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* Chemical synthesis
* Enzyme-mediated exchange
* Recombinant protein expression in isotopic labeled media. | 7 | Physical Chemistry |
In this pathway the enzyme xylose isomerase converts D-xylose directly into D-xylulose. D-xylulose is then phosphorylated to D-xylulose-5-phosphate as in the oxido-reductase pathway. At equilibrium, the isomerase reaction results in a mixture of 83% D-xylose and 17% D-xylulose because the conversion of xylose to xylulose is energetically unfavorable. | 1 | Biochemistry |
Fionn Patrick Edward Dunne is a Professor of Materials Science at Imperial College London and holds the Chair in Micromechanics and the Royal Academy of Engineering/Rolls-Royce Research Chair. Professor Dunne specialises in computational crystal plasticity and microstructure-sensitive nucleation and growth of short fatigue cracks in engineering materials, mainly Nickel, Titanium and Zirconium alloys. | 8 | Metallurgy |
When exposed to air, warmth and light (especially without antioxidants), the oil loses its taste and psychoactivity due to aging. Cannabinoid carboxylic acids (THCA, CBDA, and maybe others) have an antibiotic effect on gram-positive bacteria such as (penicillin-resistant) Staphylococcus aureus, but gram-negative bacteria such as Escherichia coli are unaffected. | 7 | Physical Chemistry |
Chloride ion channels vary from many other ion channels due to being controlled by the anionic chloride ions. Chloride ion channels are pore-forming membrane proteins that allow the passive transport of chloride ions across biological membranes. Chloride ion channels involve both voltage-gated and ligand-gated mechanisms to transport the ions across cellular membranes. Chloride ion channels have been found to play crucial roles in the development of human diseases, for example, mutations in the genes encoding chloride ion channels lead to a variety of deleterious diseases in muscle, kidney, bone, and brain, including cystic fibrosis, osteoporosis, and epilepsy, and similarly their activation is supposed to be responsible for the progression of glioma in the brain and the growth of malaria-parasite in the red blood cells. Currently, chloride ion channels are not completely understood, and more research is necessary. | 7 | Physical Chemistry |
Phosphorus chains (with organic substituents) have been prepared, although these tend to be quite fragile. Small rings or clusters are more common. | 0 | Organic Chemistry |
Cytomegalovirus (CMV) is part of the β-herpesvirus subfamily that includes roseoloviruses. CMV coevolved with an assortment of mammalian hosts, including human CMV (HCMV), murine CMV (MCMV) and rhesus CMV (RhCMV). CMVs are characterized by large DNA genomes and typically asymptomatic infection in healthy hosts.
The first investigation into cytomegalovirus (CMV) as a gene therapy vector was published in 2000. CMV's tropism for hematopoietic progenitor cells and its large genome (230 kbp) initially attracted researchers. CMV-based vaccine vectors have since been used to induce T Cell response. More recently, CMV containing telomerase and follistatin was intravenously and intranasally delivered in mouse studies with the intention of extending healthspan. | 1 | Biochemistry |
Various microorganisms are involved in a two-stage process of degradation of PCBs, which happens in aerobic and anaerobic environments. Degrading PCBs is similar to the degradation of biphenyl. However, the chlorines on PCBs prevent them from being utilized as a substrate of biphenyl degradation. Due to high chemical stability, PCBs cannot be used as energy sources. However, due to the chlorination, PCBs can be used as electron acceptors in anaerobic respiration to store energy, which is also the first stage of the degradation pathway, reductive dechlorination. Once the PCBs are dechlorinated to a certain degree, usually lower than five chlorines presenting in the structure and one aromatic ring has no chlorine, they can undergo the biphenyl degradation pathway (BP pathway) to be degraded to accessible carbon or CO in the aerobic environment. BP pathway is a pathway that utilizes series of enzymes (BphA, B, C, D, E, F, G) to convert biphenyl to TCA cycle intermediates (pyruvate and Acyl-CoA) and benzoate. However, there are few microorganisms that can dechlorinate substrate under natural conditions. Even with selective media, the accumulation of PCB dechlorinating microorganisms is still slow, which is one reason for the slow degradation rate. As a result, PCBs usually go through a co-metabolism pathway that involving different microorganism species.
Generally speaking, there are four steps in this process:
# In order for PCBs to enter the cell, they firstly need to be solubilized.
# PCBs are dechlorinated by anaerobic bacteria, then transport the metabolites to aerobic bacteria or fungi through a biofilm.
# The presence of PCBs metabolites triggers the expression of enzymes in BP pathway.
# PCBs are broken down to Acetyl-CoA and then can be utilized or carbon dioxide.
The Figure below shows the complete degradation pathway. | 1 | Biochemistry |
All current methods of covalent organic framework (COF) synthesis use DCvC. Boronic acid dehydration, as demonstrated by Yaghi et al. is the most common type of reaction used. COFs have been used in gas storage, catalysis, . Possible morphologies include infinite covalent 3D frameworks, 2D polymers, or discrete molecular cages. | 6 | Supramolecular Chemistry |
It has been suggested that biominerals could be important indicators of extraterrestrial life and thus could play an important role in the search for past or present life on the planet Mars. Furthermore, organic components (biosignatures) that are often associated with biominerals are believed to play crucial roles in both pre-biotic and biotic reactions.
On January 24, 2014, NASA reported that current studies by the Curiosity and Opportunity rovers on Mars will now be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic and/or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars is now a primary NASA objective. | 1 | Biochemistry |
Symbiotic and kleptoplastic organisms excluded:
*The glaucophytes and the red and green algae—clade Archaeplastida (uni- and multicellular)
*The cryptophytes—clade Cryptista (unicellular)
*The haptophytes—clade Haptista (unicellular)
*The dinoflagellates and chromerids in the superphylum Myzozoa, and Pseudoblepharisma in the phylum Ciliophora—clade Alveolata (unicellular)
*The ochrophytes—clade Stramenopila (uni- and multicellular)
*The chlorarachniophytes and three species of Paulinella in the phylum Cercozoa—clade Rhizaria (unicellular)
*The euglenids—clade Excavata (unicellular)
Except for the euglenids, which are found within the Excavata, all of these belong to the Diaphoretickes. Archaeplastida and the photosynthetic Paulinella got their plastids, which are surrounded by two membranes, through primary endosymbiosis in two separate events, by engulfing a cyanobacterium. The plastids in all the other groups have either a red or green algal origin, and are referred to as the "red lineages" and the "green lineages". The only known exception is the ciliate Pseudoblepharisma tenue, which in addition to its plastids that originated from green algae also has a purple sulfur bacterium as symbiont. In dinoflagellates and euglenids the plastids are surrounded by three membranes, and in the remaining lines by four. A nucleomorph, remnants of the original algal nucleus located between the inner and outer membranes of the plastid, is present in the cryptophytes (from a red alga) and chlorarachniophytes (from a green alga).
Some dinoflagellates that lost their photosynthetic ability later regained it again through new endosymbiotic events with different algae.
While able to perform photosynthesis, many of these eukaryotic groups are mixotrophs and practice heterotrophy to various degrees. | 5 | Photochemistry |
Stanford dedicated the BIL gate's design to the public domain, which may speed its adoption. According to Endy, other researchers were already using the gates to reprogram metabolism when the Stanford team published its research.
Computing by transcriptor is still very slow; it can take a few hours between receiving an input signal and generating an output. Endy doubted that biocomputers would ever be as fast as traditional computers, but added that is not the goal of his research. "Were building computers that will operate in a place where your cellphone isnt going to work", he said. Medical devices with built-in biological computers could monitor, or even alter, cell behavior from inside a patients body. ExtremeTech' writes:
UC Berkeley biochemical engineer Jay Keasling said the transcriptor "clearly demonstrates the power of synthetic biology and could revolutionize how we compute in the future". | 1 | Biochemistry |
A common assumption is that the Casimir force is of little practical use; the argument is made that the only way to actually gain energy from the two plates is to allow them to come together (getting them apart again would then require more energy), and therefore it is a one-use-only tiny force in nature. In 1984 Robert Forward published work showing how a "vacuum-fluctuation battery" could be constructed; the battery can be recharged by making the electrical forces slightly stronger than the Casimir force to reexpand the plates.
In 1999, Pinto, a former scientist at NASAs Jet Propulsion Laboratory at Caltech in Pasadena, published in Physical Review' his thought experiment (Gedankenexperiment) for a "Casimir engine". The paper showed that continuous positive net exchange of energy from the Casimir effect was possible, even stating in the abstract "In the event of no other alternative explanations, one should conclude that major technological advances in the area of endless, by-product free-energy production could be achieved."
Garret Moddel at University of Colorado has highlighted that he believes such devices hinge on the assumption that the Casimir force is a nonconservative force, he argues that there is sufficient evidence (e.g. analysis by Scandurra (2001)) to say that the Casimir effect is a conservative force and therefore even though such an engine can exploit the Casimir force for useful work it cannot produce more output energy than has been input into the system.
In 2008, DARPA solicited research proposals in the area of Casimir Effect Enhancement (CEE). The goal of the program is to develop new methods to control and manipulate attractive and repulsive forces at surfaces based on engineering of the Casimir force.
A 2008 patent by Haisch and Moddel details a device that is able to extract power from zero-point fluctuations using a gas that circulates through a Casimir cavity. A published test of this concept by Moddel was performed in 2012 and seemed to give excess energy that could not be attributed to another source. However it has not been conclusively shown to be from zero-point energy and the theory requires further investigation. | 7 | Physical Chemistry |
One major advantage of the Stöber process is that it can produce silica particles that are nearly monodisperse, and thus provides an ideal model for use in studying colloidal phenomena. It was a pioneering discovery when first published, allowing synthesis of spherical monodisperse silica particles of controlled sizes, and in 2015 remains the most widely used wet chemistry approach to silica nanoparticles.
The process provides a convenient approach to preparing silica nanoparticles for applications including intracellular drug delivery and biosensing. The mesoporous silica nanoparticles prepared by modified Stöber processes have applications in the field of catalysis and liquid chromatography. In addition to monodispersity, these materials have very large surface areas as well as uniform, tunable, and highly ordered pore structures, which makes mesoporous silica uniquely attractive for these applications. | 7 | Physical Chemistry |
Related to η-O-bonded complexes of aldehydes and ketones are metal acetylacetonates and related species, which can be viewed as a combination of ketone and enolate ligands. | 0 | Organic Chemistry |
The term “Brownian motor” was originally invented by Swiss theoretical physicist Peter Hänggi in 1995. The Brownian motor, like the phenomenon of Brownian motion that underpinned its underlying theory, was also named after 19th century Scottish botanist Robert Brown, who, while looking through a microscope at pollen of the plant Clarkia pulchella immersed in water, famously described the random motion of pollen particles in water in 1827. In 1905, almost eighty years later, theoretical physicist Albert Einstein published a paper where he modeled the motion of the pollen as being moved by individual water molecules, and this was verified experimentally by Jean Perrin in 1908, who was awarded the Nobel Prize in Physics in 1926 "for his work on the discontinuous structure of matter". These developments helped to create the fundamentals of the present theories of the nanoscale world.
Nanoscience has traditionally long remained at the intersection of the physical sciences of physics and chemistry, but more recent developments in research increasingly position it beyond the scope of either of these two traditional fields. | 7 | Physical Chemistry |
UNSCEAR recommends a reference value of 9 nSv (Bq·h/m).
For example, a person living (7000 h/year) in a concentration of 40 Bq/m receives an effective dose of 1 mSv/year.
Studies of miners exposed to radon and its decay products provide a direct basis for assessing their lung cancer risk. The BEIR VI report, entitled Health Effects of Exposure to Radon, reported an excess relative risk from exposure to radon that was equivalent to 1.8% per megabecquerel hours per cubic meter (MBq·h/m) (95% confidence interval: 0.3, 35) for miners with cumulative exposures below 30 MBq·h/m. Estimates of risk per unit exposure are 5.38×10 per WLM; 9.68×10/WLM for ever smokers; and 1.67×10 per WLM for never smokers.
According to the UNSCEAR modeling, based on these miner's studies, the excess relative risk from long-term residential exposure to radon at 100 Bq/m is considered to be about 0.16 (after correction for uncertainties in exposure assessment), with about a threefold factor of uncertainty higher or lower than that value.
In other words, the absence of ill effects (or even positive hormesis effects) at 100 Bq/m are compatible with the known data.
The ICPR 65 model follows the same approach, and estimates the relative lifelong risk probability of radon-induced cancer death to 1.23 × 10 per Bq/(m·year). This relative risk is a global indicator; the risk estimation is independent of sex, age, or smoking habit. Thus, if a smokers chances of dying of lung cancer are 10 times that of a nonsmokers, the relative risks for a given radon exposure will be the same according to that model, meaning that the absolute risk of a radon-generated cancer for a smoker is (implicitly) tenfold that of a nonsmoker.
The risk estimates correspond to a unit risk of approximately 3–6 × 10 per Bq/m, assuming a lifetime risk of lung cancer of 3%. This means that a person living in an average European dwelling with 50 Bq/m has a lifetime excess lung cancer risk of 1.5–3 × 10. Similarly, a person living in a dwelling with a high radon concentration of 1000 Bq/m has a lifetime excess lung cancer risk of 3–6%, implying a doubling of background lung cancer risk.
The BEIR VI model proposed by the National Academy of Sciences of the USA is more complex. It is a multiplicative model that estimates an excess risk per exposure unit. It takes into account age, elapsed time since exposure, and duration and length of exposure, and its parameters allow for taking smoking habits into account.
In the absence of other causes of death, the absolute risks of lung cancer by age 75 at usual radon concentrations of 0, 100, and 400 Bq/m would be about 0.4%, 0.5%, and 0.7%, respectively, for lifelong nonsmokers, and about 25 times greater (10%, 12%, and 16%) for cigarette smokers.
There is great uncertainty in applying risk estimates derived from studies in miners to the effects of residential radon, and direct estimates of the risks of residential radon are needed.
As with the miner data, the same confounding factor of other carcinogens such as dust applies. | 2 | Environmental Chemistry |
The EPOC effect can be observed in a wide range of catalytic reactions with several kinds of metal or metal oxide catalysts mostly coupled with solid electrolytes. Versatile catalytic reactions including hydrogenations, dehydrogenations, oxidations, reductions, isomerizations, and chemical decompositions have been known to be promoted electrochemically on various transition metal and oxide catalysts (e.g., Pt, Pd, Rh, Ag, Au, Ni, Cu, Fe, IrO, RuO) deposited on O (YSZ), Na or K, H, F, aqueous, CeO conductors, and molten salts. The main focus and purpose of numerous studies regarding the EPOC effect have been reported so far can be classified as follows: 1) the elucidation of examples for the EPOC effects on specific catalytic reactions with environmental or industrial interest (ex. NOx reduction and hydrocarbons oxidations), 2) the mechanistic investigation of the origin of the EPOC effects (mainly focusing on the system with oxygen-ion conducting electrolytes), 3) the large-scale application and commercialization of the chemical reactions promoted by the EPOC effects along with development of novel compact monolithic reactors and 4) the utilization and incorporation of the EPOC effect in high or low-temperature fuel cell systems. | 7 | Physical Chemistry |
A microprobe is an instrument that applies a stable and well-focused beam of charged particles (electrons or ions) to a sample. | 7 | Physical Chemistry |
The halides of low-valent early metals often are clusters with extensive M-M bonding. The situation contrasts with the higher halides of these metals and virtually all halides of the late transition metals, where metal-halide bonding is replete.
Transition metal halide clusters are prevalent for the heavier metals: Zr, Hf, Nb, Ta, Mo, W, and Re. For the earliest metals Zr and Hf, interstitial carbide ligands are also common. One example is ZrCCl. One structure type features six terminal halides and 12 edge-bridging halides. This motif is exemplified by tungsten(III) chloride, [TaCl], Another common structure has six terminal halides and 8 bridging halides, e.g. MoCl.
Many of the early metal clusters can only be prepared when they incorporate interstitial atoms.
In terms of history, Linus Pauling showed that "MoCl" consisted of Mo octahedra. F. Albert Cotton established that "ReCl" in fact features subunits of the cluster ReCl, which could be converted to a host of adducts without breaking the Re-Re bonds. Because this compound is diamagnetic and not paramagnetic the rhenium bonds are double bonds and not single bonds. In the solid state further bridging occurs between neighbours and when this compound is dissolved in hydrochloric acid a ReCl complex forms. An example of a tetranuclear complex is hexadecamethoxytetratungsten W(OCH) with tungsten single bonds. A related group of clusters with the general formula MMoX such as PbMoS. These sulfido clusters are called Chevrel phases. | 7 | Physical Chemistry |
*Lovelock, James. The Independent. [https://web.archive.org/web/20060408121826/http://comment.independent.co.uk/commentators/article338830.ece The Earth is about to catch a morbid fever], 16 January 2006.
*Lovelock, James (2006), interviewed in How to think about science, CBC Ideas (radio program), broadcast January 3, 2008. [http://www.cbc.ca/ideas/episodes/2009/01/02/how-to-think-about-science-part-1---24-listen/ Link] | 9 | Geochemistry |
Radical polymerization of vinyl monomers, like methyl (metha)acrylate of vinyl acetate is a common (industrial) method to prepare polymeric materials. One of the problems associated with this method is, however, that the radical polymerisation reaction rate is so high that even at short reaction times the polymeric chains are exceedingly long. This has several practical disadvantages, especially for polymer processing (e.g. melt-processing). A solution to this problem is catalytic chain transfer, which is a way to make shorter polymer chains in radical polymerisation processes. The method involves adding a catalytic chain transfer agent to the reaction mixture of the monomer and the radical initiator. | 7 | Physical Chemistry |
Atta-ur-Rahman (Urdu: عطاالرحمان; b. 22 September 1942), h-index 75, with 36,000 citations is a Pakistani organic chemist and is currently serving as Professor Emeritus at the International Center for Chemical and Biological Sciences at the University of Karachi and as Chairman of PM Task Force on Science and Technology. He has twice served as the President of Pakistan Academy of Sciences (2003-2006, and 2011–2014). He was the Federal Minister of Science and Technology (2000-2002), Federal Minister of Education (2002) and Chairman Higher Education Commission with status of Federal Minister (2002-2008) He is also the President of the Network of Academies of Sciences in Countries of the Organisation of Islamic Countries (NASIC). After returning to Pakistan from Cambridge after completing his tenure as Fellow of Kings College, Cambridge University, he contributed to the development of the International Center for Chemical and Biological Sciences at the University of Karachi, and transforming the landscape of higher education, science and technology of Pakistan. He is Fellow of Royal Society (London), Life Fellow of Kings College, Cambridge University, UK.,, Academician Chinese Academy of Sciences and Professor Emeritus at University of Karachi | 0 | Organic Chemistry |
George Hammond published a hypothesis in physical organic chemistry which describes the geometric structure of the transition state in an organic chemical reaction in his publication, Hammond's principle.
His 1955 publication asserted:
Therefore, the geometric structure of a state can be predicted by comparing its energy to the species neighboring it along the reaction coordinate. For example, in an exothermic reaction the transition state is closer in energy to the reactants than to the products. Therefore, the transition state will be more geometrically similar to the reactants than to the products. In contrast, however, in an endothermic reaction the transition state is closer in energy to the products than to the reactants. So, according to Hammond's postulate the structure of the transition state would resemble the products more than the reactants. This type of comparison is especially useful because most transition states cannot be characterized experimentally.
Hammonds postulate also helps to explain and rationalize the Bell–Evans–Polanyi principle. Namely, this principle describes the experimental observation that the rate of a reaction, and therefore its activation energy, is affected by the enthalpy change of that reaction. Hammonds postulate explains this observation by describing how varying the enthalpy of a reaction would also change the structure of the transition state. In turn, this change in geometric structure would alter the energy of the transition state, and therefore the activation energy and reaction rate as well.
The postulate has also been used to predict the shape of reaction coordinate diagrams. For example, electrophilic aromatic substitutions involves a distinct intermediate and two less well defined states. By measuring the effects of aromatic substituents and applying Hammond's postulate it was concluded that the rate-determining step involves formation of a transition state that should resemble the intermediate complex.
During the 1940s and 1950s, chemists had trouble explaining why even slight changes in the reactants caused significant differences in the rate and product distributions of a reaction. In 1955 George S. Hammond, a young professor at Iowa State University, postulated that transition-state theory could be used to qualitatively explain the observed structure-reactivity relationships. Notably, John E. Leffler of Florida State University proposed a similar idea in 1953. However, Hammonds version has received more attention since its qualitative nature was easier to understand and employ than Lefflers complex mathematical equations. Hammond's postulate is sometimes called the Hammond-Leffler postulate to give credit to both scientists. | 7 | Physical Chemistry |
In metazoans, in order to respond to environmental stress, differentiate properly, and progress normally through the cell cycle, a eukaryotic cell needs a specific and coordinated gene expression program, which involves the highly regulated transcription of thousands of genes. This gene regulation is in large part controlled, in a tissue-specific manner, by the binding of transcription factors to noncoding genomic regions referred to as cis-regulatory modules (CRMs), activating or repressing gene expression by modulating the structure of the chromatin and therefore having a positive or negative effect on transcription regulation. CRMs activating gene expression are often referred to as transcriptional enhancers, whereas those repressing gene expression are referred to as transcriptional silencers. | 1 | Biochemistry |
Hydroacylation is a type of organic reaction in which an electron-rich unsaturated hydrocarbon inserts into a formyl C-H bond. With alkenes, the product is a ketone:
:RCHO + CH=CHR → RC(O)CHCHR
With an alkyne instead, the reaction produces an α,β-unsaturated ketone.
The reaction requires a metal catalyst or a radical initiator. It is almost invariably practiced as an intramolecular reaction using homogeneous catalysts, often based on rhodium phosphines. | 0 | Organic Chemistry |
Mixtures can be either homogeneous or heterogeneous: a mixture of uniform composition and in which all components are in the same phase, such as salt in water, is called homogeneous, whereas a mixture of non-uniform composition and of which the components can be easily identified, such as sand in water, it is called heterogeneous.
In addition, "uniform mixture" is another term for homogeneous mixture and "non-uniform mixture" is another term for heterogeneous mixture. These terms are derived from the idea that a homogeneous mixture has a uniform appearance, or only one visible phase, because the particles are evenly distributed. However, a heterogeneous mixture has non-uniform composition, and its constituent substances are easily distinguishable from one another (often, but not always, in different phases).
Several solid substances, such as salt and sugar, dissolve in water to form a special type of homogeneous mixture called a solution, in which there is both a solute (dissolved substance) and solvent (dissolving medium) present. Air is an example of a solution as well: a homogeneous mixture of gaseous nitrogen solvent, in which oxygen and smaller amounts of other gaseous solutes are dissolved. Mixtures are not limited in either their number of substances or the amounts of those substances, though in a homogeneous mixture the solute-to-solvent proportion can only reach a certain point before the mixture separates and becomes heterogeneous.
A homogeneous mixture is characterized by uniform dispersion of its constituent substances throughout; the substances exist in equal proportion everywhere within the mixture. Differently put, a homogeneous mixture will be the same no matter from where in the mixture it is sampled. For example, if a solid-liquid solution is divided into two halves of equal volume, the halves will contain equal amounts of both the liquid medium and dissolved solid (solvent and solute).
In physical chemistry and materials science, "homogeneous" more narrowly describes substances and mixtures which are in a single phase. | 7 | Physical Chemistry |
Along with ubiquitination and phosphorylation, methylation is a major biochemical process for modifying protein function. The most prevalent protein methylations affect arginine and lysine residue of specific histones. Otherwise histidine, glutamate, asparagine, cysteine are susceptible to methylation. Some of these products include S-methylcysteine, two isomers of N-methylhistidine, and two isomers of N-methylarginine. | 0 | Organic Chemistry |
It is category A in Australia meaning that no evidence of harm has been found after being taken by many pregnant women. Use during breast feeding is generally safe. | 4 | Stereochemistry |
Asymmetric stereoinduction can be achieved with the use of chiral auxiliaries. Chiral auxiliaries may be reversibly attached to the substrate, inducing a diastereoselective reaction prior to cleavage, overall producing an enantioselective process. Examples of chiral auxiliaries include, Evans’ chiral oxazolidinone auxiliaries (for asymmetric aldol reactions) pseudoephedrine amides and tert-butanesulfinamide imines. | 4 | Stereochemistry |
Klein-Seetharaman was born in Germany. She completed her undergraduate training at the University of Cologne, where she earned dual honours in biology and chemistry. After earning her doctorate, she moved to the United States, where she worked in the laboratory of Har Gobind Khorana at the Massachusetts Institute of Technology. Her research considered conformational changes in rhodopsin, the G protein coupled receptor. She was a postdoctoral researcher at MIT with Harald Schwalbe, focusing on nuclear magnetic resonance spectroscopy. After eight months as a postdoc, Klein-Seetharaman moved Carnegie Mellon University where she worked with Raj Reddy in biology. She was eventually appointed to the faculty at Carnegie Mellon. | 1 | Biochemistry |
Studies on insect cell lines and in vivo experiments on D. melanogaster have revealed active expression of Hexo1 and Hexo2, and, most importantly, the fused lobe (fdl) gene encoding fused ß-lobe (FDL), also known as GNase, an orthologue of A. thaliana and human Hex. FDL is expressed in high abundance in vesicles and the plasma membrane and has, unlike Hexo1 and Hexo2, been linked to fruit fly paucimannosidic protein production. However, except for the well-studied D. melanogaster and other common insect model organisms, solid evidence for active involvement of Hex and/or the possible concerted usage of the GnT-I-independent pathway or alternative truncation pathways for paucimannosidic protein production remains unavailable across the diverse class of insects. | 1 | Biochemistry |
Recycling chromatography is mode practiced in both HPLC and CCC. In recycling chromatography, the target compounds are reintroduced into the column after they elute. Each pass through the column increases the number of theoretical plates the compounds experience and enhances chromatographic resolution. Direct recycling must be done with an isocratic solvent system. With this mode, the eluant can be selectively re-chromatographed on the same or a different column in order to facilitate the separation. This process of selective recycling has been termed a "heart-cut" and is especially effective in purifying selected target compounds with some sacrificial loss of recovery. The process of re-separating selected fractions from one chromatography experiment with another chromatographic method has long been practiced by scientists. Recycling and sequential chromatography is a streamlined version of this process. In CCC, the separation characteristics of the column may be modified simply by changing the composition of the biphasic solvent system. | 3 | Analytical Chemistry |
The one-step Stöber process may be modified to manufacture porous silica by adding a surfactant template to the reaction mixture and calcining the resulting particles. Surfactants that have been used include cetrimonium bromide, cetyltrimethylammonium chloride, and glycerol. The surfactant forms micelles, small near-spherical balls with a hydrophobic interior and a hydrophilic surface, around which the silica network grows, producing particles with surfactant- and solvent-filled channels. Calcining the solid leads to removal of the surfactant and solvent molecules by combustion and/or evaporation, leaving mesopore voids throughout the structure, as seen in the illustration at right.
Varying the surfactant concentration allows control over the diameter and volume of pores, and thus of the surface area of the product material. Increasing the amount of surfactant leads to increases in total pore volume and hence particle surface area, but with individual pore diameters remaining unchanged. Altering the pore diameter can be achieved by varying the amount of ammonia used relative to surfactant concentration; additional ammonia leads to pores with greater diameters, but with a corresponding decrease in total pore volume and particle surface area. The time allowed for the reaction to proceed also influences porosity, with greater reaction times leading to increases in total pore volume and particle surface area. Longer reaction times also lead to increases in overall silica particle size and related decreases in the uniformity of the size distribution. | 7 | Physical Chemistry |
In February, the first ever gene therapy for Tay–Sachs disease was announced, it uses an adeno-associated virus to deliver the correct instruction for the HEXA gene on brain cells which causes the disease. Only two children were part of a compassionate trial presenting improvements over the natural course of the disease and no vector-related adverse events.
In May, eladocagene exuparvovec is recommended for approval by the European Commission.
In July results of a gene therapy candidate for haemophilia B called FLT180 were announced, it works using an adeno-associated virus (AAV) to restore the clotting factor IX (FIX) protein, normal levels of the protein were observed with low doses of the therapy but immunosuppression was necessitated to decrease the risk of vector-related immune responses.
In December, a 13-year girl that had been diagnosed with T-cell acute lymphoblastic leukaemia was successfully treated at Great Ormond Street Hospital (GOSH) in the first documented use of therapeutic gene editing for this purpose, after undergoing six months of an experimental treatment, where all attempts of other treatments failed. The procedure included reprogramming a healthy T-cell to destroy the cancerous T-cells to first rid her of leukaemia, and then rebuilding her immune system using healthy immune cells. The GOSH team used BASE editing and had previously treated a case of acute lymphoblastic leukaemia in 2015 using TALENs. | 1 | Biochemistry |
If required, farmers' responses to waterlogging and soil salinity can be automatically accounted for. The method can gradually decrease:
# The amount of irrigation water applied when the water table becomes shallower depending on the kind of crop (paddy rice and non-rice)
# The fraction of irrigated land when the available irrigation water is scarce;
# The fraction of irrigated land when the soil salinity increases; for this purpose, the salinity is given a stochastic interpretation;
# The groundwater abstraction by pumping from wells when the water table drops.
The farmers' responses influence the water and salt balances, which, in turn, slows down the process of water logging and salinization. Ultimately a new equilibrium situation will arise.
The user can also introduce farmers responses by manually changing the relevant input data. Perhaps it will be useful first to study the automatic farmers responses and their effect first and thereafter decide what the farmers' responses will be in the view of the user. | 9 | Geochemistry |
URhGes critical temperature (T') is normally about 280 millikelvins.
The Grenoble team in France, headed by Andrew D. Huxley, first cooled down the sample below its critical temperature and raised the magnetic field to 2 T. As expected, the sample's superconducting properties vanished. However, when the team raised the magnetic field to 8 T, the superconducting behavior continued. The critical temperature at that field strength increased to about 400 millikelvins. The sample retained the superconducting state until 13 T. They also found that at 12 T, the URhGe sample experienced a magnetic phase transition. | 8 | Metallurgy |
* Sinyan Shen, Surface Second Sound in Superfluid Helium. PhD Dissertation (1973). http://adsabs.harvard.edu/abs/1973PhDT.......142S
* V. Peshkov, "Second Sound in Helium II," J. Phys. (Moscow) 8, 381 (1944)
* U. Piram, [http://www.inf.ethz.ch/personal/fcellier/MS/piram_ms.pdf "Numerical investigation of second sound in liquid helium,"] Dipl.-Ing. Dissertation (1991). Retrieved on April 15, 2007. | 7 | Physical Chemistry |
The article concerns the total synthesis of galanthamine, a drug used for the treatment of mild to moderate Alzheimer's disease.
The natural source of galantamine are certain species of daffodil and because these species are scarce and because the isolation of galanthamine from daffodil is expensive (a 1996 figure specifies 50,000 US dollar per kilogram, the yield from daffodil is 0.1–0.2% dry weight) alternative synthetic sources are under development by means of total synthesis. | 0 | Organic Chemistry |
In one version of the laser spray interface, explosive vaporization and mist formation occur when an aqueous solution effusing from the tip of the stainless steel capillary is irradiated from the opposite side of the capillary by a 10.6 μm infrared laser. Weak ion signals could be detected when the plume was sampled through the ion sampling orifice. When a high voltage (3–4 kV) was applied to the stainless-steel capillary, strong ion signals appeared. The ion abundances were found to be orders of magnitude greater than those obtained by conventional electrospray ionization in the case of aqueous solutions. This approach to laser spray ionization is a hybrid of three basic techniques for the generation of gaseous ions from the condensed phase, i.e., energy-sudden activation, nebulization and the action of an electric field.
Laser spray mass spectrometry can faithfully reflect the solution-phase characteristics of biomolecules. It has been successfully applied to evaluate the binding affinities of protein-DNA.
Laser spray has better ionization efficiency than conventional electrospray ionization (ESI). In particular, the sensitivity became more than one order of magnitude higher in negative ion modes. It was also found that this technique has a potential benefit for the low concentration samples due to condensation effect of the formed droplet by the irradiation of laser. Higher the solvation energies of triply charged metal ions, stronger are the signals for ions. | 3 | Analytical Chemistry |
Normally, angiotensin I is converted to angiotensin II by an angiotensin-converting enzyme (ACE). Angiotensin II constricts blood vessels, increasing blood pressure. Enalaprilat, the active metabolite of enalapril, inhibits ACE. Inhibition of ACE decreases levels of angiotensin II, leading to less vasoconstriction and decreased blood pressure. | 4 | Stereochemistry |
Cyclamin is an organic compound that has been used by the pharmaceutical industry as an ingredient for nasal sprays. | 0 | Organic Chemistry |
Although they are derivatives of phosphonous acid (RP(OH)), they are not prepared from such precursors. Phosphonites are prepared by alcoholysis of organophosphinous chlorides. For example, treatment of dichlorophenylphosphine with methanol and base gives dimethyl phenylphosphonite:
:ClPPh + 2 CHOH → (CHO)PPh + 2 HCl | 0 | Organic Chemistry |
Fragmented genomic DNA or complementary DNA (cDNA) of interest is cloned into plasmid vectors. The cloning sites are flanked with adaptor sequences that contain restriction sites for endonucleases (discussed below). Inserts are ligated to the plasmid vectors and individual vectors are then transformed into E. coli making the PET library. PET sequences are obtained by purifying plasmid and digesting with specific endonuclease leaving two short sequences on the ends of the vectors. Under intramolecular (dilute) conditions, vectors are re-circularized and ligated, leaving only the ditags in the vector. The sequences unique to the clone are now paired together. Depending on the next-generation sequencing technique, PET sequences can be left singular, dimerized, or concatenated into long chains. | 1 | Biochemistry |
The first electron crystallographic protein structure to achieve atomic resolution was bacteriorhodopsin, determined by Richard Henderson and coworkers at the Medical Research Council Laboratory of Molecular Biology in 1990. However, already in 1975 Unwin and Henderson had determined the first membrane protein structure at intermediate resolution (7 Ångström), showing for the first time the internal structure of a membrane protein, with its alpha-helices standing perpendicular to the plane of the membrane. Since then, several other high-resolution structures have been determined by electron crystallography, including the light-harvesting complex, the nicotinic acetylcholine receptor, and the bacterial flagellum. The highest resolution protein structure solved by electron crystallography of 2D crystals is that of the water channel aquaporin-0. In 2012, Jan Pieter Abrahams and coworkers extended electron crystallography to 3D protein nanocrystals by rotation electron diffraction (RED). | 3 | Analytical Chemistry |
Azide has become a popular target for chemoselective protein modification, because they are small in size and have a favorable thermodynamic reaction potential. One such azide reactions is the [3+2] cycloaddition reaction with alkyne, but the reaction requires high temperature and often gives mixtures of regioisomers.
An improved reaction developed by chemist Karl Barry Sharpless involves the copper (I) catalyst, which couples azide with terminal alkyne that only give 1,4 substituted 1,2,3 triazoles in high yields (shown below in Figure 11). The mechanistic study suggests a stepwise reaction. The Cu (I) first couples with acetylenes, and then it reacts with azide to generate a six-membered intermediate. The process is very robust that it occurs at pH ranging from 4 to 12, and copper (II) sulfate is often used as a catalyst in the presence of a reducing agent. | 1 | Biochemistry |
1,10-Phenanthroline is an inhibitor of metallopeptidases, with one of the first observed instances reported in carboxypeptidase A. Inhibition of the enzyme occurs by removal and chelation of the metal ion required for catalytic activity, leaving an inactive apoenzyme. 1,10-Phenanthroline targets mainly zinc metallopeptidases, with a much lower affinity for calcium. | 3 | Analytical Chemistry |
It is important to note that the list given above is qualitative and describes trends. The ability of a group to leave is contextual. For example, in SAr reactions, the rate is generally increased when the leaving group is fluoride relative to the other halogens. This effect is due to the fact that the highest energy transition state for this two step addition-elimination process occurs in the first step, where fluoride's greater electron withdrawing capability relative to the other halides stabilizes the developing negative charge on the aromatic ring. The departure of the leaving group takes place quickly from this high energy Meisenheimer complex, and since the departure is not involved in the rate limiting step, it does not affect the overall rate of the reaction. This effect is general to conjugate base eliminations.
Even when the departure of the leaving group is involved in the rate limiting step of a reaction there can still exist contextual differences that can change the order of leaving group ability. In Friedel-Crafts alkylations, the normal halogen leaving group order is reversed so that the rate of the reaction follows RF > RCl > RBr > RI. This effect is due to their greater ability to complex the Lewis acid catalyst, and the actual group that leaves is an "ate" complex between the Lewis acid and the departing leaving group. This situation is broadly defined as leaving group activation.
There can still exist contextual differences in leaving group ability in the purest form, that is when the actual group that leaves is not affected by the reaction conditions (by protonation or Lewis acid complexation) and the departure of the leaving group occurs in the rate determining step. In the situation where other variables are held constant (nature of the alkyl electrophile, solvent, etc.), a change in nucleophile can lead to a change in the order of reactivity for leaving groups. In the case below, tosylate is the best leaving group when ethoxide is the nucleophile, but iodide and even bromide become better leaving groups in the case of the thiolate nucleophile. | 0 | Organic Chemistry |
For the first time pyruvate kinase M2 enzyme was reported with two missense mutations, H391Y and K422R, found in cells from Bloom syndrome patients, prone to develop cancer. Results show that despite the presence of mutations in the inter-subunit contact domain, the K422R and H391Y mutant proteins maintained their homotetrameric structure, similar to the wild-type protein, but showed a loss of activity of 75 and 20%, respectively. H391Y showed a 6-fold increase in affinity for its substrate phosphoenolpyruvate and behaved like a non-allosteric protein with compromised cooperative binding. However, the affinity for phosphoenolpyruvate was lost significantly in K422R. Unlike K422R, H391Y showed enhanced thermal stability, stability over a range of pH values, a lesser effect of the allosteric inhibitor Phe, and resistance toward structural alteration upon binding of the activator (fructose 1,6-bisphosphate) and inhibitor (Phe). Both mutants showed a slight shift in the pH optimum from 7.4 to 7.0. The co-expression of homotetrameric wild type and mutant PKM2 in the cellular milieu resulting in the interaction between the two at the monomer level was substantiated further by in vitro experiments. The cross-monomer interaction significantly altered the oligomeric state of PKM2 by favoring dimerisation and heterotetramerization. In silico study provided an added support in showing that hetero-oligomerization was energetically favorable. The hetero-oligomeric populations of PKM2 showed altered activity and affinity, and their expression resulted in an increased growth rate of Escherichia coli as well as mammalian cells, along with an increased rate of polyploidy. These features are known to be essential to tumor progression. | 1 | Biochemistry |
The use of progesterone tests in dog breeding to pinpoint ovulation is becoming more widely used. There are several tests available but the most reliable test is a blood test with blood drawn by a veterinarian and sent to a lab for processing. Results can usually be obtained with 24 to 72 hours. The rationale for using progesterone tests is that increased numbers begin in close proximity to preovulatory surge in gonadotrophins and continue through ovulation and estrus. When progesterone levels reach certain levels they can signal the stage of estrus the female is. Prediction of birth date of the pending litter can be very accurate if ovulation date is known. Puppies deliver with a day or two of 9 weeks gestation in most cases. It is not possible to determine pregnancy using progesterone tests once a breeding has taken place, however. This is due to the fact that, in dogs, progesterone levels remain elevated throughout the estrus period. | 0 | Organic Chemistry |
Photoelectrochemical reduction of carbon dioxide, also known as photoelectrolysis of carbon dioxide, is a chemical process whereby carbon dioxide is reduced to carbon monoxide or hydrocarbons by the energy of incident light. This process requires catalysts, most of which are semiconducting materials. The feasibility of this chemical reaction was first theorised by Giacomo Luigi Ciamician, an Italian photochemist. Already in 1912 he stated that "[b]y using suitable catalyzers, it should be possible to transform the mixture of water and carbon dioxide into oxygen and methane, or to cause other endo-energetic processes."
Furthermore, the reduced species may prove to be a valuable feedstock for other processes. If the incident light utilized is solar then this process also potentially represents energy routes which combine renewable energy with CO reduction. | 5 | Photochemistry |
Mechanistic target of rapamycin has been shown to interact with:
* ABL1,
* AKT1,
* IGF-IR,
* InsR,
* CLIP1,
* EIF3F
* EIF4EBP1,
* FKBP1A,
* GPHN,
* KIAA1303,
* PRKCD,
* RHEB,
* RICTOR,
* RPS6KB1,
* STAT1,
* STAT3,
* Two-pore channels: TPCN1; TPCN2, and
* UBQLN1. | 1 | Biochemistry |
Many synthetic ionophores are based on crown ethers, cryptands, and calixarenes. Pyrazole-pyridine and bis-pyrazole derivatives have also been synthesized. These synthetic species are often macrocyclic. Some synthetic agents are not macrocyclic, e.g. carbonyl cyanide-p-trifluoromethoxyphenylhydrazone. Even simple organic compounds, such as phenols, exhibit ionophoric properties. The majority of synthetic receptors used in the carrier-based anion-selective electrodes employ transition elements or metalloids as anion carriers, although simple organic urea- and thiourea-based receptors are known. | 7 | Physical Chemistry |
In solid rocket propellants and some translucent smokeless powders, the primary method of heat transfer into the propellant grain from the combustion process is by radiation, and opacifiers such as "lamp black" may be added to the propellant mixture to ensure the heat does not penetrate far below the surface of the grain, which could cause detonation. The opacifiers also prevent sub-surface overheating and localized premature ignition in the grains where imperfections absorbing the thermal radiation are present. Carbon black is commonly used for this purpose; other possible additives are nigrosin, Prussian blue, methylene blue, etc. in amounts ranging commonly between 0.1 and 0.5%. | 7 | Physical Chemistry |
Another species that exhibits alarm calls is the Barbary macaque. Barbary macaque mothers are able to recognize their own offspring's calls and behave accordingly. | 1 | Biochemistry |
Initiation of translation usually involves the interaction of certain key proteins, the initiation factors, with a special tag bound to the 5-end of an mRNA molecule, the 5 cap, as well as with the 5' UTR. These proteins bind the small (40S) ribosomal subunit and hold the mRNA in place.
eIF3 is associated with the 40S ribosomal subunit and plays a role in keeping the large (60S) ribosomal subunit from prematurely binding. eIF3 also interacts with the eIF4F complex, which consists of three other initiation factors: eIF4A, eIF4E, and eIF4G. eIF4G is a scaffolding protein that directly associates with both eIF3 and the other two components. eIF4E is the cap-binding protein. Binding of the cap by eIF4E is often considered the rate-limiting step of cap-dependent initiation, and the concentration of eIF4E is a regulatory nexus of translational control. Certain viruses cleave a portion of eIF4G that binds eIF4E, thus preventing cap-dependent translation to hijack the host machinery in favor of the viral (cap-independent) messages. eIF4A is an ATP-dependent RNA helicase that aids the ribosome by resolving certain secondary structures formed along the mRNA transcript. The poly(A)-binding protein (PABP) also associates with the eIF4F complex via eIF4G, and binds the poly-A tail of most eukaryotic mRNA molecules. This protein has been implicated in playing a role in circularization of the mRNA during translation.
This 43S preinitiation complex (43S PIC) accompanied by the protein factors moves along the mRNA chain toward its 3-end, in a process known as scanning', to reach the start codon (typically AUG). In eukaryotes and archaea, the amino acid encoded by the start codon is methionine. The Met-charged initiator tRNA (Met-tRNA) is brought to the P-site of the small ribosomal subunit by eukaryotic initiation factor 2 (eIF2). It hydrolyzes GTP, and signals for the dissociation of several factors from the small ribosomal subunit, eventually leading to the association of the large subunit (or the 60S subunit). The complete ribosome (80S) then commences translation elongation.
Regulation of protein synthesis is partly influenced by phosphorylation of eIF2 (via the α subunit), which is a part of the eIF2-GTP-Met-tRNA ternary complex (eIF2-TC). When large numbers of eIF2 are phosphorylated, protein synthesis is inhibited. This occurs under amino acid starvation or after viral infection. However, a small fraction of this initiation factor is naturally phosphorylated. Another regulator is 4EBP, which binds to the initiation factor eIF4E and inhibits its interactions with eIF4G, thus preventing cap-dependent initiation. To oppose the effects of 4EBP, growth factors phosphorylate 4EBP, reducing its affinity for eIF4E and permitting protein synthesis.
While protein synthesis is globally regulated by modulating the expression of key initiation factors as well as the number of ribosomes, individual mRNAs can have different translation rates due to the presence of regulatory sequence elements. This has been shown to be important in a variety of settings including yeast meiosis and ethylene response in plants. In addition, recent work in yeast and humans suggest that evolutionary divergence in cis-regulatory sequences can impact translation regulation. Additionally, RNA helicases such as DHX29 and Ded1/DDX3 may participate in the process of translation initiation, especially for mRNAs with structured 5'UTRs. | 1 | Biochemistry |
NRIP1 has been shown to interact with:
* AHR,
* CTBP1
* CTBP2,
* DAX1,
* HDAC5,
* NR1B1,
* NR2B1,
* NR3A1,
* NR3C1,
* NR5A1, and
* YWHAQ. | 1 | Biochemistry |
Urine excretion of pregnanetriol can be measured over a period of 24 hours. Elevated urine pregnanetriol levels suggest adrenogenital syndrome. In monitoring treatment with cortisol replacement, elevated urine pregnanetriol levels indicate insufficient dosage of cortisol. | 1 | Biochemistry |
Avacopan was approved for medical use in the United States to treat anti-neutrophil cytoplasmic autoantibody-associated vasculitis in October 2021. | 1 | Biochemistry |
In humans, the protein is encoded by the RB1 gene located on chromosome 13—more specifically, 13q14.1-q14.2. If both alleles of this gene are mutated in a retinal cell, the protein is inactivated and the cells grow uncontrollably, resulting in development of retinoblastoma cancer, hence the "RB" in the name pRb. Thus most pRb knock-outs occur in retinal tissue when UV radiation-induced mutation inactivates all healthy copies of the gene, but pRb knock-out has also been documented in certain skin cancers in patients from New Zealand where the amount of UV radiation is significantly higher.
Two forms of retinoblastoma were noticed: a bilateral, familial form and a unilateral, sporadic form. Sufferers of the former were over six times more likely to develop other types of cancer later in life, compared to individuals with sporadic retinoblastoma. This highlighted the fact that mutated pRb could be inherited and lent support for the two-hit hypothesis. This states that only one working allele of a tumour suppressor gene is necessary for its function (the mutated gene is recessive), and so both need to be mutated before the cancer phenotype will appear. In the familial form, a mutated allele is inherited along with a normal allele. In this case, should a cell sustain only one mutation in the other RB gene, all pRb in that cell would be ineffective at inhibiting cell cycle progression, allowing cells to divide uncontrollably and eventually become cancerous. Furthermore, as one allele is already mutated in all other somatic cells, the future incidence of cancers in these individuals is observed with linear kinetics. The working allele need not undergo a mutation per se, as loss of heterozygosity (LOH) is frequently observed in such tumours.
However, in the sporadic form, both alleles would need to sustain a mutation before the cell can become cancerous. This explains why sufferers of sporadic retinoblastoma are not at increased risk of cancers later in life, as both alleles are functional in all their other cells. Future cancer incidence in sporadic pRb cases is observed with polynomial kinetics, not exactly quadratic as expected because the first mutation must arise through normal mechanisms, and then can be duplicated by LOH to result in a tumour progenitor.
RB1 orthologs have also been identified in most mammals for which complete genome data are available.
RB/E2F-family proteins repress transcription. | 1 | Biochemistry |
*Ag-O-Cs, also called S-1. This was the first compound photocathode material, developed in 1929. Sensitivity from 300 nm to 1200 nm. Since Ag-O-Cs has a higher dark current than more modern materials, photomultiplier tubes with this photocathode material are nowadays used only in the infrared region with cooling.
*Sb-Cs (antimony-caesium) has a spectral response from UV to visible and is mainly used in reflection-mode photocathodes.
*Bialkali (antimony-rubidium-caesium Sb-Rb-Cs, antimony-potassium-caesium Sb-K-Cs). Spectral response range similar to the Sb-Cs photocathode, but with higher sensitivity and lower dark current than Sb-Cs. They have sensitivity well matched to the most common scintillator materials and so are frequently used for ionizing radiation measurement in scintillation counters.
*High temperature bialkali or low noise bialkali (sodium-potassium-antimony, Na-K-Sb). This material is often used in oil well logging since it can withstand temperatures up to 175 °C. At room temperatures, this photocathode operates with very low dark current, making it ideal for use in photon counting applications.
*Multialkali (sodium-potassium-antimony-caesium, Na-K-Sb-Cs), also called S-20. The multialkali photocathode has a wide spectral response from the ultraviolet to near infrared region. It is widely used for broad-band spectrophotometers and photon counting applications. The long wavelength response can be extended to 930 nm by a special photocathode activation processing. With the broadened response, this is sometimes referred to as S-25.
*GaAs (gallium(II) arsenide). This photocathode material covers a wider spectral response range than multialkali, from ultraviolet to 930 nm. GaAs photocathodes are also used in accelerator facilities where polarized electrons are required. One of the important property of GaAs photocathode is, it can achieve Negative Electron Affinity due to Cs deposition on the surface. However GaAs is very delicate and loses Quantum Efficiency(QE) due to couple of damage mechanism. Ion Back Bombardment is one of the main cause of GaAs cathode QE decay.
*InGaAs (indium gallium arsenide). Extended sensitivity in the infrared range compared to GaAs. Moreover, in the range between 900 nm and 1000 nm, InGaAs has a much better signal-to-noise ratio than Ag-O-Cs. With special manufacturing techniques this photocathode can operate up to 1700 nm.
*Cs-Te, Cs-I (caesium-telluride, caesium iodide). These materials are sensitive to vacuum UV and UV rays but not to visible light and are therefore referred to as solar blind. Cs-Te is insensitive to wavelengths longer than 320 nm, and Cs-I to those longer than 200 nm. | 7 | Physical Chemistry |
A metamorphic reaction is a chemical reaction that takes place during the geological process of metamorphism wherein one assemblage of minerals is transformed into a second assemblage which is stable under the new temperature/pressure conditions resulting in the final stable state of the observed metamorphic rock.
Examples include the production of talc under varied metamorphic conditions:
:serpentine + carbon dioxide → talc + magnesite + water
:chlorite + quartz → kyanite + talc + water | 9 | Geochemistry |
For general application of the Rietveld method, irrespective of the software used, the observed Bragg peaks in a powder diffraction pattern are best described by the so-called peak shape function (PSF). The PSF is a convolution of three functions: the instrumental broadening , wavelength dispersion , and the specimen function , with the addition of a background function, . It is represented as follows:
where denotes convolution, which is defined for two functions and as an integral:
The instrumental function depends on the location and geometry of the source, monochromator, and sample. Wavelength function accounts for the distribution of the wavelengths in the source, and varies with the nature of the source and monochromatizing technique. The specimen function depends on several things. First is dynamic scattering, and secondly the physical properties of the sample such as crystallite size, and microstrain.
A short aside: unlike the other contributions, those from the specimen function can be interesting in materials characterization. As such, average crystallite size, , and microstrain, , effects on Bragg peak broadening, (in radians), can be described as follows, where is a constant:
: and .
Returning to the peak shape function, the goal is to correctly model the Bragg peaks which exist in the observed powder diffraction data. In the most general form, the intensity, , of the point (, where is the number of measured points) is the sum of the contributions from the overlapped Bragg peaks (), and the background, , and can be described as follows:
where is the intensity of the Bragg peak, and . Since is a multiplier, it is possible to analyze the behaviour of different normalized peak functions independently of peak intensity, under the condition that the integral over infinity of the PSF is unity. There are various functions that can be chosen to do this with varying degrees of complexity. The most basic functions used in this way to represent Bragg reflections are the Gauss, and Lorentzian functions. Most commonly though, is the pseudo-Voigt function, a weighted sum of the former two (the full Voigt profile is a convolution of the two, but is computationally more demanding). The pseudo-Voigt profile is the most common and is the basis for most other PSF's. The pseudo-Voigt function can be represented as:
where
and
are the Gaussian and Lorentzian contributions, respectively.
Thus,
where:
* and are the full widths at half maximum (FWHM)
* is essentially the Bragg angle of the point in the powder pattern with its origin in the position of the peak divided by the peak's FWHM.
* , and and are normalization factors such that and respectively.
* , known as the Caglioti formula, is the FWHM as a function of for Gauss, and pseudo-Voigt profiles. , , and are free parameters.
* is the FWHM vs. for the Lorentz function. and are free variables
* , where is the pseudo-Voigt mixing parameter, and are free variables.
The pseudo-Voigt function, like the Gaussian and Lorentz functions, is a centrosymmetric function, and as such does not model asymmetry. This can be problematic for non-ideal powder XRD data, such as those collected at synchrotron radiation sources, which generally exhibit asymmetry due to the use of multiple focusing optics.
The Finger–Cox–Jephcoat function is similar to the pseudo-Voigt, but has better handling of asymmetry, which is treated in terms of axial divergence. The function is a convolution of pseudo-Voigt with the intersection of the diffraction cone and a finite receiving slit length using two geometrical parameters, , and , where and are the sample and the detector slit dimensions in the direction parallel to the goniometer axis, and is the goniometer radius. | 3 | Analytical Chemistry |
Trimethylsilyldiazomethane is highly toxic. It has been implicated in the death of at least two chemists, a pharmaceutical worker in Windsor, Nova Scotia, Canada and one in New Jersey. Inhalation of diazomethane is known to cause pulmonary edema; trimethylsilyldiazomethane is suspected to behave similarly.
When used as a reagent in organic synthesis to convert carboxylic acids to their methyl esters, trimethylsilyldiazomethane undergoes acid-catalysed methanolysis, forming diazomethane in situ. A similar hydrolysis reaction may take place when trimethylsilyldiazomethane comes into contact with water on the surface of a human lung.
Trimethylsilyldiazomethane is nonexplosive. | 0 | Organic Chemistry |
Reaction intermediates are chemical species, often unstable and short-lived (however sometimes can be isolated), which are not reactants or products of the overall chemical reaction, but are temporary products and/or reactants in the mechanism's reaction steps. Reaction intermediates are often free radicals or ions.
The kinetics (relative rates of the reaction steps and the rate equation for the overall reaction) are explained in terms of the energy needed for the conversion of the reactants to the proposed transition states (molecular states that correspond to maxima on the reaction coordinates, and to saddle points on the potential energy surface for the reaction). | 7 | Physical Chemistry |
Petite mutants can be generated in the laboratory by using high-efficiency treatments such as acriflavine, ethidium bromide, and other intercalating agents. Their mechanisms work to break down and cause the eventual loss of mitochondrial DNA: if the treatment time increases, the amount of mitochondrial DNA will decrease. After prolonged treatment, petites containing no detectable mitochondrial DNA were obtained. It is useful approach to illustrate the function of mitochondrial DNA in yeast growth. | 1 | Biochemistry |
There are currently a number of on-going efforts to solve the structures for every protein in a given proteome. | 1 | Biochemistry |
Depending on the conditions in which the titration is performed, the manganese is reduced from an oxidation of +7 to +2, +4, or +6.
In most cases, permanganometry is performed in a very acidic solution in which the following electrochemical reaction occurs:
: + 8 H + 5 e → Mn + 4 HO; E° = +1.51 V
which shows that KMnO (in an acidic medium) is a very strong oxidizing agent, able to oxidize Fe (E°/Fe (E°/Sn (E°/Cl</sub> = +1.36 V).
In weak acidic medium can not accept 5 electrons to form Mn. Instead, it accepts only 3 electrons and forms solid MnO by the following reaction:
: + 4 H + 3 e → MnO + 2 HO; E° = +1.69 V
In a strongly basic solution, with the concentration c >1 mol dm, only one electron is accepted to produce manganate:
: + e → ; E° = +0.56 V | 3 | Analytical Chemistry |
The partial order with respect to a given reactant can be evaluated by the method of flooding (or of isolation) of Ostwald. In this method, the concentration of one reactant is measured with all other reactants in large excess so that their concentration remains essentially constant. For a reaction with rate law the partial order with respect to is determined using a large excess of . In this case
with
and may be determined by the integral method. The order with respect to under the same conditions (with in excess) is determined by a series of similar experiments with a range of initial concentration so that the variation of can be measured. | 7 | Physical Chemistry |
Several heterocycles related to porphyrins are found in nature, almost always bound to metal ions. These include | 1 | Biochemistry |
Due to recent innovations to the laser spray technique, a new method of laser ablation using the spray method has surfaced. Laserspray inlet ionization (LSII) involves a matrix/analyte sample at atmospheric pressure being ablated, and the ionization process will take place in an ion transfer capillary tube located in the mass spectrometer inlet. The LSII method is also known as laserspray ionization vacuum (LSIV). | 3 | Analytical Chemistry |
With radioligand therapy, there is always the risk of damage to non-cancerous surrounding tissues along with radioisotope toxicity which is always a challenge in determining how to administer and create the radioligand. Furthermore, the radioligand vial is only viable for a limited time and under specific conditions which challenges transport and storage along with feasible application to the patient.
Another limitation is the lack of centers that have trained personnel and equipment for radioligand therapy. Furthermore, individual characteristics affect the exact radiosensitivity to the therapy (thus affecting dosimetry) and are hard to predict without radiobiological models. | 1 | Biochemistry |
In this mechanism, proposed in 1938 by D. D. Eley and E. K. Rideal, only one of the molecules adsorbs and the other one reacts with it directly from the gas phase, without adsorbing ("nonthermal surface reaction"):
: A(g) + S(s) ⇌ AS(s)
: AS(s) + B(g) → Products
Constants are and and rate equation is . Applying steady state approximation to AS and proceeding as before (considering the reaction the limiting step once more) we get . The order is one with respect to B. There are two possibilities, depending on the concentration of reactant A:
:* At low concentrations of A, , and the order is one with respect to A.
:* At high concentrations of A, , and the order is zero with respect to A.
The following reactions follow an Eley–Rideal mechanism:
* CH + ½ O (adsorbed) → (CHCH)O The dissociative adsorption of oxygen is also possible, which leads to secondary products carbon dioxide and water.
* CO + H (ads.) → HO + CO
* 2 NH + 1½ O (ads.) → N + 3HO on a platinum catalyst
* CH + H (ads.) → CH on nickel or iron catalysts | 7 | Physical Chemistry |
A solution of the amide (0.365 g, 0.809 mmol), Pd(PPh) (0.187 g, 0.162 mmol), and triethylamine (1.12 mL, 8.08 mmol) in MeCN (8 mL) in a sealed tube was heated slowly to 120°. After stirring for 4 hours, the reaction mixture was cooled to room temperature, and the solvent was evaporated. The residue was chromatographed (loaded with CHCl) to give the title product 316 (0.270 g, 90%) as a colorless oil; R 0.42 (EtOAc/petroleum ether 10:1); [α] +14.9 (c, 1.0, CHCl); IR 3027, 2930, 1712, 1673, 1608, 1492, 1343, 1248 cm; H NMR (400 MHz) δ 7.33–7.21 (m, 6 H), 7.07 (dd, J = 7.3, 16.4 Hz, 1 H), 7.00 (t, J = 7.5 Hz, 1 H), 6.77 (d, J = 7.7 Hz, 1 H), 6.30 (dd, J = 8.7, 11.4 Hz, 1 H), 5.32 (d, J = 15.7 Hz, 1 H), 5.04 (s, 1 H), 4.95 (s, 1 H), 4.93 (d, J = 11.1 Hz, 1 H), 4.17 (s, 1 H), 3.98 (d, J = 15.7 Hz, 1 H), 3.62 (d, J = 8.7 Hz, 1 H), 3.17 (s, 3 H), 2.56 (dd, J = 3.5, 15.5 Hz, 1 H), 2.06 (dd, J = 2.8, 15.5 Hz, 1 H); C NMR (100 MHz) δ 177.4, 172.9, 147.8, 142.2, 136.5, 132.2, 131.6, 128.8, 128.4, 128.2, 127.7, 127.1, 123.7, 122.9, 107.9, 105.9, 61.0, 54.7, 49.9, 44.4, 38.2, 26.4; HRMS Calcd. for CHNO: 370.1681. Found: 370.1692. | 0 | Organic Chemistry |
The Falcon Ultra-Fine (UF) centrifugal concentrator is primarily used for the separation of heavy minerals which occur in ore concentrations above 0.1% by weight, such as cassiterite, tantalum and scheelite when the majority of the particles are smaller than 75 µm. The machine generates forces up to 600 times the force of gravity (600 G's) and uses a smooth-walled bowl for particle stratification with a pneumatically controlled rubber lip for heavy material collection. The machine is stopped periodically to rinse and collect the valuable concentrate from the bowl. Studies have found that the deposition of heavy material within the bowl can be predicted by a hindered settling model. The Falcon UF concentrator is used in a number of process plants around the world such as the Tanco mine in Canada and the Bluestone tin mine in Tasmania. | 8 | Metallurgy |
The MCHO group is planar. A C=O double bond is indicated by X-ray crystallography. A second resonance structure has a M=C double bond, with negative charge on oxygen. | 0 | Organic Chemistry |
Sepro Tyre Driven Grinding Mills are designed for small and medium capacity grinding applications, specifically small tonnage plants, regrinding mills, reagent prep and lime slaking. Sepro Pneumatic Tyre Driven (PTD) mills provide an alternative to standard trunnion drive systems. The drive consists of multiple gears boxes and electric motors directly connected and controlled through an AC variable frequency drive. Shell supported mills such as the Sepro PTD mills minimize stress on the mill shell by spreading the power drive over the full length of the mill. Sepro Mills are suitable for ball, rod and pebble charges and are available with overflow or grate discharge to suit the application. Shell supported mills such as the Sepro PTD Grinding Mills minimize stress on the shell by spreading the power drive over the full length of the unit. | 8 | Metallurgy |
In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below, which is referred to as the biological pump. Export production is the amount of organic matter produced in the ocean by primary production that is not recycled (remineralised) before it sinks into the aphotic zone. Because of the role of export production in the ocean's biological pump, it is typically measured in units of carbon (e.g. mg C m d). The term was coined by explorer William Beebe as observed from his bathysphere. As the origin of marine snow lies in activities within the productive photic zone, the prevalence of marine snow changes with seasonal fluctuations in photosynthetic activity and ocean currents. Marine snow can be an important food source for organisms living in the aphotic zone, particularly for organisms that live very deep in the water column. | 9 | Geochemistry |
Follicle-stimulating hormone (FSH) is an agonist of the FSHR.
Small-molecule positive allosteric modulators of the FSHR have been developed. | 1 | Biochemistry |
If there is an electropositive substituent (e.g. –SiR, –SnR, –HgR, etc.) at the β-position of carbocation, the positive charge could be stabilized which is also due largely to the stereoelectronic effect (illustrated below using –SiR3 as an example). The orientation of the two interacting orbitals can have a significant effect on the stabilization effect (σ(C–Si) → empty p orbital), where antiperiplanar (180°) > perpendicular (90°) > syn (0°). | 4 | Stereochemistry |
Main routes that can lead to human exposure to the toxic effects of bracken fern include ingestion of the plant (particularly the croziers and young fronds), inhalation of the airborne spores, consumption of the milk and meat of affected animals, and drinking ptaquiloside contaminated water. | 0 | Organic Chemistry |
The European Journal of Organic Chemistry is a weekly peer-reviewed scientific journal covering organic chemistry. It is published by Wiley-VCH on behalf of Chemistry Europe.
The journal, along with the European Journal of Inorganic Chemistry, was established in 1998 as the result of a merger of Chemische Berichte/Recueil, Bulletin de la Société Chimique de France, Bulletin des Sociétés Chimiques Belges, Gazzetta Chimica Italiana, Recueil des Travaux Chimiques des Pays-Bas, Anales de Química, Chimika Chronika, Revista Portuguesa de Química, and ACH-Models in Chemistry.
According to the Journal Citation Reports, the journal has a 2021 impact factor of 3.261. | 0 | Organic Chemistry |
As E is varied by descending group 15, there is a clear shift in the weights of the resonance structures towards the phosphaketene analogue . This reflects the decrease in effective orbital overlap between E and C which in turn disfavours multiple bond formation. This increasing tendency to form double and not triple E-C bonds is also reflected in calculated E-C bond lengths . The data from Table 1 is evidence of E-C bond elongation which correlates with the change from triple to double bond.
In addition, NBO analysis highlights that the greatest electron delocalisation within the anions stems from the donation of an oxygen lone pair into the E−C π antibonding orbital. The energy value associated with this donation is seen to increase down the group . This explains the increasing resonance weight towards the ketene like isomer as populating antibonding orbitals usually suggests the breaking of a bond.
The shift towards the ketene isomer will also cause an increase in charge density on the elemental E atom; this makes the elemental atom an increasing source of nucleophilicity . | 7 | Physical Chemistry |
Biomolecules are often purified via solvent gradient batch chromatography. Here smooth linear solvent gradients are applied to carefully handle the separation between the desired component and hundreds of impurities. The desired product is usually intermediate between weakly and strongly absorbing impurities. A center cut is required to get the desired pure product. Often the preparative resins have a low efficiency due to strong axial dispersion and slow mass transfer. Then a purification in one chromatographic step is not possible. Countercurrent movement as known from the SMB process would be required. For large scale productions and for very valuable molecules countercurrent solid movement need to be applied to increase the separation efficiency, the yield and the productivity of the purification. The MCSGP process combines both techniques in one process, the countercurrent SMB principle and the solvent gradient batch technique.
Discontinuous mode consists of equilibration, loading, washing, purification and regeneration steps. The discontinuous mode of operation allows exploiting the advantage of solvent gradients, but it implies high solvent consumptions and low productivities with respect to continuous countercurrent processes. An established process of this kind is the simulated moving bed technique (SMB) that requires the solvent-consuming steps of equilibration, washing, regeneration only once per operation and has a better resin utilization. However, major drawbacks of SMB are the inability of separating a mixture into three fractions and the lack of solvent gradient applicability.
In the case of antibodies, the state-of-the-art technique is based on batch affinity chromatography (with Protein A or Protein G as ligands) which is able to selectively bind antibody molecules. In general, affinity techniques have the advantage of purifying biomolecules with high yields and purities but the disadvantages are in general the high stationary phase cost, ligand leaching and reduced cleanability.
The MCSGP process can result in purities and yields comparable to those of purification using Protein A. The second application example for the MCSGP prototype is the separation of three MAb variants using a preparative weak cation-exchange resin. Although the intermediately eluting MAb variant can only be obtained with 80% purity at recoveries close to zero in a batch chromatographic process, the MCSGP process can provide 90% purity at 93% yield. A numerical comparison of the MCSGP process with the batch chromatographic process, and a batch chromatographic process including ideal recycling, has been performed using an industrial polypeptide purification as the model system. It shows that the MCSGP process can increase the productivity by a factor of 10 and reduce the solvent requirement by 90%.
The main advantages with respect to solvent gradient batch chromatography are high yields also for difficult separations, less solvent consumption, higher productivity, usage of countercurrent solid movement, which increases the separation efficiency. The process is continuous. Once a steady state is reached, it delivers continuously purified product in constant quality and quantity. Automatic cleaning in place is integrated. A pure empirical design of the operating conditions from a single solvent gradient batch chromatogram is possible. | 3 | Analytical Chemistry |
Mixed anion compounds exist that contain hydride with other anions. These include boride hydrides, carbohydrides, hydridonitrides, oxyhydrides and others. | 0 | Organic Chemistry |
Loss of function mutations have been shown in a number of adhesion GPCRs, including GPR56, GPR126 and VLRG1. Many mutations affect function via decreased cell surface expression or inhibition of autoproteolysis within the GAIN domain.
Mutations in GPR56 result in bilateral frontoparietal polymicrogyria in humans, characterized by abnormal neuronal migration and surface ectopias., Variants of GPR126 have been associated with adolescent idiopathic scoliosis, as well as being responsible for severe arthrogryposis multiplex congenita. Gain of function mutations within the GAIN domain of EMR2 have been shown to result in excessive degranulation by mast cells resulting in vibratory urticaria. | 1 | Biochemistry |
This quantity can be calculated from the slope of the function of two concentration cells, without or with ionic transport.
The EMF of transport concentration cell involves both the transport number of the cation and its activity coefficient:
where and are activities of HCl solutions of right and left hand electrodes, respectively, and is the transport number of . | 7 | Physical Chemistry |
The Buchner–Curtius–Schlotterbeck reaction is the reaction of aldehydes or ketones with aliphatic diazoalkanes to form homologated ketones. It was first described by Eduard Buchner and Theodor Curtius in 1885 and later by Fritz Schlotterbeck in 1907. Two German chemists also preceded Schlotterbeck in discovery of the reaction, Hans von Pechmann in 1895 and Viktor Meyer in 1905. The reaction has since been extended to the synthesis of β-keto esters from the condensation between aldehydes and diazo esters. The general reaction scheme is as follows:
The reaction yields two possible carbonyl compounds (I and II) along with an epoxide (III). The ratio of the products is determined by the reactant used and the reaction conditions. | 0 | Organic Chemistry |
For steel, the first step will be the volatilization of the inhibitor into the airspace. This may entail simple evolution of the molecule or the chemical may dissociate first and then volatilize. The molecules will then diffuse through the enclosed airspace until some of the molecules reach the metallic surface to be protected. There are two likely paths once the molecules reach the metallic surface. First the molecule may adsorb onto the metal surface thereby forming a barrier to aggressive ions and displacing any condensed water.
The second path involves the condensed water layer that has been shown to exist on the metallic surface. The VCI molecules will dissolve into the condensed water layer, raising the pH. An alkaline pH has been shown to have a beneficial effect on the corrosion resistance for steel.
The mechanism for copper begins the same as for steel, evolution of the inhibitor. Once at the copper surface however, the inhibitor will form a copper benzotriazole complex which is protective.
Vapor pressure is critical parameter in VCI effectiveness. The most favorable range of pressure is 10 to 10 Pa at room temperature. Insufficient pressure leads to the slow establishment of the protective layer; if the pressure is too high, VCI effectiveness is limited to a short time. | 8 | Metallurgy |
FACIT collagen (Fibril Associated Collagens with Interrupted Triple helices) is a type of collagen and also a proteoglycan that have two or more triple-helical domains that connect to collagen fibrils and share protein domains with non-collagen matrix molecules. FACIT collagens derive their name from their association and interaction with fibrillar collagens. Unlike fibrillar collagens, which form long fibers.
FACIT collagens have interruptions in their triple helical structure. They are involved in assembling fibrillar collagens and other ECM components. Interruptions in the triple helical structure of FACIT collagens occur due to the presence of non-triple helical domains within the collagen molecule. These collagens are typically found alongside fibrillar collagens in various tissues and organs. Fibril-associated collagens with interrupted triple helices (FACIT collagens) are a subset of collagens that contribute to the organization and stabilization of the extracellular matrix (ECM). These collagens are typically found alongside fibrillar collagens in various tissues and organs. These domains vary in length and composition and provide flexibility and additional binding sites for other components of the extracellular matrix. There are eight known types of FACIT collagens: collagens IX, XII, XIV, XVI, XIX, XXI, and XXII.
The general FACIT collagen structure contains short triple helical COL domains (COL1, COL2, COL3) interrupted by NC domains with an N-terminal NC domain facing toward the interfibrillar space. FACIT collagen is found in various tissue areas to modulate the surface properties of collagen fibrils and generate tissue-specific three-dimensional patterns in the extracellular matrix. For example, collagen XIV connects the fibrillar networks of the cartilage and skin, and XII is found in connective tissues, particularly at the tendons, ligaments, and periodontium. These collagen types can be directly or indirectly associated with fibrils at different affinities to modulate the frictional properties of fibril surfaces. In addition, collagen XIV association with a propeptide suggests FACIT function can extend to providing binding sites for fibril-modifying extracellular enzymes.
Other collagen types such as Collagen XX, which are smaller in size are mostly expressed in the connective tissue such as cartilage, tendon, and cornea while Collagen XIX is found in the skin, muscle cells, and the hippocampus. There are also collagens that are expressed in the basement membrane zones, which are extracellular matrices composed of macromolecule networks, and collagen XXII is one example located in the myotendinous junctions in the skeletal and heart muscles.
COL22A1 is also included in this class. | 1 | Biochemistry |
According to the FDA, "ibuprofen can interfere with the antiplatelet effect of low-dose aspirin, potentially rendering aspirin less effective when used for cardioprotection and stroke prevention". Allowing sufficient time between doses of ibuprofen and immediate-release (IR) aspirin can avoid this problem. The recommended elapsed time between a dose of ibuprofen and a dose of aspirin depends on which is taken first. It would be 30 minutes or more for ibuprofen taken after IR aspirin, and 8 hours or more for ibuprofen taken before IR aspirin. However, this timing cannot be recommended for enteric-coated aspirin. If ibuprofen is taken only occasionally without the recommended timing, though, the reduction of the cardioprotection and stroke prevention of a daily aspirin regimen is minimal. | 4 | Stereochemistry |
* Thure Cerling; Iain Douglas-Hamilton; Lee Siegel: "Elephant Tracks" University of Utah News Release, January 2, 2006. | 9 | Geochemistry |
Cudbear is a dye extracted from orchil lichens that produces colours in the purple range. It can be used to dye wool and silk, without the use of mordant. The lichen is first boiled in a solution of ammonium carbonate. The mixture is then cooled and ammonia is added and the mixture is kept damp for 3–4 weeks. Then the lichen is dried and ground to powder.
Cudbear was the first dye to be invented in modern times, and one of the few dyes to be credited to a named individual: Dr Cuthbert Gordon of Scotland: production began in 1758, and it was patented in 1758, British patent 727. John Glassford invested in the new process with funds from his slave-labor tobacco business by establishing a dyeworks in Dennistoun in 1777. The manufacture details were carefully protected, with a ten-feet high wall being built around the manufacturing facility, and staff consisting of Highlanders sworn to secrecy. The lichen consumption soon reached 250 tons per year and import from Norway and Sweden had to be arranged.
A similar process was developed in France. The lichen is extracted by urine or ammonia, then the extract is acidified, the dissolved dye precipitates out and is washed. Then it is dissolved in ammonia again, the solution is heated in air until it becomes purple, then it is precipitated out with calcium chloride. The resulting insoluble purple solid is known as French purple, a fast lichen dye that was much more stable than other lichen dyes. | 3 | Analytical Chemistry |
A dendrimer is a highly branched macromolecule with a spherical shape. The surface of the particle may be functionalized in many ways and many of the properties of the resulting construct are determined by its surface.
In particular it is possible to construct a cationic dendrimer, i.e. one with a positive surface charge. When in the presence of genetic material such as DNA or RNA, charge complementarity leads to a temporary association of the nucleic acid with the cationic dendrimer. On reaching its destination the dendrimer-nucleic acid complex is then taken into the cell via endocytosis.
In recent years the benchmark for transfection agents has been cationic lipids. Limitations of these competing reagents have been reported to include: the lack of ability to transfect some cell types, the lack of robust active targeting capabilities, incompatibility with animal models, and toxicity. Dendrimers offer robust covalent construction and extreme control over molecule structure, and therefore size. Together these give compelling advantages compared to existing approaches.
Producing dendrimers has historically been a slow and expensive process consisting of numerous slow reactions, an obstacle that severely curtailed their commercial development. The Michigan-based company Dendritic Nanotechnologies discovered a method to produce dendrimers using kinetically driven chemistry, a process that not only reduced cost by a magnitude of three, but also cut reaction time from over a month to several days. These new "Priostar" dendrimers can be specifically constructed to carry a DNA or RNA payload that transfects cells at a high efficiency with little or no toxicity. | 1 | Biochemistry |
Reversed phase liquid chromatography (RPLC) is the most important chromatographic method for measuring solute hydrophobicity. The non polar stationary phase mimics biological membranes. Peptide usage has many advantages because partition is not extended by the terminal charges in RPLC. Also, secondary structures formation is avoided by using short sequence peptides. Derivatization of amino acids is necessary to ease its partition into a C18 bonded phase. Another scale had been developed in 1971 and used peptide retention on hydrophilic gel. 1-butanol and pyridine were used as the mobile phase in this particular scale and glycine was used as the reference value. Pliska and his coworkers used thin layer chromatography to relate mobility values of free amino acids to their hydrophobicities. About a decade ago, another hydrophilicity scale was published, this scale used normal phase liquid chromatography and showed the retention of 121 peptides on an amide-80 column.
The absolute values and relative rankings of hydrophobicity determined by chromatographic methods can be affected by a number of parameters. These parameters include the silica surface area and pore diameter, the choice and pH of aqueous buffer, temperature and the bonding density of stationary phase chains. | 6 | Supramolecular Chemistry |
The van t Hoff factor (named after Dutch chemist Jacobus Henricus van t Hoff) is a measure of the effect of a solute on colligative properties such as osmotic pressure, relative lowering in vapor pressure, boiling-point elevation and freezing-point depression. The van t Hoff factor is the ratio between the actual concentration of particles produced when the substance is dissolved and the concentration of a substance as calculated from its mass. For most non-electrolytes dissolved in water, the van t Hoff factor is essentially 1.
For most ionic compounds dissolved in water, the van t Hoff factor is equal to the number of discrete ions in a formula unit of the substance. This is true for ideal solutions only, as occasionally ion pairing occurs in solution. At a given instant a small percentage of the ions are paired and count as a single particle. Ion pairing occurs to some extent in all electrolyte solutions. This causes the measured van t Hoff factor to be less than that predicted in an ideal solution. The deviation for the van 't Hoff factor tends to be greatest where the ions have multiple charges.
The factor binds osmolarity to molarity and osmolality to molality. | 7 | Physical Chemistry |
3-Methylfentanyl (3-MF, mefentanyl) is an opioid analgesic that is an analog of fentanyl. 3-Methylfentanyl is one of the most potent opioids, estimated to be between 400 and 6000 times stronger than morphine, depending on which isomer is used (with the cis isomers being the more potent ones). | 1 | Biochemistry |
Ionochromism, similar to chromic methods such as photochromism, thermochromism and other chromism phenomena, is the reversible process of changing the color of a material by absorption or emission spectra of molecules using ions. Electrochromism is similar to ionochromism as it involves the use of electrons in order to change the color of materials. Both electrochromic and ionochromic materials undergo a change in color by the flow of charged particles, where electrochromic materials only involve an anionic species or negatively charged species such as electrons. An example of an ionochromic dye is a complexometric indicator. A complexometric indicator involves the presence of metal ions in order to facilitate color change and is often used in complexometric titration. | 3 | Analytical Chemistry |
In metallurgy, exfoliation corrosion (also called lamellar corrosion) is a severe type of intergranular corrosion that raises surface grains from metal by forming corrosion products at grain boundaries under the surface. It is frequently found on extruded sections where grain thickness is not as thick as the rolled grain. It can affect aircraft structures, marine vessels, heaters and other objects. | 8 | Metallurgy |
* Alkalinity
* Biochemical oxygen demand (BOD)
* Chemical oxygen demand (COD)
* Dissolved oxygen (DO)
* Total hardness (TH)
* Heavy metals
* Nitrate
* Orthophosphates
* pH
* Pesticides
* Residual sodium carbonate index (RSC)
* Sodium adsorption ratio (SAR)
* Surfactants | 3 | Analytical Chemistry |
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