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Isothiocyanates occur widely in nature and are of interest in food science and medical research. Vegetable foods with characteristic flavors due to isothiocyanates include bok choy, broccoli, cabbage, cauliflower, kale, wasabi, horseradish, mustard, radish, Brussels sprouts, watercress, papaya seeds, nasturtiums, and capers. These species generate isothiocyanates in different proportions, and so have different, but recognizably related, flavors. They are all members of the order Brassicales, which is characterized by the production of glucosinolates, and of the enzyme myrosinase, which acts on glucosinolates to release isothiocyanates.
* Sinigrin is the precursor to allyl isothiocyanate
* Glucotropaeolin is the precursor to benzyl isothiocyanate
* Gluconasturtiin is the precursor to phenethyl isothiocyanate
* Glucoraphanin is the precursor to sulforaphane | 0 | Theoretical and Fundamental Chemistry |
In general, DPP-4 inhibitors are not very stable compounds. Therefore, many researchers focus on enhancing the stability for cyanopyrrolidines. The most widespread technique to improve chemical stability is to incorporate a steric bulk. The two cyanopyrrolidines that have been most pronounced, vildagliptin and saxagliptin, were created in this manner. K579 is a DPP-4 inhibitor discovered by researchers at Kyowa Hakko Kyogo. It had improved not only chemical stability but also a longer-lasting action. That long-lasting action was most likely due to slow dissociation of the enzyme-inhibitor complex and an active oxide metabolite that undergoes enterohepatic circulation. The discovery of the active oxide was in fact a big breakthrough as it led to the development of vildagliptin and saxagliptin. One major problem in DPP-4 inhibitor stability is intramolecular cyclization. The precondition for the intramolecular cyclization is the conversion of the trans-rotamer, which is the DPP-4 binding rotamer (Figure 5). Thus, preventing this conversion will increase stability. This prevention was successful when incorporating an amide group into a ring, creating a compound that kept the DPP-4 inhibitory activity that, did not undergo the intramolecular cyclization and was even more selective over different DPP enzymes. It has also been reported that a cyanoazetidine in the P1 position and a β-amino acid in the P2 position increased stability. | 1 | Applied and Interdisciplinary Chemistry |
Drugs are also used to inhibit enzymes needed for the survival of pathogens. For example, bacteria are surrounded by a thick cell wall made of a net-like polymer called peptidoglycan. Many antibiotics such as penicillin and vancomycin inhibit the enzymes that produce and then cross-link the strands of this polymer together. This causes the cell wall to lose strength and the bacteria to burst. In the figure, a molecule of penicillin (shown in a ball-and-stick form) is shown bound to its target, the transpeptidase from the bacteria Streptomyces R61 (the protein is shown as a ribbon diagram).
Antibiotic drug design is facilitated when an enzyme that is essential to the pathogen's survival is absent or very different in humans. Humans do not make peptidoglycan, therefore antibiotics that inhibit this process are selectively toxic to bacteria. Selective toxicity is also produced in antibiotics by exploiting differences in the structure of the ribosomes in bacteria, or how they make fatty acids. | 1 | Applied and Interdisciplinary Chemistry |
The Bermuda Atlantic Time-series Study (BATS) is a long-term oceanographic study by the Bermuda Institute of Ocean Sciences (BIOS). Based on regular (monthly or better) research cruises, it samples an area of the western Atlantic Ocean nominally at the coordinates . The cruise programme routinely samples physical properties such as ocean temperature and salinity, but focuses on variables of biological or biogeochemical interest including: nutrients (nitrate, nitrite, phosphate and silicic acid), dissolved inorganic carbon, oxygen, HPLC of pigments, primary production and sediment trap flux. The BATS cruises began in 1988 but are supplemented by biweekly Hydrostation "S" cruises to a neighbouring location () that began in 1954. The data collected by these cruises are available online. | 0 | Theoretical and Fundamental Chemistry |
The concept of pH was defined in 1909 by S. P. L. Sørensen, and electrodes were used for pH measurement in the 1920s.
In October 1934, Arnold Orville Beckman registered the first patent for a complete chemical instrument for the measurement of pH, U.S. Patent No. 2,058,761, for his "acidimeter", later renamed the pH meter. Beckman developed the prototype as an assistant professor of chemistry at the California Institute of Technology, when asked to devise a quick and accurate method for measuring the acidity of lemon juice for the California Fruit Growers Exchange (Sunkist).
On April 8, 1935, Beckman's renamed National Technical Laboratories focused on the manufacture of scientific instruments, with the Arthur H. Thomas Company as a distributor for its pH meter. In its first full year of sales, 1936, the company sold 444 pH meters for $60,000 in sales. In years to come, the company sold millions of the units. In 2004 the Beckman pH meter was designated an ACS National Historic Chemical Landmark in recognition of its significance as the first commercially successful electronic pH meter.
The Radiometer Corporation of Denmark was founded in 1935, and began marketing a pH meter for medical use around 1936, but "the development of automatic pH-meters for industrial purposes was neglected. Instead American instrument makers successfully developed industrial pH-meters with a wide variety of applications, such as in breweries, paper works, alum works, and water treatment systems."
In the 1940s the electrodes for pH meters were often difficult to make, or unreliable due to brittle glass. Dr. Werner Ingold began to industrialize the production of single-rod measuring cells, a combination of measurement and reference electrode in one construction unit, which led to broader acceptance in a wide range of industries including pharmaceutical production.
Beckman marketed a portable "Pocket pH Meter" as early as 1956, but it did not have a digital read-out.
In the 1970s Jenco Electronics of Taiwan designed and manufactured the first portable digital pH meter. This meter was sold under the label of the Cole-Parmer Corporation. | 0 | Theoretical and Fundamental Chemistry |
The initial stage of the natural transition process is known as the Receptivity phase and consists of the transformation of environmental disturbances – both acoustic (sound) and vortical (turbulence) – into small perturbations within the boundary layer. The mechanisms by which these disturbances arise are varied and include freestream sound and/or turbulence interacting with surface curvature, shape discontinuities and surface roughness. These initial conditions are small, often unmeasurable perturbations to the basic state flow. From here, the growth (or decay) of these disturbances depends on the nature of the disturbance and the nature of the basic state. Acoustic disturbances tend to excite two-dimensional instabilities such as Tollmien–Schlichting waves (T-S waves), while vortical disturbances tend to lead to the growth of three-dimensional phenomena such as the crossflow instability.
Numerous experiments in recent decades have revealed that the extent of the amplification region, and hence the location of the transition point on the body surface, is strongly dependent not only upon the amplitude and/or the spectrum of external disturbances but also on their physical nature. Some of the disturbances easily penetrate into the boundary layer whilst others do not. Consequently, the concept of boundary layer transition is a complex one and still lacks a complete theoretical exposition. | 1 | Applied and Interdisciplinary Chemistry |
Chloroformates are a class of organic compounds with the formula ROC(O)Cl. They are formally esters of chloroformic acid. Most are colorless, volatile liquids that degrade in moist air. A simple example is methyl chloroformate, which is commercially available.
Chloroformates are used as reagents in organic chemistry. For example, benzyl chloroformate is used to introduce the Cbz (carboxybenzyl) protecting group and fluorenylmethyloxycarbonyl chloride is used to introduce the FMOC protecting group. Chloroformates are popular in the field of chromatography as derivatization agents. They convert polar compounds into less polar more volatile derivatives. In this way, chloroformates enable relatively simple transformation of large array of metabolites (aminoacids, amines, carboxylic acids, phenols) for analysis by gas chromatography / mass spectrometry. | 0 | Theoretical and Fundamental Chemistry |
No heterogeneous catalyst has been commercialized for asymmetric hydrogenation.
The first asymmetric hydrogenation focused on palladium deposited on a silk support. Cinchona alkaloids have been used as chiral modifiers for enantioselectivity hydrogenation.
An alternative technique and one that allows more control over the structural and electronic properties of active catalytic sites is the immobilization of catalysts that have been developed for homogeneous catalysis on a heterogeneous support. Covalent bonding of the catalyst to a polymer or other solid support is perhaps most common, although immobilization of the catalyst may also be achieved by adsorption onto a surface, ion exchange, or even physical encapsulation. One drawback of this approach is the potential for the proximity of the support to change the behaviour of the catalyst, lowering the enantioselectivity of the reaction. To avoid this, the catalyst is often bound to the support by a long linker though cases are known where the proximity of the support can actually enhance the performance of the catalyst.
The final approach involves the construction of MOFs that incorporate chiral reaction sites from a number of different components, potentially including chiral and achiral organic ligands, structural metal ions, catalytically active metal ions, and/or preassembled catalytically active organometallic cores. One of these involved ruthenium-based catalysts. As little as 0.005 mol% of such catalysts proved sufficient to achieve the asymmetric hydrogenation of aryl ketones, although the usual conditions featured 0.1 mol % of catalyst and resulted in an enantiomeric excess of 90.6–99.2%.
<br /> | 0 | Theoretical and Fundamental Chemistry |
Scrutiny of the land includes examination of potential soil contamination, groundwater quality, surface water quality, vapor intrusion, and sometimes issues related to hazardous substance uptake by biota. The examination of a site may include: definition of any chemical residues within structures; identification of possible asbestos containing building materials; inventory of hazardous substances stored or used on site; assessment of mold and mildew; and evaluation of other indoor air quality parameters.
Depending upon precise protocols utilized, there are a number of variations in the scope of a Phase I study. The tasks listed here are common to almost all Phase I ESAs:
* Performance of an on-site visit to view present conditions (chemical spill residue, die-back of vegetation, etc.); hazardous substances or petroleum products usage (presence of above ground or underground storage tanks, storage of acids, etc.); and evaluate any likely environmentally hazardous site history.
*Evaluation of risks of neighboring properties upon the subject property
*Review of Federal, State, Local and Tribal Records out to distances specified by the ASTM 1528 and AAI Standards (ranging from 1/8 to 1 mile depending on the database)
* Interview of persons knowledgeable regarding the property history (past owners, present owner, key site manager, present tenants, neighbors).
*Examine municipal or county planning files to check prior land usage and permits granted.
*Conduct file searches with public agencies (State water board, fire department, county health department, etc.) having oversight relative to water quality and soil contamination issues.
*Examine historical aerial photography of the vicinity.
*Examine current USGS maps to scrutinize drainage patterns and topography.
*Examine chain-of-title for Environmental Liens and/or Activity and Land Use Limitations (AULs).
In most cases, the public file searches, historical research and chain-of-title examinations are outsourced to information services that specialize in such activities. Non-Scope Items in a Phase I Environmental Site Assessment can include visual inspections or records review searches for:
*Asbestos Containing Building Materials (ACBM)
*Lead-Based Paint
*Lead in Drinking Water
*Mold
*Radon
*Wetlands
*Threatened and Endangered Species
*Mercury poisoning
*Debris flow
*Earthquake Hazard
*Vapor intrusion
*Emerging contaminants
Observations of Non-scope Items can be reported as "findings" if requested by the report user, however, these items do not constitute recognized environmental conditions. | 1 | Applied and Interdisciplinary Chemistry |
Acylsilanes are a group of chemical compounds sharing a common functional group with the general structure RC(O)-SiR. | 0 | Theoretical and Fundamental Chemistry |
A direct electron ionization liquid chromatography–mass spectrometry interface (Direct-EI LC-MS interface) is a technique for coupling liquid chromatography and mass spectrometry (LC-MS) based on the direct introduction of the liquid effluent into an electron ionization (EI) source. Library searchable mass spectra are generated. Gas-phase EI has many applications for the detection of HPLC amenable compounds showing minimal adverse matrix effects. The direct-EI LC-MS interface provides access to well-characterized electron ionization data for a variety of LC applications and readily interpretable spectra from electronic libraries for environmental, food safety, pharmaceutical, biomedical, and other applications. | 0 | Theoretical and Fundamental Chemistry |
Diisopropylfluorophosphate (DFP) is an example of an irreversible protease inhibitor (see the "DFP reaction" diagram). The enzyme hydrolyses the phosphorus–fluorine bond, but the phosphate residue remains bound to the serine in the active site, deactivating it. Similarly, DFP also reacts with the active site of acetylcholine esterase in the synapses of neurons, and consequently is a potent neurotoxin, with a lethal dose of less than 100mg.
Suicide inhibition is an unusual type of irreversible inhibition where the enzyme converts the inhibitor into a reactive form in its active site. An example is the inhibitor of polyamine biosynthesis, α-difluoromethylornithine (DFMO), which is an analogue of the amino acid ornithine, and is used to treat African trypanosomiasis (sleeping sickness). Ornithine decarboxylase can catalyse the decarboxylation of DFMO instead of ornithine (see the "DFMO inhibitor mechanism" diagram). However, this decarboxylation reaction is followed by the elimination of a fluorine atom, which converts this catalytic intermediate into a conjugated imine, a highly electrophilic species. This reactive form of DFMO then reacts with either a cysteine or lysine residue in the active site to irreversibly inactivate the enzyme.
Since irreversible inhibition often involves the initial formation of a non-covalent enzyme inhibitor (EI) complex, it is sometimes possible for an inhibitor to bind to an enzyme in more than one way. For example, in the figure showing trypanothione reductase from the human protozoan parasite Trypanosoma cruzi, two molecules of an inhibitor called quinacrine mustard are bound in its active site. The top molecule is bound reversibly, but the lower one is bound covalently as it has reacted with an amino acid residue through its nitrogen mustard group. | 1 | Applied and Interdisciplinary Chemistry |
Hydroamination reactions are atom-efficient processes that generally use readily available and cheap starting materials, therefore a general catalytic strategy is highly desirable. Also, direct catalytic hydroamination strategies have in principle significant benefits over more classical methods to prepare amine containing compounds, including the reduction in the number of synthetic steps required.
However, hydroamination reactions pose some tough challenges for catalysis: Strong electron repulsion of the nitrogen atom lone pair and the electron rich carbon-carbon multiple bond, coupled with hydroamination reactions being entropically disfavoured (particularly the intermolecular version), results in a large reaction barrier. Regioselectivity issues also hamper the synthetic utility of the resulting products, with Markovnikov addition of the amine being the most common outcome over the less favoured anti-Markovnikov addition (see figure). As a result, there are now numerous catalysts that can be utilised in the hydroamination of alkene, allene and alkyne substrates, including various metal based heterogeneous catalysts, early-transition metal complexes (e.g. titanium and zirconium), late-transition metal complexes (e.g. ruthenium and palladium), lanthanide and actinide complexes (e.g. samarium and lanthanum), as well as Brønsted acids and bases. | 0 | Theoretical and Fundamental Chemistry |
Nucleotides can undergo enzyme-catalyzed intramolecular cyclization in order to produce several important biological molecules. These cyclizations typically proceed through an oxocarbenium intermediate. An example of this reaction can be seen in the cyclization cyclic ADP ribose, which is an important molecule for intracellular calcium signaling. | 0 | Theoretical and Fundamental Chemistry |
Thiols show little association by hydrogen bonding, both with water molecules and among themselves. Hence, they have lower boiling points and are less soluble in water and other polar solvents than alcohols of similar molecular weight. For this reason also, thiols and their corresponding sulfide functional group isomers have similar solubility characteristics and boiling points, whereas the same is not true of alcohols and their corresponding isomeric ethers. | 0 | Theoretical and Fundamental Chemistry |
The history of quantum mechanics is a fundamental part of the history of modern physics. The major chapters of this history begin with the emergence of quantum ideas to explain individual phenomena—blackbody radiation, the photoelectric effect, solar emission spectra—an era called the Old or Older quantum theories. Building on the technology developed in classical mechanics, the invention of wave mechanics by Erwin Schrödinger and expansion by many others triggers the "modern" era beginning around 1925. Paul Dirac's relativistic quantum theory work lead him to explore quantum theories of radiation, culminating in quantum electrodynamics, the first quantum field theory. The history of quantum mechanics continues in the history of quantum field theory. The history of quantum chemistry, theoretical basis of chemical structure, reactivity, and bonding, interlaces with the events discussed in this article.
The phrase "quantum mechanics" was coined (in German, Quantenmechanik) by the group of physicists including Max Born, Werner Heisenberg, and Wolfgang Pauli, at the University of Göttingen in the early 1920s, and was first used in Borns 1925 paper "Zur Quantenmechanik"'.
The word quantum comes from the Latin word for "how much" (as does quantity). Something that is quantized, as the energy of Plancks harmonic oscillators, can only take specific values. For example, in most countries, money is effectively quantized, with the quantum of money' being the lowest-value coin in circulation. Mechanics is the branch of science that deals with the action of forces on objects. So, quantum mechanics is the part of mechanics that deals with objects for which particular properties are quantized. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, the capped square antiprismatic molecular geometry describes the shape of compounds where nine atoms, groups of atoms, or ligands are arranged around a central atom, defining the vertices of a gyroelongated square pyramid. The symmetry group of the resulting object is C
The gyroelongated square pyramid is a square pyramid with a square antiprism connected to the square base. In this respect, it can be seen as a "capped" square antiprism (a square antiprism with a pyramid erected on one of the square faces).
It is very similar to the tricapped trigonal prismatic molecular geometry, and there is some dispute over the specific geometry exhibited by certain molecules.
Examples:
*[SiCo(CO)], defined by the Co framework, which encapsulates the Si atom
*[Pb(phen)(OClO)], defined by the NO framework, which encapsulates the Pb ion
*[Ge], a zintl ion
*Th(troopolonate)(HO), defined by the O framework, which encapsulates the Th ion
*Potassium nonahydridorhenate| is sometimes described as having a capped square antiprismatic geometry, although its geometry is most often described as tricapped trigonal prismatic.
*, a lanthanum(III) complex with a La–La bond. | 0 | Theoretical and Fundamental Chemistry |
Ultraviolet-visible (UV-Vis) absorption spectroelectrochemistry (SEC) is a multiresponse technique that analyzes the evolution of the absorption spectra in UV-Vis regions during an electrode process. This technique provides information from an electrochemical and spectroscopic point of view. In this way, it enables a better perception about the chemical system of interest. On one hand, molecular information related to the electronic levels of the molecules is obtained from the evolution of the spectra. On the other hand, kinetic and thermodynamic information of the processes is obtained from the electrochemical signal.
UV-Vis absorption SEC allows qualitative analysis, through the characterization of the different present compounds, and quantitative analysis, by determining the concentration of the analytes of interest. Furthermore, it helps to determine different electrochemical parameters such as absorptivity coefficients, standard potentials, diffusion coefficients, electronic transfer rate constants, etc. Throughout history, reversible processes have been studied with colored reagents or electrolysis products. Nowadays, it is possible to study all kinds of electrochemical processes in the entire UV-Vis spectral range, even in the near infrared (NIR). | 0 | Theoretical and Fundamental Chemistry |
To lower the concentration of airborne dust concentrations during woodworking, dust extraction systems are used. These can be divided into two types. The first are local exhaust ventilation systems, the second are room ventilation systems. Use of personal respirators, a form of personal protective equipment, can also isolate workers from dust. | 1 | Applied and Interdisciplinary Chemistry |
The Croatian Society of Medical Biochemists (CSMB) was founded in 1953. Until 1988, CSMB had been part of the Croatian Pharmaceutical Society and afterwards became an autonomous association. In 2012, it changed its name to the Croatian Society of Medical Biochemistry and Laboratory Medicine (CSMBLM), in line with the current trends within the profession and with the recommendations of European and global professional associations. In 2015 it had 750 members. | 1 | Applied and Interdisciplinary Chemistry |
An emission intensity (also carbon intensity or C.I.) is the emission rate of a given pollutant relative to the intensity of a specific activity, or an industrial production process; for example grams of carbon dioxide released per megajoule of energy produced, or the ratio of greenhouse gas emissions produced to gross domestic product (GDP). Emission intensities are used to derive estimates of air pollutant or greenhouse gas emissions based on the amount of fuel combusted, the number of animals in animal husbandry, on industrial production levels, distances traveled or similar activity data. Emission intensities may also be used to compare the environmental impact of different fuels or activities. In some case the related terms emission factor and carbon intensity are used interchangeably. The jargon used can be different, for different fields/industrial sectors; normally the term "carbon" excludes other pollutants, such as particulate emissions. One commonly used figure is carbon intensity per kilowatt-hour (CIPK), which is used to compare emissions from different sources of electrical power. | 1 | Applied and Interdisciplinary Chemistry |
BLOSUM scores was used to predict and understand the surface gene variants among hepatitis B virus carriers and T-cell epitopes. | 1 | Applied and Interdisciplinary Chemistry |
Children with acute otitis media who are younger than six months of age are generally treated with amoxicillin or other antibiotics. Although most children with acute otitis media who are older than two years old do not benefit from treatment with amoxicillin or other antibiotics, such treatment may be helpful in children younger than two years old with acute otitis media that is bilateral or accompanied by ear drainage. In the past, amoxicillin was dosed three times daily when used to treat acute otitis media, which resulted in missed doses in routine ambulatory practice. There is now evidence that two times daily dosing or once daily dosing has similar effectiveness. | 0 | Theoretical and Fundamental Chemistry |
In a Compton scattering process, an incident photon collides with an electron in a material. The amount of energy exchanged varies with angle, and is given by the formula:
or
* E is the energy of the incident photon.
* E ' is the energy of the outgoing photon, which escapes the material.
* is the mass of the electron.
* c is the speed of light.
* is the angle of deflection for the photon.
The amount of energy transferred to the material varies with the angle of deflection. As approaches zero, none of the energy is transferred. The maximum amount of energy is transferred when approaches 180 degrees.
It is impossible for the photon to transfer any more energy via this process; thus, there is a sharp cutoff at this energy, leading to the name Compton edge. If an isotope has multiple photopeaks, each inflection point will have its own Compton edge.
The region between zero energy transfer and the Compton edge is known as the Compton continuum. | 0 | Theoretical and Fundamental Chemistry |
This concept was suggested by the 19th-century chemist Emil Fischer. He proposed that the active site and substrate are two stable structures that fit perfectly without any further modification, just like a key fits into a lock. If one substrate perfectly binds to its active site, the interactions between them will be strongest, resulting in high catalytic efficiency.
As time went by, limitations of this model started to appear. For example, the competitive enzyme inhibitor methylglucoside can bind tightly to the active site of 4-alpha-glucanotransferase and perfectly fits into it. However, 4-alpha-glucanotransferase is not active on methylglucoside and no glycosyl transfer occurs. The Lock and Key hypothesis cannot explain this, as it would predict a high efficiency of methylglucoside glycosyl transfer due to its tight binding. Apart from competitive inhibition, this theory cannot explain the mechanism of action of non-competitive inhibitors either, as they do not bind to the active site but nevertheless influence catalytic activity. | 1 | Applied and Interdisciplinary Chemistry |
Thiosulfines, also called thiocarbonyl S-sulfides, are compounds with the formula RCSS. Although superficially appearing to be cumulenes, with the linkage RC=S=S, they are more usefully classified as 1,3-dipoles and indeed participate in 1,3-dipolar cycloadditions. Thiosulfines are proposed to exist in equilibrium with dithiiranes, three-membered CS rings. Thiosulfines are often invoked as intermediates in mechanistic discussions of the chemistry of thiones. For example, thiobenzophenone decomposes upon oxidation to the 1,2,4-trithiolane (PhC)S, which arises via the cycloaddition of PhCSS to its parent PhCS. | 0 | Theoretical and Fundamental Chemistry |
2,6-Di-tert-butylpyridine is an organic compound with the formula (MeC)CHN. This colourless, oily liquid is derived from pyridine by replacement of the two H atoms with tert-butyl groups. It is a hindered base. For example, it can be protonated, but it does not form an adduct with boron trifluoride. | 0 | Theoretical and Fundamental Chemistry |
Given n genes and k replicates, let the rank of gene g in the i-th replicate.
Compute the rank product via the geometric mean: | 1 | Applied and Interdisciplinary Chemistry |
Deulinoleate ethyl is recognized by cells as identical to the natural linoleic acid. But when taken up, it is converted into 13,13-d-arachidonic acid, a heavy isotope version of arachidonic acid, that gets incorporated into lipid membranes. The deuterated compound resists the non-enzymatic lipid peroxidation (LPO) through isotope effect — a non-antioxidant based mechanism that protects mitochondrial, neuronal and other lipid membranes, thereby greatly reducing the levels of numerous LPO-derived toxic products such as reactive carbonyls.
Deulinoleate ethyl inhibits ferroptosis by stopping the autoxidation process through the kinetic isotope effect. The protective effect of D-PUFAs was verified in erastin- and RSL3-induced ferroptosis models, with demonstrated efficacy in various disease models, particularly neurodegenerative disorders and clinical trials of deulinoleate ethyl begun in 2018. | 1 | Applied and Interdisciplinary Chemistry |
Topochemical polymerization can also be triggered by pressure. It has been reported that the cocrystal of diododiacetylene (guest) and bispyridyl oxalamide (host) could be polymerized under pressure. Interestingly, no polymerization was observed under light or heat due to the unfavorable distance between diacetylene units. The researcher postulated that the high pressure might "squeeze" the reactive site together and initiate the polymerization. | 0 | Theoretical and Fundamental Chemistry |
During the Middle Ages, between the 5th and 16th century AD, Western Europe saw a period of growth in the mining industry. The first important mines were those at Goslar in the Harz mountains, taken into commission in the 10th century. Another notable mining town is Falun in Sweden where copper has been mined since at least the 10th century and possibly even earlier. (Olsson 2010)
The rise of the Western European mining industry depended on the increasing influence of Western Europe on the world stage. Advances in medieval mining and metallurgy enabled the flourishing of Western European civilization. Accessible ores and improved extraction techniques supported economic growth and trade. Innovations like water-powered machinery and better smelting methods increased the productivity and quality of metals.
Metallurgical activities were also encouraged by the central political powers, regional authorities, monastic orders, and ecclesiastical overlords. These powers attempted to claim royal rights over the mines and a share in the output, both on private lands and regions belonging to The Crown. They were particularly interested in the extraction of the precious metal ores, and for this reason, the mines in their territories were open to all miners (Nef 1987, 706–715). | 1 | Applied and Interdisciplinary Chemistry |
* Allinger, Cava, de Jongh, Johnson, Lebel, Stevens: Organische Chemie, 1. Auflage, Walter de Gruyter, Berlin 1980, , p. 749.
* Beyer / Walter: Lehrbuch der Organischen Chemie, 19. Auflage, S. Hirzel Verlag, Stuttgart 1981, , pp. 98–99, 122.
* K. Peter C. Vollhardt, Neil E. Schore: Organische Chemie, 4. Auflage, Wiley-VCH, Weinheim 2005, , p. 632. | 0 | Theoretical and Fundamental Chemistry |
Yeasts naturally harbour various plasmids. Notable among them are 2 μm plasmids—small circular plasmids often used for genetic engineering of yeast—and linear pGKL plasmids from Kluyveromyces lactis, that are responsible for killer phenotypes.
Other types of plasmids are often related to yeast cloning vectors that include:
* Yeast integrative plasmid (YIp), yeast vectors that rely on integration into the host chromosome for survival and replication, and are usually used when studying the functionality of a solo gene or when the gene is toxic. Also connected with the gene URA3, that codes an enzyme related to the biosynthesis of pyrimidine nucleotides (T, C);
* Yeast Replicative Plasmid (YRp), which transport a sequence of chromosomal DNA that includes an origin of replication. These plasmids are less stable, as they can be lost during budding. | 1 | Applied and Interdisciplinary Chemistry |
In the early 1940s, Bradley reported the observation of sidebands around the Bragg peaks in the X-ray diffraction pattern of a Cu-Ni-Fe alloy that had been quenched and then annealed inside the miscibility gap. Further observations on the same alloy were made by Daniel and Lipson, who demonstrated that the sidebands could be explained by a periodic modulation of composition in the <100> directions. From the spacing of the sidebands, they were able to determine the wavelength of the modulation, which was of the order of 100 angstroms (10 nm).
The growth of a composition modulation in an initially homogeneous alloy implies uphill diffusion or a negative diffusion coefficient. Becker and Dehlinger had already predicted a negative diffusivity inside the spinodal region of a binary system. But their treatments could not account for the growth of a modulation of a particular wavelength, such as was observed in the Cu-Ni-Fe alloy. In fact, any model based on Fick's law yields a physically unacceptable solution when the diffusion coefficient is negative.
The first explanation of the periodicity was given by Mats Hillert in his 1955 Doctoral Dissertation at MIT. Starting with a regular solution model, he derived a flux equation for one-dimensional diffusion on a discrete lattice. This equation differed from the usual one by the inclusion of a term, which allowed for the effect of the interfacial energy on the driving force of adjacent interatomic planes that differed in composition. Hillert solved the flux equation numerically and found that inside the spinodal it yielded a periodic variation of composition with distance. Furthermore, the wavelength of the modulation was of the same order as that observed in the Cu-Ni-Fe alloys.
Building on Hillert's work, a more flexible continuum model was subsequently developed by John W. Cahn and John Hilliard, who included the effects of coherency strains as well as the gradient energy term. The strains are significant in that they dictate the ultimate morphology of the decomposition in anisotropic materials. | 0 | Theoretical and Fundamental Chemistry |
Most oxyanions are weak bases and can be protonated to give acids or acid salts. For example, the phosphate ion can be successively protonated to form phosphoric acid.
The extent of protonation in aqueous solution will depend on the acid dissociation constants and pH. For example, AMP (adenosine monophosphate) has a pK value of 6.21, so at pH 7 it will be about 10% protonated. Charge neutralization is an important factor in these protonation reactions. By contrast, the univalent anions perchlorate and permanganate ions are very difficult to protonate and so the corresponding acids are strong acids.
Although acids such as phosphoric acid are written as , the protons are attached to oxygen atoms forming hydroxyl groups, so the formula can also be written as to better reflect the structure. Sulfuric acid may be written as ; this is the molecule observed in the gas phase.
The phosphite ion, , is a strong base, and so always carries at least one proton. In this case the proton is attached directly to the phosphorus atom with the structure . In forming this ion, the phosphite ion is behaving as a Lewis base and donating a pair of electrons to the Lewis acid, .
As mentioned above, a condensation reaction is also an acid–base reaction. In many systems, both protonation and condensation reactions can occur. The case of the chromate ion provides a relatively simple example. In the predominance diagram for chromate, shown at the right, pCr stands for the negative logarithm of the chromium concentration and pH stands for the negative logarithm of ion concentration. There are two independent equilibria. Equilibrium constants are defined as follows.
The predominance diagram is interpreted as follows.
*The chromate ion, , is the predominant species at high pH. As pH rises the chromate ion becomes ever more predominant, until it is the only species in solutions with pH > 6.75.
*At pH the hydrogen chromate ion, is predominant in dilute solution.
*The dichromate ion, , is predominant in more concentrated solutions, except at high pH.
The species and are not shown as they are formed only at very low pH.
Predominance diagrams can become very complicated when many polymeric species can be formed, such as in vanadates, molybdates, and tungstates. Another complication is that many of the higher polymers are formed extremely slowly, such that equilibrium may not be attained even in months, leading to possible errors in the equilibrium constants and the predominance diagram. | 0 | Theoretical and Fundamental Chemistry |
If an elastic band is first stretched and then subjected to heating, it will shrink rather than expand. This effect was first observed by John Gough in 1802, and was investigated further by Joule in the 1850s, when it then became known as the Gough–Joule effect.
<br />Examples in Literature:
* Popular Science magazine, January 1972: "A stretched piece of rubber contracts when heated. In doing so, it exerts a measurable increase in its pull. This surprising property of rubber was first observed by James Prescott Joule about a hundred years ago and is known as the Joule effect."
* Rubber as an Engineering Material (book), by Khairi Nagdi: "The Joule effect is a phenomenon of practical importance that machine designers must consider. The simplest way of demonstrating this effect is to suspend a weight on a rubber band sufficient to elongate it by at least 50%. When an infrared lamp warms up the stretched rubber band, it does not elongate because of thermal expansion, as may be expected, but it retracts and lifts the weight." | 0 | Theoretical and Fundamental Chemistry |
The method reported by Beemelmanns & Reissig (racemic, 2010) is another formal synthesis leading to the Rawal pentacycle (see amine 5 in the Rawal method). In this method indole 1 was converted to tetracycle 2 (together with by-product) in a single cascade reaction using samarium diiodide and HMPA. Raney nickel/ H reduction gave amine 3 and a one-pot reaction using methyl chloroformate, DMAP and TEA then MsCl, DMAP and TEA and then DBU gave Rawal precursor 4 with key hydrogen atoms in the desired anti configuration.
In an aborted route intermediate 2 was first reduced to imine 5 then converted to carbamate 6, then dehydrated to diene 7 (Burgess reagent) and finally reduced to 8 (sodium cyanoborohydride). The hydrogen atoms in 8 are in an undesired cis-relationship which contradicts the results obtained in 2002 by Bodwell/Li for the same reaction. | 0 | Theoretical and Fundamental Chemistry |
In late 1891, she left Poland for France. In Paris, Maria (or Marie, as she would be known in France) briefly found shelter with her sister and brother-in-law before renting a garret closer to the university, in the Latin Quarter, and proceeding with her studies of physics, chemistry, and mathematics at the University of Paris, where she enrolled in late 1891. She subsisted on her meagre resources, keeping herself warm during cold winters by wearing all the clothes she had. She focused so hard on her studies that she sometimes forgot to eat. Skłodowska studied during the day and tutored evenings, barely earning her keep. In 1893, she was awarded a degree in physics and began work in an industrial laboratory of Gabriel Lippmann. Meanwhile, she continued studying at the University of Paris and with the aid of a fellowship she was able to earn a second degree in 1894.
Skłodowska had begun her scientific career in Paris with an investigation of the magnetic properties of various steels, commissioned by the Society for the Encouragement of National Industry. That same year, Pierre Curie entered her life: it was their mutual interest in natural sciences that drew them together. Pierre Curie was an instructor at The City of Paris Industrial Physics and Chemistry Higher Educational Institution (ESPCI Paris). They were introduced by Polish physicist Józef Wierusz-Kowalski, who had learned that she was looking for a larger laboratory space, something that Wierusz-Kowalski thought Pierre could access. Though Curie did not have a large laboratory, he was able to find some space for Skłodowska where she was able to begin work.
Their mutual passion for science brought them increasingly closer, and they began to develop feelings for one another. Eventually, Pierre proposed marriage, but at first Skłodowska did not accept as she was still planning to go back to her native country. Curie, however, declared that he was ready to move with her to Poland, even if it meant being reduced to teaching French. Meanwhile, for the 1894 summer break, Skłodowska returned to Warsaw, where she visited her family. She was still labouring under the illusion that she would be able to work in her chosen field in Poland, but she was denied a place at Kraków University because of sexism in academia. A letter from Pierre convinced her to return to Paris to pursue a PhD. At Skłodowskas insistence, Curie had written up his research on magnetism and received his own doctorate in March 1895; he was also promoted to professor at the School. A contemporary quip would call Skłodowska "Pierres biggest discovery".
On 26 July 1895, they were married in Sceaux; neither wanted a religious service. Curie's dark blue outfit, worn instead of a bridal gown, would serve her for many years as a laboratory outfit. They shared two pastimes: long bicycle trips and journeys abroad, which brought them even closer. In Pierre, Marie had found a new love, a partner, and a scientific collaborator on whom she could depend. | 0 | Theoretical and Fundamental Chemistry |
The word is an Algonquian word referring to a village at a big river. It is the seventh-oldest surviving English placename in the United States, first applied as Chesepiook by explorers heading north from the Roanoke Colony into a Chesapeake tributary in 1585 or 1586. The name may also refer to the Chesapeake people or the Chesepian, a Native American tribe who inhabited the area now known as South Hampton Roads in the U.S. state of Virginia. They occupied an area that is now the Norfolk, Portsmouth, Chesapeake, and Virginia Beach areas. In 2005, Algonquian linguist Blair Rudes "helped to dispel one of the areas most widely held beliefs: that Chesapeake means something like great shellfish bay. It does not, Rudes said. The name might have actually meant something like great water, or it might have just referred to a village location at the Bays mouth." | 1 | Applied and Interdisciplinary Chemistry |
Ouabain or (from Somali waabaayo, "arrow poison" through French ouabaïo) also known as g-strophanthin, is a plant derived toxic substance that was traditionally used as an arrow poison in eastern Africa for both hunting and warfare. Ouabain is a cardiac glycoside and in lower doses, can be used medically to treat hypotension and some arrhythmias. It acts by inhibiting the Na/K-ATPase, also known as the sodium–potassium ion pump. However, adaptations to the alpha-subunit of the -ATPase via amino acid substitutions, have been observed in certain species, namely some herbivore- insect species, that have resulted in toxin resistance.
It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities. | 0 | Theoretical and Fundamental Chemistry |
A rare-cutter enzyme is a restriction enzyme with a recognition sequence which occurs only rarely in a genome. An example is NotI, which cuts after the first GC of a 5-GCGGCCGC-3 sequence; restriction enzymes with seven and eight base pair recognition sequences are often also called rare-cutter enzymes (six bp recognition sequences are much more common).
For example, rare-cutter enzymes with 7-nucleotide recognition sites cut once every 4 bp (16,384 bp), and those with 8-nucleotide recognition sites cut every 4 bp (65,536 bp) respectively. They are used in top-down mapping to cut a chromosome into chunks of these sizes on average. | 1 | Applied and Interdisciplinary Chemistry |
Scientists Francisco Gasulla, Leonardo Casano and Alfredo Guéra, observed the lichen's metabolic response when placed in dark conditions. The light harvesting complex (LHC) inside the chloroplasts of Lichen is activated when subjected to darkness. Gasulla, Casano and Guéra, noticed that this increase in LHC activity caused PS II and the PQ pool within lichen to decrease, indicating the initiation of chlororespiration.
Immunodetection analysis was used to determine the amount of LHC molecules inside lichen in a dark environment, and a luminous environment. By determining the amount of LHC within the chloroplast, scientists were able to notice the reduction in PS II activity. This reduction was caused by a loss in excitation energy in the PS II ETC, which then stimulated an incline in chlororespiratory pathways. Gasulla, Casano and Guéra, gathered this result, when both light-adapted and dark-adapted lichen were placed in darkness. They found that the level of LHC molecules in dark-adapted lichen had doubled compared to light adapted lichen. It was also noted that the chlororespiratory ETCs were triggered at a much earlier time in dark-adapted lichen, than compared to light-adapted lichen. This resulted in a faster metabolic rate and chemical synthesis response in dark-adapted lichen due to chlororespiration. | 1 | Applied and Interdisciplinary Chemistry |
A hull with a blunt bow has to push the water away very quickly to pass through, and this high acceleration requires large amounts of energy. By using a fine bow, with a sharper angle that pushes the water out of the way more gradually, the amount of energy required to displace the water will be less. A modern variation is the wave-piercing design. The total amount of water to be displaced by a moving hull, and thus causing wave making drag, is the cross sectional area of the hull times distance the hull travels, and will not remain the same when prismatic coefficient is increased for the same lwl and same displacement and same speed. | 1 | Applied and Interdisciplinary Chemistry |
The white allotrope can be produced using several methods. In the industrial process, phosphate rock is heated in an electric or fuel-fired furnace in the presence of carbon and silica. Elemental phosphorus is then liberated as a vapour and can be collected under phosphoric acid. An idealized equation for this carbothermal reaction is shown for calcium phosphate (although phosphate rock contains substantial amounts of fluoroapatite):
White phosphorus has an appreciable vapour pressure at ordinary temperatures. The vapour density indicates that the vapour is composed of molecules up to about 800 °C. Above that temperature, dissociation into diphosphorus| molecules occurs.
In base, white phosphorus spontaneously disproportionates to phosphine and various phosphorus oxyacids.
It ignites spontaneously in air at about , and at much lower temperatures if finely divided (due to melting-point depression). Phosphorus reacts with oxygen, usually forming two oxides depending on the amount of available oxygen: (phosphorus trioxide) when reacted with a limited supply of oxygen, and when reacted with excess oxygen. On rare occasions, , , and are also formed, but in small amounts. This combustion gives phosphorus(V) oxide:
Because of this property, white phosphorus is used as a weapon.
Phosphorus pentachloride is prepared by the reaction of white phosphorus with excess of dry chlorine.
It can also be prepared by the action of sulfuryl chloride on white phosphorus. | 0 | Theoretical and Fundamental Chemistry |
Liquid foams can be used in fire retardant foam, such as those that are used in extinguishing fires, especially oil fires.
In some ways, leavened bread is a foam, as the yeast causes the bread to rise by producing tiny bubbles of gas in the dough. The dough has traditionally been understood as a closed-cell foam, in which the pores do not connect with each other. Cutting the dough releases the gas in the bubbles that are cut, but the gas in the rest of the dough cannot escape. When dough is allowed to rise too far, it becomes an open-cell foam, in which the gas pockets are connected. Cutting the dough or the surface otherwise breaking at that point would cause a large volume of gas to escape, and the dough would collapse. The open structure of an over-risen dough is easy to observe: instead of consisting of discrete gas bubbles, the dough consists of a gas space filled with threads of the flour-water paste. Recent research has indicated that the pore structure in bread is 99% interconnected into one large vacuole, thus the closed-cell foam of the moist dough is transformed into an open cell solid foam in the bread.
The unique property of gas-liquid foams having very high specific surface area is exploited in the chemical processes of froth flotation and foam fractionation.
Foam depopulation or foaming is a means of mass killing farm animals by spraying foam over a large area to obstruct breathing and ultimately cause suffocation. It is usually used to attempt to stop disease spread. | 0 | Theoretical and Fundamental Chemistry |
Many different systems for detecting mutagen have been developed. Animal systems may more accurately reflect the metabolism of human, however, they are expensive and time-consuming (may take around three years to complete), they are therefore not used as a first screen for mutagenicity or carcinogenicity. | 0 | Theoretical and Fundamental Chemistry |
Metabolites are the substrates, intermediates and products of metabolism. Within the context of metabolomics, a metabolite is usually defined as any molecule less than 1.5 kDa in size. However, there are exceptions to this depending on the sample and detection method. For example, macromolecules such as lipoproteins and albumin are reliably detected in NMR-based metabolomics studies of blood plasma. In plant-based metabolomics, it is common to refer to "primary" and "secondary" metabolites. A primary metabolite is directly involved in the normal growth, development, and reproduction. A secondary metabolite is not directly involved in those processes, but usually has important ecological function. Examples include antibiotics and pigments. By contrast, in human-based metabolomics, it is more common to describe metabolites as being either endogenous (produced by the host organism) or exogenous. Metabolites of foreign substances such as drugs are termed xenometabolites.
The metabolome forms a large network of metabolic reactions, where outputs from one enzymatic chemical reaction are inputs to other chemical reactions. Such systems have been described as hypercycles. | 1 | Applied and Interdisciplinary Chemistry |
A possible nutrient source is wastewater from the treatment of sewage, agricultural, or flood plain run-off, all currently major pollutants and health risks. However, this waste water cannot feed algae directly and must first be processed by bacteria, through anaerobic digestion. If waste water is not processed before it reaches the algae, it will contaminate the algae in the reactor, and at the very least, kill much of the desired algae strain. In biogas facilities, organic waste is often converted to a mixture of carbon dioxide, methane, and organic fertilizer. Organic fertilizer that comes out of the digester is liquid, and nearly suitable for algae growth, but it must first be cleaned and sterilized.
The utilization of wastewater and ocean water instead of freshwater is strongly advocated due to the continuing depletion of freshwater resources. However, heavy metals, trace metals, and other contaminants in wastewater can decrease the ability of cells to produce lipids biosynthetically and also impact various other workings in the machinery of cells. The same is true for ocean water, but the contaminants are found in different concentrations. Thus, agricultural-grade fertilizer is the preferred source of nutrients, but heavy metals are again a problem, especially for strains of algae that are susceptible to these metals. In open pond systems the use of strains of algae that can deal with high concentrations of heavy metals could prevent other organisms from infesting these systems. In some instances it has even been shown that strains of algae can remove over 90% of nickel and zinc from industrial wastewater in relatively short periods of time. | 1 | Applied and Interdisciplinary Chemistry |
SBPase and FBPase (fructose-1,6-bisphosphatase, EC 3.1.3.11) are both phosphatases that catalyze similar during the Calvin cycle. The genes for SBPase and FBPase are related. Both genes are found in the nucleus in plants, and have bacterial ancestry. SBPase is found across many species. In addition to being universally present in photosynthetic organism, SBPase is found in a number of evolutionarily-related, non-photosynthetic microorganisms. SBPase likely originated in red algae. | 0 | Theoretical and Fundamental Chemistry |
Drospirenone is a progestin and antiandrogen medication which is used in birth control pills to prevent pregnancy and in menopausal hormone therapy, among other uses. It is available both alone under the brand name Slynd and in combination with an estrogen under the brand name Yasmin among others. The medication is an analog of the drug spironolactone. Drospirenone is taken by mouth.
Common side effects include acne, headache, breast tenderness, weight increase, and menstrual changes. Rare side effects may include high potassium levels and blood clots (when taken as a combined oestrogen-progestogen pill), among others. Drospirenone is a progestin, or a synthetic progestogen, and hence is an agonist of the progesterone receptor, the biological target of progestogens like progesterone. It has additional antimineralocorticoid and antiandrogenic activity and no other important hormonal activity. Because of its antimineralocorticoid activity and lack of undesirable off-target activity, drospirenone is said to more closely resemble bioidentical progesterone than other progestins.
Drospirenone was patented in 1976 and introduced for medical use in 2000. It is available widely throughout the world. The medication is sometimes referred to as a "fourth-generation" progestin. It is available as a generic medication. In 2020, a formulation of drospirenone with ethinylestradiol was the 145th most commonly prescribed medication in the United States, with more than 4million prescriptions. | 0 | Theoretical and Fundamental Chemistry |
Alexander Butlerov showed in 1861 that the formose reaction created sugars including tetroses, pentoses, and hexoses when formaldehyde is heated under basic conditions with divalent metal ions like calcium. R. Breslow proposed that the reaction was autocatalytic in 1959. | 0 | Theoretical and Fundamental Chemistry |
In 1998, Andrew Fire at Carnegie Institution for Science in Washington DC and Craig Mello at University of Massachusetts in Worcester discovered the RNAi mechanism while working on the gene expression in the nematode, Caenorhabditis elegans. They won the Nobel prize for their research with RNAi in 2006. siRNAs and their role in post-transcriptional gene silencing (PTGS) was discovered in plants by David Baulcombes group at the Sainsbury Laboratory in Norwich, England and reported in Science in 1999. Thomas Tuschl and colleagues soon reported in Nature' that synthetic siRNAs could induce RNAi in mammalian cells. In 2001, the expression of a specific gene was successfully silenced by introducing chemically synthesized siRNA into mammalian cells (Tuschl et al.) These discoveries led to a surge in interest in harnessing RNAi for biomedical research and drug development. Significant developments in siRNA therapies have been made with both organic (carbon based) and inorganic (non-carbon based) nanoparticles, which have been successful in drug delivery to the brain, offering promising methods to deliver therapeutics into human subjects. However, human applications of siRNA have had significant limitations to its success. One of these being off-targeting. There is also a possibility that these therapies can trigger innate immunity. Animal models have not been successful in accurately representing the extent of this response in humans. Hence, studying the effects of siRNA therapies has been a challenge.
In recent years, siRNA therapies have been approved and new methods have been established to overcome these challenges. There are approved therapies available for commercial use and several currently in the pipeline waiting to get approval. | 1 | Applied and Interdisciplinary Chemistry |
The biosynthesis of fatty acids begins with acetyl-CoA precursors that are brought together to make long straight chain lipids. Acetyl-CoA is produced in aerobic organisms by pyruvate dehydrogenase, an enzyme that has been shown to express a large, 2.3% isotope effect on the C2 site of pyruvate and a small fractionation on the C3 site. These become the odd and even carbon positions of fatty acids respectively and in theory would result in a pattern of C depletions and enrichments at odd and even positions, respectively. In 1982, Monson and Hayes developed technology for measuring the position specific carbon isotope abundances of fatty acids. Their experiments on Escherichia coli revealed the predicted relative C enrichments at odd numbered carbon sites. However, this pattern was not found in Saccharomyces cerevisiae that were fed glucose. Instead, its fatty acids were C enriched at the odd positions. This has been interpreted as either a product of isotope effects during fatty acid degradation or the intramolecular isotopic heterogeneity of glucose that ultimately is reflected in the position-specific patterns of fatty acids. | 0 | Theoretical and Fundamental Chemistry |
In protein folding, a native contact is a contact between the side chains of two amino acids that are not neighboring in the amino acid sequence (i.e., they are more than four residues apart in the primary sequence in order to remove trivial i to i+4 contacts along alpha helices) but are spatially close in the protein's native state tertiary structure. The fraction of native contacts reproduced in a particular structure is often used as a reaction coordinate for measuring the deviation from the native state of structures produced during molecular dynamics simulations or in benchmarks of protein structure prediction methods.
The contact order is a measure of the locality of a protein's native contacts; that is, the sequence distance between amino acids that form contacts. Proteins with low contact order are thought to fold faster and some may be candidates for downhill folding. | 1 | Applied and Interdisciplinary Chemistry |
The disulfide binding of the inhibitor takes place in the luminal sector of the H/K ATPase were 2 mol of inhibitor is bound per 1 mol of active site H/K ATPase.
All PPIs react with cysteine 813 in the loop between TM5 and TM6 on the H/K ATPase, fixing the enzyme in the E2 configuration. Omeprazole reacts with cysteine 813 and 892. Rabeprazole binds to cysteine 813 and both 892 and 321. Lansoprazole reacts with cysteine 813 and cysteine 321, whereas pantoprazole and tenatoprazole react with cysteine 813 and 822.
Reaction with cysteine 822 confers a rather special property to the covalently inhibited enzyme, namely irreversibility to reducing agents. The likely first step is binding of the prodrug protonated on the pyridine of the compound with cysteine 813. Then the second proton is added with acid transport by the H/K ATPase, and the compound is activated. Recent data suggest the hydrated sulfenic acid to be the reactive species forming directly from the mono-protonated benzimidazole bound on the surface of the pump. | 1 | Applied and Interdisciplinary Chemistry |
DNA condensation can be induced in vitro either by applying external force to bring the double helices together, or by inducing attractive interactions between the DNA segments. The former can be achieved e.g. with the help of the osmotic pressure exerted by crowding neutral polymers in the presence of monovalent salts. In this case, the forces pushing the double helices together are coming from entropic random collisions with the crowding polymers surrounding DNA condensates, and salt is required to neutralize DNA charges and decrease DNA-DNA repulsion. The second possibility can be realized by inducing attractive interactions between the DNA segments by multivalent cationic charged ligands (multivalent metal ions, inorganic cations, polyamines, protamines, peptides, lipids, liposomes and proteins). | 1 | Applied and Interdisciplinary Chemistry |
Spectrum analyzer types are distinguished by the methods used to obtain the spectrum of a signal. There are swept-tuned and fast Fourier transform (FFT) based spectrum analyzers:
*A swept-tuned analyzer uses a superheterodyne receiver to down-convert a portion of the input signal spectrum to the center frequency of a narrow band-pass filter, whose instantaneous output power is recorded or displayed as a function of time. By sweeping the receiver's center-frequency (using a voltage-controlled oscillator) through a range of frequencies, the output is also a function of frequency. But while the sweep centers on any particular frequency, it may be missing short-duration events at other frequencies.
*An FFT analyzer computes a time-sequence of periodograms. FFT refers to a particular mathematical algorithm used in the process. This is commonly used in conjunction with a receiver and analog-to-digital converter. As above, the receiver reduces the center-frequency of a portion of the input signal spectrum, but the portion is not swept. The purpose of the receiver is to reduce the sampling rate that the analyzer must contend with. With a sufficiently low sample-rate, FFT analyzers can process all the samples (100% duty-cycle), and are therefore able to avoid missing short-duration events. | 0 | Theoretical and Fundamental Chemistry |
Chemfluence was started in the year 1994 by the students of The Department of Chemical Engineering of Anna University. Since then, Chemfluence had been a massive success and been attracting more participants and has become a phenomenal hit among the events by other Chemical Engineers around the country. | 1 | Applied and Interdisciplinary Chemistry |
A rather intuitive route to cyclic isomers is the intramolecular conjugate addition to α,β–unsaturated carbonyls (intramolecular Michael addition or IMA). Competent Michael acceptors include conjugated enones, enals or nitroalkene derivatives and examples of other acceptors are sparse. Despite IMA reactions being ubiquitous in synthesis, very few examples of asymmetric IMA transformations exist.
Thiourea catalysts with pendant chiral backbones have shown to activate systems with tethered nitroalkane and ester motifs to induce asymmetric IMA. The utility of this transformation was demonstrated in the synthesis of cyclic γ– amino acid precursors (figure 1). It is proposed that activation occurs via H–bonding of both the nitronate and the ester to the thiourea catalyst and explains the interesting selectivity for the E–ester.
A functional stereodivergent organocatalyzed IMA/lactonization transformation in the synthesis of substituted dihydrofurans and tetrahydrofurans has been studied for its ability to construct important structural motifs in numerous natural products (figure 2). When ethers such as 3 are subject to (S)–(–)–tetramisole hydrochloride (4) catalyst the result is the syn–2,3–substituted THF while the complementary anti–product is easily accessible via a Cinchona alkaloid catalyst such as 7. | 0 | Theoretical and Fundamental Chemistry |
Interfering with insects' reproduction can be accomplished by sterilizing males of the target species and releasing them, so that they mate with females but do not produce offspring. This technique was first used on the screwworm fly in 1958 and has since been used with the medfly, the tsetse fly, and the gypsy moth. This is a costly and slow approach that only works on some types of insects. | 1 | Applied and Interdisciplinary Chemistry |
TILLING (Targeting Induced Local Lesions in Genomes) is a method in molecular biology that allows directed identification of mutations in a specific gene. TILLING was introduced in 2000, using the model plant Arabidopsis thaliana, and expanded on into other uses and methodologies by a small group of scientists including Luca Comai. TILLING has since been used as a reverse genetics method in other organisms such as zebrafish, maize, wheat, rice, soybean, tomato and lettuce. | 1 | Applied and Interdisciplinary Chemistry |
The Shields parameter, also called the Shields criterion or Shields number, is a nondimensional number used to calculate the initiation of motion of sediment in a fluid flow. It is a nondimensionalization of a shear stress, and is typically denoted or . This parameter has been developed by Albert F. Shields, and is called later Shields parameter. The Shields parameter is the main parameter of the Shields formula. It is given by:
where:
* is a dimensional shear stress;
* is the density of the sediment;
* is the density of the fluid;
* is acceleration due to gravity;
* is a characteristic particle diameter of the sediment. | 1 | Applied and Interdisciplinary Chemistry |
The terms isoelectric point (IEP) and point of zero charge (PZC) are often used interchangeably, although under certain circumstances, it may be productive to make the distinction.
In systems in which H/OH are the interface potential-determining ions, the point of zero charge is given in terms of pH. The pH at which the surface exhibits a neutral net electrical charge is the point of zero charge at the surface. Electrokinetic phenomena generally measure zeta potential, and a zero zeta potential is interpreted as the point of zero net charge at the shear plane. This is termed the isoelectric point. Thus, the isoelectric point is the value of pH at which the colloidal particle remains stationary in an electrical field. The isoelectric point is expected to be somewhat different from the point of zero charge at the particle surface, but this difference is often ignored in practice for so-called pristine surfaces, i.e., surfaces with no specifically adsorbed positive or negative charges. In this context, specific adsorption is understood as adsorption occurring in a Stern layer or chemisorption. Thus, point of zero charge at the surface is taken as equal to isoelectric point in the absence of specific adsorption on that surface.
According to Jolivet, in the absence of positive or negative charges, the surface is best described by the point of zero charge. If positive and negative charges are both present in equal amounts, then this is the isoelectric point. Thus, the PZC refers to the absence of any type of surface charge, while the IEP refers to a state of neutral net surface charge. The difference between the two, therefore, is the quantity of charged sites at the point of net zero charge. Jolivet uses the intrinsic surface equilibrium constants, pK and pK to define the two conditions in terms of the relative number of charged sites:
For large ΔpK (>4 according to Jolivet), the predominant species is MOH while there are relatively few charged species – so the PZC is relevant. For small values of ΔpK, there are many charged species in approximately equal numbers, so one speaks of the IEP. | 0 | Theoretical and Fundamental Chemistry |
For a given cation, Pauling defined the electrostatic bond strength to each coordinated anion as , where z is the cation charge and ν is the cation coordination number. A stable ionic structure is arranged to preserve local electroneutrality, so that the sum of the strengths of the electrostatic bonds to an anion equals the charge on that anion.
where is the anion charge and the summation is over the adjacent cations. For simple solids, the are equal for all cations coordinated to a given anion, so that the anion coordination number is the anion charge divided by each electrostatic bond strength. Some examples are given in the table.
Pauling showed that this rule is useful in limiting the possible structures to consider for more complex crystals such as the aluminosilicate mineral orthoclase, , with three different cations. However, from data analysis of oxides from the Inorganic Crystal Structure Database (ICSD), the result showed that only 20% of all oxygen atoms matched with the prediction from second rule (using a cutoff of 0.01). | 0 | Theoretical and Fundamental Chemistry |
BARDS has significant potential as an analytical technique. Applications researched so far include:
* Batch consistency analysis
* Blend uniformity analysis
* Polymorph and pseudopolymorph discrimination
* Monitoring of supersaturation of solutions and rates of outgassing | 0 | Theoretical and Fundamental Chemistry |
The BC200 RNA is the product of an unprocessed monomeric Alu sequence. It is 200 nucleotides long and non-translatable.
BC200 has three distinct structural domains. The 5 region of the RNA defines one domain and consists of Alu repeat elements. The other two structural domains are a central A-rich region, and a C-rich 3 region specific to BC200. The 5 end of this molecule has both primary and secondary structure that is very similar to 7SL RNA, a signal recognition particle RNA (SRP) which also includes a 5 Alu domain.
The BC200 RNA gene has two pseudogenes: BC200 beta and BC200 gamma. These two pseudogenes each have a single gene in the genome, located on separate chromosomes. The beta pseudogene is composed of a BC200 RNA gene and additional Alu sequences. The gamma pseudogene contains an inverted long interspersed nuclear element (LINE). They both have transpositional ability, but the exact mechanism is unknown. | 1 | Applied and Interdisciplinary Chemistry |
Researchers from Britain and Switzerland have previously found antibodies that work in Group 1 influenza A viruses or against most Group 2 viruses (CR8020), but not against both.
This team developed a method using single-cell screening to test very large numbers of human plasma cells, to increase their odds of finding an antibody even if it was extremely rare. When they identified FI6, they injected it into mice and ferrets and found that it protected the animals against infection by either a Group 1 or Group 2 influenza A virus.
Scientists screened 104,000 peripheral-blood plasma cells from eight recently infected or vaccinated donors for antibodies that recognize each of three diverse influenza strains: H1N1 (swine-origin) and H5N1 and H7N7 (highly pathogenic avian influenzas.) From one donor, they isolated four plasma cells that produced an identical antibody, which they called FI6. This antibody binds all 16 HA subtypes, neutralizes infection, and protects mice and ferrets from lethal infection. The most broadly reactive antibodies that had previously been discovered recognized either one group of HA subtypes or the other, highlighting how remarkable FI6 is in its ability to target the gamut of influenza subtypes. | 1 | Applied and Interdisciplinary Chemistry |
Cytidine diphosphate glucose, often abbreviated CDP-glucose, is a nucleotide-linked sugar consisting of cytidine diphosphate and glucose. | 1 | Applied and Interdisciplinary Chemistry |
Many different microscopy techniques are used in metallographic analysis.
Prepared specimens should be examined with the unaided eye after etching to detect any visible areas that have responded to the etchant differently from the norm as a guide to where microscopical examination should be employed. Light optical microscopy (LOM) examination should always be performed prior to any electron metallographic (EM) technique, as these are more time-consuming to perform and the instruments are much more expensive.
Further, certain features can be best observed with the LOM, e.g., the natural color of a constituent can be seen with the LOM but not with EM systems. Also, image contrast of microstructures at relatively low magnifications, e.g., <500X, is far better with the LOM than with the scanning electron microscope (SEM), while transmission electron microscopes (TEM) generally cannot be utilized at magnifications below about 2000 to 3000X. LOM examination is fast and can cover a large area. Thus, the analysis can determine if the more expensive, more time-consuming examination techniques using the SEM or the TEM are required and where on the specimen the work should be concentrated. | 1 | Applied and Interdisciplinary Chemistry |
The pH of a natural soil depends on the mineral composition of the parent material of the soil, and the weathering reactions undergone by that parent material. In warm, humid environments, soil acidification occurs over time as the products of weathering are leached by water moving laterally or downwards through the soil. In dry climates, however, soil weathering and leaching are less intense and soil pH is often neutral or alkaline. | 0 | Theoretical and Fundamental Chemistry |
For the process of extracting the DNA/RNA, there are a number of essential guidelines. This includes a description of the extraction process done, a statement on what DNA extraction kit was used and any changes made to the directions, details on whether any DNase or RNase treatment was used, a statement on whether any contamination was assessed, a quantification of the amount of genetic material extracted, a description of the instruments used for the extraction, the methods used to retain RNA integrity, a statement on the RNA integrity number and quality indicator and the quantification cycle (Cq) reached, and lastly what testing was done to determine the presence or absence of inhibitors. Four desired pieces of information are where the reagents used were obtained from, what level of genetic purity was obtained, what yield was obtained, and an electrophoresis gel image for confirmation. | 1 | Applied and Interdisciplinary Chemistry |
Cytidine diphosphate, abbreviated CDP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside cytidine. CDP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase cytosine.
In Bacillus subtilis and Staphylococcus aureus, CDP-activated glycerol and ribitol are necessary to build wall teichoic acid. | 1 | Applied and Interdisciplinary Chemistry |
Froth flotation depends on the selective adhesion of air bubbles to mineral surfaces in a mineral/water slurry. The air bubbles attach to more hydrophobic particles, as determined by the interfacial energies between the solid, liquid, and gas phases. This energy is determined by the Young–Dupré equation:
where:
* γ is the surface energy of the liquid/vapor interface
* γ is the surface energy of the solid/vapor interface
* γ is the surface energy of the solid/liquid interface,
* θ is the contact angle, the angle formed at the junction between vapor, solid, and liquid phases.
Minerals targeted for separation may be chemically surface-modified with collectors so that they are more hydrophobic. Collectors are a type of surfactant that increase the natural hydrophobicity of the surface, increasing the separability of the hydrophobic and hydrophilic particles. Collectors either chemically bond via chemisorption to the mineral or adsorb onto the surface via physisorption. | 1 | Applied and Interdisciplinary Chemistry |
*Arc discharge: this is a high power thermal discharge of very high temperature (≈10,000 K). It can be generated using various power supplies. It is commonly used in metallurgical processes. For example, it is used to smelt minerals containing AlO to produce aluminium.
*Corona discharge: this is a non-thermal discharge generated by the application of high voltage to sharp electrode tips. It is commonly used in ozone generators and particle precipitators.
*Dielectric barrier discharge (DBD): this is a non-thermal discharge generated by the application of high voltages across small gaps wherein a non-conducting coating prevents the transition of the plasma discharge into an arc. It is often mislabeled "Corona" discharge in industry and has similar application to corona discharges. A common usage of this discharge is in a plasma actuator for vehicle drag reduction. It is also widely used in the web treatment of fabrics. The application of the discharge to synthetic fabrics and plastics functionalizes the surface and allows for paints, glues and similar materials to adhere. The dielectric barrier discharge was used in the mid-1990s to show that low temperature atmospheric pressure plasma is effective in inactivating bacterial cells. This work and later experiments using mammalian cells led to the establishment of a new field of research known as plasma medicine. The dielectric barrier discharge configuration was also used in the design of low temperature plasma jets. These plasma jets are produced by fast propagating guided ionization waves known as plasma bullets.
*Capacitive discharge: this is a nonthermal plasma generated by the application of RF power (e.g., 13.56 MHz) to one powered electrode, with a grounded electrode held at a small separation distance on the order of 1 cm. Such discharges are commonly stabilized using a noble gas such as helium or argon.
*"Piezoelectric direct discharge plasma:" is a nonthermal plasma generated at the high-side of a piezoelectric transformer (PT). This generation variant is particularly suited for high efficient and compact devices where a separate high voltage power supply is not desired. | 0 | Theoretical and Fundamental Chemistry |
; Nausea and vomiting
:This is not a general side effect of radiation therapy, and mechanistically is associated only with treatment of the stomach or abdomen (which commonly react a few hours after treatment), or with radiation therapy to certain nausea-producing structures in the head during treatment of certain head and neck tumors, most commonly the vestibules of the inner ears. As with any distressing treatment, some patients vomit immediately during radiotherapy, or even in anticipation of it, but this is considered a psychological response. Nausea for any reason can be treated with antiemetics.
; Damage to the epithelial surfaces
:Epithelial surfaces may sustain damage from radiation therapy. Depending on the area being treated, this may include the skin, oral mucosa, pharyngeal, bowel mucosa, and ureter. The rates of onset of damage and recovery from it depend upon the turnover rate of epithelial cells. Typically the skin starts to become pink and sore several weeks into treatment. The reaction may become more severe during the treatment and for up to about one week following the end of radiation therapy, and the skin may break down. Although this moist desquamation is uncomfortable, recovery is usually quick. Skin reactions tend to be worse in areas where there are natural folds in the skin, such as underneath the female breast, behind the ear, and in the groin.
; Mouth, throat and stomach sores
:If the head and neck area is treated, temporary soreness and ulceration commonly occur in the mouth and throat. If severe, this can affect swallowing, and the patient may need painkillers and nutritional support/food supplements. The esophagus can also become sore if it is treated directly, or if, as commonly occurs, it receives a dose of collateral radiation during treatment of lung cancer. When treating liver malignancies and metastases, it is possible for collateral radiation to cause gastric, stomach, or duodenal ulcers This collateral radiation is commonly caused by non-targeted delivery (reflux) of the radioactive agents being infused. Methods, techniques and devices are available to lower the occurrence of this type of adverse side effect.
; Intestinal discomfort
:The lower bowel may be treated directly with radiation (treatment of rectal or anal cancer) or be exposed by radiation therapy to other pelvic structures (prostate, bladder, female genital tract). Typical symptoms are soreness, diarrhoea, and nausea. Nutritional interventions may be able to help with diarrhoea associated with radiotherapy. Studies in people having pelvic radiotherapy as part of anticancer treatment for a primary pelvic cancer found that changes in dietary fat, fibre and lactose during radiotherapy reduced diarrhoea at the end of treatment.
; Swelling
:As part of the general inflammation that occurs, swelling of soft tissues may cause problems during radiation therapy. This is a concern during treatment of brain tumors and brain metastases, especially where there is pre-existing raised intracranial pressure or where the tumor is causing near-total obstruction of a lumen (e.g., trachea or main bronchus). Surgical intervention may be considered prior to treatment with radiation. If surgery is deemed unnecessary or inappropriate, the patient may receive steroids during radiation therapy to reduce swelling.
; Infertility
:The gonads (ovaries and testicles) are very sensitive to radiation. They may be unable to produce gametes following direct exposure to most normal treatment doses of radiation. Treatment planning for all body sites is designed to minimize, if not completely exclude dose to the gonads if they are not the primary area of treatment. | 0 | Theoretical and Fundamental Chemistry |
STAT1 loss of function, therefore STAT1 deficiency can have many variants. There are two main genetic impairments that can cause response to interferons type I and III. First there can be autosomal recessive partial or even complete deficiency of STAT1. That causes intracellular bacterial diseases or viral infections and impaired IFN a, b, g and IL27 responses are diagnosed. In partial form there can also be found high levels of IFNg in blood serum. When tested from whole blood, monocytes do not respond to BCG and IFNg doses with IL-12 production. In complete recessive form there is a very low response to anti-viral and antimycotical medication. Second, partial STAT1 deficiency can also be an autosomal dominant mutation; phenotypically causing impaired IFNg responses and causing patients to suffer with selective intracellular bacterial diseases (MSMD).
In knock-out mice prepared in the 90s, a low amount of CD4 and CD25 regulatory T-cells and almost no IFNa, b and g response was discovered, which lead to parasital, viral and bacterial infections. The very first reported case of STAT1 deficiency in human was an autosomal dominant mutation and patients were showing propensity to mycobacterial infections. Another case reported was about an autosomal recessive form. 2 related patients had a homozygous missense STAT1 mutation which caused impaired splicing, therefore a defect in mature protein. Patients had partially damaged response to both IFNa and IFNg. Scientists now claim that recessive STAT1 deficiency is a new form of primary immunodeficiency and whenever a patient suffers sudden, severe and unexpected bacterial and viral infections, should be considered as potentially STAT1 deficient.
Interferons induce the formation of two transcriptional activators: gamma-activating factor (GAF) and interferon-stimulated gamma factor 3 (ISGF3). A natural heterozygous germline STAT1 mutation associated with susceptibility to mycobacterial but not viral disease was found in two unrelated patients with unexplained mycobacterial disease. This mutation caused a loss of GAF and ISGF3 activation but was dominant for one cellular phenotype and recessive for the other. It impaired the nuclear accumulation of GAF but not of ISGF3 in cells stimulated by interferons, implying that the antimycobacterial but not the antiviral effects of human interferons are mediated by GAF. More recently, two patients have been identified with homozygous STAT-1 mutations who developed both post–BCG vaccination disseminated disease and lethal viral infections. The mutations in these patients caused a complete lack of STAT-1 and resulted in a lack of formation of both GAF and ISGF3. | 1 | Applied and Interdisciplinary Chemistry |
Molecules have various states referred to as energy levels. Fluorescence spectroscopy is primarily concerned with electronic and vibrational states. Generally, the species being examined has a ground electronic state (a low energy state) of interest, and an excited electronic state of higher energy. Within each of these electronic states there are various vibrational states.
In fluorescence, the species is first excited, by absorbing a photon, from its ground electronic state to one of the various vibrational states in the excited electronic state. Collisions with other molecules cause the excited molecule to lose vibrational energy until it reaches the lowest vibrational state from the excited electronic state. This process is often visualized with a Jablonski diagram.
The molecule then drops down to one of the various vibrational levels of the ground electronic state again, emitting a photon in the process. As molecules may drop down into any of several vibrational levels in the ground state, the emitted photons will have different energies, and thus frequencies. Therefore, by analysing the different frequencies of light emitted in fluorescent spectroscopy, along with their relative intensities, the structure of the different vibrational levels can be determined.
For atomic species, the process is similar; however, since atomic species do not have vibrational energy levels, the emitted photons are often at the same wavelength as the incident radiation. This process of re-emitting the absorbed photon is "resonance fluorescence" and while it is characteristic of atomic fluorescence, is seen in molecular fluorescence as well.
In a typical fluorescence (emission) measurement, the excitation wavelength is fixed and the detection wavelength varies, while in a fluorescence excitation measurement the detection wavelength is fixed and the excitation wavelength is varied across a region of interest. An emission map is measured by recording the emission spectra resulting from a range of excitation wavelengths and combining them all together. This is a three dimensional surface data set: emission intensity as a function of excitation and emission wavelengths, and is typically depicted as a contour map. | 0 | Theoretical and Fundamental Chemistry |
The so-called Sedov-Taylor solution has become useful in astrophysics. For example, it can be applied to quantify an estimate for the outcome from supernova-explosions. The Sedov-Taylor expansion is also known as the Blast Wave phase, which is an adiabatic expansion phase in the life cycle of supernova. The temperature of the material in a supernova shell decreases with time, but the internal energy of the material is always 72% of E, the initial energy released. This is helpful for astrophysicists interested in predicting the behavior of supernova remnants. | 1 | Applied and Interdisciplinary Chemistry |
"Fast ignition" appeared in the late nineties, as part of a push by LLE to build the Omega EP system, which finished in 2008. Fast ignition showed dramatic power savings and moved ICF into the race for energy production. The HiPER experimental facility became dedicated to fast ignition.
In 2001 the United States, China and Republic of Korea joined ITER while Canada withdrew.
In April 2005, a UCLA team announced a way of producing fusion using a machine that "fits on a lab bench", using lithium tantalate to generate enough voltage to fuse deuterium. The process did not generate net power.
The next year, China's EAST test reactor was completed. This was the first tokamak to use superconducting magnets to generate both toroidal and poloidal fields.
In the early 2000s, LANL researchers claimed that an oscillating plasma could reach local thermodynamic equilibrium. This prompted the POPS and Penning trap designs.
In 2005 NIF fired its first bundle of eight beams, achieving the most powerful laser pulse to date - 152.8 kJ (infrared).
MIT researchers became interested in fusors for space propulsion, using fusors with multiple inner cages. Greg Piefer founded Phoenix Nuclear Labs and developed the fusor into a neutron source for medical isotope production. Robert Bussard began speaking openly about the polywell in 2006.
In March 2009, NIF became operational.
In the early 2000s privately backed fusion companies launched to develop commercial fusion power. Tri Alpha Energy, founded in 1998, began by exploring a field-reversed configuration approach. In 2002, Canadian company General Fusion began proof-of-concept experiments based on a hybrid magneto-inertial approach called Magnetized Target Fusion. Investors included Jeff Bezos (General Fusion) and Paul Allen (Tri Alpha Energy). Toward the end of the decade, Tokamak Energy started exploring spherical tokamak devices using reconnection. | 0 | Theoretical and Fundamental Chemistry |
Engineers have studied the various heat-engine cycles to improve the amount of usable work they could extract from a given power source. The Carnot cycle limit cannot be reached with any gas-based cycle, but engineers have found at least two ways to bypass that limit and one way to get better efficiency without bending any rules:
#Increase the temperature difference in the heat engine. The simplest way to do this is to increase the hot side temperature, which is the approach used in modern combined-cycle gas turbines. Unfortunately, physical limits (such as the melting point of the materials used to build the engine) and environmental concerns regarding NO production (if the heat source is combustion with ambient air) restrict the maximum temperature on workable heat-engines. Modern gas turbines run at temperatures as high as possible within the range of temperatures necessary to maintain acceptable NO output . Another way of increasing efficiency is to lower the output temperature. One new method of doing so is to use mixed chemical working fluids, then exploit the changing behavior of the mixtures. One of the most famous is the so-called Kalina cycle, which uses a 70/30 mix of ammonia and water as its working fluid. This mixture allows the cycle to generate useful power at considerably lower temperatures than most other processes.
#Exploit the physical properties of the working fluid. The most common such exploitation is the use of water above the critical point (supercritical water). The behavior of fluids above their critical point changes radically, and with materials such as water and carbon dioxide it is possible to exploit those changes in behavior to extract greater thermodynamic efficiency from the heat engine, even if it is using a fairly conventional Brayton or Rankine cycle. A newer and very promising material for such applications is supercritical CO. SO and xenon have also been considered for such applications. Downsides include issues of corrosion and erosion, the different chemical behavior above and below the critical point, the needed high pressures and – in the case of sulfur dioxide and to a lesser extent carbon dioxide – toxicity. Among the mentioned compounds xenon is least suitable for use in a nuclear reactor due to the high neutron absorption cross section of almost all isotopes of xenon, whereas carbon dioxide and water can also double as a neutron moderator for a thermal spectrum reactor.
#Exploit the chemical properties of the working fluid. A fairly new and novel exploit is to use exotic working fluids with advantageous chemical properties. One such is nitrogen dioxide (NO), a toxic component of smog, which has a natural dimer as di-nitrogen tetraoxide (NO). At low temperature, the NO is compressed and then heated. The increasing temperature causes each NO to break apart into two NO molecules. This lowers the molecular weight of the working fluid, which drastically increases the efficiency of the cycle. Once the NO has expanded through the turbine, it is cooled by the heat sink, which makes it recombine into NO. This is then fed back by the compressor for another cycle. Such species as aluminium bromide (AlBr), NOCl, and GaI have all been investigated for such uses. To date, their drawbacks have not warranted their use, despite the efficiency gains that can be realized. | 0 | Theoretical and Fundamental Chemistry |
The density of water is about 1000 kg/m or 1 g/cm, because the size of the gram was originally based on the mass of a cubic centimetre of water.
In chemistry, g/cm is more commonly used. | 0 | Theoretical and Fundamental Chemistry |
A phonovoltaic (pV) cell converts vibrational (phonons) energy into a direct current much like the photovoltaic effect in a photovoltaic (PV) cell converts light (photon) into power. That is, it uses a p-n junction to separate the electrons and holes generated as valence electrons absorb optical phonons more energetic than the band gap, and then collects them in the metallic contacts for use in a circuit. The pV cell is an application of heat transfer physics and competes with other thermal energy harvesting devices like the thermoelectric generator.
While the thermoelectric generator converts heat, a broad spectrum of phonon and electron energy, to electricity, the pV cell converts only a narrow band of phonon energy, i.e., only the most energetic optical phonon modes. A narrow band of excited optical phonons has much less entropy than heat. Thus, the pV cell can exceed the thermoelectric efficiency. However, exciting and harvesting the optical phonon poses a challenge. | 0 | Theoretical and Fundamental Chemistry |
These sweet glycosides found in the stevia plant Stevia rebaudiana Bertoni have 40–300 times the sweetness of sucrose. The two primary glycosides, stevioside and rebaudioside A, are used as natural sweeteners in many countries. These glycosides have steviol as the aglycone part. Glucose or rhamnose-glucose combinations are bound to the ends of the aglycone to form the different compounds. | 0 | Theoretical and Fundamental Chemistry |
Ligand-based methods typically require a fraction of a second for a single structure comparison operation. Sometimes a single CPU is enough to perform a large screening within hours. However, several comparisons can be made in parallel in order to expedite the processing of a large database of compounds. | 1 | Applied and Interdisciplinary Chemistry |
To track the progress of a SELEX reaction, the number of target bound molecules, which is equivalent to the number of oligonucleotides eluted, can be compared to the estimated total input of oligonucleotides following elution at each round. The number of eluted oligonucleotides can be estimated through elution concentration estimations via 260 nm wavelength absorbance or fluorescent labeling of oligonucleotides. As the SELEX reaction approaches completion, the fraction of the oligonucleotide library that binds target approaches 100%, such that the number of eluted molecules approaches the total oligonucleotide input estimate, but may converge at a lower number. | 1 | Applied and Interdisciplinary Chemistry |
There have been proposals for reactors that consume nuclear waste and transmute it to other, less-harmful or shorter-lived, nuclear waste. In particular, the integral fast reactor was a proposed nuclear reactor with a nuclear fuel cycle that produced no transuranic waste and, in fact, could consume transuranic waste. It proceeded as far as large-scale tests but was eventually canceled by the U.S. Government. Another approach, considered safer but requiring more development, is to dedicate subcritical reactors to the transmutation of the left-over transuranic elements.
An isotope that is found in nuclear waste and that represents a concern in terms of proliferation is Pu-239. The large stock of plutonium is a result of its production inside uranium-fueled reactors and of the reprocessing of weapons-grade plutonium during the weapons program. An option for getting rid of this plutonium is to use it as a fuel in a traditional light-water reactor (LWR). Several fuel types with differing plutonium destruction efficiencies are under study.
Transmutation was banned in the United States in April 1977 by President Carter due to the danger of plutonium proliferation, but President Reagan rescinded the ban in 1981. Due to economic losses and risks, the construction of reprocessing plants during this time did not resume. Due to high energy demand, work on the method has continued in the EU. This has resulted in a practical nuclear research reactor called Myrrha in which transmutation is possible. Additionally, a new research program called ACTINET has been started in the EU to make transmutation possible on a large, industrial scale. According to President Bush's Global Nuclear Energy Partnership (GNEP) of 2007, the United States is actively promoting research on transmutation technologies needed to markedly reduce the problem of nuclear waste treatment.
There have also been theoretical studies involving the use of fusion reactors as so-called "actinide burners" where a fusion reactor plasma such as in a tokamak, could be "doped" with a small amount of the "minor" transuranic atoms which would be transmuted (meaning fissioned in the actinide case) to lighter elements upon their successive bombardment by the very high energy neutrons produced by the fusion of deuterium and tritium in the reactor. A study at MIT found that only 2 or 3 fusion reactors with parameters similar to that of the International Thermonuclear Experimental Reactor (ITER) could transmute the entire annual minor actinide production from all of the light-water reactors presently operating in the United States fleet while simultaneously generating approximately 1 gigawatt of power from each reactor. | 0 | Theoretical and Fundamental Chemistry |
Among the diverse range of defense strategies plants utilize against pathogens, Ca signaling is very common. Free Ca levels in the cytoplasm increases in response to a pathogenic infection. Ca signatures of this nature usually activate the plant defense system by inducing defense-related genes and the hypersensitive cell death. CaMs, CMLs and CaM-binding proteins are some of the recently identified elements of the plant defense signaling pathways. Several CML genes in tobacco, bean and tomato are responsive to pathogens. CML43 is a CaM-related protein that, as isolated from APR134 gene in the disease-resistant leaves of Arabidopsis for gene expression analysis, is rapidly induced when the leaves are inoculated with Pseudomonas syringae. These genes are also found in tomatoes (Solanum lycopersicum). The CML43 from the APR134 also binds to Ca ions in vitro which shows that CML43 and APR134 are, hence, involved in the Ca-dependent signaling during the plant immune response to bacterial pathogens. The CML9 expression in Arabidopsis thaliana is rapidly induced by phytopathogenic bacteria, flagellin and salicylic acid. Expression of soybean SCaM4 and SCaM5 in transgenic tobacco and Arabidopsis causes an activation of genes related to pathogen resistance and also results in enhanced resistance to a wide spectrum of pathogen infection. The same is not true for soybean SCaM1 and SCaM2 that are highly conserved CaM isoforms. The AtBAG6 protein is a CaM-binding protein that binds to CaM only in the absence of Ca and not in the presence of it. AtBAG6 is responsible for the hypersensitive response of programmed cell death in order to prevent the spread of pathogen infection or to restrict pathogen growth. Mutations in the CaM binding proteins can lead to severe effects on the defense response of the plants towards pathogen infections. Cyclic nucleotide-gated channels (CNGCs) are functional protein channels in the plasma membrane that have overlapping CaM binding sites transport divalent cations such as Ca. However, the exact role of the positioning of the CNGCs in this pathway for plant defense is still unclear. | 1 | Applied and Interdisciplinary Chemistry |
Vasdev grew up in Oakville, Ontario, Canada. He attended Oakville Trafalgar High School and graduated from McMaster University in 1998 with double bachelor degrees, summa cum laude, Hon. BSc in chemistry and B.A. in psychology. He concurrently worked as chemist at Astra Pharma and Glaxo-Wellcome. He then earned his Doctorate of Chemistry, supported by NSERC, at McMaster University in 2003, under the supervision of Professors Raman Chirakal and Gary J. Schrobilgen. He continued training with a NSERC postdoctoral fellowship in the Department of Nuclear Medicine and Functional Imaging at the Lawrence Berkeley National Laboratory, mentored by Henry F. VanBrocklin. | 0 | Theoretical and Fundamental Chemistry |
The photovoltaic effect was experimentally demonstrated first by French physicist Edmond Becquerel. In 1839, at age 19, he built the worlds first photovoltaic cell in his fathers laboratory. Willoughby Smith first described the "Effect of Light on Selenium during the passage of an Electric Current" in a 20 February 1873 issue of Nature. In 1883 Charles Fritts built the first solid state photovoltaic cell by coating the semiconductor selenium with a thin layer of gold to form the junctions; the device was only around 1% efficient. Other milestones include:
* 1888 – Russian physicist Aleksandr Stoletov built the first cell based on the outer photoelectric effect discovered by Heinrich Hertz in 1887.
* 1904 – Julius Elster, together with Hans Friedrich Geitel, devised the first practical photoelectric cell.
* 1905 – Albert Einstein proposed a new quantum theory of light and explained the photoelectric effect in a landmark paper, for which he received the Nobel Prize in Physics in 1921.
* 1941 – Vadim Lashkaryov discovered p-n-junctions in CuO and AgS protocells.
* 1946 – Russell Ohl patented the modern junction semiconductor solar cell, while working on the series of advances that would lead to the transistor.
* 1948 - Introduction to the World of Semiconductors states Kurt Lehovec may have been the first to explain the photo-voltaic effect in the peer reviewed journal Physical Review.
* 1954 – The first practical photovoltaic cell was publicly demonstrated at Bell Laboratories. The inventors were Calvin Souther Fuller, Daryl Chapin and Gerald Pearson.
* 1958 – Solar cells gained prominence with their incorporation onto the Vanguard I satellite. | 0 | Theoretical and Fundamental Chemistry |
The two principal groups which were involved in the conflict over element naming were:
* An American group at Lawrence Berkeley Laboratory.
* A Russian group at Joint Institute for Nuclear Research in Dubna.
and, as a kind of arbiter,
* The IUPAC Commission on Nomenclature of Inorganic Chemistry, which introduced its own proposal to the IUPAC General Assembly.
The German group at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, who had (undisputedly) discovered elements 107 to 109, were dragged into the controversy when the Commission suggested that the name "hahnium", proposed for element 105 by the Americans, be used for GSI's element 108 instead. | 1 | Applied and Interdisciplinary Chemistry |
The power required to run a supersonic wind tunnel is enormous, of the order of 50 MW per square meter of test section cross-sectional area. For this reason most wind tunnels operate intermittently using energy stored in high-pressure tanks. These wind tunnels are also called intermittent supersonic blowdown wind tunnels (of which a schematic preview is given below). Another way of achieving the huge power output is with the use of a vacuum storage tank. These tunnels are called indraft supersonic wind tunnels, and are seldom used because they are restricted to low Reynolds numbers. Some large countries have built major supersonic tunnels that run continuously; one is shown in the photo.
Other problems operating a supersonic wind tunnel include:
*starting and unstart of the test section (related to maintaining at least a minimum pressure ratio)
*adequate supply of dry air
*wall interference effects due to shock wave reflection and (sometimes) blockage
*high-quality instruments capable of rapid measurements due to short run times in intermittent tunnels
Tunnels such as a Ludwieg tube have short test times (usually less than one second), relatively high Reynolds number, and low power requirements. | 1 | Applied and Interdisciplinary Chemistry |
Strontium-90 () is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.8 years. It undergoes β decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine and industry and is an isotope of concern in fallout from nuclear weapons, nuclear weapons testing, and nuclear accidents. | 0 | Theoretical and Fundamental Chemistry |
A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid. It can effuse through porous solids like a gas, overcoming the mass transfer limitations that slow liquid transport through such materials. SCF are superior to gases in their ability to dissolve materials like liquids or solids. Also, near the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be "fine-tuned".
Supercritical fluids occur in the atmospheres of the gas giants Jupiter and Saturn, the terrestrial planet Venus, and probably in those of the ice giants Uranus and Neptune. Supercritical water is found on Earth, such as the water issuing from black smokers, a type of hydrothermal vent. SCF’s are used as a substitute for organic solvents in a range of industrial and laboratory processes. Carbon dioxide and water are the most commonly used supercritical fluids; they are often used for decaffeination and power generation, respectively. Some substances are soluble in the supercritical state of a solvent (e.g. carbon dioxide) but insoluble in the gaseous or liquid state—or vice versa. This can be used to extract a substance and transport it elsewhere in solution before depositing it in the desired place by simply allowing or inducing a phase transition in the solvent. | 0 | Theoretical and Fundamental Chemistry |
Like most other community analysis methods, TRFLP is also based on PCR amplification of a target gene. In the case of TRFLP, the amplification is performed with one or both the primers having their 5’ end labeled with a fluorescent molecule. In case both primers are labeled, different fluorescent dyes are required. While several common fluorescent dyes can be used for the purpose of tagging such as 6-carboxyfluorescein (6-FAM), ROX, carboxytetramethylrhodamine (TAMRA, a rhodamine-based dye), and [https://en.wiktionary.org/wiki/hexachlorofluorescein hexachlorofluorescein] (HEX), the most widely used dye is 6-FAM. The mixture of amplicons is then subjected to a restriction reaction, normally using a four-cutter restriction enzyme. Following the restriction reaction, the mixture of fragments is separated using either capillary or polyacrylamide electrophoresis in a DNA sequencer and the sizes of the different terminal fragments are determined by the fluorescence detector. Because the excised mixture of amplicons is analyzed in a sequencer, only the terminal fragments (i.e. the labeled end or ends of the amplicon) are read while all other fragments are ignored. Thus, T-RFLP is different from ARDRA and RFLP in which all restriction fragments are visualized. In addition to these steps the TRFLP protocol often includes a cleanup of the PCR products prior to the restriction and in case a capillary electrophoresis is used a desalting stage is also performed prior to running the sample. | 1 | Applied and Interdisciplinary Chemistry |
Mycosubtilin has strong antifungal and hemolytic activities. It is active against fungi and yeasts such as Candida albicans, Candida tropicalis, Saccharomyces cerevisiae, Penicillium notatum, and Fusarium oxysporum.
Its antibacterial activity is quite limited to bacteria such as Micrococcus luteus. | 0 | Theoretical and Fundamental Chemistry |
In thermodynamics, the volume of a system is an important extensive parameter for describing its thermodynamic state. The specific volume, an intensive property, is the system's volume per unit mass. Volume is a function of state and is interdependent with other thermodynamic properties such as pressure and temperature. For example, volume is related to the pressure and temperature of an ideal gas by the ideal gas law.
The physical region covered by a system may or may not coincide with a control volume used to analyze the system. | 0 | Theoretical and Fundamental Chemistry |
Following oral administration, dextromethorphan is rapidly absorbed from the gastrointestinal tract, where it enters the bloodstream and crosses the blood–brain barrier.
At therapeutic doses, dextromethorphan acts centrally (meaning that it acts on the brain) as opposed to locally (on the respiratory tract). It elevates the threshold for coughing, without inhibiting ciliary activity. Dextromethorphan is rapidly absorbed from the gastrointestinal tract and converted into the active metabolite dextrorphan in the liver by the cytochrome P450 enzyme CYP2D6. The average dose necessary for effective antitussive therapy is between 10 and 45 mg, depending on the individual. The International Society for the Study of Cough recommends "an adequate first dose of medication is 60 mg in the adult and repeat dosing should be infrequent rather than qds recommended."
Dextromethorphan has an elimination half-life of approximately 4 hours in individuals with an extensive metabolizer phenotype; this is increased to approximately 13 hours when dextromethorphan is given in combination with quinidine. The duration of action after oral administration is about three to eight hours for dextromethorphan hydrobromide, and 10 to 12 hours for dextromethorphan polistirex. Around one in 10 of the Caucasian population has little or no CYP2D6 enzyme activity, leading to long-lived high drug levels. | 0 | Theoretical and Fundamental Chemistry |
In water-borne coatings, an aqueous polymer dispersion creates a film on the substrate once the solvent has evaporated. Surface functionalization of the polymer particles is a key component of a coating formulation allowing control over such properties as dispersion, film formation temperature, and the coating rheology. Dispersing aids often involve steric or electrostatic repulsion of the polymer particles, providing colloidal stability. The dispersing aids adsorb (as in a grafting onto scheme) onto latex particles giving them functionality. The association of other additives, such as thickeners shown in the schematic to the right, with adsorbed polymer material give rise to complex rheological behavior and excellent control over a coating's flow properties. | 0 | Theoretical and Fundamental Chemistry |
Arslantepe was first investigated by the French archaeologist Louis Delaporte from 1932 to 1939. From 1946 to 1951 Claude F.A. Schaeffer carried out some soundings.
The first Italian excavations at the site of Arslantepe started in 1961, and were conducted under the direction of Professors Piero Meriggi and Salvatore M. Puglisi until 1968. The choice of the site was initially due to their desire to investigate the Neo-Hittite phases of occupation at the site, a period in which Malatya was the capital of one of the most important reigns born after the destruction of the Hittite Empire in its most eastern borders. Majestic remains of this period had been known from Arslantepe since the 1930s after they were brought to light by a French expedition. The Hittitologist Meriggi only took part in the first few campaigns and later left the direction to Puglisi, a palaeoethnologist, who expanded and regularly conducted yearly investigations under regular permit from the Turkish government. Alba Palmieri took over the supervision of the excavation during the 1970s. In the early 21st century, the archaeological investigation was led by Marcella Frangipane. | 1 | Applied and Interdisciplinary Chemistry |
Mesoporous carbon nanoparticles (MCN) are similar to MSNs. They have a similar structure and share key physical properties and characteristics. However, it has been found that MCNs can exhibit lower toxicity that MSNs. To date, not much research has been done on MCNs. The Du lab based in Nanjing, China took made MSN templates using the common method of combining CTAB and TEOS. The researchers then took the MSN templates and dispersed them in a glucose solution followed by autoclaving the mixture to produce a reaction. The product was then subjected to carbonization at 900 degrees Celsius and the MCNs were generated. The researchers found that MCNs had a surface area of 1575 m^2/g, a pore size of 2.2 nm, and an average diameter of 115 nm. | 1 | Applied and Interdisciplinary Chemistry |
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