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The ratio r between the apparent molar volume of a dissolved electrolyte in a concentrated solution and the molar volume of the solvent (water) can be linked to the statistical component of the activity coefficient of the electrolyte and its solvation shell number h: where ν is the number of ions due to dissociation of the electrolyte, and b is the molality as above.

Physical Chemistry

A Brønsted-Lowry acids strength corresponds with its ability to release a hydrogen ion. One common measure of acid strength for concentrated, superacidic liquid media is the Hammett acidity function, H. Based on its ability to quantitatively protonate benzene, the chlorinated carborane acid was conservatively estimated to have an H value at or below −18, leading to the common assertion that carborane acids are at least a million times stronger than 100% sulfuric acid (H = −12). However, since the H value measures the protonating ability of a liquid medium, the crystalline and high-melting nature of these acids precludes direct measurement of this parameter. In terms of pK, a slightly different measure of acidity defined as the ability of a given solute to undergo ionization in a solvent, carborane acids are estimated to have pK values below −20, even without electron-withdrawing substituents on the boron atoms (e.g., is estimated to have a pK of −24), with the (yet unknown) fully fluorinated analog having a calculated pK of −46. The known acid with one fewer fluorine is expected to be only slightly weaker (pK' < −40). In the gas phase, has a computed acidity of 216 kcal/mol, compared to an experimentally determined acidity of 241 kcal/mol (in reasonable agreement with the computed value of 230 kcal/mol) for . In contrast, HSbF (a simplified model for the proton donating species in fluoroantimonic acid) has a computed gas phase acidity of 255 kcal/mol, while the previous experimentally determined record holder was (CFSO)NH, a congener of bistriflimide, at 291 kcal/mol. Thus, is likely the most acidic substance so far synthesized in bulk, in terms of its gas phase acidity. In view of its unique reactivity, it is also a strong contender for being the most acidic substance in the condensed phase (see above). Some even more strongly acidic derivatives have been predicted, with gas phase acidities < 200 kcal/mol. Carborane acids differ from classical superacids in being well-defined one component substances. In contrast, classical superacids are often mixtures of a Brønsted acid and Lewis acid (e.g. HF/SbF). Despite being the strongest acid, the boron-based carborane acids are described as being "gentle", cleanly protonating weakly basic substances without further side reactions. Whereas conventional superacids decompose fullerenes due to their strongly oxidizing Lewis acidic component, carborane acid has the ability to protonate fullerenes at room temperature to yield an isolable salt. Furthermore, the anion that forms as a result of proton transfer is nearly completely inert. This property is what makes the carborane acids the only substances that are comparable in acidity to the mixed superacids that can also be stored in a glass bottle, as various fluoride-donating species (which attack glass) are not present or generated.

Physical Chemistry

UV disinfection is most effective for treating high-clarity, purified reverse osmosis distilled water. Suspended particles are a problem because microorganisms buried within particles are shielded from the UV light and pass through the unit unaffected. However, UV systems can be coupled with a pre-filter to remove those larger organisms that would otherwise pass through the UV system unaffected. The pre-filter also clarifies the water to improve light transmittance and therefore UV dose throughout the entire water column. Another key factor of UV water treatment is the flow rate—if the flow is too high, water will pass through without sufficient UV exposure. If the flow is too low, heat may build up and damage the UV lamp. A disadvantage of UVGI is that while water treated by chlorination is resistant to reinfection (until the chlorine off-gasses), UVGI water is not resistant to reinfection. UVGI water must be transported or delivered in such a way as to avoid reinfection.

Photochemistry

Brownian motion is the mathematical model used to describe the random movement of particles suspended in a fluid. The gas particle animation, using pink and green particles, illustrates how this behavior results in the spreading out of gases (entropy). These events are also described by particle theory. Since it is at the limit of (or beyond) current technology to observe individual gas particles (atoms or molecules), only theoretical calculations give suggestions about how they move, but their motion is different from Brownian motion because Brownian motion involves a smooth drag due to the frictional force of many gas molecules, punctuated by violent collisions of an individual (or several) gas molecule(s) with the particle. The particle (generally consisting of millions or billions of atoms) thus moves in a jagged course, yet not so jagged as would be expected if an individual gas molecule were examined.

Physical Chemistry

Calcium is stored in geologic reservoirs, most commonly in the form of calcium carbonate or as calcium silicate. Calcium-containing rocks include calcite, dolomite, phosphate, and gypsum. Rocks slowly dissolve by physical and chemical processes, carrying calcium ions into rivers and oceans. Calcium ions (Ca) and magnesium ions (Mg) have the same charge (+2) and similar sizes, so they react similarly and are able to substitute for each other in some minerals, such as carbonates. Ca-containing minerals are often more easily weathered than Mg minerals, so Ca is often more enriched in waterways than Mg. Rivers containing more dissolved Ca are generally considered more alkaline. Calcium is one of the most common elements found in seawater. Inputs of dissolved calcium (Ca) to the ocean include the weathering of calcium sulfate, calcium silicate, and calcium carbonate, basalt-seawater reaction, and dolomitization.

Biochemistry

The original Fischer glycal synthesis was the reductive elimination with zinc of a glycosyl halide. This glycosyl halide was formed from a monosaccharide starting material. Some other synthetic routes include: *Ring-closing metathesis *Reaction of thioglycosides with lithium napthalenide. *Mesylation of the anomeric hydroxyl and formation of the anomeric palladium complex, which undergoes beta-elimination A general example of each synthetic route is given below (drawn with first discussed synthesis bottom right, moving clockwise):

Organic Chemistry

Chromatographic peak resolution is given by where t is the retention time and w is the peak width at baseline. Here compound 1 elutes before compound 2. If the peaks have the same width

Analytical Chemistry

Public Analysts are scientists in the British Isles whose principal task is to ensure the safety and correct description of food by testing for compliance with legislation. Most Public Analysts are also Agricultural Analysts who carry out similar work on animal feedingstuffs and fertilisers. Nowadays this includes checking that the food labelling is accurate. They also test drinking water, and may carry out chemical and biological tests on other consumer products. While much of the work is done by other scientists and technicians in the laboratory, the Public Analyst has legal responsibility for the accuracy of the work and the validity of any opinion expressed on the results reported. The UK-based Association of Public Analysts includes members with similar roles if different titles in other countries.

Environmental Chemistry

Minigenes were first described as the somatic assembly of DNA segments and consisted of DNA regions known to encode the protein and the flanking regions required to express the protein. The term was first used in a paper in 1977 to describe the cloning of two minigenes that were designed to express a peptide. RNA splicing was discovered in the late 1970s through the study of adenoviruses that invade mammals and replicate inside them. Researchers identified RNA molecules that contained sequences from noncontiguous parts of the virus’s genome. This discovery led to the conclusion that regulatory mechanisms existed which affected mature RNA and the genes it expresses. Using minigenes as a splice reporting vector to explore the effects of RNA splicing regulation naturally followed and remains the major use of minigenes to date.

Biochemistry

The divinylcyclopropane-cycloheptadiene rearrangement is an organic chemical transformation that involves the isomerization of a 1,2-divinylcyclopropane into a cycloheptadiene or -triene. It is conceptually related to the Cope rearrangement, but has the advantage of a strong thermodynamic driving force due to the release of ring strain. This thermodynamic power is recently being considered as an alternative energy source.

Organic Chemistry

Laser-induced breakdown spectroscopy (LIBS) is a type of atomic emission spectroscopy which uses a highly energetic laser pulse as the excitation source. The laser is focused to form a plasma, which atomizes and excites samples. The formation of the plasma only begins when the focused laser achieves a certain threshold for optical breakdown, which generally depends on the environment and the target material.

Physical Chemistry

Born in Sydney, Cornforth was the son and the second of four children of English-born, Oxford-educated schoolmaster and teacher John Warcup Cornforth and Hilda Eipper (1887–1969), a granddaughter of pioneering missionary and Presbyterian minister Christopher Eipper. Before her marriage, Eipper had been a maternity nurse. Cornforth was raised in Sydney as well as Armidale, in the north of New South Wales, where he undertook primary school education. At about 10 years old, Cornforth had noted signs of deafness, which led to a diagnosis of otosclerosis, a disease of the middle ear which causes progressive hearing loss. This left him completely deaf by the age of 20 but also fatefully influenced his career direction away from law, his original intended field of study, and towards chemistry. In an interview with Sir Harry Kroto for the Vega Science Trust, Cornforth explained:

Organic Chemistry

Indirect calorimetry measures O consumption and CO production. On the assumption that all the oxygen is used to oxidize degradable fuels and all the CO thereby evolved is recovered, it is possible to estimate the total amount of energy produced from the chemical energy of nutrients and converted into the chemical energy of ATP, with some loss of energy during the oxidation process. Respiratory indirect calorimetry (IC) is a noninvasive and highly accurate method of metabolic rate, which has an error of less than 1%. It has high reproducibility and has been considered a gold standard method. This method allows estimating BEE and REE as well as identification of energy substrates that are predominantly metabolized by the body at a specific moment. It is based on the indirect measurement of the heat produced by oxidation of macronutrients, which is estimated by monitoring O consumption and CO production for a certain period of time. The calorimeter has a gas collector that adapts to the subject and through a unidirectional valve minute by minute collects and quantifies the volume and concentration of O inspired and CO expired by the subject. After a volume is met, Resting Energy Expenditure is calculated by the Weir formula and results are displayed in software attached to the system. Another formula used is: where RQ is the respiratory quotient (ratio of volume CO produced to volume of O consumed), is , the heat released per litre of oxygen by the oxidation of carbohydrate, and is , the value for fat. This gives the same result as the Weir formula at RQ = 1 (burning only carbohydrates), and almost the same value at RQ = 0.7 (burning only fat).

Biochemistry

Similar principles guide the lowest energy conformations of larger ring systems. Along with the acyclic stereocontrol principles outlined below, subtle interactions between remote substituents in large rings, analogous to those observed for 8-10 membered rings, can influence the conformational preferences of a molecule. In conjunction with remote substituent effects, local acyclic interactions can also play an important role in determining the outcome of macrocyclic reactions. The conformational flexibility of larger rings potentially allows for a combination of acyclic and macrocyclic stereocontrol to direct reactions.

Organic Chemistry

Grinding is abrasion of the surface of interest by abrasive particles, usually diamond, that are bonded to paper or a metal disc. Grinding erases saw marks, coarsely smooths the surface, and removes stock to a desired depth. A typical grinding sequence for ceramics is one minute on a 240-grit metal-bonded diamond wheel rotating at 240 rpm and lubricated by flowing water, followed by a similar treatment on a 400-grit wheel. The specimen is washed in an ultrasonic bath after each step.

Metallurgy

Synapses can be classified by the type of cellular structures serving as the pre- and post-synaptic components. The vast majority of synapses in the mammalian nervous system are classical axo-dendritic synapses (axon synapsing upon a dendrite), however, a variety of other arrangements exist. These include but are not limited to axo-axonic, dendro-dendritic, axo-secretory, axo-ciliary, somato-dendritic, dendro-somatic, and somato-somatic synapses. In fact, the axon can synapse onto a dendrite, onto a cell body, or onto another axon or axon terminal, as well as into the bloodstream or diffusely into the adjacent nervous tissue.

Biochemistry

At a temperature below the boiling point, any matter in liquid form will evaporate until reaching equilibrium with the reverse process of condensation of its vapor. At this point the vapor will condense at the same rate as the liquid evaporates. Thus, a liquid cannot exist permanently if the evaporated liquid is continually removed. A liquid at or above its boiling point will normally boil, though superheating can prevent this in certain circumstances. At a temperature below the freezing point, a liquid will tend to crystallize, changing to its solid form. Unlike the transition to gas, there is no equilibrium at this transition under constant pressure, so unless supercooling occurs, the liquid will eventually completely crystallize. However, this is only true under constant pressure, so that (for example) water and ice in a closed, strong container might reach an equilibrium where both phases coexist. For the opposite transition from solid to liquid, see melting.

Physical Chemistry

Cyclic salt is salt that is carried by the wind when it comes in contact with breaking waves. It is estimated that more than 300 million tons of cyclic salt is deposited on the Earths surface each year, and it is considered to be a significant factor in the chlorine content of the Earths river water. In general, cyclic salt deposits are lower at sites further inland and are most abundant along the shoreline, although this pattern varies depending on the given environmental conditions. Use of the term "cyclic" refers to the cycle in which the salt moves from sea to land and is then washed by rainwater back to the sea. The salt (and other solid matter) cannot evaporate as water does. Instead it leaves the ocean surface in fine droplets of drop impacts or bubble bursts. Wave-crests and other turbulence form foam. When drops splash or bubbles burst, fine droplets of solute are ejected from the water or bubble surface into the air. Some of the droplets are small enough to allow the water to evaporate before it falls back into the sea, leaving in the air a mote of the light enough to stay suspended by Brownian motion and be carried away on the wind.

Geochemistry

5,6-Dichloro-1-β--ribofuranosylbenzimidazole (DRB) is a chemical compound that inhibits transcription elongation by RNA Polymerase II. Sensitivity to DRB is dependent on DRB sensitivity inducing factor (DSIF), negative elongation factor (NELF), and positive transcription elongation factor b (P-TEFb). DRB is a nucleoside analog and also inhibits some protein kinases.

Biochemistry

According to Entertainment Weekly, "The Navi can commune with animals on their planet by literally plugging their braid into the creatures nerve systems. To become a warrior, a Navi must tame and ride a flying creature known as Ikran." The Navi also use this neural bonding system, called "tsaheylu", to mate with a "life partner", a bond that, when made, cannot be broken in the Navis lifetime. This is akin to human marriage. The Navi way of life revolves around their religion, and the Home Tree. The Navi sleep in hammocks in large groups for comfort and as a warning system. Conceived for the film was the Navi language, a constructed language often spoken by the actors when they played Navi characters. The Navi language was created by communications professor emeritus and linguistics consultant Paul Frommer of the University of Southern California. He designed the language so as to be speakable by human actors, combining syntactic and grammatical rules from other existing languages. Frommer created over a thousand words for the Navi language and coached the actors who narrated Navi characters. When communicating to humans in the film, Navi characters – especially Neytiri – speak in accented and broken English. Human visitors see the Navi as possessing a religion, whose chief and possibly sole deity is a benevolent goddess known as Eywa. The Navi are able to physically connect to Eywa when they use their braids to connect to the Tree of Souls and other similar flora which function as the global brain's interfaces. Eywa is said to have a connection to all things Pandoran. Political power is exceedingly diffused, with each clan being a sovereign entity under either the diarchical rule of both a temporal chieftain (known as an Oloeyktan) and a spiritual chieftain (known as a Tsahik), or the monarchical rule of a single individual who holds the two separate offices simultaneously. The numerous clans are seemingly only ever brought together as a tribe by Toruk Makto, a messianic war chief whose office is both non-permanent and apparently the only one with an authority that covers the entire race of Navi. By the time of the film, there had only been five Toruk Maktos in the history of the tribe, and the last one had ruled no fewer than four generations before the present day. This may be due to the fact that the Toruk Maktos seem to draw their power from a situation of explicitly external danger, and therefore are not really necessary for the day to day internal running of the tribal clans. Succession to the various offices is smooth, however, based more on popular recognition and customary worthiness than on anything else, and respect for hierarchical superiors appears to be high.

Biochemistry

* Reduced cellular defense mechanisms ** Children younger than 4 months exposed to various environmental agents ** Pregnant women are considered vulnerable to exposure of high levels of nitrates in drinking water ** Cytochrome b5 reductase deficiency ** G6PD deficiency ** Hemoglobin M disease ** Pyruvate kinase deficiency * Various pharmaceutical compounds ** Local anesthetic agents, especially prilocaine and benzocaine. ** Amyl nitrite, chloroquine, dapsone, nitrates, nitrites, nitroglycerin, nitroprusside, phenacetin, phenazopyridine, primaquine, quinones and sulfonamides * Environmental agents ** Aromatic amines (e.g. p-nitroaniline, [http://www.gtfch.org/cms/images/stories/media/tk/tk73_2/Bakdash.pdf patient case]) ** Arsine ** Chlorobenzene ** Chromates ** Nitrates/nitrites ** Umbellulone * Inherited disorders ** Some family members of the Fugate family in Kentucky, due to a recessive gene, had blue skin from an excess of methemoglobin. * In cats **Ingestion of paracetamol (i.e. acetaminophen, tylenol)

Biochemistry

The high intensity of the Jameson Cell means that it is much shorter than conventional column flotation cells (see Figure 1), and it does not require air compressors to aerate the suspension of ground ore particles and water (known as a slurry or pulp) in the flotation cell. The lack of a requirement for compressed air and the lack of moving parts means that power consumption is less than for the equivalent mechanical or conventional column flotation cell. In contrast to most types of flotation cell, the Cell introduces the feed and the air to the Cell in a combined stream via one or more cylindrical columns referred to as "downcomers". Other types of flotation cell typically introduce the feed and the air separately to the cell. The Cell produces fast mineral flotation rates, especially for very fine mineral particles. It produces high concentrate grades from fast floating liberated particles and is able to do this from a single stage of flotation. The high carrying capacity of the Jameson Cell is particularly beneficial when high yields (mass pulls) are required, such as in recleaning in metals flotation and in the flotation of metallurgical coal, where yields can exceed 80%. The Cell was initially developed as a lower-cost alternative to conventional column flotation cells for recovering fine particles, and was first used in the Mount Isa lead–zinc concentrator in 1988. Since then, use of the technology has spread to include coal flotation, base and precious metal flotation, potash flotation, oil sands flotation, molybdenum flotation, graphite flotation and cleaning solvent extraction liquors. Xstrata Technology, Glencore Xstratas technology marketing arm, listed 328 Jameson Cell installations in May 2013. Cells have been installed by 94 companies in 27 countries. Today, the technology is the standard in the Australian Coal Industry where well over one hundred Cells have been installed to recover coal fines. It is mainly used in metals applications to solve final grade and capacity issues from conventional cell cleaner circuits. It has found a niche in transforming traditional circuit designs where its inclusion allows cleaner circuits to be designed with fewer cells in a smaller footprint, while achieving cleaner and/or higher grade concentrates. It has also made possible the recovery of previously discarded fine materials, such as coal and phosphate fines, thereby increasing the efficiency and extending the life of the worlds non-renewable natural resources.

Metallurgy

Despite the highly attractive nature of 3D optical data storage, the development of commercial products has taken a significant length of time. This results from limited financial backing in the field, as well as technical issues, including: Destructive reading. Since both the reading and the writing of data are carried out with laser beams, there is a potential for the reading process to cause a small amount of writing. In this case, the repeated reading of data may eventually serve to erase it (this also happens in phase change materials used in some DVDs). This issue has been addressed by many approaches, such as the use of different absorption bands for each process (reading and writing), or the use of a reading method that does not involve the absorption of energy. Thermodynamic stability. Many chemical reactions that appear not to take place in fact happen very slowly. In addition, many reactions that appear to have happened can slowly reverse themselves. Since most 3D media are based on chemical reactions, there is therefore a risk that either the unwritten points will slowly become written or that the written points will slowly revert to being unwritten. This issue is particularly serious for the spiropyrans, but extensive research was conducted to find more stable chromophores for 3D memories. Media sensitivity. two-photon absorption is a weak phenomenon, and therefore high power lasers are usually required to produce it. Researchers typically use Ti-sapphire lasers or Nd:YAG lasers to achieve excitation, but these instruments are not suitable for use in consumer products.

Photochemistry

A characteristic reaction of is its easy hydrolysis, signaled by the release of HCl vapors and titanium oxides and oxychlorides. Titanium tetrachloride has been used to create naval smokescreens, as the hydrochloric acid aerosol and titanium dioxide that is formed scatter light very efficiently. This smoke is corrosive, however. Alcohols react with to give alkoxides with the formula (R = alkyl, n = 1, 2, 4). As indicated by their formula, these alkoxides can adopt complex structures ranging from monomers to tetramers. Such compounds are useful in materials science as well as organic synthesis. A well known derivative is titanium isopropoxide, which is a monomer. Titanium bis(acetylacetonate)dichloride results from treatment of titanium tetrachloride with excess acetylacetone: Organic amines react with to give complexes containing amido (-containing) and imido (-containing) complexes. With ammonia, titanium nitride is formed. An illustrative reaction is the synthesis of tetrakis(dimethylamido)titanium , a yellow, benzene-soluble liquid: This molecule is tetrahedral, with planar nitrogen centers.

Organic Chemistry

To determine five-day biochemical oxygen demand (BOD), several dilutions of a sample are analyzed for dissolved oxygen before and after a five-day incubation period at 20 °C in the dark. In some cases, bacteria are used to provide a standardized community to uptake oxygen while consuming the organic matter in the sample; these bacteria are known as "seed". The difference in DO and the dilution factor are used to calculated BOD. The resulting number (usually reported in parts per million or milligrams per liter) is useful in determining the relative organic strength of sewage or other polluted waters. The BOD test is an example of analysis that determines classes of materials in a sample.

Analytical Chemistry

The injection loop is a segment of tubing of known volume which is filled with the sample solution before it is injected into the column. Loop volume can range from a few microliters to 50 ml or more.

Analytical Chemistry

For a circular bleach spot of radius and diffusion-dominated recovery, the fluorescence is described by an equation derived by Soumpasis (which involves modified Bessel functions and ) with the characteristic timescale for diffusion, and is the time. is the normalized fluorescence (goes to 1 as goes to infinity). The diffusion timescale for a bleached spot of radius is , with D the diffusion coefficient. Note that this is for an instantaneous bleach with a step function profile, i.e., the fraction of protein assumed to be bleached instantaneously at time is , and , for is the distance from the centre of the bleached area. It is also assumed that the recovery can be modelled by diffusion in two dimensions, that is also both uniform and isotropic. In other words, that diffusion is occurring in a uniform medium so the effective diffusion constant D is the same everywhere, and that the diffusion is isotropic, i.e., occurs at the same rate along all axes in the plane. In practice, in a cell none of these assumptions will be strictly true. #Bleaching will not be instantaneous. Particularly if strong bleaching of a large area is required, bleaching may take a significant fraction of the diffusion timescale . Then a significant fraction of the bleached protein will diffuse out of the bleached region actually during bleaching. Failing to take account of this will introduce a significant error into D. #The bleached profile will not be a radial step function. If the bleached spot is effectively a single pixel then the bleaching as a function of position will typically be diffraction limited and determined by the optics of the confocal laser scanning microscope used. This is not a radial step function and also varies along the axis perpendicular to the plane. #Cells are of course three-dimensional not two-dimensional, as is the bleached volume. Neglecting diffusion out of the plane (we take this to be the xy plane) will be a reasonable approximation only if the fluorescence recovers predominantly via diffusion in this plane. This will be true, for example, if a cylindrical volume is bleached with the axis of the cylinder along the z axis and with this cylindrical volume going through the entire height of the cell. Then diffusion along the z axis does not cause fluorescence recovery as all protein is bleached uniformly along the z axis, and so neglecting it, as Soumpasis equation does, is harmless. However, if diffusion along the z' axis does contribute to fluorescence recovery then it must be accounted for. #There is no reason to expect the cell cytoplasm or nucleoplasm to be completely spatially uniform or isotropic. Thus, the equation of Soumpasis is just a useful approximation, that can be used when the assumptions listed above are good approximations to the true situation, and when the recovery of fluorescence is indeed limited by the timescale of diffusion . Note that just because the Soumpasis can be fitted adequately to data does not necessarily imply that the assumptions are true and that diffusion dominates recovery.

Biochemistry

Engine manufacturers typically rate their engines fuel consumption by the lower heating values since the exhaust is never condensed in the engine, and doing this allows them to publish more attractive numbers than are used in conventional power plant terms. The conventional power industry had used HHV (high heat value) exclusively for decades, even though virtually all of these plants did not condense exhaust either. American consumers should be aware that the corresponding fuel-consumption figure based on the higher heating value will be somewhat higher. The difference between HHV and LHV definitions causes endless confusion when quoters do not bother to state the convention being used. since there is typically a 10% difference between the two methods for a power plant burning natural gas. For simply benchmarking part of a reaction the LHV may be appropriate, but HHV should be used for overall energy efficiency calculations if only to avoid confusion, and in any case, the value or convention should be clearly stated.

Physical Chemistry

The G-less assay can be performed on a circular plasmid to measure levels of transcription. A circular plasmid provides a more efficient template in many systems when compared to other assays such as runoff transcription, in which a cleaved end is required. This method generates radiolabeled transcripts very efficiently because it bypasses the unnecessary process of performing other indirect mRNA product measurements. The promoter is inserted into a circular plasmid containing the G-less cassette, which will generate a transcript of a certain length that omits random and nonspecific transcription throughout the plasmid. Most crude systems, such as HeLa nuclear extracts, are used because they contain low amounts of contaminating GTP that lead to background transcription and may occasionally cause random transcription to read through the G-less cassette.

Biochemistry

Naturally occurring siRNAs have a well-defined structure that is a short (usually 20 to 24-bp) double-stranded RNA (dsRNA) with phosphorylated 5 ends and hydroxylated 3 ends with two overhanging nucleotides. The Dicer enzyme catalyzes production of siRNAs from long dsRNAs and small hairpin RNAs. siRNAs can also be introduced into cells by transfection. Since in principle any gene can be knocked down by a synthetic siRNA with a complementary sequence, siRNAs are an important tool for validating gene function and drug targeting in the post-genomic era.

Biochemistry

The interpretation of scattering measurements made at the multiangular locations relies upon some knowledge of the a priori properties of the particles or molecules measured. The scattering characteristics of different classes of such scatterers may be interpreted best by application of an appropriate theory. For example, the following theories are most often applied. Rayleigh scattering is the simplest and describes elastic scattering of light or other electromagnetic radiation by objects much smaller than the incident wavelength. This type of scattering is responsible for the blue color of the sky during the day and is inversely proportional to the fourth power of wavelength. The Rayleigh–Gans approximation is a means of interpreting MALS measurements with the assumption that the scattering particles have a refractive index, n, very close to the refractive index of the surrounding medium, n. If we set m = n/n and assume that , then such particles may be considered as composed of very small elements, each of which may be represented as a Rayleigh-scattering particle. Thus each small element of the larger particle is assumed to scatter independently of any other. Lorenz–Mie theory is used to interpret the scattering of light by homogeneous spherical particles. The Rayleigh–Gans approximation and the Lorenz–Mie theory produce identical results for homogeneous spheres in the limit as . Lorenz–Mie theory may be generalized to spherically symmetric particles per reference. More general shapes and structures have been treated by Erma. Scattering data is usually represented in terms of the so-called excess Rayleigh ratio defined as the Rayleigh ratio of the solution or single particle event from which is subtracted the Rayleigh ratio of the carrier fluid itself and other background contributions, if any. The Rayleigh Ratio measured at a detector lying at an angle θ and subtending a solid angle ΔΩ is defined as the intensity of light per unit solid angle per unit incident intensity, I, per unit illuminated scattering volume ΔV. The scattering volume ΔV from which scattered light reaches the detector is determined by the detectors field of view generally restricted by apertures, lenses and stops. Consider now a MALS measurement made in a plane from a suspension of N identical particles/molecules per ml illuminated by a fine beam of light produced by a laser. Assuming that the light is polarized perpendicular to the plane of the detectors. The scattered light intensity measured by the detector at angle θ' in excess of that scattered by the suspending fluid would be where i(θ) is the scattering function of a single particle, k = 2πn/λ, n is the refractive index of the suspending fluid, and λ is the vacuum wavelength of the incident light. The excess Rayleigh ratio, R(θ), is then given by Even for a simple homogeneous sphere of radius a whose refractive index, n, is very nearly the same as the refractive index "n" of the suspending fluid, i.e. Rayleigh–Gans approximation, the scattering function in the scattering plane is the relatively complex quantity :, where and λ is the wavelength of the incident light in vacuum.

Physical Chemistry

Cell engineering is the purposeful process of adding, deleting, or modifying genetic sequences in living cells to achieve biological engineering goals such as altering cell production, changing cell growth and proliferation requirements, adding or removing cell functions, and many more. Cell engineering often makes use of DNA technology to achieve these modifications as well as closely related tissue engineering methods. Cell engineering can be characterized as an intermediary level in the increasingly specific disciplines of biological engineering which includes organ engineering, tissue engineering, protein engineering, and genetic engineering. The field of cellular engineering is gaining more traction as biomedical research advances in tissue engineering and becomes more specific. Publications in the field have gone from several thousand in the early 2000s to nearly 40,000 in 2020.

Biochemistry

Because the net variation in state properties during a thermodynamic cycle is zero, it forms a closed loop on a PV diagram. A PV diagrams Y axis shows pressure (P) and X axis shows volume (V). The area enclosed by the loop is the work (W') done by the process: This work is equal to the balance of heat (Q) transferred into the system: Equation (2) is consistent with the First Law; even though the internal energy changes during the course of the cyclic process, when the cyclic process finishes the system's internal energy is the same as the energy it had when the process began. If the cyclic process moves clockwise around the loop, then W will be positive, and it represents a heat engine. If it moves counterclockwise, then W will be negative, and it represents a heat pump.

Physical Chemistry

A buffer solution contains an acid and its conjugate base or a base and its conjugate acid. Addition of the conjugate ion will result in a change of pH of the buffer solution. For example, if both sodium acetate and acetic acid are dissolved in the same solution they both dissociate and ionize to produce acetate ions. Sodium acetate is a strong electrolyte, so it dissociates completely in solution. Acetic acid is a weak acid, so it only ionizes slightly. According to Le Chatelier's principle, the addition of acetate ions from sodium acetate will suppress the ionization of acetic acid and shift its equilibrium to the left. Thus the percent dissociation of the acetic acid will decrease, and the pH of the solution will increase. The ionization of an acid or a base is limited by the presence of its conjugate base or acid. : NaCHCO(s) → Na(aq) + CHCO(aq) : CHCOH(aq) H(aq) + CHCO(aq) This will decrease the hydronium concentration, and thus the common-ion solution will be less acidic than a solution containing only acetic acid.

Physical Chemistry

In this technique siRNA first must be designed against the target gene. Once the siRNA is configured against the gene it has to be effectively delivered through a transfection protocol. Delivery is usually done by cationic liposomes, polymer nanoparticles, and lipid conjugation. This method is advantageous because it can deliver siRNA to most types of cells, has high efficiency and reproducibility, and is offered commercially. The most common commercial reagents for transfection of siRNA are Lipofectamine and Neon Transfection. However, it is not compatible with all cell types and has low in vivo efficiency.

Biochemistry

Self-interstitial defects are interstitial defects which contain only atoms which are the same as those already present in the lattice. The structure of interstitial defects has been experimentally determined in some metals and semiconductors. Contrary to what one might intuitively expect, most self-interstitials in metals with a known structure have a split structure, in which two atoms share the same lattice site. Typically the center of mass of the two atoms is at the lattice site, and they are displaced symmetrically from it along one of the principal lattice directions. For instance, in several common face-centered cubic (fcc) metals such as copper, nickel and platinum, the ground state structure of the self-interstitial is the split [100] interstitial structure, where two atoms are displaced in a positive and negative [100] direction from the lattice site. In body-centered cubic (bcc) iron the ground state interstitial structure is similarly a [110] split interstitial. These split interstitials are often called dumbbell interstitials, because plotting the two atoms forming the interstitial with two large spheres and a thick line joining them makes the structure resemble a dumbbell weight-lifting device. In other bcc metals than iron, the ground state structure is believed based on recent density-functional theory calculations to be the [111] crowdion interstitial, which can be understood as a long chain (typically some 10–20) of atoms along the [111] lattice direction, compressed compared to the perfect lattice such that the chain contains one extra atom. In semiconductors the situation is more complex, since defects may be charged and different charge states may have different structures. For instance, in silicon, the interstitial may either have a split [110] structure or a tetrahedral truly interstitial one. Carbon, notably in graphite and diamond, has a number of interesting self-interstitials - recently discovered using Local-density approximation-calculations is the "spiro-interestitial" in graphite, named after spiropentane, as the interstitial carbon atom is situated between two basal planes and bonded in a geometry similar to spiropentane.

Metallurgy

The Derjaguin approximation (or sometimes also referred to as the proximity approximation), named after the Russian scientist Boris Derjaguin, expresses the force profile acting between finite size bodies in terms of the force profile between two planar semi-infinite walls. This approximation is widely used to estimate forces between colloidal particles, as forces between two planar bodies are often much easier to calculate. The Derjaguin approximation expresses the force F(h) between two bodies as a function of the surface separation as where W(h) is the interaction energy per unit area between the two planar walls and R the effective radius. When the two bodies are two spheres of radii R and R, respectively, the effective radius is given by Experimental force profiles between macroscopic bodies as measured with the surface forces apparatus (SFA) or colloidal probe technique are often reported as the ratio F(h)/R.

Physical Chemistry

This technique is most commonly used by mineralogists and petrologists. Most rocks are aggregates of small mineral grains. These grains may preserve chemical information acquired during their formation and subsequent alteration. This information may illuminate geologic processes such as crystallization, lithification, volcanism, metamorphism, orogenic events (mountain building), and plate tectonics. This technique is also used for the study of extraterrestrial rocks (meteorites), and provides chemical data which is vital to understanding the evolution of the planets, asteroids, and comets. The change in elemental composition from the center (also known as core) to the edge (or rim) of a mineral can yield information about the history of the crystal's formation, including the temperature, pressure, and chemistry of the surrounding medium. Quartz crystals, for example, incorporate a small, but measurable amount of titanium into their structure as a function of temperature, pressure, and the amount of titanium available in their environment. Changes in these parameters are recorded by titanium as the crystal grows.

Analytical Chemistry

This reagent was originally prepared by Conrad Willgerodt by reacting iodobenzene with a mixture of acetic acid and peracetic acid: PIDA can also be prepared from iodosobenzene and glacial acetic acid: More recent preparations direct from iodine, acetic acid, and benzene have been reported, using either sodium perborate or potassium peroxydisulfate as the oxidizing agent: The PIDA molecule is termed hypervalent as its iodine atom (technically a hypervalent iodine) is in its +III oxidation state and has more than typical number of covalent bonds. It adopts a T-shaped molecular geometry, with the phenyl group occupying one of the three equatorial positions of a trigonal bipyramid (lone pairs occupy the other two) and the axial positions occupied by oxygen atoms from the acetate groups. The "T" is distorted in that the phenyl-C to I to acetate-O bond angles are less than 90°. A separate investigation of the crystal structure confirmed that it has orthorhombic crystals in space group Pnn2 and reported unit-cell dimensions in good agreement with the original paper. The bond lengths around the iodine atom were 2.08 Å to the phenyl carbon atom and equal 2.156 Å bonds to the acetate oxygen atoms. This second crystal structure determination explained the distortion in the geometry by noting the presence of two weaker intramolecular iodine&ndash;oxygen interactions, resulting in an "overall geometry of each iodine [that] can be described as a pentagonal-planar arrangement of three strong and two weak secondary bonds."

Organic Chemistry

Pelletizing is done in a pellet mill, where feed is normally conditioned and thermal-treated in the fitted conditioners of a pellet mill. The feed is then pushed through the holes and exit the pellet mill as pelleted feed.

Metallurgy

Extrema of the spinodal in a temperature vs composition plot coincide with those of the binodal curve, and are known as critical points.

Physical Chemistry

*Transport is proportional to applied bias (resistor) *Transport can be made to move in one direction (diode) *Control of gain is possible by introduction of third pole (transistor) *Control of the forward/reverse direction by asymmetric gates (Field-effect reconfigurable diode)

Physical Chemistry

The different biomolecules that make up a plant's biogenic substances – particularly those in seed exudates - can be identified by using different varieties of chromatography in a lab environment. For metabolite profiling, gas chromatography-mass spectrometry is used to find flavonoids such as quercetin. Compounds can then be further differentiated using reversed-phase high-performance liquid chromatography-mass spectrometry. When it comes to measuring biogenic substances in a natural environment such as a body of water, a hydroecological CNPSi model can be used to calculate the spatial transport of biogenic substances, in both the horizontal and vertical dimensions. This model takes into account the water exchange and flow rate, and yields the values of biogenic substance rates for any area or layer of the water for any month. There are two main evaluation methods involved: measuring per unit water volume (mg/m year) and measuring substances per entire water volume of layer (t of element/year). The former is mostly used to observe biogenic substance dynamics and individual pathways for flux and transformations, and is useful when comparing individual regions of the strait or waterway. The second method is used for monthly substance fluxes and must take into account that there are monthly variations in the water volume in the layers. In the study of geochemistry, biogenic substances can be isolated from fossils and sediments through a process of scraping and crushing the target rock sample, then washing with 40% hydrofluoric acid, water, and benzene/methanol in the ratio 3:1. Following this, the rock pieces are ground and centrifuged to produce a residue. Chemical compounds are then derived through various chromatography and mass spectrometry separations. However, extraction should be accompanied by rigorous precautions to ensure there is no amino acid contaminants from fingerprints, or silicone contaminants from other analytical treatment methods.

Organic Chemistry

Cycling probe technology makes use of a chimeric nucleic acid probe to detect the presence of a particular DNA sequence. The chimeric probe consists of an RNA segment sandwiched between two DNA segments. The RNA segment contains 4 contiguous purine nucleotides. The probes should be less than 30 nucleotides in length and designed to minimize intra-probe and inter-probe interactions.

Biochemistry

In eukaryotic cells the pyruvate decarboxylation occurs inside the mitochondrial matrix, after transport of the substrate, pyruvate, from the cytosol. The transport of pyruvate into the mitochondria is via the transport protein pyruvate translocase. Pyruvate translocase transports pyruvate in a symport fashion with a proton (across the inner mitochondrial membrane), which may be considered to be a form of secondary active transport, but further confirmation/support may be needed for the usage of "secondary active transport" desciptor here (Note: the pyruvate transportation method via the pyruvate translocase appears to be coupled to a proton gradient according to S. Papa et al., 1971, seemingly matching secondary active transport in definition). Alternative sources say "transport of pyruvate across the outer mitochondrial membrane appears to be easily accomplished via large non-selective channels such as voltage-dependent anion channels, which enable passive diffusion" and transport across inner mitochondrial membrane is mediated by mitochondrial pyruvate carrier 1 (MPC1) and mitochondrial pyruvate carrier 2 (MPC2). Upon entry into the mitochondrial matrix, the pyruvate is decarboxylated, producing acetyl-CoA (and carbon dioxide and NADH). This irreversible reaction traps the acetyl-CoA within the mitochondria (the acetyl-CoA can only be transported out of the mitochondrial matrix under conditions of high oxaloacetate via the citrate shuttle, a TCA intermediate that is normally sparse). The carbon dioxide produced by this reaction is nonpolar and small, and can diffuse out of the mitochondria and out of the cell. In prokaryotes, which have no mitochondria, this reaction is either carried out in the cytosol, or not at all.

Biochemistry

Nowadays, most radical photopolymerization pathways are based on addition reactions of carbon double bonds in acrylates or methacrylates, and these pathways are widely employed in photolithography and stereolithography. Before the free radical nature of certain polymerizations was determined, certain monomers were observed to polymerize when exposed to light. The first to demonstrate the photoinduced free radical chain reaction of vinyl bromide was Ivan Ostromislensky, a Russian chemist who also studied the polymerization of synthetic rubber. Subsequently, many compounds were found to become dissociated by light and found immediate use as photoinitiators in the polymerization industry. In the free radical mechanism of radiation curable systems, light absorbed by a photoinitiator generates free-radicals which induce cross-linking reactions of a mixture of functionalized oligomers and monomers to generate the cured film Photocurable materials that form through the free-radical mechanism undergo chain-growth polymerization, which includes three basic steps: initiation, chain propagation, and chain termination. The three steps are depicted in the scheme below, where R• represents the radical that forms upon interaction with radiation during initiation, and M is a monomer. The active monomer that is formed is then propagated to create growing polymeric chain radicals. In photocurable materials the propagation step involves reactions of the chain radicals with reactive double bonds of the prepolymers or oligomers. The termination reaction usually proceeds through combination, in which two chain radicals are joined, or through disproportionation, which occurs when an atom (typically hydrogen) is transferred from one radical chain to another resulting in two polymeric chains. ;Initiation ;Propagation ;Termination :combination :disproportionation Most composites that cure through radical chain growth contain a diverse mixture of oligomers and monomers with functionality that can range from 2-8 and molecular weights from 500 to 3000. In general, monomers with higher functionality result in a tighter crosslinking density of the finished material. Typically these oligomers and monomers alone do not absorb sufficient energy for the commercial light sources used, therefore photoinitiators are included.

Photochemistry

Bioenergetics is the part of biochemistry concerned with the energy involved in making and breaking of chemical bonds in the molecules found in biological organisms. It can also be defined as the study of energy relationships and energy transformations and transductions in living organisms. The ability to harness energy from a variety of metabolic pathways is a property of all living organisms. Growth, development, anabolism and catabolism are some of the central processes in the study of biological organisms, because the role of energy is fundamental to such biological processes. Life is dependent on energy transformations; living organisms survive because of exchange of energy between living tissues/ cells and the outside environment. Some organisms, such as autotrophs, can acquire energy from sunlight (through photosynthesis) without needing to consume nutrients and break them down. Other organisms, like heterotrophs, must intake nutrients from food to be able to sustain energy by breaking down chemical bonds in nutrients during metabolic processes such as glycolysis and the citric acid cycle. Importantly, as a direct consequence of the First Law of Thermodynamics, autotrophs and heterotrophs participate in a universal metabolic network—by eating autotrophs (plants), heterotrophs harness energy that was initially transformed by the plants during photosynthesis. In a living organism, chemical bonds are broken and made as part of the exchange and transformation of energy. Energy is available for work (such as mechanical work) or for other processes (such as chemical synthesis and anabolic processes in growth), when weak bonds are broken and stronger bonds are made. The production of stronger bonds allows release of usable energy. Adenosine triphosphate (ATP) is the main "energy currency" for organisms; the goal of metabolic and catabolic processes are to synthesize ATP from available starting materials (from the environment), and to break- down ATP (into adenosine diphosphate (ADP) and inorganic phosphate) by utilizing it in biological processes. In a cell, the ratio of ATP to ADP concentrations is known as the "energy charge" of the cell. A cell can use this energy charge to relay information about cellular needs; if there is more ATP than ADP available, the cell can use ATP to do work, but if there is more ADP than ATP available, the cell must synthesize ATP via oxidative phosphorylation. Living organisms produce ATP from energy sources via oxidative phosphorylation. The terminal phosphate bonds of ATP are relatively weak compared with the stronger bonds formed when ATP is hydrolyzed (broken down by water) to adenosine diphosphate and inorganic phosphate. Here it is the thermodynamically favorable free energy of hydrolysis that results in energy release; the phosphoanhydride bond between the terminal phosphate group and the rest of the ATP molecule does not itself contain this energy. An organism's stockpile of ATP is used as a battery to store energy in cells. Utilization of chemical energy from such molecular bond rearrangement powers biological processes in every biological organism. Living organisms obtain energy from organic and inorganic materials; i.e. ATP can be synthesized from a variety of biochemical precursors. For example, lithotrophs can oxidize minerals such as nitrates or forms of sulfur, such as elemental sulfur, sulfites, and hydrogen sulfide to produce ATP. In photosynthesis, autotrophs produce ATP using light energy, whereas heterotrophs must consume organic compounds, mostly including carbohydrates, fats, and proteins. The amount of energy actually obtained by the organism is lower than the amount present in the food; there are losses in digestion, metabolism, and thermogenesis. Environmental materials that an organism intakes are generally combined with oxygen to release energy, although some nutrients can also be oxidized anaerobically by various organisms. The utilization of these materials is a form of slow combustion because the nutrients are reacted with oxygen (the materials are oxidized slowly enough that the organisms do not produce fire). The oxidation releases energy, which may evolve as heat or be used by the organism for other purposes, such as breaking chemical bonds.

Biochemistry

At slow scan rates there should be no separation between the oxidative and reductive peaks. * A one-electron site (e.g. a heme or FeS cluster) gives a broad peak (fig 1A). The equation that gives the shape and intensity of the peak is: : Ideally, the peak position is in both directions. The peak current is (it is proportional to scan rate, , and to the amount of redox sites on the electrode, ). The ideal half width at half height (HWHH) equates mV at 20 °C. Non-ideal behaviour may result in the peak being broader than the ideal limit. * The peak shape for a two-electron redox site (e.g. a flavin) depends on the stability of the half-reduced state (fig 1B). If the half-reduced state is stable over a large range of electrode potential, the signal is the sum of two one-electron peaks (purple line in fig 1B). If the half reduced state is unstable, the signal is a single peak (red line in fig 1B), which may have up to four times the height and half the width of a one-electron peak. * A protein that contains multiple redox centers should give multiple peaks which all have the same area (scaled by ).

Physical Chemistry

While FeAl is a B2 alloy, the observed yield strength anomaly in FeAl is due to another mechanism. If cross-slip were the mechanism, then the yield strength anomaly would be rate dependent, as expected for a thermally activated process. Instead, yield strength anomaly is state dependent, which is a property that is dependent on the state of the material. As a result, vacancy activated strengthening is the most widely-accepted mechanism. The vacancy formation energy is low for FeAl, allowing for an unusually high concentration of vacancies in FeAl at high temperatures (2.5% at 1000C for Fe-50Al). The vacancy formed in either aluminum-rich FeAl or through heating is an aluminum vacancy. At low temperatures around 300K, the yield strength either decreases or does not change with temperature. At moderate temperatures (0.35-0.45 T), yield strength has been observed to increase with an increased vacancy concentration, providing further evidence for a vacancy driven strengthening mechanism. The increase in yield strength from increased vacancy concentration is believed to be the result of dislocations being pinned by vacancies on the slip plane, causing the dislocations to bow. Then, above the peak stress temperature, vacancies can migrate as vacancy migration is easier with elevated temperatures. At those temperatures, vacancies no longer hinder dislocation motion but rather aid climb. In the vacancy strengthening model, the increased strength below the peak stress temperature is approximated as proportional to the vacancy concentration to the one-half with the vacancy concentration estimated using Maxwell-Boltzmann statistics. Thus, the strength can be estimated as , with being the vacancy formation energy and T being the absolute temperature. Above the peak stress temperature, a diffusion-assisted deformation mechanism can be used to describe strength since vacancies are now mobile and assist dislocation motion. Above the peak, the yield strength is strain rate dependent and thus, the peak yield strength is rate dependent. As a result, the peak stress temperature increases with an increased strain rate. Note, this is different than the yield strength anomaly, which is the yield strength below the peak, being rate dependent. The peak yield strength is also dependent on percent aluminum in the FeAl alloy. As the percent aluminum increases, the peak yield strength occurs at lower temperatures. The yield strength anomaly in FeAl alloys can be hidden if thermal vacancies are not minimized through a slow anneal at a relatively low temperature (~400 °C for ~5 days). Further, the yield strength anomaly is not present in systems that use a very low strain rate as the peak yield strength is strain rate dependent and thus, would occur at temperatures too low to observe the yield strength anomaly. Additionally, since the formation of vacancies requires time, the peak yield strength magnitude is dependent on how long the material is held at the peak stress temperature. Also, the peak yield strength has been found not to be dependent on crystal orientation. Other mechanisms have been proposed including a cross slip mechanism similar to that for L1, dislocation decomposition into less mobile segments at jogs, dislocation pinning, climb-lock mechanism, and slip vector transition. The slip vector transition from MnAl is not dependent on strain rate and thus, may not follow the vacancy activated strengthening mechanism. Instead, there an order-strengthening mechanism has been proposed.

Metallurgy

Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds. Selective herbicides control specific weed species while leaving the desired crop relatively unharmed, while non-selective herbicides (sometimes called "total weed killers") kill plants indiscriminately. The combined effects of herbicides, nitrogen fertilizer, and improved cultivars has increased yields (per acre) of major crops by 3x to 6x from 1900 to 2000. In the United States in 2012, about 91% of all herbicide usage, determined by weight applied, was in agriculture. In 2012, world pesticide expenditures totaled nearly $24.7 billion; herbicides were about 44% of those sales and constituted the biggest portion, followed by insecticides, fungicides, and fumigants. Herbicide is also used in forestry, where certain formulations have been found to suppress hardwood varieties in favor of conifers after clearcutting, as well as pasture systems.

Environmental Chemistry

Exfoliation (or onion skin weathering) is the gradual removing of spall due to the cyclic increase and decrease in the temperature of the surface layers of the rock. Rocks do not conduct heat well, so when they are exposed to extreme heat, the outermost layer becomes much hotter than the rock underneath causing differential thermal expansion. This differential expansion causes sub-surface shear stress, in turn causing spalling. Extreme temperature change, such as forest fires, can also cause spalling of rock. This mechanism of weathering causes the outer surface of the rock to fall off in thin fragments, sheets or flakes, hence the name exfoliation or onion skin weathering.

Metallurgy

Copper is a biologically important metal to detect. It has many sensors developed for it including: *CTAP-1, a sensor that shows a response in the UV region when Cu(I) binds to an azatetrathiacrown motif that in turn excites a pyrazoline-based dye that is attached. To use the probe, one excites it at 365 nm. If it is bound to Cu, then it will increase its fluorescence intensity. CTAP-1 is effective as it has a large modulation in its spectrum upon binding Cu, and is selective for the binding of Cu over other metals. *Coppersensor-1 (CS1) that comprises a thioether rich motif that binds to Cu(I) causing the excitation of a boron-dipyrromethene (BODIPY) dye in the visible region. The probe has good selectivity for Cu(I) over alkaline earth metals, Cu(II), and d-block metals.

Photochemistry

The Intronerator is a database of alternatively spliced genes and a database of introns for Caenorhabditis elegans.

Biochemistry

PCET is thought to be pervasive. Important examples include water oxidation in photosynthesis, nitrogen fixation, oxygen reduction reaction, and the function of hydrogenases. These processes are relevant to respiration.

Physical Chemistry

pRb has also been implicated in regulating metabolism through interactions with components of cellular metabolic pathways. RB1 mutations can cause alterations in metabolism, including reduced mitochondrial respiration, reduced activity in the electron transport chain, and changes in flux of glucose and/or glutamine. Particular forms of pRb have been found to localize to the outer mitochondrial membrane and directly interacts with Bax to promote apoptosis.

Biochemistry

Myzocytosis (from Greek: myzein, () meaning "to suck" and kytos () meaning "container", hence referring to "cell") is a method of feeding found in some heterotrophic organisms. It is also called "cellular vampirism" as the predatory cell pierces the cell wall and/or cell membrane of the prey cell with a feeding tube, the conoid, sucks out the cellular content and digests it. Myzocytosis is found in Myzozoa and also in some species of Ciliophora (both comprise the alveolates). A classic example of myzocytosis is the feeding method of the infamous predatory ciliate, Didinium, where it is often depicted devouring a hapless Paramecium. The suctorian ciliates were originally thought to have fed exclusively through myzocytosis, sucking out the cytoplasm of prey via superficially drinking straw-like pseudopodia. It is now understood that suctorians do not feed through myzocytosis, but actually, instead, manipulate and envenomate captured prey with their tentacle-like pseudopodia.

Biochemistry

The presence of nitrogen activates the csiR gene located downstream of the gabP gene. The csiR gene encodes a protein that acts as a transcriptional repressor for csiD-ygaF-gab operon hence shutting off the GABA degradation pathway.

Biochemistry

Macrophages and related cells employ a different mechanism to recognize the pathogen. Their receptors recognize certain motifs present on the invading pathogen that are very unlikely to be present on a host cell. Such repeating motifs are recognized by pattern recognition receptors (PRRs) like the toll-like receptors (TLRs) expressed by the macrophages. Since the same receptor could bind to a given motif present on surfaces of widely disparate microorganisms, this mode of recognition is relatively nonspecific, and constitutes an innate immune response.

Biochemistry

In a small number of cases, plant genes are effective against an entire pathogen species, even though that species is pathogenic on other genotypes of that host species. Examples include barley MLO against powdery mildew, wheat Lr34 against leaf rust and wheat Yr36 against wheat stripe rust. An array of mechanisms for this type of resistance may exist depending on the particular gene and plant-pathogen combination. Other reasons for effective plant immunity can include a lack of coadaptation (the pathogen and/or plant lack multiple mechanisms needed for colonization and growth within that host species), or a particularly effective suite of pre-formed defenses.

Biochemistry

The first heteropoly molybdate and first heteropolymetallate, yellow ammonium phosphomolybdate, (NH)PMoO was discovered by Berzelius in 1826. The phosphorus atom in the anion is termed the heteroatom, other heteroatoms are silicon and arsenic. The heteropoly-molybdenum blues have structures based on the Keggin structure. The blue colour arises because the near-colourless anion, such as the phosphomolybdate anion, , can accept more electrons (i.e. be reduced) to form an intensely coloured mixed-valence complex. This can occur in one electron or two electron steps. The reduction process is reversible and the structure of the anion is essentially unchanged. : PMo + 4 e ⇌ PMoMo The structure of the anion, PMoMo, has been determined in the solid state and is a β-isomer (i.e. with one of the four groups of edge-shared octahedra on the α-Keggin ion rotated through 60°). Similar structures have been found with silicon, germanium or arsenic heteroatoms. The intense blue colour of the reduced anion is the basis for the use of heteropoly-molybdenum blues in quantitative and qualitative analytical techniques. This property is exploited as follows: *the sample to be analysed is reacted to produce the reduced blue heteropoly-molybdate in order to: **detect the presence of a hetero atom in e.g. a spot test ** measure the amount of a hetero atom present in the sample colorimetrically *the sample is added to a solution of the near colourless, unreduced complex in order to: **detect the presence of a reducing compound e.g. a reducing sugar such as glucose **measure the amount of a reducing compound in a two step procedure

Physical Chemistry

Phosphoric acid units can be bonded together in rings (cyclic structures). The simplest such compound is trimetaphosphoric acid or cyclo-triphosphoric acid having the formula . Its structure is shown in the illustration. Since the ends are condensed, its formula has one less (water) than tripolyphosphoric acid. The general formula of a phosphoric acid is , where n is the number of phosphorus atoms and x is the number of fundamental cycles in the molecule's structure; that is, the minimum number of bonds that would have to be broken to eliminate all cycles. The limiting case of internal condensation, where all oxygen atoms are shared and there are no hydrogen atoms (x = ) is an anhydride , phosphorus pentoxide .

Organic Chemistry

Brown MX-5BR or Reactive Brown 10 has a formula of CHClCrNNaOS and a molecular weight of 1163.6 g/mol, containing two dichlorotriazine rings. Brown MX-5BR, for example, can be used to purify lysozyme, phosphinothricin acetyltransferase. It also shown that it can elute tryptophanyl-tRNA synthetase using Trp as eluant, however, tryptophanyl-tRNA and tyrosyl-tRNA synthetase are the only t-RNA that can be elute out using Brown MX-5BR.

Analytical Chemistry

Metallization pressure is the pressure required for a non-metallic chemical element to become a metal. Every material is predicted to turn into a metal if the pressure is high enough, and temperature low enough. Some of these pressures are beyond the reach of diamond anvil cells, and are thus theoretical predictions. Neon has the highest metallization pressure for any element. The value for phosphorus refers to pressurizing black phosphorus. The value for arsenic refers to pressurizing metastable black arsenic; grey arsenic, the standard state, is already a metallic conductor at standard conditions. No value is known or theoretically predicted for radon.

Physical Chemistry

Based on atomicity, molecules can be classified as: *Monoatomic (composed of one atom). Examples include He (helium), Ne (neon), Ar (argon), and Kr (krypton). All noble gases are monoatomic. * Diatomic (composed of two atoms). Examples include H (hydrogen), N (nitrogen), O (oxygen), F (fluorine), and Cl (chlorine). Halogens are usually diatomic. *Triatomic (composed of three atoms). Examples include O (ozone). *Polyatomic (composed of three or more atoms). Examples include S. Atomicity may vary in different allotropes of the same element. The exact atomicity of metals, as well as some other elements such as carbon, cannot be determined because they consist of a large and indefinite number of atoms bonded together. They are typically designated as having an atomicity of 1. The atomicity of homonuclear molecule can be derived by dividing the molecular weight by the atomic weight. For example, the molecular weight of oxygen is 31.999, while its atomic weight is 15.879; therefore, its atomicity is approximately 2 (31.999/15.879 ≈ 2).

Physical Chemistry

Reinhold and coworkers performed a systematical experiment to study the kinetics and mechanisms of hydrolysis of such compounds. They prepared a series of α-silanes and γ-silanes and tested their reactivity in different pH (acidic and basic regime), functional group X and the spacer between the silicon atom and the functional group X. In general, they find that under basic conditions, the rate of hydrolysis is mainly controlled by the electrophilicity of the silicon center and the rate of the hydrolysis of the γ-silanes is less influenced by the generally electronegative functional groups than α-silanes. More electronegative the functional groups are, the higher the rate of hydrolysis. However, under acidic conditions, the rate of hydrolysis depends on both the electrophilicity of the silicon center (determining the molecular reactivity) and the concentration of the (protonated) reactive species. Under acidic conditions, the nucleophile changes from OH to HO, so it involves the process of protonation and the atoms are protonated could be either silicon or the functional group X. As a result, the general trend in acidic solution is more complicated.

Physical Chemistry

Solid phosphorus pentachloride is an ionic compound, formulated , that is, a salt containing the tetrachlorophosphonium cation. Dilute solutions dissociate according to the following equilibrium: :PCl + Cl Triphenylphosphine dichloride (PhPCl) exists both as the pentacoordinate phosphorane and as the chlorotriphenylphosphonium chloride, depending on the medium. The situation is similar to that of PCl. It is an ionic compound (PPhCl)Cl in polar solutions and a molecular species with trigonal bipyramidal molecular geometry in apolar solution.

Organic Chemistry

In SEC, mass is not measured so much as the hydrodynamic volume of the polymer molecules, that is, how much space a particular polymer molecule takes up when it is in solution. However, the approximate molecular weight can be calculated from SEC data because the exact relationship between molecular weight and hydrodynamic volume for polystyrene can be found. For this, polystyrene is used as a standard. But the relationship between hydrodynamic volume and molecular weight is not the same for all polymers, so only an approximate measurement can be obtained. Another drawback is the possibility of interaction between the stationary phase and the analyte. Any interaction leads to a later elution time and thus mimics a smaller analyte size. When performing this method, the bands of the eluting molecules may be broadened. This can occur by turbulence caused by the flow of the mobile phase molecules passing through the molecules of the stationary phase. In addition, molecular thermal diffusion and friction between the molecules of the glass walls and the molecules of the eluent contribute to the broadening of the bands. Besides broadening, the bands also overlap with each other. As a result, the eluent usually gets considerably diluted. A few precautions can be taken to prevent the likelihood of the bands broadening. For instance, one can apply the sample in a narrow, highly concentrated band on the top of the column. The more concentrated the eluent is, the more efficient the procedure would be. However, it is not always possible to concentrate the eluent, which can be considered as one more disadvantage.

Biochemistry

G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily related proteins that are cell surface receptors that detect molecules outside the cell and activate cellular responses. They are coupled with G proteins. They pass through the cell membrane seven times in the form of six loops (three extracellular loops interacting with ligand molecules, three intracellular loops interacting with G proteins, an N-terminal extracellular region and a C-terminal intracellular region) of amino acid residues, which is why they are sometimes referred to as seven-transmembrane receptors. Ligands can bind either to the extracellular N-terminus and loops (e.g. glutamate receptors) or to the binding site within transmembrane helices (rhodopsin-like family). They are all activated by agonists, although a spontaneous auto-activation of an empty receptor has also been observed. G protein-coupled receptors are found only in eukaryotes, including yeast, and choanoflagellates. The ligands that bind and activate these receptors include light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters, and vary in size from small molecules to peptides to large proteins. G protein-coupled receptors are involved in many diseases. There are two principal signal transduction pathways involving the G protein-coupled receptors: *the cAMP signal pathway and *the phosphatidylinositol signal pathway. When a ligand binds to the GPCR it causes a conformational change in the GPCR, which allows it to act as a guanine nucleotide exchange factor (GEF). The GPCR can then activate an associated G protein by exchanging the GDP bound to the G protein for a GTP. The G protein's α subunit, together with the bound GTP, can then dissociate from the β and γ subunits to further affect intracellular signaling proteins or target functional proteins directly depending on the α subunit type (G, G, G, G). GPCRs are an important drug target and approximately 34% of all Food and Drug Administration (FDA) approved drugs target 108 members of this family. The global sales volume for these drugs is estimated to be 180 billion US dollars . It is estimated that GPCRs are targets for about 50% of drugs currently on the market, mainly due to their involvement in signaling pathways related to many diseases i.e. mental, metabolic including endocrinological disorders, immunological including viral infections, cardiovascular, inflammatory, senses disorders, and cancer. The long ago discovered association between GPCRs and many endogenous and exogenous substances, resulting in e.g. analgesia, is another dynamically developing field of the pharmaceutical research.

Biochemistry

The transformation that converts 7-dehydrocholesterol to vitamin D occurs in two steps. First, 7-dehydrocholesterol is photolyzed by ultraviolet light in a 6-electron conrotatory ring-opening electrocyclic reaction; the product is previtaminD. Second, previtaminD spontaneously isomerizes to vitaminD (cholecalciferol) in an antarafacial [[Sigmatropic shift#.5B1,7.5D Shifts|sigmatropic [1,7] hydride shift]]. At room temperature, the transformation of previtaminD to vitamin D in an organic solvent takes about 12 days to complete. The conversion of previtaminD to vitamin D in the skin is about 10 times faster than in an organic solvent. The conversion from ergosterol to vitamin D follows a similar procedure, forming previtaminD by photolysis, which isomerizes to vitamin D (ergocalciferol). The transformation of previtaminD to vitamin D in methanol has a rate comparable to that of previtaminD. The process is faster in white button mushrooms.

Biochemistry

TFH participates in nucleotide excision repair (NER) by opening the DNA double helix after damage is initially recognized. NER is a multi-step pathway that removes a wide range of different damages that distort normal base pairing, including bulky chemical damages and UV-induced damages. Individuals with mutational defects in genes specifying protein components that catalyze the NER pathway, including the TFH components, often display features of premature aging (see DNA damage theory of aging).

Biochemistry

In chemistry, a phosphoric acid, in the general sense, is a phosphorus oxoacid in which each phosphorus (P) atom is in the oxidation state +5, and is bonded to four oxygen (O) atoms, one of them through a double bond, arranged as the corners of a tetrahedron. Two or more of these tetrahedra may be connected by shared single-bonded oxygens, forming linear or branched chains, cycles, or more complex structures. The single-bonded oxygen atoms that are not shared are completed with acidic hydrogen atoms. The general formula of a phosphoric acid is , where n is the number of phosphorus atoms and x is the number of fundamental cycles in the molecule's structure, between 0 and . Removal of protons () from k hydroxyl groups –OH leaves anions generically called phosphates (if ) or hydrogen phosphates (if k is between 1 and ), with general formula . The fully dissociated anion () has formula . The term phosphate is also used in organic chemistry for the functional groups that result when one or more of the hydrogens are replaced by bonds to other groups. These acids, together with their salts and esters, include some of the best-known compounds of phosphorus, of high importance in biochemistry, mineralogy, agriculture, pharmacy, chemical industry, and chemical research.

Organic Chemistry

Jonathan David Sarfati (born 1 October 1964) is a young Earth creationist who writes articles for Creation Ministries International (CMI), a non-profit Christian apologetics ministry. Sarfati has a PhD in chemistry, and was New Zealand national chess champion in 1987 and 1988.

Physical Chemistry

Polyhydroxyalkanoates (PHA) are linear polyesters produced in nature by bacterial fermentation of sugar or lipids. They are produced by the bacteria to store carbon and energy. In industrial production, the polyester is extracted and purified from the bacteria by optimizing the conditions for the fermentation of sugar. More than 150 different monomers can be combined within this family to give materials with extremely different properties. PHA is more ductile and less elastic than other plastics, and it is also biodegradable. These plastics are being widely used in the medical industry.

Physical Chemistry

Heme C differs from heme B in that the two vinyl side chains of heme B are replaced by covalent, thioether linkages to the apoprotein. The two thioether linkages are typically made by cysteine residues of the protein. These linkages do not allow the heme C to easily dissociate from the holoprotein, cytochrome c, compared with the more easily dissociated heme B that may dissociate from the holoprotein, the heme-protein complex, even under mild conditions. This allows a very wide range of cytochrome c structure and function, with myriad c type cytochromes acting primarily as electron carriers. The redox potential for cytochrome c can also be "fine-tuned" by small changes in protein structure and solvent interaction. The number of heme C units bound to a holoprotein is highly variable. For vertebrate cells one heme C per protein is the rule but for bacteria this number is often 2, 4, 5, 6 or even 16 heme C groups per holoprotein. It is generally agreed the number and arrangement of heme C groups are related and even required for proper holoprotein function. For instance, those proteins containing several heme C groups are involved with multiple electron transfer reactions, particularly important is the 6 electron reduction required to reduce atmospheric nitrogen into two organic ammonia molecules. It is common for the heme C to amino acid ratio to be high for bacterial hemeproteins, so the interiors of some cytochrome c proteins appear packed with many heme C groups compared with other hemeproteins. Some hemeproteins, often from single cell organisms, may contain five hemes C. The bc complex is another important enzyme that contains a C type heme. The thioether linkages seem to allow a great freedom of function for the holoproteins. In general, the c type cytochromes can be "fine tuned" over a wider range of oxidation-reduction potential than cytochromes b. This may be an important reason why cytochrome c is nearly ubiquitous throughout life. Heme C also plays an important role in apoptosis where just a few molecules of cytoplasmic cytochrome c, which must still contain heme C, leads to programmed cell death. Cytochrome c can be measured in human serum and can be used as a marker for inflammation. In addition to these equatorial covalent bonds, the heme iron is also usually axially coordinated to the side chains of two amino acids, making the iron hexacoordinate. For example, mammalian and tuna cytochrome c contain a single heme C that is axially coordinated to side chains of both histidine and methionine. Perhaps because of the two covalent bonds holding the heme to the protein, the iron of heme C is sometimes axially ligated to the amino group of lysine or even water.

Biochemistry

AuAl has low electrical conductivity and relatively low melting point. AuAl's formation at the joint causes increase of electrical resistance, which can lead to electrical failure. AuAl typically forms at 95% of Au and 5% of Al by mass, its melting point is about 575 °C, which is the lowest among the major gold-aluminum intermetallic compounds. AuAl is a bright-purple compound and a brittle, its composition is about 78.5% Au and 21.5% Al by mass. AuAl is the most thermally stable specie of the Au–Al intermetallic compounds, it has a melting point of 1060 °C (see phase diagram), which is similar to the melting point of pure gold. AuAl can react with Au, therefore is often replaced by AuAl, a tan-colored substancewhich forms at composition of 93% of Au and 7% of Al by mass. It is also a poor conductor and can cause electrical failure of the joint, which further lead to mechanical failure.

Metallurgy

Hilbert Spectroscopy uses Hilbert transforms to analyze broad spectrum signals from gigahertz to terahertz frequency radio. One suggested use is to quickly analyze liquids inside airport passenger luggage.

Physical Chemistry

Denaturing gels are run under conditions that disrupt the natural structure of the analyte, causing it to unfold into a linear chain. Thus, the mobility of each macromolecule depends only on its linear length and its mass-to-charge ratio. Thus, the secondary, tertiary, and quaternary levels of biomolecular structure are disrupted, leaving only the primary structure to be analyzed. Nucleic acids are often denatured by including urea in the buffer, while proteins are denatured using sodium dodecyl sulfate, usually as part of the SDS-PAGE process. For full denaturation of proteins, it is also necessary to reduce the covalent disulfide bonds that stabilize their tertiary and quaternary structure, a method called reducing PAGE. Reducing conditions are usually maintained by the addition of beta-mercaptoethanol or dithiothreitol. For a general analysis of protein samples, reducing PAGE is the most common form of protein electrophoresis. Denaturing conditions are necessary for proper estimation of molecular weight of RNA. RNA is able to form more intramolecular interactions than DNA which may result in change of its electrophoretic mobility. Urea, DMSO and glyoxal are the most often used denaturing agents to disrupt RNA structure. Originally, highly toxic methylmercury hydroxide was often used in denaturing RNA electrophoresis, but it may be method of choice for some samples. Denaturing gel electrophoresis is used in the DNA and RNA banding pattern-based methods temperature gradient gel electrophoresis (TGGE) and denaturing gradient gel electrophoresis (DGGE).

Biochemistry

HABs occur naturally off coasts all over the world. Marine dinoflagellates produce ichthyotoxins. Where HABs occur, dead fish wash up on shore for up to two weeks after a HAB has been through the area. In addition to killing fish, the toxic algae contaminate shellfish. Some mollusks are not susceptible to the toxin, and store it in their fatty tissues. By consuming the organisms responsible for HABs, shellfish can accumulate and retain saxitoxin produced by these organisms. Saxitoxin blocks sodium channels and ingestion can cause paralysis within 30 minutes. In addition to directly harming marine animals and vegetation loss, harmful algal blooms can also lead to ocean acidification, which occurs when the amount of carbon dioxide in the water is increased to unnatural levels. Ocean acidification slows the growth of certain species of fish and shellfish, and even prevents shell formation in certain species of mollusks. These subtle, small changes can add up over time to cause chain reactions and devastating effects on whole marine ecosystems. Other animals that eat exposed shellfish are susceptible to the neurotoxin, which may lead to neurotoxic shellfish poisoning and sometimes even death. Most mollusks and clams filter feed, which results in higher concentrations of the toxin than just drinking the water. Scaup, for example, are diving ducks whose diet mainly consists of mollusks. When scaup eat the filter-feeding shellfish that have accumulated high levels of the HAB toxin, their population becomes a prime target for poisoning. However, even birds that do not eat mollusks can be affected by simply eating dead fish on the beach or drinking the water. The toxins released by the blooms can kill marine animals including dolphins, sea turtles, birds, and manatees. The Florida Manatee, a subspecies of the West Indian Manatee, is a species often impacted by red tide blooms. Florida manatees are often exposed to the poisonous red-tide toxins either by consumption or inhalation. There are many small barnacles, crustaceans, and other [https://edis.ifas.ufl.edu/publication/SG188 epiphytes] that grow on the blades of seagrass. These tiny creatures filter particles from the water around them and use these particles as their main food source. During red tide blooms, they also filter the toxic red tide cells from the water, which then becomes concentrated inside them. Although these toxins do not harm epiphytes, they are extremely poisonous to marine creatures who consume (or accidentally consume) the exposed epiphytes, such as manatees. When manatees unknowingly consume exposed epiphytes while grazing on sea grass, the toxins are subsequently released from the epiphytes and ingested by the manatees. In addition to consumption, manatees may also become exposed to air-borne Brevetoxins released from harmful red-tide cells when passing through algal blooms. Manatees also have an immunoresponse to HABs and their toxins that can make them even more susceptible to other stressors. Due to this susceptibility, manatees can die from either the immediate, or the after effects of the HAB. In addition to causing manatee mortalities, red-tide exposure also causes severe [https://www.researchgate.net/publication/271274562_Sublethal_red_tide_toxin_exposure_in_free-ranging_manatees_Trichechus_manatus_affects_the_immune_system_through_reduced_lymphocyte_proliferation_responses_inflammation_and_oxidative_stress sublethal health problems among Florida manatee populations]. Studies have shown that red-tide exposure among free-ranging Florida manatees has been shown to negatively impact immune functioning by causing increased inflammation, a reduction in lymphocyte proliferation responses, and oxidative stress. Fish such as Atlantic herring, American pollock, winter flounder, Atlantic salmon, and cod were dosed orally with these toxins in an experiment, and within minutes the subjects started to exhibit a loss of equilibrium and began to swim in an irregular, jerking pattern, followed by paralysis and shallow, arrhythmic breathing and eventually death, after about an hour. HABs have been shown to have a negative effect also in the memory functions of sea lions.

Analytical Chemistry

Palladacycles are used as pre-catalysts, usually by the reductive elimination from palladium(II) to the catalytically active palladium(0). In the example of 2-aminobiphenyl palladacycles, a kinetically active 12-electrons Pd(0) species is formed, allowing for further oxidative addition with reactants. A series of 2-aminobiphenyl bearing various X and L groups were synthesized to better understand the electron/steric effect. By employing palladacycles as pre-catalysts, high reactivity and selectivity have been achieved in Heck reaction[2] and a variety of cross-coupling reactions, such as Suzuki, Sonogashira, Stille, Buchwald–Hartwig reactions. Total synthesis containing palladacycles have been demonstrated.

Organic Chemistry

While the aggregates can explain much of the protein fouling found in milk processing, this does not account for it all. A third type of fouling has been discovered that is explained by the chemical interactions of the denatured β-lg proteins. β-lg contains 5 cysteine residues, four of which are covalently bonded to each other, forming an S-S bond. When β-lg is denatured, the fifth cysteine residue is exposed to the water. This residue then bonds to other β-lg proteins, including those already adsorbed to the surface. This produces a strong interaction between the denatured proteins and the surface of the container.

Biochemistry

In 2005 there were "several types of commercial cyclic olefin copolymers based on different types of cyclic monomers and polymerization methods. Cyclic olefin copolymers are produced by chain copolymerization of cyclic monomers such as 8,9,10-trinorborn-2-ene (norbornene) or 1,2,3,4,4a,5,8,8a-octahydro-1,4:5,8-dimethanonaphthalene (tetracyclododecene) with ethene (such as Polyplastics subsidiary TOPAS Advanced Polymers TOPAS, Mitsui Chemicals APEL), or by ring-opening metathesis polymerization of various cyclic monomers followed by hydrogenation (Japan Synthetic Rubbers ARTON, Zeon Chemicals Zeonex and Zeonor)." These later materials using a single type of monomer are more properly named cyclic olefin polymers (COP).

Physical Chemistry

A rezas crystallization depends on the time it takes for layers of its chains to fold and orient themselves in the same direction. This time increases with a molecules weight and branching. The table below shows that the growth rate is higher for Sclair 14B.1 than Sclair 2907 (20%), where 2907 is less highly branched than 14B.1. Here Gc is the crystal growth rate, or how quickly it orders itself depending on the layers, and t is the time it takes to order.

Physical Chemistry

The photodegradation of pesticides is of great interest because of the scale of agriculture and the intensive use of chemicals. Pesticides are however selected in part not to photodegrade readily in sunlight in order to allow them to exert their biocidal activity. Thus, more modalities are implemented to enhance their photodegradation, including the use of photosensitizers, photocatalysts (e.g., titanium dioxide), and the addition of reagents such as hydrogen peroxide that would generate hydroxyl radicals that would attack the pesticides.

Photochemistry

The Reststrahlen effect (German: “residual rays”) is a reflectance phenomenon in which electromagnetic radiation within a narrow energy band cannot propagate within a given medium due to a change in refractive index concurrent with the specific absorbance band of the medium in question; this narrow energy band is termed the Reststrahlen band. As a result of this inability to propagate, normally incident Reststrahlen band radiation experiences strong-reflection or total-reflection from that medium. The energies at which Reststrahlen bands occur vary and are particular to the individual compound. Numerous physical attributes of a compound will have an effect on the appearance of the Reststrahlen band. These include phonon band-gap, particle/grain size, strongly absorbing compounds, compounds with optically opaque bands in the infrared.

Physical Chemistry

DNA methylation in cancer plays a variety of roles, helping to change the healthy cells by regulation of gene expression to a cancer cells or a diseased cells disease pattern. One of the most widely studied DNA methylation dysregulation is the promoter hypermethylation where the CPGs islands in the promoter regions are methylated contributing or causing genes to be silenced. All mammalian cells descended from a fertilized egg (a zygote) share a common DNA sequence (except for new mutations in some lineages). However, during development and formation of different tissues epigenetic factors change. The changes include histone modifications, CpG island methylations and chromatin reorganizations which can cause the stable silencing or activation of particular genes. Once differentiated tissues are formed, CpG island methylation is generally stably inherited from one cell division to the next through the DNA methylation maintenance machinery. In cancer, a number of mutational changes are found in protein coding genes. Colorectal cancers typically have 3 to 6 driver mutations and 33 to 66 hitchhiker or passenger mutations that silence protein expression in the genes affected. However, transcriptional silencing may be more important than mutation in causing gene silencing in progression to cancer. In colorectal cancers about 600 to 800 genes are transcriptionally silenced, compared to adjacent normal-appearing tissues, by CpG island methylation. Such CpG island methylation has also been described in glioblastoma and mesothelioma. Transcriptional repression in cancer can also occur by other epigenetic mechanisms, such as altered expression of microRNAs.

Biochemistry

Although the nuclearity of binary metal carbonyl clusters is usually six or fewer, carbido clusters often have higher nuclearities. Metal carbonyls of the iron and cobalt triads are well known to form carbido derivatives. Examples include [RhC(CO)] and [RuC(CO)]. Carbonyl carbides exist not only with fully encapsulated carbon (e.g., [FeC(CO)]) but also with exposed carbon centres as in FeC(CO) and FeC(CO).

Physical Chemistry

A number of organic compounds form charge-transfer complex, which are often described as electron-donor-acceptor complexes (EDA complexes). Typical acceptors are nitrobenzenes or tetracyanoethylene (TCNE). The strength of their interaction with electron donors correlates with the ionization potentials of the components. For TCNE, the stability constants (L/mol) for its complexes with benzene derivatives correlates with the number of methyl groups: benzene (0.128), 1,3,5-trimethylbenzene (1.11), 1,2,4,5-tetramethylbenzene (3.4), and hexamethylbenzene (16.8). 1,3,5-Trinitrobenzene and related polynitrated aromatic compounds, being electron-deficient, form charge-transfer complexes with many arenes. Such complexes form upon crystallization, but often dissociate in solution to the components. Characteristically, these CT salts crystallize in stacks of alternating donor and acceptor (nitro aromatic) molecules, i.e. A-B-A-B.

Physical Chemistry

Reactions in chemical processes are either unimolecular or bimolecular. The rate of a unimolecular reaction is an average over a vast ensemble of the rate coefficients for the microscopic events of collisional energy transfer and of reaction of a completely isolated molecule. Gilberts work in the field of unimolecular processes started with the development of theorems for this relationship. These theorems are elegant developments in matrix algebra, proving relations that had been previously known only for particular cases. His theorems also became the basis for numerical methods that he developed to perform the requisite calculations. For this purpose, he created a computer code, UNIMOL', which is widely used by researchers. He developed, with Prof J Troe, easily used approximate solutions for the pressure dependence of the rate coefficient. He provided the first solutions for cases where angular momentum conservation needs to be incorporated. His methods are used by experimentalists to fit data and extrapolate to different pressure regimes, supplanting previous tools which were of dubious validity and accuracy. His coworkers and he obtained data on the collisional energy transfer process and used them to prove the conjecture that each collision involves only a small exchange of energy. He then developed the first rigorous means to calculate these quantities from basic theory, and the first physical model for the process. His work is widely used, both for basic understanding of the transition states and by atmospheric and combustion modellers. Predicting climate change and effects on the ozone layer rely critically on this modelling.

Organic Chemistry

Howard E. Zimmerman was a native of Connecticut. During World War II, he served in the U.S. Armored Corps in Europe where he was a tank gunner. His final rank was technical sergeant. He obtained a B. S. in Chemistry in 1950 and a Ph.D. in 1953 both from Yale University. He was a Postdoctoral Research Fellow with a National Research Council fellowship from 1953 to 1954 working with R. B. Woodward (Harvard). From 1954 to 1960 he was assistant professor at Northwestern University. Beginning in 1960 he was Associate Professor and then Professor at the University of Wisconsin, and from 1990 he was Hilldale and A. C. Cope Professor of Chemistry. His publications number over 285 (including 11 chapters). Zimmerman gave ACS Short Courses on organic quantum chemistry and molecular orbital theory. He authored a 1975 textbook entitled Quantum Mechanics for Organic Chemists. Zimmerman was the organizer of the 1972 IUPAC Photochemistry Symposium (Baden-Baden) and of five Pacifichem Symposia – the last being Pacifichem 2010.

Photochemistry

The DNA of interest needs to be fragmented to provide a relevant DNA segment of suitable size. Preparation of DNA fragments for cloning is achieved by means of PCR, but it may also be accomplished by restriction enzyme digestion and fractionation by gel electrophoresis.

Biochemistry

Monomers capable of forming single, double, triple or quadruple hydrogen bonding has been utilized for making supramolecular polymers, and increased association of monomers obviously possible when monomers have maximum number of hydrogen bonding donor/acceptor motifs. For instance, ureidopyrimidinone-based monomer with self-complementary quadruple hydrogen bonding termini polymerized in solution, accordingly with the theory of conventional polymers and displayed a distinct viscoelastic nature at ambient temperatures.

Supramolecular Chemistry

DLVO theory describes the interaction potential between charged surfaces. It is the sum of electrostatic double layer, which can be either attractive of repulsive, and attractive Van der Waals interactions of the charge surfaces. DLVO theory is applied widely in explaining the aggregation and deposition of colloidal and nano particles such as Fullerene C60 in aquatic system. Because bacteria and colloid particles both share the similarities in size and surface charge, the deposition of bacteria also can be describe by the DLVO theory. The prediction is based on sphere-plate interaction for one cell and the surface.<br /> The electrostatic double layer interactions could be describes by the expression for the constant surface potential Where εis the vacuum permittivity, ε is the relative dielectric permittivity of water, a is the equivalent spherical radius of the bacteria, κ is the inverse of Debye length, h is the separation distance between the bacterium and the collector surface; ψ and ψ are the surface potentials of the bacterial cell and the collector surface. Zeta potential at the surface of the bacteria and the collector were used instead of the surface potential. The retarded Van der Waals interaction potential was calculated using the expression from Gregory, 1981 . With A is Hamaker constant for bacteria-water-surface collector (quartz) = 6.5 x 10 J and λ is the characteristic wavelength of the dielectric and could be assumed 100 nm, a is the equivalent radius of the bacteria, h is the separation distance from the surface collector to the bacteria. Thus, the total interaction between bacteria and charged surface can be expressed as follow

Physical Chemistry

Ethene and oxygen are passed co-currently in a reaction tower at about 130 °C and 400 kPa. The catalyst is an aqueous solution of PdCl and CuCl. The acetaldehyde is purified by extractive distillation followed by fractional distillation. Extractive distillation with water removes the lights ends having lower boiling points than acetaldehyde (chloromethane, chloroethane, and carbon dioxide) at the top, while water and higher-boiling byproducts, such as acetic acid, crotonaldehyde or chlorinated acetaldehydes, are withdrawn together with acetaldehyde at the bottom. Due to the corrosive nature of catalyst, the reactor is lined with acid-proof ceramic material and the tubing is made of titanium.

Organic Chemistry

Thiiranes occur very rarely in nature and are of no significance medicinally. Very few commercial applications exist, although the polymerization of episulfide has been reported.

Organic Chemistry

The crystal structures of the Thf.rst.immplexes of the Reformatsky reagents tert-butyl bromozincacetate and ethyl bromozincacetate have been determined. Both form cyclic eight-membered dimers in the solid state, but differ in stereochemistry: the eight-membered ring in the ethyl derivative adopts a tub-shaped conformation and has cis bromo groups and cis THF ligands, whereas in the tert-butyl derivative, the ring is in a chair form and the bromo groups and THF ligands are trans. Note that, in contrast to lithium and boron enolates, which have the metal(loid)s exclusively bond to oxygen, the zinc enolate moiety in the Reformatsky reagents have zinc atoms that are simultaneously O- and C-bound and can therefore be described as "organometallic".

Organic Chemistry

One case study investigated the formation of gaseous intermediates in the decomposition of CCl in the presence of steam over LaO using Fourier-transform infrared spectroscopy. This experiment produced useful information about the reaction mechanism, active site orientation, and about which species compete for the active site.

Physical Chemistry

Arsenite inhibits not only the formation of acetyl-CoA but also the enzyme succinic dehydrogenase. Arsenate can replace phosphate in many reactions. It is able to form Glc-6-arsenate in vitro; therefore it has been argued that hexokinase could be inhibited. (Eventually this may be a mechanism leading to muscle weakness in chronic arsenic poisoning.) In the glyceraldehyde 3-phosphate dehydrogenase reaction arsenate attacks the enzyme-bound thioester. The formed 1-arseno-3-phosphoglycerate is unstable and hydrolyzes spontaneously. Thus, ATP formation in glycolysis is inhibited while bypassing the phosphoglycerate kinase reaction. (Moreover, the formation of 2,3-bisphosphoglycerate in erythrocytes might be affected, followed by a higher oxygen affinity of hemoglobin and subsequently enhanced cyanosis.) As shown by Gresser (1981), submitochondrial particles synthesize adenosine-5'-diphosphate-arsenate from ADP and arsenate in presence of succinate. Thus, by a variety of mechanisms arsenate leads to an impairment of cell respiration and subsequently diminished ATP formation. This is consistent with observed ATP depletion of exposed cells and histopathological findings of mitochondrial and cell swelling, glycogen depletion in liver cells and fatty change in liver, heart and kidney. Experiments demonstrated enhanced arterial thrombosis in a rat animal model, elevations of serotonin levels, thromboxane A[2] and adhesion proteins in platelets, while human platelets showed similar responses. The effect on vascular endothelium may eventually be mediated by the arsenic-induced formation of nitric oxide. It was demonstrated that +3 As concentrations substantially lower than concentrations required for inhibition of the lysosomal protease cathepsin L in B cell line TA3 were sufficient to trigger apoptosis in the same B cell line, while the latter could be a mechanism mediating immunosuppressive effects. Its comutagenic effects may be explained by interference with base and nucleotide excision repair, eventually through interaction with zinc finger structures. Dimethylarsinic acid, DMA(V), caused DNA single strand breaks resulting from inhibition of repair enzymes at levels of 5 to 100 mM in human epithelial cells. MMA(III) and DMA(III) were also shown to be directly genotoxic by effectuating scissions in supercoiled ΦX174 DNA. Increased arsenic exposure is associated with an increased frequency of chromosomal aberrations, micronuclei and sister-chromatid exchanges. An explanation for chromosomal aberrations is the sensitivity of the protein tubulin and the mitotic spindle to arsenic. Histological observations confirm effects on cellular integrity, shape and locomotion. DMA(III) is able to form reactive oxygen species by reaction with molecular oxygen. Resulting metabolites are the dimethylarsenic radical and the dimethylarsenic peroxyl radical. Both DMA(III) and DMA(V) were shown to release iron from horse spleen as well as from human liver ferritin if ascorbic acid was administered simultaneously. Thus, formation of reactive oxygen species can be promoted. Moreover, arsenic could cause oxidative stress by depleting the cell's antioxidants, especially the ones containing thiol groups. The accumulation of reactive oxygen species like that cited above and hydroxyl radicals, superoxide radicals and hydrogen peroxides causes aberrant gene expression at low concentrations and lesions of lipids, proteins and DNA in higher concentrations which eventually lead to cellular death. In a rat animal model, urine levels of 8-hydroxy-2'-deoxyguanosine (as a biomarker of DNA damage byreactive oxygen species) were measured after treatment with DMA(V). In comparison to control levels, they turned out to be significantly increased. This theory is further supported by a cross-sectional study which found elevated mean serum lipid peroxides in the As exposed individuals which correlated with blood levels of inorganic arsenic and methylated metabolites and inversely correlated with nonprotein sulfhydryl (NPSH) levels in whole blood. Another study found an association of As levels in whole blood with the level of reactive oxidants in plasma and an inverse relationship with plasma antioxidants. A finding of the latter study indicates that methylation might in fact be a detoxification pathway with regard to oxidative stress: the results showed that the lower the As methylation capacity was, the lower the level of plasma antioxidant capacity. As reviewed by Kitchin (2001), the oxidative stress theory provides an explanation for the preferred tumor sites connected with arsenic exposure. Considering that a high partial pressure of oxygen is present in lungs and DMA(III) is excreted in gaseous state via the lungs, this seems to be a plausible mechanism for special vulnerability. The fact that DMA is produced by methylation in the liver, excreted via the kidneys and later on stored in the bladder accounts for the other tumor localizations. Regarding DNA methylation, some studies suggest interaction of As with methyltransferases which leads to an inactivation of tumor suppressor genes through hypermethylation; others state that hypomethylation might occur due to a lack of SAM resulting in aberrant gene activation. An experiment by Zhong et al. (2001) with arsenite-exposed human lung A549, kidney UOK123, UOK109 and UOK121 cells isolated eight different DNA fragments by methylation-sensitive arbitrarily primed polymerase chain reactions. It turned out that six of the fragments were hyper- and two of them were hypomethylated. Higher levels of DNA methyltransferase mRNA and enzyme activity were found. Kitchin (2001) proposed a model of altered growth factors which lead to cell proliferation and thus to carcinogenesis. From observations, it is known that chronic low-dose arsenic poisoning can lead to increased tolerance to its acute toxicity. MRP1-overexpressing lung tumor GLC4/Sb30 cells poorly accumulate arsenite and arsenate. This is mediated through MRP-1 dependent efflux. The efflux requires glutathione, but no arsenic-glutathione complex formation. Although many mechanisms have been proposed, no definite model can be given for the mechanisms of chronic arsenic poisoning. The prevailing events of toxicity and carcinogenicity might be quite tissue-specific. Current consensus on the mode of carcinogenesis is that it acts primarily as a tumor promoter. Its co-carcinogenicity has been demonstrated in several models. However, the finding of several studies that chronically arsenic-exposed Andean populations (as most extremely exposed to UV-light) do not develop skin cancer with chronic arsenic exposure, is puzzling.

Biochemistry

In the ovary, the LHCG receptor is necessary for follicular maturation and ovulation, as well as luteal function. Its expression requires appropriate hormonal stimulation by FSH and estradiol. The LHCGR is present on granulosa cells, theca cells, luteal cells, and interstitial cells The LCGR is restimulated by increasing levels of chorionic gonadotropins in case a pregnancy is developing. In turn, luteal function is prolonged and the endocrine milieu is supportive of the nascent pregnancy.

Biochemistry

Even though glycosylation is the most common form of protein modification, with highly complex carbohydrate structures, the bioinformatics on glycome is still very poor. Unlike proteins and nucleic acids which are linear, carbohydrates are often branched and extremely complex. For instance, just four sugars can be strung together to form more than 5 million different types of carbohydrates or nine different sugars may be assembled into 15 million possible four-sugar-chains. Also, the number of simple sugars that make up glycans is more than the number of nucleotides that make up DNA or RNA. Therefore, it is more computationally expensive to evaluate their structures. One of the main constrains in the glycoinformatics is the difficulty of representing sugars in the sequence form especially due to their branching nature. Owing to the lack of a genetic blue print, carbohydrates do not have a "fixed" sequence. Instead, the sequence is largely determined by the presence of a variety of enzymes, their kinetic differences and variations in the biosynthetic micro-environment of the cells. This increases the complexity of analysis and experimental reproducibility of the carbohydrate structure of interest. It is for this reason that carbohydrates are often considered as the "information poor" molecules.

Organic Chemistry

In more general use, a calibration curve is a curve or table for a measuring instrument which measures some parameter indirectly, giving values for the desired quantity as a function of values of sensor output. For example, a calibration curve can be made for a particular pressure transducer to determine applied pressure from transducer output (a voltage). Such a curve is typically used when an instrument uses a sensor whose calibration varies from one sample to another, or changes with time or use; if sensor output is consistent the instrument would be marked directly in terms of the measured unit.

Biochemistry