text stringlengths 105 4.57k | label int64 0 1 | label_text stringclasses 2
values |
|---|---|---|
That Flockhart supplied Simpsons self-experiment on 4 November 1847, was not the original plan, but his method for ensuring the chemicals purity was still broadly being used in the 1960s. Another name for it, in his time, was a perchloride of formyle, which had been planned by Dr. Simpson to come from David Waldie, another Scottish doctor/chemist from Linlithgow, based in Liverpool , but the laboratory suffered a fire. The process of making it could be dangerous; once one of their chloroform retorts exploded but Flockhart and Duncan both wore spectacles, which had protected their eyes.
The circumstances and different opinions on how Flockhart came to supply the surgeon with this drug is discussed in the Pharmaceutical Historian including statements by Simpsons daughter that Flockhart and his partner worked until 2 a.m. to prepare the first perchloride of formyle for her fathers trial. The success of the doctors experiment was communicated widely such that within three months demand was already high for this new anaesthetic and the firm were exporting to England. Flockharts product was exhibited in the London 1851 Exhibition, and that year Simpson paid Flockhart to supply it to Florence Nightingale. The total sales across the market was estimated as 750,000 doses a week by 1895.
From 1862 to 1875 the partners were Chemists and Druggists in Ordinary to Queen Victoria, supplying to Balmoral Castle, and she used chloroform in childbirth.
The firm extended to London and became the main supplier of chloroform in Britain, including to its armed forces, which continued during both World Wars. Duncan, Flockhart and Company was also used for sourcing reference samples on chloroform quality by drug firms in the United States.
At the 1947 centenary of the chloroform use experiment, the companys contribution and Flockharts role was noted in the press. | 1 | Applied and Interdisciplinary Chemistry |
This is made from rolled mild steel plate, usually between 15 and 30 mm thick, welded to form a cylinder which may be up to 230 m in length and up to 6 m in diameter.
Upper limits on diameter are set by the tendency of the shell to deform under its own weight to an oval cross section, with consequent flexure during rotation. Length is not necessarily limited, but it becomes difficult to cope with changes in length on heating and cooling (typically around 0.1 to 0.5% of the length) if the kiln is very long. | 1 | Applied and Interdisciplinary Chemistry |
Protein-directed DCC system must be amenable to efficient screening. Several analytical techniques have been applied to the analysis of protein-directed DCL. These include HPLC, mass spectrometry, NMR spectroscopy, and X-ray crystallography. | 1 | Applied and Interdisciplinary Chemistry |
Hyper-IL-6 is a designer cytokine, which was generated by the German biochemist Stefan Rose-John. Hyper-IL-6 is a fusion protein of the four-helical cytokine Interleukin-6 and the soluble Interleukin-6 receptor which are covalently linked by a flexible peptide linker. Interleukin-6 on target cells binds to a membrane bound Interleukin-6 receptor. The complex of Interleukin-6 and the Interleukin-6 receptor associate with a second receptor protein called gp130, which dimerises and initiates intracellular signal transduction. Gp130 is expressed on all cells of the human body whereas the Interleukin-6 receptor is only found on few cells such as hepatocytes and some leukocytes. Neither Interleukin-6 nor the Interleukin-6 receptor have a measurable affinity for gp130. Therefore, cells, which only express gp130 but no Interleukin-6 receptor are not responsive to Interleukin-6. It was found, however, that the membrane-bound Interleukin-6 receptor can be cleaved from the cell membrane generating a soluble Interleukin-6 receptor. The soluble Interleukin-6 receptor can bind the ligand Interleukin-6 with similar affinity as the membrane-bound Interleukin-6 receptor and the complex of Interleukin-6 and the soluble Interleukin-6 receptor can bind to gp130 on cells, which only express gp130 but no Interleukin-6 receptor. The mode of signaling via the soluble Interleukin-6 receptor has been named Interleukin-6 trans-signaling whereas Interleukin-6 signaling via the membrane-bound Interleukin-6 receptor is referred to as Interleukin-6 classic signaling. Therefore, the generation of the soluble Interleukin-6 receptor enables cells to respond to Interleukin-6, which in the absence of soluble Interleukin-6 receptor would be completely unresponsive to the cytokine. | 1 | Applied and Interdisciplinary Chemistry |
Compounds containing thiol groups on adjacent carbon centers are common. Ethane-1,2-dithiol reacts with aldehydes () and ketones () to give 1,3-dithiolanes:
Some dithiols are used in chelation therapy, i.e. the removal of heavy metal poisons. Examples include dimercaptopropanesulfate (DMPS), dimercaprol ("BAL"), and meso-2,3-dimercaptosuccinic acid. | 0 | Theoretical and Fundamental Chemistry |
Sulfuric acid reacts with most bases to give the corresponding sulfate or bisulfate.
Sulfuric acid reacts with sodium chloride, and gives hydrogen chloride gas and sodium bisulfate:
Aluminium sulfate, also known as paper maker's alum, aluminium sulfate is made by treating bauxite with sulfuric acid:
Sulfuric acid can also be used to displace weaker acids from their salts. Reaction with sodium acetate, for example, displaces acetic acid, , and forms sodium bisulfate:
Similarly, treating potassium nitrate with sulfuric acid produces nitric acid.
When combined with nitric acid, sulfuric acid acts both as an acid and a dehydrating agent, forming the nitronium ion , which is important in nitration reactions involving electrophilic aromatic substitution. This type of reaction, where protonation occurs on an oxygen atom, is important in many organic chemistry reactions, such as Fischer esterification and dehydration of alcohols.
When allowed to react with superacids, sulfuric acid can act as a base and can be protonated, forming the ion. Salts of have been prepared (e.g. trihydroxyoxosulfonium hexafluoroantimonate(V) ) using the following reaction in liquid HF:
The above reaction is thermodynamically favored due to the high bond enthalpy of the Si–F bond in the side product. Protonation using simply fluoroantimonic acid, however, has met with failure, as pure sulfuric acid undergoes self-ionization to give ions:
which prevents the conversion of to by the HF/ system. | 0 | Theoretical and Fundamental Chemistry |
Sulfur concrete was developed and promoted as a building material to get rid of large amounts of stored sulfur produced by hydrodesulfurization of gas and oil (Claus process). As of 2011, sulfur concrete has only been used in small quantities when fast curing or acid resistance is necessary.The material has been suggested by researchers as a potential building material on Mars, where water and limestone are not easily available, but sulfur is. | 1 | Applied and Interdisciplinary Chemistry |
Mn-SOD is the type of SOD present in eukaryotic mitochondria, and also in most bacteria (this fact is in keeping with the bacterial-origin theory of mitochondria). The Mn-SOD enzyme is probably one of the most ancient, for nearly all organisms living in the presence of oxygen use it to deal with the toxic effects of superoxide (), formed from the 1-electron reduction of dioxygen. The exceptions, which are all bacteria, include Lactobacillus plantarum and related lactobacilli, which use a different nonenzymatic mechanism with manganese (Mn) ions complexed with polyphosphate, suggesting a path of evolution for this function in aerobic life. | 1 | Applied and Interdisciplinary Chemistry |
The reaction is initiated by homolytic cleavage of a radical initiator, in this case 2,2'-azobisisobutyronitrile (AIBN), upon heating. A hydrogen is then abstracted from the hydrogen source (tributylstannane in this case) to leave a tributylstannyl radical that attacks the sulfur atom of the thiohydroxamate ester. The N-O bond of the thiohydroxamate ester undergoes homolysis to form a carboxyl radical which then undergoes decarboxylation and carbon dioxide (CO) is lost. The remaining alkyl radical (R·) then abstracts a hydrogen atom from remaining tributylstannane to form the reduced alkane (RH). (See Scheme 2) The tributyltin radical enters into another cycle of the reaction until all thiohydroxamate ester is consumed.
N-O bond cleavage of the Barton ester can also occur spontaneously upon heating or by irradiation with light to initiate the reaction. In this case a radical initiator is not required but a hydrogen-atom (H-atom) donor is still necessary to form the reduced alkane (RH). Alternative H-atom donors to tributylstannane include tertiary thiols and organosilanes. The relative expense, smell, and toxicity associated with tin, thiol or silane reagents can be avoided by carrying the reaction out using chloroform as both solvent and H-atom donor.
It is also possible to functionalize the alkyl radical by use of other radical trapping species (X-Y + R· -> R-X + Y·). The reaction proceeds due to the formation of the stable S-Sn bond and increasing aromaticity of the thiohydroxamate ester. There is also an overall increase in entropy due to the formation of gas which drives the reaction forward. | 0 | Theoretical and Fundamental Chemistry |
In an early example of the use of a chiral auxiliary in asymmetric synthesis, E. J. Corey and coworkers conducted an asymmetric Diels-Alder reaction between (−)-8-phenylmenthol acrylate ester and 5-benzyloxymethylcyclopentadiene. The cycloaddition product was carried forward to the iodolactone shown below, an intermediate in the classic Corey synthesis of the prostaglandins. It is proposed that the back face of the acrylate is blocked by the auxiliary, so that cycloaddition occurs at the front face of the alkene.
(−)-8-phenylmenthol can be prepared from either enantiomer of pulegone,
though neither route is very efficient. Because of the widespread utility of the 8-phenylmenthol auxiliary, alternative compounds that are more easily synthesized, such as trans-2-phenyl-1-cyclohexanol
and trans-2-(1-pheyl-1-methylethyl)cyclohexanol have been explored. | 0 | Theoretical and Fundamental Chemistry |
The carboxy-terminal domain is also the binding site for spliceosome factors that are part of RNA splicing. These allow for the splicing and removal of introns (in the form of a lariat structure) during RNA transcription. | 1 | Applied and Interdisciplinary Chemistry |
There exists no theory elucidating correlations among -amino acids. If one takes, for example, alanine, which has a small methyl group, and phenylalanine, which has a larger benzyl group, a simple question is in what aspect, -alanine resembles -phenylalanine more than -phenylalanine, and what kind of mechanism causes the selection of all -amino acids, because it might be possible that alanine was and phenylalanine was .
It was reported in 2004 that excess racemic ,-asparagine (Asn), which spontaneously forms crystals of either isomer during recrystallization, induces asymmetric resolution of a co-existing racemic amino acid such as arginine (Arg), aspartic acid (Asp), glutamine (Gln), histidine (His), leucine (Leu), methionine (Met), phenylalanine (Phe), serine (Ser), valine (Val), tyrosine (Tyr), and tryptophan (Trp). The enantiomeric excess of these amino acids was correlated almost linearly with that of the inducer, i.e., Asn. When recrystallizations from a mixture of 12 ,-amino acids (Ala, Asp, Arg, Glu, Gln, His, Leu, Met, Ser, Val, Phe, and Tyr) and excess ,-Asn were made, all amino acids with the same configuration with Asn were preferentially co-crystallized. It was incidental whether the enrichment took place in - or -Asn, however, once the selection was made, the co-existing amino acid with the same configuration at the α-carbon was preferentially involved because of thermodynamic stability in the crystal formation. The maximal ee was reported to be 100%. Based on these results, it is proposed that a mixture of racemic amino acids causes spontaneous and effective optical resolution, even if asymmetric synthesis of a single amino acid does not occur without an aid of an optically active molecule.
This is the first study elucidating reasonably the formation of chirality from racemic amino acids with experimental evidences. | 0 | Theoretical and Fundamental Chemistry |
Protein structure prediction is important in several fields of science, including bioinformatics, molecular biology, and medicine. Identifying natural proteins' structural configurations enables scientists to understand them better. This can lead to creating novel proteins by design, advances in treating disease, and solutions for other real-world problems such as invasive species, waste, and pollution.
The process by which living beings create the primary structure of proteins, protein biosynthesis, is reasonably well understood, as is the means by which proteins are encoded as DNA. However, determining how a given proteins primary structure becomes a functioning three-dimensional structure, how the molecule folds, is more difficult. The general process is understood, but predicting a proteins eventual, functioning structure is computationally demanding. | 1 | Applied and Interdisciplinary Chemistry |
Quantization of the orbital angular momentum of the electron combined with the magnetic moment of the electron suggested that atoms with a magnetic moment should show quantized behavior in a magnetic field.
In 1922, Otto Stern and Walther Gerlach set out to test this theory. They heated silver in a vacuum tube equipped with a series of narrow aligned slits, creating a molecular beam of silver atoms. They shot this beam through an inhomogeneous magnetic field. Rather than a continuous pattern of Silver atoms, they found two bunches.
Relative to its northern pole, pointing up, down, or somewhere in between, in classical mechanics, a magnet thrown through a magnetic field may be deflected a small or large distance upwards or downwards. The atoms that Stern and Gerlach shot through the magnetic field acted similarly. However, while the magnets could be deflected variable distances, the atoms would always be deflected a constant distance either up or down. This implied that the property of the atom that corresponds to the magnet's orientation must be quantized, taking one of two values (either up or down), as opposed to being chosen freely from any angle.
The choice of the orientation of the magnetic field used in the Stern–Gerlach experiment is arbitrary. In the animation shown here, the field is vertical and so the atoms are deflected either up or down. If the magnet is rotated a quarter turn, the atoms are deflected either left or right. Using a vertical field shows that the spin along the vertical axis is quantized, and using a horizontal field shows that the spin along the horizontal axis is quantized.
The results of the Stern-Gelach experiment caused a sensation, most especially because leading scientists, including Einstein and Paul Ehrenfest argued that the silver atoms should have random orientations in the conditions of the experiment: quantization should not have been observable. At least five years would elapse before this mystery was resolved: quantization was observed but it was not due to orbital angular momentum.
In 1925 Ralph Kronig proposed that electrons behave as if they self-rotate, or "spin", about an axis. Spin would generate a tiny magnetic moment that would split the energy levels responsible for spectral lines, in agreement with existing measurements. Two electrons in the same orbital would occupy distinct quantum states if they "spun" in opposite directions, thus satisfying the exclusion principle. Unfortunately, the theory had two significant flaws: two values computed by Kronig were off by a factor of two. Kronig's senior colleagues discouraged his work and it was never published.
Ten months later, Dutch physicists George Uhlenbeck and Samuel Goudsmit at Leiden University published their theory of electron self rotation. The model, like Kronig's was essentially classical but resulted in a quantum prediction. | 1 | Applied and Interdisciplinary Chemistry |
Faster GC methods have shorter times but Kovats indexes of the compounds may be conserved if proper method translation is applied.
Temperatures of the temperature program stay the same, but ramps and times change when using a smaller column or faster carrier gas.
If column dimensions Length×diameter×film are divided by 2 and gas velocity is doubled by using H2 in place of Helium, the hold times must be divided by 4 and the ramps must be multiplied by 4 to keep the same index and the same retention temperature for the same compound analyzed. Method translation rules are incorporated in some chromatography data systems. | 0 | Theoretical and Fundamental Chemistry |
There are two main groups of paired receptors, distinguished by extracellular regions containing immunoglobulin or C-type lectin domains. Nomenclature within these families is complex and has changed over time as new members were identified. In general, the example of the LILR family applies; genes designated A represent the inhibitory receptor and genes designated B represent the activating receptor. | 1 | Applied and Interdisciplinary Chemistry |
Thiamine triphosphate (ThTP) was chemically synthesized in 1948 at a time when the only organic triphosphate known was ATP. The first claim of the existence of ThTP in living organisms was made in rat liver, followed by baker’s yeast. Its presence was later confirmed in rat tissues and in plants germs, but not in seeds, where thiamine was essentially unphosphorylated. In all those studies, ThTP was separated from other thiamine derivatives using a paper chromatographic method, followed by oxidation in fluorescent thiochrome compounds with ferricyanide in alkaline solution. This method is at best semi-quantitative, and the development of liquid chromatographic methods suggested that ThTP represents far less than 10% of total thiamine in animal tissues. | 1 | Applied and Interdisciplinary Chemistry |
Luminous bacteria in light organ symbioses are successively acquired by host (squid, fish) from the seawater while they are juveniles, then regularly released into the ocean.
In the diagram on the right, depending on the light organ position, luminous bacteria are released from their guts into fecal pellets or directly into the seawater (step 1). Motile luminous bacteria colonize organic matter sinking along the water column. Bioluminescent bacteria colonising fecal pellets and particles influence zooplankton consumption rates. Such visual markers increase detection (“bait hypothesis”), attraction and finally predation by upper trophic levels (step 2). In the mesopelagic, zooplankton and their predators feed on sinking luminous particles and fecal pellets, which form either aggregates (repackaging) of faster sinking rates or fragment organic matter (due to sloppy feeding) with slower sinking rates (step 3).
Filter feeders also aggregate sinking organic matter without particular visual detection and selection of luminous matter. Diel (and seasonal) vertical migrators feeding on luminous food metabolize and release glowing fecal pellets from the surface to the mesopelagic zone (step 4). This implies bioluminescent bacteria dispersion at large spatial scales, for zooplankton or even some fish actively swimming long distances. Luminous bacteria attached to particles sink down to the seafloor, and sediment can be resuspended by oceanographic physical conditions (step 5) and consumed by epi-benthic organisms. Instruments are (a) plankton net, (b) fish net, (c) Niskin water sampler, (d) bathyphotometer, (e) sediment traps, (f) autonomous underwater vehicles, (g) photomultiplier module, (h) astrophysics optical modules ANTARES and (i–j) remotely operated vehicles. | 0 | Theoretical and Fundamental Chemistry |
Modern applications of the Wilfley table (and other wet shaking tables) are predominantly observed in the following roles:
# Laboratories. Small shaking tables are an excellent tool for see if a material will be responsive to gravity separation techniques
# Gold rooms. Wilfley tables typically act as rougher tables on gravity gold concentrate ahead final concentration methods (e.g. panning)
# High value heavy mineral concentrate cleaners. In mining, the vast majority of Wilfley-type tables are installed globally to concentrate (e.g.) tin, tungsten, tantalum, niobium, zircon, rutile, leucoxene, xenotime, monazite
# Zircon finishing table – a specialist application
Tables are now also being used in the recycling of electronic scrap to recover precious metals. | 1 | Applied and Interdisciplinary Chemistry |
A central battery system consisting of lead–acid cell units is provided to supply emergency electric power, when needed, to essential items such as the power station's control systems, communication systems, generator hydrogen seal system, turbine lube oil pumps, and emergency lighting. This is essential for a safe, damage-free shutdown of the units in an emergency situation. | 1 | Applied and Interdisciplinary Chemistry |
Intramolecular reactions of diazocarbonyl compounds include addition to carbon–carbon double bonds to form fused cyclopropanes and insertion into carbon–hydrogen bonds or carbon–carbon bonds. | 0 | Theoretical and Fundamental Chemistry |
In 2005–06, fragrance mix was the third-most-prevalent allergen in patch tests (11.5%). Fragrance was voted Allergen of the Year in 2007 by the American Contact Dermatitis Society. An academic study in the United States published in 2016 has shown that "34.7 % of the population reported health problems, such as migraine headaches and respiratory difficulties, when exposed to fragranced products".
The composition of fragrances is usually not disclosed in the label of the products, hiding the actual chemicals of the formula, which raises concerns among some consumers. In the United States, this is because the law regulating cosmetics protects trade secrets.
In the United States, fragrances are regulated by the Food and Drug Administration if present in cosmetics or drugs, by the Consumer Products Safety Commission if present in consumer products. No pre-market approval is required, except for drugs. Fragrances are also generally regulated by the Toxic Substances Control Act of 1976 that "grandfathered" existing chemicals without further review or testing and put the burden of proof that a new substance is not safe on the EPA. The EPA, however, does not conduct independent safety testing but relies on data provided by the manufacturer.
A 2019 study of the top-selling skin moisturizers found 45% of those marketed as "fragrance-free" contained fragrance. | 0 | Theoretical and Fundamental Chemistry |
While the anomeric effect can cause stabilization of molecules, it does have a magnitude to its stabilization, and this value can be overcome by other, more destabilizing effects in some cases.
In the example of spiroketals, the orientation on the upper left shows stabilization by the hyperconjugative anomeric effect twice, thus greatly stabilizing the orientation of the molecule. The orientation on the upper right only shows this hyperconjugative anomeric stabilization once, causing it to be the lesser preferred structure. However, when substituent are added onto the spiroketal backbone, the more preferred structure can be changed. When a large substituent is added to the spiroketal backbone, as seen in the lower left, the strain from having this large substituent, R, in the axial position is greatly destabilizing to the molecule. In the molecule on the lower right, R is now in the equatorial position, which no longer causes destabilization on the molecule. Therefore, without substituents, the upper equilibrium reaction is favored on the left hand side, while the lower equilibrium is favored on the right hand side, simply from the addition of a large, destabilizing substituent. | 0 | Theoretical and Fundamental Chemistry |
Salbutamol, also known as albuterol and sold under the brand name Ventolin among others, is a medication that opens up the medium and large airways in the lungs. It is a short-acting β adrenergic receptor agonist that causes relaxation of airway smooth muscle. It is used to treat asthma, including asthma attacks and exercise-induced bronchoconstriction, as well as chronic obstructive pulmonary disease (COPD). It may also be used to treat high blood potassium levels. Salbutamol is usually used with an inhaler or nebulizer, but it is also available in a pill, liquid, and intravenous solution. Onset of action of the inhaled version is typically within 15 minutes and lasts for two to six hours.
Common side effects include shakiness, headache, fast heart rate, dizziness, and feeling anxious. Serious side effects may include worsening bronchospasm, irregular heartbeat, and low blood potassium levels. It can be used during pregnancy and breastfeeding, but safety is not entirely clear.
Salbutamol was patented in 1966 in Britain and became commercially available in the UK in 1969. It was approved for medical use in the United States in 1982. It is on the World Health Organization's List of Essential Medicines. Salbutamol is available as a generic medication. In 2021, it was the seventh most commonly prescribed medication in the United States, with more than 61million prescriptions. | 0 | Theoretical and Fundamental Chemistry |
Neculai Costăchescu (18 February 1876–14 July 1939) was a Romanian chemist and politician.
Born in Huși, he obtained a degree in physics and chemistry from Iași University in 1901. Costăchescu earned a doctorate from the same institution in 1905, with a thesis on the gases found in Romanias salt deposits and muddy volcanoes; he was the universitys first doctor in chemistry. He took specialty courses at the University of Zurich from 1906 to 1908, then was hired as professor of mineral chemistry at the Iași science faculty in 1912. There, he set up an organic chemistry laboratory. Thanks to his scientific activity, he was elected a corresponding member of the Romanian Academy in 1925, and was granted honorary membership in 1936.
Costăchescu entered politics in December 1918, at the close of World War I, and was a founding member of the Peasants Party, serving as vice president until its 1926 merger with the Romanian National Party to form the National Peasants Party (PNȚ). A prominent member of the latter, he was elected senator in 1926 and deputy in 1928. Between November 1928 and April 1931, he served as Public Instruction Minister in the PNȚ cabinets of Iuliu Maniu and Gheorghe Mironescu. He was Senate President from August 1932 to November 1933.
Costăchescu contributed to a number of specialized publications in Iași, such as Annales scientifiques de la Université de Jassy and Revista științifică V. Adamachi. His works included Fluosels de cobalt et de nikel (1911), Sels complexes de fer (1912) and Fluorures complexes de chrôme (1912–14). | 0 | Theoretical and Fundamental Chemistry |
The only known place in the universe where the baryon density might possibly be high enough to produce quark matter, and the temperature is low enough for color superconductivity to occur, is the core of a compact star (often called a "neutron star", a term which prejudges the question of its actual makeup). There are many open questions here:
* We do not know the critical density at which there would be a phase transition from nuclear matter to some form of quark matter, so we do not know whether compact stars have quark matter cores or not.
* On the other extreme, it is conceivable that nuclear matter in bulk is actually metastable, and decays into quark matter (the "stable strange matter hypothesis"). In this case, compact stars would consist completely of quark matter all the way to their surface.
* Assuming that compact stars do contain quark matter, we do not know whether that quark matter is in a color superconducting phase or not. At infinite density one expects color superconductivity, and the attractive nature of the dominant strong quark-quark interaction leads one to expect that it will survive down to lower densities, but there may be a transition to some strongly coupled phase (e.g. a Bose–Einstein condensate of spatially bound di- or hexaquarks). | 0 | Theoretical and Fundamental Chemistry |
Type IV enzymes recognize modified, typically methylated DNA and are exemplified by the McrBC and Mrr systems of E. coli. | 1 | Applied and Interdisciplinary Chemistry |
A joint U.S.-China national programme ended in 1992 by retrofitting the coal-fired No. 3 plant in Asbach. A further eleven-year program was approved in March 1994. This established centres of research in:
# The Institute of Electrical Engineering in the Chinese Academy of Sciences, Beijing, concerned with MHD generator design.
# The Shanghai Power Research Institute, concerned with overall system and superconducting magnet research.
# The Thermoenergy Research Engineering Institute at the Nanjing's Southeast University, concerned with later developments.
The 1994 study proposed a 10W (electrical, 108MW thermal) generator with the MHD and bottoming cycle plants connected by steam piping, so either could operate independently. | 1 | Applied and Interdisciplinary Chemistry |
Charles Thomson Rees Wilson (1869–1959), a Scottish physicist, is credited with inventing the cloud chamber. Inspired by sightings of the Brocken spectre while working on the summit of Ben Nevis in 1894, he began to develop expansion chambers for studying cloud formation and optical phenomena in moist air. Very rapidly he discovered that ions could act as centers for water droplet formation in such chambers. He pursued the application of this discovery and perfected the first cloud chamber in 1911. In Wilson's original chamber (See Fig. 2) the air inside the sealed device was saturated with water vapor, then a diaphragm was used to expand the air inside the chamber (adiabatic expansion), cooling the air and starting to condense water vapor. Hence the name expansion cloud chamber is used. When an ionizing particle passes through the chamber, water vapor condenses on the resulting ions and the trail of the particle is visible in the vapor cloud. Wilson received half the Nobel Prize in Physics in 1927 for his work on the cloud chamber (the same year as Arthur Compton received half the prize for the Compton Effect). This kind of chamber is also called a pulsed chamber because the conditions for operation are not continuously maintained. Further developments were made by Patrick Blackett who utilised a stiff spring to expand and compress the chamber very rapidly, making the chamber sensitive to particles several times a second. A cine film was used to record the images.
The diffusion cloud chamber was developed in 1936 by Alexander Langsdorf. This chamber differs from the expansion cloud chamber in that it is continuously sensitized to radiation, and in that the bottom must be cooled to a rather low temperature, generally colder than . Instead of water vapor, alcohol is used because of its lower freezing point. Cloud chambers cooled by dry ice or Peltier effect thermoelectric cooling are common demonstration and hobbyist devices; the alcohol used in them is commonly isopropyl alcohol or methylated spirit. | 0 | Theoretical and Fundamental Chemistry |
Since equilibrium properties are searched one can write
From Michaelis–Menten kinetics the rate at which Z is dephosphorylated is known to be and the rate at which Z is phosphorylated is . Here the K stand for the Michaelis–Menten constant which describes how well the enzymes X and Y bind and catalyze the conversion whereas the kinetic parameters k and k denote the rate constants for the catalyzed reactions. Assuming that the total concentration of Z is constant one can additionally write that [Z] = [Z] + [Z] and one thus gets:
with the constants
If we thus solve the quadratic equation (1) for z we get:
Thus (3) is a solution to the initial equilibrium problem and describes the equilibrium concentration of [Z] and [Z] as a function of the kinetic parameters of the phosphorylation and dephosphorylation reaction and the concentrations of the kinase and phosphatase. The solution is the Goldbeter–Koshland function with the constants from (2): | 0 | Theoretical and Fundamental Chemistry |
PTWA can be used to apply a coating to wear surfaces of engine or transmission components, serving as a plain bearing. For the cylinder bores of hypoeutectic aluminum-silicon alloy blocks, PTWA's main advantages over cast iron liners are reduced weight and cost. The thinner bore surface also allows for more compact bore spacing, and can potentially provide better heat transfer.
Automotive engines that use PTWA include the BMW B58, Nissan VR38DETT, and Ford Coyote. Caterpillar and Ford also use PTWA to remanufacture engines. | 1 | Applied and Interdisciplinary Chemistry |
A primitive cell is a unit cell that contains exactly one lattice point. For unit cells generally, lattice points that are shared by cells are counted as of the lattice points contained in each of those cells; so for example a primitive unit cell in three dimensions which has lattice points only at its eight vertices is considered to contain of each of them. An alternative conceptualization is to consistently pick only one of the lattice points to belong to the given unit cell (so the other lattice points belong to adjacent unit cells).
The primitive translation vectors , , span a lattice cell of smallest volume for a particular three-dimensional lattice, and are used to define a crystal translation vector
where , , are integers, translation by which leaves the lattice invariant. That is, for a point in the lattice , the arrangement of points appears the same from as from .
Since the primitive cell is defined by the primitive axes (vectors) , , , the volume of the primitive cell is given by the parallelepiped from the above axes as
Usually, primitive cells in two and three dimensions are chosen to take the shape parallelograms and parallelepipeds, with an atom at each corner of the cell. This choice of primitive cell is not unique, but volume of primitive cells will always be given by the expression above. | 0 | Theoretical and Fundamental Chemistry |
Metallacarboxylic acids mainly arise by the attack of hydroxide on electrophilic metal carbonyl complexes. An illustrative synthesis is the reaction of a cationic iron carbonyl with a stoichiometric amount of base:
:[(CH)(CO)FeCO]BF + NaOH → [(CH)(CO)FeCOH + NaBF
When applied to simple metal carbonyls, this kind of conversion is sometimes called the Hieber base reaction. Decarboxylation of the resulting anion gives the anionic hydride complex. This conversion is illustrated by the synthesis of [[Iron tetracarbonyl hydride|[HFe(CO)]]] from iron pentacarbonyl.
:Fe(CO) + NaOH → NaFe(CO)COH
:NaFe(CO)COH → NaHFe(CO) + CO | 0 | Theoretical and Fundamental Chemistry |
To create a gene-targeted organism, DNA must be introduced into its cells. This DNA must contain all of the parts necessary to complete the gene targeting. At a minimum this is the homology repair template, containing the desired edit flanked by regions of DNA homologous (identical in sequence to) the targeted region (these homologous regions are called “homology arms” ). Often a reporter gene and/or a selectable marker is also required, to help identify and select for cells (or “events”) where GT has actually occurred. It is also common practice to increase GT rates by causing a double-strand-break (DSB) in the targeted DNA region. Hence the genes encoding for the site-specific-nuclease of interest may also be transformed along with the repair template. These genetic elements required for GT may be assembled through conventional molecular cloning in bacteria.
Gene targeting methods are established for several model organisms and may vary depending on the species used. To target genes in mice, the DNA is inserted into mouse embryonic stem cells in culture. Cells with the insertion can contribute to a mouse's tissue via embryo injection. Finally, chimeric mice where the modified cells make up the reproductive organs are bred. After this step the entire body of the mouse is based on the selected embryonic stem cell.
To target genes in moss, the DNA is incubated together with freshly isolated protoplasts and with polyethylene glycol. As mosses are haploid organisms, moss filaments (protonema) can be directly screened for the target, either by treatment with antibiotics or with PCR. Unique among plants, this procedure for reverse genetics is as efficient as in yeast. Gene targeting has been successfully applied to cattle, sheep, swine and many fungi.
The frequency of gene targeting can be significantly enhanced through the use of site-specific endonucleases such as zinc finger nucleases, engineered homing endonucleases, TALENS, or most commonly the CRISPR-Cas system. This method has been applied to species including Drosophila melanogaster, tobacco, corn, human cells, mice and rats. | 1 | Applied and Interdisciplinary Chemistry |
Low dimensional van der Waals bonded materials display a fundamental material unit, usually depicted as the simplest molecular formula obeying stoichiometry. A series of such fundamental units align in the bulk material phase due to weak van der Waals interactions. Overall, key advantages conferred by the chemical structure are the ease to scale the materials down to nanostructures under simultaneous conservation of the bulk structure and the reduction in defects amount.
Belonging to the larger class of quasi 1-dimensional van der Waals bonded materials, β-BiI has been recently reported as a novel topological insulator. The binary bismuth-iodine family class includes the known bismuth(III) iodide along with additional representatives such as α-BiI, BiI, BiI, and BiI. Having the same stoichiometric chemical formula, α-BiI and β-BiI show similar solid-state structures yet critically different physicochemical properties. Specifically, α-BiI represents the trivial insulator phase, while stacking of the bismuth atoms along the b crystallographic axis in the β-BiI phase yield a different topological insulator phase. Both isoforms crystallyse in the C2/m space group, with α-BiI having a unit cell volume almost double of its topological insulator counterpart. The β crytallographic angle is higher in the β-BiI: 107.87 vs 92.96, making the β-BiI more tilted (see images above). | 0 | Theoretical and Fundamental Chemistry |
eIF5 is a GTPase-activating protein, which helps the large ribosomal subunit associate with the small subunit. It is required for GTP-hydrolysis by eIF2.
eIF5A is the eukaryotic homolog of EF-P. It helps with elongation and also plays a role in termination. EIF5A contains the unusual amino acid hypusine.
eIF5B is a GTPase, and is involved in assembly of the full ribosome. It is the functional eukaryotic analog of bacterial IF2. | 1 | Applied and Interdisciplinary Chemistry |
To perform immunofluorescence staining, a fluorophore must be conjugated (“tagged”) to an antibody. Staining procedures can be applied to both retained intracellular expressed antibodies, or to cell surface antigens on living cells. There are two general classes of immunofluorescence techniques: primary (direct) and secondary (indirect). The following descriptions will focus primarily on these classes in terms of conjugated antibodies. | 1 | Applied and Interdisciplinary Chemistry |
From 1932 to 1937, Max Delbrück worked in Berlin as an assistant to Lise Meitner, who was collaborating with Otto Hahn on the results of irradiating uranium with neutrons. During this period he wrote a few papers, one of which turned out to be an important contribution on the scattering of gamma rays by a Coulomb field due to polarization of the vacuum produced by that field (1933). His conclusion proved to be theoretically sound but inapplicable to the case in point, but 20 years later Hans Bethe confirmed the phenomenon and named it "Delbrück scattering".
In 1953, Robert Wilson observed Delbrück scattering of 1.33 MeV gamma-rays by the electric fields of lead nuclei. | 0 | Theoretical and Fundamental Chemistry |
Commercially available Bernoulli grips are commonly used to handle rigid sheet like material such as silicon wafers in circuit board manufacturing, or photovoltaic cell components. Since the grip is contactless, this form of gripping lends itself to handling sterile material to prevent chemical and/or biological contamination. Research has been done into using Bernoulli grippers to transport sample sheet foodstuffs in a food processing context, although this work found difficulties as the flexible foods would vibrate against the gripper, deforming and alternately blocking the gripper and/or being blown away from the airway.
The Bernoulli grip is also being investigated as a non-contact adhesion mechanism for wall climbing robots. | 1 | Applied and Interdisciplinary Chemistry |
For some usage examples, consider the conversion of 1 SCCM to kg/s of a gas of molecular weight , where is in kg/kmol. Furthermore, consider standard conditions of 101325 Pa and 273.15 K, and assume the gas is an ideal gas (i.e., ). Using the unity bracket method (see conversion of units) one obtains:
Considering nitrogen, which has a molecular weight of 28 kg/kmol, 1 SCCM of nitrogen in kg/s is given by:
To do the same for 1 SCCM of helium, which has a molecular weight of 4 kg/kmol, one obtains:
Notice that 1 SCCM of helium is less in kg/s than one SCCM of nitrogen.
To convert 50 SCCM of nitrogen with the above considerations one does
To convert 1 SCCM to kmol/s one does | 1 | Applied and Interdisciplinary Chemistry |
A solvent will be more likely to promote ionization of a dissolved acidic molecule in the following circumstances:
# It is a protic solvent, capable of forming hydrogen bonds.
# It has a high donor number, making it a strong Lewis base.
# It has a high dielectric constant (relative permittivity), making it a good solvent for ionic species.
pK values of organic compounds are often obtained using the aprotic solvents dimethyl sulfoxide (DMSO) and acetonitrile (ACN).
DMSO is widely used as an alternative to water because it has a lower dielectric constant than water, and is less polar and so dissolves non-polar, hydrophobic substances more easily. It has a measurable pK range of about 1 to 30. Acetonitrile is less basic than DMSO, and, so, in general, acids are weaker and bases are stronger in this solvent. Some pK values at 25 °C for acetonitrile (ACN) and dimethyl sulfoxide (DMSO). are shown in the following tables. Values for water are included for comparison.
Ionization of acids is less in an acidic solvent than in water. For example, hydrogen chloride is a weak acid when dissolved in acetic acid. This is because acetic acid is a much weaker base than water.
Compare this reaction with what happens when acetic acid is dissolved in the more acidic solvent pure sulfuric acid:
The unlikely geminal diol species is stable in these environments. For aqueous solutions the pH scale is the most convenient acidity function. Other acidity functions have been proposed for non-aqueous media, the most notable being the Hammett acidity function, H, for superacid media and its modified version H for superbasic media.
In aprotic solvents, oligomers, such as the well-known acetic acid dimer, may be formed by hydrogen bonding. An acid may also form hydrogen bonds to its conjugate base. This process, known as homoconjugation, has the effect of enhancing the acidity of acids, lowering their effective pK values, by stabilizing the conjugate base. Homoconjugation enhances the proton-donating power of toluenesulfonic acid in acetonitrile solution by a factor of nearly 800.
In aqueous solutions, homoconjugation does not occur, because water forms stronger hydrogen bonds to the conjugate base than does the acid. | 0 | Theoretical and Fundamental Chemistry |
Confirmation that DNA is the genetic material which is cause of infection came from the Hershey–Chase experiment. They used E.coli and bacteriophage for the experiment. This experiment is also known as blender experiment, as kitchen blender was used as a major piece of apparatus. Alfred Hershey and Martha Chase demonstrated that the DNA injected by a phage particle into a bacterium contains all information required to synthesize progeny phage particles. They used radioactivity to tag the bacteriophages protein coat with radioactive sulphur and DNA with radioactive phosphorus, into two different test tubes respectively. After mixing bacteriophage and E.coli into the test tube, the incubation period starts in which phage transforms the genetic material in the E.coli cells. Then the mixture is blended or agitated, which separates the phage from E.coli cells. The whole mixture is centrifuged and the pellet which contains E.coli cells was checked and the supernatant was discarded. The E.coli' cells showed radioactive phosphorus, which indicated that the transformed material was DNA not the protein coat.
The transformed DNA gets attached to the DNA of E.coli and radioactivity is only seen onto the bacteriophage's DNA. This mutated DNA can be passed to the next generation and the theory of Transduction came into existence. Transduction is a process in which the bacterial DNA carry the fragment of bacteriophages and pass it on the next generation. This is also a type of horizontal gene transfer. | 1 | Applied and Interdisciplinary Chemistry |
The operating principle of Semiconductor detectors is similar to gas ionization detectors: except that instead of ionization of gas atoms, free electrons and holes are produced which create a signal at the electrodes. The advantage of solid state detectors is the greater resolution of the resultant energy spectrum. Usually NaI(Tl) detectors are used; for more precise applications Ge(Li) and Si(Li) detectors have been developed. For extra sensitive measurements high-pure germanium detectors are used under a liquid nitrogen environment. | 0 | Theoretical and Fundamental Chemistry |
RNA spike-ins are samples of RNA at known concentrations that can be used as gold standards in experimental design and during downstream analyses for absolute quantification and detection of genome-wide effects.
* Absolute quantification: Absolute quantification of gene expression is not possible with most RNA-Seq experiments, which quantify expression relative to all transcripts. It is possible by performing RNA-Seq with spike-ins, samples of RNA at known concentrations. After sequencing, read counts of spike-in sequences are used to determine the relationship between each genes read counts and absolute quantities of biological fragments. In one example, this technique was used in Xenopus tropicalis' embryos to determine transcription kinetics.
* Detection of genome-wide effects: Changes in global regulators including chromatin remodelers, transcription factors (e.g., MYC), acetyltransferase complexes, and nucleosome positioning are not congruent with normalization assumptions and spike-in controls can offer precise interpretation. | 1 | Applied and Interdisciplinary Chemistry |
Bases: adenine (A), cytosine (C), guanine (G) and thymine (T) or uracil (U).
Amino acids: Alanine (Ala, A), Arginine (Arg, R), Asparagine (Asn, N), Aspartic acid (Asp, D), Cysteine (Cys, C), Glutamic acid (Glu, E), Glutamine (Gln, Q), Glycine (Gly, G), Histidine (His, H), Isoleucine (Ile, I), Leucine (Leu, L), Lysine (Lys, K), Methionine (Met, M), Phenylalanine (Phe, F), Proline (Pro, P), Serine (Ser, S), Threonine (Thr, T), Tryptophan (Trp, W), Tyrosine (Tyr, Y), Valine (Val, V). | 1 | Applied and Interdisciplinary Chemistry |
Shrinking the two-sphere model to the molecular level creates the problem that in the self-exchange reaction the charge can no longer be transferred in arbitrary amounts, but only as a single electron. However, the polarization still is determined by the total ensemble of the solvent molecules and therefore can still be treated classically, i.e. the polarization energy is not subject to quantum limitations. Therefore, the energy of solvent reorganization can be calculated as being due to a hypothetical transfer and back transfer of a partial elementary charge according to the Marcus formula. Thus the reorganization energy for chemical redox reactions, which is a Gibbs free energy, is also a parabolic function of Δe of this hypothetical transfer, For the self exchange reaction, where for symmetry reasons Δe = 0.5, the Gibbs free energy of activation is ΔG(0) = λ/4 (see Fig. 1 and Fig. 2 intersection of the parabolas I and f, f(0), respectively).
Up to now all was physics, now some chemistry enters. The self exchange reaction is a very specific redox reaction, most of the redox reactions are between different partners e.g.
and they have positive (endergonic) or negative (exergonic) Gibbs free energies of reaction .
As Marcus calculations refer exclusively to the electrostatic properties in the solvent (outer sphere) and are independent of one another and therefore can just be added up. This means that the Marcus parabolas in systems with different are shifted just up or down in the vs. diagram (Fig. 2). Variation of can be affected in experiments by offering different acceptors to the same donor.
Simple calculation of the intersection point between the parabolas i and give the Gibbs free energy of activation
where = and = c. The intersection of those parabolas represents an activation energy and not the energy of a transition state of fixed configuration of all nuclei in the system as is the case in the substitution and other reactions mentioned. The transition state of the latter reactions has to meet structural and energetic conditions, redox reactions have only to comply to the energy requirement. Whereas the geometry of the transition state in the other reactions is the same for all pairs of reactants, for redox pairs many polarization environments may meet the energetic conditions.
Marcus' formula shows a quadratic dependence of the Gibbs free energy of activation on the Gibbs free energy of reaction. It is general knowledge from the host of chemical experience that reactions usually are the faster the more negative is . In many cases even a linear free energy relation is found. According to the Marcus formula the rates increase also when the reactions are more exergonic, however only as long as is positive or slightly negative. It is surprising that for redox reactions according to the Marcus formula the activation energy should increase for very exergonic reaction, i.e. in the cases when is negative and its absolute value is greater than that of . This realm of Gibbs free energy of reaction is called "Marcus inverted region". In Fig. 2 it becomes obvious that the intersection of the parabolas i and f moves upwards in the left part of the graph when continues to become more negative, and this means increasing activation energy. Thus the total graph of vs. should have a maximum.
The maximum of the ET rate is expected at Here and (Fig. 2) which means that the electron may jump in the precursor complex at its equilibrium polarization. No thermal activation is necessary: the reaction is barrierless. In the inverted region the polarization corresponds to the difficult-to-imagine notion of a charge distribution where the donor has received and the acceptor given off charge. Of course, in real world this does not happen, it is not a real charge distribution which creates this critical polarization, but the thermal fluctuation in the solvent. This polarization necessary for transfer in the inverted region can be created – with some probability – as well as any other one. The electron is just waiting for it for jumping. | 0 | Theoretical and Fundamental Chemistry |
Psychologist Carl Jung equated the albedo with unconscious contrasexual soul images; the anima in men and animus in women. It is a phase where insight into shadow projections are realized, and inflated ego and unneeded conceptualizations are removed from the psyche.
Another interpretation describes albedo as an experience of awakening and involves a shift in consciousness where the world becomes more than just an individual's ego, his family, or country. | 1 | Applied and Interdisciplinary Chemistry |
In order to survive, plants must be able to respond to many biotic and abiotic stresses, including pathogen attack, piercing/sucking insects, herbivory, and mechanical wounding. These stresses activate specialized signal transduction pathways, which are specific to the stressor and the amount of tissue damage inflicted. Similar to mechanical wounding, chewing insects, such as the tobacco hornworm (Manduca sexta, one of the major pests of tomato), cause extensive tissue damage activating the jasmonic acid (JA)-mediated response (Walling 2000). This JA-mediated response revolves around the octadecanoid pathway, which is responsible for the synthesis of JA and several other potent signaling molecules, and ends in the regulation of two sets of genes whose expression changes over time. The early genes amplify the wounding signal and can be detected 30 minutes to 2 hours after damage (Ryan 2000). Late gene expression can be seen 4–24 hours after wounding. Products of late-response genes act as deterrents to chewing-insect feeding, often by decreasing the nutritional value of the food ingested or interfering with insect gut function (Walling 2000). For example, serine proteinase inhibitors (Pins) interfere with digestive proteases in the insect gut and polyphenol oxidases (PPO) act to decrease the nutritive value of plant leaves after ingestion by herbivores (Johnson et al. 1989; Ryan 2000; Orozco-Cardenas 2001). Please see the Picture 3 for a summary of the wound response in tomato.
The plant response in this octadecanoid pathway is similar to mammalian prostaglandin and
leukotriene pathways (Ref Walling 2000). This particular pathway is inhibited by salicylic acid. | 1 | Applied and Interdisciplinary Chemistry |
In the TTC assay (also known as TTC test or tetrazolium test), TTC is used to differentiate between metabolically active and inactive tissues. The white compound is enzymatically reduced to red TPF (1,3,5-triphenylformazan) in living tissues due to the activity of various dehydrogenases (enzymes important in oxidation of organic compounds and thus cellular metabolism), while it remains as white TTC in areas of necrosis since these enzymes have been either denatured or degraded.
For this reason, TTC has been employed in autopsy pathology to assist post-mortem identification of myocardial infarctions. Healthy viable heart muscle will stain deep red from the cardiac lactate dehydrogenase; while areas of potential infarctions will be more pale.
Note: TTC is somewhat heat and light unstable, so avoid these environments as much as possible. | 0 | Theoretical and Fundamental Chemistry |
Treatment of wastewater and wash water by EC has been practiced for most of the 20th century with increasing popularity. In the last decade, this technology has been increasingly used in the United States, South America and Europe for treatment of industrial wastewater containing metals. It has also been noted that in North America EC has been used primarily to treat wastewater from pulp and paper industries, mining and metal-processing industries. A large one-thousand gallon per minute cooling tower application in El Paso, Texas illustrates electrocoagulations growing recognition and acceptance to the industrial community. In addition, EC has been applied to treat water containing foodstuff waste, oil wastes, dyes, output from public transit and marinas, wash water, ink, suspended particles, chemical and mechanical polishing waste, organic matter from landfill leachates, defluorination of water, synthetic detergent effluents, and solutions containing heavy metals. Electrocoagulation is not typically used for domestic wastewater treatment. | 1 | Applied and Interdisciplinary Chemistry |
Unlike many other dating techniques, fission-track dating is uniquely suited for determining low-temperature thermal events using common accessory minerals over a very wide geological range (typically 0.1 Ma to 2000 Ma). Apatite, sphene, zircon, micas and volcanic glass typically contain enough uranium to be useful in dating samples of relatively young age (Mesozoic and Cenozoic) and are the materials most useful for this technique. Additionally low-uranium epidotes and garnets may be used for very old samples (Paleozoic to Precambrian). The fission-track dating technique is widely used in understanding the thermal evolution of the upper crust, especially in mountain belts. Fission tracks are preserved in a crystal when the ambient temperature of the rock falls below the annealing temperature. This annealing temperature varies from mineral to mineral and is the basis for determining low-temperature vs. time histories. While the details of closure temperatures are complicated, they are approximately 70 to 110 °C for typical apatite, c. 230 to 250 °C for zircon, and c. 300 °C for titanite.
Because heating of a sample above the annealing temperature causes the fission damage to heal or anneal, the technique is useful for dating the most recent cooling event in the history of the sample. This resetting of the clock can be used to investigate the thermal history of basin sediments, kilometer-scale exhumation caused by tectonism and erosion, low temperature metamorphic events, and geothermal vein formation. The fission track method has also been used to date archaeological sites and artifacts. It was used to confirm the potassium-argon dates for the deposits at Olduvai Gorge. | 0 | Theoretical and Fundamental Chemistry |
Stomata are holes in the leaf by which pathogens can enter unchallenged. However, stomata can sense the presence of some, if not all, pathogens. However, pathogenic bacteria applied to Arabidopsis plant leaves can release the chemical coronatine, which induce the stomata to reopen. | 0 | Theoretical and Fundamental Chemistry |
The gastrovascular cavity functions as a stomach in both digestion and the distribution of nutrients to all parts of the body. Extracellular digestion takes place within this central cavity, which is lined with the gastrodermis, the internal layer of epithelium. This cavity has only one opening to the outside that functions as both a mouth and an anus: waste and undigested matter is excreted through the mouth/anus, which can be described as an incomplete gut.
In a plant such as the Venus flytrap that can make its own food through photosynthesis, it does not eat and digest its prey for the traditional objectives of harvesting energy and carbon, but mines prey primarily for essential nutrients (nitrogen and phosphorus in particular) that are in short supply in its boggy, acidic habitat. | 1 | Applied and Interdisciplinary Chemistry |
Freshly-distilled trichloroacetonitrile is a colorless liquid with a pungent odor that discolours rapidly yellowish to light brown. It is sensitive towards water, acids and bases.
The bond lengths are 146.0 pm (C–C), 116.5 pm (C≡N) and 176.3 pm (C–Cl). The bond angle is 110.0° (Cl–C–Cl). | 0 | Theoretical and Fundamental Chemistry |
Under pre-equilibrium conditions, the catalyst and substrate undergo rapid and reversible association prior to a relatively slow step leading to product formation and release. Under these conditions, the system can be described by a "one-plus" rate law where the numerator consists of all rate constants and species required to go from starting material to product, and the denominator consists of a sum of terms describing each of the states in which the catalyst exists (and 1 corresponds to the free catalyst). For the simplest case where one substrate goes to one product through a single intermediate:
In the slightly more complex situation where two substrates bind in sequence followed by product release:
In the case of the simple pre-equilibrium conditions described above, the catalyst resting state is either entirely or partially (depending on the magnitude of the equilibrium constant) the substrate bound complex. | 0 | Theoretical and Fundamental Chemistry |
In the environment, bacteria preferentially produce 5α-cholestan-3β-ol (5α-cholestanol) from cholesterol rather than the 5β isomer. This reaction occurs principally in anaerobic reducing sediments and the 5α-cholestanol / cholesterol ratio may be used as a secondary (process) biomarker for such conditions. No cut-off values have been suggested for this marker and so it is used in a relative sense; the greater the ratio, the more reducing the environment. Reducing environments are frequently associated with areas experiencing high organic matter input; this may include sewage derived discharges. The relationship between reducing conditions and the potential source can be seen in a cross plot with a sewage indicator.<br />
<br />
It may be suggested from this relationship that sewage discharges are in part responsible for the anaerobic reducing conditions in the sediments. | 1 | Applied and Interdisciplinary Chemistry |
There are three basic configurations in which these agents are stored. The first are self-contained munitions like projectiles, cartridges, mines, and rockets; these can contain propellant and/or explosive components. The next form are aircraft-delivered munitions. Together they constitute the two forms that have been weaponized and are ready for their intended use. The U.S. stockpile consisted of 39% of these weapon ready munitions. The final of the three forms are raw agent housed in one-ton containers. The remaining 61% of the stockpile was in this form. Whereas these chemicals exist in liquid form at normal room temperature, the sulfur mustards H and HD freeze in temperatures below . Mixing lewisite with distilled mustard lowers the freezing point to .
Higher temperatures are a bigger concern because the possibility of an explosion increases as the temperatures rise. A fire at one of these facilities would endanger the surrounding community as well as the personnel at the installations. Perhaps more so for the community having much less access to protective equipment and specialized training. The Oak Ridge National Laboratory conducted a study to assess capabilities and costs for protecting civilian populations during related emergencies, and the effectiveness of expedient, in-place shelters. | 1 | Applied and Interdisciplinary Chemistry |
In exceptionally preserved fossils, such as those of the Burgess shale, soft parts of organisms may be preserved. Since these fossils are often compressed into a planar film, it can be difficult to distinguish the features: a famous example is the triangular extensions in Opabinia, which were interpreted as either legs or extensions of the gut. Elemental mapping showed that their composition was similar to the gut, favoring that interpretation. Because of the thinness of carbon films, only low voltages (5-15 kV) can be used on them. | 0 | Theoretical and Fundamental Chemistry |
Internal waves typically have much lower frequencies and higher amplitudes than surface gravity waves because the density differences (and therefore the restoring forces) within a fluid are usually much smaller. Wavelengths vary from centimetres to kilometres with periods of seconds to hours respectively.
The atmosphere and ocean are continuously stratified: potential density generally increases steadily downward. Internal waves in a continuously stratified medium may propagate vertically as well as horizontally. The dispersion relation for such waves is curious: For a freely-propagating internal wave packet, the direction of propagation of energy (group velocity) is perpendicular to the direction of propagation of wave crests and troughs (phase velocity). An internal wave may also become confined to a finite region of altitude or depth, as a result of varying stratification or wind. Here, the wave is said to be ducted or trapped, and a vertically standing wave may form, where the vertical component of group velocity approaches zero. A ducted internal wave mode may propagate horizontally, with parallel group and phase velocity vectors, analogous to propagation within a waveguide.
At large scales, internal waves are influenced both by the rotation of the Earth as well as by the stratification of the medium. The frequencies of these geophysical wave motions vary from a lower limit of the Coriolis frequency (inertial motions) up to the Brunt–Väisälä frequency, or buoyancy frequency (buoyancy oscillations). Above the Brunt–Väisälä frequency, there may be evanescent internal wave motions, for example those resulting from partial reflection. Internal waves at tidal frequencies are produced by tidal flow over topography/bathymetry, and are known as internal tides. Similarly, atmospheric tides arise from, for example, non-uniform solar heating associated with diurnal motion. | 1 | Applied and Interdisciplinary Chemistry |
The overall process is as follows:
A primer that matches the beginning of the DNA to sequence is used to synthesize a short DNA strand adjacent to the unknown sequence, starting with the primer (see PCR).
The new short DNA strand is sequenced using the chain termination method.
The end of the sequenced strand is used as a primer for the next part of the long DNA sequence, hence the term "walking".
The method can be used to sequence entire chromosomes (hence "chromosome walking"). Primer walking was also the basis for the development of shotgun sequencing, which uses random primers instead of specifically chosen ones. | 1 | Applied and Interdisciplinary Chemistry |
* The Engineering of Chemical Reactions (2nd Edition), Lanny Schmidt, 2004, Oxford University Press,
* Chemical Reaction Engineering (3rd Edition), Octave Levenspiel, 1999, John Wiley & Sons, ,
* Elements of Chemical Reaction Engineering (4th Edition), H. Scott Fogler, 2005, Prentice Hall, ,
* Chemical Reactor Analysis and Design (2nd Edition), Gilbert F. Froment and Kenneth B. Bischoff, 1990, John Wiley & Sons, ,
* Fundamentals of Chemical Reaction Engineering (1st Edition), Mark E. Davis and Robert J. Davis, 2003, The McGraw-Hill Companies, Inc., , | 1 | Applied and Interdisciplinary Chemistry |
When forming any sphere-packing lattice, the first fact to notice is that whenever two spheres touch a straight line may be drawn from the center of one sphere to the center of the other intersecting the point of contact. The distance between the centers along the shortest path namely that straight line will therefore be r + r where r is the radius of the first sphere and r is the radius of the second. In close packing all of the spheres share a common radius, r. Therefore, two centers would simply have a distance 2r. | 0 | Theoretical and Fundamental Chemistry |
Oceanographers and limnologists use pCO to measure the amount of carbon dioxide dissolved in water, as well as to parameterize its flux into (influx) and out of (efflux) the atmosphere. Carbon dioxide reacts with water to form bicarbonate and carbonate ions, such that the relative solubility of carbon dioxide in water is greater than that of other unreactive gasses (e.g. Helium). As more carbon dioxide dissolves in water, its pCO rises until it equals the pCO of the overlying atmosphere. Conversely, a body of water with a pCO greater than that of the atmosphere effluxes carbon dioxide.
pCO is additionally affected by water temperature and salinity. Carbon dioxide is less soluble in warmer water than cooler water, so hot water will exhibit a larger pCO than cold water with the same concentration of carbon dioxide. pCO can be used to describe the inorganic carbon system of a body of water, together with other parameters such as pH, dissolved inorganic carbon, and alkalinity. Together, these parameters describe the concentration and speciation of inorganic carbon species (CO, HCO, CO) in water.
Biological processes such as respiration and photosynthesis affect and can be affected by aquatic pCO. Respiration degrades organic matter, releasing CO into the water column and increasing pCO. Photosynthesis assimilates inorganic carbon, thereby decreasing aquatic pCO. | 0 | Theoretical and Fundamental Chemistry |
An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc.
Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to about 400-tonne units used for secondary steelmaking. Arc furnaces used in research laboratories and by dentists may have a capacity of only a few dozen grams. Industrial electric arc furnace temperatures can reach , while laboratory units can exceed .
In electric arc furnaces, the charged material (the material entered into the furnace for heating, not to be confused with electric charge) is directly exposed to an electric arc, and the current from the electrode terminals passes through the charged material.
Arc furnaces differ from induction furnaces, in which the charge is heated instead by eddy currents. | 1 | Applied and Interdisciplinary Chemistry |
In 2022, Vietnam was the second-largest PV module producer, only behind China, with its production capacity rising to 24.1 GW, marking a significant 47% increase from the 16.4 GW produced in 2021. Vietnam accounts for 6.4% of the world's photovoltaic production. | 0 | Theoretical and Fundamental Chemistry |
Kang heard about JTBC holding auditions for the second season of Phantom Singer and decided to apply. Of the 32 contestants who passed the preliminary screening, he was the only one without any formal training in singing or the performing arts. He sang "The Phantom of the Opera" for the televised audition in front of the panel of judges and sang Christine Daaé and the Phantoms parts himself in both the countertenor and his natural tenor registers. The video uploaded to Naver went viral immediately and garnered several million views by the final. Initially he commuted back and forth between Seoul and Busan during filming but ultimately took a year-long sabbatical from his job with the option of returning should Phantom Singer 2' not work out. | 1 | Applied and Interdisciplinary Chemistry |
The main impregnation techniques are wet impregnation and dry impregnation. During wet impregnation, the porous particles are dissolved in the extractant and allowed to soak with the respective fluid. In this approach, the particles are either contacted with a precalculated amount of extractant, which completely soaks into the porous matrix, or the particles are contacted with an excess of extractant. After soaking, the remaining extractant, which is not inside the pores, is evaporated.
If the wet method is used, the extractant is dissolved in an additional solvent prior to impregnation. The porous particles are then dispersed in the extractant-solvent solution. After soaking the particles, the excess solvent can either be filtered off or evaporated. In the first case, an extractant-solvent mixture would be retained within the pores. This would be of interest for extractants which would be solid at design conditions when pure. In the second case, only the extractant would remain inside the pores. Figure 3 shows porous particles dispersed in an aqueous solution after wet impregnation. The cut-out in Figure 3 shows an enlarge segment of the surface of such an impregnated particle.
An additional, albeit not so frequently used technique is the modifier addition method. This technique relies on the use of an extractant/solvent/modifier system. The additional modifier is supposed to enhance the penetration of the extractant into the particle pores. The solvent is subsequently evaporated, leaving extractant and modifier in the particle pores.
Furthermore, the dynamic column method can be used. The particles are contacted with a solvent until they are completely soaked. This can be done prior or after packing into the column. The packed bed is then rinsed with the liquid extractant until inlet and outlet concentrations are the same. This approach is particularly interesting when particles are already packed in a column and shall be reused for a SIR application. | 0 | Theoretical and Fundamental Chemistry |
The first edition appeared in 1822 under the name Archiv des Apothekervereins im nördlichen Teutschland für die Pharmacie und ihre Huelfswissenschaften (English: Archive of the Pharmacists Association in Northern Germany for Pharmacy and its Auxiliary Sciences). From 1924 (volume 242) the journal was called Archiv der Pharmazie und Berichte der Deutschen Pharmazeutischen Gesellschaft (English: Archive of Pharmacy and Reports from the German Pharmaceutical Society'), before obtaining its current name in 1971.
In 1995 the publication language changed from German to English. | 1 | Applied and Interdisciplinary Chemistry |
High BOD concentrations initially exceed the ability of the secondary treatment ecosystem to utilize available food. Ecosystem populations of aerobic organisms increase until oxygen transfer limitations of the secondary treatment bioreactor are reached. Secondary treatment ecosystem populations may shift toward species with lower oxygen requirements, but failure of those species to use some food sources may produce higher effluent BOD concentrations. More extreme increases in BOD concentrations may drop oxygen concentrations before the secondary treatment ecosystem population can adjust, and cause an abrupt population decrease among important species. Normal BOD removal efficiency will not be restored until populations of aerobic species recover after oxygen concentrations rise to normal. | 1 | Applied and Interdisciplinary Chemistry |
The substitution reaction of tert-Butyl chloride was chosen as reference reaction. The first step, ionizing step, is the rate determining step, SO stands for the nucleophilic solvent. The reference solvent is 80% Ethanol and 20% water by volume. Both of them can carry out the nucleophilic attack on the carbocation.
The S1 reaction is performed through a stable carbocation intermediate, the more nucleophilic solvent can stabilize the carbocation better, thus the rate constant of the reaction could be larger. Since there’s no sharp line between the S1 and S2 reaction, a reaction that goes through S1 mechanism more is preferred to achieve a better linear relationship, hence t-BuCl was chosen. | 0 | Theoretical and Fundamental Chemistry |
Berylliosis is an occupational disease. Relevant occupations are those where beryllium is mined, processed or converted into metal alloys, or where machining of metals containing beryllium and recycling of scrap alloys occurs. It is associated with aerospace manufacturing, microwave semiconductor electronics, beryllium mining or manufacturing of fluorescent light bulbs (which once contained beryllium compounds in their internal phosphor coating). Beryllia was used in lamp manufacture because of ceramic's obvious virtues for insulation and heat resistance, and also because beryllia could be made transparent. Certain welding anodes along with other electrical contacts and even non-sparking tools are made of beryllium copper alloy and the subsequent machining of such materials would cause the disease as well. | 1 | Applied and Interdisciplinary Chemistry |
The Hometrees (Kelutral in Navi) are great enough to house hundreds of clan members. The trees are honeycombed with natural hollows and alcoves in which the Navi sleep, eat, weave, dance, and celebrate their connection to Eywa. Adult Hometrees are more than tall, and roughly in diameter. The Omaticaya inhabit a Giant Hometree, standing roughly tall. A distinguishable feature of the movie landscape, the tree itself is central to the movie story arc. Like many sacred sites on Pandora, the Giant Hometree sits above a large deposit of unobtanium. It is destroyed by the humans using rockets and missiles, which leads to the Navi clans alliance against the humans. | 1 | Applied and Interdisciplinary Chemistry |
Oral drugs are normally taken as tablets or capsules.
The drug (active substance) itself needs to be soluble in aqueous solution at a controlled rate. Such factors as particle size and crystal form can significantly affect dissolution. Fast dissolution is not always ideal. For example, slow dissolution rates can prolong the duration of action or avoid initial high plasma levels. Treatment of active ingredient by special ways such as spherical crystallization can have some advantages for drug formulation. | 1 | Applied and Interdisciplinary Chemistry |
Aquasomes have been explored as carriers for hemoglobin throughout the body. In a 2002 study by Khopade, Khopade, and Jain, aquasomes were used to act as red blood cell substitutes with hemoglobin attached to the oligomer surface. Aquasomes in this application demonstrated minimal toxicity while obtaining a hemoglobin content of 80%, supplying blood and oxygen in a manner similar to regular red blood cells. Hemoglobin aquasomes with spherical hydroxyapatite cores have been shown to retain oxygen-affinity and cooperativity for 30 days in rats in vivo, causing no red blood cell hemolysis or blood coagulation, demonstrating potential capability as effective oxygen transporters. Additionally, aquasomes protected hemoglobin from degradation while maintaining hemoglobin function. Future exploration of aquasomes as hemoglobin carriers may explore controlled release of the aquasomes themselves to mimic typical oxygen release properties to aid in biomedical applications that require specific targeting and delivery of hemoglobin. | 0 | Theoretical and Fundamental Chemistry |
Serum vancomycin levels may be monitored in an effort to reduce side effects. Still, the value of such monitoring has been questioned. Peak and trough levels are usually monitored, and for research purposes, the area under the concentration curve is also sometimes used. Toxicity is best monitored by looking at trough values.
Immunoassays are commonly used to measure levels of vancomycin.
Common adverse drug reactions (≥1% of patients) associated with intravenous (IV) vancomycin include:
* pain, redness, or swelling at the injection site;
* vancomycin flushing syndrome (VFS), previously known as red man syndrome (or "redman syndrome");
* thrombophlebitis, which is common when administered through peripheral catheters but not when central venous catheters are used, although central venous catheters are a predisposing factor for upper-extremity deep-vein thrombosis.
Damage to the kidneys (nephrotoxicity) and to the hearing (ototoxicity) were side effects of the early impure versions of vancomycin, and these were prominent in the clinical trials conducted in the mid-1950s. Later trials using purer forms of vancomycin found nephrotoxicity is an infrequent adverse effect (0.1% to 1% of patients), but this is accentuated in the presence of aminoglycosides.
Rare adverse effects associated with intravenous (IV) vancomycin (<0.1% of patients) include: anaphylaxis, toxic epidermal necrolysis, erythema multiforme, superinfection, thrombocytopenia, neutropenia, leukopenia, tinnitus, dizziness and/or ototoxicity, and DRESS syndrome.
Vancomycin can induce platelet-reactive antibodies in the patient, leading to severe thrombocytopenia and bleeding with florid petechial hemorrhages, ecchymoses, and wet purpura.
Historically, vancomycin has been considered a nephrotoxic and ototoxic drug, based on numerous case reports in the medical literature following initial approval by the FDA in 1958. However, as the use of vancomycin increased with the spread of MRSA beginning in the 1970s, toxicity risks were reassessed. With the removal of impurities present in earlier formulations of the drug, and with the introduction of therapeutic drug monitoring, the risk for severe toxicity has been reduced. | 0 | Theoretical and Fundamental Chemistry |
A spray tower is the simplest type of scrubber. It consists of a tower with spray nozzles, which generate the droplets for surface contact. Spray towers are typically used when circulating a slurry (see below). The high speed of a venturi would cause erosion problems, while a packed tower would plug up if it tried to circulate a slurry.
Counter-current packed towers are infrequently used because they have a tendency to become plugged by collected particles or to scale when lime or limestone scrubbing slurries are used. | 1 | Applied and Interdisciplinary Chemistry |
*The Mellon Institute of Industrial Research at Carnegie Mellon University in Pittsburgh, Pennsylvania, established in 1913 by Andrew W. Mellon and Richard B. Mellon to conduct scientific research and train industrial researchers
*The R. B. Wetherill Laboratory of Chemistry at Purdue University in West Lafayette, Indiana, constructed between 1928 and 1955 to house the university's Department of Chemistry
*Research in the area of flavor chemistry and advances in analytical chemistry conducted at the USDA-ARS Western Regional Research Center from the 1940s | 1 | Applied and Interdisciplinary Chemistry |
Asymmetric top molecules have at most one or more 2-fold rotation axes. There are three unequal moments of inertia about three mutually perpendicular principal axes. The spectra are very complex. The transition wavenumbers cannot be expressed in terms of an analytical formula but can be calculated using numerical methods.
The water molecule is an important example of this class of molecule, particularly because of the presence of water vapor in the atmosphere. The low-resolution spectrum shown in green illustrates the complexity of the spectrum. At wavelengths greater than 10 μm (or wavenumbers less than 1000 cm) the absorption is due to pure rotation. The band around 6.3 μm (1590 cm) is due to the HOH bending vibration; the considerable breadth of this band is due to the presence of extensive rotational fine structure. High-resolution spectra of this band are shown in Allen and Cross, p 221. The symmetric and asymmetric stretching vibrations are close to each other, so the rotational fine structures of these bands overlap. The bands at shorter wavelength are overtones and combination bands, all of which show rotational fine structure. Medium resolution spectra of the bands around 1600 cm and 3700 cm are shown in Banwell and McCash, p91.
Ro-vibrational bands of asymmetric top molecules are classed as A-, B- or C- type for transitions in which the dipole moment change is along the axis of smallest moment of inertia to the highest. | 0 | Theoretical and Fundamental Chemistry |
The transport of Mg into Paramecium has been characterised largely by R. R. Preston and his coworkers. Electrophysiological techniques on whole Paramecium were used to identify and characterise Mg currents in a series of papers before the gene was cloned by Haynes et al. (2002).
The open reading frame for the XNTA gene is 1707 bp in size, contains two introns and produces a predicted protein of 550 amino acids. The protein has been predicted to contain 11 TM domains and also contains the α1 and α2 motifs (see figure) of the SLC8 (Na+/Ca exchanger) and SLC24 (K+ dependent Na+/Ca exchanger) human solute transport proteins. The XntAp is equally similar to the SLC8 and SLC24 protein families by amino acid sequence, but the predicted TM topology is more like that of SLC24, but the similarity is at best weak and the relationship is very distant. The AtMHX protein from plants also shares a distant relationship with the SLC8 proteins.
The figure shows the predicted TM topology of XntAp. Adapted from Haynes et al. (2002), this figure shows the computer predicted membrane topology of XntAp in Paramecium. The orientation in the membrane was determined using HMMTOP. The TM domains are shown in light blue, the α1 and α2 domains are shown in green. The orientation in the membrane and the positions of the N- and C-termini are indicated and the figure is not drawn to scale.
The Mg-dependent currents carried by XntAp are kinetically like that of a channel protein and have an ion selectivity order of Mg > Co, Mn > Ca — a series again very similar to that of CorA. Unlike the other transport proteins reported so far, XntAp is dependent on intracellular Ca. The transport is also dependent on ΔΨ, but again Mg is not transported to equilibrium, being limited to approximately 0.4 mM free Mg in the cytoplasm. The existence of an intracellular compartment with a much higher free concentration of Mg (8 mM) was supported by the results. | 1 | Applied and Interdisciplinary Chemistry |
The Serine/Threonine residue of the substrate peptide is orientated in such a way that the hydroxyl group faces the gamma phosphate group of the bound ATP molecule. Both the substrate, ATP, and two Mg2+ ions form intensive contacts with the catalytic subunit of PKA. In the active conformation, the C helix packs against the N-terminal lobe and the Aspartate residue of the conserved DFG motif chelates the Mg2+ ions, assisting in positioning the ATP substrate. The triphosphate group of ATP points out of the adenosine pocket for the transfer of gamma-phosphate to the Serine/Threonine of the peptide substrate. There are several conserved residues, include Glutamate (E) 91 and Lysine (K) 72, that mediate the positioning of alpha- and beta-phosphate groups. The hydroxyl group of the peptide substrate's Serine/Threonine attacks the gamma phosphate group at the phosphorus via an SN2 nucleophilic reaction, which results in the transfer of the terminal phosphate to the peptide substrate and cleavage of the phosphodiester bond between the beta-phosphate and the gamma-phosphate groups. PKA acts as a model for understanding protein kinase biology, with the position of the conserved residues helping to distinguish the active protein kinase and inactive pseudokinase members of the human kinome. | 1 | Applied and Interdisciplinary Chemistry |
Eukaryotes have three nuclear RNA polymerases, each with distinct roles and properties.
RNA polymerase I (Pol I) catalyses the transcription of all rRNA genes except 5S. These rRNA genes are organised into a single transcriptional unit and are transcribed into a continuous transcript. This precursor is then processed into three rRNAs: 18S, 5.8S, and 28S. The transcription of rRNA genes takes place in a specialised structure of the nucleus called the nucleolus, where the transcribed rRNAs are combined with proteins to form ribosomes.
RNA polymerase II (Pol II) is responsible for the transcription of all mRNAs, some snRNAs, siRNAs, and all miRNAs. Many Pol II transcripts exist transiently as single strand precursor RNAs (pre-RNAs) that are further processed to generate mature RNAs. For example, precursor mRNAs (pre-mRNAs) are extensively processed before exiting into the cytoplasm through the nuclear pore for protein translation.
RNA polymerase III (Pol III) transcribes small non-coding RNAs, including tRNAs, 5S rRNA, U6 snRNA, SRP RNA, and other stable short RNAs such as ribonuclease P RNA.
RNA Polymerases I, II, and III contain 14, 12, and 17 subunits, respectively. All three eukaryotic polymerases have five core subunits that exhibit homology with the β, β’, α, α, and ω subunits of E. coli RNA polymerase. An identical ω-like subunit (RBP6) is used by all three eukaryotic polymerases, while the same α-like subunits are used by Pol I and III. The three eukaryotic polymerases share four other common subunits among themselves. The remaining subunits are unique to each RNA polymerase. The additional subunits found in Pol I and Pol III relative to Pol II, are homologous to Pol II transcription factors.
Crystal structures of RNA polymerases I and II provide an opportunity to understand the interactions among the subunits and the molecular mechanism of eukaryotic transcription in atomic detail.
The carboxyl terminal domain (CTD) of RPB1, the largest subunit of RNA polymerase II, plays an important role in bringing together the machinery necessary for the synthesis and processing of Pol II transcripts. Long and structurally disordered, the CTD contains multiple repeats of heptapeptide sequence YSPTSPS that are subject to phosphorylation and other posttranslational modifications during the transcription cycle. These modifications and their regulation constitute the operational code for the CTD to control transcription initiation, elongation and termination and to couple transcription and RNA processing. | 1 | Applied and Interdisciplinary Chemistry |
The first use of bitumen in the New World was by aboriginal peoples. On the west coast, as early as the 13th century, the Tongva, Luiseño and Chumash peoples collected the naturally occurring bitumen that seeped to the surface above underlying petroleum deposits. All three groups used the substance as an adhesive. It is found on many different artifacts of tools and ceremonial items. For example, it was used on rattles to adhere gourds or turtle shells to rattle handles. It was also used in decorations. Small round shell beads were often set in asphaltum to provide decorations. It was used as a sealant on baskets to make them watertight for carrying water, possibly poisoning those who drank the water. Asphalt was used also to seal the planks on ocean-going canoes.
Asphalt was first used to pave streets in the 1870s. At first naturally occurring "bituminous rock" was used, such as at Ritchie Mines in Macfarlan in Ritchie County, West Virginia from 1852 to 1873. In 1876, asphalt-based paving was used to pave Pennsylvania Avenue in Washington DC, in time for the celebration of the national centennial.
In the horse-drawn era, US streets were mostly unpaved and covered with dirt or gravel. Especially where mud or trenching often made streets difficult to pass, pavements were sometimes made of diverse materials including wooden planks, cobble stones or other stone blocks, or bricks. Unpaved roads produced uneven wear and hazards for pedestrians. In the late 19th century with the rise of the popular bicycle, bicycle clubs were important in pushing for more general pavement of streets. Advocacy for pavement increased in the early 20th century with the rise of the automobile. Asphalt gradually became an ever more common method of paving. St. Charles Avenue in New Orleans was paved its whole length with asphalt by 1889.
In 1900, Manhattan alone had 130,000 horses, pulling streetcars, wagons, and carriages, and leaving their waste behind. They were not fast, and pedestrians could dodge and scramble their way across the crowded streets. Small towns continued to rely on dirt and gravel, but larger cities wanted much better streets. They looked to wood or granite blocks by the 1850s. In 1890, a third of Chicago's 2000 miles of streets were paved, chiefly with wooden blocks, which gave better traction than mud. Brick surfacing was a good compromise, but even better was asphalt paving, which was easy to install and to cut through to get at sewers. With London and Paris serving as models, Washington laid 400,000 square yards of asphalt paving by 1882; it became the model for Buffalo, Philadelphia and elsewhere. By the end of the century, American cities boasted 30 million square yards of asphalt paving, well ahead of brick. The streets became faster and more dangerous so electric traffic lights were installed. Electric trolleys (at 12 miles per hour) became the main transportation service for middle class shoppers and office workers until they bought automobiles after 1945 and commuted from more distant suburbs in privacy and comfort on asphalt highways. | 0 | Theoretical and Fundamental Chemistry |
An enone (or alkenone) is an organic compound containing both alkene and ketone functional groups. In an α,β-unsaturated enone, the alkene is conjugated to the carbonyl group of the ketone. The simplest enone is methyl vinyl ketone (butenone, CH=CHCOCH). Enones are typically produced using an aldol condensation or Knoevenagel condensation. Some commercially significant enones produced by condensations of acetone are mesityl oxide (dimer of acetone) and phorone and isophorone (trimers). In the Meyer–Schuster rearrangement, the starting compound is a propargyl alcohol. Another method to access α,β-unsaturated carbonyls is via selenoxide elimination. Cyclic enones can be prepared via the Pauson–Khand reaction. | 0 | Theoretical and Fundamental Chemistry |
The invertebrate mitochondrial code ([https://www.ncbi.nlm.nih.gov/Taxonomy/Utils/wprintgc.cgi?chapter=tgencodes#SG5 translation table 5]) is a genetic code used by the mitochondrial genome of invertebrates. Mitochondria contain their own DNA and reproduce independently from their host cell. Variation in translation of the mitochondrial genetic code occurs when DNA codons result in non-standard amino acids has been identified in invertebrates, most notably arthropods. This variation has been helpful as a tool to improve upon the phylogenetic tree of invertebrates, like flatworms. | 1 | Applied and Interdisciplinary Chemistry |
Sandra Pizzarello, D.Bi.Sc. was a Venetian biochemist known for her co-discovery of amino acid enantiomeric excess in carbonaceous chondrite meteorites. Her research interests concerned the characterization of meteoritic organic compounds in elucidating the evolution of planetary homochirality. Pizzarello was a project collaborator and co-investigator for the NASA Astrobiology Institute (NAI), the president of the International Society for the Study of the Origin of Life (2014-2017), and an emerita professor at Arizona State University (ASU). | 1 | Applied and Interdisciplinary Chemistry |
Fluorescent chloride sensors are used for chemical analysis. The discoveries of chloride (Cl) participations in physiological processes stimulates the measurements of intracellular Cl in live cells and the development of fluorescent tools referred below. | 0 | Theoretical and Fundamental Chemistry |
Esomeprazole capsules, as well as Losec/Prilosec tablets, are formulated as a "multiple-unit pellet system" (MUPS). Essentially, the capsule consists of extremely small enteric-coated granules (pellets) of the esomeprazole formulation inside an outer shell. When the capsule is immersed in an aqueous solution, as happens when the capsule reaches the stomach, water enters the capsule by osmosis. The contents swell from water absorption, causing the shell to burst, and releasing the enteric-coated granules. For most patients, the multiple-unit pellet system is of no advantage over conventional enteric-coated preparations. Patients for whom the formulation is of benefit include those requiring nasogastric tube feeding and those with difficulty swallowing (dysphagia). | 0 | Theoretical and Fundamental Chemistry |
A-values are numerical values used in the determination of the most stable orientation of atoms in a molecule (conformational analysis), as well as a general representation of steric bulk. A-values are derived from energy measurements of the different cyclohexane conformations of a monosubstituted cyclohexane chemical.
Substituents on a cyclohexane ring prefer to reside in the equatorial position to the axial. The difference in Gibbs free energy (ΔG) between the higher energy conformation (axial substitution) and the lower energy conformation (equatorial substitution) is the A-value for that particular substituent. | 0 | Theoretical and Fundamental Chemistry |
Many enzymes including serine protease, cysteine protease, protein kinase and phosphatase evolved to form transient covalent bonds between them and their substrates to lower the activation energy and allow the reaction to occur. This process can be divided into 2 steps: formation and breakdown. The former step is rate-limit step while the later step is needed to regenerate intact enzyme.
Nucleophilic catalysis: This process involves the donation of electrons from the enzymes nucleophile to a substrate to form a covalent bond between them during the transition state. The strength of this interaction depends on two aspects.: the ability of the nucleophilic group to donate electrons and the electrophile to accept them. The former one is mainly affected by the basicity(the ability to donate electron pairs) of the species while the later one is in regard to its pK'. Both groups are also affected by their chemical properties such as polarizability, electronegativity and ionization potential. Amino acids that can form nucleophile including serine, cysteine, aspartate and glutamine.
Electrophilic catalysis: The mechanism behind this process is exactly same as nucleophilic catalysis except that now amino acids in active site act as electrophile while substrates are nucleophiles. This reaction usually requires cofactors as the amino acid side chains are not strong enough in attracting electrons. | 1 | Applied and Interdisciplinary Chemistry |
ECST is the official conference proceedings publication of The Electrochemical Society. This publication features full-text content of proceedings from ECS meetings and ECS-sponsored meetings. ECST is a high-quality venue for authors and an excellent resource for researchers. The papers appearing in ECST are reviewed to ensure that submissions meet generally accepted scientific standards. | 0 | Theoretical and Fundamental Chemistry |
The Hiyama coupling is limited by the need for fluoride in order to activate the organo­silicon reagent. Addition of fluoride cleaves any silicon protecting groups (e.g. silyl ethers), which are frequently employed in organic synthesis. The fluoride ion is also basic, so base sensitive protecting groups, acidic protons, and functional groups may be affected by the addition of this activator. Most of the active research concerning this reaction involves circumventing this problem. To overcome this issue, many groups have looked to the use of other basic additives for activation, or use of a different organo­silane reagent all together, leading to the multiple variations of the original Hiyama coupling. | 0 | Theoretical and Fundamental Chemistry |
All four HCN subunits are expressed in the brain. In addition to their proposed roles in pacemaking rhythmic or oscillatory activity, HCN channels may control the way that neurons respond to synaptic input. Initial studies suggest roles for HCN channels in sour taste, coordinated motor behavior and aspects of learning and memory. Clinically, there is evidence that HCN channels play roles in epilepsy and neuropathic pain. HCN channels have been shown to be important for activity-dependent mechanisms for olfactory sensory neuron growth.
HCN1 and 2 channels have been found in dorsal root ganglia, basal ganglia, and the dendrites of neurons in the hippocampus. It has been found that human cortical neurons have particularly high amount of HCN1 channel expression in all layers. HCN channel trafficking along dendrites in the hippocampus of rats has shown that HCN channels are quickly shuttled to the surface in response to neural activity. HCN channels have also been observed in the retrotrapezoid nucleus (RTN), a respiratory control center that responds to chemical signals such as CO. When HCN is inhibited, serotonin fails to stimulate chemoreceptors in the RTN. This illustrates a connection between HCN channels and respiratory regulation. Due to the complex nature of HCN channel regulation, as well as the complex interactions between multiple ion channels, HCN channels are fine-tuned to respond to certain thresholds and agonists. This complexity is believed to affect neural plasticity. | 1 | Applied and Interdisciplinary Chemistry |
Historically, pyridine was extracted from coal tar or obtained as a byproduct of coal gasification. The process is labor-consuming and inefficient: coal tar contains only about 0.1% pyridine, and therefore a multi-stage purification was required, which further reduced the output. Nowadays, most pyridines are synthesized from ammonia, aldehydes, and nitriles, a few combinations of which are suited for pyridine itself. Various name reactions are also known, but they are not practiced on scale.
In 1989, 26,000 tonnes of pyridine was produced worldwide. Other major derivatives are 2-, 3-, 4-methylpyridines and 5-ethyl-2-methylpyridine. The combined scale of these alkylpyridines matches that of pyridine itself. Among the largest 25 production sites for pyridine, eleven are located in Europe (as of 1999). The major producers of pyridine include Evonik Industries, Rütgers Chemicals, Jubilant Life Sciences, Imperial Chemical Industries, and Koei Chemical. Pyridine production significantly increased in the early 2000s, with an annual production capacity of 30,000 tonnes in mainland China alone. The US–Chinese joint venture Vertellus is currently the world leader in pyridine production. | 0 | Theoretical and Fundamental Chemistry |
In this chemical procedure, a "sol" (a colloidal solution) is formed that then gradually evolves towards the formation of a gel-like diphasic system containing both a liquid phase and solid phase whose morphologies range from discrete particles to continuous polymer networks. In the case of the colloid, the volume fraction of particles (or particle density) may be so low that a significant amount of fluid may need to be removed initially for the gel-like properties to be recognized. This can be accomplished in any number of ways. The simplest method is to allow time for sedimentation to occur, and then pour off the remaining liquid. Centrifugation can also be used to accelerate the process of phase separation.
Removal of the remaining liquid (solvent) phase requires a drying process, which is typically accompanied by a significant amount of shrinkage and densification. The rate at which the solvent can be removed is ultimately determined by the distribution of porosity in the gel. The ultimate microstructure of the final component will clearly be strongly influenced by changes imposed upon the structural template during this phase of processing.
Afterwards, a thermal treatment, or firing process, is often necessary in order to favor further polycondensation and enhance mechanical properties and structural stability via final sintering, densification, and grain growth. One of the distinct advantages of using this methodology as opposed to the more traditional processing techniques is that densification is often achieved at a much lower temperature.
The precursor sol can be either deposited on a substrate to form a film (e.g., by dip-coating or spin coating), cast into a suitable container with the desired shape (e.g., to obtain monolithic ceramics, glasses, fibers, membranes, aerogels), or used to synthesize powders (e.g., microspheres, nanospheres). The sol–gel approach is a cheap and low-temperature technique that allows the fine control of the product's chemical composition. Even small quantities of dopants, such as organic dyes and rare-earth elements, can be introduced in the sol and end up uniformly dispersed in the final product. It can be used in ceramics processing and manufacturing as an investment casting material, or as a means of producing very thin films of metal oxides for various purposes. Sol–gel derived materials have diverse applications in optics, electronics, energy, space, (bio)sensors, medicine (e.g., controlled drug release), reactive material, and separation (e.g., chromatography) technology.
The interest in sol–gel processing can be traced back in the mid-1800s with the observation that the hydrolysis of tetraethyl orthosilicate (TEOS) under acidic conditions led to the formation of SiO in the form of fibers and monoliths. Sol–gel research grew to be so important that in the 1990s more than 35,000 papers were published worldwide on the process. | 0 | Theoretical and Fundamental Chemistry |
Solar-blind technology is a set of technologies to produce images without interference from the Sun. This is done by using wavelengths of ultraviolet light that are totally absorbed by the ozone layer, yet are transmitted in the Earth's atmosphere. Wavelengths from 240 to 280 nm are completely absorbed by the ozone layer. Elements of this technology are ultraviolet light sources, ultraviolet image detectors, and filters that only transmit the range of wavelengths that are blocked by ozone. A system will also have a signal processing system, and a way to display the results (image). | 0 | Theoretical and Fundamental Chemistry |
Tantalum capacitors are, under some conditions, prone to self-destruction by thermal runaway. The capacitor typically consists of a sintered tantalum sponge acting as the anode, a manganese dioxide cathode, and a dielectric layer of tantalum pentoxide created on the tantalum sponge surface by anodizing. It may happen that the tantalum oxide layer has weak spots that undergo dielectric breakdown during a voltage spike. The tantalum sponge then comes into direct contact with the manganese dioxide, and increased leakage current causes localized heating; usually, this drives an endothermic chemical reaction that produces manganese(III) oxide and regenerates (self-heals) the tantalum oxide dielectric layer.
However, if the energy dissipated at the failure point is high enough, a self-sustaining exothermic reaction can start, similar to the thermite reaction, with metallic tantalum as fuel and manganese dioxide as oxidizer. This undesirable reaction will destroy the capacitor, producing smoke and possibly flame.
Therefore, tantalum capacitors can be freely deployed in small-signal circuits, but application in high-power circuits must be carefully designed to avoid thermal runaway failures. | 1 | Applied and Interdisciplinary Chemistry |
Analysis of water hardness in major Australian cities by the Australian Water Association shows a range from very soft (Melbourne) to hard (Adelaide).
Total hardness levels of calcium carbonate in ppm are:
*Canberra: 40
* Melbourne: 10–26
* Sydney: 39.4–60.1
* Perth: 29–226
* Brisbane: 100
* Adelaide: 134–148
* Hobart: 5.8–34.4
* Darwin: 31 | 0 | Theoretical and Fundamental Chemistry |
Polanyi described that the “turning point” of the acceptance of his model of adsorption occurred when Fritz Haber asked him to defend his theory in full in the Kaiser Wilhelm Institute for Physical Chemistry in Berlin, Germany. Many key players in the scientific world were present in this meeting including Albert Einstein. After hearing Polanyi's full explanation of his model, Haber and Einstein claimed that Polanyi “had displayed a total disregard for the scientifically established structure of the matter”. Years later, Polanyi described his ordeal by concluding,
Polanyi continued to provide supporting evidence in proving the validity of his model years after this meeting. | 0 | Theoretical and Fundamental Chemistry |
A bond angle is the geometric angle between two adjacent bonds. Some common shapes of simple molecules include:
* Linear: In a linear model, atoms are connected in a straight line. The bond angles are set at 180°. For example, carbon dioxide and nitric oxide have a linear molecular shape.
* Trigonal planar: Molecules with the trigonal planar shape are somewhat triangular and in one plane (flat). Consequently, the bond angles are set at 120°. For example, boron trifluoride.
* Angular: Angular molecules (also called bent or V-shaped) have a non-linear shape. For example, water (HO), which has an angle of about 105°. A water molecule has two pairs of bonded electrons and two unshared lone pairs.
* Tetrahedral: Tetra- signifies four, and -hedral relates to a face of a solid, so "tetrahedral" literally means "having four faces". This shape is found when there are four bonds all on one central atom, with no extra unshared electron pairs. In accordance with the VSEPR (valence-shell electron pair repulsion theory), the bond angles between the electron bonds are arccos(−) = 109.47°. For example, methane (CH) is a tetrahedral molecule.
* Octahedral: Octa- signifies eight, and -hedral relates to a face of a solid, so "octahedral" means "having eight faces". The bond angle is 90 degrees. For example, sulfur hexafluoride (SF) is an octahedral molecule.
* Trigonal pyramidal: A trigonal pyramidal molecule has a pyramid-like shape with a triangular base. Unlike the linear and trigonal planar shapes but similar to the tetrahedral orientation, pyramidal shapes require three dimensions in order to fully separate the electrons. Here, there are only three pairs of bonded electrons, leaving one unshared lone pair. Lone pair – bond pair repulsions change the bond angle from the tetrahedral angle to a slightly lower value. For example, ammonia (NH). | 0 | Theoretical and Fundamental Chemistry |
The steam injector is a common device used for delivering water to steam boilers, especially in steam locomotives. It is a typical application of the injector principle used to deliver cold water to a boiler against its own pressure, using its own live or exhaust steam, replacing any mechanical pump. When first developed, its operation was intriguing because it seemed paradoxical, almost like perpetual motion, but it was later explained using thermodynamics. Other types of injector may use other pressurised motive fluids such as air. | 1 | Applied and Interdisciplinary Chemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.