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*This test is done to ascertain the nature of fluid in the vagina during pregnancy especially when premature rupture of membranes (PROM) is suspect. This test involves putting a drop of fluid obtained from the vagina onto paper strips containing nitrazine dye. The strips change color depending on the pH of the fluid. The strips will turn blue if the pH is greater than 6.0. A blue strip means it's more likely the membranes have ruptured.
This test, however, can produce false positives. If blood gets in the sample or if there is an infection present, the pH of the vaginal fluid may be higher than normal. Semen also has a higher pH, so recent vaginal intercourse can produce a false reading.
* To perform a fecal pH test for diagnosing intestinal infections or other digestive problems
* In civil engineering, to determine the carbonatation spread in concrete structures and therefore assess the state of the rebar's passivation film. | 3 | Analytical Chemistry |
*If are the solutions for a particular value of , then solutions for other values of are obtained from the following integro-differential equations
* For conservative case, this integral property reduces to
*If the abbreviations for brevity are introduced, then we have a relation stating In the conservative, this reduces to
*If the characteristic function is , where are two constants, then we have .
*For conservative case, the solutions are not unique. If are solutions of the original equation, then so are these two functions , where is an arbitrary constant. | 7 | Physical Chemistry |
A covalent bond joining atoms in an organic molecule consists of a group of two electrons. Such a group is referred to as an electron pair. Reactions in organic chemistry proceed through the sequential breaking and formation of such bonds. Organic chemists recognize two processes for the breaking of a chemical bond. These processes are known as homolytic cleavage and heterolytic cleavage. | 0 | Organic Chemistry |
Koded membranes are described by the construct and the concentration of FSL (in μg/mL) used to create them. For example, kodecytes created with a 100 μg/mL solution of FSL-A would be termed A100 kodecytes. If multiple FSL constructs were used then the definition is expanded accordingly, e.g. A100+B300 kodecytes are created with a solution containing 100 μg/mL solution of FSL-A and 300 μg/mL solution of FSL-B. The "+" symbol is used to separate the construct mixes, e.g. A100+B300. If FSL concentrations are constant then the μg/mL component of the terminology can be dropped, e.g. A kodecytes. Alternatively unrelated constructs such as FSL-A and FSL-biotin will create A+biotin kodecytes, etc. If different cells are used in the same study then inclusion of the cell type into the name is recommended, e.g. RBC A100 kodecytes vs WBC A100 kodecytes, or platelet A100 kodecytes, etc. | 1 | Biochemistry |
The Riemschneider thiocarbamate synthesis for aromatic compounds does not work efficiently for ortho-substituted compounds such as ortho-carboxy, ortho-methoxy or ortho-nitro derivative compounds. The reaction is also not as efficient for compounds that are sensitive to concentrated acid, such as thiocyanophenols. The reaction works well for other compounds. Various thiocyanate compounds underwent the Riemschneider synthesis to form thiocarbamates, and all had melting points similar to the predicted value. | 0 | Organic Chemistry |
Molten urea decomposes into ammonium cyanate at about 152 °C, and into ammonia and isocyanic acid above 160 °C:
Heating above 160 °C yields biuret and triuret via reaction with isocyanic acid:
At higher temperatures it converts to a range of condensation products, including cyanuric acid , guanidine , and melamine.
In aqueous solution, urea slowly equilibrates with ammonium cyanate. This hydrolysis cogenerates isocyanic acid, which can carbamylate proteins, in particular the N-terminal amino group, the side chain amino of lysine, and to a lesser extent the side chains of arginine and cysteine. Each carbamylation event adds 43 daltons to the mass of the protein, which can be observed in protein mass spectrometery. For this reason, pure urea solutions should be freshly prepared and used, as aged solutions may develop a significant concentration of cyanate (20 mM in 8 M urea). Dissolving urea in ultrapure water followed by removing ions (i.e. cyanate) with a mixed-bed ion-exchange resin and storing that solution at 4 °C is a recommended preparation procedure. However, cyanate will build back up to significant levels within a few days. Alternatively, adding 25–50 mM ammonium chloride to a concentrated urea solution decreases formation of cyanate because of the common ion effect. | 0 | Organic Chemistry |
Exposure assessment is a branch of environmental science and occupational hygiene that focuses on the processes that take place at the interface between the environment containing the contaminant of interest and the organism being considered. These are the final steps in the path to release an environmental contaminant, through transport to its effect in a biological system. It tries to measure how much of a contaminant can be absorbed by an exposed target organism, in what form, at what rate and how much of the absorbed amount is actually available to produce a biological effect. Although the same general concepts apply to other organisms, the overwhelming majority of applications of exposure assessment are concerned with human health, making it an important tool in public health. | 2 | Environmental Chemistry |
Two kinds of lithium–halogen exchange can be considered: reactions involving organolithium compounds and reactions involving lithium metal. Commercial organolithium compounds are produced by the heterogeneous (slurry) reaction of lithium with organic bromides and chlorides:
: 2 Li + R−X → LiX + R−Li
Often the lithium halide remains in the soluble product.
Most of this article is about the homogeneous (one-phase) reaction of preformed organolithium compounds:
: R−Li + R′−X → R−X + R′−Li
Butyllithium is commonly used. Gilman and Wittig independently discovered this method in the late 1930s. It is not a salt metathesis reaction, as no salt is produced.
Lithium–halogen exchange is frequently used to prepare vinyl-, aryl- and primary alkyllithium reagents. Vinyl halides usually undergo lithium–halogen exchange with retention of the stereochemistry of the double bond. The presence of alkoxyl or related chelating groups accelerates lithium–halogen exchange. Lithium halogen exchange is typically a fast reaction. It is usually faster than nucleophilic addition and can sometimes exceed the rate of proton transfer.
Exchange rates usually follow the trend I > Br > Cl. Alkyl- and arylfluoride are generally unreactive toward organolithium reagents. Lithium–halogen exchange is kinetically controlled, and the rate of exchange is primarily influenced by the stabilities of the carbanion intermediates (sp > sp > sp) of the organolithium reagents. | 0 | Organic Chemistry |
Bacteriorhodopsin molecule is purple and is most efficient at absorbing green light (in the wavelength range 500-650 nm). In the native membrane, the protein has a maximum absorbance at 553 nm, however addition of detergent disrupts the trimeric form, leading a loss of exciton coupling between the chromophores, and the monomeric form consequently has an absorption maximum of 568 nm.
Bacteriorhodopsin has a broad excitation spectrum. For a detection wavelength between 700 and 800 nm, it has an appreciable detected emission for excitation wavelengths between 470 nm and 650 nm (with a peak at 570 nm).
When pumped at 633 nm, the emission spectrum has appreciable intensity between 650 nm and 850 nm. | 5 | Photochemistry |
By the first law of thermodynamics, the excitation driving electron generation in both photo- and phonovoltaic cells, i.e., the photon or phonon, must have more energy than the semiconductor band gap. For a PV cell, many materials are available with a band gap () well matched to the solar photon spectrum, like Silicon or Gallium Arsenide. For a pV cell, however, no current semiconducting materials have a band gap smaller than the energy of their most energetic (optical) phonon modes (). Thus, novel materials are required with both energetic optical phonon modes ( meV, e.g., graphene, diamond, or boron nitride) and a small band gap (, e.g., graphene).
By the second law of thermodynamics, the excitation must be "hotter" than the cell for power generation to occur. In a PV, the light comes from an outside source, for example, the sun, which is nearly 6000 kelvins, whereas the PV is around 300 kelvins. Thus, the second law is satisfied and energy conversion is possible. However, the crystal vibrations driving power generation in a pV are intrinsic to the material itself. As such, they can not be imported from an outside source like the sun, but must instead be excited by some other process until they are hotter than the cell. The temperature of the optical phonon population is calculated by comparing the number of optical phonon to the number expected at a given temperature, which comes from the Bose–Einstein statistics. | 7 | Physical Chemistry |
In chemistry and materials science, ultrahydrophobic (or superhydrophobic) surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet on an ultrahydrophobic material exceed 150°. This is also referred to as the lotus effect, after the superhydrophobic leaves of the lotus plant. A droplet striking these kinds of surfaces can fully rebound like an elastic ball. Interactions of bouncing drops can be further reduced using special superhydrophobic surfaces that promote symmetry breaking, pancake bouncing or waterbowl bouncing. | 6 | Supramolecular Chemistry |
Binding to the solid phase may be achieved by column chromatography whereby the solid medium is packed onto a column, the initial mixture run through the column to allow settling, a wash buffer run through the column and the elution buffer subsequently applied to the column and collected. These steps are usually done at ambient pressure. Alternatively, binding may be achieved using a batch treatment, for example, by adding the initial mixture to the solid phase in a vessel, mixing, separating the solid phase, removing the liquid phase, washing, re-centrifuging, adding the elution buffer, re-centrifuging and removing the elute.
Sometimes a hybrid method is employed such that the binding is done by the batch method, but the solid phase with the target molecule bound is packed onto a column and washing and elution are done on the column.
The ligands used in affinity chromatography are obtained from both organic and inorganic sources. Examples of biological sources are serum proteins, lectins and antibodies. Inorganic sources are moronic acid, metal chelates and triazine dyes.
A third method, expanded bed absorption, which combines the advantages of the two methods mentioned above, has also been developed. The solid phase particles are placed in a column where liquid phase is pumped in from the bottom and exits at the top. The gravity of the particles ensure that the solid phase does not exit the column with the liquid phase.
Affinity columns can be eluted by changing salt concentrations, pH, pI, charge and ionic strength directly or through a gradient to resolve the particles of interest.
More recently, setups employing more than one column in series have been developed. The advantage compared to single column setups is that the resin material can be fully loaded since non-binding product is directly passed on to a consecutive column with fresh column material. These chromatographic processes are known as periodic counter-current chromatography (PCC). The resin costs per amount of produced product can thus be drastically reduced. Since one column can always be eluted and regenerated while the other column is loaded, already two columns are sufficient to make full use of the advantages. Additional columns can give additional flexibility for elution and regeneration times, at the cost of additional equipment and resin costs. | 3 | Analytical Chemistry |
Recently, the Woodward–Hoffmann rules have been reinterpreted using conceptual density functional theory (DFT). The key to the analysis is the dual descriptor function, proposed by Christophe Morell, André Grand and Alejandro Toro-Labbé , the second derivative of the electron density with respect to the number of electrons . This response function is important as the reaction of two components A and B involving a transfer of electrons will depend on the responsiveness of the electron density to electron donation or acceptance, i.e. the derivative of the Fukui function . In fact, from a simplistic viewpoint, the dual descriptor function gives a readout on the electrophilicity or nucleophilicity of the various regions of the molecule. For , the region is electrophilic, and for , the region is nucleophilic. Using the frontier molecular orbital assumption and a finite difference approximation of the Fukui function, one may write the dual descriptor as
This makes intuitive sense as if a region is better at accepting electrons than donating, then the LUMO must dominate and dual descriptor function will be positive. Conversely, if a region is better at donating electrons then the HOMO term will dominate and the descriptor will be negative. Notice that although the concept of phase and orbitals are replaced simply by the notion of electron density, this function still takes both positive and negative values.
The Woodward–Hoffmann rules are reinterpreted using this formulation by matching favorable interactions between regions of electron density for which the dual descriptor has opposite signs. This is equivalent to maximizing predicted favorable interactions and minimizing repulsive interactions. For the case of a [4+2] cycloaddition, a simplified schematic of the reactants with the dual descriptor function colored (red=positive, blue=negative) is shown in the optimal supra/supra configuration to the left. This method correctly predicts the WH rules for the major classes of pericyclic reactions. | 7 | Physical Chemistry |
Microorganisms can be used as indicators of aquatic or terrestrial ecosystem health. Found in large quantities, microorganisms are easier to sample than other organisms. Some microorganisms will produce new proteins, called stress proteins, when exposed to contaminants such as cadmium and benzene. These stress proteins can be used as an early warning system to detect changes in levels of pollution. | 2 | Environmental Chemistry |
Trifluoromethanesulfonic anhydride, also known as triflic anhydride, is the chemical compound with the formula (CFSO)O. It is the acid anhydride derived from triflic acid. This compound is a strong electrophile, useful for introducing the triflyl group, CFSO. Abbreviated TfO, triflic anhydride is the acid anhydride of the superacid triflic acid, CFSOOH. | 0 | Organic Chemistry |
In atmospheric sciences, one often refers to the optical depth of the atmosphere as corresponding to the vertical path from Earths surface to outer space; at other times the optical path is from the observers altitude to outer space. The optical depth for a slant path is , where τ′ refers to a vertical path, m is called the relative airmass, and for a plane-parallel atmosphere it is determined as where θ is the zenith angle corresponding to the given path. Therefore,The optical depth of the atmosphere can be divided into several components, ascribed to Rayleigh scattering, aerosols, and gaseous absorption. The optical depth of the atmosphere can be measured with a Sun photometer.
The optical depth with respect to the height within the atmosphere is given by and it follows that the total atmospheric optical depth is given by
In both equations:
* k is the absorption coefficient
* w is the mixing ratio
* ρ is the density of air at sea level
* H is the scale height of the atmosphere
* z is the height in question
The optical depth of a plane parallel cloud layer is given bywhere:
* Q is the extinction efficiency
* L is the liquid water path
* H is the geometrical thickness
* N is the concentration of droplets
* ρ is the density of liquid water
So, with a fixed depth and total liquid water path, . | 7 | Physical Chemistry |
Synergetics is an interdisciplinary science explaining the formation and self-organization of patterns and structures in open systems far from thermodynamic equilibrium. It is founded by Hermann Haken, inspired by the laser theory. Hakens interpretation of the laser principles as self-organization of non-equilibrium systems paved the way at the end of the 1960s to the development of synergetics. One of his successful popular books is Erfolgsgeheimnisse der Natur, translated into English as The Science of Structure: Synergetics'.
Self-organization requires a macroscopic system, consisting of many nonlinearly interacting subsystems. Depending on the external control parameters (environment, energy fluxes) self-organization takes place. | 7 | Physical Chemistry |
In macromolecular crystallography, the term additive is used instead of adjutant. An additive can either interact directly with the protein, and become incorporated at a fixed position in the resulting crystal or have a role within the disordered solvent, that in protein crystals constitute roughly 50% of the lattice volume.
Polyethylene glycols of various molecular weights and high-ionic strength salts such as ammonium sulfate and sodium citrate that induce protein precipitation when used in high concentrations are classified as precipitants, while certain other salts such as zinc sulfate or calcium sulfate that may cause a protein to precipitate vigorously even when used in small amounts are considered adjutants. Crystallization adjutants are considered additives when they are effective at relatively low concentrations.
The distinction between buffers and adjutants is also fuzzy. Buffer molecules can become part of the lattice (for example HEPES in becomes incorporated in crystals of human neutrophil collagenase) but their main use is to maintain the rather precise pH requirements for crystallization that many proteins have. Commonly used buffers such as citrate have a high ionic strength and at the typical buffer concentrations they also act as precipitants. Various species such as Ca and Zn are a biological requirement for certain proteins to fold correctly and certain co-factors are needed to maintain a well defined conformation. Certain strategies, like replacing precipitants and buffers with others intended to have a similar effect, have been used to differentiate between the roles played in protein crystallization by the various components in the crystallization solution. | 3 | Analytical Chemistry |
* P. aeruginosa also uses 2-heptyl-3-hydroxy-4-quinolone (PQS) for quorum sensing. This molecule is noteworthy because it does not belong to the homoserine lactone class of autoinducers. PQS is believed to provide an additional regulatory link between the Las and Rhl circuits involved in virulence and infection.
* Agrobacterium tumefaciens is a plant pathogen that induces tumors on susceptible hosts. Infection by A. tumefaciens involves the transfer of an oncogenic plasmid from the bacterium to the host cell nucleus, while quorum sensing controls the conjugal transfer of plasmids between bacteria. Conjugation, on the other hand, requires the HSL autoinducer, N-(3-oxooctanoyl)-homoserine lactone.
* Erwinia carotovora is another plant pathogen that causes soft-rot disease. These bacteria secrete cellulases and pectinases, which are enzymes that degrade plant cell walls. ExpI/ExpR are LuxI/LuxR homologs in E. carotovora believed to control secretion of these enzymes only when a high enough local cell density is achieved. The autoinducer involved in quorum sensing in E. carotovora is N-(3-oxohexanoyl)-L-homoserine lactone. | 1 | Biochemistry |
Metabolomics is the scientific study of chemical processes involving metabolites, the small molecule substrates, intermediates, and products of cell metabolism. Specifically, metabolomics is the "systematic study of the unique chemical fingerprints that specific cellular processes leave behind", the study of their small-molecule metabolite profiles. The metabolome represents the complete set of metabolites in a biological cell, tissue, organ, or organism, which are the end products of cellular processes. Messenger RNA (mRNA), gene expression data, and proteomic analyses reveal the set of gene products being produced in the cell, data that represents one aspect of cellular function. Conversely, metabolic profiling can give an instantaneous snapshot of the physiology of that cell, and thus, metabolomics provides a direct "functional readout of the physiological state" of an organism. There are indeed quantifiable correlations between the metabolome and the other cellular ensembles (genome, transcriptome, proteome, and lipidome), which can be used to predict metabolite abundances in biological samples from, for example mRNA abundances. One of the ultimate challenges of systems biology is to integrate metabolomics with all other -omics information to provide a better understanding of cellular biology. | 1 | Biochemistry |
Agriculture-
Gravity separation tables are used for the removal of impurities, admixture, insect damage and immature kernels from the following examples: wheat, barley, oilseed rape, peas, beans, cocoa beans, linseed. They can be used to separate and standardize coffee beans, cocoa beans, peanuts, corn, peas, rice, wheat, sesame and other food grains.
The gravity separator separates products of same size but with difference in specific weight. It has a vibrating rectangular deck, which makes it easy for the product to travel a longer distance, ensuring improved quality of the end product. The pressurized air in the deck enables the material to split according to its specific weight. As a result, the heavier particles travel to the higher level while the lighter particles travel to the lower level of the deck. It comes with easily adjustable air fans to control the volume of air distribution at different areas of the vibrating deck to meet the air supply needs of the deck. The table inclination, speed of eccentric motion and the feed rate can be precisely adjusted to achieve smooth operation of the machine. | 3 | Analytical Chemistry |
In chemistry the descriptor vicinal (from Latin vicinus = neighbor), abbreviated vic, is a descriptor that identifies two functional groups as bonded to two adjacent carbon atoms (i.e., in a 1,2-relationship). It may arise from vicinal difunctionalization. | 4 | Stereochemistry |
The nitrate ion can easily be identified by heating copper turnings along with concentrated sulfuric acid. Effervescence of a brown, pungent gas is observed which turns moist blue litmus paper red.
Here sulfuric acid reacts with the nitrate ion to form nitric acid. Nitric acid then reacts with the copper turnings to form nitric oxide. Nitric oxide is thus oxidised to nitrogen dioxide. | 3 | Analytical Chemistry |
Researchers from Britain and Switzerland have previously found antibodies that work in Group 1 influenza A viruses or against most Group 2 viruses (CR8020), but not against both.
This team developed a method using single-cell screening to test very large numbers of human plasma cells, to increase their odds of finding an antibody even if it was extremely rare. When they identified FI6, they injected it into mice and ferrets and found that it protected the animals against infection by either a Group 1 or Group 2 influenza A virus.
Scientists screened 104,000 peripheral-blood plasma cells from eight recently infected or vaccinated donors for antibodies that recognize each of three diverse influenza strains: H1N1 (swine-origin) and H5N1 and H7N7 (highly pathogenic avian influenzas.) From one donor, they isolated four plasma cells that produced an identical antibody, which they called FI6. This antibody binds all 16 HA subtypes, neutralizes infection, and protects mice and ferrets from lethal infection. The most broadly reactive antibodies that had previously been discovered recognized either one group of HA subtypes or the other, highlighting how remarkable FI6 is in its ability to target the gamut of influenza subtypes. | 1 | Biochemistry |
Mesophillic Thermoproteota were recently placed into a new phylum of Archaea called the Nitrososphaerota (formerly Thaumarchaeota). However there are very few molecular markers that can distinguish this group of archaea from the phylum Thermoproteota (formerly Crenarchaeota). A detailed phylogenetic study using the CSI approach was conducted to distinguish these phyla in molecular terms. 6 CSIs were uniquely found in various Nitrososphaerota, namely Cenarchaeum symbiosum, Nitrosopumilus maritimus and a number of uncultured marine Thermoproteota. 3 CSIs were found that were commonly shared between species belonging to Nitrososphaerota and Thermoproteota. Additionally, a number of CSIs were found that are specific for different orders of Thermoproteota—3 CSIs for Sulfolobales, 5 CSIs for Thermoproteales, lastly 2 CSIs common for Sulfolobales and Desulfurococcales. The signatures described provide novel means for distinguishing Thermoproteota and Nitrososphaerota, additionally they could be used as a tool for the classification and identification of related species. | 1 | Biochemistry |
Establishing body axes is a critical step in animal development. During mouse embryonic development, Nodal, a transforming growth factor-beta superfamily ligand, is a key gene involved in patterning both the anterior-posterior axis and the left-right axis of the early embryo. The Nodal gene contains two enhancers: the Proximal Epiblast Enhancer (PEE) and the Asymmetric Enhancer (ASE). The PEE is upstream of the Nodal gene and drives Nodal expression in the portion of the primitive streak that will differentiate into the node (also referred to as the primitive node). The PEE turns on Nodal expression in response to a combination of Wnt signaling plus a second, unknown signal; thus, a member of the LEF/TCF transcription factor family likely binds to a TCF binding site in the cells in the node. Diffusion of Nodal away from the node forms a gradient which then patterns the extending anterior-posterior axis of the embryo. The ASE is an intronic enhancer bound by the fork head domain transcription factor Fox1. Early in development, Fox1-driven Nodal expression establishes the visceral endoderm. Later in development, Fox1 binding to the ASE drives Nodal expression on the left side of the lateral plate mesoderm, thus establishing left-right asymmetry necessary for asymmetric organ development in the mesoderm.
Establishing three germ layers during gastrulation is another critical step in animal development. Each of the three germ layers has unique patterns of gene expression that promote their differentiation and development. The endoderm is specified early in development by Gata4 expression, and Gata4 goes on to direct gut morphogenesis later. Gata4 expression is controlled in the early embryo by an intronic enhancer that binds another forkhead domain transcription factor, FoxA2. Initially the enhancer drives broad gene expression throughout the embryo, but the expression quickly becomes restricted to the endoderm, suggesting that other repressors may be involved in its restriction. Late in development, the same enhancer restricts expression to the tissues that will become the stomach and pancreas. An additional enhancer is responsible for maintaining Gata4 expression in the endoderm during the intermediate stages of gut development. | 1 | Biochemistry |
As the result of substrate effects producing preferred crystallite orientations, pronounced textures tend to occur in thin films. Modern technological devices to a large extent rely on polycrystalline thin films with thicknesses in the nanometer and micrometer ranges. This holds, for instance, for all microelectronic and most optoelectronic systems or sensoric and superconducting layers. Most thin film textures may be categorized as one of two different types: (1) for so-called fiber textures the orientation of a certain lattice plane is preferentially parallel to the substrate plane; (2) in biaxial textures the in-plane orientation of crystallites also tend to align with respect to the sample. The latter phenomenon is accordingly observed in nearly epitaxial growth processes, where certain crystallographic axes of crystals in the layer tend to align along a particular crystallographic orientation of the (single-crystal) substrate.
Tailoring the texture on demand has become an important task in thin film technology. In the case of oxide compounds intended for transparent conducting films or surface acoustic wave (SAW) devices, for instance, the polar axis should be aligned along the substrate normal. Another example is given by cables from high-temperature superconductors that are being developed as oxide multilayer systems deposited on metallic ribbons. The adjustment of the biaxial texture in YBaCuO layers turned out as the decisive prerequisite for achieving sufficiently large critical currents.
The degree of texture is often subjected to an evolution during thin film growth and the most pronounced textures are only obtained after the layer has achieved a certain thickness. Thin film growers thus require information about the texture profile or the texture gradient in order to optimize the deposition process. The determination of texture gradients by x-ray scattering, however, is not straightforward, because different depths of a specimen contribute to the signal. Techniques that allow for the adequate deconvolution of diffraction intensity were developed only recently. | 8 | Metallurgy |
Torsional strain is the resistance to bond twisting. In cyclic molecules, it is also called Pitzer strain.
Torsional strain occurs when atoms separated by three bonds are placed in an eclipsed conformation instead of the more stable staggered conformation. The barrier of rotation between staggered conformations of ethane is approximately 2.9 kcal mol. It was initially believed that the barrier to rotation was due to steric interactions between vicinal hydrogens, but the Van der Waals radius of hydrogen is too small for this to be the case. Recent research has shown that the staggered conformation may be more stable due to a hyperconjugative effect. Rotation away from the staggered conformation interrupts this stabilizing force.
More complex molecules, such as butane, have more than one possible staggered conformation. The anti conformation of butane is approximately 0.9 kcal mol (3.8 kJ mol) more stable than the gauche conformation. Both of these staggered conformations are much more stable than the eclipsed conformations. Instead of a hyperconjugative effect, such as that in ethane, the strain energy in butane is due to both steric interactions between methyl groups and angle strain caused by these interactions. | 4 | Stereochemistry |
Carborane acid consists of 11 boron atoms; each boron atom is bound to a chlorine atom. The chlorine atoms serve to enhance acidity and act as shields against attacks from the outside due to the steric hindrance they form around the cluster. The cluster, consisting of the 11 borons, 11 chlorines, and a single carbon atom, is paired with a hydrogen atom, bound to the carbon atom. The boron and carbon atoms are allowed to form six bonds due to boron's ability to form three-center, two-electron bonds.
Although the structure of the carborane acid differs greatly from conventional acids, both distribute charge and stability in a similar fashion. The carboranate anion distributes its charge by delocalizing the electrons throughout the 12 cage atoms. This was shown in a single crystal X-ray diffraction study revealing shortened bond lengths in the heterocyclic portion of the ring suggesting electronic delocalization.
The chlorinated carba-closo-dodecaborate anion is an outstandingly stable anion with what has previously been described as "substitutionally inert" B–Cl vertices. The descriptor closo indicates that the molecule is formally derived (by B-to-C replacement) from a borane of stoichiometry and charge [BH] (n = 12 for known carborane acids). The cagelike structure formed by the 11 boron atoms and 1 carbon atom allows the electrons to be highly delocalized through the 3D cage (the special stabilization of the carborane system has been termed "σ-aromaticity"), and the high energy required to disrupt the boron cluster portion of the molecule is what gives the anion its remarkable stability. Because the anion is extremely stable, it will not behave as a nucleophile toward the protonated substrate, while the acid itself is completely non-oxidizing, unlike the Lewis acidic components of many superacids like antimony pentafluoride. Hence, sensitive molecules like C can be protonated without decomposition. | 7 | Physical Chemistry |
Several studies have demonstrated the possibility to develop chemical cells inspired by biological models to produce molecular hydrogen, for example: Selvaggi et al. explored the possibility to use energy captured by the PSII, developing for that goal, an organic-inorganic hybrid system replacing the PSII protein complex by microspheres of TiO a photo-inducible compound. In order to get the hydrogen production, the TiO microspheres were covered with hydrogenases extracted from the marine thermophile Pyrococcus furiosus, in that way the energy of the light was captured by the TiO microspheres and used to generate protons and electrons from water with the subsequent production of 29 µmol de H hour.
The obtained results from immobilization of hydrogenases on the surface of electrodes have demonstrated the viability of incorporating these enzymes in electrochemical cells, due to their ability to produce gaseous hydrogen through a redox reaction. (Hallenbeck and Benemann). This opens the possibility of using biomimetic compounds in electrodes to generate hydrogen.
Until the present day several bio-mimetic compounds have been developed: Collman et al. produced ruthenium porphyrins, furthermore of the bio-mimetic compounds published by the research teams of Rauchfuss, Darensbourg and Pickett (in Artero and Fontecave) who developed bio-mimetic compounds of the [Fe] hydrogenase. More recently Manor and Rauchfuss presented a very interesting mimic compound based in the [NiFe] hydrogenase with bidirectional properties, this compound has the characteristic that it carries two borane protected cyanide ligands at the iron atom. Some works about bio-mimetic compounds of hydrogenases are summarized in table 1.
Table 1. Bio-mimetic compounds of hydrogenases
However, obtaining bio-mimetic compounds able to hydrogen production on an industrial scale still is elusive. For that reason, the research of this topic is a hot spot in science which has taken the efforts of researchers around the world. Recently a review of the works done in bio-mimetic compounds was published by Schilter et al.. Showing that some studies have got promising results in bio-mimetic compounds synthesized in laboratory. | 1 | Biochemistry |
n-BuLi exists as a cluster both in the solid state and in a solution. The tendency to aggregate is common for organolithium compounds. The aggregates are held together by delocalized covalent bonds between lithium and the terminal carbon of the butyl chain. In the case of n-BuLi, the clusters are tetrameric (in ether) or hexameric (in cyclohexane). The cluster is a distorted cubane-type cluster with Li and CHR groups at alternating vertices. An equivalent description describes the tetramer as a Li tetrahedron interpenetrated with a tetrahedron [CHR]. Bonding within the cluster is related to that used to describe diborane, but more complex since eight atoms are involved. Reflecting its electron-rich character, n-butyllithium is highly reactive toward Lewis acids.
Due to the large difference between the electronegativities of carbon (2.55) and lithium (0.98), the C−Li bond is highly polarized. The charge separation has been estimated to be 55–95%. For practical purposes, n-BuLi can often be considered to react as the butyl anion, n-Bu, and a lithium cation, Li. | 0 | Organic Chemistry |
Two classes of reaction centres are recognized. Type I, found in green-sulfur bacteria, Heliobacteria, and plant/cyanobacterial PS-I, use iron sulfur clusters as electron acceptors. Type II, found in chloroflexus, purple bacteria, and plant/cyanobacterial PS-II, use quinones. Not only do all members inside each class share common ancestry, but the two classes also, by means of common structure, appear related.
Cyanobacteria, the precursor to chloroplasts found in green plants, have both photosystems with both types of reaction centers. Combining the two systems allows for producing oxygen. | 5 | Photochemistry |
Meibom currently leads the laboratory for biological geochemistry at EPFL. Research performed in his laboratory is interdisciplinary in nature, at the interface between isotope geochemistry and biology. Active themes in the laboratory include the use of NanoSIMS to visualize and characterize the diagenesis of biogenic substrates, as well as the study of metabolic processes in symbiotic organisms (notably corals) and how these processes may be influenced by environmental stress, in particular climate change. | 9 | Geochemistry |
Firefly luciferase is the light-emitting enzyme responsible for the bioluminescence of fireflies and click beetles. The enzyme catalyses the oxidation of firefly luciferin, requiring oxygen and ATP. Because of the requirement of ATP, firefly luciferases have been used extensively in biotechnology. | 1 | Biochemistry |
Silver ions form alkene complexes. The binding is reversible, but sufficient to impede the elution of the alkene-containing analytes. | 3 | Analytical Chemistry |
Fumarate, produced from the purine nucleotide cycle, is an intermediate of TCA cycle and enters the mitochondria by converting into malate and utilizing the malate shuttle where it is converted into oxaloacetic acid (OAA). During exercise, OAA either enters into TCA cycle or converts into aspartate in the mitochondria.
As the purine nucleotide cycle produces ammonia (see below in ammonia synthesis), skeletal muscle needs to synthesize glutamate in a way that does not further increase ammonia, and as such the use of glutaminase to produce glutamate from glutamine would not be ideal. Also, plasma glutamine (released from the kidneys) requires active transport into the muscle cell (consuming ATP). Consequently, during exercise when the ATP reservoir is low (ADP>ATP), glutamate is produced from branch-chained amino acids (BCAAs) and α-ketoglutarate, as well as from alanine and α-ketoglutarate. Glutamate is then used to produce aspartate. The aspartate enters the purine nucleotide cycle, where it is used to convert IMP into S-AMP.
:BCAAs + α-Ketoglutarate ⇌ Glutamate + Branch-chain keto acids (BCKAs) (catalyzed by Branched-chain aminotransferases (BCAT))
:Alanine + α-Ketoglutarate ⇌ Pyruvate + Glutamate (catalyzed by alanine transaminase)
:Oxaloacetic acid + Glutamate ⇌ α-Ketoglutarate + Aspartate (catalyzed by aspartate aminotransferase)
When skeletal muscle is at rest (ADP | 1 | Biochemistry |
Phosphoinositide phospholipase C (PLC, EC 3.1.4.11, triphosphoinositide phosphodiesterase, phosphoinositidase C, 1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase, monophosphatidylinositol phosphodiesterase, phosphatidylinositol phospholipase C, PI-PLC, 1-phosphatidyl--myo-inositol-4,5-bisphosphate inositoltrisphosphohydrolase; systematic name 1-phosphatidyl-1-myo-inositol-4,5-bisphosphate inositoltrisphosphohydrolase) is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. These enzymes belong to a larger superfamily of Phospholipase C. Other families of phospholipase C enzymes have been identified in bacteria and trypanosomes. Phospholipases C are phosphodiesterases.
Phospholipase Cs participate in phosphatidylinositol 4,5-bisphosphate (PIP) metabolism and lipid signaling pathways in a calcium-dependent manner. At present, the family consists of six sub-families comprising a total of 13 separate isoforms that differ in their mode of activation, expression levels, catalytic regulation, cellular localization, membrane binding avidity and tissue distribution. All are capable of catalyzing the hydrolysis of PIP into two important second messenger molecules, which go on to alter cell responses such as proliferation, differentiation, apoptosis, cytoskeleton remodeling, vesicular trafficking, ion channel conductance, endocrine function and neurotransmission. | 1 | Biochemistry |
The relatively small number of atomic absorption lines (compared to atomic emission lines) and their narrow width (a few pm) make spectral overlap rare; there are only few examples known that an absorption line from one element will overlap with another. Molecular absorption, in contrast, is much broader, so that it is more likely that some molecular absorption band will overlap with an atomic line. This kind of absorption might be caused by un-dissociated molecules of concomitant elements of the sample or by flame gases. We have to distinguish between the spectra of di-atomic molecules, which exhibit a pronounced fine structure, and those of larger (usually tri-atomic) molecules that don't show such fine structure. Another source of background absorption, particularly in ET AAS, is scattering of the primary radiation at particles that are generated in the atomization stage, when the matrix could not be removed sufficiently in the pyrolysis stage.
All these phenomena, molecular absorption and radiation scattering, can result in artificially high absorption and an improperly high (erroneous) calculation for the concentration or mass of the analyte in the sample. There are several techniques available to correct for background absorption, and they are significantly different for LS AAS and HR-CS AAS. | 3 | Analytical Chemistry |
Fermentation is the main source of ethanol in the production of ethanol fuel. Common crops such as sugar cane, potato, cassava, and maize are fermented by yeast to produce ethanol which is further processed to become fuel. | 1 | Biochemistry |
The TTSI is used as a screening parameter for resistance to thyroid hormone due to mutations in the THRB gene, where it is elevated. It is also beneficial for assessing the severity of already confirmed thyroid hormone resistance, even on replacement therapy with L-T4, and for monitoring the pituitary response to substitution therapy with thyromimetics (e.g. TRIAC) in RTH Beta.
In autoimmune thyroiditis the TTSI is moderately elevated.
A large cohort study demonstrated TTSI to be strongly influenced by genetic factors. A variant of the TTSI that is not corrected for the upper limit of the FT4 reference range was shown to be significantly increased in offspring from long-lived siblings compared to their partners.
Conversely, an elevated set point of thyroid homeostasis, as quantified by the TT4RI, is associated to higher prevalence of metabolic syndrome and several harmonized criteria by the International Diabetes Federation, including triglyceride and HDL concentration and blood pressure.
In certain phenotypes of non-thyroidal illness syndrome, especially in cases with concomitant sepsis, the TTSI is reduced. This reflects a reduced set point of thyroid homeostasis, as also experimentally predicted in rodent models of inflammation and sepsis.
Negative correlation of the TTSI with the urinary excretion of certain phthalates suggests that endocrine disruptors may affect the central set point of thyroid homeostasis. | 1 | Biochemistry |
Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility (or in thermodynamics lexicon a lower exergy or higher entropy) than the original energy source. Sources of waste heat include all manner of human activities, natural systems, and all organisms, for example, incandescent light bulbs get hot, a refrigerator warms the room air, a building gets hot during peak hours, an internal combustion engine generates high-temperature exhaust gases, and electronic components get warm when in operation.
Instead of being "wasted" by release into the ambient environment, sometimes waste heat (or cold) can be used by another process (such as using hot engine coolant to heat a vehicle), or a portion of heat that would otherwise be wasted can be reused in the same process if make-up heat is added to the system (as with heat recovery ventilation in a building).
Thermal energy storage, which includes technologies both for short- and long-term retention of heat or cold, can create or improve the utility of waste heat (or cold). One example is waste heat from air conditioning machinery stored in a buffer tank to aid in night time heating. Another is seasonal thermal energy storage (STES) at a foundry in Sweden. The heat is stored in the bedrock surrounding a cluster of heat exchanger equipped boreholes, and is used for space heating in an adjacent factory as needed, even months later. An example of using STES to use natural waste heat is the Drake Landing Solar Community in Alberta, Canada, which, by using a cluster of boreholes in bedrock for interseasonal heat storage, obtains 97 percent of its year-round heat from solar thermal collectors on the garage roofs. Another STES application is storing winter cold underground, for summer air conditioning.
On a biological scale, all organisms reject waste heat as part of their metabolic processes, and will die if the ambient temperature is too high to allow this.
Anthropogenic waste heat can contribute to the urban heat island effect. The biggest point sources of waste heat originate from machines (such as electrical generators or industrial processes, such as steel or glass production) and heat loss through building envelopes. The burning of transport fuels is a major contribution to waste heat. | 7 | Physical Chemistry |
*[http://www.alittihad.ae/details.php?id=26368&y=2011&article=full Alittihad Newspaper]
*[http://www.alkhaleej.ae/portal/7ce19b8d-8888-4057-8d05-373ecb13d683.aspx Alkhaleej Newspaper]
*[https://archive.today/20130418015423/http://www.akhirlahza.sd/akhir/index.php?option=com_content&view=article&id=18360:----005--&catid=44:africa&Itemid=124 Akhir lahza Newspaper]
*[https://archive.today/20130221034709/http://www.alintibaha.net/portal/%D8%A7%D9%84%D9%85%D9%84%D9%81-%D8%A7%D9%84%D8%AB%D9%82%D8%A7%D9%81%D9%8A-%D9%88-%D8%A7%D9%84%D9%81%D9%86%D9%8A/18644-%D8%A7%D9%84%D9%85%D8%AE%D8%AA%D8%B1%D8%B9-%D8%A7%D9%84%D8%B3%D9%88%D8%AF%D8%A7%D9%86%D9%8A-%D8%A7%D9%84%D8%B9%D8%A7%D9%84%D9%85%D9%8A-%D9%85%D8%AD%D9%85%D8%AF-%D8%B9%D8%AB%D9%85%D8%A7%D9%86-%D9%84%D9%80-%D8%AA%D9%82%D8%A7%D8%B3%D9%8A%D9%85 Alintibaha Newspaper] | 7 | Physical Chemistry |
The word ketone is derived from Aketon, an old German word for acetone.
According to the rules of IUPAC nomenclature, ketone names are derived by changing the suffix -ane of the parent alkane to -anone. Typically, the position of the carbonyl group is denoted by a number, but traditional nonsystematic names are still generally used for the most important ketones, for example acetone and benzophenone. These nonsystematic names are considered retained IUPAC names, although some introductory chemistry textbooks use systematic names such as "2-propanone" or "propan-2-one" for the simplest ketone () instead of "acetone".
The derived names of ketones are obtained by writing separately the names of the two alkyl groups attached to the carbonyl group, followed by "ketone" as a separate word. Traditionally the names of the alkyl groups were written in order of increasing complexity, for example methyl ethyl ketone. However, according to the rules of IUPAC nomenclature, the alkyl groups are written alphabetically, for example ethyl methyl ketone. When the two alkyl groups are the same, the prefix "di-" is added before the name of alkyl group. The positions of other groups are indicated by Greek letters, the α-carbon being the atom adjacent to carbonyl group.
Although used infrequently, oxo is the IUPAC nomenclature for the oxo group (=O) and used as prefix when the ketone does not have the highest priority. Other prefixes, however, are also used. For some common chemicals (mainly in biochemistry), keto refer to the ketone functional group. | 0 | Organic Chemistry |
Glycals can be formed as pyranose (six-membered) or furanose (five-membered) rings, depending on the monosaccharide used as a starting material to synthesize the glycal. Glycals can also be classified as endo-glycals or exo-glycals. A glycal is an endo-glycal when the double bond is within the ring. If the hydroxyl group on carbon 1 has been replaced with another carbon atom, a double bond can also form outside the ring between carbon 1 and this new carbon. In this case, the product is called an exo-glycal. The glycal conformation that has been studied in most depth is that of the pyranose endo-glycal. The favoured conformation of this glycal is the half-chair, a result which has been confirmed by quantum mechanical calculations. | 0 | Organic Chemistry |
One case study monitored the dehydrogenation of propane to propene using micro-GC. Reproducibility for the experiment was high. The study found that the catalyst (Cr/AlO) activity increased to a sustained maximum of 10% after 28 minutes — an industrially useful insight into the working stability of a catalyst. | 7 | Physical Chemistry |
Relatively effective polymer solar cells are built by thermal annealing of caesium carbonate. Caesium carbonate increases the energy effectiveness of the power conversion of solar cells and enhances the life times of the equipment. The studies done on UPS and XPS reveal that the system will do less work due to the thermal annealing of the layer. Caesium carbonate breaks down into Caesium monoxide| and Caesium peroxide| by thermal evaporation. It was suggested that, when combines with they produce n-type dopes that supplies additional conducting electrons to the host devices. This produces a highly efficient inverted cell that can be used to further improve the efficiency of polymer solar cells or to design adequate multijunction photovoltaic cells.
The nanostructure layers of can be used as cathodes for organic electronic materials due to its capacity to increase the kinetic energy of the electrons. The nanostructure layers of caesium carbonate had been probed for various fields using different techniques. The fields include such as photovoltaic studies, current-voltage measurements, UV photoelectron spectroscopy, X-ray photoelectron spectroscopy, and impedance spectroscopy. The n-type semiconductor produced by thermal evaporation of reacts intensively with metals like Al, and Ca in the cathode. This reaction will cut down the work the cathode metals. Polymer solar cells based on solution process are under extensive studies due to their advantage in producing low cost solar cells. Lithium fluoride has been used to raise the power conversion efficiency of polymer solar cells. However, it requires high temperatures (> 500 degree), and high vacuum states raise the cost of production. The devices with layers have produced equivalent power conversion efficiency compared with the devices that use lithium fluoride. Placing a layer in between the cathode and the light-emitting polymer improves the efficiency of the white OLED. | 0 | Organic Chemistry |
The first successful economizer design was used to increase the steam-raising efficiency of the boilers of stationary steam engines. It was patented by Edward Green in 1845, and since then has been known as Greens economiser. It consisted of an array of vertical cast iron tubes connected to a tank of water above and below, between which the boilers exhaust gases passed. This is the reverse arrangement to that usually but not always seen in the fire tubes of a boiler; there the hot gases usually pass through tubes immersed in water, whereas in an economizer the water passes through tubes surrounded by hot gases. While both are heat exchange devices, in a boiler the burning gases heat the water to produce steam to drive an engine, whether piston or turbine, whereas in an economizer, some of the heat energy that would otherwise all be lost to the atmosphere is instead used to heat the water and/or air that will go into the boiler, thus saving fuel. The most successful feature of Green's design of economizer was its mechanical scraping apparatus, which was needed to keep the tubes free of deposits of soot.
Economizers were eventually fitted to virtually all stationary steam engines in the decades following Greens invention. Some preserved stationary steam engine sites still have their Greens economisers although usually they are not used. One such preserved site is the Claymills Pumping Engines Trust in Staffordshire, England, which is in the process of restoring one set of economisers and the associated steam engine which drove them. Another such example is the British Engineerium in Brighton & Hove, where the economiser associated with the boilers for Number 2 Engine is in use, complete with its associated small stationary engine. A third site is Coldharbour Mill Working Wool Museum, where the Green's economiser is in working order, complete with the drive shafts from the Pollit and Wigzell steam engine. | 7 | Physical Chemistry |
Firesetting is the process of exposing a rock face to high temperatures to induce cracking, spalling, and an overall increase to the brittleness of the rock in order to make it more susceptible to mining processes. Understanding the process of firesetting has been a crucial element to the development of an archaeological history of mining and as such has been the subject of several experiments to reproduce the technique. Typically firesetting experiments are conducted by setting a fire next to a predetermined rock face while taking measurements on the amount of and type of fuel used, temperatures of the fire and rock face, the amount of spalling before and after excavation, as well as the amount of time required for the different procedures. This examination allows for several possible inferences to be made about the mining process including the total amount of fuel a mining site may have needed to complete and its effects on the surrounding environment as well as how mining labor could have been organized. One outcome of firesetting experimentation is the realization that the quenching, or dousing the rock face with water after heating, is not necessary to making the rock face easier to excavate. The quenching process had been a standard step in most experiments with firesetting, but now more research is necessary to answer the new question of why quenching was used if it was not effective. | 8 | Metallurgy |
A macromolecule is a very large molecule important to biological processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. The most common macromolecules in biochemistry are biopolymers (nucleic acids, proteins, and carbohydrates) and large non-polymeric molecules such as lipids, nanogels and macrocycles. Synthetic fibers and experimental materials such as carbon nanotubes are also examples of macromolecules. | 7 | Physical Chemistry |
mTOR is the catalytic subunit of two structurally distinct complexes: mTORC1 and mTORC2. The two complexes localize to different subcellular compartments, thus affecting their activation and function. Upon activation by Rheb, mTORC1 localizes to the Ragulator-Rag complex on the lysosome surface where it then becomes active in the presence of sufficient amino acids. | 1 | Biochemistry |
Stereochemistry is conveniently denoted in skeletal formulae:
The relevant chemical bonds can be depicted in several ways:
* Solid lines represent bonds in the plane of the paper or screen.
* Solid wedges represent bonds that point out of the plane of the paper or screen, towards the observer.
* Hashed wedges or dashed lines (thick or thin) represent bonds that point into the plane of the paper or screen, away from the observer.
* Wavy lines represent either unknown stereochemistry or a mixture of the two possible stereoisomers at that point.
*An obsolescent depiction of hydrogen stereochemistry that used to be common in steroid chemistry is the use of a filled circle centered on a vertex (sometimes called H-dot/H-dash/H-circle, respectively) for an upward pointing hydrogen atom and two hash marks next to vertex or a hollow circle for a downward pointing hydrogen atom.
An early use of this notation can be traced back to Richard Kuhn who in 1932 used solid thick lines and dotted lines in a publication. The modern solid and hashed wedges were introduced in the 1940s by Giulio Natta to represent the structure of high polymers, and extensively popularised in the 1959 textbook Organic Chemistry by Donald J. Cram and George S. Hammond.
Skeletal formulae can depict cis and trans isomers of alkenes. Wavy single bonds are the standard way to represent unknown or unspecified stereochemistry or a mixture of isomers (as with tetrahedral stereocenters). A crossed double-bond has been used sometimes; it is no longer considered an acceptable style for general use but may still be required by computer software. | 0 | Organic Chemistry |
As a derivative of EDTA, dexrazoxane chelates iron and thus reduces the number of metal ions complexed with anthracycline and, consequently, decrease the formation of superoxide radicals. The exact chelation mechanism is unknown, but it has been postulated that dexrazoxane can be converted into ring-opened form intracellularly and interfere with iron-mediated free radical generation that is in part thought to be responsible for anthryacycline induced cardiomyopathy. It was speculated that dexrazoxane could be used for further investigation to synthesize new antimalarial drugs. | 4 | Stereochemistry |
In organic chemistry glycerolysis refers to any process in which chemical bonds are broken via a reaction with glycerol. The term refers almost exclusively to the transesterification reaction of glycerol with triglycerides (fats/oils) to form mixtures of monoglycerides and diglycerides. These find a variety of uses; as food emulsifiers (e.g. E471), low fat cooking oils (e.g. diacylglycerol oil) and surfactants (such as monolaurin).
The transesterification process gives a complex mixture of products, however not all of these are of equivalent use. This has led to the development of optimized processes able to produce better defined products; in particular by using enzymes, reactions in supercritical carbon dioxide and flow chemistry. The production of diglycerides (often called diacylglycerols or DAGs) have been investigated extensively due to their use in foods, with total annual sales of approximately US$200 million in Japan since its introduction in the late 1990s until 2009. | 0 | Organic Chemistry |
Cleavage and polyadenylation specificity factor (CPSF) is involved in the cleavage of the 3 signaling region from a newly synthesized pre-messenger RNA (pre-mRNA) molecule in the process of gene transcription. In eukaryotes, messenger RNA precursors (pre-mRNA) are transcribed in the nucleus from DNA by the enzyme, RNA polymerase II. The pre-mRNA must undergo post-transcriptional modifications, forming mature RNA (mRNA), before they can be transported into the cytoplasm for translation into proteins. The post-transcriptional modifications are: the addition of a 5 m7G cap, splicing of intronic sequences, and 3' cleavage and polyadenylation.
According to Schönemann et al., "CPSF recognizes the polyadenylation signal (PAS), providing sequence specificity in pre-mRNA cleavage and polyadenylation, and catalyzes pre-mRNA cleavage." It is required to induce RNA polymerase pausing once it recognizes a functional PAS. It is the first protein to bind to the signaling region near the cleavage site of the pre-mRNA, to which the poly(A) tail will be added by polynucleotide adenylyltransferase. The 10-30 nucleotide upstream signaling region of the cleavage site, polyadenylation signal (PAS), has the canonical nucleotide sequence AAUAAA, which is highly conserved across the vast majority of pre-mRNAs. The AAUAAA region is usually defined by a cytosine/adenine (CA) dinucleotide, which is the preferred sequence, that is 5' to the site of the endonucleolytic cleavage. A second downstream signaling region, located approximately 40 nucleotides downstream from the cleavage site on the portion of the pre-mRNA that is cleaved before polyadenylation, consists of a U/GU-rich region required for efficient processing. This downstream fragment is degraded. The mature RNA are transported into the cytoplasm, where they are translated into proteins. | 1 | Biochemistry |
A sensor device embedded on microprocessors used to monitor the temperature of the processor's die is also known as a "thermal diode".
This application of thermal diode is based on the property of electrical diodes to change voltage across it linearly according to temperature. As the temperature increases, diodes forward voltage decreases. Microprocessors having high clock rate encounter high thermal loads. To monitor the temperature limits thermal diodes are used. They are usually placed in that part of the processor core where highest temperature is encountered. Voltage developed across it varies with the temperature of the diode. All modern AMD and Intel CPUs, as well as AMD and Nvidia GPUs have on-chip thermal diodes. As the sensor is located directly on the processor die, it provides most local and relevant CPU and GPU temperature readings. The silicon diodes have temperature dependency of -2mV per degree Celsius. Thus the junction temperature can be determined by passing a set current through the diode and then measuring voltage developed across it. In addition to processors, the same technology is widely used in dedicated temperature sensor ICs. | 7 | Physical Chemistry |
Use of Tramadol during pregnancy is generally avoided, as it may cause some reversible withdrawal effects in the newborn. A small prospective study in France found, while an increased risk of miscarriages existed, no major malformations were reported in the newborn. Its use during lactation is also generally advised against, but a small trial found that infants breastfed by mothers taking tramadol were exposed to about 2.88% of the dose the mothers were taking. No evidence of this dose harming the newborn was seen. | 4 | Stereochemistry |
Most neuropeptides act on G-protein coupled receptors (GPCRs). Neuropeptide-GPCRs fall into two families: rhodopsin-like and the secretin class. Most peptides activate a single GPCR, while some activate multiple GPCRs (e.g. AstA, AstC, DTK). Peptide-GPCR binding relationships are highly conserved across animals. Aside from conserved structural relationships, some peptide-GPCR functions are also conserved across the animal kingdom. For example, neuropeptide F/neuropeptide Y signaling is structurally and functionally conserved between insects and mammals.
Although peptides mostly target metabotropic receptors, there is some evidence that neuropeptides bind to other receptor targets. Peptide-gated ion channels (FMRFamide-gated sodium channels) have been found in snails and Hydra. Other examples of non-GPCR targets include: insulin-like peptides and tyrosine-kinase receptors in Drosophila and atrial natriuretic peptide and eclosion hormone with membrane-bound guanylyl cyclase receptors in mammals and insects. | 1 | Biochemistry |
Tertiary phosphine oxides, compounds with the formula RPO cannot tautomerize. The situation is different for the secondary and primary phosphine oxides, with the respective formulas R(H)PO and R(H)PO. | 0 | Organic Chemistry |
Cleavage, in mineralogy and materials science, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the microscope and to the naked eye. If bonds in certain directions are weaker than others, the crystal will tend to split along the weakly bonded planes. These flat breaks are termed "cleavage". The classic example of cleavage is mica, which cleaves in a single direction along the basal pinacoid, making the layers seem like pages in a book. In fact, mineralogists often refer to "books of mica".
Diamond and graphite provide examples of cleavage. Each is composed solely of a single element, carbon. In diamond, each carbon atom is bonded to four others in a tetrahedral pattern with short covalent bonds. The planes of weakness (cleavage planes) in a diamond are in four directions, following the faces of the octahedron. In graphite, carbon atoms are contained in layers in a hexagonal pattern where the covalent bonds are shorter (and thus even stronger) than those of diamond. However, each layer is connected to the other with a longer and much weaker van der Waals bond. This gives graphite a single direction of cleavage, parallel to the basal pinacoid. So weak is this bond that it is broken with little force, giving graphite a slippery feel as layers shear apart. As a result, graphite makes an excellent dry lubricant.
While all single crystals will show some tendency to split along atomic planes in their crystal structure, if the differences between one direction or another are not large enough, the mineral will not display cleavage. Corundum, for example, displays no cleavage. | 3 | Analytical Chemistry |
Alexey Ekimov or Aleksey Yekimov (; born 1945) is a Russian solid state physicist and a pioneer in nanomaterials research. He discovered the semiconductor nanocrystals known as quantum dots in 1981, while working at the Vavilov State Optical Institute. In 2023, he was awarded the Nobel Prize in Chemistry for this discovery. | 7 | Physical Chemistry |
In the Horner–Wadsworth–Emmons reaction dialkyl-phosphonates are deprotonated to give stabilized carbanions, which react with aldehydes to give E-alkenes with elimination of a dialkyl-phosphate. | 0 | Organic Chemistry |
Glycogen: Glycogen is the most common form of glucose in animals and is especially abundant in cells of muscles, and liver. It appears in electron micrograph as clusters, or a rosette of beta particles that resemble ribosomes, located near the smooth endoplasmic reticulum. Glycogen is an important energy source of the cell; therefore, it will be available on demand. The enzymes responsible for glycogenolysis degrade glycogen into individual molecules of glucose and can be utilized by multiple organs of the body.
Lipids: Lipids are triglycerides in storage form is the common form of inclusions, not only are stored in specialized cells (adipocytes) but also are located as individuals droplets in various cell type especially hepatocytes. These are fluid at body temperature and appear in living cells as refractile spherical droplets. Lipid yields more than twice as many calories per gram as does carbohydrate. On demand, they serve as a local store of energy and a potential source of short carbon chains that are used by the cell in its synthesis of membranes and other lipid containing structural components or secretory products.
Crystals: Crystalline inclusions have long been recognized as normal constituents of certain cell types such as Sertoli cells and Leydig cells of the human testis, and occasionally in macrophages. It is believed that these structures are crystalline forms of certain proteins which is located everywhere in the cell such as in nucleus, mitochondria, endoplasmic reticulum, Golgi body, and free in cytoplasmic matrix.
Pigments: The most common pigment in the body, besides hemoglobin of red blood cells is melanin, manufactured by melanocytes of the skin and hair, pigments cells of the retina and specialized nerve cells in the substantia nigra of the brain. These pigments have protective functions in skin and aid in the sense of sight in the retina but their functions in neurons is not understood completely. Furthermore, cardiac tissue and central nervous system neurons shows yellow to brown pigment called lipofuscin, some believed that they have lysosomal activity. | 1 | Biochemistry |
Ions are ubiquitous in nature and are responsible for diverse phenomena from the luminescence of the Sun to the existence of the Earth's ionosphere. Atoms in their ionic state may have a different color from neutral atoms, and thus light absorption by metal ions gives the color of gemstones. In both inorganic and organic chemistry (including biochemistry), the interaction of water and ions is extremely important; an example is energy that drives the breakdown of adenosine triphosphate (ATP). | 7 | Physical Chemistry |
The electrical double layer can be regarded as behaving like a parallel plate capacitor with a compressible dielectric filling. When sound waves induce a local pressure variation, the spacing of the plates varies at the frequency of the excitation, generating an AC displacement current normal to the interface. For practical reasons this is most readily observed at a conducting surface. It is therefore possible to use an electrode immersed in a conducting electrolyte as a microphone, or indeed as a loudspeaker when the effect is applied in reverse. | 7 | Physical Chemistry |
FSP can also be used to fabricate metal matrix composites at the nugget zone where we need the change of properties. Al 5052/SiC and some other composites were successfully fabricated. Even nano composites can also be fabricated by FSP. | 8 | Metallurgy |
One of the most outspoken critics of some concepts of "molecular assemblers" was Professor Richard Smalley (1943–2005) who won the Nobel prize for his contributions to the field of nanotechnology. Smalley believed that such assemblers were not physically possible and introduced scientific objections to them. His two principal technical objections were termed the "fat fingers problem" and the "sticky fingers problem". He believed these would exclude the possibility of "molecular assemblers" that worked by precision picking and placing of individual atoms. Drexler and coworkers responded to these two issues in a 2001 publication.
Smalley also believed that Drexlers speculations about apocalyptic dangers of self-replicating machines that have been equated with "molecular assemblers" would threaten the public support for development of nanotechnology. To address the debate between Drexler and Smalley regarding molecular assemblers Chemical & Engineering News' published a point-counterpoint consisting of an exchange of letters that addressed the issues. | 6 | Supramolecular Chemistry |
John Garton and his two brothers, Robert and Thomas, were in business with their father, Peter, in Golborne and Newton-le-Willows in Lancashire, England, as corn and agricultural merchants.
As a young man, John Garton (1863–1922), was the first to understand that whilst some agricultural plants were self-pollinating, others were cross-pollinating. He began experimenting with the artificial cross pollination firstly of cereal plants, then herbage species and root crops.
He attracted the friendship and encouragement of a young Scottish seedsman, George Peddie Miln (1861–1928) who had trained in Dundee and was seed manager of Dicksons Limited of Chester.
Knowing he had developed a far reaching new technique in plant breeding John Garton began to carry out many thousands of controlled crosses on fields at the family farm in Newton-le-Willows. He and his colleagues tried in 1889 to interest the UK Government’s new Board of Agriculture in the invention they called Scientific Farm Plant Breeding. But this was to no avail. | 1 | Biochemistry |
Its use in children is generally advised against, although it may be done under the supervision of a specialist. On 21 September 2015, the FDA started investigating the safety of tramadol in use in persons under the age of 17. The investigation was initiated because some of these people have experienced slowed or difficult breathing. The FDA lists age under 12 years old as a contraindication. | 4 | Stereochemistry |
The stability of individual atropisomers is conferred by the repulsive interactions that inhibit rotation. Both the steric bulk and, in principle, the length and rigidity of the bond connecting the two subunits contribute. Commonly, atropisomerism is studied by dynamic nuclear magnetic resonance spectroscopy, since atropisomerism is a form of fluxionality. Inferences from theory and results of reaction outcomes and yields also contribute.
Atropisomers exhibit axial chirality (planar chirality). When the barrier to racemization is high, as illustrated by the BINAP ligands, the phenomenon becomes of practical value in asymmetric synthesis. Methaqualone, the anxiolytic and hypnotic-sedative, is a classical example of a drug molecule that exhibits the phenomenon of atropisomerism. | 4 | Stereochemistry |
This class is defined by loss of two beta-strands and additional N-terminal strands. Both namesakes of this superfamily, myosin and kinesin, have shifted to use ATP. | 1 | Biochemistry |
Nitric acid plays a key role in PUREX and other nuclear fuel reprocessing methods, where it can dissolve many different actinides. The resulting nitrates are converted to various complexes that can be reacted and extracted selectively in order to separate the metals from each other. | 3 | Analytical Chemistry |
The HMG proteins are subdivided into 3 superfamilies each containing a characteristic functional domain:
* HMGA – contains an AT-hook domain
** HMGA1
** HMGA2
* HMGB – contains a HMG-box domain
** HMGB1
** HMGB2
** HMGB3
** HMGB4
* HMGN – contains a nucleosomal binding domain
** HMGN1
** HMGN2
** HMGN3
** HMGN4
** HMGN5
Proteins containing any of these embedded in their sequence are known as HMG motif proteins.
HMG-box proteins are found in a variety of eukaryotic organisms.
They were originally isolated from mammalian cells, and named according to their electrophoretic mobility in polyacrylamide gels. | 1 | Biochemistry |
In the first part of the test, the patient is given radiolabeled vitamin B to drink or eat. The most commonly used radiolabels are Co and Co. An intramuscular injection of unlabeled vitamin B is given an hour later. This is not enough to replete or saturate body stores of B. The purpose of the single injection is to temporarily saturate B receptors in the liver with enough normal vitamin B to prevent radioactive vitamin B binding in body tissues (especially in the liver), so that if absorbed from the G.I. tract, it will pass into the urine. The patient's urine is then collected over the next 24 hours to assess the absorption.
Normally, the ingested radiolabeled vitamin B will be absorbed into the body. Since the body already has liver receptors for transcobalamin/vitamin B saturated by the injection, much of the ingested vitamin B will be excreted in the urine.
* A normal result shows at least 10% of the radiolabeled vitamin B in the urine over the first 24 hours.
* In patients with pernicious anemia or with deficiency due to impaired absorption, less than 10% of the radiolabeled vitamin B is detected.
The normal test will result in a higher amount of the radiolabeled cobalamin in the urine because it would have been absorbed by the intestinal epithelium, but passed into the urine because all hepatic B12 receptors were occupied. An abnormal result is caused by less of the labeled cobalamin to appear in the urine because it will remain in the intestine and be passed into the feces. | 1 | Biochemistry |
Kenneth H. Cooper conducted a study for the United States Air Force in the late 1960s. One of the results of this was the Cooper test in which the distance covered running in 12 minutes is measured. Based on the measured distance, an estimate of V̇O max [in mL/(kg·min)] can be calculated by inverting the linear regression equation, giving us:
where d is the distance (in metres) covered in 12 minutes.
An alternative equation is:
where d′ is distance (in miles) covered in 12 minutes. | 1 | Biochemistry |
Messenger RNA is the bridge between the genetic code and the resulting proteins, as it is what carries the necessary information that gets translated into proteins. Modifications to the actual, physical genetic code are likely to be deleterious; therefore, minor modifications, such as methylation, done to mRNA are preferable (nevertheless, modifications are still seen throughout the genome). The four major types of modifications done to mRNA are N7-methylguanine (at the 5′ cap), N-methyladenosine, 5-methylcytosine, and 2′-O-methylation. The modification seen at the 5 cap perfectly demonstrates how modifications to mRNA can impact its function, as the 5 cap is necessary to initiate translation. Therefore, modifications, such as N7-methylguanine during RNA processing, to the 5' cap may effect the ability of the ribosome to initiate translation. It is important to note that not all modifications happening to the mRNA are epigenetic, some, like the N7-methylguanosine cap, are RNA editing.
mRNA molecules demonstrate something known as "modification stoichiometry". Modification stoichiometry is when only a portion of transcripts have a specific modification at a particular modification site. Typically, under normal cell conditions, the modification stoichiometry is very low, there are a very few number of transcripts that have specific modifications. However, as cell conditions change, the fraction of modified transcripts can change as well. As with other types of RNA, modifications impact the overall structure of the mRNA. Altering its structure may cause the mRNA to take different paths. For example, a normal transcript might be fated to be translated; however, the introduction of a modified base can disrupt its structure and send it down a different path, and that particular transcript may now be targeted for degradation. | 1 | Biochemistry |
Parting is a process by which gold is purified to a commercially-tradeable standard, typically ≥99.5%. Removal of silver is of particular interest since the two metals often co-purify. The standard procedure is based on the Miller process. The separation is achieved by passing chlorine gas into a molten alloy. The technique is practiced on a large scale (e.g. 500 kg). The principle of the method exploits the nobility of gold, such that at high temperatures, gold does not react with chlorine, but virtually all contaminating metals do. Thus, at c. 500 °C, as the chlorine gas is passed through molten mixture (again, mainly gold), a low-density slag forms on top, which can be decanted from the liquid gold. Silver chloride and other precious metals can be recovered from this slag. The slag layer is often diluted with a flux like borax to facilitate the separation.
Alternative methods exist for parting gold. Silver can be dissolved selectively by boiling the mixture with 30% nitric acid, a process sometimes called inquartation. Affination is a largely obsolete process of removing silver from gold using concentrated sulfuric acid. Electrolysis using the Wohlwill process is yet another approach. | 8 | Metallurgy |
Alkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecting alkylation. Alkyl groups can also be removed in a process known as dealkylation. Alkylating agents are often classified according to their nucleophilic or electrophilic character. In oil refining contexts, alkylation refers to a particular alkylation of isobutane with olefins. For upgrading of petroleum, alkylation produces a premium blending stock for gasoline. In medicine, alkylation of DNA is used in chemotherapy to damage the DNA of cancer cells. Alkylation is accomplished with the class of drugs called alkylating antineoplastic agents. | 0 | Organic Chemistry |
Perhaps the most prevalent carbamate is the one involved in the capture of CO by plants. This process is necessary for their growth. The enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) fixes a molecule of carbon dioxide as phosphoglycerate in the Calvin cycle. At the active site of the enzyme, a Mg ion is bound to glutamate and aspartate residues as well as a lysine carbamate. The carbamate is formed when an uncharged lysine side chain near the ion reacts with a carbon dioxide molecule from the air (not the substrate carbon dioxide molecule), which then renders it charged, and, therefore, able to bind the Mg ion. | 0 | Organic Chemistry |
Diphoterine solution contains an amphoteric, chelating molecule: a substance which is capable of reacting with both acids and alkalis when applied to either type of chemical spill, stopping the aggressive action of a corrosive or irritant chemical, halting the reaction with the body.
However, it is not fully effective at halting the body's reaction with hydrofluoric acid. This is because hydrofluoric acid is poisonous as well as corrosive. Treatment with either Hexafluorine or calcium gluconate is required to deal with hydrofluoric acid contamination.
Like all of the emergency treatments, Diphoterine solution is not a substitute for professional medical attention, so immediate attention from emergency medical personnel should always be sought, especially if the chemical spill was to the eye. | 7 | Physical Chemistry |
CN-PAGE (commonly referred to as Native PAGE) separates acidic water-soluble and membrane proteins in a polyacrylamide gradient gel. It uses no charged dye so the electrophoretic mobility of proteins in CN-PAGE (in contrast to the charge shift technique BN-PAGE) is related to the intrinsic charge of the proteins. The migration distance depends on the protein charge, its size and the pore size of the gel. In many cases this method has lower resolution than BN-PAGE, but CN-PAGE offers advantages whenever Coomassie dye would interfere with further analytical techniques, for example it has been described as a very efficient microscale separation technique for FRET analyses. Additionally, as CN-PAGE does not require the harsh conditions of BN-PAGE, it can retain the supramolecular assemblies of membrane protein complexes that would be dissociated in BN-PAGE. | 1 | Biochemistry |
Labeling studies establish the following regiochemistry:
:RCDO + CH=CHR → RC(O)CHCHDR
In terms of the reaction mechanism, hydroacylation begins with oxidative addition of the aldehydic carbon-hydrogen bond. The resulting acyl hydride complex next binds the alkene. The sequence of oxidative addition and alkene coordination is often unclear. Via migratory insertion, the alkene inserts into either the metal-acyl or the metal-hydride bonds. In the final step, the resulting alkyl-acyl or beta-ketoalkyl-hydride complex undergoes reductive elimination. A competing side-reaction is decarbonylation of the aldehyde. This process also proceeds via the intermediacy of the acyl metal hydride:
:R"C(O)-ML-H → R"-M(CO)L-H
This step can be followed by reductive elimination of the alkane:
:R"-M(CO)L-H → R"-H + M(CO)L | 0 | Organic Chemistry |
Keiko Hattori is a geochemist and mineralogist. She is Distinguished University Professor of Geochemistry and Mineral Deposits in the Department of Earth and Environmental Sciences at the University of Ottawa.
Hattori is most known for her research on aspects of Earth's atmospheric and mantle evolution, as well as the formation of arc volcanoes and the generation of metal-fertile volcanic arcs. Her application of this knowledge has led to insights regarding the origins and locations of mineral deposits. Specifically, she has conducted research on the transfer of chalcophile elements (copper-like elements) from slabs to arc magmas through mantle wedges, as well as from arc magmas to mineral deposits. Additionally, her work has encompassed exploration geochemistry, where she has investigated the dispersion of metals from buried deposits including platinum and palladium in surface media. She was appointed as the 2022 International Exchange Lecturer of the Society of Economic Geologists (SEG), and has been the recipient of the Island Arc Award and the Takeo Kato Gold Medal.
Hattori is an elected Fellow of the Royal Society of Canada and Mineralogical Society of America. | 9 | Geochemistry |
Aluminium chloride finds a wide variety of other applications in organic chemistry. For example, it can catalyse the ene reaction, such as the addition of 3-buten-2-one (methyl vinyl ketone) to carvone:
It is used to induce a variety of hydrocarbon couplings and rearrangements.
Aluminium chloride combined with aluminium in the presence of an arene can be used to synthesize bis(arene) metal complexes, e.g. bis(benzene)chromium, from certain metal halides via the Fischer–Hafner synthesis. Dichlorophenylphosphine is prepared by reaction of benzene and phosphorus trichloride catalyzed by aluminium chloride. | 0 | Organic Chemistry |
The starting of Townsend discharge sets the upper limit to the blocking voltage a glow discharge gas-filled tube can withstand. This limit is the Townsend discharge breakdown voltage, also called ignition voltage of the tube.
The occurrence of Townsend discharge, leading to glow discharge breakdown shapes the current–voltage characteristic of a gas-discharge tube such as a neon lamp in a way such that it has a negative differential resistance region of the S-type. The negative resistance can be used to generate electrical oscillations and waveforms, as in the relaxation oscillator whose schematic is shown in the picture on the right. The sawtooth shaped oscillation generated has frequency
:where
:* is the glow discharge breakdown voltage,
:* is the Townsend discharge breakdown voltage,
:*, and are respectively the capacitance, the resistance and the supply voltage of the circuit.
:Since temperature and time stability of the characteristics of gas diodes and neon lamps is low, and also the statistical dispersion of breakdown voltages is high, the above formula can only give a qualitative indication of what the real frequency of oscillation is. | 7 | Physical Chemistry |
Changes in ocean chemistry can have extensive direct and indirect effects on organisms and their habitats. One of the most important repercussions of increasing ocean acidity relates to the production of shells out of calcium carbonate (). This process is called calcification and is important to the biology and survival of a wide range of marine organisms. Calcification involves the precipitation of dissolved ions into solid structures, structures for many marine organisms, such as coccolithophores, foraminifera, crustaceans, mollusks, etc. After they are formed, these structures are vulnerable to dissolution unless the surrounding seawater contains saturating concentrations of carbonate ions ().
Very little of the extra carbon dioxide that is added into the ocean remains as dissolved carbon dioxide. The majority dissociates into additional bicarbonate and free hydrogen ions. The increase in hydrogen is larger than the increase in bicarbonate, creating an imbalance in the reaction:
To maintain chemical equilibrium, some of the carbonate ions already in the ocean combine with some of the hydrogen ions to make further bicarbonate. Thus the ocean's concentration of carbonate ions is reduced, removing an essential building block for marine organisms to build shells, or calcify:
The increase in concentrations of dissolved carbon dioxide and bicarbonate, and reduction in carbonate, are shown in the Bjerrum plot. | 9 | Geochemistry |
Dietary selenium comes from nuts, cereals, meat, mushrooms, fish, and eggs. Brazil nuts are the richest ordinary dietary source and could cause selenium toxicity if consumed regularly – though the actual concentration of selenium (as with any plant-based food sources, such as another selenium-accumulating "paradise nut" Lecythis, belonging to the same family Lecythidaceae) is soil-dependent and may vary significantly by geographic location. In descending order of concentration, high levels are also found in kidney, tuna, crab, and lobster.
The human body's content of selenium is believed to be in the 13–20 milligram range. | 1 | Biochemistry |
Compared to time domain reflectometer (TDR), FD sensors are cheaper to build and have a faster response time. However, because of the complex electrical field around the probe, the sensor needs to be calibrated for different soil types. Some commercial sensors have been able to remove the soil type sensitivity by using a high frequency. | 7 | Physical Chemistry |
Strader and colleagues designed the first GPCR which could be activated only by a synthetic compound and has gradually been gaining momentum. The first international RASSL meeting was scheduled for April 6, 2006. A simple example of the use of a RASSL system in behavioral genetics was illustrated by Mueller et al. (2005) where they showed that expressing a RASSL receptor in sweet taste cells of the mouse tongue led to a strong preference for oral consumption of the synthetic ligand, whereas expressing the RASSL in bitter taste cells caused dramatic taste aversion for the same compound.
The attenuating effects of the hM4Di-DREADD were originally explored in 2007, before being confirmed in 2014. | 1 | Biochemistry |
Particle size distribution can greatly affect the efficiency of any collection device.
Settling chambers will normally only collect very large particles, those that can be separated using sieve trays.
Centrifugal collectors will normally collect particles down to about 20 μm. Higher efficiency models can collect particles down to 10 μm.
Fabric filters are one of the most efficient and cost effective types of dust collectors available and can achieve a collection efficiency of more than 99% for very fine particles.
Wet scrubbers that use liquid are commonly known as wet scrubbers. In these systems, the scrubbing liquid (usually water) comes into contact with a gas stream containing dust particles. The greater the contact of the gas and liquid streams, the higher the dust removal efficiency.
Electrostatic precipitators use electrostatic forces to separate dust particles from exhaust gases. They can be very efficient at the collection of very fine particles.
Filter Press used for filtering liquids by cake filtration mechanism. The PSD plays an important part in the cake formation, cake resistance, and cake characteristics. The filterability of the liquid is determined largely by the size of the particles. | 7 | Physical Chemistry |
On 1 August 2009 it was announced that the decision by Corby Borough Council regarding whether or not to appeal the ruling would be taken on 18 August 2009, the day before the deadline for appeal decisions to be submitted to Mr Justice Akenhead. Unusually, the authority decided that openness and public opinion were required at the extraordinary full council sitting after which councillors will vote on whether to appeal or instead pay the compensation to 16 children who were born with birth defects.
Chief Executive Chris Mallender stated: "The council is doing the right thing by reaching the decision in public. We will be starting the meeting at 6pm so we can give the opportunity for [the public] to speak," a move he said would make sure councillors' decisions reflected public opinion.
The council, which has an annual budget of £12m, has already spent £1.9m fighting the case and has now received a bill for £4.7m from the families' solicitor.
At the meeting the council voted to appeal against the ruling but said that they would follow a "twin track" approach, preferring to attend independent mediation sessions to come to an out-of-court settlement with the families. They also stated that any mediation would include the cases of the two youngest claimants despite these not being covered by the ruling. The chief executive gave a statement that if a causal link between the toxins and the limb deformities was ever proven he would "offer an unreserved apology", however he believed "that the judgement is unsound and will be found wanting on appeal." | 2 | Environmental Chemistry |
Wetlands are sources of extreme biodiversity and ecological benefit. They contain a multitude of species of plants and animals, including 79 species classified as rare, threatened, or endangered. An estimate by the U.S. Fish and Wildlife Service indicates that wetlands provide for, directly and indirectly, up to 43% of federally threatened or endangered species. Wetlands are the leading producer of oysters, 50% of the shrimp crop, 75% of the alligator harvest, 27% of the oil and gas, and the largest port complex in the United States. The world’s wetlands have an estimated worth of $14.9 trillion.
Wetlands also provide for disaster protection, including surge protection from hurricanes, as they and barrier islands help to break down the power of a storm before it reaches mainland. They also provide flood relief, as they are able to hold about three-acre feet (one million gallons) of water. This holding of water allows for rejuvenation of ecosystems, as new sediment is able to settle. Flooding also affects factors such as root penetration, soil temperature, conductivity, and bulk density.
Wetlands are highly effective at removing pollutants and excess nutrients due to the slow water flow and absorption by the plant systems. This has been shown to be effective in the removal of nitrogen and phosphorus, the major nutrients involved in “dead zones”. They are also major sinks for heavy metals and sulfur. | 9 | Geochemistry |
The process occurs in two cellular locations: the cytosol and the mitochondria matrix. A cycle is formed by the system, ensuring that the conversion between acetylene, oxaloacetate, citrate, and malate can continue without the need for foreign molecule addition.
It involves six major steps: | 1 | Biochemistry |
After tin and lead, the next metal smelted appears to have been copper. How the discovery came about is debated. Campfires are about 200 °C short of the temperature needed, so some propose that the first smelting of copper may have occurred in pottery kilns. (The development of copper smelting in the Andes, which is believed to have occurred independently of the Old World, may have occurred in the same way.)
The earliest current evidence of copper smelting, dating from between 5500 BC and 5000 BC, has been found in Pločnik and Belovode, Serbia. A mace head found in Turkey and dated to 5000 BC, once thought to be the oldest evidence, now appears to be hammered, native copper.
Combining copper with tin and/or arsenic in the right proportions produces bronze, an alloy that is significantly harder than copper. The first copper/arsenic bronzes date from 4200 BC from Asia Minor. The Inca bronze alloys were also of this type. Arsenic is often an impurity in copper ores, so the discovery could have been made by accident. Eventually, arsenic-bearing minerals were intentionally added during smelting.
Copper–tin bronzes, harder and more durable, were developed around 3500 BC, also in Asia Minor.
How smiths learned to produce copper/tin bronzes is unknown. The first such bronzes may have been a lucky accident from tin-contaminated copper ores. However, by 2000 BC, people were mining tin on purpose to produce bronze—which is remarkable as tin is a semi-rare metal, and even a rich cassiterite ore only has 5% tin. However early peoples learned about tin, they understood how to use it to make bronze by 2000 BC.
The discovery of copper and bronze manufacture had a significant impact on the history of the Old World. Metals were hard enough to make weapons that were heavier, stronger, and more resistant to impact damage than wood, bone, or stone equivalents. For several millennia, bronze was the material of choice for weapons such as swords, daggers, battle axes, and spear and arrow points, as well as protective gear such as shields, helmets, greaves (metal shin guards), and other body armor. Bronze also supplanted stone, wood, and organic materials in tools and household utensils—such as chisels, saws, adzes, nails, blade shears, knives, sewing needles and pins, jugs, cooking pots and cauldrons, mirrors, and horse harnesses. Tin and copper also contributed to the establishment of trade networks that spanned large areas of Europe and Asia and had a major effect on the distribution of wealth among individuals and nations. | 8 | Metallurgy |
Supercritical water oxidation uses supercritical water as a medium in which to oxidize hazardous waste, eliminating production of toxic combustion products that burning can produce.
The waste product to be oxidised is dissolved in the supercritical water along with molecular oxygen (or an oxidising agent that gives up oxygen upon decomposition, e.g. hydrogen peroxide) at which point the oxidation reaction occurs. | 7 | Physical Chemistry |
Neocarzinostatin is a natural product of Streptomyces carzinostaticus. It forms an apoprotein with a 113-amino acid polypeptide which can cleave histone protein H1. Neocarzinostatin is an example of an enediyne that undergoes triggering via Myers-Saito cyclization. An analog of neocarzinostatin, SMANCS, has been approved for use in Japan as an antitumor drug for liver cancer. | 0 | Organic Chemistry |
Tetracycline, aminoglycosides, polymyxins and clindamycin potentiate neuromuscular blockage by inhibiting ACh release or desensitisation of post-synpatic nAChRs to ACh. This interaction happens mostly during maintenance of anesthesia. As antibiotics typically are given after a dose of NMBA, this interaction needs to be considered when re-dosing NMBA. | 1 | Biochemistry |
The position of equilibrium in both cyclic and acyclic systems may be predicted from the structures of the two equilibrating epoxides. In acyclic systems, these rules have been established:
* Greater substitution on the epoxide ring is favored.
* Among disubstituted epoxides, trans isomers are favored over cis isomers.
* Isomers with primary hydroxyl groups are favored.
* Electron-donating substituents on the epoxide are stabilizing and electron-withdrawing substituents are destabilizing.
Pyranosides are the most heavily studied cyclic systems. Studies of epoxide migration in pyranosides and other cyclic epoxy alcohols have revealed three generalizations:
* As in acyclic systems, greater substitution on the epoxide ring is favored.
* The favored isomer is the one with more pseudoequatorial substituents.
* Intramolecular hydrogen bonding and other through-space interactions do not play a role in equilibrium ratios.
Conformationally locked pyranosides reveal the thermodynamic preference of cyclic substrates for more pseudoequatorial groups.
Under aprotic conditions, nucleophilic opening of epoxide isomers can be achieved with hydrides or organocuprates. Nucleophilic attack generally takes place at the least substituted carbon, yielding the more substituted diol product.
Under protic conditions, opening at the least substituted position is also usually favored. Nucleophiles that may be used under protic conditions include phenols, secondary amines, azide anion, and sulfides.
Intermolecular nucleophilic trapping of a single epoxide isomer is difficult, as reaction of the epoxy alcohol with the electrophile is typically faster than migration. However, intramolecular electrophies are often effective for trapping a single epoxide isomer. For instance, a second nearby epoxide in the starting material of equation (9) is trapped by a single epoxide isomer, leading to a tetrahydrofuran. | 0 | Organic Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), Valine (Val, V). | 1 | Biochemistry |
*One part per hundred is generally represented by the percent sign (%) and denotes one part per 100 () parts, and a value of . This is equivalent to about fourteen minutes out of one day.
*One part per thousand should generally be spelled out in full and not as "ppt" (which is usually understood to represent "parts per trillion"). It may also be denoted by the permille sign (‰). Note however, that specific disciplines such as oceanography, as well as educational exercises, do use the "ppt" abbreviation. "One part per thousand" denotes one part per 1,000 () parts, and a value of . This is equivalent to about ninety seconds out of one day.
*One part per ten thousand is denoted by the permyriad sign (‱). Although rarely used in science (ppm is typically used instead), one permyriad has an unambiguous value of one part per 10,000 () parts, and a value of . This is equivalent to about nine seconds out of one day. <br/>In contrast, in finance, the basis point is typically used to denote changes in or differences between percentage interest rates (although it can also be used in other cases where it is desirable to express quantities in hundredths of a percent). For instance, a change in an interest rate from 5.15% per annum to 5.35% per annum could be denoted as a change of 20 basis points (per annum). As with interest rates, the words "per annum" (or "per year") are often omitted. In that case, the basis point is a quantity with a dimension of (time).
* One part per hundred thousand, per cent mille (pcm) or milli-percent denotes one part per 100,000 () parts, and a value of . It is commonly used in epidemiology for mortality, crime and disease prevalence rates, and nuclear reactor engineering as a unit of reactivity. In time measurement it is equivalent to about 5 minutes out of a year; in distance measurement, it is equivalent to 1 cm of error per km of distance traversed.
* One part per million (ppm) denotes one part per 1,000,000 () parts, and a value of . It is equivalent to about 32 seconds out of a year or 1 mm of error per km of distance traversed. In mining, it is also equivalent to one gram per metric ton, expressed as g/t.
* One part per billion (ppb) denotes one part per 1,000,000,000 () parts, and a value of . This is equivalent to about three seconds out of a century.
* One part per trillion (ppt) denotes one part per 1,000,000,000,000 () parts, and a value of . This is equivalent to about thirty seconds out of every million years.
* One part per quadrillion (ppq) denotes one part per 1,000,000,000,000,000 () parts, and a value of . This is equivalent to about two and a half minutes out of the age of the Earth (4.5 billion years). Although relatively uncommon in analytical chemistry, measurements at the ppq level are sometimes performed. | 2 | Environmental Chemistry |
Operation of the modified Q cycle in Complex III results in the reduction of Cytochrome c, oxidation of ubiquinol to ubiquinone, and the transfer of four protons into the intermembrane space, per two-cycle process.
Ubiquinol (QH) binds to the Q site of complex III via hydrogen bonding to His182 of the Rieske iron-sulfur protein and Glu272 of Cytochrome b. Ubiquinone (Q), in turn, binds the Q site of complex III. Ubiquinol is divergently oxidized (gives up one electron each) to the Rieske iron-sulfur (FeS) protein and to the b heme. This oxidation reaction produces a transient semiquinone before complete oxidation to ubiquinone, which then leaves the Q site of complex III.
Having acquired one electron from ubiquinol, the FeS protein is freed from its electron donor and is able to migrate to the Cytochrome c subunit. FeS protein then donates its electron to Cytochrome c, reducing its bound heme group. The electron is from there transferred to an oxidized molecule of Cytochrome c externally bound to complex III, which then dissociates from the complex. In addition, the reoxidation of the FeS protein releases the proton bound to His181 into the intermembrane space.
The other electron, which was transferred to the b heme, is used to reduce the b heme, which in turn transfers the electron to the ubiquinone bound at the Q site. The movement of this electron is energetically unfavourable, as the electron is moving towards the negatively charged side of the membrane. This is offset by a favourable change in E from −100 mV in B to +50mV in the B heme. The attached ubiquinone is thus reduced to a semiquinone radical. The proton taken up by Glu272 is subsequently transferred to a hydrogen-bonded water chain as Glu272 rotates 170° to hydrogen bond a water molecule, in turn hydrogen-bonded to a propionate of the b heme.
Because the last step leaves an unstable semiquinone at the Q site, the reaction is not yet fully completed. A second Q cycle is necessary, with the second electron transfer from cytochrome b reducing the semiquinone to ubiquinol. The ultimate products of the Q cycle are four protons entering the intermembrane space, two from the matrix and two from the reduction of two molecules of cytochrome c. The reduced cytochrome c is eventually reoxidized by complex IV. The process is cyclic as the ubiquinol created at the Q site can be reused by binding to the Q site of complex III. | 1 | Biochemistry |
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