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After finishing his Ph.D., Willard returned to Michigan to rejoin the faculty; he became a full professor in 1922 and retired from the university, assuming professor emeritus status, in 1951. He was designated the Henry Russel Lecturer in 1948, noted as the university's highest distinction. He was known for his strong teaching skills and continued teaching at a variety of institutions after his retirement.
During his tenure at Michigan, Willard wrote several widely used and positively reviewed chemistry textbooks and laboratory course manuals, often with former students as coauthors. He also performed consulting work for local industry throughout his career, serving as the Director of the Chemistry and Metallurgy Laboratories for Detroit's Bureau of Aircraft Production in 1917-18 and as a long-term consultant for the Parker Rust-Proof Company.
Willard served as a director of the American Chemical Society from 1934 to 1940 and received the ACS' Fisher Award in Analytical Chemistry in 1951. He was the inaugural recipient of the Anachem Award given by the Association of Analytical Chemists in 1953. | 0 | Theoretical and Fundamental Chemistry |
Research carried out in 2008 in the Siberian Arctic showed methane releases on the annual scale of millions of tonnes, which was a substantial increase on the previous estimate of 0.5 millions of tonnes per year. apparently through perforations in the seabed permafrost, with concentrations in some regions reaching up to 100 times normal levels. The excess methane has been detected in localized hotspots in the outfall of the Lena River and the border between the Laptev Sea and the East Siberian Sea. At the time, some of the melting was thought to be the result of geological heating, but more thawing was believed to be due to the greatly increased volumes of meltwater being discharged from the Siberian rivers flowing north.
By 2013, the same team of researchers used multiple sonar observations to quantify the density of bubbles emanating from subsea permafrost into the ocean (a process called ebullition), and found that 100–630 mg methane per square meter is emitted daily along the East Siberian Arctic Shelf (ESAS), into the water column. They also found that during storms, when wind accelerates air-sea gas exchange, methane levels in the water column drop dramatically. Observations suggest that methane release from seabed permafrost will progress slowly, rather than abruptly. However, Arctic cyclones, fueled by global warming, and further accumulation of greenhouse gases in the atmosphere could contribute to more rapid methane release from this source. Altogether, their updated estimate had now amounted to 17 millions of tonnes per year.
However, these findings were soon questioned, as this rate of annual release would mean that the ESAS alone would account for between 28% and 75% of the observed Arctic methane emissions, which contradicts many other studies. In January 2020, it was found that the rate at which methane enters the atmosphere after it had been released from the shelf deposits into the water column had been greatly overestimated, and observations of atmospheric methane fluxes taken from multiple ship cruises in the Arctic instead indicate that only around 3.02 million tonnes of methane are emitted annually from the ESAS. A modelling study published in 2020 suggested that under the present-day conditions, annual methane release from the ESAS may be as low as 1000 tonnes, with 2.6 – 4.5 million tonnes representing the peak potential of turbulent emissions from the shelf. | 0 | Theoretical and Fundamental Chemistry |
The Taylor–Goldstein equation is an ordinary differential equation used in the fields of geophysical fluid dynamics, and more generally in fluid dynamics, in presence of quasi-2D flows. It describes the dynamics of the Kelvin–Helmholtz instability, subject to buoyancy forces (e.g. gravity), for stably stratified fluids in the dissipation-less limit. Or, more generally, the dynamics of internal waves in the presence of a (continuous) density stratification and shear flow. The Taylor–Goldstein equation is derived from the 2D Euler equations, using the Boussinesq approximation.
The equation is named after G.I. Taylor and S. Goldstein, who derived the equation independently from each other in 1931. The third independent derivation, also in 1931, was made by B. Haurwitz. | 1 | Applied and Interdisciplinary Chemistry |
Devapamil in rats can be used to decrease glutathione levels and increase oxidation of lipids, which makes it effective in preclusion of ulcers caused by stress. The medical characteristics of this drug, and other phenylalkylamines, depends greatly on the state of the calcium channels being targeted which results in a greater affinity and drug efficiency. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, subhalide usually refers to inorganic compounds that have a low ratio of halide to metal, made possible by metal–metal bonding (or element–element bonding for nonmetals), sometimes extensive. Many compounds meet this definition. | 0 | Theoretical and Fundamental Chemistry |
Nucleic acids, so-called because of their prevalence in cellular nuclei, is the generic name of the family of biopolymers. They are complex, high-molecular-weight biochemical macromolecules that can convey genetic information in all living cells and viruses. The monomers are called nucleotides, and each consists of three components: a nitrogenous heterocyclic base (either a purine or a pyrimidine), a pentose sugar, and a phosphate group.
The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The phosphate group and the sugar of each nucleotide bond with each other to form the backbone of the nucleic acid, while the sequence of nitrogenous bases stores the information. The most common nitrogenous bases are adenine, cytosine, guanine, thymine, and uracil. The nitrogenous bases of each strand of a nucleic acid will form hydrogen bonds with certain other nitrogenous bases in a complementary strand of nucleic acid (similar to a zipper). Adenine binds with thymine and uracil, thymine binds only with adenine, and cytosine and guanine can bind only with one another. Adenine and Thymine & Adenine and Uracil contains two hydrogen Bonds, while Hydrogen Bonds formed between cytosine and guanine are three in number.
Aside from the genetic material of the cell, nucleic acids often play a role as second messengers, as well as forming the base molecule for adenosine triphosphate (ATP), the primary energy-carrier molecule found in all living organisms. Also, the nitrogenous bases possible in the two nucleic acids are different: adenine, cytosine, and guanine occur in both RNA and DNA, while thymine occurs only in DNA and uracil occurs in RNA. | 1 | Applied and Interdisciplinary Chemistry |
Since plasmas are very good electrical conductors, electric potentials play an important role. The average potential in the space between charged particles, independent of how it can be measured, is called the "plasma potential", or the "space potential". If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a Debye sheath. The good electrical conductivity of plasmas makes their electric fields very small. This results in the important concept of "quasineutrality", which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma (), but on the scale of the Debye length, there can be charge imbalance. In the special case that double layers are formed, the charge separation can extend some tens of Debye lengths.
The magnitude of the potentials and electric fields must be determined by means other than simply finding the net charge density. A common example is to assume that the electrons satisfy the Boltzmann relation:
Differentiating this relation provides a means to calculate the electric field from the density:
It is possible to produce a plasma that is not quasineutral. An electron beam, for example, has only negative charges. The density of a non-neutral plasma must generally be very low, or it must be very small, otherwise, it will be dissipated by the repulsive electrostatic force. | 0 | Theoretical and Fundamental Chemistry |
Mitogens are important in cancer research due to their effects on the cell cycle. Cancer is in part defined by a lack of, or failure of, control in the cell cycle. This is usually a combination of two abnormalities: first, cancer cells lose their dependence on mitogens. Second, cancer cells are resistant to anti-mitogens. | 1 | Applied and Interdisciplinary Chemistry |
Nanoparticles have the ability to assemble chemically through covalent or noncovalent interactions with their capping ligand. The terminal functional group(s) on the particle are known as capping ligands. As these ligands tend to be complex and sophisticated, self-assembly can provide a simpler pathway for nanoparticle organization by synthesizing efficient functional groups. For instance, DNA oligomers have been a key ligand for nanoparticle building blocks to be self-assembling via sequence-based specific organization. However, to deliver precise and scalable (programmable) assembly for a desired structure, a careful positioning of ligand molecules onto the nanoparticle counterpart should be required at the building block (precursor) level, such as direction, geometry, morphology, affinity, etc. The successful design of ligand-building block units can play an essential role in manufacturing a wide-range of new nano systems, such as nanosensor systems,
nanomachines/nanobots, nanocomputers, and many more uncharted systems. | 0 | Theoretical and Fundamental Chemistry |
Natural phenols are reactive species toward oxidation, notably the complex mixture of phenolics, found in food for example, can undergo autoxidation during the ageing process. Simple natural phenols can lead to the formation of B type proanthocyanidins in wines or in model solutions. This is correlated to the non-enzymatic browning color change characteristic of this process. This phenomenon can be observed in foods like carrot purees.
Browning associated with oxidation of phenolic compounds has also been given as the cause of cells death in calli formed in in vitro cultures. Those phenolics originate both from explant tissues and from explant secretions. | 0 | Theoretical and Fundamental Chemistry |
A powerful solution is the multi-wavelength anomalous dispersion (MAD) method. In this technique, atoms inner electrons absorb X-rays of particular wavelengths, and reemit the X-rays after a delay, inducing a phase shift in all of the reflections, known as the anomalous dispersion effect'. Analysis of this phase shift (which may be different for individual reflections) results in a solution for the phases. Since X-ray fluorescence techniques (like this one) require excitation at very specific wavelengths, it is necessary to use synchrotron radiation when using the MAD method. | 0 | Theoretical and Fundamental Chemistry |
Electrophilic amination reactions can be classified as either additions or substitutions. Although the resulting product is not always an amine, these reactions are unified by the formation of a carbon–nitrogen bond and the use of an electrophilic aminating agent. A wide variety of electrophiles have been used; for substitutions, these are most commonly amines substituted with electron-withdrawing groups: chloramines, hydroxylamines, hydrazines, and oxaziridines, for instance. Addition reactions have employed imines, oximes, azides, azo compounds, and others. | 0 | Theoretical and Fundamental Chemistry |
There is a lack of scientific research regarding EWSS. Other issues that may affect the effectiveness of an EWSS:
* Sprinkler performance in high wind conditions typical in a bushfire
* Home design
** High vulnerability areas. e.g. decking
** Garden beds near walls
** Window sills
** Large windows (heat radiation)
** Internal furnishings (e.g. curtains)
* Home location
** Slope
** Surrounding vegetation
* If defended by occupiers
* Preparation (if prepared for defense)
* If intended for remote (unattended) defense
* Available water supply
* Ember attack
* Fire front (radiant heat)
* Adjacent building or vegetation fire | 1 | Applied and Interdisciplinary Chemistry |
The important characteristic of these tests is that the strain rate is low, for example extension rates selected in the range from 10 to 10 s. The selection of the strain rate is very important because the susceptibility to cracking may not be evident from result of tests at too low or too high strain rate. For numerous material-environment systems, strain rates in range 10 - 10 s are used; however, the observed absence of cracking at a given strain rate should not be taken as a proof of immunity to cracking. There are known cases wherein the susceptibility to stress-corrosion cracking only became evident at strain rates as low as 10 or 10 s. Nevertheless, the method is very suitable for mechanistic studies, as well as for relative ranking of susceptibility to cracking of different alloys, or the aggressiveness of environments and the effect of temperature, pH, metallurgical condition etc.
The fastest strain rate that will still promote SCC for a given environment-material system is sometimes called the "critical strain rate", some values are given in the table: | 1 | Applied and Interdisciplinary Chemistry |
The calicheamicins are a sub-family of enediynes that were isolated from Micromonospora echinospora calichensis. All calicheamicin family members demonstrate potent antimicrobial activity against Gram-positive and Gram-negative organisms. Calicheamicin γ1 exhibited significant antitumor activity against leukemia and melanoma cells in vivo. The calicheamicins are notably similar in structure to the esperamicins.</p> | 0 | Theoretical and Fundamental Chemistry |
* 2016 GIAN fellow (Indian Ministry of Human Resource Development)
* 2015 Catalysis Society of South Africa (CATSA eminent visitor)
* 2014 European Research Council Consolidator Grant
* 2013 Bessel Award (Humboldt Foundation)
* 2011 Fellow of the Royal Society of Chemistry (RSC)
* 2008 Visiting Professor (University of Otago, New Zealand)
* 2007 European Research Council Starting Grant
* 2002 Alfred Werner Assistant Professorship (Alfred Werner Foundation)
* 2001 Bakker price from the Royal Dutch Chemical Society (KNCV) | 0 | Theoretical and Fundamental Chemistry |
Even though many studies conduct testing under experimental or enriched conditions, oxidation-reduction reactions occur naturally and allow for chemicals to go through processes such as biodegradation, outlined above. Oxidation is defined as the loss of an electron to another species, while reduction is the gaining of an electron from another species. As compounds go through oxidation and reduction in sediments, the preservative compounds are altered to form new chemicals, leading to decomposition. An example of the oxidation of p-cresol and phenol can be seen in the figures below: | 0 | Theoretical and Fundamental Chemistry |
Crystallography is a technique that characterizes the chemical structure of materials at the atomic level by analyzing the diffraction patterns of electromagnetic radiation or particles that have been deflected by atoms in the material. X-rays are most commonly used. From the raw data, the relative placement of atoms in space may be determined. | 0 | Theoretical and Fundamental Chemistry |
Comparing the functions of the characterised Mg transport proteins is currently almost impossible, even though the proteins have been investigated in different biological systems using different methodologies and technologies. Finding a system where all the proteins can be compared directly would be a major advance. If the proteins could be shown to be functional in bacteria (S. typhimurium), then a combination of the techniques of mag-fura 2, quantification of protein in the envelope membrane, and structure of the proteins (X-ray crystal or cryo-TEM) might allow the determination of the basic mechanisms involved in the recognition and transport of the Mg ion. However, perhaps the best advance would be the development of methods allowing the measurement of the protein's function in the patch-clamp system using artificial membranes. | 1 | Applied and Interdisciplinary Chemistry |
Polarization gradient cooling (PG cooling) is a technique in laser cooling of atoms. It was proposed to explain the experimental observation of cooling below the doppler limit. Shortly after the theory was introduced experiments were performed that verified the theoretical predictions. While Doppler cooling allows atoms to be cooled to hundreds of microkelvin, PG cooling allows atoms to be cooled to a few microkelvin or less.
The superposition of two counterpropagating beams of light with orthogonal polarizations creates a gradient where the polarization varies in space. The gradient depends on which type of polarization is used. Orthogonal linear polarizations (the lin⊥lin configuration) results in the polarization varying between linear and circular polarization in the range of half a wavelength. However, if orthogonal circular polarizations (the σσ configuration) are used, the result is a linear polarization that rotates along the axis of propagation. Both configurations can be used for cooling and yield similar results, however, the physical mechanisms involved are very different. For the lin⊥lin case, the polarization gradient causes periodic light shifts in Zeeman sublevels of the atomic ground state that allows for a Sisyphus effect to occur. In the σ-σ configuration, the rotating polarization creates a motion-induced population imbalance in the Zeeman sublevels of the atomic ground state resulting in an imbalance in the radiation pressure that opposes the motion of the atom. Both configurations achieve sub-Doppler cooling and instead reach the recoil limit. While the limit of PG cooling is lower than that of Doppler cooling, the capture range of PG cooling is lower and thus an atomic gas must be pre-cooled before PG cooling. | 0 | Theoretical and Fundamental Chemistry |
Chinese mythology generally reflects a time when metallurgy had long been practiced. According to the Romanian anthropologist, orientalist, and philosopher Mircea Eliade, the Iron Age produced a large number of rites, myths and symbols; the blacksmith was the main agent of diffusion of mythology, rites and metallurgical mysteries. The secret knowledge of metallurgists and their powers made them founders of the human world and masters of the spirit world. This metallurgical model was reinterpreted again by Taoist alchemists.
Some metalworkers illustrate the close relationship between Chinese mystical and sovereign power and the mining and metallurgy industries. Although the name Huangdi is absent from Shang or Zhou inscriptions, it appears in the Spring and Autumn periods Guoyu and Zuo zhuan'. According to Mitarai (1984), Huangdi may have lived in early antiquity and led a regional ethnic group who worshiped him as a deity; "The Yellow Emperor fought Chiyou at Mount Kunwu whose summit was covered with a large quantity of red copper".
"The seventy-two brothers of Chiyou had copper heads and iron fronts; they ate iron and stones [...] In the province of Ji where Chiyou is believed to have lived (Chiyou shen), when we dig the earth and we find skulls that seem to be made of copper and iron, they are identified as the bones of Chiyou." Chiyou was the leader of the indigenous Sanmiao (or Jiuli) tribes who defeated Xuanyuan, the future Yellow Emperor. Chiyou, a rival of the Yellow Emperor, belonged to a clan of blacksmiths. The advancement of weaponry is sometimes attributed to the Yellow Emperor and Chiyou, and Chiyou reportedly discovered the process of casting. Kunwu is associated with a people, a royal blacksmith, a mountain which produces metals, and a sword. Kui, a master of music and dance cited by Shun, was succeeded by Yu the Great. Yu the Great, reported founder of the Xia dynasty (China's first), spent many years working on flood control and is credited with casting the Nine Tripod Cauldrons. Helped by dragons descended from heaven, he died on Mount Xianglu in Zhejiang. In these myths and legends, mines and forges are associated with leadership. | 1 | Applied and Interdisciplinary Chemistry |
Total synthesis of (+)-Absinthin was conducted in 2004 by Zhang, et al. The final yield reported for the synthesis was 18.6% over a course of 10 steps originating from Santonin (1), a commercially available reagent. The basis of the synthesis was the ring expansion of the original 6-membered carbon ring to the 7-membered ring, engendering the formation of the guaianolide monomer (2) scaffold, followed by Diels Alder coupling (3) and final stereochemical modifications resulting in (+)-Absinthin (4). | 0 | Theoretical and Fundamental Chemistry |
NBS will react with alkenes 1 in aqueous solvents to give bromohydrins 2. The preferred conditions are the portionwise addition of NBS to a solution of the alkene in 50% aqueous DMSO, DME, THF, or tert-butanol at 0 °C. Formation of a bromonium ion and immediate attack by water gives strong Markovnikov addition and anti stereochemical selectivities.
Side reactions include the formation of α-bromoketones and dibromo compounds. These can be minimized by the use of freshly recrystallized NBS.
With the addition of nucleophiles, instead of water, various bifunctional alkanes can be synthesized. | 0 | Theoretical and Fundamental Chemistry |
Orbifold notation for wallpaper groups, advocated by John Horton Conway (Conway, 1992) (Conway 2008), is based not on crystallography, but on topology. One can fold the infinite periodic tiling of the plane into its essence, an orbifold, then describe that with a few symbols.
*A digit, n, indicates a centre of n-fold rotation corresponding to a cone point on the orbifold. By the crystallographic restriction theorem, n must be 2, 3, 4, or 6.
*An asterisk, *, indicates a mirror symmetry corresponding to a boundary of the orbifold. It interacts with the digits as follows:
*#Digits before * denote centres of pure rotation (cyclic).
*#Digits after * denote centres of rotation with mirrors through them, corresponding to "corners" on the boundary of the orbifold (dihedral).
*A cross, ×, occurs when a glide reflection is present and indicates a crosscap on the orbifold. Pure mirrors combine with lattice translation to produce glides, but those are already accounted for so need no notation.
*The "no symmetry" symbol, o, stands alone, and indicates there are only lattice translations with no other symmetry. The orbifold with this symbol is a torus; in general the symbol o denotes a handle on the orbifold.
The group denoted in crystallographic notation by cmm will, in Conway's notation, be 2*22. The 2 before the * says there is a 2-fold rotation centre with no mirror through it. The * itself says there is a mirror. The first 2 after the * says there is a 2-fold rotation centre on a mirror. The final 2 says there is an independent second 2-fold rotation centre on a mirror, one that is not a duplicate of the first one under symmetries.
The group denoted by pgg will be 22×. There are two pure 2-fold rotation centres, and a glide reflection axis. Contrast this with pmg, Conway 22*, where crystallographic notation mentions a glide, but one that is implicit in the other symmetries of the orbifold.
Coxeter's bracket notation is also included, based on reflectional Coxeter groups, and modified with plus superscripts accounting for rotations, improper rotations and translations. | 0 | Theoretical and Fundamental Chemistry |
The serendipitous discovery and subsequent clinical success of penicillin prompted a large-scale search for other environmental microorganisms that might produce anti-infective natural products. Soil and water samples were collected from all over the world, leading to the discovery of streptomycin (derived from Streptomyces griseus), and the realization that bacteria, not just fungi, represent an important source of pharmacologically active natural products. This, in turn, led to the development of an impressive arsenal of antibacterial and antifungal agents including amphotericin B, chloramphenicol, daptomycin and tetracycline (from Streptomyces spp.), the polymyxins (from Paenibacillus polymyxa), and the rifamycins (from Amycolatopsis rifamycinica). Antiparasitic and antiviral drugs have similarly been derived from bacterial metabolites.
Although most of the drugs derived from bacteria are employed as anti-infectives, some have found use in other fields of medicine. Botulinum toxin (from Clostridium botulinum) and bleomycin (from Streptomyces verticillus) are two examples. Botulinum, the neurotoxin responsible for botulism, can be injected into specific muscles (such as those controlling the eyelid) to prevent muscle spasm. Also, the glycopeptide bleomycin is used for the treatment of several cancers including Hodgkin's lymphoma, head and neck cancer, and testicular cancer. Newer trends in the field include the metabolic profiling and isolation of natural products from novel bacterial species present in underexplored environments. Examples include symbionts or endophytes from tropical environments, subterranean bacteria found deep underground via mining/drilling, and marine bacteria. | 1 | Applied and Interdisciplinary Chemistry |
Antimony-125 decays with a half life of over two years to which itself decays with a half life of almost two months via isomeric transition to the ground state. While its relatively short half life and the significant gamma emissions (144.77 keV) of its daughter nuclide make usage in an RTG less attractive, Sb-125 could deliver a relatively high power density of 3.4 W/g.
Fluoride volatility can recover antimony as the mildly volatile (solid at room temperature) Antimony trifluoride or the more volatile (boiling point ) Antimony pentafluoride. | 0 | Theoretical and Fundamental Chemistry |
Approximately 100 million years ago (mya), within the yeast lineage there was a whole genome duplication (WGD). A majority of Crabtree-positive yeasts are post-WGD yeasts. It was believed that the WGD was a mechanism for the development of the Crabtree effect in these species due to the duplication of alcohol dehydrogenase (ADH) encoding genes and hexose transporters. However, recent evidence has shown that aerobic fermentation originated before the WGD and evolved as a multi-step process, potentially aided by the WGD. The origin of aerobic fermentation, or the first step, in Saccharomyces Crabtree-positive yeasts likely occurred in the interval between the ability to grow under anaerobic conditions, horizontal transfer of anaerobic DHODase (encoded by URA1 with bacteria), and the loss of respiratory chain Complex I. A more pronounced Crabtree effect, the second step, likely occurred near the time of the WGD event. Later evolutionary events that aided in the evolution of aerobic fermentation are better understood and outlined in the section discussing the genomic basis of the Crabtree effect. | 1 | Applied and Interdisciplinary Chemistry |
a. Fructose is not the only sugar found in fruits. Glucose and sucrose are also found in varying quantities in various fruits, and sometimes exceed the fructose present. For example, 32% of the edible portion of a date is glucose, compared with 24% fructose and 8% sucrose. However, peaches contain more sucrose (6.66%) than they do fructose (0.93%) or glucose (1.47%). | 1 | Applied and Interdisciplinary Chemistry |
The Rabi frequency is the frequency at which the probability amplitudes of two atomic energy levels fluctuate in an oscillating electromagnetic field. It is proportional to the transition dipole moment of the two levels and to the amplitude (not intensity) of the electromagnetic field. Population transfer between the levels of such a 2-level system illuminated with light exactly resonant with the difference in energy between the two levels will occur at the Rabi frequency; when the incident light is detuned from this energy difference (detuned from resonance) then the population transfer occurs at the generalized Rabi frequency. The Rabi frequency is a semiclassical concept since it treats the atom as an object with quantized energy levels and the electromagnetic field as a continuous wave.
In the context of a nuclear magnetic resonance experiment, the Rabi frequency is the nutation frequency of a sample's net nuclear magnetization vector about a radio-frequency field. (Note that this is distinct from the Larmor frequency, which characterizes the precession of a transverse nuclear magnetization about a static magnetic field.) | 0 | Theoretical and Fundamental Chemistry |
Stromatolites are layered biochemical accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by biofilms (microbial mats) of microorganisms, especially cyanobacteria.
During the Precambrian, stromatolite communities of microorganisms grew in most marine and non-marine environments in the photic zone. After the Cambrian explosion of marine animals, grazing on the stromatolite mats by herbivores greatly reduced the occurrence of the stromatolites in marine environments. Since then, they are found mostly in hypersaline conditions where grazing invertebrates cannot live (e.g. Shark Bay, Western Australia). Stromatolites provide ancient records of life on Earth by fossil remains which date from 3.5 Ga ago. The oldest undisputed evidence of cyanobacteria is dated to be 2.1 Ga ago, but there is some evidence for them as far back as 2.7 Ga ago. Cyanobacteria might have also emerged 3.5 Ga ago. Oxygen concentrations in the atmosphere remained around or below 0.001% of today's level until 2.4 Ga ago (the Great Oxygenation Event). The rise in oxygen may have caused a fall in the concentration of atmospheric methane, and triggered the Huronian glaciation from around 2.4 to 2.1 Ga ago. In this way, cyanobacteria may have killed off most of the other bacteria of the time.
Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are similar to stromatolites, but instead of forming columns, they form approximately spherical structures that were not attached to the underlying substrate as they formed. The oncoids often form around a central nucleus, such as a shell fragment, and a calcium carbonate structure is deposited by encrusting microbes. Oncolites are indicators of warm waters in the photic zone, but are also known in contemporary freshwater environments. These structures rarely exceed 10 cm in diameter.
One former classification scheme of cyanobacterial fossils divided them into the porostromata and the spongiostromata. These are now recognized as form taxa and considered taxonomically obsolete; however, some authors have advocated for the terms remaining informally to describe form and structure of bacterial fossils. | 0 | Theoretical and Fundamental Chemistry |
Lactams can be formed from cyclisation of amino acids via the coupling between an amine and a carboxylic acid within the same molecule.
Lactamization is most efficient in this way if the product is a γ-lactam. For example, Fmoc-Dab(Mtt)-OH, although its side-chain amine is sterically protected by extremely bulky 4-Methyltrityl (Mtt) group, the amine can still intramolecularly couple with the carboxylic acid to form a γ-lactam. This reaction almost finished within 5 minutes with many coupling reagents (e.g. HATU and PyAOP). | 0 | Theoretical and Fundamental Chemistry |
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.
The process is called anodizing because the part to be treated forms the anode electrode of an electrolytic cell. Anodizing increases resistance to corrosion and wear, and provides better adhesion for paint primers and glues than bare metal does. Anodic films can also be used for several cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add reflected light wave interference effects.
Anodizing is also used to prevent galling of threaded components and to make dielectric films for electrolytic capacitors. Anodic films are most commonly applied to protect aluminium alloys, although processes also exist for titanium, zinc, magnesium, niobium, zirconium, hafnium, and tantalum. Iron or carbon steel metal exfoliates when oxidized under neutral or alkaline micro-electrolytic conditions; i.e., the iron oxide (actually ferric hydroxide or hydrated iron oxide, also known as rust) forms by anoxic anodic pits and large cathodic surface, these pits concentrate anions such as sulfate and chloride accelerating the underlying metal to corrosion. Carbon flakes or nodules in iron or steel with high carbon content (high-carbon steel, cast iron) may cause an electrolytic potential and interfere with coating or plating. Ferrous metals are commonly anodized electrolytically in nitric acid or by treatment with red fuming nitric acid to form hard black Iron(II,III) oxide. This oxide remains conformal even when plated on wiring and the wiring is bent.
Anodizing changes the microscopic texture of the surface and the crystal structure of the metal near the surface. Thick coatings are normally porous, so a sealing process is often needed to achieve corrosion resistance. Anodized aluminium surfaces, for example, are harder than aluminium but have low to moderate wear resistance that can be improved with increasing thickness or by applying suitable sealing substances. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, but also more brittle. This makes them less likely to crack and peel from ageing and wear, but more susceptible to cracking from thermal stress. | 1 | Applied and Interdisciplinary Chemistry |
Uroporphyrinogens are cyclic tetrapyrroles with four propionic acid groups ("P" groups) and four acetic acid groups ("A" groups).
There are four forms, which vary based upon the arrangements of the "P" and "A" groups (in clockwise order):
* In the "I" variety (i.e. uroporphyrinogen I), the order repeats four times: AP-AP-AP-AP.
* In the "III" variety (i.e. uroporphyrinogen III), the fourth is reversed: AP-AP-AP-PA.
*:This is the most common form. In the synthesis of porphyrin, it is created from the linear tetrapyrrole hydroxymethylbilane by the enzyme uroporphyrinogen III synthase, and is further converted into coproporphyrinogen III by the enzyme uroporphyrinogen III decarboxylase.
* The "II" and "IV" varieties can be created synthetically, but do not appear in nature. | 1 | Applied and Interdisciplinary Chemistry |
Polymerization, an anabolic pathway used to build macromolecules such as nucleic acids, proteins, and polysaccharides, uses condensation reactions to join monomers. Macromolecules are created from smaller molecules using enzymes and cofactors. | 1 | Applied and Interdisciplinary Chemistry |
Levobetaxolol should not be used by people who have sinus bradycardia, atrioventricular block, cardiogenic shock, or overt cardiac failure. The drug has been associated with bradycardia and hypertension. | 0 | Theoretical and Fundamental Chemistry |
The United Nations Economic Commission for Europe and the EU National Emission Ceilings Directive (2016) require countries to produce annual National Air Pollution Emission Inventories under the provisions of the Convention on Long-Range Transboundary Air Pollution (CLRTAP).
The European Monitoring and Evaluation Programme (EMEP) Task Force of the European Environment Agency has developed methods to estimate emissions and the associated emission factors for air pollutants, which have been published in the EMEP/CORINAIR Emission Inventory Guidebook on Emission Inventories and Projections TFEIP. | 1 | Applied and Interdisciplinary Chemistry |
All atomic nuclei are composed of protons and neutrons bound together by the nuclear force. There are 286 primordial nuclides that occur naturally on earth, each corresponding to a unique number of protons, called the atomic number, Z, and a unique number of neutrons, called the neutron number, N. The mass number, A, of a nuclide is the sum of atomic and neutron numbers, A = Z + N. Not all nuclides are stable, however. According to Byrne, stable nuclides are defined as those having a half-life greater than 10 years, and there are many combinations of protons and neutrons that form nuclides that are unstable. A common example of an unstable nuclide is carbon-14 that decays by beta decay into nitrogen-14 with a half-life of about 5,730 years:
In this form of decay, the original element becomes a new chemical element in a process known as nuclear transmutation and a beta particle and an electron antineutrino are emitted. An essential property of this and all nuclide decays is that the total energy of the decay product is less than that of the original nuclide. The difference between the initial and final nuclide binding energies is carried away by the kinetic energies of the decay products, often the beta particle and its associated neutrino.
The concept of the valley of stability is a way of organizing all of the nuclides according to binding energy as a function of neutron and proton numbers. Most stable nuclides have roughly equal numbers of protons and neutrons, so the line for which Z = N forms a rough initial line defining stable nuclides. The greater the number of protons, the more neutrons are required to stabilize a nuclide; nuclides with larger values for Z require an even larger number of neutrons, N > Z, to be stable. The valley of stability is formed by the negative of binding energy, the binding energy being the energy required to break apart the nuclide into its proton and neutron components. The stable nuclides have high binding energy, and these nuclides lie along the bottom of the valley of stability. Nuclides with weaker binding energy have combinations of N and Z that lie off of the line of stability and further up the sides of the valley of stability. Unstable nuclides can be formed in nuclear reactors or supernovas, for example. Such nuclides often decay in sequences of reactions called decay chains that take the resulting nuclides sequentially down the slopes of the valley of stability. The sequence of decays take nuclides toward greater binding energies, and the nuclides terminating the chain are stable. The valley of stability provides both a conceptual approach for how to organize the myriad stable and unstable nuclides into a coherent picture and an intuitive way to understand how and why sequences of radioactive decay occur. | 0 | Theoretical and Fundamental Chemistry |
From about the 14th century, water-power began to be applied to bloomeries, but fewer than ten such sites are suspected. | 1 | Applied and Interdisciplinary Chemistry |
According to a 2022 systematic review, inadequate resources (financial and subject matter expertise), barriers to accessing shelved compounds and their trial data, and the lack of traditional IP protections for repurposed compounds are the key barriers to drug repurposing. There is a lack of financial incentives for pharmaceutical companies to explore the repurposing of generic drugs. Indeed, doctors can prescribe the drug off-label and pharmacists can switch the branded version for a cheaper generic alternative. According to Pharmacologist Alasdair Breckenridge and patent judge Robin Jacob this issue is so significant that: "If a generic version of a drug is available, developers have little or no opportunity to recoup their investment in the development of the drug for a new indication".
Drug repositioning present other challenges. First, the dosage required for the treatment of a novel disease usually differs from that of its original target disease, and if this happens, the discovery team will have to begin from Phase I clinical trials, which effectively strips drug repositioning of its advantages of over de novo drug discovery. Second, the finding of new formulation and distribution mechanisms of existing drugs to the novel-disease-affected areas rarely includes the efforts of "pharmaceutical and toxicological" scientists. Third, patent right issues can be very complicated for drug repurposing due to the lack of experts in the legal area of drug repositioning, the disclosure of repositioning online or via publications, and the extent of the novelty of the new drug purpose. | 1 | Applied and Interdisciplinary Chemistry |
In ultrashort pulse physics, a so-called nonthermal melting may take place. It occurs not because of the increase of the atomic kinetic energy, but because of changes of the interatomic potential due to excitation of electrons. Since electrons are acting like a glue sticking atoms together, heating electrons by a femtosecond laser alters the properties of this "glue", which may break the bonds between the atoms and melt a material even without an increase of the atomic temperature.
In genetics, melting DNA means to separate the double-stranded DNA into two single strands by heating or the use of chemical agents, polymerase chain reaction. | 0 | Theoretical and Fundamental Chemistry |
The term neopolarogram refers to mathematical derivatives of polarograms or cyclic voltammograms that in effect deconvolute diffusion and electrochemical kinetics. This is achieved by analog or digital implementations of fractional calculus. The implementation of fractional derivative calculations by means of numerical methods is straight forward. The G1- (Grünwald–Letnikov derivative) and the RL0-algorithms (Riemann–Liouville integral) are recursive methods to implement a numerical calculation of fractional differintegrals. Yet differintegrals are faster to compute in discrete fourier space using FFT. | 0 | Theoretical and Fundamental Chemistry |
The Tim9-Tim10 complex is made up of three Tim9 molecules and three Tim10 molecules. Each Tim9 and Tim10 subunit consists of 80-110 amino acid residues with four conserved cysteine residues that form two intramolecular disulfide bonds. Each subunit folds into a helix-loop-helix structure, with each loop forming a donut shape that comprises the upper face of the complex. The structure of the Tim9-Tim10 complex takes on the form of an α-propeller, with two helical blades radiating from a narrow central pore. | 1 | Applied and Interdisciplinary Chemistry |
The study of planar chiral metamaterials has revealed that planar chirality is also associated with an optical effect in non-diffracting structures: the directionally asymmetric transmission (reflection and absorption) of circularly polarized waves. Planar chiral metamaterials, which are also anisotropic and lossy exhibit different total transmission (reflection and absorption) levels for the same circularly polarized wave incident on their front and back.
The asymmetric transmission phenomenon arises from different, e.g. left-to-right, circular polarization conversion efficiencies for opposite propagation directions of the incident wave and therefore the effect is referred to as circular conversion dichroism.
Like the twist of a planar chiral pattern appears reversed for opposite directions of observation, planar chiral metamaterials have interchanged properties for left-handed and right-handed circularly polarized waves that are incident on their front and back. In particular left-handed and right-handed circularly polarized waves experience opposite directional transmission (reflection and absorption) asymmetries. | 0 | Theoretical and Fundamental Chemistry |
Commonly fluorophores (such as rhodamine or fluorescein) are linked to the ring linked to the sugar (in para) via a flexible arm, presumably extruding from the major groove of the helix. Due to low processivity of the nucleotides linked to bulky adducts such as florophores by [Taq polymerase]s, the sequence is typically copied using a nucleotide with an arm and later coupled with a reactive fluorophore (indirect labelling):
* Amine reactive: aminoallyl nucleotides contain a primary amine group on a linker that reacts with the amino-reactive dye such as cyanine or Alexa Fluor dyes, which contain a reactive leaving group like succinimidyl ester (NHS). Base-pairing amino groups are not affected.
* Thiol reactive: thiol-containing nucleotides react with the fluorophore linked to a reactive leaving group like maleimide.
* Biotin-linked nucleotides rely on the same indirect labelling principle (and fluorescent streptavidin) and are used in Affymetrix DNAchips.
Fluorophores find a variety of uses in medicine and biochemistry. | 1 | Applied and Interdisciplinary Chemistry |
Diarylethene photoswitches have reversible cyclization and cycloreversion reactions that are photoinduced. They are a class of compounds that have aromatic functional groups bonded to each end of a carbon-carbon double bond. An example of this class of molecule that is used in photopharmacology is stilbene. Under the influence of light, stilbene switches between its two isomers (E and Z).
Figure 4. Figure showing stilbene isomerizations under light from E to Z
Diarylethenes have been shown to have some advantages over the more researched azobenzenes switches, such as thermal irreversibility, high photoswitching efficiency, favorable cellular stability, and low toxicity. Diarylethenes have been shown to have promise in fields other than photopharmacology as well. These fields include optical data storage, optoelectronic devices, supramolecular self-assembly and anti-counterfeiting. | 1 | Applied and Interdisciplinary Chemistry |
IL-22 mediates inflammation and binds class II cytokine receptor heterodimers IL-22 RA1/CRF2-4; is involved in immuno-regulatory responses | 1 | Applied and Interdisciplinary Chemistry |
A starting point for the development can be taken as the virial equation of state for a gas.
where is the pressure, is the volume, is the temperature and ... are known as virial coefficients. The first term on the right-hand side is for an ideal gas. The remaining terms quantify the departure from the ideal gas law with changing pressure, . It can be shown by statistical mechanics that the second virial coefficient arises from the intermolecular forces between pairs of molecules, the third virial coefficient involves interactions between three molecules, etc. This theory was developed by McMillan and Mayer.
Solutions of uncharged molecules can be treated by a modification of the McMillan-Mayer theory. However, when a solution contains electrolytes, electrostatic interactions must also be taken into account. The Debye–Hückel theory was based on the assumption that each ion was surrounded by a spherical "cloud" or ionic atmosphere made up of ions of the opposite charge. Expressions were derived for the variation of single-ion activity coefficients as a function of ionic strength. This theory was very successful for dilute solutions of 1:1 electrolytes and, as discussed below, the Debye–Hückel expressions are still valid at sufficiently low concentrations. The values calculated with Debye–Hückel theory diverge more and more from observed values as the concentrations and/or ionic charges increases. Moreover, Debye–Hückel theory takes no account of the specific properties of ions such as size or shape.
Brønsted had independently proposed an empirical equation,
in which the activity coefficient depended not only on ionic strength, but also on the concentration, m, of the specific ion through the parameter β. This is the basis of SIT theory. It was further developed by Guggenheim. Scatchard extended the theory to allow the interaction coefficients to vary with ionic strength. Note that the second form of Brønsted's equation is an expression for the osmotic coefficient. Measurement of osmotic coefficients provides one means for determining mean activity coefficients. | 0 | Theoretical and Fundamental Chemistry |
If the constituents of a mixture are completely miscible in all proportions with each other, the type of azeotrope is called a homogeneous azeotrope. Homogeneous azeotropes can be of the low-boiling or high-boiling azeotropic type. For example, any amount of ethanol can be mixed with any amount of water to form a homogeneous solution.
If the components of a mixture are not completely miscible, an azeotrope can be found inside the miscibility gap. This type of azeotrope is called a heterogeneous azeotrope or heteroazeotrope. A heteroazeotropic distillation will have two liquid phases. Heterogeneous azeotropes are only known in combination with temperature-minimum azeotropic behavior. For example, if equal volumes of chloroform (water solubility 0.8 g/100 ml at 20 °C) and water are shaken together and then left to stand, the liquid will separate into two layers. Analysis of the layers shows that the top layer is mostly water with a small amount of chloroform dissolved in it, and the bottom layer is mostly chloroform with a small amount of water dissolved in it. If the two layers are heated together, the system of layers will boil at 53.3 °C, which is lower than either the boiling point of chloroform (61.2 °C) or the boiling point of water (100 °C). The vapor will consist of 97.0% chloroform and 3.0% water regardless of how much of each liquid layer is present provided both layers are indeed present. If the vapor is re-condensed, the layers will reform in the condensate, and will do so in a fixed ratio, which in this case is 4.4% of the volume in the top layer and 95.6% in the bottom layer.
Combinations of solvents that do not form an azeotrope when mixed in any proportion are said to be zeotropic. Azeotropes are useful in separating zeotropic mixtures. An example is acetic acid and water, which do not form an azeotrope. Despite this, it is very difficult to separate pure acetic acid (boiling point: 118.1 °C) from a solution of acetic acid and water by distillation alone. As progressive distillations produce solutions with less and less water, each further distillation becomes less effective at removing the remaining water. Distilling the solution to dry acetic acid is therefore economically impractical. But ethyl acetate forms an azeotrope with water that boils at 70.4 °C. By adding ethyl acetate as an entrainer, it is possible to distill away the azeotrope and leave nearly pure acetic acid as the residue. | 1 | Applied and Interdisciplinary Chemistry |
Antisense oligonucleotides were discovered in 1978 by Paul Zamecnik and Mary Stephenson. Oligonucleotides, which are short nucleic acid fragments, bind to complementary target mRNA molecules when added to the cell. These molecules can be composed of single-stranded DNA or RNA and are generally 13–25 nucleotides long. The antisense oligonucleotides can affect gene expression in two ways: by using an RNase H-dependent mechanism or by using a steric blocking mechanism. RNase H-dependent oligonucleotides cause the target mRNA molecules to be degraded, while steric-blocker oligonucleotides prevent translation of the mRNA molecule. The majority of antisense drugs function through the RNase H-dependent mechanism, in which RNase H hydrolyzes the RNA strand of the DNA/RNA heteroduplex. expression. | 1 | Applied and Interdisciplinary Chemistry |
Color change materials have been used in several very common outlets but also in an increasing number of new ones. Commercial applications include photochromics in ophthalmics, fashion/cosmetics, security, sensors, optical memory and optical switches, thermochromics in paints, inks, plastics and textiles as indicators/sensors and in architecture, ionochromics in copy paper, direct thermal printing and textile sensors, electrochromics in car mirrors, smart windows, flexible devices and solar protection, solvatochromics in biological probes and sensors, gasochromics in windows and gas sensors. | 0 | Theoretical and Fundamental Chemistry |
In 2014, Southern Research and the University of Alabama at Birmingham formed the Alliance for Innovative Medical Technology (AIMTech) to develop new medical devices to improve healthcare.
The creation of medical devices are across all five specializations: Cardiology, Orthopedics, Ophthalmology, Rehabilitation and Trauma. The goal is for the first group of AIMTech-created medical devices to hit the market by 2020. By comparison, it can take 10 years to create an FDA approved drug.
In 2016, AIMTech was awarded a $500,000 U.S. Department of Commerce grant to expand medical device innovation and commercialization. | 1 | Applied and Interdisciplinary Chemistry |
SINEs are classified as non-LTR retrotransposons because they do not contain long terminal repeats (LTRs). There are three types of SINEs common to vertebrates and invertebrates: CORE-SINEs, V-SINEs, and AmnSINEs. SINEs have 50-500 base pair internal regions which contain a tRNA-derived segment with A and B boxes that serve as an internal promoter for RNA polymerase III. | 1 | Applied and Interdisciplinary Chemistry |
Apart from some production of puddled steel, English steel continued to be made by the cementation process, sometimes followed by remelting to produce crucible steel. These were batch-based processes whose raw material was bar iron, particularly Swedish oregrounds iron.
The problem of mass-producing cheap steel was solved in 1855 by Henry Bessemer, with the introduction of the Bessemer converter at his steelworks in Sheffield, England. (An early converter can still be seen at the city's Kelham Island Museum). In the Bessemer process, molten pig iron from the blast furnace was charged into a large crucible, and then air was blown through the molten iron from below, igniting the dissolved carbon from the coke. As the carbon burned off, the melting point of the mixture increased, but the heat from the burning carbon provided the extra energy needed to keep the mixture molten. After the carbon content in the melt had dropped to the desired level, the air draft was cut off: a typical Bessemer converter could convert a 25-ton batch of pig iron to steel in half an hour.
In the 1860s development of regenerative furnaces and higher temperature refractory lining allowed to melt steel in an open hearth. That was slow and energy intensive, but allowed to better control the chemical makeup of the product and recycle iron scrap.
The acidic refractory lining of Bessemer converters and early open hearths didn't allow to remove phosphorus from steel with lime, which prolonged the life of puddling furnaces in order to utilize phosphorous iron ores abundant in Continental Europe. However in the 1870s Gilchrist–Thomas process was developed, and later basic lining was adopted for the open hearths as well.
Finally, the basic oxygen process was introduced at the Voest-Alpine works in 1952; a modification of the basic Bessemer process, it lances oxygen from above the steel (instead of bubbling air from below), reducing the amount of nitrogen uptake into the steel. The basic oxygen process is used in all modern steelworks; the last Bessemer converter in the U.S. was retired in 1968. Furthermore, the last three decades have seen a massive increase in the mini-mill business, where scrap steel only is melted with an electric arc furnace. These mills only produced bar products at first, but have since expanded into flat and heavy products, once the exclusive domain of the integrated steelworks.
Until these 19th-century developments, steel was an expensive commodity and only used for a limited number of purposes where a particularly hard or flexible metal was needed, as in the cutting edges of tools and springs. The widespread availability of inexpensive steel powered the Second Industrial Revolution and modern society as we know it. Mild steel ultimately replaced wrought iron for almost all purposes, and wrought iron is no longer commercially produced. With minor exceptions, alloy steels only began to be made in the late 19th century. Stainless steel was developed on the eve of World War I and was not widely used until the 1920s. | 1 | Applied and Interdisciplinary Chemistry |
Syngenta was the Chinese owned worldwide leader in agrochemical sales in 2013 at approximately US$10.9 billion, followed by Bayer CropScience, BASF, Dow AgroSciences, Monsanto, and then DuPont with about $3.6 billion. It is still in the worldwide leading position based on sales of year 2019. Based on a statistics by statistica, In 2019, the agrochemical market worldwide was worth approximately $234.2 billion. This is expected to increase to more than $300 billion in 2025. | 1 | Applied and Interdisciplinary Chemistry |
The most direct method for measuring atmospheric carbon dioxide concentrations for periods before instrumental sampling is to measure bubbles of air (fluid or gas inclusions) trapped in the Antarctic or Greenland ice sheets. The most widely accepted of such studies come from a variety of Antarctic cores and indicate that atmospheric concentrations were about 260–280 ppm immediately before industrial emissions began and did not vary much from this level during the preceding 10,000 years. The longest ice core record comes from East Antarctica, where ice has been sampled to an age of 800,000 years. During this time, the atmospheric carbon dioxide concentration has varied between 180 and 210 ppm during ice ages, increasing to 280–300 ppm during warmer interglacials.
mole fractions in the atmosphere have gone up by around 35 percent since the 1900s, rising from 280 parts per million by volume to 387 parts per million in 2009. One study using evidence from stomata of fossilized leaves suggests greater variability, with mole fractions above 300 ppm during the period ten to seven thousand years ago, though others have argued that these findings more likely reflect calibration or contamination problems rather than actual CO variability. Because of the way air is trapped in ice (pores in the ice close off slowly to form bubbles deep within the firn) and the time period represented in each ice sample analyzed, these figures represent averages of atmospheric concentrations of up to a few centuries rather than annual or decadal levels.
Ice cores provide evidence for greenhouse gas concentration variations over the past 800,000 years. Both CO and concentrations vary between glacial and interglacial phases, and these variations correlate strongly with temperature. Direct data does not exist for periods earlier than those represented in the ice core record, a record that indicates that CO mole fractions stayed within a range of 180 ppm to 280 ppm throughout the last 800,000 years, until the increase of the last 250 years. However, various proxy measurements and models suggest larger variations in past epochs: 500 million years ago CO levels were likely 10 times higher than now.
Various proxy measurements have been used to try to determine atmospheric CO concentrations millions of years in the past. These include boron and carbon isotope ratios in certain types of marine sediments, and the numbers of stomata observed on fossil plant leaves.
Phytane is a type of diterpenoid alkane. It is a breakdown product of chlorophyll, and is now used to estimate ancient levels. Phytane gives both a continuous record of concentrations but it also can overlap a break in the record of over 500 million years. | 1 | Applied and Interdisciplinary Chemistry |
The closed loop recirculation is a proven method of directly monitoring hydrogen in molten aluminium. A small volume of carrier gas, usually nitrogen, is brought in contact with the melt by means of an immersed probe, and is continuously recirculated in the closed loop until its hydrogen content reaches equilibrium with the vapor pressure of H in the melt. The H concentration in the gas is measured and converted into a reading of the gas concentration in the metal. This method is fast, reproducible, and accurate, and can be used online on the factory floor.
The amount of H in the gas loop of the instrument is determined by a thermal conductivity sensor, which provides high reproducibility and a broad measurement range. | 1 | Applied and Interdisciplinary Chemistry |
Termination by disproportionation occurs when an atom is transferred from one polymer free radical to another. The atom is usually hydrogen, and this results in two polymer chains.
With this type of termination and no chain transfer, the number average degree of polymerization (DP) is then equal to the average kinetic chain length: | 0 | Theoretical and Fundamental Chemistry |
The A. V. Shubnikov Institute of Crystallography is a scientific institute of the Department of Physical Sciences of the Russian Academy of Sciences (RAS) located in Moscow, Russia. The institute was created by the order of the Presidium of the Academy of Sciences of the USSR on 16November 1943. The first director of the Institute was a corresponding member of the Academy of Sciences of the USSR Alexei Vasilievich Shubnikov. In 1969, the institute was awarded the Order of the Red Banner of Labour.
Areas of scientific interest:
* Crystal growth: research into crystal formation and growth, development of synthesis methods and creation of equipment for crystallography
* Crystal structure: study of idealialized (theoretical) and real-world crystal structures
* Crystal properties: study of symmetry and physical properties of crystals; search for crystals with valuable properties | 0 | Theoretical and Fundamental Chemistry |
Pontecorvo was never able to prove his theory, but he was on to something with his thinking. In 2002, results from an experiment conducted 2100 meters underground at the Sudbury Neutrino Observatory proved and supported Pontecorvo's theory and discovered that neutrinos released from the Sun can in fact change form or flavor because they are not completely massless. This discovery of neutrino oscillation solved the solar neutrino problem, nearly 40 years after Davis and Bahcall began studying solar neutrinos. | 0 | Theoretical and Fundamental Chemistry |
The solution for axisymmetric stagnation point flow in the presence of a solid wall was first obtained by Homann (1936). A typical example of this flow is the forward stagnation point appearing in a flow past a sphere. Paul A. Libby (1974)(1976) extended Homann's work by allowing the solid wall to translate along its own plane with a constant speed and allowing constant suction or injection at the solid surface.
The solution for this problem is obtained in the cylindrical coordinate system by introducing
where is the translational speed of the wall and is the injection (or, suction) velocity at the wall. The problem is axisymmetric only when . The pressure is given by
The Navier–Stokes equations then reduce to
along with boundary conditions,
When , the classical Homann problem is recovered. | 1 | Applied and Interdisciplinary Chemistry |
Based on air resistance, for example, the terminal speed of a skydiver in a belly-to-earth (i.e., face down) free fall position is about . This speed is the asymptotic limiting value of the speed, and the forces acting on the body balance each other more and more closely as the terminal speed is approached. In this example, a speed of 50% of terminal speed is reached after only about 3 seconds, while it takes 8 seconds to reach 90%, 15 seconds to reach 99% and so on.
Higher speeds can be attained if the skydiver pulls in their limbs (see also freeflying). In this case, the terminal speed increases to about , which is almost the terminal speed of the peregrine falcon diving down on its prey. The same terminal speed is reached for a typical .30-06 bullet dropping downwards—when it is returning to the ground having been fired upwards, or dropped from a tower—according to a 1920 U.S. Army Ordnance study.
Competition speed skydivers fly in a head-down position and can reach speeds of . The current record is held by Felix Baumgartner who jumped from an altitude of and reached , though he achieved this speed at high altitude where the density of the air is much lower than at the Earth's surface, producing a correspondingly lower drag force.
The biologist J. B. S. Haldane wrote, | 1 | Applied and Interdisciplinary Chemistry |
Group 6 and group 7 transition metal complexes have been found to be the most prominent in regards to dissociation of the CO cis to ligand X. CO is a neutral ligand that donates 2 electrons to the complex, and therefore lacks anionic or cationic properties that would affect the electron count of the complex. For transition metal complexes that have the formula , group 6 metals (M, where the oxidation state of the metal is zero) paired with neutral ligand X, and group 7 metals (M, where the oxidation state of the metal is +1), paired anionic ligands, will create very stable 18 electron complexes. Transition metal complexes have 9 valence orbitals, and 18 electrons will in turn fill these valences shells, creating a very stable complex, which satisfies the 18-electron rule. The cis-labilization of 18 e complexes suggests that dissociation of ligand X in the cis position creates a square pyramidal transition state, which lowers the energy of the complex, enhancing the rate of reaction. The scheme below shows the dissociation pathway of a CO ligand in the cis and trans position to the X, followed by the association of ligand Y. This is an example of a dissociative mechanism, where an 18 e complex loses a CO ligand, making a 16 e intermediate, and a final complex of 18 e results from an incoming ligand inserting in place of the CO. This mechanism resembles the S1 mechanism in organic chemistry, and applies to coordination compounds as well.
Figure 1. Intermediates in the substitution of complexes.
If ligands X and Y are neutral donors to the complex:
M = Group 6 metal (m = 0)
M = Group 7 metal (m = +1) | 0 | Theoretical and Fundamental Chemistry |
Semicarbazide is the chemical compound with the formula OC(NH)(NH). It is a water-soluble white solid. It is a derivative of urea. | 0 | Theoretical and Fundamental Chemistry |
Independent research conducted by Antibody Solutions and published or presented at scientific conferences include the following:
* Generation of Neutralizing Human Monoclonal Antibodies Against a Therapeutic Target from the Alloy Therapeutics Mouse
* Generation Using a Molecular Modeling Platform to Guide Therapeutic Antibody Discovery
* Optimization of Therapeutic Discovery Strategies for Human Antibody Transgenic Animal Platforms
* Development of Antibody and PK, and ADA Assays for a Cystine Knot Fusion Protein
* A Rapid, High-Throughput Recombinant Antibody Expression System for Therapeutic Antibody Discovery and Validation
* Generation of Agonist and Antagonist Human Monoclonal Antibodies Against an Immune Checkpoint Target from the H2L2 Mouse
* Generation and Selection of Human Monoclonal Antibodies from the OmniRat
* Therapeutic Antibody Discovery at Antibody Solutions using the OmniAb Platform
* Development of human antibodies to human vascular endothelial growth factor -C (VEGF-C) and -D (VEGF-D)
* Obtaining Antibodies to Difficult Membrane Targets through DNA and Cell Immunization
* Next-Generation Therapeutic Antibody Discovery from Single B-cells
* Generation and Selection of Human Monoclonal Antibodies from the H2L2 Mouse
* Generation of Antibodies to Difficult Membrane Protein Targets
* Development of Antibodies and ELISAs to measure Free and Total Obiltoxaximab (ETI-204) in the Presence of Anthrax Protective Antigen PA63
* Discovery of Therapeutic Antibodies to Difficult Membrane Proteins | 1 | Applied and Interdisciplinary Chemistry |
Surfactin is a broad-spectrum antibiotic with detergent-like activity increasing the permeability of cell membranes in all bacteria, regardless of their Gram stain classification. The minimum inhibitory concentration (MIC) of surfactin is between 12-50 μg/ml.
Surfactin is also capable of degrading viral envelope lipids and forming ion channels in the inner capsid with experimental evidence showing inhibition of HIV and HSV. However, surfactin can only degrade viruses when they are outside of host cells. Furthermore, when the environment is packed with proteins and lipids, surfactin faces a buffer effect lowering its antiviral activity. | 0 | Theoretical and Fundamental Chemistry |
Design parameters include type of mill, milling container, milling speed, milling time, type, size, and size distribution of the grinding medium, ball-to-powder weight ratio, extent of filling the vial, milling atmosphere, process control agent, temperature of milling, and the reactivity of the species. | 1 | Applied and Interdisciplinary Chemistry |
The dashboard provides support for mass spectrometry providing searches against the chemical data contained in the database based on mass and molecular formula. The dashboard has been applied to non-targeted analysis searching for "known unknowns". Both targeted mass spectrometry and non-targeted mass spectrometry are supported. The searches utilize a search based on "MS-Ready" forms of chemical compounds. Individual chemical substances are collapsed into a form that would be detected by mass spectrometry such that salts are desalted and neutralized and multi-component chemicals are separated into their individual components. | 1 | Applied and Interdisciplinary Chemistry |
The center's projects are:
* Analysis of potential glycan-binding proteins on various glycan arrays (CFG glycan array, Microbial glycan array, NCFG-derived arrays)
* Structural analysis of glycans
* Production of naturally occurring glycans by isolation | 0 | Theoretical and Fundamental Chemistry |
During the 1990s, when the term ecosan was something new, discussions were heated and confrontational. Supporters of ecosan claimed the corner on containment, treatment and reuse. The proponents of conventional sanitation systems on the other side defended pit latrines and waterborne sewage systems. Ecosan supporters criticized conventional sanitation for contaminating waterways with nutrients and pathogens. Since about 2007, the two opposing sides have slowly found ways of dealing with each other, and the formation of the Sustainable Sanitation Alliance in that year has further helped to provide a space for all sanitation actors to meet and push into the same direction of sustainable sanitation. | 1 | Applied and Interdisciplinary Chemistry |
Pseudo-response regulator (PRR) refers to a group of genes that regulate the circadian oscillator in plants. There are four primary PRR proteins (PRR9, PRR7, PRR5 and TOC1/PRR1) that perform the majority of interactions with other proteins within the circadian oscillator, and another (PRR3) that has limited function. These genes are all paralogs of each other, and all repress the transcription of Circadian Clock Associated 1 (CCA1) and Late Elongated Hypocotyl (LHY) at various times throughout the day. The expression of PRR9, PRR7, PRR5 and TOC1/PRR1 peak around morning, mid-day, afternoon and evening, respectively. As a group, these genes are one part of the three-part repressilator system that governs the biological clock in plants. | 1 | Applied and Interdisciplinary Chemistry |
*Dystonia: involuntary muscle contractions
*Axial hypotonia: low muscle tone and strength
*Dysarthria: impairment in muscles used for speech
*Muscle stiffness and tremors
*Seizures
*Coordination and balance impairment
*Oculogyric crises: abnormal rotation of the eyes
The oculogyric crises usually occur in the later half of the day and during these episodes patients undergo extreme agitation and irritability along with uncontrolled head and neck movements. Apart from the aforementioned symptoms, patients can also display parkinsonism, sleep disturbances, small head size (microcephaly), behavioral abnormalities, weakness, drooling, and gastrointestinal symptoms. | 1 | Applied and Interdisciplinary Chemistry |
Generally, the rates of ligand dissociation from low spin complexes are lower than dissociation rates from high spin complexes. In the case of octahedral complexes, electrons in the e levels are anti-bonding with respect to the metal-ligand bonds. Famous "exchange inert" complexes are octahedral complexes of d and low-spin d metal ions, illustrated respectfully by Cr and Co. | 0 | Theoretical and Fundamental Chemistry |
Simplified sewerage is most widely used in Brazil. It is estimated that in Brazil some 5 million people in over 200 towns and cities are served with simplified sewerage - or condominial sewerage. This corresponds to about 3% of the population of Brazil and about 6% of the population connected to sewers. They serve poor and rich alike.
Simplified sewerage has also been used in
*Bolivia, beginning with a pilot project in El Alto;
*Honduras, primarily in marginal areas of Tegucigalpa where simplified sewerage has been introduced in 20 communities with 24,000 inhabitants;
*Peru, primarily in marginal areas of Lima;
*in South Africa, where pilot projects were carried out in Johannesburg and Durban;
* in Sri Lanka, where the National Housing Development Authority implemented over 20 schemes in the 1980s and 90s.
In Pakistan, beginning with the Orangi Pilot Project in Karachi, a variation of simplified sewerage using larger diameter pipes has been used. | 1 | Applied and Interdisciplinary Chemistry |
S. Finch and R. H. Collier, in a paper entitled "Insects can see clearly now the weeds have gone", showed experimentally that flying pests are far less successful if their host-plants are surrounded by other plants or even "decoy-plants" coloured green. Pests find hosts in stages, first detecting plant odours which induce it to try to land on the host plant, avoiding bare soil. If the plant is isolated, then the insect simply lands on the patch of green near the odour, making an "appropriate landing". If it finds itself on the wrong plant, an "inappropriate landing", it takes off and flies to another plant; it eventually leaves the area if there are too many "inappropriate" landings. Companion planting of clover as ground cover was equally disruptive to eight pest species from four different insect orders. In a test, 36% of cabbage root flies laid eggs beside cabbages growing in bare soil (destroying the crop), compared to only 7% beside cabbages growing in clover (which allowed a good crop). Simple decoys of green cardboard worked just as well as the live ground cover. | 1 | Applied and Interdisciplinary Chemistry |
Paquette's 1982 organic synthesis takes about 29 steps with raw materials cyclopentadiene (2 equivalents 10 carbon atoms), dimethyl acetylenedicarboxylate (4 carbon atoms) and allyltrimethylsilane (2 equivalents, 6 carbon atoms).
In the first leg of the procedure two molecules of cyclopentadiene 1 are coupled together by reaction with elemental sodium (forming the cyclopentadienyl complex) and iodine to dihydrofulvalene 2. Next up is a tandem Diels–Alder reaction with dimethyl acetylenedicarboxylate 3 with desired sequence pentadiene-acetylene-pentadiene as in symmetrical adduct 4. An equal amount of asymmetric pentadiene-pentadiene-acetylene compound (4b) is formed and discarded.
In the next step of the sequence iodine is temporarily introduced via an iodolactonization of the diacid of 4 to dilactone 5. The ester group is cleaved next by methanol to the halohydrin 6, the alcohol groups converted to ketone groups in 7 by Jones oxidation and the iodine groups reduced by a zinc-copper couple in 8.
The final 6 carbon atoms are inserted in a nucleophilic addition to the ketone groups of the carbanion 10 generated from allyltrimethylsilane 9 and n-butyllithium. In the next step the vinyl silane 11 reacts with peracetic acid in acetic acid in a radical substitution to the dilactone 12 followed by an intramolecular Friedel-Crafts alkylation with phosphorus pentoxide to diketone 13. This molecule contains all required 20 carbon atoms and is also symmetrical which facilitates the construction of the remaining 5 carbon-carbon bonds.
Reduction of the double bonds in 13 to 14 is accomplished with hydrogenation with palladium on carbon and that of the ketone groups to alcohol groups in 15 by sodium borohydride. Replacement of hydroxyl by chlorine in 17 via nucleophilic aliphatic substitution takes place through the dilactone 16 (tosyl chloride). The first C–C bond forming reaction is a kind of Birch alkylation (lithium, ammonia) with the immediate reaction product trapped with chloromethyl phenyl ether, the other chlorine atom in 17 is simply reduced. This temporary appendix will in a later stage prevent unwanted enolization. The newly formed ketone group then forms another C–C bond by photochemical Norrish reaction to 19 whose alcohol group is induced to eliminate with TsOH to alkene 20.
The double bond is reduced with hydrazine and sequential diisobutylaluminum hydride reduction and pyridinium chlorochromate oxidation of 21 forms the aldehyde 22. A second Norrish reaction then adds another C–C bond to alcohol 23 and having served its purpose the phenoxy tail is removed in several steps: a Birch reduction to diol 24, oxidation with pyridinium chlorochromate to ketoaldehyde 25 and a reverse Claisen condensation to ketone 26. A third Norrish reaction produces alcohol 27 and a second dehydration 28 and another reduction 29 at which point the synthesis is left completely without functional groups. The missing C-C bond is put in place by hydrogen pressurized dehydrogenation with palladium on carbon at 250 °C to dodecahedrane 30. | 0 | Theoretical and Fundamental Chemistry |
WeNMR aims at bringing together complementary research teams in the structural biology and life science area into a virtual research community at a worldwide level and provide them with a platform integrating and streamlining the computational approaches necessary for NMR and SAXS data analysis and structural modelling. Access to the infrastructure is provided through a portal integrating commonly used software and GRID technology. | 1 | Applied and Interdisciplinary Chemistry |
X-ray crystallography is the primary method for determining the molecular conformations of biological macromolecules, particularly protein and nucleic acids such as DNA and RNA. The double-helical structure of DNA was deduced from crystallographic data. The first crystal structure of a macromolecule was solved in 1958, a three-dimensional model of the myoglobin molecule obtained by X-ray analysis. The Protein Data Bank (PDB) is a freely accessible repository for the structures of proteins and other biological macromolecules. Computer programs such as RasMol, Pymol or VMD can be used to visualize biological molecular structures.
Neutron crystallography is often used to help refine structures obtained by X-ray methods or to solve a specific bond; the methods are often viewed as complementary, as X-rays are sensitive to electron positions and scatter most strongly off heavy atoms, while neutrons are sensitive to nucleus positions and scatter strongly even off many light isotopes, including hydrogen and deuterium.
Electron crystallography has been used to determine some protein structures, most notably membrane proteins and viral capsids. | 0 | Theoretical and Fundamental Chemistry |
In the Hunterian Museum at the University of Glasgow are two pitch-based demonstrations by Lord Kelvin from the 19th century. Kelvin placed some bullets on top of a dish of pitch, and corks at the bottom: over time, the bullets sank and the corks floated.
Lord Kelvin also showed that the pitch flows like glaciers, with a mahogany ramp that allowed it to slide slowly downward and form shapes and patterns similar to glaciers in the Alps. This model was considered as an inspiration for the expected properties of luminiferous aether. | 1 | Applied and Interdisciplinary Chemistry |
The Mg-Mg bond for a neutral magnesium(I) dimer has shown to be significantly sigma-bonding. This arises from the s-orbital overlap of the two metals. The bonding interaction that occurs may be connected to the highest occupied molecular orbital (HOMO), giving the highest energy bond of the molecule. This can be reflected through the Wiberg Bond Index (WBI). The sigma single bond gives a WBI value of 0.9, having 90% s-character. Further theoretical investigations have proved that this does not hold for every complex. There can be notable p-orbital contribution to the Mg—Mg, with it being determined to be 55% in some complexes as the charge changes. There were also findings regarding the lowest unoccupied molecular orbital (LUMO). For example, bonding character was also discovered in nearly degenerate LUMO and LUMO+1, with a HOMO-LUMO gap of 93 kcal mol. | 0 | Theoretical and Fundamental Chemistry |
Archaeal transcription factor B (ATFB or TFB) is a protein family of extrinsic transcription factors that guide the initiation of RNA transcription in organisms that fall under the domain of Archaea. It is homologous to eukaryotic TFIIB and, more distantly, to bacterial sigma factor. Like these proteins, it is involved in forming transcription preinitiation complexes. Its structure includes several conserved motifs which interact with DNA and other transcription factors, notably the single type of RNA polymerase that performs transcription in Archaea. | 1 | Applied and Interdisciplinary Chemistry |
DnaA consists mainly in two different forms, the active ATP-form and the inactive ADP. The level of active DnaA within a cell is low immediately after a cell has divided. Although the active form of DnaA requires ATP, the formation of the oriC/DnaA complex and subsequent DNA unwinding does not require ATP hydrolysis.
The oriC site in E. coli has three AT rich 13 base pair regions (DUEs) followed by four 9 bp regions with the sequence TTAT(C or A)CA(C or A)A. Around 10 DnaA molecules bind to the 9 bp regions, which wrap around the proteins causing the DNA at the AT-rich region to unwind. There are 8 DnaA binding sites within oriC, to which DnaA binds with differential affinity. When DNA replication is about to commence, DnaA occupies all of the high and low affinity binding sites. The denatured AT-rich region allows for the recruitment of DnaB (helicase), which complexes with DnaC (helicase loader). DnaC helps the helicase to bind to and to properly accommodate the ssDNA at the 13 bp region; this is accomplished by ATP hydrolysis, after which DnaC is released. Single-strand binding proteins (SSBs) stabilize the single DNA strands in order to maintain the replication bubble. DnaB is a 5→3 helicase, so it travels on the lagging strand. It associates with DnaG (a primase) to form the only primer for the leading strand and to add RNA primers on the lagging strand. The interaction between DnaG and DnaB is necessary to control the longitude of Okazaki fragments on the lagging strand. DNA polymerase III is then able to start DNA replication.
DnaA is made up of four domains: the first is the N-terminal that associates with regulatory proteins, the second is a helical linker region, the third domain is a AAA+ region that binds to ATP, and the fourth domain is the C-terminal DNA binding region. DnaA contains two conserved regions: the first is located in the central part of the protein and corresponds to the ATP-binding domain, the second is located in the C-terminal half and is involved in DNA-binding. | 1 | Applied and Interdisciplinary Chemistry |
PNRC1 functions as a coactivator for several nuclear receptors including AR, ERα, ERRα, ERRγ, GR, SF1, PR, TR, RAR and RXR. The interaction between PNRC1 with nuclear receptors occurs through the SH3 domain of PNRC1. | 1 | Applied and Interdisciplinary Chemistry |
The third edition of the Green Book () was first published by IUPAC in 2007. A second printing of the third edition was released in 2008; this printing made several minor revisions to the 2007 text. A third printing of the third edition was released in 2011. The text of the third printing is identical to that of the second printing.
A Japanese translation of the third edition of the Green Book () was published in 2009. A French translation of the third edition of the Green Book () was published in 2012. A [http://www.sbq.org.br/livroverde/ Portuguese translation] (Brazilian Portuguese and European Portuguese) of the third edition of the Green Book () was published in 2018, with updated values of the physical constants and atomic weights; it is referred to as the "Livro Verde".
A concise four-page summary of the most important material in the Green Book was published in the July–August 2011 issue of Chemistry International, the IUPAC news magazine.
The second edition of the Green Book () was first published in 1993. It was reprinted in 1995, 1996, and 1998.
The Green Book is a direct successor of the Manual of Symbols and Terminology for Physicochemical Quantities and Units, originally prepared for publication on behalf of IUPACs Physical Chemistry Division by M. L. McGlashen in 1969. A full history of the Green Books various editions is provided in the historical introduction to the third edition.
The second edition and the third edition (second printing) of the Green Book have both been made available online as PDF files; the PDF version of the third edition is fully searchable. The four-page concise summary is also available online as a PDF file. External Links (below). | 0 | Theoretical and Fundamental Chemistry |
Glycobiology is a monthly peer-reviewed scientific journal covering all aspects of the field of glycobiology and the official journal of the Society for Glycobiology. It is published by Oxford University Press. The journal was established in September 1990. It publishes primary research on the "biological functions of glycans, including glycoproteins, glycolipids, proteoglycans and free oligosaccharides, and on proteins that specifically interact with glycans." | 1 | Applied and Interdisciplinary Chemistry |
In coordination chemistry, hydration isomerism is a kind of isomerism that is observed in some solids. Hydration isomers have identical formula but differ with respect to the numbers of water ligands. | 0 | Theoretical and Fundamental Chemistry |
Cyclic PPA is obtained through a cationic polymerization of o-phthalaldehyde using a Lewis acid, typically Boron trifluoride etherate, as an initiator. When Aso and Tagami first reported the successful synthesis of PPA using this technique in 1967, they were unaware of the fact that the polymer they prepared was cyclic and instead reported the structure as linear in their research paper. It was not until 2013 that polymer chemists proved that the structure is cyclic using a combination of characterization techniques including Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FT-IR), Gel Permeation Chromatography (GPC), and Mass Spectrometry (MS). Cyclic PPA is easy to synthesize; it is reported by Prof. Jeffrey Moore that the cationic polymerization of o-phthalaldehyde is very fast, yielding cyclic PPA within few minutes. Furthermore, the polymer can be isolated without the addition of pyridine nor methanol nor a strong base terminator, which in general makes this polymerization technique easy, fast, and cheap. Nevertheless, a known issue of this technique is the fact that the molecular weight cannot be controlled based on the initial concentration of the monomer used, which has led typically to cyclic PPA with a wide variety of molecular weights ranging between 3 kDa to 100 kDa using the same starting conditions. Furthermore, because of its cyclic structure, no end caps are used or needed. The absence of functionalized end caps in the structure has limited the usage of cyclic PPA especially in stimuli responsive applications. | 0 | Theoretical and Fundamental Chemistry |
The first mutagens to be identified were carcinogens, substances that were shown to be linked to cancer. Tumors were described more than 2,000 years before the discovery of chromosomes and DNA; in 500 B.C., the Greek physician Hippocrates named tumors resembling a crab karkinos (from which the word "cancer" is derived via Latin), meaning crab. In 1567, Swiss physician Paracelsus suggested that an unidentified substance in mined ore (identified as radon gas in modern times) caused a wasting disease in miners, and in England, in 1761, John Hill made the first direct link of cancer to chemical substances by noting that excessive use of snuff may cause nasal cancer. In 1775, Sir Percivall Pott wrote a paper on the high incidence of scrotal cancer in chimney sweeps, and suggested chimney soot as the cause of scrotal cancer. In 1915, Yamagawa and Ichikawa showed that repeated application of coal tar to rabbit's ears produced malignant cancer. Subsequently, in the 1930s the carcinogen component in coal tar was identified as a polyaromatic hydrocarbon (PAH), [[benzo(a)pyrene|benzo[a]pyrene]]. Polyaromatic hydrocarbons are also present in soot, which was suggested to be a causative agent of cancer over 150 years earlier.
The association of exposure to radiation and cancer had been observed as early as 1902, six years after the discovery of X-ray by Wilhelm Röntgen and radioactivity by Henri Becquerel. Georgii Nadson and German Filippov were the first who created fungi mutants under ionizing radiation in 1925. The mutagenic property of mutagens was first demonstrated in 1927, when Hermann Muller discovered that x-rays can cause genetic mutations in fruit flies, producing phenotypic mutants as well as observable changes to the chromosomes, visible due to the presence of enlarged "polytene" chromosomes in fruit fly salivary glands. His collaborator Edgar Altenburg also demonstrated the mutational effect of UV radiation in 1928. Muller went on to use x-rays to create Drosophila mutants that he used in his studies of genetics. He also found that X-rays not only mutate genes in fruit flies, but also have effects on the genetic makeup of humans. Similar work by Lewis Stadler also showed the mutational effect of X-rays on barley in 1928, and ultraviolet (UV) radiation on maize in 1936. The effect of sunlight had previously been noted in the nineteenth century where rural outdoor workers and sailors were found to be more prone to skin cancer.
Chemical mutagens were not demonstrated to cause mutation until the 1940s, when Charlotte Auerbach and J. M. Robson found that mustard gas can cause mutations in fruit flies. A large number of chemical mutagens have since been identified, especially after the development of the Ames test in the 1970s by Bruce Ames that screens for mutagens and allows for preliminary identification of carcinogens. Early studies by Ames showed around 90% of known carcinogens can be identified in Ames test as mutagenic (later studies however gave lower figures), and ~80% of the mutagens identified through Ames test may also be carcinogens. | 0 | Theoretical and Fundamental Chemistry |
The shape memory effect (SME) occurs because a temperature-induced phase transformation reverses deformation, as shown in the previous hysteresis curve. Typically the martensitic phase is monoclinic or orthorhombic (B19' or [https://www.atomic-scale-physics.de/lattice/struk/b19.html B19]). Since these crystal structures do not have enough slip systems for easy dislocation motion, they deform by twinning—or rather, detwinning.
Martensite is thermodynamically favored at lower temperatures, while austenite ([https://www.atomic-scale-physics.de/lattice/struk/b2.html B2] cubic) is thermodynamically favored at higher temperatures. Since these structures have different lattice sizes and symmetry, cooling austenite into martensite introduces internal strain energy in the martensitic phase. To reduce this energy, the martensitic phase forms many twins—this is called "self-accommodating twinning" and is the twinning version of geometrically necessary dislocations. Since the shape memory alloy will be manufactured from a higher temperature and is usually engineered so that the martensitic phase is dominant at operating temperature to take advantage of the shape memory effect, SMAs "start" highly twinned.
When the martensite is loaded, these self-accommodating twins provide an easy path for deformation. Applied stresses will detwin the martensite, but all of the atoms stay in the same position relative to the nearby atoms—no atomic bonds are broken or reformed (as they would be by dislocation motion). Thus, when the temperature is raised and austenite becomes thermodynamically favored, all of the atoms rearrange to the B2 structure which happens to be the same macroscopic shape as the B19' pre-deformation shape. This phase transformation happens extremely quickly and gives SMAs their distinctive "snap".
Repeated use of the shape-memory effect may lead to a shift of the characteristic transformation temperatures (this effect is known as functional fatigue, as it is closely related with a change of microstructural and functional properties of the material). The maximum temperature at which SMAs can no longer be stress induced is called M, where the SMAs are permanently deformed. | 1 | Applied and Interdisciplinary Chemistry |
Among the group 10 and 11 elements, nickel and copper feature most prominently in literature reactions with yellow arsenic. Nickel tetrafluoroborate salts react analogously to cobalt complexes in the presence of triphos to form a sandwich structure with a central cyclic As moiety. Much like iron, the reaction of nickel cyclopentadienyl carbonyl complexes with As yields a variety of bi- and multi-metallic products depending on the size of the attending ligands, though the nature and geometric structure of these compounds differ from those observed with iron. These include trimers with bridging As and As moieties in cubane structural arrangements when smaller Cp ligands are employed, and distorted hexagonal prism complexes with two nickel fragments and four arsenic atoms when bulkier Cp groups are introduced.
The reaction of the copper complex [LCu(NCMe)] (L = [{N(CHiPr-2,6)C(Me)}CH]) with yellow arsenic yields the As-bridged dimer [{LCu}- (μ,η-As)]. The four-atom arsenic moiety in this complex was deemed to be "intact" yellow arsenic through the use of density functional theory calculations determining the change in bond critical points between the free and bound arsenic molecules. Specifically, only a small shift was observed in the bond critical points between arsenic atoms involved in binding to copper; the remaining bond critical points were very similar to free yellow arsenic. | 0 | Theoretical and Fundamental Chemistry |
Single-crystal superalloys (SX or SC superalloys) are formed as a single crystal using a modified version of the directional solidification technique, leaving no grain boundaries. The mechanical properties of most other alloys depend on the presence of grain boundaries, but at high temperatures, they participate in creep and require other mechanisms. In many such alloys, islands of an ordered intermetallic phase sit in a matrix of disordered phase, all with the same crystal lattice. This approximates the dislocation-pinning behavior of grain boundaries, without introducing any amorphous solid into the structure.
Single crystal (SX) superalloys have wide application in the high-pressure turbine section of aero- and industrial gas turbine engines due to the unique combination of properties and performance. Since introduction of single crystal casting technology, SX alloy development has focused on increased temperature capability, and major improvements in alloy performance are associated with rhenium (Re) and ruthenium (Ru).
The creep deformation behavior of superalloy single crystal is strongly temperature-, stress-, orientation- and alloy-dependent. For a single-crystal superalloy, three modes of creep deformation occur under regimes of different temperature and stress: rafting, tertiary, and primary. At low temperature (~750 °C), SX alloys exhibits mostly primary creep behavior. Matan et al. concluded that the extent of primary creep deformation depends strongly on the angle between the tensile axis and the <001>/<011> symmetry boundary. At temperatures above 850 °C, tertiary creep dominates and promotes strain softening behavior. When temperature exceeds 1000 °C, the rafting effect is prevalent where cubic particles transform into flat shapes under tensile stress. The rafts form perpendicular to the tensile axis, since γ phase is transported out of the vertical channels and into the horizontal ones. Reed et al. studied unaxial creep deformation of <001> oriented CMSX-4 single crystal superalloy at 1105 °C and 100 MPa. They reported that rafting is beneficial to creep life since it delays evolution of creep strain. In addition, rafting occurs quickly and suppresses the accumulation of creep strain until a critical strain is reached. | 1 | Applied and Interdisciplinary Chemistry |
Urea is readily quantified by a number of different methods, such as the diacetyl monoxime colorimetric method, and the Berthelot reaction (after initial conversion of urea to ammonia via urease). These methods are amenable to high throughput instrumentation, such as automated flow injection analyzers and 96-well micro-plate spectrophotometers. | 0 | Theoretical and Fundamental Chemistry |
Trimethylamine N-oxide (MeNO) can be used in the nucleophilic abstraction of carbonyl. There is an nucleophilic attack of MeNO on the carbon of the carbonyl group which pushes electrons on the metal. The reaction then proceeds to kick out CO and NMe.
An article from the Bulletin of Korean Chemical Society journal showed interesting results where one iridium complex undergoes carbonyl abstraction while a very similar iridium complex undergoes hydride extraction. | 0 | Theoretical and Fundamental Chemistry |
With a pK near 3.4, thioacetic acid is about 15 times more acidic than acetic acid. The conjugate base is thioacetate:
In neutral water, thioacetic acid is fully ionized. | 0 | Theoretical and Fundamental Chemistry |
Born in Moscow to a Russian-Jewish family, she later traveled to Geneva in the 1890s to study chemistry at Geneva University. | 0 | Theoretical and Fundamental Chemistry |
Demethylation often refers to cleavage of ethers, especially aryl ethers.
Historically, aryl methyl ethers, including natural products such as codeine (O-methylmorphine), have been demethylated by heating the substance in molten pyridine hydrochloride (melting point ) at , sometimes with excess hydrogen chloride, in a process known as the Zeisel–Prey ether cleavage. Quantitative analysis for aromatic methyl ethers can be performed by argentometric determination of the N-methylpyridinium chloride formed. The mechanism of this reaction starts with proton transfer from pyridinium ion to the aryl methyl ether, a highly unfavorable step (K ) that accounts for the harsh conditions required, given the much weaker acidity of pyridinium (pK = 5.2) compared to the protonated aryl methyl ether (an arylmethyloxonium ion, pK = –6.7 for aryl = Ph). This is followed by S2 attack of the arylmethyloxonium ion at the methyl group by either pyridine or chloride ion (depending on the substrate) to give the free phenol and, ultimately, N-methylpyridinium chloride, either directly or by subsequent methyl transfer from methyl chloride to pyridine.
Another classical (but, again, harsh) method for the removal of the methyl group of an aryl methyl ether is to heat the ether in a solution of hydrogen bromide or hydrogen iodide sometimes also with acetic acid. The cleavage of ethers by hydrobromic or hydroiodic acid proceeds by protonation of the ether, followed by displacement by bromide or iodide. A slightly milder set of conditions uses cyclohexyl iodide (CyI, 10.0 equiv) in N,N-dimethylformamide to generate a small amount of hydrogen iodide in situ.
Boron tribromide, which can be used at room temperature or below, is a more specialized reagent for the demethylation of aryl methyl ethers. The mechanism of ether dealkylation proceeds via the initial reversible formation of a Lewis acid-base adduct between the strongly Lewis acidic BBr and the Lewis basic ether. This Lewis adduct can reversibly dissociate to give a dibromoboryl oxonium cation and Br. Rupture of the ether linkage occurs through the subsequent nucleophilic attack on the oxonium species by Br to yield an aryloxydibromoborane and methyl bromide. Upon completion of the reaction, the phenol is liberated along with boric acid (HBO) and hydrobromic acid (aq. HBr) upon hydrolysis of the dibromoborane derivative during aqueous workup.
Stronger nucleophiles such as diorganophosphides (LiPPh) also cleave aryl ethers, sometimes under mild conditions. Other strong nucleophiles that have been employed include thiolate salts like EtSNa.
Aromatic methyl ethers, particularly those with an adjacent carbonyl group, can be regioselectively demethylated using magnesium iodide etherate. An example of this being used is in the synthesis of the natural product Calphostin A, as seen below.
Methyl esters also are susceptible to demethylation, which is usually achieved by saponification. Highly specialized demethylations are abundant, such as the Krapcho decarboxylation:
A mixture of anethole, KOH, and alcohol was heated in an autoclave. Although the product of this reaction was the expected anol, a highly reactive dimerization product in the mother liquors called dianol was also discovered by Charles Dodds. | 0 | Theoretical and Fundamental Chemistry |
Photochromic, thermochromic, solvatochromic and electrochromic characteristics of spiropyrans make them especially important in the technology area. Most of their applications are based on their photochromic properties.
Photochromic compounds based on spiropyrans, spirooxazines, and [2H]chromenes are being investigated because of their silver-free light-sensitive properties that could be used for optical recording data, including thin films, photoswitches (sensors that discern light of certain wavelength), light filters with modulated transmission and miniature hybrid multifunctional materials.
Thanks to the creation of novel media sensitive to IR radiation and the potential of spiropyrans for optical recording data, semiconductor lasers as activating source of radiation are possible.
Spiropyrans with ion complexes and spiropyran copolymers which are part of powdered and film materials have been used too to record optical data and increase the length of time of its storage.
Another group of spiropyrans which contain indoline or nitrogen heterocycles and the indolinospirothiapyrans found their application in film forms of photochromic materials using polyester resins. Those resins with a high refractive index were used to make photochromic lenses. Moreover, spiropyrans are being used in cosmetics.
New types of modified spiropyrans polymers contained in photochromic compounds found their use in the creation of photoreceptors. The ones with rhodopsin as a compound are adopted to raise the level of the photosignal.
Another collection of spiropyrans characterized for their sensitivity to UV radiation are detectors for the protection of organs, for the production of light filters with modulated transmission, or photochromic lenses.
The determination of peroxidase activity and NO levels in the atmosphere are applications of carboxylated spiropyrans.
Today, spiropyrans are most used as molecular logic devices, photochromic and electrooptical devices, molecular and supramolecular logic switches, photoswitches and multifunctional artificial receptors.
Spiropyrans can be used to probe the conformational state of DNA, as certain derivatives can intercalate into DNA when in the open form.
Spiropyrans are used in photo controlled transfer of amino acids across bilayers and membranes because of nucleophilic interaction between zwitterionic merocyanine and polar amino acids. Certain types of spiropyrans display ring opening upon recognition of an analyte, for example zinc ions. | 0 | Theoretical and Fundamental Chemistry |
A coarctate reaction is a concerted reaction whose transition state involves two rings, in which at least one atom undergoes the simultaneous making and breaking of two bonds. It is an uncommon reaction topology, compared with linear topology and pericyclic topology (itself subdivided into Hückel and Möbius topologies). The name is derived from the Latin , meaning . | 0 | Theoretical and Fundamental Chemistry |
Products of the reaction include not only biodiesel, but also the byproducts soap, glycerol, excess alcohol, and trace amounts of water. All of these byproducts must be removed to meet the standards, but the order of removal is process-dependent.
The density of glycerol is greater than that of biodiesel, and this property difference is exploited to separate the bulk of the glycerol coproduct. Residual methanol is typically recovered by distillation and reused. Soaps can be removed or converted into acids. Residual water is also removed from the fuel. | 0 | Theoretical and Fundamental Chemistry |
hESCs and hiPSCs are the primary cells used to generate hECTs. Human pluripotent stem cells are differentiated into cardiomyocytes (hPSC-CMs) in culture through a milieu containing small-molecule mediators (e.g. cytokines, growth and transcription factors). Transforming hPSC-CMs into hECTs incorporates the use of 3-dimensional (3D) tissue scaffolds to mimic the natural physiological environment of the heart. This 3D scaffold, along with collagen – a major component of the cardiac extracellular matrix – provides the appropriate conditions to promote cardiomyocyte organization, growth and differentiation. | 1 | Applied and Interdisciplinary Chemistry |
The first developments in thin layer chromatography occurred in the 1940s, and techniques advanced rapidly in the 1950s after the introduction of relatively large plates and relatively stable materials for sorbent layers. | 1 | Applied and Interdisciplinary Chemistry |
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