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The cyano group in HCN can add to the carbonyl group to form cyanohydrins, . In this reaction the ion is the nucleophile that attacks the partially positive carbon atom of the carbonyl group. The mechanism involves a pair of electrons from the carbonyl-group double bond transferring to the oxygen atom, leaving it single-bonded to carbon and giving the oxygen atom a negative charge. This intermediate ion rapidly reacts with , such as from the HCN molecule, to form the alcohol group of the cyanohydrin.
Organometallic compounds, such as organolithium reagents, Grignard reagents, or acetylides, undergo nucleophilic addition reactions, yielding a substituted alcohol group. Related reactions include organostannane additions, Barbier reactions, and the Nozaki–Hiyama–Kishi reaction.
In the aldol reaction, the metal enolates of ketones, esters, amides, and carboxylic acids add to aldehydes to form β-hydroxycarbonyl compounds (aldols). Acid or base-catalyzed dehydration then leads to α,β-unsaturated carbonyl compounds. The combination of these two steps is known as the aldol condensation.
The Prins reaction occurs when a nucleophilic alkene or alkyne reacts with an aldehyde as electrophile. The product of the Prins reaction varies with reaction conditions and substrates employed. | 0 | Theoretical and Fundamental Chemistry |
A 2008 study explored the usage of femtosecond laser irradiation to create permanent spatial arrangements in transparent materials, particularly in its usage to form a singular foamed layer upon biopolymers such as collagen or curcumin. Foaming these surfaces results in a variety of surface modifications that may improve the material's ability for cell adhesion, permeability of fluids due to cell structure, and the formation of nanoscopic fibers.
Additionally, an iron-nitrogen co-doped carbon nanofoam was purposed to be fabricated through the acile salt-assisted pyrolysis process of chitooligosaccharides. | 0 | Theoretical and Fundamental Chemistry |
Pharmacoinformatics is also referred to as pharmacy informatics. According to the article "Pharmacy Informatics: What You Need to Know Now" by the University of Illinois at Chicago Pharmacoinformatics may be defined as: “the scientific field that focuses on medication-related data and knowledge within the continuum of healthcare systems.” It is the application of computers to the storage, retrieval and analysis of drug and prescription information. Pharmacy informaticists work with pharmacy information management systems that help the pharmacist safe decisions about patient drug therapies with respect to, medical insurance records, drug interactions, as well as prescription and patient information.
Pharmacy informatics can be thought of as a sub-domain of the larger professional discipline of health informatics. Health informatics is the study of interactions between people, their work processes and engineered systems within health care with a focus on pharmaceutical care and improved patient safety. For example, the Health Information Management Systems Society (HIMSS) defines pharmacy informatics as, "the scientific field that focuses on medication-related data and knowledge within the continuum of healthcare systems - including its acquisition, storage, analysis, use and dissemination - in the delivery of optimal medication-related patient care and health outcomes" | 1 | Applied and Interdisciplinary Chemistry |
If half of the tetrahedral sites of the parent FCC lattice are filled by ions of opposite charge, the structure formed is the zincblende crystal structure. If all the tetrahedral sites of the parent FCC lattice are filled by ions of opposite charge, the structure formed is the fluorite structure or antifluorite structure. If all the octahedral sites of the parent FCC lattice are filled by ions of opposite charge, the structure formed is the rock-salt structure. | 0 | Theoretical and Fundamental Chemistry |
The Navier–Stokes momentum equation can be derived as a particular form of the Cauchy momentum equation, whose general convective form is
By setting the Cauchy stress tensor to be the sum of a viscosity term (the deviatoric stress) and a pressure term (volumetric stress), we arrive at
where
* is the material derivative, defined as ,
* is the (mass) density,
* is the flow velocity,
* is the divergence,
* is the pressure,
* is time,
* is the deviatoric stress tensor, which has order 2,
* represents body accelerations acting on the continuum, for example gravity, inertial accelerations, electrostatic accelerations, and so on.
In this form, it is apparent that in the assumption of an inviscid fluid – no deviatoric stress – Cauchy equations reduce to the Euler equations.
Assuming conservation of mass, with the known properties of divergence and gradient we can use the mass continuity equation, which represents the mass per unit volume of a homogenous fluid with respect to space and time (i.e., material derivative ) of any finite volume (V) to represent the change of velocity in fluid media:
where
* is the material derivative of mass per unit volume (density, ),
* is the mathematical operation for the integration throughout the volume (V),
* is the partial derivative mathematical operator,
* is the divergence of the flow velocity (), which is a scalar field,
* is the gradient of density (), which is the vector derivative of a scalar field,
) symbol.</sup>
to arrive at the conservation form of the equations of motion. This is often written:
where is the outer product of the flow velocity ():
The left side of the equation describes acceleration, and may be composed of time-dependent and convective components (also the effects of non-inertial coordinates if present). The right side of the equation is in effect a summation of hydrostatic effects, the divergence of deviatoric stress and body forces (such as gravity).
All non-relativistic balance equations, such as the Navier–Stokes equations, can be derived by beginning with the Cauchy equations and specifying the stress tensor through a constitutive relation. By expressing the deviatoric (shear) stress tensor in terms of viscosity and the fluid velocity gradient, and assuming constant viscosity, the above Cauchy equations will lead to the Navier–Stokes equations below. | 1 | Applied and Interdisciplinary Chemistry |
Among aquatic vegetation, the lily pad is perhaps the most recognizable, commonly associated with ponds and lakes. Their flexibility allows for increased loads, enabling them to support animals, such as frogs, many times their own weight.
Some aquatic flowers, such as the daisy Bellis perennis, use compliance as a survival mechanism. Such flowers have roots that extend down to the underlying soil, anchoring the flower to the surface of the water. When flooding occurs, the petals pull inward and deform the water line, shielding the genetic material in the core. Some flowers are even known to completely close up into a shell in this fashion, trapping air inside. | 1 | Applied and Interdisciplinary Chemistry |
A prototype 2 nanometer thick COF layer on a graphene substrate was used to filter dye from industrial wastewater. Once full, the COF can be cleaned and reused. | 0 | Theoretical and Fundamental Chemistry |
As of 2015, several bodies of water in the state of Washington were contaminated with PCBs, including the Columbia River, the Duwamish River, Green Lake, Lake Washington, the Okanogan River, Puget Sound, the Spokane River, the Walla Walla River, the Wenatchee River, and the Yakima River. A study by Washington State published in 2011 found that the two largest sources of PCB flow into the Spokane River were City of Spokane stormwater (44%) and municipal and industrial discharges (20%).
PCBs entered the environment through paint, hydraulic fluids, sealants, inks and have been found in river sediment and wildlife. Spokane utilities will spend $300 million to prevent PCBs from entering the river in anticipation of a 2017 federal deadline to do so. In August 2015 Spokane joined other U.S. cities like San Diego and San Jose, California, and Westport, Massachusetts, in seeking damages from Monsanto. | 1 | Applied and Interdisciplinary Chemistry |
Transvection is an epigenetic phenomenon that results from an interaction between an allele on one chromosome and the corresponding allele on the homologous chromosome. Transvection can lead to either gene activation or repression. It can also occur between nonallelic regions of the genome as well as regions of the genome that are not transcribed.
The first observation of mitotic (i.e. non-meiotic) chromosome pairing was discovered via microscopy in 1908 by Nettie Stevens. Edward B. Lewis at Caltech discovered transvection at the bithorax complex in Drosophila in the 1950s. Since then, transvection has been observed at a number of additional loci in Drosophila, including the genes known as white, decapentaplegic, eyes absent, vestigial, and yellow.
As defined by Lewis, "Operationally, transvection is occurring if the phenotype of a given genotype can be altered solely by disruption of somatic (or meiotic) pairing. Such disruption can generally be accomplished by introduction of a heterozygous rearrangement that disrupts pairing in the relevant region but has no position effect of its own on the phenotype" (cited by Ting Wu and Jim Morris, 1999). Recently, pairing-mediated phenomena have been observed in species other than Drosophila, including mice, humans, plants, nematodes, insects, and fungi. In light of these findings, transvection may represent a potent and widespread form of gene regulation.
Transvection appears to be dependent upon chromosome pairing. In some cases, if one allele is placed on a different chromosome by a translocation, transvection does not occur. Transvection can sometimes be restored in a translocation homozygote, where both alleles may once again be able to pair. Restoration of phenotype has been observed at bithorax, decapentaplegic, eyes absent, and vestigial, and with transgenes of white. In some cases, transvection between two alleles leads to intragenic complementation while disruption of transvection disrupts the complementation.
Transvection is believed to occur through a variety of mechanisms. In one mechanism, the enhancers of one allele activate the promoter of a paired second allele. Other mechanisms include pairing-sensitive silencing and enhancer bypass of a chromatin insulator through pairing-mediated changes in gene structure.
The physiological relevance of transvection has recently been documented in the context of sex-biased gene expression. In Drosophila, transvection acts on the female X-linked gene yellow, which is homozygous in females (XX) versus hemizygous in males (XY). | 1 | Applied and Interdisciplinary Chemistry |
Berthelots reagent is an alkaline solution of phenol and hypochlorite, used in analytical chemistry. It is named after its inventor, Marcellin Berthelot. Ammonia reacts with Berthelots reagent to form a blue product which is used in a colorimetric method for determining ammonia. The reagent can also be used for determining urea. In this case the enzyme urease is used to catalyze the hydrolysis of urea into carbon dioxide and ammonia. The ammonia is then determined with Berthelot's reagent. | 0 | Theoretical and Fundamental Chemistry |
A reversible reaction is a reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously.
A and B can react to form C and D or, in the reverse reaction, C and D can react to form A and B. This is distinct from a reversible process in thermodynamics.
Weak acids and bases undergo reversible reactions. For example, carbonic acid:
: HCO + HO ⇌ HCO + HO.
The concentrations of reactants and products in an equilibrium mixture are determined by the analytical concentrations of the reagents (A and B or C and D) and the equilibrium constant, K. The magnitude of the equilibrium constant depends on the Gibbs free energy change for the reaction. So, when the free energy change is large (more than about 30 kJ mol), the equilibrium constant is large (log K > 3) and the concentrations of the reactants at equilibrium are very small. Such a reaction is sometimes considered to be an irreversible reaction, although small amounts of the reactants are still expected to be present in the reacting system. A truly irreversible chemical reaction is usually achieved when one of the products exits the reacting system, for example, as does carbon dioxide (volatile) in the reaction
: CaCO + 2HCl → CaCl + HO + CO↑ + HO | 0 | Theoretical and Fundamental Chemistry |
Isocyanates can present respiratory hazards as particulates, vapors or aerosols. Autobody shop workers are a very commonly examined population for isocyanate exposure as they are repeatedly exposed when spray painting automobiles and can be exposed when installing truck bed liners. Hypersensitivity pneumonitis has slower onset and features chronic inflammation that can be seen on imaging of the lungs. Occupational asthma is a worrisome outcome of respiratory sensitization to isocyanates as it can be acutely fatal. Diagnosis of occupational asthma is generally performed using pulmonary function testing (PFT) and performed by pulmonology or occupational medicine physicians. Occupational asthma is much like asthma in that it causes episodic shortness of breath and wheezing. Both the dose and duration of exposure to isocyanates can lead to respiratory sensitization. Dermal exposures to isocyanates can sensitize an exposed person to respiratory disease.
Dermal exposures can occur via mixing, spraying coatings or applying and spreading coatings manually. Dermal exposures to isocyanates is known to lead to respiratory sensitization. Even when the right personal protective equipment (PPE) is used, exposures can occur to body areas not completely covered. Isocyanates can also permeate improper PPE, necessitating frequent changes of both disposable gloves and suits if they become over exposed. | 0 | Theoretical and Fundamental Chemistry |
Another class of high performance polymer frameworks with regular porosity and high surface area is based on triazine materials which can be achieved by dynamic trimerization reaction of simple, cheap, and abundant aromatic nitriles in ionothermal conditions (molten zinc chloride at high temperature (400 °C)). CTF-1 is a good example of this chemistry. | 0 | Theoretical and Fundamental Chemistry |
From 1966 to 1980 Fraser-Reid was on the faculty of the University of Waterloo in Waterloo, Ontario where he established a research group known as "Fraser-Reid's Rowdies". The primary emphasis of his work at this point was the synthesis of chiral natural products using carbohydrates as the starting materials. In 1975, Fraser-Reid was the first to publish a method for making nonsugar compounds with simple sugars. In 1980, he was hired at the University of Maryland, College Park, and then at Duke University in North Carolina in 1983. In 1985 he was appointed the James B. Duke Professor of Chemistry. At Duke University, his research shifted to exploring the role of oligosaccharides in immune responses, and particularly on the effect of molecules on human diseases like malaria and AIDS. After retiring from Duke in 1996, due to an undisclosed harassment claim, he established the Natural Products & Glycotechnology Research Institute, a nonprofit, to study the carbohydrate chemistry/biology of tropical parasitic diseases in developing countries and to develop a carbohydrate-based malaria vaccine. Fraser-Reid and his team achieved a milestone in oligosaccharide synthesis by assembling a molecule consisting of 28 monosaccharide units. | 0 | Theoretical and Fundamental Chemistry |
A material may have lower melting point in nanoparticle form than in the bulk form. For example, 2.5 nm gold nanoparticles melt at about 300 °C, whereas bulk gold melts at 1064 °C. | 0 | Theoretical and Fundamental Chemistry |
Bioaccumulation should be considered during the utilization of the triad approach depending on the study goals. It preparation for measuring bioaccumulation, it must be specified if the test will serve to assess secondary poisoning or biomagnification (Chapman, 1997). Bioaccumulation analysis should be conducted appropriately based on the contaminants of concern (for example, metals do not biomagnify). This can be done with field-collected, caged organisms, or laboratory exposed organisms (Chapman, 1997). While the bioaccumulation portion is recommended, it is not required. However, it serves an important role with the purpose of quantifying effects due to trophic transfer of contaminants through consumption of contaminated prey. | 1 | Applied and Interdisciplinary Chemistry |
The fundamental thermodynamic relation and statistical mechanical principles can be derived from one another. | 0 | Theoretical and Fundamental Chemistry |
Campbell was a faculty member in the Department of Chemistry at the University of Otago from 1948 to 1988. He was appointed as an assistant lecturer in 1948, rising to become a professor in 1971, and the Mellor Professor of Chemistry in 1983. He served as a member of the University Council from 1963 to 1971, dean of the Faculty of Science from 1980 to 1982, and head of the Department of Chemistry from 1983 to 1988. When he retired in 1988, he was conferred the title of professor emeritus.
Campbells early research centred on carboxylic acid derivatives. However, he became interested in organic microanalysis, and developed many analytical procedures, and improved techniques for analysing perfluorinated organic compounds. Campbell served as chair of the Chemical Testing Registration Advisory Committee of the Testing Laboratory Registration Council of New Zealand from 1973 to 1985. Internationally, he was a Bureau Member of the International Union of Pure and Applied Chemistry from 1981 to 1989. The University of Otagos Campbell Microanalytical Laboratory is named in his honour.
Between 1979 and 1980, Campbell was president of the New Zealand Institute of Chemistry. | 0 | Theoretical and Fundamental Chemistry |
RNases are ubiquitous and can often contaminate and subsequently degrade RNA samples in the laboratory, so RNA integrity can very easily be compromised, leading to a number of laboratory techniques designed to eliminate their impact. However, these methods are not fool-proof, and so samples can still be degraded, necessitating a method of measuring RNA integrity to ensure the trustworthiness and reproducibility of molecular assays, as RNA integrity is critical for proper results in gene expression studies, such as microarray analysis, Northern blots, or quantitative real-time PCR (qPCR). RNA that has been degraded has a direct impact on calculated expression levels, often leading to significantly decreased apparent expression.
qPCR and similar techniques are very expensive, taking a good deal of both time and money, so continuing research being undertaken to decrease the cost while maintaining qPCRs accuracy and reproducibility for gene expression and other applications. RIN assessment allows a scientist to evaluate an experiments trustworthiness and reproducibility before incurring substantial costs in performing the gene expression studies.
RIN is a standard method of measuring RNA integrity and can be used to evaluate the quality of RNA produced by new RNA isolation techniques. | 1 | Applied and Interdisciplinary Chemistry |
The chromosome loops shown in the figure, bringing an enhancer to the promoter of its target gene, may be directed and formed by the eRNA transcribed from the enhancer after the enhancer is activated.
A transcribed enhancer RNA (eRNA) interacting with the complex of Mediator proteins (see Figure), especially Mediator subunit 12 (MED12), appears to be essential in forming the chromosome loop that brings the enhancer into close association with the promoter of the target gene of the enhancer in the case of five genes studied by Lai et al. Hou and Kraus, describe two other studies reporting similar results. Arnold et al. review another 5 instances where eRNA is active in forming the enhancer-promoter loop. | 1 | Applied and Interdisciplinary Chemistry |
Molybdenum is an essential element in most organisms. It is most notably present in nitrogenase which is an essential part of nitrogen fixation. | 1 | Applied and Interdisciplinary Chemistry |
The following table lists some reported reactions that are relevant to photogeochemical study, including reactions that involve only naturally occurring compounds as well as complementary reactions that involve synthetic but related compounds. The selection of reactions and references given is merely illustrative and may not exhaustively reflect current knowledge, especially in the case of popular reactions such as nitrogen photofixation for which there is a large body of literature. Furthermore, although these reactions have natural counterparts, the probability of encountering optimal reaction conditions may be low in some cases; for example, most experimental work concerning CO photoreduction is intentionally performed in the absence of O, since O almost always suppresses the reduction of CO. In natural systems, however, it is uncommon to find an analogous context where CO and a catalyst are reached by light but there is no O present. | 0 | Theoretical and Fundamental Chemistry |
Adhesion is the tendency of dissimilar particles or surfaces to cling to one another (cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another).
The forces that cause adhesion and cohesion can be divided into several types. The intermolecular forces responsible for the function of various kinds of stickers and sticky tape fall into the categories of chemical adhesion, dispersive adhesion, and diffusive adhesion. In addition to the cumulative magnitudes of these intermolecular forces, there are also certain emergent mechanical effects. | 0 | Theoretical and Fundamental Chemistry |
Modified Active Gas Sampling (MAGS) is an environmental engineering assessment technique which rapidly detects unsaturated soil source areas impacted by volatile organic compounds. The technique was developed by HSA Engineers & Scientists in Fort Myers, Florida in 2002, led by Richard Lewis, Steven Folsom, and Brian Moore. It is being used all over the United States, and has been adopted by the state of Florida in its Dry-cleaning Solvent Cleanup Program. | 1 | Applied and Interdisciplinary Chemistry |
Some other plants live in association with a cyanobiont (cyanobacteria such as Nostoc) which fix nitrogen for them:
* Some lichens such as Lobaria and Peltigera
* Mosquito fern (Azolla species)
* Cycads
* Gunnera
* Blasia (liverwort)
* Hornworts
Some symbiotic relationships involving agriculturally-important plants are:
* Sugarcane and unclear endophytes
* Foxtail millet and Azospirillum brasilense
* Kallar grass and Azoarcus sp. strain BH72
* Rice and Herbaspirillum seropedicae
* Wheat and Klebsiella pneumoniae
* Maize landrace Sierra Mixe / olotón and various Bacteroidota and Pseudomonadota | 1 | Applied and Interdisciplinary Chemistry |
An oil dispersant is a mixture of emulsifiers and solvents that helps break oil into small droplets following an oil spill. Small droplets are easier to disperse throughout a water volume, and small droplets may be more readily biodegraded by microbes in the water. Dispersant use involves a trade-off between exposing coastal life to surface oil and exposing aquatic life to dispersed oil. While submerging the oil with dispersant may lessen exposure to marine life on the surface, it increases exposure for animals dwelling underwater, who may be harmed by toxicity of both dispersed oil and dispersant. Although dispersant reduces the amount of oil that lands ashore, it may allow faster, deeper penetration of oil into coastal terrain, where it is not easily biodegraded. | 1 | Applied and Interdisciplinary Chemistry |
The major component of the Earth's upper mantle is silica (SiO), which makes it the primary source of silica in hydrothermal fluids. SiO is a stable component. It often appears as quartz in volcanic rocks. Some quartz that is derived from pre-existing rocks, appear in the form of sand and detrital quartz that interact with seawater to produce siliceous fluids. In some cases, silica in siliceous rocks are subjected to hydrothermal alteration and react with seawater at certain temperatures, forming an acidic solution for silicification of nearby materials. In the rock cycle, the chemical weathering of rocks also releases silica in the form of silicic acid as by-products. Silica from weathered rocks is washed into waters and deposit into shallow-marine environments. | 0 | Theoretical and Fundamental Chemistry |
The termination of transcription of pre-rRNA genes by polymerase Pol I is performed by a system that needs a specific transcription termination factor. The mechanism used bears some resemblance to the rho-dependent termination in prokaryotes. Eukaryotic cells contain hundreds of ribosomal DNA repeats, sometimes distributed over multiple chromosomes. Termination of transcription occurs in the ribosomal intergenic spacer region that contains several transcription termination sites upstream of a Pol I pausing site. Through a yet unknown mechanism, the 3’-end of the transcript is cleaved, generating a large primary rRNA molecule that is further processed into the mature 18S, 5.8S and 28S rRNAs.
As Pol II reaches the end of a gene, two protein complexes carried by the CTD, CPSF (cleavage and polyadenylation specificity factor) and CSTF (cleavage stimulation factor), recognize the poly-A signal in the transcribed RNA. Poly-A-bound CPSF and CSTF recruit other proteins to carry out RNA cleavage and then polyadenylation. Poly-A polymerase adds approximately 200 adenines to the cleaved 3’ end of the RNA without a template. The long poly-A tail is unique to transcripts made by Pol II.
In the process of terminating transcription by Pol I and Pol II, the elongation complex does not dissolve immediately after the RNA is cleaved. The polymerase continues to move along the template, generating a second RNA molecule associated with the elongation complex. Two models have been proposed to explain how termination is achieved at last. The allosteric model states that when transcription proceeds through the termination sequence, it causes disassembly of elongation factors and/or an assembly of termination factors that cause conformational changes of the elongation complex. The torpedo model suggests that a 5 to 3 exonuclease degrades the second RNA as it emerges from the elongation complex. Polymerase is released as the highly processive exonuclease overtakes it. It is proposed that an emerging view will express a merge of these two models. | 1 | Applied and Interdisciplinary Chemistry |
Base saturation expresses the percentage of potential CEC occupied by the cations Ca, Mg, K or Na. These are traditionally termed "base cations" because they are non-acidic, although they are not bases in the usual chemical sense. Base saturation provides an index of soil weathering and reflects the availability of exchangeable cationic nutrients to plants. | 0 | Theoretical and Fundamental Chemistry |
Receptors on the opposite side of the synaptic gap bind neurotransmitter molecules. Receptors can respond in either of two general ways. First, the receptors may directly open ligand-gated ion channels in the postsynaptic cell membrane, causing ions to enter or exit the cell and changing the local transmembrane potential. The resulting change in voltage is called a postsynaptic potential. In general, the result is excitatory in the case of depolarizing currents, and inhibitory in the case of hyperpolarizing currents. Whether a synapse is excitatory or inhibitory depends on what type(s) of ion channel conduct the postsynaptic current(s), which in turn is a function of the type of receptors and neurotransmitter employed at the synapse. The second way a receptor can affect membrane potential is by modulating the production of chemical messengers inside the postsynaptic neuron. These second messengers can then amplify the inhibitory or excitatory response to neurotransmitters. | 1 | Applied and Interdisciplinary Chemistry |
Relative permittivity is typically denoted as (sometimes , lowercase kappa) and is defined as
where ε(ω) is the complex frequency-dependent permittivity of the material, and ε is the vacuum permittivity.
Relative permittivity is a dimensionless number that is in general complex-valued; its real and imaginary parts are denoted as:
The relative permittivity of a medium is related to its electric susceptibility, , as .
In anisotropic media (such as non cubic crystals) the relative permittivity is a second rank tensor.
The relative permittivity of a material for a frequency of zero is known as its static relative permittivity. | 0 | Theoretical and Fundamental Chemistry |
The GEBIK and GEBIF equations describe the dynamics of the following state variables
:; S : substrate concentration
:; P : product concentration
:; E : enzyme concentration
:; C : complex concentration
:; B : biomass concentration
Both S and P contain at least one isotopic expression of a tracer atom. For instance, if the carbon element is used as a tracer, both S and P contain at least one C atom, which may appear as and . The isotopic expression within a molecule is
where is the number of tracer atoms within S, while is the number of isotopic substitutions in the same molecule. The condition must be satisfied. For example, the product in which 1 isotopic substitution occurs (e.g., ) will be described by .
Substrates and products appear in a chemical reaction with specific stoichiometric coefficients. When chemical reactions comprise combinations of reactants and products with various isotopic expressions, the stoichiometric coefficients are functions of the isotope substitution number. If and are the stoichiometric coefficient for substrate and product, a reaction takes the form
For example, in the reaction , the notation is with for both isotopologue reactants of the same substrate with substitution number and , and with for and because the reaction does not comprise production of and .
For isotopomers, the substitution location is taken into account as and , where and indicate a different expressions of the same isotopologue . Isotopomers only exist when and . The substitution location has to be specifically defined depending on the number of tracer atoms , number of substitutions , and molecule structure. For multiatomic molecules that are symmetric with respect to tracer position, there is no need to specify the substitution position when . For example, one substitution of deuterium in the symmetric methane molecule does not require the use of the right superscript. In the case that , the substitution location has to be specified, while for and it is not required. For example, two D substitutions in can occur in adjacent or non-adjacent locations. Using this notation, the reaction can be written as
where in defines only one of the two methane forms (either with adjacent or non-adjacent D atoms). The location of D in the two isotopologue water molecules produced on the right-hand side of the reaction has not been indicated because D is present in only one water molecule at saturation, and because the water molecule is symmetric. For asymmetric and multiatomic molecules with and , definition of the substitution location is always required. For instance, the isotopomers of the (asymmetric) nitrous oxide molecule are and .
Reactions of asymmetric isotopomers can be written using the partitioning coefficient as
where . For example, using N isotope tracers, the isotopomer reactions
can be written as one reaction in which each isotopomer product is multiplied by its partition coefficient as
with . More generally, the tracer element does not necessarily occur in only one substrate and one product. If substrates react releasing products, each having an isotopic expression of the tracer element, then the generalized reaction notation is
For instance, consider the and tracers in the reaction
In this case the reaction can be written as
with two substrates and two products without indication of the substitution location because all molecules are symmetric.
Biochemical kinetic reactions of type () are often catalytic reactions in which one or more substrates, , bind to an enzyme, E, to form a reversible activated complex, C, which releases one or more
products, , and free, unchanged enzyme. These reactions belong to the type of reactions that can be described by Michaelis–Menten kinetics. Using this approach for substrate and product isotopologue and isotopomer expressions, and under the prescribed stoichiometric relationships among them, leads to the general reactions of the Michaelis–Menten type
with the index , where depends on the number of possible atomic combinations among all isotopologues and isotopomers. Here, , , and are the rate constants indexed for each of the m reactions. | 0 | Theoretical and Fundamental Chemistry |
*Bailyn, M. (1994). A Survey of Thermodynamics, American Institute of Physics Press, New York, .
*Callen, H.B. (1960/1985). Thermodynamics and an Introduction to Thermostatistics, (1st edition 1960) 2nd edition 1985, Wiley, New York, .
*Münster, A. (1970), Classical Thermodynamics, translated by E.S. Halberstadt, Wiley–Interscience, London, .
*Prigogine, I., Defay, R. (1950/1954). Chemical Thermodynamics, translated by D.H. Everett, Longmans, Green & Co, London. | 0 | Theoretical and Fundamental Chemistry |
Although trials are commonly conducted at major medical centers, some participants are excluded due to the distance and expenses required for travel, leading to hardship, disadvantage, and inequity for participants, especially those in rural and underserved communities. In the 21st century, efforts are made to collect information within a participant's home, a capability improved by telehealth and wearable technologies. | 1 | Applied and Interdisciplinary Chemistry |
In medicine, the number needed to harm (NNH) is an epidemiological measure that indicates how many persons on average need to be exposed to a risk factor over a specific period to cause harm in an average of one person who would not otherwise have been harmed. It is defined as the inverse of the absolute risk increase, and computed as , where is the incidence in the treated (exposed) group, and is the incidence in the control (unexposed) group. Intuitively, the lower the number needed to harm, the worse the risk factor, with 1 meaning that every exposed person is harmed.
NNH is similar to number needed to treat (NNT), where NNT usually refers to a positive therapeutic result and NNH to a detrimental effect or risk factor.
Marginal metrics:
* NNT for an additional beneficial outcome (NNTB)
* NNT for an additional harmful outcome (NNTH)
are also used.
__TOC__ | 1 | Applied and Interdisciplinary Chemistry |
Intrastrand DNA crosslinks have strong effects on organisms because these lesions interfere with transcription and replication. These effects can be put to good use (addressing cancer) or they can be lethal to the host organism. The drug cisplatin functions by formation of intrastrand crosslinks in DNA. Other crosslinking agents include mustard gas, mitomycin, and psoralen. | 0 | Theoretical and Fundamental Chemistry |
His numerous awards include:
*1972: Awarded the Corday-Morgan medal in Inorganic Chemistry by the Royal Society of Chemistry (RSC)
*1977: Medal in Transition Metal Chemistry from the RSC
*1982: Tilden Prize and Lectureship, RSC
*1984: American Chemical Society Award in Inorganic Chemistry
*1985: Elected a Fellow of the Royal Society (FRS)
*1985: Medal in Organometallic Chemistry, RSC
*1988: Sir Edward Frankland Prize Lecturership, RSC
*1995: Awarded the Davy Medal by the Royal Society
*1997: Medal in Organometallic Chemistry from the American Chemical Society
*1992: From the Gesellschaft Deutscher Chemiker, the Karl-Ziegler Prize
*2000: Sir Geoffrey Wilkinson Medal and Prize, RSC
* Elected a Fellow of the Royal Society of Chemistry (FRSC)
*2015: From the European Association for Chemical and Molecular Sciences, the European Prize for Organometallic Chemistry | 0 | Theoretical and Fundamental Chemistry |
Wastewater quality indicators are laboratory test methodologies to assess suitability of wastewater for disposal, treatment or reuse. The main parameters in sewage that are measured to assess the sewage strength or quality as well as treatment options include: solids, indicators of organic matter, nitrogen, phosphorus, indicators of fecal contamination. Tests selected vary with the intended use or discharge location. Tests can measure physical, chemical, and biological characteristics of the wastewater. Physical characteristics include temperature and solids. Chemical characteristics include pH value, dissolved oxygen concentrations, biochemical oxygen demand (BOD) and chemical oxygen demand (COD), nitrogen, phosphorus, chlorine. Biological characteristics are determined with bioassays and aquatic toxicology tests.
Both the BOD and COD tests are a measure of the relative oxygen-depletion effect of a waste contaminant. Both have been widely adopted as a measure of pollution effect. Any oxidizable material present in an aerobic natural waterway or in an industrial wastewater will be oxidized both by biochemical (bacterial) or chemical processes. The result is that the oxygen content of the water will be decreased. | 0 | Theoretical and Fundamental Chemistry |
A superhelix is a molecular structure in which a helix is itself coiled into a helix. This is significant to both proteins and genetic material, such as overwound circular DNA.
The earliest significant reference in molecular biology is from 1971, by F. B. Fuller:
About the writhing number, mathematician W. F. Pohl says:
Contrary to intuition, a topological property, the linking number, arises from the geometric properties twist and writhe according to the following relationship:
:L= T + W,
where L is the linking number, W is the writhe and T is the twist of the coil.
The linking number refers to the number of times that one strand wraps around the other. In DNA this property does not change and can only be modified by specialized enzymes called topoisomerases. | 0 | Theoretical and Fundamental Chemistry |
In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e.g. a battery), or sound (e.g. explosion heard when burning hydrogen). The term exothermic was first coined by 19th-century French chemist Marcellin Berthelot.
The opposite of an exothermic process is an endothermic process, one that absorbs energy usually in the form of heat. The concept is frequently applied in the physical sciences to chemical reactions where chemical bond energy is converted to thermal energy (heat). | 0 | Theoretical and Fundamental Chemistry |
For example, an enzyme that catalyzed this reaction would be an oxidoreductase:
:A + B → A + B
In this example, A is the reductant (electron donor) and B is the oxidant (electron acceptor).
In biochemical reactions, the redox reactions are sometimes more difficult to see, such as this reaction from glycolysis:
:P + glyceraldehyde-3-phosphate + NAD → NADH + H + 1,3-bisphosphoglycerate
In this reaction, NAD is the oxidant (electron acceptor), and glyceraldehyde-3-phosphate is the reductant (electron donor). | 0 | Theoretical and Fundamental Chemistry |
Several techniques of re-utilising the spoil tips exist, usually including either geotechnics or recycling. Most commonly, old spoil tips are partially revegetated to provide valuable green spaces since they are inappropriate for building purposes. At Nœux-les-Mines, an artificial ski slope has been constructed on the tip. If spoil tips are considered to contain sufficient amounts of residual material, various methods are employed to remove the spoil from the site for subsequent processing.
The oldest coal-based spoil tips may still contain enough coal to begin spontaneous slow combustion. This results in a form of vitrification of the shale, which then acquires sufficient mechanical strength to be of use in road construction. Some can therefore have a new life in being thus exploited; for example, the flattened pile of residue from the 11/19 site of Loos-en-Gohelle. Conversely, others are painstakingly preserved on account of their ecological wealth. With the passage of time, they become colonised with a variety of flora and fauna, sometimes foreign to the region. This diversity follows the mining exploitation. In South Wales some spoil tips are protected as Sites of Special Scientific Interest because they provide a unique habitat for 57 species of Lichen, several of which are at risk due to their limited environment being developed and by vegetation development.
For example, because the miners threw their apple or pear cores into the wagons, the spoil tips became colonised with fruit trees. One can even observe the proliferation of buckler-leaved sorrel (French sorrel – Rumex scutatus), the seeds of which have been carried within the cracks in the pine timber used in the mines. Furthermore, on account of its dark colour, the south face of the spoil tip is significantly warmer than its surroundings, which contributes to the diverse ecology of the area. In this way, the spoil tip of Pinchonvalles, at Avion, hosts 522 different varieties of higher plants. Some sixty species of birds nest there.
Some are used to cultivate vines, as in the case of Spoil Tip No. 7 of the coal-mining region of Mariemont-Bascoup near Chapelle-lez-Herlaimont (province of Hainaut). It produces some 3,000 litres of wine each year from a vineyard on its slopes.
Some spoil tips are used for various sporting activities. The slopes of the spoil tips of 11/19 at Loos-en-Gohelle, or again, at Nœux-les-Mines, are used for winter sports, for example ski and luge. A piste was built on the flank of the heap. In Belgium, a long distance footpath along the spoil tips (GR-412, Sentier des terrils) was opened in 2005. It leads from Bernissart in western Hainaut to Blegny in the province of Liège.
In the United States, coal mining companies have not been allowed to leave behind abandoned piles since the Surface Mining Control and Reclamation Act was passed in 1977. The Virginia City Hybrid Energy Center uses coal gob as a fuel source for energy production. | 1 | Applied and Interdisciplinary Chemistry |
The Dda gene is 31,219 base pair long. The GenBank accession number is AAD42555. The coding strand (see also: sense strand) begins in base number 9,410 and ends in base number 10,729. | 1 | Applied and Interdisciplinary Chemistry |
Cholesterol 7 alpha-hydroxylase is a cytochrome P450 heme enzyme that oxidizes cholesterol in the position 7 using molecular oxygen. It is an oxidoreductase. CYP7A1 is located in the endoplasmic reticulum (ER) and is important for the synthesis of bile acid and the regulation of cholesterol levels. | 1 | Applied and Interdisciplinary Chemistry |
Ultraviolet (UV) light is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs, Cherenkov radiation, and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights.
The photons of ultraviolet have greater energy than those of visible light, from about 3.1 to 12 electron volts, around the minimum energy required to ionize atoms. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack sufficient energy, it can induce chemical reactions and cause many substances to glow or fluoresce. Many practical applications, including chemical and biological effects, are derived from the way that UV radiation can interact with organic molecules. These interactions can involve absorption or adjusting energy states in molecules, but do not necessarily involve heating. Short-wave ultraviolet light is ionizing radiation. Consequently, short-wave UV damages DNA and sterilizes surfaces with which it comes into contact.
For humans, suntan and sunburn are familiar effects of exposure of the skin to UV light, along with an increased risk of skin cancer. The amount of UV light produced by the Sun means that the Earth would not be able to sustain life on dry land if most of that light were not filtered out by the atmosphere. More energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground. However, ultraviolet light (specifically, UVB) is also responsible for the formation of vitamin D in most land vertebrates, including humans. The UV spectrum, thus, has effects both beneficial and detrimental to life.
The lower wavelength limit of the visible spectrum is conventionally taken as 400 nm, so ultraviolet rays are not visible to humans, although people can sometimes perceive light at shorter wavelengths than this. Insects, birds, and some mammals can see near-UV (NUV), i.e., slightly shorter wavelengths than what humans can see. | 0 | Theoretical and Fundamental Chemistry |
Dissolved free sulfides (HS, HS and S) are very aggressive species for the corrosion of many metals such as steel, stainless steel, and copper. Sulfides present in aqueous solution are responsible for stress corrosion cracking (SCC) of steel, and is also known as sulfide stress cracking. Corrosion is a major concern in many industrial installations processing sulfides: sulfide ore mills, deep oil wells, pipelines transporting soured oil and Kraft paper factories.
Microbially-induced corrosion (MIC) or biogenic sulfide corrosion are also caused by sulfate reducing bacteria producing sulfide that is emitted in the air and oxidized in sulfuric acid by sulfur oxidizing bacteria. Biogenic sulfuric acid reacts with sewerage materials and most generally causes mass loss, cracking of the sewer pipes and ultimately, structural collapse. This kind of deterioration is a major process affecting sewer systems worldwide and leading to very high rehabilitation costs.
Oxidation of sulfide can also form thiosulfate () an intermediate species responsible for severe problems of pitting corrosion of steel and stainless steel while the medium is also acidified by the production of sulfuric acid when oxidation is more advanced. | 0 | Theoretical and Fundamental Chemistry |
Automated mineralogy is a generic term describing a range of analytical solutions, areas of commercial enterprise, and a growing field of scientific research and engineering applications involving largely automated and quantitative analysis of minerals, rocks and man-made materials. | 0 | Theoretical and Fundamental Chemistry |
Zinc is an efficient Lewis acid, making it a useful catalytic agent in hydroxylation and other enzymatic reactions. The metal also has a flexible coordination geometry, which allows proteins using it to rapidly shift conformations to perform biological reactions. Two examples of zinc-containing enzymes are carbonic anhydrase and carboxypeptidase, which are vital to the processes of carbon dioxide () regulation and digestion of proteins, respectively.
In vertebrate blood, carbonic anhydrase converts into bicarbonate and the same enzyme transforms the bicarbonate back into for exhalation through the lungs. Without this enzyme, this conversion would occur about one million times slower at the normal blood pH of 7 or would require a pH of 10 or more. The non-related β-carbonic anhydrase is required in plants for leaf formation, the synthesis of indole acetic acid (auxin) and alcoholic fermentation.
Carboxypeptidase cleaves peptide linkages during digestion of proteins. A coordinate covalent bond is formed between the terminal peptide and a C=O group attached to zinc, which gives the carbon a positive charge. This helps to create a hydrophobic pocket on the enzyme near the zinc, which attracts the non-polar part of the protein being digested. | 1 | Applied and Interdisciplinary Chemistry |
Trimethyl orthoformate (TMOF) is the organic compound with the formula HC(OCH). A colorless liquid, it is the simplest orthoester. It is a reagent used in organic synthesis for the formation of methyl ethers. The product of reaction of an aldehyde with trimethyl orthoformate is an acetal. In general cases, these acetals can be deprotected back to the aldehyde by using hydrochloric acid. | 0 | Theoretical and Fundamental Chemistry |
The molecular mechanism of RNAa is not fully understood. Similar to RNAi, it has been shown that mammalian RNAa requires members of the Ago clade of Argonaute proteins, particularly Ago2, but possesses kinetics distinct from RNAi. In contrast to RNAi, promoter-targeted saRNAs induce prolonged activation of gene expression associated with epigenetic changes. It is currently suggested that saRNAs are first loaded and processed by an Ago protein to form an Ago-RNA complex which is then guided by the RNA to its promoter target. The target can be a non-coding transcript overlapping the promoter or the chromosomal DNA. The RNA-loaded Ago then recruits other proteins such as RHA, also known as nuclear DNA helicase II, and CTR9 to form an RNA-induced transcriptional activation (RITA) complex. RITA can directly interacts with RNAP II to stimulate transcription initiation and productive transcription elongation which is related to increased ubiquitination of H2B. | 1 | Applied and Interdisciplinary Chemistry |
Vat leaching involves contacting material, which has usually undergone size reduction and classification, with leach solution in large vats. | 1 | Applied and Interdisciplinary Chemistry |
Latent semantic structure indexing (LaSSI) is a technique for calculating chemical similarity derived from latent semantic analysis (LSA).
LaSSI was developed at Merck & Co. and patented in 2007 by Richard Hull, Eugene Fluder, Suresh Singh, Robert Sheridan, Robert Nachbar and Simon Kearsley. | 1 | Applied and Interdisciplinary Chemistry |
RT-PCR can also be very useful in the insertion of eukaryotic genes into prokaryotes. Because most eukaryotic genes contain introns, which are present in the genome but not in the mature mRNA, the cDNA generated from a RT-PCR reaction is the exact (without regard to the error-prone nature of reverse transcriptases) DNA sequence that would be directly translated into protein after transcription. When these genes are expressed in prokaryotic cells for the sake of protein production or purification, the RNA produced directly from transcription need not undergo splicing as the transcript contains only exons. (Prokaryotes, such as E. coli, lack the mRNA splicing mechanism of eukaryotes). | 1 | Applied and Interdisciplinary Chemistry |
The solvothermal approach is the most common used in the literature but typically requires long reaction times due to the insolubility of the organic SBUs in nonorganic media and the time necessary to reach thermodynamic COF products. | 0 | Theoretical and Fundamental Chemistry |
If , the resulting flow is a sort of hexagonal version of the case considered above. Streamlines are given by, and the flow in this case may be interpreted as flow into a 60° corner. | 1 | Applied and Interdisciplinary Chemistry |
Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidized for energy production.
Coenzyme A (CoASH or CoA) consists of a β-mercaptoethylamine group linked to pantothenic acid (vitamin B5) through an amide linkage and 3'-phosphorylated ADP. The acetyl group (indicated in blue in the structural diagram on the right) of acetyl-CoA is linked to the sulfhydryl substituent of the β-mercaptoethylamine group. This thioester linkage is a "high energy" bond, which is particularly reactive. Hydrolysis of the thioester bond is exergonic (−31.5 kJ/mol).
CoA is acetylated to acetyl-CoA by the breakdown of carbohydrates through glycolysis and by the breakdown of fatty acids through β-oxidation. Acetyl-CoA then enters the citric acid cycle, where the acetyl group is oxidized to carbon dioxide and water, and the energy released is captured in the form of 11 ATP and one GTP per acetyl group.
Konrad Bloch and Feodor Lynen were awarded the 1964 Nobel Prize in Physiology or Medicine for their discoveries linking acetyl-CoA and fatty acid metabolism. Fritz Lipmann won the Nobel Prize in 1953 for his discovery of the cofactor coenzyme A. | 1 | Applied and Interdisciplinary Chemistry |
The nucleotide sequences of interest are preserved as inserts to a plasmid or the genome of a bacteriophage that has been used to infect bacterial cells.
Vectors are propagated most commonly in bacterial cells, but if using a YAC (Yeast Artificial Chromosome) then yeast cells may be used. Vectors could also be propagated in viruses, but this can be time-consuming and tedious. However, the high transfection efficiency achieved by using viruses (often phages) makes them useful for packaging the vector (with the ligated insert) and then introducing them into the bacterial (or yeast) cell.
Additionally, for cDNA libraries, a system using the Lambda Zap II phage, ExAssist, and 2 E. coli species has been developed. A Cre-Lox system using loxP sites and the in vivo expression of the recombinase enzyme can also be used instead. These are examples of in vivo excision systems. In vitro excision involves subcloning often using traditional restriction enzymes and cloning strategies. In vitro excision can be more time-consuming and may require more "hands-on" work than in vivo excision systems. In either case, the systems allow the movement of the vector from the phage into a live cell, where the vector can replicate and propagate until the library is to be used. | 1 | Applied and Interdisciplinary Chemistry |
Alzheimers disease is the most common cause of severe memory impairment and is caused by senile plaques, neurofibrillary tangles, dystrophic neuritis, and neuronal loss. It is thought that Alzheimers disease may be due to unnecessary protein accumulation of β Amyloid. In fact, Senile plaques are dense, protein deposits composed of amyloid β peptide. The two types of senile plaques are diffuse plaques and neuritic plaques, and differ in morphology. In addition to the amyloid, the microtubule-associated Tau protein has also been in involved with Alzheimers disease and a variety of other neurodegenerative diseases. Inherited forms of Alzheimers have been linked to mutation in the APP genes or presenilins which regulate APP processing.
Because cholinergic neurons of the nucleus basalis are significantly altered during Alzheimer's progression, cholinergic agents such as choline and lecithin were hypothesized to augment the progression. However, these attempts were unsuccessful and the only clinically useful drugs used in the United States are cholinesterase inhibitors, which prolong the time before choline degradation. Although receptor antagonists and anti-inflammatory drugs were tested in a clinical environment, more promising clinical trials are underway to targeting the Aβ with the immune system. | 1 | Applied and Interdisciplinary Chemistry |
The red form of HgO can be made by heating Hg in oxygen at roughly 350 °C, or by pyrolysis of Hg(NO). The yellow form can be obtained by precipitation of aqueous Hg with alkali. The difference in color is due to particle size; both forms have the same structure consisting of near linear O-Hg-O units linked in zigzag chains with an Hg-O-Hg angle of 108°. | 0 | Theoretical and Fundamental Chemistry |
Effectively, the postulate states that the structure of a transition state resembles that of the species nearest to it in free energy. This can be explained with reference to potential energy diagrams:
In case (a), which is an exothermic reaction, the energy of the transition state is closer in energy to that of the reactant than that of the intermediate or the product. Therefore, from the postulate, the structure of the transition state also more closely resembles that of the reactant. In case (b), the energy of the transition state is close to neither the reactant nor the product, making none of them a good structural model for the transition state. Further information would be needed in order to predict the structure or characteristics of the transition state. Case (c) depicts the potential diagram for an endothermic reaction, in which, according to the postulate, the transition state should more closely resemble that of the intermediate or the product.
Another significance of Hammond’s postulate is that it permits us to discuss the structure of the transition state in terms of the reactants, intermediates, or products. In the case where the transition state closely resembles the reactants, the transition state is called “early” while a “late” transition state is the one that closely resembles the intermediate or the product.
An example of the “early” transition state is chlorination. Chlorination favors the products because it is an exothermic reaction, which means that the products are lower in energy than the reactants. When looking at the adjacent diagram (representation of an "early" transition state), one must focus on the transition state, which is not able to be observed during an experiment. To understand what is meant by an “early” transition state, the Hammond postulate represents a curve that shows the kinetics of this reaction. Since the reactants are higher in energy, the transition state appears to be right after the reaction starts.
An example of the “late” transition state is bromination. Bromination favors the reactants because it is an endothermic reaction, which means that the reactants are lower in energy than the products. Since the transition state is hard to observe, the postulate of bromination helps to picture the “late” transition state (see the representation of the "late" transition state). Since the products are higher in energy, the transition state appears to be right before the reaction is complete.
One other useful interpretation of the postulate often found in textbooks of organic chemistry is the following:
:Assume that the transition states for reactions involving unstable intermediates can be closely approximated by the intermediates themselves.
This interpretation ignores extremely exothermic and endothermic reactions which are relatively unusual and relates the transition state to the intermediates which are usually the most unstable. | 0 | Theoretical and Fundamental Chemistry |
Self-replicating stretches of eukaryotic genomes known as retrotransposons utilize reverse transcriptase to move from one position in the genome to another via an RNA intermediate. They are found abundantly in the genomes of plants and animals. Telomerase is another reverse transcriptase found in many eukaryotes, including humans, which carries its own RNA template; this RNA is used as a template for DNA replication.
Initial reports of reverse transcriptase in prokaryotes came as far back as 1971 in France (Beljanski et al., 1971a, 1972) and a few years later in the USSR (Romashchenko 1977). These have since been broadly described as part of bacterial Retrons, distinct sequences that code for reverse transcriptase, and are used in the synthesis of msDNA. In order to initiate synthesis of DNA, a primer is needed. In bacteria, the primer is synthesized during replication.
Valerian Dolja of Oregon State argues that viruses, due to their diversity, have played an evolutionary role in the development of cellular life, with reverse transcriptase playing a central role. | 1 | Applied and Interdisciplinary Chemistry |
When iodide is added to a solution of hexacyanoferrate(III), the following equilibrium exists:
Under strongly acidic solution, the above equilibrium lies far to the right hand side, but is reversed in almost neutral solution. This makes analysis of hexacyanoferrate(III) troublesome as the iodide and thiosulfate decomposes in strongly acidic medium. To drive the reaction to completion, an excess amount of zinc salt can be added to the reaction mixture containing potassium ions, which precipitates the hexacyanoferrate(II) ion quantitatively:
The precipitation occurs in slightly acidic medium, thus avoids the problem of decomposition of iodide and thiosulfate in strongly acidic medium, and the hexacyanoferrate(III) can be determined by iodometry as usual. | 0 | Theoretical and Fundamental Chemistry |
Neuropeptides are often co-released with other neurotransmitters and neuropeptides to modulate synaptic activity. Synaptic vesicles and dense core vesicles can have differential activation properties for release, resulting in context-dependent corelease combinations. For example, insect motor neurons are glutamatergic and some contain dense core vesicles with proctolin. At low frequency activation, only glutamate is released, yielding fast and rapid excitation of the muscle. At high frequency activation however, dense core vesicles release proctolin, inducing prolonged contractions. Thus, neuropeptide release can be fine-tuned to modulate synaptic activity in certain contexts.
Some regions of the nervous system are specialized to release distinctive sets of peptides. For example, the hypothalamus and the pituitary gland release peptides (e.g. TRH, GnRH, CRH, SST) that act as hormones In one subpoplation of the arcuate nucleus of the hypothalamus, three anorectic peptides are co-expressed: α-melanocyte-stimulating hormone (α-MSH), galanin-like peptide, and cocaine-and-amphetamine-regulated transcript (CART), and in another subpopulation two orexigenic peptides are co-expressed, neuropeptide Y and agouti-related peptide (AGRP). These peptides are all released in different combinations to signal hunger and satiation cues.
The following is a list of neuroactive peptides coreleased with other neurotransmitters. Transmitter names are shown in bold.
Norepinephrine (noradrenaline).
In neurons of the A2 cell group in the nucleus of the solitary tract), norepinephrine co-exists with:
* Galanin
* Enkephalin
* Neuropeptide Y
GABA
* Somatostatin (in the hippocampus)
* Cholecystokinin
* Neuropeptide Y (in the arcuate nucleus)
Acetylcholine
* VIP
* Substance P
Dopamine
* Cholecystokinin
* Neurotensin
* Glucagon-like peptide-1 (in the nucleus accumbens)
Epinephrine (adrenaline)
* Neuropeptide Y
* Neurotensin
Serotonin (5-HT)
* Substance P
* TRH
* Enkephalin
Some neurons make several different peptides. For instance,
vasopressin co-exists with dynorphin and galanin in magnocellular neurons of the supraoptic nucleus and paraventricular nucleus, and with CRF (in parvocellular neurons of the paraventricular nucleus)
Oxytocin in the supraoptic nucleus co-exists with enkephalin, dynorphin, cocaine-and amphetamine regulated transcript (CART) and cholecystokinin. | 1 | Applied and Interdisciplinary Chemistry |
Ethyl eicosapentaenoic acid (E-EPA) is an ethyl ester of eicosapentaenoic acid, which is an omega-3 fatty acid. | 1 | Applied and Interdisciplinary Chemistry |
The interpretation of scattering measurements made at the multiangular locations relies upon some knowledge of the a priori properties of the particles or molecules measured. The scattering characteristics of different classes of such scatterers may be interpreted best by application of an appropriate theory. For example, the following theories are most often applied.
Rayleigh scattering is the simplest and describes elastic scattering of light or other electromagnetic radiation by objects much smaller than the incident wavelength. This type of scattering is responsible for the blue color of the sky during the day and is inversely proportional to the fourth power of wavelength.
The Rayleigh–Gans approximation is a means of interpreting MALS measurements with the assumption that the scattering particles have a refractive index, n, very close to the refractive index of the surrounding medium, n. If we set m = n/n and assume that , then such particles may be considered as composed of very small elements, each of which may be represented as a Rayleigh-scattering particle. Thus each small element of the larger particle is assumed to scatter independently of any other.
Lorenz–Mie theory is used to interpret the scattering of light by homogeneous spherical particles. The Rayleigh–Gans approximation and the Lorenz–Mie theory produce identical results for homogeneous spheres in the limit as .
Lorenz–Mie theory may be generalized to spherically symmetric particles per reference.
More general shapes and structures have been treated by Erma.
Scattering data is usually represented in terms of the so-called excess Rayleigh ratio defined as the Rayleigh ratio of the solution or single particle event from which is subtracted the Rayleigh ratio of the carrier fluid itself and other background contributions, if any. The Rayleigh Ratio measured at a detector lying at an angle θ and subtending a solid angle ΔΩ is defined as the intensity of light per unit solid angle per unit incident intensity, I, per unit illuminated scattering volume ΔV. The scattering volume ΔV from which scattered light reaches the detector is determined by the detectors field of view generally restricted by apertures, lenses and stops. Consider now a MALS measurement made in a plane from a suspension of N identical particles/molecules per ml illuminated by a fine beam of light produced by a laser. Assuming that the light is polarized perpendicular to the plane of the detectors. The scattered light intensity measured by the detector at angle θ' in excess of that scattered by the suspending fluid would be
where i(θ) is the scattering function of a single particle, k = 2πn/λ, n is the refractive index of the suspending fluid, and λ is the vacuum wavelength of the incident light. The excess Rayleigh ratio, R(θ), is then given by
Even for a simple homogeneous sphere of radius a whose refractive index, n, is very nearly the same as the refractive index "n" of the suspending fluid, i.e. Rayleigh–Gans approximation, the scattering function in the scattering plane is the relatively complex quantity
:, where
and λ is the wavelength of the incident light in vacuum. | 0 | Theoretical and Fundamental Chemistry |
Taylor–Maccoll flow refers to the steady flow behind a conical shock wave that is attached to a solid cone. The flow is named after G. I. Taylor and J. W. Maccoll, whom described the flow in 1933, guided by an earlier work of Theodore von Kármán. | 1 | Applied and Interdisciplinary Chemistry |
Polymerase chain reaction (PCR) is the primary gene amplification technique that has revolutionized modern biochemistry. Polymerase chain reaction was developed by Kary Mullis in 1983. There are four steps to a proper polymerase chain reaction: 1) denaturation 2) extension 3) insertion (of gene to be expressed) and finally 4) amplification of the inserted gene. These steps with simple illustrative examples of this process can be seen in the image below and to the right of this section. This technique allows for the copy of a single gene to be amplified into hundreds or even millions of copies and has become a cornerstone in the protocol for any biochemist that wishes to work with bacteria and gene expression. PCR is not only used for gene expression research but is also capable of aiding laboratories in diagnosing certain diseases such a lymphomas, some types of leukemia, and other malignant diseases that can sometimes puzzle doctors. Without polymerase chain reaction development, there are many advancements in the field of bacterial study and protein expression study that would not have come to fruition. The development of the theory and process of polymerase chain reaction is essential but the invention of the thermal cycler is equally as important because the process would not be possible without this instrument. This is yet another testament to the fact that the advancement of technology is just as crucial to sciences such as biochemistry as is the painstaking research that leads to the development of theoretical concepts. | 1 | Applied and Interdisciplinary Chemistry |
Fermentative hydrogen production is the fermentative conversion of organic substrates to H. Hydrogen produced in this manner is often called biohydrogen. The conversion is effected by bacteria and protozoa, which employ enzymes. Fermentative hydrogen production is one of several anaerobic conversions. | 1 | Applied and Interdisciplinary Chemistry |
Isocyanide dichlorides are organic compounds containing the RN=CCl functional group. Classically they are obtained by chlorination of isocyanides. Phenylcarbylamine chloride is a well-characterized example. | 0 | Theoretical and Fundamental Chemistry |
A very small minority of free neutron decays (about four per million) are so-called "two-body decays", in which the proton, electron and antineutrino are produced, but the electron fails to gain the 13.6 eV energy necessary to escape the proton, and therefore simply remains bound to it, as a neutral hydrogen atom. In this type of beta decay, in essence all of the neutron decay energy is carried off by the antineutrino.
For fully ionized atoms (bare nuclei), it is possible in likewise manner for electrons to fail to escape the atom, and to be emitted from the nucleus into low-lying atomic bound states (orbitals). This cannot occur for neutral atoms with low-lying bound states which are already filled by electrons.
Bound-state β decays were predicted by Daudel, Jean, and Lecoin in 1947, and the phenomenon in fully ionized atoms was first observed for Dy in 1992 by Jung et al. of the Darmstadt Heavy-Ion Research Center. Although neutral is a stable isotope, the fully ionized Dy undergoes β decay into the K and L shells with a half-life of 47 days. The resulting nucleus - - is stable only in the fully ionized state and will decay via electron capture into in the neutral state. The half life for neutral is 4750 years.
Another possibility is that a fully ionized atom undergoes greatly accelerated β decay, as observed for Re by Bosch et al., also at Darmstadt. Neutral Re does undergo β decay with a half-life of years, but for fully ionized Re this is shortened to only 32.9 years. For comparison the variation of decay rates of other nuclear processes due to chemical environment is less than 1%. Due to the difference in the price of rhenium and osmium and the high share of in rhenium samples found on earth, this could some day be of commercial interest in the synthesis of precious metals. | 0 | Theoretical and Fundamental Chemistry |
The Grignard reaction is conducted under anhydrous conditions. Otherwise, the reaction will fail because the Grignard reagent will act as a base rather than a nucleophile and pick up a labile proton rather than attacking the electrophilic site. This will result in no formation of the desired product as the R-group of the Grignard reagent will become protonated while the MgX portion will stabilize the deprotonated species.
To prevent this, Grignard reactions are completed in an inert atmosphere to remove all water from the reaction flask and ensure that the desired product is formed. Additionally, if there are acidic protons in the starting material, as shown in the figure on the right, one can overcome this by protecting the acidic site of the reactant by turning it into an ether or a silyl ether to eliminate the labile proton from the solution prior to the Grignard reaction. | 0 | Theoretical and Fundamental Chemistry |
The field of chemical ecology has elucidated additional types of plant multitrophic interactions that entail the transfer of defensive compounds across multiple trophic levels. For example, certain plant species in the Castilleja and Plantago genera have been found to produce defensive compounds called iridoid glycosides that are sequestered in the tissues of the Taylor's checkerspot butterfly larvae that have developed a tolerance for these compounds and are able to consume the foliage of these plants. These sequestered iridoid glycosides then confer chemical protection against bird predators to the butterfly larvae. Another example of this sort of multitrophic interaction in plants is the transfer of defensive alkaloids produced by endophytes living within a grass host to a hemiparasitic plant that is also using the grass as a host. | 1 | Applied and Interdisciplinary Chemistry |
NSAIDs such as ibuprofen work by inhibiting the cyclooxygenase (COX) enzymes, which convert arachidonic acid to prostaglandin H (PGH). PGH, in turn, is converted by other enzymes to several other prostaglandins (which are mediators of pain, inflammation, and fever) and to thromboxane A (which stimulates platelet aggregation, leading to the formation of blood clots).
Like aspirin and indomethacin, ibuprofen is a nonselective COX inhibitor, in that it inhibits two isoforms of cyclooxygenase, COX-1 and COX-2. The analgesic, antipyretic, and anti-inflammatory activity of NSAIDs appears to operate mainly through inhibition of COX-2, which decreases the synthesis of prostaglandins involved in mediating inflammation, pain, fever, and swelling. Antipyretic effects may be due to action on the hypothalamus, resulting in an increased peripheral blood flow, vasodilation, and subsequent heat dissipation. Inhibition of COX-1 instead would be responsible for unwanted effects on the gastrointestinal tract. However, the role of the individual COX isoforms in the analgesic, anti-inflammatory, and gastric damage effects of NSAIDs is uncertain, and different compounds cause different degrees of analgesia and gastric damage.
Ibuprofen is administered as a racemic mixture. The R-enantiomer undergoes extensive interconversion to the S-enantiomer in vivo. The S-enantiomer is believed to be the more pharmacologically active enantiomer. The R-enantiomer is converted through a series of three main enzymes. These enzymes include acyl-CoA-synthetase, which converts the R-enantiomer to (−)-R-ibuprofen I-CoA; 2-arylpropionyl-CoA epimerase, which converts (−)-R-ibuprofen I-CoA to (+)-S-ibuprofen I-CoA; and hydrolase, which converts (+)-S-ibuprofen I-CoA to the S-enantiomer. In addition to the conversion of ibuprofen to the S-enantiomer, the body can metabolize ibuprofen to several other compounds, including numerous hydroxyl, carboxyl and glucuronyl metabolites. Virtually all of these have no pharmacological effects.
Unlike most other NSAIDs, ibuprofen also acts as an inhibitor of Rho kinase and may be useful in recovery from spinal-cord injury. Another unusual activity is inhibition of the sweet taste receptor. | 0 | Theoretical and Fundamental Chemistry |
For decades after Libby performed the first radiocarbon dating experiments, the only way to measure the in a sample was to detect the radioactive decay of individual carbon atoms. In this approach, what is measured is the activity, in number of decay events per unit mass per time period, of the sample. This method is also known as "beta counting", because it is the beta particles emitted by the decaying atoms that are detected. In the late 1970s an alternative approach became available: directly counting the number of and atoms in a given sample, via accelerator mass spectrometry, usually referred to as AMS. AMS counts the / ratio directly, instead of the activity of the sample, but measurements of activity and / ratio can be converted into each other exactly. For some time, beta counting methods were more accurate than AMS, but AMS is now more accurate and has become the method of choice for radiocarbon measurements. In addition to improved accuracy, AMS has two further significant advantages over beta counting: it can perform accurate testing on samples much too small for beta counting, and it is much faster – an accuracy of 1% can be achieved in minutes with AMS, which is far quicker than would be achievable with the older technology. | 0 | Theoretical and Fundamental Chemistry |
In homogeneous catalysis, C-symmetric ligands refer to ligands that lack mirror symmetry but have C symmetry (two-fold rotational symmetry). Such ligands are usually bidentate and are valuable in catalysis. The C symmetry of ligands limits the number of possible reaction pathways and thereby increases enantioselectivity, relative to asymmetrical analogues. C-symmetric ligands are a subset of chiral ligands. Chiral ligands, including C-symmetric ligands, combine with metals or other groups to form chiral catalysts. These catalysts engage in enantioselective chemical synthesis, in which chirality in the catalyst yields chirality in the reaction product. | 0 | Theoretical and Fundamental Chemistry |
The commercial development of the Cell occurred indirectly as a result of problems being experienced in MIMs Mount Isa lead–zinc concentrator (sometimes referred to as a "mill" in the mining industry). MIM had been operating a lead–zinc concentrator at Mount Isa since 1931, although lead–zinc ore was substituted with copper ore for a time between mid-1943 and mid-1946. Over time, the lead, zinc and other mineral grains in the ore became progressively finer, the ore grade decreased and it became more difficult to treat. These trends, combined with an increase in the concentrators throughput, significantly reduced the concentrator's performance in the 1980s, resulting in a "tense" period of "an endless circle of circuit changes, reagent changes, operator changes, metallurgist changes, and so on". The decreasing grain size and pushing the grinding circuit beyond its design throughput meant a reduction in the degree of separation of the individual mineral grains (referred to as "liberation") during grinding. From 1984 to 1991, the liberation of sphalerite (the zinc-bearing mineral, ZnS) decreased from almost 70% to just over 50%. This decrease in liberation resulted in a reduction in the recovery of zinc to saleable zinc concentrate.
The initial response to the problem of decreased zinc recovery was in 1986 to start to produce a lower-grade concentrate that was a mixture of zinc and lead (known in the industry as a "bulk concentrate" and referred to at Mount Isa as the "low-grade middlings concentrate"). This concentrate typically contained 34% zinc and 13% lead, compared to the normal zinc concentrate composition of at least 50% zinc and less than 3% lead.
By producing the bulk concentrate, the total recovery of zinc for sale was maintained at over 70% until 1989. However, the high lead content meant that the bulk concentrate could not be treated by the electrolytic zinc process, and it had to be sold to zinc smelters using the more-expensive Imperial Smelting Process. Initially, MIM received good revenue from its bulk concentrate, but as the nature of the ore continued to deteriorate, the production of the bulk concentrate increased and saturated the market. Payment terms declined until MIM received less than half the payment for zinc in the bulk concentrate than it received for zinc in the zinc concentrate.
The problems in the concentrator also affected the performance of MIMs Mount Isa lead smelter. The lead–zinc ore also contained increasing amounts of fine-grained, carbonaceous pyrite (FeS). This material was naturally hydrophobic and floated without the aid of a collector into the lead concentrate, diluting it. The additional sulfur from the pyrite in the lead concentrate reduced the lead smelters lead production because the ability to eliminate sulfur from the concentrate was lead smelter's capacity bottleneck.
As part of the effort to try to fix the problems, MIM installed some column flotation cells in the zinc concentrate and bulk concentrate sections of the plant. In those days, the air was introduced into flotation columns using air spargers, usually in the form of a bag or sheath around a pipe. The spargers were high-maintenance items, and their performance was critical to the operation of the column. | 1 | Applied and Interdisciplinary Chemistry |
Degeneracy or redundancy of codons is the redundancy of the genetic code, exhibited as the multiplicity of three-base pair codon combinations that specify an amino acid. The degeneracy of the genetic code is what accounts for the existence of synonymous mutations. | 1 | Applied and Interdisciplinary Chemistry |
Enzymes are biological catalysts: biopolymers that catalyze a reaction. Although a small number of natural enzymes are built from RNA–termed Ribozymes–most enzymes are proteins. Like any other protein, an enzyme is an amino acid polymer with added cofactors and other post-translational modifications. Often, most of the amino acid polymer is indirectly involved with the enzymes function, perhaps providing ancillary structure or connectivity, indirect activity regulation, or molecular identification of the enzyme. As a result, most enzymes are large molecules weighing many kilodaltons. This bulk can obscure various investigative techniques such as NMR, EPR, electrochemistry, crystallography, among others. It is standard practice to compare spectroscopic data from enzymes to similar spectroscopic data derived from better characterized small molecules. In this way, the understanding of metalloenzymes and other metalloproteins have developed. In many cases, the small molecule analogs were created for other reasons; however, it has been increasingly common for groups to intentionally make small molecule analogs also known as enzyme mimics. These enzyme mimics are prime examples of bioinorganic chemistry. | 0 | Theoretical and Fundamental Chemistry |
Different types of kerogen have differing potentials to produce oil during maturation. These various types of kerogen can be distinguished on a van Krevelen diagram. | 0 | Theoretical and Fundamental Chemistry |
PDE5 inhibitors have been shown to have various macrovascular, microvascular and metabolic benefits in diabetes mellitus, and in a large study of men with type 2 diabetes mellitus the agents were found to significantly reduce patients' risk of death from any cause. It is unclear to what extent this observation reflects the protective effects of PDE5 inhibitors against cardiovascular and renal disease. | 1 | Applied and Interdisciplinary Chemistry |
Large numbers of samples can be automatically injected onto an HPLC system, by the use of HPLC autosamplers. In addition, HPLC autosamplers have an injection volume and technique which is exactly the same for each injection, consequently they provide a high degree of injection volume precision.
It is possible to enable sample stirring within the sampling-chamber, thus promoting homogeneity. | 0 | Theoretical and Fundamental Chemistry |
Synapses are functional connections between neurons, or between neurons and other types of cells. A typical neuron gives rise to several thousand synapses, although there are some types that make far fewer. Most synapses connect axons to dendrites, but there are also other types of connections, including axon-to-cell-body, axon-to-axon, and dendrite-to-dendrite. Synapses are generally too small to be recognizable using a light microscope except as points where the membranes of two cells appear to touch, but their cellular elements can be visualized clearly using an electron microscope.
Chemical synapses pass information directionally from a presynaptic cell to a postsynaptic cell and are therefore asymmetric in structure and function. The presynaptic axon terminal, or synaptic bouton, is a specialized area within the axon of the presynaptic cell that contains neurotransmitters enclosed in small membrane-bound spheres called synaptic vesicles (as well as a number of other supporting structures and organelles, such as mitochondria and endoplasmic reticulum). Synaptic vesicles are docked at the presynaptic plasma membrane at regions called active zones.
Immediately opposite is a region of the postsynaptic cell containing neurotransmitter receptors; for synapses between two neurons the postsynaptic region may be found on the dendrites or cell body. Immediately behind the postsynaptic membrane is an elaborate complex of interlinked proteins called the postsynaptic density (PSD).
Proteins in the PSD are involved in anchoring and trafficking neurotransmitter receptors and modulating the activity of these receptors. The receptors and PSDs are often found in specialized protrusions from the main dendritic shaft called dendritic spines.
Synapses may be described as symmetric or asymmetric. When examined under an electron microscope, asymmetric synapses are characterized by rounded vesicles in the presynaptic cell, and a prominent postsynaptic density. Asymmetric synapses are typically excitatory. Symmetric synapses in contrast have flattened or elongated vesicles, and do not contain a prominent postsynaptic density. Symmetric synapses are typically inhibitory.
The synaptic cleft—also called synaptic gap—is a gap between the pre- and postsynaptic cells that is about 20 nm (0.02 μ) wide. The small volume of the cleft allows neurotransmitter concentration to be raised and lowered rapidly.
An autapse is a chemical (or electrical) synapse formed when the axon of one neuron synapses with its own dendrites. | 1 | Applied and Interdisciplinary Chemistry |
Beletskaya was born in Leningrad (St. Petersburg, Russia) in 1933. She graduated from the Department of Chemistry of Lomonosov Moscow State University in 1955 where she focused her undergraduate research on organoarsenic chemistry. She obtained the Candidate of Chemistry (analogous to Ph.D.) degree in 1958. For this degree she investigated electrophilic substitution reactions. More specifically, she explored the influence of ammonia on a-bromomercurophenylacetic acid reactions. In 1963 she received her Dr.Sci. degree from the same institution. In 1970 she became a Full Professor of Chemistry at Moscow State University, where she currently serves as head of the [http://www.chem.msu.su/eng/lab/orgcomp.html Organoelement Chemistry Laboratory]. Beletskaya was elected a corresponding member of the Academy of Science of USSR in 1974. In 1992 she became a full member (academician) of the Russian Academy of Sciences. Between 1991 and 1993 she served as president of the Division of Organic Chemistry of IUPAC. Until 2001 she served on the IUPAC Committee on Chemical Weapons Destruction Technology (CWDT). She is editor-in chief of the [https://link.springer.com/journal/11178 Russian Journal of Organic Chemistry].
Beletskaya initially researched the reaction mechanisms of organic reactions, focusing on compounds with metal-carbon bonds. Her research included Grignard-like reactions and lanthanide complexes in the context of catalysts. She and Prof. O. Reutov worked on electrophilic reactions at saturated carbon. She also investigated the reaction mechanisms of organometallic compounds. She also researched carbanion reactivity, emphasizing the reactivity and structure of ion pairs. Once more advanced in her career, Beltskaya focused more on transition metal catalysts and developing economically favorable catalysts. Currently, she serves as the head of the Laboratory of Organoelement Compounds within the Department of Chemistry at Moscow State University, where she has concentrated her research on carbon dioxide utilization and its utility in renewable energy and reactions with epoxides. | 0 | Theoretical and Fundamental Chemistry |
Deutetrabenazine is a deuterated version of tetrabenazine. It was developed by Auspex then acquired by Teva in 2015 and approved by the FDA in 2017 as a treatment for chorea associated with Huntington's disease; it has a longer half life than the non-deuterated form of tetrabenazine, which had been approved earlier for the same use.
Deucravacitinib is a deuterated JAK inhibitor (specifically, TYK2 inhibitor) approved for the treatment of plaque psoriasis.
Concert Pharmaceuticals focuses on deuterated drugs for various conditions. Concert was acquired by Sun Pharma in March 2023.
The company Retrotope discovered and has been developing a deuterated fatty acid RT001 as a treatment for neurodegenerative diseases such as Friedreich's ataxia and infantile neuroaxonal dystrophy. Their premise is that fatty acids in cell membranes are a source of reactive oxygen species and deuterated versions will be less prone to generating them.
Poxel SA, a French clinical-stage biopharmaceutical company focused on therapies for rare metabolic diseases, is developing PXL065 to target non-alcoholic steatohepatitis (NASH). The company acquired PXL065 (the deuterium-stabilized (R)-enantiomer of pioglitazone) and a portfolio of deuterated thiazolidinediones (TZDs) from DeuteRx, LLC, in 2018, and published positive results from the Phase 2 trial in March 2023. | 1 | Applied and Interdisciplinary Chemistry |
With the major breakthrough of commercial application of laser peening on the F101 engine to resolve a major operational problem, laser peening attracted attention around the globe. Researchers in many countries and industries undertook investigations to extend understanding of the laser shock peening process and material property effects. As a result, a large volume of research papers and patents were generated in the United States, France, and Japan. In addition to the work being done in these countries and Spain, laser peening programs were initiated in China, Britain, Germany and several other countries. The continuing growth of the technology and its applications led to the appearance of several commercial laser shock peening providers in the early 2000s.
GE Aviation and LSP Technologies were the first companies performing laser peening commercially, having licensed the technology from Battelle. GE Aviation performed laser peening for its aerospace engine components and LSP Technologies marketed laser shock peening services and equipment to a broader industrial base. In the late 1990s, Metal Improvement Company (MIC is now part of Curtis Wright Surface Technologies) partnered with Lawrence Livermore National Laboratory (LLNL) to develop its own laser peening capabilities. In Japan, Toshiba Corporation expanded the commercial applications of its LPwC system to pressurized water reactors, and in 2002 implemented fiber optic beam delivery to the underwater laser peening head. Toshiba also redesigned the laser and beam delivery into a compact system, enabling the entire system to be inserted into the pressure vessel. This system was ready for commercial use in 2013 MIC developed and adapted laser shock peening for forming the wing shapes on the Boeing 747-8.
The growth of industrial suppliers and commercial proof of laser peening technology lead to many companies adopting laser peening technology to solve and prevent problems. Some of the companies who have adopted laser peening include: GE, Rolls-Royce, Siemens, Boeing, Pratt & Whitney, and others.
In the 1990s and continuing through present day, laser peening developments have targeted decreasing costs and increasing throughput to reach markets outside of high-cost low-volume components. High costs in the laser peening process were previously attributable to laser system complexity, processing rates, manual labor and overlay applications. Numerous ongoing advancements addressing these challenges have reduced laser peening costs dramatically: laser peening systems are designed to handle robust operations; pulse rates of laser systems are increasing; routine labor operations are increasingly automated; application of overlays are automated in many cases. These reduced operational costs of laser peening have made it a valuable tool for solving an extended range of fatigue and related applications. | 1 | Applied and Interdisciplinary Chemistry |
When block copolymer micelles do not display the characteristic relaxation processes of surfactant micelles, these are called kinetically frozen micelles. These can be achieved in two ways: when the unimers forming the micelles are not soluble in the solvent of the micelle solution, or if the core forming blocks are glassy at the temperature in which the micelles are found. Kinetically frozen micelles are formed when either of these conditions is met. A special example in which both of these conditions are valid is that of polystyrene-b-poly(ethylene oxide). This block copolymer is characterized by the high hydrophobicity of the core forming block, PS, which causes the unimers to be insoluble in water. Moreover, PS has a high glass transition temperature which is, depending on the molecular weight, higher than room temperature. Thanks to these two characteristics, a water solution of PS-PEO micelles of sufficiently high molecular weight can be considered kinetically frozen. This means that none of the relaxation processes, which would drive the micelle solution towards thermodynamic equilibrium, are possible. Pioneering work on these micelles was done by Adi Eisenberg. It was also shown how the lack of relaxation processes allowed great freedom in the possible morphologies formed. Moreover, the stability against dilution and vast range of morphologies of kinetically frozen micelles make them particularly interesting, for example, for the development of long circulating drug delivery nanoparticles. | 0 | Theoretical and Fundamental Chemistry |
Another accepted explanation for the anomeric effect is the equatorial configuration has the dipoles involving both heteroatoms partially aligned, and therefore repelling each other. By contrast the axial configuration has these dipoles roughly opposing, thus representing a more stable and lower energy state.
Both the hyperconjugation and the dipole minimization contribute to the preferred (Z)-conformation of esters over the (E)-conformation. In the (Z) conformation the lone pair of electrons in the alpha oxygen can donate into the neighboring σ* C-O orbital. In addition, the dipole is minimized in the (Z)-conformation and maximized in the (E)-conformation. | 0 | Theoretical and Fundamental Chemistry |
Cyclohexane conformations are any of several three-dimensional shapes adopted by molecules of cyclohexane. Because many compounds feature structurally similar six-membered rings, the structure and dynamics of cyclohexane are important prototypes of a wide range of compounds.
The internal angles of a regular, flat hexagon are 120°, while the preferred angle between successive bonds in a carbon chain is about 109.5°, the tetrahedral angle (the arc cosine of −). Therefore, the cyclohexane ring tends to assume non-planar (warped) conformations, which have all angles closer to 109.5° and therefore a lower strain energy than the flat hexagonal shape.
Consider the carbon atoms numbered from 1 to 6 around the ring. If we hold carbon atoms 1, 2, and 3 stationary, with the correct bond lengths and the tetrahedral angle between the two bonds, and then continue by adding carbon atoms 4, 5, and 6 with the correct bond length and the tetrahedral angle, we can vary the three dihedral angles for the sequences (2,3,4), (3,4,5), and (4,5,6). The next bond, from atom 6, is also oriented by a dihedral angle, so we have four degrees of freedom. But that last bond has to end at the position of atom 1, which imposes three conditions in three-dimensional space. If the bond angle in the chain (6,1,2) should also be the tetrahedral angle then we have four conditions. In principle this means that there are no degrees of freedom of conformation, assuming all the bond lengths are equal and all the angles between bonds are equal. It turns out that, with atoms 1, 2, and 3 fixed, there are two solutions called chair, depending on whether the dihedral angle for (1,2,3,4) is positive or negative, and these two solutions are the same under a rotation. But there is also a continuum of solutions, a topological circle where angle strain is zero, including the twist boat and the boat conformations. All the conformations on this continuum have a twofold axis of symmetry running through the ring, whereas the chair conformations do not (they have D symmetry, with a threefold axis running through the ring). It is because of the symmetry of the conformations on this continuum that it is possible to satisfy all four constraints with a range of dihedral angles at (1,2,3,4). On this continuum the energy varies because of Pitzer strain related to the dihedral angles. The twist boat has a lower energy than the boat. In order to go from the chair conformation to a twist-boat conformation or the other chair conformation, bond angles have to be changed, leading to a high-energy half-chair conformation. So the relative stabilities are: . All relative conformational energies are shown below. At room temperature the molecule can easily move among these conformations, but only chair and twist-boat can be isolated in pure form, because the others are not at local energy minima.
The boat and twist-boat conformations, as said, lie along a continuum of zero angle strain. If there are substituents that allow the different carbon atoms to be distinguished, then this continuum is like a circle with six boat conformations and six twist-boat conformations between them, three "right-handed" and three "left-handed". (Which should be called right-handed is unimportant.) But if the carbon atoms are indistinguishable, as in cyclohexane itself, then moving along the continuum takes the molecule from the boat form to a "right-handed" twist-boat, and then back to the same boat form (with a permutation of the carbon atoms), then to a "left-handed" twist-boat, and then back again to the achiral boat. The passage boat⊣twist-boat⊣boat⊣twist-boat⊣boat constitutes a pseudorotation. | 0 | Theoretical and Fundamental Chemistry |
Clustering of genes in prokaryotes was known for a long time. Their genes are grouped in operons, genes within operons share a common promoter unit. These genes are mostly functionally related. The genome of prokaryotes is relatively very simple and compact. In eukaryotes the genome is huge and only a small amount of it are functionally genes, furthermore the genes are not arranged in operons. Except for nematodes and trypanosomes; although their operons are different from the prokaryotic operons. In eukaryotes each gene has a transcription regulation site of its own. Therefore, genes don't have to be in close proximity to be co-expressed. Therefore, it was long assumed that eukaryotic genes were randomly distributed across the genome due to the high rate of chromosome rearrangements. But because the complete sequence of genomes became available it became possible to absolutely locate a gene and measure its distance to other genes.
The first eukaryote genome ever sequenced was that of Saccharomyces cerevisiae, or budding yeast, in 1996. Half a year after that Velculescu et al. (1997) published a research in which they had integrated SAGE data with the now available genome map. During a cell cycle different genes are active in a cell. Therefore, they used SAGE data from three moments of the cell cycle (log phase, S phase-arrested and G2/M-phase arrested cells). Because in yeast all genes have a promoter unit of their own it was not suspected that genes would cluster near to each other but they did. Clusters were present on all 16 yeast chromosomes.
A year later Cho et al. also reported (although in more detail) that certain genes are located near to each other in yeast. | 1 | Applied and Interdisciplinary Chemistry |
Calcium looping compares favorably with several post-combustion capture technologies. Amine scrubbing is the capture technology closest to being market-ready, and calcium looping has several marked benefits over it. When modeled on a 580 MW coal-fired power plant, Calcium looping experienced not only a smaller efficiency penalty (6.7-7.9% points compared to 9.5% for monoethanolamine and 9% for chilled ammonia) but also a less complex retrofitting process. Both technologies would require the plant to be retrofitted for adoption, but the calcium looping retrofitting process would result in twice the net power output of the scrubbing technology. Furthermore, this advantage can be compounded by introducing technology such as cryogenic O separation systems. This ups the efficiency of the calcium looping technology by increasing the energy density by 57.4%, making the already low energy penalties even less of an issue.
Calcium looping already has an energy advantage over amine scrubbing, but the main problem is that amine scrubbing is the more market-ready technology. However, the accompanying infrastructure for amine scrubbing include large solvent scrubbing towers, the likes of which have never been used on an industrial scale. The accompanying infrastructure for calcium looping capture technologies are circulating fluidized beds, which have already been implemented on an industrial scale. Although the individual technologies differ in terms of current technological viability, the fact that the infrastructure needed to properly implement an amine scrubbing system has yet to be developed keeps calcium looping competitive from a viability standpoint. | 1 | Applied and Interdisciplinary Chemistry |
The regulation of transcription by enhancers has been studied since the 1980s. Large or multi-component transcription regulators with a range of mechanistic properties, including locus control regions, clustered open regulatory elements, and transcription initiation platforms, were observed shortly thereafter. More recent research has suggested that these different categories of regulatory elements may represent subtypes of super-enhancer.
In 2013, two labs identified large enhancers near several genes especially important for establishing cell identities. While Richard A. Young and colleagues identified super-enhancers, Francis Collins and colleagues identified stretch enhancers. Both super-enhancers and stretch enhancers are clusters of enhancers that control cell-specific genes and may be largely synonymous.
As currently defined, the term “super-enhancer” was introduced by Young’s lab to describe regions identified in mouse embryonic stem cells (ESCs). These particularly large, potent enhancer regions were found to control the genes that establish the embryonic stem cell identity, including Oct-4, Sox2, Nanog, Klf4, and Esrrb. Perturbation of the super-enhancers associated with these genes showed a range of effects on their target genes’ expression. Super-enhancers have been since identified near cell identity-regulators in a range of mouse and human tissues. | 1 | Applied and Interdisciplinary Chemistry |
Multiferroic composite structures in bulk form are explored for high-sensitivity ac magnetic field sensors and electrically tunable microwave devices such as filters, oscillators and phase shifters (in which the ferri-, ferro- or antiferro-magnetic resonance is tuned electrically instead of magnetically). | 0 | Theoretical and Fundamental Chemistry |
Tim Requarth, reviewing The Vital Question for The New York Times, finds the book "seductive and often convincing, though speculation far outpaces evidence in many of the book’s passages. But perhaps for a biological theory of everything, that's to be expected, even welcomed."
Peter Forbes, reviewing The Vital Question in The Guardian, noted that the origin of life was once thought to be "safely consigned to wistful armchair musing", but that in the past 20 years new research in genomics, geology, biochemistry and molecular biology have transformed thinking in the field. "Here is the book that presents all this hard evidence and tightly interlocking theory to a wider audience.", writes Forbes.
Michael LePage, reviewing the book in New Scientist, writes that the fact that complex cells only evolved once is "very peculiar when you think about it", but it is just one of many large mysteries that Lane addresses, including aging and death, sex, and speciation. LePage finds Lane's arguments "powerful and persuasive", with many testable ideas. The book is not, he writes, the easiest to read, but "it does tell an incredible, epic story", from the dawn of life to the present day.
Caspar Henderson, in his book review in The Telegraph, writes that Lanes book "succeeds brilliantly" as good science writing can, expanding the readers horizons "in ways not previously imagined." Lane explains why the counterintuitive idea "that cross-membrane proton gradients power all living cells" is no mere technical detail: per gram, he notes, the power is 10,000 times denser than the sun, and it is conserved across every form of life, telling us something about how life began and how it was constrained to evolve. Henderson recommends the book as amazing and gripping, only criticising the publisher for the "pedestrian" quality of the design and printing.
The founder of Microsoft, Bill Gates, reviewed the book under the heading "This Biology Book Blew Me Away". It moved him to read two of Lanes other books, and to bring him to New York to interview him. Gates noted that "As much as I loved The Vital Question, its not for everyone. Some of the explanations are pretty technical. But this is a technical subject, and I doubt anyone else will make it much easier to understand without sacrificing crucial details."
Lane won the Michael Faraday Prize in 2016 for "excellence in communicating science to UK audiences". | 1 | Applied and Interdisciplinary Chemistry |
The beta particles from small amounts of tritium cause chemicals called phosphors to glow. This radioluminescence is used in self-powered lighting devices called betalights, which are used for night illumination of firearm sights, watches, exit signs, map lights, navigational compasses (such as current-use M-1950 U.S. military compasses), knives and a variety of other devices. , commercial demand for tritium is per year and the cost is or more. | 0 | Theoretical and Fundamental Chemistry |
Phonon-electron scattering can also contribute when the material is heavily doped. The corresponding relaxation time is given as:
The parameter is conduction electrons concentration, ε is deformation potential, ρ is mass density and m* is effective electron mass. It is usually assumed that contribution to thermal conductivity by phonon-electron scattering is negligible . | 0 | Theoretical and Fundamental Chemistry |
Two examples of natural phosphoramidates are phosphocreatine and the phosphoramidate formed when histidine residues in histidine kinases are phosphorylated.
An example of a phosphorodiamidate is morpholino which is used in molecular biology. | 0 | Theoretical and Fundamental Chemistry |
Emma Schymanski (born Emma Craven) is chemist known for her work identifying unknown organic compounds, particularly pollutants, and is an advocate for open science. | 0 | Theoretical and Fundamental Chemistry |
GLVs can also have antimicrobial effects. Some plants express HPL, the main enzyme of GLV synthesis. The rates of fungal spore growth in HPL over-expressing have been compared with HPL silencing mutants to the wild type plants. Results from the study showed lower rates of fungal growth and higher GLV emissions on the HPL over-expressing mutants, while the HPL silencing mutants showed higher rates of fungal growth and lower GLV emissions, which supports the hypothesis that GLVs have antimicrobial properties.
The antimicrobial properties of GLVs have also been proposed to be part of an evolutionary arms race. During an infection, plants emit GLVs to act as microbial agents, but bacteria and viruses have adapted to use these GLVs to their own benefit. The most common example of this is found in the red raspberry. When the red raspberry plant is infected, the virus influences it to produce more GLVs, which attract the red raspberry aphid. These GLVs cause more aphids to come and to feed on the plant for longer, giving the virus better chances of being ingested and spread more widely. Researchers are now trying to determine whether under infectious conditions plants emit GLVs for their benefit, or if bacteria and viruses induce the release of these compounds for their own benefit. Studies in this area have been inconclusive and contradictory. | 1 | Applied and Interdisciplinary Chemistry |
The proposed mechanism for cationic photopolymerization begins with the photoexcitation of the initiator. Once excited, both homolytic cleavage and dissociation of a counter anion takes place, generating a cationic radical (R), an aryl radical (R') and an unaltered counter anion (X). The abstraction of a lewis acid by the cationic radical produces a very weakly bound hydrogen and a free radical. The acid is further deprotonated by the anion (X) in solution, generating a lewis acid with the starting anion (X) as a counter ion. It is thought that the acidic proton generated is what ultimately initiates the polymerization. | 0 | Theoretical and Fundamental Chemistry |
The measure of the promoter activity has a broad meaning. The promoter activity could be measured for different situations or research questions, such as:
* estimation of the level of expression in comparison (relative) to some known value
* how fast a gene is expressed after induction
* the timing of expression relative to others genes
* the specific spatial location of expression
Methods to study promoter activity commonly are based in the expression of a reporter gene from the promoter of the gene of interest. Mutations and deletions are made in a promoter region, and their changes on couple expression of the reporter gene are measured.
The most important reporter genes are the fluorescence proteins as GFP. These reporters allow to measure promoter activation by increasing fluorescent signals, and deactivation by decrease in the rate of fluorescence. | 1 | Applied and Interdisciplinary Chemistry |
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