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In chemistry, nuclear physics, and particle physics, inelastic scattering is a process in which the kinetic energy of a particle or a system of particles changes after a collision. Formally, the kinetic energy of the incident particle is not conserved (in contrast to elastic scattering). In an inelastic scattering process, some of the energy of the incident particle is lost or increased. Although inelastic scattering is historically related to the concept of inelastic collision in dynamics, the two concepts are quite distinct; inelastic collision in dynamics refers to processes in which the total macroscopic kinetic energy is not conserved. In general, scattering due to inelastic collisions will be inelastic, but, since elastic collisions often transfer kinetic energy between particles, scattering due to elastic collisions can also be inelastic, as in Compton scattering meaning the two particles in the collision transfer energy causing a loss of energy in one particle. | 7 | Physical Chemistry |
A proper rotation refers to simple rotation about an axis. Such operations are denoted by where is a rotation of or performed times. The superscript is omitted if it is equal to one. is a rotation through 360°, where . It is equivalent to the Identity () operation. is a rotation of 180°, as is a rotation of 120°, as and so on.
Here the molecule can be rotated into equivalent positions around an axis. An example of a molecule with symmetry is the water () molecule. If the molecule is rotated by 180° about an axis passing through the oxygen atom, no detectable difference before and after the operation is observed.
Order of an axis can be regarded as a number of times that, for the least rotation which gives an equivalent configuration, that rotation must be repeated to give a configuration identical to the original structure (i.e. a 360° or 2 rotation). An example of this is proper rotation, which rotates by represents the first rotation around the axis by is the rotation by while is the rotation by is the identical configuration because it gives the original structure, and it is called an identity element (). Therefore, is an order of three, and is often referred to as a threefold axis. | 7 | Physical Chemistry |
Converting a mixture of H and CO into aliphatic products is a multi-step reaction with several intermediate compounds. The growth of the hydrocarbon chain may be visualized as involving a repeated sequence in which hydrogen atoms are added to carbon and oxygen, the C–O bond is split and a new C–C bond is formed.
For one –CH– group produced by CO + 2 H → (CH) + HO, several reactions are necessary:
* Associative adsorption of CO
* Splitting of the C–O bond
* Dissociative adsorption of 2 H
* Transfer of 2 H to the oxygen to yield HO
* Desorption of HO
* Transfer of 2 H to the carbon to yield CH
The conversion of CO to alkanes involves hydrogenation of CO, the hydrogenolysis (cleavage with H) of C–O bonds, and the formation of C–C bonds. Such reactions are assumed to proceed via initial formation of surface-bound metal carbonyls. The CO ligand is speculated to undergo dissociation, possibly into oxide and carbide ligands. Other potential intermediates are various C fragments including formyl (CHO), hydroxycarbene (HCOH), hydroxymethyl (CHOH), methyl (CH), methylene (CH), methylidyne (CH), and hydroxymethylidyne (COH). Furthermore, and critical to the production of liquid fuels, are reactions that form C–C bonds, such as migratory insertion. Many related stoichiometric reactions have been simulated on discrete metal clusters, but homogeneous Fischer–Tropsch catalysts are of no commercial importance.
Addition of isotopically labelled alcohol to the feed stream results in incorporation of alcohols into product. This observation establishes the facility of C–O bond scission. Using C-labelled ethylene and propene over cobalt catalysts results in incorporation of these olefins into the growing chain. Chain growth reaction thus appears to involve both olefin insertion as well as CO-insertion. | 0 | Organic Chemistry |
Before the use of gas chromatography-mass spectrometry and biomarkers, correlation of locations' geology was used to find how different formations relate to each other and to their environment. Oil-oil correlations (comparing petroleum to other oil found locally or in other areas) and oil-source correlations (comparing petroleum and its source) were performed; infrared spectrometry, refractive indices, solvent extractable organic matter, compound class distribution, and elemental analysis are all methods of doing oil-source correlations. | 9 | Geochemistry |
Due to its relatively short turnover time of ~6 weeks in the human body, Cu serves as an important indicator of cancer and other diseases that rapidly evolve. The serum of cancer patients contains significantly higher levels of Cu than that of healthy patients due to copper chelation by lactate, which is produced via anaerobic glycolysis by tumor cells. These imbalances in Cu homeostasis are reflected isotopically in the serum and organ tissues of patients with various types of cancer, where the serum of cancer patients is generally Cu-depleted relative to the serum of healthy patients, while organ tumors are generally Cu-enriched. In one study, the blood components of patients with hepatocellular carcinomas (HCC) was found to be, on average, depleted in Cu by 0.4‰ relative to the blood of non-cancer patients. In particular, the δCu values of the serum in patients with HCC ranged from -0.66 to +0.47‰ (compared to serum δCu values of -0.39 to +0.38‰ in matched control patients), and the δCu values of the erythrocytes in the HCC patients ranged from -0.07 to +0.92‰ (compared to erythrocyte δCu values of +0.57 to +1.24‰ in matched control patients). The liver tumor tissues in the HCC patients were Cu-enriched relative to healthy liver tissue in the same patients (δCu = -0.02 to +0.43‰; δCu = -0.45 to -0.11‰), and the magnitude of Cu-enrichment mirrored that of the Cu-depletion observed in the cancer patients' serum. Though our understanding of how copper isotopes are fractionated during cancer physiologies is still limited, it is clear that copper isotope ratios may serve as a powerful biomarker of cancer presence and progression. | 9 | Geochemistry |
B3/B4 tRNA-binding domain - B5 protein domain - BAC - back mutation - bacteria - bacterial artificial chromosome - bacteriophage - bacteriophage lambda - bacteriophage scaffolding proteins - band shift assay - base - base pair - benzoyl-CoA 2,3-dioxygenase - benzyl benzoate/disulfiram - benzyl-2-methyl-hydroxybutyrate dehydrogenase - beta-carotene 3-hydroxylase - beta-cyclopiazonate dehydrogenase - beta-glucan-transporting ATPase - beta2-adaptin C-terminal domain - binding site - biological organisation - biological process - Biomolecular gradient - Biomolecule Stretching Database - biotin - birth defect - blotting - blunt end - bone marrow transplantation - box - BP - BRCA1 - BRCA2 - Brix (database) - BSD domain - BURP domain - | 1 | Biochemistry |
Related to the Fermi energy, a few useful quantities also occur often in modern literature.
The Fermi temperature is defined as , where is the Boltzmann constant. The Fermi temperature can be thought of as the temperature at which thermal effects are comparable to quantum effects associated with Fermi statistics. The Fermi temperature for a metal is a couple of orders of magnitude above room temperature. Other quantities defined in this context are Fermi momentum , and Fermi velocity , which are the momentum and group velocity, respectively, of a fermion at the Fermi surface. The Fermi momentum can also be described as , where is the radius of the Fermi sphere and is called the Fermi wave vector.
Note that these quantities are not well-defined in cases where the Fermi surface is non-spherical. | 7 | Physical Chemistry |
In metallurgy, non-ferrous metals are metals or alloys that do not contain iron (allotropes of iron, ferrite, and so on) in appreciable amounts.
Generally more costly than ferrous metals, non-ferrous metals are used because of desirable properties such as low weight (e.g. aluminium), higher conductivity (e.g. copper), non-magnetic properties or resistance to corrosion (e.g. zinc). Some non-ferrous materials are also used in the iron and steel industries. For example, bauxite is used as flux for blast furnaces, while others such as wolframite, pyrolusite, and chromite are used in making ferrous alloys.
Important non-ferrous metals include aluminium, copper, lead, tin, titanium, and zinc, and alloys such as brass. Precious metals such as gold, silver, and platinum and exotic or rare metals such as mercury, tungsten, beryllium, bismuth, cerium, cadmium, niobium, indium, gallium, germanium, lithium, selenium, tantalum, tellurium, vanadium, and zirconium are also non-ferrous. They are usually obtained through minerals such as sulfides, carbonates, and silicates. Non-ferrous metals are usually refined through electrolysis. | 8 | Metallurgy |
Pyruvate molecules produced by glycolysis are actively transported across the inner mitochondrial membrane, and into the matrix where they can either be oxidized and combined with coenzyme A to form CO, acetyl-CoA, and NADH, or they can be carboxylated (by pyruvate carboxylase) to form oxaloacetate. This latter reaction "fills up" the amount of oxaloacetate in the citric acid cycle and is therefore an anaplerotic reaction, increasing the cycles capacity to metabolize acetyl-CoA when the tissues energy needs (e.g., in muscle) are suddenly increased by activity.
In the citric acid cycle, all the intermediates (e.g. citrate, iso-citrate, alpha-ketoglutarate, succinate, fumarate, malate and oxaloacetate) are regenerated during each turn of the cycle. Adding more of any of these intermediates to the mitochondrion therefore means that the additional amount is retained within the cycle, increasing all the other intermediates as one is converted into the other. Hence, the addition of any one of them to the cycle has an anaplerotic effect, and its removal has a cataplerotic effect. These anaplerotic and cataplerotic reactions will, during the course of the cycle, increase or decrease the amount of oxaloacetate available to combine with acetyl-CoA to form citric acid. This in turn increases or decreases the rate of ATP production by the mitochondrion, and thus the availability of ATP to the cell.
Acetyl-CoA, on the other hand, derived from pyruvate oxidation, or from the beta-oxidation of fatty acids, is the only fuel to enter the citric acid cycle. With each turn of the cycle one molecule of acetyl-CoA is consumed for every molecule of oxaloacetate present in the mitochondrial matrix, and is never regenerated. It is the oxidation of the acetate portion of acetyl-CoA that produces CO and water, with the energy thus released captured in the form of ATP.
In the liver, the carboxylation of cytosolic pyruvate into intra-mitochondrial oxaloacetate is an early step in the gluconeogenic pathway, which converts lactate and de-aminated alanine into glucose, under the influence of high levels of glucagon and/or epinephrine in the blood. Here, the addition of oxaloacetate to the mitochondrion does not have a net anaplerotic effect, as another citric acid cycle intermediate (malate) is immediately removed from the mitochondrion to be converted to cytosolic oxaloacetate, and ultimately to glucose, in a process that is almost the reverse of glycolysis.
The enzymes of the citric acid cycle are located in the mitochondrial matrix, with the exception of succinate dehydrogenase, which is bound to the inner mitochondrial membrane as part of Complex II. The citric acid cycle oxidizes the acetyl-CoA to carbon dioxide, and, in the process, produces reduced cofactors (three molecules of NADH and one molecule of FADH) that are a source of electrons for the electron transport chain, and a molecule of GTP (which is readily converted to an ATP). | 1 | Biochemistry |
The novel MEMS cantilever approach detects pressure changes in a photoacoustic cell. High sensitivity is achieved by using a cantilever pressure sensor that is over hundred times more sensitive compared to a membrane, which is conventionally used in photoacoustic spectroscopy. A laser-based readout interferometer is able to accurately measure displacement from well under a picometer up to millimeters. | 7 | Physical Chemistry |
In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct bonds between them. The term metamer was formerly used for the same concept.
For example, butanol , methyl propyl ether , and diethyl ether have the same molecular formula but are three distinct structural isomers.
The concept applies also to polyatomic ions with the same total charge. A classical example is the cyanate ion and the fulminate ion . It is also extended to ionic compounds, so that (for example) ammonium cyanate and urea are considered structural isomers, and so are methylammonium formate and ammonium acetate .
Structural isomerism is the most radical type of isomerism. It is opposed to stereoisomerism, in which the atoms and bonding scheme are the same, but only the relative spatial arrangement of the atoms is different. Examples of the latter are the enantiomers, whose molecules are mirror images of each other, and the cis and trans versions of 2-butene.
Among the structural isomers, one can distinguish several classes including skeletal isomers, positional isomers (or regioisomers), functional isomers, tautomers, and structural topoisomers. | 4 | Stereochemistry |
Lakes and ponds can be very large and support a complex eco-system in which environmental parameters vary widely in all three physical dimensions and with time. Large lakes in the temperate zone often stratify in the warmer months into a warmer upper layers rich in oxygen and a colder lower layer with low oxygen levels. In the autumn, falling temperatures and occasional high winds result in the mixing of the two layers into a more homogeneous whole. When stratification occurs it not only affects oxygen levels but also many related parameters such as iron, phosphate and manganese which are all changed in their chemical form by change in the redox potential of the environment.
Lakes also receive waters, often from many different sources with varying qualities. Solids from stream inputs will typically settle near the mouth of the stream and depending on a variety of factors the incoming water may float over the surface of the lake, sink beneath the surface or rapidly mix with the lake water. All of these phenomena can skew the results of any environmental monitoring unless the process are well understood. | 2 | Environmental Chemistry |
* [http://gpsprot.org GPS-Prot] Web-based data visualization for protein interactions
* PINV - [http://biosual.cbio.uct.ac.za/pinv.html Protein Interaction Network Visualizer] | 1 | Biochemistry |
Some atmospheric effects on the functionality of adhesive devices can be characterized by following the theory of surface energy and interfacial tension. It is known that γ = (1/2)W = (1/2)W. If γ is high, then each species finds it favorable to cohere while in contact with a foreign species, rather than dissociate and mix with the other. If this is true, then it follows that when the interfacial tension is high, the force of adhesion is weak, since each species does not find it favorable to bond to the other. The interfacial tension of a liquid and a solid is directly related to the liquid's wettability (relative to the solid), and thus one can extrapolate that cohesion increases in non-wetting liquids and decreases in wetting liquids. One example that verifies this is polydimethyl siloxane rubber, which has a work of self-adhesion of 43.6 mJ/m in air, 74 mJ/m in water (a nonwetting liquid) and 6 mJ/m in methanol (a wetting liquid).
This argument can be extended to the idea that when a surface is in a medium with which binding is favorable, it will be less likely to adhere to another surface, since the medium is taking up the potential sites on the surface that would otherwise be available to adhere to another surface. Naturally this applies very strongly to wetting liquids, but also to gas molecules that could adsorb onto the surface in question, thereby occupying potential adhesion sites. This last point is actually fairly intuitive: Leaving an adhesive exposed to air too long gets it dirty, and its adhesive strength will decrease. This is observed in the experiment: when mica is cleaved in air, its cleavage energy, W or W, is smaller than the cleavage energy in vacuum, W, by a factor of 13. | 6 | Supramolecular Chemistry |
An ubiquitous example of a hydrogen bond is found between water molecules. In a discrete water molecule, there are two hydrogen atoms and one oxygen atom. The simplest case is a pair of water molecules with one hydrogen bond between them, which is called the water dimer and is often used as a model system. When more molecules are present, as is the case with liquid water, more bonds are possible because the oxygen of one water molecule has two lone pairs of electrons, each of which can form a hydrogen bond with a hydrogen on another water molecule. This can repeat such that every water molecule is H-bonded with up to four other molecules, as shown in the figure (two through its two lone pairs, and two through its two hydrogen atoms). Hydrogen bonding strongly affects the crystal structure of ice, helping to create an open hexagonal lattice. The density of ice is less than the density of water at the same temperature; thus, the solid phase of water floats on the liquid, unlike most other substances.
Liquid water's high boiling point is due to the high number of hydrogen bonds each molecule can form, relative to its low molecular mass. Owing to the difficulty of breaking these bonds, water has a very high boiling point, melting point, and viscosity compared to otherwise similar liquids not conjoined by hydrogen bonds. Water is unique because its oxygen atom has two lone pairs and two hydrogen atoms, meaning that the total number of bonds of a water molecule is up to four.
The number of hydrogen bonds formed by a molecule of liquid water fluctuates with time and temperature. From TIP4P liquid water simulations at 25 °C, it was estimated that each water molecule participates in an average of 3.59 hydrogen bonds. At 100 °C, this number decreases to 3.24 due to the increased molecular motion and decreased density, while at 0 °C, the average number of hydrogen bonds increases to 3.69. Another study found a much smaller number of hydrogen bonds: 2.357 at 25 °C. Defining and counting the hydrogen bonds is not straightforward however.
Because water may form hydrogen bonds with solute proton donors and acceptors, it may competitively inhibit the formation of solute intermolecular or intramolecular hydrogen bonds. Consequently, hydrogen bonds between or within solute molecules dissolved in water are almost always unfavorable relative to hydrogen bonds between water and the donors and acceptors for hydrogen bonds on those solutes. Hydrogen bonds between water molecules have an average lifetime of 10 seconds, or 10 picoseconds. | 6 | Supramolecular Chemistry |
Most of the iron in the body is hoarded and recycled by the reticuloendothelial system, which breaks down aged red blood cells. In contrast to iron uptake and recycling, there is no physiologic regulatory mechanism for excreting iron. People lose a small but steady amount by gastrointestinal blood loss, sweating and by shedding cells of the skin and the mucosal lining of the gastrointestinal tract. The total amount of loss for healthy people in the developed world amounts to an estimated average of a day for men, and 1.5–2 mg a day for women with regular menstrual periods. People with gastrointestinal parasitic infections, more commonly found in developing countries, often lose more. Those who cannot regulate absorption well enough get disorders of iron overload. In these diseases, the toxicity of iron starts overwhelming the body's ability to bind and store it. | 1 | Biochemistry |
Corundum is the name for a structure prototype in inorganic solids, derived from the namesake polymorph of aluminum oxide (α-AlO). Other compounds, especially among the inorganic solids, exist in corundum structure, either in ambient or other conditions. Corundum structures are associated with metal-insulator transition, ferroelectricity, polar magnetism, and magnetoelectric effects. | 3 | Analytical Chemistry |
After a library is created, the genome of an organism can be sequenced to elucidate how genes affect an organism or to compare similar organisms at the genome-level. The aforementioned genome-wide association studies can identify candidate genes stemming from many functional traits. Genes can be isolated through genomic libraries and used on human cell lines or animal models to further research. Furthermore, creating high-fidelity clones with accurate genome representation and no stability issues would contribute well as intermediates for shotgun sequencing or the study of complete genes in functional analysis. | 1 | Biochemistry |
According to the m + n + o + p − q rule, ferrocene requires 2 + 11 + 1 + 2 − 0 = 16 SEPs. 10 CH units provide 15 pairs while Fe provides one pair. | 7 | Physical Chemistry |
The work of Koch, Muller, Rafelski predicts that in a quark–gluon plasma hadronization process the enhancement for each particle species increases with the strangeness content of the particle. The enhancements for particles carrying one, two and three strange or antistrange quarks were measured and this effect was demonstrated by the CERN WA97 experiment in time for the CERN announcement in 2000 of a possible quark–gluon plasma formation in its experiments. These results were elaborated by the successor collaboration NA57 as shown in the enhancement of antibaryon figure. The gradual rise of the enhancement as a function of the variable representing the amount of nuclear matter participating in the collisions, and thus as a function of the geometric centrality of nuclear collision strongly favors the quark–gluon plasma source over normal matter reactions.
A similar enhancement was obtained by the STAR experiment at the RHIC. Here results obtained when two colliding systems at 100 A GeV in each beam are considered: in red the heavier gold–gold collisions and in blue the smaller copper–copper collisions. The energy at RHIC is 11 times greater in the CM frame of reference compared to the earlier CERN work. The important result is that enhancement observed by STAR also increases with the number of participating nucleons. We further note that for the most peripheral events at the smallest number of participants, copper and gold systems show, at the same number of participants, the same enhancement as expected.
Another remarkable feature of these results, comparing CERN and STAR, is that the enhancement is of similar magnitude for the vastly different collision energies available in the reaction. This near energy independence of the enhancement also agrees with the quark–gluon plasma approach regarding the mechanism of production of these particles and confirms that a quark–gluon plasma is created over a wide range of collision energies, very probably once a minimal energy threshold is exceeded. | 7 | Physical Chemistry |
* Definition of the K or P-value
: The K or P-value always only refers to a single species or substance:
: with:
:* concentration of species i of a substance in the octanol-rich phase
:* concentration of species i of a substance in the water-rich phase
: If different species occur in the octanol-water system by dissociation or association, several P-values and one D-value exist for the system. If, on the other hand, the substance is only present in a single species, the P and D values are identical.
: P is usually expressed as a common logarithm, i.e. Log P (also Log P or, less frequently, Log pOW):
: Log P is positive for lipophilic and negative for hydrophilic substances or species.
* Definition of the D-value
: The P-value only correctly refers to the concentration ratio of a single substance distributed between the octanol and water phases. In the case of a substance that occurs as multiple species, it can therefore be calculated by summing the concentrations of all n species in the octanol phase and the concentrations of all n species in the aqueous phase:
: with:
:* concentration of the substance in the octanol-rich phase
:* concentration of the substance in the water-rich phase
: D values are also usually given in the form of the common logarithm as Log D:
: Like Log P, Log D is positive for lipophilic and negative for hydrophilic substances. While P values are largely independent of the pH value of the aqueous phase due to their restriction to only one species, D values are often strongly dependent on the pH value of the aqueous phase. | 7 | Physical Chemistry |
It should first be noted that the first inelastic mechanism of these polymers is the mobility of the chains and the conformational rearrangement of the groups. Then the effect on semi-crystalline and amorphous polymers must be distinguished. In both cases, anchor points must be created that act as "triggers" for the effect. In the case of amorphous polymers, these will be the knots or "tangles" of the chains, and in the case of semi-crystalline polymers, the crystals themselves will form these anchor points.
By modifying the shape of the material under minimal critical stress, the chains slide and a metastable structure is created, which increases the organization and order of the chains (lower entropy), when the deformation load is eliminated, the anchor points provide a storage mechanism for macroscopic stresses in the form of small localized stresses and decreasing entropy.
In the glassy state the rotational motions of the molecules are frozen and impeded, as the temperature increases and the glassy state is reached, these motions thaw and rotations and relaxations occur, the molecules take the form that is entropically most favorable to them, the one with the lowest energy. These movements are called relaxation process and the formation of "random strings" to eliminate stresses is called shape-memory loss.
A polymer will exhibit the shape-memory effect if it is susceptible to being stabilized in a given state of deformation, preventing the molecules from slipping and regaining their higher entropy (lower energy) form. This can be achieved almost entirely by creating crosslinking or vulcanization, these new bonds act as anchors and prevent the relaxation of the chains, the anchor points can be physical or chemical. | 7 | Physical Chemistry |
Lichens are pioneer species, among the first living things to grow on bare rock or areas denuded of life by a disaster. Lichens may have to compete with plants for access to sunlight, but because of their small size and slow growth, they thrive in places where higher plants have difficulty growing. Lichens are often the first to settle in places lacking soil, constituting the sole vegetation in some extreme environments such as those found at high mountain elevations and at high latitudes. Some survive in the tough conditions of deserts, and others on frozen soil of the Arctic regions.
A major ecophysiological advantage of lichens is that they are poikilohydric (poikilo- variable, hydric- relating to water), meaning that though they have little control over the status of their hydration, they can tolerate irregular and extended periods of severe desiccation. Like some mosses, liverworts, ferns and a few resurrection plants, upon desiccation, lichens enter a metabolic suspension or stasis (known as cryptobiosis) in which the cells of the lichen symbionts are dehydrated to a degree that halts most biochemical activity. In this cryptobiotic state, lichens can survive wider extremes of temperature, radiation and drought in the harsh environments they often inhabit.
Lichens do not have roots and do not need to tap continuous reservoirs of water like most higher plants, thus they can grow in locations impossible for most plants, such as bare rock, sterile soil or sand, and various artificial structures such as walls, roofs, and monuments. Many lichens also grow as epiphytes (epi- on the surface, phyte- plant) on plants, particularly on the trunks and branches of trees. When growing on plants, lichens are not parasites; they do not consume any part of the plant nor poison it. Lichens produce allelopathic chemicals that inhibit the growth of mosses. Some ground-dwelling lichens, such as members of the subgenus Cladina (reindeer lichens), produce allelopathic chemicals that leach into the soil and inhibit the germination of seeds, spruce and other plants. Stability (that is, longevity) of their substrate is a major factor of lichen habitats. Most lichens grow on stable rock surfaces or the bark of old trees, but many others grow on soil and sand. In these latter cases, lichens are often an important part of soil stabilization; indeed, in some desert ecosystems, vascular (higher) plant seeds cannot become established except in places where lichen crusts stabilize the sand and help retain water.
Lichens may be eaten by some animals, such as reindeer, living in arctic regions. The larvae of a number of Lepidoptera species feed exclusively on lichens. These include common footman and marbled beauty. They are very low in protein and high in carbohydrates, making them unsuitable for some animals. The Northern flying squirrel uses it for nesting, food and winter water. | 2 | Environmental Chemistry |
Transition metal carbyne complexes are most common for the early transition metals, especially niobium, tantalum, molybdenum, tungsten, and rhenium. They can also have low-valence metals as well as high-valence metals.
The first Fischer carbyne complex was reported in 1973. Two years later in 1975, the first "Schrock carbyne" was reported.
Many high-valent carbyne complexes have since been prepared, often by dehydrohalogenation of carbene complexes. Alternatively, amino-substituted carbyne ligands sometimes form upon protonation of electron-rich isonitrile complexes. Similarly, O-protonation of μ-CO ligands in clusters gives hydroxycarbyne complexes. Vinyl ligands have been shown to rearrange into carbyne ligands. Addition of electrophiles to vinylidene ligands also affords carbyne complexes. | 0 | Organic Chemistry |
Pebble circuits are a very advantageous location for the application of sensor-based ore sorters. Usually it is hard waste recirculating and limiting the total mill capacity. In addition, the tonnage is significantly lower in comparison to the total run-of-mine stream, the size range is applicable and usually uniform and the particles' surfaces are clean. High impact on total mill capacity is reported in the literature. | 3 | Analytical Chemistry |
In chemistry, peroxydicarbonate (sometimes peroxodicarbonate) is a divalent anion with the chemical formula . It is one of the oxocarbon anions, which consist solely of carbon and oxygen. Its molecular structure can be viewed as two carbonate anions joined so as to form a peroxide bridge –O–O–.
The anion is formed, together with peroxocarbonate , at the negative electrode during electrolysis of molten lithium carbonate. The anion can also be obtained by electrolysis of a saturated solution of rubidium carbonate in water.
In addition, the peroxodicarbonate anion can be obtained by electrosynthesis on boron doped diamond (BDD) during water oxidation. The formal oxidation of two carbonate ions takes place at the anode. Due to the high oxidation potential of the peroxodicarbonate anion, a high anodic overpotential is necessary. This is even more important if hydroxyl radicals are involved in the formation process. Recent publications show that a concentration of 282 mmol/L of peroxodicarbonate can be reached in an undivided cell with sodium carbonate as starting material at current densities of 720 mA/cm. The described process is suitable for the pilot scale production of sodium peroxodicarbonate.
Potassium peroxydicarbonate KCO was obtained by Constam and von Hansen in 1895; its crystal structure was determined only in 2002. It too can be obtained by electrolysis of a saturated potassium carbonate solution at −20 °C. It is a light blue crystalline solid that decomposes at 141 °C, releasing oxygen and carbon dioxide, and decomposes slowly at lower temperatures.
Rubidium peroxodicarbonate is a light blue crystalline solid that decomposes at . Its structure was published in 2003. In both salts, each of the two carbonate units is planar. In the rubidium salt the whole molecule is planar, whereas in the potassium salt the two units lie on different and nearly perpendicular planes, both of which contain the O–O bond. | 7 | Physical Chemistry |
In the early years of serious research into the locations of stations on the Antonine Itineraries, the location of Ariconium was in doubt, and William Camden (1551–1623) suggested Magnis, the site of modern Kenchester, some northwest of modern Hereford. Later analysis of the Antonine Itineraries, notably by John Horsley (1685–1732), refined previous estimates and ultimately placed Ariconium at Bury Hill, Weston under Penyard, west-northwest of Glevum (at modern Gloucester), and northeast of Blestium (at modern Monmouth). With confidence that the overgrown ruins near Weston under Penyard were actually the site of Ariconium, local people began clearing away the brush, revealing the enormous magnitude of the cinder piles, and further revealing the walls of buildings. Stories emerged of significant Roman-era relics, and there were unverified stories that existing relics having no provenance had actually been found in Ariconium.
Such capable modern research as has been done so far supports the characterisation of a large iron working site with massive refuse piles covering approximately , pottery remnants, and numerous artefacts. Finds have included pre-Roman British coins, including one minted by Cunobelin, and coins from the Roman arrival until 360, after which there are no coins found. | 8 | Metallurgy |
The Novartis-Drew Award for Biomedical Research is an award jointly presented by Novartis and Drew University. It comprises a cash award (originally $2000) and a plaque. The award was initially created as the Ciba-Drew Award for Biomedical Research and renamed following the change of company name from Ciba-Geigy to Novartis in 1996. | 1 | Biochemistry |
Drosha shares striking structural similarity with the downstream ribonuclease Dicer, suggesting an evolutionary relationship, though Drosha and related enzymes are found only in animals while Dicer relatives are widely distributed, including among protozoans. Both components of the microprocessor complex are conserved among the vast majority of metazoans with known genomes. Mnemiopsis leidyi, a ctenophore, lacks both Drosha and DGCR8 homologs, as well as recognizable miRNAs, and is the only known metazoan with no detectable genomic evidence of Drosha. In plants, the miRNA biogenesis pathway is somewhat different; neither Drosha nor DGCR8 has a homolog in plant cells, where the first step in miRNA processing is usually executed by a different nuclear ribonuclease, DCL1, a homolog of Dicer.
It has been suggested based on phylogenetic analysis that the key components of RNA interference based on exogenous substrates were present in the ancestral eukaryote, likely as an immune mechanism against viruses and transposable elements. Elaboration of this pathway for miRNA-mediated gene regulation is thought to have evolved later. | 1 | Biochemistry |
Flutamide has been identified as an agonist of the aryl hydrocarbon receptor. This may be involved in the hepatotoxicity of flutamide. | 4 | Stereochemistry |
Crosslinking is often measured by swelling tests. The crosslinked sample is placed into a good solvent at a specific temperature, and either the change in mass or the change in volume is measured. The more crosslinking, the less swelling is attainable. Based on the degree of swelling, the Flory Interaction Parameter (which relates the solvent interaction with the sample), and the density of the solvent, the theoretical degree of crosslinking can be calculated according to Flory's Network Theory. Two ASTM standards are commonly used to describe the degree of crosslinking in thermoplastics. In ASTM D2765, the sample is weighed, then placed in a solvent for 24 hours, weighed again while swollen, then dried and weighed a final time. The degree of swelling and the soluble portion can be calculated. In another ASTM standard, F2214, the sample is placed in an instrument that measures the height change in the sample, allowing the user to measure the volume change. The crosslink density can then be calculated. | 7 | Physical Chemistry |
Cleaving relies on planar weaknesses of the chemical bonds in the crystal structure of a mineral. If a sharp blow is applied at the correct angle, the stone may split cleanly apart. While cleaving is sometimes used to split uncut gemstones into smaller pieces, it is never used to produce facets. Cleaving of diamonds was once common, but as the risk of damaging a stone is too high, undesirable diamond pieces often resulted. The preferred method of splitting diamonds into smaller pieces is now sawing.
An older and more primitive style of faceting machine called a jamb peg machine used wooden dop sticks of precise length and a "mast" system consisting of a plate with holes carefully placed in it. By placing the back end of the dop into one of the many holes, the stone could be introduced to the lap at precise angles. These machines took considerable skill to operate effectively.
Another method of facet cutting involves the use of cylinders to produce curved, concave facets. This technique can produce many unusual and artistic variations of the traditional faceting process. | 3 | Analytical Chemistry |
Benzene is used mainly as an intermediate to make other chemicals, above all ethylbenzene (and other alkylbenzenes), cumene, cyclohexane, and nitrobenzene. In 1988 it was reported that two-thirds of all chemicals on the American Chemical Societys lists contained at least one benzene ring. More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene, which is used to make polymers and plastics like polystyrene. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. Cyclohexane consumes around 10% of the worlds benzene production; it is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. In 2013, the biggest consumer country of benzene was China, followed by the USA. Benzene production is currently expanding in the Middle East and in Africa, whereas production capacities in Western Europe and North America are stagnating.
Toluene is now often used as a substitute for benzene, for instance as a fuel additive. The solvent-properties of the two are similar, but toluene is less toxic and has a wider liquid range. Toluene is also processed into benzene. | 2 | Environmental Chemistry |
*Bisulfite sequencing – the biochemical method used to determine the presence or absence of methyl groups on a DNA sequence
*MethDB DNA Methylation Database
*Microscale thermophoresis – a biophysical method to determine the methylisation state of DNA
*Remethylation, the reversible removal of methyl group in methionine and 5-methylcytosine | 0 | Organic Chemistry |
The ten-step catabolic pathway of glycolysis is the initial phase of free-energy release in the breakdown of glucose and can be split into two phases, the preparatory phase and payoff phase. ADP and phosphate are needed as precursors to synthesize ATP in the payoff reactions of the TCA cycle and oxidative phosphorylation mechanism. During the payoff phase of glycolysis, the enzymes phosphoglycerate kinase and pyruvate kinase facilitate the addition of a phosphate group to ADP by way of substrate-level phosphorylation. | 1 | Biochemistry |
One of the first substances that was reported to produce an oxygen diffusion-enhancing effect was crocetin, a carotenoid that occurs naturally in plants such as crocus sativus, and is related to another carotenoid, saffron. Saffron has been used culturally (e.g., as a dye) and medicinally since ancient times.
Trans sodium crocetinate (TSC), a synthetic drug containing the carotenoid structure of trans crocetin has been extensively investigated in animal disease models and in human clinical trials. Clinical trials of TSC have focused on testing the compound's effectiveness in sensitizing hypoxic cancer cells to radiation therapy in patients with glioblastoma, an aggressive form of brain cancer.
TSC, which is being developed by Diffusion Pharmaceuticals, has been shown to enhance the oxygenation of hypoxic tumor tissue and belongs to a subclass of oxygen diffusion-enhancing compounds known as bipolar trans carotenoid salts. Diffusion Pharmaceuticals is currently investigating the use of trans sodium crocetinate in the treatment of COVID-19, acute stroke, and solid cancerous tumors. | 1 | Biochemistry |
The KDPG is then converted into pyruvate and glyceraldehyde-3-phosphate in the presence of enzyme KDPG aldolase. For the pyruvate, the ED pathway ends here, and the pyruvate then goes into further metabolic pathways (TCA cycle, ETC cycle, etc).
The other product (glyceraldehyde-3-phosphate) is further converted by entering into the glycolysis pathway, via which it, too, gets converted into pyruvate for further metabolism. | 1 | Biochemistry |
This process was developed by the St. Joseph Mineral Company in 1930, and is the only pyrometallurgical process still used in the US to smelt zinc. The advantage of this system is that it is able to smelt a wide variety of zinc-bearing materials, including electric arc furnace dust. The disadvantage of this process is that it is less efficient than the electrolysis process.
The process begins with a downdraft sintering operation. The sinter, which is a mixture of roaster calcine and EAF (electric arc furnace) calcine, is loaded onto a gate type conveyor and then combustions gases are pumped through the sinter. The carbon in the combustion gases react with some impurities, such as lead, cadmium, and halides. These impurities are driven off into filtration bags. The sinter after this process, called product sinter, usually has a composition of 48% zinc, 8% iron, 5% aluminium, 4% silicon, 2.5% calcium, and smaller quantities of magnesium, lead, and other metals. The sinter product is then charged with coke into an electric retort furnace. A pair of graphite electrodes from the top and bottom of the furnace produce current flow through the mixture. The coke provides electrical resistance to the mixture in order to heat the mixture to and produce carbon monoxide. These conditions allow for the following chemical reaction to occur:
The zinc vapour and carbon dioxide pass to a vacuum condenser, where zinc is recovered by bubbling through a molten zinc bath. Over 95% of the zinc vapour leaving the retort is condensed to liquid zinc. The carbon dioxide is regenerated with carbon, and the carbon monoxide is recycled back to the retort furnace. | 8 | Metallurgy |
The Nernst–Planck equation is a continuity equation for the time-dependent concentration of a chemical species:
where is the flux. It is assumed that the total flux is composed of three elements: diffusion, advection, and electromigration. This implies that the concentration is affected by an ionic concentration gradient , flow velocity , and an electric field :
where is the diffusivity of the chemical species, is the valence of ionic species, is the elementary charge, is the Boltzmann constant, and is the absolute temperature. The electric field may be further decomposed as:
where is the electric potential and is the magnetic vector potential. Therefore, the Nernst–Planck equation is given by: | 7 | Physical Chemistry |
The Cape York meteorite, also known as the Innaanganeq meteorite, is one of the largest known iron meteorites, classified as a medium octahedrite in chemical group IIIAB. In addition to many small fragments, at least eight large fragments with a total mass of 58 tonnes have been recovered, the largest weighing . The meteorite is named after the location where the largest fragment was found: east of Cape York, in Savissivik, Meteorite Island, Greenland.
The date of the meteorite fall is debated, but was likely within the last few thousand years. It was known to the Inughuit (the local Inuit) for centuries, who used it as a source of meteoritic iron for tools. The first foreigner to reach the meteorite was Robert Peary in 1894, with the assistance of Inuit guides. Large pieces are on display at the American Museum of Natural History and the University of Copenhagen Geological Museum. | 8 | Metallurgy |
Structuring of absorbing materials has both positive and negative affects on cell performance. Structuring allows for light absorption and carrier collection to occur in different places, which loosens the requirements for pure materials and helps with catalysis. This allows for the use of non-precious and oxide catalysts that may be stable in more oxidizing conditions. However, these devices have lower open-circuit potentials which may contribute to lower performance. | 5 | Photochemistry |
Hematochrome is a yellow, orange, or (most commonly) red biological pigment present in some green algae, especially when exposed to intense light. It is a name used mainly in older literature. Hematochrome is a mixture of carotenoid pigments and their derivates. | 1 | Biochemistry |
The earliest reported synthesis of a rotaxane in 1967 relied on the statistical probability that if two halves of a dumbbell-shaped molecule were reacted in the presence of a macrocycle that some small percentage would connect through the ring. To obtain a reasonable quantity of rotaxane, the macrocycle was attached to a solid-phase support and treated with both halves of the dumbbell 70 times and then severed from the support to give a 6% yield. However, the synthesis of rotaxanes has advanced significantly and efficient yields can be obtained by preorganizing the components utilizing hydrogen bonding, metal coordination, hydrophobic forces, covalent bonds, or coulombic interactions. The three most common strategies to synthesize rotaxane are "capping", "clipping", and "slipping", though others do exist. Recently, Leigh and co-workers described a new pathway to mechanically interlocked architectures involving a transition-metal center that can catalyse a reaction through the cavity of a macrocycle. | 6 | Supramolecular Chemistry |
Aliphatic metal alkoxides decompose in water: where R is an organic substituent and L is an unspecified ligand (often an alkoxide). A well-studied case is the irreversible hydrolysis of titanium isopropoxide:
By controlling the stoichiometry and steric properties of the alkoxide, such reactions can be arrested leading to metal-oxy-alkoxides, which usually are oligonuclear. Other alcohols can be employed in place of water. In this way one alkoxide can be converted to another, and the process is properly referred to as alcoholysis (although there is an issue of terminology confusion with transesterification, a different process - see below). The position of the equilibrium can be controlled by the acidity of the alcohol; for example phenols typically react with alkoxides to release alcohols, giving the corresponding phenoxide. More simply, the alcoholysis can be controlled by selectively evaporating the more volatile component. In this way, ethoxides can be converted to butoxides, since ethanol (b.p. 78 °C) is more volatile than butanol (b.p. 118 °C). | 0 | Organic Chemistry |
Modern coupling chemistries allow other properties of polyfluorenes to be controlled through implementation of complex molecular designs.
The above polymer structure pictured has excellent photoluminescent quantum yields (partly due to its fluorene monomer) excellent stability (due to its oxadiazole comonomer) good solubility (due to its many and branched alkyl side chains) and has an amine functionalized side chain for ease of tethering to other molecules or to a substrate.
The luminescent color of polyfluorenes can be changed, for example, (from blue to green-yellow) by adding functional groups which participate in excited state intramolecular proton transfer. Exchanging the alkoxy side chains for alcohol side groups allows for energy dissipation (and a red-shift in emission) through reversible transfer of a proton from the alcohol to the nitrogen (on the oxadiazole). These complicated molecular structures were engineered to have these properties and were only able to be realized through careful control of their ordering and side group functionality. | 7 | Physical Chemistry |
In 1835, Charles Wheatstone reported that different metals could be easily distinguished by the different bright lines in the emission spectra of their sparks, thereby introducing an alternative mechanism to flame spectroscopy. In 1849, J. B. L. Foucault experimentally demonstrated that absorption and emission lines appearing at the same wavelength are both due to the same material, with the difference between the two originating from the temperature of the light source. In 1853, the Swedish physicist Anders Jonas Ångström presented observations and theories about gas spectra in his work Optiska Undersökningar (Optical investigations) to the [[Royal Swedish Academy of Sciences. Ångström postulated that an incandescent gas emits luminous rays of the same wavelength as those it can absorb. Ångström was unaware of Foucalt's experimental results. At the same time George Stokes and William Thomson (Kelvin) were discussing similar postulates. Ångström also measured the emission spectrum from hydrogen later labeled the Balmer lines. In 1854 and 1855, David Alter published observations on the spectra of metals and gases, including an independent observation of the Balmer lines of hydrogen.
The systematic attribution of spectra to chemical elements began in the 1860s with the work of German physicists Robert Bunsen and Gustav Kirchhoff, who found that Fraunhofer lines correspond to emission spectral lines observed in laboratory light sources. This laid way for spectrochemical analysis in laboratory and astrophysical science. Bunsen and Kirchhoff applied the optical techniques of Fraunhofer, Bunsens improved flame source and a highly systematic experimental procedure to a detailed examination of the spectra of chemical compounds. They established the linkage between chemical elements and their unique spectral patterns. In the process, they established the technique of analytical spectroscopy. In 1860, they published their findings on the spectra of eight elements and identified these elements presence in several natural compounds. They demonstrated that spectroscopy could be used for trace chemical analysis and several of the chemical elements they discovered were previously unknown. Kirchhoff and Bunsen also definitively established the link between absorption and emission lines, including attributing solar absorption lines to particular elements based on their corresponding spectra. Kirchhoff went on to contribute fundamental research on the nature of spectral absorption and emission, including what is now known as Kirchhoffs law of thermal radiation. Kirchhoffs applications of this law to spectroscopy are captured in three laws of spectroscopy:
#An incandescent solid, liquid or gas under high pressure emits a continuous spectrum.
#A hot gas under low pressure emits a "bright-line" or emission-line spectrum.
#A continuous spectrum source viewed through a cool, low-density gas produces an absorption-line spectrum.
In the 1860s the husband-and-wife team of William and Margaret Huggins used spectroscopy to determine that the stars were composed of the same elements as found on earth. They also used the non-relativistic Doppler shift (redshift) equation on the spectrum of the star Sirius in 1868 to determine its axial speed. They were the first to take a spectrum of a planetary nebula when the Cat's Eye Nebula (NGC 6543) was analyzed. Using spectral techniques, they were able to distinguish nebulae from stars.
August Beer observed a relationship between light absorption and concentration and created the color comparator which was later replaced by a more accurate device called the spectrophotometer. | 7 | Physical Chemistry |
Medium-sized rings (7–13 carbons) experience more strain energy than cyclohexane, due mostly to deviation from ideal vicinal angles, or Pitzer strain. Molecular mechanics calculations indicate that transannular strain, also known as Prelog strain, does not play an essential role. Transannular reactions however, such as 1,5-shifts in cyclooctane substitution reactions, are well known. | 4 | Stereochemistry |
Glycosyl iodides were first introduced for use in glycosylation reactions in 1901 by Koenigs and Knorr although were often considered too reactive for synthetic use. Recently several research groups have shown these donors to have unique reactive properties and can differ from other glycosyl chlorides or bromides with respect to reaction time, efficiency, and stereochemistry. Glycosyl iodides may be made under a variety of conditions, one method of note is the reaction of a 1-O-acetylpyranoside with TMSI.
Iodide donors may typically be activated under basic conditions to give β-glycosides with good selectivity. The use of tetraalkylammonium iodide salts such as tetrabutylammonium iodide (TBAI) allows for in-situ anomerization of the α-glycosyl halide to the β-glycosyl halide and provides the α-glycoside in good selectivity. | 0 | Organic Chemistry |
Soil gases have been used for multiple scientific studies to explore topics such as microseepage, earthquakes, and gaseous exchange between the soil and the atmosphere. Microseepage refers to the limited release of hydrocarbons on the soil surface and can be used to look for petroleum deposits based on the assumption that hydrocarbons vertically migrate to the soil surface in small quantities. Migration of soil gases, specifically radon, can also be examined as earthquake precursors. Furthermore, for processes such as soil thawing and rewetting, for example, large sudden changes in soil respiration can cause increased flux of soil gases such as carbon dioxide and methane, which are greenhouse gases. These fluxes and interactions between soil gases and atmospheric air can further be analyzed by distance from the soil surface. | 9 | Geochemistry |
YAC (yeast artificial chromosome) - Ycf9 protein domain - YchF-GTPase C terminal protein domain - Ydc2 protein domain - YDG SRA protein domain - YecM bacterial protein domain - YjeF N terminal protein domain - YopH, N-terminal - YopR bacterial protein domain - Y Y Y - | 1 | Biochemistry |
Iron plays an essential role in marine systems and can act as a limiting nutrient for planktonic activity. Because of this, too much of a decrease in iron may lead to a decrease in growth rates in phytoplanktonic organisms such as diatoms. Iron can also be oxidized by marine microbes under conditions that are high in iron and low in oxygen.
Iron can enter marine systems through adjoining rivers and directly from the atmosphere. Once iron enters the ocean, it can be distributed throughout the water column through ocean mixing and through recycling on the cellular level. In the arctic, sea ice plays a major role in the store and distribution of iron in the ocean, depleting oceanic iron as it freezes in the winter and releasing it back into the water when thawing occurs in the summer. The iron cycle can fluctuate the forms of iron from aqueous to particle forms altering the availability of iron to primary producers. Increased light and warmth increases the amount of iron that is in forms that are usable by primary producers. | 1 | Biochemistry |
The formation of dropwise condensation on PDRC surfaces can alter the infrared emittance of the surface of selective PDRC emitters, which can weaken their performance. Even in semi-arid environments, dew formation on PDRC surfaces can occur. Thus, the cooling power of selective emitters "may broaden the narrowband emittances of the selective emitter and reduce their sub-ambient cooling power and their supposed cooling benefits over broadband emitters," as per Simsek et al., who discuss the implications on the performance of selective emitters: | 7 | Physical Chemistry |
Bischofberger has received a Bachelor of Science in Chemistry from the University of Innsbruck, a Ph.D. in Organic Chemistry at the ETH Zurich with Oskar Jeger, and has done postdoctoral work at Harvard University with George M. Whitesides and Syntex Research. | 0 | Organic Chemistry |
The isomeric shift (also called isomer shift) is the shift on atomic spectral lines and gamma spectral lines, which occurs as a consequence of replacement of one nuclear isomer by another. It is usually called isomeric shift on atomic spectral lines and Mössbauer isomeric shift respectively. If the spectra also have hyperfine structure the shift refers to the center of gravity of the spectra. The isomeric shift provides important information about the nuclear structure and the physical, chemical or biological environment of atoms. More recently the effect has also been proposed as a tool in the search for the time variation of fundamental constants of nature. | 7 | Physical Chemistry |
In geometry, the dyakis dodecahedron /ˈdʌɪəkɪsˌdəʊdɪkəˈhiːdrən/ or diploid is a variant of the deltoidal icositetrahedron with pyritohedral symmetry, transforming the kite faces into chiral quadrilaterals. It is the dual of the cantic snub octahedron. It can be constructed by enlarging 24 of the 48 faces of the disdyakis dodecahedron, and is inscribed in the dyakis dodecahedron, thus it exists as a hemihedral form of it with indices {hkl}. It can be constructed into two non regular pentagonal dodecahedra, the pyritohedron and the tetartoid. The transformation to the pyritohedron can be made by combining two adjacent trapezoids that share a long edge together into one hexagon face, which is a pyritohedral pentagon with an extra vertex added. The edges that bend at it can be combined and the vertex removed to finally get the pentagon. The transformation to the tetartoid can be made by enlarging 12 of the dyakis dodecahedron's 24 faces.
Since the quadrilaterals are chiral and non-regular, the dyakis dodecahedron is a non-uniform polyhedron, a type of polyhedron that isnt vertex transitive and doesnt have regular polygon faces. Since it is face-transitive, it is an isohedron. The name diploid derives from the Greek word διπλάσιος (diplásios), meaning twofold since it has 2-fold symmetry along its 6 octahedral vertices. It has the same number of faces, edges and vertices as the deltoidal icositetrahedron as they are topologically identical. | 3 | Analytical Chemistry |
Following 2D SDS PAGE the proteins can be transferred to a polyvinylidene difluoride (PVDF) blotting membrane for further analysis. Edman degradations can be performed directly from a PVDF membrane. N-terminal residue sequencing resulting in five to ten amino acid may be sufficient to identify a Protein of Interest (POI). | 0 | Organic Chemistry |
Quark matter or QCD matter (quantum chromodynamic) refers to any of a number of hypothetical phases of matter whose degrees of freedom include quarks and gluons, of which the prominent example is quark-gluon plasma. Several series of conferences in 2019, 2020, and 2021 were devoted to this topic.
Quarks are liberated into quark matter at extremely high temperatures and/or densities, and some of them are still only theoretical as they require conditions so extreme that they cannot be produced in any laboratory, especially not at equilibrium conditions. Under these extreme conditions, the familiar structure of matter, where the basic constituents are nuclei (consisting of nucleons which are bound states of quarks) and electrons, is disrupted. In quark matter it is more appropriate to treat the quarks themselves as the basic degrees of freedom.
In the standard model of particle physics, the strong force is described by the theory of QCD. At ordinary temperatures or densities this force just confines the quarks into composite particles (hadrons) of size around 10 m = 1 femtometer = 1 fm (corresponding to the QCD energy scale Λ ≈ 200 MeV) and its effects are not noticeable at longer distances.
However, when the temperature reaches the QCD energy scale (T of order 10 kelvins) or the density rises to the point where the average inter-quark separation is less than 1 fm (quark chemical potential μ around 400 MeV), the hadrons are melted into their constituent quarks, and the strong interaction becomes the dominant feature of the physics. Such phases are called quark matter or QCD matter.
The strength of the color force makes the properties of quark matter unlike gas or plasma, instead leading to a state of matter more reminiscent of a liquid. At high densities, quark matter is a Fermi liquid, but is predicted to exhibit color superconductivity at high densities and temperatures below 10 K. | 7 | Physical Chemistry |
There are several design considerations and mitigation techniques that can be used to reduce the susceptibility to CAF. Certain material selection (i.e. laminate) and design rules (i.e. via spacing) can help reduce CAF risk. Poor adhesion between the resin and glass fibers in the PCB can create a path for CAF to occur. This may depend on parameters of the silane finish applied to the glass fibers, which is used to promote adhesion to the resin. There are also testing standards that can be performed to assess CAF risk. IPC TM-650 2.6.25 provides a test method to assess CAF susceptibility. Additionally, IPC TM-650 2.6.16 provides a pressure vessel test method to rapidly evaluate glass epoxy laminate integrity. This is helpful but it may often be better to use design rules and proper material selection to proactively mitigate the issue. | 7 | Physical Chemistry |
The visual cycle occurs via G-protein coupled receptors called retinylidene proteins which consists of a visual opsin and a chromophore 11-cis-retinal. The 11-cis-retinal is covalently linked to the opsin receptor via Schiff base. When it absorbs a photon, 11-cis-retinal undergoes photoisomerization to all-trans-retinal, which changes the conformation of the opsin GPCR leading to signal transduction cascades which causes closure of cyclic GMP-gated cation channel, and hyperpolarization of the photoreceptor cell. Following photoisomerization, all-trans-retinal is released from the opsin protein and reduced to all-trans-retinol, which travels to the retinal pigment epithelium to be "recharged". It is first esterified by lecithin retinol acyltransferase (LRAT) and then converted to 11-cis-retinol by the isomerohydrolase RPE65. The isomerase activity of RPE65 has been shown; it is uncertain whether it also acts as the hydrolase. Finally, it is oxidized to 11-cis-retinal before traveling back to the photoreceptor cell outer segment where it is again conjugated to an opsin to form new, functional visual pigment (retinylidene protein), namely photopsin or rhodopsin. | 1 | Biochemistry |
* F. Asinger: Methanol, Chemie- und Energierohstoff. Akademie-Verlag, Berlin, 1987, , .
* Martin Bertau, Heribert Offermanns, Ludolf Plass, Friedrich Schmidt, Hans-Jürgen Wernicke: Methanol: The Basic Chemical and Energy Feedstock of the Future: Asingers Vision Today', 750 Seiten, Verlag Springer; 2014,
* †George A. Olah, Alain Goeppert, G. K. Surya Prakash, Beyond Oil and Gas: The Methanol Economy – Third, Updated and Enlarged Edition, Wiley-VCH, 2018, . | 2 | Environmental Chemistry |
The basic driving force for protein crystallization is to optimize the number of bonds one can form with another protein through intermolecular interactions. These interactions depend on electron densities of molecules and the protein side chains that change as a function of pH. The tertiary and quaternary structure of proteins are determined by intermolecular interactions between the amino acids’ side groups, in which the hydrophilic groups are usually facing outwards to the solution to form a hydration shell to the solvent (water). As the pH changes, the charge on these polar side group also change with respect to the solution pH and the protein's pKa. Hence, the choice of pH is essential either to promote the formation of crystals where the bonding between molecules to each other is more favorable than with water molecules. pH is one of the most powerful manipulations that one can assign for the optimal crystallization condition. | 3 | Analytical Chemistry |
A possible alternative to the detection of epitranscriptomic modifications by SMRT sequencing is the direct detection using the Nanopore sequencing technologies. This technique exploits nanometer-sized protein channels embedded into a membrane or solid materials, and coupled to sensors, able to detect the amplitude and duration of the variations of the ionic current passing through the pore. As the RNA passes through the nanopore, the blockage leads to a disruption in current stream, which is different for the different bases, included modified ones, and therefore can be used to identify possible modifications. By producing single-molecule reads, without previous RNA amplification and conversion to cDNA, these techniques can lead to the production of quantitative transcriptome-wide maps.
In particular, the Nanopore technology proved to be effective in detecting the presence of two nucleotide analogs in RNA: N-methyladenosine (m6A) and 5-methylcytosine (5-mC). Using Hidden Markov Models (HMM) or recurrent neural networks (RNN) trained with known sequences, it was possible to demonstrate that the modified nucleotides produce a characteristic disruption in the ionic current when passing through the pore, and that these data can be used to identify the nucleotide. | 1 | Biochemistry |
HACs were first constructed de novo in 1997 by adding alpha-satellite DNA to telomeric and genomic DNA in human HT1080 cells. This resulted in an entirely new microchromosome that contained DNA of interest, as well as elements allowing it to be structurally and mitotically stable, such as telomeric and centromeric sequences. Due to the difficulty of de novo HAC formation, this method has largely been abandoned. | 1 | Biochemistry |
Geoffrey Norman Malcolm (23 April 1931 – 11 August 2019) was a New Zealand physical chemist. Appointed in 1969, he was the first chemistry professor at Massey University. | 7 | Physical Chemistry |
The history and evolution of reversed phase stationary phases in described in detail in an article by Majors, Dolan, Carr and Snyder.
In the 1970s, most liquid chromatography runs were performed using solid particles as the stationary phases, made of unmodified silica gel or alumina. This type of technique is now referred to as normal-phase chromatography. Since the stationary phase is hydrophilic in this technique, and the mobile phase is non-polar (consisting of organic solvents such as hexane and heptane), biomolecules with hydrophilic properties in the sample adsorb to the stationary phase strongly. Moreover, they were not dissolved easily in the mobile phase solvents. At the same time hydrophobic molecules experience less affinity to the polar stationary phase, and elute through it early with not enough retention. This was the reasons why during the 1970s the silica based particles were treated with hydrocarbons, immobilized or bonded on their surface, and the mobile phases were switched to aqueous and polar in nature, to accommodate biomedical substances.
The use of a hydrophobic stationary phase and polar mobile phases is essentially the reverse of normal phase chromatography, since the polarity of the mobile and stationary phases have been inverted – hence the term reversed-phase chromatography. As a result, hydrophobic molecules in the polar mobile phase tend to adsorb to the hydrophobic stationary phase, and hydrophilic molecules in the sample pass through the column and are eluted first. Hydrophobic molecules can be eluted from the column by decreasing the polarity of the mobile phase using an organic (non-polar) solvent, which reduces hydrophobic interactions. The more hydrophobic the molecule, the more strongly it will bind to the stationary phase, and the higher the concentration of organic solvent that will be required to elute the molecule.
Many of the mathematical parameters of the theory of chromatography and experimental considerations used in other chromatographic methods apply to RP-LC as well (for example, the selectivity factor, chromatographic resolution, plate count, etc. It can be used for the separation of a wide variety of molecules. It is typically used for separation of proteins, because the organic solvents used in normal-phase chromatography can denature many proteins.
Today, RP-LC is a frequently used analytical technique. There are huge variety of stationary phases available for use in RP-LC, allowing great flexibility in the development of the separation methods. | 3 | Analytical Chemistry |
The Brønsted–Lowry theory (also called proton theory of acids and bases) is an acid–base reaction theory which was first developed by Johannes Nicolaus Brønsted and Thomas Martin Lowry independently in 1923. The basic concept of this theory is that when an acid and a base react with each other, the acid forms its conjugate base, and the base forms its conjugate acid by exchange of a proton (the hydrogen cation, or H). This theory generalises the Arrhenius theory. | 7 | Physical Chemistry |
Most NONOates are stable in alkaline solution above pH 8.0 (e. g. 10 mM NaOH) and can be stored at −20 °C in this way for the short term. To generate NO from NONOates, the pH is lowered accordingly. Typically, a dilution of the stock NONOate solution is made in a phosphate buffer (pH 7.4; tris buffers can also be used) and incubated at room temperature for the desired time to allow NO to accumulate in solution. This is often visible as bubbles at high NONOate concentrations. Incubation time is important, since the different NONOates have different half-lives (t) in phosphate buffer at pH 7.4. For example, the half-life of MAHMA NONOate under these conditions is ~3.5 minutes, whilst the t of DPTA NONOate is 300 minutes. This is often useful in biological systems, where a combination of different NONOates can be used to give a sustained release of nitric oxide. At pH 5.0, most NONOates are considered to decompose almost instantaneously. | 0 | Organic Chemistry |
* Oxime compounds are used as antidotes for nerve agents. A nerve agent inactivates acetylcholinesterase by phosphorylation. Oxime compounds can reactivate acetylcholinesterase by attaching to phosphorus, forming an oxime-phosphonate, which then splits away from the acetylcholinesterase molecule. Oxime nerve-agent antidotes are pralidoxime (also known as 2-PAM), obidoxime, methoxime, HI-6, Hlo-7, and TMB-4. The effectiveness of the oxime treatment depends on the particular nerve agent used.
* Perillartine, the oxime of perillaldehyde, is used as an artificial sweetener in Japan. It is 2000 times sweeter than sucrose.
* Diaminoglyoxime is a key precursor to various compounds containing the highly reactive furazan ring.
* Methyl ethyl ketoxime is a skin-preventing additive in many oil-based paints.
* Buccoxime and 5-methyl-3-heptanone oxime ("Stemone") are perfume ingredients.
*Fluvoxamine is used as an antidepressant. | 0 | Organic Chemistry |
The CRC Handbook of Chemistry and Physics defines specific rotation as:
= α/γl, where α is the angle through which plane polarized light is rotated by a solution of mass concentration γ and path length l. Here θ is the Celsius temperature and λ the wavelength of the light at which the measurement is carried out.</blockquote>
Values for specific rotation are reported in units of deg·mL·g·dm, which are typically shortened to just degrees, wherein the other components of the unit are tacitly assumed. These values should always be accompanied by information about the temperature, solvent and wavelength of light used, as all of these variables can affect the specific rotation. As noted above, temperature and wavelength are frequently reported as a superscript and subscript, respectively, while the solvent is reported parenthetically, or omitted if it happens to be water. | 4 | Stereochemistry |
Starting in the 2010s, despite a global ban on the production of CFCs, five of these ozone-damaging emissions were on the rise.
The atmospheric abundance of CFC-13 rose from 3.0 parts per trillion (ppt) in year 2010 to 3.3 ppt in year 2020 based on analysis of air samples gathered from sites around the world.
Contrary to the Montreal Protocol, the atmospheric emissions of CFC-13 and four other chlorofluorocarbons (CFCs), increased between 2010 and 2020.
As of 2023, the drivers behind the increase in CFC-13 and CFC-112a emissions were not certain. | 2 | Environmental Chemistry |
In analytical chemistry, a standard solution (titrant or titrator) is a solution containing an accurately known concentration. Standard solutions are generally prepared by dissolving a solute of known mass into a solvent to a precise volume, or by diluting a solution of known concentration with more solvent.
Standard solutions are used to determine the concentration of solutions with unknown concentration, such as solutions in titrations. The concentrations of standard solutions are normally expressed in units of moles per litre (mol/L, often abbreviated to M for molarity), moles per cubic decimetre (mol/dm), kilomoles per cubic metre (kmol/m), grams per milliliters (g/mL), or in terms related to those used in particular titrations (such as titres). | 3 | Analytical Chemistry |
Although ischemic cell death is the accepted name of the process, the alternative name of oncosis was introduced as the process involves the affected cell(s) swelling to an abnormally large size in known models. This is thought to be caused by failure of the plasma membranes ionic pumps. The name oncosis (derived from ónkos, meaning largeness, and ónkosis', meaning swelling) was first introduced in 1910 by pathologist Friedrich Daniel von Recklinghausen. | 1 | Biochemistry |
Shrimp trawlers first reported a dead zone in the Gulf of Mexico in 1950, but it was not until 1970 when the size of the hypoxic zone had increased that scientists began to investigate.
After 1950, the conversion of forests and wetlands for agricultural and urban developments accelerated. "Missouri River Basin has had hundreds of thousands of acres of forests and wetlands (66,000,000 acres) replaced with agriculture activity [. . .] In the Lower Mississippi one-third of the valley's forests were converted to agriculture between 1950 and 1976."
In July 2007, a dead zone was discovered off the coast of Texas where the Brazos River empties into the Gulf. | 9 | Geochemistry |
Green death is a solution used to test the resistance of metals and alloys to corrosion. It consists of a mixture of sulfuric acid, hydrochloric acid, iron(III) chloride and copper(II) chloride and its boiling point is at approximately 103 °C. Its typical chemical composition is given in the table hereafter:
The chemical composition of the green death solution allows it to achieve a particularly aggressive oxidizing chloride solution. Indeed, among the four reagents, all are oxidizing species (, , ) except hydrochloric acid (HCl) in which the chlorine atom is present in its lowest oxidation state as anion. The chloride anions, also added to the solution as counter-ions of iron(III) and copper(II) species, are very aggressive for the localized corrosion of metals and alloys as they induce severe pitting corrosion problems. The green death solution is also used to determine the critical pitting temperature (CPT) and the critical crevice temperature (CCT) of metals and alloys. | 8 | Metallurgy |
MPSS allows mRNA transcripts to be identified through the generation of a 17–20 bp (base pair) signature sequence adjacent to the 3-end of the 3-most site of the designated restriction enzyme (commonly Sau3A or DpnII). Each signature sequence is cloned onto one of a million microbeads. The technique ensures that only one type of DNA sequence is on a microbead. So if there are 50 copies of a specific transcript in the biological sample, these transcripts will be captured onto 50 different microbeads, each bead holding roughly 100,000 amplified copies of the specific signature sequence. The microbeads are then arrayed in a flow cell for sequencing and quantification. The sequence signatures are deciphered by the parallel identification of four bases by hybridization to fluorescently labeled encoders (Figure 5). Each of the encoders has a unique label which is detected after hybridization by taking an image of the microbead array. The next step is to cleave and remove that set of four bases and reveal the next four bases for a new round of hybridization to encoders and image acquisition. The raw output is a list of 17–20 bp signature sequences, that can be annotated to the human genome for gene identification. | 1 | Biochemistry |
RNase cleavage of the last six nucleotides is the next step following the ligation, ultimately extending the primer strand by a single base. Such cleavage allows rezipping of 6 nucleotides of the hairpin, signaled by a decrease in hairpin length of ~4 nm. Therefore, an incorporation of a complementary nucleotide is indicated by an increase in 7 nucleotides (+5 nm) followed by a decrease in 6 nucleotides (-4 nm). | 1 | Biochemistry |
The Purnell equation is an equation used in analytical chemistry to calculate the resolution R between two peaks in a chromatogram.
where
::R is the resolution between the two peaks
::N is the plate number of the second peak
::α is the separation factor between the two peaks
::k ' is the retention factor of the second peak.
The higher the resolution, the better the separation. | 3 | Analytical Chemistry |
Metal ions are Lewis acids, and in aqueous solution they form metal aquo complexes of the general formula . The aqua ions undergo hydrolysis, to a greater or lesser extent. The first hydrolysis step is given generically as
Thus the aqua cations behave as acids in terms of Brønsted–Lowry acid–base theory. This effect is easily explained by considering the inductive effect of the positively charged metal ion, which weakens the bond of an attached water molecule, making the liberation of a proton relatively easy.
The dissociation constant, pK, for this reaction is more or less linearly related to the charge-to-size ratio of the metal ion. Ions with low charges, such as are very weak acids with almost imperceptible hydrolysis. Large divalent ions such as , , and have a pK of 6 or more and would not normally be classed as acids, but small divalent ions such as undergo extensive hydrolysis. Trivalent ions like and are weak acids whose pK is comparable to that of acetic acid. Solutions of salts such as or in water are noticeably acidic; the hydrolysis can be suppressed by adding an acid such as nitric acid, making the solution more acidic.
Hydrolysis may proceed beyond the first step, often with the formation of polynuclear species via the process of olation. Some "exotic" species such as are well characterized. Hydrolysis tends to proceed as pH rises leading, in many cases, to the precipitation of a hydroxide such as or . These substances, major constituents of bauxite, are known as laterites and are formed by leaching from rocks of most of the ions other than aluminium and iron and subsequent hydrolysis of the remaining aluminium and iron. | 7 | Physical Chemistry |
In metallurgy, the Scheil-Gulliver equation (or Scheil equation) describes solute redistribution during solidification of an alloy. | 8 | Metallurgy |
The age of the Earth is 4.54 Gya as found by radiometric dating of calcium-aluminium-rich inclusions in carbonaceous chrondrite meteorites, the oldest material in the Solar System. The Hadean Earth (from its formation until 4 Gya) was at first inhospitable to any living organisms. During its formation, the Earth lost a significant part of its initial mass, and consequentially lacked the gravity to hold molecular hydrogen and the bulk of the original inert gases. Soon after initial accretion of Earth at 4.48 Ga, its collision with Theia, a hypothesised impactor, is thought to have created the ejected debris that would eventually form the Moon. This impact would have removed the Earth's primary atmosphere, leaving behind clouds of viscous silicates and carbon dioxide. This unstable atmosphere was short-lived and condensed shortly after to form the bulk silicate Earth, leaving behind an atmosphere largely consisting of water vapor, nitrogen, and carbon dioxide, with smaller amounts of carbon monoxide, hydrogen, and sulfur compounds. The solution of carbon dioxide in water is thought to have made the seas slightly acidic, with a pH of about 5.5.
Condensation to form liquid oceans is theorised to have occurred as early as the Moon-forming impact. This scenario has found support from the dating of 4.404 Gya zircon crystals with high δO values from metamorphosed quartzite of Mount Narryer in Western Australia. The Hadean atmosphere has been characterized as a "gigantic, productive outdoor chemical laboratory," similar to volcanic gases today which still support some abiotic chemistry. Despite the likely increased volcanism from early plate tectonics, the Earth may have been a predominantly water world between 4.4 and 4.3 Gya. It is debated whether or not crust was exposed above this ocean due to uncertainties of what early plate tectonics looked like. For early life to have developed, it is generally thought that a land setting is required, so this question is essential to determining when in Earth's history life evolved. The post-Moon-forming impact Earth likely existed with little if any continental crust, a turbulent atmosphere, and a hydrosphere subject to intense ultraviolet light from a T Tauri stage Sun, from cosmic radiation, and from continued asteroid and comet impacts. Despite all this, niche environments likely existed conducive to life on Earth in the Late-Hadean to Early-Archaean.
The Late Heavy Bombardment hypothesis posits that a period of intense impact occurred at ~3.9 Gya during the Hadean. A cataclysmic impact event would have had the potential to sterilise all life on Earth by volatilising liquid oceans and blocking the Sun needed for photosynthesising primary producers, pushing back the earliest possible emergence of life to after Late Heavy Bombardment. Recent research questions both the intensity of the Late Heavy Bombardment as well as its potential for sterilisation. Uncertainties as to whether Late Heavy Bombardment was one giant impact or a period of greater impact rates greatly changed the implication of its destructive power. The 3.9 Ga date arises from dating of Apollo return mission samples collected mostly near the Imbrium Basin, biasing the age of recorded impacts. Impact modelling of the lunar surface reveals that rather than a cataclysmic event at 3.9 Ga, multiple small-scale, short-lived periods of bombardment likely occurred. Terrestrial data backs this idea by showing multiple periods of ejecta in the rock record both before and after the 3.9 Ga marker, suggesting that the early Earth was subject to continuous impacts that would not have had as great an impact on extinction as previously thought. If the Late Heavy Bombardment did not take place, this allows for the emergence of life to have taken place far before 3.9 Ga.
If life evolved in the ocean at depths of more than ten meters, it would have been shielded both from late impacts and the then high levels of ultraviolet radiation from the sun. Geothermically heated oceanic crust could have yielded far more organic compounds through deep hydrothermal vents than the Miller–Urey experiments indicated. The available energy is maximized at 100–150 °C, the temperatures at which hyperthermophilic bacteria and thermoacidophilic archaea live. | 9 | Geochemistry |
Enzymatic deficiency in alpha-oxidation (most frequently in phytanoyl-CoA dioxygenase) leads to Refsum's disease, in which the accumulation of phytanic acid and its derivatives leads to neurological damage. Other disorders of peroxisome biogenesis also prevent alpha-oxidation from occurring. | 1 | Biochemistry |
Pure Togni reagent II is metastable at room temperature. Heating it above the melting point will lead to strong exothermic decomposition, in which trifluoroiodomethane (CFI) is released. The heat of composition at a temperature of 149 °C and higher has been determined to be 502 J·g. From recrystallization in acetonitrile, small amounts of trifluoromethyl-2-iodobenzoate and 2-iodobenzyl fluoride were observed as decomposition products. Togni reagent II reacts violently with strong bases and acids, as well as reductants. In tetrahydrofuran, the compound polymerizes. | 0 | Organic Chemistry |
There are two aspects to surface integrity: topography characteristics and surface layer characteristics. The topography is made up of surface roughness, waviness, errors of form, and flaws. The surface layer characteristics that can change through processing are: plastic deformation, residual stresses, cracks, hardness, overaging, phase changes, recrystallization, intergranular attack, and hydrogen embrittlement. When a traditional manufacturing process is used, such as machining, the surface layer sustains local plastic deformation.
The processes that affect surface integrity can be conveniently broken up into three classes: traditional processes, non-traditional processes, and finishing treatments. Traditional processes are defined as processes where the tool contacts the workpiece surface; for example: grinding, turning, and machining. These processes will only damage the surface integrity if the improper parameters are used, such as dull tools, too high feed speeds, improper coolant or lubrication, or incorrect grinding wheel hardness. Nontraditional processes are defined as processes where the tool does not contact the workpiece; examples of this type of process include EDM, electrochemical machining, and chemical milling. These processes will produce different surface integrity depending on how the processes are controlled; for instance, they can leave a stress-free surface, a remelted surface, or excessive surface roughness. Finishing treatments are defined as processes that negate surface finishes imparted by traditional and non-traditional processes or improve the surface integrity. For example, compressive residual stress can be enhanced via peening or roller burnishing or the recast layer left by EDMing can be removed via chemical milling.
Finishing treatments can affect the workpiece surface in a wide variety of manners. Some clean and/or remove defects, such as scratches, pores, burrs, flash, or blemishes. Other processes improve or modify the surface appearance by improving smoothness, texture, or color. They can also improve corrosion resistance, wear resistance, and/or reduce friction. Coatings are another type of finishing treatment that may be used to plate an expensive or scarce material onto a less expensive base material. | 8 | Metallurgy |
Modafinil is contraindicated during pregnancy and 2 months before getting pregnant. Women who take modafinil should not become pregnant, and, additionally, should be aware that modafinil reduces effectiveness of hormonal contraceptives, increasing chances of getting pregnant. Modafinil therapy during pregnancy increases the risk of birth defects, such as with congenital torticollis, hypospadias, and congenital heart defects.
Modafinil is contraindicated for individuals with known hypersensitivity to either modafinil or armodafinil.
Modafinil is also contraindicated in certain cardiac conditions, including uncontrolled moderate to severe hypertension, arrhythmia, cor pulmonale, and in cases with signs of CNS stimulant-induced mitral valve prolapse or left ventricular hypertrophy. The package insert in the United States cautions about using modafinil in people with a documented medical history of left ventricular hypertrophy or those diagnosed with mitral valve prolapse who have previously exhibited symptoms associated with the mitral valve prolapse syndrome while undergoing treatment involving central nervous system stimulants. The reasons why modafinil is contraindicated in certain cardiac conditions are because modafinil affects the autonomic nervous system and, in particular, exerts significant effects on autonomic cardiovascular regulation, leading in some people to notable increases in heart rate and blood pressure. These substantial changes in the autonomic system warrant careful consideration when prescribing modafinil to people with pre-existing cardiovascular conditions. The increase in heart rate and blood pressure can worsen the symptoms of such pre-existing conditions as hypertension, arrhythmia, and cor pulmonale. These changes in the autonomic system induced by modafinil can increase the risk of heart attack, stroke, and heart failure. Modafinil can stimulate the release of norepinephrine and epinephrine, hormones that activate the sympathetic nervous system. This can cause vasoconstriction, which is the narrowing of blood vessels, and increase the heart's workload, which is not desired in people with pre-existing heart conditions. In particular, modafinil can worsen the consequences of mitral valve prolapse or left ventricular hypertrophy, which are structural abnormalities of the heart. These can affect the blood flow and oxygen delivery to the heart and other organs.
Modafinil is also contraindicated in people with congenital problems like galactose intolerance, lactase deficiency, or glucose-galactose malabsorption. | 4 | Stereochemistry |
Higher selectivity: for example, positive, negative and neutral substances could be separated by a reversed phase (RP)/anion-cation exchange (ACE) column in a single run.
Higher loading capacity,
for example, loading capacity of ACE/ hydrophilic interaction chromatography (HILIC) increased 10-100 times when compared with RPLC,
which offered a new selection and idea for developing semi-preparative and preparative chromatography.
One mixed-mode column can replace two or even more single mode columns, which is economic and eco-friendly for employing the stationary phase more sufficiently and reducing the consuming and ‘waste’ of raw materials.
Single mixed-mode column can be applied for on-line two-dimensional (2D) analysis in a sealed system via establishing corresponding chromatographic system or off-line 2D analysis as two columns. | 3 | Analytical Chemistry |
The following table lists pharmaceuticals that have been available in both racemic and single-enantiomer form. These single-enantiomer drug switched from the respective racemic drug are referred to as chiral switch.
The following are cases where the individual enantiomers have markedly different effects:
*Thalidomide: Thalidomide is racemic. One enantiomer is effective against morning sickness, whereas the other is teratogenic. However, the enantiomers are converted into each other in vivo. As a result, dosing with a single-enantiomer form of the drug will still lead to both the enantiomers eventually being present in the patients serum and thus would not prevent adverse effects—at best, it might reduce them if the rate of in vivo' conversion can be slowed.
*Ethambutol: Whereas the (S,S)-(+)-enantiomer is used to treat tuberculosis, the (R,R)-(–)-ethambutol may cause blindness.
*Steroid receptor sites also show stereoisomer specificity.
*Penicillin's activity is stereodependent. The antibiotic must mimic the -alanine chains that occur in the cell walls of bacteria in order to react with and subsequently inhibit bacterial transpeptidase enzyme.
*Propranolol: -propranolol is a powerful adrenoceptor antagonist, whereas -propranolol is not. However, both have local anesthetic effect.
*Methorphan: The -isomer of methorphan, levomethorphan, is a potent opioid analgesic, while the -isomer, dextromethorphan, is a dissociative cough suppressant.
*Carvedilol: (S)-(–)-isomer interacts with adrenoceptors with 100 times greater potency as β adrenoreceptor blocker than (R)-(+)-isomer. However, both the isomers are approximately equipotent as α adrenoreceptor blockers.
*Amphetamine and methamphetamine: The -isomers of these drugs are strong central nervous system (CNS) stimulants, while the -isomers lack appreciable CNS stimulant effects, but instead stimulate the peripheral nervous system. For this reason, the -isomer of methamphetamine is available as an over-the-counter nasal inhaler in some countries, while the -isomer is banned from medical use in all but a few countries in the world, and highly regulated in those countries which do allow it to be used medically.
*Ketamine: This drug is available as a mixture of both (S)-(+)-ketamine, also known as esketamine, and (R)-(–)-ketamine, also known as arketamine. Pure esketamine is also available. The two have different dissociative and hallucinogenic properties, with esketamine being more potent in isolation as a dissociative. The two enantiomers have inverse effects on the rate of glucose metabolism in the frontal cortex.
*Dihydroxy-3, 4 phenylalanine (Dopa): Dopa is a racemic mixture where one enantiomer, L-Dopa, is used as a treatment for Parkinson's Disease, and the other enantiomer, D-Dopa is considered to be toxic. D-Dopa can cause headaches, abdominal pains, nausea, vomiting, and dizziness. | 4 | Stereochemistry |
Ion exchange sorbents separate analytes based on electrostatic interactions between the analyte of interest and the positively or negatively charged groups on the stationary phase. For ion exchange to occur, both the stationary phase and sample must be at a pH where both are charged. | 3 | Analytical Chemistry |
After a cell has established a resting potential, that cell has the capacity to undergo depolarization. Depolarization is the process by which the membrane potential becomes less negative, facilitating the generation of an action potential. For this rapid change to take place within the interior of the cell, several events must occur along the plasma membrane of the cell. While the sodium–potassium pump continues to work, the voltage-gated sodium and calcium channels that had been closed while the cell was at resting potential are opened in response to an initial change in voltage. As a change in the neuronal charge leads to the opening of voltage-gated sodium channels, this results in an influx of sodium ions down their electrochemical gradient. Sodium ions enter the cell, and they contribute a positive charge to the cell interior, causing a change in the membrane potential from negative to positive. The initial sodium ion influx triggers the opening of additional sodium channels (positive-feedback loop), leading to further sodium ion transfer into the cell and sustaining the depolarization process until the positive equilibrium potential is reached. Sodium channels possess an inherent inactivation mechanism that prompts rapid reclosure, even as the membrane remains depolarized. During this equilibrium, the sodium channels enter an inactivated state, temporarily halting the influx of sodium ions until the membrane potential becomes negatively charged again.Once the cell's interior is sufficiently positively charged, depolarization concludes, and the channels close once more. | 7 | Physical Chemistry |
A phosphodiesterase (PDE) is an enzyme that breaks a phosphodiester bond. Usually, phosphodiesterase refers to cyclic nucleotide phosphodiesterases, which have great clinical significance and are described below. However, there are many other families of phosphodiesterases, including phospholipases C and D, autotaxin, sphingomyelin phosphodiesterase, DNases, RNases, and restriction endonucleases (which all break the phosphodiester backbone of DNA or RNA), as well as numerous less-well-characterized small-molecule phosphodiesterases.
The cyclic nucleotide phosphodiesterases comprise a group of enzymes that degrade the phosphodiester bond in the second messenger molecules cAMP and cGMP. They regulate the localization, duration, and amplitude of cyclic nucleotide signaling within subcellular domains. PDEs are therefore important regulators of signal transduction mediated by these second messenger molecules. | 1 | Biochemistry |
As defined above, the light compensation point I is when no net carbon assimilation occurs. At this point, the organism is neither consuming nor building biomass. The net gaseous exchange is also zero at this point.
I is a practical value that can be reached during early mornings and early evenings. Respiration is relatively constant with regard to light, whereas photosynthesis depends on the intensity of sunlight. | 5 | Photochemistry |
Gene deserts are regions of the genome that are devoid of protein-coding genes. Gene deserts constitute an estimated 25% of the entire genome, leading to the recent interest in their true functions. Originally believed to contain inessential and “junk” DNA due to their inability to create proteins, gene deserts have since been linked to several vital regulatory functions, including distal enhancing and conservatory inheritance. Thus, an increasing number of risks that lead to several major diseases, including a handful of cancers, have been attributed to irregularities found in gene deserts. One of the most notable examples is the 8q24 gene region, which, when affected by certain single nucleotide polymorphisms, lead to a myriad of diseases. The major identifying factors of gene deserts lay in their low GpC content and their relatively high levels of repeats, which are not observed in coding regions. Recent studies have even further categorized gene deserts into variable and stable forms; regions are categorized based on their behavior through recombination and their genetic contents. Although current knowledge of gene deserts is rather limited, ongoing research and improved techniques are beginning to open the doors for exploration on the various important effects of these noncoding regions. | 1 | Biochemistry |
Suppose that we are studying an isolated, quantum mechanical many-body system. In this context, "isolated" refers to the fact that the system has no (or at least negligible) interactions with the environment external to it. If the Hamiltonian of the system is denoted , then a complete set of basis states for the system is given in terms of the eigenstates of the Hamiltonian,
where is the eigenstate of the Hamiltonian with eigenvalue . We will refer to these states simply as "energy eigenstates." For simplicity, we will assume that the system has no degeneracy in its energy eigenvalues, and that it is finite in extent, so that the energy eigenvalues form a discrete, non-degenerate spectrum (this is not an unreasonable assumption, since any "real" laboratory system will tend to have sufficient disorder and strong enough interactions as to eliminate almost all degeneracy from the system, and of course will be finite in size). This allows us to label the energy eigenstates in order of increasing energy eigenvalue. Additionally, consider some other quantum-mechanical observable , which we wish to make thermal predictions about. The matrix elements of this operator, as expressed in a basis of energy eigenstates, will be denoted by
We now imagine that we prepare our system in an initial state for which the expectation value of is far from its value predicted in a microcanonical ensemble appropriate to the energy scale in question (we assume that our initial state is some superposition of energy eigenstates which are all sufficiently "close" in energy). The eigenstate thermalization hypothesis says that for an arbitrary initial state, the expectation value of will ultimately evolve in time to its value predicted by a microcanonical ensemble, and thereafter will exhibit only small fluctuations around that value, provided that the following two conditions are met:
# The diagonal matrix elements vary smoothly as a function of energy, with the difference between neighboring values, , becoming exponentially small in the system size.
# The off-diagonal matrix elements , with , are much smaller than the diagonal matrix elements, and in particular are themselves exponentially small in the system size.
These conditions can be written as
where and are smooth functions of energy, is the many-body Hilbert space dimension, and is a random variable with zero mean and unit variance. Conversely if a quantum many-body system satisfies the ETH, the matrix representation of any local operator in the energy eigen basis is expected to follow the above ansatz. | 7 | Physical Chemistry |
In organic chemistry, Zaytsevs rule (or Zaitsevs rule, Saytzeffs rule, Saytzevs rule) is an empirical rule for predicting the favored alkene product(s) in elimination reactions. While at the University of Kazan, Russian chemist Alexander Zaytsev studied a variety of different elimination reactions and observed a general trend in the resulting alkenes. Based on this trend, Zaytsev proposed that the alkene formed in greatest amount is that which corresponded to removal of the hydrogen from the alpha-carbon having the fewest hydrogen substituents. For example, when 2-iodobutane is treated with alcoholic potassium hydroxide (KOH), but-2-ene is the major product and but-1-ene is the minor product.
More generally, Zaytsevs rule predicts that in an elimination reaction the most substituted product will be the most stable, and therefore the most favored. The rule makes no generalizations about the stereochemistry of the newly formed alkene, but only the regiochemistry of the elimination reaction. While effective at predicting the favored product for many elimination reactions, Zaytsevs rule is subject to many exceptions.
Many of them include exceptions under Hofmann product (analogous to Zaytsev product). These include compounds having quaternary nitrogen and leaving groups like NR, SOH, etc. In these eliminations the Hofmann product is preferred. In case the leaving group is halogens, except fluorine; others give the Zaytsev product. | 7 | Physical Chemistry |
Geoksyur Oasis, located in the foothills of the Kopetdag, to the east of Altyndepe, is in the center of a cluster of tepes in the desert region on the northern Iranian border. It extends over an area of 12 ha. It is to the east of the city of Tedzhen. Even though in the Aneolithic Period (4th – early 3rd century BC), the space between houses was used for burials, the settlement was not a cemetery but rather a settlement which was affected by shifting sand dunes and scarcity of water. Geoksyr was revealed to contain "adobe multi-room houses and group burial chambers". Ceramics were also found with dichromatic paintings and many female terracotta figurines. The culture of Geoksyurtepe was correlated with an eastern Anau group of tribes linked to Elam and Mesopotamia. | 8 | Metallurgy |
Nucleofection is a method to transfer substrates into mammalian cells so far considered difficult or even impossible to transfect. Examples for such substrates are nucleic acids, like the DNA of an isolated gene cloned into a plasmid, or small interfering RNA (siRNA) for knocking down expression of a specific endogenous gene.
Primary cells, for example stem cells, especially fall into this category, although many other cell lines are also difficult to transfect. Primary cells are freshly isolated from body tissue and thus cells are unchanged, closely resembling the in-vivo situation, and are therefore of particular relevance for medical research purposes. In contrast, cell lines have often been cultured for decades and may significantly differ from their origin. | 1 | Biochemistry |
Coffee Joulies are small, stainless-steel capsules containing a phase-change material; the capsules were designed to be placed in a cup of coffee in order to cool coffee that is too hot then slowly release the heat to keep the coffee warm. The company was founded by Dave Petrillo and Dave Jackson, mechanical engineers from Pennington, New Jersey.
They made prototypes in their basement, then in 2011 started refining and producing them in rented space at Sherrill Manufacturing in Sherrill, New York, a former Oneida silverware factory that had changed its business model to hosting startups and small companies in 2010, after Oneida had moved most of its manufacturing overseas in 2004 but had left a small amount of business with the factory under contract. The company received help on manufacturing costs from Sherrill and raised money on Kickstarter in 2011. The team decided to continue with production in the United States, rather than moving to Mexico, as was their initial plan.
A similar concept using phase change materials, but integrated into the walls and bottom of a cup, had been invented by the Fraunhofer Institute for Building Physics in 2009.
Some reviews show Joulies work while others have expressed doubts over the product's effectiveness. After doing some tests, they reported that the product does not work very well if at all.
Specifically it is stated that the promised effect, while existing, is "barely noticeable", especially when compared to adding other objects of similar heat capacity, thus being far from the creators' claims that the drink “will be ready to drink three times sooner and will remain hot twice as long.”
In 2013 the founders were contestants on Shark Tank and raised $150,000. | 7 | Physical Chemistry |
Adding more mirrors does not add more possibilities (in the plane), because they can always be rearranged to cause cancellation. | 3 | Analytical Chemistry |
The quinhydrone electrode provides an alternative to the most commonly used glass electrode. however, it is not reliable above pH 8 (at 298 K) and cannot be used with solutions that contain a strong oxidizing or reducing agent. | 3 | Analytical Chemistry |
TET processivity can be viewed at three levels, the physical, chemical and genetic levels. Physical processivity refers to the ability of a TET protein to slide along the DNA from one CpG site to another. An in vitro study showed that DNA-bound TET does not preferentially oxidize other CpG sites on the same DNA molecule, indicating that TET is not physically processive. Chemical processivity refers to the ability of TET to catalyze the oxidation of 5mC iteratively to 5caC without releasing its substrate. It appears that TET can work through both chemically processive and non‑processive mechanisms depending on reaction conditions. Genetic processivity refers to the genetic outcome of TET‑mediated oxidation in the genome, as shown by mapping of the oxidized bases. In mouse embryonic stem cells, many genomic regions or CpG sites are modified so that 5mC is changed to 5hmC but not to 5fC or 5caC, whereas at many otherCpG sites 5mCs are modified to 5fC or 5caC but not 5hmC, suggesting that 5mC is processed to different states at different genomic regions or CpG sites. | 1 | Biochemistry |
He was awarded by the President of Chile, Eduardo Frei Ruiz-Tagle the Presidential Chair in Science in 1996 by a Committee chaired by a Nobel Prize in Chemistry Rudolph Marcus and including Physics Nobel Laureate David Gross. He received the Silver Medal “University Merit” in 1998 and the Gold Medal in 2002 and the Manuel Bulnes Medal in 2013. He was distinguished by Conicyt with “Fondecyt Diploma” for being awarded more than 10 consecutive research grants without rejects in 2012. He still remains unbeaten in Fondecyt. He has been awarded two Milenium Projects as Alternative Responsible Scientist and has participated in many other associative research projects in Chile and abroad. He was appointed by the President of Chile Sebastian Piñera Echeñique and the Minister of Education, Member of the Superior Council of Research of Conicyt for the period 2010–2013. In 2014 he received the Dr. Alberto Zanlungo Prize. He has received several distinctions from international scientific societies. He was appointed Fellow by the Royal Society of Chemistry (RSC) of the UK in 2018. He became a Member of the RSC in 2017. He received the Fellow Medal from the International Society of Electrochemistry based in Europe and the Fellow Medal from the US-based Electrochemical Society (ECS) both in 2014. This year he was incorporated as an Active Member to the Academy of Sciences of Latin America (ACAL) and became an Emeritus Member of The Electrochemical Society of the United States of America. He created the Chilean Secretary of ISE in 2003 and was his first chilean representative. He also created the Chile Section of ECS in 2011 and is presently its Chairman. He was a co-founder of the Chilean Society of Carbonaceous Materials and is presently its President. He is also the President of the Iberoamerican Chemical Society. | 7 | Physical Chemistry |
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