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Calcineurin inhibitors such as tacrolimus are used to suppress the immune system in organ allotransplant recipients to prevent rejection of the transplanted tissue. | 1 | Biochemistry |
Deoxydehydration (DODH) is a chemical reaction for removing two adjacent hydroxyl groups in a vicinal diol to form an alkene. In contrast to hydrodeoxygenation which uses hydrogen as a reductant, deoxydehydration is able to use a variety of other reductants such as alcohols and organic phosphines. In research, the most common homogeneous catalysts for this reaction use rhenium.
Recently, research has focused on the use of vanadium heterogeneous catalysts for deoxydehydration, such as the conversion of 2,3-butanediol to butene. Although deoxydehydration over vanadium catalysts requires higher temperatures than over rhenium catalysts, the reaction can proceed without the need for hydrogen or external reductants, which can reduce waste products. | 0 | Organic Chemistry |
Marion McQuillan (30 October 1921 – 24 June 1998) was a British metallurgist who specialised in the engineering uses for titanium and its alloys. She researched jet engine metals and was on the first team to research titanium for the Royal Aircraft Establishment Farnborough (RAE). | 8 | Metallurgy |
In conventional seasoning, the oil or fat is converted into a hard surface at or above the high temperatures used for cooking, analogous to the reaction of drying oils. When oils or fats are heated, multiple degradation reactions occur, including decomposition, autoxidation, thermal oxidation, polymerization, and cyclization.
Often cookware's seasoning is uneven, and over time it will spread to the whole item. Heating the cookware (such as in a hot oven or on a stovetop) facilitates the oxidation of the iron; the fats and/or oils protect the metal from contact with the air during the reaction, which would otherwise cause rust to form. Some cast iron users advocate heating the cookware slightly before applying the fat or oil to ensure it is completely dry.
The seasoned surface is hydrophobic and highly attractive to oils and fats used for cooking (oleophilic). These form a layer that prevents foods, which typically contain water, from touching and cooking on to the hydrophilic metallic cooking surface underneath.
The seasoned surface will deteriorate at the temperature where the coating breaks down. This is typically higher than the smoke point of the original oils and fats used to season the cookware. Thus old seasoning can be removed at a sufficiently high temperature (~500 °C), as found in oven self-cleaning cycles. | 7 | Physical Chemistry |
Colored dissolved organic matter (CDOM) absorbs light, making the water appear darker or tea-colored. Absorption by CDOM is one measure of water clarity. Clarity can still be quite high in terms of visibility with high amounts of CDOM in the water, but the color of the water will be altered to yellow or brown, and the water will appear darker than water with low CDOM concentrations. CDOM absorbs blue light more strongly than other colors, shifting the color of the water toward the yellow and red part of the visible light spectrum as the water gets darker. For example, in lakes with high CDOM concentrations, the bottom of the lake may be clearly visible to the human eye, but a white surface in the same lake water may appear yellow or brown. | 3 | Analytical Chemistry |
Rather than internal displacement coordinates, an alternative approach to write the potential energy of a molecule as explained by Decius is to write it as a quadratic form in terms of generalized displacement forces (negative gradient) .
: (eq. 5)
This gradient is the first derivative of the potential energy with respect to the displacement coordinates, which can be expressed as shown:
: (eq. 6)
By substituting the expression of in eq. 5 into equation 5, equation 7 is obtained.
: (eq. 7)
Thus, with the knowledge that is positive definite, the only possible value of which is the compliance matrix then must be:
: (eq. 8)
Equation 7 offers a surrogate formulation of the potential energy which proves to be significantly advantageous in defining chemical bonds. Specially, this method is independent on coordinate selection and also eliminates such issue with redundant Hessian that the common force constant calculation method suffers with. Intriguingly, compliance constants calculation can be employed regardless of the redundancy of the coordinates. | 6 | Supramolecular Chemistry |
According to a laboratory procedure hydroxylamine-O-sulfonic acid can be prepared by treating hydroxylamine sulfate with fuming sulfuric acid (oleum). The industrial process is similar.
:(NHOH)SO + 2SO → 2HNOSOH + HSO
The sulfonation of hydroxylamine can also be effected with chlorosulfonic acid by a method first published in 1925 and refined for Organic Syntheses.
The hydroxylamine-O-sulfonic acid, which should be stored at 0 °C to prevent decomposition, can be checked by iodometric titration. | 0 | Organic Chemistry |
In 1978, Walter Gilbert published "Why Genes in Pieces" which first began to explore the idea that the gene is a mosaic—that each full nucleic acid strand is not coded continuously but is interrupted by "silent" non-coding regions. This was the first indication that there needed to be a distinction between the parts of the genome that code for protein, now called coding regions, and those that do not. | 1 | Biochemistry |
As of 2015, several bodies of water in the state of Washington were contaminated with PCBs, including the Columbia River, the Duwamish River, Green Lake, Lake Washington, the Okanogan River, Puget Sound, the Spokane River, the Walla Walla River, the Wenatchee River, and the Yakima River. A study by Washington State published in 2011 found that the two largest sources of PCB flow into the Spokane River were City of Spokane stormwater (44%) and municipal and industrial discharges (20%).
PCBs entered the environment through paint, hydraulic fluids, sealants, inks and have been found in river sediment and wildlife. Spokane utilities will spend $300 million to prevent PCBs from entering the river in anticipation of a 2017 federal deadline to do so. In August 2015 Spokane joined other U.S. cities like San Diego and San Jose, California, and Westport, Massachusetts, in seeking damages from Monsanto. | 2 | Environmental Chemistry |
As with many other places in Britain, there have been speculative articles written that connect Ariconium to the characters in Arthurian tales. Some are careful with their wording and state that they are not asserting historical facts; others are less careful and propagate fiction in the guise of hypothesis.
There are occasional mentions of Ariconium in poetic works, but there is nothing to connect them with the Ariconium of this article. They may be references to Kenchester at a time when Camden placed the site there, or to a similar-sounding word such as Uriconium, or to some other place or person; or as works of poetry, they may refer to nothing in particular at all. | 8 | Metallurgy |
A materials oscilloscope is a time-resolved synchrotron
high-energy X-ray technique to study rapid phase composition and microstructural related changes in a polycrystalline sample. Such device has been developed for in-situ studies of specimens undergoing physical thermo-mechanical simulation. | 7 | Physical Chemistry |
Janet Gretchen Jones was born in Pittsburgh, Pennsylvania, and grew up in Vero Beach, Florida. She was an undergraduate student at Swarthmore College, where she was a Merit scholar. Jones was a graduate student at California Institute of Technology, where she worked alongside Fred Anson on ligand bridging in charge transfer reactions. Robert Osteryoung was a Visiting Associate in the Department of Chemistry at Caltech at this same time. After marrying, Janet and Robert Osteryoung both continued to carry out research in the field of electroanalytical chemistry. | 3 | Analytical Chemistry |
During high-energy milling the powder particles are repeatedly flattened, cold welded, fractured and rewelded. Whenever two steel balls collide, some powder is trapped between them. Typically, around 1000 particles with an aggregate weight of about 0.2 mg are trapped during each collision. The force of the impact plastically deforms the powder particles, leading to work hardening and fracture. The new surfaces thus created enable the particles to weld together; this leads to an increase in particle size. Since in the early stages of milling, the particles are soft (if using either ductile-ductile or ductile-brittle material combination), their tendency to weld together and form large particles is high. A broad range of particle sizes develops, with some as large as three times larger than the starting particles. The composite particles at this stage have a characteristic layered structure consisting of various combinations of the starting constituents. With continued deformation particles become work hardened, and fracture by a fatigue failure mechanism and/or by the fragmentation of fragile flakes. | 8 | Metallurgy |
As mentioned previously, Pseudomonas aeruginosa produces a host of virulence factors in concert, under the control of the quorum sensing system. Many studies show that inhibiting quorum sensing down-regulates the pathogenicity of Pseudomonas aeruginosa. However, it has been shown that rhamnolipids specifically are a key virulence determinant in Pseudomonas aeruginosa. A variety of virulence factors were analysed in Pseudomonas aeruginosa strains isolated from pneumonia patients. Rhamnolipids were found to be the only virulence factor that was associated with the deterioration of the patients to ventilator-associated pneumonia. Several other reports also support the role of rhamnolipids in lung infections. The effect of rhamnolipids in Pseudomonas aeruginosa virulence has been further noted in corneal infections (Alarcon et al., 2009; Zhu et al., 2004). It has been shown that rhamnolipids are able to integrate into the epithelial cell membrane and disrupt tight-junctions. This study used reconstituted epithelial membranes and purified rhamnolipids to demonstrate this mechanism. In addition to inhibition and killing of epithelial cells, rhamnolipids are able to kill polymorphonuclear (PMN) leukocytes and macrophages and inhibit phagocytosis. In summary, rhamnolipids have been shown unequivocally to be a potent virulence factor in the human host, however, they are also produced outside of the host, for example in a soil environment.
Rhamnolipids contribute to the establishment and maintenance of infection in cystic fibrosis patients in a number of ways, they disrupt the bronchial epithelium by disrupting the cell membranes, which promotes paracellular invasion of Pseudomonas aeruginosa and causes ciliostasis, further preventing the clearing of mucus. They also solubilise lung surfactant, allowing phospholipase C access to cell membranes and are necessary for correct biofilm formation. | 0 | Organic Chemistry |
Porphine or porphin is an organic compound of empirical formula . It is heterocyclic and aromatic. The molecule is a flat macrocycle, consisting of four pyrrole-like rings joined by four methine bridges, which makes it the simplest of the tetrapyrroles.
The nonpolar tetrapyrrolic ring structure of porphine means it is poorly soluble in most organic solvents and hardly water soluble. As a result, porphine is mostly of theoretical interest. It has been detected in GC-MS of certain fractions of Piper betle. | 1 | Biochemistry |
Laser-induced incandescence (LII) is an in situ method of measuring aerosol particle volume fraction, primary particle sizes, and other thermophysical properties in flames, during gas-phase nanoparticle synthesis, and in aerosol streams more broadly. The technique is prominently used to characterize soot.
The technique can broadly be separated into applications involving continuous or pulsed laser sources, with the former implemented in the Single Particle Soot Photometer (SP2) and the latter used in time-resolved laser-induced incandescence (TiRe-LII) analyses. | 7 | Physical Chemistry |
HO is a diatomic molecule. The electronic angular momentum along the molecular axis is +1 or -1, and the electronic spin angular momentum S=1/2. Because of the orbit-spin coupling, the spin angular momentum can be oriented in parallel or anti parallel directions to the orbital angular momentum, producing the splitting into Π and Π states. The Π ground state of HO is split by lambda doubling interaction (an interaction between the nuclei rotation and the unpaired electron motion around its orbit). Hyperfine interaction with the unpaired spin of the proton further splits the levels. | 2 | Environmental Chemistry |
The respiratory quotient (RQ) is the ratio:
RQ = CO / O
where the term "eliminated" refers to carbon dioxide (CO) removed from the body.
In this calculation, the CO and O must be given in the same units, and in quantities proportional to the number of molecules. Acceptable inputs would be either moles, or else volumes of gas at standard temperature and pressure.
Many metabolized substances are compounds containing only the elements carbon, hydrogen, and oxygen. Examples include fatty acids, glycerol, carbohydrates, deamination products, and ethanol. For complete oxidation of such compounds, the chemical equation is
CHO + (x + y/4 - z/2) O
→ x CO + (y/2) HO
and thus metabolism of this compound gives an RQ of x/(x + y/4 - z/2).
For glucose, with the molecular formula, CHO, the complete oxidation equation is CHO + 6 O
→ 6 CO + 6 HO. Thus, the RQ= 6 CO/ 6 O=1.
For fats, the RQ depends on the specific fatty acids present. Amongst the commonly stored fatty acids in vertebrates, RQ varies from 0.692 (stearic acid) to as high as 0.759 (docosahexaenoic acid). Historically, it was assumed that average fat had an RQ of about 0.71, and this holds true for most mammals including humans. However, a recent survey showed that aquatic animals, especially fish, have fat that should yield higher RQs on oxidation, reaching as high as 0.73 due to high amounts of docosahexaenoic acid.
The range of respiratory coefficients for organisms in metabolic balance usually ranges from 1.0 (representing the value expected for pure carbohydrate oxidation) to ~0.7 (the value expected for pure fat oxidation). In general, molecules that are more oxidized (e.g., glucose) require less oxygen to be fully metabolized and, therefore, have higher respiratory quotients. Conversely, molecules that are less oxidized (e.g., fatty acids) require more oxygen for their complete metabolism and have lower respiratory quotients. See BMR for a discussion of how these numbers are derived. A mixed diet of fat and carbohydrate results in an average value between these numbers.
RQ value corresponds to a caloric value for each liter (L) of CO produced. If O consumption numbers are available, they are usually used directly, since they are more direct and reliable estimates of energy production.
RQ as measured includes a contribution from the energy produced from protein. However, due to the complexity of the various ways in which different amino acids can be metabolized, no single RQ can be assigned to the oxidation of protein in the diet.
Insulin, which increases lipid storage and decreases fat oxidation, is positively associated with increases in the respiratory quotient. A positive energy balance will also lead to an increased respiratory quotient. | 1 | Biochemistry |
Based on current evidence, the term of endothelium-derived hyperpolarising factor should represent a mechanism rather than a specific factor. The mechanism(s) of endothelium-dependent hyperpolarization (i.e., EDHF-mediated relaxation) seems to be heterogeneous depending on several factors (e.g., size and vascular bed), surrounding environment (oxidative stress, hypercholesterolemia) and demand (compensatory). Different endothelial mediators or pathways involved in EDHF-mediated relaxation may also work simultaneously and/or substitute each other. It implies a reasonable physiological sense, although to some extent and when EDHF acts as backup mechanism for endothelium-dependent relaxation in the present of compromised NO contribution. Thus, alternatives for EDHF-typed responses (HO, K etc.) will provide a guarantee for compensation of endothelial function. However, once the involvement of a certain endothelium-derived vasodilator for a given vascular bed is confirmed, it is preferred that they be described by their proper name (i.e., endothelium-derived HO, or CNP), and no longer be termed as “EDHF”. Although the role of EDHF in the genesis of Cardiovascular Disease remains to be further elucidated, the EDHF contribution and its importance at the level of small arteries delivers a theoretical opportunity to control systemic blood pressure. There is an increasing experimental evidence to suggest that treatment of the EDHF system could provide a means to control blood pressure and blood flow to target organs in compatible way achieved by manipulations of NO system.
Since “EDHF story” is particularly heterogeneous and based mainly on animal studies, the most important and demanding current task is to strengthen our knowledge about EDHF action in human arteries in health and disease. | 1 | Biochemistry |
As of 2013, bottromycin has not been approved for any clinical applications, nor has it been tested in humans. The in vivo stability of bottromycin must be improved before it can be considered as a drug candidate. Work by Kobayashi and colleagues has already begun to address this issue, but more work may be in progress. The need to find new antibiotics to combat antibiotic resistance means that biologic and synthetic interest in bottromycin will likely continue. A combination of biologic and synthetic techniques may yield both an efficacious and stable bottromycin analog for development as a potential drug candidate. | 0 | Organic Chemistry |
TMAO is an organic osmolyte that has the useful biological function of protecting proteins against denaturing stresses such as high concentration of urea. Various bacteria grow anaerobically using TMAO as an alternative electron transport chain, allowing for growth on non-fermentable carbon sources such as glycerol. Bacteria capable of reducing TMAO to TMA are found throughout three different ecological niches. TMAO-reducing, to date, has been observed in marine bacteria, photosynthetic bacteria living in shallow ponds, and in enterobacteria.
TMAO reductases have been studied in several organisms, and a common conserved feature is the presence of a molybdenum cofactor in all the known terminal enzymes.
Based on their substrate specificity, these enzymes can be divided into two groups:
* TMAO reductases which have high substrate specificity
* DMSO/TMAO reductases which can reduce a broad range of N and S-oxide substrates.
The first group consists of species such as Escherichia coli, Shewanella putrefaciens, and Roseobacter denitrificans while the second group consists of species such as Proteus vulgaris, Rhodobacter capsulatus, and Rhodobacter sphaeroides.
The TMAO respiratory system has been mostly widely studied at the molecular level in E. coli and Rhodobacter species. | 1 | Biochemistry |
Di(2-ethylhexyl)phosphoric acid (DEHPA or HDEHP) is an organophosphorus compound with the formula (CHO)POH. The colorless liquid is a diester of phosphoric acid and 2-ethylhexanol. It is used in the solvent extraction of uranium, vanadium and the rare-earth metals. | 3 | Analytical Chemistry |
Perindopril shares the indications of ACE inhibitors as a class, including essential hypertension, stable coronary artery disease (reduction of risk of cardiac events in patients with a history of myocardial infarction and/or revascularization), treatment of symptomatic coronary artery disease or heart failure, and diabetic nephropathy. | 4 | Stereochemistry |
pRb is known to interact with more than 300 proteins, some of which are listed below:
* Abl gene
* Androgen receptor
* Apoptosis-antagonizing transcription factor
* ARID4A
* Aryl hydrocarbon receptor
* BRCA1
* BRF1
* C-jun
* C-Raf
* CDK9
* CUTL1
* Cyclin A1
* Cyclin D1
* Cyclin T2
* DNMT1
* E2F1
* E2F2,
* E4F1
* EID1
* ENC1
* FRK
* HBP1
* HDAC1
* HDAC3
* Histone deacetylase 2
* Insulin
* JARID1A
* Large tumor antigen
* LIN9
* MCM7
* MORF4L1
* MRFAP1,
* MyoD
* NCOA6
* PA2G4
* Peroxisome proliferator-activated receptor gamma
* PIK3R3
* Plasminogen activator inhibitor-2
* Polymerase (DNA directed), alpha 1
* PRDM2
* PRKRA
* Prohibitin
* Promyelocytic leukemia protein
* RBBP4
* RBBP7
* RBBP8
* RBBP9
* SNAPC1
* SKP2
* SNAPC3
* SNW1
* SUV39H1
* TAF1
* THOC1
* TRAP1
* TRIP11
* UBTF
* USP4. | 1 | Biochemistry |
Galaxy IV was a telecommunications satellite that was disabled and lost due to short circuits caused by tin whiskers in 1998. It was initially thought that space weather contributed to the failure, but later it was discovered that a conformal coating had been misapplied, allowing whiskers formed in the pure tin plating to find their way through a missing coating area, causing a failure of the main control computer. The manufacturer, Hughes, has moved to nickel plating, rather than tin, to reduce the risk of whisker growth. The trade-off has been an increase in weight, adding per payload. | 8 | Metallurgy |
The National Institutes of Health announced on 27 February 2015 the commencement of a randomized controlled trial of ZMapp to be conducted in Liberia and the United States. From March 2015 through November 2015, 72 individuals infected with the Ebola virus were enrolled in the trial; investigators stopped enrolling new subjects in January 2016, having failed to reach its enrollment goal of 200 due to the waning of the Ebola outbreak. As a result, although a 40% lower risk of death was calculated for those who received ZMapp, the difference was not statistically significant and ultimately it could not be determined whether the use of ZMapp was superior to the optimized standard of care alone. However, ZMapp was found to be safe and well tolerated. | 1 | Biochemistry |
radioisotope - radioisotopic labelling - Raman spectroscopy - random coil - Ras gene - Ras protein - reading frame - receptor (biochemistry) - receptor antagonist - receptor protein-tyrosine kinase - recombinant fusion protein - recombinant interferon-gamma - recombinant protein - recombination - redox - redox reaction - redox system - reflux - replication origin - replicon - repressor - repressor protein - respiration (physiology) - restriction enzyme - retinoblastoma protein - retinoic acid receptor - retinol-binding protein - retroelement - retroviridae protein - retrovirus - Reverse transcriptase - RFLP - rho factor - rhodopsin - ribonucleoprotein - ribose - ribosomal protein - ribosomal protein S6 kinase - ribosome - RNA - RNA virus - RNA-binding protein - RNA-directed DNA polymerase - rod outer segment - rough ER | 1 | Biochemistry |
Most supramolecular catalysts are developed from rigid building blocks because rigid blocks are less complicated than flexible parts in constructing a desired shape and placing functional groups where the designer wants. Due to the rigidity, however, a slight mismatch from the transition state inevitably leads to poor stabilization and thus poor catalysis. In nature, enzymes are flexible and could change their structures to bind a transition state better than their native form. | 6 | Supramolecular Chemistry |
Any periodic tiling can be seen as a wallpaper. More particularly, we can consider as a wallpaper a tiling by identical tiles edge‑to‑edge, necessarily periodic, and conceive from it a wallpaper by decorating in the same manner every tiling element, and eventually erase partly or entirely the boundaries between these tiles. Conversely, from every wallpaper we can construct such a tiling by identical tiles edge‑to‑edge, which bear each identical ornaments, the identical outlines of these tiles being not necessarily visible on the original wallpaper. Such repeated boundaries delineate a repetitive surface added here in dashed lines.
Such pseudo‑tilings connected to a given wallpaper are in infinite number. For example image 1 shows two models of repetitive squares in two different positions, which have Another repetitive square has an We could indefinitely conceive such repetitive squares larger and larger. An infinity of shapes of repetitive zones are possible for this Pythagorean tiling, in an infinity of positions on this wallpaper. For example in red on the bottom right‑hand corner of image 1, we could glide its repetitive parallelogram in one or another position. In common on the first two images: a repetitive square concentric with each small square tile, their common center being a point symmetry of the wallpaper.
Between identical tiles edge‑to‑edge, an edge is not necessarily a segment of a straight line. On the top left‑hand corner of image 3, point C is a vertex of a repetitive pseudo‑rhombus with thick stripes on its whole surface, called pseudo‑rhombus because of a concentric repetitive rhombus constructed from it by taking out a bit of surface somewhere to append it elsewhere, and keep the area unchanged. By the same process on image 4, a repetitive regular hexagon filled with vertical stripes is constructed from a rhombic repetitive zone Conversely, from elementary geometric tiles edge‑to‑edge, an artist like M. C. Escher created attractive surfaces many times repeated. On image 2, the minimum area of a repetitive surface by disregarding colors, each repetitive zone in dashed lines consisting of five pieces in a certain arrangement, to be either a square or a hexagon, like in a proof of the Pythagorean theorem.
In the present article, a pattern is a repetitive parallelogram of minimal area in a determined position on the wallpaper. Image 1 shows two parallelogram‑shaped patterns — a square is a particular parallelogram —. Image 3 shows rhombic patterns — a rhombus is a particular parallelogram —.
On this page, all repetitive patterns (of minimal area) are constructed from two translations that generate the group of all translations under which the wallpaper is invariant. With the circle shaped symbol ⵔ of function composition, a pair like or generates the group of all translations that transform the Pythagorean tiling into itself. | 3 | Analytical Chemistry |
Industrially, most alkylations are typically conducted using alcohols, not alkyl halides. Alcohols are less expensive than alkyl halides and their alkylation does not produce salts, the disposal of which can be problematic. Key to the alkylation of alcohols is the use of catalysts that render the hydroxyl group a good leaving group. The largest scale N-alkylation is the production of the methylamines from ammonia and methanol, resulting in approximately 500,000 tons/y of methylamine, dimethylamine, and trimethylamine. The reaction is poorly selective, requiring separation of the three products. Many other industrially significant alkyl amines are produced, again on a large scale, from the alcohols. Epoxides are another class of halide-free N-alkylating agents, useful in the production of ethanolamines. | 0 | Organic Chemistry |
Raytec Vision is a camera and sensor-based manufacturer based in Parma and specialized in food sorting. The applications of Raytec Vision's machines are many: tomatoes, tubers, fruit, fresh cut, vegetables and confectionery products. Each machine can separate good products from wastes, foreign bodies and defects and guarantees high levels of food safety for the final consumer. | 3 | Analytical Chemistry |
Hemoglobin (Hb) is synthesized in a complex series of steps. The heme part is synthesized in a series of steps in the mitochondria and the cytosol of immature red blood cells, while the globin protein parts are synthesized by ribosomes in the cytosol. Production of Hb continues in the cell throughout its early development from the proerythroblast to the reticulocyte in the bone marrow. At this point, the nucleus is lost in mammalian red blood cells, but not in birds and many other species. Even after the loss of the nucleus in mammals, residual ribosomal RNA allows further synthesis of Hb until the reticulocyte loses its RNA soon after entering the vasculature (this hemoglobin-synthetic RNA in fact gives the reticulocyte its reticulated appearance and name). | 7 | Physical Chemistry |
Resonance is to be distinguished from isomerism. Isomers are molecules with the same chemical formula but are distinct chemical species with different arrangements of atomic nuclei in space. Resonance contributors of a molecule, on the other hand, can only differ in the way electrons are formally assigned to atoms in the Lewis structure depictions of the molecule. Specifically, when a molecular structure is said to be represented by a resonance hybrid, it does not mean that electrons of the molecule are "resonating" or shifting back and forth between several sets of positions, each one represented by a Lewis structure. Rather, it means that the set of contributing structures represents an intermediate structure (a weighted average of the contributors), with a single, well-defined geometry and distribution of electrons. It is incorrect to regard resonance hybrids as rapidly interconverting isomers, even though the term "resonance" might evoke such an image. (As described below, the term "resonance" originated as a classical physics analogy for a quantum mechanical phenomenon, so it should not be construed too literally.) Symbolically, the double headed arrow is used to indicate that A and B are contributing forms of a single chemical species (as opposed to an equilibrium arrow, e.g., ; see below for details on usage).
A non-chemical analogy is illustrative: one can describe the characteristics of a real animal, the narwhal, in terms of the characteristics of two mythical creatures: the unicorn, a creature with a single horn on its head, and the leviathan, a large, whale-like creature. The narwhal is not a creature that goes back and forth between being a unicorn and being a leviathan, nor do the unicorn and leviathan have any physical existence outside the collective human imagination. Nevertheless, describing the narwhal in terms of these imaginary creatures provides a reasonably good description of its physical characteristics.
Due to confusion with the physical meaning of the word resonance, as no entities actually physically "resonate", it has been suggested that the term resonance be abandoned in favor of delocalization and resonance energy abandoned in favor of delocalization energy. A resonance structure becomes a contributing structure and the resonance hybrid becomes the hybrid structure. The double headed arrows would be replaced by commas to illustrate a set of structures, as arrows of any type may suggest that a chemical change is taking place. | 7 | Physical Chemistry |
Zelinsky's scientific activity was very versatile: his works on the chemistry of thiophene and the stereochemistry of organic dibasic acids are widely known. In the summer of 1891, Zelinsky participated in an expedition to survey the waters of the Black Sea and the Odessa estuaries on the gunboat Zaporozhets, where he proved for the first time that the hydrogen sulfide contained in the water was of bacterial origin. During the period of life and work in Odessa, Nikolai Zelinsky wrote 40 scientific papers.
A number of his works were also devoted to electrical conductivity in non-aqueous solutions and to the chemistry of amino acids, but his main works were related to the chemistry of hydrocarbons and organic catalysis.
In 1895-1907 he was the first to synthesize a number of cyclopentane and cyclohexane hydrocarbons, which served as standards for studying the chemical composition and the basis for artificial modeling of oil and oil fractions.
In 1910 he discovered the phenomenon of dehydrogenation catalysis, which consists in the exclusively selective action of platinum and palladium on cyclohexane and aromatic hydrocarbons and in the ideal reversibility of hydro- and dehydrogenation reactions only depending on temperature. In 1911 he carried out a smooth dehydrogenation of cyclohexane and its homologues into aromatic hydrocarbons in the presence of platinum and palladium catalysts; he widely used this reaction to determine the content of cyclohexane hydrocarbons in gasoline and kerosene fractions of oil (1920-1930), and also as an industrial method for obtaining aromatic hydrocarbons from oil. These Zelinsky’s studies underlie the modern processes of catalytic reforming of petroleum fractions.
Subsequent research led Zelinsky and his students to the discovery of the reaction of hydrogenolysis of cyclopentane hydrocarbons with their transformation into alkanes in the presence of platinized coal and excess hydrogen in 1934.
In 1915, Zelinsky successfully used oxide catalysts for oil cracking, which led to a decrease in the process temperature and an increase in the yield of aromatic hydrocarbons. In 1918-1919, he developed a method for producing gasoline by solar oil and petroleum cracking in the presence of aluminum chloride and aluminum bromide; the implementation of this method on an industrial scale played an important role in providing gasoline to the Soviet state. Zelinsky improved the reaction of catalytic conversion of acetylene into benzene by suggesting the use of activated carbon as a catalyst. Zelinsky and his students also studied the dehydrogenation of paraffins and olefins in the presence of oxide catalysts.
Being a supporter of the theory of the organic origin of oil, Zelinsky conducted a series of studies to connect its genesis with sapropels, oil shale and other natural and synthetic organic substances.
Zelinsky and his students proved the intermediate formation of methylene radicals in many heterogeneous catalytic reactions: in the decomposition of cyclohexane, in the synthesis of hydrocarbons from carbon monoxide and hydrogen on a cobalt catalyst, in the reactions of hydrocondensation of olefins with carbon monoxide and hydropolymerization of olefins in the presence of small amounts of oxide carbon which were discovered by him.
The works of Zelinsky and his scientific team on the adsorption of gases on activated carbons were important for the countrys defense ability, the creation of a coal gas mask in cooperation with Kumant (1915) and its adoption during the First World War in the Russian and allied armies were significant for the countrys defense ability. | 0 | Organic Chemistry |
EBSD detectors can have forward scattered electron diodes (FSD) at the bottom, in the middle (MSD) and at the top of the detector. Forward-scattered electron (FSE) imaging involves collecting electrons scattered at small angles from the surface of a sample, which provides information about the surface topography and composition. The FSE signal is also sensitive to the crystallographic orientation of the sample. By analysing the intensity and contrast of the FSE signal, researchers can determine the crystallographic orientation of each pixel in the image.
The FSE signal is typically collected simultaneously with the BSE signal in EBSD analysis. The BSE signal is sensitive to the average atomic number of the sample, and is used to generate an image of the surface topography and composition. The FSE signal is superimposed on the BSE image to provide information about the crystallographic orientation.
Image generation has a lot of freedom when using the EBSD detector as an imaging device. An image created using a combination of diodes is called virtual or VFSD. It is possible to acquire images at a rate akin to slow scan imaging in the SEM by excessive binning of the EBSD CCD camera. It is possible to suppress or isolate the contrast of interest by creating composite images from simultaneously captured images, which offers a wide range of combinations for assessing various microstructure characteristics. Nevertheless, VFSD images do not include the quantitative information inherent to traditional EBSD maps; they simply offer representations of the microstructure. | 7 | Physical Chemistry |
Heterosynaptic plasticity (or also heterotropic modulation) is a change in synaptic strength that results from the activity of other neurons. Again, the plasticity can alter the number of vesicles or their replenishment rate or the relationship between calcium and vesicle release. Additionally, it could directly affect calcium influx. Heterosynaptic plasticity can also be postsynaptic in nature, affecting receptor sensitivity.
One example is again neurons of the sympathetic nervous system, which release noradrenaline, which, in addition, generates an inhibitory effect on presynaptic terminals of neurons of the parasympathetic nervous system. | 1 | Biochemistry |
Stress corrosion cracking is a phenomenon where a synergistic action of corrosion and tensile stress leads to brittle fracture of normally ductile materials at generally lower stress levels. During stress corrosion cracking, the material is relatively unattacked by the corrosive agent (no general corrosion, only localized corrosion), but fine cracks form within it. This process has serious implications on the utilisation of the material because the applicable safe stress levels are drastically reduced in the corrosive medium. Season cracking and caustic embrittlement are two stress corrosion cracking processes which affected the serviceability of brass cartridge cases and riveted steel boilers respectively. | 8 | Metallurgy |
LC–MS is widely used in the field of bioanalysis and is specially involved in pharmacokinetic studies of pharmaceuticals. Pharmacokinetic studies are needed to determine how quickly a drug will be cleared from the body organs and the hepatic blood flow. MS analyzers are useful in these studies because of their shorter analysis time, and higher sensitivity and specificity compared to UV detectors commonly attached to HPLC systems. One major advantage is the use of tandem MS–MS, where the detector may be programmed to select certain ions to fragment. The measured quantity is the sum of molecule fragments chosen by the operator. As long as there are no interferences or ion suppression in LC–MS, the LC separation can be quite quick. | 3 | Analytical Chemistry |
Several software graphic tools will let you create 2D patterns using wallpaper symmetry groups. Usually you can edit the original tile and its copies in the entire pattern are updated automatically.
* [http://www.madpattern.com/ MadPattern], a free set of Adobe Illustrator templates that support the 17 wallpaper groups
* [http://www.peda.com/tess/ Tess], a shareware tessellation program for multiple platforms, supports all wallpaper, frieze, and rosette groups, as well as Heesch tilings.
*[http://math.hws.edu/eck/js/symmetry/wallpaper.html Wallpaper Symmetry] is a free online JavaScript drawing tool supporting the 17 groups. The [http://math.hws.edu/eck/js/symmetry/symmetry-info.html main page] has an explanation of the wallpaper groups, as well as drawing tools and explanations for the other planar symmetry groups as well.
* [https://en.oiler.education/tales TALES GAME], a free software designed for educational purposes which includes the tessellation function.
* [http://www.scienceu.com/geometry/handson/kali/ Kali] , online graphical symmetry editor Java applet (not supported by default in browsers).
* [http://www.geometrygames.org/Kali/index.html Kali] , free downloadable Kali for Windows and Mac Classic.
* Inkscape, a free vector graphics editor, supports all 17 groups plus arbitrary scales, shifts, rotates, and color changes per row or per column, optionally randomized to a given degree. (See [http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Tiles-Symmetries.html])
* [http://www.artlandia.com/products/SymmetryWorks/ SymmetryWorks] is a commercial plugin for Adobe Illustrator, supports all 17 groups.
* [https://eschersket.ch/ EscherSketch] is a free online JavaScript drawing tool supporting the 17 groups.
* [https://repper.app/ Repper] is a commercial online drawing tool supporting the 17 groups plus a number of non-periodic tilings | 3 | Analytical Chemistry |
Some physical constraints are usually incorporated in the calculations. For example, all the concentrations of free reactants and species must have positive values and association constants must have positive values.
With spectrophotometric data the calculated molar absorptivity (or emissivity) values should all be positive. Most computer programs do not impose this constraint on the calculations. | 7 | Physical Chemistry |
The precise mechanism of action for thalidomide was not known until the twenty-first century, although efforts to identify thalidomide's teratogenic action generated more than 2,000 research papers and the proposal of 15 or 16 plausible mechanisms by 2000. The primary mechanism of action of thalidomide and its analogs in both their anti-cancer and teratogenic effects is now known to be as cereblon E3 ligase modulators.
Thalidomide also binds to and acts as an antagonist of the androgen receptor and hence is a nonsteroidal antiandrogen of some capacity. In accordance, it can produce gynecomastia and sexual dysfunction as side effects in men. | 4 | Stereochemistry |
A traditional version of the second law of thermodynamics states: Heat does not spontaneously flow from a colder body to a hotter body.
The second law refers to a system of matter and radiation, initially with inhomogeneities in temperature, pressure, chemical potential, and other intensive properties, that are due to internal constraints, or impermeable rigid walls, within it, or to externally imposed forces. The law observes that, when the system is isolated from the outside world and from those forces, there is a definite thermodynamic quantity, its entropy, that increases as the constraints are removed, eventually reaching a maximum value at thermodynamic equilibrium, when the inhomogeneities practically vanish. For systems that are initially far from thermodynamic equilibrium, though several have been proposed, there is known no general physical principle that determines the rates of approach to thermodynamic equilibrium, and thermodynamics does not deal with such rates. The many versions of the second law all express the general irreversibility of the transitions involved in systems approaching thermodynamic equilibrium.
In macroscopic thermodynamics, the second law is a basic observation applicable to any actual thermodynamic process; in statistical thermodynamics, the second law is postulated to be a consequence of molecular chaos. | 7 | Physical Chemistry |
Mesocrystals have unique structural features and the physical and physiochemical properties that come from that structure have made them become a subject of interest. Mesocrystals are expected to have a role in many different applications. These include heterogeneous photocatalysts, electrodes, optoelectronics, biomedical materials, and lightweight structural materials.
The properties that make mesocrystals viable for future applications are their shared properties with nanoparticulate, mesoporous, and single-crystal materials. Because mesocrystals are made up of nanoparticles, the properties of the nanoparticles themselves are, in some cases, passed to the whole mesocrystal structure. This allows for the practical application of mesocrystals because they are "potentially more stable analogues of nanoparticulate materials." High porosity is generally a quality of mesocrystals, this is the property shared with mesoporous materials. Closed, internal pores are good for thermal and dielectric insulation and the open pores then aid in absorption and could be utilized for medical delivery. Alternatively, a mesocrystal could have its pores filled and then it would be similar to a single-crystal material and have some unusual electronic and optical properties. The diversity of the properties of mesocrystals could allow them to be effectively utilized in many applications. | 7 | Physical Chemistry |
The Caspian Summit is a head of state-level meeting of the five littoral states. The fifth Caspian Summit took place on August 12, 2018, in the Kazakh port city of Aktau. The five leaders signed the Convention on the Legal Status of the Caspian Sea.
Representatives of the Caspian littoral states held a meeting in the capital of Kazakhstan on September 28, 2018, as a follow-up to the Aktau Summit. The conference was hosted by the Kazakh Ministry of Investment and Development. The participants in the meeting agreed to host an investment forum for the Caspian region every two years. | 2 | Environmental Chemistry |
The Science and Technology Council (STC) coordinates the scientific and technical activities of the IIR. The Science and Technology Council includes five distinct Sections that are in turn divided into ten Commissions. The Science and Technology Council includes:
* one President
* six Vice-presidents
* ten Commission Presidents
* one congress liaison contact person. | 7 | Physical Chemistry |
The biological pump is accompanied by a physico-chemical counterpart known as the solubility pump. This pump transports significant amounts of carbon in the form of dissolved inorganic carbon (DIC) from the ocean's surface to its interior. It involves physical and chemical processes only, and does not involve biological processes.
The solubility pump is driven by the coincidence of two processes in the ocean:
* The solubility of carbon dioxide is a strong inverse function of seawater temperature (i.e. solubility is greater in cooler water)
* The thermohaline circulation is driven by the formation of deep water at high latitudes where seawater is usually cooler and denser
Since deep water (that is, seawater in the oceans interior) is formed under the same surface conditions that promote carbon dioxide solubility, it contains a higher concentration of dissolved inorganic carbon than might be expected from average surface concentrations. Consequently, these two processes act together to pump carbon from the atmosphere into the oceans interior. One consequence of this is that when deep water upwells in warmer, equatorial latitudes, it strongly outgasses carbon dioxide to the atmosphere because of the reduced solubility of the gas. | 9 | Geochemistry |
Over the past few decades, AMMs have diversified rapidly and their design principles, properties, and characterization methods have been outlined more clearly. A major starting point for the design of AMMs is to exploit the existing modes of motion in molecules. For instance, single bonds can be visualized as axes of rotation, as can be metallocene complexes. Bending or V-like shapes can be achieved by incorporating double bonds, that can undergo cis-trans isomerization in response to certain stimuli (typically irradiation with a suitable wavelength), as seen in numerous designs consisting of stilbene and azobenzene units. Similarly, ring-opening and -closing reactions such as those seen for spiropyran and diarylethene can also produce curved shapes. Another common mode of movement is the circumrotation of rings relative to one another as observed in mechanically interlocked molecules (primarily catenanes). While this type of rotation can not be accessed beyond the molecule itself (because the rings are confined within one another), rotaxanes can overcome this as the rings can undergo translational movements along a dumbbell-like axis. Another line of AMMs consists of biomolecules such as DNA and proteins as part of their design, making use of phenomena like protein folding and unfolding.
AMM designs have diversified significantly since the early days of the field. A major route is the introduction of bistability to produce molecular switches, featuring two distinct configurations for the molecule to convert between. This has been perceived as a step forward from the original molecular shuttle which consisted of two identical sites for the ring to move between without any preference, in a manner analogous to the ring flip in an unsubstituted cyclohexane. If these two sites are different from each other in terms of features like electron density, this can give rise to weak or strong recognition sites as in biological systems — such AMMs have found applications in catalysis and drug delivery. This switching behavior has been further optimized to acquire useful work that gets lost when a typical switch returns to its original state.
Inspired by the use of kinetic control to produce work in natural processes, molecular motors are designed to have a continuous energy influx to keep them away from equilibrium to deliver work.
Various energy sources are employed to drive molecular machines today, but this was not the case during the early years of AMM development. Though the movements in AMMs were regulated relative to the random thermal motion generally seen in molecules, they could not be controlled or manipulated as desired. This led to the addition of stimuli-responsive moieties in AMM design, so that externally applied non-thermal sources of energy could drive molecular motion and hence allow control over the properties. Chemical energy (or "chemical fuels") was an attractive option at the beginning, given the broad array of reversible chemical reactions (heavily based on acid-base chemistry) to switch molecules between different states. However, this comes with the issue of practically regulating the delivery of the chemical fuel and the removal of waste generated to maintain the efficiency of the machine as in biological systems. Though some AMMs have found ways to circumvent this, more recently waste-free reactions such based on electron transfers or isomerization have gained attention (such as redox-responsive viologens). Eventually, several different forms of energy (electric, magnetic, optical and so on) have become the primary energy sources used to power AMMs, even producing autonomous systems such as light-driven motors. | 6 | Supramolecular Chemistry |
Gestonorone caproate was studied in the treatment of prostate cancer in men at a dosage of 400 mg per week by intramuscular injection but, in contrast to the case of benign prostatic hyperplasia, was found to be ineffective.
SH-834 was a combination of 90 mg estradiol valerate and 300 mg gestonorone caproate for weekly intramuscular injection that was developed by Schering in the 1960s and 1970s. It was investigated clinically as a treatment for breast cancer and was found to be effective. However, its effectiveness was found to be no better than that of an estrogen alone, and the combination was ultimately never marketed.
Gestonorone caproate was studied by Schering for use as a progestogen-only injectable contraceptive across a dose range of 2.5 to 200 mg once every one or two months but was never marketed. There is very little clinical experience of gestonorone caproate for this indication.
Gestonorone caproate has been studied in the treatment of ovarian cancer (in combination with cyclophosphamide), menstrual cycle-related mouth ulcers, and as a component of menopausal hormone therapy. | 4 | Stereochemistry |
The Middle Bronze Age settlement is smaller than its precursor and no evidence for a palace has been found. | 8 | Metallurgy |
There are two main sources of new research projects, namely ideas originating from the researchers themselves ("supply push") and those coming from customers ("demand pull"). Ideas for new processes typically originate from researchers, ideas for new products from customers, respectively customer contacts. Particularly in custom manufacturing, "demand pull" prevails industrial reality. The "new product committee" is the body of choice for evaluating new and monitoring ongoing research activities. It has the assignment to evaluate all new product ideas. It decides whether a new product idea should be taken up in research, reassesses a project at regular intervals and, last but not least decides also about the abandonment of a project, once it becomes evident that the objectives cannot be reached. In a typical project the overall responsibility for the economic and technical success lies with the project champion. He is assisted by the project manager, who is responsible for the technical success. In custom manufacturing, a typical project starts with the acceptance of the product idea, which originates mainly from business development, by the new product committee, followed by the preparation of a laboratory process, and ends with the successful completion of demonstration runs on industrial scale and the signature of a multiyear supply contract, respectively. The input from the customer is contained in the "technology package". Its main constituents are (1) reaction scheme, (2) target of project & deliverables (product, quantity, required dates, specifications), (3) list of analytical methods, (4) process development opportunities (stepwise assessment), (5) list of required reports, (6) Safety, Health and Environment (SHE) issues, (7) materials to be supplied by customer and (8) packaging & shipping information The technical part of a project usually determines its duration. Depending on the quality of the information contained in the "technology package" received from the customer and the complexity of the project as such, particularly the number of steps that have to be performed; it can be any time between 12 and 24 months. Depending on the number of researches involved, the total budget easily amounts to several million US dollars. | 0 | Organic Chemistry |
The detection of optical scattering and the gradient forces on micron sized particles was first reported in 1970 by Arthur Ashkin, a scientist working at Bell Labs. Years later, Ashkin and colleagues reported the first observation of what is now commonly referred to as an optical tweezer: a tightly focused beam of light capable of holding microscopic particles stable in three dimensions. In 2018, Ashkin was awarded the Nobel Prize in Physics for this development.
One author of this seminal 1986 paper, Steven Chu, would go on to use optical tweezing in his work on cooling and trapping neutral atoms. This research earned Chu the 1997 Nobel Prize in Physics along with Claude Cohen-Tannoudji and William D. Phillips. In an interview, Steven Chu described how Ashkin had first envisioned optical tweezing as a method for trapping atoms. Ashkin was able to trap larger particles (10 to 10,000 nanometers in diameter) but it fell to Chu to extend these techniques to the trapping of neutral atoms (0.1 nanometers in diameter) using resonant laser light and a magnetic gradient trap (cf. Magneto-optical trap).
In the late 1980s, Arthur Ashkin and Joseph M. Dziedzic demonstrated the first application of the technology to the biological sciences, using it to trap an individual tobacco mosaic virus and Escherichia coli bacterium. Throughout the 1990s and afterwards, researchers like Carlos Bustamante, James Spudich, and Steven Block pioneered the use of optical trap force spectroscopy to characterize molecular-scale biological motors. These molecular motors are ubiquitous in biology, and are responsible for locomotion and mechanical action within the cell. Optical traps allowed these biophysicists to observe the forces and dynamics of nanoscale motors at the single-molecule level; optical trap force-spectroscopy has since led to greater understanding of the stochastic nature of these force-generating molecules.
Optical tweezers have proven useful in other areas of biology as well. They are used in synthetic biology to construct tissue-like networks of artificial cells, and to fuse synthetic membranes together to initiate biochemical reactions. They are also widely employed in genetic studies and research on chromosome structure and dynamics. In 2003 the techniques of optical tweezers were applied in the field of cell sorting; by creating a large optical intensity pattern over the sample area, cells can be sorted by their intrinsic optical characteristics. Optical tweezers have also been used to probe the cytoskeleton, measure the visco-elastic properties of biopolymers, and study cell motility. A bio-molecular assay in which clusters of ligand coated nano-particles are both optically trapped and optically detected after target molecule induced clustering was proposed in 2011 and experimentally demonstrated in 2013.
Optical tweezers are also used to trap laser-cooled atoms in vacuum, mainly for applications in quantum science. Some achievements in this area include trapping of a single atom in 2001, trapping of 2D arrays of atoms in 2002, trapping of strongly interacting entangled pairs in 2010, trapping precisely assembled 2-dimensional arrays of atoms in 2016 and 3-dimensional arrays in 2018. These techniques have been used in quantum simulators to obtain programmable arrays of 196 and 256 atoms in 2021 and represent a promising platform for quantum computing.
Researchers have worked to convert optical tweezers from large, complex instruments to smaller, simpler ones, for use by those with smaller research budgets. | 1 | Biochemistry |
For a substance in solution (solute), the standard state is usually chosen as the hypothetical state it would have at the standard state molality or amount concentration but exhibiting infinite-dilution behavior (where there are no solute-solute interactions, but solute-solvent interactions are present). The reason for this unusual definition is that the behavior of a solute at the limit of infinite dilution is described by equations which are very similar to the equations for ideal gases. Hence taking infinite-dilution behavior to be the standard state allows corrections for non-ideality to be made consistently for all the different solutes. The standard state molality is , while the standard state molarity is .
Other choices are possible. For example, the use of a standard state concentration of 10 mol/L for the hydrogen ion in a real, aqueous solution is common in the field of biochemistry. In other application areas such as electrochemistry, the standard state is sometimes chosen as the actual state of the real solution at a standard concentration (often ). The activity coefficients will not transfer from convention to convention and so it is very important to know and understand what conventions were used in the construction of tables of standard thermodynamic properties before using them to describe solutions. | 7 | Physical Chemistry |
Optimal conditions for enantio-selective nucleophilic epoxidation depend on the substrate employed. Although a variety of substrates may be epoxidized using nucleophilic methods, each particular method tends to have limited substrate scope. This section describes asymmetric nucleophilic epoxidation methods, organizing them according to the constitution and configuration of the unsaturated substrate. | 0 | Organic Chemistry |
Norlevorphanol is an opioid analgesic of the morphinan family that was never marketed. It is the levo-isomer of 3-hydroxymorphinan (morphinan-3-ol). Norlevorphanol is a Schedule I Narcotic controlled substance in the United States with an ACSCN of 9634 and in 2014 it had an annual aggregate manufacturing quota of 52 grams. It is used as the hydrobromide (free base conversion ratio 0.750) and hydrochloride (0.870). | 4 | Stereochemistry |
Double Helix (2004), a novel by Nancy Werlin, is about 18-year-old Eli Samuels, who works for a famous molecular biologist named Dr. Quincy Wyatt. There is a mysterious connection between Dr. Wyatt and Elis parents, and all Eli knows about the connection is that it has something to do with his mother, who has Huntingtons disease. Because of the connection between Dr. Wyatt and the Samuels family, Elis father is strongly against Eli working there. The job is perfect, and the wages are great, but Eli cant help but notice that Dr. Wyatt seems to be a little too interested in him. Later on, as Eli continues to work in the lab, he discovers with the help of Kayla Matheson, Dr. Wyatt's supposed "niece," that he and Kayla are the product of a highly unethical eugenics experiment. | 1 | Biochemistry |
In dendritic spines, SK channels are directly coupled to NMDA receptors. In addition to being activated by calcium flow through voltage-gated calcium channels, SK channels can be activated by calcium flowing through NMDA receptors, which occurs after depolarization of the postsynaptic membrane. Experiments using apamin have shown that specifically blocking SK channels can increase learning and long-term potentiation. In addition, brain-derived neurotrophic factor (BDNF) causes the down-regulation of SK channels, which facilitates long-term potentiation. Increasing SK channel activity has the opposite effect and serves to impair learning. An increase in SK channel activity that occurs over time may be related to decreases in plasticity and memory that is seen with aging. | 1 | Biochemistry |
The sum activity of peripheral deiodinases (G, also referred to as deiodination capacity, total deiodinase activity or, if calculated from levels of thyroid hormones, as SPINA-GD) is the maximum amount of triiodothyronine produced per time-unit under conditions of substrate saturation. It is assumed to reflect the activity of deiodinases outside the central nervous system and other isolated compartments. GD is therefore expected to reflect predominantly the activity of type I deiodinase. | 1 | Biochemistry |
Phosphoramide arises from the reaction of phosphoryl chloride with ammonia. In moist air, it hydrolyzes to an ammonium salt:
It reacts with sodium hydroxide with loss of ammonia:
The related thiophosphoryl triamide compound was made from the reaction of thiophosphoryl chloride with ammonia. | 0 | Organic Chemistry |
The point of zero charge (pzc) is generally described as the pH at which the net charge of total particle surface (i.e. absorbent's surface) is equal to zero, which concept has been introduced in the studies dealt with colloidal flocculation to explain pH affecting the phenomenon.
A related concept in electrochemistry is the electrode potential at the point of zero charge. Generally, the pzc in electrochemistry is the value of the negative decimal logarithm of the activity of the potential-determining ion in the bulk fluid. The pzc is of fundamental importance in surface science. For example, in the field of environmental science, it determines how easily a substrate is able to adsorb potentially harmful ions. It also has countless applications in technology of colloids, e.g., flotation of minerals. Therefore, the pzc value has been examined in many application of adsorption to the environmental science. The pzc value is typically obtained by titrations and several titration method has been developed. Related values associated with the soil characteristics exist along with the pzc value, including zero point of charge (zpc), point of zero net charge (pznc), etc. | 7 | Physical Chemistry |
Rapamycin and rapalogs crosslink the immunophilin FK506 binding protein, tacrolimus or FKBP-12, through its methoxy group. The rapamycin-FKBP12 complex interferes with FRB domain of mTOR. Molecular interaction between FKBP12, mTOR, and rapamycin can last for about three days (72 hours). The inhibition of mTOR blocks the binding of the accessory protein raptor (regulatory-associated protein of mTOR) to mTOR, but that is necessary for downstream phosphorylation of S6K1 and 4EBP1.
As a consequence, S6K1 dephosphorylates, which reduces protein synthesis and decreases cell mortality and size. Rapamycin induces dephosphorylation of 4EBP1 as well, resulting in an increase in p27 and a decrease in cyclin D1 expression. That leads to late blockage of G1/S cell cycle. Rapamycin has shown to induce cancer cell death by stimulating autophagy or apoptosis, but the molecular mechanism of apoptosis in cancer cells has not yet been fully resolved. One suggestion of the relation between mTOR inhibition and apoptosis might be through the downstream target S6K1, which can phosphorylate BAD, a pro-apoptotic molecule, on Ser136. That reaction breaks the binding of BAD to BCL-XL and BCL2, a mitochondrial death inhibitors, resulting in inactivation of BAD and decreased cell survival. Rapamycin has also shown to induce p53-independent apoptosis in certain types of cancer. | 1 | Biochemistry |
Cyanobacteria are capable of natural genetic transformation. Natural genetic transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous DNA from its surroundings. For bacterial transformation to take place, the recipient bacteria must be in a state of competence, which may occur in nature as a response to conditions such as starvation, high cell density or exposure to DNA damaging agents. In chromosomal transformation, homologous transforming DNA can be integrated into the recipient genome by homologous recombination, and this process appears to be an adaptation for repairing DNA damage. | 5 | Photochemistry |
Gelbart's early interest in science was inspired by his time as an undergraduate researcher in the molecular spectroscopy group of William Klemperer at Harvard. As a graduate student at the University of Chicago, with his mentors Stuart A. Rice, Karl Freed, and Joshua Jortner, he developed the modern theory of non-radiative processes ("radiationless transitions") in molecular photophysics. He was a US National Science Foundation/NATO Postdoctoral Fellow at the, University of Paris in 1971, and a Miller Institute Postdoctoral Fellow at UC Berkeley in 1972, during which time he switched fields and formulated a general theory of collision-induced optical properties of simple fluids.
He was appointed Assistant Professor of Chemistry, at UC Berkeley in 1972, continuing his researches on the quantum mechanical theory of molecular spectroscopy and on the statistical mechanical theory of intermolecular and multiple light scattering in liquids away from and near their critical points. He moved to UCLA as Associate Professor of Chemistry in 1975, and was promoted to full Professor in 1979 and to Distinguished Professor in 1999. He was Chair of the Department of Chemistry and Biochemistry at UCLA from 2000-2004 and has been a member of UCLA's California NanoSystems Institute since 2004 and of its Molecular Biology Institute from 2008.
At UCLA he became a leader in the then-emerging fields of "complex fluids" and " soft matter physics". Shortly after moving there he began a 40-year collaboration with Avinoam Ben-Shaul on statistical-thermodynamic models of liquid crystal systems, polymer and polyelectrolyte (in particular, DNA) solutions, and colloidal suspensions, and on the self-assembly theory of micelles, surfactant monolayers, and biological membranes.
During a sabbatical year in 1998-99 at the Institute for Theoretical Physics in UC Santa Barbara and at the Curie Institute in Paris, Gelbart became deeply intrigued by viruses and over the course of the next several years, with his UCLA colleague Charles Knobler, established a laboratory to investigate simple viruses outside their hosts and isolated in test tubes. Early results included: the first measurement of pressure inside DNA viruses, establishing that it is as high as tens of atmospheres depending on genome length and ambient salt concentrations; and the demonstration that capsid proteins from certain viruses are capable of complete in vitro packaging of a broad range of lengths of heterologous RNA. This work, along with that of several other groups in the United States and Europe, helped launch the field of "physical virology". Most recently he moved his viruses from test tubes to host cells, and from wildtype viruses to artificial viruses and virus-like particles, engineered for purposes of delivering self-replicating RNA genes, RNA vaccines, and therapeutic microRNA to targeted mammalian cells. | 7 | Physical Chemistry |
As in any technology that has long been conducted on the multi-million ton per year scale, flotation technologies have the potential to threaten the environment beyond the disruption caused by mining. Froth flotation employs a host of organic chemicals and relies upon elaborate machinery. Some of the chemicals (cyanide) are acutely toxic but hydrolyze to innocuous products. Naturally occurring fatty acids are widely used. Tailings and effluents are contained in lined ponds. Froth flotation is "poised for increased activity due to their potential usefulness in environmental site cleanup operations" including recycling of plastics and metals, not to mention water treatment. | 8 | Metallurgy |
The EQCM sensitivity factor K can be calculated by combing the electrochemical cell measured charge density and QCM measured frequency shift. The sensitivity factor is only valid when the mass change on the electrode is homogenous. Otherwise, K is taken as the average sensitivity factor of the EQCM.
where is the measured frequency shift (Hz), S is the quartz crystal active area (cm), ρ is the density of quartz crystal, is the quartz crystal shear modulus and is the fundamental quartz crystal frequency. K is the intrinsic sensitivity factor of the EQCM.
In a certain electrolyte solution, a metal film will deposited on the working electrode, which is the QCM sensor surface of QCM.
The charge density () is involved in the electro-reduction of metal ions at a constant current , in a period of time ().
The active areal mass density is calculated by
where is the atomic weight of deposited metal, z is the electrovalency, and F is the Faraday constant.
The experimental sensitivity of the EQCM is calculated by combing and . | 7 | Physical Chemistry |
Thermocouples ideally should be very simple measurement devices, with each type being characterized by a precise curve, independent of any other details.
In reality, thermocouples are affected by issues such as alloy manufacturing uncertainties, aging effects, and circuit design mistakes/misunderstandings. | 8 | Metallurgy |
International law has prohibited the use of chemical weapons since 1899, under the Hague Convention: Article 23 of the Regulations Respecting the Laws and Customs of War on Land adopted by the First Hague Conference "especially" prohibited employing "poison and poisoned arms". A separate declaration stated that in any war between signatory powers, the parties would abstain from using projectiles "the object of which is the diffusion of asphyxiating or deleterious gases".
The Washington Naval Treaty, signed February 6, 1922, also known as the Five-Power Treaty, aimed at banning chemical warfare but did not succeed because France rejected it. The subsequent failure to include chemical warfare has contributed to the resultant increase in stockpiles.
The Geneva Protocol, officially known as the Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or other Gases, and of Bacteriological Methods of Warfare, is an International treaty prohibiting the use of chemical and biological weapons in international armed conflicts. It was signed at Geneva June 17, 1925, and entered into force on February 8, 1928. 133 nations are listed as state parties to the treaty. Ukraine is the newest signatory, acceding August 7, 2003.
This treaty states that chemical and biological weapons are "justly condemned by the general opinion of the civilised world". And while the treaty prohibits the use of chemical and biological weapons, it does not address the production, storage, or transfer of these weapons. Treaties that followed the Geneva Protocol did address those omissions and have been enacted. | 1 | Biochemistry |
The adsorption of gases and solutes is usually described through isotherms, that is, the amount of adsorbate on the adsorbent as a function of its pressure (if gas) or concentration (for liquid phase solutes) at constant temperature. The quantity adsorbed is nearly always normalized by the mass of the adsorbent to allow comparison of different materials. To date, 15 different isotherm models have been developed. | 7 | Physical Chemistry |
An MDC is constructed similarly to a microbial fuel cell by including two
chambers with two electrodes, an anode and a cathode, in addition to both a third chamber separated by an anion exchange membrane (AEM) and cation exchange membrane (CEM), and a peripheral, external circuit that is responsible for aerobic and anaerobic processes at each respective electrode. Organic matter from the sludge proliferates in the anode chamber and creates a biofilm that generates an electric current. The biofilm thus begins to oxidize the pollutants in the sludge by strictly adhering to the anode, freeing both electrons and protons from the bio-sludge, creating a current of atoms that are collected by the electrodes through circuit transportation. Electrical current is produced by the potential difference generated between the anode and cathode due to the aerobic nature of the cathode chamber. | 7 | Physical Chemistry |
In plants and some algae, another enzyme, RuBisCO activase (Rca, , ), is required to allow the rapid formation of the critical carbamate in the active site of RuBisCO. This is required because ribulose 1,5-bisphosphate (RuBP) binds more strongly to the active sites of RuBisCO when excess carbamate is present, preventing processes from moving forward. In the light, RuBisCO activase promotes the release of the inhibitory (or — in some views — storage) RuBP from the catalytic sites of RuBisCO. Activase is also required in some plants (e.g., tobacco and many beans) because, in darkness, RuBisCO is inhibited (or protected from hydrolysis) by a competitive inhibitor synthesized by these plants, a substrate analog 2-carboxy-D-arabitinol 1-phosphate (CA1P). CA1P binds tightly to the active site of carbamylated RuBisCO and inhibits catalytic activity to an even greater extent. CA1P has also been shown to keep RuBisCO in a conformation that is protected from proteolysis. In the light, RuBisCO activase also promotes the release of CA1P from the catalytic sites. After the CA1P is released from RuBisCO, it is rapidly converted to a non-inhibitory form by a light-activated CA1P-phosphatase. Even without these strong inhibitors, once every several hundred reactions, the normal reactions with carbon dioxide or oxygen are not completed; other inhibitory substrate analogs are still formed in the active site. Once again, RuBisCO activase can promote the release of these analogs from the catalytic sites and maintain the enzyme in a catalytically active form. However, at high temperatures, RuBisCO activase aggregates and can no longer activate RuBisCO. This contributes to the decreased carboxylating capacity observed during heat stress. | 5 | Photochemistry |
The first example of ring-closing metathesis was reported by Dider Villemin in 1980 when he synthesized an Exaltolide precursor using a WCl/MeSn catalyzed metathesis cyclization in 60-65% yield depending on ring size (A). In the following months, Jiro Tsuji reported a similar metathesis reaction describing the preparation of a macrolide catalyzed by WCl and dimethyltitanocene (CpTiMe) in a modest 17.9% yield (B). Tsuji describes the olefin metathesis reaction as “…potentially useful in organic synthesis” and addresses the need for the development of a more versatile catalyst to tolerate various functional groups.
In 1987, Siegfried Warwel and Hans Kaitker published a synthesis of symmetric macrocycles through a cross-metathesis dimerization of starting cycloolefins to afford C, C, and C dienes in 58-74% yield, as well as C in 30% yield, using ReO on AlO and MeSn for catalyst activation.
After a decade since its initial discovery, Grubbs and Fu published two influential reports in 1992 detailing the synthesis of O- and N- heterocycles via RCM utilizing Schrock’s molybdenum alkylidene catalysts, which had proven more robust and functional group tolerant than the tungsten chloride catalysts. The synthetic route allowed access to dihydropyrans in high yield (89-93%) from readily available starting materials. In addition, synthesis of substituted pyrrolines, tetrahydropyridines, and amides were illustrated in modest to high yield (73-89% ). The driving force for the cyclization reaction was attributed to entropic favorability by forming two molecules per one molecule of starting material. The loss of the second molecule, ethylene, a highly volatile gas, drives the reaction in the forward direction according to Le Châtelier's principle.
In 1993, Grubbs and others not only published a report on carbocycle synthesis using a molybdenum catalyst, but also detailed the initial use of a novel ruthenium carbene complex for metathesis reactions, which later became a popular catalyst due to its extraordinary utility. The ruthenium catalysts are not sensitive to air and moisture, unlike the molybdenum catalysts. The ruthenium catalysts, known better as the Grubbs Catalysts, as well as molybdenum catalysts, or Schrock’s Catalysts, are still used today for many metathesis reactions, including RCM. Overall, it was shown that metal-catalyzed RCM reactions were very effective in C-C bond forming reactions, and would prove of great importance in organic synthesis, chemical biology, materials science, and various other fields to access a wide variety of unsaturated and highly functionalized cyclic analogues. | 0 | Organic Chemistry |
Ostromislensky was born in Oryol, Russia to a family of a nobleman, a poruchik of elite corps. He received his education first at the Moscow cadet corps and then, from 1898 to 1902 at the Moscow Technical School. After graduation, in April 1902, Ostromislensky went to Germany, and enrolled to the Technical School in Karlsruhe. There, he specialized in physical chemistry, organic chemistry and electrochemistry. In July 1906 he returned to Russia and in February 1907 was hired at the Moscow State University (MSU) as an assistant in the laboratory of inorganic and physical chemistry, led by Professor Sabaneev. In 1909, Ostromislensky became a privatdozent of MSU. During his work at MSU, he actively collaborated with Professor L. Chugayev, who headed the laboratory of organic and general chemistry, and started his work on synthetic rubber.
In 1912, after an internal quarrel, Ostromislensky resigned from the MSU. He continued his work on rubber (1912–1917) at Bogatyr (Russian: Богатырь), which was Russia's main rubber company. The company director showed great interest in the emerging synthetic rubber and readily financed the work of Ostromislensky, who was the pioneer of synthetic rubber in Russia.
In 1905, Ostromislensky started reporting his research on the polymerization of dienes and on the synthesis of the starting monomers for synthetic rubber. He had patented more than 20 ways to produce butadiene (buta-1,3-diene), which were implemented industrially in the Soviet Union. The butadiene production method, which was based on aldol condensation of acetaldehyde (1905), was also implemented on industrial scale in Germany in 1936. Another method was based on passing vapors of ethanol and acetaldehyde at 440–460 °C over aluminium oxide (1915) and received industrial use in 1942–1943 in the United States. In 1915, Ostromislensky also synthesized isoprene via pyrolysis of turpentine and polymerized it using light. Ostromislensky pioneered the studies of non-sulfur activators of vulcanization of rubber. He also proposed organic additions to rubber, such as toluidine and naphthylamine, in order to improve its properties. Those additives were later exploited by US companies, such as Union Carbide.
In 1913, Ostromislensky published a book on "Rubber and its analogs", which was the first Russian textbook on chemistry and technology of rubber. It summarized most available bibliography on the subject, including foreign patents which were inaccessible to most Russian readers. The book also described 16 original methods of industrial synthesis and polymerization of dialkenes (alkadienes).
In 1910s, Ostromislensky also started shifting his attention toward biochemical, immunochemical and pharmaceutical research, as indicated by that he had two doctoral degrees from University of Zurich, in philosophy and medicine. In 1913, he started his own company named "private chemical and bacteriological laboratory". There he performed a number of studies on the immunological specificity and chemical nature of antibodies and antigens and published the results in the Journal of Physical and Chemical Society in 1915. Ostromislensky investigated the possibility of synthesis of antibodies in vitro and proposed a theory of antibody synthesis, which is regarded as one of the first versions of the so-called matrix theory of antibody synthesis. The theory had strong influence on the development of immunochemistry, but was later proven incorrect. Medical interests of Ostromislensky are also illustrated by his essay on "dream in humans and animals", which examined the toxicological, immunological and physiological aspects of a dream. He considered sleep as a process of self-poisoning by some toxin, which shortens the lifetime.
Between 1918 and 1920, Ostromislensky headed a chemical therapeutic laboratory of the Chemical-Pharmaceutical Institute in Moscow. There he studied the structure and properties of the popular foreign drug Salvarsan and developed the method of manufacturing a domestic analogue called Arsol. Arsol was based on relatively cheap production of colloidal arsenic that was important in the time of the Civil Wars and economic crisis in Russia. | 0 | Organic Chemistry |
Chairman, Gordon Research Conference on Analytical Chemistry; James B. Himes Merit Award of the Chicago Chromatography Discussion Group; M.S. Tswett Award and Medal in Chromatography; American Chemical Society Award in Chromatography; ISCO Award in Biochemical Instrumentation; Eastern Analytical Symposium Award in Chromatography; Chemical Instrumentation Award of the American Chemical Society; Distinguished Faculty Research Lecture, Indiana University. | 3 | Analytical Chemistry |
The approximate knife advance rate can be determined for a set of operating conditions using table 6 below. The table indicates the number of hours that the filter can operate in a one-inch pre coat cake; the required condition is that the advance blade must be at a constant position. This method can be used to check for optimum operation range.
If the operating parameter is higher than the optimum range, the user can reduce the knife advance rate and use a tighter grade of filter aid. This will result in less filter aid used (lower capital cost) and less filter aid being removed (lower disposal cost). However, if the operating parameter is lower than the optimum range, the user can increase the knife advanced rate (more production) and decrease the drum speed for less filter air usage (reduced operating cost). | 3 | Analytical Chemistry |
A solution of 1.485 g 1,10-phenanthroline monohydrate is added to a solution of 695 mg FeSO·7HO in distilled water, and the resulting red solution is diluted to 100 mL. | 9 | Geochemistry |
The word solder comes from the Middle English word , via Old French and , from the Latin , meaning "to make solid". | 8 | Metallurgy |
The compounds are pale-yellow viscous liquids. They are hydrophobic, with low water solubilities: 0.0027–0.42 ng/L for Aroclors brand, but they have high solubilities in most organic solvents, oils, and fats. They have low vapor pressures at room temperature. They have dielectric constants of 2.5–2.7, very high thermal conductivity, and high flash points (from 170 to 380 °C).
The density varies from 1.182 to 1.566 g/cm. Other physical and chemical properties vary widely across the class. As the degree of chlorination increases, melting point and lipophilicity increase, and vapour pressure and water solubility decrease.
PCBs do not easily break down or degrade, which made them attractive for industries. PCB mixtures are resistant to acids, bases, oxidation, hydrolysis, and temperature change. They can generate extremely toxic dibenzodioxins and dibenzofurans through partial oxidation. Intentional degradation as a treatment of unwanted PCBs generally requires high heat or catalysis (see Methods of destruction below).
PCBs readily penetrate skin, PVC (polyvinyl chloride), and latex (natural rubber). PCB-resistant materials include Viton, polyethylene, polyvinyl acetate (PVA), polytetrafluoroethylene (PTFE), butyl rubber, nitrile rubber, and Neoprene. | 2 | Environmental Chemistry |
It was first produced in 1878 by the German chemists August Michaelis (1847–1916) and Wilhelm La Coste (1854–1885). It is prepared by the reduction of diphenylarsinic acid with sulfur dioxide. An idealized equation is shown:
:PhAsOH + SO + HCl → PhAsCl + HSO
The process adopted by Edgewood Arsenal, the "sodium process", for the production of DA for chemical warfare purposes employed a reaction between chlorobenzene and arsenic trichloride in the presence of sodium.
The German process, used in the first war, applied at Hochstam-Main, used the Sandmeyer reaction between phenyldiazonium chloride and sodium arsenite. The acidified product was reduced and then neutralized. The salt was condensed again by the Sandmeyer reaction and reduced again, the final product was then acidified, resulting in DA.
The structure consists of pyramidal As centre. The As-Cl distance is 2.26 A and the Cl-As-C and C-As-C angles are 96 and 105°, respectively. | 1 | Biochemistry |
The compound was protected by a patent which was assigned to the German pharmaceutical company Hoechst AG (since merged into Aventis) on 29 October 1991. The patent was scheduled to expire on 29 October 2008. On 11 September 2007, in an appeal by the Indian company Lupin Ltd., the United States Court of Appeals for the Federal Circuit reversed a district court trial verdict and found that Aventis's patent on ramipril was invalid for "obviousness", opening this drug to generic manufacturers. | 4 | Stereochemistry |
Indirect calorimetry calculates heat that living organisms produce by measuring either their production of carbon dioxide and nitrogen waste (frequently ammonia in aquatic organisms, or urea in terrestrial ones), or from their consumption of oxygen. Indirect calorimetry estimates the type and rate of substrate utilization and energy metabolism in vivo starting from gas exchange measurements (oxygen consumption and carbon dioxide production during rest and steady-state exercise). This technique provides unique information, is noninvasive, and can be advantageously combined with other experimental methods to investigate numerous aspects of nutrient assimilation, thermogenesis, the energetics of physical exercise, and the pathogenesis of metabolic diseases. | 1 | Biochemistry |
Except in acid or siliceous igneous rocks containing greater than 66% of silica, known as felsic rocks, quartz is not abundant in igneous rocks. In basic rocks (containing 20% of silica or less) it is rare for them to contain as much silicon, these are referred to as mafic rocks. If magnesium and iron are above average while silica is low, olivine may be expected; where silica is present in greater quantity over ferromagnesian minerals, such as augite, hornblende, enstatite or biotite, occur rather than olivine. Unless potash is high and silica relatively low, leucite will not be present, for leucite does not occur with free quartz. Nepheline, likewise, is usually found in rocks with much soda and comparatively little silica. With high alkalis, soda-bearing pyroxenes and amphiboles may be present. The lower the percentage of silica and alkali's, the greater is the prevalence of plagioclase feldspar as contracted with soda or potash feldspar.
Earths crust is composed of 90% silicate minerals and their abundance in the Earth is as follows: plagioclase feldspar (39%), alkali feldspar (12%), quartz (12%), pyroxene (11%), amphiboles (5%), micas (5%), clay minerals (5%); the remaining silicate minerals make up another 3% of Earths crust. Only 8% of the Earth is composed of non-silicate minerals such as carbonates, oxides, and sulfides.
The other determining factor, namely the physical conditions attending consolidation, plays, on the whole, a smaller part, yet is by no means negligible. Certain minerals are practically confined to deep-seated intrusive rocks, e.g., microcline, muscovite, diallage. Leucite is very rare in plutonic masses; many minerals have special peculiarities in microscopic character according to whether they crystallized in-depth or near the surface, e.g., hypersthene, orthoclase, quartz. There are some curious instances of rocks having the same chemical composition, but consisting of entirely different minerals, e.g., the hornblendite of Gran, in Norway, which contains only hornblende, has the same composition as some of the camptonites of the same locality that contain feldspar and hornblende of a different variety. In this connection, we may repeat what has been said above about the corrosion of porphyritic minerals in igneous rocks. In rhyolites and trachytes, early crystals of hornblende and biotite may be found in great numbers partially converted into augite and magnetite. Hornblende and biotite were stable under the pressures and other conditions below the surface, but unstable at higher levels. In the ground-mass of these rocks, augite is almost universally present. But the plutonic representatives of the same magma, granite, and syenite contain biotite and hornblende far more commonly than augite. | 9 | Geochemistry |
Shihwa Bay is a costal resevior created in 1994 to supply surrounding agricultural lands with water, and act as a run-off lake for nearby industrial plants. The Bay was made without much enviornmental consideration, and by 1999, water quality had a significant drop. This drop in water quality is attributed to the bay not having enough circulation or new water flow to accomadate for the domestic and industrial waste being dumped. In response, the Korean government set up a pollution management system within the bay, and has a gate system that allows the Bay to mix with water in the sea. Shihwa Bay is also experiencing an imbalance of phosphorus to nitrogen, but also large sources of Ammonium. | 9 | Geochemistry |
As stated previously, two diastereomers will not have identical chemical properties. This knowledge is harnessed in chiral synthesis to separate a mixture of enantiomers. This is the principle behind chiral resolution. After preparing the diastereomers, they are separated by chromatography or recrystallization. Note also the example of the stereochemistry of ketonization of enols and enolates. | 4 | Stereochemistry |
* Qualitative Chemical Analysis: Principles and methods, 1931
* General Chemistry for Colleges, 1935
* The Structure and properties of Matter, 1935
* An Introduction to College Chemistry, 1937 | 3 | Analytical Chemistry |
Some fluorescent chemicals exhibit significant fluorescent quenching when exposed to increasing temperatures. This effect has been used to measure and examine the thermogenic properties of mitochondria. This involves placing mitochondria-targeting thermosensitive fluorophores inside cells, which naturally localise inside the mitochondria due to the inner mitochondrial membrane matrix-faces negative charge (as the fluorophores are cationic). The temperature of these fluorophores is inversely proportional to their fluorescence emission, and thus by measuring the fluorescent output, the temperature of actively-respiring mitochondria can be deduced. The fluorophores used are typically lipophilic cations derived from Rhodamine-B, such as ThermoFishers MitoTracker probes. This technique has contributed significantly to the general scientific consensus that mitochondria are physiologically maintained at close to 50 ˚C, more than 10˚C above the rest of the cell.
The inverse relationship between fluorescence and temperature can be explained by the change in the number of atomic collisions in the fluorophore's environment, depending on the kinetic energy. Collisions promote radiationless decay and loss of extra energy as heat, so more collisions or more forceful collisions will promote radiationless decay and reduce fluorescence emission.
This temperature-measurement technique is, however, limited. These cationic fluorophores are heavily influenced by the charge of the inner mitochondrial membrane matrix-face, dependent on the cell type. For example, the thermosensitive fluorophore MTY (MitoTracker Yellow) shows a sudden and drastic drop in fluorescence after the addition of oligomycin (an ATP synthase inhibitor) to the mitochondria of human primary fibroblasts. This would suggest a sharp increase in mitochondrial temperature but is, in reality, explained by the hyperpolarisation of the mitochondrial inner membrane by oligomycin - leading to the breakdown of the positively-charged MTY fluorophore. | 1 | Biochemistry |
Metal dusting is "a catastrophic form of corrosion that occurs when susceptible materials are exposed to environments with high carbon activities." The corrosion manifests itself as a break-up of bulk metal to metal powder. The suspected mechanism is firstly the deposition of a graphite layer on the surface of the metal, usually from carbon monoxide (CO) in the vapour phase. This graphite layer is then thought to form metastable MC species (where M is the metal), which migrate away from the metal surface. However, in some regimes no MC species are observed indicating a direct transfer of metal atoms into the graphite layer.
The temperatures normally associated with metal dusting are high (300–850 °C). From a general understanding of chemistry, it can be deduced that at lower temperatures, the rate of reaction to form the metastable MC species is too low to be significant, and at much higher temperatures the graphite layer is unstable and so CO deposition does not occur (at least to any appreciable degree).
Very briefly, there are several proposed methods for prevention or reduction of metal dusting; the most common seem to be aluminide coatings, alloying with copper and addition of steam.
There is a significant amount of literature in existence that describes proposed mechanisms, prevention methods etc. There is also a good summary of metal dusting and some prevention methods in Corrosion by Carbon and Nitrogen - Metal Dusting, Carburisation and Nitridation | 8 | Metallurgy |
The table below lists some of the properties of the BTX aromatic hydrocarbons, all of which are liquids at typical room conditions: | 7 | Physical Chemistry |
In a "relaxed" double-helical segment of B-DNA, the two strands twist around the helical axis once every 10.4–10.5 base pairs of sequence. Adding or subtracting twists, as some enzymes do, imposes strain. If a DNA segment under twist strain is closed into a circle by joining its two ends, and then allowed to move freely, it takes on different shape, such as a figure-eight. This shape is referred to as a supercoil. (The noun form "supercoil" is often used when describing DNA topology.)
The DNA of most organisms is usually negatively supercoiled. It becomes temporarily positively supercoiled when it is being replicated or transcribed. These processes are inhibited (regulated) if it is not promptly relaxed. The simplest shape of a supercoil is a figure eight; a circular DNA strand assumes this shape to accommodate more or few helical twists. The two lobes of the figure eight will appear rotated either clockwise or counterclockwise with respect to one another, depending on whether the helix is over- or underwound. For each additional helical twist being accommodated, the lobes will show one more rotation about their axis.
Lobal contortions of a circular DNA, such as the rotation of the figure-eight lobes above, are referred to as writhe. The above example illustrates that twist and writhe are interconvertible. Supercoiling can be represented mathematically by the sum of twist and writhe. The twist is the number of helical turns in the DNA and the writhe is the number of times the double helix crosses over on itself (these are the supercoils). Extra helical twists are positive and lead to positive supercoiling, while subtractive twisting causes negative supercoiling. Many topoisomerase enzymes sense supercoiling and either generate or dissipate it as they change DNA topology.
In part because chromosomes may be very large, segments in the middle may act as if their ends are anchored. As a result, they may be unable to distribute excess twist to the rest of the chromosome or to absorb twist to recover from underwinding—the segments may become supercoiled, in other words. In response to supercoiling, they will assume an amount of writhe, just as if their ends were joined.
Supercoiled DNA forms two structures; a plectoneme or a toroid, or a combination of both. A negatively supercoiled DNA molecule will produce either a one-start left-handed helix, the toroid, or a two-start right-handed helix with terminal loops, the plectoneme. Plectonemes are typically more common in nature, and this is the shape most bacterial plasmids will take. For larger molecules it is common for hybrid structures to form – a loop on a toroid can extend into a plectoneme. If all the loops on a toroid extend then it becomes a branch point in the plectonemic structure. DNA supercoiling is important for DNA packaging within all cells, and seems to also play a role in gene expression. | 1 | Biochemistry |
Solubility values of organic acids, bases, and ampholytes of pharmaceutical interest may be obtained by a process called "Chasing equilibrium solubility". In this procedure, a quantity of substance is first dissolved at a pH where it exists predominantly in its ionized form and then a precipitate of the neutral (un-ionized) species is formed by changing the pH. Subsequently, the rate of change of pH due to precipitation or dissolution is monitored and strong acid and base titrant are added to adjust the pH to discover the equilibrium conditions when the two rates are equal. The advantage of this method is that it is relatively fast as the quantity of precipitate formed is quite small. However, the performance of the method may be affected by the formation supersaturated solutions. | 7 | Physical Chemistry |
In Australia, modafinil is considered to be a Schedule 4 prescription-only medicine. This means that it is a drug with a perceived low potential for abuse and low risk of dependence; still, the use of Schedule 4 drugs in Australia is restricted to those who have a valid prescription from a medical practitioner; import from abroad is illegal. | 4 | Stereochemistry |
The volatilome (sometimes termed volatolome or volatome) contains all of the volatile metabolites as well as other volatile organic and inorganic compounds that originate from an organism, super-organism, or ecosystem. The atmosphere of a living planet could be regarded as its volatilome. While all volatile metabolites in the volatilome can be thought of as a subset of the metabolome, the volatilome also contains exogenously derived compounds that do not derive from metabolic processes (e.g. environmental contaminants), therefore the volatilome can be regarded as a distinct entity from the metabolome. The volatilome is a component of the aura of molecules and microbes (the microbial cloud) that surrounds all organisms. | 1 | Biochemistry |
Heterotrimeric G protein complexes are composed of three distinct protein subunits named alpha (α), beta (β) and gamma (γ) subunits. The alpha subunits contain the GTP binding/GTPase domain flanked by long regulatory regions, while the beta and gamma subunits form a stable dimeric complex referred to as the beta-gamma complex. When activated, a heterotrimeric G protein dissociates into activated, GTP-bound alpha subunit and separate beta-gamma subunit, each of which can perform distinct signaling roles. The α and γ subunit are modified by lipid anchors to increase their association with the inner leaflet of the plasma membrane.
Heterotrimeric G proteins act as the transducers of G protein-coupled receptors, coupling receptor activation to downstream signaling effectors and second messengers. In unstimulated cells, heterotrimeric G proteins are assembled as the GDP bound, inactive trimer (G-GDP-G complex). Upon receptor activation, the activated receptor intracellular domain acts as GEF to release GDP from the G protein complex and to promote binding of GTP in its place. The GTP-bound complex undergoes an activating conformation shift that dissociates it from the receptor and also breaks the complex into its component G protein alpha and beta-gamma subunit components. While these activated G protein subunits are now free to activate their effectors, the active receptor is likewise free to activate additional G proteins – this allows catalytic activation and amplification where one receptor may activate many G proteins.
G protein signaling is terminated by hydrolysis of bound GTP to bound GDP. This can occur through the intrinsic GTPase activity of the α subunit, or be accelerated by separate regulatory proteins that act as GTPase-activating proteins (GAPs), such as members of the Regulator of G protein signaling (RGS) family). The speed of the hydrolysis reaction works as an internal clock limiting the length of the signal. Once G is returned to being GDP bound, the two parts of the heterotrimer re-associate to the original, inactive state.
The heterotrimeric G proteins can be classified by sequence homology of the α unit and by their functional targets into four families: G family, G family, G family and G family. Each of these G protein families contains multiple members, such that the mammals have 16 distinct -subunit genes. The G and G are likewise composed of many members, increasing heterotrimer structural and functional diversity. Among the target molecules of the specific G proteins are the second messenger-generating enzymes adenylyl cyclase and phospholipase C, as well as various ion channels. | 1 | Biochemistry |
An eluotropic series, which orders solvents by how much they move compounds, can help in selecting a mobile phase. Solvents are also divided into solvent selectivity groups. Using solvents with different elution strengths or different selectivity groups can often give very different results. While single-solvent mobile phases can sometimes give good separation, some cases may require solvent mixtures.
In normal-phase TLC, the most common solvent mixtures include ethyl acetate/hexanes (EtOAc/Hex) for less-polar compounds and methanol/dichloromethane (MeOH/DCM) for more polar compounds. Different solvent mixtures and solvent ratios can help give better separation. In reverse-phase TLC, solvent mixtures are typically water with a less-polar solvent: Typical choices are water with tetrahydrofuran (THF), acetonitrile (ACN), or methanol. | 3 | Analytical Chemistry |
The Museum of the History of Donetsk Metallurgical Plant was created in 1955, and it is located in the Technology House. The idea for its creation came from the director of the DMZ, Pavel Vasilyevich Andreev. The museum consists of more than 3000 exhibits. In 1971 the museum was awarded the title of national museum. Among the exhibits are certificates for products manufactured by the plant in 1900, original photographs of the Nizhny Novgorod industrial exhibition in 1896 and others.
On February 16, 2012, a branch of the Museum of the History of the Donetsk Metallurgical Plant was opened in the lower floor of the St. Ignatius Church, which is dedicated to Ignatius of Mariupol. | 8 | Metallurgy |
There are six steps in the mechanism of TFIIB action in the formation of the PIC and transcription initiation:
#RNA polymerase II is recruited to DNA through the TFIIB B core and B ribbon.
#RNA polymerase II unwinds DNA, aided by the TFIIB B linker and B reader (open complex formation).
#RNA polymerase II selects a transcription start site, aided by the TFIIB B reader.
#RNA polymerase II forms the first phosphodiester bond.
#RNA polymerase II produces short abortive transcripts due to clashes between nascent RNA and the TFIIB B reader loop.
#Extension of nascent RNA to 12-13 nucleotides leads to ejection of TFIIB due to further clashes with TFIIB. | 1 | Biochemistry |
Retention uniformity, or R, is a concept in thin layer chromatography. It is designed for the quantitative measurement of equal-spreading of the spots on the chromatographic plate and is one of the Chromatographic response functions. | 3 | Analytical Chemistry |
Eutrophication is a common phenomenon in coastal waters, where nitrogenous sources are the main culprit. In coastal waters, nitrogen is commonly the key limiting nutrient of marine waters (unlike the freshwater systems where phosphorus is often the limiting nutrient). Therefore, nitrogen levels are more important than phosphorus levels for understanding and controlling eutrophication problems in salt water. Estuaries, as the interface between freshwater and saltwater, can be both phosphorus and nitrogen limited and commonly exhibit symptoms of eutrophication. Eutrophication in estuaries often results in bottom water hypoxia or anoxia, leading to fish kills and habitat degradation. Upwelling in coastal systems also promotes increased productivity by conveying deep, nutrient-rich waters to the surface, where the nutrients can be assimilated by algae.
Examples of anthropogenic sources of nitrogen-rich pollution to coastal waters include sea cage fish farming and discharges of ammonia from the production of coke from coal. In addition to runoff from land, wastes from fish farming and industrial ammonia discharges, atmospheric fixed nitrogen can be an important nutrient source in the open ocean. This could account for around one third of the ocean's external (non-recycled) nitrogen supply, and up to 3% of the annual new marine biological production.
Coastal waters embrace a wide range of marine habitats from enclosed estuaries to the open waters of the continental shelf. Phytoplankton productivity in coastal waters depends on both nutrient and light supply, with the latter an important limiting factor in waters near to shore where sediment resuspension often limits light penetration.
Nutrients are supplied to coastal waters from land via river and groundwater and also via the atmosphere. There is also an important source from the open ocean, via mixing of relatively nutrient rich deep ocean waters. Nutrient inputs from the ocean are little changed by human activity, although climate change may alter the water flows across the shelf break. By contrast, inputs from land to coastal zones of the nutrients nitrogen and phosphorus have been increased by human activity globally. The extent of increases varies greatly from place to place depending on human activities in the catchments. A third key nutrient, dissolved silicon, is derived primarily from sediment weathering to rivers and from offshore and is therefore much less affected by human activity. | 2 | Environmental Chemistry |
Although the native biological role of APP is of obvious interest to Alzheimers research, thorough understanding has remained elusive. Experimental models of Alzheimers disease are commonly used by researchers to gain better understandings about the biological function of APP in disease pathology and progression. | 1 | Biochemistry |
Metals such as aluminum naturally form a passivating oxide layer which provides moderate protection against corrosion. The layer is strongly adherent to the metal surface, and it will regrow quickly if scratched off. In conventional anodizing, this layer of oxide is grown on the surface of the metal by the application of electrical potential, while the part is immersed in an acidic electrolyte.
In plasma electrolytic oxidation, higher potentials are applied. For example, in the plasma electrolytic oxidation of aluminum, at least 200 V must be applied. This locally exceeds the dielectric breakdown potential of the growing oxide film, and discharges occur. These discharges result in localized plasma reactions, with conditions of high temperature and pressure which modify the growing oxide. Processes include melting, melt-flow, re-solidification, sintering and densification of the growing oxide. One of the most significant effects, is that the oxide is partially converted from amorphous alumina into crystalline forms such as corundum (α-AlO) which is much harder. As a result, mechanical properties such as wear resistance and toughness are enhanced. | 8 | Metallurgy |
The thermal noise on the nanoscale is so great that moving in a particular direction is as difficult as “walking in a hurricane” or “swimming in molasses”. The theoretical operation of the Brownian motor can be explained by ratchet theory, wherein strong random thermal fluctuations are allowed to move the particle in the desired direction, while energy is expended to counteract forces that would produce motion in the opposite direction. This motion can be both linear and rotational. In the biological sense and in the extent to which this phenomenon appears in nature, this exists as chemical energy is sourced from the molecule adenosine triphosphate (ATP).
The Brownian ratchet is an apparent perpetual motion machine that appears to violate the Second Law of Thermodynamics, but was later debunked upon more detailed analysis by Richard Feynman and other physicists. The difference between real Brownian motors and fictional Brownian ratchets is that only in Brownian motors is there an input of energy in order to provide the necessary force to hold the motor in place to counteract the thermal noise that try to move the motor in the opposite direction.
Because Brownian motors rely on the random nature of thermal noise to achieve directed motion, they are stochastic in nature, in that they can be analysed statistically but not predicted precisely. | 7 | Physical Chemistry |
Concern about the increasing discoveries of bay pollution problems, and of the institutional challenges of organizing bay restoration programs over a large geographical area, led to Congress directing the US Environmental Protection Agency (EPA) to take a greater role in studying the scientific and technical aspects of the problems beginning in the late 1970s. The agency conducted its research over a seven-year period and published a major report in 1983. The report stated that the bay was an "ecosystem in decline" and cited numerous instances of declines in the populations of oysters, crabs, freshwater fish and other wildlife.
The growing concerns about pollution also prompted the legislatures of Maryland and Virginia to establish the Chesapeake Bay Commission, an advisory body, in 1980. The commission consults with the state legislatures and executive agencies, as well as Congress, about environmental, economic and social issues related to the bay.
As an initial follow-up to the EPA report, the Chesapeake Bay Commission and EPA developed the Chesapeake Bay Agreement in 1983. The agreement was signed by the governors of Maryland, Virginia and Pennsylvania; the Mayor of the District of Columbia; and the EPA Administrator. The parties agreed to:
* Creation of an "Executive Council" consisting of cabinet-level appointees from each state and Washington, D.C., and the EPA Regional Administrator
* The council's creation of an implementation committee to coordinate technical issues and development management plans for bay restoration
* The establishment of the Chesapeake Bay Program as a liaison office for all of the participating organizations. The program's office, based in Annapolis, is partially funded by EPA and staffed by experts from the member states, EPA and other federal agencies, and academic institutions.
Concurrent with the 1983 agreement EPA began providing matching grants to the bay states for research and restoration projects.
In 1987 the parties agreed to set a goal of reducing the amount of nutrients that enter the bay by 40 percent by 2000. In 1992, the bay program partners agreed to continue the 40 percent reduction goal beyond 2000 and to attack nutrients at their source: upstream, in the bay tributaries. | 2 | Environmental Chemistry |
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