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Helical wheels can be drawn by a variety of software packages including [https://CRAN.R-project.org/package=helixvis helixvis] in R, [https://github.com/smsaladi/heliquest heliquest] in R, or via the HELIQUEST server. | 1 | Biochemistry |
Thermal composites is a term given to combinations of phase change materials (PCMs) and other (usually solid) structures. A simple example is a copper mesh immersed in paraffin wax. The copper mesh within paraffin wax can be considered a composite material, dubbed a thermal composite. Such hybrid materials are created to achieve specific overall or bulk properties (an example being the encapsulation of paraffin into distinct silicon dioxide nanospheres for increased surface area-to-volume ratio and, thus, higher heat transfer speeds ).
Thermal conductivity is a common property targeted for maximization by creating thermal composites. In this case, the basic idea is to increase thermal conductivity by adding a highly conducting solid (such as the copper mesh or graphite) into the relatively low-conducting PCM, thus increasing overall or bulk (thermal) conductivity. If the PCM is required to flow, the solid must be porous, such as a mesh.
Solid composites such as fiberglass or kevlar prepreg for the aerospace industry usually refer to a fiber (the kevlar or the glass) and a matrix (the glue, which solidifies to hold fibers and provide compressive strength). A thermal composite is not so clearly defined but could similarly refer to a matrix (solid) and the PCM, which is of course usually liquid and/or solid depending on conditions. They are also meant to discover minor elements in the earth. | 7 | Physical Chemistry |
Magnetic isotope effects arise when a chemical reaction involves spin-selective processes, such as the radical pair mechanism. The result is that some isotopes react preferentially, depending on their nuclear spin quantum number I. This is in contrast to more familiar mass-dependent isotope effects. | 7 | Physical Chemistry |
The majority of quorum sensing systems that fall under the "two-gene" (an autoinducer synthase coupled with a receptor molecule) paradigm as defined by the Vibrio fischeri system occur in the gram-negative Pseudomonadota. A comparison between the Pseudomonadota phylogeny as generated by 16S ribosomal RNA sequences and phylogenies of LuxI-, LuxR-, or LuxS-homologs shows a notably high level of global similarity. Overall, the quorum sensing genes seem to have diverged along with the Pseudomonadota phylum as a whole. This indicates that these quorum sensing systems are quite ancient, and arose very early in the Pseudomonadota lineage.
Although examples of horizontal gene transfer are apparent in LuxI, LuxR, and LuxS phylogenies, they are relatively rare. This result is in line with the observation that quorum sensing genes tend to control the expression of a wide array of genes scattered throughout the bacterial chromosome. A recent acquisition by horizontal gene transfer would be unlikely to have integrated itself to this degree. Given that the majority of autoinducer–synthase/receptor pairs occur in tandem in bacterial genomes, it is also rare that they switch partners and so pairs tend to co-evolve.
In quorum sensing genes of Gammaproteobacteria, which includes Pseudomonas aeruginosa and Escherichia coli, the LuxI/LuxR genes form a functional pair, with LuxI as the auto-inducer synthase and LuxR as the receptor. Gammaproteobacteria are unique in possessing quorum sensing genes, which, although functionally similar to the LuxI/LuxR genes, have a markedly divergent sequence. This family of quorum-sensing homologs may have arisen in the Gammaproteobacteria ancestor, although the cause of their extreme sequence divergence yet maintenance of functional similarity has yet to be explained. In addition, species that employ multiple discrete quorum sensing systems are almost all members of the Gammaproteobacteria, and evidence of horizontal transfer of quorum sensing genes is most evident in this class. | 1 | Biochemistry |
Mar Menor (, "minor/smaller sea") is a coastal saltwater lagoon in the Iberian Peninsula located south-east of the Autonomous Community of Murcia, Spain, near Cartagena.
Its name is the opposite of the Mediterranean, which is the (greater/larger sea) of the region.
Four municipalities border the Mar Menor: Cartagena, Los Alcázares, San Javier and San Pedro del Pinatar.
With a surface area of 135 km, a coastal length of 70 km, and warm and clear water no more than 7 metres in depth, it is the largest lagoon in Spain.
The lagoon is separated from the Mediterranean Sea by La Manga ("the sleeve"), a sandbar 22 km in length whose width ranges from 100 to 1,200 metres, with Cape Palos in its south-eastern vertex making for the lagoon's roughly triangular shape. There are five islets located within the lagoon: Perdiguera islet, Mayor or El Barón islet, Ciervo islet, Redonda islet and del Sujeto islet.
Its relatively high salinity (which aids flotation), low waves, and remarkable sporting infrastructures makes it a popular place for a wide variety of water sports. | 2 | Environmental Chemistry |
An algae scrubber is a water filtering device (not to be confused with a scrubber pad used to clean glass) which uses light to grow algae; in this process, undesirable chemicals are removed from the water. Algae scrubbers allow saltwater, freshwater and pond hobbyists to operate their tanks using natural filtration in the form of primary production, much like oceans and lakes. | 5 | Photochemistry |
While the production and consumption of CFCs are regulated under the Montreal Protocol, emissions from existing banks of CFCs are not regulated under the agreement. In 2002, there were an estimated 5,791 kilotons of CFCs in existing products such as refrigerators, air conditioners, aerosol cans and others. Approximately one-third of these CFCs are projected to be emitted over the next decade if action is not taken, posing a threat to both the ozone layer and the climate. A proportion of these CFCs can be safely captured and destroyed by means of high temperature, controlled incineration which destroys the CFC molecule. | 2 | Environmental Chemistry |
Welan gum is an exopolysaccharide used as a rheology modifier in industrial applications such as cement manufacturing. It is produced by fermentation of sugar by bacteria of the genus Alcaligenes. The molecule consists of repeating tetrasaccharide units with single branches of L-mannose or L-rhamnose. In solution, the gum retains viscosity at elevated temperature, and is stable in a wide pH range, in the presence of calcium ion, and with high concentration of glycols. | 0 | Organic Chemistry |
It has been suggested that L1s may directly contribute to telomere reprogramming at the 2-cell stage of embryo development. | 1 | Biochemistry |
The epidermis is the outer layer of cells covering the leaf. It is covered with a waxy cuticle which is impermeable to liquid water and water vapor and forms the boundary separating the plant's inner cells from the external world. The cuticle is in some cases thinner on the lower epidermis than on the upper epidermis, and is generally thicker on leaves from dry climates as compared with those from wet climates. The epidermis serves several functions: protection against water loss by way of transpiration, regulation of gas exchange and secretion of metabolic compounds. Most leaves show dorsoventral anatomy: The upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions.
The epidermis tissue includes several differentiated cell types; epidermal cells, epidermal hair cells (trichomes), cells in the stomatal complex; guard cells and subsidiary cells. The epidermal cells are the most numerous, largest, and least specialized and form the majority of the epidermis. They are typically more elongated in the leaves of monocots than in those of dicots.
Chloroplasts are generally absent in epidermal cells, the exception being the guard cells of the stomata. The stomatal pores perforate the epidermis and are surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts, forming a specialized cell group known as the stomatal complex. The opening and closing of the stomatal aperture is controlled by the stomatal complex and regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Stomata therefore play the important role in allowing photosynthesis without letting the leaf dry out. In a typical leaf, the stomata are more numerous over the abaxial (lower) epidermis than the adaxial (upper) epidermis and are more numerous in plants from cooler climates. | 5 | Photochemistry |
Chromosome jumping is a tool of molecular biology that is used in the physical mapping of genomes. It is related to several other tools used for the same purpose, including chromosome walking.
Chromosome jumping is used to bypass regions difficult to clone, such as those containing repetitive DNA, that cannot be easily mapped by chromosome walking, and is useful in moving along a chromosome rapidly in search of a particular gene. Unlike chromosome walking, chromosome jumping is able to start on one point of the chromosome in order to traverse potential distant point of the same chromosome without cloning the intervening sequences. The ends of a large DNA fragment is the target cloning section of the chromosome jumping while the middle section gets removed by sequences of chemical manipulations prior to the cloning step. | 1 | Biochemistry |
Affinity chromatography can be used in a number of applications, including nucleic acid purification, protein purification from cell free extracts, and purification from blood.
By using affinity chromatography, one can separate proteins that bind to a certain fragment from proteins that do not bind that specific fragment. Because this technique of purification relies on the biological properties of the protein needed, it is a useful technique and proteins can be purified many folds in one step. | 3 | Analytical Chemistry |
Protein adsorption is critical for many industrial and biomedical applications. Accurate prediction of protein adsorption will enable progress to be made in these areas. | 1 | Biochemistry |
In the last step of glycolysis, phosphoenolpyruvate (PEP) is converted to pyruvate by pyruvate kinase. This reaction is strongly exergonic and irreversible; in gluconeogenesis, it takes two enzymes, pyruvate carboxylase and PEP carboxykinase, to catalyze the reverse transformation of pyruvate to PEP. | 1 | Biochemistry |
Dynamic allele-specific hybridization (DASH) genotyping takes advantage of the differences in the melting temperature in DNA that results from the instability of mismatched base pairs. The process can be vastly automated and encompasses a few simple principles.
In the first step, a genomic segment is amplified and attached to a bead through a PCR reaction with a biotinylated primer. In the second step, the amplified product is attached to a streptavidin column and washed with NaOH to remove the unbiotinylated strand. An allele-specific oligonucleotide is then added in the presence of a molecule that fluoresces when bound to double-stranded DNA. The intensity is then measured as temperature is increased until the melting temperature (Tm) can be determined. A SNP will result in a lower than expected Tm.
Because DASH genotyping is measuring a quantifiable change in Tm, it is capable of measuring all types of mutations, not just SNPs. Other benefits of DASH include its ability to work with label free probes and its simple design and performance conditions. | 1 | Biochemistry |
DNA-dependent ATPase, abbreviated Dda and also known as Dda helicase and Dda DNA helicase, is the 439-amino acid 49,897-atomic mass unit protein coded by the Dda gene of the bacteriophage T4 phage, a virus that infects enterobacteria. | 1 | Biochemistry |
In animals and humans, after ingestion, natural phenols become part of the xenobiotic metabolism. In subsequent phase II reactions, these activated metabolites are conjugated with charged species such as glutathione, sulfate, glycine or glucuronic acid. These reactions are catalysed by a large group of broad-specificity transferases. UGT1A6 is a human gene encoding a phenol UDP glucuronosyltransferase active on simple phenols. The enzyme encoded by the gene UGT1A8 has glucuronidase activity with many substrates including coumarins, anthraquinones and flavones. | 0 | Organic Chemistry |
Twintrons were discovered by Donald W. Copertino and Richard B. Hallick as a group II intron within another group II intron in Euglena chloroplast genome. They found that splicing of both the internal and external introns occurs via lariat intermediates. Additionally, twintron splicing was found to proceed by a sequential pathway, the internal intron being removed prior to the excision of the external intron.
Since the original discovery, there have been other reports of Group III twintrons and GroupII/III twintrons in the chloroplast of Euglena gracilis. In 1993 a new type of complex twintron composed of four individual group III introns has been characterized. The external intron was interrupted by an internal intron containing two additional introns. In 1995 scientists discovered the first non-Euglena twintron in cryptomonad alga Pyrenomonas salina. In 2004, several twintrons were discovered in Drosophila. | 1 | Biochemistry |
High temperature materials are valuable for energy conversion and energy production applications. Maximum energy conversion efficiency is desired in such applications, in accord with the Carnot cycle. Because Carnot efficiency is limited by the temperature difference between the hot and cold reservoirs, higher operating temperatures increase energy conversion efficiency. Operating temperatures are limited by superalloys, limiting applications to around 1000 °C-1400 °C. Energy applications include:
* Solar thermal power plants (stainless steel rods containing heated water)
* Steam turbines (turbine blades and boiler housing)
* Heat exchangers for nuclear reactor systems
Alumina-forming stainless steel is weldable and has potential for use in automotive applications, such as for high temperature exhaust piping and in heat capture and reuse. | 8 | Metallurgy |
The emitted photons from excited lanthanides are detected by highly sensitive devices and techniques such as single-photon detection. If the lifetime of the excited emitting level is long enough, then time-resolved detection (TRD) can be used to enhance the signal-to-noise ratio. The instrumentation used to perform LRET is relatively simple, although slightly more complex than conventional fluorimeters. The general requirements are a pulsed UV excitation source and time-resolved detection.
Light sources which emit short duration pulses can be divided into the following categories:
* Flash tubes
* Mechanically or electronically chopped discharge lamps
* Spark gaps
* Pulsed lasers
The most important factors in the selection of the pulsed light source for are the duration and intensity of the light. Pulsed lasers for the 300 to 500 nm range have now replaced spark caps in fluorescence spectroscopy. There are four general types of pulsing lasers used: lasers with pulsed excitation, lasers with G-switching, mode locked lasers and cavity dumped lasers. Pulsed nitrogen lasers (337 nm) have often been used as an excitation source in time resolved fluorometry.
In time resolved fluorometry the fast photomultiplier tube is the only practical single photon detector. Good single photon resolution is also an advantage in counting photons from long decay fluorescent probes, such as lanthanide chelates.
These commercial instruments are available in the market today: Perkin-Elmer Micro Filter Fluorometer LS-2, Perkin-Elmer Luminescence Spectrometer Model LS 5, and LKB-Wallac Time-Resolved Fluorometer Model 1230. | 1 | Biochemistry |
In physics, work output is the work done by a simple machine, compound machine, or any type of engine model. In common terms, it is the energy output, which for simple machines is always less than the energy input, even though the forces may be drastically different.
In [thermodynamics], work output can refer to the thermodynamic work done by a heat engine, in which case the amount of work output must be less than the input as energy is lost to heat, as determined by the engine's efficiency. | 7 | Physical Chemistry |
Engine oil is filtered to remove impurities. Filtration of oil is normally done with volume filtration. Filter papers for lubrication oils are impregnated to resist high temperatures. | 3 | Analytical Chemistry |
Recently, there had been discussion connecting copy number variations to gene families. Gene families are defined as a set of related genes that serve similar functions but have minor temporal or spatial differences and these genes likely derived from one ancestral gene. The main reason copy number variations are connected to gene families is that there is a possibility that genes in a family may have derived from one ancestral gene which got duplicated into different copies. Mutations accumulate through time in the genes and with natural selection acting on the genes, some mutations lead to environmental advantages allowing those genes to be inherited and eventually clear gene families are separated out. An example of a gene family that may have been created due to copy number variations is the globin gene family. The globin gene family is an elaborate network of genes consisting of alpha and beta globin genes including genes that are expressed in both embryos and adults as well as pseudogenes. These globin genes in the globin family are all well conserved and only differ by a small portion of the gene, indicating that they were derived from a common ancestral gene, perhaps due to duplication of the initial globin gene.
Research has shown that copy number variations are significantly more common in genes that encode proteins that directly interact with the environment than proteins that are involved in basic cellular activities. It was suggested that the gene dosage effect accompanying copy number variation may lead to detrimental effects if essential cellular functions are disrupted, therefore proteins involved in cellular pathways are subjected to strong purifying selection. In addition, proteins function together and interact with proteins of other pathways, therefore it is important to view the effects of natural selection on bio-molecular pathways rather than on individual proteins. With that being said, it was found that proteins in the periphery of the pathway are enriched in copy number variations whereas proteins in the center of the pathways are depleted in copy number variations. It was explained that proteins in the periphery of the pathway interact with fewer proteins and so a change in protein dosage affected by a change in copy number may have a smaller effect on the overall outcome of the cellular pathway.
In the past few years, researchers seem to have shifted their focus from detecting, locating, and sequencing copy number variations to in depth analyses of the role of these copy number variations in the human genome and in nature in general. Evidence is needed to further validate the relationship between copy number variations and gene families as well as the role that natural selection plays in shaping these relationships and changes. Furthermore, researchers are also aiming to elucidate the molecular mechanisms involved in copy number variations as it may reveal essential information regarding structural variations in general. Taking a step back, the area of structural variation in the human genome seems to be a rapidly growing research topic. Not only can these research data provide additional evidence for evolution and natural selection, it can also be used to develop treatments for a wide range of genetic diseases. | 1 | Biochemistry |
The purpose of this technique is to analyze the activity of a gene transcription promoter (in terms of expression of a so-called reporter gene under the regulatory control of that promoter) either in a quantitative manner, involving some measure of activity, or qualitatively (on versus off) through visualization of its activity in different cells, tissues, or organs. The technique utilizes the uidA gene of Escherichia coli, which codes for the enzyme, β-glucuronidase; this enzyme, when incubated with specific colorless or non-fluorescent substrates, can convert them into stable colored or fluorescent products. The presence of the GUS-induced color indicates where the gene has been actively expressed. In this way, strong promoter activity produces much staining and weak promoter activity produces less staining.
The uidA gene can also be fused to a gene of interest, creating a gene fusion. The insertion of the uidA gene will cause production of GUS, which can then be detected using various glucuronides as substrates. | 1 | Biochemistry |
Carbonate in marine sediments predominantly comes from calcifying organisms, with a minor contribution from diagenesis and precipitation. Biogenic calcium carbonate has two polymorphs; calcite by foraminifera and coccolith and aragonite by corals and pteropods. While the distribution of foraminifera is generally global, that of corals is subtropical to tropical. Hence the distribution of fossil corals is commonly used as proxy for paleolatitudes. Kiessling et al. (1999) have compiled a database for the “Phanerozoic reefs” including their paleopostions for paleoclimatological reconstructions Maillet et al. (2021), based on the distribution of Carboniferous coral reefs demonstrated the warm paleoclimatic conditions during the Mississippian, characterized by the wide spread of coral reefs on the supercontinent of Pangea, and this is followed by early Pennsylvanian cooling, marked by rare occurrence of coral reefs. | 9 | Geochemistry |
EPIC-seq, (short for Epigenetic Expression Inference by Cell-free DNA Sequencing), is a high-throughput method that specifically targets gene promoters using cell-free DNA (cfDNA) sequencing. By employing non-invasive techniques such as blood sampling, it infers the expression levels of targeted genes. It consists of both wet and dry lab stages.
EPIC-seq involves deep sequencing of the transcription start sites (TSS). It hypothesizes that with deep sequencing of these TSSs, usage of fragmentomic features, chromatin fragmentation patterns or properties, can allow high-resolution analyses, as opposed to its alternatives.
The method has been shown effective for gene-level expression inference, molecular subtyping of diffuse large B cell lymphoma (DLBCL), histological classification of nonsmall-cell lung cancer (NSCLC), evaluation of results of immunotherapy agents, and assessment of the genes' prognostic importance. EPIC-seq uses machine learning to deduce the RNA expression of the genes and proposes two new metrics: promoter fragmentation entropy (PFE), an adjusted Shannon Index for entropy, and nucleosome-depleted region (NDR) score, the depth of sequencing in NDR regions. PFE showed superior performance compared to earlier metrics for fragmentomic features.
Additionally, EPIC-seq has been mentioned as a possible solution for detecting tissue damage and esophagus cancer using methylation profiles of cfDNAs, profiling of donor liver molecular networks, and inflammatory bowel disease (IBD) detection. | 1 | Biochemistry |
Iron smelting was unknown in pre-Columbian America.
Excavations at LAnse aux Meadows, Newfoundland, have found considerable evidence for the processing of bog iron and the production of iron in a bloomery by the Norse. The cluster of Viking Age (–1022 AD) at LAnse aux Meadows are situated on a raised marine terrace, between a sedge peat bog and the ocean. Estimates from the smaller amount of slag recovered archaeologically suggest 15 kg of slag was produced during what appears to have been a single smelting attempt. By comparing the iron content of the primary bog iron ore found in the purpose built furnace hut with the iron remaining in that slag, an estimated 3 kg iron bloom was produced. At a yield of at best 20% from what is a good iron rich ore, this suggests the workers processing the ore had not been particularly skilled. This supports the idea that iron processing knowledge was widespread and not restricted to major centers of trade and commerce. Archaeologists also found 98 nail, and importantly, ship rivet fragments, at the site as well as considerable evidence for woodworking – which points to boat or possibly ship repairs being undertaken at the site. (An important consideration remains that a potential 3 kg raw bloom most certainly does not make enough refined bar to manufacture the 3 kg of recovered nails and rivets.)
In the Spanish colonization of the Americas, bloomeries or "Catalan forges" were part of "self-sufficiency" at some of the missions, , and . As part of the Franciscan Spanish missions in Alta California, the "Catalan forges" at Mission San Juan Capistrano from the 1790s are the oldest existing facilities of their kind in the present day state of California. The bloomeries sign proclaims the site as being "part of Orange Countys first industrial complex".
The archaeology at Jamestown Virginia (circa 1610–1615) had recovered the remains of a simple short-shaft bloomery furnace, likely intended as yet another "resource test" like the one in Vinland much earlier. The English settlers of the Thirteen Colonies were prevented by law from manufacture; for a time, the British sought to situate most of the skilled artisanry at domestic locations. In fact, this was one of the problems that led to the revolution. The Falling Creek Ironworks was the first in the United States. The Neabsco Iron Works is an example of the early Virginian effort to form a workable American industry.
The earliest iron forge in colonial Pennsylvania was Thomas Rutter's bloomery near Pottstown, founded in 1716. In the Adirondacks, New York, new bloomeries using the hot blast technique were built in the 19th century. | 8 | Metallurgy |
As the group 2 elements (also referred to as the alkaline earth metals) contain two valence electrons, their chemistries have similarities group 12 organometallic compounds. Both readily assume a +2 oxidation states with higher and lower states being rare, and are less electronegative than carbon. However, as the group two elements (with the exception of beryllium) have considerably low electronegativity the resulting C-M bonds are more highly polarized and ionic-like, if not entirely ionic for the heavier barium compounds. The lighter organoberyllium and organomagnesium compounds are often considered covalent, but with some ionic bond characteristics owing to the attached carbon bearing a negative dipole moment. This higher ionic character and bond polarization tends to produce high coordination numbers and many compounds (particularly dialklys) are polymeric in solid or liquid states with highly complex structures in solution, though in the gaseous state they are often monomeric.
Metallocene compounds with group 2 elements are rare, but some do exist. Bis(cyclopentadienyl)beryllium or beryllocene (CpBe), with a molecular dipole moment of 2.2 D, is so-called slipped η/η sandwich. While magnesocene (CpMg) is a regular metallocene, bis(pentamethylcyclopentadienyl)calcium (Cp)Ca is bent with an angle of 147°. | 0 | Organic Chemistry |
When the excited chlorophyll P passes the electron to pheophytin, it converts to high-energy P, which can oxidize the tyrosine (or Y) molecule by ripping off one of its hydrogen atoms. The high-energy oxidized tyrosine gives off its energy and returns to the ground state by taking up a proton and removing an electron from the oxygen-evolving complex and ultimately from water. Kok's S-state diagram shows the reactions of water splitting in the oxygen-evolving complex. | 5 | Photochemistry |
The per base accuracy achieved in house by Ion Torrent on the [http://www.lifetechnologies.com/iontorrent Ion Torrent] Ion semiconductor sequencer as of February 2011 was 99.6% based on 50 base reads, with 100 Mb per run. The read-length as of February 2011 was 100 base pairs. The accuracy for homopolymer repeats of 5 repeats in length was 98%. Later releases show a read length of 400 base pairs These figures have not yet been independently verified outside of the company. | 1 | Biochemistry |
The reaction occurring between double bonds and ozone is known as ozonolysis when one molecule of the gas reacts with the double bond:
The immediate result is formation of an ozonide, which then decomposes rapidly so that the double bond is cleaved. This is the critical step in chain breakage when polymers are attacked. The strength of polymers depends on the chain molecular weight or degree of polymerization: The higher the chain length the greater the mechanical strength (such as tensile strength). By cleaving the chain, the molecular weight drops rapidly and there comes a point when it has little strength whatsoever, and a crack forms. Further attack occurs in the freshly exposed crack surfaces and the crack grows steadily until it completes a circuit and the product separates or fails. In the case of a seal or a tube, failure occurs when the wall of the device is penetrated.
The carbonyl end groups that are formed are usually aldehydes or ketones, which can oxidise further to carboxylic acids. The net result is a high concentration of elemental oxygen on the crack surfaces, which can be detected using EDX in the ESEM. For example, two EDX spectra were obtained during an investigation into ozone cracking of diaphragm seals in a semiconductor fabrication factory. The EDX spectrum of the crack surface shows the high-oxygen peak compared with a constant sulfur peak. In contrast, the EDX spectrum of the unaffected elastomer surface spectrum shows a relatively low-oxygen peak compared with the sulfur peak. | 7 | Physical Chemistry |
SMA actuators are typically actuated electrically, where an electric current results in Joule heating. Deactivation typically occurs by free convective heat transfer to the ambient environment. Consequently, SMA actuation is typically asymmetric, with a relatively fast actuation time and a slow deactuation time. A number of methods have been proposed to reduce SMA deactivation time, including forced convection, and lagging the SMA with a conductive material in order to manipulate the heat transfer rate.
Novel methods to enhance the feasibility of SMA actuators include the use of a conductive "lagging". this method uses a thermal paste to rapidly transfer heat from the SMA by conduction. This heat is then more readily transferred to the environment by convection as the outer radii (and heat transfer area) are significantly greater than for the bare wire. This method results in a significant reduction in deactivation time and a symmetric activation profile. As a consequence of the increased heat transfer rate, the required current to achieve a given actuation force is increased. | 8 | Metallurgy |
The concept of selectivity is used to quantify the extent to which one chemical substance, A, binds each of two other chemical substances, B and C. The simplest case is where the complexes formed have 1:1 stoichiometry. Then, the two interactions may be characterized by equilibrium constants and .
where [X] represents the concentration of substance X (A, B, C, …).
A selectivity coefficient is defined as the ratio of the two equilibrium constants.
This selectivity coefficient is in fact the equilibrium constant for the displacement reaction
It is easy to show that the same definition applies to complexes of a different stoichiometry, AB and AC. The greater the selectivity coefficient, the more the ligand C will displace the ligand B from the complex formed with the substrate A. An alternative interpretation is that the greater the selectivity coefficient, the lower the concentration of C that is needed to displace B from AB. Selectivity coefficients are determined experimentally by measuring the two equilibrium constants, and . | 7 | Physical Chemistry |
The majority of benzylic functionalization reactions of tricarbonyl(arene)chromium complexes proceed by mechanisms analogous to those followed by the free arenes. The aromatic ring and benzylic position are activated towards solvolysis, deprotonation, and nucleophilic attack (at the ortho and para positions of the arene) upon complexation to chromium, which is able to stabilize developing charges in the arene ligand. As a result, these reactions of chromium arene complexes are often faster than analogous reactions of free arenes.
Second, in benzylic cations and anions of chromium arene complexes, rotation about the bond connecting the benzylic carbon and aromatic ring is severely restricted. This bond possesses a significant amount of double bond character due to the delocalization of charge into the aromatic ring (and the stabilization of that charge by chromium).
Finally, the chromium tri(carbonyl) moiety serves as a sterically bulky group in reactions of arene chromium complexes, preventing the approach of a reagent endo to chromium. In addition, ortho-substituted aromatic aldehydes and styrenes prefer to adopt a conformation in which the doubly bound oxygen or carbon is pointed away from the ortho substituent. As a result, only one face of the double bond is exposed on the exo face of the aromatic ring. If this were not the case, addition to styrenes and aromatic aldehydes would not be diastereoselective, despite the presence of the chromium tri(carbonyl) group. The ortho substituent is necessary for high stereoselectivity; meta-substituted arenes exhibit very low diastereoselectivity. | 0 | Organic Chemistry |
Virus survival through inclusion of AMGs is governed by the laws of natural selection and has been made highly selective through co-evolution with their hosts. As such, the AMGs that confer a fitness advantage to the virus's ability to infect a host and reproduce will be more abundant. AMG abundance is largely dictated by the lifestyle of the virus, environmental conditions surrounding it, and host characteristics. | 1 | Biochemistry |
Modified bisulfite sequencing was optimized for rRNA, tRNA, and miRNA molecules from Drosophila.
Bisulfite treatment has been most widely used to detect dm5C (DNA m5C). The treatment essentially converts a cytosine to a uridine, but methylated cytosines would be unchanged by the treatment.
Previous attempts to develop m5C sequencing protocols using bisulfite treatment were not able to effectively address the problem of the harsh treatment of RNA which causes significant degradation of the molecules. Specifically, bisulfite deamination treatment (high pH) of RNA is detrimental to the stability of phosphodiester bonds. As a result, it is difficult to pre-enrich RNA molecules or to obtain enough PCR product of the correct size for deep sequencing.
A modified version of bisulfite sequencing was developed by Schaefer et al. (2009) which decreased the temperature at which bisulfite treatment of RNA from 95 °C to 60 °C. The rationale behind the modification was that since RNA, unlike DNA, is not double-stranded, but rather, consists of regions of single-strandedness, double-stranded stem structures and loops, it could be possible to unwind RNA at a much lower temperature. Indeed, RNA could be treated for 180 minutes at 60C without significant loss of PCR amplicons of the expected size. Deamination rates were determined to be 99% at 180min of treatment.
After bisulfite treatment of fragmented RNA, reverse transcription is performed, followed by PCR amplification of the cDNA products, and finally deep sequencing was done using the Roche 454 platform.
Since the developers of the method used the Roche platform, they also used GS Amplicon Variant Analyzer (Roche) for analyzing deep sequencing data to quantify sequence-specific cytosine content.
However, recent papers have suggested that the method have several flaws: (1) Incomplete conversion of regular cytosines in double-stranded regions of RNA; (2) areas containing other modifications that resulted in bisulfite-treatment resistance; and (3) sites containing potential false-positives due to (1) and (2) In addition, it is possible the sequencing depth is still not high enough to correctly detect all methylated sites. | 1 | Biochemistry |
An optical spectrum analyzer uses reflective or refractive techniques to separate out the wavelengths of light. An electro-optical detector is used to measure the intensity of the light, which is then normally displayed on a screen in a similar manner to a radio- or audio-frequency spectrum analyzer.
The input to an optical spectrum analyzer may be simply via an aperture in the instrument's case, an optical fiber or an optical connector to which a fiber-optic cable can be attached.
Different techniques exist for separating out the wavelengths. One method is to use a monochromator, for example a Czerny–Turner design, with an optical detector placed at the output slit. As the grating in the monochromator moves, bands of different frequencies (colors) are seen by the detector, and the resulting signal can then be plotted on a display. More precise measurements (down to MHz in the optical spectrum) can be made with a scanning Fabry–Pérot interferometer along with analog or digital control electronics, which sweep the resonant frequency of an optically resonant cavity using a voltage ramp to piezoelectric motor that varies the distance between two highly reflective mirrors. A sensitive photodiode embedded in the cavity provides an intensity signal, which is plotted against the ramp voltage to produce a visual representation of the optical power spectrum.
The frequency response of optical spectrum analyzers tends to be relatively limited, e.g. (near-infrared), depending on the intended purpose, although (somewhat) wider-bandwidth general purpose instruments are available. | 7 | Physical Chemistry |
One of the main sources of information about the Earths composition comes from understanding the relationship between peridotite and basalt melting. Peridotite makes up most of Earths mantle. Basalt, which is highly concentrated in the Earths oceanic crust, is formed when magma reaches the Earths surface and cools down at a very fast rate. When magma cools, different minerals crystallize at different times depending on the cooling temperature of that respective mineral. This ultimately changes the chemical composition of the melt as different minerals begin to crystallize. Fractional crystallization of elements in basaltic liquids has also been studied to observe the composition of lava in the upper mantle. This concept can be applied by scientists to give insight on the evolution of Earth's mantle and how concentrations of lithophile trace elements have varied over the last 3.5 billion years. | 9 | Geochemistry |
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, plastics, and other materials. The nanoparticles in the sintered material diffuse across the boundaries of the particles, fusing the particles together and creating a solid piece.
Since the sintering temperature does not have to reach the melting point of the material, sintering is often chosen as the shaping process for materials with extremely high melting points, such as tungsten and molybdenum. The study of sintering in metallurgical powder-related processes is known as powder metallurgy.
An example of sintering can be observed when ice cubes in a glass of water adhere to each other, which is driven by the temperature difference between the water and the ice. Examples of pressure-driven sintering are the compacting of snowfall to a glacier, or the formation of a hard snowball by pressing loose snow together.
The material produced by sintering is called sinter. The word sinter comes from the Middle High German , a cognate of English cinder. | 8 | Metallurgy |
Metal-coded affinity tag is a method used for quantitative proteomics by mass spectrometry that uses a metal chelate complex 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) coupled to different lanthanide ions. The metal complexes attach to the cysteine residues of proteins in a sample. | 3 | Analytical Chemistry |
Knowles was educated at Toller Porcorum primary school, Beaminster School and St Catharine's College, Cambridge, graduating from the university in 1988, with triple first class honours in natural sciences (taking Materials Science and Metallurgy in Part II). He then went on to complete a PhD in 1991 - on the topic of the fatigue and fracture behaviour of aluminium-lithium based composites - under the supervision of Dr Julia King (now Baroness Brown of Cambridge). | 8 | Metallurgy |
In boilers, economizers are heat exchange devices that heat fluids, usually water, up to but not normally beyond the boiling point of that fluid. Economizers are so named because they can make use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boilers efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used to fill it (the feed water').
Steam boilers use large amounts of energy raising feed water to the boiling temperature, converting the water to steam and sometimes superheating that steam above saturation temperature. Heat transfer efficiency is improved when the highest temperatures near the combustion sources are used for boiling and superheating, while using the residual heat of the cooled combustion gases exhausting from the boiler through an economizer to raise the temperature of feed water entering the steam drum.
An indirect contact or direct contact condensing economizer will recover the residual heat from the combustion products. A series of dampers, an efficient control system, as well as a ventilator, allow all or part of the combustion products to pass through the economizer, depending on the demand for make-up water and/or process water. The temperature of the gases can be lowered from the boiling temperature of the fluid to little more than the incoming feed water temperature while preheating that feed water to the boiling temperature. High pressure boilers typically have larger economizer surfaces than low pressure boilers. Economizer tubes often have projections like fins to increase the heat transfer surface on the combustion gas side. On average over the years, boiler combustion efficiency has risen from 80% to more than 95%. The efficiency of heat produced is directly linked to boiler efficiency. The percentage of excess air and the temperature of the combustion products are two key variables in evaluating this efficiency.
The combustion of natural gas needs a certain quantity of air in order to be complete, so the burners need a flow of excess air in order to operate. Combustion produces water steam, and the quantity depends on the amount of natural gas burned. Also, the evaluation of the dew point depends on the excess air. Natural gas has different combustion efficiency curves linked to the temperature of the gases and the excess air. For example, if the gases are chilled to 38 °C and there is 15% excess air, then the efficiency will be 94%. The condensing economizer can thus recover the sensible and latent heat in the steam condensate contained in the flue gases for the process.
The economizer is made of an aluminium and stainless steel alloy. The gases pass through the cylinder, and the water passes through the finned tubes. It condenses about 11% of the water contained in the gases. | 7 | Physical Chemistry |
The quasistatic equations that describe the scattering and absorbance cross-sections for very small spherical nanoparticles are:
where is the wavenumber of the electric field, is the radius of the particle, is the relative permittivity of the dielectric medium and is the relative permittivity of the nanoparticle defined by
also known as the Drude Model for free electrons where is the plasma frequency, is the relaxation frequency of the charge carries, and is the frequency of the electromagnetic radiation. This equation is the result of solving the differential equation for a harmonic oscillator with a driving force proportional to the electric field that the particle is subjected to. For a more thorough derivation, see surface plasmon.
It logically follows that the resonance conditions for these equations is reached when the denominator is around zero such that
When this condition is fulfilled the cross-sections are at their maximum.
These cross-sections are for single, spherical particles. The equations change when particles are non-spherical, or are coupled to 1 or more other nanoparticles, such as when their geometry changes. This principle is important for several applications.
Rigorous electrodynamic analysis of plasma oscillations in a spherical metal nanoparticle of a finite size was performed in. | 7 | Physical Chemistry |
A Light-oxygen-voltage-sensing domain (LOV domain) is a protein sensor used by a large variety of higher plants, microalgae, fungi and bacteria to sense environmental conditions. In higher plants, they are used to control phototropism, chloroplast relocation, and stomatal opening, whereas in fungal organisms, they are used for adjusting the circadian temporal organization of the cells to the daily and seasonal periods. They are a subset of PAS domains. | 1 | Biochemistry |
Pittsfield, in western Massachusetts, was home to the General Electric (GE) transformer, capacitor, and electrical generating equipment divisions. The electrical generating division built and repaired equipment that was used to power the electrical utility grid throughout the nation. PCB-contaminated oil routinely migrated from GE's industrial plant located in the very center of the city to the surrounding groundwater, nearby Silver Lake, and to the Housatonic River, which flows through Massachusetts, Connecticut, and down to Long Island Sound. PCB-containing solid material was widely used as fill, including oxbows of the Housatonic River. Fish and waterfowl who live in and around the river contain significant levels of PCBs and are not safe to eat. EPA designated the Pittsfield plant and several miles of the river as a Superfund site in 1997, and ordered GE to remediate the site. EPA and GE began a cleanup of the area in 1999.
New Bedford Harbor, which is a listed Superfund site, contained some of the highest sediment concentrations of PCBs in the marine environment. Cleanup of the area began in 1994 and is mostly complete as of 2020.
Investigations into historic waste dumping in the Bliss Corner neighborhood have revealed the existence of PCBs, among other hazardous materials, buried into soil and waste material. | 2 | Environmental Chemistry |
An important microstructural feature of a polymer is its architecture and shape, which relates to the way branch points lead to a deviation from a simple linear chain. A branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Types of branched polymers include star polymers, comb polymers, polymer brushes, dendronized polymers, ladder polymers, and dendrimers. There exist also two-dimensional polymers (2DP) which are composed of topologically planar repeat units. A polymer's architecture affects many of its physical properties including solution viscosity, melt viscosity, solubility in various solvents, glass-transition temperature and the size of individual polymer coils in solution. A variety of techniques may be employed for the synthesis of a polymeric material with a range of architectures, for example living polymerization. | 7 | Physical Chemistry |
A "black body" is a body which has the property of allowing all incident rays to enter without surface reflection and not allowing them to leave again.
Blackbodies are idealized surfaces that act as the perfect absorber and emitter. They serve as the standard against which real surfaces are compared when characterizing thermal radiation. A blackbody is defined by three characteristics:
# A blackbody absorbs all incident radiation, regardless of wavelength and direction.
# No surface can emit more energy than a blackbody for a given temperature and wavelength.
# A blackbody is a diffuse emitter. | 7 | Physical Chemistry |
Multiplex polymerase chain reaction (Multiplex PCR) refers to the use of polymerase chain reaction to amplify several different DNA sequences simultaneously (as if performing many separate PCR reactions all together in one reaction). This process amplifies DNA in samples using multiple primers and a temperature-mediated DNA polymerase in a thermal cycler. The primer design for all primers pairs has to be optimized so that all primer pairs can work at the same annealing temperature during PCR.
Multiplex-PCR was first described in 1988 as a method to detect deletions in the dystrophin gene. It has also been used with the steroid sulfatase gene. In 2008, multiplex-PCR was used for analysis of microsatellites and SNPs. In 2020, RT-PCR multiplex assays were designed that combined multiple gene targets from the Center for Diseases and Control in a single reaction to increase molecular testing accessibility and throughput for SARS-CoV-2 diagnostics.
Multiplex-PCR consists of multiple primer sets within a single PCR mixture to produce amplicons of varying sizes that are specific to different DNA sequences. By targeting multiple sequences at once, additional information may be gained from a single test run that otherwise would require several times the reagents and more time to perform. Annealing temperatures for each of the primer sets must be optimized to work correctly within a single reaction, and amplicon sizes, i.e., their base pair length, should be different enough to form distinct bands when visualized by gel electrophoresis. Alternatively, if amplicon sizes overlap, the different amplicons may be differentiated and visualised using primers that have been dyed with different colour fluorescent dyes. Commercial multiplexing kits for PCR are available and used by many forensic laboratories to amplify degraded DNA samples. | 1 | Biochemistry |
Nucleotide (abbreviated "nt") is a common unit of length for single-stranded nucleic acids, similar to how base pair is a unit of length for double-stranded nucleic acids. | 1 | Biochemistry |
Minerals that have the same structure (isomorphic minerals) may have epitaxic relations. An example is albite on microcline . Both these minerals are triclinic, with space group , and with similar unit cell parameters, a = 8.16 Å, b = 12.87 Å, c = 7.11 Å, α = 93.45°, β = 116.4°, γ = 90.28° for albite and a = 8.5784 Å, b = 12.96 Å, c = 7.2112 Å, α = 90.3°, β = 116.05°, γ = 89° for microcline. | 3 | Analytical Chemistry |
Diphenylcyanoarsine, also called Clark 2 (Chlor-Arsen-Kampfstoff 2, being the successor of Clark 1) by the Germans, was discovered in 1918 by Sturniolo and Bellinzoni and shortly thereafter used like the related Clark 1 gas by the Germans for chemical warfare in the First World War. The substance causes nausea, vomiting, and headaches. It can subsequently lead to e.g. pulmonary edema (fluid in the lungs). | 1 | Biochemistry |
Nickel is both naturally abundant – it is the fifth most common element on earth – and widely used in industry and commercial goods. Workplace nickel exposure is common in many industries, and the performance of normal work tasks can result in nickel skin levels sufficient to elicit dermatitis. Within the workplace, individuals may be exposed to significant amounts of nickel, airborne from the combustion of fossil fuels or from contact with tools that are nickel plated. Historically, workplaces where prolonged contact with soluble nickel has been high have shown high risks for allergic contact nickel dermatitis. For example, nickel dermatitis was common in the past among nickel platers. Outbreaks of nickel allergy from consumer goods have been documented throughout the 20th century, with jewelry, stocking suspenders, and metallic buttons on blue jeans each resulting in dermatitis at the point of contact. Nickel can also be present in food and drinking water; ingestion of increased nickel is not associated with systemic allergic disease, but is associated with flare-ups of dermatitis or aggravation of vesicular hand eczema. Similarly, aggravation of dermatitis has been reported in response to nickel-containing surgical implants or dental gear.
The risk of an object eliciting nickel allergy is linked to the amount of nickel released by its surface (and not to its total nickel content). Suspected objects can be screened by wiping the surface with a 1% dimethylglyoxime solution that turns pink if more than 0.5 μg/cm per week is released by the surface. Various methods exist to test the skin or nails for nickel exposure, typically relying on wiping the skin, then quantifying the nickel on the wipe via mass spectrometry.
Dietary nickel exposure may come from high-nickel foods, possibly canned food (via the packaging), possibly stainless steel cookware (whereas some grades of stainless steel contain more nickel than others), or plumbing (especially the first water run from the tap in the morning). | 1 | Biochemistry |
DNA printing can thus be used to produce DNA parts, which are defined as sequences of DNA that encode a specific biological function (for example, promoters, transcription regulatory sequences or open reading frames). However, because oligonucleotide synthesis typically cannot accurately produce oligonucleotides sequences longer than a few hundred base pairs, DNA assembly methods have to be employed to assemble these parts together to create functional genes, multi-gene circuits or even entire synthetic chromosomes or genomes. Some DNA assembly techniques only define protocols for joining DNA parts, while other techniques also define the rules for the format of DNA parts that are compatible with them. These processes can be scaled up to enable the assembly of entire chromosomes or genomes. In recent years, there has been proliferation in the number of different DNA assembly standards with 14 different assembly standards developed as of 2015, each with their pros and cons. Overall, the development of DNA assembly standards has greatly facilitated the workflow of synthetic biology, aided the exchange of material between research groups and also allowed for the creation of modular and reusable DNA parts.
The various DNA assembly methods can be classified into three main categories – endonuclease-mediated assembly, site-specific recombination, and long-overlap-based assembly. Each group of methods has its distinct characteristics and their own advantages and limitations. | 1 | Biochemistry |
Inclusion of plasticizers tends to lower T and increase polymer flexibility. Addition of the plasticizer will also modify dependence of the glass-transition temperature T on the cooling rate. The mobility of the chain can further change if the molecules of plasticizer give rise to hydrogen bonding formation. Plasticizers are generally small molecules that are chemically similar to the polymer and create gaps between polymer chains for greater mobility and fewer interchain interactions. A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. A uPVC, or unplasticized polyvinylchloride, is used for things such as pipes. A pipe has no plasticizers in it, because it needs to remain strong and heat-resistant. Plasticized PVC is used in clothing for a flexible quality. Plasticizers are also put in some types of cling film to make the polymer more flexible. | 7 | Physical Chemistry |
Automated mineralogy solutions are applied in a variety of fields requiring statistically reliable, quantitative mineralogical information. These include the following sectors: mining; O&G; coal; environmental sciences; forensic geosciences; archaeology;agribusiness; built environment and planetary geology. | 7 | Physical Chemistry |
For a molecule to be considered a photosensitizer:
* The photosensitizer must impart a physicochemical change upon a substrate after absorbing incident light.
* Upon imparting a chemical change, the photosensitizer returns to its original chemical form.
It is important to differentiate photosensitizers from other photochemical interactions including, but not limited to, photoinitiators, photocatalysts, photoacids and photopolymerization. Photosensitizers utilize light to enact a chemical change in a substrate; after the chemical change, the photosensitizer returns to its initial state, remaining chemically unchanged from the process. Photoinitiators absorb light to become a reactive species, commonly a radical or an ion, where it then reacts with another chemical species. These photoinitiators are often completely chemically changed after their reaction. Photocatalysts accelerate chemical reactions which rely upon light. While some photosensitizers may act as photocatalysts, not all photocatalysts may act as photosensitizers. Photoacids (or photobases) are molecules which become more acidic (or basic) upon the absorption of light. Photoacids increase in acidity upon absorbing light and thermally reassociate back into their original form upon relaxing. Photoacid generators undergo an irreversible change to become an acidic species upon light absorption. Photopolymerization can occur in two ways. Photopolymerization can occur directly wherein the monomers absorb the incident light and begin polymerizing, or it can occur through a photosensitizer-mediated process where the photosensitizer absorbs the light first before transferring energy into the monomer species. | 5 | Photochemistry |
Escitalopram, like other SSRIs, has been shown to affect sexual function, causing side effects such as decreased libido, delayed ejaculation, and anorgasmia.
There is also evidence that SSRIs may cause an increase in suicidal ideation. An analysis conducted by the FDA found a statistically insignificant 1.5 to 2.4-fold (depending on the statistical technique used) increase of suicidality among the adults treated with escitalopram for psychiatric indications. The authors of a related study note the general problem with statistical approaches: due to the rarity of suicidal events in clinical trials, it is hard to draw firm conclusions with a sample smaller than two million patients.
Citalopram and escitalopram are associated with dose-dependent QT interval prolongation and should not be used in those with congenital long QT syndrome or known pre-existing QT interval prolongation, or in combination with other medicines that prolong the QT interval. ECG measurements should be considered for patients with cardiac disease, and electrolyte disturbances should be corrected before starting treatment. In December 2011, the UK implemented new restrictions on the maximum daily doses at 20 mg for adults and 10 mg for those older than 65 years or with liver impairment. There are concerns of higher rates of QT prolongation and torsades de pointes compared with other SSRIs. The US Food and Drug Administration and Health Canada did not similarly order restrictions on escitalopram dosage, only on its predecessor citalopram. | 4 | Stereochemistry |
In electrochemistry, a thermoneutral voltage is a voltage drop across an electrochemical cell which is sufficient not only to drive the cell reaction, but to also provide the heat necessary to maintain a constant temperature. For a reaction of the form
The thermoneutral voltage is given by
where is the change in enthalpy and F is the Faraday constant. | 7 | Physical Chemistry |
In pharmacology, Schild regression analysis, based upon the Schild equation, both named for Heinz Otto Schild, are tools for studying the effects of agonists and antagonists on the response caused by the receptor or on ligand-receptor binding. | 1 | Biochemistry |
Enalapril has an L-proline moiety as a part of the molecule which is responsible for the oral bioavailability of the drug. It is a pro-drug, which means that it exerts its function after being metabolized. The "-OCH2CH3" part of the molecule will split during the metabolism and at the carbon will be a carboxylate, which then interacts with the Zn+2 site of the ACE enzyme. This structural feature and mechanism of metabolism that must occur before the drug can inhibit the enzyme explains why it has a greater duration of action than another similar drug used for the same indication, Captopril. Duration of effect is dose-related; at recommended doses, antihypertensive and haemodynamic effects have been shown to be maintained for at least 24 hours. Enalapril has a slower onset of action than Captopril but a greater duration of action. However, unlike Captopril, Enalapril does not have a thiol moiety. | 4 | Stereochemistry |
The 3rd group of anions consist of SO, PO and BO. They react neither with concentrated nor diluted HSO.
* Sulfates give a white precipitate of BaSO with BaCl which is insoluble in any acid or base.
* Phosphates give a yellow crystalline precipitate upon addition of HNO and ammonium molybdate and heating the solution.
* Borates give a green flame characteristic of ethyl borate when ignited with concentrated HSO and ethanol. | 3 | Analytical Chemistry |
Mitochondria play a central role in many other metabolic tasks, such as:
* Signaling through mitochondrial reactive oxygen species
* Regulation of the membrane potential
* Apoptosis-programmed cell death
* Calcium signaling (including calcium-evoked apoptosis)
* Regulation of cellular metabolism
* Certain heme synthesis reactions (see also: Porphyrin)
* Steroid synthesis
* Hormonal signaling – mitochondria are sensitive and responsive to hormones, in part by the action of mitochondrial estrogen receptors (mtERs). These receptors have been found in various tissues and cell types, including brain and heart
* Immune signaling
* Neuronal mitochondria also contribute to cellular quality control by reporting neuronal status towards microglia through specialised somatic-junctions.
* Mitochondria of developing neurons contribute to intercellular signaling towards microglia, which communication is indispensable for proper regulation of brain development.
Some mitochondrial functions are performed only in specific types of cells. For example, mitochondria in liver cells contain enzymes that allow them to detoxify ammonia, a waste product of protein metabolism. A mutation in the genes regulating any of these functions can result in mitochondrial diseases.
Mitochondrial proteins (proteins transcribed from mitochondrial DNA) vary depending on the tissue and the species. In humans, 615 distinct types of proteins have been identified from cardiac mitochondria, whereas in rats, 940 proteins have been reported. The mitochondrial proteome is thought to be dynamically regulated. | 1 | Biochemistry |
Trifluoroacetic acid is a corrosive strong acid but it does not pose the hazards associated with hydrofluoric acid because the carbon-fluorine bond is not labile. TFA is harmful when inhaled, causes severe skin burns and is toxic for aquatic organisms even at low concentrations.
TFA's reaction with bases and metals, especially light metals, is strongly exothermic. The reaction with lithium aluminium hydride (LAH) results in an explosion.
TFA is a metabolic breakdown product of the volatile anaesthetic agent halothane. It is thought to be responsible for halothane induced hepatitis. | 0 | Organic Chemistry |
Several additives, including polystyrene, cyclen, and polyamines, to the Stöber process allow the creation of shell-core silica particles. Two configurations of the shell-core morphology have been described. One is a silica core with an outer shell of an alternative material such as polystyrene. The second is a silica shell with a morphologically different core such as a polyamine.
The creation of the polystrene/silica core composite particles begins with creation of the silica cores via the one-step Stöber process. Once formed, the particles are treated with oleic acid, which is proposed to react with the surface silanol groups. Styrene is polymerized around the fatty-acid-modified silica cores. By virtue of size distribution of the silica cores, the styrene polymerizes around them evenly resulting composite particles are similarly sized.
The silica shell particles created with cyclen and other polyamine ligands are created in a much different fashion. The polyamines are added to the Stöber reaction in the initial steps along with the TEOS precursor. These ligands interact with the TEOS precursor, resulting in an increase in the speed of hydrolysis; however, as a result they get incorporated into the resulting silica colloids. The ligands have several nitrogen sites that contain lone pairs of electrons that interact with the hydrolyzed end groups of TEOS. Consequently, the silica condense around the ligands encapsulating them. Subsequently, the silica/ligand capsules stick together to create larger particles. Once all of the ligand has been consumed by the reaction the remaining TEOS aggregates around the outside of the silica/ligand nanoparticles, creating a solid silica outer shell. The resultant particle has a solid silica shell and an internal core of silica-wrapped ligands. The sizes of the particles cores and shells can be controlled through selection of the shape of the ligands along with the initial concentrations added to the reaction. | 7 | Physical Chemistry |
1,4-alpha-glucan-branching enzyme, also known as brancher enzyme or glycogen-branching enzyme is an enzyme that in humans is encoded by the GBE1 gene.
Glycogen branching enzyme is an enzyme that adds branches to the growing glycogen molecule during the synthesis of glycogen, a storage form of glucose. More specifically, during glycogen synthesis, a glucose 1-phosphate molecule reacts with uridine triphosphate (UTP) to become UDP-glucose, an activated form of glucose. The activated glucosyl unit of UDP-glucose is then transferred to the hydroxyl group at the C-4 of a terminal residue of glycogen to form an α-1,4-glycosidic linkage, a reaction catalyzed by glycogen synthase. Importantly, glycogen synthase can only catalyze the synthesis of α-1,4-glycosidic linkages. Since glycogen is a readily mobilized storage form of glucose, the extended glycogen polymer is branched by glycogen branching enzyme to provide glycogen breakdown enzymes, such as glycogen phosphorylase, with many terminal residues for rapid degradation. Branching also importantly increases the solubility and decreases the osmotic strength of glycogen.
The protein encoded by this gene is a glycogen branching enzyme that catalyzes the transfer of alpha-1,4-linked glucosyl units from the outer end of a glycogen chain to an alpha-1,6 position on the same or a neighboring glycogen chain. Branching of the chains is essential to increase the solubility of the glycogen molecule and, consequently, in reducing the osmotic pressure within cells. The highest levels of this enzyme are found in liver and muscle cells. Mutations in this gene are associated with glycogen storage disease type IV (also known as Andersen's disease). | 1 | Biochemistry |
This family of clusters includes the closo cages and their derivatives.
Isomerism is well established in this family:
*2,3- and 2,4-
*2,3- and 2,4-
*1,2- and 1,6-
*1,10-, 1,6-, and 1,2-
*1,2 and 1,3-. | 7 | Physical Chemistry |
Electrostatic precipitators, ESPs, have recently gained renewed interest for bioaerosol sampling due to their highly efficient particle removal efficiencies and gentler sampling method as compared with impinging. ESPs charge and remove incoming aerosol particles from an air stream by employing a non-uniform electrostatic field between two electrodes, and a high field strength. This creates a region of high density ions, a corona discharge, which charges incoming aerosol droplets, and the electric field deposits the charges particles onto a collection surface.
Since biological particles are typically analysed using liquid-based assays (PCR, immunoassays, viability assay) it is preferable to sample directly into a liquid volume for downstream analysis. For example, Pardon et al. show sampling of aerosols down to a microfluidic air-liquid interface, and Ladhani et al., show sampling of airborne Influenza down to a small liquid droplet. The use of low-volume liquids is ideal for minimising sample dilution, and has the potential to be couple to lab-on-chip technologies for rapid point-of-care analysis. | 7 | Physical Chemistry |
Network motifs are recurrent and statistically significant subgraphs or patterns of a larger graph. All networks, including biological networks, social networks, technological networks (e.g., computer networks and electrical circuits) and more, can be represented as graphs, which include a wide variety of subgraphs.
Network motifs are sub-graphs that repeat themselves in a specific network or even among various networks. Each of these sub-graphs, defined by a particular pattern of interactions between vertices, may reflect a framework in which particular functions are achieved efficiently. Indeed, motifs are of notable importance largely because they may reflect functional properties. They have recently gathered much attention as a useful concept to uncover structural design principles of complex networks. Although network motifs may provide a deep insight into the network's functional abilities, their detection is computationally challenging. | 1 | Biochemistry |
As the concentration of particles in a suspension is increased, a point is reached where particles are so close together that they no longer settle independently of one another and the velocity fields of the fluid displaced by adjacent particles, overlap. There is also a net upward flow of liquid displaced by the settling particles. This results in a reduced particle-settling velocity and the effect is known as hindered settling.
There is a common case for hindered settling occurs. the whole suspension tends to settle as a ‘blanket’ due to its extremely high particle concentration. This is known as zone settling, because it is easy to make a distinction between several different zones which separated by concentration discontinuities. Fig. 3 represents a typical batch-settling column tests on a suspension exhibiting zone-settling characteristics. There is a clear interface near the top of the column would be formed to separating the settling sludge mass from the clarified supernatant as long as leaving such a suspension to stand in a settling column. As the suspension settles, this interface will move down at the same speed. At the same time, there is an interface near the bottom between that settled suspension and the suspended blanket. After settling of suspension is complete, the bottom interface would move upwards and meet the top interface which moves downwards. | 3 | Analytical Chemistry |
In quantum mechanics the basis for a spectroscopic selection rule is the value of the transition moment integral
where and are the wave functions of the two states, "state 1" and "state 2", involved in the transition, and is the transition moment operator. This integral represents the propagator (and thus the probability) of the transition between states 1 and 2; if the value of this integral is zero then the transition is "forbidden".
In practice, to determine a selection rule the integral itself does not need to be calculated: It is sufficient to determine the symmetry of the transition moment function
If the transition moment function is symmetric over all of the totally symmetric representation of the point group to which the atom or molecule belongs, then the integrals value is (in general) not zero and the transition is' allowed. Otherwise, the transition is "forbidden".
The transition moment integral is zero if the transition moment function, is anti-symmetric or odd, i.e. holds. The symmetry of the transition moment function is the direct product of the parities of its three components. The symmetry characteristics of each component can be obtained from standard character tables. Rules for obtaining the symmetries of a direct product can be found in texts on character tables. | 7 | Physical Chemistry |
Lithium tert-butoxide is the metalorganic compound with the formula LiOC(CH). A white solid, it is used as a strong base in organic synthesis. The compound is often depicted as a salt, and it often behaves as such, but it is not ionized in solution. Both octameric and hexameric forms have been characterized by X-ray crystallography | 0 | Organic Chemistry |
Non-ferrous metals are used in residential,
commercial and industrial applications. Material selection for a mechanical or structural application requires some important considerations, including how easily the material can be shaped into a finished part and how its properties can be either intentionally or inadvertently altered in the process. Depending on the end use, metals can be simply cast into the finished part, or cast into an intermediate form, such as an ingot, then worked, or wrought, by rolling, forging, extruding, or other deformation process. Although the same operations are used with ferrous as well as nonferrous metals and alloys, the reaction of nonferrous metals to these forming processes is often more severe. Consequently, properties may differ considerably between the cast and wrought forms of the same metal or alloy. | 8 | Metallurgy |
Levan is a naturally occurring fructan present in many plants and microorganisms. This polymer is made up of fructose, a monosaccharide sugar, connected by 2,6 beta glycosidic linkages. Levan can have both branched and linear structures of relatively low molecular weight. Branched levan forms a very small, sphere-like structure with basal chains 9 units long. The 2,1 branching allows methyl ethers to form and create a spherical shape. The ends of levan also tend to contain a glucosyl residue. Branched levan tends to be more stable than linear polysaccharides. However, the amount of branching and length of polymerization tends to vary among different species. The shortest levan is 6-kestose, a chain of two fructose molecules and a terminal glucose molecule. | 1 | Biochemistry |
Many metal complexes catalyze the dehydrogenation of amine-borane (AB). Catalysis in the absence of metals has also been observed. | 0 | Organic Chemistry |
In general, radical cyclization to produce small rings is difficult. However, it is possible to trap the cyclized radical before re-opening. This process can be facilitated by fragmentation (see the three-membered case below) or by stabilization of the cyclized radical (see the four-membered case). Five- and six-membered rings are the most common sizes produced by radical cyclization.
Polycycles and macrocycles can also be formed using radical cyclization reactions. In the former case, rings can be pre-formed and a single ring closed with radical cyclization, or multiple rings can be formed in a tandem process (as below). Macrocyclizations, which lack the FMO requirement of cyclizations of smaller substrates, have the unique property of exhibiting endo selectivity. | 0 | Organic Chemistry |
KaiC is a gene belonging to the KaiABC gene cluster (with KaiA, and KaiB) that, together, regulate bacterial circadian rhythms, specifically in cyanobacteria. KaiC encodes for the KaiC protein, which interacts with the KaiA and KaiB proteins in a post-translational oscillator (PTO). The PTO is cyanobacteria master clock that is controlled by sequences of phosphorylation of KaiC protein. Regulation of KaiABC expression and KaiABC phosphorylation is essential for cyanobacteria circadian rhythmicity, and is particularly important for regulating cyanobacteria processes such as nitrogen fixation, photosynthesis, and cell division. Studies have shown similarities to Drosophila, Neurospora, and mammalian clock models in that the kaiABC regulation of the cyanobacteria slave circadian clock is also based on a transcription translation feedback loop (TTFL). KaiC protein has both auto-kinase and auto-phosphatase activity and functions as the circadian regulator in both the PTO and the TTFL. KaiC has been found to not only suppress kaiBC when overexpressed, but also suppress circadian expression of all genes in the cyanobacterial genome. | 1 | Biochemistry |
A collection of matter may be entirely isolated from its surroundings. If it has been left undisturbed for an indefinitely long time, classical thermodynamics postulates that it is in a state in which no changes occur within it, and there are no flows within it. This is a thermodynamic state of internal equilibrium. (This postulate is sometimes, but not often, called the "minus first" law of thermodynamics. One textbook calls it the "zeroth law", remarking that the authors think this more befitting that title than its more customary definition, which apparently was suggested by Fowler.)
Such states are a principal concern in what is known as classical or equilibrium thermodynamics, for they are the only states of the system that are regarded as well defined in that subject. A system in contact equilibrium with another system can by a thermodynamic operation be isolated, and upon the event of isolation, no change occurs in it. A system in a relation of contact equilibrium with another system may thus also be regarded as being in its own state of internal thermodynamic equilibrium. | 7 | Physical Chemistry |
Plants produce a large number of secondary metabolites thanks to enzymes that, unlike those involved in primary metabolism, are less catalytically efficient but have a larger mechanistic elasticity (reaction types) and broader specificities. The liberal drift threshold (caused by the low selective pressure due to the small population size) allows the fitness gain endowed by one of the products to maintain the other activities even though they may be physiologically useless. | 1 | Biochemistry |
Cells observed under the electron microscope after a technique involving rapid freezing of the cells followed by substitution of water with a polymer (Fast-freeze Fixation/Freeze Substitution) contain a large number of electron dense bodies around the cell periphery. These structures correspond in size and location to the fluorescent bodies confirmed to be scintillons by their light emission, and they show colocalization of anti-luciferase and anti-LBP labeling meaning both bioluminescence proteins are found in the structures. Scintillons appear as cytoplasmic drops hanging in the vacuolar space, as they are almost completely surrounded by the vacuolar membrane. This structure led to the proposal that a voltage gated proton channel in the vacuolar membrane could allow an action potential to be propagated along the vacuolar membrane. This would in turn let protons enter into the cytoplasm around all the scintillons in the cells virtually simultaneously producing an intense but brief flash of light. Voltage gated proton channels were subsequently identified in a dinoflagellate confirming their predicted existence. | 1 | Biochemistry |
Metallic bonding refers to the specific bonding between positive metal ions and surrounding valence electron clouds. This intermolecular force is relatively strong, and gives rise to the repeated crystalline orientation of atoms, also referred to as its lattice system. There are several types of common lattice formations, and each has its own unique packing density and atomic closeness. The negatively charged electron clouds of the metal ions will sterically hinder the adhesion of negatively charged protein regions due to charge repulsion, thus limiting the available binding sites of a protein to a metal surface.
The lattice formation can lead to connection with exposed potential metal-ion-dependent adhesion sites (MIDAS) which are binding sites for collagen and other proteins. The surface of the metal has different properties than the bulk since the normal crystalline repeating subunits is terminated at the surface. This leaves the surface atoms without a neighboring atom on one side, which inherently alters the electron distribution. This phenomenon also explains why the surface atoms have a higher energy than the bulk, often simply referred to as surface energy. This state of higher energy is unfavorable, and the surface atoms will try to reduce it by binding to available reactive molecules. This is often accomplished by protein adsorption, where the surface atoms are reduced to a more advantageous energy state.
The internal environment of the body is often modeled to be an aqueous environment at 37 °C at pH 7.3 with plenty of dissolved oxygen, electrolytes, proteins, and cells. When exposed to oxygen for an extended period of time, many metals may become oxidized and increase their surface oxidation state by losing electrons. This new cationic state leaves the surface with a net positive charge, and a higher affinity for negatively charged protein side groups. Within the vast diversity of metals and metal alloys, many are susceptible to corrosion when implanted in the body. Elements that are more electronegative are corroded faster when exposed to an electrolyte-rich aqueous environment such as the human body. Both oxidation and corrosion will lower the free energy, thus affecting protein adsorption as seen in Eq. 1. | 1 | Biochemistry |
Arteriviruses are small, enveloped, animal viruses with an icosahedral core containing a positive-sense RNA genome. The family includes equine arteritis virus (EAV), porcine reproductive and respiratory syndrome virus (PRRSV), lactate dehydrogenase elevating virus (LDV) of mice and simian haemorrhagic fever virus (SHFV). | 1 | Biochemistry |
Because the ratio of hydrogen to oxygen atoms in all carbohydrates is always the same as that in water—that is, 2 to 1—all of the oxygen consumed by the cells is used to oxidize the carbon in the carbohydrate molecule to form carbon dioxide. Consequently, during the complete oxidation of a glucose molecule, six molecules of carbon dioxide and six molecules of water are produced and six molecules of oxygen are consumed.
The overall equation for this reaction is
(30–32 ATP molecules produced depending on type of mitochondrial shuttle, 5–5.33 ATP molecules per molecule of oxygen.)
Because the gas exchange in this reaction is equal, the respiratory quotient (R.Q.) for carbohydrate is unity or 1.0: | 1 | Biochemistry |
The earliest recorded use of the internal standard method dates back to Gouy's flame spectroscopy work in 1877, where he used an internal standard to determine if the excitation in his flame was consistent. His experimental procedure was later reintroduced in the 1940s, when recording flame photometers became readily available. The use of internal standards continued to grow, being applied to a wide range of analytical techniques including nuclear magnetic resonance (NMR) spectroscopy, chromatography, and inductively coupled plasma spectroscopy. | 3 | Analytical Chemistry |
The density of surface seawater ranges from about 1020 to 1029 kg/m, depending on the temperature and salinity. At a temperature of 25 °C, the salinity of 35 g/kg and 1 atm pressure, the density of seawater is 1023.6 kg/m. Deep in the ocean, under high pressure, seawater can reach a density of 1050 kg/m or higher. The density of seawater also changes with salinity. Brines generated by seawater desalination plants can have salinities up to 120 g/kg. The density of typical seawater brine of 120 g/kg salinity at 25 °C and atmospheric pressure is 1088 kg/m. | 9 | Geochemistry |
Different proteins are degraded at different rates. Abnormal proteins are quickly degraded, whereas the rate of degradation of normal proteins may vary widely depending on their functions. Enzymes at important metabolic control points may be degraded much faster than those enzymes whose activity is largely constant under all physiological conditions. One of the most rapidly degraded proteins is ornithine decarboxylase, which has a half-life of 11 minutes. In contrast, other proteins like actin and myosin have a half-life of a month or more, while, in essence, haemoglobin lasts for the entire life-time of an erythrocyte.
The N-end rule may partially determine the half-life of a protein, and proteins with segments rich in proline, glutamic acid, serine, and threonine (the so-called PEST proteins) have short half-life. Other factors suspected to affect degradation rate include the rate deamination of glutamine and asparagine and oxidation of cystein, histidine, and methionine, the absence of stabilizing ligands, the presence of attached carbohydrate or phosphate groups, the presence of free α-amino group, the negative charge of protein, and the flexibility and stability of the protein. Proteins with larger degrees of intrinsic disorder also tend to have short cellular half-life, with disordered segments having been proposed to facilitate efficient initiation of degradation by the proteasome.
The rate of proteolysis may also depend on the physiological state of the organism, such as its hormonal state as well as nutritional status. In time of starvation, the rate of protein degradation increases. | 1 | Biochemistry |
Historically, many places kept left, while many others kept right, often within the same country. There are many myths that attempt to explain why one or the other is preferred. About 90 percent of people are right-handed, and many explanations reference this. Horses are traditionally mounted from the left, and led from the left, with the reins in the right hand. So people walking horses might use RHT, to keep the animals separated. Also referenced is the need for pedestrians to keep their swords in the right hand and pass on the left as in LHT, for self-defence. It has been suggested that wagon-drivers whipped their horses with their right hand, and thus sat on the left-hand side of the wagon, as in RHT. Academic Chris McManus notes that writers have stated that in the year 1300, Pope Boniface VIII directed pilgrims to keep left; however, others suggest that he directed them to keep to the right, and there is no documented evidence to back either claim. | 4 | Stereochemistry |
Microthermometry is the process of reheating a melt inclusion to its original melt temperature and then rapidly quenching to form a homogenous glass phase free of daughter minerals or vapor bubbles that may have been originally contained within the melt inclusion. | 9 | Geochemistry |
In general, increased levels of fecal coliforms provide a warning of failure in water treatment, a break in the integrity of the distribution system, possible contamination with pathogens. When levels are high there may be an elevated risk of waterborne gastroenteritis. Tests for the bacteria are cheap, reliable and rapid (1-day incubation). | 3 | Analytical Chemistry |
dPCR enables the absolute and reproducible quantification of target nucleic acids at single-molecule resolution. Unlike analogue quantitative PCR (qPCR), however, absolute quantification with dPCR does not require a standard curve. dPCR also has a greater tolerance for inhibitor substances and PCR assays that amplify inefficiently as compared to qPCR.
dPCR can quantify, for example, the presence of specific sequences from contaminating genetically modified organisms in foodstuffs, viral load in the blood, PBMCs, serum samples, chorionic villi tissues, biomarkers of neurodegenerative disease in cerebral spinal fluid, and fecal contamination in drinking water. | 1 | Biochemistry |
Marquis reagent is used as a simple spot-test to presumptively identify alkaloids as well as other compounds. It is composed of a mixture of formaldehyde and concentrated sulfuric acid, which is dripped onto the substance being tested. The United States Department of Justice method for producing the reagent is the addition of 100 mL of concentrated (95–98%) sulfuric acid to 5 mL of 40% formaldehyde. Different compounds produce different color reactions. Methanol may be added to slow down the reaction process to allow better observation of the colour change. | 3 | Analytical Chemistry |
Cyanobacteria have fundamentally transformed the geochemistry of the planet. Multiple lines of geochemical evidence support the occurrence of intervals of profound global environmental change at the beginning and end of the Proterozoic (2,500–542 Mya).
While it is widely accepted that the presence of molecular oxygen in the early fossil record was the result of cyanobacteria activity, little is known about how cyanobacteria evolution (e.g., habitat preference) may have contributed to changes in biogeochemical cycles through Earth history. Geochemical evidence has indicated that there was a first step-increase in the oxygenation of the Earths surface, which is known as the Great Oxidation Event (GOE), in the early Paleoproterozoic (2,500–1,600 Mya). A second but much steeper increase in oxygen levels, known as the Neoproterozoic Oxygenation Event (NOE), occurred at around 800 to 500 Mya. Recent chromium isotope data point to low levels of atmospheric oxygen in the Earths surface during the mid-Proterozoic, which is consistent with the late evolution of marine planktonic cyanobacteria during the Cryogenian; both types of evidence help explain the late emergence and diversification of animals.
Understanding the evolution of planktonic cyanobacteria is important because their origin fundamentally transformed the nitrogen and carbon cycles towards the end of the Pre-Cambrian. It remains unclear, however, what evolutionary events led to the emergence of open-ocean planktonic forms within cyanobacteria and how these events relate to geochemical evidence during the Pre-Cambrian. So far, it seems that ocean geochemistry (e.g., euxinic conditions during the early- to mid-Proterozoic) and nutrient availability likely contributed to the apparent delay in diversification and widespread colonization of open ocean environments by planktonic cyanobacteria during the Neoproterozoic. | 5 | Photochemistry |
Prior to further mechanistic investigation, it is important to determine the kinetic dependence of the reaction of interest on the catalyst. The turnover frequency (TOF) of the catalyst can be expressed as the reaction rate normalized to the concentration of catalyst:
:TOF =
This TOF is determined by running any two or more same-excess experiments in which the absolute catalyst concentration is varied. Because the catalyst concentration is constant over the course of the reaction, the resulting plots are normalized by an unchanging value. If the resulting plots overlay perfectly, then the reaction is, in fact, first-order in catalyst. If the reaction fails to overlay, higher-order processes are at work and require a more detailed analysis than described here. It is also worth noting that the normalization-overlay manipulation described here is only one approach for interpretation of the raw data. Equally valid results may be obtained by fitting the observed kinetic behavior to simulated rate laws. | 7 | Physical Chemistry |
The transparent window, on to which the sample is deposited, is usually cooled using a compressed helium or similar refrigerant. Experiments must be performed under a high vacuum to prevent contaminants from unwanted gases freezing to the cold window. Lower temperatures are preferred, due to the improved rigidity and "glassiness" of the matrix material. Noble gases such as argon are used not just because of their unreactivity but also because of their broad optical transparency in the solid state. Mono-atomic gases have relatively simple face-centered cubic (fcc) crystal structure, which can make interpretations of the site occupancy and crystal-field splitting of the guest easier. In some cases a reactive material, for example, methane, hydrogen or ammonia, may be used as the host material so that the reaction of the host with the guest species may be studied.
Using the matrix isolation technique, short-lived, highly-reactive species such as radical ions and reaction intermediates may be observed and identified by spectroscopic means. For example, the solid noble gas krypton can be used to form an inert matrix within which a reactive F ion can sit in chemical isolation. The reactive species can either be generated outside (before deposition) the apparatus and then be condensed, inside the matrix (after deposition) by irradiating or heating a precursor, or by bringing together two reactants on the growing matrix surface. For the deposition of two species it can be crucial to control the contact time and temperature. In twin jet deposition the two species have a much shorter contact time (and lower temperature) than in merged jet. With concentric jet the contact time is adjustable. | 7 | Physical Chemistry |
David Israel Schuster is a chemist who is currently a professor emeritus at New York University. His research program focused on organic photochemistry and later on fullerenes. | 5 | Photochemistry |
In E for Ecstasy (a book examining the uses of the street drug ecstasy in the UK) the writer, activist and ecstasy advocate Nicholas Saunders highlighted test results showing that certain consignments of the drug also contained selegiline. Consignments of ecstasy known as "Strawberry" contained what Saunders described as a "potentially dangerous combination of ketamine, ephedrine and selegiline," as did a consignment of "Sitting Duck" Ecstasy tablets.
David Pearce wrote The Hedonistic Imperative six weeks after starting taking selegiline.
In Gregg Hurwitzs novel Out of the Dark, selegiline (Emsam') and tyramine-containing food were used to assassinate the president of the United States. | 4 | Stereochemistry |
Many commercial elastomers contain polysulfides as crosslinks. These crosslinks interconnect neighboring polymer chains, thereby conferring rigidity. The degree of rigidity is related to the number of crosslinks. Elastomers, therefore, have a characteristic ability to return to their original shape after being stretched or compressed. Because of this memory for their original cured shape, elastomers are commonly referred to as rubbers. The process of crosslinking the polymer chains in these polymers with sulfur is called vulcanization. The sulfur chains attach themselves to the allylic carbon atoms, which are adjacent to C=C linkages. Vulcanization is a step in the processing of several classes of rubbers, including polychloroprene (Neoprene), styrene-butadiene, and polyisoprene, which is chemically similar to natural rubber. Charles Goodyear's discovery of vulcanization, involving the heating of polyisoprene with sulfur, was revolutionary because it converted a sticky and almost useless material into an elastomer that could be fabricated into useful products. | 8 | Metallurgy |
The ion is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a formal charge of −1. This charge results from a combination formal charge in which each of the three oxygens carries a − charge, whereas the nitrogen carries a +1 charge, all these adding up to formal charge of the polyatomic nitrate ion. This arrangement is commonly used as an example of resonance. Like the isoelectronic carbonate ion, the nitrate ion can be represented by resonance structures: | 0 | Organic Chemistry |
Within molecular and cell biology, Qa-1b is a MHC class I molecule and is the functional homolog of HLA-E in humans. Qa-1b is characterised by its limited polymorphisms and small peptide repertoire. Qa-1b binds to peptides derived from signal peptides of MHC class Ia molecule and interact with the CD94/NKG2 receptors on natural killer cells. The Qa-1b-peptide complex signals natural killer cells not to engage in cell lysis. Despite its homology with HLA-E, it seems that Qa-1b evolved a similar function to HLA-E coincidentally. | 1 | Biochemistry |
N-formylmethionine - N-formylmethionine leucyl-phenylalanine - N-methyl-D-aspartate receptor - N-methylaspartate - N-terminus - NADH - NADPH - NaKATPase - native state - nef gene product - neoplasm protein - Nernst equation - nerve - nerve growth factor - nerve growth factor receptor - nerve tissue protein - nerve tissue protein S 100 - nervous system - neurobiology - neurofilament protein - neurokinin A - neurokinin K - neurokinin-1 receptor - neurokinin-2 receptor - neuron - neuronal cell adhesion molecule - neuropeptide - neuropeptide receptor - neuropeptide Y - neuropeptide Y receptor - neuroscience - neurotensin - neurotensin receptor - neurotransmitter - neurotransmitter receptor - neutral theory of molecular evolution - neutron - neutron activation analysis - NF-kappa B - nicotinic receptor - nitrogen - nitroglycerine - Nobel Prize in Chemistry - non-competitive inhibition - nuclear lamina - nuclear localization signal - nuclear magnetic resonance - NMR - nuclear protein - nucleic acid - nucleic acid regulatory sequence - nucleic acid repetitive sequence - nucleic acid sequence homology - nucleon - nucleophile - nucleoside - nucleosome - nucleotide - nutrition | 1 | Biochemistry |
The surfaces of cancer cells often exhibit aberrant glycosylation, which serves to mediate cell proliferation, metastasis, and tumor progression. However, because these glycans often differ from those present on healthy cells, they also serve as candidates to act as cancer biomarkers for use in diagnostics and in developing targeted therapies that discriminate between cancerous cells and normal host tissue. One such therapy involves the use of enzyme inhibitors that target those enzymes involved in the biosynthesis of cancer-associated glycans. Another treatment is cancer immunotherapy, which directs the immune system to attack tumor cells expressing the targeted altered glycoconjugates.
For example, modifying CD44 antigens using glycosyltransferase-programmed stereosubstitution (GPS), the HCELL expression on the surfaces of human mesenchymal stem cells and hematopoietic stem cells can be enforced, effectively homing those cells to the bone marrow of their host. Once mesenchymal stem cells transmigrate through the bone marrow endothelium, they differentiate into osteoblasts and begin contributing to bone formation. This technique has been proposed as a potential treatment for numerous bone diseases, including osteogenesis imperfecta.
Other therapeutic measures involving glycans include epitope recognition for both vaccine and antibody production. This has been an area of interest especially in the field of HIV vaccines, as the immense genetic diversity of strains and high degree of glycosylation leads to much difficulty in developing antibodies that bind to viral particles. The heavy glycosylation of these proteins can mask peptide epitopes, making designing antibodies targeted to certain proteins sections all the more difficult. Therefore, some have turned to translational glycobiology to develop antibodies using semi-synthetic and fully synthetic oligosaccharides as antigens. Many of these discoveries have focused on the GP120 surface glycoprotein, which is naturally heavily glycosylated with high mannose glycans. | 1 | Biochemistry |
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