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*pimaric acid
**pimara-8(14),15-dien-18-oic acid
*isopimaric acids
*simplified formula CHO or CHCOOH
*molecular weight 302 | 1 | Applied and Interdisciplinary Chemistry |
In spite of the stepwise, radical mechanism, both stereoselective intra- and intermolecular variants have emerged. Cyclic enones are employed, otherwise competitive cis-trans isomerization ensues.
The mechanism of [2+2] photocyclization is proposed to begin with photoexcitation of the enone to a singlet excited state. The singlet state is typically very short lived, and decays by intersystem crossing to the triplet state. At this point, the enone forms an exciplex with the ground state alkene, eventually giving the triplet diradical. Spin inversion to the singlet diradical allows closure to the cyclobutane. As an alternative a pericyclic reaction mechanism is proposed, in which after intersystem crossing a radical cation and a radical anion are formed, which then recombine to the cyclobutane. | 0 | Theoretical and Fundamental Chemistry |
The structure of binary oxides can be predicted on the basis of the relative sizes of the metal and oxide ions and the filling of holes in a close packed oxide lattice. However, the predictions of structure are more difficult for ternary oxides. The combination of two or more metals in an oxide creates a lot of structural possibilities. Also, the stoichiometry of ternary oxide may be changed by varying the proportions of the two components and their oxidation states. For example, at least twenty ternary oxide phases are formed between strontium and vanadium including SrVO, SrVO, SrVO and SrVO. The structural chemistry of ternary and more complex oxides is an extensive subject, but there are a few structures that are widely adopted by ternary oxides, such as the perovskite structure. | 0 | Theoretical and Fundamental Chemistry |
Later in the 20th century several British pathologists, Mikey Rochman, Francis Camps, Sydney Smith and Keith Simpson pioneered new forensic science methods. Alec Jeffreys pioneered the use of DNA profiling in forensic science in 1984. He realized the scope of DNA fingerprinting, which uses variations in the genetic code to identify individuals. The method has since become important in forensic science to assist police detective work, and it has also proved useful in resolving paternity and immigration disputes. DNA fingerprinting was first used as a police forensic test to identify the rapist and killer of two teenagers, Lynda Mann and Dawn Ashworth, who were both murdered in Narborough, Leicestershire, in 1983 and 1986 respectively. Colin Pitchfork was identified and convicted of murder after samples taken from him matched semen samples taken from the two dead girls.
Forensic science has been fostered by a number of national and international forensic science learned bodies including the American Academy of Forensic Sciences (founded 1948), publishers of the Journal of Forensic Sciences; the Canadian Society of Forensic Science (founded 1953), publishers of the Journal of the Canadian Society of Forensic Science; the Chartered Society of Forensic Sciences, (founded 1959), then known as the Forensic Science Society, publisher of Science & Justice; the British Academy of Forensic Sciences (founded 1960), publishers of Medicine, Science and the Law; the Australian Academy of Forensic Sciences (founded 1967), publishers of the Australian Journal of Forensic Sciences; and the European Network of Forensic Science Institutes (founded 1995). | 0 | Theoretical and Fundamental Chemistry |
Extensional viscosity (also known as elongational viscosity) is a viscosity coefficient when the applied stress is extensional stress. It is often used for characterizing polymer solutions.
Extensional viscosity can be measured using rheometers that apply extensional stress. Acoustic rheometer is one example of such devices.
Extensional viscosity is defined as the ratio of the normal stress difference to the rate of strain. For uniaxial extension along direction :
where
: is the extensional viscosity or elongational viscosity
: is the normal stress along direction n.
: is the rate of strain:
The ratio between the extensional viscosity and the dynamic viscosity is known as Trouton's Ratio, . For a Newtonian Fluid, the Trouton ratio equals three. | 1 | Applied and Interdisciplinary Chemistry |
K-Mold is a fracture test method. Liquid metal is cast into a mold containing notches. Once solidified, the resulting bar is bent to expose a fracture surface. The visual observation of inclusions on the fracture is used to determine a K-value for the melt and compared to a preset standard. This method is rather imprecise and therefore only suitable when metal contains large inclusions and inclusion clusters. | 1 | Applied and Interdisciplinary Chemistry |
By studying the peaks of nuclear magnetic resonance spectra, chemists can determine the structure of many compounds. It can be a very selective technique, distinguishing among many atoms within a molecule or collection of molecules of the same type but which differ only in terms of their local chemical environment. NMR spectroscopy is used to unambiguously identify known and novel compounds, and as such, is usually required by scientific journals for identity confirmation of synthesized new compounds. See the articles on carbon-13 NMR and proton NMR for detailed discussions.
A chemist can determine the identity of a compound by comparing the observed nuclear precession frequencies to known frequencies. Further structural data can be elucidated by observing spin-spin coupling, a process by which the precession frequency of a nucleus can be influenced by the spin orientation of a chemically bonded nucleus. Spin-spin coupling is easily observed in NMR of hydrogen-1 ( NMR) since its natural abundance is nearly 100%.
Because the nuclear magnetic resonance timescale is rather slow, compared to other spectroscopic methods, changing the temperature of a T* experiment can also give information about fast reactions, such as the Cope rearrangement or about structural dynamics, such as ring-flipping in cyclohexane. At low enough temperatures, a distinction can be made between the axial and equatorial hydrogens in cyclohexane.
An example of nuclear magnetic resonance being used in the determination of a structure is that of buckminsterfullerene (often called "buckyballs", composition C). This now famous form of carbon has 60 carbon atoms forming a sphere. The carbon atoms are all in identical environments and so should see the same internal H field. Unfortunately, buckminsterfullerene contains no hydrogen and so nuclear magnetic resonance has to be used. spectra require longer acquisition times since carbon-13 is not the common isotope of carbon (unlike hydrogen, where is the common isotope). However, in 1990 the spectrum was obtained by R. Taylor and co-workers at the University of Sussex and was found to contain a single peak, confirming the unusual structure of buckminsterfullerene. | 0 | Theoretical and Fundamental Chemistry |
Polymer degradation is the reduction in the physical properties of a polymer, such as strength, caused by changes in its chemical composition. Polymers and particularly plastics are subject to degradation at all stages of their product life cycle, including during their initial processing, use, disposal into the environment and recycling. The rate of this degradation varies significantly; biodegradation can take decades, whereas some industrial processes can completely decompose a polymer in hours.
Technologies have been developed to both inhibit or promote degradation. For instance, polymer stabilizers ensure plastic items are produced with the desired properties, extend their useful lifespans, and facilitate their recycling. Conversely, biodegradable additives accelerate the degradation of plastic waste by improving its biodegradability. Some forms of plastic recycling can involve the complete degradation of a polymer back into monomers or other chemicals.
In general, the effects of heat, light, air and water are the most significant factors in the degradation of plastic polymers. The major chemical changes are oxidation and chain scission, leading to a reduction in the molecular weight and degree of polymerization of the polymer. These changes affect physical properties like strength, malleability, melt flow index, appearance and colour. The changes in properties are often termed "aging". | 0 | Theoretical and Fundamental Chemistry |
A thermodynamic cycle is constructed as a sequence of stages or steps. Each stage consists of a thermodynamic operation followed by a thermodynamic process. For example, an initial thermodynamic operation of a cycle of a Carnot heat engine could be taken as the setting of the working body, at a known high temperature, into contact with a thermal reservoir at the same temperature (the hot reservoir), through a wall permeable only to heat, while it remains in mechanical contact with the work reservoir. This thermodynamic operation is followed by a thermodynamic process, in which the expansion of the working body is so slow as to be effectively reversible, while internal energy is transferred as heat from the hot reservoir to the working body and as work from the working body to the work reservoir. Theoretically, the process terminates eventually, and this ends the stage. The engine is then subject to another thermodynamic operation, and the cycle proceeds into another stage. The cycle completes when the thermodynamic variables (the thermodynamic state) of the working body return to their initial values. | 0 | Theoretical and Fundamental Chemistry |
In naphtha cracking process, C4R3 refers to C4 residual obtained after separation of 1,3-butadiene, isobutylene, and 1-butene from C4 raffinate stream which mainly consists of cis- or trans-2-butene, n-butane, and unseparated 1-butene. Normally C4R3 is being process through a selective hydrogenation unit (SHU) and CDHydro deisobutenizer unit to produce isobutylene as a feed to tert-butyl alcohol plant. | 0 | Theoretical and Fundamental Chemistry |
Spectroscopy is a branch of science concerned with the spectra of electromagnetic radiation as a function of its wavelength or frequency measured by spectrographic equipment, and other techniques, in order to obtain information concerning the structure and properties of matter. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers. Most spectroscopic analysis in the laboratory starts with a sample to be analyzed, then a light source is chosen from any desired range of the light spectrum, then the light goes through the sample to a dispersion array (diffraction grating instrument) and captured by a photodiode. For astronomical purposes, the telescope must be equipped with the light dispersion device. There are various versions of this basic setup that may be employed.
Spectroscopy began with Isaac Newton splitting light with a prism; a key moment in the development of modern optics. Therefore, it was originally the study of visible light which we call color that later under the studies of James Clerk Maxwell came to include the entire electromagnetic spectrum. Although color is involved in spectroscopy, it is not equated with the color of elements or objects which involve the absorption and reflection of certain electromagnetic waves to give objects a sense of color to our eyes. Rather spectroscopy involves the splitting of light by a prism, diffraction grating, or similar instrument, to give off a particular discrete line pattern called a "spectrum" unique to each different type of element. Most elements are first put into a gaseous phase to allow the spectra to be examined although today other methods can be used on different phases. Each element that is diffracted by a prism-like instrument displays either an absorption spectrum or an emission spectrum depending upon whether the element is being cooled or heated.
Until recently all spectroscopy involved the study of line spectra and most spectroscopy still does. Vibrational spectroscopy is the branch of spectroscopy that studies the spectra. However, the latest developments in spectroscopy can sometimes dispense with the dispersion technique. In biochemical spectroscopy, information can be gathered about biological tissue by absorption and light scattering techniques. Light scattering spectroscopy is a type of reflectance spectroscopy that determines tissue structures by examining elastic scattering. In such a case, it is the tissue that acts as a diffraction or dispersion mechanism.
Spectroscopic studies were central to the development of quantum mechanics, because the first useful atomic models described the spectra of hydrogen which models include the Bohr model, the Schrödinger equation, and Matrix mechanics which all can produce the spectral lines of hydrogen, therefore providing the basis for discrete quantum jumps to match the discrete hydrogen spectrum. Also, Max Planck's explanation of blackbody radiation involved spectroscopy because he was comparing the wavelength of light using a photometer to the temperature of a Black Body. Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms and molecules. Spectroscopy is also used in astronomy and remote sensing on Earth. Most research telescopes have spectrographs. The measured spectra are used to determine the chemical composition and physical properties of astronomical objects (such as their temperature, density of elements in a star, velocity, black holes and more). An important use for spectroscopy is in biochemistry. Molecular samples may be analyzed for species identification and energy content. | 0 | Theoretical and Fundamental Chemistry |
The Stöber process is a chemical process used to prepare silica () particles of controllable and uniform size for applications in materials science. It was pioneering when it was reported by Werner Stöber and his team in 1968, and remains today the most widely used wet chemistry synthetic approach to silica nanoparticles. It is an example of a sol-gel process wherein a molecular precursor (typically tetraethylorthosilicate) is first reacted with water in an alcoholic solution, the resulting molecules then joining together to build larger structures. The reaction produces silica particles with diameters ranging from 50 to 2000 nm, depending on conditions. The process has been actively researched since its discovery, including efforts to understand its kinetics and mechanisma particle aggregation model was found to be a better fit for the experimental data than the initially hypothesized LaMer model. The newly acquired understanding has enabled researchers to exert a high degree of control over particle size and distribution and to fine-tune the physical properties of the resulting material in order to suit intended applications.
In 1999 a two-stage modification was reported that allowed the controlled formation of silica particles with small holes. The process is undertaken at low pH in the presence of a surface-active molecule. The hydrolysis step is completed with the formation of a microemulsion before adding sodium fluoride to start the condensation process. The non-ionic surfactant is burned away to produce empty pores, increasing the surface area and altering the surface characteristics of the resulting particles, allowing for much greater control over the physical properties of the material. Development work has also been undertaken for larger pore structures such as macroporous monoliths, shell-core particles based on polystyrene, cyclen, or polyamines, and carbon spheres.
Silica produced using the Stöber process is an ideal material to serve as a model for studying colloid phenomena because of the monodispersity (uniformity) of its particle sizes. Nanoparticles prepared using the Stöber process have found applications including in the delivery of medications to within cellular structures and in the preparation of biosensors. Porous silica Stöber materials have applications in catalysis and liquid chromatography due to their high surface area and their uniform, tunable, and highly ordered pore structures. Highly effective thermal insulators known as aerogels can also be prepared using Stöber methods, and Stöber techniques have been applied to prepare non-silica aerogel systems. Applying supercritical drying techniques, a Stöber silica aerogel with a specific surface area of 700 m g and a density of 0.040 g cm can be prepared. NASA has prepared silica aerogels with a Stöber-process approach for both the Mars Pathfinder and Stardust missions. | 0 | Theoretical and Fundamental Chemistry |
Carbides are predicted to be more likely lower in the mantle as experiments have shown a much lower oxygen fugacity for high pressure iron silicates. Cohenite remains stable to over 187 GPa, but is predicted to have a denser orthorhombic Cmcm form in the inner core. | 0 | Theoretical and Fundamental Chemistry |
Spoil tips sometimes increased to millions of tons, and, having been abandoned, remain as huge piles today. They trap solar heat, making it difficult (although not impossible) for vegetation to take root; this encourages erosion and creates dangerous, unstable slopes. Existing techniques for regreening spoil tips include the use of geotextiles to control erosion as the site is resoiled and simple vegetation such as grass is seeded on the slope.
The piles also create acid rock drainage, which pollutes streams and rivers. Environmental problems have included surface runoff of silt, and leaching of noxious chemical compounds from spoil banks exposed to weathering. These cause contamination of ground water, and other problems.
In the United States, current state and federal coal mining regulations require that the earth materials from excavations be removed in such a fashion that they can be replaced after the mining operations cease in a process called mine reclamation, with oversight of mining corporations. This requires adequate reserves of monetary bonds to guarantee a completion of the reclamation process when mining becomes unprofitable or stops. (See for example, the Surface Mining Control and Reclamation Act of 1977.) | 1 | Applied and Interdisciplinary Chemistry |
Indigotindisulfonate sodium, sold under the brand name Bludigo, is used as a diagnostic dye during surgical procedures. It is indicated for use as a visualization aid in the cystoscopic assessment of the integrity of the ureters in adults following urological and gynecological open, robotic, or endoscopic surgical procedures. It was approved for medical use in the United States in July 2022.
In obstetric surgery, indigo carmine solutions are sometimes employed to detect amniotic fluid leaks. In urologic surgery, intravenous injection of indigo carmine is often used to highlight portions of the urinary tract. The dye is filtered rapidly by the kidneys from the blood, and colors the urine blue. This enables structures of the urinary tract to be seen in the surgical field, and demonstrate if there is a leak. However, the dye can cause a potentially dangerous increase in blood pressure in some cases.
Although not absorbed by the cells, indigo carmine stain, sprayed onto regions of interest, highlights the topography of the mucosal surface with its blue coloring. Generally used at a concentration around 0.2%, indigo carmine stain is useful as a screening method for diagnosing minute lesions, to differentiate between benign and malignant lesions, as well as to facilitate application of magnifying endoscopes to observe and analyze the surface structure of a lesion, delineate boundaries of early stage malignant lesions and estimate the invasion depth of cancer. It has been used to diagnose Barrett’s esophagus, evaluate villous atrophy, diagnose and discriminate polypoid and non-polypoid lesions in the colon, and diagnose gastric adenoma and cancer. | 0 | Theoretical and Fundamental Chemistry |
Pentane interference or syn-pentane interaction is the steric hindrance that the two terminal methyl groups experience in one of the chemical conformations of n-pentane. The possible conformations are combinations of anti conformations and gauche conformations and are anti-anti, anti-gauche, gauche - gauche and gauche - gauche of which the last one is especially energetically unfavorable. In macromolecules such as polyethylene pentane interference occurs between every fifth carbon atom. The 1,3-diaxial interactions of cyclohexane derivatives is a special case of this type of interaction, although there are additional gauche interactions shared between substituents and the ring in that case. A clear example of the syn-pentane interaction is apparent in the diaxial versus diequatorial heats of formation of cis 1,3-dialkyl cyclohexanes. Relative to the diequatorial conformer, the diaxial conformer is 2-3 kcal/mol higher in energy than the value that would be expected based on gauche interactions alone. Pentane interference helps explain molecular geometries in many chemical compounds, product ratios, and purported transition states. One specific type of syn-pentane interaction is known as 1,3 allylic strain or (A strain).
For instance in certain aldol adducts with 2,6-disubstituted aryl groups the molecular geometry has the vicinal hydrogen atoms in an antiperiplanar configuration both in a crystal lattice (X-ray diffraction) and in solution proton (NMR coupling constants) normally reserved for the most bulky groups i.d. both arenes:
The other contributing factor explaining this conformation is reduction in allylic strain by minimizing the dihedral angle between the arene double bond and the methine proton.
Syn-pentane interactions are responsible for the backbone-conformation dependence of protein side chain rotamer frequencies and their mean dihedral angles, which is evident from statistical analysis of protein side-chain rotamers in the Backbone-dependent rotamer library. | 0 | Theoretical and Fundamental Chemistry |
The erosive effect of electrical discharges was first noted in 1770 by English physicist Joseph Priestley. | 1 | Applied and Interdisciplinary Chemistry |
Singapore installed a green roof on a bus in 2019 as part of an experiment led by researchers at the National University of Singapore. Green roofs on bus stops in Singapore were found to reduce ambient temperatures by up to 2C. | 1 | Applied and Interdisciplinary Chemistry |
The process of carrying salts by water to the sea or a land-locked lake from a river basin is called salt export. When adequate salt export is not occurring, the river basin area gradually converts into saline soils and/or alkali soils, particularly in lower reaches. | 0 | Theoretical and Fundamental Chemistry |
Sequencing batch reactors (SBRs) treat wastewater in batches within the same vessel. This means that the bioreactor and final clarifier are not separated in space but in a timed sequence. The installation consists of at least two identically equipped tanks with a common inlet, which can be alternated between them. While one tank is in settle/decant mode the other is aerating and filling. | 1 | Applied and Interdisciplinary Chemistry |
On May 9, 2006, a New Drug Application was submitted to the United States Food and Drug Administration (FDA) by Pharmacyclics, Inc.
In December 2007, the FDA issued a not approvable letter for motexafin gadolinium. | 1 | Applied and Interdisciplinary Chemistry |
The ammonia fountain is a type of chemical demonstration. The experiment consists of introducing water through an inlet to a container filled with ammonia gas. Ammonia dissolves into the water and the pressure in the container drops. As a result, more water is forced into the container from another inlet creating a fountain effect. The demonstration introduces concepts like solubility and the gas laws at entry level.
A different gas of comparable solubility in water, such as hydrogen chloride, can be used instead of ammonia.
If the ammonia is replaced by a liquid vapor, such as water vapor, at a pressure higher than its room-temperature vapor pressure, a similar effect is produced. In this case, the reduction in pressure in the container is due to condensation of the vapor as the container cools to room temperature. Another reported variation involves copper sulfate. | 1 | Applied and Interdisciplinary Chemistry |
Ida Noddack (25 February 1896 – 24 September 1978), née Tacke, was a German chemist and physicist. In 1934 she was the first to mention the idea later named nuclear fission. With her husband Walter Noddack, and Otto Berg, she discovered element 75, rhenium. She was nominated three times for the Nobel Prize in Chemistry. | 1 | Applied and Interdisciplinary Chemistry |
Between 1950 and 2020, the average pH value of the ocean surface is estimated to have decreased from approximately 8.15 to 8.05. This represents an increase of around 26% in hydrogen ion concentration in the world's oceans (the pH scale is logarithmic, so a change of one in pH unit is equivalent to a tenfold change in hydrogen ion concentration). For example, in the 15-year period 1995–2010 alone, acidity has increased 6 percent in the upper 100 meters of the Pacific Ocean from Hawaii to Alaska.
The IPCC Sixth Assessment Report in 2021 stated that "present-day surface pH values are unprecedented for at least 26,000 years and current rates of pH change are unprecedented since at least that time. The pH value of the ocean interior has declined over the last 20–30 years everywhere in the global ocean. The report also found that "pH in open ocean surface water has declined by about 0.017 to 0.027 pH units per decade since the late 1980s".
The rate of decline differs by region. This is due to complex interactions between different types of forcing mechanisms: "In the tropical Pacific, its central and eastern upwelling zones exhibited a faster pH decline of minus 0.022 to minus 0.026 pH unit per decade." This is thought to be "due to increased upwelling of -rich sub-surface waters in addition to anthropogenic uptake." Some regions exhibited a slower acidification rate: a pH decline of minus 0.010 to minus 0.013 pH unit per decade has been observed in warm pools in the western tropical Pacific.
The rate at which ocean acidification will occur may be influenced by the rate of surface ocean warming, because warm waters will not absorb as much . Therefore, greater seawater warming could limit CO absorption and lead to a smaller change in pH for a given increase in CO. The difference in changes in temperature between basins is one of the main reasons for the differences in acidification rates in different localities.
Current rates of ocean acidification have been likened to the greenhouse event at the Paleocene–Eocene boundary (about 56 million years ago), when surface ocean temperatures rose by 5–6 degrees Celsius. In that event, surface ecosystems experienced a variety of impacts, but bottom-dwelling organisms in the deep ocean actually experienced a major extinction. Currently, the rate of carbon addition to the atmosphere-ocean system is about ten times the rate that occurred at the Paleocene–Eocene boundary.
Extensive observational systems are now in place or being built for monitoring seawater chemistry and acidification for both the global open ocean and some coastal systems. | 0 | Theoretical and Fundamental Chemistry |
Lake Chichoj is located within 2 km of the Chixoy-Polochic fault, a major fault of the North America-Caribbean plate boundary, which constitutes the closest and largest seismic hazard for San Cristóbal Verapaz, but lies within a broader array of large to intermediate seismogenic faults. The latest noticeable earthquakes include a M 4.1 quake in 2006 on the Polochic fault and a M4.8 in June 2009 on a secondary fault, NW of the lake. The sediments of the lake host a rich record of disruptions produced by past earthquakes, most notably the M 7.8 February 4th 1978 earthquake on the Motagua fault as well as a series of older M 7 earthquakes along the Polochic fault between 850 CE and 1450 CE. The lake adds hazard to the ground shaking of earthquakes. The low-lying marshlands that surround the lake are increasingly filled and urbanized. They are susceptible to seismic wave amplification, seismic wave refraction, and soil liquefaction during earthquakes, but also susceptible to flooding during earthquakes if the lake spillovers. Large waves can be produced during earthquakes, either as a result of landslides affecting the lake inner slopes, or by seismic resonance (seiche waves). | 1 | Applied and Interdisciplinary Chemistry |
*Obligate aerobes need oxygen to grow. In a process known as cellular respiration, these organisms use oxygen to oxidize substrates (for example sugars and fats) and generate energy.
*Facultative anaerobes use oxygen if it is available, but also have anaerobic methods of energy production.
*Microaerophiles require oxygen for energy production, but are harmed by atmospheric concentrations of oxygen (21% O).
*Aerotolerant anaerobes do not use oxygen but are not harmed by it.
When an organism is able to survive in both oxygen and anaerobic environments, the use of the Pasteur effect can distinguish between facultative anaerobes and aerotolerant organisms. If the organism is using fermentation in an anaerobic environment, the addition of oxygen will cause facultative anaerobes to suspend fermentation and begin using oxygen for respiration. Aerotolerant organisms must continue fermentation in the presence of oxygen.
Facultative organisms grow in both oxygen rich media and oxygen free media. | 1 | Applied and Interdisciplinary Chemistry |
The three related TET genes, TET1, TET2 and TET3 code respectively for three related mammalian proteins TET1, TET2, and TET3. All three proteins possess 5mC oxidase activity, but they differ in terms of domain architecture. TET proteins are large (~180- to 230-kDa) multidomain enzymes. All TET proteins contain a conserved double-stranded β-helix (DSBH) domain, a cysteine-rich domain, and binding sites for the cofactors Fe(II) and 2-oxoglutarate (2-OG) that together form the core catalytic region in the C terminus. In addition to their catalytic domain, full-length TET1 and TET3 proteins have an N-terminal CXXC zinc finger domain that can bind DNA. The TET2 protein lacks a CXXC domain, but the IDAX gene, that's a neighbor of the TET2 gene, encodes a CXXC4 protein. IDAX is thought to play a role in regulating TET2 activity by facilitating its recruitment to unmethylated CpGs. | 1 | Applied and Interdisciplinary Chemistry |
The Molecular Kink Paradigm proceeds from the intuitive notion that molecular chains that make up a natural rubber (polyisoprene) network are constrained by surrounding chains to remain within a ‘tube’. Elastic forces produced in a chain, as a result of some applied strain, are propagated along the chain contour within this tube. Fig. 2 shows a representation of a four-carbon isoprene backbone unit with an extra carbon atom at each end to indicate its connections to adjacent units on a chain. It has three single C-C bonds and one double bond. It is principally by rotating about the C-C single bonds that a polyisoprene chain randomly explores its possible conformations. Sections of chain containing between two and three isoprene units have sufficient flexibility that they may be considered statistically de-correlated from one another. That is, there is no directional correlation along the chain for distances greater than this distance, referred to as a Kuhn length. These non-straight regions evoke the concept of ‘kinks’ and are in fact a manifestation of the random-walk nature of the chain. Since a kink is composed of several isoprene units, each having three carbon-carbon single bonds, there are many possible conformations available to a kink, each with a distinct energy and end-to-end distance. Over time scales of seconds to minutes, only these relatively short sections of the chain, i.e. kinks, have sufficient volume to move freely amongst their possible rotational conformations. The thermal interactions tend to keep the kinks in a state of constant flux, as they make transitions between all of their possible rotational conformations. Because the kinks are in thermal equilibrium, the probability that a kink resides in any rotational conformation is given by a Boltzmann distribution and we may associate an entropy with its end-to-end distance. The probability distribution for the end-to-end distance of a Kuhn length is approximately Gaussian and is determined by the Boltzmann probability factors for each state (rotational conformation). As a rubber network is stretched, some kinks are forced into a restricted number of more extended conformations having a greater end-to-end distance and it is the resulting decrease in entropy that produces an elastic force along the chain.
There are three distinct molecular mechanisms that produce these forces, two of which arise from changes in entropy that we shall refer to as low chain extension regime, Ia and moderate chain extension regime, Ib. The third mechanism occurs at high chain extension, as it is extended beyond its initial equilibrium contour length by the distortion of the chemical bonds along its backbone. In this case, the restoring force is spring-like and we shall refer to it as regime II. The three force mechanisms are found to roughly correspond to the three regions observed in tensile stress vs. strain experiments, shown in Fig. 1.
The initial morphology of the network, immediately after chemical cross-linking, is governed by two random processes: (1) The probability for a cross-link to occur at any isoprene unit and, (2) the random walk nature of the chain conformation. The end-to-end distance probability distribution for a fixed chain length, i.e. fixed number of isoprene units, is described by a random walk. It is the joint probability distribution of the network chain lengths and the end-to-end distances between their cross-link nodes that characterizes the network morphology. Because both the molecular physics mechanisms that produce the elastic forces and the complex morphology of the network must be treated simultaneously, simple analytic elasticity models are not possible; an explicit 3-dimensional numerical model is required to simulate the effects of strain on a representative volume element of a network. | 0 | Theoretical and Fundamental Chemistry |
The neon-burning process is a set of nuclear fusion reactions that take place in evolved massive stars with at least 8 Solar masses. Neon burning requires high temperatures and densities (around 1.2×10 K or 100 keV and 4×10 kg/m).
At such high temperatures photodisintegration becomes a significant effect, so some neon nuclei decompose, absorbing 4.73 MeV and releasing alpha particles. This free helium nucleus can then fuse with neon to produce magnesium, releasing 9.316 MeV.
Alternatively:
where the neutron consumed in the first step is regenerated in the second.
A secondary reaction causes helium to fuse with magnesium to produce silicon:
: + → Silicon| + γ
Contraction of the core leads to an increase of temperature, allowing neon to fuse directly as follows:
Neon burning takes place after carbon burning has consumed all carbon in the core and built up a new oxygen–neon–sodium–magnesium core. The core ceases producing fusion energy and contracts. This contraction increases density and temperature up to the ignition point of neon burning. The increased temperature around the core allows carbon to burn in a shell, and there will be shells burning helium and hydrogen outside.
During neon burning, oxygen and magnesium accumulate in the central core while neon is consumed. After a few years the star consumes all its neon and the core ceases producing fusion energy and contracts. Again, gravitational pressure takes over and compresses the central core, increasing its density and temperature until the oxygen-burning process can start. | 0 | Theoretical and Fundamental Chemistry |
In a laminar flow reactor, the fluid flows through a long tube or parallel plate reactor and the flow is in layers parallel to the walls of the tube. The velocity of the flow is a parabolic function of radius. In the absence of molecular diffusion, the RTD is
The variance is infinite. In a real reactor, diffusion will eventually mix the layers so that the tail of the RTD becomes exponential and the variance finite; but laminar flow reactors can have variance greater than 1, the maximum for CTSD reactors. | 0 | Theoretical and Fundamental Chemistry |
The original Jameson Cell design had the following features:
* small (200 mm diameter) downcomers
* no wash water
* no tailings recycle
* no bubble dispersers
* low capacity.
In 1994 MIM launched the Mark II model Cell. It incorporated the following changes:
* the downcomer diameter was increased to 280 mm
* wash-water trays were included for froth washing
* a tailings recycle system was added to maintain constant downcomer flow and higher recoveries
* conical bubble dispersers were added
* increased depth of tank from the bottom of the downcomer
* increased distance between the downcomers.
These changes resulted in a higher capacity design.
One of the problems encountered with the Mark I Cell was that its performance was reduced if the feed rate to the cell varied, which was a common occurrence arising from normal fluctuations in operating concentrators. This problem was resolved by recycling some of the tailings to the cell feed via an external splitter box called an "External Recycle Mechanism" or "ERM" box separate to the flotation cell. Thus, when the production of the feed stream to the Jameson Cell decreased as a result of a fluctuation elsewhere in the concentrator, a higher percentage of the tailings was automatically recycled to the downcomers, producing a constant flow rate, hence feed pressure, to the cell. This had the added benefit of giving a proportion of the tailings (typically 40%) a second pass through the system, which resulted in higher recoveries. In coal fines flotation, this allowed a single Cell to achieve the same recovery of combustibles as had previously been achieved in some two-stage Cell systems.
Subsequently, an internal recycling system, referred to as the "internal recycle control" or "IRC" was developed. This was mainly used in integrated rectangular cells (see Figure 6), where the feed tank and tailings recycling system could easily be built in a single unit with the flotation cell. This system reduced the cell installation costs and made the cell more compact.
During this period, the orifice diameter was increased from the 28 mm design used in 1990 to 34 mm with the Mark II model and 38 mm in 1997. This, together with the larger Mark II downcomer diameter, allowed the slurry flow per downcomer to be doubled from 30 m/h in 1990 to 60 m/h in 1997.
The increased distance between the downcomers reduced the interaction of aerated slurry discharging from adjacent downcomers. This interaction could reduce overall cell recovery by causing particles collected by bubbles in the downcomer to detach in the pulp tank.
There was significant turbulence in the areas beneath the downcomers. that could result in particles detaching from bubbles. These turbulent areas were calmed by the addition of conical diffusers beneath each downcomer. They allowed uniform bubble rise velocities across the surface of the cell by slowing the superficial gas velocity in the high void-fraction area immediately around the downcomer and provided a more even bubble dispersion. It was reported that the diffusers reduced the turbulence by 69% compared with a standard downcomer with no diffuser. | 1 | Applied and Interdisciplinary Chemistry |
Reticular synthesis enables facile bottom-up synthesis of the framework materials to introduce precise perturbations in chemical composition, resulting in the highly controlled tunability of framework properties. Through a bottom-up approach, a material is built from atomic or molecular components synthetically as opposed to a top-down approach, which forms a material from the bulk through approaches such as exfoliation, lithography, or other varieties of post-synthetic modification. The bottom-up approach is especially advantageous with respect to materials such as COFs because the synthetic methods are designed to directly result in an extended, highly crosslinked framework that can be tuned with exceptional control at the nanoscale level. Geometrical and dimensional principles govern the framework's resulting topology as the SBUs combine to form predetermined structures. This level of synthetic control has also been termed "molecular engineering", abiding by the concept termed by Arthur R. von Hippel in 1956.
It has been established in the literature that, when integrated into an isoreticular framework, such as a COF, properties from monomeric compounds can be synergistically enhanced and amplified. COF materials possess the unique ability for bottom-up reticular synthesis to afford robust, tunable frameworks that synergistically enhance the properties of the precursors, which, in turn, offers many advantages in terms of improved performance in different applications. As a result, the COF material is highly modular and tuned efficiently by varying the SBUs’ identity, length, and functionality depending on the desired property change on the framework scale. Ergo, there exists the ability to introduce diverse functionality directly into the framework scaffold to allow for a variety of functions which would be cumbersome, if not impossible, to achieve through a top-down method, such as lithographic approaches or chemical-based nanofabrication. Through reticular synthesis, it is possible to molecularly engineer modular, framework materials with highly porous scaffolds that exhibit unique electronic, optical, and magnetic properties while simultaneously integrating desired functionality into the COF skeleton.
Reticular synthesis is different from retrosynthesis of organic compounds, because the structural integrity and rigidity of the building blocks in reticular synthesis remain unaltered throughout the construction process—an important aspect that could help to fully realize the benefits of design in crystalline solid-state frameworks. Similarly, reticular synthesis should be distinguished from supramolecular assembly, because in the former, building blocks are linked by strong bonds throughout the crystal. | 0 | Theoretical and Fundamental Chemistry |
Henry's law describes the tendency of a compound to join air in the vapor phase or dissolve in water. The Henry’s Law constant, sometimes called coefficient, is specific to each compound and depends on the system temperature. The constant is used to predict the amount of contaminant what will remain in the vapor phase (or transfer to the liquid phase), upon exiting the condenser. | 1 | Applied and Interdisciplinary Chemistry |
The Russian Journal of Physical Chemistry A: Focus on Chemistry () is an English-language translation of the eponymous Russian-language peer-reviewed scientific journal published by Springer Science+Business Media on behalf of Pleiades Publishing. It was established in 1930 and focuses on review articles pertaining to global coverage of all theory and experiment in physical chemistry. The editor-in-chief is Aslan Yu. Tsivadze (Russian Academy of Sciences). | 0 | Theoretical and Fundamental Chemistry |
1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC, EDAC or EDCI) is a water-soluble carbodiimide usually handled as the hydrochloride.
It is typically employed in the 4.0-6.0 pH range. It is generally used as a carboxyl activating agent for the coupling of primary amines to yield amide bonds. While other carbodiimides like dicyclohexylcarbodiimide (DCC) or diisopropylcarbodiimide (DIC) are also employed for this purpose, EDC has the advantage that the urea byproduct formed (often challenging to remove in the case of DCC or DIC) can be washed away from the amide product using dilute acid. Additionally, EDC can also be used to activate phosphate groups in order to form phosphomonoesters and phosphodiesters. Common uses for this carbodiimide include peptide synthesis, protein crosslinking to nucleic acids, but also in the preparation of immunoconjugates. EDC is often used in combination with N-hydroxysuccinimide (NHS) for the immobilisation of large biomolecules. Recent work has also used EDC to assess the structure state of uracil nucleobases in RNA. | 1 | Applied and Interdisciplinary Chemistry |
The equation of motion for the superfluid component, in a somewhat simplified form, is given by Newton's law
The mass M is the molar mass of He, and is the velocity of the superfluid component. The time derivative is the so-called hydrodynamic derivative, i.e. the rate of increase of the velocity when moving with the fluid. In the case of superfluid He in the gravitational field the force is given by
In this expression μ is the molar chemical potential, g the gravitational acceleration, and z the vertical coordinate. Thus we get the equation which states that the thermodynamics of a certain constant will be amplified by the force of the natural gravitational acceleration
Eq. only holds if v is below a certain critical value, which usually is determined by the diameter of the flow channel.
In classical mechanics the force is often the gradient of a potential energy. Eq. shows that, in the case of the superfluid component, the force contains a term due to the gradient of the chemical potential. This is the origin of the remarkable properties of He-II such as the fountain effect. | 1 | Applied and Interdisciplinary Chemistry |
In laser physics however, the atomic ratio may refer to the doping ratio or the doping fraction.
*For example, theoretically, a 100% doping ratio of Yb YAlO is pure YbAlO.
*The doping fraction equals, | 0 | Theoretical and Fundamental Chemistry |
* 1.F.1 The Synaptosomal Vesicle Fusion Pore (SVF-Pore) Family
* 1.F.2 The Octameric Exocyst (Exocyst) Family | 1 | Applied and Interdisciplinary Chemistry |
Acoustic theory is a scientific field that relates to the description of sound waves. It derives from fluid dynamics. See acoustics for the engineering approach.
For sound waves of any magnitude of a disturbance in velocity, pressure, and density we have
In the case that the fluctuations in velocity, density, and pressure are small, we can approximate these as
Where is the perturbed velocity of the fluid, is the pressure of the fluid at rest, is the perturbed pressure of the system as a function of space and time, is the density of the fluid at rest, and is the variance in the density of the fluid over space and time.
In the case that the velocity is irrotational (), we then have the acoustic wave equation that describes the system:
Where we have | 1 | Applied and Interdisciplinary Chemistry |
There are multiple approaches to measuring a persons exposure to pesticides, each of which provides an estimate of an individuals internal dose. Two broad approaches include measuring biomarkers and markers of biological effect. The former involves taking direct measurement of the parent compound or its metabolites in various types of media: urine, blood, serum. Biomarkers may include a direct measurement of the compound in the body before its been biotransformed during metabolism. Other suitable biomarkers may include the metabolites of the parent compound after theyve been biotransformed during metabolism. Toxicokinetic data can provide more detailed information on how quickly the compound is metabolized and eliminated from the body, and provide insights into the timing of exposure.
Markers of biological effect provide an estimation of exposure based on cellular activities related to the mechanism of action. For example, many studies investigating exposure to pesticides often involve the quantification of the acetylcholinesterase enzyme at the neural synapse to determine the magnitude of the inhibitory effect of organophosphate and carbamate pesticides.
Another method of quantifying exposure involves measuring, at the molecular level, the amount of pesticide interacting with the site of action. These methods are more commonly used for occupational exposures where the mechanism of action is better understood, as described by WHO guidelines published in "Biological Monitoring of Chemical Exposure in the Workplace". Better understanding of how pesticides elicit their toxic effects is needed before this method of exposure assessment can be applied to occupational exposure of agricultural workers.
Alternative methods to assess exposure include questionnaires to discern from participants whether they are experiencing symptoms associated with pesticide poisoning. Self-reported symptoms may include headaches, dizziness, nausea, joint pain, or respiratory symptoms. | 1 | Applied and Interdisciplinary Chemistry |
Konrad Seppelt (born September 2, 1944 in Leipzig) is an academic, author, professor and former vice president of the Free University of Berlin. | 0 | Theoretical and Fundamental Chemistry |
National Pipe Taper Fuel (NPTF, also called Dryseal American National Standard Taper Pipe Thread, defined by ASME B1.20.3) is designed to provide a more leak-free seal without the use of PTFE tape (often referred to by the popular brand name "Teflon") or another sealant compound. NPTF threads have the same basic shape but with crest and root heights adjusted for an interference fit, eliminating the spiral leakage path. | 1 | Applied and Interdisciplinary Chemistry |
Chemotaxis receptors are expressed in the surface membrane with diverse dynamics, some of them have long-term characteristics as they are determined genetically, others have short-term moiety as their assembly is induced ad hoc in the presence of the ligand. The diverse feature of the chemotaxis receptors and ligands provides the possibility to select chemotactic responder cells with a simple chemotaxis assay. By chemotactic selection we can determine whether a still not characterized molecule acts via the long- or the short-term receptor pathway. Recent results proved that chemokines (e.g. IL-8, RANTES) are working on long-term chemotaxis receptors, while vasoactive peptides (e.g. endothelin) act more on the short-term ones. Term chemotactic selection is also used to design a technique which separates eukaryotic or prokaryotic cells upon their chemotactic responsiveness to selector ligands. | 1 | Applied and Interdisciplinary Chemistry |
Since [http://sourceforge.net/project/showfiles.php?group_id=71971&package_id=76633 Level 2 Version 2] SBML provides a mechanism to annotate model components with SBO terms, therefore increasing the semantics of the
model beyond the sole topology of interaction and mathematical expression. Modelling tools such as [https://github.com/draeger-lab/SBMLsqueezer SBMLsqueezer] interpret SBO terms to augment the mathematics in the SBML file. Simulation tools can check the consistency of a rate law, convert reaction from one modelling framework to another (e.g., continuous to discrete), or distinguish between identical mathematical expressions based on different assumptions (e.g., Michaelis–Menten vs. Briggs–Haldane). To add missing SBO terms to models, software such as [https://github.com/draeger-lab/SBOannotator SBOannotator] can be used. Other tools such as [http://www.semanticsbml.org/ semanticSBML] can use the SBO annotation to integrate individual models into a larger one. The use of SBO is not restricted to the development of models. Resources providing quantitative experimental information such as [https://web.archive.org/web/20061117195025/http://sabio.villa-bosch.de/SABIORK/ SABIO Reaction Kinetics] will be able to annotate the parameters (what do they mean exactly, how were they calculated) and determine relationships between them. | 1 | Applied and Interdisciplinary Chemistry |
The Bosch–Meiser process is an industrial process, which was patented in 1922 and named after its discoverers, the German chemists Carl Bosch and Wilhelm Meiser for the large-scale manufacturing of urea, a valuable nitrogenous chemical.
The whole process consists of two main equilibrium reactions, with incomplete conversion of the reactants.
* The first, called carbamate formation: the fast exothermic reaction of liquid ammonia with gaseous carbon dioxide () at high temperature and pressure to form ammonium carbamate ():
:(ΔH = −117 kJ/mol at 110 atm and 160 °C)
* The second, called urea conversion: the slower endothermic decomposition of ammonium carbamate into urea and water:
:(ΔH = +15.5 kJ/mol at 160–180 °C)
The overall conversion of and to urea is exothermic, with the reaction heat from the first reaction driving the second. The conditions that favor urea formation (high temperature) have an unfavorable effect on the carbamate formation equilibrium. The process conditions are a compromise: the ill-effect on the first reaction of the high temperature (around 190 °C) needed for the second is compensated for by conducting the process under high pressure (140–175 bar), which favors the first reaction. Although it is necessary to compress gaseous carbon dioxide to this pressure, the ammonia is available from the ammonia production plant in liquid form, which can be pumped into the system much more economically. To allow the slow urea formation reaction time to reach equilibrium, a large reaction space is needed, so the synthesis reactor in a large urea plant tends to be a massive pressure vessel. | 0 | Theoretical and Fundamental Chemistry |
James Thomas Brenna (born October 15, 1959) is an American scientist specializing in analytical chemistry, and in human nutrition and foods, specifically fats. He is a professor of Paediatrics at Dell Medical School, having previously been a professor of human nutrition, chemistry, chemical biology and food science at Cornell University. | 0 | Theoretical and Fundamental Chemistry |
India needs infrastructure for logistics and the movement of freight. Using connected rivers as navigation is a cleaner, low carbon footprint form of transport infrastructure, particularly for ores and food grains. | 1 | Applied and Interdisciplinary Chemistry |
The expressions for the T-matrix resulting from both methods can be related to certain class of variational principles. In the case of first iteration of MCFV method we get the same result as from Schwinger variational principle with trial function . The higher iterations with N-terms in the continuous fraction reproduce exactly 2N terms (2N + 1) of Born series for the MCFV (or MCFG) method respectively. The method was tested on calculation of collisions of electrons from hydrogen atom in static-exchange approximation. In this case the method reproduces exact results for scattering cross-section on 6 significant digits in 4 iterations. It can also be shown that both methods reproduce exactly the solution of the Lippmann-Schwinger equation with the potential given by finite-rank operator. The number of iterations is then equal to the rank of the potential. The method has been successfully used for solution of problems in both nuclear and molecular physics. | 0 | Theoretical and Fundamental Chemistry |
Organometallic compounds are distinguished by the prefix "organo-" (e.g., organopalladium compounds), and include all compounds which contain a bond between a metal atom and a carbon atom of an organyl group. In addition to the traditional metals (alkali metals, alkali earth metals, transition metals, and post transition metals), lanthanides, actinides, semimetals, and the elements boron, silicon, arsenic, and selenium are considered to form organometallic compounds. Examples of organometallic compounds include Gilman reagents, which contain lithium and copper, and Grignard reagents, which contain magnesium. Boron-containing organometallic compounds are often the result of hydroboration and carboboration reactions. Tetracarbonyl nickel and ferrocene are examples of organometallic compounds containing transition metals. Other examples of organometallic compounds include organolithium compounds such as n-butyllithium (n-BuLi), organozinc compounds such as diethylzinc (EtZn), organotin compounds such as tributyltin hydride (BuSnH), organoborane compounds such as triethylborane (EtB), and organoaluminium compounds such as trimethylaluminium (MeAl).
A naturally occurring organometallic complex is methylcobalamin (a form of Vitamin B), which contains a cobalt-methyl bond. This complex, along with other biologically relevant complexes are often discussed within the subfield of bioorganometallic chemistry. | 0 | Theoretical and Fundamental Chemistry |
Pneumatic cylinder, also known as air cylinder, is a mechanical device which uses the power of compressed gas to produce a force in a reciprocating linear motion.
Like in a hydraulic cylinder, something forces a piston to move in the desired direction. The piston is a disc or cylinder, and the piston rod transfers the force it develops to the object to be moved. Engineers sometimes prefer to use pneumatics because they are quieter, cleaner, and do not require large amounts of space for fluid storage.
Because the operating fluid is a gas, leakage from a pneumatic cylinder will not drip out and contaminate the surroundings, making pneumatics more desirable where cleanliness is a requirement. For example, in the mechanical puppets of the Disney Tiki Room, pneumatics are used to prevent fluid from dripping onto people below the puppets. | 1 | Applied and Interdisciplinary Chemistry |
In their 2010 Synlett article, Martina Wernerova and organic chemist, Tomáš Hudlický, raised concerns about inaccurate reporting of yields, and offered solutions—including the proper characterization of compounds. After performing careful control experiments, Wernerova and Hudlický said that each physical manipulation (including extraction/washing, drying over desiccant, filtration, and column chromatography) results in a loss of yield of about 2%. Thus, isolated yields measured after standard aqueous workup and chromatographic purification should seldom exceed 94%. They called this phenomenon "yield inflation" and said that yield inflation had gradually crept upward in recent decades in chemistry literature. They attributed yield inflation to careless measurement of yield on reactions conducted on small scale, wishful thinking and a desire to report higher numbers for publication purposes. Hudlickýs 2020 article published in Angewandte Chemie—since retracted—honored and echoed Dieter Seebachs often-cited 1990 thirty-year review of organic synthesis, which had also been published in Angewandte Chemie. In his 2020 Angewandte Chemie 30-year review, Hudlický said that the suggestions that he and Wernerova had made in their 2010 Synlett article, were "ignored by the editorial boards of organic journals, and by most referees." | 0 | Theoretical and Fundamental Chemistry |
"Sustainable engineering" and "green engineering" are terms that are often used interchangeably. The main difference between the two being that green engineering is "optimized to minimize negative impacts without exhausting resources available in the natural environment" and sustainable engineering is "more directed toward building a better future for the next generations". The idea of sustainable development became intertwined with engineering and chemistry early in the 21st century. One often cited book that brought the idea of sustainable development to engineers was the publishing of: "Sustainable Infrastructure: Principles into Practice", written by Charles Ainger and Richard Fenner. | 1 | Applied and Interdisciplinary Chemistry |
Human breast milk contains unique and highly diverse human milk oligosaccharides. These oligosaccharides are considered to be a "Bifidus Factor" because they form highly desired intestinal bacteria; it is for this reason that baby formula contains added oligosaccharides in order to help build a child's immune system. Studies showed that infants, who were bottled fed, lacked intestinal colonization of bifidobacteria. This lack of bacteria made the babies susceptible to other infectious bacteria and ailments. The infants who were breast fed had higher concentration of the bacteria and their vulnerability too infections was significantly lower. Breast milk had high amounts of oligosaccharides. As, a result, oligosaccharides were added to milk formula. This method worked and the colonization of bifidobacteria leveled. This suggested that the oligosaccharides found in human milk were candidates for the bifidus factor. | 1 | Applied and Interdisciplinary Chemistry |
*2015 Friedrich Wilhelm Bessel Award, granted by the Alexander Von Humboldt Foundation
*2013 William H. Kiekhofer Distinguished Teaching Award, presented by University of Wisconsin-Madison
*2010 Eli Lilly Grantee Award, conferred by Eli Lilly & Company
*2010 Camille Dreyfus Teacher-Scholar Award, granted by the Camille & Henry Dreyfus Foundation
*2009 Amgen Young Investigator Award, sponsored by Amgen
*2009 Alfred P. Sloan Research Fellowship, awarded by the Alfred P. Sloan Foundation
*2008 Cottrell Scholar Award, presented by Research Corporation for Scientific Advancement (RCSA)
*2008 Beckman Young Investigator Award, granted by the Arnold and Mabel Beckman Foundation
*2007 NSF CAREER Award, initiated through the National Science Foundation CAREER Awards | 0 | Theoretical and Fundamental Chemistry |
In most cases, organisms containing recombinant DNA have apparently normal phenotypes. That is, their appearance, behavior and metabolism are usually unchanged, and the only way to demonstrate the presence of recombinant sequences is to examine the DNA itself, typically using a polymerase chain reaction (PCR) test. Significant exceptions exist, and are discussed below.
If the rDNA sequences encode a gene that is expressed, then the presence of RNA and/or protein products of the recombinant gene can be detected, typically using RT-PCR or western hybridization methods. Gross phenotypic changes are not the norm, unless the recombinant gene has been chosen and modified so as to generate biological activity in the host organism. Additional phenotypes that are encountered include toxicity to the host organism induced by the recombinant gene product, especially if it is over-expressed or expressed within inappropriate cells or tissues.
In some cases, recombinant DNA can have deleterious effects even if it is not expressed. One mechanism by which this happens is insertional inactivation, in which the rDNA becomes inserted into a host cell's gene. In some cases, researchers use this phenomenon to "knock out" genes to determine their biological function and importance. Another mechanism by which rDNA insertion into chromosomal DNA can affect gene expression is by inappropriate activation of previously unexpressed host cell genes. This can happen, for example, when a recombinant DNA fragment containing an active promoter becomes located next to a previously silent host cell gene, or when a host cell gene that functions to restrain gene expression undergoes insertional inactivation by recombinant DNA. | 1 | Applied and Interdisciplinary Chemistry |
Apixaban shows a similar binding mode as rivaroxaban and forms a tight inhibitor-enzyme complex when connected to FXa. The p-methoxy group of apixaban connects to S1 pocket of FXa but does not appear to have any interaction with any residues in this region of FXa. The pyrazole N-2 nitrogen atom of apixaban interacts with Gln-192 and the carbonyl oxygen interacts with Gly-216. The phenyl lactam group of apixaban is positioned between Tyr-99 and Phe-174 and due to its orientation, it is able to interact with Trp-215 of the S4 pocket. The carbonyl oxygen group of the lactam moiety interacts with a water molecule and does not seem to interact with any residues in the S4 pocket. | 1 | Applied and Interdisciplinary Chemistry |
The limitations of currently available rapalogs have led to new approaches to mTOR targeting. Studies suggest that mTOR inhibitors may have anticancer activity in many cancer types, such as RCC, neuroendocrine tumors, breast cancer, hepatocellular carcinoma, sarcoma, and large B-cell lymphoma.
One major limitation for the development of mTOR inhibition therapy is that biomarkers are not presently available to predict which patient will respond to them. A better understanding of the molecular mechanisms that are involved in the response of cancer cells to mTOR inhibitors are still required so this can be possible.
A way to overcome the resistance and improve efficacy of mTOR targeting agents may be with stratification of patients and selection of drug combination therapies. This may lead to a more effective and personalized cancer therapy. Although further research is needed, mTOR targeting still remains an attractive and promising therapeutic option for the treatment of cancer. | 1 | Applied and Interdisciplinary Chemistry |
When multiple copies of a polypeptide encoded by a gene self-assemble to form a complex, this protein structure is referred to as a "multimer". Genes that encode multimer-forming polypeptides appear to be common. When a multimer is formed from polypeptides produced by two different mutant alleles of a particular gene, the mixed multimer may exhibit greater functional activity than the unmixed multimers formed by each of the mutants alone. In such a case, the phenomenon is referred to as intragenic complementation. Jehle pointed out that, when immersed in a liquid and intermingled with other molecules, charge fluctuation forces favor the association of identical molecules as nearest neighbors. | 0 | Theoretical and Fundamental Chemistry |
Hexachlorophosphazene has also found applications in research by enabling aromatic coupling reactions between pyridine and either N,N-dialkylanilines or indole, resulting in 4,4'-substituted phenylpyridine derivatives, postulated to go through a cyclophosphazene pyridinium salt intermediate.
The compound may also be used as a peptide coupling reagent for the synthesis of oligopeptides in chloroform, though for this application the tetramer octachlorotetraphosphazene usually proves more effective. | 0 | Theoretical and Fundamental Chemistry |
1,1-Difluoroethane is a synthetic substance that is produced by the mercury-catalyzed addition of hydrogen fluoride to acetylene:
:HCCH + 2 HF → CHCHF
The intermediate in this process is vinyl fluoride (CHF), the monomeric precursor to polyvinyl fluoride. | 1 | Applied and Interdisciplinary Chemistry |
The lost-wax technique came to be known in the Mediterranean during the Bronze Age. It was a major metalworking technique utilized in the ancient Mediterranean world, notably during the Classical period of Greece for large-scale bronze statuary and in the Roman world.
Direct imitations and local derivations of Oriental, Syro-Palestinian and Cypriot figurines are found in Late Bronze Age Sardinia, with a local production of figurines from the 11th to 10th century BC. The cremation graves (mainly 8th-7th centuries BC, but continuing until the beginning of the 4th century) from the necropolis of Paularo (Italian Oriental Alps) contained fibulae, pendants and other copper-based objects that were made by the lost-wax process. Etruscan examples, such as the bronze anthropomorphic handle from the Bocchi collection (National Archaeological Museum of Adria), dating back to the 6th to 5th centuries BC, were made by cire perdue. Most of the handles in the Bocchi collection, as well as some bronze vessels found in Adria (Rovigo, Italy) were made using the lost-wax technique. The better known lost-wax produced items from the classical world include the "Praying Boy" (in the Berlin Museum), the statue of Hera from Vulci (Etruria), which, like most statues, was cast in several parts which were then joined. Geometric bronzes such as the four copper horses of San Marco (Venice, probably 2nd century) are other prime examples of statues cast in many parts.
Examples of works made using the lost-wax casting process in Ancient Greece largely are unavailable due to the common practice in later periods of melting down pieces to reuse their materials. Much of the evidence for these products come from shipwrecks. As underwater archaeology became feasible, artifacts lost to the sea became more accessible. Statues like the Artemision Bronze Zeus or Poseidon (found near Cape Artemision), as well as the Victorious Youth (found near Fano), are two such examples of Greek lost-wax bronze statuary that were discovered underwater.
Some Late Bronze Age sites in Cyprus have produced cast bronze figures of humans and animals. One example is the male figure found at Enkomi. Three objects from Cyprus (held in the Metropolitan Museum of Art in New York) were cast by the lost-wax technique from the 13th and 12th centuries BC, namely, the amphorae rim, the rod tripod, and the cast tripod.
Other, earlier examples that show this assembly of lost-wax cast pieces include the bronze head of the Chatsworth Apollo and the bronze head of Aphrodite from Satala (Turkey) from the British Museum. | 1 | Applied and Interdisciplinary Chemistry |
* Kumar, A., et al. "Sustainability in Environmental Engineering and Science." (2021): 253–262.
* Sharma, Abhinav. "Effect of ozone pretreatment on biodegradability enhancement and biogas production of biomethanated distillery effluent."
* Sharma, Asheesh, et al. "NutriL-GIS: A Tool for Assessment of Agricultural Runoff and Nutrient Pollution in a Watershed." National Environmental Engineering Research Institute (NEERI). India (2010).
* Sinnarkar, S. N., and Rajesh Kumar Lohiya. "External user in an environmental research library." Annals of library and information studies 55.4 (2008): 275–280.
* Schools, Greywater Reuse In Rural. "Guidance Manual." National Environmental Engineering Research Institute (2007).
* Thawale, P. R., Asha A. Juwarkar, and S. K. Singh. "Resource conservation through land treatment of municipal wastewater." Current Science (2006): 704–711.
* Rao, Padma S., et al. "Performance evaluation of a green belt in a petroleum refinery: a case study". Ecological engineering 23.2 (2004): 77–84.
* Murty , K. S. "Groundwater in India." Studies in Environmental Science. Vol. 17. Elsevier, 1981. 733–736. | 1 | Applied and Interdisciplinary Chemistry |
In analytical chemistry, a reagent is a compound or mixture used to detect the presence or absence of another substance, e.g. by a color change, or to measure the concentration of a substance, e.g. by colorimetry. Examples include Fehlings reagent, Millons reagent, and Tollens' reagent. | 0 | Theoretical and Fundamental Chemistry |
* Borax – for brazing
* Beeswax
* Citric acid – for soldering copper/electronics
* Tallow and lead
* Paraffin wax
* Palm oil
* Zinc chloride ("killed spirits")
* Zinc chloride and ammonium chloride
* Olive oil and ammonium chloride – for iron
* Rosin, tallow, olive oil, and zinc chloride – for aluminium
* Cryolite (sodium hexafluoroaluminate)
* Cryolite and phosphoric acid
* Phosphoric acid and alcohol
* Cryolite and barium chloride
* Oleic acid
* Lithium chloride
* Magnesium chloride
* Sodium chloride
* Potassium chloride
* Unslaked lime | 1 | Applied and Interdisciplinary Chemistry |
Xanthate salts are prepared by the action of alkoxides on carbon disulfide. The alkoxide is often generated in situ from potassium hydroxide:
Potassium ethyl xanthate is a pale yellow powder that is stable at high pH, but rapidly hydrolyses below pH = 9:
Oxidation gives diethyl dixanthogen disulfide:
KEX is a source of ethylxanthate coordination complexes. For example have been prepared from KEX for M = Cr, In, Co. | 1 | Applied and Interdisciplinary Chemistry |
Holmium titanate is an inorganic compound with the chemical formula HoTiO.
Holmium titanate is a spin ice material like dysprosium titanate and holmium stannate. | 0 | Theoretical and Fundamental Chemistry |
cfDNA, cell death-related and chromatin fragmented DNA molecules contained in blood plasma, has been used to detect transplant tissue rejection, prenatal fetal aneuploidy testing, tumour profiling, and early cancer detection in previous research. Nevertheless, prevalent liquid biopsy methods for cfDNA profiling depend on detecting germline or somatic genetic variations, which may be absent even in high disease burden-bearing patients and cancers with high tumour mutation rates.
Historically, the usage of fragmentomic features of cfDNA samples was shown to be another method to approach the problems mentioned. They demonstrated the capability to inform about the originated tissue classification of cfDNA molecules, which can help segregate tumour-related somatic mutations. However, current methods that use fragmentomic features, such as shallow whole genome sequencing (WGS) on cfDNA, do not fully cover all the tissues' effects and provide low sequencing depth and breadth to infer low-level, for example, gene level, properties. Hence, these methods require a high tumour burden from the patients. | 1 | Applied and Interdisciplinary Chemistry |
In crystallography, a Wyckoff position is any point in a set of points whose site symmetry groups (see below) are all conjugate subgroups one of another. Crystallography tables give the Wyckoff positions for different space groups. | 0 | Theoretical and Fundamental Chemistry |
The endocannabinoid system has been shown to have a homeostatic role by controlling several metabolic functions, such as energy storage and nutrient transport. It acts on peripheral tissues such as adipocytes, hepatocytes, the gastrointestinal tract, the skeletal muscles and the endocrine pancreas. It has also been implied in modulating insulin sensitivity. Through all of this, the endocannabinoid system may play a role in clinical conditions, such as obesity, diabetes, and atherosclerosis, which may also give it a cardiovascular role. | 1 | Applied and Interdisciplinary Chemistry |
The biopolymers that comprise DNA, RNA and (poly)peptides are linear polymers (i.e.: each monomer is connected to at most two other monomers). The sequence of their monomers effectively encodes information. The transfers of information from one molecule to another are faithful, deterministic transfers, wherein one biopolymers sequence is used as a template for the construction of another biopolymer with a sequence that is entirely dependent on the original biopolymers sequence. When DNA is transcribed to RNA, its complement is paired to it. DNA codes A, G, T, and C are transferred to RNA codes U, C, A, and G, respectively. The encoding of proteins is done in groups of three, known as codons. The standard codon table applies for humans and mammals, but some other lifeforms (including human mitochondria) use different translations. | 1 | Applied and Interdisciplinary Chemistry |
In nutritional science, which covers the intake of nutrients and non-drug dietary ingredients, the concept of bioavailability lacks the well-defined standards associated with the pharmaceutical industry. The pharmacological definition cannot apply to these substances because utilization and absorption is a function of the nutritional status and physiological state of the subject, resulting in even greater differences from individual to individual (inter-individual variation). Therefore, bioavailability for dietary supplements can be defined as the proportion of the administered substance capable of being absorbed and available for use or storage.
In both pharmacology and nutrition sciences, bioavailability is measured by calculating the area under curve (AUC) of the drug concentration time profile. | 1 | Applied and Interdisciplinary Chemistry |
Azobilirubin is a coloured compound formed by the condensation of diazotized sulfanilic acid with bilirubin in the van den Bergh reaction. The quantity of bilirubin in patients with jaundice can be determined by the formation of azobilirubin in the presence of methanol.
The Van den Bergh chemical reaction which is used to measure bilirubin levels, couples bilirubin with diazotized sulfanilic acid. This reaction produced azo pigments, or azobilirubin. The presence of azobilirubin is best indicated by the emergence of a pink-purple color. The intensity of the color will also indicate how much bilirubin is in the blood. Color markers and indicators can be changed. Adding alkaline tartrate can make the purple azobilirubin into a blue azobilirubin. If we have high levels of bilirubin in the blood, the Van den Bergh chemical reaction is used to determine if the bilirubin is conjugated or unconjugated.
Azobilirubin can also be used to determine how much conjugated bilirubin is the blood compared to that of unconjugated bilirubin. This process is done by using both forms of bilirubin alongside a diazo reagent and a caffeine-benzoate reagent. Conjugated bilirubin with the azo reagent will react, whilst the unconjugated bilirubin will not react with the azo reagent. | 1 | Applied and Interdisciplinary Chemistry |
Oral ingestion is the most common route of administration of pharmaceuticals. Passing through the esophagus to the stomach, the contents of the capsule or tablet are absorbed by the GI tract. The absorbed pharmaceutical is then passed through the liver and kidneys.
The rate of dissolution is a key target for controlling the duration of a drug's effect, and as such, several dosage forms that contain the same active ingredient may be available, differing only in the rate of dissolution. If a drug is supplied in a form that is not readily dissolved, it may be released gradually and act for longer. Having a longer duration of action may improve compliance since the medication will not have to be taken as often. Additionally, slow-release dosage forms may maintain concentrations within an acceptable therapeutic range over a longer period, whereas quick-release dosage forms may have sharper peaks and troughs in serum concentration.
The rate of dissolution is described by the Noyes–Whitney equation as shown below:
Where:
* is the rate of dissolution.
*A is the surface area of the solid.
*C is the concentration of the solid in the bulk dissolution medium.
* is the concentration of the solid in the diffusion layer surrounding the solid.
*D is the diffusion coefficient.
*L is the diffusion layer thickness.
As can be inferred from the Noyes–Whitney equation, the rate of dissolution may be modified primarily by altering the surface area of the solid by altering the particle size (e.g., with micronization). For many drugs, reducing the particle size reduces the dose needed to achieve the same therapeutic effect. The particle size reduction increases the specific surface area and the dissolution rate and does not affect solubility.
The rate of dissolution may also be altered by choosing a suitable polymorph of a compound. Different polymorphs have different solubility and dissolution rate characteristics. Specifically, crystalline forms dissolve slower than amorphous forms since they require more energy to leave the lattice during dissolution. The stablest crystalline polymorph has the lowest dissolution rate. Dissolution also differs between anhydrous and hydrous forms of a drug. Anhydrous forms often dissolve faster but sometimes are less soluble.
Esterification is also used to control solubility. For example, stearate and estolate esters of drugs have decreased solubility in gastric fluid. Later, esterases in the gastrointestinal tract (GIT) wall and blood hydrolyze these esters to release the parent drug.
Coatings on a tablet or pellet may act as barriers to reducing the dissolution rate. Coatings may also be used to control where dissolution takes place. For example, enteric coatings only dissolve in the basic environment of the intestines.
Drugs held in solution do not need to be dissolved before being absorbed.
Lipid-soluble drugs are absorbed more rapidly than water-soluble drugs. | 1 | Applied and Interdisciplinary Chemistry |
Full-mold casting is an evaporative-pattern casting process which is a combination of sand casting and lost-foam casting. It uses an expanded polystyrene foam pattern which is then surrounded by sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the foam upon contact. | 1 | Applied and Interdisciplinary Chemistry |
Typical arene tricarbonyl piano stool complexes of Mn(I) and Re(I) are cationic and thus exhibit enhanced reactivity toward nucleophiles. Subsequent to nucleophilic addition, the modified arene can be recovered from the metal. | 0 | Theoretical and Fundamental Chemistry |
The protein is a member of the tripartite motif family. This motif includes three zinc-binding domains:
* RING
* B-box type 1 zinc finger
* B-box type 2 zinc finger
and a coiled-coil region.
Three alternatively spliced transcript variants for this gene have been described, however, the full-length nature of one variant has not been determined. | 1 | Applied and Interdisciplinary Chemistry |
Phillips conducted various studies on protein structures and their functional implications. He examined the structural features of type 6 streptococcal M proteins, highlighting their predominantly alpha-helical coiled-coil, which demonstrates a unique conformation in bacterial surface projections. His research on the crystal structure of tropomyosin filaments proposed a model in which tropomyosin exhibited distinct conformations related to muscle contraction, suggesting a statistical mechanism for regulating muscle function.
In one of his highly cited studies, Phillips, alongside Fan Yang and Larry G. Moss, described the crystal structure of recombinant wild-type green fluorescent protein, unveiling a unique structure referred to as the "ß-can." This study also delved into the protective environment for the fluorophores within the cylinder and its applications in elucidating the effects of GFP mutants.
Phillips has utilized X-ray crystallography and various advanced spectroscopy techniques to provide details about the dynamic structural changes in proteins. He used X-ray crystallography to determine the structure of unstable intermediate caused by photodissociation of CO from myoglobin and provided insights into the dynamics and structural alterations involved in this protein reaction. In addition, his study focused on capturing the structural evolution of the protein on a picosecond timescale used time-resolved X-ray diffraction and mid-infrared spectroscopy on a myoglobin (Mb) mutant (L29F mutant) revealing conformational changes within the protein. | 1 | Applied and Interdisciplinary Chemistry |
Since kinetic isotope effects arise from differences in isotopic masses, the largest observable kinetic isotope effects are associated with isotopic substitutions of hydrogen with deuterium (100% increase in mass) or tritium (200% increase in mass). Kinetic isotope effects from isotopic mass ratios can be as large as 36.4 using muons. They have produced the lightest hydrogen atom, H (0.113 amu), in which an electron orbits around a positive muon (μ) "nucleus" that has a mass of 206 electrons. They have also prepared the heaviest hydrogen atom analogue by replacing one electron in helium with a negative muon (μ) to form Heμ with an atomic mass of 4.116 amu. Since the negative muon is much heavier than an electron, it orbits much closer to the nucleus, effectively shielding one proton, making Heμ to behave as H. With these exotic species, the reaction of H with H was investigated. Rate constants from reacting the lightest and the heaviest hydrogen analogues with H were then used to calculate the k/k kinetic isotope effect, in which there is a 36.4 fold difference in isotopic masses. For this reaction, isotopic substitution happens to produce an inverse kinetic isotope effect, and the authors report a kinetic isotope effect as low as 1.74 x 10, which is the smallest kinetic isotope effect ever reported.
The kinetic isotope effect leads to a specific distribution of deuterium isotopes in natural products, depending on the route they were synthesized in nature. By NMR spectroscopy, it is therefore easy to detect whether the alcohol in wine was fermented from glucose, or from illicitly added saccharose.
Another reaction mechanisms that was elucidated using the kinetic isotope effect is the halogenation of toluene:
In this particular "intramolecular KIE" study, a benzylic hydrogen undergoes radical substitution by bromine using N-bromosuccinimide as the brominating agent. It was found that PhCH brominates 4.86x faster than PhCD. A large KIE of 5.56 is associated with the reaction of ketones with bromine and sodium hydroxide.
In this reaction the rate-limiting step is formation of the enolate by deprotonation of the ketone. In this study the KIE is calculated from the reaction rate constants for regular 2,4-dimethyl-3-pentanone and its deuterated isomer by optical density measurements.
In asymmetric catalysis, there are rare instances in which a kinetic isotope effect manifests as a significant difference in the enantioselectivity observed for a deuterated substrate compared to a non-deuterated one. One example was reported by Toste and coworkers, in which a deuterated substrate produced an enantioselectivity of 83% ee, compared to 93% ee for the undeuterated substrate. The effect was taken to corroborate additional inter- and intramolecular competition KIE data that suggested cleavage of the C-H/D bond in the enantiodetermining step. | 0 | Theoretical and Fundamental Chemistry |
Selenium is incorporated into several prokaryotic selenoprotein families in bacteria, archaea, and eukaryotes as selenocysteine, where selenoprotein peroxiredoxins protect bacterial and eukaryotic cells against oxidative damage. Selenoprotein families of GSH-Px and the deiodinases of eukaryotic cells seem to have a bacterial phylogenetic origin. The selenocysteine-containing form occurs in species as diverse as green algae, diatoms, sea urchin, fish and chicken. Selenium enzymes are involved in utilization of the small reducing molecules glutathione and thioredoxin.
Trace elements involved in GSH-Px and superoxide dismutase enzymes activities, i.e. selenium, vanadium, magnesium, copper, and zinc, may have been lacking in some terrestrial mineral-deficient areas. Marine organisms retained and sometimes expanded their seleno-proteomes, whereas the seleno-proteomes of some terrestrial organisms were reduced or completely lost. These findings suggest that aquatic life supports selenium utilization, whereas terrestrial habitats lead to reduced use of this trace element. Marine fishes and vertebrate thyroid glands have the highest concentration of selenium and iodine. From about 500 Mya, freshwater and terrestrial plants slowly optimized the production of "new" endogenous antioxidants such as ascorbic acid (Vitamin C), polyphenols (including flavonoids), tocopherols, etc. A few of these appeared more recently, in the last 50–200 million years, in fruits and flowers of angiosperm plants. In fact, the angiosperms (the dominant type of plant today) and most of their antioxidant pigments evolved during the late Jurassic period.
About 200 Mya, new selenoproteins were developed as mammalian GSH-Px enzymes. | 1 | Applied and Interdisciplinary Chemistry |
Micromeritics is the science and technology of small particles pioneered by Joseph M. DallaValle. It is thus the study of the fundamental and derived properties of individual as well as a collection of particles. The knowledge and control of the size of particles has importance in pharmacy and materials science. The size, and hence the surface area of a particle, can be related to the physical, chemical and pharmacological properties of drugs. Clinically, the particle size of a drug can affect its release from dosage forms that are administered orally, parenterally, rectally and topically. The successful formulation of suspensions, emulsions and tablets; both physical stability and pharmacological response also depends on the particle size achieved in the product. | 0 | Theoretical and Fundamental Chemistry |
Silicothermic reactions are thermic chemical reactions using silicon as the reducing agent at high temperature (800-1400°C). The most prominent example is the Pidgeon process for reducing magnesium metal from ores. Other processes include the Bolzano process and the magnetherm process. All three are commercially used for magnesium production.
The silicothermic process for magnesium production was developed commercially in Canada during the Second World War by Lloyd Montgomery Pidgeon. | 1 | Applied and Interdisciplinary Chemistry |
Fatal infantile lactic acidosis: Defective SCS has been implicated as a cause of fatal infantile lactic acidosis, which is a disease in infants that is characterized by the build-up of toxic levels of lactic acid. The condition (when it is most severe) results in death usually within 2–4 days after birth. It has been determined that patients with the condition display a two base pair deletion within the gene known as SUCLG1 that encodes the α subunit of SCS. As a result, functional SCS is absent in metabolism causing a major imbalance in flux between glycolysis and the citric acid cycle. Since the cells do not have a functional citric acid cycle, acidosis results because cells are forced to choose lactic acid production as the primary means of producing ATP. | 1 | Applied and Interdisciplinary Chemistry |
A neurochemical is a small organic molecule or peptide that participates in neural activity. The science of neurochemistry studies the functions of neurochemicals. | 1 | Applied and Interdisciplinary Chemistry |
The Eigen-Wilkins mechanism, named after chemists Manfred Eigen and R. G. Wilkins, is a mechanism and rate law in coordination chemistry governing associative substitution reactions of octahedral complexes. It was discovered for substitution by ammonia of a chromium-(III) hexaaqua complex. The key feature of the mechanism is an initial rate-determining pre-equilibrium to form an encounter complex ML-Y from reactant ML and incoming ligand Y. This equilibrium is represented by the constant K:
:ML + Y ML-Y
The subsequent dissociation to form product is governed by a rate constant k:
:ML-Y → MLY + L
A simple derivation of the Eigen-Wilkins rate law follows:
:[ML-Y] = K[ML][Y]
:[ML-Y] = [M] - [ML]
:rate = k[ML-Y]
:rate = kK[Y][ML]
Leading to the final form of the rate law, using the steady-state approximation (d[ML-Y] / dt = 0),
:rate = kK[Y][M] / (1 + K[Y]) | 0 | Theoretical and Fundamental Chemistry |
The Knudsen layer, also known as evaporation layer, is the thin layer of vapor near a liquid or solid. It is named after Danish physicist Martin Knudsen (1871–1949). | 1 | Applied and Interdisciplinary Chemistry |
The identity of this complex anion is uncertain, suggestions include [Co(κ-CO)], [Co(κ-COH)(OH)], and [Co(κ-CO)(κ-CO)(OH)]. Thermal gravimetric analysis favors the presence of one aquo ligand, and infra-red spectroscopy indicates the presence of both bi- and unidentate carbonate ligands. The addition of [[hexaamminecobalt(III) chloride|[Co(NH)]Cl]] to fresh solutions of sodium tris(carbonato)cobalt(III) precipitates anhydrous salt [Co(NH)] [Co(κ-CO)]. This salt has been characterized by X-ray crystallography, which established that the anionic complex features three bidentate (κ-) carbonate ligands.
To some extent, the exact description of the title salt is unimportant since it is only used as a synthetic intermediate, it has no intrinsic value. Products include [Co(HO)], [Co(κ-CO)(HO)], and [Co(κ-CO)(HO)] and their derivatives where the aquo ligand has been displaced. The closely related potassium tris(carbonatocobalt(III) has also been used for the preparation of diverse complexes. These derivatives include [Co(NH)(κ-CO)] and [Co(CN)(κ-CO)], rare examples of biscarbonato cobalt(III) complexes. Other derivatives include the dinitrite [Co(NH)(κ-CO)(NO)] and the oxalate [Co(NH)(κ-CO)(CO)]. | 0 | Theoretical and Fundamental Chemistry |
The nuclear genetic code is flexible as illustrated by variant genetic codes that reassign standard stop codons to amino acids. | 1 | Applied and Interdisciplinary Chemistry |
Oil-eating bacteria biodegrade oil that has escaped to the surface. Oil sands are reservoirs of partially biodegraded oil still in the process of escaping and being biodegraded, but they contain so much migrating oil that, although most of it has escaped, vast amounts are still present—more than can be found in conventional oil reservoirs. The lighter fractions of the crude oil are destroyed first, resulting in reservoirs containing an extremely heavy form of crude oil, called crude bitumen in Canada, or extra-heavy crude oil in Venezuela. These two countries have the world's largest deposits of oil sands.
On the other hand, oil shales are source rocks that have not been exposed to heat or pressure long enough to convert their trapped hydrocarbons into crude oil. Technically speaking, oil shales are not always shales and do not contain oil, but are fined-grain sedimentary rocks containing an insoluble organic solid called kerogen. The kerogen in the rock can be converted into crude oil using heat and pressure to simulate natural processes. The method has been known for centuries and was patented in 1694 under British Crown Patent No. 330 covering, "A way to extract and make great quantities of pitch, tar, and oil out of a sort of stone." Although oil shales are found in many countries, the United States has the world's largest deposits. | 0 | Theoretical and Fundamental Chemistry |
An emulator for the APEXC series has been developed by MESS. They describe its functioning as follows:
<blockquote>The APEXC is an incredibly simple machine.
<br/>
Instruction and data words are always 32 bits long. The processor uses integer arithmetic with 2's complement representation. Addresses are 10 bits long. The APEXC has no RAM, except for a 32-bit accumulator and a 32-bit data register (used along with the 32-bit accumulator to implement 64-bit shift instructions and hold the 64-bit result of a multiplication). Instructions and data are stored in two magnetic drums, for a total of 32 circular magnetic tracks of 32 words. Since the rotation rate is 3750rpm (62.5 rotations per second), the program execution speed can go from as high as the theoretical maximum of 1 kIPS to lower than 100IPS if program instructions and data are not contiguous. Nowadays, many say a pocket calculator is faster.
<br/>
One oddity is that there is no program counter: each machine instruction includes the address of the next instruction. This design may sound weird, but it is the only way to achieve optimal performance with this cylinder-based memory.
<br/>
The machine code is made of 15 instructions only, namely addition, subtraction, multiplication, load (3 variants), store (2 variants), conditional branch, right arithmetic bit shift, right bit rotation, punched-card input, punched-card output, machine stop, and bank-switching (which is never used on the APEXC, since it only has 1024 words of storage, and addresses are 10-bit-long). A so-called vector mode enables to repeat the same operation 32 times with 32 successive memory locations. Note the lack of bitwise and/or/xor and division. Also, note the lack of indirect addressing modes: dynamic modification of opcodes is the only way one may simulate it.
<br/>
Another oddity is that the memory bus and the ALU are 1-bit-wide. There is a 64 kHz bit-clock and a 2 kHz word-clock, and each word memory and arithmetic operation is decomposed into 32 1-bit memory and arithmetic operations: this takes 32 bit cycles, for a total of 1 word cycle.
<br/>
The processor is fairly efficient: most instructions take only 2 word cycles (1 for fetch, 1 for read operand and execute), with the exception of stores, shifts and multiplications. The APEXC CPU qualifies as RISC; there is no other adequate word.
<br/>
Note there is no read-only memory (ROM), and therefore no bootstrap loader or default start-up program whatsoever. It is believed that no executive or operating system was ever written for the APEXC, although there were subroutine libraries of sorts for common arithmetic, I/O and debug tasks.
<br/>
Operation of the machine is normally done through a control panel which allows the user to start, stop and resume the central processing unit, and to alter registers and memory when the CPU is stopped. When starting the machine, the address of the first instruction of the program to be executed must be entered in the control panel, then the run switch must be pressed. Most programs end with a stop instruction, which enables the operator to check the state of the machine, possibly run some post-mortem debugging procedures (a core dump routine is described in an APEXC programming book), then enter the address of another program and run it.
<br/>
Two I/O devices were supported: a paper tape reader, and a paper tape puncher. The puncher output could be fed to a printer (teletyper) unit when desirable. Printer output is emulated and is displayed on screen. Tape input was either computer-generated by the APEXC, or hand-typed with a special 32-key keyboard (each tape row had 5 data holes ( | 0 | Theoretical and Fundamental Chemistry |
The original sulfur isotopic reference material was the Canyon Diablo Troilite (CDT), a meteorite recovered from Meteor Crater in Arizona. The Canyon Diablo Meteorite was chosen because it was thought to have a sulfur isotopic composition similar to the bulk Earth. However, the meteorite was later found to be isotopically heterogeneous with variations up to 0.4‰ (Beaudoin et al., 1994). This isotopic variability resulted in problems for the interlaboratory calibration of sulfur isotope measurements. A meeting of the IAEA in 1993 defined Vienna Canyon Diablo Troilite (VCDT) in an allusion to the earlier establishment of VSMOW. Like the original SMOW and VPDB, VCDT was never a physical material that could be measured but was still used as the definition of the sulfur isotopic scale. For the purposes of actually measuring S/S ratios, the IAEA defined the δS of IAEA-S-1 (originally called IAEA-NZ1) to be -0.30‰ relative to VCDT. These fairly recent changes to the sulfur isotope reference materials have greatly improved interlaboratory reproducibility (Coplen & Krouse, 1998). | 0 | Theoretical and Fundamental Chemistry |
Sieverts' law, in physical metallurgy and in chemistry, is a rule to predict the solubility of gases in metals. It is named after German chemist Adolf Sieverts (1874–1947). The law states that the solubility of a diatomic gas in metal is proportional to the square root of the partial pressure of the gas in thermodynamic equilibrium. Hydrogen, oxygen and nitrogen are examples of dissolved diatomic gases of frequent interest in metallurgy. | 1 | Applied and Interdisciplinary Chemistry |
Fusion ignition is the point at which a nuclear fusion reaction becomes self-sustaining. This occurs when the energy being given off by the reaction heats the fuel mass more rapidly than it cools. In other words, fusion ignition is the point at which the increasing self-heating of the nuclear fusion removes the need for external heating.
This is quantified by the Lawson criterion.
Ignition can also be defined by the fusion energy gain factor.
In the laboratory, fusion ignition defined by the Lawson criterion was first achieved in August 2021,
and ignition defined by the energy gain factor was achieved in December 2022,
both by the U.S. National Ignition Facility. | 0 | Theoretical and Fundamental Chemistry |
* Chemical engineer
* Chemical reaction
* Distillation Design
* Fluid mechanics
* Heat transfer
* Mass transfer and equilibrium stages
* Operations involving particulate solids.
* Process design
* Transport Phenomena
* Unit operations
* Polymerization
* 3D Plant Design
* FEED | 1 | Applied and Interdisciplinary Chemistry |
The MAM is a critical signaling, metabolic, and trafficking hub in the cell that allows for the integration of ER and mitochondrial physiology. Coupling between these organelles is not simply structural but functional as well and critical for overall cellular physiology and homeostasis. The MAM thus offers a perspective on mitochondria that diverges from the traditional view of this organelle as a static, isolated unit appropriated for its metabolic capacity by the cell. Instead, this mitochondrial-ER interface emphasizes the integration of the mitochondria, the product of an endosymbiotic event, into diverse cellular processes. Recently it has also been shown, that mitochondria and MAM-s in neurons are anchored to specialised intercellular communication sites (so called somatic-junctions). Microglial processes monitor and protect neuronal functions at these sites, and MAM-s are supposed to have an important role in this type of cellular quality-control. | 1 | Applied and Interdisciplinary Chemistry |
Biochemical receptors are large protein molecules that can be activated by the binding of a ligand such as a hormone or a drug. Receptors can be membrane-bound, as cell surface receptors, or inside the cell as intracellular receptors, such as nuclear receptors including those of the mitochondrion. Binding occurs as a result of non-covalent interactions between the receptor and its ligand, at locations called the binding site on the receptor. A receptor may contain one or more binding sites for different ligands. Binding to the active site on the receptor regulates receptor activation directly. The activity of receptors can also be regulated by the binding of a ligand to other sites on the receptor, as in allosteric binding sites. Antagonists mediate their effects through receptor interactions by preventing agonist-induced responses. This may be accomplished by binding to the active site or the allosteric site. In addition, antagonists may interact at unique binding sites not normally involved in the biological regulation of the receptor's activity to exert their effects.
The term antagonist was originally coined to describe different profiles of drug effects. The biochemical definition of a receptor antagonist was introduced by Ariens and Stephenson in the 1950s. The current accepted definition of receptor antagonist is based on the receptor occupancy model. It narrows the definition of antagonism to consider only those compounds with opposing activities at a single receptor. Agonists were thought to turn "on" a single cellular response by binding to the receptor, thus initiating a biochemical mechanism for change within a cell. Antagonists were thought to turn "off" that response by blocking the receptor from the agonist. This definition also remains in use for physiological antagonists, substances that have opposing physiological actions, but act at different receptors. For example, histamine lowers arterial pressure through vasodilation at the histamine H receptor, while adrenaline raises arterial pressure through vasoconstriction mediated by alpha-adrenergic receptor activation.
Our understanding of the mechanism of drug-induced receptor activation and receptor theory and the biochemical definition of a receptor antagonist continues to evolve. The two-state model of receptor activation has given way to multistate models with intermediate conformational states. The discovery of functional selectivity and that ligand-specific receptor conformations occur and can affect interaction of receptors with different second messenger systems may mean that drugs can be designed to activate some of the downstream functions of a receptor but not others. This means efficacy may actually depend on where that receptor is expressed, altering the view that efficacy at a receptor is receptor-independent property of a drug. | 1 | Applied and Interdisciplinary Chemistry |
Blasius developed an expression of friction factor in 1913 for the flow in the regime .
Koo introduced another explicit formula in 1933 for a turbulent flow in region of | 1 | Applied and Interdisciplinary Chemistry |
The development of effective anti-HIV drugs is difficult due to wide variations in nucleotide and amino acid sequences. The perfect anti-HIV drug chemical should be effective against drug resistance mutation. Understanding the target RT enzyme and its structure, mechanism of drug action and the consequence of drug resistance mutations provide useful information which can be helpful to design more effective NNRTIs. The RT enzyme can undergo change due to mutations that can disturb NNRTI binding. | 1 | Applied and Interdisciplinary Chemistry |
Chromatin relaxation is one of the earliest cellular responses to DNA damage. Several experiments have been performed on the recruitment kinetics of proteins involved in the response to DNA damage. The relaxation appears to be initiated by PARP1, whose accumulation at DNA damage is half complete by 1.6 seconds after DNA damage occurs. This is quickly followed by accumulation of chromatin remodeler Alc1, which has an ADP-ribose–binding domain, allowing it to be quickly attracted to the product of PARP1. The maximum recruitment of Alc1 occurs within 10 seconds of DNA damage. About half of the maximum chromatin relaxation, presumably due to action of Alc1, occurs by 10 seconds. PARP1 action at the site of a double-strand break allows recruitment of the two DNA repair enzymes MRE11 and NBS1. Half maximum recruitment of these two DNA repair enzymes takes 13 seconds for MRE11 and 28 seconds for NBS1.
Another process of chromatin relaxation, after formation of a DNA double-strand break, employs γH2AX, the phosphorylated form of the H2AX protein. The histone variant H2AX constitutes about 10% of the H2A histones in human chromatin. γH2AX (phosphorylated on serine 139 of H2AX) was detected at 20 seconds after irradiation of cells (with DNA double-strand break formation), and half maximum accumulation of γH2AX occurred in one minute. The extent of chromatin with phosphorylated γH2AX is about two million base pairs at the site of a DNA double-strand break.
γH2AX does not, by itself, cause chromatin decondensation, but within seconds of irradiation the protein "Mediator of the DNA damage checkpoint 1" (MDC1) specifically attaches to γH2AX. This is accompanied by simultaneous accumulation of RNF8 protein and the DNA repair protein NBS1 which bind to MDC1 as MDC1 attaches to γH2AX. RNF8 mediates extensive chromatin decondensation, through its subsequent interaction with CHD4 protein, a component of the nucleosome remodeling and deacetylase complex NuRD. CHD4 accumulation at the site of the double-strand break is rapid, with half-maximum accumulation occurring by 40 seconds after irradiation.
The fast initial chromatin relaxation upon DNA damage (with rapid initiation of DNA repair) is followed by a slow recondensation, with chromatin recovering a compaction state close to its pre-damage level in ~ 20 min. | 1 | Applied and Interdisciplinary Chemistry |
The rate of reaction for the ionization reaction
:2 HO → HO + OH
depends on the activation energy, ΔE. According to the Boltzmann distribution the proportion of water molecules that have sufficient energy, due to thermal population, is given by
where k is the Boltzmann constant. Thus some dissociation can occur because sufficient thermal energy is available. The following sequence of events has been proposed on the basis of electric field fluctuations in liquid water. Random fluctuations in molecular motions occasionally (about once every 10 hours per water molecule) produce an electric field strong enough to break an oxygen–hydrogen bond, resulting in a hydroxide (OH) and hydronium ion (HO); the hydrogen nucleus of the hydronium ion travels along water molecules by the Grotthuss mechanism and a change in the hydrogen bond network in the solvent isolates the two ions, which are stabilized by solvation. Within 1 picosecond, however, a second reorganization of the hydrogen bond network allows rapid proton transfer down the electric potential difference and subsequent recombination of the ions. This timescale is consistent with the time it takes for hydrogen bonds to reorientate themselves in water.
The inverse recombination reaction
:HO + OH → 2 HO
is among the fastest chemical reactions known, with a reaction rate constant of at room temperature. Such a rapid rate is characteristic of a diffusion-controlled reaction, in which the rate is limited by the speed of molecular diffusion. | 0 | Theoretical and Fundamental Chemistry |
In natural systems, secondary minerals may form as a byproduct of bacterial metal reduction. Commonly observed secondary minerals produced during experimental bio-reduction by dissimilatory metal reducers include magnetite, siderite, green rust, vivianite, and hydrous Fe(II)-carbonate. | 1 | Applied and Interdisciplinary Chemistry |
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