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IMFP data can be collected from the National Institute of Standards and Technology (NIST) Electron Inelastic-Mean-Free-Path Database or the NIST Database for the Simulation of Electron Spectra for Surface Analysis (SESSA). The data contains IMFPs determined by EPES for energies below 2 keV. Otherwise, IMFPs can be determined from the TPP-2M or the S1 formula. | 0 | Theoretical and Fundamental Chemistry |
An alternative method for analyzing the autocorrelation function can be achieved through an inverse Laplace transform known as CONTIN developed by Steven Provencher. The CONTIN analysis is ideal for heterodisperse, polydisperse, and multimodal systems that cannot be resolved with the cumulant method. The resolution for separating two different particle populations is approximately a factor of five or higher and the difference in relative intensities between two different populations should be less than 1:10. | 0 | Theoretical and Fundamental Chemistry |
Biophysical organic chemistry is a term used when attempting to describe intimate details of molecular recognition by bioorganic chemistry.
Natural product chemistry is the process of Identifying compounds found in nature to determine their properties. Compound discoveries have and often lead to medicinal uses, development of herbicides and insecticides. | 1 | Applied and Interdisciplinary Chemistry |
First a strongly hydrophobic essential oil such as trans-anethole is dissolved in a water-miscible solvent, such as ethanol, and the ethanol itself forms a solution (a homogenous mixture) with water.
If then the concentration of ethanol is lowered by addition of more water the hydrophobic substance precipitates from the solution and forms an emulsion with the remaining ethanol-water-mixture. The tiny droplets of the substance in the emulsion scatter light and thus make the mixture appear white.
Oil-in-water emulsions are not normally stable. Oil droplets coalesce until complete phase separation is achieved at macroscopic levels. Addition of a small amount of surfactant or the application of high shear rates (strong stirring) can stabilize the oil droplets.
In a water-rich ouzo mixture the droplet coalescence is dramatically slowed without mechanical agitation, dispersing agents, or surfactants. It forms a stable homogeneous fluid dispersion by liquid–liquid nucleation. The size of the droplets when measured by small-angle neutron scattering was found to be on the order of a micron.
Using dynamic light scattering, Sitnikova et al. showed that the droplets of oil in the emulsion grow by Ostwald ripening, and that droplets do not coalesce. The Ostwald ripening rate is observed to diminish with increasing ethanol concentrations until the droplets stabilize in size with an average diameter of .
Based on thermodynamic considerations of the multi-component mixture, the emulsion derives its stability from trapping between the binodal and spinodal curves in the phase diagram. However, the microscopic mechanisms responsible for the observed slowing of Ostwald ripening rates at increasing ethanol concentrations appear not fully understood. | 0 | Theoretical and Fundamental Chemistry |
The Hertz–Knudsen equation describes the non-dissociative adsorption of a gas molecule on a surface by expressing the variation of the number of molecules impacting on the surfaces per unit of time as a function of the pressure of the gas and other parameters which characterise both the gas phase molecule and the surface:
where:
Since the equation result has the units of s it can be assimilated to a rate constant for the adsorption process. | 0 | Theoretical and Fundamental Chemistry |
In general, ligands are viewed as electron donors and the metals as electron acceptors, i.e., respectively, Lewis bases and Lewis acids. This description has been semi-quantified in many ways, e.g. ECW model. Bonding is often described using the formalisms of molecular orbital theory.
Ligands and metal ions can be ordered in many ways; one ranking system focuses on ligand hardness (see also hard/soft acid/base theory). Metal ions preferentially bind certain ligands. In general, hard metal ions prefer weak field ligands, whereas soft metal ions prefer strong field ligands. According to the molecular orbital theory, the HOMO (Highest Occupied Molecular Orbital) of the ligand should have an energy that overlaps with the LUMO (Lowest Unoccupied Molecular Orbital) of the metal preferential. Metal ions bound to strong-field ligands follow the Aufbau principle, whereas complexes bound to weak-field ligands follow Hund's rule.
Binding of the metal with the ligands results in a set of molecular orbitals, where the metal can be identified with a new HOMO and LUMO (the orbitals defining the properties and reactivity of the resulting complex) and a certain ordering of the 5 d-orbitals (which may be filled, or partially filled with electrons). In an octahedral environment, the 5 otherwise degenerate d-orbitals split in sets of 3 and 2 orbitals (for a more in-depth explanation, see crystal field theory):
*3 orbitals of low energy: d, d and d and
*2 orbitals of high energy: d−y</sub>.
The energy difference between these 2 sets of d-orbitals is called the splitting parameter, Δ. The magnitude of Δ is determined by the field-strength of the ligand: strong field ligands, by definition, increase Δ more than weak field ligands. Ligands can now be sorted according to the magnitude of Δ (see the table below). This ordering of ligands is almost invariable for all metal ions and is called spectrochemical series.
For complexes with a tetrahedral surrounding, the d-orbitals again split into two sets, but this time in reverse order:
*2 orbitals of low energy: d−y</sub> and
*3 orbitals of high energy: d, d and d.
The energy difference between these 2 sets of d-orbitals is now called Δ. The magnitude of Δ is smaller than for Δ, because in a tetrahedral complex only 4 ligands influence the d-orbitals, whereas in an octahedral complex the d-orbitals are influenced by 6 ligands. When the coordination number is neither octahedral nor tetrahedral, the splitting becomes correspondingly more complex. For the purposes of ranking ligands, however, the properties of the octahedral complexes and the resulting Δ has been of primary interest.
The arrangement of the d-orbitals on the central atom (as determined by the strength of the ligand), has a strong effect on virtually all the properties of the resulting complexes. E.g., the energy differences in the d-orbitals has a strong effect in the optical absorption spectra of metal complexes. It turns out that valence electrons occupying orbitals with significant 3 d-orbital character absorb in the 400–800 nm region of the spectrum (UV–visible range). The absorption of light (what we perceive as the color) by these electrons (that is, excitation of electrons from one orbital to another orbital under influence of light) can be correlated to the ground state of the metal complex, which reflects the bonding properties of the ligands. The relative change in (relative) energy of the d-orbitals as a function of the field-strength of the ligands is described in Tanabe–Sugano diagrams.
In cases where the ligand has low energy LUMO, such orbitals also participate in the bonding. The metal–ligand bond can be further stabilised by a formal donation of electron density back to the ligand in a process known as back-bonding. In this case a filled, central-atom-based orbital donates density into the LUMO of the (coordinated) ligand. Carbon monoxide is the preeminent example a ligand that engages metals via back-donation. Complementarily, ligands with low-energy filled orbitals of pi-symmetry can serve as pi-donor. | 0 | Theoretical and Fundamental Chemistry |
Porous turf, if properly constructed, can be used for occasional parking like that at churches and stadia. Plastic turf reinforcing grids can be used to support the increased load. Living turf transpires water, actively counteracting the "heat island" with what appears to be a green open lawn. | 1 | Applied and Interdisciplinary Chemistry |
Azomethine ylides are nitrogen-based 1,3-dipoles, consisting of an iminium ion next to a carbanion. They are used in 1,3-dipolar cycloaddition reactions to form five-membered heterocycles, including pyrrolidines and pyrrolines. These reactions are highly stereo- and regioselective, and have the potential to form four new contiguous stereocenters. Azomethine ylides thus have high utility in total synthesis, and formation of chiral ligands and pharmaceuticals. Azomethine ylides can be generated from many sources, including aziridines, imines, and iminiums. They are often generated in situ, and immediately reacted with dipolarophiles. | 0 | Theoretical and Fundamental Chemistry |
Active blue roof systems control the rate at which water drains from a rooftop through mechanical means. Sometimes referred to as automated roof runoff management systems, active blue roofs use valve configurations and controls to monitor and regulate the discharge of stormwater runoff from roofs. Water ponded on the roof can be released in several ways, including via a pneumatically or hydraulically actuated pinch valve, an electronically controlled valve connected to a timer, or manually opening the valve. Active blue roofs for stormwater detention using forecast integration were first proposed in 2008. | 1 | Applied and Interdisciplinary Chemistry |
Molecular fly-by collisions take little time, something like 10 s.
Optical transition of collisional complexes of molecules generate spectral
"lines" that are very broad - roughly five orders of magnitude broader
than the most familiar "ordinary" spectral lines (Heisenberg's uncertainty
relation). The resulting spectral "lines" usually strongly
overlap so that collision-induced spectral bands typically appear as continua
(as opposed to the bands of often discernible lines of ordinary molecules).
Collision-induced spectra appear at the frequencies of the rotovibrational and
electronic transition bands of the unperturbed molecules, and also at sums and
differences of such transition frequencies: simultaneous transitions in two (or
more) interacting molecules are well known to generate optical transitions of
molecular complexes. | 0 | Theoretical and Fundamental Chemistry |
The concept of pressure is central to the study of both fluid statics and fluid dynamics. A pressure can be identified for every point in a body of fluid, regardless of whether the fluid is in motion or not. Pressure can be measured using an aneroid, Bourdon tube, mercury column, or various other methods.
Some of the terminology that is necessary in the study of fluid dynamics is not found in other similar areas of study. In particular, some of the terminology used in fluid dynamics is not used in fluid statics. | 1 | Applied and Interdisciplinary Chemistry |
Calcareous is used as an adjectival term applied to anatomical structures which are made primarily of calcium carbonate, in animals such as gastropods, i.e., snails, specifically in relation to such structures as the operculum, the clausilium, and the love dart. The term also applies to the calcium carbonate tests of, often, more-or-less microscopic Foraminifera. Not all tests are calcareous; diatoms and radiolaria have siliceous tests.
The molluscs are calcareous organisms, as are the calcareous sponges (Calcarea), that have spicules which are made of calcium carbonate.
Additionally, reef-building corals, or Scleractinia, are calcareous organisms that form their rigid skeletal structure through the precipitation of aragonite (i.e., a polymorph of calcium carbonate). | 0 | Theoretical and Fundamental Chemistry |
Arylsulfonic acids are susceptible to hydrolysis, the reverse of the sulfonation reaction. Whereas benzenesulfonic acid hydrolyzes above 200 °C, most related derivatives are easier to hydrolyze. Thus, heating aryl sulfonic acids in aqueous acid produces the parent arene. This reaction is employed in several scenarios. In some cases the sulfonic acid serves as a water-solubilizing protecting group, as illustrated by the purification of para-xylene via its sulfonic acid derivative. In the synthesis of 2,6-dichlorophenol, phenol is converted to its 4-sulfonic acid derivative, which then selectively chlorinates at the positions flanking the phenol. Hydrolysis releases the sulfonic acid group. | 0 | Theoretical and Fundamental Chemistry |
A third element was presently supplied in the rich repertory of decorative motives, Egyptian and Assyrian, that was brought to Europe by Phoenician traders or fetched from Asia by adventurous Greeks. A vast amount of oriental merchandise found its way into Greece and Italy around 800 BC. There is some uncertainty about the place of manufacture of much of the surviving bronze work, but the same doubt serves to emphasize the close resemblance that these pieces, Phoenician, Greek or Etruscan, bear to their Assyrian or Egyptian models. Foremost among them are the bowls and shields from the Idaean cave in Crete. These interesting bowls are embossed with simple bands of animals, the shields with bold and complicated designs of purely oriental character. It is unlikely that a Greek craftsman in this vigorous Geometric age could suppress his style and produce mechanical copies such as these. So in Etruscan graves beside inscribed Phoenician bowls there have been found great cauldrons, adorned with jutting heads of lions and griffins, and set on conical stands which are embossed with Assyrian winged monsters. | 1 | Applied and Interdisciplinary Chemistry |
V̇O max is expressed either as an absolute rate in (for example) litres of oxygen per minute (L/min) or as a relative rate in (for example) millilitres of oxygen per kilogram of the body mass per minute (e.g., mL/(kg·min)). The latter expression is often used to compare the performance of endurance sports athletes. However, V̇O max generally does not vary linearly with body mass, either among individuals within a species or among species, so comparisons of the performance capacities of individuals or species that differ in body size must be done with appropriate statistical procedures, such as analysis of covariance. | 1 | Applied and Interdisciplinary Chemistry |
Quasi-equilibrium is different from classical chemical equilibrium, but can be described using a similar thermodynamic treatment. Consider the reaction below
where complete equilibrium is achieved between all the species in the system including activated complexes, [AB] . Using statistical mechanics, concentration of [AB] can be calculated in terms of the concentration of A and B.
TST assumes that even when the reactants and products are not in equilibrium with each other, the activated complexes are in quasi-equilibrium with the reactants. As illustrated in Figure 2, at any instant of time, there are a few activated complexes, and some were reactant molecules in the immediate past, which are designated [AB] (since they are moving from left to right). The remainder of them were product molecules in the immediate past ([AB]).
In TST, it is assumed that the flux of activated complexes in the two directions are independent of each other. That is, if all the product molecules were suddenly removed from the reaction system, the flow of [AB] stops, but there is still a flow from left to right. Hence, to be technically correct, the reactants are in equilibrium only with [AB], the activated complexes that were reactants in the immediate past. | 0 | Theoretical and Fundamental Chemistry |
Construction on bay mud sites is difficult because of the soil's low strength and high compressibility. Very lightweight buildings can be constructed on bay mud sites if there is a thick enough layer of non-bay-mud soil above the bay mud, but buildings which impose significant loads must be supported on deep foundations bearing on stiffer layers below the bay mud, or obtaining support from friction in the bay mud. Even with deep foundations, difficulties arise because the surrounding ground will likely settle over time, potentially damaging utility connections to the building and causing the entryway to sink below street level.
A number of notable buildings have been constructed over bay muds, typically employing special mitigation designs to withstand seismic risks and settlement issues. Complicating design issues, fill (beginning about 1850 CE) is sometimes found deposited on the surface level. For example, the Dakin Building in Brisbane, California, was designed in 1985 to sit on piles 150 feet deep, anchoring to the Franciscan formation, below the bay muds and through an upper fill layer. Furthermore, the structures entrance ramp has been set on a giant hinge to allow the surrounding land to settle, while the building absolute height remains constant. The Crowne Plaza high-rise hotel in Burlingame, California was also designed to sit over bay muds, as was the Westin Hotel in Millbrae, California, and Trinity Church in Bostons Copley Square. Indeed, Boston's entire Back Bay district is named for the tidal bay that it now covers. Logan International Airport and the San Francisco International Airport are also constructed over bay mud. | 1 | Applied and Interdisciplinary Chemistry |
Hydrogen embrittlement (HE), also known as hydrogen-assisted cracking or hydrogen-induced cracking (HIC), is a reduction in the ductility of a metal due to absorbed hydrogen. Hydrogen atoms are small and can permeate solid metals. Once absorbed, hydrogen lowers the stress required for cracks in the metal to initiate and propagate, resulting in embrittlement. Hydrogen embrittlement occurs most notably in steels, as well as in iron, nickel, titanium, cobalt, and their alloys. Copper, aluminium, and stainless steels are less susceptible to hydrogen embrittlement.
The essential facts about the nature of hydrogen embrittlement have been known since the 19th century.
Hydrogen embrittlement is maximised at around room temperature in steels, and most metals are relatively immune to hydrogen embrittlement at temperatures above 150 °C. Hydrogen embrittlement requires the presence of both atomic ("diffusible") hydrogen and a mechanical stress to induce crack growth, although that stress may be applied or residual. Hydrogen embrittlement increases at lower strain rates. In general, higher-strength steels are more susceptible to hydrogen embrittlement than mid-strength steels.
Metals can be exposed to hydrogen from two types of sources: gaseous hydrogen and hydrogen chemically generated at the metal surface. Gaseous hydrogen is molecular hydrogen and does not cause embrittlement though it can cause hot hydrogen attack (see below). It is the atomic hydrogen from chemical attack which causes embrittlement because the atomic hydrogen dissolves quickly into the metal at room temperature. Gaseous hydrogen is found in pressure vessels and pipelines. Electrochemical sources of hydrogen include acids (as may be encountered during pickling, etching, or cleaning), corrosion (typically due to aqueous corrosion or cathodic protection), and electroplating. Hydrogen can be introduced into the metal during manufacturing by the presence of moisture during welding or while the metal is molten. The most common causes of failure in practice are poorly-controlled electroplating or damp welding rods.
Hydrogen embrittlement as a term can be used to refer specifically to the embrittlement that occurs in steels and similar metals at relatively low hydrogen concentrations, or it can be used to encompass all embrittling effects that hydrogen has on metals. These broader embrittling effects include hydride formation, which occurs in titanium and vanadium but not in steels, and hydrogen-induced blistering, which only occurs at high hydrogen concentrations and does not require the presence of stress. However, hydrogen embrittlement is almost always distinguished from high temperature hydrogen attack (HTHA), which occurs in steels at temperatures above 400 °C and involves the formation of methane pockets. The mechanisms (there are many) by which hydrogen causes embrittlement in steels are not comprehensively understood and continue to be explored and studied. | 0 | Theoretical and Fundamental Chemistry |
Empirical scales are based on the measurement of physical parameters that express the property of interest to be measured through some formal, most commonly a simple linear, functional relationship. For the measurement of temperature, the formal definition of thermal equilibrium in terms of the thermodynamic coordinate spaces of thermodynamic systems, expressed in the zeroth law of thermodynamics, provides the framework to measure temperature.
All temperature scales, including the modern thermodynamic temperature scale used in the International System of Units, are calibrated according to thermal properties of a particular substance or device. Typically, this is established by fixing two well-defined temperature points and defining temperature increments via a linear function of the response of the thermometric device. For example, both the old Celsius scale and Fahrenheit scale were originally based on the linear expansion of a narrow mercury column within a limited range of temperature, each using different reference points and scale increments.
Different empirical scales may not be compatible with each other, except for small regions of temperature overlap. If an alcohol thermometer and a mercury thermometer have the same two fixed points, namely the freezing and boiling point of water, their readings will not agree with each other except at the fixed points, as the linear 1:1 relationship of expansion between any two thermometric substances may not be guaranteed.
Empirical temperature scales are not reflective of the fundamental, microscopic laws of matter. Temperature is a universal attribute of matter, yet empirical scales map a narrow range onto a scale that is known to have a useful functional form for a particular application. Thus, their range is limited. The working material only exists in a form under certain circumstances, beyond which it no longer can serve as a scale. For example, mercury freezes below 234.32 K, so temperatures lower than that cannot be measured in a scale based on mercury. Even ITS-90, which interpolates among different ranges of temperature, has a range of only 0.65 K to approximately 1358 K (−272.5 °C to 1085 °C). | 0 | Theoretical and Fundamental Chemistry |
Drugs or toxic chemicals are useful in killing pathogenic bacteria or tumor cells, and studying how they mechanistically develop tolerance to a wide range of drugs can improve anti-bacterial and cancer therapeutics. Pdr5p has a similar mechanism of actions and functions to human multidrug resistance protein, whose overexpression is shown to provide chemical tolerance to cancer cells. Studying Pdr5p and how it is regulated by Pdr1p in yeast can give insights into how multi drug resistance occurs in mammals.
By using pdr1-3 and fusing the promoter of Pdr5p to genes that code for membrane proteins of interests, yeast membrane proteins such as Pdr5p, Yor1, and Drs2 can be expressed highly so that they can be efficiently cloned and purified for further studies. | 1 | Applied and Interdisciplinary Chemistry |
11β-hydroxylase has strong catalytic activity during conversion of 11-deoxycortisol to cortisol and 11-deoxycorticosterone to corticosterone, by catalyzing the hydroxylation of carbon hydrogen bond at 11-beta position. Note the extra "–OH" added at the 11 position (near the center, on ring "C"): | 1 | Applied and Interdisciplinary Chemistry |
Glycoconjugate is the covalently bonded product of oligosaccharides to the biomolecules such as proteins and lipids. They play indispensable role in the biological activities of mammalian cells from energy generation to cell signalling. These glycoconjugates with short oligosaccharide structures are important for the characterization and purification in the course glycoconjucate vaccine developements. Therefore, research in the engineering of the glycosyl precursors that create oligosaccharides with controlled size is important in carbohydrate synthesis. | 0 | Theoretical and Fundamental Chemistry |
A grant of £670,000 was awarded in 1985 by the then Science and Engineering Research Council (SERC) to establish a national Mass Spectrometry Center at Swansea University to provide an analytical service to British Universities. It was officially opened in April 1987 by Lord Callaghan. In 2002, the center was enlarged and the new laboratories were opened by Lord Morgan. Following successful £3,000,000 contract renewal Edwina Hart, the Minister for Economy, Science and Transport, officially re-opened the EPSRC National Research Facility after refurbishment in 2015. | 0 | Theoretical and Fundamental Chemistry |
Analyses are done to assist in design, operation, maintenance and optimization of water distribution systems. There are two main types of analyses: hydraulic, and water quality behavior as it flows through a water distribution system. Optimizing the design of water distribution networks is a complex task. However, a large number of methods have already been proposed, mainly based on metaheuristics. Employing mathematical optimization techniques can lead to substantial construction savings in these kinds of infrastructures. | 1 | Applied and Interdisciplinary Chemistry |
All metal castings experience segregation to some extent, and a distinction is made between macrosegregation and microsegregation. Microsegregation refers to localized differences in composition between dendrite arms, and can be significantly reduced by a homogenizing heat treatment. This is possible because the distances involved (typically on the order of 10 to 100 μm) are sufficiently small for diffusion to be a significant mechanism. This is not the case in macrosegregation. Therefore, macrosegregation in metal castings cannot be remedied or removed using heat treatment. | 0 | Theoretical and Fundamental Chemistry |
Decellularization (also spelled decellularisation in British English) is the process used in biomedical engineering to isolate the extracellular matrix (ECM) of a tissue from its inhabiting cells, leaving an ECM scaffold of the original tissue, which can be used in artificial organ and tissue regeneration. Organ and tissue transplantation treat a variety of medical problems, ranging from end organ failure to cosmetic surgery. One of the greatest limitations to organ transplantation derives from organ rejection caused by antibodies of the transplant recipient reacting to donor antigens on cell surfaces within the donor organ. Because of unfavorable immune responses, transplant patients suffer a lifetime taking immunosuppressing medication. Stephen F. Badylak pioneered the process of decellularization at the McGowan Institute for Regenerative Medicine at the University of Pittsburgh. This process creates a natural biomaterial to act as a scaffold for cell growth, differentiation and tissue development. By recellularizing an ECM scaffold with a patient’s own cells, the adverse immune response is eliminated. Nowadays, commercially available ECM scaffolds are available for a wide variety of tissue engineering. Using peracetic acid to decellularize ECM scaffolds have been found to be false and only disinfects the tissue.
With a wide variety of decellularization-inducing treatments available, combinations of physical, chemical, and enzymatic treatments are carefully monitored to ensure that the ECM scaffold maintains the structural and chemical integrity of the original tissue. Scientists can use the acquired ECM scaffold to reproduce a functional organ by introducing progenitor cells, or adult stem cells (ASCs), and allowing them to differentiate within the scaffold to develop into the desired tissue. The produced organ or tissue can be transplanted into a patient. In contrast to cell surface antibodies, the biochemical components of the ECM are conserved between hosts, so the risk of a hostile immune response is minimized. Proper conservation of ECM fibers, growth factors, and other proteins is imperative to the progenitor cells differentiating into the proper adult cells. The success of decellularization varies based on the components and density of the applied tissue and its origin. The applications to the decellularizing method of producing a biomaterial scaffold for tissue regeneration are present in cardiac, dermal, pulmonary, renal, and other types of tissues. Complete organ reconstruction is still in the early levels of development. | 1 | Applied and Interdisciplinary Chemistry |
When the two intersecting planes are described in terms of Cartesian coordinates by the two equations
the dihedral angle, between them is given by:
and satisfies It can easily be observed that the angle is independent of and .
Alternatively, if and are normal vector to the planes, one has
where is the dot product of the vectors and is the product of their lengths.
and b and through b and b, respectively. -->
The absolute value is required in above formulas, as the planes are not changed when changing all coefficient signs in one equation, or replacing one normal vector by its opposite.
However the absolute values can be and should be avoided when considering the dihedral angle of two half planes whose boundaries are the same line. In this case, the half planes can be described by a point of their intersection, and three vectors , and such that , and belong respectively to the intersection line, the first half plane, and the second half plane. The dihedral angle of these two half planes is defined by
and satisfies In this case, switching the two half-planes gives the same result, and so does replacing with In chemistry (see below), we define a dihedral angle such that replacing with changes the sign of the angle, which can be between and . | 0 | Theoretical and Fundamental Chemistry |
The utility of palladium-catalyzed cross-coupling reactions is enhanced by the use of N-heterocyclic carbene ligands. Indeed, Pd-NHC complexes have been proven effective in Suzuki-Miyaura, Negishi, Sonogashira, Kumada-Tamao-Corriu, Hiyama, and Stille cross-coupling. Compared to the corresponding Pd-phosphine catalysts, Pd-NHC catalysts can be faster, exhibit broader substrate scope, all with higher turnover numbers. | 0 | Theoretical and Fundamental Chemistry |
Valve positions are operating conditions determined by the position of the disc or rotor in the valve. Some valves are made to be operated in a gradual change between two or more positions. Return valves and non-return valves allow fluid to move in 2 or 1 directions respectively. | 1 | Applied and Interdisciplinary Chemistry |
Seizures are characterized by high levels of synchronized neuronal activity. One important regulator of neuronal activity is the hyperpolarizing A-type current mediated by potassium channel KV4.2. miR-324-5p downregulates KV4.2, exacerbating conditions that lead to seizure onset, and downregulation of miR-324-5p in mouse models of epilepsy is seizure-suppressive.
Changes in miRNA expression are seen in epileptogenesis and in other disease pathologies. In epilepsy, miR-324-5p expression has been shown to increase and decrease at different timepoints and loci.
Importantly, miR-324-5p has increased association with the RISC complex following seizure in mice, indicating more suppressive activity.
Overall, this suggests that miR-324-5p plays a role in epileptogenesis via targeting of potassium channel KV4.2. | 1 | Applied and Interdisciplinary Chemistry |
Selenium deficiency can occur in patients with severely compromised intestinal function, those undergoing total parenteral nutrition, and in those of advanced age (over 90). Also, people dependent on food grown from selenium-deficient soil are at risk. Although New Zealand has low levels of selenium in its soil, adverse health effects have not been detected.
Selenium deficiency as defined by low (<60% of normal) selenoenzyme activity levels in brain and endocrine tissues only occurs when a low selenium status is linked with an additional stress, such as high exposures to mercury or as a result of increased oxidant stress due to vitamin E deficiency.
Selenium interacts with other nutrients, such as iodide and vitamin E. The interaction is observed in the etiology of many deficiency diseases in animals, and pure selenium deficiency is rare. The effect of selenium deficiency on health remains uncertain, particularly in relation to Kashin-Beck disease. | 1 | Applied and Interdisciplinary Chemistry |
The clearest waters occur in oligotrophic ocean regions such as the South Pacific Gyre, tropical coastal waters, glacially-formed lakes with low sediment inputs, and lakes with some kind of natural filtration occurring at the inflow point. Blue Lake in New Zealand holds the record for the highest water clarity of any lake, with a Secchi depth of 230 to 260 feet. Blue Lake is fed by an underground passage from a nearby lake, which acts as a natural filter. Some other very clear water bodies are Lake Tahoe between California and Nevada in the United States, Lake Baikal in Russia, and Crater Lake in Oregon in the United States.
In tropical coastal waters, the water is clear thanks to low nutrient inputs, low primary production, and coral reefs acting as a natural buffer that keep sediments from getting resuspended.
The clearest recorded water on Earth is either Blue Lake, New Zealand or the Weddell Sea near Antarctica, both of which claim Secchi depths of 80 meters (230 to 260 feet). | 0 | Theoretical and Fundamental Chemistry |
Sodium laureth sulfate, or sodium lauryl ether sulfate (SLES), is a detergent and surfactant found in many personal care products (soaps, shampoos, toothpastes, etc.). It is an inexpensive and effective foamer. Sodium lauryl sulfate (also known as sodium dodecyl sulfate or SDS) and ammonium lauryl sulfate (ALS) are commonly used alternatives to SLES in consumer products. | 0 | Theoretical and Fundamental Chemistry |
The punkah (fan) was used in India about 500 BCE. It was a handheld fan made from bamboo strips or other plant fiber, that could be rotated or fanned to move air. During British rule, the word came to be used by Anglo-Indians to mean a large swinging flat fan, fixed to the ceiling and pulled by a servant called the punkawallah.
For purposes of air conditioning, the Han dynasty craftsman and engineer Ding Huan (fl. 180 CE) invented a manually operated rotary fan with seven wheels that measured 3 m (10 ft) in diameter; in the 8th century, during the Tang dynasty (618–907), the Chinese applied hydraulic power to rotate the fan wheels for air conditioning, while the rotary fan became even more common during the Song dynasty (960–1279).
During the Heian period (794-1185) in Japan, fans adapted the role of symbolizing social class as well as a mechanical role. The tessen, a Japanese fan used in Feudal times, was a dangerous weapon hidden in plain sight in the shape of a regular fan, a weapon used by samurais when katanas were not ideal.
In the 17th century, the experiments of scientists including Otto von Guericke, Robert Hooke and Robert Boyle, established the basic principles of vacuum and airflow. The English architect Sir Christopher Wren applied an early ventilation system in the Houses of Parliament that used bellows to circulate air. Wren's design was the catalyst for much later improvement and innovation. The first rotary fan used in Europe was for mine ventilation during the 16th century, as illustrated by Georg Agricola (1494–1555).
John Theophilus Desaguliers, a British engineer, demonstrated the successful use of a fan system to draw out stagnant air from coal mines in 1727—ventilation was particularly important in coal mines to prevent asphyxiation—and soon afterwards he installed a similar apparatus in Parliament. The civil engineer John Smeaton, and later John Buddle installed reciprocating air pumps in the mines in the North of England, though the machinery was liable to breaking down. | 0 | Theoretical and Fundamental Chemistry |
EPE foams were first manufactured in the 1970s.
Production of the PE beads is usually by extrusion, followed by chopping, producing a pellet. Autoclave expansion is the most common route the bead foam. Butane or pentane is often used as a blowing agent (before 1992 CFCs may have been used). Depending on the specific process uses the beads may be cross-linked either by electron beam irradiation (see Electron beam processing), or by the addition of a chemical agent such as dicumyl peroxide.
An alternate route (JSP Process) to the beads uses carbon dioxide as a blowing agent which is impregnated into the pellets in an autoclave at a temperature close to the plastic's crystalline melting point. The pellets are foamed by "flashing" into the (lower pressure) atmosphere to expand.
Finally molding is done by steam chest compression molding; usually the low pressure variant of the process is used, though the high pressure variant may be used for HDPE based EPE foams. | 0 | Theoretical and Fundamental Chemistry |
Sometimes, stereoelectronic effects can win over extreme steric clash. In a similar cyclobutene ring-opening reaction, the trimethylsilyl group, which is very bulky, still favors the inward rotation. The stereoelectronic effect, which is the interaction shown above when the acceptor orbital is the σ*(Si–CH), appears to be a more predominant factor in determining the reaction selectivity against the steric hindrance and even wins over the penalty of the disrupted conjugation system of the product due to steric clash.
Furthermore, the acceptor orbitals are not limited to the antibonding orbitals of carbon-heteroatom bonds or the empty orbitals; in the following case, the acceptor orbital is the σ*(B–O) orbital. In the six-membered ring transition state, the stereoelectronic interaction is σ(C–X) → σ*(B–O). | 0 | Theoretical and Fundamental Chemistry |
Many tablets today are coated after being pressed. Although sugar-coating was popular in the past, the process has many drawbacks. Modern tablet coatings are polymer and polysaccharide based, with plasticizers and pigments included. Tablet coatings must be stable and strong enough to survive the handling of the tablet, must not make tablets stick together during the coating process, and must follow the fine contours of embossed characters or logos on tablets. Coatings are necessary for tablets that have an unpleasant taste, and a smoother finish makes large tablets easier to swallow. Tablet coatings are also useful to extend the shelf-life of components that are sensitive to moisture or oxidation. Special coatings (for example with pearlescent effects) can enhance brand recognition.
If the active ingredient of a tablet is sensitive to acid, or is irritant to the stomach lining, an enteric coating can be used, which is resistant to stomach acid, and dissolves in the less acidic area of the intestines. Enteric coatings are also used for medicines that can be negatively affected by taking a long time to reach the small intestine, where they are absorbed. Coatings are often chosen to control the rate of dissolution of the drug in the gastrointestinal tract. Some drugs are absorbed better in certain parts of the digestive system. If this part is the stomach, a coating is selected that dissolves quickly and easily in acid. If the rate of absorption is best in the large intestine or colon, a coating is used that is acid resistant and dissolves slowly to ensure that the tablet reaches that point before dispersing. To measure the disintegration time of the tablet coating and the tablet core, automatic disintegration testers are used which are able to determine the complete disintegration process of a tablet by measuring the rest height of the thickness with every upward stroke of the disintegration tester basket.
There are two types of coating machines used in the pharmaceutical industry: coating pans and automatic coaters. Coating pans are used mostly to sugar coat pellets. Automatic coaters are used for all kinds of coatings; they can be equipped with a remote control panel, a dehumidifier, and dust collectors. An explosion-proof design is required for applying coatings that contain alcohol. | 1 | Applied and Interdisciplinary Chemistry |
Section 1.3 explains the rules for writing scientific symbols and names, for example, where to use capital letters or italics, and where their use is incorrect. The typographical rules are extensive, including even such detail as whether "20°C" or "20 °C" is the correct form. | 0 | Theoretical and Fundamental Chemistry |
Adsorption is the adhesion of ions or molecules onto the surface of another phase. Adsorption may occur via physisorption and chemisorption. Ions and molecules can adsorb to many types of surfaces including polymer surfaces. A polymer is a large molecule composed of repeating subunits bound together by covalent bonds. In dilute solution, polymers form globule structures. When a polymer adsorbs to a surface that it interacts favorably with, the globule is essentially squashed, and the polymer has a pancake structure. | 0 | Theoretical and Fundamental Chemistry |
Increased carbon dioxide levels, mostly from burning fossil fuels, are changing ocean chemistry. Global warming and changes in salinity have significant implications for the ecology of marine environments. | 0 | Theoretical and Fundamental Chemistry |
RNA polymerase II (RNAP II and Pol II) is a multiprotein complex that transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. It is one of the three RNAP enzymes found in the nucleus of eukaryotic cells. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to upstream gene promoters and begin transcription. | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics, the Plateau–Rayleigh instability, often just called the Rayleigh instability, explains why and how a falling stream of fluid breaks up into smaller packets with the same volume but less surface area. It is related to the Rayleigh–Taylor instability and is part of a greater branch of fluid dynamics concerned with fluid thread breakup. This fluid instability is exploited in the design of a particular type of ink jet technology whereby a jet of liquid is perturbed into a steady stream of droplets.
The driving force of the Plateau–Rayleigh instability is that liquids, by virtue of their surface tensions, tend to minimize their surface area. A considerable amount of work has been done recently on the final pinching profile by attacking it with self-similar solutions. | 1 | Applied and Interdisciplinary Chemistry |
In the 1950s, Norwegian scientist Scholander set out to explain how Arctic fish can survive in water colder than the freezing point of their blood. His experiments led him to believe there was “antifreeze” in the blood of Arctic fish. Then in the late 1960s, animal biologist Arthur DeVries was able to isolate the antifreeze protein through his investigation of Antarctic fish. These proteins were later called antifreeze glycoproteins (AFGPs) or antifreeze glycopeptides to distinguish them from newly discovered nonglycoprotein biological antifreeze agents (AFPs). DeVries worked with Robert Feeney (1970) to characterize the chemical and physical properties of antifreeze proteins. In 1992, Griffith et al. documented their discovery of AFP in winter rye leaves. Around the same time, Urrutia, Duman and Knight (1992) documented thermal hysteresis protein in angiosperms. The next year, Duman and Olsen noted AFPs had also been discovered in over 23 species of angiosperms, including ones eaten by humans. They reported their presence in fungi and bacteria as well. | 1 | Applied and Interdisciplinary Chemistry |
Because unsaturated alanes are oxygen- and moisture-sensitive, they are most often prepared for immediate use without isolation. However, the method of preparation determines the configuration of the intermediate unsaturated alane, which is directly related to the configuration of the product (transfer of the alkenyl group occurs with retention of configuration). Thus, an understanding of available hydroalumination methods is important for the study of reactions of unsaturated alanes. This second describes the most common methods of hydroalumination, and subsequent chemical reactions that the resulting alkenylalanes may undergo. | 0 | Theoretical and Fundamental Chemistry |
The Nernst–Planck equation is applied in describing the ion-exchange kinetics in soils. It has also been applied to membrane electrochemistry. | 0 | Theoretical and Fundamental Chemistry |
The EBF was founded in the fall of 2006 at the initiative of twelve pharmaceutical companies, all of them having bioanalytical laboratory activities in Europe. The goal of bringing these companies together was to implement a platform for discussions of science and regulatory issues. Views and recommendations following from these discussions are either published in scientific journals, like for example on the controversial and much debated topic of incurred sample reproducibility or presented at international meetings. As of May 2010 the EBF consists of 28 member companies. | 0 | Theoretical and Fundamental Chemistry |
Magnetic nanoparticle synthesis can sometimes lead to a wide range of differently sized particles. The size of particles can influence their usefulness. Specifically, nanoparticles that are less than 10 nm or greater than 200 nm in size tend to be cleared from the body more quickly. | 1 | Applied and Interdisciplinary Chemistry |
Metals bound to so-called triply bonded carbyne, imide, nitride (nitrido), and oxide (oxo) ligands are generally assigned to high oxidation states with low d electron counts. The high oxidation state stabilizes the highly reduced ligands. The low d electron count allow for many bonds between ligands and the metal center. A d metal center can accommodate up to 9 bonds without violating the 18 electron rule, whereas a d species can only accommodate 6 bonds. | 0 | Theoretical and Fundamental Chemistry |
PAC is commonly used as a large capacity vector which allows propagation of large DNA inserts in Escherichia coli. This feature has been commonly used for:
* building genome libraries for human, mouse, etc, helps with projects such as Human Genome Project
* libraries served as the template for gene sequencing (example: used as gene template in mouse gene function analysis)
* genome analysis on specific functions of different genes for more complex organisms (plants, animals etc.)
* facilitate gene expression
Since PAC was derived from phages, PAC and its variants are also useful in the PAC-based phage therapy and antibiotic studies. | 1 | Applied and Interdisciplinary Chemistry |
Restriction enzymes recognize a specific sequence of nucleotides and produce a double-stranded cut in the DNA. The recognition sequences can also be classified by the number of bases in its recognition site, usually between 4 and 8 bases, and the number of bases in the sequence will determine how often the site will appear by chance in any given genome, e.g., a 4-base pair sequence would theoretically occur once every 4^4 or 256bp, 6 bases, 4^6 or 4,096bp, and 8 bases would be 4^8 or 65,536bp. Many of them are palindromic, meaning the base sequence reads the same backwards and forwards. In theory, there are two types of palindromic sequences that can be possible in DNA. The mirror-like palindrome is similar to those found in ordinary text, in which a sequence reads the same forward and backward on a single strand of DNA, as in GTAATG. The inverted repeat palindrome is also a sequence that reads the same forward and backward, but the forward and backward sequences are found in complementary DNA strands (i.e., of double-stranded DNA), as in GTATAC (GTATAC being complementary to CATATG). Inverted repeat palindromes are more common and have greater biological importance than mirror-like palindromes.
EcoRI digestion produces "sticky" ends,
whereas SmaI restriction enzyme cleavage produces "blunt" ends:
Recognition sequences in DNA differ for each restriction enzyme, producing differences in the length, sequence and strand orientation (5 end or 3 end) of a sticky-end "overhang" of an enzyme restriction.
Different restriction enzymes that recognize the same sequence are known as neoschizomers. These often cleave in different locales of the sequence. Different enzymes that recognize and cleave in the same location are known as isoschizomers. | 1 | Applied and Interdisciplinary Chemistry |
Pseudoephedrine is a sympathomimetic amine. Its principal mechanism of action relies on its direct action on the adrenergic receptor system. The vasoconstriction that pseudoephedrine produces is believed to be principally an α-adrenergic receptor response.
Pseudoephedrine acts on α- and β2-adrenergic receptors, to cause vasoconstriction and relaxation of smooth muscle in the bronchi, respectively. α-Adrenergic receptors are located on the muscles lining the walls of blood vessels. When these receptors are activated, the muscles contract, causing the blood vessels to constrict (vasoconstriction). The constricted blood vessels now allow less fluid to leave the blood vessels and enter the nose, throat, and sinus linings, which results in decreased inflammation of nasal membranes, as well as decreased mucus production. Thus, by constriction of blood vessels, mainly those located in the nasal passages, pseudoephedrine causes a decrease in the symptoms of nasal congestion. Activation of β2-adrenergic receptors produces relaxation of smooth muscle of the bronchi, causing bronchial dilation and in turn decreasing congestion (although not fluid) and difficulty breathing. | 0 | Theoretical and Fundamental Chemistry |
The Burgess reagent (methyl N-(triethylammoniumsulfonyl)carbamate) is a mild and selective dehydrating reagent often used in organic chemistry. It was developed in the laboratory of Edward M. Burgess at Georgia Tech.
The Burgess reagent is used to convert secondary and tertiary alcohols with an adjacent proton into alkenes. Dehydration of primary alcohols does not work well. The reagent is soluble in common organic solvents and alcohol dehydration takes place with syn elimination through an intramolecular elimination reaction. The Burgess reagent is a carbamate and an inner salt. A general mechanism is shown below. | 0 | Theoretical and Fundamental Chemistry |
Improvements to this early design included a focus on the weight and wear of the downcomer. The downcomer was originally built with polyurethane-lined steel, and then changed to a high-density polyethylene ("HDPE") construction with seven elements.
The orifice plate used to generate the slurry jet was a high-wear item and its materials of construction were also a focus of the development effort. After testing high-chromium hardened steel and various ceramics, high-density alumina was found to have excellent wear properties, and it became the standard. | 1 | Applied and Interdisciplinary Chemistry |
Lipidomics is the large-scale study of pathways and networks of cellular lipids in biological systems The word "lipidome" is used to describe the complete lipid profile within a cell, tissue, organism, or ecosystem and is a subset of the "metabolome" which also includes other major classes of biological molecules (such as amino acids, sugars, glycolysis & TCA intermediates, and nucleic acids). Lipidomics is a relatively recent research field that has been driven by rapid advances in technologies such as mass spectrometry (MS), nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy, dual polarisation interferometry and computational methods, coupled with the recognition of the role of lipids in many metabolic diseases such as obesity, atherosclerosis, stroke, hypertension and diabetes. This rapidly expanding field complements the huge progress made in genomics and proteomics, all of which constitute the family of systems biology.
Lipidomics research involves the identification and quantification of the thousands of cellular lipid molecular species and their interactions with other lipids, proteins, and other metabolites. Investigators in lipidomics examine the structures, functions, interactions, and dynamics of cellular lipids and the changes that occur during perturbation of the system.
Han and Gross first defined the field of lipidomics through integrating the specific chemical properties inherent in lipid molecular species with a comprehensive mass spectrometric approach. Although lipidomics is under the umbrella of the more general field of "metabolomics", lipidomics is itself a distinct discipline due to the uniqueness and functional specificity of lipids relative to other metabolites.
In lipidomic research, a vast amount of information quantitatively describing the spatial and temporal alterations in the content and composition of different lipid molecular species is accrued after perturbation of a cell through changes in its physiological or pathological state. Information obtained from these studies facilitates mechanistic insights into changes in cellular function. Therefore, lipidomic studies play an essential role in defining the biochemical mechanisms of lipid-related disease processes through identifying alterations in cellular lipid metabolism, trafficking and homeostasis. The growing attention on lipid research is also seen from the initiatives underway of the LIPID Metabolites And Pathways Strategy (LIPID MAPS Consortium). and The European Lipidomics Initiative (ELIfe). | 1 | Applied and Interdisciplinary Chemistry |
Since it is not possible to measure K for all substances, various models have been developed to allow for their prediction, e.g. Quantitative structure–activity relationships (QSAR) or linear free energy relationships (LFER) such as the Hammett equation.
A variant of the UNIFAC system can also be used to estimate octanol-water partition coefficients. | 0 | Theoretical and Fundamental Chemistry |
Reynolds operators are often given by projecting onto an invariant subspace of a group action.
*The "Reynolds operator" considered by was essentially the projection of a fluid flow to the "average" fluid flow, which can be thought of as projection to time-invariant flows. Here the group action is given by the action of the group of time-translations.
*Suppose that G is a reductive algebraic group or a compact group, and V is a finite-dimensional representation of G. Then G also acts on the symmetric algebra SV of polynomials. The Reynolds operator R is the G-invariant projection from SV to the subring SV of elements fixed by G. | 1 | Applied and Interdisciplinary Chemistry |
Neurotrophin mimetics are small molecules or peptide like molecules that can modulate the action of the neurotrophin receptor.
One of the main causes of neurodegeneration involves changes in the expression of neurotrophins (NTs) and/or their receptors (TrkA, TrkB, TrkC and p75NTR). Indeed, these imbalances or changes in their activity, lead to neuronal damage resulting in neurological and neurodegenerative conditions. The therapeutic properties of neurotrophins attracted the focus of many researchers during the years, but the poor pharmacokinetic properties, such as reduced bioavailability and low metabolic stability, the hyperalgesia, the inability to penetrate the blood–brain barrier and the short half-lives render the large neurotrophin proteins not suitable to be implemented as drugs.
For this reason, several efforts have been made to develop neurotrophin mimetics (small molecules and peptidomimetics) that can modulate the action of the neurotrophin receptors (Trks and p75NTR) and possess drug-like pharmacokinetic and pharmacodynamic profiles. Specifically, these mimetics can be classified as TrkA and TrkB receptor agonists and p75NTR modulators/antagonists. | 1 | Applied and Interdisciplinary Chemistry |
Electron crystallography is a method to determine the arrangement of atoms in solids using a transmission electron microscope (TEM). It can involve the use of high-resolution transmission electron microscopy images, electron diffraction patterns including convergent-beam electron diffraction or combinations of these. It has been successful in determining some bulk structures, and also surface structures. Two related methods are low-energy electron diffraction which has solved the structure of many surfaces, and reflection high-energy electron diffraction which is used to monitor surfaces often during growth. | 0 | Theoretical and Fundamental Chemistry |
Different kinds of stimuli result in different responses within the Arabidopsis plant. A wound or damage to the plant causes a wound-activated surface potential (WASP) changes that serve as an alert message to undamaged tissues. This wound response results in a plasma membrane depolarization, H+ and Ca efflux and K+ influx, causing an action potential. This action potential causes Ca cytosolic concentration to increase, therefore sending calcium into the phloem, where the signaling is spread, and as it arrives to systemic tissues. Because of the various stimuli perceived by the plant, abiotic and biotic stress results in different amplitudes, durations, frequencies and localizations of Ca concentrations. These “calcium signatures” encode information about the nature of the stimulus and different signatures are sensed by different sensor proteins. With herbivory being an abiotic stressor, Ca is sensed by the regulatory ubiquitin protein calmodulin, which phosphorylates JAV1. In turn, it ubiquitinates JAV1 so it no longer inhibits the biosynthesis of JA, giving a rapid increase of the JA hormone. This increase signals the defense system to begin transcribing JA inducible defense genes against herbivory. Alert messages are generated and propagated throughout the plant to undamaged tissues through WASPs, Ca, and hormonal signals, such as JA. | 0 | Theoretical and Fundamental Chemistry |
Antibody (or immunoglobulin) structure is made up of two heavy-chains and two light-chains. These chains are held together by disulfide bonds. The arrangement or processes that put together different parts of this antibody molecule play important role in antibody diversity and production of different subclasses or classes of antibodies. The organization and processes take place during the development and differentiation of B cells. That is, the controlled gene expression during transcription and translation coupled with the rearrangements of immunoglobulin gene segments result in the generation of antibody repertoire during development and maturation of B cells. | 1 | Applied and Interdisciplinary Chemistry |
The reaction of an organic substrate with phosgene is called phosgenation. Phosgenation of diols give carbonates (R = H, alkyl, aryl), which can be either linear or cyclic:
An example is the reaction of phosgene with bisphenol A to form polycarbonates. Phosgenation of diamines gives di-isocyanates, like toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). In these conversions, phosgene is used in excess to increase yield and minimize side reactions. The phosgene excess is separated during the work-up of resulting end products and recycled into the process, with any remaining phosgene decomposed in water using activated carbon as the catalyst. Diisocyanates are precursors to polyurethanes. More than 90% of the phosgene is used in these processes, with the biggest production units located in the United States (Texas and Louisiana), Germany, Shanghai, Japan, and South Korea. The most important producers are Dow Chemical, Covestro, and BASF. Phosgene is also used to produce monoisocyanates, used as pesticide precursors (e.g. methyl isocyanate (MIC).
Aside from the widely used reactions described above, phosgene is also used to produce acyl chlorides from carboxylic acids:
For this application, thionyl chloride is commonly used instead of phosgene. | 0 | Theoretical and Fundamental Chemistry |
Most enzyme mimic studies are motivated by a combination of factors, including factors that are unrelated to the enzyme. Several of the factors that are related to the enzyme are listed below.
Defining the active site structure. A number of important active sites are still poorly defined. This includes the oxygen evolving complex and nitrogenase. In an effort to understand these enzymes, small molecule analogs are created and compared to the data which exists for the proteins.
Understanding the active site function. The structure of some enzymes are very well characterized, however, the function of some component of the active site is poorly understood. This is often investigated through site-directed mutagenesis. In addition, the synthesis of a model complex can suggest the function of various components.
Reproducing the enzymes function. A number of enzymes are an interest since they catalyze a reaction chemist find challenging. These reactions include the partial oxidation of a hydrocarbon by methane monooxygenase (MMO) or the oxidation and production of hydrogen by hydrogenase. "Functional" enzyme mimics or bioinspired catalysts are designed with characteristics of the enzyme in hopes of reproducing the enzymes functionality. | 0 | Theoretical and Fundamental Chemistry |
Lithium toxicity, which is also called lithium overdose and lithium poisoning, is the condition of having too much lithium in the blood. This condition also happens in persons that are taking lithium in which the lithium levels are affected by drug interactions in the body.
In acute toxicity, people have primarily gastrointestinal symptoms such as vomiting and diarrhea, which may result in volume depletion. During acute toxicity, lithium distributes later into the central nervous system resulting in mild neurological symptoms, such as dizziness.
In chronic toxicity, people have primarily neurological symptoms which include nystagmus, tremor, hyperreflexia, ataxia, and change in mental status. During chronic toxicity, the gastrointestinal symptoms seen in acute toxicity are less prominent. The symptoms are often vague and nonspecific.
If the lithium toxicity is mild or moderate, lithium dosage is reduced or stopped entirely. If the toxicity is severe, lithium may need to be removed from the body. | 1 | Applied and Interdisciplinary Chemistry |
In covalent imprinting, the template molecule is covalently bonded to the functional monomers that are then polymerized together. After polymerization, the polymer matrix is cleaved from the template molecule, leaving a cavity shaped as the template. Upon rebinding with the original molecule, the binding sites will interact with the target molecule, reestablishing the covalent bonds. During this reestablishment, kinetics associated with bond binding and bond breakage are obtained back. The imprinted molecule is then released from the template, in which it would then rebind with the target molecule, forming the same covalent bonds that were formed before polymerization. Advantages through utilizing this approach include the functional group being solely associated with the binding sites, avoiding any non-specific binding. The imprinted molecule also displays a homogenous distribution of binding sites, increasing the stability of the template-polymer complex. However, there are a few number of compounds that can be used to imprint with template molecules via covalent bonding, such as alcohols, aldehydes and ketones, all of which have high formation kinetics. In some cases, the rebinding of the polymer matrix with the template can be very slow, making this approach time inefficient for applications that require fast kinetics, such as chromatography. | 0 | Theoretical and Fundamental Chemistry |
The Prix Michel-Sarrazin is awarded annually in the Canadian province of Quebec by the Club de Recherches Clinique du Québec to a celebrated Québécois scientist who, by their dynamism and productivity, have contributed in an important way to the advancement of research biomedical. It is named in honour of Michel Sarrazin (1659–1734) who was the first Canadian scientist. | 1 | Applied and Interdisciplinary Chemistry |
The Yeast Metabolome Database is a freely accessible, online database of >2,000 small molecule metabolites found in or produced by Saccharomyces cerevisiae (Baker's yeast). The YMDB contains two kinds of information:
# Chemical information and
# Biochemical information.
The chemical information in YMDB includes 2,027 metabolite structures with detailed metabolite descriptions, extensive chemical classifications, synthesis information and observed/calculated chemical properties. It also contains nearly 4,000 NMR, GC-MS and LC/MS spectra obtained from more than 500 different metabolites. The biochemical information in YMDB includes >1,100 protein (and DNA) sequences and >900 biochemical reactions. The YMDB supports a wide variety of queries including text searches, chemical structure searches, sequence similarity searches and spectral similarity searches. This makes it particularly useful for metabolomic researchers who are studying yeast as a model organism or who are looking into optimizing the production of fermented beverages (wine, beer).
Secondary electrospray ionization-high resolution mass spectrometry SESI-HRMS is a non-invasive analytical technique that allows us to monitor the yeast metabolic activities. SESI-HRMS has found around 300 metabolites in the yeast fermentation process, this suggests that a large number of glucose metabolites are not reported in the literature. | 1 | Applied and Interdisciplinary Chemistry |
At a given point of time, degree distribution , is the probability that a randomly chosen monomer has connected neighbours. The central idea of the random graph theory of gelation is that a cross-linked or branched polymer can be studied separately at two levels: 1) monomer reaction kinetics that predicts and 2) random graph with a given degree distribution. The advantage of such a decoupling is that the approach allows one to study the monomer kinetics with relatively simple rate equations, and then deduce the degree distribution serving as input for a random graph model. In several cases the aforementioned rate equations have a known analytical solution. | 0 | Theoretical and Fundamental Chemistry |
In electrochemistry, concentration polarization denotes the part of the polarization of an electrolytic cell resulting from changes in the electrolyte concentration due to the passage of current through the electrode/solution interface. Here polarization is understood as the shift of the electrochemical potential difference across the cell from its equilibrium value. When the term is used in this sense, it is equivalent to “concentration overpotential”.
the changes in concentration (emergence of concentration gradients in the solution adjacent to the electrode surface) is the difference in the rate of electrochemical reaction at the electrode and the rate of ion migration in the solution from/to the surface. When a chemical species participating in an electrochemical electrode reaction is in short supply, the concentration of this species at the surface decreases causing diffusion, which is added to the migration transport towards the surface in order to maintain the balance of consumption and delivery of that species. | 0 | Theoretical and Fundamental Chemistry |
Walsh diagrams, often called angular coordinate diagrams or correlation diagrams, are representations of calculated orbital binding energies of a molecule versus a distortion coordinate (bond angles), used for making quick predictions about the geometries of small molecules. By plotting the change in molecular orbital levels of a molecule as a function of geometrical change, Walsh diagrams explain why molecules are more stable in certain spatial configurations (e.g. why water adopts a bent conformation).
A major application of Walsh diagrams is to explain the regularity in structure observed for related molecules having identical numbers of valence electrons (e.g. why HO and HS look similar), and to account for how molecules alter their geometries as their number of electrons or spin state changes. Additionally, Walsh diagrams can be used to predict distortions of molecular geometry from knowledge of how the LUMO (Lowest Unoccupied Molecular Orbital) affects the HOMO (Highest Occupied Molecular Orbital) when the molecule experiences geometrical perturbation.
Walsh's rule for predicting shapes of molecules states that a molecule will adopt a structure that best provides the most stability for its HOMO. If a particular structural change does not perturb the HOMO, the closest occupied molecular orbital governs the preference for geometrical orientation. | 0 | Theoretical and Fundamental Chemistry |
Ghodsi Mohammadi Ziarani (born 1964) is an Iranian chemist and Professor of Organic Chemistry at Alzahra University. Mohammadi Ziarani is among the most-cited Iranian researchers and is known for her works on organic chemistry, nanochemistry, multi-component reactions, natural product synthesis, and asymmetric synthesis. | 0 | Theoretical and Fundamental Chemistry |
The Ferrier carbocyclization (or Ferrier II reaction) is an organic reaction that was first reported by the carbohydrate chemist Robert J. Ferrier in 1979. It is a metal-mediated rearrangement of enol ether pyrans to cyclohexanones. Typically, this reaction is catalyzed by mercury salts, specifically mercury(II) chloride.
Several reviews have been published. | 0 | Theoretical and Fundamental Chemistry |
Topography is "classically" applied to inorganic crystals, such a metals and semiconductors. However, it is nowadays applied more and more often also to organic crystals, most notably proteins. Topographic investigations can help to understand and optimize crystal growth processes also for proteins. Numerous studies have been initiated in the last 5–10 years, using both white-beam and plane-wave topography.
Although considerable progress has been achieved, topography on protein crystals remains a difficult discipline: Due to large unit cells, small structure factors and high disorder, diffracted intensities are weak. Topographic imaging therefore requires long exposure times, which may lead to radiation damage of the crystals, generating in the first place the defects which are then imaged. In addition, the low structure factors lead to small Darwin widths and thus to broad dislocation images, i.e. rather low spatial resolution.
Nevertheless, in some cases, protein crystals were reported to be perfect enough to achieve images of single dislocations.
Literature: | 0 | Theoretical and Fundamental Chemistry |
Nevado was born in Madrid and grew up in Spain. She was the first scientist in her family. At high school she was inspired by her chemistry and physics teachers to pursue a career in science. She eventually studied chemistry at the Autonomous University of Madrid, and earned her bachelor's degree in 2000. During one summer holiday she worked at the Menéndez Pelayo International University, where she met international students and realised the scientific community was global. She remained at the Autonomous University for her doctoral research, where she worked on organic chemistry and the cyclisation of enynes that had been catalysed by gold and platinum complexes. After earning her doctorate, Nevado moved to the Max Planck Institute for Coal Research, where she worked as a postdoctoral fellow with Alois Fürstner. Her postdoctoral research considered natural product synthesis. She spent three months working alongside Eiichi Nakamura at the University of Tokyo. | 0 | Theoretical and Fundamental Chemistry |
The Norrish type I reaction is the photochemical cleavage or homolysis of aldehydes and ketones into two free radical intermediates (α-scission). The carbonyl group accepts a photon and is excited to a photochemical singlet state. Through intersystem crossing the triplet state can be obtained. On cleavage of the α-carbon bond from either state, two radical fragments are obtained. The size and nature of these fragments depends upon the stability of the generated radicals; for instance, the cleavage of 2-butanone largely yields ethyl radicals in favor of less stable methyl radicals.
Several secondary reaction modes are open to these fragments depending on the exact molecular structure.
* The fragments can simply recombine to the original carbonyl compound, with racemisation at the α-carbon.
* The acyl radical can lose a molecule of carbon monoxide, forming a new carbon radical at the other α-carbon, followed by formation of a new carbon–carbon bond between the radicals. The ultimate effect is simple extraction of the carbonyl unit from the carbon chain. The rate and yield of this product depends upon the bond-dissociation energy of the ketone's α substituents. Typically the more α substituted a ketone is, the more likely the reaction will yield products in this way.
* The abstraction of an α-proton from the carbonyl fragment may form a ketene and an alkane.
* The abstraction of a β-proton from the alkyl fragment may form an aldehyde and an alkene.
The synthetic utility of this reaction type is limited, for instance it often is a side reaction in the Paternò–Büchi reaction. One organic synthesis based on this reaction is that of bicyclohexylidene. | 0 | Theoretical and Fundamental Chemistry |
There are relatively few CRESU apparatuses in existence for the simple reason that the gas throughput and pumping requirements are huge, which makes them expensive to run. Two of the leading centres have been the University of Rennes (France) and the University of Birmingham (UK). A more recent development has been a pulsed version of the CRESU, which requires far less gas and therefore smaller pumps. | 0 | Theoretical and Fundamental Chemistry |
Vitamin D toxicity is rare. It is caused by supplementing with high doses of vitamin D rather than sunlight. The threshold for vitamin D toxicity has not been established; however, according to some research:
* 100μg/day (4k IU), have been show to not cause toxic levels. ages 9–71
* 240 μg/day (10k IU), over 5 months have been show not to cause toxicity.
* 1250μg/day (50k IU) over several months can increase serum 25-hydroxyvitamin D levels to 150ng/mL.
Those with certain medical conditions, such as primary hyperparathyroidism, are far more sensitive to vitamin D and develop hypercalcemia in response to any increase in vitamin D nutrition, while maternal hypercalcemia during pregnancy may increase fetal sensitivity to effects of vitamin D and lead to a syndrome of intellectual disability and facial deformities.
Idiopathic infantile hypercalcemia is caused by a mutation of the CYP24A1 gene, leading to a reduction in the degradation of vitamin D. Infants who have such a mutation have an increased sensitivity to vitamin D and in case of additional intake a risk of hypercalcaemia. The disorder can continue into adulthood.
A review published in 2015 noted that adverse effects have been reported only at 25(OH)D serum concentrations above 200nmol/L.
Published cases of toxicity involving hypercalcemia in which the vitamin D dose and the 25-hydroxy-vitamin D levels are known all involve an intake of ≥40,000IU (1,000μg) per day.
Those who are pregnant or breastfeeding should consult a doctor before taking a vitamin D supplement. The FDA advised manufacturers of liquid vitamin D supplements that droppers accompanying these products should be clearly and accurately marked for 400 international units (1IU is the biological equivalent of 25ng cholecalciferol/ergocalciferol). In addition, for products intended for infants, the FDA recommends the dropper hold no more than 400IU. For infants (birth to 12 months), the tolerable upper limit (maximum amount that can be tolerated without harm) is set at 25μg/day (1,000IU). One thousand micrograms per day in infants has produced toxicity within one month. After being commissioned by the Canadian and American governments, the Institute of Medicine (IOM) , has increased the tolerable upper limit (UL) to 2,500IU per day for ages 1–3 years, 3,000IU per day for ages 4–8 years and 4,000IU per day for ages 9–71+ years (including pregnant or lactating women).
Calcitriol itself is auto-regulated in a negative feedback cycle, and is also affected by parathyroid hormone, fibroblast growth factor 23, cytokines, calcium, and phosphate.
A study published in 2017 assessed the prevalence of high daily intake levels of supplemental vitamin D among adults ages 20+ in the United States, based on publicly available NHANES data from 1999 through 2014. Its data shows the following:
* Over 18% of the population exceeds the NIH daily recommended allowance (RDA) of 600–800 IU, by taking over 1000 IU, which suggests intentional supplement intake.
* Over 3% of the population exceeds the NIH daily tolerable upper intake level (UL) of 4000 IU, above which level the risk of toxic effects increases.
* The percentage of the population taking over 1000 IU/day, as well as the percentage taking over 4000 IU/day, have both increased since 1999, according to trend analysis. | 1 | Applied and Interdisciplinary Chemistry |
Before the discovery of msDNA in myxobacteria, a group of swarming, soil-dwelling bacteria, it was thought that the enzymes known as reverse transcriptases (RT) existed only in eukaryotes and viruses. The discovery led to an increase in research of the area. As a result, msDNA has been found to be widely distributed among bacteria, including various strains of Escherichia coli and pathogenic bacteria. Further research discovered similarities between HIV-encoded reverse transcriptase and an open reading frame (ORF) found in the msDNA coding region. Tests confirmed the presence of reverse transcriptase activity in crude lysates of retron-containing strains. Although an RNase H domain was tentatively identified in the retron ORF, it was later found that the RNase H activity required for msDNA synthesis is actually supplied by the host. | 1 | Applied and Interdisciplinary Chemistry |
As the first line strategy, the troops were given synthetic drugs. Drug combinations using pyrimethamine and dapsone, pyrimethamine and sulfadoxine, and sulfadoxine and piperaquine phosphate were tested in the battlefield. Because these drugs had serious adverse effects, the primary focus was to examine traditional Chinese medicines and look for new compounds. The first drug of interest was chángshān (), an extract from the roots of Dichroa febrifuga depicted in the Shennong Ben Cao Jing. Another early candidate was huanghuahao (sweet wormwood or Artemisia annua). These two plants became a huge success in modern pharmacology. | 1 | Applied and Interdisciplinary Chemistry |
This diagram shows an o-alkylation between phenol and methanol. Unlike the c-alkylation, the o-alkylation replaces the hydrogen atom on the -OH group with the methyl group (from the methanol). The product of the o-alkylation is methoxybenzene, better-known as anisole, and water, which is not shown in the diagram. Anisole is listed as an acute hazard to aquatic life with long-term effects. | 0 | Theoretical and Fundamental Chemistry |
Recent research has implicated the UPR in the transformation of cells in to cancer cells. Researchers have identified the SIRT3 axis of UPR as a marker to differentiate between metastatic and non-metastatic breast cancer. As many cancers exhibit a metabolic shift from oxidative phosporylation-depentent energy production to aerobic glycolysis dependent energy production, also known as the Warburg effect, researchers suggest that cancer cells rely on the UPR to maintain the mitochondrial integrity. Furthermore, multiple studies have shown that inhibition of UPR, specifically ATF5, selectively kills human and rat cancer cells rather than non-cancer cells. | 1 | Applied and Interdisciplinary Chemistry |
N-Oleoylsarcosine is a clear, yellow to brown, viscous liquid, which is sparsely soluble in water and acts acidic. As long-chain N-acylamino acid, the surfactant is soluble in many organic solvents and in mineral oil. In the alkaline it dissolves well in water. Because of its carboxamide structure, Sarkosyl O is chemically stable even at high pH values and strongly foaming as an anionic surfactant. N-oleyl sarcosine is only slightly toxic and easily biodegradable. | 0 | Theoretical and Fundamental Chemistry |
The C-terminus of RPB1 is appended to form the C-terminal domain (CTD). The carboxy-terminal domain of RNA polymerase II typically consists of up to 52 repeats of the sequence Tyr-Ser-Pro-Thr-Ser-Pro-Ser. The domain stretches from the core of the RNAPII enzyme to the exit channel, this placement is effective due to its inductions of "RNA processing reactions, through direct or indirect interactions with components of the RNA processing machinery". The CTD domain does not exist in RNA Polymerase I or RNA Polymerase III. The RNA Polymerase CTD was discovered first in the laboratory of C.J.Ingles at the University of Toronto and also in the laboratory of J Corden at Johns Hopkins University during the processes of sequencing the DNA encoding the RPB1 subunit of RNA polymerase from Yeast and Mice respectively. Other proteins often bind the C-terminal domain of RNA polymerase in order to activate polymerase activity. It is the protein domain that is involved in the initiation of transcription, the capping of the RNA transcript, and attachment to the spliceosome for RNA splicing. | 1 | Applied and Interdisciplinary Chemistry |
Cyclic AMP-dependent protein kinases (protein kinase A) are activated by the signal cascade originated by the activation of the G protein Gs by the LHCG-receptor. Activated Gs binds the enzyme adenylate cyclase and this leads to the production of cyclic AMP (cAMP). Cyclin AMP-dependent protein kinases are present as tetramers with two regulatory subunits and two catalytic subunits. Upon binding of cAMP to the regulatory subunits, the catalytic units are released and initiate the phosphorylation of proteins leading to the physiologic action. Cyclic AMP is degraded by phosphodiesterase and release 5’AMP. One of the targets of protein kinase A is the Cyclic AMP Response Element Binding Protein, CREB, which binds DNA in the cell nucleus via direct interactions with specific DNA sequences called cyclic AMP response elements (CRE); this process results in the activation or inactivation of gene transcription.
The signal is amplified by the involvement of cAMP and the resulting phosphorylation. The process is modified by prostaglandins. Other cellular regulators that participate are the intracellular calcium concentration regulated by phospholipase C activation, nitric oxide, and other growth factors.
Other pathways of signaling exist for the LHCGR. | 1 | Applied and Interdisciplinary Chemistry |
A receptor antagonist is a type of receptor ligand or drug that blocks or dampens a biological response by binding to and blocking a receptor rather than activating it like an agonist. Antagonist drugs interfere in the natural operation of receptor proteins. They are sometimes called blockers; examples include alpha blockers, beta blockers, and calcium channel blockers. In pharmacology, antagonists have affinity but no efficacy for their cognate receptors, and binding will disrupt the interaction and inhibit the function of an agonist or inverse agonist at receptors. Antagonists mediate their effects by binding to the active site or to the allosteric site on a receptor, or they may interact at unique binding sites not normally involved in the biological regulation of the receptor's activity. Antagonist activity may be reversible or irreversible depending on the longevity of the antagonist–receptor complex, which, in turn, depends on the nature of antagonist–receptor binding. The majority of drug antagonists achieve their potency by competing with endogenous ligands or substrates at structurally defined binding sites on receptors. | 1 | Applied and Interdisciplinary Chemistry |
Hydraulic jumps can be seen in both a stationary form, which is known as a "hydraulic jump", and a dynamic or moving form, which is known as a positive surge or "hydraulic jump in translation". They can be described using the same analytic approaches and are simply variants of a single phenomenon. | 1 | Applied and Interdisciplinary Chemistry |
Two major modifications of the biuret test are commonly applied in modern colorimetric analysis of peptides: the bicinchoninic acid (BCA) assay and the Lowry assay. In these tests, the Cu formed during the biuret reaction reacts further with other reagents, leading to a deeper color.
In the BCA test, Cu forms a deep purple complex with bicinchoninic acid (BCA), which absorbs around 562 nm, producing the signature mauve color. The water-soluble BCA/copper complex absorbs much more strongly than the peptide/copper complex, increasing the sensitivity of the biuret test by a factor of around 100: the BCA assay allows to detect proteins in the range of 0.0005 to 2 mg/mL). Additionally, the BCA protein assay gives the important benefit of compatibility with substances such as up to 5% surfactants in protein samples.
In the Lowry protein assay Cu is oxidized back to Cu by Mo in the Folin–Ciocalteu reagent, which forms molybdenum blue (Mo). Tyrosine residues in the protein also form molybdenum blue under these circumstances. In this way, proteins can be detected in concentrations between 0.005 and 2 mg/mL. Molybdenum blue in turn can bind certain organic dyes such as malachite green and Auramine O, resulting in further amplification of the signal. | 0 | Theoretical and Fundamental Chemistry |
Neglecting the carbon utilised for biomass formation (known to be a small fraction of the total carbon utilised) basic biochemistry balances can be performed based on the established metabolic pathways of these organisms. Using glucose as substrate the natural producing succinic acid producers are first considered. These organisms use the excretion of acetic acid (and sometimes formic acid) to balance the NADH requirement of succinic acid production. Two possible paths exist as indicated in Figure 1 and Figure 2. The difference between the two pathways lies in the pyruvate oxidation step where pyruvate formate lyase is employed in Figure 1 and pyruvate dehydrogenase employed in Figure 2. The additional NADH generated in Figure 2 results in 66% of the molar glucose flux ending up as succinic acid compared to the 50% of Figure 1. The overall yields can be expressed on a mass basis where the pathway in Figure 1 results in a 0.66 gram succinic acid per gram of glucose consumed (g/g). The pathway in Figure 2 results in a yield of 0.87 g/g.
The metabolic pathway can be genetically engineered in order to have succinic acid as the only excretion product. This can be achieved by using the oxidative section of the tricarboxylic acid cycle (TCA) under anaerobic conditions as illustrated in Figure 3. Alternatively the glyoxylate bypass can be utilised (Figure 4) to give the same result. For both these scenarios the mass based succinic acid yield is 1.12 g/g. This implies that the theoretical maximum yield is such that more succinic acid is formed than glucose consumed due to the fixation of carbon dioxide. | 1 | Applied and Interdisciplinary Chemistry |
The basic property of fluorescence are extensively used, such as a marker of labelled components in cells (fluorescence microscopy) or as an indicator in solution (Fluorescence spectroscopy), but other additional properties, not found with radioactivity, make it even more extensively used. | 1 | Applied and Interdisciplinary Chemistry |
The Confederation of European Environmental Engineering Societies (CEEES) was created as a co-operative international organization for information exchange regarding environmental engineering between the various European societies in this field.
The CEEES maintains an online public discussion forum for the interchange of information. | 1 | Applied and Interdisciplinary Chemistry |
β-elimination or elimination reactions occur through the loss of a substituent leaving group and loss of a proton to form a pi bond. E1 and E2 are two different mechanisms for elimination reactions, and E1 involves a carbocation intermediate. In E1, a leaving group detaches from a carbon to form a carbocation reaction intermediate. Then, a solvent removes a proton, but the electrons used to form the proton bond form a pi bond, as shown in the pictured reaction on the right. | 0 | Theoretical and Fundamental Chemistry |
In 1956 a heterogeneous catalyst made of palladium deposited on silk was shown to effect asymmetric hydrogenation. Later, in 1968, the groups of William Knowles and Leopold Horner independently published the examples of asymmetric hydrogenation using a homogeneous catalysts. While exhibiting only modest enantiomeric excesses, these early reactions demonstrated feasibility. By 1972, enantiomeric excess of 90% was achieved, and the first industrial synthesis of the Parkinson's drug L-DOPA commenced using this technology.
The field of asymmetric hydrogenation continued to experience a number of notable advances. Henri Kagan developed DIOP, an easily prepared C-symmetric diphosphine that gave high ees in certain reactions. Ryōji Noyori introduced the ruthenium-based catalysts for the asymmetric hydrogenated polar substrates, such as ketones and aldehydes. Robert H. Crabtree demonstrated the ability for Iridium compounds to catalyse asymmetric hydrogenation reactions in 1979 with the invention of Crabtrees catalyst. In the early 1990's, the introduction of P,N ligands by several groups independently then further expanded the scope of the C-symmetric ligands, although they are not fundamentally superior to chiral ligands lacking rotational symmetry.
Today, asymmetric hydrogenation is a routine methodology in laboratory and industrial scale organic chemistry. The importance of asymmetric hydrogenation was recognized by the 2001 Nobel Prize in Chemistry awarded to William Standish Knowles and Ryōji Noyori. | 0 | Theoretical and Fundamental Chemistry |
"Tar" and "pitch" can be used interchangeably. Asphalt (naturally occurring pitch) may also be called either "mineral tar" or "mineral pitch". There is a tendency to use "tar" for more liquid substances and "pitch" for more solid (viscoelastic) substances. Both "tar" and "pitch" are applied to viscous forms of asphalt, such as the asphalt found in naturally occurring tar pits (e.g., the La Brea Tar Pits in Los Angeles). "Rangoon tar", also known as "Burmese oil" or "Burmese naphtha", is also a form of petroleum. Oil sands, found extensively in Alberta, Canada, and composed of asphalt, are colloquially referred to as "tar sands". | 0 | Theoretical and Fundamental Chemistry |
Mitochondrial phosphoenolpyruvate carboxykinase is thought to participate in the transfer of the phosphorylation potential from the matrix to the cytosol and vice versa. However, it is strongly favored towards GTP hydrolysis, thus it is not really considered as an important source of intra-mitochondrial substrate-level phosphorylation. | 1 | Applied and Interdisciplinary Chemistry |
*BAT1 aka DDX39B which is involved in RNA splicing
*BSG Basigin Immunoglobulin Superfamily, extracellular metalloproteinase
*MIF macrophage migration inhibitory factor
*TAPBP | 1 | Applied and Interdisciplinary Chemistry |
Flow systems can be scaled to the tons per hour scale. Plant redesign (batch to conti for an existing plant), Unit Operation (exchanging only one reaction step) and Modular Multi-purpose (Cutting a continuous plant into modular units) are typical realization solutions for flow processes. | 1 | Applied and Interdisciplinary Chemistry |
*4.C.1 The Proposed Fatty Acid Transporter (FAT) Family
*4.C.2 The Carnitine O-Acyl Transferase (CrAT) Family
*4.C.3 The Acyl-CoA Thioesterase (AcoT) Family | 1 | Applied and Interdisciplinary Chemistry |
At room temperature and below, hydroxylamine-O-sulfonic acid reacts with ketones and aldehydes as a nucleophile to the corresponding oxime-O-sulfonic acids or their salts. The oxime-O-sulfonic acids of aldehydes react above room temperature upon elimination of sulfuric acid in high yields to nitriles.
Aliphatic ketones provide under similar conditions in very high yields oximes, arylalkyl ketones react in a Beckmann rearrangement to amides. When heated to reflux for several hours under acidic conditions (e.g., in the presence of concentrated formic acid) alicyclic ketones react to provide lactams in high yields.
Under basic conditions in the presence of primary amines, hydroxylamine-O-sulfonic acid forms with aldehydes and ketones (e.g. cyclohexanone) diaziridines, which can easily be oxidized to the more stable diazirines.
The reaction also provides substituted aziridines from simple aldehydes and ketones with high yield and diastereoselectivity.
1,2-Benzisoxazole is efficiently produced by nucleophilic attack of hydroxylamine-O-sulfonic acid to the carbonyl group of 2-hydroxybenzaldehyde followed by cyclization.
1,2-Benzisoxazole is a structural element in the antipsychotic risperidone and paliperidone, as well as the anticonvulsant zonisamide.
In a one-pot reaction, N-aryl[3,4-d]pyrazolopyrimidines are obtained in good yields from simple 4,6-dichloropyrimidine-5-carboxaldehyde,
which can be used as purine analogs for a wide range of diagnostic and therapeutic applications. | 0 | Theoretical and Fundamental Chemistry |
A revolution in this area occurred in the 1990s with the introduction of the [[Tetrakis(3,5-bis(trifluoromethyl)phenyl)borate|tetrakis[3,5-bis(trifluoromethyl)phenyl]borate]] ion, , commonly abbreviated as and colloquially called "BARF". This anion is far less coordinating than tetrafluoroborate, hexafluorophosphate, and perchlorate, and consequently has enabled the study of still more electrophilic cations. Related tetrahedral anions include tetrakis(pentafluorophenyl)borate , and .
In the bulky borates and aluminates, the negative charge is symmetrically distributed over many electronegative atoms. Related anions are derived from tris(pentafluorophenyl)boron B(CF). Another advantage of these anions is that their salts are more soluble in non-polar organic solvents such as dichloromethane, toluene, and, in some cases, even alkanes. Polar solvents, such as acetonitrile, THF, and water, tend to bind to electrophilic centers, in which cases, the use of a non-coordinating anion is pointless.
Salts of the anion were first reported by Kobayashi and co-workers. For that reason, it is sometimes referred to as Kobayashis anion. Kobayashis method of preparation has been superseded by a safer route.
The neutral molecules that represent the parents to the non-coordinating anions are strong Lewis acids, e.g. boron trifluoride, BF and phosphorus pentafluoride, PF. A notable Lewis acid of this genre is tris(pentafluorophenyl)borane, B(CF), which abstracts alkyl ligands:
:(CH)Zr(CH) + B(CF) → [(CH)Zr(CH)][(CH)B(CF)] | 0 | Theoretical and Fundamental Chemistry |
NTA has been used by commercial, academic, and government laboratories working with nanoparticle toxicology, drug delivery, exosomes, microvesicles, bacterial membrane vesicles, and other small biological particles, virology and vaccine production, ecotoxicology, protein aggregation, orthopedic implants, inks and pigments, and nanobubbles. | 0 | Theoretical and Fundamental Chemistry |
In the liver and peripheral tissues of humans, retinol is reversibly converted to retinal by the action of alcohol dehydrogenases, which are also responsible for the conversion of ethanol to acetaldehyde. Retinal is irreversibly oxidized to retinoic acid (RA) by the action of aldehyde dehydrogenases. RA regulates the activation or deactivation of genes. The oxidative degradation of RA is induced by RA - its presence triggers its removal, making for a short-acting gene transcription signal. This deactivation is mediated by a cytochrome P450 (CYP) enzyme system, specifically enzymes CYP26A1, CYP26B1 and CYP26C1. CYP26A1 is the predominant form in the human liver; all other human adult tissues contained higher levels of CYP26B1. CYP26C1 is expressed mainly during embryonic development. All three convert retinoic acid into 4-oxo-RA, 4-OH-RA and 18-OH-RA. Glucuronic acid forms water-soluble glucuronide conjugates with the oxidized metabolites, which are then excreted in urine and feces. | 1 | Applied and Interdisciplinary Chemistry |
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