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Several complexes of disulfur monoxide are known. Most are formed by oxidation peroxide oxidation of a disulfur ligand. In these complexes, the ligand is invariably bound in an manner. Selected examples: , , , , , .
arises when the dithiocarbamate complex is oxidized with elemental sulfur in air. Another way to form these complexes is to combine complexes with hydrogen sulfide. Complexes formed in this way are: ; . With hydrosulfide and a base followed by oxygen, can be made. | 0 | Theoretical and Fundamental Chemistry |
In materials science, environmental stress fracture or environment assisted fracture is the generic name given to premature failure under the influence of tensile stresses and harmful environments of materials such as metals and alloys, composites, plastics and ceramics.
Metals and alloys exhibit phenomena such as stress corrosion cracking, hydrogen embrittlement, liquid metal embrittlement and corrosion fatigue all coming under this category. Environments such as moist air, sea water and corrosive liquids and gases cause environmental stress fracture. Metal matrix composites are also susceptible to many of these processes.
Plastics and plastic-based composites may suffer swelling, debonding and loss of strength when exposed to organic fluids and other corrosive environments, such as acids and alkalies. Under the influence of stress and environment, many structural materials, particularly the high-specific strength ones become brittle and lose their resistance to fracture. While their fracture toughness remains unaltered, their threshold stress intensity factor for crack propagation may be considerably lowered. Consequently, they become prone to premature fracture because of sub-critical crack growth. This article aims to give a brief overview of the various degradation processes mentioned above. | 1 | Applied and Interdisciplinary Chemistry |
The methyl radical has the formula . It exists in dilute gases, but in more concentrated form it readily dimerizes to ethane. It is routinely produced by various enzymes of the radical SAM and methylcobalamin varieties. | 0 | Theoretical and Fundamental Chemistry |
(Bis(trifluoroacetoxy)iodo)benzene, , is a hypervalent iodine compound used as a reagent in organic chemistry. It can be used to carry out the Hofmann rearrangement under acidic conditions. | 0 | Theoretical and Fundamental Chemistry |
The society was founded in 1911 by Benjamin Moore, W.D. Halliburton and others, under the name of the Biochemical Club. It acquired the existing Biochemical Journal in 1912.
The society name changed to the Biochemical Society in 1913.
In 2005, the headquarters of the society moved from Portland Place to purpose-built offices in Holborn.
In 2009, the headquarters moved again to Charles Darwin House, near Gray's Inn Road.
Past presidents include Professor Ron Laskey, Sir Philip Cohen, and Sir Tom Blundell. | 1 | Applied and Interdisciplinary Chemistry |
Foot-and-mouth disease virus (FMDV) is a member of the Aphthovirus genus in the Picornaviridae family and is the cause of foot-and-mouth disease in pigs, cattle, sheep and goats. It is a non-enveloped, positive strand, RNA virus. FMDV is a highly contagious virus. It enters the body through inhalation. | 1 | Applied and Interdisciplinary Chemistry |
The isotope was first hypothesized and subsequently imaged by Patrick Blackett in Rutherford's lab in 1925:
It was a product out of the first man-made transmutation of N and He conducted by Frederick Soddy and Ernest Rutherford in 1917–1919. Its natural abundance in Earth's atmosphere was later detected in 1929 by Giauque and Johnson in absorption spectra. | 0 | Theoretical and Fundamental Chemistry |
Vinegar, petroleum jelly, milk and lemon juice solutions have also been used by activists. It is unclear how effective these remedies are. In particular, vinegar itself can burn the eyes and prolonged inhalation can also irritate the airways. Vegetable oil and vinegar have been reported as helping relieve burning caused by pepper spray, Kräuter suggests the usage of baking soda or toothpaste, stating that they trap the particles emanating from the gas near the airways that are more feasible to inhale. A small trial of baby shampoo for washing out the eyes did not show any benefit. | 1 | Applied and Interdisciplinary Chemistry |
Baron Axel Fredrik Cronstedt (/kroonstet/ 23 December 1722 – 19 August 1765) was a Swedish mineralogist and chemist who discovered the element nickel in 1751 as a mining expert with the Bureau of Mines.
Cronstedt is considered a founder of modern mineralogy, for introducing the blowpipe as a tool for mineralogists, and for proposing that the mineral kingdom be organized on the basis of chemical analysis in his book Försök til mineralogie, eller mineral-rikets upställning (“An attempt at mineralogy or arrangement of the Mineral Kingdom”, 1758). | 1 | Applied and Interdisciplinary Chemistry |
An early medieval writer Theophilus Presbyter, believed to be the Benedictine monk and metalworker Roger of Helmarshausen, wrote a treatise in the early-to-mid-12th century that includes original work and copied information from other sources, such as the Mappae clavicula and Eraclius, De dolorous et artibus Romanorum. It provides step-by-step procedures for making various articles, some by lost-wax casting: "The Copper Wind Chest and Its Conductor" (Chapter 84); "Tin Cruets" (Chapter 88), and "Casting Bells" (Chapter 85), which call for using "tallow" instead of wax; and "The Cast Censer". In Chapters 86 and 87 Theophilus details how to divide the wax into differing ratios before moulding and casting to achieve accurately tuned small musical bells. The 16th-century Florentine sculptor Benvenuto Cellini may have used Theophilus writings when he cast his bronze Perseus with the Head of Medusa'. | 1 | Applied and Interdisciplinary Chemistry |
Pedagogical work was an important part of the life of Pigulevsky. From 1911 to 1964, with a break for the duration of the war, he taught at Leningrad State University and lectured at other universities and institutes. During this time, he read many lecture courses: “Fats and oils”, “About derivatives of aliphatic terpenes”, “Resins”, “Terpenes”, “Essential oils”, etc.
Pigulevsky was a member of the Academic Council of the Leningrad branch of the D.I. Mendeleev All-Union Chemical Society, as well as a member of the Central Council of the D.I. Mendeleev All-Union Chemical Society. In 1946-1947, he was a member of the editorial board of the journal "Sovietskaya Botanica". From 1937 until the end of his life, he was a member of the editorial committee of the Journal of Applied Chemistry of the USSR. | 0 | Theoretical and Fundamental Chemistry |
Crystal structures for the E. coli SCS provide evidence that the coenzyme A binds within each α-subunit (within a Rossmann fold) in close proximity to a histidine residue (His246α). This histidine residue becomes phosphorylated during the succinate forming step in the reaction mechanism. The exact binding location of succinate is not well-defined. The formation of the nucleotide triphosphate occurs in an ATP grasp domain, which is located near the N-terminus of the each β subunit. However, this grasp domain is located about 35 Å away from the phosphorylated histidine residue. This leads researchers to believe that the enzyme must undergo a major change in conformation to bring the histidine to the grasp domain and facilitate the formation of the nucleoside triphosphate. Mutagenesis experiments have determined that two glutamate residues (one near the catalytic histidine, Glu208α and one near the ATP grasp domain, Glu197β) play a role in the phosphorylation and dephosphorylation of the histidine, but the exact mechanism by which the enzyme changes conformation is not fully understood. | 1 | Applied and Interdisciplinary Chemistry |
The link between protein chemical shifts and protein secondary structure (specifically alpha helices) was first described by John Markley and colleagues in 1967. With the development of modern 2-dimensional NMR techniques, it became possible to measure more protein chemical shifts. With more peptides and proteins were being assigned in the early 1980s it soon became obvious that amino acid chemical shifts were sensitive not only to helical conformations, but also to β-strand conformations. Specifically, the secondary Hα chemical shifts of all amino acids exhibit a clear upfield trend on helix formation and an obvious downfield trend on β-sheet formation. By the early 1990s, a sufficient body of C and N chemical shift assignments for peptides and proteins had been collected to determine that similar upfield/downfield trends were evident for essentially all backbone Cα, Cβ, C', HN and N (weakly) chemical shifts. It was these rather striking chemical shift trends that were exploited in the development of the chemical shift index. | 0 | Theoretical and Fundamental Chemistry |
There have been disputes on metamerism being included with other isomerisms such as position as well as chain isomerism, some authors still keep using it in their textbooks, mostly citing the examples of ethers and secondary amines. | 0 | Theoretical and Fundamental Chemistry |
This type of flow provides important information about flow in front part of streamlined body. It is probable that at the boundary, flow is not properly represented for real flow. The pressure and velocity of flow near to boundary layer is calculated by applying the Bernoulli's principle and is approximated with potential flow. The above equations may be used to calculate the stress on the body placed into the flow stream. | 1 | Applied and Interdisciplinary Chemistry |
Acyl halides are rather reactive compounds often synthesized to be used as intermediates in the synthesis of other organic compounds. For example, an acyl halide can react with:
*water, to form a carboxylic acid. This hydrolysis is the most heavily exploited reaction for acyl halides as it occurs in the industrial synthesis of acetic acid.
*an alcohol to form an ester
*an amine to form an amide
*an aromatic compound, using a Lewis acid catalyst such as AlCl, to form an aromatic ketone. See Friedel-Crafts acylation.
*carboxylic acids to form an organic acid anhydrides.
In the above reactions, HX (hydrogen halide or hydrohalic acid) is also formed. For example, if the acyl halide is an acyl chloride, HCl (hydrogen chloride or hydrochloric acid) is also formed. | 0 | Theoretical and Fundamental Chemistry |
The first structure of a creatine kinase solved by X-ray protein crystallography was that of the octameric, sarcomeric muscle-type mitochondrial CK (s-mtCK) in 1996., followed by the structure of ubiquitous mitochondrial CK (u-mtCK) in 2000. Both mt-CK isoforms form octameric structures (built of 4 banana-like dimers) with a four-fold symmetry and a central channel.
The atomic structure of the banana-shaped, dimeric cytosolic brain-type BB-CK was solved in 1999 at a resolution of 1,4 Å. Cytosolic BB-CK, as well as muscle-type MM-CK both form banana-shaped symmetric dimers, with one catalytic active site in each subunit. | 1 | Applied and Interdisciplinary Chemistry |
Crystallographic features of HCP systems, such as vectors and atomic plane families, can be described using a four-value Miller index notation ( hkil ) in which the third index i denotes a convenient but degenerate component which is equal to −h − k. The h, i and k index directions are separated by 120°, and are thus not orthogonal; the l component is mutually perpendicular to the h, i and k index directions. | 0 | Theoretical and Fundamental Chemistry |
It is useful to distinguish between global and local thermodynamic equilibrium. In thermodynamics, exchanges within a system and between the system and the outside are controlled by intensive parameters. As an example, temperature controls heat exchanges. Global thermodynamic equilibrium (GTE) means that those intensive parameters are homogeneous throughout the whole system, while local thermodynamic equilibrium (LTE) means that those intensive parameters are varying in space and time, but are varying so slowly that, for any point, one can assume thermodynamic equilibrium in some neighborhood about that point.
If the description of the system requires variations in the intensive parameters that are too large, the very assumptions upon which the definitions of these intensive parameters are based will break down, and the system will be in neither global nor local equilibrium. For example, it takes a certain number of collisions for a particle to equilibrate to its surroundings. If the average distance it has moved during these collisions removes it from the neighborhood it is equilibrating to, it will never equilibrate, and there will be no LTE. Temperature is, by definition, proportional to the average internal energy of an equilibrated neighborhood. Since there is no equilibrated neighborhood, the concept of temperature doesn't hold, and the temperature becomes undefined.
It is important to note that this local equilibrium may apply only to a certain subset of particles in the system. For example, LTE is usually applied only to massive particles. In a radiating gas, the photons being emitted and absorbed by the gas do not need to be in a thermodynamic equilibrium with each other or with the massive particles of the gas for LTE to exist. In some cases, it is not considered necessary for free electrons to be in equilibrium with the much more massive atoms or molecules for LTE to exist.
As an example, LTE will exist in a glass of water that contains a melting ice cube. The temperature inside the glass can be defined at any point, but it is colder near the ice cube than far away from it. If energies of the molecules located near a given point are observed, they will be distributed according to the Maxwell–Boltzmann distribution for a certain temperature. If the energies of the molecules located near another point are observed, they will be distributed according to the Maxwell–Boltzmann distribution for another temperature.
Local thermodynamic equilibrium does not require either local or global stationarity. In other words, each small locality need not have a constant temperature. However, it does require that each small locality change slowly enough to practically sustain its local Maxwell–Boltzmann distribution of molecular velocities. A global non-equilibrium state can be stably stationary only if it is maintained by exchanges between the system and the outside. For example, a globally-stable stationary state could be maintained inside the glass of water by continuously adding finely powdered ice into it to compensate for the melting, and continuously draining off the meltwater. Natural transport phenomena may lead a system from local to global thermodynamic equilibrium. Going back to our example, the diffusion of heat will lead our glass of water toward global thermodynamic equilibrium, a state in which the temperature of the glass is completely homogeneous. | 0 | Theoretical and Fundamental Chemistry |
These compounds are related to SO. They have planar C–N=S=N–C cores with bent C–N=S and N=S=N geometries, and various combinations of E and Z isomers are observed for the two N=S bonds.
Sulfur diimides are electrophilic. They undergo Diels–Alder reactions with dienes. Organolithium reagents attack at the sulfur to give the corresponding nitrogen anion:
:RLi + S(NR) → RS(NR)(NRLi)
The triimido analogues of sulfite can be generated by treating the sulfur diimides with a metal amide:
::4 LiNHBu-t + 2 S(NBu-t) → 2 LiS(NBu-t) + 2 t-BuNH | 0 | Theoretical and Fundamental Chemistry |
The salt effects (salting in and salting-out) refers to the fact that the presence of a salt which has no ion in common with the solute, has an effect on the ionic strength of the solution and hence on activity coefficients, so that the equilibrium constant, expressed as a concentration quotient, changes. | 0 | Theoretical and Fundamental Chemistry |
A marine outfall (or ocean outfall) is a pipeline or tunnel that discharges municipal or industrial wastewater, stormwater, combined sewer overflows (CSOs), cooling water, or brine effluents from water desalination plants to the sea. Usually they discharge under the sea's surface (submarine outfall). In the case of municipal wastewater, effluent is often being discharged after having undergone no or only primary treatment, with the intention of using the assimilative capacity of the sea for further treatment. Submarine outfalls are common throughout the world and probably number in the thousands. The light intensity and salinity in natural sea water disinfects the wastewater to ocean outfall system significantly. More than 200 outfalls alone have been listed in a single international database maintained by the Institute for Hydromechanics at Karlsruhe University for the International Association of Hydraulic Engineering and Research (IAHR) / International Water Association (IWA) Committee on Marine Outfall Systems.
The worlds first marine outfall was built in Santa Monica, United States, in 1910. In Latin America and the Caribbean there were 134 outfalls with more than 500 m length in 2006 for wastewater disposal alone, according to a survey by the Pan American Center for Sanitary Engineering and Environmental Sciences (CEPIS) of PAHO. According to the survey, the largest number of municipal wastewater outfalls in the region exist in Venezuela (39), Chile (39) and Brazil (22). The worlds largest marine outfall stems from the Deer Island Waste Water Treatment Plant located in Boston, United States. Currently, Boston has approximately 235 miles of combined sewers and 37 active CSO outfalls. Many outfalls are simply known by a public used name, e.g. Boston Outfall. | 1 | Applied and Interdisciplinary Chemistry |
In the 1910s, Wint-O-Green Life Savers were used to create soda geysers. The tubes of candies were threaded onto a pipe cleaner and dropped into the soft drink to create a geyser. At the end of the 1990s, the manufacturer of Wintergreen Lifesavers increased the size of the mints, and they no longer fit in the mouth of soda bottles. Science teachers found that Mentos candies had the same effect when dropped into a bottle of any carbonated soft drink.
Lee Marek and "Mareks Kid Scientists" performed the Diet Coke and Mentos experiment on the Late Show with David Letterman in 1999. In March 2002, Steve Spangler, a science educator, did the demonstration on KUSA-TV, an NBC affiliate, in Denver, Colorado. The Diet Coke and Mentos geyser experiment became an internet sensation in September 2005. The experiment became a subject of the television show MythBusters in 2006. Spangler signed a licensing agreement with Perfetti Van Melle, the maker of Mentos, after inventing an apparatus aimed to make it easier to drop the Mentos into the bottle and produce a large soda geyser. Amazing Toys, Spanglers toy company, released the Geyser Tube toys in February 2007. In October 2010, a Guinness World Record of 2,865 simultaneous geysers was set at an event organized by Perfetti Van Melle at the SM Mall of Asia Complex, in Manila, Philippines. This record was afterward beaten in November 2014 by another event organized by Perfetti Van Melle and Chupa Chups in León, Guanajuato, Mexico, where 4,334 Mentos and soda fountains were set off simultaneously. | 1 | Applied and Interdisciplinary Chemistry |
For decades β-blockers have been used in cardiovascular medicine. They have proved to reduce morbidity and mortality. In acute coronary syndrome, β-blockers have been recommended as a class I-A indication in clinical practice guidelines, because the treatment decreases the mortality rate. β-blockers, along with calcium channel blockers, reduce the workload of the heart and its oxygen requirement. β-blockers are sometimes used in a combination therapy to treat angina, if a β-blocker doesn't work well enough on its own. They are used as anti-arrhythmic drugs in patients with hyperthyroidism, cardiac dysrhythmia, atrial fibrillation, atrial flutter and ventricular tachycardia. The treatment with β-blockers reduces the incidence of sudden heart failure when the patient has already had a myocardial infarction. The reason is probably because of their anti-arrhythmic effects and also anti-ischemic effects. A β-blocker therapy is also useful in myocardial infarction, independent to heart failure. The therapy has been very helpful for high-risk patients. Although beta-blockers effectively lower blood pressure, they are not recommended as a first-line agent in the treatment of hypertension, as thiazides diuretics, ACE inhibitors, and calcium channel blockers show greater benefit. Therefore, β-blockers are usually used alongside other blood pressure medications such as calcium channel blockers. They also have an effect on cardiomyopathy, postural orthostatic tachycardia syndrome and portal hypertension, to name a few. | 1 | Applied and Interdisciplinary Chemistry |
Photons have a momentum given by (where is the reduced Planck constant and the photon wavenumber), which is conserved in all atom-photon interactions. Thus, when an atom absorbs a photon, it is given a momentum kick in the direction of the photon before absorption. By detuning a laser beam to a frequency less than the resonant frequency (also known as red detuning), laser light is only absorbed if the light is frequency up-shifted by the Doppler effect, which occurs whenever the atom is moving towards the laser source. This applies a friction force to the atom whenever it moves towards a laser source.
For cooling to occur along all directions, the atom must see this friction force along all three Cartesian axes; this is most easily achieved by illuminating the atom with three orthogonal laser beams, which are then reflected back along the same direction. | 0 | Theoretical and Fundamental Chemistry |
Genome-wide knockdown studies are an example of the reverse genetics made possible by the acquisition of whole genome sequences, and the advent of genomics and gene-silencing technologies, mainly siRNA and deletion mapping. Genome-wide knockdown studies involve systematic knockdown or deletion of genes or segments of the genome. This is generally done in prokaryotes or in a tissue culture environment due to the massive number of knockdowns that must be performed. After the systematic knockout is completed (and possibly confirmed by mRNA expression analysis), the phenotypic results of the knockdown/knockout can be observed. Observation parameters can be selected to target a highly specific phenotype. The resulting dataset is then queried for samples which exhibit phenotypes matching the disease in question – the gene(s) knocked down/out in said samples can then be considered candidate disease genes for the individual in question. | 1 | Applied and Interdisciplinary Chemistry |
Absolute bioavailability compares the bioavailability of the active drug in systemic circulation following non-intravenous administration (i.e., after oral, buccal, ocular, nasal, rectal, transdermal, subcutaneous, or sublingual administration), with the bioavailability of the same drug following intravenous administration. It is the fraction of exposure to a drug (AUC) through non-intravenous administration compared with the corresponding intravenous administration of the same drug. The comparison must be dose normalized (e.g., account for different doses or varying weights of the subjects); consequently, the amount absorbed is corrected by dividing the corresponding dose administered.
In pharmacology, in order to determine absolute bioavailability of a drug, a pharmacokinetic study must be done to obtain a plasma drug concentration vs time plot for the drug after both intravenous (iv) and extravascular (non-intravenous, i.e., oral) administration. The absolute bioavailability is the dose-corrected area under curve (AUC) non-intravenous divided by AUC intravenous. The formula for calculating the absolute bioavailability, F, of a drug administered orally (po) is given below (where D is dose administered).
Therefore, a drug given by the intravenous route will have an absolute bioavailability of 100% (f = 1), whereas drugs given by other routes usually have an absolute bioavailability of less than one.
If we compare the two different dosage forms having same active ingredients and compare the two drug bioavailability is called comparative bioavailability.
Although knowing the true extent of systemic absorption (referred to as absolute bioavailability) is clearly useful, in practice it is not determined as frequently as one may think. The reason for this is that its assessment requires an intravenous reference; that is, a route of administration that guarantees all of the administered drug reaches systemic circulation. Such studies come at considerable cost, not least of which is the necessity to conduct preclinical toxicity tests to ensure adequate safety, as well as potential problems due to solubility limitations. These limitations may be overcome, however, by administering a very low dose (typically a few micrograms) of an isotopically labelled drug concomitantly with a therapeutic non-isotopically labelled oral dose (the isotopically labelled intravenous dose is sufficiently low so as not to perturb the systemic drug concentrations achieved from the non-labelled oral dose). The intravenous and oral concentrations can then be deconvoluted by virtue of their different isotopic constitution, and can thus be used to determine the oral and intravenous pharmacokinetics from the same dose administration. This technique eliminates pharmacokinetic issues with non-equivalent clearance as well as enabling the intravenous dose to be administered with a minimum of toxicology and formulation. The technique was first applied using stable-isotopes such as C and mass-spectrometry to distinguish the isotopes by mass difference. More recently, C labelled drugs are administered intravenously and accelerator mass spectrometry (AMS) used to measure the isotopically labelled drug along with mass spectrometry for the unlabelled drug.
There is no regulatory requirement to define the intravenous pharmacokinetics or absolute bioavailability however regulatory authorities do sometimes ask for absolute bioavailability information of the extravascular route in cases in which the bioavailability is apparently low or variable and there is a proven relationship between the pharmacodynamics and the pharmacokinetics at therapeutic doses. In all such cases, to conduct an absolute bioavailability study requires that the drug be given intravenously.
Intravenous administration of a developmental drug can provide valuable information on the fundamental pharmacokinetic parameters of volume of distribution (V) and clearance (CL). | 1 | Applied and Interdisciplinary Chemistry |
Peramivir has a guanidino group similar to zanamivir and a hydrophobic group similar to oseltamivir. Mutations that effect the efficiency of oseltamivir and zanamivir can also effect peramivir efficiency. Resistances to peramivir have been seen at the mutation of H274Y residue in vitro. One of these resistances is associated with cross-resistance to peramivir and oseltamivir. Peramivir is approved in Japan as Rapiacta and also available in South Korea as Peramiflu. | 1 | Applied and Interdisciplinary Chemistry |
In physics, a bipolaron is a bound pair of two polarons. An electron in a material may cause a distortion in the underlying lattice. The combination of electron and distortion (which may also be understood as a cloud of phonons) is known as a polaron (in part because the interaction between electron and lattice is via a polarization). When two polarons are close together, they can lower their energy by sharing the same distortions, which leads to an effective attraction between the polarons. If the interaction is sufficiently large, then that attraction leads to a bound bipolaron. For strong attraction, bipolarons may be small. Small bipolarons have integer spin and thus share some of the properties of bosons. If many bipolarons form without coming too close, they might be able to form a Bose–Einstein condensate. This has led to a suggestion that bipolarons could be a possible mechanism for high-temperature superconductivity. For example, they can lead to a very direct interpretation of the isotope effect.
Recently, bipolarons were predicted theorethically in a Bose-Einstein condensate. Two polarons interchange sound waves and they attract to each other, forming a bound-state when the strength coupling between the single polarons and the condensate is strong in comparison with the interactions of the host gas. | 0 | Theoretical and Fundamental Chemistry |
Historically, small muffle ovens were often used for a second firing of porcelain at a relatively low temperature to fix overglaze enamels; these tend to be called muffle kilns. The pigments for most enamel colours discoloured at the high temperatures required for the body and glaze of the porcelain. They were used for painted enamels on metal for the same reason.
Like other types of muffle furnaces, the design isolates the objects from the flames producing the heat (with electricity this is not so important). For historical overglaze enamels the kiln was generally far smaller than that for the main firing, and produced firing temperatures in the approximate range of 750 to 950 °C, depending on the colours used. Typically, wares were fired for between five and twelve hours and then cooled over twelve hours. | 1 | Applied and Interdisciplinary Chemistry |
The most thorough fluid mechanics studies in gas have been performed using the RELIEF scheme and the APART scheme. Both techniques can be used in ambient air without the need for additional seeding.
In RELIEF, excited oxygen is used as a tracer. The method takes advantage of quantum mechanical properties that prohibit relaxation of the molecule so that the excited oxygen has a relatively long lifetime.
APART is based on the "photosynthesis" of nitric oxide. Since NO is a stable molecule, patterns written with it can, in principle, be followed almost indefinitely.
Another well-developed and widely documented technique that yields extremely high accuracy is hydroxyl tagging velocimetry (HTV). It is based on photo-dissociation of water vapor followed by visualization of the resulting OH radical using LIF. HTV has been successfully demonstrated in many test conditions ranging from room air temperature flows to Mach 2 flows within a cavity. | 1 | Applied and Interdisciplinary Chemistry |
The ferric chloride test is used to determine the presence of phenols in a given sample or compound (for instance natural phenols in a plant extract). Enols, hydroxamic acids, oximes, and sulfinic acids give positive results as well. The bromine test is useful to confirm the result, although modern spectroscopic techniques (e.g. NMR and IR spectroscopy) are far superior in determining the identity of the unknown. The quantity of total phenols may be spectroscopically determined by the Folin–Ciocalteau assay. | 0 | Theoretical and Fundamental Chemistry |
The inside of pipes can be cleaned with a tube cleaning process, if they are contaminated with debris or fouling. This depends on the process that the pipe will be used for and the cleanliness needed for the process. In some cases the pipes are cleaned using a displacement device formally known as a Pipeline Inspection Gauge or "pig"; alternately the pipes or tubes may be chemically flushed using specialized solutions that are pumped through. In some cases, where care has been taken in the manufacture, storage, and installation of pipe and tubing, the lines are blown clean with compressed air or nitrogen. | 1 | Applied and Interdisciplinary Chemistry |
Deuterium is often represented by the chemical symbol D. Since it is an isotope of hydrogen with mass number 2, it is also represented by H. IUPAC allows both D and H, though H is preferred. A distinct chemical symbol is used for convenience because of the isotopes common use in various scientific processes. Also, its large mass difference with protium (H) confers non-negligible chemical differences with protium compounds. Deuterium has a mass of , about twice the mean hydrogen atomic weight of , or twice protiums mass of . The isotope weight ratios within other chemical elements are largely insignificant in this regard. | 0 | Theoretical and Fundamental Chemistry |
The DLVO theory (named after Boris erjaguin and Lev andau, Evert erwey and Theodoor verbeek) explains the aggregation and kinetic stability of aqueous dispersions quantitatively and describes the force between charged surfaces interacting through a liquid medium.
It combines the effects of the van der Waals attraction and the electrostatic repulsion due to the so-called double layer of counterions.
The electrostatic part of the DLVO interaction is computed in the mean field approximation in the limit of low surface potentials - that is when the potential energy of an elementary charge on the surface is much smaller than the thermal energy scale, . For two spheres of radius each having a charge (expressed in units of the elementary charge) separated by a center-to-center distance in a fluid of dielectric constant containing a concentration of monovalent ions, the electrostatic potential takes the form of a screened-Coulomb or Yukawa potential,
where
* is the Bjerrum length,
* is the potential energy,
* ≈ 2.71828 is Euler's number,
* is the inverse of the Debye–Hückel screening length (); is given by , and
* is the thermal energy scale at absolute temperature | 0 | Theoretical and Fundamental Chemistry |
A systematic review of clinical studies found an association between low vitamin D levels with cognitive impairment and a higher risk of developing Alzheimer's disease. However, lower vitamin D concentrations are also associated with poor nutrition and spending less time outdoors. Therefore, alternative explanations for the increase in cognitive impairment exist and hence a direct causal relationship between vitamin D levels and cognition could not be established. | 1 | Applied and Interdisciplinary Chemistry |
In this pathway CO is fixed (i.e. incorporated) by the action of two enzymes, acetyl-CoA carboxylase and propionyl-CoA carboxylase. These enzymes generate malonyl-CoA and (S)-methylmalonyl-CoA, respectively. | 1 | Applied and Interdisciplinary Chemistry |
In optics the noise-equivalent flux density (NEFD) or noise-equivalent irradiance (NEI) of a system is the level of flux density required to be equivalent to the noise present in the system. It is a measure used by astronomers in determining the accuracy of observations.
The NEFD can be related to a light detectors noise-equivalent power for a collection area A' and a photon bandwidth by:
where a factor (often 2, in the case of switching between measuring a source and measuring off-source) accounts for the photon statistics for the mode of operation. | 0 | Theoretical and Fundamental Chemistry |
Organic compounds containing conjugate (i.e., alternate single-double) bonds can have semiconducting properties. The conductivity and mobility of those organic compounds however, are very low compared to inorganic semiconductors. Assuming the molecules of the organic semiconductor are lattices, the same procedure of electroreflectance of inorganic semiconductors can be applied for the organic ones. It should be noted though that there is a certain dualism in semiconductors: intra-molecular conduction (inside a molecule) and inter-molecular conduction (between molecules), which one should take into account doing measurements. Especially for thin films the band gaps of organic semiconductors can be accurately determined using this method. | 0 | Theoretical and Fundamental Chemistry |
Bürgi–Dunitz angle theory was initially developed based on "frozen" interactions in crystals, while most chemistry takes place via collisions of molecules tumbling in solution; remarkably, the theories of the , with the complexity they reflect, evolved not from crystallographic work, but from studying reaction outcomes in such practical reactions as addition of enolates to aldehydes (e.g., in study of diastereoselection in particular aldol reactions). In applying both angles of the nucleophile trajectory to real chemical reactions, the HOMO-LUMO centered view of the Bürgi-Dunitz angle, , is modified to include further complex, electrophile-specific attractive and repulsive electrostatic and van der Waals interactions that can alter and bias toward one substituent or the other (see above). As well, dynamics are at play in each system (e.g., changing torsional angles) and are implicitly included in studies of reaction outcomes in solution, as in the early studies of ,—though not in crystallographic structure correlation approaches as gave birth to the BD concept.
Finally, in constrained environments (e.g., in enzyme and nanomaterial binding sites), these angles, when characterized, appear to be quite distinct, an observation conjectured to arise because reactivity is not based on random collision, and so the relationship between orbital overlap principles and reactivity is more complex. For instance, while a simple amide addition study with relatively small substituents gave an of ≈50° in solution, the crystallographic value determined for an enzymatic cleavage of an amide by the serine protease subtilisin gave an of 8°, and a compilation of literature crystallographic values for the same reaction in different catalysts clustered at 4 ± 6° (i.e., only slightly offset from directly behind the carbonyl, despite significant dissymmetry of the substrate electrophiles). At the same time, the subtilisin was 88° (quite distinct from the hydride-formaldehyde value of 107°, see the Bürgi–Dunitz article), and angle values from the careful literature compilation clustered at 89 ± 7° (i.e., only slightly offset from directly above or below the carbonyl carbon). | 0 | Theoretical and Fundamental Chemistry |
In France, the only academy where conservators and curators can receive training is at the Institut national du patrimoine (The National Institute of Cultural Heritage). A five-year training program for aspiring conservators is offered which grants students with a Master's in Conservation-Restoration, with specialties in earthenware and glassware. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, a carbonate ester (organic carbonate or organocarbonate) is an ester of carbonic acid. This functional group consists of a carbonyl group flanked by two alkoxy groups. The general structure of these carbonates is and they are related to esters (), ethers () and also to the inorganic carbonates.
Monomers of polycarbonate (e.g. Makrolon or Lexan) are linked by carbonate groups. These polycarbonates are used in eyeglass lenses, compact discs, and bulletproof glass. Small carbonate esters like dimethyl carbonate, ethylene carbonate, propylene carbonate are used as solvents, dimethyl carbonate is also a mild methylating agent. | 0 | Theoretical and Fundamental Chemistry |
In 1832, lacking his own laboratory facilities at Kassel, Wöhler worked with Justus Liebig in his Giessen laboratory. In that year, Wöhler and Liebig published an investigation of the oil of bitter almonds. Through their detailed analysis of the chemical composition of this oil, they proved by their experiments that a group of carbon, hydrogen, and oxygen atoms can behave chemically as if it were the equivalent of a single atom, take the place of an atom in a chemical compound, and be exchanged for other atoms in chemical compounds. Specifically, their research on the oil of bitter almonds showed that a group of elements with the chemical composition CHO can be thought of as a single functional group, which came to be known as a benzoyl radical. In this way, the investigations of Wöhler and Liebig established a new concept in organic chemistry referred to as compound radicals, which had a profound influence on the development of organic chemistry. Many more functional groups were later identified by subsequent investigators with wide utility in chemistry.
Liebig and Wöhler explored the concept of chemical isomerism, the idea that two chemical compounds with identical chemical compositions could be different substances because of different arrangements of the atoms in the chemical structure. Aspects of chemical isomerism originated in the research of Berzelius. Liebig and Wöhler investigated silver fulminate and silver cyanate. These two compounds have the same chemical composition yet are chemically different. Silver fulminate is explosive, while silver cyanate is a stable compound. Liebig and Wöhler recognized these as examples of structural isomerism, which was a significant advance in understanding chemical isomerism.
Wöhler has also been regarded as a pioneering researcher in organic chemistry as a result of his 1828 demonstration of the laboratory synthesis of urea from ammonium cyanate, in a chemical reaction that came to be known as the "Wöhler synthesis". Urea and ammonium cyanate are further examples of structural isomers of chemical compounds. Heating ammonium cyanate converts it into urea, which is its isomer. In a letter to Swedish chemist Jöns Jacob Berzelius the same year, he wrote, In a manner of speaking, I can no longer hold my chemical water. I must tell you that I can make urea without the use of kidneys of any animal, be it man or dog.
Wöhler's demonstration of urea synthesis has become regarded as a refutation of vitalism, the hypothesis that living things are alive because of some special "vital force".
It was the beginning of the end for one popular vitalist hypothesis, the idea that "organic" compounds could be made only by living things.
In responding to Wöhler, Jöns Jakob Berzelius acknowledged that Wöhlers results were highly significant for the understanding of organic chemistry, calling the findings a "jewel" for Wöhlers "laurel wreath". Both scientists also recognized the work's importance to the study of isomerism, a new area of research.
Wöhlers role in overturning vitalism is said to have become exaggerated over time. This tendency can be traced back to Hermann Kopps History of Chemistry (in four volumes, 1843–1847). He emphasized the importance of Wöhler's research as a refutation of vitalism but ignored its importance in understanding chemical isomerism, setting a tone for subsequent writers.
The notion that Wöhler single-handedly overturned vitalism also gained popularity after it appeared in a popular history of chemistry published in 1931, which, "ignoring all pretense of historical accuracy, turned Wöhler into a crusader".
Contrary to what was thought in Wöhler's time, cyanate is not a purely inorganic anion, as it is formed in various metabolic pathways. Thus the conversion of ammonium cyanate into urea was not an example of production of an organic compound from an inorganic precursor. | 1 | Applied and Interdisciplinary Chemistry |
Under Carl Duisbergs leadership, Bayer was firmly committed to the standards of ethical drugs, as opposed to patent medicines. Ethical drugs were drugs that could be obtained only through a pharmacist, usually with a doctors prescription. Advertising drugs directly to consumers was considered unethical and strongly opposed by many medical organizations; that was the domain of patent medicines. Therefore, Bayer was limited to marketing Aspirin directly to doctors.
When production of Aspirin began in 1899, Bayer sent out small packets of the drug to doctors, pharmacists and hospitals, advising them of Aspirins uses and encouraging them to publish about the drugs effects and effectiveness. As positive results came in and enthusiasm grew, Bayer sought to secure patent and trademark wherever possible. It was ineligible for patent in Germany (despite being accepted briefly before the decision was overturned), but Aspirin was patented in Britain (filed 22 December 1898) and the United States (US Patent 644,077 issued 27 February 1900). The British patent was overturned in 1905, the American patent was also besieged but was ultimately upheld.
Faced with growing legal and illegal competition for the globally marketed ASA, Bayer worked to cement the connection between Bayer and Aspirin. One strategy it developed was to switch from distributing Aspirin powder for pharmacists to press into pill form to distributing standardized tablets—complete with the distinctive Bayer cross logo. In 1903 the company set up an American subsidiary, with a converted factory in Rensselaer, New York, to produce Aspirin for the American market without paying import duties. Bayer also sued the most egregious patent violators and smugglers. The company's attempts to hold onto its Aspirin sales incited criticism from muckraking journalists and the American Medical Association, especially after the 1906 Pure Food and Drug Act that prevented trademarked drugs from being listed in the United States Pharmacopeia; Bayer listed ASA with an intentionally convoluted generic name (monoacetic acid ester of salicylic acid) to discourage doctors referring to anything but Aspirin. | 1 | Applied and Interdisciplinary Chemistry |
A number of implanted ceramics have not actually been designed for specific biomedical applications. However, they manage to find their way into different implantable systems because of their properties and their good biocompatibility. Among these ceramics, we can cite silicon carbide, titanium nitrides and carbides, and boron nitride. TiN has been suggested as the friction surface in hip prostheses. While cell culture tests show a good biocompatibility, the analysis of implants shows significant wear, related to a delaminating of the TiN layer. Silicon carbide is another modern-day ceramic which seems to provide good biocompatibility and can be used in bone implants. | 0 | Theoretical and Fundamental Chemistry |
Vortex dynamics is a vibrant subfield of fluid dynamics, commanding attention at major scientific conferences and precipitating workshops and symposia that focus fully on the subject.
A curious diversion in the history of vortex dynamics was the Vortex theory of the atom of William Thomson, later Lord Kelvin. His basic idea was that atoms were to be represented as vortex motions in the ether. This theory predated the quantum theory by several decades and because of the scientific standing of its originator received considerable attention. Many profound insights into vortex dynamics were generated during the pursuit of this theory. Other interesting corollaries were the first counting of simple knots by P. G. Tait, today considered a pioneering effort in graph theory, topology and knot theory. Ultimately, Kelvins vortex atom was seen to be wrong-headed but the many results in vortex dynamics that it precipitated have stood the test of time. Kelvin himself originated the notion of circulation and proved that in an inviscid fluid circulation around a material contour would be conserved. This result singled out by Einstein in "Zum hundertjährigen Gedenktag von Lord Kelvins Geburt, Naturwissenschaften, 12 (1924), 601–602," (title translation: "On the 100th Anniversary of Lord Kelvins Birth"), as one of the most significant results of Kelvin's work provided an early link between fluid dynamics and topology.
The history of vortex dynamics seems particularly rich in discoveries and re-discoveries of important results, because results obtained were entirely forgotten after their discovery and then were re-discovered decades later. Thus, the integrability of the problem of three point vortices on the plane was solved in the 1877 thesis of a young Swiss applied mathematician named Walter Gröbli. In spite of having been written in Göttingen in the general circle of scientists surrounding Helmholtz and Kirchhoff, and in spite of having been mentioned in Kirchhoffs well known lectures on theoretical physics and in other major texts such as Lambs Hydrodynamics, this solution was largely forgotten. A 1949 paper by the noted applied mathematician J. L. Synge created a brief revival, but Synges paper was in turn forgotten. A quarter century later a 1975 paper by E. A. Novikov and a 1979 paper by H. Aref on chaotic advection finally brought this important earlier work to light. The subsequent elucidation of chaos in the four-vortex problem, and in the advection of a passive particle by three vortices, made Gröblis work part of "modern science".
Another example of this kind is the so-called "localized induction approximation" (LIA) for three-dimensional vortex filament motion, which gained favor in the mid-1960s through the work of Arms, Hama, Betchov and others, but turns out to date from the early years of the 20th century in the work of Da Rios, a gifted student of the noted Italian mathematician T. Levi-Civita. Da Rios published his results in several forms but they were never assimilated into the fluid mechanics literature of his time. In 1972 H. Hasimoto used Da Rios' "intrinsic equations" (later re-discovered independently by R. Betchov) to show how the motion of a vortex filament under LIA could be related to the non-linear Schrödinger equation. This immediately made the problem part of "modern science" since it was then realized that vortex filaments can support solitary twist waves of large amplitude. | 1 | Applied and Interdisciplinary Chemistry |
The Bengal Iron Works was founded at Kulti, Bengal, in 1870 which began its production in 1874 followed by The Tata Iron and Steel Company (TISCO) was established by Dorabji Tata in 1907, as part of his father's conglomerate. By 1939 it operated the largest steel plant in the British Empire. The company launched a major modernization and expansion program in 1951.
Prime Minister Jawaharlal Nehru, a believer in socialism, decided that the technological revolution in India needed maximization of steel production. He, therefore, formed a government owned company, Hindustan Steel Limited (HSL) and set up three steel plants in the 1950s.
The Indian steel industry began expanding into Europe in the 21st century. In January 2007 Indias Tata Steel made a successful $11.3 billion offer to buy European steel maker Corus Group. In 2006 Mittal Steel (based in London but with Indian management) merged with Arcelor after a takeover bid for $34.3 billion to become the worlds biggest steel maker, ArcelorMittal (based in Luxembourg City), with 10% of the world's output. | 1 | Applied and Interdisciplinary Chemistry |
An MRI pulse sequence in magnetic resonance imaging (MRI) is a particular setting of pulse sequences and pulsed field gradients, resulting in a particular image appearance.
A multiparametric MRI is a combination of two or more sequences, and/or including other specialized MRI configurations such as spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
If the initial, environmentally-generated disturbance is small enough, the next stage of the transition process is that of primary mode growth. In this stage, the initial disturbances grow (or decay) in a manner described by linear stability theory. The specific instabilities that are exhibited in reality depend on the geometry of the problem and the nature and amplitude of initial disturbances. Across a range of Reynolds numbers in a given flow configuration, the most amplified modes can and often do vary.
There are several major types of instability which commonly occur in boundary layers. In subsonic and early supersonic flows, the dominant two-dimensional instabilities are T-S waves. For flows in which a three-dimensional boundary layer develops such as a swept wing, the crossflow instability becomes important. For flows navigating concave surface curvature, Görtler vortices may become the dominant instability. Each instability has its own physical origins and its own set of control strategies - some of which are contraindicated by other instabilities – adding to the difficulty in controlling laminar-turbulent transition. | 1 | Applied and Interdisciplinary Chemistry |
Many evaluation criteria apply globally to an entire experimental structure, most notably the resolution, the anisotropy or incompleteness of the data, and the residual or R-factor that measures overall model-to-data match (see below). Those help a user choose the most accurate among related Protein Data Bank entries to answer their questions. Other criteria apply to individual residues or local regions in the 3D structure, such as fit to the local electron density map or steric clashes between atoms. Those are especially valuable to the structural biologist for making improvements to the model, and to the user for evaluating the reliability of that model right around the place they care about - such as a site of enzyme activity or drug binding. Both types of measures are very useful, but although global criteria are easier to state or publish, local criteria make the greatest contribution to scientific accuracy and biological relevance. As expressed in the Rupp textbook, "Only local validation, including assessment of both geometry and electron density, can give an accurate picture of the reliability of the structure model or any hypothesis based on local features of the model." | 1 | Applied and Interdisciplinary Chemistry |
Nutrition polysaccharides are common sources of energy. Many organisms can easily break down starches into glucose; however, most organisms cannot metabolize cellulose or other polysaccharides like cellulose, chitin, and arabinoxylans. Some bacteria and protists can metabolize these carbohydrate types. Ruminants and termites, for example, use microorganisms to process cellulose.
Even though these complex polysaccharides are not very digestible, they provide important dietary elements for humans. Called dietary fiber, these carbohydrates enhance digestion. The main action of dietary fiber is to change the nature of the contents of the gastrointestinal tract and how other nutrients and chemicals are absorbed. Soluble fiber binds to bile acids in the small intestine, making them less likely to enter the body; this, in turn, lowers cholesterol levels in the blood. Soluble fiber also attenuates the absorption of sugar, reduces sugar response after eating, normalizes blood lipid levels and, once fermented in the colon, produces short-chain fatty acids as byproducts with wide-ranging physiological activities (discussion below). Although insoluble fiber is associated with reduced diabetes risk, the mechanism by which this occurs is unknown.
Not yet formally proposed as an essential macronutrient (as of 2005), dietary fiber is nevertheless regarded as important for the diet, with regulatory authorities in many developed countries recommending increases in fiber intake. | 0 | Theoretical and Fundamental Chemistry |
* 2023: Yoshida Prize, International Organic Chemistry Foundation
* 2022: Sang-Chul Shim Academic Award, Korean Chemical Society
* 2007: NUS Young Investigator Award
* 2005: Career Award, National Science Foundation | 0 | Theoretical and Fundamental Chemistry |
The ARC fusion reactor (affordable, robust, compact) is a design for a compact fusion reactor developed by the Massachusetts Institute of Technology (MIT) Plasma Science and Fusion Center (PSFC). ARC aims to achieve an engineering breakeven of three (to produce three times the electricity required to operate the machine). The key technical innovation is to use high-temperature superconducting magnets in place of ITER's low-temperature superconducting magnets. The proposed device would be about half the diameter of the ITER reactor and cheaper to build.
The ARC has a conventional advanced tokamak layout. ARC uses rare-earth barium copper oxide (REBCO) high-temperature superconductor magnets in place of copper wiring or conventional low-temperature superconductors. These magnets can be run at much higher field strengths, 23 T, roughly doubling the magnetic field on the plasma axis. The confinement time for a particle in plasma varies with the square of the linear size, and power density varies with the fourth power of the magnetic field, so doubling the magnetic field offers the performance of a machine 4 times larger. The smaller size reduces construction costs, although this is offset to some degree by the expense of the REBCO magnets.
The use of REBCO may allow the magnet windings to be flexible when the machine is not operational. This would allow them to be "folded open" to allow access to the interior of the machine. This would greatly lower maintenance costs, eliminating the need to perform maintenance through small access ports using remote manipulators. If realized, this could improve the reactor's capacity factor, an important metric in power generation costs.
The first machine planned to come from the project is a scaled-down demonstrator named SPARC (as Soon as Possible ARC). It is to be built by Commonwealth Fusion Systems, with backing led by Eni, Breakthrough Energy Ventures, Khosla Ventures, Temasek, and Equinor. | 0 | Theoretical and Fundamental Chemistry |
The method has been in use since World War I. Prior to this, the process and purity of hydrogen generation relying on steam passing over hot iron was difficult to control. The chemical reaction uses sodium hydroxide (NaOH), ferrosilicon, and water (HO). While in the "silicol" process, a heavy steel pressure vessel is filled with sodium hydroxide and ferrosilicon, and upon closing, a controlled amount of water is added; the dissolving of the hydroxide heats the mixture to about and starts the reaction; sodium silicate, hydrogen and steam are produced. The overall reaction of the process is believed to be:
: 2NaOH + Si + HO → NaSiO + 2H
Ferrosilicon is used by the military to quickly produce hydrogen for balloons by the ferrosilicon method. The generator may be small enough to fit in a truck and requires only a small amount of electric power, the materials are stable and not combustible, and they do not generate hydrogen until mixed.
One report notes that this method of hydrogen production wasn't thoroughly investigated for about century despite being reported by the US military in the beginning of 20th century. | 1 | Applied and Interdisciplinary Chemistry |
MsO catalyzes the esterification of alcohols by carboxylic acids. 2-Naphthyl acetate was prepared from 2-naphthol and glacial (anhydrous) acetic acid in the presence of MsO. Both alcohols on ethylene glycol successfully benzoylated with benzoic acid and MsO. However, for free alcohols on monosaccharides, the acetylation was not completed. | 0 | Theoretical and Fundamental Chemistry |
Since discovery of ribozymes by Thomas Cech and Sidney Altman in the early 1980s, ribozymes have been shown to be a distinct class of metalloenzymes. Many ribozymes require metal ions in their active sites for chemical catalysis; hence they are called metalloenzymes. Additionally, metal ions are essential for structural stabilization of ribozymes. Group I intron is the most studied ribozyme which has three metals participating in catalysis. Other known ribozymes include group II intron, RNase P, and several small viral ribozymes (such as hammerhead, hairpin, HDV, and VS) and the large subunit of ribosomes. Several classes of ribozymes have been described.
Deoxyribozymes, also called DNAzymes or catalytic DNA, are artificial DNA-based catalysts that were first produced in 1994. Almost all DNAzymes require metal ions. Although ribozymes mostly catalyze cleavage of RNA substrates, a variety of reactions can be catalyzed by DNAzymes including RNA/DNA cleavage, RNA/DNA ligation, amino acid phosphorylation and dephosphorylation, and carbon–carbon bond formation. Yet, DNAzymes that catalyze RNA cleavage reaction are the most extensively explored ones. 10-23 DNAzyme, discovered in 1997, is one of the most studied catalytic DNAs with clinical applications as a therapeutic agent. Several metal-specific DNAzymes have been reported including the GR-5 DNAzyme (lead-specific), the CA1-3 DNAzymes (copper-specific), the 39E DNAzyme (uranyl-specific) and the NaA43 DNAzyme (sodium-specific). | 1 | Applied and Interdisciplinary Chemistry |
The dietary reference intake for vitamin D issued in 2010 by the Institute of Medicine (IoM) (renamed National Academy of Medicine in 2015), superseded previous recommendations which were expressed in terms of adequate intake. The recommendations were formed assuming the individual has no skin synthesis of vitamin D because of inadequate sun exposure. The reference intake for vitamin D refers to total intake from food, beverages and supplements, and assumes that calcium requirements are being met. The tolerable upper intake level (UL) is defined as "the highest average daily intake of a nutrient that is likely to pose no risk of adverse health effects for nearly all persons in the general population." Although ULs are believed to be safe, information on the long-term effects is incomplete and these levels of intake are not recommended for long-term consumption.
For US food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV). For vitamin D labeling purposes, 100% of the daily value was 400IU (10μg), but in May 2016, it was revised to 800IU (20μg) to bring it into agreement with the recommended dietary allowance (RDA). Compliance with the updated labeling regulations was required by 1 January 2020 for manufacturers with or more in annual food sales, and by 1 January 2021 for manufacturers with lower volume food sales. A table of the old and new adult daily values is provided at Reference Daily Intake. | 1 | Applied and Interdisciplinary Chemistry |
A volatile oil was extracted from waterwort distillery (Artemisia vulgaris) and tarragon (Artemisia dracunculus), from which the sesquiterpene alcohol spathulenol was isolated for the first time in 1975 as a colorless, viscous compound with an earth-aromatic odor and bitter-spicy taste. | 1 | Applied and Interdisciplinary Chemistry |
Some of the first reported organotantalum complexes were cyclopentadienyl derivatives. These arise from the salt metathesis reactions of sodium cyclopentadienide and tantalum pentachloride. An example of this is the first transition metal trihydride, CpTaH. More soluble and better developed are derivatives of pentamethylcyclopentadiene such as Cp*TaCl, Cp*TaCl, and Cp*TaH. | 0 | Theoretical and Fundamental Chemistry |
While the definition of sublimation is simple, there is often confusion as to what counts as a sublimation. | 0 | Theoretical and Fundamental Chemistry |
Dexchlorpheniramine (trade name Polaramine) is an antihistamine with anticholinergic properties used to treat allergic conditions such as hay fever or urticaria. It is the pharmacologically active dextrorotatory isomer of chlorpheniramine.
It came into medical use in 1959 and was patented in 1962. | 0 | Theoretical and Fundamental Chemistry |
In the case of NMR, nuclei with spin ≥ 1/2 have a magnetic dipole moment so that their energies are split by a magnetic field, allowing resonance absorption of energy related to the Larmor frequency:
where is the gyromagnetic ratio and is the (normally applied) magnetic field external to the nucleus.
In the case of NQR, nuclei with spin ≥ 1, such as N, O, Cl and Cu, also have an electric quadrupole moment. The nuclear quadrupole moment is associated with non-spherical nuclear charge distributions. As such it is a measure of the degree to which the nuclear charge distribution deviates from that of a sphere; that is, the prolate or oblate shape of the nucleus. NQR is a direct observation of the interaction of the quadrupole moment with the local electric field gradient (EFG) created by the electronic structure of its environment. The NQR transition frequencies are proportional to the product of the electric quadrupole moment of the nucleus and a measure of the strength of the local EFG:
where q is related to the largest principal component of the EFG tensor at the nucleus. is referred to as the quadrupole coupling constant.
In principle, the NQR experimenter could apply a specified EFG in order to influence just as the NMR experimenter is free to choose the Larmor frequency by adjusting the magnetic field. However, in solids, the strength of the EFG is many kV/m^2, making the application of EFG's for NQR in the manner that external magnetic fields are chosen for NMR impractical. Consequently, the NQR spectrum of a substance is specific to the substance - and NQR spectrum is a so called "chemical fingerprint." Because NQR frequencies are not chosen by the experimenter, they can be difficult to find making NQR a technically difficult technique to carry out. Since NQR is done in an environment without a static (or DC) magnetic field, it is sometimes called "zero field NMR". Many NQR transition frequencies depend strongly upon temperature. | 0 | Theoretical and Fundamental Chemistry |
Liebig and Wöhler observed in 1832 in an investigation of benzoin resin (benzoic acid) that the compounds almond oil (benzaldehyde), "Benzoestoff" (benzyl alcohol), benzoyl chloride and benzamide all share a common CHO fragment and that these compounds could all be synthesized from almond oil by simple substitutions. The CHO fragment was considered a "radical of benzoic acid" and called benzoyl. Organic radicals were thus placed on the same level as the inorganic elements. Just like the inorganic elements (simple radicals) the organic radicals (compound radicals) were indivisible. The theory was developed thanks to improvements in elemental analysis by von Liebig. Laurent contributed to the theory by reporting the isolation of benzoyl itself in 1835, however the isolated chemical is today recognised at its dimer dibenzoyl. Raffaele Piria reported the salicyl radical as the base for salicylic acid. Liebig published a definition of a radical in 1838
Berzelius and Robert Bunsen investigated the radical cacodyl (reaction of cacodyl chloride with zinc) around 1841, now also known as a dimer species (CH)As—As(CH). Edward Frankland and Hermann Kolbe contributed to the radical theory by investigating the ethyl and the methyl radicals. Frankland first reported diethylzinc in 1848. Frankland and Kolbe together investigated the reaction of ethyl cyanide and zinc in 1849 reporting the isolation of not the ethyl radical but the methyl radical (CH) which in fact was ethane. Kolbe also investigated the electrolysis of potassium salts of some fatty acids. Acetic acid was regarded as the combination of the methyl radical and oxalic acid and electrolysis of the salt yielded as gas again ethane misidentified as the liberated methyl radical.
In 1850 Frankland investigated ethyl radicals. In the course of this work butane formed by reaction of ethyl iodide and zinc was mistakenly identified as the ethyl radical. | 0 | Theoretical and Fundamental Chemistry |
In blood vessels Endothelium-Derived Hyperpolarizing Factor or EDHF is proposed to be a substance and/or electrical signal that is generated or synthesized in and released from the endothelium; its action is to hyperpolarize vascular smooth muscle cells, causing these cells to relax, thus allowing the blood vessel to expand in diameter. | 1 | Applied and Interdisciplinary Chemistry |
How much gas is present could be specified by giving the mass instead of the chemical amount of gas. Therefore, an alternative form of the ideal gas law may be useful. The chemical amount, n (in moles), is equal to total mass of the gas (m) (in kilograms) divided by the molar mass, M (in kilograms per mole):
By replacing n with m/M and subsequently introducing density ρ = m/V, we get:
Defining the specific gas constant R as the ratio R/M,
This form of the ideal gas law is very useful because it links pressure, density, and temperature in a unique formula independent of the quantity of the considered gas. Alternatively, the law may be written in terms of the specific volume v, the reciprocal of density, as
It is common, especially in engineering and meteorological applications, to represent the specific gas constant by the symbol R. In such cases, the universal gas constant is usually given a different symbol such as or to distinguish it. In any case, the context and/or units of the gas constant should make it clear as to whether the universal or specific gas constant is being used. | 0 | Theoretical and Fundamental Chemistry |
The separating funnel relies on the concept of "like dissolves like", which describes the ability of polar solvents to dissolve polar solutes and non-polar solvents to dissolve non-polar solutes. When the separating funnel is agitated, each solute migrates to the solvent (also referred to as "phase") in which it is more soluble.
The solvents normally do not form a unified solution together because they are immiscible. When the funnel is kept stationary after agitation, the liquids form distinct physical layers - lower density liquids will stay above higher density liquids. A mixture of solutes is thus separated into two physically separate solutions, each enriched in different solutes.
The stopcock may be opened after the two phases separate to allow the bottom layer to escape the separator funnel. The top layer may be retained in the separating funnel for further extractions with additional batches of solvent or drained out into a separate vessel for other uses. If it is desired to retain the bottom layer in the separating funnel for further extractions, both layers are taken out separately, and then the former bottom layer is returned to the separating funnel.
Each independent solution can then be extracted again with additional batches of solvent, used for other physical or chemical processes. If the goal was to separate a soluble material from mixture, the solution containing that desired product can sometimes simply be evaporated to leave behind the purified solute. For this reason, it is a practical benefit to use volatile solvents for extracting the desired material from the mixture. | 0 | Theoretical and Fundamental Chemistry |
Other techniques for writing data in three-dimensions have also been examined, including:
Persistent spectral hole burning (PSHB), which also allows the possibility of spectral multiplexing to increase data density. However, PSHB media currently requires extremely low temperatures to be maintained in order to avoid data loss.
Void formation, where microscopic bubbles are introduced into a media by high intensity laser irradiation.
Chromophore poling, where the laser-induced reorientation of chromophores in the media structure leads to readable changes. | 0 | Theoretical and Fundamental Chemistry |
The original membership fee was very steep for the time: The first subscription fee was set at one guinea, which would be equivalent to nearly £400 today. Four grades of membership were agreed at the time: member, associate, student and honorary, with most appointments made on the basis of a review of their eligibility by the SCI council. Despite the high fee, by the time of the first official meeting of the Society of Chemical Industry in June 1881, it had attracted over 300 members. | 1 | Applied and Interdisciplinary Chemistry |
Ammonotelism is the excretion of ammonia and ammonium ions. Ammonia (NH) forms with the oxidation of amino groups.(-NH), which are removed from the proteins when they convert into carbohydrates. It is a very toxic substance to tissues and extremely soluble in water. Only one nitrogen atom is removed with it. A lot of water is needed for the excretion of ammonia, about 0.5 L of water is needed per 1 g of nitrogen to maintain ammonia levels in the excretory fluid below the level in body fluids to prevent toxicity. Thus, the marine organisms excrete ammonia directly into the water and are called ammonotelic. Ammonotelic animals include crustaceans, platyhelminths, cnidarians, poriferans, echinoderms, and other aquatic invertebrates. | 1 | Applied and Interdisciplinary Chemistry |
Microscopic simulation methods work directly with the equations of motion (classical or quantum) of the constituent molecules. | 0 | Theoretical and Fundamental Chemistry |
In organic chemistry, a ketene is an organic compound of the form , where R and R' are two arbitrary monovalent chemical groups (or two separate substitution sites in the same molecule). The name may also refer to the specific compound ethenone , the simplest ketene.
Although they are highly useful, most ketenes are unstable. When used as reagents in a chemical procedure, they are typically generated when needed, and consumed as soon as (or while) they are produced. | 0 | Theoretical and Fundamental Chemistry |
At the beginning of the 20th century, the entire Russian industry was in a deep crisis, the consequences of which affected the factories of the Urals until 1909. In 1909, the Ural iron and steel plants smelted 34.7 million tons of iron, which is 30.9% less than in 1900. During the crisis years, the share of finished iron increased, new markets were searched for, syndicates and associations were created to fight the competition of factories in Southern Russia. To a lesser extent, the crisis affected the copper smelting industry, thanks to continued demand and an increase in customs duties on copper imports. In the first decade of the 20th century, small technically backward factories with worn-out equipment, which had become unprofitable, were closed. Of the 111 metallurgical plants operating in the Urals in 1900, 35 plants were shut down by 1913. In conditions of tough competition, factories were forced to modernize: blast furnaces with a lightweight casing were erected, hot blast was introduced everywhere, steam engines and ore preparation for smelting, furnaces and puddling furnaces were replaced by open-hearth furnaces, more powerful rolling mills were built, and factories received electricity. In the mountainous districts, the optimization and reorganization of capacities were carried out: the final processing was concentrated, as a rule, at the main plant of the district, the rest of the factories provided supplies of iron. During the Russo-Japanese War, the Izhevsk, Perm, and Zlatoust arms factories sharply increased the production of guns, rifles, and shells.
In 1908, the construction of the Porogi electrometallurgical plant for the production of ferroalloys, and one of the first hydroelectric power plants in Russia to provide the plant with electricity began. Until 1931, the plant was the only producer of ferroalloys in the country.
In 1910, an industrial boom began, which continued until the First World War. From 1910 to 1913, the production of iron increased to 55.3 million poods (by 29.9%), finished metal products - up to 40.8 million poods (by 9.6%). But the share of the Ural factories in the all-Russian iron smelting fell to 21.6%. Commercial banks actively invested in the development of the metallurgy of the Urals. The most important role in the Urals was played by the Azov-Don Commercial Bank, Saint Petersburg International Commercial Bank, and Russo-Asiatic Bank. The volume of investments at the turn of the 20th century was estimated at 10.8 million rubles. Modernization and reconstruction of mountain districts continued. In 1911, a new blast furnace with a volume of 150 m³ and an open-hearth furnace with a capacity of 25 tons were launched at the Nizhniy Tagil plant; two Bessemer converters and two new blast furnaces were installed at the Nizhnesaldinsky plant. The Votkinsk plant was reconstructed for the production of steam locomotives and river vessels. The factories that produced weapons were reconstructed and switched over to the production of civilian products. Also in the pre-war years, the concentration of production at large factories increased: in 1914, out of 49 Ural plants, 16 had the productivity of more than 1 million poods of iron per year and produced 65% of the total volume, including 5 factories with a capacity of more than 2 million poods of iron per year. Nadezhdinsky, Nizhnesaldinsky, Zlatoustovsky, Chusovskoy, and Votkinsky produced 36.1% of the total volume.
Copper smelters of the Urals at the beginning of the 20th century mastered pyrite smelting, which made it possible to process poor sulfur ores. In the pre-war years, the Nizhnekyshtymsky Copper Electrolytic Plant, the Karabashsky, and Kalatinsky plants were launched. Through syndicates formed, British companies owned 65.5% of the copper mined in the Urals. The gold-platinum mining industry underwent mechanization. The first Dutch dredges appeared in 1900 at the Neozhidany Mine on the Is River. By 1913, the number of dredges in the Urals reached 50, they ensured the extraction of 20% of gold and 50% of platinum. Until 1913, the average production of gold in the Urals was 550-650 poods per year, while the average production of platinum was 300-350 poods per year. | 1 | Applied and Interdisciplinary Chemistry |
Thermomechanical processing is a metallurgical process that combines mechanical or plastic deformation process like compression or forging, rolling, etc. with thermal processes like heat-treatment, water quenching, heating and cooling at various rates into a single process. | 1 | Applied and Interdisciplinary Chemistry |
A well dispersed colloidal suspension consists of individual, separated particles and is stabilized by repulsive inter-particle forces. When the repulsive forces weaken or become attractive through the addition of a coagulant, particles start to aggregate. Initially, particle doublets A will form from singlets A according to the scheme
In the early stage of the aggregation process, the suspension mainly contains individual particles. The rate of this phenomenon is characterized by the aggregation rate coefficient . Since doublet formation is a second order rate process, the units of this coefficients are ms since particle concentrations are expressed as particle number per unit volume (m). Since absolute aggregation rates are difficult to measure, one often refers to the dimensionless stability ratio , defined as where is the aggregation rate coefficient in the fast regime, and the coefficient at the conditions of interest. The stability ratio is close to unity in the fast regime, increases in the slow regime, and becomes very large when the suspension is stable.
Often, colloidal particles are suspended in water. In this case, they accumulate a surface charge and an electrical double layer forms around each particle. The overlap between the diffuse layers of two approaching particles results in a repulsive double layer interaction potential, which leads to particle stabilization. When salt is added to the suspension, the electrical double layer repulsion is screened, and van der Waals attraction become dominant and induce fast aggregation. The figure on the right shows the typical dependence of the stability ratio versus the electrolyte concentration, whereby the regimes of slow and fast aggregation are indicated.
The table below summarizes the critical coagulation concentration (CCC) ranges for different net charge of the counter ion.
The charge is expressed in units of elementary charge. This dependence reflects the Schulze–Hardy rule, which states that the CCC varies as the inverse sixth power of the counter ion charge. The CCC also depends on the type of ion somewhat, even if they carry the same charge. This dependence may reflect different particle properties or different ion affinities to the particle surface. Since particles are frequently negatively charged, multivalent metal cations thus represent highly effective coagulants.
Adsorption of oppositely charged species (e.g., protons, specifically adsorbing ions, surfactants, or polyelectrolytes) may destabilize a particle suspension by charge neutralization or stabilize it by buildup of charge, leading to a fast aggregation near the charge neutralization point, and slow aggregation away from it.
Quantitative interpretation of colloidal stability was first formulated within the DLVO theory. This theory confirms the existence slow and fast aggregation regimes, even though in the slow regime the dependence on the salt concentration is often predicted to be much stronger than observed experimentally. The Schulze–Hardy rule can be derived from DLVO theory as well.
Other mechanisms of colloid stabilization are equally possible, particularly, involving polymers. Adsorbed or grafted polymers may form a protective layer around the particles, induce steric repulsive forces, and lead to steric stabilization at it is the case with polycarboxylate ether (PCE), the last generation of chemically tailored superplasticizer specifically designed to increase the workability of concrete while reducing its water content to improve its properties and durability. When polymers chains adsorb to particles loosely, a polymer chain may bridge two particles, and induce bridging forces. This situation is referred to as bridging flocculation.
When particle aggregation is solely driven by diffusion, one refers to perikinetic aggregation. Aggregation can be enhanced through shear stress (e.g., stirring). The latter case is called orthokinetic aggregation. | 0 | Theoretical and Fundamental Chemistry |
NMR signals are usually detected inductively, but the low frequencies of the electromagnetic radiation emitted by samples in a ZULF experiment makes inductive detection impractical at low fields. Hence, the earliest approach for measuring zero-field NMR in solid samples was via field-cycling techniques. The field cycling involves three steps: preparation, evolution and detection. In the preparation stage, a field is applied in order to magnetize the nuclear spins. Then the field is suddenly switched to zero to initiate the evolution interval and the magnetization evolves under the zero-field Hamiltonian. After a time period, the field is again switched on and the signal is detected inductively at high field. In a single field cycle, the magnetization observed corresponds only to a single value of the zero-field evolution time. The time-varying magnetization can be detected by repeating the field cycle with incremented lengths of the zero-field interval, and hence the evolution and decay of the magnetization is measured point by point. The Fourier transform of this magnetization will result to the zero-field absorption spectrum.
The emergence of highly sensitive magnetometry techniques has allowed for the detection of zero-field NMR signals in situ. Examples include superconducting quantum interference devices (SQUIDs), magnetoresistive sensors, and SERF atomic magnetometers. SQUIDs have high sensitivity, but require cryogenic conditions to operate, which makes them practically somewhat difficult to employ for the detection of chemical or biological samples. Magnetoresistive sensors are less sensitive, but are much easier to handle and to bring close to the NMR sample which is advantageous since proximity improves sensitivity. The most common sensors employed in ZULF NMR experiments are optically-pumped magnetometers, which have high sensitivity and can be placed in close proximity to an NMR sample. | 0 | Theoretical and Fundamental Chemistry |
Members of the Hedgehog protein family act by binding to a transmembrane "Patched" receptor, which is bound to the "Smoothened" protein, by which the Hedgehog signal can be transduced. In the absence of Hedgehog, the Patched receptor inhibits Smoothened action. Inhibition of Smoothened causes the Cubitus interruptus (Ci), Fused, and Cos protein complex attached to microtubules to remain intact. In this conformation, the Ci protein is cleaved so that a portion of the protein is allowed to enter the nucleus and act as a transcriptional repressor. In the presence of Hedgehog, Patched no longer inhibits Smoothened. Then active Smoothened protein is able to inhibit PKA and Slimb, so that the Ci protein is not cleaved. This intact Ci protein can enter the nucleus, associate with CPB protein and act as a transcriptional activator, inducing the expression of Hedgehog-response genes. | 1 | Applied and Interdisciplinary Chemistry |
Type III restriction enzymes (e.g., EcoP15) recognize two separate non-palindromic sequences that are inversely oriented. They cut DNA about 20–30 base pairs after the recognition site. These enzymes contain more than one subunit and require AdoMet and ATP cofactors for their roles in DNA methylation and restriction digestion, respectively. They are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. Type III enzymes are hetero-oligomeric, multifunctional proteins composed of two subunits, Res () and Mod (). The Mod subunit recognises the DNA sequence specific for the system and is a modification methyltransferase; as such, it is functionally equivalent to the M and S subunits of type I restriction endonuclease. Res is required for restriction digestion, although it has no enzymatic activity on its own. Type III enzymes recognise short 5–6 bp-long asymmetric DNA sequences and cleave 25–27 bp downstream to leave short, single-stranded 5' protrusions. They require the presence of two inversely oriented unmethylated recognition sites for restriction digestion to occur. These enzymes methylate only one strand of the DNA, at the N-6 position of adenine residues, so newly replicated DNA will have only one strand methylated, which is sufficient to protect against restriction digestion. Type III enzymes belong to the beta-subfamily of N6 adenine methyltransferases, containing the nine motifs that characterise this family, including motif I, the AdoMet binding pocket (FXGXG), and motif IV, the catalytic region (S/D/N (PP) Y/F). | 1 | Applied and Interdisciplinary Chemistry |
Monatomic anions are named as the element modified with an -ide ending. The charge follows in brackets, (optional for 1) e.g.:
* Cl) or chloride
* S)
Some elements take their Latin name as the root e.g
*silver, Ag, argentide
*copper, Cu, cupride
*iron, Fe, ferride
*tin, Sn, stannide
Polyatomic anions of the same element are named as the element name preceded by di-, tri-, etc., e.g.:
* O) (or peroxide as an acceptable name)
* C) (or acetylide as an acceptable name)
* S)
or sometimes as an alternative derived from a substitutive name e.g.
* S</sup> disulfanediide
Polyatomic anions made up of different elements are named either substitutively or additively, the name endings are -ide and -ate respectively e.g. :
* GeH) (additive)
*TeH</sup> tellanuide substitutive where -uide specifies anion composed of additional hydride attached to parent hydride
* [PF]-phosphanuide (substitutive), or hexafluoridophosphate(1) (additive)
*SO) (additive), or sulfite (acceptable non-systematic name)
A full list of the alternative acceptable non-systematic names for cations and anions is in the recommendations.
Many anions have names derived from inorganic acids and these are dealt with later. | 0 | Theoretical and Fundamental Chemistry |
The use of synthetic oligonucleotides as specific probes for genetic sequence variations was pioneered by R. Bruce Wallace, working at the City of Hope National Medical Center in Duarte, California. In 1979 Wallace and his coworkers reported the use of ASO probes to detect variations in a single-stranded bacterial virus, and later applied the technique to cloned human genes. In 1983 and 1985 Wallace's lab reported the detection of the mutation for sickle cell anemia in samples of whole genomic DNA, although this application was hampered by the small amount of label that could be carried by the ASO.
Fortunately PCR, a method to greatly amplify a specific segment of DNA, was also reported in 1985. In less than a year PCR had been paired with ASO analysis. This combination solved the problem of ASO labeling, since the amount of target DNA could be amplified over a million-fold. Also, the specificity of the PCR process itself could be added to that of the ASO probes, greatly reducing the problem of spurious binding of the ASO to non-target sequences. The combination was specific enough that it could be used in a simple Dot blot, avoiding the laborious and inefficient Southern blot method. | 1 | Applied and Interdisciplinary Chemistry |
Rhodopin (1,2-dihydro-ψ,ψ-caroten-1-ol) is a carotenoid. It is a major carotenoid of phototropic bacteria such as Rhodomicrobium vannielii and Rhodopseudomonas acidophila strain 7050. | 1 | Applied and Interdisciplinary Chemistry |
Harmful algal bloom in coastal areas are also often referred to as "red tides". The term "red tide" is derived from blooms of any of several species of dinoflagellate, such as Karenia brevis. However, the term is misleading since algal blooms can widely vary in color, and growth of algae is unrelated to the tides. Not all red tides are produced by dinoflagellates. The mixotrophic ciliate Mesodinium rubrum produces non-toxic blooms coloured deep red by chloroplasts it obtains from the algae it eats.
As a technical term, it is being replaced in favor of more precise terminology, including the generic term "harmful algal bloom" for harmful species, and "algal bloom" for benign species. | 0 | Theoretical and Fundamental Chemistry |
A hormone response element (HRE) is a short sequence of DNA within the promoter of a gene, that is able to bind to a specific hormone receptor complex and therefore regulate transcription. The sequence is most commonly a pair of inverted repeats separated by three nucleotides, which also indicates that the receptor binds as a dimer. Specifically, HRE responds to steroid hormones, as the activated steroid receptor is the transcription factor binding HRE. This regulates the transcription of genes signalled by the steroid hormone.
A gene may have many different response elements, allowing complex control to be exerted over the level and rate of transcription.
HRE are used in transgenic animal cells as inducers of gene expression.
Examples of HREs include estrogen response elements and androgen response elements. | 1 | Applied and Interdisciplinary Chemistry |
*[http://www.pharmetrx.de/ PharMetrX: Pharmacometrics & Computational Disease Modelling] (annual call for applications, July - Sept 15th) | 1 | Applied and Interdisciplinary Chemistry |
To solve for the concentration of all components appearing in any general biochemical reaction as in (), the Michaelis–Menten kinetics for an enzymatic reaction are coupled with the Monod kinetics for biomass dynamics. The most general case is to assume that the enzyme concentration is proportional to the biomass concentration and that the reaction is not in quasi-steady state. These hypotheses lead to the following system of equations
with , and where is the concentration of the most limiting substrate in each reaction i, z is the enzyme yield coefficient, Y is the yield coefficient expressing the biomass gain per unit of released product and is the biomass mortality rate. | 0 | Theoretical and Fundamental Chemistry |
Photoionization is the physical process in which an incident photon ejects one or more electrons from an atom, ion or molecule. This is essentially the same process that occurs with the photoelectric effect with metals. In the case of a gas or single atoms, the term photoionization is more common.
The ejected electrons, known as photoelectrons, carry information about their pre-ionized states. For example, a single electron can have a kinetic energy equal to the energy of the incident photon minus the electron binding energy of the state it left. Photons with energies less than the electron binding energy may be absorbed or scattered but will not photoionize the atom or ion.
For example, to ionize hydrogen, photons need an energy greater than 13.6 electronvolts (the Rydberg energy), which corresponds to a wavelength of 91.2 nm. For photons with greater energy than this, the energy of the emitted photoelectron is given by:
where h is the Planck constant and ν is the frequency of the photon.
This formula defines the photoelectric effect.
Not every photon which encounters an atom or ion will photoionize it. The probability of photoionization is related to the photoionization cross-section, which depends on the energy of the photon and the target being considered. For photon energies below the ionization threshold, the photoionization cross-section is near zero. But with the development of pulsed lasers it has become possible to create extremely intense, coherent light where multi-photon ionization may occur. At even higher intensities (around 10 - 10 W/cm of infrared or visible light), non-perturbative phenomena such as barrier suppression ionization and rescattering ionization are observed. | 0 | Theoretical and Fundamental Chemistry |
Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions that allows a plant to photosynthesize during the day, but only exchange gases at night. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but they open at night to collect carbon dioxide () and allow it to diffuse into the mesophyll cells. The is stored as four-carbon malic acid in vacuoles at night, and then in the daytime, the malate is transported to chloroplasts where it is converted back to , which is then used during photosynthesis. The pre-collected is concentrated around the enzyme RuBisCO, increasing photosynthetic efficiency. This mechanism of acid metabolism was first discovered in plants of the family Crassulaceae. | 0 | Theoretical and Fundamental Chemistry |
The US Government uses the Hazardous Materials Identification System (HMIS) standard for flammability ratings, as do many US regulatory agencies, and also the US National Fire Protection Association (NFPA).
The ratings are as follows: | 0 | Theoretical and Fundamental Chemistry |
In the typical porphyrin biosynthesis pathway, four molecules of porphobilinogen are concatenated by carbons 2 and 5 of the pyrrole ring (adjacent to the nitrogen atom) into hydroxymethyl bilane by the enzyme porphobilinogen deaminase, also known as hydroxymethylbilane synthase. | 1 | Applied and Interdisciplinary Chemistry |
Galactolysis refers to the catabolism of galactose.
In the liver, galactose is converted through the Leloir pathway to glucose 6-phosphate in the following reactions:
galacto- uridyl phosphogluco-
kinase transferase mutase
gal --------> gal 1 P ------------------> glc 1 P -----------> glc 6 P
/ v
UDP-glc UDP-gal
epimerase | 1 | Applied and Interdisciplinary Chemistry |
Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are also piezoelectric and pyroelectric, with the additional property that their natural electrical polarization is reversible. The term is used in analogy to ferromagnetism, in which a material exhibits a permanent magnetic moment. Ferromagnetism was already known when ferroelectricity was discovered in 1920 in Rochelle salt by Joseph Valasek. Thus, the prefix ferro, meaning iron, was used to describe the property despite the fact that most ferroelectric materials do not contain iron. Materials that are both ferroelectric and ferromagnetic are known as multiferroics. | 0 | Theoretical and Fundamental Chemistry |
The first version of SMPDB was released on January 1, 2010. This release contained more than 350 image-mapped pathways for small molecule pathways. The viewer interface was limited to scroll-bar image navigation with 3-step (small, medium, large) zooming. The pathways in this first version were limited to 1) human metabolic pathways; 2) human metabolic disease pathways; and 3) human metabolite signaling pathways. The second version of SMPDB was released in 2014. This version contained more than 620 small molecule pathways. The viewer interface was enhanced to include a Google-Map-like interface with click-n-drag image navigation and unlimited, interactive zooming. The pathways in this second version were expanded to include: 1) general human metabolic pathways; 2) human metabolic disease pathways; 3) human metabolite signaling pathways; 4) drug action pathways and 5) drug metabolism pathways. | 1 | Applied and Interdisciplinary Chemistry |
Modafinil was studied for the treatment of stimulant dependence, but the results are mixed and inconclusive. Modafinil is not a controlled substance in some countries, unlike other medications, such as bupropion, which is also used to treat depression and nicotine dependence. The clinical trials that have tested modafinil as a treatment for stimulant abuse have failed to demonstrate its efficacy and the optimal dose and duration of modafinil treatment remain unclear, and modafinil is not a recommended treatment for stimulant abuse. | 0 | Theoretical and Fundamental Chemistry |
In 1960, Atalla and Kahng fabricated the first MOSFET with a gate oxide thickness of 100 nm, along with a gate length of 20µm. In 1962, Atalla and Kahng fabricated a nanolayer-base metal–semiconductor junction (M–S junction) transistor. This device has a metallic layer with nanometric thickness sandwiched between two semiconducting layers, with the metal forming the base and the semiconductors forming the emitter and collector. With its low resistance and short transit times in the thin metallic nanolayer base, the device was capable of high operation frequency compared to bipolar transistors. Their pioneering work involved depositing metal layers (the base) on top of single crystal semiconductor substrates (the collector), with the emitter being a crystalline semiconductor piece with a top or a blunt corner pressed against the metallic layer (the point contact). They deposited gold (Au) thin films with a thickness of 10 nm on n-type germanium (n-Ge), while the point contact was n-type silicon (n-Si). Atalla resigned from BTL in 1962. | 0 | Theoretical and Fundamental Chemistry |
This reaction shows the oxidation of phenol by iron and peroxide. This combination of iron, which comes from iron oxide in the sediment, and the peroxide, commonly released by animals and plants into the environment, is known as the Fenton Reagent. This reagent is used to oxidize phenol groups by the use of a radical hydroxide group produced from the peroxide in the p-benzoquinone. This product of phenol's oxidation is now leached into the environment while other products include iron(II) and water. P-benzoquinone is listed as being a very toxic, acute environmental hazard. | 0 | Theoretical and Fundamental Chemistry |
Luminol is synthesized in a two-step process, beginning with 3-nitrophthalic acid. First, hydrazine (NH) is heated with the 3-nitrophthalic acid in a high-boiling solvent such as triethylene glycol and glycerol. An acyl substitution condensation reaction occurs, with loss of water, forming 3-nitrophthalhydrazide. Reduction of the nitro group to an amino group with sodium dithionite (NaSO), via a transient hydroxylamine intermediate, produces luminol.
The compound was first synthesized in Germany in 1902, but was not named "luminol" until 1934. | 0 | Theoretical and Fundamental Chemistry |
The process of translation is highly regulated in both eukaryotic and prokaryotic organisms. Regulation of translation can impact the global rate of protein synthesis which is closely coupled to the metabolic and proliferative state of a cell.
To delve deeper into this intricate process, scientists typically use a technique known as ribosome profiling. This method enables researchers to take a snapshot of the translatome, showing which parts of the mRNA are being translated into proteins by ribosomes at a given time. Ribosome profiling provides valuable insights into translation dynamics, revealing the complex interplay between gene sequence, mRNA structure, and translation regulation. For example, research utilizing this method has revealed that genetic differences and their subsequent expression as mRNAs can also impact translation rate in an RNA-specific manner.
Expanding on this concept, a more recent development is single-cell ribosome profiling, a technique that allows us to study the translation process at the resolution of individual cells. This is particularly significant as cells, even those of the same type, can exhibit considerable variability in their protein synthesis. Single-cell ribosome profiling has the potential to shed light on the heterogeneous nature of cells, leading to a more nuanced understanding of how translation regulation can impact cell behavior, metabolic state, and responsiveness to various stimuli or conditions. | 1 | Applied and Interdisciplinary Chemistry |
Momentum diffusion most commonly refers to the diffusion, or spread of momentum between particles (atoms or molecules) of matter, often in the fluid state.
This transport of momentum can occur in any direction of the fluid flow. Momentum diffusion can be attributed to either external pressure or shear stress or both. | 1 | Applied and Interdisciplinary Chemistry |
Geopolymerization forms aluminosilicate frameworks that are similar to those of rock-forming minerals. Yet, there are major differences. In 1994, Davidovits presented a theoretical structure for K-poly(sialate-siloxo) (K)-(Si-O-Al-O-Si-O) that was consistent with the NMR spectra. It does not show the presence of water in the structure because he only focused on the relationship between Si, Al, Na, K, atoms. Water is present only at temperatures below 150 °C – 200 °C, whereas numerous geopolymer industrial and commercial applications work at temperatures above 200 °C, up to 1400 °C, i.e. at temperatures above dehydroxylation. Nevertheless, scientists working on low temperature applications, such as cements and waste management, tried to pinpoint cation hydration and water molecules. This model shows an incompletely reacted geopolymer (left in the figure), which involves free Si-OH groups that will later with time or with temperature polycondense with opposed Al-O-K, into Si-O-Al-O sialate bonds. The water released by this reaction either remains in the pores, is associated with the framework similarly to zeolitic water, or can be released and removed. Several 3D-frameworks are described in the book Geopolymer Chemistry and Applications. After dehydroxylation (and dehydration), generally above 250 °C, geopolymers become more and more crystalline (right in the picture) and above 500-1000 °C (depending on the nature of the alkali cation present) crystallise and have X-ray diffraction patterns and framework structures identical to their geological analogues. | 0 | Theoretical and Fundamental Chemistry |
Mass-difference impurity scattering is given by:
where is a measure of the impurity scattering strength. Note that is dependent of the dispersion curves. | 0 | Theoretical and Fundamental Chemistry |
In 1947 after the Manhattan Project had been dismantled, Lathrop remained on staff at the lab as an associate biochemist as it was renamed Argonne National Laboratory. In 1954, tired of an exhausting commute, Lathrop left Argonne to pursue a career at the Argonne Cancer Research Hospital. It had opened in 1953 on the University of Chicago campus making it much closer to her home.
Lathrop was hired by the US Atomic Energy Commission facility as a research associate under the guidance of Paul Harper. Their goal was to find ways to manipulate radiation to allow for cancer detection and treatment. Their groundbreaking work on using the gamma camera to scan the body is a method still in practice to this day.
She published her last paper in 1999 and then retired in 2000. | 0 | Theoretical and Fundamental Chemistry |
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