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The water molecule has three fundamental molecular vibrations. The O-H stretching vibrations give rise to absorption bands with band origins at 3657 cm (ν, 2.734 μm) and 3756 cm (ν, 2.662 μm) in the gas phase. The asymmetric stretching vibration, of B symmetry in the point group C is a normal vibration. The H-O-H bending mode origin is at 1595 cm (ν, 6.269 μm). Both symmetric stretching and bending vibrations have A symmetry, but the frequency difference between them is so large that mixing is effectively zero. In the gas phase all three bands show extensive rotational fine structure. In the near-infrared spectrum
ν has a series of overtones at wavenumbers somewhat less than n·ν, n=2,3,4,5... Combination bands, such as ν + ν are also easily observed in the near-infrared region. The presence of water vapor in the atmosphere is important for atmospheric chemistry especially as the infrared and near infrared spectra are easy to observe. Standard (atmospheric optical) codes are assigned to absorption bands as follows. 0.718 μm (visible): α, 0.810 μm: μ, 0.935 μm: ρστ, 1.13 μm: φ, 1.38 μm: ψ, 1.88 μm: Ω, 2.68 μm: X. The gaps between the bands define the infrared window in the Earth's atmosphere.
The infrared spectrum of liquid water is dominated by the intense absorption due to the fundamental O-H stretching vibrations. Because of the high intensity, very short path lengths, usually less than 50 μm, are needed to record the spectra of aqueous solutions. There is no rotational fine structure, but the absorption bands are broader than might be expected, because of hydrogen bonding. Peak maxima for liquid water are observed at 3450 cm (2.898 μm), 3615 cm (2.766 μm) and 1640 cm (6.097 μm). Direct measurement of the infrared spectra of aqueous solutions requires that the cuvette windows be made of substances such as calcium fluoride which are water-insoluble. This difficulty can alternatively be overcome by using an attenuated total reflectance (ATR) device rather than transmission.
In the near-infrared range liquid water has absorption bands around 1950 nm (5128 cm), 1450 nm (6896 cm), 1200 nm (8333 cm) and 970 nm, (10300 cm). The regions between these bands can be used in near-infrared spectroscopy to measure the spectra of aqueous solutions, with the advantage that glass is transparent in this region, so glass cuvettes can be used. The absorption intensity is weaker than for the fundamental vibrations, but this is not important as longer path-length cuvettes can be used. The absorption band at 698 nm (14300 cm) is a 3rd overtone (n=4). It tails off onto the visible region and is responsible for the intrinsic blue color of water. This can be observed with a standard UV/vis spectrophotometer, using a 10 cm path-length. The colour can be seen by eye by looking through a column of water about 10 m in length; the water must be passed through an ultrafilter to eliminate color due to Rayleigh scattering which also can make water appear blue.
The spectrum of ice is similar to that of liquid water, with peak maxima at 3400 cm (2.941 μm), 3220 cm (3.105 μm) and 1620 cm (6.17 μm)
In both liquid water and ice clusters, low-frequency vibrations occur, which involve the stretching (TS) or bending (TB) of intermolecular hydrogen bonds (O–H•••O). Bands at wavelengths λ = 50-55 μm or 182-200 cm (44 μm, 227 cm in ice) have been attributed to TS, intermolecular stretch, and 200 μm or 50 cm (166 μm, 60 cm in ice), to TB, intermolecular bend | 0 | Theoretical and Fundamental Chemistry |
Middle and Late Minoan and Mycenaean vessels are many. First in size are some basins found at Tylissos in Crete, the largest measuring 1.40 metres in diameter. They are shallow hemispherical bowls with two or three loop-handles riveted on their edges, and are made in several sections. The largest is composed of seven hammered sheets, three at the lip, three in the body, and one at the base. This method of construction is usual in large complicated forms. The joints of necks and bodies of jugs and jars were often masked with a roll-moulding. Simpler and smaller forms were also cast. The finest specimens of such vases come from houses and tombs at Knossos. Their ornament is applied in separate bands, hammered or cast and chased, and soldered on the lip or shoulder of the vessel. A richly decorated form is a shallow bowl with wide ring-handle and flat lip, on both of which are foliate or floral patterns in relief.
A notable shape, connecting prehistoric with Hellenic metallurgy is a tripod-bowl, a hammered globular body with upright ring-handles on the lip and heavy cast legs attached to the shoulder. | 1 | Applied and Interdisciplinary Chemistry |
In its natural state, wood is not a transparent material because of its scattering and absorption of light. The tannish color in wood is due to its chemical polymer composition of cellulose, hemicellulose, and lignin. The woods lignin is mostly responsible for the woods distinctive color. Consequently, the amount of lignin determines the levels of visibility in the wood, around 80–95%. To make wood a visible and transparent material, both absorption and scattering need to be reduced in its production. The manufacturing process of transparent wood is based on removing all of the lignin called the delignification process. | 0 | Theoretical and Fundamental Chemistry |
The organic linkers for conductive MOFs are generally conjugated. 2D conductive MOFs have been explored well and several studies of 3D conductive MOFs have also been reported so far. Single crystal structure of a 2D conductive MOF Co(HHTP) [hexahydroxytriphenylene] was reported in 2012.
The conductivity of these materials are often tested by two probe method, i.e. a known potential is applied between two probes, the resulting current is measured, and resistance is calculated by using Ohm’s law. A four-probe method employs two wires on the extreme are used to supply a current and the inner two wires measure the drop in potential. This method eliminates the effect of contact resistance.
Most MOFs have conductivity less than 10 S cm and are considered as Insulator. Based on the literature reports so far, conductivity range in the MOFs can vary from 10 to 10 S cm. Charge transfer in conductive MOFs have been attributed to three pathways: 1) Through-bond:- when d orbital of transition metal ion overlaps with the p orbital of the organic linker, π electrons are delocalized across all the adjacent p orbitals. 2) Extended conjugation:- When transition metal ions are coupled with the a conjugated organic linker, the d-π conjugation allows delocalization of the charge carriers. 3) Through-space:- Organic linkers in one layer can interact with the one in the adjacent layer via π-π interaction. This will facilitate charge delocalization in the adjacent layers. | 0 | Theoretical and Fundamental Chemistry |
Thiomers are able to reversibly open tight junctions. The responsible mechanism seems to be based on the inhibition of protein tyrosine phosphatase being involved in the closing process of tight junctions. Due to thiolation the permeation enhancing effect of polymers such as polyacrylic acid or chitosan can be up to 10-fold improved. In comparison to most low molecular weight permeation enhancers, thiolated polymers offer the advantage of not being absorbed from the mucosal membrane. Hence, their permeation enhancing effect can be maintained for a comparatively longer period of time and systemic toxic side effects of the auxiliary agent can be excluded. | 0 | Theoretical and Fundamental Chemistry |
*Thomas Young's double-slit experiment demonstrating the wave nature of light. (c. 1801)
*Henri Becquerel discovers radioactivity. (1896)
*J. J. Thomson's cathode ray tube experiments (discovers the electron and its negative charge). (1897)
*The study of black-body radiation between 1850 and 1900, which could not be explained without quantum concepts.
*The photoelectric effect: Einstein explained this in 1905 (and later received a Nobel prize for it) using the concept of photons, particles of light with quantized energy.
*Robert Millikans oil-drop experiment, which showed that electric charge occurs as quanta' (whole units). (1909)
*Ernest Rutherford's gold foil experiment disproved the plum pudding model of the atom which suggested that the mass and positive charge of the atom are almost uniformly distributed. This led to the planetary model of the atom (1911).
*James Franck and Gustav Hertz's electron collision experiment shows that energy absorption by mercury atoms is quantized. (1914)
*Otto Stern and Walther Gerlach conduct the Stern–Gerlach experiment, which demonstrates the quantized nature of particle spin. (1920)
*Arthur Compton with Compton scattering experiment (1923)
*Clinton Davisson and Lester Germer demonstrate the wave nature of the electron in the electron diffraction experiment. (1927)
*Carl David Anderson with the discovery positron (1932), validated Paul Dirac's theoretical prediction of this particle (1928)
*Lamb–Retherford experiment discovered Lamb shift (1947), which led to the development of quantum electrodynamics.
*Clyde L. Cowan and Frederick Reines confirm the existence of the neutrino in the neutrino experiment. (1955)
*Clauss Jönsson's double-slit experiment with electrons. (1961)
*The quantum Hall effect, discovered in 1980 by Klaus von Klitzing. The quantized version of the Hall effect has allowed for the definition of a new practical standard for electrical resistance and for an extremely precise independent determination of the fine-structure constant.
*The experimental verification of quantum entanglement by John Clauser and Stuart Freedman. (1972)
*The Mach–Zehnder interferometer experiment conducted by Paul Kwiat, Harold Wienfurter, Thomas Herzog, Anton Zeilinger, and Mark Kasevich, providing experimental verification of the Elitzur–Vaidman bomb tester, proving interaction-free measurement is possible. (1994) | 1 | Applied and Interdisciplinary Chemistry |
Amoxicillin may interact with these drugs:
* Anticoagulants (dabigatran, warfarin).
* Methotrexate (chemotherapy and immunosuppressant).
* Typhoid, Cholera and BCG vaccines.
* Probenecid reduces renal excretion and increases blood levels of amoxicillin.
* Oral contraceptives potentially become less effective.
* Allopurinol (gout treatment).
* Mycophenolate (immunosuppressant) | 0 | Theoretical and Fundamental Chemistry |
Semi-solid and soft nanoparticles have been produced. A prototype nanoparticle of semi-solid nature is the liposome. Various types of liposome nanoparticles are currently used clinically as delivery systems for anticancer drugs and vaccines.
The breakdown of biopolymers into their nanoscale building blocks is considered a potential route to produce nanoparticles with enhanced biocompatibility and biodegradability. The most common example is the production of nanocellulose from wood pulp. Other examples are nanolignin, nanochitin, or nanostarches.
Nanoparticles with one half hydrophilic and the other half hydrophobic are termed Janus particles and are particularly effective for stabilizing emulsions. They can self-assemble at water/oil interfaces and act as pickering stabilizers.
Hydrogel nanoparticles made of N-isopropylacrylamide hydrogel core shell can be dyed with affinity baits, internally. These affinity baits allow the nanoparticles to isolate and remove undesirable proteins while enhancing the target analytes. | 0 | Theoretical and Fundamental Chemistry |
The development of enantioselective synthesis was initially slow, largely due to the limited range of techniques available for their separation and analysis.
Diastereomers possess different physical properties, allowing separation by conventional means, however at the time enantiomers could only be separated by spontaneous resolution (where enantiomers separate upon crystallisation) or kinetic resolution (where one enantiomer is selectively destroyed). The only tool for analysing enantiomers was optical activity using a polarimeter, a method which provides no structural data.
It was not until the 1950s that major progress really began. Driven in part by chemists such as R. B. Woodward and Vladimir Prelog but also by the development of new techniques.
The first of these was X-ray crystallography, which was used to determine the absolute configuration of an organic compound by Johannes Bijvoet in 1951.
Chiral chromatography was introduced a year later by Dalgliesh, who used paper chromatography to separate chiral amino acids.
Although Dalgliesh was not the first to observe such separations, he correctly attributed the separation of enantiomers to differential retention by the chiral cellulose. This was expanded upon in 1960, when Klem and Reed first reported the use of chirally-modified silica gel for chiral HPLC separation. | 0 | Theoretical and Fundamental Chemistry |
The viscous Burgers' equation can be converted to a linear equation by the Cole–Hopf transformation,
which turns it into the equation
which can be integrated with respect to to obtain
where is an arbitrary function of time. Introducing the transformation (which does not affect the function ), the required equation reduces to that of the heat equation
The diffusion equation can be solved. That is, if , then
The initial function is related to the initial function by
where the lower limit is chosen arbitrarily. Inverting the Cole–Hopf transformation, we have
which simplifies, by getting rid of the time-dependent prefactor in the argument of the logarthim, to | 1 | Applied and Interdisciplinary Chemistry |
The main advantages of marine outfalls for the discharge of wastewater are:
* the natural dilution and dispersion of organic matter, pathogens and other pollutants
* the ability to keep the sewage field submerged because of the depth at which the sewage is being released
* the greater die-off rate of pathogens due to the greater distance they will have to travel to shore.
They also tend to be less expensive than advanced wastewater treatment plants, using the natural assimilative capacity of the sea instead of energy-intensive treatment processes in a plant. For example, preliminary treatment of wastewater is sufficient with an effective outfall and diffuser. The costs of preliminary treatment are about one tenth that of secondary treatment. Preliminary treatment also requires much less land than advanced wastewater treatment. | 1 | Applied and Interdisciplinary Chemistry |
Recently, encapsulin nanocompartments have begun to receive considerable interest from bioengineers because of their potential to allow the targeted delivery of drugs, proteins, and mRNAs to specific cells of interest. | 1 | Applied and Interdisciplinary Chemistry |
The amine value is useful in helping determine the correct stoichiometry of a two component amine cure epoxy resin system.
It is the number of Nitrogens x 56.1 (Mwt of KOH) x 1000 (convert to milligrams) divided by molecular mass of the amine functional compound. So using Tetraethylenepentamine (TEPA) as an example:
Mwt = 189, number of nitrogen atoms = 5
So 5 x 1000 x 56.1/189 = 1484. So the Amine Value of TEPA = 1484 | 0 | Theoretical and Fundamental Chemistry |
Upstream contamination by floating particles is a counterintuitive phenomenon in fluid dynamics. When pouring water from a higher container to a lower one, particles floating in the latter can climb upstream into the upper container. A definitive explanation is still lacking: experimental and computational evidence indicates that the contamination is chiefly driven by surface tension gradients, however the phenomenon is also affected by the dynamics of swirling flows that remain to be fully investigated. | 1 | Applied and Interdisciplinary Chemistry |
Phosphomimetics are amino acid substitutions that mimic a phosphorylated protein, thereby activating (or deactivating) the protein. Within cells, proteins are commonly modified at serine, tyrosine and threonine amino acids by adding a phosphate group. Phosphorylation is a common mode of activating or deactivating a protein as a form of regulation. However some non-phosphorylated amino acids appear chemically similar to phosphorylated amino acids. Therefore, by replacing an amino acid, the protein may maintain a higher level of activity. For example, aspartic acid can be considered chemically similar to phospho-serine, due to it also carrying a negative charge. Therefore, when an aspartic acid replaces a serine, it is a phosphomimetic of phospho-serine and can imitate the protein always in its phosphorylated form. However, differences in between the phosphomimetics compound and the phosphorylated residue, notably differences in ramachandran distributions, charge states and size, can alter the protein sufficiently to result in significant differences in behavior. Phosphonate-based compounds have been used as phosphotyrosine analogues, as they are less enzyme labile and are physiologically more stable. | 1 | Applied and Interdisciplinary Chemistry |
Ubiquitination plays a central role in cell signaling that regulates processes including protein degradation and immunological response. Although one of the main functions of ubiquitin is to target proteins for destruction, it is also useful in signaling pathways, hormone release, apoptosis and translocation of materials throughout the cell. Ubiquitination is a component of several immune responses. Without ubiquitin's proper functioning, the invasion of pathogens and other harmful molecules would increase dramatically due to weakened immune defenses. | 1 | Applied and Interdisciplinary Chemistry |
The two most common modes of nc-AFM operation, frequency modulation (FM) and amplitude modulation (AM), are described below. | 0 | Theoretical and Fundamental Chemistry |
Since AMGs originate in hosts, distinguishing host and viral genes is critical for their study. This is not easily achieved as cultivation of viral-host systems in a laboratory setting proves challenging if even possible. Additionally, filtering out cellular sequences before entry in bioinformatic pipelines is not possible with cellular gene transfer agents and membrane vesicles are unable to distinguish from viruses due to their many shared properties at this step of analysis. The extent to which they have contaminated existing viral databases is unknown. Some genes have distinctions between host and viral versions such as cyanophage photosynthesis easing the task of computational distinction. The most definitive way developed to determine gene origin has been identification of taxonomically informative genes colocalized on assembled contigs. ViromeQC can display contamination for the dataset overall and DRAM-v assigns a confidence score for the AMG being on a viral MAG. Viral identification is most popularly performed by VIBRANT, VirSorter2, DeepVirFinder, and CheckV. | 1 | Applied and Interdisciplinary Chemistry |
Isometries requiring an odd number of mirrors — reflection and glide reflection — always reverse left and right. The even isometries — identity, rotation, and translation — never do; they correspond to rigid motions, and form a normal subgroup of the full Euclidean group of isometries. Neither the full group nor the even subgroup are abelian; for example, reversing the order of composition of two parallel mirrors reverses the direction of the translation they produce.
Since the even subgroup is normal, it is the kernel of a homomorphism to a quotient group, where the quotient is isomorphic to a group consisting of a reflection and the identity. However the full group is not a direct product, but only a semidirect product, of the even subgroup and the quotient group. | 0 | Theoretical and Fundamental Chemistry |
Plano-convex ingots are lumps of metal with a flat or slightly concave top and a convex base. They are sometimes, misleadingly, referred to as bun ingots which imply the opposite concavity. They are most often made of copper, although other materials such as copper alloy, lead and tin are used. The first examples known were from the Near East during the 3rd and 2nd Millennia BC. By the end of the Bronze Age they were found throughout Europe and in Western and South Asia. Similar ingot forms continued in use during later Roman and Medieval periods. | 1 | Applied and Interdisciplinary Chemistry |
The cross effect requires two unpaired electrons as the source of high polarization. Without special condition, such a three spins system can only generate a solid effect type of polarization. However, when the resonance frequency of each electron is separated by the nuclear Larmor frequency, and when the two electrons are dipolar coupled, another mechanism occurs: the cross-effect. In that case, the DNP process is the result of irradiation of an allowed transition (called single quantum) as a result the strength of microwave irradiation is less demanded than that in the solid effect. In practice, the correct EPR frequency separation is accomplished through random orientation of paramagnetic species with g-anisotropy. Since the "frequency" distance between the two electrons should be equal to the Larmor frequency of the targeted nucleus, cross-effect can only occur if the inhomogeneously broadened EPR lineshape has a linewidth broader than the nuclear Larmor frequency. Therefore, as this linewidth is proportional to external magnetic field B, the overall DNP efficiency (or the enhancement of nuclear polarization) scales as B. This remains true as long as the relaxation times remain constant. Usually going to higher field leads to longer nuclear relaxation times and this may partially compensate for the line broadening reduction.
In practice, in a glassy sample, the probability of having two dipolarly coupled electrons separated by the Larmor frequency is very scarce. Nonetheless, this mechanism is so efficient that it can be experimentally observed alone or in addition to the solid-effect. | 0 | Theoretical and Fundamental Chemistry |
Bacteria and Pseudomonadota, such as Geobacter and Burkholderia fungorum (strain Rifle), can reduce and fix uranium in soil and groundwater. These bacteria change soluble U(VI) into the highly insoluble complex-forming U(IV) ion, hence stopping chemical leaching.
It has been suggested that it is possible to form a reactive barrier by adding something to the soil which will cause the uranium to become fixed. One method of doing this is to use a mineral (apatite) while a second method is to add a food substance such as acetate to the soil. This will enable bacteria to reduce the uranium(VI) to uranium(IV), which is much less soluble. In peat-like soils, the uranium will tend to bind to the humic acids; this tends to fix the uranium in the soil. | 0 | Theoretical and Fundamental Chemistry |
There is ongoing research on how Genetic variants in the CYP21A2 gene may lead to pathogenic conditions. A variant of this gene has been reported to cause autosomal dominant posterior polar cataract, suggesting that steroid 21-hydroxylase may be involved in the extra-adrenal biosynthesis of aldosterone and cortisol in the lens of the eye. | 1 | Applied and Interdisciplinary Chemistry |
Disinfection of treated sewage aims to kill pathogens (disease-causing microorganisms) prior to disposal. It is increasingly effective after more elements of the foregoing treatment sequence have been completed. The purpose of disinfection in the treatment of sewage is to substantially reduce the number of pathogens in the water to be discharged back into the environment or to be reused. The target level of reduction of biological contaminants like pathogens is often regulated by the presiding governmental authority. The effectiveness of disinfection depends on the quality of the water being treated (e.g. turbidity, pH, etc.), the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Water with high turbidity will be treated less successfully, since solid matter can shield organisms, especially from ultraviolet light or if contact times are low. Generally, short contact times, low doses and high flows all militate against effective disinfection. Common methods of disinfection include ozone, chlorine, ultraviolet light, or sodium hypochlorite. Monochloramine, which is used for drinking water, is not used in the treatment of sewage because of its persistence.
Chlorination remains the most common form of treated sewage disinfection in many countries due to its low cost and long-term history of effectiveness. One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment.
Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water has no adverse effect on organisms that later consume it, as may be the case with other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the target microorganisms are not shielded from the UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from the UV light). In many countries, UV light is becoming the most common means of disinfection because of the concerns about the impacts of chlorine in chlorinating residual organics in the treated sewage and in chlorinating organics in the receiving water.
As with UV treatment, heat sterilization also does not add chemicals to the water being treated. However, unlike UV, heat can penetrate liquids that are not transparent. Heat disinfection can also penetrate solid materials within wastewater, sterilizing their contents. Thermal effluent decontamination systems provide low resource, low maintenance effluent decontamination once installed.
Ozone () is generated by passing oxygen () through a high voltage potential resulting in a third oxygen atom becoming attached and forming . Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site (highly poisonous in the event of an accidental release), ozone is generated on-site as needed from the oxygen in the ambient air. Ozonation also produces fewer disinfection by-products than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for special operators. Ozone sewage treatment requires the use of an ozone generator, which decontaminates the water as ozone bubbles percolate through the tank.
Membranes can also be effective disinfectants, because they act as barriers, avoiding the passage of the microorganisms. As a result, the final effluent may be devoid of pathogenic organisms, depending on the type of membrane used. This principle is applied in membrane bioreactors. | 1 | Applied and Interdisciplinary Chemistry |
Cholesteryl ester, a dietary lipid, is an ester of cholesterol. The ester bond is formed between the carboxylate group of a fatty acid and the hydroxyl group of cholesterol. Cholesteryl esters have a lower solubility in water due to their increased hydrophobicity. Esters are formed by replacing at least one –OH (hydroxyl) group with an –O–alkyl (alkoxy) group. They are hydrolyzed by pancreatic enzymes, cholesterol esterase, to produce cholesterol and free fatty acids. They are associated with atherosclerosis.
Cholesteryl ester is found in human brains as lipid droplets which store and transport cholesterol. Increased levels of cholesteryl ester have been found in certain parts of the brain of people with Huntington disease. Higher concentrations of cholesteryl ester have been found in the caudate and putamen, but not the cerebellum, of people with Huntington disease compared with levels in controls. Increase in cholesteryl ester has also been found in other neurological disorders like multiple sclerosis and Alzheimer's disease. | 1 | Applied and Interdisciplinary Chemistry |
In the first enantioselective synthesis of (+)-Griseofulvin, a potent antifungal agent, a Curtin–Hammett situation was observed. A key step in the synthesis is the rhodium-catalyzed formation of an oxonium ylide, which then undergoes a [2,3] sigmatropic rearrangement en route to the desired product. However, the substrate contains two ortho-alkoxy groups, either of which could presumably participate in oxonium ylide generation.
Obtaining high selectivity for the desired product was possible, however, due to differences in the activation barriers for the step following ylide formation. If the ortho-methoxy group undergoes oxonium ylide formation, a 1,4-methyl shift can then generate an undesired product. The oxonium ylide formed from the other ortho-alkoxy group is primed to undergo a [2,3] sigmatropic rearrangement to yield the desired compound. Pirrung and coworkers reported complete selectivity for the desired product over the product resulting from a 1,4-methyl shift. This result suggests that oxonium ylide formation is reversible, but that the subsequent step is irreversible. The symmetry-allowed [2,3] sigmatropic rearrangement must follow a pathway that is lower in activation energy than the 1,4-methyl shift, explaining the exclusive formation of the desired product. | 0 | Theoretical and Fundamental Chemistry |
Oxidative addition of vinylcyclopropanes primarily occurs at the proximal position, giving pi-allyl intermediates. Through subsequent insertion reactions (e.g. with alkynes, alkenes, and carbon monoxide), rings of various sizes and fused ring systems can be formed. | 0 | Theoretical and Fundamental Chemistry |
is a potent greenhouse gas. A ton of HFC-23 in the atmosphere has the same effect as 11,700 tons of carbon dioxide. This equivalency, also called a 100-yr global warming potential, is slightly larger at 14,800 for HFC-23.
The atmospheric lifetime is 270 years.
HFC-23 was the most abundant HFC in the global atmosphere until around 2001, when the global mean concentration of HFC-134a (1,1,1,2-tetrafluoroethane), the chemical now used extensively in automobile air conditioners, surpassed those of HFC-23. Global emissions of HFC-23 have in the past been dominated by the inadvertent production and release during the manufacture of the refrigerant HCFC-22 (chlorodifluoromethane).
Substantial decreases in HFC-23 emissions by developed countries were reported from the 1990s to the 2000s: from 6-8 Gg/yr in the 1990s to 2.8 Gg/yr in 2007.
The UNFCCC Clean Development Mechanism provided funding and facilitated the destruction of HFC-23.
Developing countries have become the largest producers of HCFC-23 in recent years according to data compiled by the Ozone Secretariat of the World Meteorological Organization. Emissions of all HFCs are included in the UNFCCCs Kyoto Protocol. To mitigate its impact, can be destroyed with electric plasma arc technologies or by high temperature incineration. | 1 | Applied and Interdisciplinary Chemistry |
Soon after it was discovered and recognized as the principle of meat smoking, wood-tar creosote became used as a replacement for the process. Several methods were used to apply the creosote. One was to dip the meat in pyroligneous acid or a water of diluted creosote, as Reichenbach did, or brush it over with them, and within one hour the meat would have the same quality of that of traditionally smoked preparations. Sometimes the creosote was diluted in vinegar rather than water, as vinegar was also used as a preservative. Another was to place the meat in a closed box, and place with it a few drops of creosote in a small bottle. Because of the volatility of the creosote, the atmosphere was filled with a vapour containing it, and it would cover the flesh.
The application of wood tar to seagoing vessels was practiced through the 18th century and early 19th century, before the creosote was isolated as a compound. Wood-tar creosote was found not to be as effective in wood treatments, because it was harder to infuse the creosote into the wood cells, but still experiments were done, including by many governments, because it proved to be less expensive on the market. | 0 | Theoretical and Fundamental Chemistry |
Avalanche multiplication during Townsend discharge is naturally used in gas phototubes, to amplify the photoelectric charge generated by incident radiation (visible light or not) on the cathode: achievable current is typically 10~20 times greater respect to that generated by vacuum phototubes. | 0 | Theoretical and Fundamental Chemistry |
One-dimensional flow is valid when both plates are infinitely long in the streamwise () and spanwise () directions. When the spanwise length is finite, the flow becomes two-dimensional and is a function of both and . However, the infinite length in the streamwise direction must be retained in order to ensure the unidirectional nature of the flow.
As an example, consider an infinitely long rectangular channel with transverse height and spanwise width , subject to the condition that the top wall moves with a constant velocity . Without an imposed pressure gradient, the Navier–Stokes equations reduce to
with boundary conditions
Using separation of variables, the solution is given by
When , the planar Couette flow is recovered, as shown in the figure. | 1 | Applied and Interdisciplinary Chemistry |
Molecular glue compounds, particularly those involved in targeted protein degradation (TPD), offer a novel strategy for inhibiting viral protein interactions and combating viral infections. Unlike traditional direct-acting antivirals (DAAs), TPD-based molecules exert their pharmacological activity through event-driven mechanisms, inducing target degradation. This unique approach can lead to prolonged pharmacodynamic efficacy with lower pharmacokinetic exposure, potentially reducing toxicity and the risk of antiviral resistance. The protein-protein interactions induced by TPD molecules may also enhance selectivity, making them a promising avenue for antiviral research. | 1 | Applied and Interdisciplinary Chemistry |
Some journals that deal with physical chemistry include
* Zeitschrift für Physikalische Chemie (1887)
* Journal of Physical Chemistry A (from 1896 as Journal of Physical Chemistry, renamed in 1997)
* Physical Chemistry Chemical Physics (from 1999, formerly Faraday Transactions with a history dating back to 1905)
* Macromolecular Chemistry and Physics (1947)
* Annual Review of Physical Chemistry (1950)
* Molecular Physics (1957)
* Journal of Physical Organic Chemistry (1988)
* Journal of Physical Chemistry B (1997)
* ChemPhysChem (2000)
* Journal of Physical Chemistry C (2007)
* Journal of Physical Chemistry Letters (from 2010, combined letters previously published in the separate journals)
Historical journals that covered both chemistry and physics include Annales de chimie et de physique (started in 1789, published under the name given here from 1815 to 1914). | 0 | Theoretical and Fundamental Chemistry |
Jostel's TSH index (JTI or TSHI) helps to determine thyrotropic function of anterior pituitary on a quantitative level. It is reduced in thyrotropic insufficiency and in certain cases of non-thyroidal illness syndrome.
It is calculated with
Additionally, a standardized form of TSH index may be calculated with | 1 | Applied and Interdisciplinary Chemistry |
A solar cell is made of semiconducting materials, such as silicon, that have been fabricated into a p–n junction. Such junctions are made by doping one side of the device p-type and the other n-type, for example in the case of silicon by introducing small concentrations of boron or phosphorus respectively.
In operation, photons in sunlight hit the solar cell and are absorbed by the semiconductor. When the photons are absorbed, electrons are excited from the valence band to the conduction band (or from occupied to unoccupied molecular orbitals in the case of an organic solar cell), producing electron-hole pairs.
If the electron-hole pairs are created near the junction between p-type and n-type materials the local electric field sweeps them apart to opposite electrodes, producing an excess of electrons on one side and an excess of holes on the other. When the solar cell is unconnected (or the external electrical load is very high) the electrons and holes will ultimately restore equilibrium by diffusing back across the junction against the field and recombine with each other giving off heat, but if the load is small enough then it is easier for equilibrium to be restored by the excess electrons going around the external circuit, doing useful work along the way.
An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity. An inverter can convert the power to alternating current (AC).
The most commonly known solar cell is configured as a large-area p–n junction made from silicon. Other possible solar cell types are organic solar cells, dye sensitized solar cells, perovskite solar cells, quantum dot solar cells etc. The illuminated side of a solar cell generally has a transparent conducting film for allowing light to enter into the active material and to collect the generated charge carriers. Typically, films with high transmittance and high electrical conductance such as indium tin oxide, conducting polymers or conducting nanowire networks are used for the purpose. | 0 | Theoretical and Fundamental Chemistry |
An Ambident nucleophile refers to an anionic nucleophile that exhibits resonance delocalization of its negative charge over two unlike atoms or over two like but non-equivalent atoms. Enolate ions are Ambident Nucleophile. | 0 | Theoretical and Fundamental Chemistry |
The previous discussion focused on single aerosol particles. In contrast, aerosol dynamics explains the evolution of complete aerosol populations. The concentrations of particles will change over time as a result of many processes. External processes that move particles outside a volume of gas under study include diffusion, gravitational settling, and electric charges and other external forces that cause particle migration. A second set of processes internal to a given volume of gas include particle formation (nucleation), evaporation, chemical reaction, and coagulation.
A differential equation called the Aerosol General Dynamic Equation (GDE) characterizes the evolution of the number density of particles in an aerosol due to these processes.
Change in time = Convective transport + brownian diffusion + gas-particle interactions + coagulation + migration by external forces
Where:
: is number density of particles of size category
: is the particle velocity
: is the particle Stokes-Einstein diffusivity
: is the particle velocity associated with an external force | 0 | Theoretical and Fundamental Chemistry |
The simplest method of lipid separation is the use of thin layer chromatography (TLC). Although not as sensitive as other methods of lipid detection, it offers a rapid and comprehensive screening tool prior to more sensitive and sophisticated techniques.
Solid-phase extraction (SPE) chromatography is useful for rapid, preparative separation of crude lipid mixtures into different lipid classes. This involves the use of prepacked columns containing silica or other stationary phases to separate glycerophospholipids, fatty acids, cholesteryl esters, glycerolipids, and sterols from crude lipid mixtures.
High-performance liquid chromatography (HPLC or LC) is extensively used in lipidomic analysis to separate lipids prior to mass analysis. Separation can be achieved by either normal-phase (NP) HPLC or reverse-phase (RP) HPLC. For example, NP-HPLC effectively separates glycerophospholipids on the basis of headgroup polarity, whereas RP-HPLC
effectively separates fatty acids such as eicosanoids on the basis of chain length, degree of unsaturation and substitution. For global, untargeted lipidomic studies it is common to use both RP and NP or Hydrophilic Interaction Liquid Chromatrography (HILC) columns for increased lipidome coverage. The application of nano-flow liquid chromatography (nLC) proved thereby to be most efficient to enhance both general measurement sensitivity and lipidome coverage for a global lipidomics approach. Chromatographic (HPLC/UHPLC) separation of lipids may either be performed offline or online where the eluate is integrated with the ionization source of a mass spectrometer. | 1 | Applied and Interdisciplinary Chemistry |
In physics and chemistry, motional narrowing is a phenomenon where a certain resonant frequency has a smaller linewidth than might be expected, due to motion in an inhomogeneous system. The discovery of motional narrowing has been attributed to Nicolaas Bloembergen during his thesis work in the 1940s | 0 | Theoretical and Fundamental Chemistry |
In Chinese history, the alchemical practice of concocting elixirs of immortality from metallic and mineral substances began circa the 4th century BCE in the late Warring states period, reached a peak in the 9th century CE Tang dynasty when five emperors died, and, despite common knowledge of the dangers, elixir poisoning continued until the 18th century Qing dynasty. | 1 | Applied and Interdisciplinary Chemistry |
Mitochondrial replacement therapy (MRT), sometimes called mitochondrial donation, is the replacement of mitochondria in one or more cells to prevent or ameliorate disease. MRT originated as a special form of in vitro fertilisation in which some or all of the future baby's mitochondrial DNA (mtDNA) comes from a third party. This technique is used in cases when mothers carry genes for mitochondrial diseases. The therapy is approved for use in the United Kingdom. A second application is to use autologous mitochondria to replace mitochondria in damaged tissue to restore the tissue to a functional state. This has been used in clinical research in the United States to treat cardiac-compromised newborns. | 1 | Applied and Interdisciplinary Chemistry |
The movement of terrestrial carbon in the water cycle is shown in the diagram on the right and explained below:
# Atmospheric particles act as cloud condensation nuclei, promoting cloud formation.
#Raindrops absorb organic and inorganic carbon through particle scavenging and adsorption of organic vapors while falling toward Earth.
#Burning and volcanic eruptions produce highly condensed polycyclic aromatic molecules (i.e. black carbon) that is returned to the atmosphere along with greenhouse gases such as CO.
#Terrestrial plants fix atmospheric CO through photosynthesis, returning a fraction back to the atmosphere through respiration. Lignin and celluloses represent as much as 80% of the organic carbon in forests and 60% in pastures.
#Litterfall and root organic carbon mix with sedimentary material to form organic soils where plant-derived and petrogenic organic carbon is both stored and transformed by microbial and fungal activity.
#Water absorbs plant and settled aerosol-derived dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) as it passes over forest canopies (i.e. throughfall) and along plant trunks/stems (i.e. stemflow). Biogeochemical transformations take place as water soaks into soil solution and groundwater reservoirs and overland flow occurs when soils are completely saturated, or rainfall occurs more rapidly than saturation into soils.
#Organic carbon derived from the terrestrial biosphere and in situ primary production is decomposed by microbial communities in rivers and streams along with physical decomposition (i.e. photo-oxidation), resulting in a flux of CO from rivers to the atmosphere that are the same order of magnitude as the amount of carbon sequestered annually by the terrestrial biosphere. Terrestrially-derived macromolecules such as lignin and black carbon are decomposed into smaller components and monomers, ultimately being converted to CO, metabolic intermediates, or biomass.
#Lakes, reservoirs, and floodplains typically store large amounts of organic carbon and sediments, but also experience net heterotrophy in the water column, resulting in a net flux of CO to the atmosphere that is roughly one order of magnitude less than rivers. Methane production is also typically high in the anoxic sediments of floodplains, lakes, and reservoirs.
#Primary production is typically enhanced in river plumes due to the export of fluvial nutrients. Nevertheless, estuarine waters are a source of CO to the atmosphere, globally.
#Coastal marshes both store and export blue carbon. Marshes and wetlands are suggested to have an equivalent flux of CO to the atmosphere as rivers, globally.
#Continental shelves and the open ocean typically absorb CO from the atmosphere.
#The marine biological pump sequesters a small but significant fraction of the absorbed CO as organic carbon in marine sediments (see below). | 0 | Theoretical and Fundamental Chemistry |
Oganessian was granted Armenian citizenship in July 2018 by Premier Nikol Pashinyan. Oganessian is a member of the Board of Trustees of the Foundation for Armenian Science and Technology (FAST). He is also the chairman of the international scientific board of the Alikhanian National Science Laboratory (Yerevan Physics Institute). In 2017 HayPost issued a postage stamp dedicated to Oganessian. In 2022 the Central Bank of Armenia issued a silver commemorative coin dedicated to Oganessian and the element oganesson (Og). In April 2022 he was named honorary professor of Yerevan State University. | 1 | Applied and Interdisciplinary Chemistry |
Following the work on homeotic mutants by Ed Lewis, the phenomenology of homeosis in animals was further elaborated by discovery of a conserved DNA binding sequence present in many homeotic proteins.
Thus, the 60 amino acid DNA binding protein domain was named the homeodomain, while the 180 bp nucleotide sequence encoding it was named the homeobox. The homeobox gene clusters studied by Ed Lewis were named the Hox genes, although many more homeobox genes are encoded by animal genomes than those in the Hox gene clusters.
The homeotic-function of certain proteins was first postulated to be that of a "selector" as proposed by Antonio Garcia-Bellido.
By definition selectors were imagined to be (transcription factor) proteins that stably determined one of two possible cell fates for a cell and its cellular descendants in a tissue.
While most animal homeotic functions are associated with homeobox-containing factors, not all homeotic proteins in animals are encoded by homeobox genes, and further not all homeobox genes are necessarily associated with homeotic functions or (mutant) phenotypes.
The concept of homeotic selectors was further elaborated or at least qualified by Michael Akam in a so-called "post-selector gene" model that incorporated additional findings and "walked back" the "orthodoxy" of selector-dependent stable binary switches.
The concept of tissue compartments is deeply intertwined with the selector model of homeosis because the selector-mediated maintenance of cell fate can be restricted into different organizational units of an animal's body plan.
In this context, newer insights into homeotic mechanisms were found by Albert Erives and colleagues by focusing on enhancer DNAs that are co-targeted by homeotic selectors and different combinations of developmental signals.
This work identifies a protein biochemical difference between the transcription factors that function as homeotic selectors versus the transcription factors that function as effectors of developmental signaling pathways, such as the Notch signaling pathway and the BMP signaling pathway.
This work proposes that homeotic selectors function to "license" enhancer DNAs in a restricted tissue compartment so that the enhancers are enabled to read-out developmental signals, which are then integrated via polyglutamine-mediated aggregation. | 1 | Applied and Interdisciplinary Chemistry |
It remains a challenge to develop good single-phase multiferroics with large magnetization and polarization and strong coupling between them at room temperature. Therefore, composites combining magnetic materials, such as FeRh, with ferroelectric materials, such as PMN-PT, are an attractive and established route to achieving multiferroicity. Some examples include magnetic thin films on piezoelectric PMN-PT substrates and Metglass/PVDF/Metglass trilayer structures. Recently an interesting layer-by-layer growth of an atomic-scale multiferroic composite has been demonstrated, consisting of individual layers of ferroelectric and antiferromagnetic LuFeO alternating with ferrimagnetic but non-polar LuFeO in a superlattice.
A new promising approach are core-shell type ceramics where a magnetoelectric composite is formed in-situ during synthesis. In the system (BiFeCoO)-(BiKTiO) (BFC-BKT) very strong ME coupling has been observed on a microscopic scale using PFM under magnetic field. Furthermore, switching of magnetization via electric field has been observed using MFM. Here, the ME active core-shell grains consist of magnetic CoFeO (CFO) cores and a (BiFeO)-(BiKTiO) (BFO-BKT) shell where core and shell have an epitaxial lattice structure. The mechanism of strong ME coupling is via magnetic exchange interaction between CFO and BFO across the core-shell interface, which results in an exceptionally high Neel-Temperature of 670 K of the BF-BKT phase. | 0 | Theoretical and Fundamental Chemistry |
Most applications of NMR involve full NMR spectra, that is, the intensity of the NMR signal as a function of frequency. Early attempts to acquire the NMR spectrum more efficiently than simple CW methods involved illuminating the target simultaneously with more than one frequency. A revolution in NMR occurred when short radio-frequency pulses began to be used, with a frequency centered at the middle of the NMR spectrum. In simple terms, a short pulse of a given "carrier" frequency "contains" a range of frequencies centered about the carrier frequency, with the range of excitation (bandwidth) being inversely proportional to the pulse duration, i.e. the Fourier transform of a short pulse contains contributions from all the frequencies in the neighborhood of the principal frequency. The restricted range of the NMR frequencies made it relatively easy to use short (1 - 100 microsecond) radio frequency pulses to excite the entire NMR spectrum.
Applying such a pulse to a set of nuclear spins simultaneously excites all the single-quantum NMR transitions. In terms of the net magnetization vector, this corresponds to tilting the magnetization vector away from its equilibrium position (aligned along the external magnetic field). The out-of-equilibrium magnetization vector then precesses about the external magnetic field vector at the NMR frequency of the spins. This oscillating magnetization vector induces a voltage in a nearby pickup coil, creating an electrical signal oscillating at the NMR frequency. This signal is known as the free induction decay (FID), and it contains the sum of the NMR responses from all the excited spins. In order to obtain the frequency-domain NMR spectrum (NMR absorption intensity vs. NMR frequency) this time-domain signal (intensity vs. time) must be Fourier transformed. Fortunately, the development of Fourier transform (FT) NMR coincided with the development of digital computers and the digital fast Fourier transform (FFT). Fourier methods can be applied to many types of spectroscopy.
Richard R. Ernst was one of the pioneers of pulsed NMR and won a Nobel Prize in chemistry in 1991 for his work on Fourier Transform NMR and his development of multi-dimensional NMR spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
Silicon thin-film cells are mainly deposited by chemical vapor deposition (typically plasma-enhanced, PE-CVD) from silane gas and hydrogen gas. Depending on the deposition parameters, this can yield amorphous silicon (a-Si or a-Si:H), protocrystalline silicon or nanocrystalline silicon (nc-Si or nc-Si:H), also called microcrystalline silicon.
Amorphous silicon is the most well-developed thin film technology to-date. An amorphous silicon (a-Si) solar cell is made of non-crystalline or microcrystalline silicon. Amorphous silicon has a higher bandgap (1.7 eV) than crystalline silicon (c-Si) (1.1 eV), which means it absorbs the visible part of the solar spectrum more strongly than the higher power density infrared portion of the spectrum. The production of a-Si thin film solar cells uses glass as a substrate and deposits a very thin layer of silicon by plasma-enhanced chemical vapor deposition (PECVD).
Protocrystalline silicon with a low volume fraction of nanocrystalline silicon is optimal for high open-circuit voltage. Nc-Si has about the same bandgap as c-Si and nc-Si and a-Si can advantageously be combined in thin layers, creating a layered cell called a tandem cell. The top cell in a-Si absorbs the visible light and leaves the infrared part of the spectrum for the bottom cell in nc-Si. | 0 | Theoretical and Fundamental Chemistry |
The diversity of the crystal structures of rare-earth borides results in unusual physical properties and potential applications in thermopower generation. Thermal conductivity of boron icosahedra based compounds is low because of their complex crystal structure; this property is favored for thermoelectric materials. On the other hand, these compounds exhibit very low (variable range hopping type) p-type electrical conductivity. Increasing the conductivity is a key issue for thermoelectric applications of these borides.
YB is used as a soft-X-ray monochromator for dispersing 1–2 keV synchrotron radiation at some synchrotron radiation facilities. Contrary to thermoelectric applications, high thermal conductivity is desirable for synchrotron radiation monochromators. YB exhibits low, amorphous-like thermal conductivity. However, transition metal doping increases the thermal conductivity twice in YNbB as compared to undoped YB. | 0 | Theoretical and Fundamental Chemistry |
Both of the amino analogs are prepared from the condensation of 3-aminopiperidine-2,6-dione hydrochloride (Compound 3) which is synthesized in a two step reaction from commercially available Cbz--glutamine. The Cbz--glutamine is treated with CDI in refluxing THF to yield Cbz-aminoglutarimide. To remove the Cbz protecting group hydrogenolysis, under 50–60 psi of hydrogen with 10% Pd/C mixed with ethyl acetate and HCl, was performed. The formulated hydrochloride (Compound 3 in Scheme 3) was then reacted with 3-nitrophthalic anhydride in refluxing acetic acid to yield the 4-nitro substituted thalidomide analog and the nitro group then reduced with hydrogenation to give pomalidomide.
Lenalidomide is synthesized in a similar way using compound 3 (3-aminopiperidine-2,6-dione) treated with a nitro-substituted methyl 2-(bromomethyl) benzoate, and hydrogenation of the nitro group. | 1 | Applied and Interdisciplinary Chemistry |
The rising level of the Caspian Sea between 1995 and 1996 reduced the number of habitats for rare species of aquatic vegetation. This has been attributed to a general lack of seeding material in newly formed coastal lagoons and water bodies.
Many rare and endemic plant species of Russia are associated with the tidal areas of the Volga delta and riparian forests of the Samur River delta. The shoreline is also a unique refuge for plants adapted to the loose sands of the Central Asian Deserts. The principal limiting factors to successful establishment of plant species are hydrological imbalances within the surrounding deltas, water pollution, and various land reclamation activities. The water level change within the Caspian Sea is an indirect reason for which plants may not get established.
These affect aquatic plants of the Volga Delta, such as Aldrovanda vesiculosa and the native Nelumbo caspica. About 11 plant species are found in the Samur River delta, including the unique liana forests that date back to the Tertiary period.
Since 2019 UNESCO has admitted the lush Hyrcanian forests of Mazandaran, Iran as World Heritage Site under category (ix). | 1 | Applied and Interdisciplinary Chemistry |
There is no unique and fully consistent way to define the reactivity series, but it is common to use the three types of reaction listed below, many of which can be performed in a high-school laboratory (at least as demonstrations). | 0 | Theoretical and Fundamental Chemistry |
Many crystals naturally grow in faceted shapes. For instance, common table salt forms cubes and quartz forms hexagonal prisms. These characteristic shapes are a consequence of the crystal structure of the material and the surface energy, as well as the general conditions under which the crystal formed.
The Bravais lattice of the crystal structure defines a set of possible "low-energy planes", which are usually planes on which the atoms are close-packed. For instance, a cubic crystal may have low-energy planes on the faces of the cube or on the diagonals. The planes are low-energy in the sense that if the crystal is cleaved along these planes, there will be relatively few broken bonds and a relatively small increase in energy over the unbroken crystal. Equivalently, these planes have a low surface energy. The planes with the lowest energy will form the largest facets, in order to minimize the overall thermodynamic free energy of the crystal. If the surface energy as a function of the planes is known, the equilibrium shape of the crystal may be found via the Wulff construction.
Growth conditions, including the surface the crystal is growing on top of (the substrate), may change the expected shape of the crystal; for instance, if the base of the crystal is under stress from the substrate, this may favor the crystal growing taller rather than growing outwards along the substrate. The surface energy, including the relative energies of the different planes, depend on many factors including the temperature, the composition of the surroundings (e.g. humidity), and the pressure. | 0 | Theoretical and Fundamental Chemistry |
Burks-Houck began her education in Anniston, Alabama, having attended both elementary and high school in the city. Burks-Houck continued her education and earned a Bachelor of Arts degree in chemistry from Dillard University followed by a Master of Science Degree in Organic Chemistry from Atlanta University. | 0 | Theoretical and Fundamental Chemistry |
The longitudinal invariant of a particle trapped in a magnetic mirror,
where the integral is between the two turning points, is also an adiabatic invariant. This guarantees, for example, that a particle in the magnetosphere moving around the Earth always returns to the same line of force. The adiabatic condition is violated in transit-time magnetic pumping, where the length of a magnetic mirror is oscillated at the bounce frequency, resulting in net heating. | 0 | Theoretical and Fundamental Chemistry |
* Both the two- and three-dimensional versions of Ladyzhenskaya's inequality are special cases of the Gagliardo–Nirenberg interpolation inequality
:which holds whenever
:Ladyzhenskaya's inequalities are the special cases when and when .
* A simple modification of the argument used by Ladyzhenskaya in her 1958 paper (see e.g. Constantin & Seregin 2010) yields the following inequality for , valid for all :
* The usual Ladyzhenskaya inequality on , can be generalized (see McCormick & al. 2013) to use the weak "norm" of in place of the usual norm: | 1 | Applied and Interdisciplinary Chemistry |
TLRs are believed to function as dimers. Though most TLRs appear to function as homodimers, TLR2 forms heterodimers with TLR1 or TLR6, each dimer having a different ligand specificity. TLRs may also depend on other co-receptors for full ligand sensitivity, such as in the case of TLR4's recognition of LPS, which requires MD-2. CD14 and LPS-Binding Protein (LBP) are known to facilitate the presentation of LPS to MD-2.
A set of endosomal TLRs comprising TLR3, TLR7, TLR8 and TLR9 recognize nucleic acid derived from viruses as well as endogenous nucleic acids in context of pathogenic events. Activation of these receptor leads to production of inflammatory cytokines as well as type I interferons (interferon type I) to help fight viral infection.
The adapter proteins and kinases that mediate TLR signaling have also been targeted. In addition, random germline mutagenesis with ENU has been used to decipher the TLR signaling pathways. When activated, TLRs recruit adapter molecules within the cytoplasm of cells to propagate a signal. Four adapter molecules are known to be involved in signaling. These proteins are known as MyD88, TIRAP (also called Mal), TRIF, and TRAM (TRIF-related adaptor molecule).
TLR signaling is divided into two distinct signaling pathways, the MyD88-dependent and TRIF-dependent pathway. | 1 | Applied and Interdisciplinary Chemistry |
In the area of metal carbonyl clusters, a prototypical octahedral cluster is [FeC(CO)], which is obtained by heating iron pentacarbonyl with sodium. Some of the CO ligands are bridging and many are terminal. A carbide ligand resides at the center of the cluster. A variety of analogous compounds have been reported where some or all of the Fe centres are replaced by Ru, Mn and other metals.
Outside of carbonyl clusters, gold forms octahedral clusters. | 0 | Theoretical and Fundamental Chemistry |
Chemical reactions involving thermal runaway are also called thermal explosions in chemical engineering, or runaway reactions in organic chemistry. It is a process by which an exothermic reaction goes out of control: the reaction rate increases due to an increase in temperature, causing a further increase in temperature and hence a further rapid increase in the reaction rate. This has contributed to industrial chemical accidents, most notably the 1947 Texas City disaster from overheated ammonium nitrate in a ships hold, and the 1976 explosion of zoalene, in a drier, at Kings Lynn. Frank-Kamenetskii theory provides a simplified analytical model for thermal explosion. Chain branching is an additional positive feedback mechanism which may also cause temperature to skyrocket because of rapidly increasing reaction rate.
Chemical reactions are either endothermic or exothermic, as expressed by their change in enthalpy. Many reactions are highly exothermic, so many industrial-scale and oil refinery processes have some level of risk of thermal runaway. These include hydrocracking, hydrogenation, alkylation (S2), oxidation, metalation and nucleophilic aromatic substitution. For example, oxidation of cyclohexane into cyclohexanol and cyclohexanone and ortho-xylene into phthalic anhydride have led to catastrophic explosions when reaction control failed.
Thermal runaway may result from unwanted exothermic side reaction(s) that begin at higher temperatures, following an initial accidental overheating of the reaction mixture. This scenario was behind the Seveso disaster, where thermal runaway heated a reaction to temperatures such that in addition to the intended 2,4,5-trichlorophenol, poisonous 2,3,7,8-tetrachlorodibenzo-p-dioxin was also produced, and was vented into the environment after the reactor's rupture disk burst.
Thermal runaway is most often caused by failure of the reactor vessel's cooling system. Failure of the mixer can result in localized heating, which initiates thermal runaway. Similarly, in flow reactors, localized insufficient mixing causes hotspots to form, wherein thermal runaway conditions occur, which causes violent blowouts of reactor contents and catalysts. Incorrect equipment component installation is also a common cause. Many chemical production facilities are designed with high-volume emergency venting, a measure to limit the extent of injury and property damage when such accidents occur.
At large scale, it is unsafe to "charge all reagents and mix", as is done in laboratory scale. This is because the amount of reaction scales with the cube of the size of the vessel (V ∝ r³), but the heat transfer area scales with the square of the size (A ∝ r²), so that the heat production-to-area ratio scales with the size (V/A ∝ r). Consequently, reactions that easily cool fast enough in the laboratory can dangerously self-heat at ton scale. In 2007, this kind of erroneous procedure caused an explosion of a -reactor used to metalate methylcyclopentadiene with metallic sodium, causing the loss of four lives and parts of the reactor being flung away. Thus, industrial scale reactions prone to thermal runaway are preferably controlled by the addition of one reagent at a rate corresponding to the available cooling capacity.
Some laboratory reactions must be run under extreme cooling, because they are very prone to hazardous thermal runaway. For example, in Swern oxidation, the formation of sulfonium chloride must be performed in a cooled system (−30 °C), because at room temperature the reaction undergoes explosive thermal runaway. | 1 | Applied and Interdisciplinary Chemistry |
Due to its high relative density, it gathers in low-lying areas, and at high concentrations it can cause asphyxiation. Other health effects are similar to tetrafluoromethane. | 1 | Applied and Interdisciplinary Chemistry |
*Porphyrins, and phthalocyanines have highly tunable photochemical and electrochemical activity as well as the potential to form complexes.
*Photochromic and photoisomerizable groups can change their shapes and properties, including binding properties, upon exposure to light.
*Tetrathiafulvalene (TTF) and quinones have multiple stable oxidation states, and therefore can be used in redox reactions and electrochemistry.
*Other units, such as benzidine derivatives, viologens, and fullerenes, are useful in supramolecular electrochemical devices. | 0 | Theoretical and Fundamental Chemistry |
The main approximation is that all the domains are located in an equivalent mean field.
Unfortunately, it is not the case close to the percolation threshold where the system is governed by the largest cluster of conductors, which is a fractal, and long-range correlations that are totally absent from Bruggeman's simple formula.
The threshold values are in general not correctly predicted. It is 33% in the EMA, in three dimensions, far from the 16% expected from percolation theory and observed in experiments. However, in two dimensions, the EMA gives a threshold of 50% and has been proven to model percolation relatively well. | 0 | Theoretical and Fundamental Chemistry |
Omega Chi Epsilon has chartered 80 chapters at colleges and universities in the United States, Quatar, and the United Arab Emirates. | 1 | Applied and Interdisciplinary Chemistry |
This is a derivation to obtain an expression for for an ideal gas.
An ideal gas has the equation of state:
where
:P = pressure
:V = volume
:n = number of moles
:R = universal gas constant
:T = temperature
The ideal gas equation of state can be arranged to give:
: or
The following partial derivatives are obtained from the above equation of state:
The following simple expressions are obtained for thermal expansion coefficient :
and for isothermal compressibility :
One can now calculate for ideal gases from the previously obtained general formula:
Substituting from the ideal gas equation gives finally:
where n = number of moles of gas in the thermodynamic system under consideration and R = universal gas constant. On a per mole basis, the expression for difference in molar heat capacities becomes simply R for ideal gases as follows:
This result would be consistent if the specific difference were derived directly from the general expression for . | 0 | Theoretical and Fundamental Chemistry |
In order to associate with the inner leaflet of the plasma membrane, many G proteins and small GTPases are lipidated, that is, covalently modified with lipid extensions. They may be myristoylated, palmitoylated or prenylated. | 1 | Applied and Interdisciplinary Chemistry |
The Knudsen number (Kn) is a dimensionless number defined as the ratio of the molecular mean free path length to a representative physical length scale. This length scale could be, for example, the radius of a body in a fluid. The number is named after Danish physicist Martin Knudsen (1871–1949).
The Knudsen number helps determine whether statistical mechanics or the continuum mechanics formulation of fluid dynamics should be used to model a situation. If the Knudsen number is near or greater than one, the mean free path of a molecule is comparable to a length scale of the problem, and the continuum assumption of fluid mechanics is no longer a good approximation. In such cases, statistical methods should be used. | 1 | Applied and Interdisciplinary Chemistry |
As much as 25% of the primary production from phytoplankton in the global oceans may be recycled within the microbial loop through viral shunting. The viral shunt is a mechanism whereby marine viruses prevent microbial particulate organic matter (POM) from migrating up trophic levels by recycling them into dissolved organic matter (DOM), which can be readily taken up by microorganisms. The DOM recycled by the viral shunt pathway is comparable to the amount generated by the other main sources of marine DOM. Viruses can easily infect microorganisms in the microbial loop due to their relative abundance compared to microbes. Prokaryotic and eukaryotic mortality contribute to carbon nutrient recycling through cell lysis. There is evidence as well of nitrogen (specifically ammonium) regeneration. This nutrient recycling helps stimulates microbial growth. | 0 | Theoretical and Fundamental Chemistry |
During 2006 and 2007, Bussard sought the large-scale funding necessary to design and construct a full-scale Polywell fusion power plant. His fusor design is feasible enough, he asserted, to render unnecessary the construction of larger and larger test models still too small to achieve break-even. Also, the scaling of power with size goes as the seventh power of the machine radius, while the gain scales as the fifth power, so there is little incentive to build half-scale systems; one might as well build the real thing.
On March 29, 2006, Bussard claimed on the fusor.net internet forum that EMC² had developed an inertial electrostatic confinement fusion process that was 100,000 times more efficient than previous designs, but that the US Navy budget line item that supported the work was zero-funded in FY2006.
Bussard provided more details of his breakthrough and the circumstances surrounding the end of his Navy funding in a letter to the James Randi Educational Foundation internet forum on June 23.
From October 2, 2006, to October 6, 2006, Bussard presented an informal overview of the previous decade of his work at the 57th International Astronautical Congress. This was the first publication of this work in 11 years, as the U.S. Navy had put an embargo on publications of the research, in 1994.
Bussard presented further details of his IEC fusion research at a Google Tech Talk on November 9, 2006, of which a video was widely circulated.
Bussard presented more of his thoughts on the potential world impact of fusion power at a Yahoo! Tech Talk on April 10, 2007.
(The video is only available internally for Yahoo employees.) He also spoke on the internet talk radio show The Space Show, Broadcast 709, on May 7, 2007.
He founded a non-profit organization to solicit tax-deductible donations to restart the work in 2007, EMC2 Fusion Development Corporation. | 0 | Theoretical and Fundamental Chemistry |
Heterologous gene expression is used in many biotechnological applications, including protein production and metabolic engineering. Because tRNA pools vary between different organisms, the rate of transcription and translation of a particular coding sequence can be less efficient when placed in a non-native context. For an overexpressed transgene, the corresponding mRNA makes a large percent of total cellular RNA, and the presence of rare codons along the transcript can lead to inefficient use and depletion of ribosomes and ultimately reduce levels of heterologous protein production. In addition, the composition of the gene (e.g. the total number of rare codons and the presence of consecutive rare codons) may also affect translation accuracy. However, using codons that are optimized for tRNA pools in a particular host to overexpress a heterologous gene may also cause amino acid starvation and alter the equilibrium of tRNA pools. This method of adjusting codons to match host tRNA abundances, called codon optimization, has traditionally been used for expression of a heterologous gene. However, new strategies for optimization of heterologous expression consider global nucleotide content such as local mRNA folding, codon pair bias, a codon ramp, codon harmonization or codon correlations. With the number of nucleotide changes introduced, artificial gene synthesis is often necessary for the creation of such an optimized gene.
Specialized codon bias is further seen in some endogenous genes such as those involved in amino acid starvation. For example, amino acid biosynthetic enzymes preferentially use codons that are poorly adapted to normal tRNA abundances, but have codons that are adapted to tRNA pools under starvation conditions. Thus, codon usage can introduce an additional level of transcriptional regulation for appropriate gene expression under specific cellular conditions. | 1 | Applied and Interdisciplinary Chemistry |
EDTA, ethylenediaminetetraacetic acid, has four carboxyl groups and two amine groups that can act as electron pair donors, or Lewis bases. The ability of EDTA to potentially donate its six lone pairs of electrons for the formation of coordinate covalent bonds to metal cations makes EDTA a hexadentate ligand. However, in practice EDTA is usually only partially ionized, and thus forms fewer than six coordinate covalent bonds with metal cations.
Disodium EDTA is commonly used to standardize aqueous solutions of transition metal cations. Disodium EDTA (often written as NaHY) only forms four coordinate covalent bonds to metal cations at pH values ≤ 12. In this pH range, the amine groups remain protonated and thus unable to donate electrons to the formation of coordinate covalent bonds. Note that the shorthand form NaHY can be used to represent any species of EDTA, with x designating the number of acidic protons bonded to the EDTA molecule.
EDTA forms an octahedral complex with most 2+ metal cations, M, in aqueous solution. The main reason that EDTA is used so extensively in the standardization of metal cation solutions is that the formation constant for most metal cation-EDTA complexes is very high, meaning that the equilibrium for the reaction:
:M + HY → MHY + 2H
lies far to the right. Carrying out the reaction in a basic buffer solution removes H as it is formed, which also favors the formation of the EDTA-metal cation complex reaction product. For most purposes it can be considered that the formation of the metal cation-EDTA complex goes to completion, and this is chiefly why EDTA is used in titrations and standardizations of this type. | 0 | Theoretical and Fundamental Chemistry |
Whenever a wave forms through a medium/object (organ pipe) with a closed/open end, there is a chance of error in the formation of the wave, i.e. it may not actually start from the opening of the object but instead before the opening, thus resulting on an error when studying it theoretically. Hence an end correction is sometimes required to appropriately study its properties. The end correction depends on the radius of the object.
An acoustic pipe, such as an organ pipe, marimba, or flute resonates at a specific pitch or frequency. Longer pipes resonate at lower frequencies, producing lower-pitched sounds. The details of acoustic resonance are taught in many elementary physics classes. In an ideal tube, the wavelength of the sound produced is directly proportional to the length of the tube. A tube which is open at one end and closed at the other produces sound with a wavelength equal to four times the length of the tube. A tube which is open at both ends produces sound whose wavelength is just twice the length of the tube. Thus, when a Boomwhacker with two open ends is capped at one end, the pitch produced by the tube goes down by one octave.
The analysis above applies only to an ideal tube, of zero diameter. When designing an organ or Boomwhacker, the diameter of the tube must be taken into account. In acoustics, end correction is a short distance applied or added to the actual length of a resonance pipe, in order to calculate the precise resonant frequency of the pipe. The pitch of a real tube is lower than the pitch predicted by the simple theory. A finite diameter pipe appears to be acoustically somewhat longer than its physical length.
A theoretical basis for computation of the end correction is the radiation acoustic impedance of a circular piston. This impedance represents the ratio of acoustic pressure at the piston, divided by the flow rate induced by it. The air speed is typically assumed to be uniform across the tube end. This is a good approximation, but not exactly true in reality, since air viscosity reduces the flow rate in the boundary layer very close to the tube surface. Thus, the air column inside the tube is loaded by the external fluid due to sound energy radiation. This requires an additional length to be added to the regular length for calculating the natural frequency of the pipe system.
The end correction is denoted by and sometimes by . In organ pipes, a displacement antinode is not formed exactly at the open end. Rather, the antinode is formed a little
distance away from the open end outside it.
This is known as end correction, which can be calculated as:
* for a closed pipe (with one opening):
:If you add this in total length calculated based on sound frequency the actual length will be longer. This equation will increase the flute length if flute diameter will be larger but in real sense it reduces the length as the diameter increases. It looks contradictory but in real sense this equation is not accurate for all bore / pipe diameter. For example this is correct for G bass flute for 20mm bore diameter but as diameter increases then this equation have negative effect means length will reduce. The pipe wall thickness correction also need to be added here for accuracy.
where is the radius of the neck and is the hydraulic diameter of the neck;
* and for an open pipe (with two openings):
The exact number for the end correction depends on a number of factors relating to the geometry of the pipe. Lord Rayleigh was the first experimenter to publish a figure, in 1871: it was . Other experiments have yielded results such as and . The end correction for ideal cylindrical tubes was calculated to be by Levine and Schwinger. | 1 | Applied and Interdisciplinary Chemistry |
This section explains how the saprobic index of a water body is computed according to the Zelinka & Marvan method; without adjusting for several confounding factors.
In a first iteration, the abundance A of each indicator species is counted and converted to categories ranging from 1 to 7. An abundance of 1 means that only one or two animals was found, while the class 7 means more than 1000 individuals during a survey. There are different abundance classes — for example, some methods use classes where the next-bigger class contains roughly double the number of individuals. The following table follows the DIN 38410-1 (2008) standard used in Germany, where the next-bigger class is about three times larger than the previous one.
The saprobic value s denotes how much organic matter must be present for an aquatic species to thrive. An animal with a saprobic value 1 can only survive in water with little organic matter present, while one with a value of 4 requires water bodies with a large amount of organic matter. The aforementioned example, the Lymnaea stagnalis snail, has a saprobic value of 2.0. The annelid worm Tubifex tubifex needs a lot of organic matter and has an s value of 3.6.
The weighting factor g has a value of either 1, 2, 4, 8 or 16, and denotes a tolerance range. If a species can survive in both unpolluted and heavily polluted water, g is very small because finding the species in a survey has little predictive value. In practice, only indicator species with a weighting factor g ≥ 4 are used. For example, a caddisfly, Agapetus fuscipes, has a g value of 16, while the zebra mussel's value is g = 4.
The saprobic index of a water body - the water quality - is finally computed with the following formula:
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The water body's quality, in Roman numerals, is the rounded value of S. | 1 | Applied and Interdisciplinary Chemistry |
Especially in meteorology they are used to analyze the actual state of the atmosphere derived from the measurements of radiosondes, usually obtained with weather balloons. In such diagrams, temperature and humidity values (represented by the dew point) are displayed with respect to pressure. Thus the diagram gives at a first glance the actual atmospheric stratification and vertical water vapor distribution. Further analysis gives the actual base and top height of convective clouds or possible instabilities in the stratification.
By assuming the energy amount due to solar radiation it is possible to predict the 2 m (6.6 ft) temperature, humidity, and wind during the day, the development of the boundary layer of the atmosphere, the occurrence and development of clouds and the conditions for soaring flight during the day.
The main feature of thermodynamic diagrams is the equivalence between the area in the diagram and energy. When air changes pressure and temperature during a process and prescribes a closed curve within the diagram the area enclosed by this curve is proportional to the energy which has been gained or released by the air. | 0 | Theoretical and Fundamental Chemistry |
Enzyme inhibition is a common feature of metabolic pathway control in cells. Metabolic flux through a pathway is often regulated by a pathway's metabolites acting as inhibitors and enhancers for the enzymes in that same pathway. The glycolytic pathway is a classic example. This catabolic pathway consumes glucose and produces ATP, NADH and pyruvate. A key step for the regulation of glycolysis is an early reaction in the pathway catalysed by phosphofructokinase1 (PFK1). When ATP levels rise, ATP binds an allosteric site in PFK1 to decrease the rate of the enzyme reaction; glycolysis is inhibited and ATP production falls. This negative feedback control helps maintain a steady concentration of ATP in the cell. However, metabolic pathways are not just regulated through inhibition since enzyme activation is equally important. With respect to PFK1, fructose 2,6-bisphosphate and ADP are examples of metabolites that are allosteric activators.
Physiological enzyme inhibition can also be produced by specific protein inhibitors. This mechanism occurs in the pancreas, which synthesises many digestive precursor enzymes known as zymogens. Many of these are activated by the trypsin protease, so it is important to inhibit the activity of trypsin in the pancreas to prevent the organ from digesting itself. One way in which the activity of trypsin is controlled is the production of a specific and potent trypsin inhibitor protein in the pancreas. This inhibitor binds tightly to trypsin, preventing the trypsin activity that would otherwise be detrimental to the organ. Although the trypsin inhibitor is a protein, it avoids being hydrolysed as a substrate by the protease by excluding water from trypsin's active site and destabilising the transition state. Other examples of physiological enzyme inhibitor proteins include the barstar inhibitor of the bacterial ribonuclease barnase. | 1 | Applied and Interdisciplinary Chemistry |
Chenevix went to Paris after his university studies. He was imprisoned there for 15 months during the Reign of Terror. While in custody he had two children; also, amongst his fellow prisoners were a number of chemists who whetted his interest in the topic. After his release he studied at three different schools in Paris, gaining skills in chemical analysis. In 1798 he wrote his first paper, in French: Analysis of some magnesium rocks in Annales de Chimie. Thereafter, in journals both sides of the Channel, he reported analyses of hydrochloric and sulphuric acids, compounds of lead, copper, iron, arsenic, carbon and sulphur and crystals of corundum including sapphires and rubies. He was made a fellow of the Royal Society in 1801 as a result of this work.
He wrote a paper in England in 1802 supporting French Neologist-inspired changes to chemical nomenclature. During a year in Germany, he published criticisms of the work of ground-breaking scientists: Danish chemist and physicist Hans Christian Ørsted and the German physicist, chemist and mineralogist Christian Samuel Weiss. In 1803, in the Philosophical Transactions of the Royal Society, he published a paper asserting that the palladium that the English chemist William Hyde Wollaston had extracted from platinum ore the previous year (and had announced and offered for sale anonymously) was in fact an alloy of mercury and platinum. For this seemingly astonishing result, he was awarded the Copley Medal. Wollaston, again anonymously, offered a reward to anyone who could confirm Chenevixs claims experimentally. On his part, Chenevix published a second paper supporting his result in 1805, by which time hed made Paris his permanent home. Henry Cavendish, an admirer of Wollaston, was the sole Society objector in the vote for the publication. Later that year, Wollaston publicly revealed his authorship (although he had communicated as much to the Royal Society before Chenevixs second paper) and details of how he had, correctly, isolated the element palladium. Chenevix bore no apparent animus in later meetings between the two. How damaging the affair was to Chenevixs reputation as a chemist in the scientific world has been a discussion point for different writers. In 1808 came his criticism of Abraham Werners classification of minerals. In 1809, he produced his final scientific paper, a method to produce acetone by distilling acetates. An English translation of a paper he wrote in 1808 for Annales de Chimie was published in London in 1811 as Observations on Mineralogical Systems'.
Chenevix was a member of a number of European societies. The Royal Society has (a minimum of) twenty-six papers by Chenevix. | 1 | Applied and Interdisciplinary Chemistry |
Synthesis of metallic nanofoams may be accomplished through a variety of methods. In 2006, researchers produced metal nanofoams by igniting pellets of energetic metal bis(tetrazolato)amine complexes. Nanofoams of iron, cobalt, nickel, copper, silver, and palladium have been prepared through this technique. These materials exhibit densities as low as 11 mg/cm, and surface areas as high as 258 m/g. These foams are effective catalysts and electrocatalyst supports. Also, metal nanofoams can be made by electrodeposition of metals inside templates with interconnected pores, such as 3D-porous anodic aluminum oxide (AAO). Such method gives nanofoams with an organized structure and allows to control the surface area and porosity of the fabricated material.
A 2016 study discussed a low temperature/pressure microwave solvothermal method for fabricating pure copper, silver, and nickel metal nanofoams. The process claims to be non-hazardous, novel, as well as facile, with an emphasis on its low-waste and low-cost method of manufacturing.
Additionally, a 2020 publication discussed successful synthesis of nanofoam films from silver, gold, copper, and palladium through the use of a modified vacuum thermal evaporation method. | 0 | Theoretical and Fundamental Chemistry |
Dravya () means substance or entity. According to the Jain philosophy, the universe is made up of six eternal substances: sentient beings or souls (jīva), non-sentient substance or matter (pudgala), principle of motion (dharma), the principle of rest (adharma), space (ākāśa) and time (kāla). The latter five are united as the ajiva (the non-living). As per the Sanskrit etymology, dravya means substances or entity, but it may also mean real or fundamental categories.
Jain philosophers distinguish a substance from a body, or thing, by declaring the former as a simple element or reality while the latter as a compound of one or more substances or atoms. They claim that there can be a partial or total destruction of a body or thing, but no dravya can ever be destroyed. The Vaisheshika school of Indian philosophy also deals with a concept of dravya. | 1 | Applied and Interdisciplinary Chemistry |
A goal of plasmonics is to understand and manipulate surface plasmons at the nano-scale, so characterization of surface plasmons is important. Some techniques frequently used to characterize surface plasmons are dark-field microscopy, UV-vis-NIR spectroscopy, and surface-enhanced Raman scattering (SERS). With dark-field microscopy, it is possible to monitor the spectrum of an individual metal nanostructure as the incident light polarization, wavelength, or variations in the dielectric environment is changed. | 0 | Theoretical and Fundamental Chemistry |
Ferdinand Reich (19 February 1799 – 27 April 1882) was a German chemist who co-discovered indium in 1863 with Hieronymous Theodor Richter.
Reich was born in Bernburg, Anhalt-Bernburg and died in Freiberg. He was color blind, or could only see in whites and blacks, and that is why Theodor Richter became his science partner. Richter would examine the colors produced in reactions that they studied.
Reich and Richter ended up isolating the indium, creating a small supply, although it was later found in more regions. They isolated the indium at the Freiberg University of Mining and Technology in Germany.
In 1803, Laplace and Gauss both derived that, if a heavy object is dropped from a height at latitude , and the earth rotates from west to east with angular velocity , then the object would be deflected to the east by a distance of . In 1831, Reich set out to test this prediction by actually dropping objects in a mine pit (Drei-Brüder-Schacht, with latitude 50° 53′ 12.5″ N) 158.5 m deep, in Freiberg, Saxony, for 106 times. The average deflection is 2.84 cm to the east and 0.44 cm to the south. The eastward deflection is almost exactly equal to the theoretical value of 2.75 cm, but the southward deflection remains unexplained to this day. The experiment is published in
* Fallversuche über die Umdrehung der Erde angestellt auf hohe Obergamtliche Anordnung in dem Dreibrüderschacht bei Freiberg, [http://digital.ub.uni-duesseldorf.de/urn/urn:nbn:de:hbz:061:1-500010 Digitized] (published in 1832) | 1 | Applied and Interdisciplinary Chemistry |
Louis Pasteur a French chemist, supported the idea that fermentation was a biological process. Justus von Liebig, a German chemist, supported the idea that fermentation was a mechanical process. Both chemists had different methods of experimentation, and they focused on different aspects of fermentation because they had different ideas about where the fermentation began in an organism.
The Liebig–Pasteur feud started in 1857 when Pasteur said that fermentation can occur in the absence of oxygen. The two were aware of the other's works, but continued working with their own theories. The two mention each other, as well as other scientists, in articles and other publications about the processes and causes of fermentation. | 1 | Applied and Interdisciplinary Chemistry |
Photothermal deflection spectroscopy is a kind of spectroscopy that measures the change in refractive index due to heating of a medium by light. It works via a sort of "mirage effect" where a refractive index gradient exists adjacent to the test sample surface. A probe laser beam is refracted or bent in a manner proportional to the temperature gradient of the transparent medium near the surface. From this deflection, a measure of the absorbed excitation radiation can be determined. The technique is useful when studying optically thin samples, because sensitive measurements can be obtained of whether absorption is occurring. It is of value in situations where "pass through" or transmission spectroscopy can't be used.
There are two main forms of PDS: Collinear and Transverse. Collinear PDS was introduced in a 1980 paper by A.C. Boccara, D. Fournier, et al. In collinear, two beams pass through and intersect in a medium. The pump beam heats the material and the probe beam is deflected. This technique only works for transparent media. In transverse, the pump beam heats come in normal to the surface, and the probe beam passes parallel. In a variation on this, the probe beam may reflect off the surface, and measure buckling due to heating. Transverse PDS can be done in Nitrogen, but better performance is gained in a liquid cell: usually an inert, non-absorbing material such as a perfluorocarbon is used.
In both collinear and transverse PDS, the surface is heated using a periodically modulated light source, such as an optical beam passing through a mechanical chopper or regulated with a function generator. A lock-in amplifier is then used to measure deflections found at the modulation frequency. Another scheme uses a pulsed laser as the excitation source. In that case, a boxcar average can be used to measure the temporal deflection of the probe beam to the excitation radiation. The signal falls off exponentially as a function of frequency, so frequencies around 1-10 hertz are frequently used. A full theoretical analysis of the PDS system was published by Jackson, Amer, et al. in 1981. The same paper also discussed the use of PDS as a form of microscopy, called "Photothermal Deflection Microscopy", which can yield information about impurities and the surface topology of materials.
PDS analysis of thin films can also be performed using a patterned substrate that supports optical resonances, such as guided-mode resonance and whispering-gallery modes. The probe beam is coupled into a resonant mode and the coupling efficiency is highly sensitive to the incidence angle. Due to the photoheating effect, the coupling efficiency is changed and characterized to indicate the thin film absorption. | 0 | Theoretical and Fundamental Chemistry |
Dye-sub printing is a digital printing technology using full color artwork that works with polyester and polymer-coated substrates. Also referred to as digital sublimation, the process is commonly used for decorating apparel, signs and banners, as well as novelty items such as cell phone covers, plaques, coffee mugs, and other items with sublimation-friendly surfaces. The process uses the science of sublimation, in which heat and pressure are applied to a solid, turning it into a gas through an endothermic reaction without passing through the liquid phase.
In sublimation printing, unique sublimation dyes are transferred to sheets of “transfer” paper via liquid gel ink through a piezoelectric print head. The ink is deposited on these high-release inkjet papers, which are used for the next step of the sublimation printing process. After the digital design is printed onto sublimation transfer sheets, it is placed on a heat press along with the substrate to be sublimated.
In order to transfer the image from the paper to the substrate, it requires a heat press process that is a combination of time, temperature and pressure. The heat press applies this special combination, which can change depending on the substrate, to “transfer” the sublimation dyes at the molecular level into the substrate. The most common dyes used for sublimation activate at 350 degrees Fahrenheit. However, a range of 380 to 420 degrees Fahrenheit is normally recommended for optimal color.
The result of the sublimation process is a nearly permanent, high resolution, full color print. Because the dyes are infused into the substrate at the molecular level, rather than applied at a topical level (such as with screen printing and direct to garment printing), the prints will not crack, fade or peel from the substrate under normal conditions. | 0 | Theoretical and Fundamental Chemistry |
In biology, the "%" symbol is sometimes incorrectly used to denote mass concentration, also called "mass/volume percentage". A solution with 1 g of solute dissolved in a final volume of 100 mL of solution would be labeled as "1%" or "1% m/v" (mass/volume). The notation is mathematically flawed because the unit "%" can only be used for dimensionless quantities. "Percent solution" or "percentage solution" are thus terms best reserved for "mass percent solutions" (m/m = m% = mass solute/mass total solution after mixing), or "volume percent solutions" (v/v = v% = volume solute per volume of total solution after mixing). The very ambiguous terms "percent solution" and "percentage solutions" with no other qualifiers, continue to occasionally be encountered.
This common usage of % to mean m/v in biology is because of many biological solutions being dilute and water-based or an aqueous solution. Liquid water has a density of approximately 1 g/cm (1 g/mL). Thus 100 mL of water is equal to approximately 100 g. Therefore, a solution with 1 g of solute dissolved in final volume of 100 mL aqueous solution may also be considered 1% m/m (1 g solute in 99 g water). This approximation breaks down as the solute concentration is increased (for example, in water–NaCl mixtures). High solute concentrations are often not physiologically relevant, but are occasionally encountered in pharmacology, where the mass per volume notation is still sometimes encountered. An extreme example is saturated solution of potassium iodide (SSKI) which attains 100 "%" m/v potassium iodide mass concentration (1 gram KI per 1 mL solution) only because the solubility of the dense salt KI is extremely high in water, and the resulting solution is very dense (1.72 times as dense as water).
Although there are examples to the contrary, it should be stressed that the commonly used "units" of % w/v are grams per millilitre (g/mL). 1% m/v solutions are sometimes thought of as being gram/100 mL but this detracts from the fact that % m/v is g/mL; 1g of water has a volume of approximately 1 mL (at standard temperature and pressure) and the mass concentration is said to be 100%. To make 10 mL of an aqueous 1% cholate solution, 0.1 grams of cholate are dissolved in 10mL of water. Volumetric flasks are the most appropriate piece of glassware for this procedure as deviations from ideal solution behavior can occur with high solute concentrations.
In solutions, mass concentration is commonly encountered as the ratio of mass/[volume solution], or m/v. In water solutions containing relatively small quantities of dissolved solute (as in biology), such figures may be "percentivized" by multiplying by 100 a ratio of grams solute per mL solution. The result is given as "mass/volume percentage". Such a convention expresses mass concentration of 1 gram of solute in 100 mL of solution, as "1 m/v %". | 0 | Theoretical and Fundamental Chemistry |
Equal volumes of aniline and oil are stirred continuously in a test tube and heated until the two merge into a homogeneous solution. Heating is stopped and the tube is allowed to cool. The temperature at which the two phases separate out is recorded as aniline point. | 0 | Theoretical and Fundamental Chemistry |
Rheotens is a fiber spinning rheometer, suitable for polymeric melts. The material is pumped from an upstream tube, and a set of wheels elongates the strand. A force transducer mounted on one of the wheels measures the resultant extensional force. Because of the pre-shear induced as the fluid is transported through the upstream tube, a true extensional viscosity is difficult to obtain. However, the Rheotens is useful to compare the extensional flow properties of a homologous set of materials. | 1 | Applied and Interdisciplinary Chemistry |
Somatic-cell nuclear transfer, popularly known as SCNT, can also be used to create embryos for research or therapeutic purposes. The most likely purpose for this is to produce embryos for use in stem cell research. This process is also called "research cloning" or "therapeutic cloning". The goal is not to create cloned human beings (called "reproductive cloning"), but rather to harvest stem cells that can be used to study human development and to potentially treat disease. While a clonal human blastocyst has been created, stem cell lines are yet to be isolated from a clonal source.
Therapeutic cloning is achieved by creating embryonic stem cells in the hopes of treating diseases such as diabetes and Alzheimers. The process begins by removing the nucleus (containing the DNA) from an egg cell and inserting a nucleus from the adult cell to be cloned. In the case of someone with Alzheimers disease, the nucleus from a skin cell of that patient is placed into an empty egg. The reprogrammed cell begins to develop into an embryo because the egg reacts with the transferred nucleus. The embryo will become genetically identical to the patient. The embryo will then form a blastocyst which has the potential to form/become any cell in the body.
The reason why SCNT is used for cloning is because somatic cells can be easily acquired and cultured in the lab. This process can either add or delete specific genomes of farm animals. A key point to remember is that cloning is achieved when the oocyte maintains its normal functions and instead of using sperm and egg genomes to replicate, the donors somatic cell nucleus is inserted into the oocyte. The oocyte will react to the somatic cell nucleus, the same way it would to a sperm cells nucleus.
The process of cloning a particular farm animal using SCNT is relatively the same for all animals. The first step is to collect the somatic cells from the animal that will be cloned. The somatic cells could be used immediately or stored in the laboratory for later use. The hardest part of SCNT is removing maternal DNA from an oocyte at metaphase II. Once this has been done, the somatic nucleus can be inserted into an egg cytoplasm. This creates a one-cell embryo. The grouped somatic cell and egg cytoplasm are then introduced to an electrical current. This energy will hopefully allow the cloned embryo to begin development. The successfully developed embryos are then placed in surrogate recipients, such as a cow or sheep in the case of farm animals.
SCNT is seen as a good method for producing agriculture animals for food consumption. It successfully cloned sheep, cattle, goats, and pigs. Another benefit is SCNT is seen as a solution to clone endangered species that are on the verge of going extinct. However, stresses placed on both the egg cell and the introduced nucleus can be enormous, which led to a high loss in resulting cells in early research. For example, the cloned sheep Dolly was born after 277 eggs were used for SCNT, which created 29 viable embryos. Only three of these embryos survived until birth, and only one survived to adulthood. As the procedure could not be automated, and had to be performed manually under a microscope, SCNT was very resource intensive. The biochemistry involved in reprogramming the differentiated somatic cell nucleus and activating the recipient egg was also far from being well understood. However, by 2014 researchers were reporting cloning success rates of seven to eight out of ten and in 2016, a Korean Company Sooam Biotech was reported to be producing 500 cloned embryos per day.
In SCNT, not all of the donor cells genetic information is transferred, as the donor cells mitochondria that contain their own mitochondrial DNA are left behind. The resulting hybrid cells retain those mitochondrial structures which originally belonged to the egg. As a consequence, clones such as Dolly that are born from SCNT are not perfect copies of the donor of the nucleus. | 1 | Applied and Interdisciplinary Chemistry |
Excited state intramolecular proton transfer (ESIPT) is a process in which photoexcited molecules relax their energy through tautomerization by transfer of protons. Some kinds of molecules could have different minimum-energy tautomers in different electronic states, and if the molecular structure of minimum-energy tautomer in the excited state is proton-transferred geometry between neighboring atoms, proton transfer in excited state can occur. The tautomerization often takes the form of keto-enol tautomerism. | 0 | Theoretical and Fundamental Chemistry |
Sodium iodide is used for conversion of alkyl chlorides into alkyl iodides. This method, the Finkelstein reaction, relies on the insolubility of sodium chloride in acetone to drive the reaction:
::R–Cl + NaI → R–I + NaCl | 0 | Theoretical and Fundamental Chemistry |
Plants do not carry pathogens that might be dangerous to human health. Additionally, on the level of pharmacologically active proteins, there are no proteins in plants that are similar to human proteins. On the other hand, plants are still sufficiently closely related to animals and humans that they are able to correctly process and configure both animal and human proteins. Their seeds and fruits also provide sterile packaging containers for the valuable therapeutics and guarantee a certain storage life.
Global demand for pharmaceuticals is at unprecedented levels. Expanding the existing microbial systems, although feasible for some therapeutic products, is not a satisfactory option on several grounds. Many proteins of interest are too complex to be made by microbial systems or by protein synthesis. These proteins are currently being produced in animal cell cultures, but the resulting product is often prohibitively expensive for many patients. For these reasons, science has been exploring other options for producing proteins of therapeutic value.
These pharmaceutical crops could become extremely beneficial in developing countries. The World Health Organization estimates that nearly 3 million people die each year from vaccine preventable disease, mostly in Africa. Diseases such as measles and hepatitis lead to deaths in countries where the people cannot afford the high costs of vaccines, but pharm crops could help solve this problem. | 1 | Applied and Interdisciplinary Chemistry |
Biochemistry laboratories often use in vitro studies to explore ATP-dependent molecular processes. ATP analogs are also used in X-ray crystallography to determine a protein structure in complex with ATP, often together with other substrates.
Enzyme inhibitors of ATP-dependent enzymes such as kinases are needed to examine the binding sites and transition states involved in ATP-dependent reactions.
Most useful ATP analogs cannot be hydrolyzed as ATP would be; instead, they trap the enzyme in a structure closely related to the ATP-bound state. Adenosine 5′-(γ-thiotriphosphate) is an extremely common ATP analog in which one of the gamma-phosphate oxygens is replaced by a sulfur atom; this anion is hydrolyzed at a dramatically slower rate than ATP itself and functions as an inhibitor of ATP-dependent processes. In crystallographic studies, hydrolysis transition states are modeled by the bound vanadate ion.
Caution is warranted in interpreting the results of experiments using ATP analogs, since some enzymes can hydrolyze them at appreciable rates at high concentration. | 1 | Applied and Interdisciplinary Chemistry |
Burning glasses are known to date back to about 700 BC. One of the first accurately mentions of burning glasses appears in Aristophaness comedy, The Clouds, written in 423 BC. According to the Archimedes heat ray anecdote, Archimedes is purported to have developed mirrors to concentrate heat rays in order to burn attacking Roman ships during the Siege of Syracuse ( 213–212 BC), but no sources from the time have been confirmed. Catoptrics is a book attributed to Euclid on how to focus light in order to produce heat, but the book might have been written in 300 AD. | 0 | Theoretical and Fundamental Chemistry |
For the creation of dies for producing jewelry and badges, or blanking and piercing (through use of a pancake die) by the coinage (stamping) process, the positive master may be made from sterling silver, since (with appropriate machine settings) the master is significantly eroded and is used only once. The resultant negative die is then hardened and used in a drop hammer to produce stamped flats from cutout sheet blanks of bronze, silver, or low proof gold alloy. For badges these flats may be further shaped to a curved surface by another die. This type of EDM is usually performed submerged in an oil-based dielectric. The finished object may be further refined by hard (glass) or soft (paint) enameling, or electroplated with pure gold or nickel. Softer materials such as silver may be hand engraved as a refinement. | 1 | Applied and Interdisciplinary Chemistry |
In May, onasemnogene abeparvovec (Zolgensma) was approved by the European Union for the treatment of spinal muscular atrophy in people who either have clinical symptoms of SMA type 1 or who have no more than three copies of the SMN2 gene, irrespective of body weight or age.
In August, Audentes Therapeutics reported that three out of 17 children with X-linked myotubular myopathy participating the clinical trial of a AAV8-based gene therapy treatment AT132 have died. It was suggested that the treatment, whose dosage is based on body weight, exerts a disproportionately toxic effect on heavier patients, since the three patients who died were heavier than the others. The trial has been put on clinical hold.
On 15 October, the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) adopted a positive opinion, recommending the granting of a marketing authorisation for the medicinal product Libmeldy (autologous CD34+ cell enriched population that contains hematopoietic stem and progenitor cells transduced ex vivo using a lentiviral vector encoding the human arylsulfatase A gene), a gene therapy for the treatment of children with the "late infantile" (LI) or "early juvenile" (EJ) forms of metachromatic leukodystrophy (MLD). The active substance of Libmeldy consists of the childs own stem cells which have been modified to contain working copies of the ARSA gene. When the modified cells are injected back into the patient as a one-time infusion, the cells are expected to start producing the ARSA enzyme that breaks down the build-up of sulfatides in the nerve cells and other cells of the patients body. Libmeldy was approved for medical use in the EU in December 2020.
On 15 October, Lysogene, a French biotechnological company, reported the death of a patient in who has received LYS-SAF302, an experimental gene therapy treatment for mucopolysaccharidosis type IIIA (Sanfilippo syndrome type A). | 1 | Applied and Interdisciplinary Chemistry |
For many polymeric foams, a solidified foam is formed by polymerizing and foaming a liquid polymer mixture and then allowing that foam to solidify. Thus, liquid foam aging effects do occur before solidification. In the liquid foam, gravitational forces and internal pressures cause a flow of the liquid toward the bottom of the foam. This causes some of the foam cells to form into irregular polyhedra as liquid drains, which are less stable structures than the spherical structures of a traditional foam. These structures can however be stabilized by the presence of a surfactant.
The foam structure before solidification is an inherently unstable one, as the voids present greatly increase the surface free energy of the structure. In some synthetic biofoams, a surfactant can be used in order to lower the surface free energy of the foam and therefore stabilize the foam. In some natural biofoams, proteins can act as the surfactants for the foams to form and stabilize. | 0 | Theoretical and Fundamental Chemistry |
Combinations of the above techniques produce "hybrid" or "hyphenated" techniques. Several examples are in popular use today and new hybrid techniques are under development.
Hyphenated separation techniques refer to a combination of two or more techniques to separate chemicals from solutions and detect them. Most often, the other technique is some form of chromatography. Hyphenated techniques are widely used in chemistry and biochemistry. A slash is sometimes used instead of hyphen, especially if the name of one of the methods contains a hyphen itself.
Examples of hyphenated techniques:
*Gas chromatography-mass spectrometry (GC-MS)
*Liquid chromatography–mass spectrometry (LC-MS)
*Liquid chromatography-infrared spectroscopy (LC-IR)
*High-performance liquid chromatography/electrospray ionization-mass spectrometry (HPLC/ESI-MS)
*Chromatography-diode-array detection (LC-DAD)
*Capillary electrophoresis-mass spectrometry (CE-MS)
*Capillary electrophoresis-ultraviolet-visible spectroscopy (CE-UV)
*Ion-mobility spectrometry–mass spectrometry
*Prolate trochoidal mass spectrometer | 0 | Theoretical and Fundamental Chemistry |
The problem can be prevented by adding antiozonants to the rubber before vulcanization. Ozone cracks were commonly seen in automobile tire sidewalls, but are now seen rarely thanks to the use of these additives. A common and low cost antiozonant is a wax which bleeds to the surface and forms a protective layer, but other specialist chemicals are also widely used.
On the other hand, the problem does recur in unprotected products such as rubber tubing and seals, where ozone attack is thought to be impossible. Unfortunately, traces of ozone can turn up in the most unexpected situations. Using ozone-resistant rubbers is another way of inhibiting cracking. EPDM rubber and butyl rubber are ozone resistant, for example.
For high value equipment where loss of function can cause serious problems, low cost seals may be replaced at frequent intervals so as to preclude failure.
Ozone gas is produced during electric discharge by sparking or corona discharge for example. Static electricity can build up within machines like compressors with moving parts constructed from insulating materials. If those compressors feed pressurised air into a closed pneumatic system, then all seals in the system may be at risk from ozone cracking.
Ozone is also produced by the action of sunlight on volatile organic compounds or VOCs, such as gasoline vapour present in the air of towns and cities, in a problem known as photochemical smog. The ozone formed can drift many miles before it is destroyed by further reactions. | 0 | Theoretical and Fundamental Chemistry |
Genes can be silenced by multiple methylation of CpG sites in the CpG islands of their promoters.[11] Even if silencing of a gene is initiated by another mechanism, this often is followed by methylation of CpG sites in the promoter CpG island to stabilize the silencing of the gene.[11] On the other hand, hypomethylation of CpG islands in promoters can result in gene over-expression.
Causes of DNA hypermethylation are:
- Mediation of mutated K-ras induced jun protein (Serra RW. et al. 2014; Leppä S. et al. 1998)
- the inhibitory effect of lnRNA on miRNAs causing demethylation - their "absorption" in the sponge effect or direct repression of demethylation factors TET1 and TGD (Thakur S. Brenner C. 2017; Ratti M. et al. 2020; Morita S. et al. 2013)
- Activation of DNA methylases (Kwon JJ. et al. 2018)
- Changes in isocitrate dehydrogenase (Christensen BC. et al. 2011)
- Effects of viruses (Wang X. et al. )
Causes of DNA hypomethylation:
- The effect of mutated K-ras on long non-coding RNAs, which, when acting, a) directly inhibits the activity or translation of genes encoding DNA methylases (Sarkar D. et al. 2015) b) rather, "sponges" absorb miRNAs (Ratti M. et al. 2020 ), which should ensure the functioning of DNA methylases
- The effect of mutated K-Ras through the activation of the myc-ODC axis, the mTor complex, with the consequence of the synthesis of polyamines, the activation of which, figuratively speaking, "pumps out" single-carbon fragments from the Methionine cycle and creates a lack of substrate for DNA methylation, leading to a hypomethylated state of DNA (Урба К. 1991 )
- Changes in the activity of methylases DNMT1/3A/3B, their relocalization (Hoffmann MJ, Schulz WA. 2005; Nishiyama A. et al. 2021)
- Changes in TET performance (Nishiyama A. et al. 2021)
- Changes in the synthesis of SAM from methionine due to changes in the enzymes MAT (Frau M. et al. 2013)
- Changes in serine catabolism (Snell K., Weber G. 1986), causing more intensive removal of homocysteine from the methionine cycle, when serine binds to homocysteine (Урба К. 1991)
- Other, unspecified reasons for supplying the Met cycle with single-carbon fragments, causing e.g. "methyl trap" phenomenon (Shane B. Stokstad EL. 1985; Zheng Y, Cantley LC. 2019), sietin and with disorders of vitamin B12 metabolism, disruption of the spare methionine resynthesis pathway (Ouyang Y. et al. 2020; Ozyerli-Goknar E, Bagci-Onder T. 2021; Barekatain, Yasaman et al. 2021) or other monocarbon fragment metabolism disorders (Urba K. 1991). | 1 | Applied and Interdisciplinary Chemistry |
In eukaryotes, most of the newly synthesized secretory proteins are transported from the ER to the Golgi apparatus. If these proteins have a particular 4-amino-acid retention sequence for the ERs lumen, KDEL, on their C-terminus, they are retained in the ERs lumen or are routed back to the ER's lumen (in instances where they escape) via interaction with the KDEL receptor in the Golgi apparatus. If the signal is KKXX, the retention mechanism to the ER will be similar but the protein will be transmembranal. | 1 | Applied and Interdisciplinary Chemistry |
In pyrotechnics, it is used as fuel to make special mixtures, e.g. for production of smokes, in flash compositions, and in percussion caps. Specification for pyrotechnic calcium silicide is MIL-C-324C. In some mixtures it may be substituted with ferrosilicon. Silicon-based fuels are used in some time delay mixtures, e.g. for controlling of explosive bolts, hand grenades, and infrared decoys. Smoke compositions often contain hexachloroethane; during burning they produce silicon tetrachloride, which, like titanium tetrachloride used in smoke-screens, reacts with air moisture and produces dense white fog. Gum arabic is used in some mixtures to inhibit calcium silicide decomposition. | 1 | Applied and Interdisciplinary Chemistry |
The euplotid nuclear code (translation table 10) is the genetic code used by Euplotidae. The euplotid code is a socalled "symmetrical code", which results from the symmetrical distribution of the codons. This symmetry allows for arythmic exploration of the codon distribution. In 2013, shCherbak and Makukov, reported that "the patterns are shown to match the criteria of an intelligent signal." | 1 | Applied and Interdisciplinary Chemistry |
The lac repressor (LacI) operates by a helix-turn-helix motif in its DNA-binding domain, binding base-specifically to the major groove of the operator region of the lac operon, with base contacts also made by residues of symmetry-related alpha helices, the "hinge" helices, which bind deeply in the minor groove. This bound repressor can reduce transcription of the Lac proteins by occluding the RNA polymerase binding site or by prompting DNA looping. When lactose is present, allolactose binds to the lac repressor, causing an allosteric change in its shape. In its changed state, the lac repressor is unable to bind tightly to its cognate operator. Thus, the gene is mostly off in the absence of inducer and mostly on in the presence of inducer, although the degree of gene expression depends on the number of repressors in the cell and on the repressors DNA-binding affinity. Isopropyl β-D-1-thiogalactopyranoside (IPTG) is a commonly used allolactose mimic which can be used to induce transcription of genes being regulated by lac' repressor. | 1 | Applied and Interdisciplinary Chemistry |
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