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* Order of Polonia Restituta (2018)
* [https://ptchem.pl/pl/honors/distinctions-and-medals-ptchem Medal Jana Zawidzkiego] (1997)
* Golden Cross of Merit (Poland) (1990) | 7 | Physical Chemistry |
A typical thermodynamic operation is externally imposed change of position of a piston, so as to alter the volume of the system of interest. Another thermodynamic operation is a removal of an initially separating wall, a manipulation that unites two systems into one undivided system. A typical thermodynamic process consists of a redistribution that spreads a conserved quantity between a system and its surroundings across a previously impermeable but newly semi-permeable wall between them.
More generally, a process can be considered as a transfer of some quantity that is defined by a change of an extensive state variable of the system, corresponding to a conserved quantity, so that a transfer balance equation can be written. According to Uffink, "... thermodynamic processes only take place after an external intervention on the system (such as: removing a partition, establishing thermal contact with a heat bath, pushing a piston, etc.). They do not correspond to the autonomous behaviour of a free system." For example, for a closed system of interest, a change of internal energy (an extensive state variable of the system) can be occasioned by transfer of energy as heat. In thermodynamics, heat is not an extensive state variable of the system. The quantity of heat transferred, is however, defined by the amount of adiabatic work that would produce the same change of the internal energy as the heat transfer; energy transferred as heat is the conserved quantity.
As a matter of history, the distinction, between a thermodynamic operation and a thermodynamic process, is not found in these terms in nineteenth century accounts. For example, Kelvin spoke of a "thermodynamic operation" when he meant what present-day terminology calls a thermodynamic operation followed by a thermodynamic process. Again, Planck usually spoke of a "process" when our present-day terminology would speak of a thermodynamic operation followed by a thermodynamic process. | 7 | Physical Chemistry |
These reagents are useful because, unlike related Grignard reagents and organolithium reagents, they react with organic halides to replace the halide group with an R group (the Corey–House reaction). Such displacement reactions allow for the synthesis of complex products from simple building blocks. Lewis acids can be used to modify the reagent. | 0 | Organic Chemistry |
Lactonase hydrolyzes the ester bond of the homoserine lactone ring of acylated homoserine lactones. In hydrolysing the lactone bond, lactonase prevents these signaling molecules from binding to their target transcriptional regulators, thus inhibiting quorum sensing. | 1 | Biochemistry |
Different types of kerogen have differing potentials to produce oil during maturation. These various types of kerogen can be distinguished on a van Krevelen diagram. | 9 | Geochemistry |
Generally, two major frictional systems affect adhesive wear or galling: solid surface contact and lubricated contact. In terms of prevention, they work in dissimilar ways and set different demands on the surface structure, alloys, and crystal matrix used in the materials.
In solid surface contact or unlubricated conditions, the initial contact is characterized by the interaction between asperities and the exhibition of two different sorts of attraction: cohesive surface-energy or the molecules connect and adhere the two surfaces together, notably even if a measurable distance separates them. Direct contact and plastic deformation generate another type of attraction through the constitution of a plastic zone with flowing material where induced energy, pressure, and temperature allow bonding between the surfaces on a much larger scale than cohesive surface energy.
In metallic compounds and sheet metal forming, the asperities are usually oxides, and the plastic deformation primarily consists of brittle fracture, which presupposes a very small plastic zone. The accumulation of energy and temperature is low due to the discontinuity in the fracture mechanism.
However, during the initial asperity/asperity contact, wear debris or bits and pieces from the asperities adhere to the opposing surface, creating microscopic, usually localized, roughening and creation of protrusions (in effect lumps) above the original surface. The transferred wear debris and lumps penetrate the opposing oxide surface layer and cause damage to the underlying bulk material, plowing it forward. This allows continuous plastic deformation, plastic flow, and accumulation of energy and temperature.
The prevention of adhesive material transfer is accomplished by the following or similar approaches:
* Low-temperature carburizing treatments such as Kolsterising can eliminate galling in austenitic stainless steels by increasing surface hardness up to 1200 HV0.05 (depending on the base material and surface conditions).
* Less cohesive or chemical attraction between surface atoms or molecules.
* Avoid continuous plastic deformation and plastic flow, for example, through a thicker oxide layer on the subject material in sheet-metal forming (SMF).
* Coatings deposited on the SMF work tool, such as chemical vapor deposition (CVD) or physical vapor deposition (PVD) and titanium nitride (TiN) or diamond-like carbon coatings exhibit low chemical reactivity even in high energy frictional contact, where the subject material's protective oxide layer is breached, and the frictional contact is distinguished by continuous plastic deformation and plastic flow.
Lubricated contact places other demands on the surface structure of the materials involved, and the main issue is to retain the protective lubrication thickness and avoid plastic deformation. This is important because plastic deformation raises the temperature of the oil or lubrication fluid and changes the viscosity. Any eventual material transfer or creation of protrusions above the original surface will also reduce the ability to retain a protective lubrication thickness. A proper protective lubrication thickness can be assisted or retained by:
* Surface cavities or small holes can create a favorable geometric situation for the oil to retain a protective lubrication thickness in the contact zone.
* Cohesive forces on the surface can increase the chemical attraction between the surface and lubricants and enhance the lubrication thickness.
* Oil additives may reduce the tendency for galling or adhesive wear. | 7 | Physical Chemistry |
The water in the sea was thought to come from the Earths volcanoes, starting 4 billion years ago, released by degassing from molten rock. More recent work suggests much of the Earths water may come from comets.
Scientific theories behind the origins of sea salt started with Sir Edmond Halley in 1715, who proposed that salt and other minerals were carried into the sea by rivers after rainfall washed it out of the ground. Upon reaching the ocean, these salts concentrated as more salt arrived over time (see Hydrologic cycle). Halley noted that most lakes that do not have ocean outlets (such as the Dead Sea and the Caspian Sea, see endorheic basin), have high salt content. Halley termed this process "continental weathering".
Halleys theory was partly correct. In addition, sodium leached out of the ocean floor when the ocean formed. The presence of salts other dominant ion, chloride, results from outgassing of chloride (as hydrochloric acid) with other gases from Earth's interior via volcanos and hydrothermal vents. The sodium and chloride ions subsequently became the most abundant constituents of sea salt.
Ocean salinity has been stable for billions of years, most likely as a consequence of a chemical/tectonic system which removes as much salt as is deposited; for instance, sodium and chloride sinks include evaporite deposits, pore-water burial, and reactions with seafloor basalts. | 9 | Geochemistry |
Within the CH group, commonly found in organic compounds, the two low mass hydrogens can vibrate in six different ways which can be grouped as 3 pairs of modes: 1. symmetric and asymmetric stretching, 2. scissoring and rocking, 3. wagging and twisting. These are shown here:
(These figures do not represent the "recoil" of the C atoms, which, though necessarily present to balance the overall movements of the molecule, are much smaller than the movements of the lighter H atoms). | 7 | Physical Chemistry |
The production of butanol by biological means was first performed by Louis Pasteur in 1861. In 1905, Austrian biochemist Franz Schardinger found that acetone could similarly be produced. In 1910 Auguste Fernbach (1860–1939) developed a bacterial fermentation process using potato starch as a feedstock in the production of butanol.
Industrial exploitation of ABE fermentation started in 1916, during World War I, with Chaim Weizmann's isolation of Clostridium acetobutylicum, as described in U.S. patent 1315585.
The Weizmann process was operated by Commercial Solvents Corporation from about 1920 to 1964 with plants in the US (Terre Haute, IN, and Peoria, IL), and Liverpool, England. The Peoria plant was the largest of the three. It used molasses as feedstock and had 96 fermenters with a volume of 96,000 gallons each.
After World War II, ABE fermentation became generally non-profitable, compared to the production of the same three solvents (acetone, butanol, ethanol) from petroleum. During the 1950s and 1960s, ABE fermentation was replaced by petroleum chemical plants. Due to different raw material costs, ABE fermentation was viable in South Africa until the early 1980s, with the last plant closing in 1983. Green Biologics Ltd operated the last attempt to resurrect the process at scale but the plant closed in Minnesota in June 2019.
A new ABE biorefinery has been developed in Scotland by Celtic Renewables Ltd and will begin production in early 2022. The key difference in the process is the use of low value spent materials or residues from other processes removing the variable costs of raw feedstock crops and materials. | 1 | Biochemistry |
Chan King-ming earned his Bachelor of Science and Master of Philosophy degrees at the Chinese University of Hong Kong, and his doctoral degree from Memorial University of Newfoundland in St. John's, Newfoundland, Canada.
He is now director of the Environmental Science Program at the Chinese University of Hong Kong. He teaches many different courses including Current Environmental Issues, Biochemical Toxicology and Introduction to Environmental Science in the Environmental Science Program and Molecular Endocrinology in the Biochemistry Programme. Trained as a molecular biologist for his PhD and post-doctoral research, Professor Chan's research interests include gene regulation, aquatic toxicology, marine biotechnology and environmental biochemistry and environmental policy. Prof. Chan is also chairman of CUTA (Chinese University Teachers Association), trustee of Shaw College Board of trustees, Member of Assembly of Fellows, Shaw College, and warden of Hostel 2, Shaw College. | 1 | Biochemistry |
It can be advantageous to describe the aqueous phase in terms of molality instead of concentration. The molality of a solution does not change with , since it refers to the mass of the solvent. In contrast, the concentration does change with , since the density of a solution and thus its volume are temperature-dependent. Defining the aqueous-phase composition via molality has the advantage that any temperature dependence of the Henry's law constant is a true solubility phenomenon and not introduced indirectly via a density change of the solution. Using molality, the Henry solubility can be defined as
Here is used as the symbol for molality (instead of ) to avoid confusion with the symbol for mass. The SI unit for is mol/(kg·Pa). There is no simple way to calculate from , since the conversion between concentration and molality involves all solutes of a solution. For a solution with a total of solutes with indices , the conversion is:
where is the density of the solution, and are the molar masses. Here is identical to one of the in the denominator. If there is only one solute, the equation simplifies to
Henry's law is only valid for dilute solutions where and . In this case the conversion reduces further to
and thus | 7 | Physical Chemistry |
SahysMod accepts four different reservoirs of which three are in the soil profile:
:s: a surface reservoir,
:r: an upper (shallow) soil reservoir or root zone,
:x: an intermediate soil reservoir or transition zone,
:q: a deep reservoir or main aquifer.
The upper soil reservoir is defined by the soil depth, from which water can evaporate or be taken up by plant roots. It can be taken equal to the root zone. It can be saturated, unsaturated, or partly saturated, depending on the water balance. All water movements in this zone are vertical, either upward or downward, depending on the water balance. (In a future version of Sahysmod, the upper soil reservoir may be divided into two equal parts to detect the trend in the vertical salinity distribution.)
The transition zone can also be saturated, unsaturated or partly saturated. All flows in this zone are horizontal, except the flow to subsurface drains, which is radial.
If a horizontal subsurface drainage system is present, this must be placed in the transition zone, which is then divided into two parts: an upper transition zone (above drain level) and a lower transition zone (below drain level).
If one wishes to distinguish an upper and lower part of the transition zone in the absence of a subsurface drainage system, one may specify in the input data a drainage system with zero intensity.
The aquifer has mainly horizontal flow. Pumped wells, if present, receive their water from the aquifer only. The flow in the aquifer is determined in dependence of spatially varying depths of the aquifer, levels of the water table, and hydraulic conductivity.
SahysMod permits the introduction of phreatic (unconfined) and semi-confined aquifers. The latter may develop a hydraulic over or under pressure below the slowly permeable top-layer (aquitard). | 9 | Geochemistry |
Raoults law was first observed empirically and led François-Marie Raoult to postulate that the vapor pressure above an ideal mixture of liquids is equal to the sum of the vapor pressures of each component multiplied by its mole fraction. Taking compliance with Raoults Law as a defining characteristic of ideality in a solution, it is possible to deduce that the chemical potential of each component of the liquid is given by
where is the chemical potential in the pure state and is the mole fraction of component in the ideal solution. From this equation, other thermodynamic properties of an ideal solution may be determined. If the assumption that the vapor follows the ideal gas law is added, Raoult's law may be derived as follows.
If the system is ideal, then, at equilibrium, the chemical potential of each component must be the same in the liquid and gas states. That is,
Substituting the formula for chemical potential gives
as the gas-phase mole fraction depends on its fugacity, , as a fraction of the pressure in the reference state, .
The corresponding equation when the system consists purely of component in equilibrium with its vapor is
Subtracting these equations and re-arranging leads to the result
For the ideal gas, pressure and fugacity are equal, so introducing simple pressures to this result yields Raoult's law: | 7 | Physical Chemistry |
Isostructural chemical compounds have similar chemical structures. "Isomorphous" when used in the relation to crystal structures is not synonymous: in addition to the same atomic connectivity that characterises isostructural compounds, isomorphous substances crystallise in the same space group and have the same unit cell dimensions. The IUCR definition used by crystallographers is:
Examples include:
*I-Gold(I) bromide is isostructural with gold(I) chloride
*Borazine is isostructural with benzene
*Indium(I) bromide is isostructural with β-thallium(I) iodide and has a distorted rock salt structure.
Many minerals are isostructural when they differ only in the nature of a cation.
Compounds which are isoelectronic usually have similar chemical structures. For example, methane, CH, and the ammonium ion, NH, are isoelectric and are isostructural
as both have a tetrahedral structure. The C-H and N-H bond lengths are different and crystal structures are completely different because the ammonium ion only occurs in salts. | 4 | Stereochemistry |
In molecular orbital theory, the main alternative to valence bond theory, the molecular orbitals (MOs) are approximated as sums of all the atomic orbitals (AOs) on all the atoms; there are as many MOs as AOs. Each AO has a weighting coefficient c that indicates the AOs contribution to a particular MO. For example, in benzene, the MO model gives us 6 π MOs which are combinations of the 2p AOs on each of the 6 C atoms. Thus, each π MO is delocalized over the whole benzene molecule and any electron occupying' an MO will be delocalized over the whole molecule. This MO interpretation has inspired the picture of the benzene ring as a hexagon with a circle inside. When describing benzene, the VB concept of localized σ bonds and the MO concept of delocalized π orbitals are frequently combined in elementary chemistry courses.
The contributing structures in the VB model are particularly useful in predicting the effect of substituents on π systems such as benzene. They lead to the models of contributing structures for an electron-withdrawing group and electron-releasing group on benzene. The utility of MO theory is that a quantitative indication of the charge from the π system on an atom can be obtained from the squares of the weighting coefficient c on atom C. Charge q ≈ c. The reason for squaring the coefficient is that if an electron is described by an AO, then the square of the AO gives the electron density. The AOs are adjusted (normalized) so that AO = 1, and q ≈ (cAO) ≈ c. In benzene, q = 1 on each C atom. With an electron-withdrawing group q > 1 for an electron-releasing group. | 7 | Physical Chemistry |
Calthemite coralloids (also known as popcorn), can form on the underside of concrete structures and look very similar to those which occurs in caves. Coralloids can form by a number of different methods in caves, however on concrete the most common form is created when hyperalkaline solution seeps from fine cracks in concrete. Due to solution evaporation, deposition of calcium carbonate occurs before any drop can form. The resulting coralloids are small and chalky with a cauliflower appearance. | 8 | Metallurgy |
Benefits will be realised by pursuing two overarching goals:
* To determine global ocean distributions of selected trace elements and isotopes, and to evaluate the sources, sinks, and internal cycling of these species in order to characterise more completely the physical, chemical and biological processes regulating their distributions.
* To understand the response of trace element and isotope cycles to global change, to help predict the future and to improve chemical proxies for past changes in the ocean environment. | 9 | Geochemistry |
Various solutions have been proposed for the challenging problem of network motif (NM) discovery. These algorithms can be classified under various paradigms such as exact counting methods, sampling methods, pattern growth methods and so on. However, motif discovery problem comprises two main steps: first, calculating the number of occurrences of a sub-graph and then, evaluating the sub-graph significance. The recurrence is significant if it is detectably far more than expected. Roughly speaking, the expected number of appearances of a sub-graph can be determined by a Null-model, which is defined by an ensemble of random networks with some of the same properties as the original network.
Until 2004, the only exact counting method for NM detection was the brute-force one proposed by Milo et al.. This algorithm was successful for discovering small motifs, but using this method for finding even size 5 or 6 motifs was not computationally feasible. Hence, a new approach to this problem was needed.
Here, a review on computational aspects of major algorithms is given and their related benefits and drawbacks from an algorithmic perspective are discussed. | 1 | Biochemistry |
The unambiguous mechanism of the antigen transfer is still unknown. However, there are three possible ways: I. acquisition of mTEC apoptotic bodies, which could possibly be related with low mTEC lifespan II. acquisition of exosomes and III. acquisition via trogocytosis, how antigen transfer can be mediated.
There is also an evidence, that antigen transfer and therefore indirect presentation by thymic DCs are regulated by PGE activator Aire. | 1 | Biochemistry |
Modern research topics in solid-state physics include:
*High-temperature superconductivity
*Quasicrystals
*Spin glass
*Strongly correlated materials
*Two-dimensional materials
*Nanomaterials | 8 | Metallurgy |
The relation between mass concentration and density of a pure component (mass concentration of single component mixtures) is:
where is the density of the pure component, the volume of the pure component before mixing. | 3 | Analytical Chemistry |
In crystallography and the theory of infinite vertex-transitive graphs, the coordination sequence of a vertex is an integer sequence that counts how many vertices are at each possible distance from . That is, it is a sequence
where each is the number of vertices that are steps away from . If the graph is vertex-transitive, then the sequence is an invariant of the graph that does not depend on the specific choice of . Coordination sequences can also be defined for sphere packings, by using either the contact graph of the spheres or the Delaunay triangulation of their centers, but these two choices may give rise to different sequences.
As an example, in a square grid, for each positive integer , there are grid points that are steps away from the origin. Therefore, the coordination sequence of the square grid is the sequence
in which, except for the initial value of one, each number is a multiple of four.
The concept was proposed by Georg O. Brunner and Fritz Laves and later developed by Michael O'Keefe. The coordination sequences of many low-dimensional lattices and uniform tilings are known.
The coordination sequences of periodic structures are known to be quasi-polynomial. | 3 | Analytical Chemistry |
The litmus mixture has the CAS number 1393-92-6 and contains 10 to around 15 different dyes. All of the chemical components of litmus are likely to be the same as those of the related mixture known as orcein but in different proportions. In contrast with orcein, the principal constituent of litmus has an average molecular mass of 3300. Acid-base indicators on litmus owe their properties to a 7-hydroxyphenoxazone chromophore. Some fractions of litmus were given specific names including erythrolitmin (or erythrolein), azolitmin, spaniolitmin, leucoorcein, and leucazolitmin. Azolitmin shows nearly the same effect as litmus.
A recipe to make litmus out of the lichens, as outlined on a UC Santa Barbara website says: | 3 | Analytical Chemistry |
Organosulfur compounds can be classified according to the sulfur-containing functional groups, which are listed (approximately) in decreasing order of their occurrence. | 9 | Geochemistry |
3-Indolepropionic acid (IPA), or indole-3-propionic acid, has been studied for its therapeutic therapeutic value in the treatment of Alzheimer's disease. As of 2022 IPA shows potential in the treatment of this disease, though the therapeutic effect of IPA depends on dose and time of therapy initiation.
Though promising in some historical clinical trials, IPA is not clinically listed as a useful therapeutic in managing Alzheimer's as of 2023.
This compound endogenously produced by human microbiota and has only been detected in vivo when the species Clostridium sporogenes is present in the gastrointestinal tract. , C. sporogenes, which uses tryptophan to synthesize IPA, is the only species of bacteria known to synthesize IPA in vivo at levels which are subsequently detectable in the blood plasma of the host.
IPA is an even more potent scavenger of hydroxyl radicals than melatonin, the most potent scavenger of hydroxyl radicals that is synthesized by human enzymes. Similar to melatonin but unlike other antioxidants, it scavenges radicals without subsequently generating reactive and pro-oxidant intermediate compounds. In 2017, elevated concentrations of IPA in human blood plasma were found to be correlated with a lower risk of type 2 diabetes and higher consumption of fiber-rich foods. | 1 | Biochemistry |
The use of the chiral pool is illustrated by the synthesis of the anticancer drug paclitaxel (Taxol). The incorporation of the C10 precursor verbenone, a member of the chiral pool, makes the production of paclitaxel more efficient than most alternatives.
Chiral pool synthesis is used to build a part of epothilone (an alternative to paclitaxel) from readily available enantiopure (–)-pantolactone. | 0 | Organic Chemistry |
and , with constants and and rate equations ; and
The integrated rate equations are then ; and
One important relationship in this case is | 7 | Physical Chemistry |
Functional genomics is a field of molecular biology that attempts to describe gene (and protein) functions and interactions. Functional genomics make use of the vast data generated by genomic and transcriptomic projects (such as genome sequencing projects and RNA sequencing). Functional genomics focuses on the dynamic aspects such as gene transcription, translation, regulation of gene expression and protein–protein interactions, as opposed to the static aspects of the genomic information such as DNA sequence or structures. A key characteristic of functional genomics studies is their genome-wide approach to these questions, generally involving high-throughput methods rather than a more traditional "candidate-gene" approach. | 1 | Biochemistry |
Homogeneous metallocene catalysts, e.g., derived from or related to zirconocene dichloride introduced a level of microstructural control that was unavailable with heterogeneous systems. Metallocene catalysts are homogeneous single-site systems, implying that a uniform catalyst is present in the solution. In contrast, commercially important Ziegler-Natta heterogeneous catalysts contain a distribution of catalytic sites. The catalytic properties of single-site catalysts can be controlled by modification of the ligand. Initially ligand modifications focused on various cyclopentadienyl derivatives, but great diversity was uncovered through high throughput screening. These post-metallocene catalysts employ a range of chelating ligands, often including pyridine and amido (RN). These ligands are available in great diversity with respect to their steric and electronic properties. Such postmetallocene catalysts enabled the introduction of Chain shuttling polymerization. | 7 | Physical Chemistry |
In physical therapy, occupational therapy, and athletic training, a goniometer measures range of motion of limbs and joints of the body. These measurements help accurately track progress in a rehabilitation program. When a patient has decreased range of motion, a therapist assesses the joint before performing an intervention, and continues to use the tool to monitor progress. The therapist can take these range of motion measurements at any joint. They typically require knowledge about the anatomy of the body, particularly bony landmarks. For example, when measuring the knee joint, the therapist places the axis (point of rotation) on the lateral epicondyle of the femur, and lines up the stationary arm with the greater trochanter of the femur. Finally, the therapist lines up the moveable arm of the goniometer with the lateral malleolus of the fibula, and records a measurement using the degree scale on the circular portion of the tool. Reading accuracy is sometimes a problem with goniometers. Issues with the intra-measure (between measures) and inter-tester (between clinicians) reliability may increase as the experience of the examiner decreases. Some studies suggest that these errors can be anywhere between 5 and 10 degrees.
These goniometers come in different forms that some argue increase reliability. The universal standard goniometer is a plastic or metal tool with 1 degree increments. The arms are usually not longer than 12-inches, so it can be hard to accurately pinpoint the exact landmark for measurement. The telescopic-armed goniometer is more reliable—with a plastic circular axis like a classic goniometer, but with arms that extend to as long as two feet in either direction.
More recently in the twenty-first century, smartphone application developers have created mobile applications that provide the functions of a goniometer. These applications (such as Knee Goniometer and Goniometer Pro) use the accelerometers in phones to calculate joint angles. Recent research supports these applications and their devices as reliable and valid tools with as much accuracy as a universal goniometer.
Modern rehabilitative therapy motion capture systems perform goniometry at the very least measuring active range of motion. While in some cases accuracy may be inferior to a goniometer, measuring angles with a motion capture system is superior at measuring during dynamic, as opposed to static situations. Furthermore, using a traditional goniometer takes valuable time. In the clinical context, performing manual measurements takes valuable time and may not be practical. | 7 | Physical Chemistry |
The evolution of ATP synthase is thought to have been modular whereby two functionally independent subunits became associated and gained new functionality. This association appears to have occurred early in evolutionary history, because essentially the same structure and activity of ATP synthase enzymes are present in all kingdoms of life. The F-ATP synthase displays high functional and mechanistic similarity to the V-ATPase. However, whereas the F-ATP synthase generates ATP by utilising a proton gradient, the V-ATPase generates a proton gradient at the expense of ATP, generating pH values of as low as 1.
The F region also shows significant similarity to hexameric DNA helicases (especially the Rho factor), and the entire enzyme region shows some similarity to -powered T3SS or flagellar motor complexes. The αβ hexamer of the F region shows significant structural similarity to hexameric DNA helicases; both form a ring with 3-fold rotational symmetry with a central pore. Both have roles dependent on the relative rotation of a macromolecule within the pore; the DNA helicases use the helical shape of DNA to drive their motion along the DNA molecule and to detect supercoiling, whereas the αβ hexamer uses the conformational changes through the rotation of the γ subunit to drive an enzymatic reaction.
The motor of the F particle shows great functional similarity to the motors that drive flagella. Both feature a ring of many small alpha-helical proteins that rotate relative to nearby stationary proteins, using a potential gradient as an energy source. This link is tenuous, however, as the overall structure of flagellar motors is far more complex than that of the F particle and the ring with about 30 rotating proteins is far larger than the 10, 11, or 14 helical proteins in the F complex. More recent structural data do however show that the ring and the stalk are structurally similar to the F particle.
The modular evolution theory for the origin of ATP synthase suggests that two subunits with independent function, a DNA helicase with ATPase activity and a motor, were able to bind, and the rotation of the motor drove the ATPase activity of the helicase in reverse. This complex then evolved greater efficiency and eventually developed into today's intricate ATP synthases. Alternatively, the DNA helicase/ motor complex may have had pump activity with the ATPase activity of the helicase driving the motor in reverse. This may have evolved to carry out the reverse reaction and act as an ATP synthase. | 5 | Photochemistry |
Vitamin A receptor, Stimulated by retinoic acid 6 or STRA6 protein was originally discovered as a transmembrane cell-surface receptor for retinol-binding protein. STRA6 is unique as it functions both as a membrane transporter and a cell surface receptor, particularly as a cytokine receptor. In fact, STRA6 may be the first of a whole new class of proteins that might be known as "cytokine signaling transporters." STRA6 is primarily known as the receptor for retinol binding protein and for its relevance in the transport of retinol to specific sites such as the eye (Vitamin A). It does this through the removal of retinol (ROH) from the holo-Retinol Binding Protein (RBP) and transports it into the cell to be metabolized into retinoids and/or kept as a retinylester. As a receptor, after holo-RBP is bound, STRA6 activates the JAK/STAT pathway, resulting in the activation of transcription factor, STAT5. These two functions—retinol transporter and cytokine receptor—while using different pathways, are processes that depend on each other. | 1 | Biochemistry |
A recent study highlights the first report of thermo-responsive rare-earth elements (REE)-selective protein. The ELP and the REE-binding domain are genetically fused to form REE-selective and thermo-responsive genetically encoded ELP called RELP for the selective extraction and recovery of total REEs. RELP shows a selective and repeatable biosorption platform for REE recovery. The authors highlighted that technology can be adapted to recover other precious metals and commodities. | 7 | Physical Chemistry |
Vitamin D supplementation has been tentatively found to lead to a reduced risk of death in the elderly, but the effect has not been deemed pronounced, or certain enough, to make taking supplements recommendable. Other forms (vitamin D, alfacalcidol, and calcitriol) do not appear to have any beneficial effects with regard to the risk of death. High blood levels appear to be associated with a lower risk of death, but it is unclear if supplementation can result in this benefit. Both an excess and a deficiency in vitamin D appear to cause abnormal functioning and premature aging. The relationship between serum calcifediol concentrations and all-cause mortality is "U-shaped": mortality is elevated at high and low calcifediol levels, relative to moderate levels. Harm from vitamin D appears to occur at a lower vitamin D level in the black population than in the white population. | 1 | Biochemistry |
In his 1960 novel Trouble with Lichen, John Wyndham gives the name Lichenin to a biochemical extract of lichen used to extend life expectancy beyond 300 years. | 1 | Biochemistry |
Organotantalum reagents arise via transmetalation of organotin compounds with tantalum(V) chloride. These organotantalum reagents promote the conjugate allylation of enones. Although the direct allylation of carbonyl groups is prevalent throughout the literature, little has been reported on the conjugate allylation of enones. | 0 | Organic Chemistry |
The cam is actuated by a user by rotating the handle, causing a cam to lift the weight and let it fall freely on the frame attached to the ram head. This produces a standard compacting action to a pre-measured amount of sand. Demonstration of this apparatus can be seen here:
Variety of standard specimen for Green Sand and Silicate based (CO)sand are prepared using a sand rammer along with accessories
The object for producing the standard cylindrical specimen is to have the specimen become 2 inches high (plus or minus 1/32 inch) with three rams of the machine. After the specimen has been prepared inside the specimen tube, the specimen can be used for various standard sand tests such as the permeability test, the green sand compression test, the shear test, or other standard foundry tests.
The sand rammer machine can be used to measure compactability of prepared sand by filling the specimen tube with prepared sand so that it is level with the top of the tube. The tube is then placed under the ram head in the shallow cup and rammed three times. Compactability in percentage is then calculated from the resultant height of the sand inside the specimen tube.
A rammer is mounted on a base block on a solid foundation, which provides vibration damping to ensure consistent ramming. | 8 | Metallurgy |
Gene silencing techniques have been widely used by researchers to study genes associated with disorders. These disorders include cancer, infectious diseases, respiratory diseases, and neurodegenerative disorders. Gene silencing is also currently being used in drug discovery efforts, such as synthetic lethality, high-throughput screening, and miniaturized RNAi screens. | 1 | Biochemistry |
The Ostwald law of dilution provides a satisfactory description of the concentration dependence of the conductivity of weak electrolytes like CHCOOH and NHOH. The variation of molar conductivity is essentially due to the incomplete dissociation of weak electrolytes into ions.
For strong electrolytes, however, Lewis and Randall recognized that the law fails badly since the supposed equilibrium constant is actually far from constant. This is because the dissociation of strong electrolytes into ions is essentially complete below a concentration threshold value. The decrease in molar conductivity as a function of concentration is actually due to attraction between ions of opposite charge as expressed in the Debye-Hückel-Onsager equation and later revisions.
Even for weak electrolytes the equation is not exact. Chemical thermodynamics shows that the true equilibrium constant is a ratio of thermodynamic activities, and that each concentration must be multiplied by an activity coefficient. This correction is important for ionic solutions due to the strong forces between ionic charges. An estimate of their values is given by the Debye–Hückel theory at low concentrations. | 7 | Physical Chemistry |
In plants, algae, cyanobacteria, and phototrophic and chemoautotrophic Pseudomonadota (formerly proteobacteria), the enzyme usually consists of two types of protein subunit, called the large chain (L, about 55,000 Da) and the small chain (S, about 13,000 Da). The large-chain gene (rbcL) is encoded by the chloroplast DNA in plants. There are typically several related small-chain genes in the nucleus of plant cells, and the small chains are imported to the stromal compartment of chloroplasts from the cytosol by crossing the outer chloroplast membrane. The enzymatically active substrate (ribulose 1,5-bisphosphate) binding sites are located in the large chains that form dimers in which amino acids from each large chain contribute to the binding sites. A total of eight large chains (= four dimers) and eight small chains assemble into a larger complex of about 540,000 Da. In some Pseudomonadota and dinoflagellates, enzymes consisting of only large subunits have been found.
Magnesium ions () are needed for enzymatic activity. Correct positioning of in the active site of the enzyme involves addition of an "activating" carbon dioxide molecule (Carbon dioxide|) to a lysine in the active site (forming a carbamate). operates by driving deprotonation of the Lys210 residue, causing the Lys residue to rotate by 120 degrees to the trans conformer, decreasing the distance between the nitrogen of Lys and the carbon of . The close proximity allows for the formation of a covalent bond, resulting in the carbamate. is first enabled to bind to the active site by the rotation of His335 to an alternate conformation. is then coordinated by the His residues of the active site (His300, His302, His335), and is partially neutralized by the coordination of three water molecules and their conversion to OH. This coordination results in an unstable complex, but produces a favorable environment for the binding of . Formation of the carbamate is favored by an alkaline pH. The pH and the concentration of magnesium ions in the fluid compartment (in plants, the stroma of the chloroplast) increases in the light. The role of changing pH and magnesium ion levels in the regulation of RuBisCO enzyme activity is discussed below. Once the carbamate is formed, His335 finalizes the activation by returning to its initial position through thermal fluctuation. | 5 | Photochemistry |
In medicine, the partial pressure of carbon dioxide in arterial blood is called or PaCO. Measurement of in the systemic circulation indicates the effectiveness of ventilation at the lungs' alveoli, given the diffusing capacity of the gas. It is a good indicator of respiratory function and the closely related factor of acid–base homeostasis, reflecting the amount of acid in the blood (without lactic acid). Normal values for humans are in the range 35–45 mmHg. Values less than this may indicate hyperventilation and (if blood pH is greater than 7.45) respiratory alkalosis. Values greater than 45 mmHg may indicate hypoventilation, and (if blood pH is less than 7.35) respiratory acidosis. | 7 | Physical Chemistry |
* Bacteriophytochrome
* sensory bacteriorhodopsin
* Halorhodopsin
* Proteorhodopsin
* Cyanobacteriochrome | 1 | Biochemistry |
Phosphoribosylaminoimidazole carboxylase is a fusion protein in plants and fungi, but consists of two non-interacting proteins in bacteria, PurK and PurE.
The crystal structure of PurE indicates a unique quaternary structure that confirms the octameric nature of the enzyme. | 1 | Biochemistry |
Amination is the process by which an amine group is introduced into an organic molecule. This type of reaction is important because organonitrogen compounds are pervasive. | 0 | Organic Chemistry |
Burying biomass (such as trees) directly mimics the natural processes that created fossil fuels. The global potential for carbon sequestration using wood burial is estimated to be 10 ± 5 GtC/yr and largest rates in tropical forests (4.2 GtC/yr), followed by temperate (3.7 GtC/yr) and boreal forests (2.1 GtC/yr). In 2008, Ning Zeng of the University of Maryland estimated 65 GtC lying on the floor of the world's forests as coarse woody material which could be buried and costs for wood burial carbon sequestration run at 50 USD/tC which is much lower than carbon capture from e.g. power plant emissions. CO fixation into woody biomass is a natural process carried out through photosynthesis. This is a nature-based solution and suggested methods include the use of "wood vaults" to store the wood-containing carbon under oxygen-free conditions.
In 2022 a certification organization published methodologies for biomass burial. Other biomass storage proposals have included the burial of biomass deep underwater, including at the bottom of the Black Sea. | 5 | Photochemistry |
It was not until 1987 when two chemists, Hedrick and Schlemper, from the University of Freiburg proposed the use of phosphazene bases to speed up the reaction and lower the polydispersity index. Up until 2023, three different phosphazene bases have been used in PPA polymerization. Moreover, most of the published research articles describing PPA synthesis between 2008 and 2023 revolve around the usage of LAP, rendering it the most common and effective polymerization technique. | 7 | Physical Chemistry |
Milk lipids are secreted in a unique manner by lactocytes, which are specialized epithelial cells within the alveoli of the lactating mammary gland.
The process takes place in multiple stages. First, fat synthesized within the endoplasmic reticulum accumulates in droplets between the inner and outer phospholipid monolayers of the endoplasmic reticulum membrane. As these droplets increase in size, the two monolayers separate further and eventually pinch off. This leads to the surrounding of the droplet in a phospholipid monolayer that allows it to disperse within the aqueous cytoplasm. In the next stage, lipid droplets then migrate to the apical surface of the cell, where plasma membrane subsequently envelops the droplet and extrudes together with it. It fully encases the fat droplet in an additional bilayer of phospholipids. The milk fat globule thus released into the glandular lumen, measuring 3-6 μm in average diameter, is surrounded by a phospholipid trilayer containing associated proteins, carbohydrates, and lipids derived primarily from the membrane of the secreting lactocyte. This trilayer is collectively known as MFGM.
This secretion process occurs in all types of mammalian milk, including human and bovine. However, it is distinct from the lipid secretion mechanism used by all other non-mammary cells. That makes MFGM unique to milk and it is not present in non-dairy food products. | 1 | Biochemistry |
Liver of sulfur is a loosely defined mixture of potassium sulfide, potassium polysulfide, potassium thiosulfate, and likely potassium bisulfide. Synonyms include hepar sulfuris, sulfur, sulfurated potash and sulfurated potassa. There are two distinct varieties: "potassic liver of sulfur" and "ammoniacal liver of sulfur". | 7 | Physical Chemistry |
The adverse effect profile of mecillinam is similar to that of other penicillins. Its most common side effects are rash and gastrointestinal upset, including nausea and vomiting. | 4 | Stereochemistry |
Sliding ferroelectricity is widely found but only in two-dimensional (2D) van der Waals stacked layers. The vertical electric polarization is switched by in-plane interlayer sliding. | 7 | Physical Chemistry |
In cancerous cells, initiation factors assist in cellular transformation and development of tumors. The survival and growth of cancer is directly related to the modification of initiation factors and is used as a target for pharmaceuticals. Cells need increased energy when cancerous and derive this energy from proteins. Over-expression of initiation factors correlates with cancers, as they increase protein synthesis for proteins needed in cancers. Some initiation factors, such as eIF4E, are important in synthesizing specific proteins needed for the proliferation and survival of cancer. The careful selection of proteins ensures that proteins that are usually limited in translation and only proteins needed for cancer cell growth will be synthesized. This includes proteins involved in growth, malignancy, and angiogenesis. The eIF4E factor, along with eIF4A and eIF4G, also play a role in transitioning benign cancer cells to metastatic.
The largest initiation factor, eIF3, is another significant initiation factor in human cancers. Due to its role in creating the 43S pre-initiation complex, it helps to bind the ribosomal subunit to the mRNA. The initiation factor has been linked to cancers through over-expression. For example, one of the thirteen eIF3 proteins, eIF3c, interacts with and represses proteins used in tumor suppression. Limited expression of certain eIF3 proteins, such as eIF3a an eIF3d, has been proven to decrease the vigorous growth of cancer cells. The over-expression of eIF3a has been linked to breast, lung, cervix, esophagus, stomach, and colon cancers. It is prevalent during early stages of oncogenesis and likely selectively translates proteins needed for cell proliferation. When eIF3a is suppressed, it has shown to decrease the malignancy of breast and lung cancer, most likely due to its role in tumor growth. | 1 | Biochemistry |
Bis(trifluoromethanesulfonyl)aniline is the organic compound with the formula CHN(SOCF). It is a white solid. The compound is used to install the triflyl group (SOCF). Its behavior is akin to that of triflic anhydride, but milder. | 0 | Organic Chemistry |
* ATOMIC, MOLECULAR AND OPTICAL PHYSICS: NEW RESEARCH by L.T. Chen ; Nova Science Publishers, Inc. New York | 7 | Physical Chemistry |
He taught courses on General and Inorganic Chemistry, Photochemistry, Supramolecular chemistry. He was chairman of the PhD course on Chemical Sciences from 2002 to 2007 and of the “laurea specialistica” in Photochemistry and Material Chemistry from 2004 to 2007. In the Academic Year 2008–2009, he founded at the University of Bologna an interdisciplinary course on Science and Society. | 5 | Photochemistry |
In terms of representation theory, what has happened is that the two conjugate 2-dimensional spin representations of the spin group SU(2) = Spin(3) (as it sits inside the 3-dimensional Clifford algebra) have tensored to produce a 4-dimensional representation. The 4-dimensional representation descends to the usual orthogonal group SO(3) and so its objects are tensors, corresponding to the integrality of their spin. The 4-dimensional representation decomposes into the sum of a one-dimensional trivial representation (singlet, a scalar, spin zero) and a three-dimensional representation (triplet, spin 1) that is nothing more than the standard representation of SO(3) on . Thus the "three" in triplet can be identified with the three rotation axes of physical space. | 7 | Physical Chemistry |
A variety of different polymerization methods may be utilized for the synthesis of the polymer chains that make up hydrogels. Their properties depend on how these chains are crosslinked. | 7 | Physical Chemistry |
The optical activity (absorption and scattering of light) and hydrodynamic properties (translational diffusion, sedimentation coefficients, and rotational correlation times) of formamide denatured nucleic acids are similar to those of heat-denatured nucleic acids. Therefore, depending on the desired effect, chemically denaturing DNA can provide a gentler procedure for denaturing nucleic acids than denaturation induced by heat. Studies comparing different denaturation methods such as heating, beads mill of different bead sizes, probe sonication, and chemical denaturation show that chemical denaturation can provide quicker denaturation compared to the other physical denaturation methods described. Particularly in cases where rapid renaturation is desired, chemical denaturation agents can provide an ideal alternative to heating. For example, DNA strands denatured with alkaline agents such as NaOH renature as soon as phosphate buffer is added. | 1 | Biochemistry |
Benzene, toluene, and xylenes can be made by various processes. However, most BTX production is based on the recovery of aromatics derived from the catalytic reforming of naphtha in a petroleum refinery.
Catalytic reforming usually utilizes a feedstock naphtha that contains non-aromatic hydrocarbons with 6 to 12 carbon atoms and typically produces a reformate product containing C to C aromatics (benzene, toluene, xylenes) as well as paraffins and heavier aromatics containing 9 to 12 carbon atoms.
Another process for producing BTX aromatics involves the steam cracking of hydrocarbons which typically produces a cracked naphtha product commonly referred to as pyrolysis gasoline, pyrolysis gas or pygas. The pyrolysis gasoline typically consists of C to C aromatics, heavier aromatics containing 9 to 12 carbon atoms, and non-aromatic cyclic hydrocarbons (naphthenes) containing 6 or more carbon atoms.
The adjacent table compares the BTX content of pyrolysis gasoline produced at standard cracking severity or at medium cracking severity with the BTX content of catalytic reformate produced by either a continuous catalytic regenerative (CCR) reformer or by a semi-regenerative catalytic reformer. About 70 percent of the global production of benzene is by extraction from either reformate or pyrolysis gasoline.
The BTX aromatics can be extracted from catalytic reformate or from pyrolysis gasoline by many different methods. Most of those methods, but not all, involve the use of a solvent either for liquid-liquid extraction or extractive distillation. Many different solvents are suitable, including sulfolane (CHOS), furfural (CHO), tetraethylene glycol (CHO), dimethylsulfoxide (CHOS), and N-methyl-2-pyrrolidone (CHNO).
Below is a schematic flow diagram of one method, involving extractive distillation, for extraction of the BTX aromatics from a catalytic reformate:<br />
<br /> | 7 | Physical Chemistry |
The primary form of inorganic carbon that is fixed is carbon dioxide (CO). It is estimated that approximately 250 billion tons of carbon dioxide are converted by photosynthesis annually. The majority of the fixation occurs in terrestrial environments, especially the tropics. The gross amount of carbon dioxide fixed is much larger since approximately 40% is consumed by respiration following photosynthesis. Historically it is estimated that approximately 2×10 billion tons of carbon has been fixed since the origin of life. | 5 | Photochemistry |
The self-ionization of water was first proposed in 1884 by Svante Arrhenius as part of the theory of ionic dissociation which he proposed to explain the conductivity of electrolytes including water. Arrhenius wrote the self-ionization as . At that time, nothing was yet known of atomic structure or subatomic particles, so he had no reason to consider the formation of an ion from a hydrogen atom on electrolysis as any less likely than, say, the formation of a ion from a sodium atom.
In 1923 Johannes Nicolaus Brønsted and Martin Lowry proposed that the self-ionization of water actually involves two water molecules: . By this time the electron and the nucleus had been discovered and Rutherford had shown that a nucleus is very much smaller than an atom. This would include a bare ion which would correspond to a proton with zero electrons. Brønsted and Lowry proposed that this ion does not exist free in solution, but always attaches itself to a water (or other solvent) molecule to form the hydronium ion (or other protonated solvent).
Later spectroscopic evidence has shown that many protons are actually hydrated by more than one water molecule. The most descriptive notation for the hydrated ion is , where aq (for aqueous) indicates an indefinite or variable number of water molecules. However the notations and are still also used extensively because of their historical importance. This article mostly represents the hydrated proton as , corresponding to hydration by a single water molecule. | 7 | Physical Chemistry |
RA regulates gene transcription by binding to nuclear receptors known as retinoic acid receptors (RARs; RARα, RARβ, RARγ) which are bound to DNA as heterodimers with retinoid "X" receptors (RXRs; RXRα, RXRβ, RXRγ). RARs and RXRs must dimerize before they can bind to the DNA. Expression of more than 500 genes is responsive to retinoic acid. The process is that RAR-RXR heterodimers recognize retinoic acid response elements on DNA. The receptors undergo a conformational change that causes co-repressors to dissociate from the receptors. Coactivators can then bind to the receptor complex, which may help to loosen the chromatin structure from the histones or may interact with the transcriptional machinery. This response upregulates or downregulates the expression of target genes, including the genes that encode for the receptors themselves. To prevent excess accumulation of RA it must be metabolized and eliminated. Three cytochromes (Cyp26A1, Cyp26B1 Cyp26C1) catalyze the oxidation of RA. The genes for these proteins are induced by high concentrations of RA, thus providing a regulatory feedback mechanism. | 1 | Biochemistry |
Chemical warfare involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from nuclear warfare and biological warfare, which together make up NBC, the military initialism for Nuclear, Biological, and Chemical (warfare or weapons). None of these fall under the term conventional weapons, which are primarily effective because of their destructive potential. Chemical warfare does not depend upon explosive force to achieve an objective. It depends upon the unique properties of the chemical agent weaponized.
A lethal agent is designed to injure, incapacitate, or kill an opposing force, or deny unhindered use of a particular area of terrain. Defoliants are used to quickly kill vegetation and deny its use for cover and concealment. Chemical warfare can also be used against agriculture and livestock to promote hunger and starvation. Chemical payloads can be delivered by remote controlled container release, aircraft, or rocket. Protection against chemical weapons includes proper equipment, training, and decontamination measures. | 1 | Biochemistry |
Traditional virus diagnostic procedures are being replaced by sensitive immunoassays with lanthanides. The time resolved fluorescence based technique is generally applicable and its performance has also been tested in the assay of viral antigens in clinical specimens. | 1 | Biochemistry |
Products of carotenoid degradation such as ionones, damascones and damascenones are also important fragrance chemicals that are used extensively in the perfumes and fragrance industry. Both β-damascenone and β-ionone although low in concentration in rose distillates are the key odor-contributing compounds in flowers. In fact, the sweet floral smells present in black tea, aged tobacco, grape, and many fruits are due to the aromatic compounds resulting from carotenoid breakdown. | 5 | Photochemistry |
During sewage treatment, 5β-coprostanol may be converted to 5β-cholestan-3α-ol form, epi-coprostanol. There is also a slow conversion of 5β-coprostanol to epi-coprostanol in the environment and so this ratio will indicate either the degree of treatment of sewage or its age in the environment. A cross-plot of the 5β-coprostanol / cholesterol ratio with the epi-coprostanol / 5β-coprostanol can indicate both faecal contamination and treatment.<br /> | 2 | Environmental Chemistry |
The reaction rate varies depending upon what substances are reacting. Acid/base reactions, the formation of salts, and ion exchange are usually fast reactions. When covalent bond formation takes place between the molecules and when large molecules are formed, the reactions tend to be slower.
The nature and strength of bonds in reactant molecules greatly influence the rate of their transformation into products. | 7 | Physical Chemistry |
When the two bodies come in contact, surface deformation may occur on both bodies. This deformation may either be plastic or elastic, depending on the material properties and the contact pressure. When a surface undergoes plastic deformation, contact resistance is lowered, since the deformation causes the actual contact area to increase | 7 | Physical Chemistry |
In systematics, an ideotype is a specimen identified as belonging to a specific taxon by the author of that taxon, but collected from somewhere other than the type locality.
The concept of ideotype in plant breeding was introduced by Donald in 1968 to describe the idealized appearance of a plant variety. It literally means a form denoting an idea. According to Donald, an ideotype is a biological model which is expected to perform or behave in a particular manner within a defined environment: "a crop ideotype is a plant model, which is expected to yield a greater quantity or quality of grain, oil or other useful product when developed as a cultivar." Donald and Hamblin (1976) proposed the concepts of isolation, competition and crop ideotypes. Market ideotype, climatic ideotype, edaphic ideotype, stress ideotype and disease/pest ideotypes are its other concepts. The term ideotype has the following synonyms: model plant type, ideal model plant type and ideal plan type.
The term is also used in cognitive science and cognitive psychology, where Ronaldo Vigo (2011, 2013, 2014) introduced it to refer to a type of concept metarepresentation that is a compound memory trace consisting of the structural information detected by humans in categorical stimuli. | 1 | Biochemistry |
Related to the title concept are the ideas of a van der Waals volume, V, and a van der Waals surface area, abbreviated variously as A, vdWSA, VSA, and WSA.
A van der Waals surface area is an abstract conception of the surface area of atoms or molecules from a mathematical estimation, either computing it from first principles or by integrating over a corresponding van der Waals volume.
In simplest case, for a spherical monatomic gas, it is simply the computed surface area of a sphere of radius equal to the van der Waals radius of the gaseous atom:
The van der Waals volume, a type of atomic or molecular volume, is a property directly related to the van der Waals radius, and is defined as the volume occupied by an individual atom, or in a combined sense, by all atoms of a molecule.
It may be calculated for atoms if the van der Waals radius is known, and for molecules if its atoms radii and the inter-atomic distances and angles are known.
As above, in simplest case, for a spherical monatomic gas, V is simply the computed volume of a sphere of radius equal to the van der Waals radius of the gaseous atom:
For a molecule, V is the volume enclosed by the van der Waals surface; hence, computation of V presumes ability to describe and compute a van der Waals surface. van der Waals volumes of molecules are always smaller than the sum of the van der Waals volumes of their constituent atoms, due to the fact that the interatomic distances resulting from chemical bond are less than the sum of the atomic van der Waals radii.
In this sense, a van der Waals surface of a homonuclear diatomic molecule can be viewed as an pictorial overlap of the two spherical van der Waals surfaces of the individual atoms, likewise for larger molecules like methane, ammonia, etc. (see images).
van der Waals radii and volumes may be determined from the mechanical properties of gases (the original method, determining the van der Waals constant), from the critical point (e.g., of a fluid), from crystallographic measurements of the spacing between pairs of unbonded atoms in crystals, or from measurements of electrical or optical properties (i.e., polarizability or molar refractivity).
In all cases, measurements are made on macroscopic samples and results are expressed as molar quantities. van der Waals volumes of a single atom or molecules are arrived at by dividing the macroscopically determined volumes by the Avogadro constant.
The various methods give radius values which are similar, but not identical—generally within 1–2 Å (100–200 pm).
Useful tabulated values of van der Waals radii are obtained by taking a weighted mean of a number of different experimental values, and, for this reason, different tables will be seen to present different values for the van der Waals radius of the same atom.
As well, it has been argued that the van der Waals radius is not a fixed property of an atom in all circumstances, rather, that it will vary with the chemical environment of the atom. | 6 | Supramolecular Chemistry |
For polyatomic molecules, progressions are most often observed when the change in bond lengths upon electronic excitation coincides with the change due to a ″totally symmetric″ vibration. This is the same process that occurs in resonance Raman spectroscopy. For example, in formaldehyde (methanal), HCO, the n → π* transition involves excitation of an electron from a non-bonding orbital to an antibonding pi orbital which weakens and lengthens the C-O bond. This produces a long progression in the C-O stretching vibration. Another example is furnished by benzene, CH. In both gas and liquid phase the band around 250 nm shows a progression in the symmetric ring-breathing vibration.
As an example from inorganic chemistry the permanganate ion, , in aqueous solution has an intense purple colour due to an O → Mn ligand-to-metal charge transfer band (LMCT) in much of the visible region. This band shows a progression in the symmetric Mn-O stretching vibration. The individual lines overlap each other extensively, giving rise to a broad overall profile with some coarse structure.
Progressions in vibrations which are not totally symmetric may also be observed.
d-d electronic transitions in atoms in a centrosymmetric environment are electric-dipole forbidden by the Laporte rule. This will apply to octahedral coordination compounds of the transition metals. The spectra of many of these complexes have some vibronic character. The same rule also applies to f-f transitions in centrosymmetric complexes of lanthanides and actinides. In the case of the octahedral actinide chloro-complex of uranium(IV), UCl the observed electronic spectrum is entirely vibronic. At the temperature of liquid helium, 4K, the vibronic structure was completely resolved, with zero intensity for the purely electronic transition, and three side-lines corresponding to the asymmetric U-Cl stretching vibration and two asymmetric Cl-U-Cl bending modes. Later studies on the same anion were also able to account for vibronic transitions involving low-frequency lattice vibrations. | 7 | Physical Chemistry |
Thermal degradation of DOC has been found at high-temperature hydrothermal ridge-flanks, where outflow DOC concentrations are lower than in the inflow. While the global impact of these processes has not been investigated, current data suggest it is a minor DOC sink. Abiotic DOC flocculation is often observed during rapid (minutes) shifts in salinity when fresh and marine waters mix. Flocculation changes the DOC chemical composition, by removing humic compounds and reducing molecular size, transforming DOC to particulate organic flocs which can sediment and/or be consumed by grazers and filter feeders, but it also stimulates the bacterial degradation of the flocculated DOC. The impacts of flocculation on the removal of DOC from coastal waters are highly variable with some studies suggesting it can remove up to 30% of the DOC pool, while others find much lower values (3–6%;). Such differences could be explained by seasonal and system differences in the DOC chemical composition, pH, metallic cation concentration, microbial reactivity, and ionic strength. | 2 | Environmental Chemistry |
Imines are common ligands in coordination chemistry. Particularly popular examples are found with Schiff base ligands derived from salicylaldehyde, the salen ligands. Metal-catalyzed reactions of imines proceed through such complexes. In classical coordination complexes, imines bind metals through nitrogen. For low-valent metals, η-imine ligands are observed. | 0 | Organic Chemistry |
Adenylylation, more commonly known as AMPylation, is a process in which an adenosine monophosphate (AMP) molecule is covalently attached to the amino acid side chain of a protein. This covalent addition of AMP to a hydroxyl side chain of the protein is a post-translational modification. Adenylylation involves a phosphodiester bond between a hydroxyl group of the molecule undergoing adenylylation, and the phosphate group of the adenosine monophosphate nucleotide (i.e. adenylic acid). Enzymes that are capable of catalyzing this process are called AMPylators.
The known amino acids to be targeted in the protein are tyrosine and threonine, and sometimes serine. When charges on a protein undergo a change, it affects the characteristics of the protein, normally by altering its shape via interactions of the amino acids which make up the protein. AMPylation can have various effects on the protein. These are properties of the protein like, stability, enzymatic activity, co-factor binding, and many other functional capabilities of a protein. Another function of adenylylation is amino acids activation, which is catalyzed by tRNA aminoacyl synthetase. The most commonly identified protein to receive AMPylation are GTPases, and glutamine synthetase. | 1 | Biochemistry |
Nitric acid reacts with proteins to form yellow nitrated products. This reaction is known as the xanthoproteic reaction. This test is carried out by adding concentrated nitric acid to the substance being tested, and then heating the mixture. If proteins that contain amino acids with aromatic rings are present, the mixture turns yellow. Upon adding a base such as ammonia, the color turns orange. These color changes are caused by nitrated aromatic rings in the protein. Xanthoproteic acid is formed when the acid contacts epithelial cells. Respective local skin color changes are indicative of inadequate safety precautions when handling nitric acid. | 3 | Analytical Chemistry |
TMSCl is prepared on a large scale by the direct process, the reaction of methyl chloride with a silicon-copper alloy. The principal target of this process is dimethyldichlorosilane, but substantial amounts of the trimethyl and monomethyl products are also obtained. The relevant reactions are (Me = methyl, ):
Typically about 2–4% of the product stream is the monochloride, which forms an azeotrope with . | 0 | Organic Chemistry |
Generally the conductivity of a solution increases with temperature, as the mobility of the ions increases. For comparison purposes reference values are reported at an agreed temperature, usually 298 K (≈ 25 °C or 77 °F), although occasionally 20 °C (68 °F) is used. So called compensated measurements are made at a convenient temperature but the value reported is a calculated value of the expected value of conductivity of the solution, as if it had been measured at the reference temperature. Basic compensation is normally done by assuming a linear increase of conductivity versus temperature of typically 2% per kelvin. This value is broadly applicable for most salts at room temperature. Determination of the precise temperature coefficient for a specific solution is simple and instruments are typically capable of applying the derived coefficient (i.e. other than 2%).
Measurements of conductivity versus temperature can be used to determine the activation energy , using the Arrhenius equation:
where is the exponential prefactor, the gas constant, and the absolute temperature in Kelvin. | 7 | Physical Chemistry |
Fibulin (FY-beau-lin) (now known as Fibulin-1 FBLN1) is the prototypic member of a multigene family, currently with seven members. Fibulin-1 is a calcium-binding glycoprotein. In vertebrates, fibulin-1 is found in blood and extracellular matrices. In the extracellular matrix, fibulin-1 associates with basement membranes and elastic fibers. The association with these matrix structures is mediated by its ability to interact with numerous extracellular matrix constituents including fibronectin, proteoglycans, laminins and tropoelastin. In blood, fibulin-1 binds to fibrinogen and incorporates into clots.
Fibulins are secreted glycoproteins that become incorporated into a fibrillar extracellular matrix when expressed by cultured cells or added exogenously to cell monolayers. The five known members of the family share an elongated structure and many calcium-binding sites, owing to the presence of tandem arrays of epidermal growth factor-like domains. They have overlapping binding sites for several basement-membrane proteins, tropoelastin, fibrillin, fibronectin and proteoglycans, and they participate in diverse supramolecular structures. The amino-terminal domain I of fibulin consists of three anaphylatoxin-like (AT) modules, each approximately 40 residues long and containing four or six cysteines. The structure of an AT module was determined for the complement-derived anaphylatoxin C3a, and was found to be a compact alpha-helical fold that is stabilized by three disulphide bridges in the pattern Cys14, Cys25 and Cys36 (where Cys is cysteine). The bulk of the remaining portion of the fibulin molecule is a series of nine EGF-like repeats. | 1 | Biochemistry |
Chloramphenicol is a rare example of a naturally occurring nitro compound. At least some naturally occurring nitro groups arose by the oxidation of amino groups. 2-Nitrophenol is an aggregation pheromone of ticks.
Examples of nitro compounds are rare in nature. 3-Nitropropionic acid found in fungi and plants (Indigofera). Nitropentadecene is a defense compound found in termites. Aristolochic acids are found in the flowering plant family Aristolochiaceae. Nitrophenylethane is found in Aniba canelilla. Nitrophenylethane is also found in members of the Annonaceae, Lauraceae and Papaveraceae. | 0 | Organic Chemistry |
Yeast artificial chromosome are used as vectors to clone DNA fragments of more than 1 mega base (1Mb=1000kb) in size. They are useful in cloning larger DNA fragments as required in mapping genomes such as in the Human Genome Project. It contains a telomeric sequence, an autonomously replicating sequence (features required to replicate linear chromosomes in yeast cells). These vectors also contain suitable restriction sites to clone foreign DNA as well as genes to be used as selectable markers. | 1 | Biochemistry |
The Norrish reaction has been studied in relation to environmental chemistry with respect to the photolysis of the aldehyde heptanal, a prominent compound in Earth's atmosphere. Photolysis of heptanal in conditions resembling atmospheric conditions results in the formation of 1-pentene and acetaldehyde in 62% chemical yield together with cyclic alcohols (cyclobutanols and cyclopentanols) both from a Norrish type II channel and around 10% yield of hexanal from a Norrish type I channel (the initially formed n-hexyl radical attacked by oxygen).
In one study the photolysis of an acyloin derivative in water in presence of hydrogen tetrachloroaurate (HAuCl) generated nanogold particles with 10 nanometer diameter. The species believed to responsible for reducing Au to Au is the Norrish generated ketyl radical.
Leo Paquette's 1982 synthesis of dodecahedrane involves three separate Norrish-type reactions in its approximately 29-step sequence.
An example of a synthetically useful Norrish type II reaction can be found early in the total synthesis of the biologically active cardenolide ouabagenin by Phil Baran and coworkers. The optimized conditions minimize side reactions, such as the competing Norrish type I pathway, and furnish the desired intermediate in good yield on a multi-gram scale. | 5 | Photochemistry |
*[http://www-ssrl.slac.stanford.edu/absorb.html The SSRL Absorption Package] —
*[http://www.gwyndafevans.co.uk/chooch.html CHOOCH] —
*[http://www.hwi.buffalo.edu/SnB/ Shake-and-Bake] (SnB) —
*[http://shelx.uni-ac.gwdg.de/SHELX/ SHELX] — | 3 | Analytical Chemistry |
To conduct a topographic experiment, three groups of instruments are required: an x-ray source, potentially including appropriate x-ray optics; a sample stage with sample manipulator (diffractometer); and a two-dimensionally resolving detector (most often X-ray film or camera). | 3 | Analytical Chemistry |
-Photo-leucine is a synthetic derivative of the -leucine amino acid that is used as its natural analog and is characterized for having photo-reactivity, which makes it suitable for observing and characterizing protein-protein interactions (PPI). When a protein containing this amino acid (A) is exposed to
ultraviolet light while interacting with another protein (B), the complex formed from these two proteins (AB) remains attached and can be isolated for study.
Photo-leucine, as well as another photo-reactive amino acid derived from methionine, photo-methionine, were first synthesized in 2005 by Monika Suchanek, Anna Radzikoska and Christoph Thiele from the Max Planck Institute of Molecular Cell Biology and Genetics with the objective of identifying protein to protein interaction throughout a simple western blot test that would provide high specificity.
The resemblance of the photo-reactive amino acids to the natural ones allows the former ones to avoid the extensive control mechanisms that take place during the protein synthesis within the cell. | 5 | Photochemistry |
Two-color microarrays or two-channel microarrays are typically hybridized with cDNA prepared from two samples to be compared (e.g. diseased tissue versus healthy tissue) and that are labeled with two different fluorophores. Fluorescent dyes commonly used for cDNA labeling include Cy3, which has a fluorescence emission wavelength of 570 nm (corresponding to the green part of the light spectrum), and Cy5 with a fluorescence emission wavelength of 670 nm (corresponding to the red part of the light spectrum). The two Cy-labeled cDNA samples are mixed and hybridized to a single microarray that is then scanned in a microarray scanner to visualize fluorescence of the two fluorophores after excitation with a laser beam of a defined wavelength. Relative intensities of each fluorophore may then be used in ratio-based analysis to identify up-regulated and down-regulated genes.
Oligonucleotide microarrays often carry control probes designed to hybridize with RNA spike-ins. The degree of hybridization between the spike-ins and the control probes is used to normalize the hybridization measurements for the target probes. Although absolute levels of gene expression may be determined in the two-color array in rare instances, the relative differences in expression among different spots within a sample and between samples is the preferred method of data analysis for the two-color system. Examples of providers for such microarrays includes Agilent with their Dual-Mode platform, Eppendorf with their DualChip platform for colorimetric Silverquant labeling, and TeleChem International with Arrayit.
In single-channel microarrays or one-color microarrays, the arrays provide intensity data for each probe or probe set indicating a relative level of hybridization with the labeled target. However, they do not truly indicate abundance levels of a gene but rather relative abundance when compared to other samples or conditions when processed in the same experiment. Each RNA molecule encounters protocol and batch-specific bias during amplification, labeling, and hybridization phases of the experiment making comparisons between genes for the same microarray uninformative. The comparison of two conditions for the same gene requires two separate single-dye hybridizations. Several popular single-channel systems are the Affymetrix "Gene Chip", Illumina "Bead Chip", Agilent single-channel arrays, the Applied Microarrays "CodeLink" arrays, and the Eppendorf "DualChip & Silverquant". One strength of the single-dye system lies in the fact that an aberrant sample cannot affect the raw data derived from other samples, because each array chip is exposed to only one sample (as opposed to a two-color system in which a single low-quality sample may drastically impinge on overall data precision even if the other sample was of high quality). Another benefit is that data are more easily compared to arrays from different experiments as long as batch effects have been accounted for.
One channel microarray may be the only choice in some situations. Suppose samples need to be compared: then the number of experiments required using the two channel arrays quickly becomes unfeasible, unless a sample is used as a reference. | 1 | Biochemistry |
A positive balance is a result of energy intake being higher than what is consumed in external work and other bodily means of energy expenditure.
The main preventable causes are:
*Overeating, resulting in increased energy intake
*Sedentary lifestyle, resulting in decreased energy expenditure through external work
A positive balance results in energy being stored as fat and/or muscle, causing weight gain. In time, overweight and obesity may develop, with resultant complications. | 1 | Biochemistry |
** States: Dagestan, Kalmykia, Astrakhan Oblast
** Districts: North Caucasian Federal District, Southern Russia | 2 | Environmental Chemistry |
The equation parameter m, called the sensitivity factor of solvolysis, describes the compound’s ability to form the carbocation intermediate in given solvent system. It is the slope of the plot of log(k/k) vs Y values. Since the reference reaction has little solvent nucleophilic assistance, the reactions with m equal to 1 or larger than 1 have almost full ionized intermediates. If the compounds are not so sensitive to the ionizing ability of solvent, then the m values are smaller than 1. That is:
# m ≥ 1, the reactions proceed through S1 mechanism.
# m 1 and S2. | 7 | Physical Chemistry |
Suppose that a Hamiltonian is slowly time-varying, for example, a one-dimensional harmonic oscillator with a changing frequency:
The action J of a classical orbit is the area enclosed by the orbit in phase space:
Since J is an integral over a full period, it is only a function of the energy. When the Hamiltonian is constant in time, and J is constant in time, the canonically conjugate variable increases in time at a steady rate:
So the constant can be used to change time derivatives along the orbit to partial derivatives with respect to at constant J. Differentiating the integral for J with respect to J gives an identity that fixes :
The integrand is the Poisson bracket of x and p. The Poisson bracket of two canonically conjugate quantities, like x and p, is equal to 1 in any canonical coordinate system. So
and is the inverse period. The variable increases by an equal amount in each period for all values of J' it is an angle variable. | 7 | Physical Chemistry |
Intuitively, the slightly deformed eigenfunctions of the full Hamiltonian H are the in and out states. The are noninteracting states that resemble the in and out states in the infinite past and infinite future. | 7 | Physical Chemistry |
Biochar is charcoal created by pyrolysis of biomass waste. The resulting material is added to a landfill or used as a soil improver to create terra preta. Addition of pyrogenic organic carbon (biochar) is a novel strategy to increase the soil-C stock for the long term and to mitigate global warming by offsetting the atmospheric C (up to 9.5 Gigatons C annually). In the soil, the biochar carbon is unavailable for oxidation to and consequential atmospheric release. However concerns have been raised about biochar potentially accelerating release of the carbon already present in the soil.
Terra preta, an anthropogenic, high-carbon soil, is also being investigated as a sequestration mechanism. By pyrolysing biomass, about half of its carbon can be reduced to charcoal, which can persist in the soil for centuries, and makes a useful soil amendment, especially in tropical soils (biochar or agrichar). | 5 | Photochemistry |
Dai is editor of books including:
* Hai-Lung Dai, Robert W. Field (editors) (1995). [https://www.worldcat.org/oclc/31901502 Molecular dynamics and spectroscopy by stimulated emission pumping]. Singapore; New Jersey; London; Hong Kong: World Scientific. .
* Hai-Lung Dai, Wilson Ho (editors) (1995). [https://www.worldcat.org/oclc/32468614 Laser spectroscopy and photochemistry on metal surfaces]. Singapore; New Jersey; London; Hong Kong: World Scientific. . | 7 | Physical Chemistry |
The transposed Paternò−Büchi reaction involves a ππ* excited state of alkene reacting with a ground state carbonyl functionality. This is reversal of the traditional Paternò−Büchi reaction where an excited carbonyl group reacts with a ground state alkene. This strategy was first reported by Sivaguru and co-workers with reaction of enamides.
<br /> | 0 | Organic Chemistry |
In 1965, Rice and Whitehead published the seminal contribution to the theory of the transport of electrolyte solutions in long (ideally infinite) nanometer-diameter capillaries.
Briefly, the potential, ϕ, at a radial distance, r, is given by the Poisson-Boltzmann equation,
where κ is the inverse Debye length,
determined by the ion number density, n, the dielectric constant, ε, the Boltzmann constant, k, and the temperature, T. Knowing the potential, φ(r), the charge density can then be recovered from the Poisson equation, whose solution may be expressed as a modified Bessel function of the first kind, I, and scaled to the capillary radius, a. An equation of motion under combined pressure and electrically-driven flow can then be written,
where η is the viscosity, dp/dz is the pressure gradient, and F is the body force driven by the action of the applied electric field, E, on the net charge density in the double layer.
When there is no applied pressure, the radial distribution of the velocity is given by,
From the equation above, it follows that fluid flow in nanocapillaries is governed by the κa product, that is, the relative sizes of the Debye length and the pore radius.
By adjusting these two parameters and the surface charge density of the nanopores, fluid flow can be manipulated as desired. | 7 | Physical Chemistry |
Dissolved inorganic carbon (DIC) is the sum of the aqueous species of inorganic carbon in a solution. Carbon compounds can be distinguished as either organic or inorganic, and as dissolved or particulate, depending on their composition. Organic carbon forms the backbone of key component of organic compounds such as – proteins, lipids, carbohydrates, and nucleic acids.
Inorganic carbon is found primarily in simple compounds such as carbon dioxide, carbonic acid, bicarbonate, and carbonate (CO, HCO, , respectively). Dissolved inorganic carbon (DIC) includes three major aqueous species, CO, ,, and to a lesser extent their complexes in solution with metal ions. | 9 | Geochemistry |
Another class of high performance polymer frameworks with regular porosity and high surface area is based on triazine materials which can be achieved by dynamic trimerization reaction of simple, cheap, and abundant aromatic nitriles in ionothermal conditions (molten zinc chloride at high temperature (400 °C)). CTF-1 is a good example of this chemistry. | 6 | Supramolecular Chemistry |
The two forms of inorganic arsenic, reduced (trivalent As(III)) and oxidized (pentavalent As(V)), can be absorbed, and accumulated in tissues and body fluids. In the liver, the metabolism of arsenic involves enzymatic and non-enzymatic methylation; the most frequently excreted metabolite (≥ 90%) in the urine of mammals is dimethylarsinic acid or cacodylic acid, DMA(V). Dimethylarsenic acid is also known as Agent Blue and was used as herbicide in the American war in Vietnam.
In humans inorganic arsenic is reduced nonenzymatically from pentoxide to trioxide, using glutathione or it is mediated by enzymes. Reduction of arsenic pentoxide to arsenic trioxide increases its toxicity and bio availability, Methylation occurs through methyltransferase enzymes. S-adenosylmethionine (SAM) may serve as methyl donor. Various pathways are used, the principal route being dependent on the current environment of the cell. Resulting metabolites are monomethylarsonous acid, MMA(III), and dimethylarsinous acid, DMA(III).
Methylation had been regarded as a detoxification process, but reduction from +5 As to +3 As may be considered as a bioactivation instead. Another suggestion is that methylation might be a detoxification if "As[III] intermediates are not permitted to accumulate" because the pentavalent organoarsenics have a lower affinity to thiol groups than inorganic pentavalent arsenics. Gebel (2002) stated that methylation is a detoxification through accelerated excretion. With regard to carcinogenicity it has been suggested that methylation should be regarded as a toxification.
Arsenic, especially +3 As, binds to single, but with higher affinity to vicinal sulfhydryl groups, thus reacts with a variety of proteins and inhibits their activity. It was also proposed that binding of arsenite at nonessential sites might contribute to detoxification. Arsenite inhibits members of the disulfide oxidoreductase family like glutathione reductase and thioredoxin reductase.
The remaining unbound arsenic (≤ 10%) accumulates in cells, which over time may lead to skin, bladder, kidney, liver, lung, and prostate cancers. Other forms of arsenic toxicity in humans have been observed in blood, bone marrow, cardiac, central nervous system, gastrointestinal, gonadal, kidney, liver, pancreatic, and skin tissues.
The acute minimal lethal dose of arsenic in adults is estimated to be 70 to 200 mg or 1 mg/kg/day. | 1 | Biochemistry |
In the 1920s Davenport and Bain discovered a new steel microstructure which they provisionally called martensite-troostite, due to it being intermediate between the already known low-temperature martensite phase and what was then known as troostite (now fine-pearlite). This microstructure was subsequently named bainite by Bain's colleagues at the United States Steel Corporation, although it took some time for the name to be taken up by the scientific community with books as late as 1947 failing to mention bainite by name.
Bain and Davenport also noted the existence of two distinct forms: upper-range bainite which formed at higher temperatures and lower-range bainite which formed near the martensite start temperature (these forms are now known as upper- and lower-bainite respectively). The early terminology was further confused by the overlap, in some alloys, of the lower-range of the pearlite reaction and the upper-range of the bainite with the additional possibility of proeutectoid ferrite. | 8 | Metallurgy |
The European Union defines a VOC as "any organic compound as well as the fraction of creosote, having at 293.15 K a vapour pressure of 0,01 kPa or more, or having a corresponding volatility under the particular conditions of use;". The VOC Solvents Emissions Directive was the main policy instrument for the reduction of industrial emissions of volatile organic compounds (VOCs) in the European Union. It covers a wide range of solvent-using activities, e.g. printing, surface cleaning, vehicle coating, dry cleaning and manufacture of footwear and pharmaceutical products. The VOC Solvents Emissions Directive requires installations in which such activities are applied to comply either with the emission limit values set out in the Directive or with the requirements of the so-called reduction scheme. Article 13 of The Paints Directive, approved in 2004, amended the original VOC Solvents Emissions Directive and limits the use of organic solvents in decorative paints and varnishes and in vehicle finishing products. The Paints Directive sets out maximum VOC content limit values for paints and varnishes in certain applications. The Solvents Emissions Directive was replaced by the Industrial Emissions Directive from 2013. | 0 | Organic Chemistry |
Winemaking is legal in most countries. However, kilju is fermented from pure carbohydrates like white sugar (a plant extract) instead of grapes. | 1 | Biochemistry |
The hydrolysis of oximes proceeds easily by heating in the presence of various inorganic acids, and the oximes decompose into the corresponding ketones or aldehydes, and hydroxylamines. The reduction of oximes by sodium metal, sodium amalgam, hydrogenation, or reaction with hydride reagents produces amines. Typically the reduction of aldoximes gives both primary amines and secondary amines; however, reaction conditions can be altered (such as the addition of potassium hydroxide in a 1/30 molar ratio) to yield solely primary amines.
In general, oximes can be changed to the corresponding amide derivatives by treatment with various acids. This reaction is called Beckmann rearrangement. In this reaction, a hydroxyl group is exchanged with the group that is in the anti position of the hydroxyl group. The amide derivatives that are obtained by Beckmann rearrangement can be transformed into a carboxylic acid by means of hydrolysis (base or acid catalyzed). And an amine by Hoffman degradation of the amide in the presence of alkali hypoclorites. Beckmann rearrangement is used for the industrial synthesis of caprolactam (see applications below).
The Ponzio reaction (1906) concerning the conversion of m-nitrobenzaldoxime to m-nitrophenyldinitromethane using dinitrogen tetroxide was the result of research into TNT analogues:
In the Neber rearrangement certain oximes are converted to the corresponding alpha-amino ketones.
Oximes can be dehydrated using acid anhydrides to yield corresponding nitriles.
Certain amidoximes react with benzenesulfonyl chloride to make substituted ureas in the Tiemann rearrangement: | 0 | Organic Chemistry |
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