Oplophorus gracilirostris
*copepods such as Pleuromamma xiphias and Gaussia princeps
*chaetognaths
*fish including some Neoscopelidae and Myctophidae
*echinoderms such as Amphiura filiformis
The compound has also been isolated from organisms that are not luminescent, such as the Atlantic herring and several shrimp species including Pandalus borealis and Pandalus platyuros. | 1 | Biochemistry |
A beamsplitter is used to divide a single ultrashort optical pulse into two separate beams. A 50/50 beamsplitter is often used, supplying equal optical power to the terahertz generator and detector, though it is common to provide the terahertz generation path with more power given the inefficiency of the terahertz generation process compared to the detection efficiency of infrared (typically 800 nm wavelength) light. | 7 | Physical Chemistry |
Lanthipeptides are characterized by the presence lanthionine (Lan) and 3-methyllanthionine (MeLan) residues. Lan residues are formed from a thioether bridge between Cys and Ser, while MeLan residues are formed from the linkage of Cys to a Thr residue. The biosynthetic enzymes responsible for Lan and MeLan installation first dehydrate Ser and Thr to dehydroalanine (Dha) and dehydrobutyrine (Dhb), respectively. Subsequent thioether crosslinking occurs through a Michael-type addition by Cys onto Dha or Dhb.
Four classes of lanthipeptide biosynthetic enzymes have been designated. Class I lanthipeptides have dedicated lanthipeptide dehydratases, called LanB enzymes, though more specific designations are used for particular lanthipeptides (e.g. NisB is the nisin dehydratase). A separate cyclase, LanC, is responsible for the second step in Lan and MeLan biosynthesis. However, class II, III, and IV lanthipeptides have bifunctional lanthionine synthetases in their gene clusters, meaning a single enzyme carries out both dehydration and cyclization steps. Class II synthetases, designated LanM synthetases, have N-terminal dehydration domains with no sequence homology to other lanthipeptide biosynthetic enzymes; the cyclase domain has homology to LanC. Class III (LanKC) and IV (LanL) enzymes have similar N-terminal lyase and central kinase domains, but diverge in C-terminal cyclization domains: the LanL cyclase domain is homologous to LanC, but the class III enzymes lack Zn-ligand binding domains. | 1 | Biochemistry |
In cell biology, chromosome territories are regions of the nucleus preferentially occupied by particular chromosomes.
Interphase chromosomes are long DNA strands that are extensively folded, and are often described as appearing like a bowl of spaghetti. The chromosome territory concept holds that despite this apparent disorder, chromosomes largely occupy defined regions of the nucleus. Most eukaryotes are thought to have chromosome territories, although the budding yeast S. cerevisiae is an exception to this. | 1 | Biochemistry |
Eastern meadow voles are active year-round and day or night, with no clear 24-hour rhythm in many areas. Most changes in activity are imposed by season, habitat, cover, temperature, and other factors. Eastern meadow voles have to eat frequently, and their active periods (every two to three hours) are associated with food digestion. In Canada, eastern meadow voles are active the first few hours after dawn and during the two- to four-hour period before sunset. Most of the inactive period is spent in the nest. | 2 | Environmental Chemistry |
In geophysics, a common assumption is that the rock formations of the crust are locally polar anisotropic (transversely isotropic); this is the simplest case of geophysical interest. Backus upscaling is often used to determine the effective transversely isotropic elastic constants of layered media for long wavelength seismic waves.
Assumptions that are made in the Backus approximation are:
* All materials are linearly elastic
* No sources of intrinsic energy dissipation (e.g. friction)
* Valid in the infinite wavelength limit, hence good results only if layer thickness is much smaller than wavelength
* The statistics of distribution of layer elastic properties are stationary, i.e., there is no correlated trend in these properties.
For shorter wavelengths, the behavior of seismic waves is described using the superposition of plane waves. Transversely isotropic media support three types of elastic plane waves:
* a quasi-P wave (polarization direction almost equal to propagation direction)
* a quasi-S wave
* a S-wave (polarized orthogonal to the quasi-S wave, to the symmetry axis, and to the direction of propagation).
Solutions to wave propagation problems in such media may be constructed from these plane waves, using Fourier synthesis. | 3 | Analytical Chemistry |
The deepest gold mines of the Ancient world were found in the Maski region in Karnataka. There were ancient silver mines in northwest India. Dated to the middle of the 1st millennium BCE. gold and silver were also used for making utensils for the royal family and nobilities.the royal family wore costly fabrics that were made from gold and silver thin fibres embroidered or woven into fabrics or dress. | 8 | Metallurgy |
Nuclease protection assays are used to map introns and 5 and 3 ends of transcribed gene regions. Quantitative results can be obtained regarding the amount of the target RNA present in the original cellular extract - if the target is a messenger RNA, this can indicate the level of transcription of the gene in the cell.
They are also used to detect the presence of double stranded RNA, presence of which could mean RNA interference.
Northern blotting is a laboratory technique that produces similar information. It is slower and less quantitative, but also produces accurate information about the size of the target RNA. Nuclease protection assay products are limited to the size of the initial probes due to the destruction of the non-hybridized RNA during the nuclease digestion step. | 1 | Biochemistry |
The bacterial RNA polymerase, a leading enzyme involved in formation of a transcription bubble, uses DNA template to guide RNA synthesis. It is present in two main forms: as a core enzyme, when it is inactive, and as a holoenzyme, when it is activated. A sigma (σ) factor is a subunit that assists the process of transcription and it stabilizes the transcription bubble when it binds to unpaired bases. These two components, RNA polymerase and sigma factor, when paired together, build RNA polymerase holoenzyme which is then in its active form and ready to bind to a promoter and initiate DNA transcription. Once it binds to the DNA, RNA polymerase turns from a closed to an open complex, forming the transcription bubble. RNA polymerase synthesizes the new RNA in the 5 to 3 direction by adding complementary bases to the 3' end of a new strand. The holoenzyme composition dissociates after transcription initiation, where the σ factor disengages the complex and the RNA polymerase, in its core form, slides along the DNA molecule. | 1 | Biochemistry |
Markovnikovs rule addition of the cobalt hydride to primary alkenes is disfavored by steric hindrance between the cobalt centre and the secondary alkyl ligand. Bulky ligands exacerbate this steric hindrance. Hence, the mixed carbonyl/phosphine complexes offer a greater selectivity for anti-Markovnikov addition, thus favoring straight chain products (n'-) aldehydes. Modern catalysts rely increasingly on chelating ligands, especially diphosphites. | 0 | Organic Chemistry |
In acyloxy groups the acyl group is bonded to oxygen: R−C(=O)−O−R′ where R−C(=O) is the acyl group.
Acylium ions are cations of the type R−C=O ↔ R−C≡O and play an important role as intermediates in organic reactions for example the Hayashi rearrangement. | 0 | Organic Chemistry |
Strep Tamer is a technology which allows the reversible isolation and staining of antigen-specific T-cells. This technology combines a current T-cell isolation method with the Strep-Tag technology. In principle, the T-cells are separated by establishing a specific interaction between the T-cell of interest and a molecule, that is conjugated to a marker which enables the isolation. The reversibility of this interaction and the low temperatures at which it is performed allow for the isolation and characterization of functional T-cells. Because T-cells remain phenotypically and functionally indistinguishable from untreated cells, this method offers modern strategies in clinical and basic T-cell research. | 1 | Biochemistry |
Most of the solvents employed vaporize quickly and are flammable, making the extraction process dangerous. Several explosion and fire incidents related to hash oil manufacturing attempts in homes have been reported.
Solvents used to extract THC are flammable or combustible and have resulted in explosions, fires, severe injuries, and deaths. | 7 | Physical Chemistry |
The bowl and stand were favourite archaic forms. The Greek stand was a fusion of the cast-rod tripod and the embossed cone. Some early examples have large triangular plates between the legs, worked in relief; but the developed type has separate legs and stays of which the joints are masked with decorative rims and feet and covering-plates. These ornaments are cast and chased, and are modelled in floral, animal and human forms. The feet are lions' paws, which sometimes clasp a ball or stands on toads; the rims and plaques bear groups of fighting animals, warriors, revelles or athletes, nymphs and satyrs, or mythological subjects in relief. Feasters recline and horsemen gallop on the rims of bowls; handles are formed by single standing figures, arched pairs of wrestlers, lovers holding hands, or two vertical soldiers carrying a horizontal comrade. Nude athletes serve as handles for all kinds of lids and vessels, draped women support mirror-disks around which love-gods fly, and similar figures crown tall shafts of candelabra. Handle-bases are modelled as satyr-masks, palmettes and sphinxes. This is Greek ornament of the 6th and later centuries. Its centres of manufacture are not precisely known, but the style of much archaic work points to Ionia.
Etruscan fabrics approach their Greek originals so closely that it is not possible to separate them in technique or design, and the Etruscan style is no more than provincial Greek. Bronze was quite plentiful in Italy, the earliest Roman coinage was of heavy bronze, and there is literary evidence that Etruscan bronzes were exported. The process of line engraving seems to have been a Latin speciality; it was applied in pictorial subjects on the backs of mirrors and on the sides large cylindrical boxes, both of which are particularly connected with Praeneste. The finest of all such boxes, the Firconi cista in the Villa Giulia at Rome, bears the signature of a Roman artist. These belong to the 4th and 3rd centuries BC. Greek mirrors of the same period are seldom engraved; the disk is usually contained in a flat box which has a repoussé design on its lid. | 8 | Metallurgy |
A study demonstrates how the autocrine production of the IL-7 cytokine mediated by T-cell acute lymphoblastic leukemia (T-ALL) can be involved in the oncogenic development of T-ALL and offer novel insights into T-ALL spreading. | 1 | Biochemistry |
Once the nucleotides are synthesized they can exchange phosphates among one another in order to create mono-, di-, and tri-phosphate molecules. The conversion of a nucleoside-diphosphate (NDP) to a nucleoside-triphosphate (NTP) is catalyzed by nucleoside diphosphate kinase, which uses ATP as the phosphate donor. Similarly, nucleoside-monophosphate kinase carries out the phosphorylation of nucleoside-monophosphates. Adenylate kinase is a specific nucleotide kinase used for regulating cellular energy fluctuations by the interconversion of 2ADP ⇔ ATP + AMP. | 1 | Biochemistry |
Blue billy is a chemical or mineral deposit often encountered in contaminated land.
The name is a reference to its distinctive bright blue colour, which can make it immediately obvious in other mud or soil. Chemically it is a form of Prussian blue. Although several chemical industry processes could produce it, it is particularly associated with coal gasification and older town gasworks. It has been recognised as a problem effluent and land contaminant since the early industrial period and the first gasworks at the start of the 19th century.
As a visible proof of contamination, blue billy is an important signifier in contaminated land remediation projects and its discovery, especially if undisclosed, may be a cause of contract disputes. | 2 | Environmental Chemistry |
The discovery of paper chromatography in 1943 by Martin and Synge provided, for the first time, the means of surveying constituents of plants and for their separation and identification. Erwin Chargaff credits in Weintraub's history of the man the 1944 article by Consden, Gordon and Martin. There was an explosion of activity in this field after 1945. | 3 | Analytical Chemistry |
Acid-base extraction works on the fundamental principle that salts are ionic compounds with a high solubility in water, while neutral molecules typically lack solubility in water.
Consider a mixture of acidic and basic compounds dissolved in an organic solvent. Adding aqueous acid will cause the acidic component to stay uncharged, while the basic component will be protonated to form a salt. The uncharged acid component will remain dissolved in the organic solvent, while the highly charged basic salt will migrate to the aqueous solvent. Since the acidic and basic components are now in two different layers, they can easily be separated.
Alternatively, adding aqueous base will cause the acidic component to be deprotonated and form a salt, while the basic component will remain uncharged. In this case, the uncharged base will stay in the organic layer, while the highly charged acidic salt will migrate to the aqueous layer.
If the organic acid component is relatively weak and has a pK value of ~5 (such as a carboxylic acid), adding additional acid can further improve separation by lowering the pH of the solution. This minimizes the self ionization of the organic acid component and limits its tendency to enter the aqueous layer. This principle is also applicable to an organic base when it is a relatively weak base.
Although acid-base extractions are most commonly used to separate acids from bases, they can be used to separate two acids or two bases from each other. However, the acids and bases must differ greatly in strength, e.g. one strong acid and one very weak acid. Therefore, the two acids must have a pK (or pK) difference that is as large as possible. For example, the following can be separated:
* Very weak acids like phenols (pK around 10) from stronger acids like carboxylic acids (pK around 4–5).
* Very weak bases (pK around 13–14) from stronger bases (pK around 3–4). This is frequently used in purifying soil to determine trace metal concentration.
When separating two acids or two bases, the pH is usually adjusted to a value roughly between the pK (or pK) constants. Separation occurs at this intermediate pH because one component is fully ionized, while the other is fully in its neutral form. Often, the solutions used to extract the acids or bases can also be used to control the pH. When separating two acids, the mixture is first washed with a weak base (e.g. sodium bicarbonate) to extract the strong acid, then washed with a strong base (e.g. sodium hydroxide) to extract the weak acid. For separating basic components, weak acid (e.g. dilute acetic acid) is first used to extract the stronger base, then more concentrated acid (e.g. hydrochloric acid or nitric acid) is used to create strongly acidic pH values and separate the weaker base. | 7 | Physical Chemistry |
A quasi-static thermodynamic process can be visualized by graphically plotting the path of idealized changes to the system's state variables. In the example, a cycle consisting of four quasi-static processes is shown. Each process has a well-defined start and end point in the pressure-volume state space. In this particular example, processes 1 and 3 are isothermal, whereas processes 2 and 4 are isochoric. The PV diagram is a particularly useful visualization of a quasi-static process, because the area under the curve of a process is the amount of work done by the system during that process. Thus work is considered to be a process variable, as its exact value depends on the particular path taken between the start and end points of the process. Similarly, heat may be transferred during a process, and it too is a process variable. | 7 | Physical Chemistry |
Some enzymes can carry out thousands of chemical reactions each second. However, RuBisCO is slow, fixing only 3-10 carbon dioxide molecules each second per molecule of enzyme. The reaction catalyzed by RuBisCO is, thus, the primary rate-limiting factor of the Calvin cycle during the day. Nevertheless, under most conditions, and when light is not otherwise limiting photosynthesis, the speed of RuBisCO responds positively to increasing carbon dioxide concentration.
RuBisCO is usually only active during the day, as ribulose 1,5-bisphosphate is not regenerated in the dark. This is due to the regulation of several other enzymes in the Calvin cycle. In addition, the activity of RuBisCO is coordinated with that of the other enzymes of the Calvin cycle in several other ways: | 5 | Photochemistry |
An encryption system constructed by pillar[5]arene, spiropyran and pentanenitrile (free state and grafted to polymer) was constructed by Wang et al. After UV irradiation, spiropyran would transform into merocyanine. When the visible light was shined on the material, the merocyanine close to the pillar[5]arene-free pentanenitrile complex had faster transformation to spiropyran; on the contrary, the one close to pillar[5]arene-grafted pentanenitrile complex has much slower transformation rate. This spiropyran-merocyanine transformation can be used for message encryption. Another strategy is based on the metallacages and polycyclic aromatic hydrocarbons. Because of the fluorescnece emission differences between the complex and the cages, the information could be encrypted. | 6 | Supramolecular Chemistry |
Most current medical laboratories now have highly automated analyzers to accommodate the high workload typical of a hospital laboratory, and accept samples for up to about 700 different kinds of tests. Even the largest of laboratories rarely do all these tests themselves, and some must be referred to other labs. Tests performed are closely monitored and quality controlled. | 1 | Biochemistry |
Independent research conducted by Antibody Solutions and published or presented at scientific conferences include the following:
* Generation of Neutralizing Human Monoclonal Antibodies Against a Therapeutic Target from the Alloy Therapeutics Mouse
* Generation Using a Molecular Modeling Platform to Guide Therapeutic Antibody Discovery
* Optimization of Therapeutic Discovery Strategies for Human Antibody Transgenic Animal Platforms
* Development of Antibody and PK, and ADA Assays for a Cystine Knot Fusion Protein
* A Rapid, High-Throughput Recombinant Antibody Expression System for Therapeutic Antibody Discovery and Validation
* Generation of Agonist and Antagonist Human Monoclonal Antibodies Against an Immune Checkpoint Target from the H2L2 Mouse
* Generation and Selection of Human Monoclonal Antibodies from the OmniRat
* Therapeutic Antibody Discovery at Antibody Solutions using the OmniAb Platform
* Development of human antibodies to human vascular endothelial growth factor -C (VEGF-C) and -D (VEGF-D)
* Obtaining Antibodies to Difficult Membrane Targets through DNA and Cell Immunization
* Next-Generation Therapeutic Antibody Discovery from Single B-cells
* Generation and Selection of Human Monoclonal Antibodies from the H2L2 Mouse
* Generation of Antibodies to Difficult Membrane Protein Targets
* Development of Antibodies and ELISAs to measure Free and Total Obiltoxaximab (ETI-204) in the Presence of Anthrax Protective Antigen PA63
* Discovery of Therapeutic Antibodies to Difficult Membrane Proteins | 1 | Biochemistry |
The corundum structure has the space group hexagonal crystal family#Crystal classes|. It typically exists in binary compounds of the type AB, where A is metallic and B is nonmetallic, including sesquioxides (AO), sesquisulfides (AS), etc. When A is nonmetallic and B is metallic, the structure becomes the antiphase of corundum, called the anticorundum structure type, with examples including β-CaN and borates. Ternary and multinary compounds can also exists in the corundum structure. The corundum-like structure with the composition ABB'O is called double corundum. A list of examples are tabulated below. | 3 | Analytical Chemistry |
PAVA is used widely as a less lethal, temporary defence tool around the world including in the United Kingdom, India, Switzerland, and others. | 1 | Biochemistry |
With improvements in measuring techniques such as AFM, confocal microscopy and SEM, researchers were able to produce and image droplets at ever smaller scales. With the reduction in droplet size came new experimental observations of wetting. These observations confirm that the modified Young’s equation does not hold at the micro-nano scales. In addition the sign of the line tension is not maintained through the modified Young’s equation.
For a sessile droplet, the free energy of the three phase system can be expressed as:
At constant volume in thermodynamic equilibrium, this reduces to:
Usually, the VdP term has been neglected for large droplets, however, VdP work becomes significant at small scales. The variation in pressure at constant volume at the free liquid-vapor boundary is due to the Laplace pressure, which is proportional to the mean curvature of the droplet, and is non zero. Solving the above equation for both convex and concave surfaces yields:
Where the constant parameters A, B, and C are defined as:
:, and
This equation relates the contact angle , a geometric property of a sessile droplet to the bulk thermodynamics, the energy at the three phase contact boundary, and the curvature of the surface α. For the special case of a sessile droplet on a flat surface (α=0),
The first two terms are the modified Young’s equation, while the third term is due to the Laplace pressure. This nonlinear equation correctly predicts the sign and magnitude of κ, the flattening of the contact angle at very small scales, and contact angle hysteresis. | 7 | Physical Chemistry |
Cyclodextrins are well established hosts for the formation of inclusion compounds. Illustrative is the case of ferrocene which is inserted into the cyclodextrin at 100 °C under hydrothermal conditions.
Cyclodextrin also forms inclusion compounds with fragrances. As a result, the fragrance molecules have a reduced vapor pressure and are more stable towards exposure to light and air. When incorporated into textiles the fragrance lasts much longer due to the slow-release action. | 6 | Supramolecular Chemistry |
Chlorprothixene is widely available throughout Europe and elsewhere in the world. The drug was previously available in the United States under the brand name Taractan, but this formulation has since been discontinued and the drug is no longer available in this country. | 4 | Stereochemistry |
In RT-PCR, the RNA template is first converted into a complementary DNA (cDNA) using a reverse transcriptase (RT). The cDNA is then used as a template for exponential amplification using PCR. The use of RT-PCR for the detection of RNA transcript has revolutionized the study of gene expression in the following important ways:
* Made it theoretically possible to detect the transcripts of practically any gene
* Enabled sample amplification and eliminated the need for abundant starting material required when using northern blot analysis
* Provided tolerance for RNA degradation as long as the RNA spanning the primer is intact | 1 | Biochemistry |
All SOCS have certain structures in common. This includes a varying N-terminal domain involved in protein-protein interactions, a central SH2 domain, which can bind to molecules that have been phosphorylated by tyrosine kinases, and a SOCS box located at the C-terminal that enables recruitment of E3 ligases and ubiquitin signaling molecules. | 1 | Biochemistry |
dPCR’s ability to detect rare mutations may be of particular benefit in the clinic through the use of the liquid biopsy, a generally noninvasive strategy for detecting and monitoring disease via bodily fluids. Researchers have used liquid biopsy to monitor tumor load, treatment response and disease progression in cancer patients by measuring rare mutations in circulating tumor DNA (ctDNA) in a variety of biological fluids from patients including blood, urine and cerebrospinal fluid. Early detection of ctDNA (as in molecular relapse) may lead to earlier administration of an immunotherapy or a targeted therapy specific for the patient’s mutation signature, potentially improving chances of the treatment’s effectiveness rather than waiting for clinical relapse before altering treatment. Liquid biopsies can have turnaround times of a few days, compared to two to four weeks or longer for tissue-based tests. This reduced time to results has been used by physicians to expedite treatments tailored to biopsy data.
In 2016, a prospective trial using dPCR at the Dana-Farber Cancer Institute authenticated the clinical benefit of liquid biopsy as a predictive diagnostic tool for patients with non-small-cell lung cancer. The application of liquid biopsy tests have also been studied in patients with breast, colorectal, gynecologic, and bladder cancers to monitor both the disease load and the tumor’s response to treatment. | 1 | Biochemistry |
Levels of β-TG is used to index platelet activation. It is measured by ELISA in blood plasma or urine, and often in conjunction with PF4. | 1 | Biochemistry |
Enzyme-linked immunosorbent assay (ELISA) is used in diagnostic laboratories to detect ANCAs. Although IF can be used to screen for many ANCAs, ELISA is used to detect antibodies to individual antigens. The most common antigens used on an ELISA microtitre plate are MPO and PR3, which are usually tested for after a positive IF test. | 1 | Biochemistry |
In 1856, William Henry Perkin, then age 18, was given a challenge by his professor, August Wilhelm von Hofmann, to synthesize quinine. In one attempt, Perkin oxidized aniline using potassium dichromate, whose toluidine impurities reacted with the aniline and yielded a black solid, suggesting a "failed" organic synthesis. Cleaning the flask with alcohol, Perkin noticed purple portions of the solution.
Suitable as a dye of silk and other textiles, it was patented by Perkin, who the next year opened a dyeworks mass-producing it at Greenford on the banks of the Grand Union Canal in Middlesex. It was originally called aniline purple. In 1859, it was named mauve in England via the French name for the mallow flower, and chemists later called it mauveine. Between 1859 and 1861, mauve became a fashion must have. The weekly journal All the Year Round described women wearing the colour as "all flying countryward, like so many migrating birds of purple paradise". Punch magazine published cartoons poking fun at the huge popularity of the colour “The Mauve Measles are spreading to so serious an extent that it is high time to consider by what means [they] may be checked.”
By 1870, demand succumbed to newer synthetic colors in the synthetic dye industry launched by mauveine.
In the early 20th century, the U.S. National Association of Confectioners permitted mauveine as a food coloring with a variety of equivalent names: rosolan, violet paste, chrome violet, anilin violet, anilin purple, Perkins violet, indisin, phenamin, purpurin and lydin'.
Laborers in the aniline dye industry were later found to be at increased risk of bladder cancer, specifically transitional cell carcinoma, yet by the 1950s, the synthetic dye industry had helped transform medicine, including cancer treatment. | 7 | Physical Chemistry |
Flutamide has been researched and used extensively in the treatment of androgen-dependent skin and hair conditions in women including acne, seborrhea, hirsutism, and scalp hair loss, as well as in hyperandrogenism (e.g., in polycystic ovary syndrome or congenital adrenal hyperplasia), and is effective in improving the symptoms of these conditions. The dosages used are lower than those used in the treatment of prostate cancer. Although flutamide continues to be used for these indications, its use in recent years has been limited due to the risk of potentially fatal hepatotoxicity, and it is no longer recommended as a first- or second-line therapy. The related NSAA bicalutamide has also been found to be effective in the treatment of hirsutism in women and appears to have comparable effectiveness to that of flutamide, but has a far lower and only small risk of hepatotoxicity in comparison.
Aside from its risk of liver toxicity and besides other nonsteroidal antiandrogens, it has been said that flutamide is likely the best typically used antiandrogen medication for the treatment of androgen-dependent symptoms in women. This is related to its high effectiveness and minimal side effects. | 4 | Stereochemistry |
The symbol used to represent temperature in equations is T with SI units of kelvins.
The speed of a gas particle is proportional to its absolute temperature. The volume of the balloon in the video shrinks when the trapped gas particles slow down with the addition of extremely cold nitrogen. The temperature of any physical system is related to the motions of the particles (molecules and atoms) which make up the [gas] system. In statistical mechanics, temperature is the measure of the average kinetic energy stored in a molecule (also known as the thermal energy). The methods of storing this energy are dictated by the degrees of freedom of the molecule itself (energy modes). Thermal (kinetic) energy added to a gas or liquid (an endothermic process) produces translational, rotational, and vibrational motion. In contrast, a solid can only increase its internal energy by exciting additional vibrational modes, as the crystal lattice structure prevents both translational and rotational motion. These heated gas molecules have a greater speed range (wider distribution of speeds) with a higher average or mean speed. The variance of this distribution is due to the speeds of individual particles constantly varying, due to repeated collisions with other particles. The speed range can be described by the Maxwell–Boltzmann distribution. Use of this distribution implies ideal gases near thermodynamic equilibrium for the system of particles being considered. | 7 | Physical Chemistry |
Many plant nutrients in soil undergo biogeochemical cycles throughout their environment. These cycles are influenced by water, gas exchange, biological activity, immobilization, and mineralization dynamics, but each element has its own course of flow (Deemy et al., 2022). For example, nitrogen moves from an isolated gaseous form to the compounds nitrate and nitrite as it moves through soil and becomes available to plants. In comparison, an element like phosphorus transfers in mineral form, as it is contained in rock material. These cycles also greatly vary in mobility, solubility, and the rate at which they move through their natural cycles. Together, they drive all of the processes of soil chemistry. | 9 | Geochemistry |
In the partial wave expansion the scattering amplitude is represented as a sum over the partial waves,
where is the partial scattering amplitude and are the Legendre polynomials. The partial amplitude can be expressed via the partial wave S-matrix element () and the scattering phase shift as
Then the total cross section
can be expanded as
is the partial cross section. The total cross section is also equal to due to optical theorem.
For , we can write | 7 | Physical Chemistry |
Vinylphosphonic acid can be prepared by the reaction of PCl and acetaldehyde:
:PCl + CHCHO → CHCH(O)
This adduct reacts with acetic acid:
: CHCH(O) + 2 CHCOH → CHCH(Cl)PO(OH) + 2 CHCOCl
This chloride undergoes dehydrochlorination to afford the target:
:CHCH(Cl)PO(OH) → CH=CHPO(OH) + HCl
In the Kinnear–Perren reaction alkylphosphonyl dichlorides and esters are generated by alkylation of phosphorus trichloride in the presence of aluminium trichloride. Alkyltrichlorophosphonium salts are intermediates:
:PCl + RCl + AlCl → RPCl + AlCl
The RPCl product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl. | 0 | Organic Chemistry |
The formula for dimensions can be derived assuming an -dimensional real vector space with a basis and an inner product . The reciprocal lattice vectors are uniquely determined by the formula . Using the permutation
they can be determined with the following formula:
Here, is the volume form, is the inverse of the vector space isomorphism defined by and denotes the inner multiplication.
One can verify that this formula is equivalent to the known formulas for the two- and three-dimensional case by using the following facts: In three dimensions, and in two dimensions, , where is the rotation by 90 degrees (just like the volume form, the angle assigned to a rotation depends on the choice of orientation). | 3 | Analytical Chemistry |
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