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The fitting method used in Rietveld refinement is the non-linear least squares approach. A detailed derivation of non-linear least squares fitting will not be given here. Further detail can be found in Chapter 6 of Pecharsky and Zavalij's text 12 . There are a few things to note however. First, non-linear least squares fitting has an iterative nature for which convergence may be difficult to achieve if the initial approximation is too far from correct, or when the minimized function is poorly defined. The latter occurs when correlated parameters are being refined at the same time, which may result in divergence and instability of the minimization. This iterative nature also means that convergence to a solution does not occur immediately for the method is not exact. Each iteration depends on the results of the last which dictate the new set of parameters used for refinement. Thus, multiple refinement iterations are required to eventually converge to a possible solution. | 3 | Analytical Chemistry |
Some organizations publish standards for rating the lightfastness of pigments and materials. Testing is typically done by controlled exposure to sunlight, or to artificial light generated by a xenon arc lamp. Watercolors, inks, pastels, and colored pencils are particularly susceptible to fading over time, so choosing lightfast pigments is especially important in these media.
The most well known scales measuring the lightfastness are the Blue Wool Scale, Grey scale and the scale defined by ASTM (American Standard Test Measure). On the Blue Wool Scale the lightfastness is rated between 1–8. 1 being very poor and 8 being excellent lightfastness. In grey scale the lightfastness is rated between 1–5. 1 being very poor and 5 being excellent lightfastness. On ASTM scale the lightfastness is rated between I-V. I is excellent lightfastness and it corresponds to ratings 7–8 on Blue Wool Scale. V is very poor lightfastness and it corresponds to Blue Wool scale rating 1.
The actual lightfastness is dependent on the strength of the radiation of the sun, so lightfastness is relative to geographic location, season, and exposure direction. The following table is listing suggestive relations of the lightfastness ratings on different measure scales and the relation relative to time in direct sunlight and normal conditions of display: away from a window, under indirect sunlight and properly framed behind a UV protective glass. | 5 | Photochemistry |
Flutamide was first synthesized in 1967 by Neri and colleagues at Schering Plough Corporation. It was originally synthesized as a bacteriostatic agent, but was subsequently, and serendipitously found to possess antiandrogen activity. The code name of flutamide during development was SCH-13521. Clinical research of the medication began in 1971, and it was first marketed in 1983, specifically in Chile under the brand name Drogenil and in West Germany under the brand name Flugerel. Flutamide was not introduced in the United States until 1989; it was specifically approved by the U.S. Food and Drug Administration for the treatment of metastatic prostate cancer in combination with a gonadotropin-releasing hormone (GnRH) analogue. The medication was first studied for the treatment of hirsutism in women in 1989. It was the first "pure antiandrogen" to be studied in the treatment of hirsutism. Flutamide was the first NSAA to be introduced, and was followed by nilutamide in 1989 and then bicalutamide in 1995. | 4 | Stereochemistry |
The Bennett acceptance ratio method is implemented in modern molecular dynamics systems, such as Gromacs.
Python-based code for MBAR and BAR is available for download at [https://github.com/choderalab/pymbar]. | 7 | Physical Chemistry |
An example of this can be found in the Ponderosa Pine tree (Pinus ponderosa), which produces a terpene called myrcene when it is damaged by the Western pine beetle. Instead of deterring the insect, it acts synergistically with aggregation pheromones which in turn act to lure more beetles to the tree.
Specialist predatory beetles find bark beetles (their prey) using the pheromones the bark beetles produce. In this case the chemical substance produced is both a pheromone (communication between bark beetles) and a kairomone (eavesdropping). This was discovered accidentally when the predatory beetles and other enemies were attracted to insect traps baited with bark beetle pheromones.
Pheromones of different kinds may be exploited as kairomones by receivers. The German wasp, Vespula germanica, is attracted to a pheromone produced by male Mediterranean fruit flies (Ceratitis capitata) when the males gather for a mating display, causing the death of some. In contrast, it is the alarm pheromone (used to communicate the presence of a threat) of an ant (Iridomyrmex purpureus) that a spider predator is attracted to. | 1 | Biochemistry |
The Debye length arises naturally in the thermodynamic description of large systems of mobile charges. In a system of different species of charges, the -th species carries charge and has concentration at position . According to the so-called "primitive model", these charges are distributed in a continuous medium that is characterized only by its relative static permittivity, .
This distribution of charges within this medium gives rise to an electric potential that satisfies Poisson's equation:
where , is the electric constant, and is a charge density external (logically, not spatially) to the medium.
The mobile charges not only contribute in establishing but also move in response to the associated Coulomb force, .
If we further assume the system to be in thermodynamic equilibrium with a heat bath at absolute temperature , then the concentrations of discrete charges, , may be considered to be thermodynamic (ensemble) averages and the associated electric potential to be a thermodynamic mean field.
With these assumptions, the concentration of the -th charge species is described by the Boltzmann distribution,
where is the Boltzmann constant and where is the mean
concentration of charges of species .
Identifying the instantaneous concentrations and potential in the Poisson equation with their mean-field counterparts in the Boltzmann distribution yields the Poisson–Boltzmann equation:
Solutions to this nonlinear equation are known for some simple systems. Solutions for more general systems may be obtained in the high-temperature (weak coupling) limit, , by Taylor expanding the exponential:
This approximation yields the linearized Poisson–Boltzmann equation
which also is known as the Debye–Hückel equation:
The second term on the right-hand side vanishes for systems that are electrically neutral. The term in parentheses divided by , has the units of an inverse length squared and by
dimensional analysis leads to the definition of the characteristic length scale
that commonly is referred to as the Debye–Hückel length. As the only characteristic length scale in the Debye–Hückel equation, sets the scale for variations in the potential and in the concentrations of charged species. All charged species contribute to the Debye–Hückel length in the same way, regardless of the sign of their charges. For an electrically neutral system, the Poisson equation becomes
To illustrate Debye screening, the potential produced by an external point charge is
The bare Coulomb potential is exponentially screened by the medium, over a distance of the Debye length: this is called Debye screening or shielding (Screening effect).
The Debye–Hückel length may be expressed in terms of the Bjerrum length as
where is the integer charge number that relates the charge on the -th ionic
species to the elementary charge . | 7 | Physical Chemistry |
Proteins are characterized by amide linkages (-N(H)-C(O)-) formed by the condensation of amino acids. The sequence of the amino acids in the polypeptide backbone is known as the primary structure of the protein. Like almost all polymers, protein fold and twist, forming into the secondary structure, which is rigidified by hydrogen bonding between the carbonyl oxygens and amide hydrogens in the backbone, i.e. C=O---HN. Further interactions between residues of the individual amino acids form the protein's tertiary structure. For this reason, the primary structure of the amino acids in the polypeptide backbone is the map of the final structure of a protein, and it therefore indicates its biological function. Spatial positions of backbone atoms can be reconstructed from the positions of alpha carbons using computational tools for the backbone reconstruction. | 0 | Organic Chemistry |
A differential refractometer (DRI), or refractive index detector (RI or RID) is a detector that measures the refractive index of an analyte relative to the solvent. They are often used as detectors for high-performance liquid chromatography and size exclusion chromatography. They are considered to be universal detectors because they can detect anything with a refractive index different from the solvent, but they have low sensitivity. | 3 | Analytical Chemistry |
Calcitonin, as salmon calcitonin (sCT), is available in the pharmaceutical market as an injectable preparation for intravenous, intramuscular or subcutaneous application. Noninvasive sCT preparation as a nasal spray is commercially produced and received US FDA approval under the proprietary name Miacalcin® in 1975 for the treatment of postmenopausal osteoporosis. The bioavailability of Miacalcin® nasal spray relative to the injectable form is between 3% and 5%.
Currently, a number of sCT oral preparations are under clinical trials and at least one of them has reached Phase III of clinical approval. | 1 | Biochemistry |
Streak seeding is a method first described during ICCBM-3 by Enrico Stura to induce crystallization in a straight line into a sitting or hanging drop for protein crystallization by introducing microseeds. The purpose is to control nucleation and understand the parameters that make crystals grow. It is also used to test any particular set of conditions to check if crystals could grow under such conditions.
The technique is relatively simple. A cat whisker is used to dislodge seeds from a crystal. The whisker is passed through the drop starting from one side of the drop and ending on the opposite side of the drop in one smooth motion. To allow for vapour diffusion equilibration, the well in which the drop has been placed is resealed. The same procedure is repeated for all the drops whose conditions need testing. | 3 | Analytical Chemistry |
Chondroitinase treatment is a treatment of proteoglycans, a protein in the fluid among cells where (among other things) they affect neural activity (communication, plasticity). Chondroitinase treatment has been shown to allow adults vision to be restored as far as ocular dominance is concerned. Moreover, there is some evidence that Chondroitinase could be used for the treatment of spinal injuries.
In addition, the enzyme that is used in the chondroitinase treatment, chondroitinase ABC, derives from the bacterium Proteus vulgaris. In recent years, pre-clinical research involving the chondroitinase ABC enzyme has been mainly directed towards utilizing it as a way of treating spinal cord injuries in test animals using viral vectors. In general, the way chondroitinase ABC works in vivo is it cleaves off the side chains of molecules known as chondroitin sulfate proteoglycans (CSPGs) which are over produced by glial cells in the central nervous system when a spinal injury occurs. When chondroitin sulfate proteoglycans are bonded to their side chains called chondroitin sulfate glycosaminoglycans, these molecules are known to prevent neural restoration to the damaged region of the central nervous system because they form glial scar tissue which inhibits both neuroplasticity and repair of damaged axons. However, when the side chains of the chondroitin sulfate proteoglycans are cleaved by chondroitinase ABC, this promotes the damaged region of the CNS to recover from the spinal cord injury.
It has recently been proposed that chondroitinase treatment promotes plasticity by activation of Tropomyosin receptor kinase B, receptor for Brain-derived neurotrophic factor and a major plasticity orchestrator in the brain. Cleavage of CSPGs by chondroitinase ABC leads to inactivation of PTPRS, the membrane receptor for CSPGs and a phosphatase that inactivates TRKB under normal physiological conditions, which subsequently promotes TRKB phosphorylation and activation of neuroplasticity. | 1 | Biochemistry |
Diarylethene is the general name of a class of chemical compounds that have aromatic functional groups bonded to each end of a carbon–carbon double bond. The simplest example is stilbene, which has two geometric isomers, E and Z.
Under the influence of light, these compounds can generally perform two kinds of reversible isomerizations:
*E to Z isomerizations, most common for stilbenes (and azobenzenes). This process goes through an excited state energy minimum where the aromatic rings lie at 90° to each other. This conformation drops to the ground state and generally relaxes to trans and cis forms in a 1:1 ratio, thus the quantum yield for E-Z isomerization is very rarely greater than 0.5.
*6π electrocyclizations of the Z form, leading to an additional bond between the two aryl functionalities and a disruption of the aromatic character of these groups. The quantum yield of this reaction is generally less than 0.1, and in most diarylethenes the close-ring form is thermally unstable, reverting to the cis-form in a matter of seconds or minutes under ambient conditions.
Thermal isomerization is also possible. In E-Z isomerization, the thermal equilibrium lies well towards the trans-form because of its lower energy (~15 kJ mol in stilbene). The activation energy for thermal E-Z isomerization is 150–190 kJ mol for stilbene, meaning that temperatures above 200°C are required to isomerize stilbene at a reasonable rate, but most derivatives have lower energy barriers (e.g. 65 kJ mol for 4-aminostilbene). The activation energy of the electrocyclization is 73 kJ mol for stilbene.
Both processes are often applied in molecular switches and for photochromism (reversible state changes from exposure to light).
After the 6π electrocyclization of the Z form to the "close-ring" form, most unsubstituted diarylethenes are prone to oxidation, leading to a re-aromatization of the π-system. The most common example is (E)-stilbene, which upon irradiation undergoes an E to Z isomerization, which can be followed by a 6π electrocyclization. Reaction of the product of this reaction with molecular oxygen affords phenanthrene, and it has been suggested by some studies that dehydrogenation may even occur spontaneously. The dihydrophenanthrene intermediate has never been isolated, but it has been detected spectroscopically in pump-probe experiments by virtue of its long wavelength optical absorption band. Although both the E-Z isomerization and the 6π electrocyclization are reversible processes, this oxidation renders the entire sequence irreversible. | 5 | Photochemistry |
Design based on supramolecular chemistry has led to numerous applications in the creation of functional biomaterials and therapeutics. Supramolecular biomaterials afford a number of modular and generalizable platforms with tunable mechanical, chemical and biological properties. These include systems based on supramolecular assembly of peptides, host–guest macrocycles, high-affinity hydrogen bonding, and metal–ligand interactions.
A supramolecular approach has been used extensively to create artificial ion channels for the transport of sodium and potassium ions into and out of cells.
Supramolecular chemistry is also important to the development of new pharmaceutical therapies by understanding the interactions at a drug binding site. The area of drug delivery has also made critical advances as a result of supramolecular chemistry providing encapsulation and targeted release mechanisms. In addition, supramolecular systems have been designed to disrupt protein–protein interactions that are important to cellular function. | 6 | Supramolecular Chemistry |
Amagats law states that the extensive volume V = Nv of a gas mixture is equal to the sum of volumes V of the K component gases, if the temperature T and the pressure p' remain the same:
This is the experimental expression of volume as an extensive quantity.
According to Amagat's law of partial volume, the total volume of a non-reacting mixture of gases at constant temperature and pressure should be equal to the sum of the individual partial volumes of the constituent gases. So if are considered to be the partial volumes of components in the gaseous mixture, then the total volume would be represented as
Both Amagats and Daltons laws predict the properties of gas mixtures. Their predictions are the same for ideal gases. However, for real (non-ideal) gases, the results differ. Daltons law of partial pressures assumes that the gases in the mixture are non-interacting (with each other) and each gas independently applies its own pressure, the sum of which is the total pressure. Amagats law assumes that the volumes of the component gases (again at the same temperature and pressure) are additive; the interactions of the different gases are the same as the average interactions of the components.
The interactions can be interpreted in terms of a second virial coefficient B(T) for the mixture. For two components, the second virial coefficient for the mixture can be expressed as
where the subscripts refer to components 1 and 2, the X are the mole fractions, and the B are the second virial coefficients. The cross term B of the mixture is given by
: for Dalton's law
and
: for Amagat's law.
When the volumes of each component gas (same temperature and pressure) are very similar, then Amagats law becomes mathematically equivalent to Vegards law for solid mixtures. | 7 | Physical Chemistry |
In chemistry, the lever rule is a formula used to determine the mole fraction (x) or the mass fraction (w) of each phase of a binary equilibrium phase diagram. It can be used to determine the fraction of liquid and solid phases for a given binary composition and temperature that is between the liquidus and solidus line.
In an alloy or a mixture with two phases, α and β, which themselves contain two elements, A and B, the lever rule states that the mass fraction of the α phase is
where
* is the mass fraction of element B in the α phase
* is the mass fraction of element B in the β phase
* is the mass fraction of element B in the entire alloy or mixture
all at some fixed temperature or pressure. | 8 | Metallurgy |
Typically, two catalysts are needed for this reaction: a zerovalent palladium complex and a copper(I) halide salt. Common examples of palladium catalysts include those containing phosphine ligands such as Tetrakis(triphenylphosphine)palladium(0)|. Another commonly used palladium source is [, but complexes containing bidentate phosphine ligands, such as , , and (1,1'-Bis(diphenylphosphino)ferrocene)palladium(II) dichloride| have also been used. The drawback to such catalysts is the need for high loadings of palladium (up to 5 mol %), along with a larger amount of a copper co-catalyst.
Pd complexes are in fact pre-catalysts since they must be reduced to Pd before catalysis can begin. Pd complexes generally exhibit greater stability than Pd complexes and can be stored under normal laboratory conditions for months. Pd catalysts are reduced to Pd in the reaction mixture by an amine, a phosphine ligand, or another reactant in the mixture allowing the reaction to proceed. For instance, oxidation of triphenylphosphine to triphenylphosphine oxide can lead to the formation of Pd in situ when is used.
Copper(I) salts, such as CuI, react with the terminal alkyne and produce a copper(I) acetylide, which acts as an activated species for the coupling reactions. Cu(I) is a co-catalyst in the reaction, and is used to increase the rate of the reaction. | 0 | Organic Chemistry |
Converting spare electricity into heat for high-volume, long-term storage is under research at various companies, who claim that costs could be much lower than lithium-ion batteries. Graphite may be used as a storage medium, with molten tin as heat transfer, at temperatures around 2000°. See LaPotin, A., Schulte, K.L., Steiner, M.A. et al. Thermophotovoltaic efficiency of 40%. Nature 604, 287–291 (2022). https://doi.org/10.1038/s41586-022-04473-y. | 7 | Physical Chemistry |
For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For calcium labeling purposes 100% of the Daily Value was 1000 mg, but as of May 27, 2016 it was revised to 1300 mg to bring it into agreement with the RDA. A table of the old and new adult daily values is provided at Reference Daily Intake. | 1 | Biochemistry |
Plane groups can be depicted using the Hermann–Mauguin system. The first letter is either lowercase p or c to represent primitive or centered unit cells. The next number is the rotational symmetry, as given above. The presence of mirror planes are denoted m, while glide reflections are only denoted g. Screw axes do not exist in two dimension, they required 3D space. | 3 | Analytical Chemistry |
The journal is abstracted and indexed in:
According to the Journal Citation Reports, the journal has a 2021 impact factor of 3.945. | 7 | Physical Chemistry |
After the discovery of the lux operon, the use of bioluminescent bacteria as a laboratory tool is claimed to have revolutionized the area of environmental microbiology. The applications of bioluminescent bacteria include biosensors for detection of contaminants, measurement of pollutant toxicity and monitoring of genetically engineered bacteria released into the environment. Biosensors, created by placing a lux gene construct under the control of an inducible promoter, can be used to determine the concentration of specific pollutants. Biosensors are also able to distinguish between pollutants that are bioavailable and those that are inert and unavailable. For example, Pseudomonas fluorescens has been genetically engineered to be capable of degrading salicylate and naphthalene, and is used as a biosensor to assess the bioavailability of salicylate and naphthalene. Biosensors can also be used as an indicator of cellular metabolic activity and to detect the presence of pathogens. | 1 | Biochemistry |
Enolate activation is the simplest Conia-ene activation mode. In this mode, the carbonyl starting material is treated with a strong base, such as nBuLi, NaH, or tBuOK, to form a metal-stabilized enolate, which then attacks the tethered alkyne and transfers the metal cation. An early example of enolate activation was reported by Taguchi and coworkers in 1999. The authors found that in the presence of catalytic base, alkynyl-substituted malonate esters undergo facile cyclization to the corresponding cyclopentanes. High yields were also obtained with substituted cyanoacetate, sulfonylacetate, and phosphonoacetate analogs. | 0 | Organic Chemistry |
If an electron in a two level atomic system is excited by narrow line width coherent electro-magnetic radiation, like a laser, that is on resonance with the two level transition, the electron will Rabi flop. During Rabi flopping the electron oscillates between the ground and excited states and can be described by a continuous rotation around the Bloch sphere.
For a perfectly isolated system the Rabi oscillation will continue indefinitely and will undergo no phase change, making it a "coherent state". In physical systems interactions between the system and the environment introduce an unknown phase in the Rabi oscillation between the two levels with respect to the Rabi oscillation in the perfectly isolated system causing "decoherence".
If instead of a single two-level system an ensemble of identical two level systems (such as a chain of identical atoms in an ion trap) is prepared and continuously addressed with a laser, all the atoms may begin to simultaneously Rabi flop. At the beginning all two level systems will have a defined relative phase relation (they will all be in phase) and the system will be coherent.
As atoms begin to undergo random spontaneous emission their Rabi oscillations will accumulate a random relative phase with respect to each other and become decoherent. In actual experiments ambient magnetic field noise and thermal heating from collisions between atoms cause decoherence faster than random spontaneous emission and are the dominant uncertainties when running atomic clocks or trapped ion quantum computers. Atomic coherence can also apply to multi-level systems which require more than a single laser.
Atomic coherence is essential in research on several effects, such as electromagnetically induced transparency (EIT), lasing without inversion (LWI), stimulated raman adiabatic passage (STIRAP) and nonlinear optical interaction with enhanced efficiency.
Atomic systems demonstrating continuous superradiance exhibit long coherence time, a property shared with lasers. | 7 | Physical Chemistry |
Lithophile elements are those that remain on or close to the surface because they combine readily with oxygen, forming compounds that do not sink into the Earth's core. The lithophile elements include Al, B, Ba, Be, Br, Ca, Cl, Cr, Cs, F, I, Hf, K, Li, Mg, Na, Nb, O, P, Rb, Sc, Si, Sr, Ta, Th, Ti, U, V, Y, Zr, W and the lanthanides or rare earth elements (REE).
Lithophile elements mainly consist of the highly reactive metals of the s- and f-blocks. They also include a small number of reactive nonmetals, and the more reactive metals of the d-block such as titanium, zirconium and vanadium. Lithophile derives from "lithos" which means "rock", and "phileo" which means "love".
Most lithophile elements form very stable ions with an electron configuration of a noble gas (sometimes with additional f-electrons). The few that do not, such as silicon, phosphorus and boron, form extremely strong covalent bonds with oxygen – often involving pi bonding. Their strong affinity for oxygen causes lithophile elements to associate very strongly with silica, forming relatively low-density minerals that thus float to the Earth's crust. The more soluble minerals formed by the alkali metals tend to concentrate in seawater or extremely arid regions where they can crystallise. The less soluble lithophile elements are concentrated on ancient continental shields where all soluble minerals have been weathered.
Because of their strong affinity for oxygen, most lithophile elements are enriched in the Earths crust relative to their abundance in the solar system. The most reactive s- and f-block metals, which form either saline or metallic hydrides, are known to be extraordinarily enriched on Earth as a whole relative to their solar abundances. This is because during the earliest stages of the Earths formation the reaction that controlled the stable form of each chemical element was its ability to form compounds with hydrogen. Under these conditions, the s- and f-block metals were strongly enriched during the formation of the Earth. The most enriched elements are rubidium, strontium and barium, which between them account for over 50 percent by mass of all elements heavier than iron in the Earth's crust.
The nonmetallic lithophiles – phosphorus and the halogens – exist on Earth as ionic salts with s-block metals in pegmatites and seawater. With the exception of fluorine, whose hydride forms hydrogen bonds and is therefore of relatively low volatility, these elements have had their concentrations on Earth significantly reduced through escape of volatile hydrides during the Earths formation. Although they are present in the Earths crust in concentrations quite close to their solar abundances, phosphorus and the heavier halogens are probably significantly depleted on Earth as a whole relative to their solar abundances.
Several transition metals, including chromium, molybdenum, iron and manganese, show both lithophile and siderophile characteristics and can be found in both these two layers. Although these metals form strong bonds with oxygen and are never found in the Earth's crust in the free state, metallic forms of these elements are thought very likely to exist in the core of the earth as relics from when the atmosphere did not contain oxygen. Like the "pure" siderophiles, these elements (except iron) are considerably depleted in the crust relative to their solar abundances.
Owing to their strong affinity for oxygen, lithophile metals, although they form the great bulk of the metallic elements in Earth's crust, were never available as free metals before the development of electrolysis. With this development, many lithophile metals are of considerable value as structural metals (magnesium, aluminium, titanium, vanadium) or as reducing agents (sodium, magnesium, calcium).
The non-metals phosphorus and the halogens were also not known to early chemists, though production of these elements is less difficult than of metallic lithophiles since electrolysis is required only with fluorine. Elemental chlorine is particularly important as an oxidizing agent – usually being made by electrolysis of sodium chloride. | 9 | Geochemistry |
In his exposition of his scheme of closed system equilibrium thermodynamics, C. Carathéodory initially postulates that experiment reveals that a definite number of real variables define the states that are the points of the manifold of equilibria. In the words of Prigogine and Defay (1945): "It is a matter of experience that when we have specified a certain number of macroscopic properties of a system, then all the other properties are fixed." As noted above, according to A. Münster, the number of variables needed to define a thermodynamic equilibrium is the least for any state of a given isolated system. As noted above, J.G. Kirkwood and I. Oppenheim point out that a state of thermodynamic equilibrium may be defined by a special subclass of intensive variables, with a definite number of members in that subclass.
If the thermodynamic equilibrium lies in an external force field, it is only the temperature that can in general be expected to be spatially uniform. Intensive variables other than temperature will in general be non-uniform if the external force field is non-zero. In such a case, in general, additional variables are needed to describe the spatial non-uniformity. | 7 | Physical Chemistry |
Scientists are working on ways to use RT-PCR in cancer detection to help improve prognosis, and monitor response to therapy. Circulating tumor cells produce unique mRNA transcripts depending on the type of cancer. The goal is to determine which mRNA transcripts serve as the best biomarkers for a particular cancer cell type and then analyze its expression levels with RT-PCR.
RT-PCR is commonly used in studying the genomes of viruses whose genomes are composed of RNA, such as Influenzavirus A, retroviruses like HIV and SARS-CoV-2. | 1 | Biochemistry |
The insulin transduction pathway is a biochemical pathway by which insulin increases the uptake of glucose into fat and muscle cells and reduces the synthesis of glucose in the liver and hence is involved in maintaining glucose homeostasis. This pathway is also influenced by fed versus fasting states, stress levels, and a variety of other hormones.
When carbohydrates are consumed, digested, and absorbed the pancreas senses the subsequent rise in blood glucose concentration and releases insulin to promote uptake of glucose from the bloodstream. When insulin binds to the insulin receptor, it leads to a cascade of cellular processes that promote the usage or, in some cases, the storage of glucose in the cell. The effects of insulin vary depending on the tissue involved, e.g., insulin is most important in the uptake of glucose by muscle and adipose tissue.
This insulin signal transduction pathway is composed of trigger mechanisms (e.g., autophosphorylation mechanisms) that serve as signals throughout the cell. There is also a counter mechanism in the body to stop the secretion of insulin beyond a certain limit. Namely, those counter-regulatory mechanisms are glucagon and epinephrine. The process of the regulation of blood glucose (also known as glucose homeostasis) also exhibits oscillatory behavior.
On a pathological basis, this topic is crucial to understanding certain disorders in the body such as diabetes, hyperglycemia and hypoglycemia. | 1 | Biochemistry |
Sucrose is a disaccharide formed from condensation of glucose and fructose to produce α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside. Sucrose has 8 hydroxyl groups which can be reacted with fatty acid esters to produce sucrose esters. Among the 8 hydroxyl groups on sucrose, three (C6, C1, and C6) are primary while the others (C2, C3, C4, C3, and C4) are secondary. (The numbers 1-6 indicate the position of the carbons on glucose while the numbers 1-6 indicate the position of the carbons on fructose.) The three primary hydroxyl groups are more reactive due to lower steric hindrance, so they react with fatty acids first, resulting in a sucrose mono-, di-, or triester. Typical saturated fatty acids that are used to produce sucrose esters are lauric acid, myristic acid, palmitic acid, stearic acid and behenic acid, and typical unsaturated fatty acids are oleic acid and erucic acid. | 0 | Organic Chemistry |
ASF/SF2 has been shown to have a critical function in heart development, embryogenesis, tissue formation, cell motility, and cell viability in general. | 1 | Biochemistry |
"Actinic" lights are a high-color-temperature blue light. They are also used in electric fly killers to attract flies. | 7 | Physical Chemistry |
The descendants of European settlers began coming to the area of the lake in the early 20th century, first using it as a staging area for bush pilots flying to mining camps and settlements further north. In the mid-1930s, abundant gold deposits in the area triggered the establishment of Yellowknife as a permanent settlement. While at the time development was concentrated on the peninsula extending into Great Slave Lakes Yellowknife Bay, an area known today as Old Town, later analysis of lake sediments lends some support to accounts from that time of Frame Lake being used for the disposal of tailings and sewage from outlying mines. The lake took its name from Bill Frame, an early miner who owned part of the citys bus and taxi franchise.
Yellowknifes growth was briefly interrupted by World War II, but when it resumed afterwards, the higher ground closer to the lake was chosen for expansion. The area just east of the lake became New Town, today the citys downtown. McNiven Beach, named after the city's first mayor, was developed with facilities for swimming; sometimes floatplanes landed nearby as well. Residents also went boating on the lake.
At the same time, runoff from storms carried increasingly nutrient-rich waters into the lake. In colder months when the lake surface was not frozen over, the city dumped plowed snow into the lake, adding even more nutrients. Sewage dumped into nearby Niven Lake, heavily used for that purpose for almost 35 years of Yellowknife's postwar growth, may also have flowed into Frame, offering more nutrients.
By the early 1970s the lakes decline had been noted. A later study by the earth science department at Carleton University concluded that the 1970 construction of the causeway across the end of the lakes eastern arm was the "tipping point" for Frame Lake. It cut off the stream between it and Niven Lake to the north, the only outlet the lake had had during human habitation of the area. With the lack of water throughput, nutrient levels in the water column rose, nurturing aquatic plants during the summertime. In the winter, however, when the lake froze over and snow cover blocked much of the limited sunlight available, those same plants died off for lack of ability to photosynthesize. The decomposed plant matter began accumulating on the lake floor, steadily deoxygenating its waters.
In a 1973 limnological study of seven lakes in the Yellowknife area, including Frame, for a possible experimental fishery, scientists from the Fisheries Research Board noted that Frame was the only one in which they were unable to catch any fish for study. Over the preceding winter, they also observed that the lake had "become rapidly anoxic".
As the lake declined, development came closer. Yellowknife built its current city hall by the lake edge in 1975, and the Prince of Wales Northern Heritage Centre, the territorial museum, followed nearby four years later. Sometime later that decade, the number of swimmers at McNiven Beach declined sufficiently for the city to remove the facilities there, as the beach itself began to grow over with grass.
Residents were still swimming and boating in the lake in the early 1980s, but in smaller numbers. Some were scared off by reports of leeches that had in one instance supposedly covered an entire child. A local journalist recalled in 2015 how he had had to watch his step to avoid deep, malodorous deposits while catching tadpoles in the shallow waters near his home at that time. Later the Frame Lake South area was developed for residential and commercial use as the city grew. Storm sewers installed for these projects diverted the runoff that had once fed the lake, increasing the concentration of nutrients in the water. | 2 | Environmental Chemistry |
Phosphaalkenes (IUPAC name: alkylidenephosphanes) are organophosphorus compounds with double bonds between carbon and phosphorus(III) with the formula RC=PR. In the compound phosphorine one carbon atom in benzene is replaced by phosphorus. The reactivity of phosphaalkenes is often compared to that of alkenes and not to that of imines because the HOMO of phosphaalkenes is not the phosphorus lone pair (as in imines the amine lone pair) but the double bond. Therefore like alkenes, phosphaalkenes engage in Wittig reactions, Peterson reactions, Cope rearrangements and Diels-Alder reactions.
The first phosphaalkene discovered was a phosphabenzene, by Mërkl in 1969. The first localized phosphaalkene was reported in 1976 by Gerd Becker as a keto-enol tautomerism akin a Brook rearrangement:
In the same year Harold Kroto established spectroscopically that thermolysis of MePH generates CH=PMe. A general method for the synthesis of phosphaalkenes is by 1,2-elimination of suitable precursors, initiated thermally or by base such as DBU, DABCO or triethylamine:
The Becker method is used in the synthesis of the phosphorus pendant of Poly(p-phenylene vinylene):
The reduction or oxidation of phosphaalynes can produce radical phosphorus ions. | 0 | Organic Chemistry |
IUPAC nomenclature has extensive rules to cover the naming of cyclic structures, both as core structures, and as substituents appended to alicyclic structures. The term macrocycle is used when a ring-containing compound has a ring of 12 or more atoms. The term polycyclic is used when more than one ring appears in a single molecule. Naphthalene is formally a polycyclic compound, but is more specifically named as a bicyclic compound. Several examples of macrocyclic and polycyclic structures are given in the final gallery below.
The atoms that are part of the ring structure are called annular atoms. | 4 | Stereochemistry |
Evapoporometry has the significant advantage of requiring only a lab scale, 2-propanol (or another wetting fluid), and a cell in which to contain the sample and 2-propanol. The sample is immersed for some time in 2-propanol prior to measurement to ensure saturation of pores, and is then placed into the cell in an analytical balance and immersed again in 2-propanol, after which the change in mass due to evaporation of the free-standing liquid layer and then draining of liquid from pores is measured by the analytical balance. Instantaneous evaporation rates are calculated from the mass data and input into the above equation to yield a pore-size distribution for the sample. can be used to quantitatively determine value of at which pore draining begins, which is equal to , where is the standard deviation of . This analysis is enabled by the principle that evaporation from small pores will only occur after 2-propanol in larger pores has completely evaporated.
It is important to note that there exists a nanoscale layer of wetting fluid on both the membrane and the test cell material known as the "t-layer," the mass of which is to be excluded from measurement to increase accuracy, otherwise these points may be incorrectly attributed to subnanometer pores. Akhondi et al describe methods for correction of the t-layers of the test cell and membrane, as well as a correction for swelling of membranes during the experiment. The correction for the t-layer of the test cell itself can be made by performing the evapoporometry procedure as described above with an empty test cell, integrating from the start point of pore draining until the point at which = 4 nm to yield the mass of the t-layer. This mass plus the mass of the membrane's t-layer will constitute the endpoint of pore diameter calculation for the principal evapoporometry measurement. | 7 | Physical Chemistry |
Single chain cyclized polymers consist of multiple cyclized rings which afford them some unique properties, including high density, low intrinsic viscosity, low translational friction coefficients, high glass transition temperatures, and excellent elasticity of the formed network. In particular, an abundance of internal space makes the single chain cyclized polymers ideal candidates as efficient cargo-carriers. | 7 | Physical Chemistry |
In the human genome, CCL7 is encoded by the CCL7 gene which is one of the several chemokine genes clustered on chromosome 17q11.2-q12. This region contains the gene for the MCP subset of CC chemokines. The CCL7 gene has been given the locus symbol SCYA7.
The gene consists of three exons and two introns. The first exon contains a 5′-untranslated region (5′-UTR), the information for the signal sequence (23 amino acids), and the mature protein's first two amino acids. The second exon encodes amino acids 3–42 of the mature proteins. The third exon is composed of the C-terminal region of the protein, a 3′-UTR containing one or more destabilizing AU-rich sequences and a polyadenylation signal. | 1 | Biochemistry |
Homofermentative bacteria convert glucose to two molecules of lactate and use this reaction to perform substrate-level phosphorylation to make two molecules of ATP:
:Glucose + 2 ADP + 2 P → 2 Lactate + 2 ATP | 1 | Biochemistry |
Deoxygenating reagents, light, or heat all catalyze rearrangement to the amide. Acids catalyze rearrangement to the oxime ether. | 0 | Organic Chemistry |
The National Center for Functional Glycomics is an organization that is focused on the development of technology development in glycosciences. They are specifically focused on glycan analysis and molecular mechanisms of glycan recognition by proteins important in human biology and disease. The center was established at Emory University in 2013 with $5.5 million funding by National Institutes of Health under the leadership of Richard D. Cummings. The center moved to Harvard University in September 2015 and is currently located at Beth Israel Deaconess Medical Center in Boston Massachusetts. The center is affiliated with the Consortium for Functional Glycomics.
The National Center for Functional Glycomics is one of four glycomics-related biomedical technology research resource centers in the United States. These centers provide unique technology and methods in the field of glycomics research. The center is responsible for services and training for outside investigators, as well as providing access and disseminating technologies, methods and software. | 0 | Organic Chemistry |
The 3′-UTR often contains microRNA response elements (MREs), which are sequences to which miRNAs bind. miRNAs are short, non-coding RNA molecules capable of binding to mRNA transcripts and regulating their expression. One miRNA mechanism involves partial base pairing of the 5' seed sequence of an miRNA to an MRE within the 3′-UTR of an mRNA; this binding then causes translational repression. | 1 | Biochemistry |
Paquette's 1982 organic synthesis takes about 29 steps with raw materials cyclopentadiene (2 equivalents 10 carbon atoms), dimethyl acetylenedicarboxylate (4 carbon atoms) and allyltrimethylsilane (2 equivalents, 6 carbon atoms).
In the first leg of the procedure two molecules of cyclopentadiene 1 are coupled together by reaction with elemental sodium (forming the cyclopentadienyl complex) and iodine to dihydrofulvalene 2. Next up is a tandem Diels–Alder reaction with dimethyl acetylenedicarboxylate 3 with desired sequence pentadiene-acetylene-pentadiene as in symmetrical adduct 4. An equal amount of asymmetric pentadiene-pentadiene-acetylene compound (4b) is formed and discarded.
In the next step of the sequence iodine is temporarily introduced via an iodolactonization of the diacid of 4 to dilactone 5. The ester group is cleaved next by methanol to the halohydrin 6, the alcohol groups converted to ketone groups in 7 by Jones oxidation and the iodine groups reduced by a zinc-copper couple in 8.
The final 6 carbon atoms are inserted in a nucleophilic addition to the ketone groups of the carbanion 10 generated from allyltrimethylsilane 9 and n-butyllithium. In the next step the vinyl silane 11 reacts with peracetic acid in acetic acid in a radical substitution to the dilactone 12 followed by an intramolecular Friedel-Crafts alkylation with phosphorus pentoxide to diketone 13. This molecule contains all required 20 carbon atoms and is also symmetrical which facilitates the construction of the remaining 5 carbon-carbon bonds.
Reduction of the double bonds in 13 to 14 is accomplished with hydrogenation with palladium on carbon and that of the ketone groups to alcohol groups in 15 by sodium borohydride. Replacement of hydroxyl by chlorine in 17 via nucleophilic aliphatic substitution takes place through the dilactone 16 (tosyl chloride). The first C–C bond forming reaction is a kind of Birch alkylation (lithium, ammonia) with the immediate reaction product trapped with chloromethyl phenyl ether, the other chlorine atom in 17 is simply reduced. This temporary appendix will in a later stage prevent unwanted enolization. The newly formed ketone group then forms another C–C bond by photochemical Norrish reaction to 19 whose alcohol group is induced to eliminate with TsOH to alkene 20.
The double bond is reduced with hydrazine and sequential diisobutylaluminum hydride reduction and pyridinium chlorochromate oxidation of 21 forms the aldehyde 22. A second Norrish reaction then adds another C–C bond to alcohol 23 and having served its purpose the phenoxy tail is removed in several steps: a Birch reduction to diol 24, oxidation with pyridinium chlorochromate to ketoaldehyde 25 and a reverse Claisen condensation to ketone 26. A third Norrish reaction produces alcohol 27 and a second dehydration 28 and another reduction 29 at which point the synthesis is left completely without functional groups. The missing C-C bond is put in place by hydrogen pressurized dehydrogenation with palladium on carbon at 250 °C to dodecahedrane 30. | 0 | Organic Chemistry |
Three of the many proteins that are phosphorylated by MAPK are shown in the figure to the right. One effect of MAPK activation is to alter the translation of mRNA to proteins. MAPK phosphorylates the 40S ribosomal protein S6 kinase (RSK). This activates RSK, which, in turn, phosphorylates ribosomal protein S6. Mitogen-activated protein kinases that phosphorylate ribosomal protein S6 were the first to be isolated.
MAPK regulates the activities of several transcription factors. MAPK can phosphorylate C-myc. MAPK phosphorylates and activates MNK, which, in turn, phosphorylates CREB. MAPK also regulates the transcription of the C-Fos gene. By altering the levels and activities of transcription factors, MAPK leads to altered transcription of genes that are important for the cell cycle.
The 22q11, 1q42, and 19p13 genes, by affecting the ERK pathway, are associated with schizophrenia, schizoaffective disorder, bipolar disorder, and migraines. | 1 | Biochemistry |
This equation for gives satisfactory agreement with experimental measurements for low electrolyte concentrations, typically less than 10 mol/L. Deviations from the theory occur at higher concentrations and with electrolytes that produce ions of higher charges, particularly unsymmetrical electrolytes. Essentially these deviations occur because the model is oversimplified, so there is little to be gained making small adjustments to the model. The individual assumptions can be challenged in turn.
*Complete dissociation. Ion association may take place, particularly with ions of higher charge. This was followed up in detail by Niels Bjerrum. The Bjerrum length is the separation at which the electrostatic interaction between two ions is comparable in magnitude to kT.
*Weak electrolytes. A weak electrolyte is one that is not fully dissociated. As such it has a dissociation constant. The dissociation constant can be used to calculate the extent of dissociation and hence, make the necessary correction needed to calculate activity coefficients.
*Ions are spherical, not point charges and are not polarized. Many ions such as the nitrate ion, NO, are not spherical. Polyatomic ions are also polarizable.
*Role of the solvent. The solvent is not a structureless medium but is made up of molecules. The water molecules in aqueous solution are both dipolar and polarizable. Both cations and anions have a strong primary solvation shell and a weaker secondary solvation shell. Ion–solvent interactions are ignored in Debye–Hückel theory.
Moreover, ionic radius is assumed to be negligible, but at higher concentrations, the ionic radius becomes comparable to the radius of the ionic atmosphere.
Most extensions to Debye–Hückel theory are empirical in nature. They usually allow the Debye–Hückel equation to be followed at low concentration and add further terms in some power of the ionic strength to fit experimental observations. The main extensions are the Davies equation, Pitzer equations and specific ion interaction theory. | 7 | Physical Chemistry |
petite (ρ–) is a mutant first discovered in the yeast Saccharomyces cerevisiae. Due to the defect in the respiratory chain, petite yeast are unable to grow on media containing only non-fermentable carbon sources (such as glycerol or ethanol) and form small colonies when grown in the presence of fermentable carbon sources (such as glucose). The petite phenotype can be caused by the absence of, or mutations in, mitochondrial DNA (termed "cytoplasmic Petites"), or by mutations in nuclear-encoded genes involved in oxidative phosphorylation. A neutral petite produces all wild type progeny when crossed with wild type.
petite mutations can be induced using a variety of mutagens, including DNA intercalating agents, as well as chemicals that can interfere with DNA synthesis in growing cells. Mutagens that create Petites are implicated in increased rates of degenerative diseases and in the aging process. | 1 | Biochemistry |
Commonly poly(pentafluorophenyl acrylate) is synthesized by free radical polymerization of the monomer pentafluorophenyl acrylate.
Additionally, pentafluorophenyl acrylate can be successfully polymerized by RAFT polymerization yield homopolymers, copolymers, or block copolymers.
It has been shown that poly(pentafluorophenyl acrylate) can also be prepared by pulsed plasma deposition. | 7 | Physical Chemistry |
With the publication of "Expansion of C ecosystems as an indicator of global ecological change in the late Miocene" in 1993, Cerling, helped by Yang Wang and Jay Quade, made relevant studies relatively to carbon isotopes. Thanks to a deep analysis of palaeovegetation from palaeosols and palaeodiet measured in fossil tooth enamel, was demonstrated a global increase in the biomass of plants using C photosynthesis between 7 and 5 million years ago. The decrease of atmospheric concentrations over the history below a threshold that favored the C-photosynthesizing plants was considered as a valid reason for the global expansion of C biomass.
The publication "Global vegetation change through the Miocene/Pliocene boundary" in 1997 confirmed these results, demonstrating even how at lower latitudes the change appeared to occur earlier because of the threshold for C photosynthesis is higher at warmer temperatures. | 9 | Geochemistry |
The stereoisomers β--glucopyranose and β--mannopyranose are epimers because they differ only in the stereochemistry at the C-2 position. The hydroxy group in β-D-glucopyranose is equatorial (in the "plane" of the ring), while in β-D-mannopyranose the C-2 hydroxy group is axial (up from the "plane" of the ring). These two molecules are epimers but, because they are not mirror images of each other, are not enantiomers. (Enantiomers have the same name, but differ in and classification.) They are also not sugar anomers, since it is not the anomeric carbon involved in the stereochemistry. Similarly, β--glucopyranose and β--galactopyranose are epimers that differ at the C-4 position, with the former being equatorial and the latter being axial.
In the case that the difference is the -OH groups on C-1, the anomeric carbon, such as in the case of α--glucopyranose and β--glucopyranose, the molecules are both epimers and anomers (as indicated by the α and β designation).
Other closely related compounds are epi-inositol and inositol and lipoxin and epilipoxin. | 4 | Stereochemistry |
For elements in the main groups of the periodic table, the valence can vary between 1 and 8.
Many elements have a common valence related to their position in the periodic table, and nowadays this is rationalised by the octet rule.
The Greek/Latin numeral prefixes (mono-/uni-, di-/bi-, tri-/ter-, and so on) are used to describe ions in the charge states 1, 2, 3, and so on, respectively. Polyvalence or multivalence refers to species that are not restricted to a specific number of valence bonds. Species with a single charge are univalent (monovalent). For example, the cation is a univalent or monovalent cation, whereas the cation is a divalent cation, and the cation is a trivalent cation. Unlike Cs and Ca, Fe can also exist in other charge states, notably 2+ and 4+, and is thus known as a multivalent (polyvalent) ion. Transition metals and metals to the right are typically multivalent but there is no simple pattern predicting their valency.
† The same adjectives are also used in medicine to refer to vaccine valence, with the slight difference that in the latter sense, quadri- is more common than tetra-.
‡ As demonstrated by hit counts in Google web search and Google Books search corpora (accessed 2017).
§ A few other forms can be found in large English-language corpora (for example, *quintavalent, *quintivalent, *decivalent), but they are not the conventionally established forms in English and thus are not entered in major dictionaries. | 3 | Analytical Chemistry |
Aggregates begin as the colloidal fraction, which typically contains particles sized between one nanometer and several micrometers. The colloidal fraction of the ocean contains a large amount of organic matter unavailable to grazers. This fraction has a much higher total mass than either phytoplankton or bacteria but is not readily available due to size characteristics of the particles in relation to potential consumers. The colloidal fraction must aggregate in order to be more bioavailable. | 9 | Geochemistry |
Organic photosensitizers are carbon-based molecules which are capable of photosensitizing. The earliest studied photosensitizers were aromatic hydrocarbons which absorbed light in the presence of oxygen to produce reactive oxygen species. These organic photosensitizers are made up of highly conjugated systems which promote electron delocalization. Due to their high conjugation, these systems have a smaller gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) as well as a continuum of orbitals within the HOMO and LUMO. The smaller band gap and the continuum of orbitals in both the conduction band and the valence band allow for these materials to enter their triplet state more efficiently, making them better photosensitizers. Some notable organic photosensitizers which have been studied extensively include benzophenones, methylene blue, and rose Bengal. | 5 | Photochemistry |
An example of a Curtin–Hammett scenario in which the more stable conformational isomer reacts more quickly is observed during the oxidation of piperidines. In the case of N-methyl piperidine, inversion at nitrogen between diastereomeric conformers is much faster than the rate of amine oxidation. The conformation which places the methyl group in the equatorial position is 3.16 kcal/mol more stable than the axial conformation. The product ratio of 95:5 indicates that the more stable conformer leads to the major product. | 7 | Physical Chemistry |
In these cases, a plasmid is constructed in which the genes to be transferred are flanked by viral sequences that are used by viral proteins to recognize and package the viral genome into viral particles. This plasmid is inserted (usually by transfection) into a producer cell together with other plasmids (DNA constructs) that carry the viral genes required for the formation of infectious virions. In these producer cells, the viral proteins expressed by these packaging constructs bind the sequences on the DNA/RNA (depending on the type of viral vector) to be transferred and insert it into viral particles. For safety, none of the plasmids used contains all the sequences required for virus formation, so that simultaneous transfection of multiple plasmids is required to get infectious virions. Moreover, only the plasmid carrying the sequences to be transferred contains signals that allow the genetic materials to be packaged in virions so that none of the genes encoding viral proteins are packaged. Viruses collected from these cells are then applied to the cells to be altered. The initial stages of these infections mimic infection with natural viruses and lead to expression of the genes transferred and (in the case of lentivirus/retrovirus vectors) insertion of the DNA to be transferred into the cellular genome. However, since the transferred genetic material does not encode any of the viral genes, these infections do not generate new viruses (the viruses are "replication-deficient").
Some enhancers have been used to improve transduction efficiency such as polybrene, protamine sulfate, retronectin, and DEAE Dextran. | 1 | Biochemistry |
Bragg diffraction (also referred to as the Bragg formulation of X-ray diffraction) was first proposed by Lawrence Bragg and his father, William Henry Bragg, in 1913 after their discovery that crystalline solids produced surprising patterns of reflected X-rays (in contrast to those produced with, for instance, a liquid). They found that these crystals, at certain specific wavelengths and incident angles, produced intense peaks of reflected radiation.
Lawrence Bragg explained this result by modeling the crystal as a set of discrete parallel planes separated by a constant parameter . He proposed that the incident X-ray radiation would produce a Bragg peak if reflections off the various planes interfered constructively. The interference is constructive when the phase difference between the wave reflected off different atomic planes is a multiple of ; this condition (see Bragg condition section below) was first presented by Lawrence Bragg on 11 November 1912 to the Cambridge Philosophical Society. Although simple, Bragg's law confirmed the existence of real particles at the atomic scale, as well as providing a powerful new tool for studying crystals. Lawrence Bragg and his father, William Henry Bragg, were awarded the Nobel Prize in physics in 1915 for their work in determining crystal structures beginning with NaCl, ZnS, and diamond. They are the only father-son team to jointly win.
The concept of Bragg diffraction applies equally to neutron diffraction and approximately to electron diffraction. In both cases the wavelengths are comparable with inter-atomic distances (~ 150 pm). Many other types of matter waves have also been shown to diffract, and also light from objected with a larger ordered structure such as opals. | 3 | Analytical Chemistry |
Current research related to VMAT uses VMAT2 knockout mice to explore the behavioral genetics of this transporter in an animal model. VMAT2 knockouts are known to be lethal as homozygotes, but heterozygote knockouts are not lethal and are used in many studies as a durable animal model.
From knockout and knockdown mice, researchers have discovered that it is good to have over-expression or under-expression of the VMAT genes in some circumstances. Mice are also used in drug studies, particularity studies involving the effect cocaine and methamphetamine have on VMATs. Studies involving animals have prompted scientists to work on developing drugs that inhibit or enhance the function of VMATs. Drugs that inhibit VMATs may have use in addiction but further studies are needed. Enhancing the function of VMATs may also have therapeutic value. | 1 | Biochemistry |
The Grove cell was an early electric primary cell named after its inventor, Welsh physical scientist William Robert Grove, and consisted of a zinc anode in dilute sulfuric acid and a platinum cathode in concentrated nitric acid, the two separated by a porous ceramic pot. | 3 | Analytical Chemistry |
Suppose that a chemical system has elements and chemical species (elements or compounds). The latter are combinations of the former, and each species can be represented as a sum of elements:
where are the integers denoting number of atoms of element in molecule . Each species is determined by a vector (a row of this matrix), but the rows are not necessarily linearly independent. If the rank of the matrix is , then there are linearly independent vectors, and the remaining vectors can be obtained by adding up multiples of those vectors. The chemical species represented by those vectors are components of the system.
If, for example, the species are C (in the form of graphite), CO and CO, then
Since CO can be expressed as CO = (1/2)C + (1/2)CO, it is not independent and C and CO can be chosen as the components of the system.
There are two ways that the vectors can be dependent. One is that some pairs of elements always appear in the same ratio in each species. An example is a series of polymers that are composed of different numbers of identical units. The number of such constraints is given by . In addition, some combinations of elements may be forbidden by chemical kinetics. If the number of such constraints is , then
Equivalently, if is the number of independent reactions that can take place, then
The constants are related by . | 7 | Physical Chemistry |
Unloading is the release of pressure due to the removal of an overburden. When the pressure is reduced rapidly, the rapid expansion of the rock causes high surface stress and spalling. | 8 | Metallurgy |
The following are some of the signs that firefighters are looking for when they attempt to determine whether a flashover is likely to occur.
* Fast dark smoke.
* The neutral plane is moving down towards the floor. In this situation, a flashover is plausible.
* All directly exposed combustible materials are showing signs of pyrolysis.
* "Rollover" or tongues of fire appear (known as "angel fingers" to firefighters) as gases reach their auto-ignition temperatures.
* There is a rapid build-up (or "spike") in temperature due to the compound effect of rapidly burning (i.e., deflagrating) gases and the thermal cycle they produce. This is generally the best indication of a flashover.
* The fire is in a ventilated compartment, so there is no shortage of oxygen in the room.
Firefighters memorize a chant to help remember these during training: "Thick dark smoke, high heat, rollover, free burning."
The colour of the smoke is often considered as well, but there is no connection between the colour of the smoke and the risk of flashovers. Traditionally, black, dense smoke was considered particularly dangerous, but history shows this to be an unreliable indicator. For example, there was a fire in a rubber mattress factory in London in 1975 which produced white smoke. The white smoke was not considered dangerous, so firefighters decided to ventilate, which caused a smoke explosion and killed two firefighters. The white smoke from the pyrolysis of the rubber turned out to be extremely flammable. | 7 | Physical Chemistry |
In aqueous solution 3-hydroxypropionaldehyde exists in equilibrium with its hydrate (1,1,3-propanetriol), in which the aldehyde group converts to a geminal diol:
:HOCHCHCHO + HO → HOCHCHCH(OH)
The hydrate is also in equilibrium with its dimer (2-(2-hydroxyethyl)-4-hydroxy-1,3-dioxane), which dominates at high concentrations. These three components - the aldehyde, its dimer, and the hydrate are therefore in a dynamic equilibrium.
Besides, 3-hydroxypropionaldehyde suffers an spontaneous dehydration in aqueous solution, and the resulting molecule is called acrolein.
In fact, the term reuterin is the name given to the dynamic system formed by 3-hydroxypropionaldehyde, its hydrate, the dimer, and acrolein. This last molecule, acrolein, was recently included in reuterin definition. | 1 | Biochemistry |
Clathrates have been explored for many applications including: gas storage, gas production, gas separation, desalination, thermoelectrics, photovoltaics, and batteries.
* Clathrate compounds with formula ABX, where A is an alkaline earth metal, B is a group III element, and X is an element from group IV have been explored for thermoelectric devices. Thermoelectric materials follow a design strategy called the phonon glass electron crystal concept. Low thermal conductivity and high electrical conductivity is desired to produce the Seebeck Effect. When the guest and host framework are appropriately tuned, clathrates can exhibit low thermal conductivity, i.e., phonon glass behavior, while electrical conductivity through the host framework is undisturbed allowing clathrates to exhibit electron crystal.
* Methane clathrates feature the hydrogen-bonded framework contributed by water and the guest molecules of methane. Large amounts of methane naturally frozen in this form exist both in permafrost formations and under the ocean sea-bed. Other hydrogen-bonded networks are derived from hydroquinone, urea, and thiourea. A much studied host molecule is Dianin's compound.
* Hofmann clathrates are coordination polymers with the formula Ni(CN)·Ni(NH)(arene). These materials crystallize with small aromatic guests (benzene, certain xylenes), and this selectivity has been exploited commercially for the separation of these hydrocarbons. Metal organic frameworks (MOFs) form clathrates. | 6 | Supramolecular Chemistry |
The analytical near infrared (NIR) region spans the range from 780 nm to 2,500 nm. The absorption bands seen in this spectral range arise from overtones and combination bands of O-H, N-H, C-H and S-H stretching and bending vibrations. Absorption is one to two orders of magnitude smaller in the NIR compared to the MIR; this phenomenon eliminates the need for extensive sample preparation. Thick and thin samples can be analyzed without any sample preparation, it is possible to acquire NIR chemical images through some packaging materials, and the technique can be used to examine hydrated samples, within limits. Intact samples can be imaged in transmittance or diffuse reflectance.
The lineshapes for overtone and combination bands tend to be much broader and more overlapped than for the fundamental bands seen in the MIR. Often, multivariate methods are used to separate spectral signatures of sample components. NIR chemical imaging is particularly useful for performing rapid, reproducible and non-destructive analyses of known materials. NIR imaging instruments are typically based on a hyperspectral camera, a tunable filter or an FT-IR interferometer. External light source is always needed, such as sun (outdoor scans, remote sensing) or a halogen lamp (laboratory, industrial measurements). | 7 | Physical Chemistry |
The stereoisomer (S)-1-pyrroline-5-carboxylate (also referred to as L-P5C) is an intermediate metabolite in the biosynthesis and degradation of proline and arginine.
In prokaryotic proline biosynthesis, GSA is synthesized from γ-glutamyl phosphate by the enzyme γ-glutamyl phosphate reductase. In most eukaryotes, GSA is synthesised from the amino acid glutamate by the bifunctional enzyme 1-pyrroline-5-carboxylate synthase (P5CS). The human P5CS is encoded by the ALDH18A1 gene. The enzyme pyrroline-5-carboxylate reductase converts P5C into proline
In proline degradation, the enzyme proline dehydrogenase produces P5C from proline, and the enzyme 1-pyrroline-5-carboxylate dehydrogenase converts GSA to glutamate. In many prokaryotes, proline dehydrogenase and P5C dehydrogenase form a bifunctional enzyme that prevents the release of P5C during proline degradation. In arginine degradation, the enzyme ornithine-δ-aminotransferase mediates the transamination between ornithine and a 2-oxo acid (typically α-ketoglutarate) to form P5C and an L-amino acid (typically glutamate). Under specific conditions, P5C may also be used for arginine biosynthesis via the reverse reaction of ornithine-δ-aminotransferase. | 1 | Biochemistry |
Exon trapping is a molecular biology technique to identify potential exons in a fragment of eukaryote DNA of unknown intron-exon structure. This is done to determine if the fragment is part of an expressed gene.
The genomic fragment is inserted into the intron of a splicing vector consisting of a known exon - intron - exon sequence of DNA, and the vector is then inserted into an eukaryotic cell. If the fragment does not contain exons (i.e., consists solely of intron DNA), it will be spliced out together with the vectors original intron. On the other hand, if exons are contained, they will be part of the mature mRNA after transcription (with all intron material removed). The presence of trapped exons' can be detected by an increase in size of the mRNA, or through RT-PCR to amplify the DNA of interest.
The technique has largely been supplanted by the approach of sequencing cDNA generated from mRNA and then using bioinformatics tools such as NCBI's BLAST server to determine the source of the sequence, thereby identifying the appropriate exon-intron splice sites. | 1 | Biochemistry |
Denaturing gradient gel electrophoresis (DGGE) works by applying a small sample of DNA (or RNA) to an electrophoresis gel that contains a denaturing agent. Researchers have found that certain denaturing gels are capable of inducing DNA to melt at various stages. As a result of this melting, the DNA spreads through the gel and can be analyzed for single components, even those as small as 200-700 base pairs.
What is unique about the DGGE technique is that as the DNA is subjected to increasingly extreme denaturing conditions, the melted strands fragment completely into single strands. The process of denaturation on a denaturing gel is very sharp: "Rather than partially melting in a continuous zipper-like manner, most fragments melt in a step-wise process. Discrete portions or domains of the fragment suddenly become single-stranded within a very narrow range of denaturing conditions" (Helms, 1990). This makes it possible to discern differences in DNA sequences or mutations of various genes: sequence differences in fragments of the same length often cause them to partially melt at different positions in the gradient and therefore "stop" at different positions in the gel. By comparing the melting behavior of the polymorphic DNA fragments side by side on denaturing gradient gels, it is possible to detect fragments that have mutations in the first melting domain (Helms, 1990). Placing two samples side by side on the gel and allowing them to denature together, researchers can easily see even the smallest differences in two samples or fragments of DNA.
There are a number of disadvantages to this technique: "Chemical gradients such as those used in DGGE are not as reproducible, are difficult to establish and often do not completely resolve heteroduplexes" (Westburg, 2001). These problems are addressed by TGGE, which uses a temperature, rather than chemical, gradient to denature the sample. | 1 | Biochemistry |
Nuclear receptor coactivator 4, also known as Androgen Receptor Activator (ARA70), is a protein that in humans is encoded by the NCOA4 gene. It plays an important role in ferritinophagy, acting as a cargo receptor, binding to the ferritin heavy chain and latching on to ATG8 on the surface of the autophagosome. | 1 | Biochemistry |
In organic chemistry, the desulfonation reaction is the hydrolysis of sulfonic acids:
:RCHSOH + HO → RCH + HSO
The reaction applied to aryl and naphthylsulfonic acids. It is the reverse of sulfonation. The temperature of desulfonation correlates with the ease of the sulfonation. | 0 | Organic Chemistry |
The European Association of Geochemistry publishes, co-publishes, or sponsors the following:
* [http://www.geochemicalperspectives.org/ Geochemical Perspectives] – 4 issues a year
* Geochemical Perspectives Letters – an open access journal
* Elements: An International Magazine of Mineralogy, Geochemistry, and Petrology – 6 issues a year
* Chemical Geology – 24 issues a year | 9 | Geochemistry |
A number of methods for synthesis have been published. The most recent is probably the method posted by the Serbian chemical society (2004).
There is another method, though, for constructing the N-Benzyl-3-methyl-4-piperidone in a 2-stage Michael reaction, followed by Dieckmann cyclization as per usual. | 1 | Biochemistry |
Methanation is the conversion of carbon monoxide and carbon dioxide (CO) to methane (CH) through hydrogenation. The methanation reactions of CO were first discovered by Sabatier and Senderens in 1902.
CO methanation has many practical applications. It is a means of carbon oxide removal from process gases and is also being discussed as an alternative to PROX in fuel processors for mobile fuel cell applications.
Methanation as a means of producing synthetic natural gas has been considered since the 1970s. More recently it has been considered as a way to store energy produced from solar or wind power using power-to-gas systems in conjunction with existing natural gas storage. | 0 | Organic Chemistry |
Contraindications are hypersensitivity against ACE inhibitors, especially if it has resulted in angioedema; idiopathic or hereditary angioedema; kidney failure; the second and third trimesters in pregnancy; and combination with the drug aliskiren in people with diabetes. | 4 | Stereochemistry |
Backdrafts were publicized by the 1991 movie Backdraft, in which a serial arsonist in Chicago was using them as a means of assassinating conspirators in a scam.
In the film adaptation of Stephen Kings 1408', the protagonist Mike Enslin induces one as a last-ditch effort to kill the room.
The term is also used and is the title of a scene in the 2012 video game Root Double: Before Crime * After Days. | 7 | Physical Chemistry |
A biocathode is a cathode used in a microbial electrolysis cell during electromethanogenesis that utilizes microorganisms to catalyze the process of accepting electrons and protons from the anode. A biocathode is usually made of a cheap material, such as carbon or graphite, like the anode in the MEC. The microbe population that is placed on the biocathode must be able to pick up electrons from the electrode material (carbon or graphite) and convert those electrons to hydrogen. | 7 | Physical Chemistry |
The Oligomer Restriction technique was developed as a variation of the Restriction Fragment Length Polymorphism (RFLP) assay method, with the hope of avoiding the laborious Southern blotting step used in RFLP analysis. OR was conceived by Randall Saiki and Henry Erlich in the early 1980s, working at Cetus Corporation in Emeryville, California. It was patented in 1984 and published in 1985, having been applied to the genomic mutation responsible for Sickle Cell Anemia. OR was soon replaced by the more general technique of Allele Specific Oligonucleotide (ASO) probes. | 1 | Biochemistry |
* G. Gauglitz, A. Brecht, G. Kraus and W. Nahm. Sensor. Actuat. B-Chem. 11, 1993
* A. Jung. Anal. Bioanal. Chem. 372 1, 2002
* F. Gesellchen, B. Zimmermann, F. W. Herberg. Methods in Molecular Biology, 2005
* T. Nagel, E. Ehrentreich-Forster, M. Singh, et al. Sensors and Actuators B-Chemical 129 2, 2008
* P. Fechner, F. Pröll, M. Carlquist and G. Proll. Anal. Bioanal. Chem. Nov 1, 2008 | 7 | Physical Chemistry |
Missense mRNA is a messenger RNA bearing one or more mutated codons that yield polypeptides with an amino acid sequence different from the wild-type or naturally occurring polypeptide. Missense mRNA molecules are created when template DNA strands or the mRNA strands themselves undergo a missense mutation in which a protein coding sequence is mutated and an altered amino acid sequence is coded for. | 1 | Biochemistry |
The music video for glam metal band Cinderellas 1988 power ballad "Dont Know What You Got (Till Its Gone)" was filmed by the lake. | 2 | Environmental Chemistry |
In colloidal mixtures quintuple and sixtuple points have been described in violation of Gibbs phase rule but it is argued that in these systems the rule can be generalized to where accounts for additional parameters of interaction among the components like the diameter of one type of particle in relation to the diameter of the other particles in the solution. | 7 | Physical Chemistry |
A thermometric titration is one of a number of instrumental titration techniques where endpoints can be located accurately and precisely without a subjective interpretation on the part of the analyst as to their location. Enthalpy change is arguably the most fundamental and universal property of chemical reactions, so the observation of temperature change is a natural choice in monitoring their progress. It is not a new technique, with possibly the first recognizable thermometric titration method reported early in the 20th century (Bell and Cowell, 1913). In spite of its attractive features, and in spite of the considerable research that has been conducted in the field and a large body of applications that have been developed; it has been until now an under-utilized technique in the critical area of industrial process and quality control. Automated potentiometric titration systems have pre-dominated in this area since the 1970s. With the advent of cheap computers able to handle the powerful thermometric titration software, development has now reached the stage where easy to use automated thermometric titration systems can in many cases offer a superior alternative to potentiometric titrimetry. | 3 | Analytical Chemistry |
Although the nucleosome is a very stable protein-DNA complex, it is not static and has been shown to undergo a number of different structural re-arrangements including nucleosome sliding and DNA site exposure. Depending on the context, nucleosomes can inhibit or facilitate transcription factor binding. Nucleosome positions are controlled by three major contributions: First, the intrinsic binding affinity of the histone octamer depends on the DNA sequence. Second, the nucleosome can be displaced or recruited by the competitive or cooperative binding of other protein factors. Third, the nucleosome may be actively translocated by ATP-dependent remodeling complexes. | 1 | Biochemistry |
When the RNA transcript reaches 7 nucleotides long, transcription enters the elongation phase, the beginning of which is characterised by the collapsing of the DNA bubble and the ejection of TFIIB. This is thought to be because the nascent RNA clashes with the B linker helix when it is 6 bases long and upon further elongation to 12-13 bases it will clash with the B-reader and B-ribbon leading to dissociation. The DNA duplex also clashes with the B linker above the rudder (caused by rewinding of the DNA into a double helix). | 1 | Biochemistry |
For ketimines and aldimines, respectively, the five core atoms (CC=NX and C(H)C=NX, X = H or C) are coplanar. Planarity results from the sp-hybridization of the mutually double-bonded carbon and the nitrogen atoms. The C=N distance is 1.29-1.31 Å for nonconjugated imines and 1.35 Å for conjugated imines. By contrast, C-N distances in amines and nitriles are 1.47 and 1.16 Å, respectively. Rotation about the C=N bond is slow. Using NMR spectroscopy, both E- and Z-isomers of aldimines have been detected. Owing to steric effects, the E isomer is favored. | 0 | Organic Chemistry |
Starting with a zerovalent palladium species and a substrate containing a leaving group in the allylic position, the Tsuji–Trost reaction proceeds through the catalytic cycle outlined below.
First, the palladium coordinates to the alkene, forming a η -allyl-Pd Π complex. The next step is oxidative addition in which the leaving group is expelled with inversion of configuration and a η -allyl-Pd is created (also called ionization). The nucleophile then adds to the allyl group regenerating the η -allyl-Pd complex. At the completion of the reaction, the palladium detaches from the alkene and can start again in the catalytic cycle. | 0 | Organic Chemistry |
The development of the fluorocarbon industry coincided with World War II. Prior to that, fluorocarbons were prepared by reaction of fluorine with the hydrocarbon, i.e., direct fluorination. Because C-C bonds are readily cleaved by fluorine, direct fluorination mainly affords smaller perfluorocarbons, such as tetrafluoromethane, hexafluoroethane, and octafluoropropane. | 2 | Environmental Chemistry |
Metabolites are the substrates, intermediates and products of metabolism. Within the context of metabolomics, a metabolite is usually defined as any molecule less than 1.5 kDa in size. However, there are exceptions to this depending on the sample and detection method. For example, macromolecules such as lipoproteins and albumin are reliably detected in NMR-based metabolomics studies of blood plasma. In plant-based metabolomics, it is common to refer to "primary" and "secondary" metabolites. A primary metabolite is directly involved in the normal growth, development, and reproduction. A secondary metabolite is not directly involved in those processes, but usually has important ecological function. Examples include antibiotics and pigments. By contrast, in human-based metabolomics, it is more common to describe metabolites as being either endogenous (produced by the host organism) or exogenous. Metabolites of foreign substances such as drugs are termed xenometabolites.
The metabolome forms a large network of metabolic reactions, where outputs from one enzymatic chemical reaction are inputs to other chemical reactions. Such systems have been described as hypercycles. | 1 | Biochemistry |
Photocatalyst activity indicator inks are a recent advance in the visual demonstration of photocatalysis and the assessment of the activity of photocatalyst materials. They are inexpensive, easy to use and provide a very quick route to demonstrating the presence of a photocatalytic film, even under low levels of UV light. Unlike the photo-oxidative bleaching of methylene blue, they use the underlying semiconductor photocatalyst film to photoreduce the dye (D in figure 2), in the ink coating, to another (usually colourless) form, (D in figure 2) whilst simultaneously oxidising an easily oxidised organic species, a sacrificial electron donor (SED), such as glycerol, which is also present in the ink. The kinetics of reduction of the dye in a paii have been studied in great detail. Figure 2 illustrates the basic principles of operation of a paii when applied to a product that has a thin photocatalyst film coating. | 5 | Photochemistry |
TRH-stimulation testing however
continues to be useful for the differential diagnosis of secondary (pituitary disorder) and tertiary (hypothalamic disorder) hypothyroidism. Patients with these conditions
appear to have physiologically inactive TSH in their circulation that is recognized by
TSH assays to a degree such that they may yield misleading, "euthyroid" TSH
results. Use and Interpretation:
• Helpful in diagnosis in patients with confusing TFTs. In primary hyperthyroidism
TSH are low and TRH administration induces little or no change in TSH levels
• In hypothyroidism due to end organ failure, administration of TRH produces a
prompt increase in TSH
• In hypothyroidism due to pituitary disease (secondary hypothyroidism) administration of TRH does not produce
an increase in TSH
• In hypothyroidism due to hypothalamic disease (tertiary hypothyroidism), administration of TRH produces a
delayed (60–120 minutes, rather than 15–30 minutes) increase in TSH | 1 | Biochemistry |
Because carbon is more electronegative than magnesium, the carbon attached to magnesium acts as a nucleophile and attacks the electrophilic carbon atom in the polar bond of a carbonyl group. The addition of the Grignard reagent to the carbonyl group typically proceeds through a six-membered ring transition state, as shown below.
Based on the detection of radical coupling side products, an alternative single electron transfer (SET) mechanism that involves the initial formation of a ketyl radical intermediate has also been proposed. A recent computational study suggests that the operative mechanism (polar vs. radical) is substrate-dependent, with the reduction potential of the carbonyl compound serving as a key parameter. | 0 | Organic Chemistry |
Regardless of the definition of the isotopic ratio, the isotopic composition of substrate and product are expressed as
where is a standard isotopic ration. Here, definition 3 of isotopic ratio has been used, however, any of the three definitions of isotopic ratio can equally be used. | 7 | Physical Chemistry |
Cool roofs combine high solar reflectance with high infrared emittance, thereby simultaneously reducing heat gain from the sun and increasing heat removal through radiation. Radiative cooling thus offers potential for passive cooling for residential and commercial buildings. Traditional building surfaces, such as paint coatings, brick and concrete have high emittances of up to 0.96. They radiate heat into the sky to passively cool buildings at night. If made sufficiently reflective to sunlight, these materials can also achieve radiative cooling during the day.
The most common radiative coolers found on buildings are white cool-roof paint coatings, which have solar reflectances of up to 0.94, and thermal emittances of up to 0.96. The solar reflectance of the paints arises from optical scattering by the dielectric pigments embedded in the polymer paint resin, while the thermal emittance arises from the polymer resin. However, because typical white pigments like titanium dioxide and zinc oxide absorb ultraviolet radiation, the solar reflectances of paints based on such pigments do not exceed 0.95.
In 2014, researchers developed the first daytime radiative cooler using a multi-layer thermal photonic structure that selectively emits long wavelength infrared radiation into space, and can achieve 5 °C sub-ambient cooling under direct sunlight. Later researchers developed paintable porous polymer coatings, whose pores scatter sunlight to give solar reflectance of 0.96-0.99 and thermal emittance of 0.97. In experiments under direct sunlight, the coatings achieve 6 °C sub-ambient temperatures and cooling powers of 96 W/m.
Other notable radiative cooling strategies include dielectric films on metal mirrors, and polymer or polymer composites on silver or aluminum films. Silvered polymer films with solar reflectances of 0.97 and thermal emittance of 0.96, which remain 11 °C cooler than commercial white paints under the mid-summer sun, were reported in 2015. Researchers explored designs with dielectric silicon dioxide or silicon carbide particles embedded in polymers that are translucent in the solar wavelengths and emissive in the infrared. In 2017, an example of this design with resonant polar silica microspheres randomly embedded in a polymeric matrix, was reported. The material is translucent to sunlight and has infrared emissivity of 0.93 in the infrared atmospheric transmission window. When backed with silver coating, the material achieved a midday radiative cooling power of 93 W/m under direct sunshine along with high-throughput, economical roll-to-roll manufacturing. | 7 | Physical Chemistry |
The specific protein glomalin has not yet been isolated and described. What has been described is an extraction process involving heat and citrate, producing a mixture containing a substance that is reactive to a monoclonal antibody Mab32B11 raised against crushed AM fungi spores. The substance is then provisionally named "glomalin". As many laboratories do not have the equipment to perform an antibody-based isolation (ELISA), a crude mixture called glomalin-related soil proteins (GRSP) is used to refer to the extract portion reactive to the Bradford protein assay. There is significant confusion between the ideal glomalin protein, the antibody-reactive extract portion termed "glomalin", and GRSP.
"Glomalin" was first detected by the Mab32B11 ELISA assay in 1987. According to the scientist that proposed the hypothetical protein, Sarah F. Wright, it eluded extraction until 1996 because "It requires an unusual effort to dislodge glomalin for study: a bath in citrate combined with heating at 250 °F (121 °C) for at least an hour.... No other soil glue found to date required anything as drastic as this." However, using advanced analytical methods in 2010, the citrate-heating extraction procedure for GRSP was proven to co-extract humic substances, so it is still not clear if this "glue effect" comes from glomalin or the other substances that are co-extracted using that method. | 9 | Geochemistry |
Because of the equivalences between many properties and derivatives within thermodynamics (e.g., see Maxwell Relations), there are many formulations of the thermal pressure coefficient, which are equally valid, leading to distinct yet correct interpretations of its meaning.
Some formulations for the thermal pressure coefficient include:
Where is the volume thermal expansion, the isothermal bulk modulus, the Grüneisen parameter, the compressibility and the constant-volume heat capacity.
Details of the calculation: | 7 | Physical Chemistry |
Sinker EDM, also called ram EDM, cavity type EDM or volume EDM, consists of an electrode and workpiece submerged in an insulating liquid such as, more typically, oil or, less frequently, other dielectric fluids. The electrode and workpiece are connected to a suitable power supply. The power supply generates an electrical potential between the two parts. As the electrode approaches the workpiece, dielectric breakdown occurs in the fluid, forming a plasma channel, and a small spark jumps.
These sparks usually strike one at a time, because it is very unlikely that different locations in the inter-electrode space have the identical local electrical characteristics which would enable a spark to occur simultaneously in all such locations. These sparks happen in huge numbers at seemingly random locations between the electrode and the workpiece. As the base metal is eroded, and the spark gap subsequently increased, the electrode is lowered automatically by the machine so that the process can continue uninterrupted. Several hundred thousand sparks occur per second, with the actual duty cycle carefully controlled by the setup parameters. These controlling cycles are sometimes known as "on time" and "off time", which are more formally defined in the literature.
The on time setting determines the length or duration of the spark. Hence, a longer on time produces a deeper cavity from each spark, creating a rougher finish on the workpiece. The reverse is true for a shorter on time. Off time is the period of time between sparks. Although not directly affecting the machining of the part, the off time allows the flushing of dielectric fluid through a nozzle to clean out the eroded debris. Insufficient debris removal can cause repeated strikes in the same location which can lead to a short circuit. Modern controllers monitor the characteristics of the arcs and can alter parameters in microseconds to compensate. The typical part geometry is a complex 3D shape, often with small or odd shaped angles. Vertical, orbital, vectorial, directional, helical, conical, rotational, spin, and indexing machining cycles are also used. | 8 | Metallurgy |
In particle physics, deep inelastic scattering is the name given to a process used to probe the insides of hadrons (particularly the baryons, such as protons and neutrons), using electrons, muons and neutrinos. It was first attempted in the 1960s and 1970s and provided the first convincing evidence of the reality of quarks, which up until that point had been considered by many to be a purely mathematical phenomenon. It is an extension of Rutherford scattering to much higher energies of the scattering particle and thus to much finer resolution of the components of the nuclei.
Henry Way Kendall, Jerome Isaac Friedman and Richard E. Taylor were joint recipients of the Nobel Prize of 1990 "for their pioneering investigations concerning deep inelastic scattering of electrons on protons and bound neutrons, which have been of essential importance for the development of the quark model in particle physics." | 7 | Physical Chemistry |
The surface advances normal to itself without the necessity of a stepwise growth mechanism. This means that in the presence of a sufficient thermodynamic driving force, every element of surface is capable of a continuous change contributing to the advancement of the interface. For a sharp or discontinuous surface, this continuous change may be more or less uniform over large areas for each successive new layer. For a more diffuse surface, a continuous growth mechanism may require changes over several successive layers simultaneously.
Non-uniform lateral growth is a geometrical motion of steps—as opposed to motion of the entire surface normal to itself. Alternatively, uniform normal growth is based on the time sequence of an element of surface. In this mode, there is no motion or change except when a step passes via a continual change. The prediction of which mechanism will be operative under any set of given conditions is fundamental to the understanding of crystal growth. Two criteria have been used to make this prediction:
Whether or not the surface is diffuse: a diffuse surface is one in which the change from one phase to another is continuous, occurring over several atomic planes. This is in contrast to a sharp surface for which the major change in property (e.g. density or composition) is discontinuous, and is generally confined to a depth of one interplanar distance.
Whether or not the surface is singular: a singular surface is one in which the surface tension as a function of orientation has a pointed minimum. Growth of singular surfaces is known to requires steps, whereas it is generally held that non-singular surfaces can continuously advance normal to themselves. | 3 | Analytical Chemistry |
Deoxynucleotides (dNTPs) may bind Mg ions and thus affect the concentration of free magnesium ions in the reaction. In addition, excessive amounts of dNTPs can increase the error rate of DNA polymerase and even inhibit the reaction. An imbalance in the proportion of the four dNTPs can result in misincorporation into the newly formed DNA strand and contribute to a decrease in the fidelity of DNA polymerase. | 1 | Biochemistry |
The enthalpy of a chemical system is essentially its energy. The enthalpy change ΔH for a reaction is equal to the heat q transferred out of (or into) a closed system at constant pressure without in- or output of electrical energy. Heat production or absorption in a chemical reaction is measured using calorimetry, e.g. with a bomb calorimeter. One common laboratory instrument is the reaction calorimeter, where the heat flow from or into the reaction vessel is monitored. The heat release and corresponding energy change, Δ, of a combustion reaction can be measured particularly accurately.
The measured heat energy released in an exothermic reaction is converted to ΔH⚬ in Joule per mole (formerly cal/mol). The standard enthalpy change ΔH⚬ is essentially the enthalpy change when the stoichiometric coefficients in the reaction are considered as the amounts of reactants and products (in mole); usually, the initial and final temperature is assumed to be 25 °C. For gas-phase reactions, ΔH⚬ values are related to bond energies to a good approximation by:
:Δ⚬ = total bond energy of reactants − total bond energy of products
In an exothermic reaction, by definition, the enthalpy change has a negative value:
:Δ = H - H < 0
where a larger value (the higher energy of the reactants) is subtracted from a smaller value (the lower energy of the products). For example, when hydrogen burns:
:2H (g) + O (g) → 2HO (g)
:Δ⚬ = −483.6 kJ/mol | 7 | Physical Chemistry |
Ionochromism is the process of reacting an ionochromic material with a charged species, or a positively or negatively charged ion. Materials that have ionochromic properties exhibit reversible color change, where the absence of a stimulus such as an ionic species can result in the compound changing to its original color.
Various ionic color changing mechanisms that are used in chromic processes can be used in ionochromism, including:
# Halochromism
# Acidochromism
# Metallochromism | 3 | Analytical Chemistry |
Monoclonal antibodies used for autoimmune diseases include infliximab and adalimumab, which are effective in rheumatoid arthritis, Crohn's disease, ulcerative colitis and ankylosing spondylitis by their ability to bind to and inhibit TNF-α. Basiliximab and daclizumab inhibit IL-2 on activated T cells and thereby help prevent acute rejection of kidney transplants. Omalizumab inhibits human immunoglobulin E (IgE) and is useful in treating moderate-to-severe allergic asthma. | 1 | Biochemistry |
Monoclonal antibodies are more expensive to manufacture than small molecules due to the complex processes involved and the general size of the molecules, all in addition to the enormous research and development costs involved in bringing a new chemical entity to patients. They are priced to enable manufacturers to recoup the typically large investment costs, and where there are no price controls, such as the United States, prices can be higher if they provide great value. Seven University of Pittsburgh researchers concluded, "The annual price of mAb therapies is about $100,000 higher in oncology and hematology than in other disease states", comparing them on a per patient basis, to those for cardiovascular or metabolic disorders, immunology, infectious diseases, allergy, and ophthalmology. | 1 | Biochemistry |
Faraday concluded after several experiments on electric current in a non-spontaneous process that the mass of the products yielded on the electrodes was proportional to the value of current supplied to the cell, the length of time the current existed, and the molar mass of the substance analyzed. In other words, the amount of a substance deposited on each electrode of an electrolytic cell is directly proportional to the quantity of electricity passed through the cell.
Below is a simplified equation of Faraday's first law:
where
:m is the mass of the substance produced at the electrode (in grams),
:Q is the total electric charge that passed through the solution (in coulombs),
:n is the valence number of the substance as an ion in solution (electrons per ion),
:M is the molar mass of the substance (in grams per mole). | 7 | Physical Chemistry |
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