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It is easy to verify that for an ideal gas defined by suitable microscopic postulates that αT = 1, so the temperature change of such an ideal gas at a Joule–Thomson expansion is zero.
For such an ideal gas, this theoretical result implies that:
:The internal energy of a fixed mass of an ideal gas depends only on its temperature (not pressure or volume).
This rule was originally found by Joule experimentally for real gases and is known as Joule's second law. More refined experiments found important deviations from it. | 7 | Physical Chemistry |
The following equations apply to two hard spheres that undergo a perfectly elastic collision. Let and denote the radii of the scattering center and scattered sphere, respectively. The differential cross section is
and the total cross section is
In other words, the total scattering cross section is equal to the area of the circle (with radius ) within which the center of mass of the incoming sphere has to arrive for it to be deflected. | 7 | Physical Chemistry |
Euxinia or euxinic conditions occur when water is both anoxic and sulfidic. This means that there is no oxygen (O) and a raised level of free hydrogen sulfide (HS). Euxinic bodies of water are frequently strongly stratified; have an oxic, highly productive, thin surface layer; and have anoxic, sulfidic bottom water. The word "euxinia" is derived from the Greek name for the Black Sea (Εὔξεινος Πόντος (Euxeinos Pontos)) which translates to "hospitable sea". Euxinic deep water is a key component of the Canfield ocean, a model of oceans during part of the Proterozoic eon (a part specifically known as the Boring Billion) proposed by Donald Canfield, an American geologist, in 1998. There is still debate within the scientific community on both the duration and frequency of euxinic conditions in the ancient oceans. Euxinia is relatively rare in modern bodies of water, but does still happen in places like the Black Sea and certain fjords. | 9 | Geochemistry |
Time-domain diffuse optics or time-resolved functional near-infrared spectroscopy is a branch of functional near-Infrared spectroscopy which deals with light propagation in diffusive media. There are three main approaches to diffuse optics namely continuous wave (CW), frequency domain (FD) and time-domain (TD). Biological tissue in the range of red to near-infrared wavelengths are transparent to light and can be used to probe deep layers of the tissue thus enabling various in vivo applications and clinical trials. | 7 | Physical Chemistry |
SDS is mainly used in detergents for laundry with many cleaning applications. It is a highly effective surfactant and is used in any task requiring the removal of oily stains and residues. For example, it is found in higher concentrations with industrial products including engine degreasers, floor cleaners, and car exterior cleaners.
It is a component in hand soap, toothpastes, shampoos, shaving creams, and bubble bath formulations, for its ability to create a foam (lather), for its surfactant properties, and in part for its thickening effect. | 1 | Biochemistry |
DNA is almost ideally suited for UV LD detection. The molecule is very long and very thin, making it very easy to orient in flow. This gives rise to a strong LD signal. DNA systems that have been studied using UV LD include DNA-enzyme complexes and DNA-ligand complexes, the formation of the latter being easily observable through kinetic experiments. | 7 | Physical Chemistry |
Young's modulus quantifies the elasticity of the polymer. It is defined, for small strains, as the ratio of rate of change of stress to strain. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands. The modulus is strongly dependent on temperature. Viscoelasticity describes a complex time-dependent elastic response, which will exhibit hysteresis in the stress-strain curve when the load is removed. Dynamic mechanical analysis or DMA measures this complex modulus by oscillating the load and measuring the resulting strain as a function of time. | 7 | Physical Chemistry |
Quantitative aspects of electrolysis were originally developed by Michael Faraday in 1834. Faraday is also credited to have coined the terms electrolyte, electrolysis, among many others while he studied quantitative analysis of electrochemical reactions. Also he was an advocate of the law of conservation of energy. | 7 | Physical Chemistry |
When phospholipids or simple lipids like fatty acids are placed in water, the molecules spontaneously arrange such that the hydrophobic tails are shielded from the water, resulting in the formation of membrane structures such as bilayers, vesicles, and micelles. In modern cells, vesicles are involved in metabolism, transport, buoyancy control, and enzyme storage. They can also act as natural chemical reaction chambers. A typical vesicle or micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single-tail regions in the micelle center. This phase is caused by the packing behavior of single-tail lipids in a bilayer. Although the spontaneous self-assembly process that form lipid monolayer vesicles and micelles in nature resemble the kinds of primordial vesicles or protocells that might have existed at the beginning of evolution, they are not as sophisticated as the bilayer membranes of today's living organisms. However, in a prebiotic context, electrostatic interactions induced by short, positively charged, hydrophobic peptides containing seven amino acids in length or fewer, can attach RNA to a vesicle membrane, the basic cell membrane.
Rather than being made up of phospholipids, early membranes may have formed from monolayers or bilayers of simple fatty acids, which may have formed more readily in a prebiotic environment. Fatty acids have been synthesized in laboratories under a variety of prebiotic conditions and have been found on meteorites, suggesting their natural synthesis in nature. Oleic acid vesicles represent good models of membrane protocells
Cohen et al. (2022) suggest that plausible prebiotic production of fatty acids — leading to the development of early protocell membranes — is enriched on metal-rich mineral surfaces, possibly from impact craters, increasing the prebiotic environmental mass of lipids by 10 times. They evaluate three different possible synthesis pathways of fatty acids in the Hadean, and found that these metal surfaces could produce 10 - 10 kg of 6-18 carbon fatty acids. Of these products, the 8-18C fatty acids are compatible with membrane formation. They also propose that alternative amphiphiles like alcohols are co-synthesized with fatty acid, and can help improve membrane stability. However, despite this production, the authors state that net fatty acid synthesis would not yield sufficient concentrations for spontaneous membrane formation without significant evaporation of Earth's aqueous environments. | 9 | Geochemistry |
One cannot assume that under all conditions the yield of strange quarks is in thermal equilibrium. In general, the quark-flavor composition of the plasma varies during its ultra short lifetime as new flavors of quarks such as strangeness are cooked up inside. The up and down quarks from which normal matter is made are easily produced as quark–antiquark pairs in the hot fireball because they have small masses. On the other hand, the next lightest quark flavor—strange quarks—will reach its high quark–gluon plasma thermal abundance provided that there is enough time and that the temperature is high enough. This work elaborated the kinetic theory of strangness production proposed by T. Biro and J. Zimanyi who demonstrated that strange quarks could not be produced fast enough alone by quark-antiquark reactions. A new mechanism operational alone in QGP was proposed. | 7 | Physical Chemistry |
Transposable elements can be harnessed in laboratory and research settings to study genomes of organisms and even engineer genetic sequences. The use of transposable elements can be split into two categories: for genetic engineering and as a genetic tool. | 1 | Biochemistry |
In A. thaliana, the main feedback loop is proposed to involve a transcriptional regulation between several proteins. The three main components of this loop are TOC1 (also known as PRR1), CCA1 and LHY. Each individual component peaks in transcriptions at different times of day. PRR 9, 7 and 5 each significantly reduce the transcription levels of CCA1 and LHY. In the opposite manner, PRR 9 and 7 slightly increase the transcription levels of TOC1. The Constans (CO) is also indirectly regulated by the PRR proteins as well by setting up the molecular mechanism to dictate the photosensitive period in the afternoon. PRRs are also known to stabilize CO at certain times of day to mediate its accumulation. This results in the regulation of early flowering in shorter photoperiods, making light sensitivity and control of flowering time important functions of the PRR class. | 1 | Biochemistry |
An amphoteric substance is one that can act as an acid or as a base, depending on pH. Water (below) is amphoteric. Another example of an amphoteric molecule is the bicarbonate ion that is the conjugate base of the carbonic acid molecule H2CO3 in the equilibrium
but also the conjugate acid of the carbonate ion in (the reverse of) the equilibrium
Carbonic acid equilibria are important for acid–base homeostasis in the human body.
An amino acid is also amphoteric with the added complication that the neutral molecule is subject to an internal acid–base equilibrium in which the basic amino group attracts and binds the proton from the acidic carboxyl group, forming a zwitterion.
At pH less than about 5 both the carboxylate group and the amino group are protonated. As pH increases the acid dissociates according to
At high pH a second dissociation may take place.
Thus the amino acid molecule is amphoteric because it may either be protonated or deprotonated. | 7 | Physical Chemistry |
*PLC-ε (230-260kDa ) is activated by Ras and Rho GTPases.
*PLC-ζ (75kDa) is thought to play an important role in vertebrate fertilization by producing intracellular calcium oscillations important for the start of embryonic development. However, the mechanism of activation still remains unclear. This isoform is also capable of entering the early-formed pronucleus after fertilization, which seems to coincide with the cessation of calcium mobilization. It, like PLC-δ1 and PLC-β, possesses nuclear export and localization sequences.
*PLC-η has been implicated in neuronal functioning. | 1 | Biochemistry |
Direct reduction processes can be divided roughly into two categories: gas-based and coal-based. In both cases, the objective of the process is to remove the oxygen contained in various forms of iron ore (sized ore, concentrates, pellets, mill scale, furnace dust, etc.) in order to convert the ore to metallic iron, without melting it (below ).
The direct reduction process is comparatively energy efficient. Steel made using DRI requires significantly less fuel, in that a traditional blast furnace is not needed. DRI is most commonly made into steel using electric arc furnaces to take advantage of the heat produced by the DRI product. | 8 | Metallurgy |
During the curing process, single monomers and oligomers, mixed with or without a curing agent, react to form a tridimensional polymeric network.
In the very first part of the reaction branches of molecules with various architectures are formed, and their molecular weight increases in time with the extent of the reaction until the network size is equal to the size of the system. The system has lost its solubility and its viscosity tends to infinite. The remaining molecules start to coexist with the macroscopic network until they react with the network creating other crosslinks. The crosslink density increases until the system reaches the end of the chemical reaction.
Curing can be induced by heat, radiation, electron beams, or chemical additives. To quote from IUPAC: curing "might or might not require mixing with a chemical curing agent". Thus, two broad classes are curing induced by chemical additives (also called curing agents, hardeners) and curing in the absence of additives. An intermediate case involves a mixture of resin and additives that requires external stimulus (light, heat, radiation) to induce curing.
The curing methodology depends on the resin and the application. Particular attention is paid to the shrinkage induced by the curing. Usually small values of shrinkage (2–3%) are desirable. | 7 | Physical Chemistry |
Telluride-mediated polymerization or TERP first appeared to mainly operate under a reversible chain transfer mechanism by homolytic substitution under thermal initiation. However, in a kinetic study it was found that TERP predominantly proceeds by degenerative transfer rather than dissociation combination.
Alkyl tellurides of the structure Z-X-R, were Z=methyl and R= a good free radical leaving group, give the better control for a wide range of monomers, phenyl tellurides (Z=phenyl) giving poor control. Polymerization of methyl methacrylates are only controlled by ditellurides. The importance of X to chain transfer increases in the series O<S<Se<Te, makes alkyl tellurides effective in mediating control under thermally initiated conditions and the alkyl selenides and sulfides effective only under photoinitiated polymerization. | 7 | Physical Chemistry |
The biochemistry of body odor pertains to the chemical compounds in the body responsible for body odor and their kinetics. | 1 | Biochemistry |
Where the acyl chloride moiety takes priority, acyl chlorides are named by taking the name of the parent carboxylic acid, and substituting -yl chloride for -ic acid. Thus:
:butyric acid (CHCOOH) → butyryl chloride (C3H7COCl)
(Idiosyncratically, for some trivial names, -oyl chloride substitutes -ic acid. For example, pivalic acid becomes pivaloyl chloride and acrylic acid becomes acryloyl chloride. The names pivalyl chloride and acrylyl chloride are less commonly used, although they are arguably more logical.)
When other functional groups take priority, acyl chlorides are considered prefixes — chlorocarbonyl-: | 0 | Organic Chemistry |
Chemical and electrical synapses are two ways of synaptic transmission.
* In a chemical synapse, electrical activity in the presynaptic neuron is converted (via the activation of voltage-gated calcium channels) into the release of a chemical called a neurotransmitter that binds to receptors located in the plasma membrane of the postsynaptic cell. The neurotransmitter may initiate an electrical response or a secondary messenger pathway that may either excite or inhibit the postsynaptic neuron. Chemical synapses can be classified according to the neurotransmitter released: glutamatergic (often excitatory), GABAergic (often inhibitory), cholinergic (e.g. vertebrate neuromuscular junction), and adrenergic (releasing norepinephrine). Because of the complexity of receptor signal transduction, chemical synapses can have complex effects on the postsynaptic cell.
* In an electrical synapse, the presynaptic and postsynaptic cell membranes are connected by special channels called gap junctions that are capable of passing an electric current, causing voltage changes in the presynaptic cell to induce voltage changes in the postsynaptic cell. In fact, gap junctions facilitate the direct flow of electrical current without the need for neurotransmitters, as well as small molecules like calcium. Thus, the main advantage of an electrical synapse is the rapid transfer of signals from one cell to the next.
* Mixed chemical electrical synapses are synaptic sites that feature both a gap junction and neurotransmitter release. This combination allows a signal to have both a fast component (electrical) and a slow component (chemical).
The formation of neural circuits in nervous systems, appears to heavily depend on the crucial interactions between chemical and electrical synapses. Thus, these interactions govern the generation of synaptic transmission. Synaptic communication is distinct from an ephaptic coupling, in which communication between neurons occurs via indirect electric fields. An autapse is a chemical or electrical synapse that forms when the axon of one neuron synapses onto dendrites of the same neuron. | 1 | Biochemistry |
The result from the previous example can be used to solve the analogous problem in three dimensions, i.e., scattering from a perfectly reflecting sphere of radius .
The plane perpendicular to the incoming light beam can be parameterized by cylindrical coordinates and . In any plane of the incoming and the reflected ray we can write (from the previous example):
while the impact area element is
In spherical coordinates,
Together with the trigonometric identity
we obtain
The total cross section is | 7 | Physical Chemistry |
Cyanobacteria are variable in morphology, ranging from unicellular and filamentous to colonial forms. Filamentous forms exhibit functional cell differentiation such as heterocysts (for nitrogen fixation), akinetes (resting stage cells), and hormogonia (reproductive, motile filaments). These, together with the intercellular connections they possess, are considered the first signs of multicellularity.
Many cyanobacteria form motile filaments of cells, called hormogonia, that travel away from the main biomass to bud and form new colonies elsewhere. The cells in a hormogonium are often thinner than in the vegetative state, and the cells on either end of the motile chain may be tapered. To break away from the parent colony, a hormogonium often must tear apart a weaker cell in a filament, called a necridium.
Some filamentous species can differentiate into several different cell types:
* Vegetative cells – the normal, photosynthetic cells that are formed under favorable growing conditions
* Akinetes – climate-resistant spores that may form when environmental conditions become harsh
* Thick-walled heterocysts – which contain the enzyme nitrogenase vital for nitrogen fixation in an anaerobic environment due to its sensitivity to oxygen.
Each individual cell (each single cyanobacterium) typically has a thick, gelatinous cell wall. They lack flagella, but hormogonia of some species can move about by gliding along surfaces. Many of the multicellular filamentous forms of Oscillatoria are capable of a waving motion; the filament oscillates back and forth. In water columns, some cyanobacteria float by forming gas vesicles, as in archaea. These vesicles are not organelles as such. They are not bounded by lipid membranes, but by a protein sheath. | 5 | Photochemistry |
Some companion plants help prevent pest insects or pathogenic fungi from damaging the crop, through their production of aromatic volatile chemicals, another type of allelopathy. For example, the smell of the foliage of marigolds is claimed to deter aphids from feeding on neighbouring plants. A 2005 study found that oil volatiles extracted from Mexican marigold could suppress the reproduction of three aphid species (pea aphid, green peach aphid and glasshouse and potato aphid) by up to 100% after 5 days from exposure. Another example familiar to gardeners is the interaction of onions and carrots with each other's pests: it is popularly believed that the onion smell puts off carrot root fly, while the smell of carrots puts off onion fly.
Some studies have demonstrated beneficial effects. For instance, cabbage crops can be seriously damaged by the cabbage moth. It has a natural enemy, the parasitoid wasp Microplitis mediator. Companion planting of cornflowers among cabbages enables the wasp to increase sufficiently in number to control the moth. This implies the possibility of natural control, with reduced use of insecticides, benefiting the farmer and local biodiversity. In horticulture, marigolds provide good protection to tomato plants against the greenhouse whitefly (an aphid), via the aromatic limonene that they produce. Not all combinations of target and companion are effective; for instance, clover, a useful companion to many crop plants, does not mask Brassica crops.
However, effects on multi-species systems are complex and may not increase crop yields. Thus, French marigold inhibits codling moth, a serious pest whose larva destroys apples, but it also inhibits the moths insect enemies, such as the parasitoid wasp Ascogaster quadridentata', an ichneumonid. The result is that the companion planting fails to reduce damage to apples. | 1 | Biochemistry |
Ashe joined the University of Minnesota Medical School in 1992 as an assistant professor of neurology. She has also worked with the Minneapolis Veterans Affairs Health Care System. She was the founding director of the N. Bud Grossman Center for Memory Research and Care. As of 2022, she has received over $28million in grants from the U.S. National Institutes of Health.
The Minneapolis Star Tribune described Ashe as a "distinguished professor considered by many to be on the short list for a Nobel Prize for her work". | 1 | Biochemistry |
Gecko feet are the most famous reversible adhesion mechanism in nature. The anti-fouling ability of feet allows geckos to run on dusty ceilings and corners without the accumulation of dirt on their feet. In 2000, Autumn et al. revealed the origin of gecko’s strong adhesion by investigating the surface features of the toes under electron microscope. They observed a hierarchical morphology of each foot which is composed of millions of small hair called setae. Moreover, each setae is composed of a smaller hair, and each hair is tailed with a flat spatula and these spatulae are bonded by the van der Waals forces. This surface feature, regardless of the surface type (hydrophobic, hydrophilic, dry, wet, rough etc.), enables geckos to stick the surface. In addition to strong adhesion, the gecko foot has a unique self-cleaning property which does not require water as the lotus leaf. | 7 | Physical Chemistry |
Field effects can arise from the electric dipole field of a bond containing an electronegative atom or electron-withdrawing substituent, as well as from an atom or substituent bearing a formal charge. The directionality of a dipole, and concentration of charge, can both define the shape of a molecule's electric field which will manipulate the localization of electron density toward or away from sites of interest, such as an acidic hydrogen. Field effects are typically associated with the alignment of a dipole field with respect to a reaction center. Since these are through space effects, the 3D structure of a molecule is an important consideration. A field may be interrupted by other bonds or atoms before propagating to a reactive site of interest. Atoms of differing electronegativities can move closer together resulting in bond polarization through space that mimics the inductive effect through bonds. Bicycloheptane and bicyclooctane (seen left) are two compounds in which the change in acidity with substitution was attributed to the field effect. The C-X dipole is oriented away from the carboxylic acid group, and can draw electron density away because the molecule center is empty, with a low dielectric constant, so the electric field is able to propagate with minimal resistance. | 7 | Physical Chemistry |
The Compendium of Macromolecular Nomenclature, by the International Union of Pure and Applied Chemistry (IUPAC), provides definition of polymer related terms and rules of nomenclature of polymers. It is referred to as the Purple Book. It was published in 1991 () by Blackwell Science. The author of this book is W.V. Metanomski.
The expansion of this book named Compendium of Polymer Terminology and Nomenclature: IUPAC Recommendations, 2008 was published by the Royal Society of Chemistry in 2009 ().
The rules and definitions were set up by the IUPAC Commission on Macromolecular Nomenclature. The work was carried on by the Subcommittee on Polymer Terminology (IUPAC Division IV) after the Commission on Macromolecular Nomenclature was terminated. | 7 | Physical Chemistry |
The alloy contains about 35–50% uranium and 1.5–4.0% carbon. At least two intermetallic compounds of iron and uranium were identified: UFe and UFe. Small amounts of uranium can drastically lower the melting point of iron and vice versa. reportedly melts at 1230 °C, at 805 °C; a mixture of these two can have melting point as low as 725 °C, a mixture of iron and can have melting point of 1055 °C. As ferrouranium readily dissolves in mineral acids, its chemical analysis is not problematic. | 8 | Metallurgy |
Diastereomers are distinct molecular configurations that are a broader category. They usually differ in physical characteristics as well as chemical properties. If two molecules with more than one chiral centre differ in one or more (but not all) centres, they are diastereomers. All stereoisomers that are not enantiomers are diastereomers. Diastereomerism also exists in alkenes. Alkenes are designated Z or E depending on group priority on adjacent carbon atoms. E/Z notation describes the absolute stereochemistry of the double bond. Cis/trans notation is also used to describe the relative orientations of groups. | 4 | Stereochemistry |
The in vivo functionality and longevity of any implantable medical device is affected by the body's response to the foreign material. The body undergoes a cascade of processes defined under the foreign body response (FBR) in order to protect the host from the foreign material. The interactions between the device upon the host tissue/blood as well as the host tissue/blood upon the device must be understood in order to prevent complications and device failure.
Tissue injury caused by device implantation causes inflammatory and healing responses during FBR. The inflammatory response occurs within two time periods: the acute phase, and the chronic phase. The acute phase occurs during the initial hours to days of implantation, and is identified by fluid and protein exudation along with a neutrophilic reaction. During the acute phase, the body attempts to clean and heal the wound by delivering excess blood, proteins, and monocytes are called to the site. Continued inflammation leads to the chronic phase, which can be categorized by the presence of monocytes, macrophages, and lymphocytes. In addition, blood vessels and connective tissue form in order to heal the wounded area. | 1 | Biochemistry |
Lysine is a proteinaceous diamino acid (i.e. a component of proteins), and is accordingly coded by codons of the genetic material. In the pH range found inside living cells, both the amino groups are protonated, and they can be classified therefore as cationic amino acids.
Ornithine is a non-proteinaceous diamino acid.
In biochemistry, diamino acids are of particular interest. Diamino acids are used for the synthesis of specific peptide nucleic acids, such as daPNA. Artificial peptide nucleic acids are capable of forming duplex structures with individual DNA- and RNA-strands and are, therefore, not only called DNA-analog, but also they are considered as candidates for the first genetic material on Earth. The corresponding diamino acids such as 2,3-diaminopropanoic acid were detected in the Murchison meteorite and in a simulated comet. | 1 | Biochemistry |
An important feature of water is its polar nature. The structure has a bent molecular geometry for the two hydrogens from the oxygen vertex. The oxygen atom also has two lone pairs of electrons. One effect usually ascribed to the lone pairs is that the H–O–H gas-phase bend angle is 104.48°, which is smaller than the typical tetrahedral angle of 109.47°. The lone pairs are closer to the oxygen atom than the electrons sigma bonded to the hydrogens, so they require more space. The increased repulsion of the lone pairs forces the O–H bonds closer to each other.
Another consequence of its structure is that water is a polar molecule. Due to the difference in electronegativity, a bond dipole moment points from each H to the O, making the oxygen partially negative and each hydrogen partially positive. A large molecular dipole, points from a region between the two hydrogen atoms to the oxygen atom. The charge differences cause water molecules to aggregate (the relatively positive areas being attracted to the relatively negative areas). This attraction, hydrogen bonding, explains many of the properties of water, such as its solvent properties.
Although hydrogen bonding is a relatively weak attraction compared to the covalent bonds within the water molecule itself, it is responsible for several of the waters physical properties. These properties include its relatively high melting and boiling point temperatures: more energy is required to break the hydrogen bonds between water molecules. In contrast, hydrogen sulfide (), has much weaker hydrogen bonding due to sulfurs lower electronegativity. is a gas at room temperature, despite hydrogen sulfide having nearly twice the molar mass of water. The extra bonding between water molecules also gives liquid water a large specific heat capacity. This high heat capacity makes water a good heat storage medium (coolant) and heat shield. | 2 | Environmental Chemistry |
Methylene blue is employed as a medication for the treatment of methemoglobinemia, which can arise from ingestion of certain pharmaceuticals, toxins, or broad beans in those susceptible. Normally, through the NADH- or NADPH-dependent methemoglobin reductase enzymes, methemoglobin is reduced back to hemoglobin. When large amounts of methemoglobin occur secondary to toxins, methemoglobin reductases are overwhelmed. Methylene blue, when injected intravenously as an antidote, is itself first reduced to leucomethylene blue, which then reduces the heme group from methemoglobin to hemoglobin. Methylene blue can reduce the half life of methemoglobin from hours to minutes. At high doses, however, methylene blue actually induces methemoglobinemia, reversing this pathway. | 3 | Analytical Chemistry |
The fourth annual Empowering Women in Organic Chemistry Conference was a hybrid meeting on Thursday, June 23, and Friday, June 24, 2022. | 0 | Organic Chemistry |
Coenzyme A is naturally synthesized from pantothenate (vitamin B), which is found in food such as meat, vegetables, cereal grains, legumes, eggs, and milk. In humans and most living organisms, pantothenate is an essential vitamin that has a variety of functions. In some plants and bacteria, including Escherichia coli, pantothenate can be synthesised de novo and is therefore not considered essential. These bacteria synthesize pantothenate from the amino acid aspartate and a metabolite in valine biosynthesis.
In all living organisms, coenzyme A is synthesized in a five-step process that requires four molecules of ATP, pantothenate and cysteine (see figure):
# Pantothenate (vitamin B) is phosphorylated to 4′-phosphopantothenate by the enzyme pantothenate kinase (PanK; CoaA; CoaX). This is the committed step in CoA biosynthesis and requires ATP.
# A cysteine is added to 4′-phosphopantothenate by the enzyme phosphopantothenoylcysteine synthetase (PPCS; CoaB) to form 4'-phospho-N-pantothenoylcysteine (PPC). This step is coupled with ATP hydrolysis.
# PPC is decarboxylated to 4′-phosphopantetheine by phosphopantothenoylcysteine decarboxylase (PPC-DC; CoaC)
# 4′-phosphopantetheine is adenylated (or more properly, AMPylated) to form dephospho-CoA by the enzyme phosphopantetheine adenylyl transferase (COASY; PPAT; CoaD)
# Finally, dephospho-CoA is phosphorylated to coenzyme A by the enzyme dephosphocoenzyme A kinase (COASY, DPCK; CoaE). This final step requires ATP.
Enzyme nomenclature abbreviations in parentheses represent mammalian, other eukaryotic, and prokaryotic enzymes respectively. In mammals steps 4 and 5 are catalyzed by a bifunctional enzyme called COASY. This pathway is regulated by product inhibition. CoA is a competitive inhibitor for Pantothenate Kinase, which normally binds ATP. Coenzyme A, three ADP, one monophosphate, and one diphosphate are harvested from biosynthesis.
Coenzyme A can be synthesized through alternate routes when intracellular coenzyme A level are reduced and the de novo pathway is impaired. In these pathways, coenzyme A needs to be provided from an external source, such as food, in order to produce 4′-phosphopantetheine. Ectonucleotide pyrophosphates (ENPP) degrade coenzyme A to 4′-phosphopantetheine, a stable molecule in organisms. Acyl carrier proteins (ACP) (such as ACP synthase and ACP degradation) are also used to produce 4′-phosphopantetheine. This pathway allows for 4′-phosphopantetheine to be replenished in the cell and allows for the conversion to coenzyme A through enzymes, PPAT and PPCK.
A 2024 article detailed a plausible chemical synthesis mechanism for the pantetheine component (the main functional part) of coenzyme A in a primordial prebiotic world. | 1 | Biochemistry |
Beryllium can coordinate with cyclic alkyl amino carbene (CAAC) ligands and can form beryllium radicals which can be present with beryllium complexes (). A CAAC ligand coordinates a 2 electron -1 charge into the beryllium center. CAAC has an "amino" substituent and an "alkyl" sp carbon atom. CAACs are very good σ donors (higher HOMO) and π acceptors (lower LUMO) compared to NHCs. In addition, the lower heteroatom stability of the carbene center in CAAC compared to NHC results in a lower ΔE. | 0 | Organic Chemistry |
In an effort to unify the above described equations the Mayr equation is rewritten as:
with s the electrophile-dependent slope parameter and s the nucleophile-dependent slope parameter. This equation can be rewritten in several ways:
* with s = 1 for carbocations this equation is equal to the original Mayr–Patz equation of 1994,
* with s = 0.6 for most n nucleophiles the equation becomes
:or the original Scott–Swain equation written as:
* with s = 1 for carbocations and s = 0.6 the equation becomes:
:or the original Ritchie equation written as: | 7 | Physical Chemistry |
The meteorite fell to Earth after the retreat of glaciers from the area. All fragments recovered were found at the surface, partly buried, some on unstable terrain. The largest fragment was recovered in an area where the landscape consists of "flowing" gravel or clay-like sediments on permafrost, indicating that it had been in place for no more than a few thousand years. Other estimates have put the date of the fall as 10,000 years ago.
The iron masses were known to Inuit as Saviksoah (Great Iron, later renamed Ahnighito by Robert Edwin Peary) weighing ; the Woman, weighing ; and the Dog, weighing . For centuries, Inuit living near the meteorites used them as a source of metal for tools and harpoons. The Inuit would work the metal using cold forging—that is, by hammering the metal with stones. Excavations of a Norse farm in 1976 located an arrowhead made of iron from the meteorite, dating from the 11th to 14th century AD; its presence is evidence of Norse journeys to northern Greenland. Other pieces of Cape York meteoritic iron dating prior to 1450 (i.e. before the Little Ice Age) have been found throughout the Arctic Archipelago and on the North American mainland, and are evidence of an extensive Thule culture trade network which supplied iron to First Nations peoples prior to European contact.
In 1818, the British First Ross Expedition (led by Captain John Ross) made contact with Inuit on the northern shore of Melville Bay, who stated they had settled in the area to exploit a nearby source of iron. The Inuit described the location of this iron, but poor weather and sea ice prevented Ross from investigating further. Ross correctly surmised that the large iron rocks described by the Inuit were meteorites, and purchased several tools with blades made of the meteoritic iron.
Between 1818 and 1883, five further expeditions to the area were mounted by Britain, Sweden, and Denmark, which all failed to find the source of the iron. Only in 1894 did a Western explorer reach the meteorite: Robert E. Peary, of the US Navy. Peary enlisted the help of a local Inuit guide, who brought him to Saviksoah Island, just off northern Greenlands Cape York. Peary dedicated three years to planning and executing the removal of the meteorite, a process which required the building of a short railroad. Peary sold the pieces for $40,000 (equivalent to $ in ) to the American Museum of Natural History in New York City, where they are still on display. The piece named Ahnighito is on display in the Arthur Ross Hall of the American Museum of Natural History. Ahnighito' is the second-heaviest meteorite to have been relocated. It is so heavy that it was necessary to build its display stand so that the supports reached directly to the bedrock below the museum.
Peary has received significant criticism for his removal of the meteorite and treatment of the Inuit (including Minik Wallace). During his expedition to retrieve the meteorite, Peary convinced six Inughuit Greenlandic Inuit people ("three men, one woman, a boy, and a girl") to travel with him for study at the American Museum of Natural History in the United States, where four died within a few months.
In 1963, a fourth major piece of the Cape York meteorite was discovered by on Agpalilik peninsula. The , also known as the Man, weighs about , and it is currently on display in the Geological Museum of the University of Copenhagen, Denmark. Other smaller pieces have also been found, such as the Savik I meteorite found in 1911 and the Tunorput fragment found in 1984. Surveys of the area with a magnetometer in 2012 and georadar in 2014 found no evidence of further large iron fragments, either buried or on the surface. | 8 | Metallurgy |
The concept of using D-PUFAs to inhibit LPO has been tested in numerous cell and animal
models, including:
* Parkinson's disease (MPTP and a-Syn models in mice and rats)
* Huntington's disease (in mice)
* Alzheimer's disease (APP/PS1 and ALDH2 mouse models)
* Diabetic retinopathy (Akita mice)
* Age-related macular degeneration (light irradiation in rats, eye iron overload in mice)
* Atherosclerosis (Leiden mice) | 7 | Physical Chemistry |
The amount of light transmitted through a material diminishes exponentially as it travels through the material, according to the Beer–Lambert law (). Since the absorbance of a sample is measured as a logarithm, it is directly proportional to the thickness of the sample and to the concentration of the absorbing material in the sample. Some other measures related to absorption, such as transmittance, are measured as a simple ratio so they vary exponentially with the thickness and concentration of the material. | 7 | Physical Chemistry |
Dexamethasone (DEX) is a glucocorticoid that is used as an anti-inflammatory and immunosuppressive agent. PLGA nanoparticles loaded with DEX via oil-in-water emulsion/solvent evaporation method can be embedded in alginate hydrogel matrices. To quantify the amount of DEX that was successfully seeding into the nanoparticle, UV spectrophotometry can be used. It has been shown that the amount of DEX that can be successfully loaded into the nanoparticles was ≈13 wt% and the typical particle size ranged from 400 to 600 nm.
In vitro tests have revealed that the impedance of the nanoparticle-loaded hydrogel-coated electrodes have similar impedance to the non-coated electrode (bare gold). This shows that the nanoparticle-loaded hydrogel coating does not significantly hinder the electrical transport. The in vivo tests have shown that the impedance amplitude of the DEX-loaded electrodes was maintained at the same level it was at initially. However, non-coated electrodes had an impedance about 3 times greater than its original impedance 2 weeks earlier. This addition of anti-inflammatory drugs via nanoparticles indicates that this form of surface modification does not have a negative effect on the electrodes performance. | 7 | Physical Chemistry |
Callystatin A is a polyketide natural product from the leptomycin family of secondary metabolites. It was first isolated in 1997 from the marine sponge Callyspongia truncata which was collected from the Goto Islands in the Nagasaki Prefecture of Japan by the Kobayashi group. Since then its absolute configuration has been elucidated and callystatin A was discovered to have anti-fungal and anti-tumor activities with extreme potency against the human epidermoid carcinoma KB cells (IG = 10 pg/ml) and the mouse lymphocytic leukemia Ll210 cells (IG = 20 pg/ml). | 0 | Organic Chemistry |
β-halo immonium compounds can be synthesized through the halogenation reaction of enamines with halides in diethyl ether solvent. Hydrolysis will result in the formation of α-halo ketones. Chlorination, bromination, and even iodination have been shown to be possible. The general reaction is shown below: | 0 | Organic Chemistry |
Many modifications to the Hiyama coupling have been developed that avoid the use of a fluoride activator/base. Using organochlorosilanes, Hiyama found a coupling scheme utilizing NaOH as the basic activator. Modifications using alkoxysilanes have been reported with the use of milder bases like NaOH and even water. Study of these mechanisms have led to the development of the Hiyama–Denmark coupling which utilize organosilanols as coupling partners.<br />
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Another class of fluoride-free Hiyama couplings include the use of a Lewis acid additive, which allows for bases such as KPO to be utilized, or for the reaction to proceed without a basic additive. The addition of a copper co-catalyst has also been reported to allow for the use of a milder activating agent and has even been shown to get turnover in which both the palladium(II) and copper(I) turnover in the catalytic cycle rather than addition of stoichiometric Lewis acid (e.g. silver(I), copper(I)). | 0 | Organic Chemistry |
Another criticism of entropic gravity is that entropic processes should, as critics argue, break quantum coherence. There is no theoretical framework quantitatively describing the strength of such decoherence effects, though. The temperature of the gravitational field in earth gravity well is very small (on the order of 10K).
Experiments with ultra-cold neutrons in the gravitational field of Earth are claimed to show that neutrons lie on discrete levels exactly as predicted by the Schrödinger equation considering the gravitation to be a conservative potential field without any decoherent factors. Archil Kobakhidze argues that this result disproves entropic gravity, while Chaichian et al. suggest a potential loophole in the argument in weak gravitational fields such as those affecting Earth-bound experiments. | 7 | Physical Chemistry |
Because the intense red color of hemoglobin interferes with the readout of colorimetric or optical detection-based diagnostic tests, blood plasma separation is a common first step to increase diagnostic test accuracy. Plasma can be extracted from whole blood via integrated filters or via agglutination. | 1 | Biochemistry |
*1 kg/m = 1 g/L (exactly)
*1 kg/m = 0.001 g/cm (exactly)
*1 kg/m ≈ 0.06243 lb/ft (approximately)
*1 kg/m ≈ 0.1335 oz/US gal (approximately)
*1 kg/m ≈ 0.1604 oz/imp gal (approximately)
*1 g/cm = 1000 kg/m (exactly)
*1 lb/ft ≈ 16.02 kg/m (approximately)
*1 oz/(US gal) ≈ 7.489 kg/m (approximately)
*1 oz/(imp gal) ≈ 6.236 kg/m (approximately) | 3 | Analytical Chemistry |
Detailed procedures for the cobalt thiocyanate test are available. The reagent consists of 2% cobalt thiocyanate dissolved in dilute acid. Glycerol is often added to stabilise the cobalt complex, ensuring it only goes blue when in contact with an analyte and not due to drying.
Addition of the cobalt thiocyanate reagent to cocaine hydrochloride results in the surface of the particles turning a bright blue (faint blue for cocaine base). The solution changes back to pink upon adding some hydrochloric acid. Addition of chloroform, results in a blue organic layer for both cocaine hydrochloride and cocaine base. Diphenhydramine and lidocaine also give blue organic layers. These compounds are known false positives for cocaine. Lidocaine is commonly used to adulterate or mimic cocaine due to its local anaesthetic effect.
If the procedure is adjusted to basify the sample rather than acidifying it, the test can be used to test for ketamine hydrochloride. | 3 | Analytical Chemistry |
Early developments in organometallic chemistry include Louis Claude Cadets synthesis of methyl arsenic compounds related to cacodyl, William Christopher Zeises platinum-ethylene complex, Edward Franklands discovery of diethyl- and dimethylzinc, Ludwig Monds discovery of Ni(CO), and Victor Grignard's organomagnesium compounds. (Although not always acknowledged as an organometallic compound, Prussian blue, a mixed-valence iron-cyanide complex, was first prepared in 1706 by paint maker Johann Jacob Diesbach as the first coordination polymer and synthetic material containing a metal-carbon bond.) The abundant and diverse products from coal and petroleum led to Ziegler–Natta, Fischer–Tropsch, hydroformylation catalysis which employ CO, H, and alkenes as feedstocks and ligands.
Recognition of organometallic chemistry as a distinct subfield culminated in the Nobel Prizes to Ernst Fischer and Geoffrey Wilkinson for work on metallocenes. In 2005, Yves Chauvin, Robert H. Grubbs and Richard R. Schrock shared the Nobel Prize for metal-catalyzed olefin metathesis. | 0 | Organic Chemistry |
Some of the most advanced molecular switches are based on mechanically-interlocked molecular architectures where the bistable states differ in the position of the macrocycle. In 1991 Stoddart devices a molecular shuttle based on a rotaxane on which a molecular bead is able to shuttle between two docking stations situated on a molecular thread. Stoddart predicts that when the stations are dissimilar with each of the stations addressed by a different external stimulus the shuttle becomes a molecular machine. In 1993 Stoddart is scooped by supramolecular chemistry pioneer Fritz Vögtle who actually delivers a switchable molecule based not on a rotaxane but on a related catenane
This compound is based on two ring systems: one ring holds the photoswichable azobenzene ring and two paraquat docking stations and the other ring is a polyether with to arene rings with binding affinity for the paraquat units. In this system NMR spectroscopy shows that in the azo trans-form the polyether ring is free to rotate around its partner ring but then when a light trigger activates the cis azo form this rotation mode is stopped
Kaifer and Stoddart in 1994 modify their molecular shuttle such a way that an electron-poor tetracationic cyclophane bead now has a choice between two docking stations: one biphenol and one benzidine unit. In solution at room temperature NMR spectroscopy reveals that the bead shuttles at a rate comparable to the NMR timescale, reducing the temperature to 229K resolves the signals with 84% of the population favoring the benzidine station. However, on addition of trifluoroacetic acid, the benzidine nitrogen atoms are protonated and the bead is fixed permanently on the biphenol station. The same effect is obtained by electrochemical oxidation (forming the benzidine radical ion) and significantly both processes are reversible.
In 2007 molecular shuttles were utilized in an experimental DRAM circuit. The device consists of 400 bottom silicon nanowire electrodes (16 nanometer (nm) wide at 33 nm intervals) crossed by another 400 titanium top-nanowires with similar dimensions sandwiching a monolayer of a bistable rotaxane depicted below:
Each bit in the device consists of a silicon and a titanium crossbar with around 100 rotaxane molecules filling in the space between them at perpendicular angles. The hydrophilic diethylene glycol stopper on the left (gray) is specifically designed to anchor to the silicon wire (made hydrophilic by phosphorus doping) while the hydrophobic tetraarylmethane stopper on the right does the same to the likewise hydrophobic titanium wire. In the ground state of the switch, the paraquat ring is located around a tetrathiafulvalene unit (in red) but it moves to the dioxynaphthyl unit (in green) when the fulvalene unit is oxidized by application of a current. When the fulvalene is reduced back a metastable high conductance 1 state is formed which relaxes back to the ground state with a chemical half-life of around one hour. The problem of defects is circumvented by adopting a defect-tolerant architecture also found in the Teramac project. In this way a circuit is obtained consisting of 160,000 bits on an area the size of a white blood cell translating into 10 bits per square centimeter. | 6 | Supramolecular Chemistry |
Note: An e plane is a double glide plane, one having glides in two different directions. They are found in seven orthorhombic, five tetragonal and five cubic space groups, all with centered lattice. The use of the symbol e became official with .
The lattice system can be found as follows. If the crystal system is not trigonal then the lattice system is of the same type. If the crystal system is trigonal, then the lattice system is hexagonal unless the space group is one of the seven in the rhombohedral lattice system consisting of the 7 trigonal space groups in the table above whose name begins with R. (The term rhombohedral system is also sometimes used as an alternative name for the whole trigonal system.) The hexagonal lattice system is larger than the hexagonal crystal system, and consists of the hexagonal crystal system together with the 18 groups of the trigonal crystal system other than the seven whose names begin with R.
The Bravais lattice of the space group is determined by the lattice system together with the initial letter of its name, which for the non-rhombohedral groups is P, I, F, A or C, standing for the principal, body centered, face centered, A-face centered or C-face centered lattices. There are seven rhombohedral space groups, with initial letter R. | 4 | Stereochemistry |
The wide variety of methods of calculation of electronegativities, which all give results that correlate well with one another, is one indication of the number of chemical properties that might be affected by electronegativity. The most obvious application of electronegativities is in the discussion of bond polarity, for which the concept was introduced by Pauling. In general, the greater the difference in electronegativity between two atoms the more polar the bond that will be formed between them, with the atom having the higher electronegativity being at the negative end of the dipole. Pauling proposed an equation to relate the "ionic character" of a bond to the difference in electronegativity of the two atoms, although this has fallen somewhat into disuse.
Several correlations have been shown between infrared stretching frequencies of certain bonds and the electronegativities of the atoms involved: however, this is not surprising as such stretching frequencies depend in part on bond strength, which enters into the calculation of Pauling electronegativities. More convincing are the correlations between electronegativity and chemical shifts in NMR spectroscopy or isomer shifts in Mössbauer spectroscopy (see figure). Both these measurements depend on the s-electron density at the nucleus, and so are a good indication that the different measures of electronegativity really are describing "the ability of an atom in a molecule to attract electrons to itself". | 3 | Analytical Chemistry |
The difference between enzymatically active and inactive homologues has been noted (and in some cases, understood when comparing catalytically active and inactive proteins residing in recognisable families) for some time at the sequence level, and some pseudoenzymes have also been referred to as prozymes when they were analysed in protozoan parasites. The best studied pseudoenzymes reside amongst various key signalling superfamilies of enzymes, such as the proteases, the protein kinases, protein phosphatases and ubiquitin modifying enzymes. The role of pseudoenzymes as "pseudo scaffolds" has also been recognised and pseudoenzymes are now beginning to be more thoroughly studied in terms of their biology and function, in large part because they are also interesting potential targets (or anti-targets) for drug design in the context of intracellular cellular signalling complexes. | 1 | Biochemistry |
Serum creatinine (a blood measurement) is an important indicator of kidney health, because it is an easily measured byproduct of muscle metabolism that is excreted unchanged by the kidneys. Creatinine itself is produced via a biological system involving creatine, phosphocreatine (also known as creatine phosphate), and adenosine triphosphate (ATP, the body's immediate energy supply).
Creatine is synthesized primarily in the liver from the methylation of glycocyamine (guanidino acetate, synthesized in the kidney from the amino acids arginine and glycine) by S-adenosyl methionine. It is then transported through blood to the other organs, muscle, and brain, where, through phosphorylation, it becomes the high-energy compound phosphocreatine. Creatine conversion to phosphocreatine is catalyzed by creatine kinase; spontaneous formation of creatinine occurs during the reaction.
Creatinine is removed from the blood chiefly by the kidneys, primarily by glomerular filtration, but also by proximal tubular secretion. Little or no tubular reabsorption of creatinine occurs. If the filtration in the kidney is deficient, blood creatinine concentrations rise. Therefore, creatinine concentrations in blood and urine may be used to calculate the creatinine clearance (CrCl), which correlates approximately with the glomerular filtration rate (GFR). Blood creatinine concentrations may also be used alone to calculate the estimated GFR (eGFR).
The GFR is clinically important as a measurement of kidney function. In cases of severe kidney dysfunction, though, the CrCl rate will overestimate the GFR because hypersecretion of creatinine by the proximal tubules will account for a larger fraction of the total creatinine cleared. Ketoacids, cimetidine, and trimethoprim reduce creatinine tubular secretion and, therefore, increase the accuracy of the GFR estimate, in particular in severe kidney dysfunction. (In the absence of secretion, creatinine behaves like inulin).
An alternative estimation of kidney function can be made when interpreting the blood plasma concentration of creatinine along with that of urea. BUN-to-creatinine ratio (the ratio of blood urea nitrogen to creatinine) can indicate other problems besides those intrinsic to the kidney; for example, a urea concentration raised out of proportion to the creatinine may indicate a prerenal problem such as volume depletion.
Counterintuitively, supporting the observation of higher creatinine production in women compared to men, and putting into question the algorithms for GFR that do not distinguish for sex accordingly, women have higher muscle protein synthesis and higher muscle protein turnover across the life span. As HDL supports muscle anabolism, higher muscle protein turnover links increased creatine to the generally higher serum HDL in women as compared to serum HDL in men and the HDL associated benefits like reduced incidence of cardiovascular complications and reduced COVID-19 severity. | 1 | Biochemistry |
The hearths may be individually heated and the number, temperature, rotation rate, and size of each hearth determine the residence time and conditions for the calcining powder in order to achieve the desired final properties. | 8 | Metallurgy |
The combination of an estrogen and flutamide as a form of combined androgen blockade for the treatment of prostate cancer has been researched. | 4 | Stereochemistry |
LAAM undergoes extensive first-pass metabolism to the active demethylated metabolite nor-LAAM, which is further demethylated to a second active metabolite, dinor-LAAM. These metabolites are more potent than the parent drug. | 4 | Stereochemistry |
Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen embrittlement occurs most notably in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminium, and stainless steels are less susceptible to hydrogen embrittlement.
The essential facts about the nature of hydrogen embrittlement have been known since the 19th century.
Hydrogen embrittlement is maximised at around room temperature in steels, and most metals are relatively immune to hydrogen embrittlement at temperatures above 150 °C. Hydrogen embrittlement requires the presence of both atomic ("diffusible") hydrogen and a mechanical stress to induce crack growth, although that stress may be applied or residual. Hydrogen embrittlement increases at lower strain rates. In general, higher-strength steels are more susceptible to hydrogen embrittlement than mid-strength steels.
Metals can be exposed to hydrogen from two types of sources: gaseous hydrogen and hydrogen chemically generated at the metal surface. Gaseous hydrogen is molecular hydrogen and does not cause embrittlement though it can cause hot hydrogen attack (see below). It is the atomic hydrogen from chemical attack which causes embrittlement because the atomic hydrogen dissolves quickly into the metal at room temperature. Gaseous hydrogen is found in pressure vessels and pipelines. Electrochemical sources of hydrogen include acids (as may be encountered during pickling, etching, or cleaning), corrosion (typically due to aqueous corrosion or cathodic protection), and electroplating. Hydrogen can be introduced into the metal during manufacturing by the presence of moisture during welding or while the metal is molten. The most common causes of failure in practice are poorly-controlled electroplating or damp welding rods.
Hydrogen embrittlement as a term can be used to refer specifically to the embrittlement that occurs in steels and similar metals at relatively low hydrogen concentrations, or it can be used to encompass all embrittling effects that hydrogen has on metals. These broader embrittling effects include hydride formation, which occurs in titanium and vanadium but not in steels, and hydrogen-induced blistering, which only occurs at high hydrogen concentrations and does not require the presence of stress. However, hydrogen embrittlement is almost always distinguished from high temperature hydrogen attack (HTHA), which occurs in steels at temperatures above 400 °C and involves the formation of methane pockets. The mechanisms (there are many) by which hydrogen causes embrittlement in steels are not comprehensively understood and continue to be explored and studied. | 7 | Physical Chemistry |
In Complex II (succinate dehydrogenase or succinate-CoQ reductase; ) additional electrons are delivered into the quinone pool (Q) originating from succinate and transferred (via flavin adenine dinucleotide (FAD)) to Q. Complex II consists of four protein subunits: succinate dehydrogenase (SDHA); succinate dehydrogenase [ubiquinone] iron–sulfur subunit mitochondrial (SDHB); succinate dehydrogenase complex subunit C (SDHC); and succinate dehydrogenase complex subunit D (SDHD). Other electron donors (e.g., fatty acids and glycerol 3-phosphate) also direct electrons into Q (via FAD). Complex II is a parallel electron transport pathway to Complex I, but unlike Complex I, no protons are transported to the intermembrane space in this pathway. Therefore, the pathway through Complex II contributes less energy to the overall electron transport chain process. | 1 | Biochemistry |
Treat the number of colors N, which is actually 3, as a large number, and expand in powers of 1/N. It turns out that at high density the higher-order corrections are large, and the expansion gives misleading results. | 7 | Physical Chemistry |
The modern era of CCC began with the development of the planetary centrifuge by Dr. Yoichiro Ito which was first introduced in 1966 as a closed helical tube which was rotated on a "planetary" axis as is turned on a "sun" axis. A flow-through model was subsequently developed and the new technique was called countercurrent chromatography in 1970. The technique was further developed by employing test mixtures of DNP amino acids in a chloroform:glacial acetic acid:0.1 M aqueous hydrochloric acid (2:2:1 v/v) solvent system. Much development was needed to engineer the instrument so that required planetary motion could be sustained while the phases were being pumped through the coil(s). Parameters such as the relative rotation of the two axes (synchronous or non-synchronous), the direction of flow through the coil, and the rotor angles were investigated. | 3 | Analytical Chemistry |
Unlike other fluorescent proteins, PAFPs can be used as selective optical markers. An entirely labeled cell can be followed to assess cell division, migration, and morphology. Very small volumes containing PAFPs can be activated with a laser. In these cases, protein trafficking, diffusion, and turnover can be assessed. | 1 | Biochemistry |
Hydrogel modifications, as with other coatings, are designed to improve the body's response to the implant and thereby improve their consistency and long-term performance. Hydrogel surface modifications achieve this by significantly altering the hydrophilicity of the neural implant surface to one that is less favorable for protein adsorption. In general, protein adsorption increases with increasing hydrophobicity as a result of the decreased Gibbs energy from the energetically favorable reaction (as seen in the equation below)
Water molecules are bonded to both the proteins and to the surface of the implant; as the protein binds to the implant, water molecules are liberated, resulting in an entropy gain, decreasing the overall energy in the system. For hydrophilic surfaces, this reaction is energetically unfavorable due to the strong attachment of water to the surface, hence the decreased protein adsorption. The decrease in protein adsorption is beneficial for the implant as it limits the body's ability to both recognize the implant as a foreign material as well as attach potentially deleterious cells such as astrocytes and fibroblasts that can create fibrous glial scars around the implant and hinder stimulating and recording processes. Increasing the hydrophilicity can also enhance the electrical signal transfer by creating a stable ionic conductance layer. However, increasing the water content of the hydrogel too much can cause swelling and eventually mechanical instability. An appropriate water balance must be created to optimize the efficacy of the implant coating. | 7 | Physical Chemistry |
The Human-transcriptome DataBase for Alternative Splicing (H-DBAS) is a database of alternatively spliced human transcripts based on H-Invitational. | 1 | Biochemistry |
ATSDR maintains registries of people who were exposed to certain toxic substances or have certain diseases. Participation in these registries is voluntary, and individual data and personal information is kept private. The information collected is used by epidemiologists and other researchers to examine long-term health outcomes or risk factors for illness. It can also help doctors diagnose those health conditions in other individuals and treat them earlier. The agency also uses registries to contact registered individuals with important health information. | 1 | Biochemistry |
The FSHR become desensitized when exposed to FSH for some time. A key reaction of this downregulation is the phosphorylation of the intracellular (or cytoplasmic) receptor domain by protein kinases. This process uncouples Gs protein from the FSHR. Another way to desensitize is to uncouple the regulatory and catalytic units of the cAMP system. | 1 | Biochemistry |
In genetics, a silencer is a DNA sequence capable of binding transcription regulation factors, called repressors. DNA contains genes and provides the template to produce messenger RNA (mRNA). That mRNA is then translated into proteins. When a repressor protein binds to the silencer region of DNA, RNA polymerase is prevented from transcribing the DNA sequence into RNA. With transcription blocked, the translation of RNA into proteins is impossible. Thus, silencers prevent genes from being expressed as proteins.
RNA polymerase, a DNA-dependent enzyme, transcribes the DNA sequences, called nucleotides, in the 3 to 5 direction while the complementary RNA is synthesized in the 5 to 3 direction. RNA is similar to DNA, except that RNA contains uracil, instead of thymine, which forms a base pair with adenine. An important region for the activity of gene repression and expression found in RNA is the 3 untranslated region. This is a region on the 3 terminus of RNA that will not be translated to protein but includes many regulatory regions.
Not much is yet known about silencers but scientists continue to study in hopes to classify more types, locations in the genome, and diseases associated with silencers. | 1 | Biochemistry |
Vancomycin is recommended to be administered in a dilute solution slowly, over at least 60 min (maximum rate of 10 mg/min for doses >500 mg) due to the high incidence of pain and thrombophlebitis and to avoid an infusion reaction known as vancomycin flushing reaction. This phenomenon has been often clinically referred to as "red man syndrome". The reaction usually appears within 4 to 10 min after the commencement or soon after the completion of an infusion and is characterized by flushing and/or an erythematous rash that affects the face, neck, and upper torso, attributed to the release of histamine from mast cells. This reaction is caused by the interaction of vancomycin with MRGPRX2, a GPCR mediating IgE-independent mast cell degranulation. Less frequently, hypotension and angioedema may also occur. Symptoms may be treated or prevented with antihistamines, including diphenhydramine, and are less likely to occur with slow infusion. | 0 | Organic Chemistry |
The Westinghouse Lamp Plant was constructed on Arlington Avenue in 1920 near the Watsessing Station of the rail line in the Watsessing neighborhood that connected Montclair, Glen Ridge and Bloomfield. The population in the area had grown since the time that the Township of Bloomfield was incorporated as a township from portions of Newark Township by an act of the New Jersey Legislature on March 23, 1812 until World War II. The population boom was contributed by the manufacturing jobs at the Westinghouse Lamp Plant along with other manufacturing plants such as General Electric, Lehn and Fink and Schering during the war time.
The Westinghouse Lamp Plant was devoted to lamp manufacturing in its early years. The plant had a research department to find a new suitable material for a light bulb filament. After World War I, the department led by Harvey C. Rentschler, and his deputy, John W. Marden, started looking into uranium to discover whether there was any similarity with tungsten to be used as a filament. The problem at the time was to make uranium into a metal form so that researchers could work with it. Westinghouse failed to establish uranium as a viable filament material, however, the research department continued to experiment with it until they found an electrolysis method to use a fused uranium salt to produce a metal. The metal was pure enough for nuclear research in many university laboratories during the 1930s. By 1941, Westinghouse Lamp Plant had the only practical process for producing pure uranium metal. | 8 | Metallurgy |
Peatlands hold approximately 30% of the carbon in our ecosystem. When they are drained for agricultural land and urbanization, because peatlands are so vast, large quantities of carbon decompose and emit into the atmosphere. The loss of one peatland could potentially produce more carbon than 175–500 years of methane emissions.
Peat bogs act as a sink for carbon because they accumulate partially decayed biomass that would otherwise continue to decay completely. There is a variance on how much the peatlands act as a carbon sink or carbon source that can be linked to varying climates in different areas of the world and different times of the year. By creating new bogs, or enhancing existing ones, the amount of carbon that is sequestered by bogs would increase. | 5 | Photochemistry |
Hydrophobicity scales are values that define the relative hydrophobicity or hydrophilicity of amino acid residues. The more positive the value, the more hydrophobic are the amino acids located in that region of the protein. These scales are commonly used to predict the transmembrane alpha-helices of membrane proteins. When consecutively measuring amino acids of a protein, changes in value indicate attraction of specific protein regions towards the hydrophobic region inside lipid bilayer.
The hydrophobic or hydrophilic character of a compound or amino acid is its hydropathic character, hydropathicity, or hydropathy. | 6 | Supramolecular Chemistry |
Immobilized metal ion affinity chromatography (IMAC) is based on the specific coordinate covalent bond of amino acids, particularly histidine, to metals. This technique works by allowing proteins with an affinity for metal ions to be retained in a column containing immobilized metal ions, such as cobalt, nickel, or copper for the purification of histidine-containing proteins or peptides, iron, zinc or gallium for the purification of phosphorylated proteins or peptides. Many naturally occurring proteins do not have an affinity for metal ions, therefore recombinant DNA technology can be used to introduce such a protein tag into the relevant gene. Methods used to elute the protein of interest include changing the pH, or adding a competitive molecule, such as imidazole. | 3 | Analytical Chemistry |
In 1991, Ye joined the National Institute for Materials Science. She was made Director of Photocatalytic Materials Center in 2006 and Director of Environmental Remediation Materials in 2011.
Ye has dedicated her career to the realization of artificial photosynthesis. She is particularly interested in the development of materials that harvest the most sunlight. Ye has studied the reaction mechanisms, and, in an effort to overcome harsh reaction kinetics, has worked on the careful construction of interfaces. In particular, Ye has developed nano-structured surfaces that enhance reactivities, and, using localized surface plasmon resonance, broaden the spectral range of her photocatalytic materials.
Ye was elected Fellow of the Royal Society of Chemistry in 2016. In 2022, she was included by the American Chemical Society Energy Letters in their list of the world's leading women scientists in energy research. | 5 | Photochemistry |
Weder’s early research activities in the 1990s focused on polymers with special optical properties. This involved the development of nonlinear optical polymers and investigations of the structure-property relationships of photoluminescent poly(p-phenylene ethynylene)s. He demonstrated the usefulness of these semiconducting polymers as the active layer in polymer-based light-emitting diodes. His group also exploited the possibility to orient such rod-like molecules to create fluorescent materials that display linearly polarized absorption and emission. Such materials formed the basis of security features that Weder’s group developed, which were used as an anti-counterfeiting element in security paper. His team also discovered a light-polarizing energy transfer effect that can be used to produce highly efficient fluorescent polarizers. Such elements are useful in display and other applications.
Weder’s research focus turned to stimuli-responsive polymers shortly after he moved to CWRU in 2001. In 2002, Weder’s research lab developed a novel method to create polymeric materials that change their fluorescence color upon deformation. Recognizing the potential for practical applications this effect had, Weder established a research program to develop polymers that translate mechanical forces into optical signals, which is still active today, and shortly thereafter, mechanochromic polymers began to attract widespread interest. Most of the mechanochrochromic materials reported by Weder’s group in the following two decades operate on the basis of the same general transduction principle, which involves changing the interactions among optically active motifs in response to mechanical deformation. Recent discoveries include the development of new mechanically responsive motifs or “mechanophores” based on rotaxanes and loop-forming dye pairs.
Controlling the interactions between molecular or nanoscale building blocks through an external stimulus has become one of Weder’s main design tools for the creation of stimuli-responsive polymers. In 2008, in collaboration with his colleague Stuart Rowan, Weder introduced stimuli-responsive mechanically adaptive polymer nanocomposites whose architecture and function was inspired by sea cucumbers. The mechanical properties of these materials, which were made by incorporating nanocellulose crystals as a reinforcing filler into polymer matrices, depend on the interactions among the cellulose nanocrystals (CNCs), and can be regulated by an external stimulus. The approach was initially used to create mechanically morphing implant materials, which soften upon exposure to physiological conditions. This work led to sustained research efforts in Weder’s group on bio-inspired mechanically morphing polymers, the development of protocols for the processing of CNC/polymer nanocomposites, and the development of new cellulose-based nanocomposites. Adaptive polymers that show such mechanical morphing upon exposure to physiological conditions were reported to increase the functionality of cortical implants.
The possibility to heal defects in polymeric materials can increase the reliability and durability of polymer products. In 2011, also in collaboration with Rowan, Weder demonstrated that the UV-light induced temporary disassembly of metallosupramolecular polymers can be used to heal defects in these materials. Expanding on this concept, Weder’s team introduced light healable nanocomposites, and modified the structure to include different binding motifs and architectures, for example glassy hydrogen-bonded supramolecular polymer networks. His group also used this approach to develop adhesives with the capability to bond or debond on demand. Weder’s group sought to push the mechanical properties of supramolecular polymers towards those of conventional thermoplastics. In 2019, his team demonstrated that it is possible to toughen stiff but brittle glassy supramolecular polymer networks by forming blends with a rubbery component. More recent versions of such materials were shown to be healable and to display property combinations that are comparable to some conventional plastics. | 7 | Physical Chemistry |
Benefactor and corporate members can be companies, universities, national, regional or international organizations, laboratories, associations or any other structure active in or connected to the refrigeration industry or IIR activities. | 7 | Physical Chemistry |
In thermodynamics so-called "specific" quantities are quantities per unit mass (kg) and are denoted by lower-case characters. So h, u, and v are the specific enthalpy, specific internal energy, and specific volume (volume per unit mass, or reciprocal density), respectively. In a Joule–Thomson process the specific enthalpy h remains constant. To prove this, the first step is to compute the net work done when a mass m of the gas moves through the plug. This amount of gas has a volume of V = m v in the region at pressure P (region 1) and a volume V = m v when in the region at pressure P (region 2). Then in region 1, the "flow work" done on the amount of gas by the rest of the gas is: W = m Pv. In region 2, the work done by the amount of gas on the rest of the gas is: W = m Pv. So, the total work done on the mass m of gas is
The change in internal energy minus the total work done on the amount of gas is, by the first law of thermodynamics, the total heat supplied to the amount of gas.
In the Joule–Thomson process, the gas is insulated, so no heat is absorbed. This means that
where u and u denote the specific internal energies of the gas in regions 1 and 2, respectively. Using the definition of the specific enthalpy h = u + Pv, the above equation implies that
where h and h denote the specific enthalpies of the amount of gas in regions 1 and 2, respectively. | 7 | Physical Chemistry |
The Trost ligand is a diphosphine used in the palladium-catalyzed Trost asymmetric allylic alkylation. Other C-symmetric ligands derived from trans-1,2-diaminocyclohexane (DACH) have been developed, such as the (R,R)-DACH-naphthyl ligand derived from 2-diphenylphosphino-1-naphthalenecarboxylic acid. Related bidentate phosphine-containing ligands derived from other chiral diamines and 2-diphenylphosphinobenzoic acid have also been developed for applications in asymmetric synthesis. | 0 | Organic Chemistry |
Among the diverse range of defense strategies plants utilize against pathogens, Ca signaling is very common. Free Ca levels in the cytoplasm increases in response to a pathogenic infection. Ca signatures of this nature usually activate the plant defense system by inducing defense-related genes and the hypersensitive cell death. CaMs, CMLs and CaM-binding proteins are some of the recently identified elements of the plant defense signaling pathways. Several CML genes in tobacco, bean and tomato are responsive to pathogens. CML43 is a CaM-related protein that, as isolated from APR134 gene in the disease-resistant leaves of Arabidopsis for gene expression analysis, is rapidly induced when the leaves are inoculated with Pseudomonas syringae. These genes are also found in tomatoes (Solanum lycopersicum). The CML43 from the APR134 also binds to Ca ions in vitro which shows that CML43 and APR134 are, hence, involved in the Ca-dependent signaling during the plant immune response to bacterial pathogens. The CML9 expression in Arabidopsis thaliana is rapidly induced by phytopathogenic bacteria, flagellin and salicylic acid. Expression of soybean SCaM4 and SCaM5 in transgenic tobacco and Arabidopsis causes an activation of genes related to pathogen resistance and also results in enhanced resistance to a wide spectrum of pathogen infection. The same is not true for soybean SCaM1 and SCaM2 that are highly conserved CaM isoforms. The AtBAG6 protein is a CaM-binding protein that binds to CaM only in the absence of Ca and not in the presence of it. AtBAG6 is responsible for the hypersensitive response of programmed cell death in order to prevent the spread of pathogen infection or to restrict pathogen growth. Mutations in the CaM binding proteins can lead to severe effects on the defense response of the plants towards pathogen infections. Cyclic nucleotide-gated channels (CNGCs) are functional protein channels in the plasma membrane that have overlapping CaM binding sites transport divalent cations such as Ca. However, the exact role of the positioning of the CNGCs in this pathway for plant defense is still unclear. | 1 | Biochemistry |
The dissociation of salts by solvation in a solution, such as water, means the separation of the anions and cations. The salt can be recovered by evaporation of the solvent.
An electrolyte refers to a substance that contains free ions and can be used as an electrically conductive medium. Most of the solute does not dissociate in a weak electrolyte, whereas in a strong electrolyte a higher ratio of solute dissociates to form free ions.
A weak electrolyte is a substance whose solute exists in solution mostly in the form of molecules (which are said to be "undissociated"), with only a small fraction in the form of ions. Simply because a substance does not readily dissolve does not make it a weak electrolyte. Acetic acid () and ammonium () are good examples. Acetic acid is extremely soluble in water, but most of the compound dissolves into molecules, rendering it a weak electrolyte. Weak bases and weak acids are generally weak electrolytes. In an aqueous solution there will be some and some and .
A strong electrolyte is a solute that exists in solution completely or nearly completely as ions. Again, the strength of an electrolyte is defined as the percentage of solute that is ions, rather than molecules. The higher the percentage, the stronger the electrolyte. Thus, even if a substance is not very soluble, but does dissociate completely into ions, the substance is defined as a strong electrolyte. Similar logic applies to a weak electrolyte. Strong acids and bases are good examples, such as HCl and . These will all exist as ions in an aqueous medium. | 7 | Physical Chemistry |
A ubiquitous signaling motif that exhibits ultrasensitivity is the MAPK (mitogen-activated protein kinase) cascade, which can take a graded input signal and produce a switch-like output, such as gene transcription or cell cycle progression. In this common motif, MAPK is activated by an earlier kinase in the cascade, called MAPK kinase, or MAPKK. Similarly, MAPKK is activated by MAPKK kinase, or MAPKKK. These kinases are sequentially phosphorylated when MAPKKK is activated, usually via a signal received by a membrane-bound receptor protein. MAPKKK activates MAPKK, and MAPKK activates MAPK. Ultrasensitivity arises in this system due to several features:
# MAPK and MAPKK both require two separate phosphorylation events to be activated.
# The reversal of MAPK phosphorylation by specific phosphatases requires an increasing concentration of activation signals from each prior kinase to achieve an output of the same magnitude.
# The MAPKK is at a concentration above the K for its specific phosphatase and MAPK is at a concentration above the K for MAPKK.
Besides the MAPK cascade, ultrasensitivity has also been reported in muscle glycolysis, in the phosphorylation of isocitrate dehydrogenase and in the activation of the calmodulin-dependent protein kinase II (CAMKII).
An ultrasensitive switch has been engineered by combining a simple linear signaling protein (N-WASP) with one to five SH3 interaction modules that have autoinhibitory and cooperative properties. Addition of a single SH3 module created a switch that was activated in a linear fashion by exogenous SH3-binding peptide. Increasing number of domains increased ultrasensitivity. A construct with three SH3 modules was activated with an apparent Hill coefficient of 2.7 and a construct with five SH3 module was activated with an apparent Hill coefficient of 3.9. | 1 | Biochemistry |
FLAG-tag, or FLAG octapeptide, or FLAG epitope, is a peptide protein tag that can be added to a protein using recombinant DNA technology, having the sequence DYKDDDDK (where D=aspartic acid, Y=tyrosine, and K=lysine). It is one of the most specific tags and it is an artificial antigen to which specific, high affinity monoclonal antibodies have been developed and hence can be used for protein purification by affinity chromatography and also can be used for locating proteins within living cells. FLAG-tag has been used to separate recombinant, overexpressed protein from wild-type protein expressed by the host organism. FLAG-tag can also be used in the isolation of protein complexes with multiple subunits, because FLAG-tag's mild purification procedure tends not to disrupt such complexes. FLAG-tag-based purification has been used to obtain proteins of sufficient purity and quality to carry out 3D structure determination by x-ray crystallography.
A FLAG-tag can be used in many different assays that require recognition by an antibody. If there is no antibody against a given protein, adding a FLAG-tag to a protein allows the protein to be studied with an antibody against the FLAG-tag sequence. Examples are cellular localization studies by immunofluorescence, immunoprecipitation or detection by SDS PAGE protein electrophoresis and Western blotting.
The peptide sequence of the FLAG-tag from the N-terminus to the C-terminus is: DYKDDDDK (1012 Da). Additionally, FLAG-tags may be used in tandem, commonly the 3xFLAG peptide: DYKDHD-G-DYKDHD-I-DYKDDDDK (with the final tag encoding an enterokinase cleavage site). FLAG-tag can be fused to the C-terminus or the N-terminus of a protein, or inserted within a protein. Some commercially available antibodies (e.g., M1/4E11) recognize the epitope only when FLAG-tag is present at the N-terminus. However, other available antibodies (e.g., M2) are position-insensitive. The tyrosine residue in the FLAG-tag can be sulfated when expressed on certain secreted proteins, which can affect antibody recognition of the FLAG epitope. The FLAG-tag can be used in conjunction with other affinity tags, for example a polyhistidine tag (His-tag), HA-tag or myc-tag. | 1 | Biochemistry |
The lysocline is the depth in the ocean dependent upon the carbonate compensation depth (CCD), usually around 5 km, below which the rate of dissolution of calcite increases dramatically because of a pressure effect. While the lysocline is the upper bound of this transition zone of calcite saturation, the CCD is the lower bound of this zone.
CaCO content in sediment varies with different depths of the ocean, spanned by levels of separation known as the transition zone. In the mid-depth area of the ocean, sediments are rich in CaCO, content values reaching 85–95%. This area is then spanned hundreds of meters by the transition zone, ending in the abyssal depths with 0% concentration. The lysocline is the upper bound of the transition zone, where amounts of CaCO content begins to noticeably drop from the mid-depth 85–95% sediment. The CaCO content drops to 0% concentration at the lower bound, known as the calcite compensation depth.
Shallow marine waters are generally supersaturated in calcite, CaCO, because as marine organisms (which often have shells made of calcite or its polymorph, aragonite) die, they tend to fall downwards without dissolving. As depth and pressure increases within the water column, calcite solubility increases, causing supersaturated water above the saturation depth, allowing for preservation and burial of CaCO on the seafloor. However, this creates undersaturated seawater below the saturation depth, preventing CaCO burial on the sea floor as the shells start to dissolve.
The equation Ω = [Ca] X [CO]/K' expresses the CaCO saturation state of seawater. The calcite saturation horizon is where Ω =1; dissolution proceeds slowly below this depth. The lysocline is the depth that this dissolution impacts is again notable, also known as the inflection point with sedimentary CaCO versus various water depths. | 9 | Geochemistry |
Anti-centromere antibodies are associated with limited cutaneous systemic sclerosis, also known as CREST syndrome, primary biliary cirrhosis and proximal scleroderma. There are six known antigens, which are all associated with the centromere; CENP-A to CENP-F. CENP-A is a 17kDa histone H3-like protein. CENP-B is an 80kDa DNA binding protein involved in the folding of heterochromatin. CENP-C is a 140kDa protein involved in kinetochore assembly. CENP-D is a 50kDa protein of unknown function, but may be homologous to another protein involved in chromatin condensation, RCC1. CENP-E is a 312kDa protein from the kinesin motor protein family. CENP-F is a 367kDa protein from the nuclear matrix that associates with the kinetochore in late G2 phase during mitosis. CENP-A, B and C antibodies are most commonly found (16–42% of systemic sclerosis) and are associated with Raynaud's phenomenon, telangiectasias, lung involvement and early onset in systemic sclerosis. | 1 | Biochemistry |
Salbutamol was discovered in 1966, by a team led by David Jack at the Allen and Hanburys laboratory (a subsidiary of Glaxo) in Ware, Hertfordshire, England, and was launched as Ventolin in 1969.
The 1972 Munich Olympics were the first Olympics where anti-doping measures were deployed, and at that time β agonists were considered to be stimulants with high risk of abuse for doping. Inhaled salbutamol was banned from those games, but by 1986 was permitted (although oral β agonists were not). After a steep rise in the number of athletes taking β agonists for asthma in the 1990s, Olympic athletes were required to provide proof that they had asthma in order to be allowed to use inhaled β agonists.
In February 2020, the U.S. Food and Drug Administration (FDA) approved the first generic of an albuterol sulfate inhalation aerosol for the treatment or prevention of bronchospasm in people four years of age and older with reversible obstructive airway disease and the prevention of exercise-induced bronchospasm in people four years of age and older. The FDA granted approval of the generic albuterol sulfate inhalation aerosol to Perrigo Pharmaceutical.
In April 2020, the FDA approved the first generic of Proventil HFA (albuterol sulfate) metered dose inhaler, 90 μg per inhalation, for the treatment or prevention of bronchospasm in patients four years of age and older who have reversible obstructive airway disease, as well as the prevention of exercise-induced bronchospasm in this age group. The FDA granted approval of this generic albuterol sulfate inhalation aerosol to Cipla Limited. | 4 | Stereochemistry |
Benzyl chloroformate is commonly used in organic synthesis for the introduction of the benzyloxycarbonyl (formerly called carboxybenzyl) protecting group for amines. The protecting group is abbreviated Cbz or Z (in honor of discoverer Zervas), hence the alternative shorthand designation for benzyl chloroformate as Cbz-Cl or Z-Cl.
Benzyloxycarbonyl is a key protecting group for amines, suppressing the nucleophilic and basic properties of the N lone pair. This "reactivity masking" property, along with the ability to prevent racemization of Z-protected amines, made the Z group the basis of the Begmann-Zervas synthesis of oligopeptides (1932) where the following general reaction is performed to protect the N-terminus of a serially growing oligopeptide chain:
This reaction was hailed as a "revolution" and essentially started the distinct field of synthetic peptide chemistry. It remained unsurpassed in utility for peptide synthesis until the early 1950s when mixed anhydride and active ester methodologies were developed.
Although the reaction is no longer commonly used for peptides, it is nonetheless very widespread for amine protection in other applications within organic synthesis and total synthesis. Common procedures to achieve protection starting from benzyl chloroformate include:
* Benzyl chloroformate and a base, such as sodium carbonate in water at 0 °C
* Benzyl chloroformate and magnesium oxide in ethyl acetate at 70 °C to reflux
* Benzyl chloroformate, DIPEA, acetonitrile and scandium trifluoromethanesulfonate (Sc(OTf))
Alternatively, the Cbz group can be generated by the reaction of an isocyanate with benzyl alcohol (as in the Curtius rearrangement). | 0 | Organic Chemistry |
An historical example, the Pratt & Whitney J58, illustrates the significance of using corrected values.
Rotating stall occurs at low corrected speeds so occurs during starting and also above idle. It may be relieved by opening a bleed valve to increase airflow. At very high flight speeds the compressor will return to this low corrected speed area so the same operating point occurs at low rotational speed on the ground and maximum rotational speed at mach 3 at high altitude. The stalling, low efficiency, blade vibration and failure that plagued low corrected speeds on the ground has returned at 100% rotor rpm at mach 3. The same operating point on the map has the same axial and peripheral mach numbers, same velocity triangles, same efficiency despite the actual rotor speed and compressor inlet temperature being 4750 RPM/60degF on the ground and 7,000RPM/over 600 degF at Mach 3. The same corrected operating point required the same solution to prevent stalling and increase efficiency which was to bleed air from the 4th compressor stage. | 7 | Physical Chemistry |
SEC can be used as a measure of both the size and the polydispersity of a synthesized polymer, that is, the ability to find the distribution of the sizes of polymer molecules. If standards of a known size are run previously, then a calibration curve can be created to determine the sizes of polymer molecules of interest in the solvent chosen for analysis (often THF). In alternative fashion, techniques such as light scattering and/or viscometry can be used online with SEC to yield absolute molecular weights that do not rely on calibration with standards of known molecular weight. Due to the difference in size of two polymers with identical molecular weights, the absolute determination methods are, in general, more desirable. A typical SEC system can quickly (in about half an hour) give polymer chemists information on the size and polydispersity of the sample. The preparative SEC can be used for polymer fractionation on an analytical scale. | 1 | Biochemistry |
Adsorption is the first step in the viral life cycle. The next steps are penetration, uncoating, synthesis (transcription if needed, and translation), and release. The virus replication cycle, in this respect, is similar for all types of viruses. Factors such as transcription may or may not be needed if the virus is able to integrate its genomic information in the cells nucleus, or if the virus can replicate itself directly within the cells cytoplasm. | 7 | Physical Chemistry |
YSZ has a number of applications:
* For its hardness and chemical inertness (e.g., tooth crowns).
* As a refractory (e.g., in jet engines).
* As a thermal barrier coating in gas turbines.
* As an electroceramic due to its ion-conducting properties (e.g., to determine oxygen content in exhaust gases, to measure pH in high-temperature water, in fuel cells).
* Used in the production of a solid oxide fuel cell (SOFC). YSZ is used as the solid electrolyte, which enables oxygen ion conduction while blocking electronic conduction. In order to achieve sufficient ion conduction, an SOFC with a YSZ electrolyte must be operated at high temperatures (800–1000 °C). While it is advantageous that YSZ retains mechanical robustness at those temperatures, the high temperature necessary is often a disadvantage of SOFCs. The high density of YSZ is also necessary in order to physically separate the gaseous fuel from oxygen, or else the electrochemical system would produce no electrical power.
* For its hardness and optical properties in monocrystal form (see "cubic zirconia"), it is used as jewelry.
* As a material for non-metallic knife blades, produced by Boker and Kyocera companies.
* In water-based pastes for do-it-yourself ceramics and cements. These contain microscopic YSZ milled fibers or sub-micrometer particles, often with potassium silicate and zirconium acetate binders (at mildly acidic pH). The cementation occurs on removal of water. The resulting ceramic material is suitable for very high-temperature applications.
* YSZ doped with rare-earth materials can act as a thermographic phosphor and a luminescent material.
* Historically used for glowing rods in Nernst lamps.
* As a high-precision alignment sleeve for optical fiber connector ferrules. | 7 | Physical Chemistry |
Sevoflurane was discovered by Ross Terrell and independently by Bernard M Regan. A detailed report of its development and properties appeared in 1975 in a paper authored by Richard Wallin, Bernard Regan, Martha Napoli and Ivan Stern. It was introduced into clinical practice initially in Japan in 1990 by Maruishi Pharmaceutical Co., Ltd. Osaka, Japan. The rights for sevoflurane worldwide were held by AbbVie. It is now available as a generic drug. | 2 | Environmental Chemistry |
Equilibrium constant of the reaction is also not independent from the other competing equilibria. Competition would include buffer interactions and other pH-dependent reactions depending on the experimental conditions. The competition from species other than the species of interest is included in the competition factor, Q in the following equation: represents species such a buffer or protons, represents their equilibrium constant, when,</blockquote> | 7 | Physical Chemistry |
Heap leaching is an industrial mining process used to extract precious metals, copper, uranium, and other compounds from ore using a series of chemical reactions that absorb specific minerals and re-separate them after their division from other earth materials. Similar to in situ mining, heap leach mining differs in that it places ore on a liner, then adds the chemicals via drip systems to the ore, whereas in situ mining lacks these liners and pulls pregnant solution up to obtain the minerals. Heap leaching is widely used in modern large-scale mining operations as it produces the desired concentrates at a lower cost compared to conventional processing methods such as flotation, agitation, and vat leaching.
Additionally, dump leaching is an essential part of most copper mining operations and determines the quality grade of the produced material along with other factors
Due to the profitability that the dump leaching has on the mining process, i.e. it can contribute substantially to the economic viability of the mining process, it is advantageous to include the results of the leaching operation in the economic overall project evaluation.
The process has ancient origins; one of the classical methods for the manufacture of copperas (iron sulfate) was to heap up iron pyrite and collect the leachate from the heap, which was then boiled with iron to produce iron(II) sulfate. | 8 | Metallurgy |
To a large extent, portions of nucleotide repeats are quite often observed as part of rare DNA combinations. The three main repeats which are largely found in particular DNA constructs include the closely precise homopurine-homopyrimidine inverted repeats, which is otherwise referred to as H palindromes, a common occurrence in triple helical H conformations that may comprise either the TAT or CGC nucleotide triads. The others could be described as long inverted repeats having the tendency to produce hairpins and cruciform, and finally direct tandem repeats, which commonly exist in structures described as slipped-loop, cruciform and left-handed Z-DNA. | 1 | Biochemistry |
A medium that experiences no transmission () is opaque, in which case absorptivity and reflectivity sum to unity: | 7 | Physical Chemistry |
PIR was established in 1984 by the National Biomedical Research Foundation as a resource to assist researchers and customers in the identification and interpretation of protein sequence information. Prior to that, the foundation compiled the first comprehensive collection of macromolecular sequences in the Atlas of Protein Sequence and Structure, published from 1964 to 1974 under the editorship of Margaret Dayhoff. Dayhoff and her research group pioneered in the development of computer methods for the comparison of protein sequences, for the detection of distantly related sequences and duplications within sequences, and for the inference of evolutionary histories from alignments of protein sequences.
Winona Barker and Robert Ledley assumed leadership of the project after the death of Dayhoff in 1983. In 1999, Cathy H. Wu joined the National Biomedical Research Foundation, and later on Georgetown University Medical Center, to head the bioinformatics efforts of PIR, and has served first as Principal Investigator and, since 2001, as Director.
For four decades, PIR has provided many protein databases and analysis tools freely accessible to the scientific community, including the Protein Sequence Database, the first international database (see PIR-International), which grew out of Atlas of Protein Sequences and Structure.
In 2002, PIR – along with its international partners, the European Bioinformatics Institute and the Swiss Institute of Bioinformatics – were awarded a grant from NIH to create UniProt, a single worldwide database of protein sequence and function, by unifying the Protein Information Resource-Protein Sequence Database, Swiss-Prot, and TrEMBL databases. , PIR offers a wide variety of resources mainly oriented to assist the propagation and standardization of protein annotation: PIRSF, iProClass, and iProLINK.
The Protein Ontology is another popular database released by the Protein Information Resource. | 1 | Biochemistry |
Other models exist to model more complex binary systems. The above theories operate on the assumption that the segregated atoms are non-interacting. If, in a binary system, adjacent adsorbate atoms are allowed an interaction energy , such that they can attract (when is negative) or repel (when is positive) each other, the solid-state analogue of the Fowler adsorption theory is developed as
When is zero, this theory reduces to that of Langmuir and McLean. However, as becomes more negative, the segregation shows progressively sharper rises as the temperature falls until eventually the rise in segregation is discontinuous at a certain temperature, as shown in the following figure.
Guttman, in 1975, extended the Fowler theory to allow for interactions between two co-segregating species in multicomponent systems. This modification is vital to explaining the segregation behavior that results in the intergranular failures of engineering materials. More complex theories are detailed in the work by Guttmann and McLean and Guttmann. | 7 | Physical Chemistry |
Glass solder is used to join glasses to other glasses, ceramics, metals, semiconductors, mica, and other materials, in a process called glass frit bonding. The glass solder has to flow and wet the soldered surfaces well below the temperature where deformation or degradation of either of the joined materials or nearby structures (e.g., metallization layers on chips or ceramic substrates) occurs. The usual temperature of achieving flowing and wetting is between . | 8 | Metallurgy |
The al-Hijarah missile warhead was probably filled with chemical weapons and biological weapons possessed by Iraq at that time like anthrax, botulinum toxin, aflatoxin, sarin, cyclosarin and VX nerve agent. The al-Hijarah missile being a version of the al Hussein also suffered from flight instability and improper guidance. Iraq itself at that time was almost fully indigenous when it came to ballistic missile components and only lacked the ability to locally manufacture Gyroscopes. | 1 | Biochemistry |
Polytetrafluoroethylene (PTFE) filter has wide operating temperature (−120 °C ~ 260 °C) with high air permeability. The resistance to high temperature makes PTFE filter paper suitable for use in autoclaves. It is often used to filter hot oils, strong solvents and collecting airborne particulates. | 3 | Analytical Chemistry |
The General Conference of the IIR defines the general policy of the IIR and convenes once every four years during its international congress. It includes representatives appointed by member countries.
The General Conference elects the president and vice-presidents of the executive committee. | 7 | Physical Chemistry |
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