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Most studies to date have focused on the development of synthetic methodologies with the aim of maximizing pore size and surface area for gas storage. That means the functions of COFs have not yet been well explored, but COFs can be used as catalysts, or for gas separation, etc. | 0 | Theoretical and Fundamental Chemistry |
A ligand exchange (also called ligand substitution) is a chemical reaction in which a ligand in a compound is replaced by another. Two general mechanisms are recognized: associative substitution or by dissociative substitution.
Associative substitution closely resembles the S2 mechanism in organic chemistry. A typically smaller ligand can attach to an unsaturated complex followed by loss of another ligand. Typically, the rate of the substitution is first order in entering ligand L and the unsaturated complex.
Dissociative substitution is common for octahedral complexes. This pathway closely resembles the S1 mechanism in organic chemistry. The identity of the entering ligand does not affect the rate. | 0 | Theoretical and Fundamental Chemistry |
Compounds containing boron exhibit unique chemistry due to their having partially filled octets and therefore acting as Lewis acids. | 0 | Theoretical and Fundamental Chemistry |
While crystals were formed of Driesss diphosphagermylene, the X-ray structure diphosphagermylene could not be analyzed due to disordering. It has been suggested that the three lone pairs in Driesss diphosphagermylene system are composed of Ge (4s, 4p) and P (3s, 3p) valence orbitals. Driess calculated (MP2/DZ+POL//RHF/DZ+ZPE) the reaction profile for the isomerization of E(PH) (E = Si, Ge, Sn, Pb) from a σ-only, carbene-like system to a tautomer containing trivalent E with a π bond between E and phosphorus. The authors observed that the carbene-like form is preferred over its tautomer for silicon, germanium, tin, and lead analogues. | 0 | Theoretical and Fundamental Chemistry |
The resolution of DamID is a function of the availability of GATC sequences in the genome. A protein can only be mapped within two consecutive GATC sites. The median spacing between GATC fragments is 205 bp in Drosophila (FlyBase release 5), 260 in mouse (Mm9), and 460 in human (HG19). A modified protocol (DamIP), which combines immunoprecipitation of m6A with a Dam variant with less specific target site recognition, may be used to obtain higher resolution data. | 1 | Applied and Interdisciplinary Chemistry |
Water is said to "boil" when bubbles of water vapor grow without bound, bursting at the surface. For a vapor bubble to expand, the temperature must be high enough that the vapor pressure exceeds the ambient pressure (the atmospheric pressure, primarily). Below that temperature, a water vapor bubble will shrink and vanish.
Superheating is an exception to this simple rule; a liquid is sometimes observed not to boil even though its vapor pressure does exceed the ambient pressure. The cause is an additional force, the surface tension, which suppresses the growth of bubbles.
Surface tension makes the bubble act like an elastic balloon. The pressure inside is raised slightly by the "skin" attempting to contract. For the bubble to expand, the temperature must be raised slightly above the boiling point to generate enough vapor pressure to overcome both surface tension and ambient pressure.
What makes superheating so explosive is that a larger bubble is easier to inflate than a small one; just as when blowing up a balloon, the hardest part is getting started. It turns out the excess pressure due to surface tension is inversely proportional to the diameter of the bubble. That is, .
This can be derived by imagining a plane cutting a bubble into two halves. Each half is pulled towards the middle with a surface tension force , which must be balanced by the force from excess pressure . So we obtain , which simplifies to .
This means if the largest bubbles in a container are small, only a few micrometres in diameter, overcoming the surface tension may require a large , requiring exceeding the boiling point by several degrees Celsius. Once a bubble does begin to grow, the surface tension pressure decreases, so it expands explosively in a positive feedback loop. In practice, most containers have scratches or other imperfections which trap pockets of air that provide starting bubbles, and impure water containing small particles can also trap air pockets. Only a smooth container of purified liquid can reliably superheat. | 0 | Theoretical and Fundamental Chemistry |
Molecules whose framework forms a closed cage, like dodecahedrane and buckminsterfullerene, can encapsulate atoms and small molecules in the hollow space within. Those insertions are not chemically bonded to the caging compound, but merely mechanically trapped in it.
Cross, Saunders and Prinzbach succeeded in encapsulating helium atoms in dodecahedrane by shooting He ions at a film of the compound. They obtained microgram quantities of He@ (the "@" being the standard notation for encapsulation), which they described as a quite stable substance. The molecule has been described as "the world's smallest helium balloon". | 0 | Theoretical and Fundamental Chemistry |
Glaciers are large bodies of ice and snow formed in cold climates by processes involving the compaction of fallen snow. While snowy glaciers appear white from a distance, the long path lengths of internal reflected light causes glaciers to appear a deep blue when viewed up close and when shielded from direct ambient light.
Relatively small amounts of regular ice appear white because plenty of air bubbles are present, and also because small quantities of water appear to be colorless. In glaciers, on the other hand, the pressure causes the air bubbles, trapped in the accumulated snow, to be squeezed out increasing the density of the created ice. Large quantities of water appear cyan, therefore a large piece of compressed ice, or a glacier, would also appear cyan. | 0 | Theoretical and Fundamental Chemistry |
The chemical chameleon is a redox reaction, well known from classroom demonstrations, that exploits the dramatic color changes associated with the various oxidation states of manganese.
Glauber reported the first description of the production of potassium permanganate when he noted that manganese dioxide (as the mineral pyrolusite) could be reacted at high temperatures with alkali to obtain a material that dissolved in water to give a green solution which slowly shifted to a violet-red. This process, similar to that still used in the production of potassium permanganate, oxidized manganese dioxide to potassium manganate which, acidified by carbon dioxide absorbed from the air, oxidized further to purple potassium permanganate.
The chemical chameleon reaction shows the process in reverse, by reducing violet potassium permanganate first to green potassium manganate and eventually to brown manganese dioxide:
:KMnO (violet) → KMnO (green) → MnO (brown/yellow suspension)
Blue potassium hypomanganate may also form as an intermediate.
The reaction proceeds in alkaline conditions under the influence of a reducing agent. Sodium hydroxide, potassium hydroxide, and ammonium hydroxide can be used to alkalize the permanganate solution, while a variety of reducing agents can be used, sugars being common.
A similar demonstration involves soaking paper in alkalized permanganate solution, which produces the same color changes as the paper is oxidized and the permanganate reduced. | 1 | Applied and Interdisciplinary Chemistry |
* Southern blot for DNA
* northern blot for RNA
* reverse northern blot for RNA
* western blot for proteins
* far-western blot for protein–protein interactions
* eastern blot for post-translational modification
* far-eastern blot for glycolipids
* dot blot | 1 | Applied and Interdisciplinary Chemistry |
Peter Scott was born and grew up in North East England and attended Whitley Bay High School. He received his undergraduate degree with first class honors in medicinal and pharmaceutical chemistry from Loughborough University in 2001, after conducting research with Raymond Jones. He subsequently obtained his PhD in organic chemistry from Durham University in 2005, where he was a member of Ustinov College, under the mentorship of Patrick G. Steel. Scott then moved to the United States to undertake postdoctoral research in organometallic chemistry at SUNY Buffalo under Huw Davies, and PET radiochemistry at the University of Michigan with Michael Kilbourn. | 0 | Theoretical and Fundamental Chemistry |
Ilmenium was the proposed name for a new element found by the chemist R. Hermann in 1847. During the analysis of the mineral samarskite, he concluded that it does contain an element similar to niobium and tantalum. The similar reactivity of niobium and tantalum complicated preparation of pure samples of the metals and therefore several new elements were proposed, which were later found to be mixtures of niobium and tantalum.
The differences between tantalum and niobium, and the fact that no other similar element was present, were unequivocally demonstrated in 1864 by Christian Wilhelm Blomstrand, and Henri Etienne Sainte-Claire Deville, as well as Louis J. Troost, who determined the formulas of some of the compounds in 1865 and finally by the Swiss chemist Jean Charles Galissard de Marignac Although it had been proven that ilmenium is only a mixture of niobium and tantalum, Hermann continued publishing articles on ilmenium for several years.
The name "ilmenium" is a reference to the Ilmensky Mountains. | 1 | Applied and Interdisciplinary Chemistry |
Cell-specific DamID can also be achieved using recombination mediated excision of a transcriptional terminator cassette upstream of the Dam-fusion protein. The terminator cassette is flanked by FRT recombination sites which can be removed when combined with tissue specific expression of FLP recombinase. Upon removal of the cassette, the Dam-fusion is expressed at low levels under the control of a basal promoter. | 1 | Applied and Interdisciplinary Chemistry |
Check dams are a highly effective practice to reduce flow velocities in channels and waterways. In contrast to big dams, check dams are implemented faster, are cost effective, and are smaller in scope. Because of this, their implementation does not typically displace people and communities nor do they destroy natural resources if designed correctly. Moreover, the dams are simple to construct and do not rely on advanced technologies, allowing their use in rural communities with fewer resources or access to technical expertise, as they have been in India's drylands for some time now. | 1 | Applied and Interdisciplinary Chemistry |
M2DS is one of the several types of X-linked intellectual disability. The cause of M2DS is a duplication of the MECP2 or Methyl CpG binding protein 2 gene located on the X chromosome (Xq28). The MeCP2 protein plays a pivotal role in regulating brain function. Increased levels of MECP2 protein results in abnormal neural function and impaired immune system. Mutations in the MECP2 gene are also commonly associated with Rett syndrome in females. Advances in genetic testing and more widespread use of Array Comparative Genomic Hybridization has led to increased diagnosis of MECP2 duplication syndrome. It is thought to represent ~1% of X-linked male mental disability cases. Females affected by this condition often do not show symptoms. | 1 | Applied and Interdisciplinary Chemistry |
* Tenatoprazole
Tenatoprazole (TU-199), an imidazopyridine proton pump inhibitor, is a novel compound that has been designed as a new chemical entity with a substantially prolonged plasma half-life (7 hours), but otherwise has similar activity as other PPIs.
The difference in the structural backbone of tenatoprazole compared to benzimidazole PPIs, is its imidazo[4,5-b]pyridine moiety, which reduces the rate of metabolism, allowing a longer plasma residence time but also decreases the pKa of the fused imidazole N as compared to the current PPIs. Tenatoprazole has the same substituents as omeprazole, the methoxy groups at position 6 on the imidazopyridine and at position 4 on the pyridine part as well as two methyl groups at position 3 and 5 on the pyridine.
The bioavailability of tenatoprazole is double for the (S)-(−)-tenatoprazole sodium salt hydrate form when compared to the free form in dogs. This increased bioavailability is due to differences in the crystal structure and hydrophobic nature of the two forms, and therefore its more likely to be marketed as the pure (S)-(−)-enantiomer. | 1 | Applied and Interdisciplinary Chemistry |
The atmosphere of Venus is 96.5% carbon dioxide and 3.5% nitrogen. The surface pressure is 9.3 MPa (93 bar) and the surface temperature is 735 K, above the critical points of both major constituents and making the surface atmosphere a supercritical fluid.
The interior atmospheres of the solar system's gas giant planets are composed mainly of hydrogen and helium at temperatures well above their critical points. The gaseous outer atmospheres of Jupiter and Saturn transition smoothly into the dense liquid interior, while the nature of the transition zones of Neptune and Uranus is unknown. Theoretical models of extrasolar planet Gliese 876 d have posited an ocean of pressurized, supercritical fluid water with a sheet of solid high pressure water ice at the bottom. | 0 | Theoretical and Fundamental Chemistry |
In organic synthesis, reagent control is an approach to selectively forming one stereoisomer out of many, the stereoselectivity is determined by the structure and chirality of the reagent used. When chiral allylmetals are used for nucleophilic addition reaction to achiral aldehydes, the chirality of the newly generated alcohol carbon is determined by the chirality of the allymetal reagents (Figure 1). The chirality of the allymetals usually comes from the asymmetric ligands used. The metals in the allylmetal reagents include boron, tin, titanium, silicon, etc.
Various chiral ligands have been developed to prepare chiral allylmetals for the reaction with aldehydes. H. C. Brown was the first to report the chiral allylboron reagents for asymmetric allylation reactions with aldehydes. The chiral allylboron reagents were synthesized from the natural product (+)-a-pinene in two steps. The TADDOL ligands developed by Dieter Seebach has been used to prepare chiral allyltitanium compounds for asymmetric allylation with aldehydes. Jim Leighton has developed chiral allysilicon compounds in which the release of ring strain facilitated the stereoselective allylation reaction, 95% to 98% enantiomeric excess could be achieved for a range of achiral aldehydes. | 0 | Theoretical and Fundamental Chemistry |
In type III reactions, there is an electron transfer that occurs between the Sens* and the substrate resulting in an anionic Sens and a cationic substrate. Another electron transfer then occurs where the anionic Sens transfers an electron to O to form the superoxide anion, O. This transfer returns the Sens to its ground state. The superoxide anion and cationic substrate then interact to form the oxygenated product. | 0 | Theoretical and Fundamental Chemistry |
Zinc is extracted from the purified zinc sulfate solution by electrowinning, which is a specialized form of electrolysis. The process works by passing an electric current through the solution in a series of cells. This causes the zinc to deposit on the cathodes (aluminium sheets) and oxygen to form at the anodes. Sulfuric acid is also formed in the process and reused in the leaching process. Every 24 to 48 hours, each cell is shut down, the zinc-coated cathodes are removed and rinsed, and the zinc is mechanically stripped from the aluminium plates.
Electrolytic zinc smelters contain as many as several hundred cells. A portion of the electrical energy is converted into heat, which increases the temperature of the electrolyte. Electrolytic cells operate at temperature ranges from and at atmospheric pressure. A portion of the electrolyte is continuously circulated through the cooling towers both to cool and concentrate the electrolyte through evaporation of water. The cooled and concentrated electrolyte is then recycled to the cells. This process accounts for approximately one-third of all the energy usage when smelting zinc.
There are two common processes for electrowinning the metal: the low current density process, and the Tainton high current density process. The former uses a 10% sulfuric acid solution as the electrolyte, with current density of 270–325 amperes per square meter. The latter uses 22–28% sulfuric acid solution as the electrolyte with a current density of about 1,000 amperes per square metre. The latter gives better purity and has higher production capacity per volume of electrolyte, but has the disadvantage of running hotter and being more corrosive to the vessel in which it is done. In either of the electrolytic processes, each metric ton of zinc production expends about of electric power. | 1 | Applied and Interdisciplinary Chemistry |
This specific sulfinamide chiral auxiliary was initially developed by Jonathan A. Ellman, and its use has been explored extensively by his group. Thus, it is often referred to as Ellmans auxiliary or Ellmans sulfinamide. | 0 | Theoretical and Fundamental Chemistry |
The concept of retrometabolic drug design encompasses two distinct approaches. One approach is the design of soft drugs (SDs), new, active therapeutic agents, often isosteric or isolelectronic analogs of a lead compound, with a chemical structure specifically designed to allow predictable metabolism into inactive metabolites after exerting their desired therapeutic effect(s). The other approach is the design of chemical delivery systems (CDSs). CDSs are biologically inert molecules intended to enhance drug delivery to a particular organ or site and requiring several conversion steps before releasing the active drug.
Although both retrometabolic design approaches involve chemical modifications of the molecular structure and both require enzymatic reactions to fulfill drug targeting, the principles of SD and CDS design are distinctly different. While CDSs are inactive as administered and sequential enzymatic reactions provide the differential distribution and ultimately release the active drug, SDs are active as administered and are designed to be easily metabolized into inactive species. Assuming an ideal situation, with a CDS the drug is present at the site and nowhere else in the body because enzymatic processes destroy the drug at those sites. Whereas, CDSs are designed to achieve drug targeting at a selected organ or site, SDs are designed to afford a differential distribution that can be regarded as reverse targeting. | 1 | Applied and Interdisciplinary Chemistry |
Many of the first metal artifacts that archaeologists have identified have been tools or weapons, as well as objects used as ornaments such as jewellery. These early metal objects were made of the softer metals; copper, gold, and lead in particular, either as native metals or by thermal extraction from minerals, and softened by minimal heat (Craddock, 1995). While technology did advance to the point of creating surprisingly pure copper, most ancient metals are in fact alloys, the most important being bronze, an alloy of copper and tin. As metallurgical technology developed (hammering, melting, smelting, roasting, cupellation, moulding, smithing, etc.), more metals were intentionally included in the metallurgical repertoire.
By the height of the Roman Empire, metals in use included: silver, zinc, iron, mercury, arsenic, antimony, lead, gold, copper, tin (Healy 1978). As in the Bronze Age, metals were used based on many physical properties: aesthetics, hardness, colour, taste/smell (for cooking wares), timbre (instruments), resistance to corrosion, weight (i.e., density), and other factors. Many alloys were also possible, and were intentionally made in order to change the properties of the metal; e.g. the alloy of predominately tin with lead would harden the soft tin, to create pewter, which would prove its utility as cooking and tableware. | 1 | Applied and Interdisciplinary Chemistry |
In one of the syntheses, 7-aminocephalosporanic acid (7-ACA) is reacted with bromoacetyl chloride to give the amide. The halo group is then displaced by 4-thiopyridine. | 0 | Theoretical and Fundamental Chemistry |
*Calcium carbonate (limestone or chalk) decomposes into calcium oxide and carbon dioxide when heated. The chemical reaction is as follows:
::CaCO → CaO + CO
:The reaction is used to make quick lime, which is an industrially important product.
:Another example of thermal decomposition is 2Pb(NO) → 2PbO + O + 4NO.
*Some oxides, especially of weakly electropositive metals decompose when heated to high enough temperature. A classical example is the decomposition of mercuric oxide to give oxygen and mercury metal. The reaction was used by Joseph Priestley to prepare samples of gaseous oxygen for the first time.
*When water is heated to well over , a small percentage of it will decompose into OH, monatomic oxygen, monatomic hydrogen, O, and H.
*The compound with the highest known decomposition temperature is carbon monoxide at ≈3870 °C (≈7000 °F). | 0 | Theoretical and Fundamental Chemistry |
When an electron is the incident particle, the probability of inelastic scattering, depending on the energy of the incident electron, is usually smaller than that of elastic scattering. Thus in the case of gas electron diffraction (GED), reflection high-energy electron diffraction (RHEED), and transmission electron diffraction, because the energy of the incident electron is high, the contribution of inelastic electron scattering can be ignored. Deep inelastic scattering of electrons from protons provided the first direct evidence for the existence of quarks. | 0 | Theoretical and Fundamental Chemistry |
A photooxygenation is a light-induced oxidation reaction in which molecular oxygen is incorporated into the product(s). Initial research interest in photooxygenation reactions arose from Oscar Raab's observations in 1900 that the combination of light, oxygen and photosensitizers is highly toxic to cells. Early studies of photooxygenation focused on oxidative damage to DNA and amino acids, but recent research has led to the application of photooxygenation in organic synthesis and photodynamic therapy.
Photooxygenation reactions are initiated by a photosensitizer, which is a molecule that enters an excited state when exposed to light of a specific wavelength (e.g. dyes and pigments). The excited sensitizer then reacts with either a substrate or ground state molecular oxygen, starting a cascade of energy transfers that ultimately result in an oxygenated molecule. Consequently, photooxygenation reactions are categorized by the type and order of these intermediates (as type I, type II, or type III reactions). | 0 | Theoretical and Fundamental Chemistry |
The potential flow equation with well-posed boundary conditions applied is:
*Note that the integration term is evaluated only on the upper surface, while th integral term is evaluated on the upper and lower surfaces.
The continuous surface S may now be discretized into discrete panels. These panels will approximate the shape of the actual surface. This value of the various source and doublet terms may be evaluated at a convenient point (such as the centroid of the panel). Some assumed distribution of the source and doublet strengths (typically constant or linear) are used at points other than the centroid. A single source term s of unknown strength and a single doublet term m of unknown strength are defined at a given point.
where:
These terms can be used to create a system of linear equations which can be solved for all the unknown values of . | 1 | Applied and Interdisciplinary Chemistry |
Basic LIC images are grayscale images, without color and animation. While such LIC image conveys the orientation of the field vectors, it does not indicate their direction; for stationary fields, this can be remedied by animation. Basic LIC images do not show the length of the vectors (or the strength of the field). | 1 | Applied and Interdisciplinary Chemistry |
Finally, the potential at the center of each side is a natural function of the variables at the corner of that side. So, is a natural function of and , and is a natural function of and . | 0 | Theoretical and Fundamental Chemistry |
The chemical intuition suggests that the glycan-binding sites may be enriched in polar amino acid residues that form non-covalent interactions, such as hydrogen bonds, with polar carbohydrates. Indeed, a statistical analysis of carbohydrate-binding pockets shows that aspartic acid and asparagine residues are present twice as often as would be predicted by chance. Surprisingly, there is an even stronger preference for aromatic amino acids: tryptophan has a 9-fold increase in prevalence, tyrosine a 3-fold one, and histidine a 2-fold increase. It has been shown that the underlying force is the interaction between the aromatic system and the in carbohydrate as shown in Figure 1. The interaction is identified if the °, the distance (distance from to ) is less than 4.5Å. | 1 | Applied and Interdisciplinary Chemistry |
A variety of synthetic routes to acid have been developed. The first reported chemical syntheses approached HMB by oxidation of alkene, vicinal diol, and alcohol precursors:
* in 1877, Russian chemists Michael and Alexander Zaytsev reported the preparation of HMB by oxidation of 2-methylpent-4-en-2-ol with chromic acid (HCrO);
* in 1880 and 1889, Schirokoff and Reformatsky (respectively) reported that the oxidative cleavage of the vicinal diol 4-methylpentane-1,2,4-triol with acidified potassium permanganate (KMnO) yields HMB – this result is closest related to the first synthesis as cold dilute KMnO oxidises alkenes to vicinal cis-diols which hot acid KMnO further oxidises to carbonyl-containing compounds, and the diol intermediate is not obtained when hot acidic conditions are used for alkene oxidation. In other words, racemic 4-methylpentane-1,2,4-triol is a derivative of 2-methylpent-4-en-2-ol and β-hydroxy β-methylbutyric acid is a derivative of both; and,
* in 1892, Kondakow reported the preparation of HMB by permanganate oxidation of 3-methylbutane-1,3-diol.
Depending on the experimental conditions, cycloaddition of acetone and ketene produces either or 4,4-dimethyloxetan-2-one, both of which hydrolyze under basic conditions to yield the conjugate base of HMB. The haloform reaction provides another pathway to HMB involving the exhaustive halogenation of the methyl-ketone region of diacetone alcohol with sodium hypobromite or sodium hypochlorite; Diacetone alcohol is readily available from the aldol condensation of acetone. An organometallic approach to HMB involves the carboxylation of tert-butyl alcohol with carbon monoxide and Fentons reagent (hydrogen peroxide and ferrous iron). Alternatively, HMB can be prepared through microbial oxidation of acid by the fungus Galactomyces reessii'. | 1 | Applied and Interdisciplinary Chemistry |
In thermodynamics, a component is one of a collection of chemically independent constituents of a system. The number of components represents the minimum number of independent chemical species necessary to define the composition of all phases of the system.
Calculating the number of components in a system is necessary when applying Gibbs' phase rule in determination of the number of degrees of freedom of a system.
The number of components is equal to the number of distinct chemical species (constituents), minus the number of chemical reactions between them, minus the number of any constraints (like charge neutrality or balance of molar quantities). | 0 | Theoretical and Fundamental Chemistry |
Classical bioisosterism was originally formulated by James Moir and refined by Irving Langmuir as a response to the observation that different atoms with the same valence electron structure had similar biological properties.
For example, the replacement of a hydrogen atom with a fluorine atom at a site of metabolic oxidation in a drug candidate may prevent such metabolism from taking place. Because the fluorine atom is similar in size to the hydrogen atom the overall topology of the molecule is not significantly affected, leaving the desired biological activity unaffected. However, with a blocked pathway for metabolism, the drug candidate may have a longer half-life.
*Procainamide, an amide, has a longer duration of action than Procaine, an ester, because of the isosteric replacement of the ester oxygen with a nitrogen atom. Procainamide is a classical bioisostere because the valence electron structure of a disubstituted oxygen atom is the same as a trisubstituted nitrogen atom, as Langmuir showed.
Another example is seen in a series of anti-bacterial chalcones. By modifying certain substituents, the pharmacological activity of the chalcone and its toxicity are also modified. | 1 | Applied and Interdisciplinary Chemistry |
Phosphatidic acid consists of a glycerol backbone, with, in general, a saturated fatty acid bonded to carbon-1, an unsaturated fatty acid bonded to carbon-2, and a phosphate group bonded to carbon-3. | 1 | Applied and Interdisciplinary Chemistry |
Dissolving in seawater increases the hydrogen ion () concentration in the ocean, and thus decreases ocean pH, as follows:
In shallow coastal and shelf regions, a number of factors interplay to affect air-ocean exchange and resulting pH change. These include biological processes, such as photosynthesis and respiration, as well as water upwelling. Also, ecosystem metabolism in freshwater sources reaching coastal waters can lead to large, but local, pH changes.
Freshwater bodies also appear to be acidifying, although this is a more complex and less obvious phenomenon.
The absorption of CO from the atmosphere does not affect the ocean's alkalinity. This is important to know in this context as alkalinity is the capacity of water to resist acidification. Ocean alkalinity enhancement has been proposed as one option to add alkalinity to the ocean and therefore buffer against pH changes. | 0 | Theoretical and Fundamental Chemistry |
The traditional synthetic route uses Raney nickel and has been further improved over time, for example by the use of ibuprofen and AlCl.
Overall, it is a cost-effective method with moderate reaction conditions that is easy to handle and suitable for industrial production. | 0 | Theoretical and Fundamental Chemistry |
Vicat softening temperature or Vicat hardness is the determination of the softening point for materials that have no definite melting point, such as plastics. It is taken as the temperature at which the specimen is penetrated to a depth of by a flat-ended needle with a circular or square cross-section. For the Vicat A test, a load of is used. For the Vicat B test, the load is . It is named after the French engineer Louis Vicat.
Standards to determine Vicat softening point include ASTM D 1525 and ISO 306, which are largely equivalent.
The vicat softening temperature can be used to compare the heat-characteristics of different materials.
Four different methods may be used for testing.
ISO 10350 Note
ISO 10350 Vicat values are tested using the B50 method.
Similar Standards: ASTM D1525 | 0 | Theoretical and Fundamental Chemistry |
* Durable water repellent This being used for fabrics in order to protect them from water.
* Rain repellent This is made for car windshield for repelling rain water during rain in order to improve driving visibility. | 0 | Theoretical and Fundamental Chemistry |
Stable nucleic acid lipid particles (SNALPs) are microscopic particles approximately 120 nanometers in diameter, smaller than the wavelengths of visible light. They have been used to deliver siRNAs therapeutically to mammals in vivo. In SNALPs, the siRNA is surrounded by a lipid bilayer containing a mixture of cationic and fusogenic lipids, coated with diffusible polyethylene glycol. | 1 | Applied and Interdisciplinary Chemistry |
The Robinson oscillator is an electronic oscillator circuit originally devised for use in the field of continuous wave (CW) nuclear magnetic resonance (NMR). It was a development of the marginal oscillator. Strictly one should distinguish between the marginal oscillator and the Robinson oscillator, although sometimes they are conflated and referred to as a Robinson marginal oscillator. Modern magnetic resonance imaging (MRI) systems are based on pulsed (or Fourier transform) NMR; they do not rely on the use of such oscillators.
The key feature of a Robinson oscillator is a limiter in the feedback loop. This means that a square wave current, of accurately-fixed amplitude, is fed back to the tank circuit. The tank selects the fundamental of the square wave, which is amplified and fed back. This results in an oscillation with well-defined amplitude; the voltage across the tank circuit is proportional to its Q-factor.
The marginal oscillator has no limiter. It is arranged for the working point of one of the amplifier elements to operate at a nonlinear part of its characteristic and this determines the amplitude of oscillation. This is not as stable as the Robinson arrangement.
The Robinson oscillator was invented by British physicist Neville Robinson. | 0 | Theoretical and Fundamental Chemistry |
Proteolysis is widely used in biochemistry and cell biology to probe protein structure. In "limited trypsin proteolysis", low amounts of protease digest both folded and unfolded protein but at largely different rates: unstructured proteins are cut more rapidly, while structured proteins are cut at a slower rate (sometimes by orders of magnitude). Recently, several other assays of protein stability based on proteolysis have been proposed, exploiting other proteases with high specificity for cleaving unfolded proteins. These include Pulse Proteolysis, Proteolytic Scanning Calorimetry and FASTpp. | 1 | Applied and Interdisciplinary Chemistry |
Germanene is a material made up of a single layer of germanium atoms. The material is created in a process similar to that of silicene and graphene, in which high vacuum and high temperature are used to deposit a layer of germanium atoms on a substrate. High-quality thin films of germanene have revealed unusual two-dimensional structures with novel electronic properties suitable for semiconductor device applications and materials science research. | 0 | Theoretical and Fundamental Chemistry |
Bond strength and temperature certainly play important roles in the crystal grow process. For high bond strength, when atoms land on a surface, they tend to be closed to atomic surface clusters, which reduce total energy. This behavior results in many isolated cluster formations with a variety of size yielding a rough surface. Temperature, on the other hand, controls the high of the energy barrier.
Conclusion: high bond strength and low temperature is preferred to grow a smoothed surface. | 0 | Theoretical and Fundamental Chemistry |
The human leukocyte antigen (HLA) system, also referred to as the major histocompatibility complex (MHC), is a complex of genes important for the adaptive immune system. Mutations in the HLA complex have been associated with an increased risk of developing hypersensitivity reactions in response to certain medications. | 1 | Applied and Interdisciplinary Chemistry |
This piece is the larger part of the fragment broken during Bahadur Shah's reign. Henry Cousens (1902–03) measured its length as . Klaus Roessler (1995) found it to be long. It has a square cross-section. Roessler estimated its weight at .
In 1598, the Mughal emperor Akbars visit to Dhar was recorded on the pillar in form of a Persian language inscription. This piece also has some names and letters in Devanagari script. The names end in word Soni' ("goldsmith"), and seem to have been engraved while the original pillar was still intact. There are some other symbols and Persian characters scratched on the surface.
The autobiography of Akbars son Jahangir mentions that he saw this piece lying on ground in Dhar. He ordered it to be taken to Agra, intending to use it as a lamp post in the courtyard of Akbars tomb. It appears that Jahangir's orders were never carried out.
Until 1980, this piece lay in a sloping position against a masonry terrace. The local kids used it as a slide, because of which a large part of its surface gained a polished appearance. | 1 | Applied and Interdisciplinary Chemistry |
Installation of storage and pumps at residences may offset the intermittency of the water supply. Roof tanks are a common feature in countries where the water supply is intermittent. In Jordan, most houses have one or more ground or roof tanks. An intermittent supply can be supplemented with other non-piped sources such as packaged drinking and cooking water bought from local shops or delivered to the house. | 1 | Applied and Interdisciplinary Chemistry |
The Heart of Europe Bio-Crystallography Meeting (short HEC-Meeting) is an annual academic conference on structural biology, in particular protein crystallography. Researchers from universities, other research institutions and industry from Austria, Czech Republic, Germany and Poland meet to present and discuss current topics of their research. The talks are predominantly given by PhD students (doctoral students). An exception is the invited HEC lecture, which is held by a renowned scientist of the research field. The format of the HEC meeting has been adopted from the eleven years older [http://regiomeeting.eu/ Rhine-Knee Regional Meeting on Structural Biology]. | 1 | Applied and Interdisciplinary Chemistry |
The volume in the definition refers to the volume of the solution, not the volume of the solvent. One litre of a solution usually contains either slightly more or slightly less than 1 litre of solvent because the process of dissolution causes volume of liquid to increase or decrease. Sometimes the mass concentration is called titre. | 0 | Theoretical and Fundamental Chemistry |
Consider a particle under a force field that has a velocity parallel to the field direction and a speed proportional to the square of the magnitude of the electric field (any other non-linearity can be employed):
The effective mobility of the particle (the relationship between small changes in drift velocity with respect to small changes in electric field ) can be expressed in Cartesian coordinates as:
Combining (5), (6) and (7) we get:
Further consider the field E is applied in a plane and it rotates counter-clockwise at angular frequency , such that the field components are:
Substituting (10) and (11) in (8) and (9) and simplifying using trigonometric identities results in a sum of constant terms, sine and cosine, at angular frequency . The next calculations will be performed such that only the cosine terms at angular frequency will yield non-zero net drift velocity - therefore we need only evaluate these terms, which will be abbreviated and . The following is obtained:
Let and take the form of a small quadrupole field of intensity that varies in a sinusoidal manner proportional to such that:
Substituting (14) and (15) into (12) and (13) and taking the time average we obtain:
which can be summarized in vector notation to:
Equation (18) shows that for all positions the time averaged velocity is in the direction toward the origin (concentrating the particles towards the origin), with speed proportional to the mobility coefficient k, the strength of the rotating field E and the strength of the perturbing quadrupole field . | 1 | Applied and Interdisciplinary Chemistry |
Archaeological evidence has not revealed metal smelting or alloying of metals by pre-Columbian native peoples north of the Rio Grande; however, they did use native copper extensively. | 1 | Applied and Interdisciplinary Chemistry |
The effect of corrosion on a smooth-specimen S-N diagram is shown schematically on the right. Curve A shows the fatigue behavior of a material tested in air. A fatigue threshold (or limit) is seen in curve A, corresponding to the horizontal part of the curve. Curves B and C represent the fatigue behavior of the same material in two corrosive environments. In curve B, the fatigue failure at high stress levels is retarded, and the fatigue limit is eliminated. In curve C, the whole curve is shifted to the left; this indicates a general lowering in fatigue strength, accelerated initiation at higher stresses and elimination of the fatigue limit.
To meet the needs of advancing technology, higher-strength materials are developed through heat treatment or alloying. Such high-strength materials generally exhibit higher fatigue limits, and can be used at higher service stress levels even under fatigue loading. However, the presence of a corrosive environment during fatigue loading eliminates this stress advantage, since the fatigue limit becomes almost insensitive to the strength level for a particular group of alloys. This effect is schematically shown for several steels in the diagram on the left, which illustrates the debilitating effect of a corrosive environment on the functionality of high-strength materials under fatigue.
Corrosion fatigue in aqueous media is an electrochemical behavior. Fractures are initiated either by pitting or persistent slip bands. Corrosion fatigue may be reduced by alloy additions, inhibition and cathodic protection, all of which reduce pitting. Since corrosion-fatigue cracks initiate at a metals surface, surface treatments like plating, cladding, nitriding and shot peening were found to improve the materials resistance to this phenomenon. | 1 | Applied and Interdisciplinary Chemistry |
Sneaths index takes into account 134 categories of activity and structure. Dissimilarity index D is a percentage value of the sum of all properties not shared between two replaced amino acids. It is percentage value expressed by , where S' is Similarity. | 1 | Applied and Interdisciplinary Chemistry |
Let us consider the example of a system of charged particles subject to a constant external magnetic field: in this case the canonical time reversal operation that reverses the velocities and the time and keeps the coordinates untouched is no more a symmetry for the system. Under this consideration, it seems that only Onsager–Casimir reciprocal relations could hold; these equalities relate two different systems, one subject to and another to , and so their utility is limited. However, there was proved that it is possible to find other time reversal operations which preserve the dynamics and so Onsager reciprocal relations; in conclusion, one cannot state that the presence of a magnetic field always breaks T-symmetry. | 0 | Theoretical and Fundamental Chemistry |
The Darrieus–Landau instability or hydrodynamic instability is an instrinsic flame instability that occurs in premixed flames, caused by the density variation due to the thermal expansion of the gas produced by the combustion process. In simple terms, the stability inquires whether a steadily propagating plane sheet with a discontinuous jump in density is stable or not. It was predicted independently by Georges Jean Marie Darrieus and Lev Landau. Yakov Zeldovich notes that Lev Landau generously suggested this problem to him to investigate and Zeldovich however made error in calculations which led Landau himself to complete the work.
The instability analysis behind the Darrieus–Landau instability considers a planar, premixed flame front subjected to very small perturbations. It is useful to think of this arrangement as one in which the unperturbed flame is stationary, with the reactants (fuel and oxidizer) directed towards the flame and perpendicular to it with a velocity u1, and the burnt gases leaving the flame also in a perpendicular way but with velocity u2. The analysis assumes that the flow is an incompressible flow, and that the perturbations are governed by the linearized Euler equations and, thus, are inviscid. With these considerations, the main result of this analysis is that, if the density of the burnt gases is less than that of the reactants, which is the case in practice due to the thermal expansion of the gas produced by the combustion process, the flame front is unstable to perturbations of any wavelength. Another result is that the rate of growth of the perturbations is inversely proportional to their wavelength; thus small flame wrinkles (but larger than the characteristic flame thickness) grow faster than larger ones. In practice, however, diffusive and buoyancy effects that are not taken into account by the analysis of Darrieus and Landau may have a stabilizing effect. | 1 | Applied and Interdisciplinary Chemistry |
The Gouy-Chapman model fails for highly charged DLs. In 1924, Otto Stern suggested combining the Helmholtz model with the Gouy-Chapman model: in Stern's model, some ions adhere to the electrode as suggested by Helmholtz, giving an internal Stern layer, while some form a Gouy-Chapman diffuse layer.
The Stern layer accounts for ions finite size and consequently an ions closest approach to the electrode is on the order of the ionic radius. The Stern model has its own limitations, namely that it effectively treats ions as point charges, assumes all significant interactions in the diffuse layer are Coulombic, assumes dielectric permittivity to be constant throughout the double layer, and that fluid viscosity is constant plane. | 0 | Theoretical and Fundamental Chemistry |
How stereoselectivity is achieved in asymmetric nucleophilic epoxidations depends on the method employed. Covered here are various methods for the asymmetric nucleophilic epoxidation of electron-poor olefins. See below for a survey of the substrate scope of the reaction.
When chiral, non-racemic peroxides are used, the two transition states of epoxidation leading to enantiomeric products are diastereomeric. Steric interactions between the peroxide, enone, and templating cation M influence the sense of selectivity observed.
Methods that employ metal peroxides modified by chiral, non-racemic ligands operate by a similar mechanism in which the metal cation plays a templating role. Chiral zinc alkoxides under an oxygen atmosphere have been used to epoxidize some classes of enones (see equation (8) below). The evolution of ethane gas and uptake of oxygen are evidence for ligand exchange followed by oxidation of the intermediate zinc alkoxide species. A catalytic version of this transformation has been achieved using chiral zinc alkylperoxides.
Lithium, magnesium, and calcium alkylperoxides have also been employed as asymmetric nucleophilic epoxidation reagents. Simple tartrate and pseudoephedrine ligands are effective in combination with these metals; however, little detailed information about the precise mechanisms of these systems is known.
In combination with BINOL ligands and cumene hydroperoxide, lanthanide alkoxides can be used to epoxidize both trans and cis enones with high enantioselectivity. Studies of non-linear effects with these catalyst systems suggest that the active catalyst is oligomeric.
Homopolymers of amino acids (polypeptides) can also be used to effect enantioselective epoxidations in the presence of an enone and a peroxide. Structure-reactivity relationships have not emerged, but enantioselectivities in these reactions are often high, and polypeptides can often be used when other methods fail.
Phase-transfer catalysis of nucleophilic epoxidation is also possible using cinchona-based alkaloid catalysts. Phase-transfer methods allow some variability in the oxidant used: hydroperoxides, hydrogen peroxide, and hypochlorites have all been used with some success. | 0 | Theoretical and Fundamental Chemistry |
There are rigorous procedures in place to minimise the risk of accidental overexposure of radiation therapy to patients. However, mistakes do occasionally occur; for example, the radiation therapy machine Therac-25 was responsible for at least six accidents between 1985 and 1987, where patients were given up to one hundred times the intended dose; two people were killed directly by the radiation overdoses. From 2005 to 2010, a hospital in Missouri overexposed 76 patients (most with brain cancer) during a five-year period because new radiation equipment had been set up incorrectly.
Although medical errors are exceptionally rare, radiation oncologists, medical physicists and other members of the radiation therapy treatment team are working to eliminate them. In 2010 the American Society for Radiation Oncology (ASTRO) launched a safety initiative called [https://www.astro.org/Patient-Care-and-Research/Patient-Safety/Target-Safely Target Safely] that, among other things, aimed to record errors nationwide so that doctors can learn from each and every mistake and prevent them from recurring. ASTRO also publishes a list of questions for patients to ask their doctors about radiation safety to ensure every treatment is as safe as possible. | 0 | Theoretical and Fundamental Chemistry |
In physics, thermal contact conductance is the study of heat conduction between solid or liquid bodies in thermal contact. The thermal contact conductance coefficient, , is a property indicating the thermal conductivity, or ability to conduct heat, between two bodies in contact. The inverse of this property is termed thermal contact resistance. | 0 | Theoretical and Fundamental Chemistry |
"In vitro" is a latin phrase whose literal translation is "within the glass." This term is used in the English language to describe a process which occurs outside of a living organism. Within the context of muscle tissue engineering, the term "in vitro" applies to the seeding of cells into a biomaterial scaffold with growth factors and nutrients, then culturing these constructs until a functional construct, such as myofibres, is developed. These developed constructs are then implanted into the wound site with the expectation that they will continue to proliferate and integrate into host muscle tissue. The goal of in vitro muscle tissue engineering is to increase the functionality of the tissue before it is ever implanted into the body, thus increasing mechanical properties and potential to thrive in the host body.
Abdulghani & Mitchell describe in vitro muscle tissue engineering as a concept with utilizes the same basic strategies of in vivo tissue engineering. The difference between the two methods, however, is the development of a fully functional tissue engineered muscle graft (TEMG) that occurs in the in vitro technique. In vitro muscle tissue engineering includes the seeding of cells onto a biomaterial scaffold, but goes a step further by adding growth factors and biochemical and biophysical cues to promote cell growth, proliferation, differentiation, and finally regeneration into a functional muscle tissue construct. Typically, in vitro scaffolds contain specific surface features which guide the direction of cell proliferation. They are usually fibrous with aligned pores as these features encourage cell adhesion during regeneration. Beyond the types of scaffolds used in this technique, a largely important aspect of this technique is the electrical and mechanical stimulation which mimic the natural regeneration environment and encourage the expansion of intracellular communication pathways. Before TEMGs are introduced into the wound defect, they musts be vascularized to promote proper integration with the host tissue. To achieve vascularization, researchers typically seed a scaffold with multiple cell types in order to develop both muscle tissue and vascular pathways. This process prevents rejection of the TEMG upon implantation as it is able to effectively thrive in the host tissue environment. There is always a risk of immune rejection when implanting fully developed tissue, though, so this method tissue regeneration is the most closely monitored post-implantation.
The in vitro muscle tissue engineering technique is used to create muscle tissue with more successful functional and mechanical properties. According to Carnes & Pins in Skeletal Muscle Tissue Engineering: Biomaterials-Based Strategies for the Treatment of Volumetric Muscle Loss, this approach develops a microenvironment that is more conducive to enhancing tissue regeneration upon implantation, thus restoring full functionality to patients. | 1 | Applied and Interdisciplinary Chemistry |
Alkynylations, including the asymmetric variety, have been developed as metal-catalyzed reactions. Various catalytic additions of alkynes to electrophiles in water have also been developed. | 0 | Theoretical and Fundamental Chemistry |
The high pressure pump pushes water through the membrane. Typical pressures for brackish water range from 1.6 to 2.6 MPa (225 to 376 psi). In the case of seawater, they range from 5.5 to 8 MPa (800 to 1,180 psi). This requires substantial energy. Where energy recovery is used, part of the high pressure pump's work is done by the energy recovery device, reducing energy inputs. | 0 | Theoretical and Fundamental Chemistry |
22R-Hydroxycholesterol, or (3β)-cholest-5-ene-3,22-diol is an endogenous, metabolic intermediate in the biosynthesis of the steroid hormones from cholesterol. Cholesterol ((3β)-cholest-5-en-3-ol) is hydroxylated by cholesterol side-chain cleavage enzyme (P450scc) to form 22R-hydroxycholesterol, which is subsequently hydroxylated again by P450scc to form 20α,22R-dihydroxycholesterol, and finally the bond between carbons 20 and 22 is cleaved by P450scc to form pregnenolone ((3β)-3-hydroxypregn-5-en-20-one), the precursor to the steroid hormones.
It is an agonist of the liver X receptor. | 1 | Applied and Interdisciplinary Chemistry |
The old test was composed of two sections: a multiple-choice section consisting of 75 questions with five answer choices each, and a free-response section consisting of six essay prompts that required the authoring of chemical equations, solution of problems, and development of thoughtful essays in response to hypothetical scenarios.
* Section I, the multiple-choice portion, did allow the use of a calculator in 2023 exams, with additional reference material, other than a periodic table. Each question contained five answer choices or four. 90 minutes were allotted for the completion of Section I. Section I covered the breadth of the curriculum.
* Section II, the free response section, was divided into two sections: Part A, requiring the completion of three problems, and Part B, also containing three problems. Part A, lasting 55 minutes, allowed the use of calculators, Part B, lasting 40 minutes, also allowed for calculators. The first problem in Part A concerned equilibrium related to solubility, acids and bases, or pressure/concentration. The first question of Part B was a chemical equation question in which 3 scenarios were presented and the student was required to work all 3 scenarios, authoring a balanced net ionic chemical equation for each scenario and answering questions about the equations and scenarios. If time permitted, students may have edited their responses from Part A during the time allotted for responding to Part B, though without the use of a calculator. The student needed to have completed all six questions.
While the use of calculators was prohibited during Section I and Section II Part B, a periodic table, a list of selected standard reduction potentials, and two pages of equations and conventions are available for use during the entirety of Section II. | 1 | Applied and Interdisciplinary Chemistry |
Acylium ions are cations of the formula . The carbon–oxygen bond length in these cations is near 1.1 Å (110-112 pm), which is shorter than the 112.8 pm of carbon monoxide and indicates triple-bond character.
The carbon centres of acylium ions generally have a linear geometry and sp atomic hybridization, and are best represented by a resonance structure bearing a formal positive charge on the oxygen (rather than carbon): . They are characteristic fragments observed in EI-mass spectra of ketones.
Acylium ions are common reactive intermediates, for example in the Friedel–Crafts acylation and many other organic reactions such as the Hayashi rearrangement. Salts containing acylium ions can be generated by removal of the halide from acyl halides:
Acyl radicals are readily generated from aldehydes by hydrogen-atom abstraction. However, they undergo rapid decarbonylation to afford the alkyl radical:
Acyl anions are almost always unstable—usually too unstable to be exploited synthetically. They readily react with the neutral aldehyde to form an acyloin dimer. Hence, synthetic chemists have developed various acyl anion synthetic equivalents, such as dithianes, as surrogates. However, as a partial exception, hindered dialkylformamides (e.g., diisopropylformamide, HCONiPr) can undergo deprotonation at low temperature (−78 °C) with lithium diisopropylamide as the base to form a carbamoyl anion stable at these temperatures. | 0 | Theoretical and Fundamental Chemistry |
Pseudomonas aeruginosa is a known opportunistic pathogen. One of its virulence factors is its ability to produce pyocyanin, a toxin released to kill both microbes and mammalian cells alike. The pyocyanin production occurs when activated by PhoB. This implies that P. aeruginosa uses the low Pi as a signal that the host has been damaged and to start producing toxin to improve chances of its survival.
In contrast to P. aeruginosa, Vibrio cholerae has its toxin genes repressed by PhoB. It is thought that PhoB in V. cholerae is activated when Pi is low to prevent the production of toxins. It could be activated by other signals in the environment, but it has been shown that PhoB directly inhibits the toxins production by binding to the tcpPH promoter and stopping the ToxR regulon from being activated. Evidence supporting Pi as the signal is given by how the regulon is not repressed under high Pi conditions. The regulatory cascade is only repressed under low Pi conditions. | 1 | Applied and Interdisciplinary Chemistry |
The lower heating value (LHV; net calorific value; NCV, or lower calorific value; LCV) is another measure of available thermal energy produced by a combustion of fuel, measured as a unit of energy per unit mass or volume of substance. In contrast to the HHV, the LHV considers energy losses such as the energy used to vaporize water - although its exact definition is not uniformly agreed upon. One definition is simply to subtract the heat of vaporization of the water from the higher heating value. This treats any HO formed as a vapor that is released as a waste. The energy required to vaporize the water is therefore lost.
LHV calculations assume that the water component of a combustion process is in vapor state at the end of combustion, as opposed to the higher heating value (HHV) (a.k.a. gross calorific value or gross CV) which assumes that all of the water in a combustion process is in a liquid state after a combustion process.
Another definition of the LHV is the amount of heat released when the products are cooled to . This means that the latent heat of vaporization of water and other reaction products is not recovered. It is useful in comparing fuels where condensation of the combustion products is impractical, or heat at a temperature below cannot be put to use.
One definition of lower heating value, adopted by the American Petroleum Institute (API), uses a reference temperature of .
Another definition, used by Gas Processors Suppliers Association (GPSA) and originally used by API (data collected for API research project 44), is the enthalpy of all combustion products minus the enthalpy of the fuel at the reference temperature (API research project 44 used 25 °C. GPSA currently uses 60 °F), minus the enthalpy of the stoichiometric oxygen (O) at the reference temperature, minus the heat of vaporization of the vapor content of the combustion products.
The definition in which the combustion products are all returned to the reference temperature is more easily calculated from the higher heating value than when using other definitions and will in fact give a slightly different answer. | 0 | Theoretical and Fundamental Chemistry |
Current trends in organic chemistry include (as of 2020):
*Biocatalysis
*Catalysis
*Chemosensors
*Chiral synthesis
* Flow chemistry
* Green chemistry
*Mechanochemistry
*Photoredox catalysis | 0 | Theoretical and Fundamental Chemistry |
Adenoviral E1A-associated protein of 300kDa (p300) and the CREB-binding protein (CBP) make up the next family of HATs. This family of HATs contain HAT domains that are approximately 500 residues long and contain bromodomains as well as three cysteine-histidine rich domains that help with protein interactions. These HATs are known to acetylate all of the histone subunits in the nucleosome. They also have the ability to acetylate and mediate non-histone proteins involved in transcription and are also involved in the cell-cycle, differentiation and apoptosis. | 0 | Theoretical and Fundamental Chemistry |
Starting with
We can have these equations work for a moving medium by setting , where is the constant velocity that the whole fluid is moving at before being disturbed (equivalent to a moving observer) and is the fluid velocity.
In this case the equations look very similar:
Note that setting returns the equations at rest. | 1 | Applied and Interdisciplinary Chemistry |
Endoglin has been shown to interact with high affinity to TGF beta receptor 3 and TGF beta receptor 1, and with lower affinity to TGF beta receptor 2. It has high sequence similarity to another TGF beta binding protein, betaglycan, which was one of the first cues that indicated that endoglin is a TGF beta binding proteins. However, it has been shown that TGF beta binds with high affinity to only a small amount of the available endoglin, which suggests that there is another factor regulating this binding.
Endoglin itself doesnt bind the TGF beta ligands, but is present with the TGF beta receptors when the ligand is bound, indicating an important role for endoglin. The full length endoglin will bind to the TGF beta receptor complex whether TGF beta is bound or not, but the truncated forms of endoglin have more specific binding. The amino acid (aa) region 437–558 in the extracellular domain of endoglin will bind to TGF beta receptor II. TGF beta receptor I binds to the 437-588 aa region and to the aa region between 437 and the N-terminus. Unlike TGF beta receptor I which can only bind the cytoplasmic tail when its kinase domain is inactive, TGF beta receptor II can bind endoglin with an inactive and active kinase domain. The kinase is active when it is phosphorylated. Furthermore, TGF beta receptor I will dissociate from endoglin soon after it phosphorylates its cytoplasmic tail, leaving TGF beta receptor I inactive. Endoglin is constituitively phosphorylated at the serine and threonine residues in the cytoplasmic domain. The high interaction between endoglins cytoplasmic and extracellular tail with the TGF beta receptor complexes indicates an important role for endoglin in the modulation of the TGF beta responses, such as cellular localization and cellular migration.
Endoglin can also mediate F-actin dynamics, focal adhesions, microtubular structures, endocytic vesicular transport through its interaction with zyxin, ZRP-1, beta-arrestin and Tctex2beta, LK1, ALK5, TGF beta receptor II, and GIPC. In one study with mouse fibroblasts, the overexpression of endoglin resulted in a reduction of some ECM components, decreased cellular migration, a change in cellular morphology and intercellular cluster formation. | 1 | Applied and Interdisciplinary Chemistry |
The bodys generation of heat is known as thermogenesis and it can be measured to determine the amount of energy expended. BMR generally decreases with age, and with the decrease in lean body mass (as may happen with aging). Increasing muscle mass has the effect of increasing BMR. Aerobic (resistance) fitness level, a product of cardiovascular exercise, while previously thought to have effect on BMR, has been shown in the 1990s not to correlate with BMR when adjusted for fat-free body mass. But anaerobic exercise does increase resting energy consumption (see "aerobic vs. anaerobic exercise"). Illness, previously consumed food and beverages, environmental temperature, and stress levels can affect ones overall energy expenditure as well as one's BMR.
BMR is measured under very restrictive circumstances when a person is awake. An accurate BMR measurement requires that the person's sympathetic nervous system not be stimulated, a condition which requires complete rest. A more common measurement, which uses less strict criteria, is resting metabolic rate (RMR).
BMR may be measured by gas analysis through either direct or indirect calorimetry, though a rough estimation can be acquired through an equation using age, sex, height, and weight. Studies of energy metabolism using both methods provide convincing evidence for the validity of the respiratory quotient (RQ), which measures the inherent composition and utilization of carbohydrates, fats and proteins as they are converted to energy substrate units that can be used by the body as energy. | 1 | Applied and Interdisciplinary Chemistry |
Nicolas Dauphas (born December 10, 1975) is a planetary scientist and isotope geochemist. He is a professor of geochemistry and cosmochemistry in the Department of the Geophysical Sciences and Enrico Fermi Institute at the University of Chicago. Within cosmochemistry, his research focus is on isotope geochemistry. He studies the origin and evolution of planets and other objects in the solar system by analyzing the natural distributions of elements and their isotopes using mass spectrometers. | 0 | Theoretical and Fundamental Chemistry |
This type of carbon-concentrating mechanism (CCM) relies on a contained compartment within the cell into which is shuttled, and where RuBisCO is highly expressed. In many species, biophysical CCMs are only induced under low carbon dioxide concentrations. Biophysical CCMs are more evolutionary ancient than biochemical CCMs. There is some debate as to when biophysical CCMs first evolved, but it is likely to have been during a period of low carbon dioxide, after the Great Oxygenation Event (2.4 billion years ago). Low periods occurred around 750, 650, and 320–270 million years ago. | 0 | Theoretical and Fundamental Chemistry |
Prior to the widespread use of herbicides, cultural controls, such as altering soil pH, salinity, or fertility levels, were used to control weeds. Mechanical control including tillage and flooding were also used to control weeds. In the late 19th and early 20th centuries, inorganic chemicals such as sulfuric acid, arsenic, copper salts, kerosene and sodium chlorate were used to control weeds, but these chemicals were either toxic, flammable or corrosive and were expensive and ineffective at controlling weeds. | 1 | Applied and Interdisciplinary Chemistry |
* 1946 Harvard University: Instructor; 1948 Assistant Professor
* 1953 Columbia University: Associate Professor; 1955 Professor; 1967–1993 Eugene Higgins Professor; *1993 Professor Emeritus | 0 | Theoretical and Fundamental Chemistry |
In fluid dynamics, vortex stretching is the lengthening of vortices in three-dimensional fluid flow, associated with a corresponding increase of the component of vorticity in the stretching direction—due to the conservation of angular momentum.
Vortex stretching is associated with a particular term in the vorticity equation. For example, vorticity transport in an incompressible inviscid flow is governed by
where D/Dt is the material derivative. The source term on the right hand side is the vortex stretching term. It amplifies the vorticity when the velocity is diverging in the direction parallel to .
A simple example of vortex stretching in a viscous flow is provided by the Burgers vortex.
Vortex stretching is at the core of the description of the turbulence energy cascade from the large scales to the small scales in turbulence. In general, in turbulence fluid elements are more lengthened than squeezed, on average. In the end, this results in more vortex stretching than vortex squeezing. For incompressible flow—due to volume conservation of fluid elements—the lengthening implies thinning of the fluid elements in the directions perpendicular to the stretching direction. This reduces the radial length scale of the associated vorticity. Finally, at the small scales of the order of the Kolmogorov microscales, the turbulence kinetic energy is dissipated into heat through the action of molecular viscosity. | 1 | Applied and Interdisciplinary Chemistry |
PSD is usually defined by the method by which it is determined. The most easily understood method of determination is sieve analysis, where powder is separated on sieves of different sizes. Thus, the PSD is defined in terms of discrete size ranges: e.g. "% of sample between 45 μm and 53 μm", when sieves of these sizes are used. The PSD is usually determined over a list of size ranges that covers nearly all the sizes present in the sample. Some methods of determination allow much narrower size ranges to be defined than can be obtained by use of sieves, and are applicable to particle sizes outside the range available in sieves. However, the idea of the notional "sieve", that "retains" particles above a certain size, and "passes" particles below that size, is universally used in presenting PSD data of all kinds.
The PSD may be expressed as a "range" analysis, in which the amount in each size range is listed in order. It may also be presented in "cumulative" form, in which the total of all sizes "retained" or "passed" by a single notional "sieve" is given for a range of sizes. Range analysis is suitable when a particular ideal mid-range particle size is being sought, while cumulative analysis is used where the amount of "under-size" or "over-size" must be controlled.
The way in which "size" is expressed is open to a wide range of interpretations. A simple treatment assumes the particles are spheres that will just pass through a square hole in a "sieve". In practice, particles are irregular – often extremely so, for example in the case of fibrous materials – and the way in which such particles are characterized during analysis is very dependent on the method of measurement used. | 0 | Theoretical and Fundamental Chemistry |
Some countries use the International Maximum Residue Limits -Codex Alimentarius to define the residue limits; this was established by Food and Agriculture Organization of the United Nations (FAO) and World Health Organization (WHO) in 1963 to develop international food standards, guidelines codes of practices, and recommendation for food safety. Currently the CODEX has 185 Member Countries and 1 member organization (EU).
The following is the list of maximum residue limits (MRLs) for spices adopted by the commission. | 1 | Applied and Interdisciplinary Chemistry |
A quasistatic process is an idealized or fictive model of a thermodynamic "process" considered in theoretical studies. It does not occur in physical reality. It may be imagined as happening infinitely slowly so that the system passes through a continuum of states that are infinitesimally close to equilibrium. | 0 | Theoretical and Fundamental Chemistry |
Channelization has several predictable and negative effects. One of them is loss of wetlands. Wetlands are an excellent habitat for many forms of wildlife, and additionally serve as a "filter" for much of the worlds surface fresh water. Another is the fact that channelized streams are almost invariably straightened. For example, the channelization of Floridas Kissimmee River has been cited as a cause contributing to the loss of wetlands. This straightening causes the streams to flow more rapidly, which can, in some instances, vastly increase soil erosion. It can also increase flooding downstream from the channelized area, as larger volumes of water traveling more rapidly than normal can reach choke points over a shorter period of time than they otherwise would, with a net effect of flood control in one area coming at the expense of greatly aggravated flooding in another. In addition, studies have shown that stream channelization results in declines of river fish populations.
A 1971 study of the Chariton River in northern Missouri, United States, found that the channelized section of the river contained only 13 species of fish, whereas the natural segment of the stream was home to 21 species of fish. The biomass of fish able to be caught in the dredged segments of the river was 80 percent less than in the natural parts of the same stream. This loss of fish diversity and abundance is thought to occur because of reduction in habitat, elimination of riffles and pools, greater fluctuation of stream levels and water temperature, and shifting substrates. The rate of recovery for a stream once it has been dredged is extremely slow, with many streams showing no significant recovery 30 to 40 years after the date of channelization. | 1 | Applied and Interdisciplinary Chemistry |
Deflectors are generally wooden or rock structures installed at a bank toe and extending towards the center of a stream, in order to concentrate stream flow away from its banks. They can limit bank erosion and generate varying flow conditions in terms of depth and velocity, which can positively impact fish habitat. | 1 | Applied and Interdisciplinary Chemistry |
Electrolyte solutions are normally formed when salt is placed into a solvent such as water and the individual components dissociate due to the thermodynamic interactions between solvent and solute molecules, in a process called "solvation". For example, when table salt (sodium chloride), NaCl, is placed in water, the salt (a solid) dissolves into its component ions, according to the dissociation reaction
:NaCl → Na + Cl
It is also possible for substances to react with water, producing ions. For example, carbon dioxide gas dissolves in water to produce a solution that contains hydronium, carbonate, and hydrogen carbonate ions.
Molten salts can also be electrolytes as, for example, when sodium chloride is molten, the liquid conducts electricity. In particular, ionic liquids, which are molten salts with melting points below 100 °C, are a type of highly conductive non-aqueous electrolytes and thus have found more and more applications in fuel cells and batteries.
An electrolyte in a solution may be described as "concentrated" if it has a high concentration of ions, or "dilute" if it has a low concentration. If a high proportion of the solute dissociates to form free ions, the electrolyte is strong; if most of the solute does not dissociate, the electrolyte is weak. The properties of electrolytes may be exploited using electrolysis to extract constituent elements and compounds contained within the solution.
Alkaline earth metals form hydroxides that are strong electrolytes with limited solubility in water, due to the strong attraction between their constituent ions. This limits their application to situations where high solubility is required.
In 2021 researchers have found that electrolyte can "substantially facilitate electrochemical corrosion studies in less conductive media". | 0 | Theoretical and Fundamental Chemistry |
Another useful way of determining how many protons a carbon in a molecule is bonded to is to use an attached proton test (APT), which distinguishes between carbon atoms with even or odd number of attached hydrogens. A proper spin-echo sequence is able to distinguish between S, IS and IS, IS spin systems: the first will appear as positive peaks in the spectrum, while the latter as negative peaks (pointing downwards), while retaining relative simplicity in the spectrum since it is still broadband proton decoupled.
Even though this technique does not distinguish fully between CH groups, it is so easy and reliable that it is frequently employed as a first attempt to assign peaks in the spectrum and elucidate the structure. Additionally, signals from quaternary carbons and other carbons with no attached protons are still detectable, so in many cases an additional conventional C spectrum is not required, which is an advantage over DEPT. It is, however, sometimes possible that a CH and CH signal have coincidentally equivalent chemical shifts resulting in annulment in the APT spectrum due to the opposite phases. For this reason the conventional C{H} spectrum or HSQC are occasionally also acquired. | 0 | Theoretical and Fundamental Chemistry |
DEP is mainly used for characterising cells measuring the changes in their electrical properties. To do this, many techniques are available to quantify the dielectrophoretic response, as it is not possible to directly measure the DEP force.
These techniques rely on indirect measures, obtaining a proportional response of the strength and direction of the force that needs to be scaled to the model spectrum. So most models only consider the Clausius-Mossotti factor of a particle.
The most used techniques are collection rate measurements: this is the simplest and most used technique – electrodes are submerged in a suspension with a known concentration of particles and the particles that collect at the electrode are counted; crossover measurements: the crossover frequency between positive and negative DEP is measured to characterise particles – this technique is used for smaller particles (e.g. viruses), that are difficult to count with the previous technique; particle velocity measurements: this technique measures the velocity and direction of the particles in an electric field gradient; measurement of the levitation height: the levitation height of a particle is proportional to the negative DEP force that is applied. Thus, this technique is good for characterising single particles and is mainly used for larger particles such as cells; impedance sensing: particles collecting at the electrode edge have an influence on the impedance of the electrodes – this change can be monitored to quantify DEP.
In order to study larger populations of cells, the properties can be obtained by analysing the dielectrophoretic spectra. | 0 | Theoretical and Fundamental Chemistry |
Many chloroplast DNAs contain two inverted repeats, which separate a long single copy section (LSC) from a short single copy section (SSC).
While a given pair of inverted repeats are rarely completely identical, they are always very similar to each other, apparently resulting from concerted evolution.
The inverted repeats vary wildly in length, ranging from 4,000 to 25,000 base pairs long each and containing as few as four or as many as over 150 genes. Inverted repeats in plants tend to be at the upper end of this range, each being 20,000–25,000 base pairs long.
The inverted repeat regions are highly conserved among land plants, and accumulate few mutations. Similar inverted repeats exist in the genomes of cyanobacteria and the other two chloroplast lineages (glaucophyta and rhodophyceae), suggesting that they predate the chloroplast, though some chloroplast DNAs have since lost or flipped the inverted repeats (making them direct repeats). It is possible that the inverted repeats help stabilize the rest of the chloroplast genome, as chloroplast DNAs which have lost some of the inverted repeat segments tend to get rearranged more. | 0 | Theoretical and Fundamental Chemistry |
Stevens is the author or co-author of over 70 scientific publications and books. These include:
* Carly Stevens, The impact of atmospheric nitrogen deposition on grasslands: species composition and biogeochemistry, VDM Verlag, 2009. ISBN 978-3639144147
* Carly J Stevens, Nancy B Dise, J Owen Mountford, David J Gowing (2004) Impact of nitrogen deposition on the species richness of grasslands. Science 303 1876-1879 | 0 | Theoretical and Fundamental Chemistry |
Bacteria reproduce rapidly if conditions are right for growth. Most bacteria grow best in dark, warm, moist environments with food. When grown on solid media, some bacteria form colonies as they multiply which may grow large enough to be seen. By growing and counting colonies of fecal coliform bacteria from a sample of water, the amount of bacteria originally present can be determined.
Membrane filtration is the method of choice for the analysis of fecal coliforms in water. Samples to be tested are passed through a filter of particular pore size (generally 0.45 micrometre). The microorganisms present in the water remain on the filter surface. The filter is placed in a sterile Petri dish with a selective medium, growth of the desired organisms is encouraged, while other non-target organisms is suppressed. Each cell develops into a separate colony, which can be counted directly, and the initial inoculum size can be determined. Typically sample volumes of 100 ml will be used for water testing and filtered, with the goal of achieving a final desirable colony density range of 20 to 60 colonies per filter. Contaminated sources may require dilution to achieve a "countable" membrane. The filter is placed on a Petri dish containing M-FC agar and incubated for 24 hours at 44.5 °C (112.1 degrees F). This elevated temperature heat shocks non-fecal bacteria and suppresses their growth. As the fecal coliform colonies grow they produce an acid (through fermenting lactose) that reacts with the aniline dye in the agar thus giving the colonies their blue color.
Newer methods for coliform detection are based on specific enzyme substrates as indicators of coliforms. These assays make use of a sugar linked to a dye which, when acted on by the enzyme beta-galactosidase, produces a characteristic color. The enzyme beta-galactosidase is a marker for coliforms generally and may be assayed by hydrolysis of enzyme specific glycosides such as o-nitrophenyl-beta-D-galactose. Assays typically include a second sugar linked to a different dye which, when acted on by the enzyme beta-glucuronidase, produces a fluorescent product. Because E. coli produces both beta-galactosidase and beta-glucuronidase, a combination of two dyes makes it possible to differentiate and quantify coliforms and E. coli in the same pot.
More recently, the chemistry behind enzymatic detection compounds has been updated so that the indicating component is redox active, as opposed to the more usual chromogenic format, allowing fecal indicator bacteria such as E. coli and E. faecalis to be detected electrochemically without any sample pre-treatment. Since the colour of the detection compound is of no consequence, this allows detection in deeply coloured matrices. | 0 | Theoretical and Fundamental Chemistry |
Today, a muffle furnace is often a front-loading box-type oven or kiln for high-temperature applications such as fusing glass, creating enamel coatings, ceramics and soldering and brazing articles. They are also used in many research facilities, for example by chemists in order to determine what proportion of a sample is non-combustible and non-volatile (i.e., ash). Some models incorporate programmable digital controllers, allowing automatic execution of ramping, soaking, and sintering steps. Also, advances in materials for heating elements, such as molybdenum disilicide, can now produce working temperatures up to , which facilitate more sophisticated metallurgical applications. The heat source may be gas or oil burners, but more often they are now electric.
The term muffle furnace may also be used to describe another oven constructed on many of the same principles as the box-type kiln mentioned above, but takes the form of a long, wide, and thin hollow tube used in roll-to-roll manufacturing processes.
Both of the above-mentioned furnaces are usually heated to desired temperatures by conduction, convection, or blackbody radiation from electrical resistance heater elements. Therefore, there is (usually) no combustion involved in the temperature control of the system, which allows for much greater control of temperature uniformity and assures isolation of the material being heated from the byproducts of fuel combustion. | 1 | Applied and Interdisciplinary Chemistry |
In parallel kinetic resolution (PKR), a racemic mixture reacts to form two non-enantiomeric products, often through completely different reaction pathways. With PKR, there is no tradeoff between conversion and ee, as the formed products are not enantiomers. One strategy for PKR is to remove the less reactive enantiomer (towards the desired chiral catalyst) from the reaction mixture by subjecting it to a second set of reaction conditions that preferentially react with it, ideally with an approximately equal reaction rate. Thus, both enantiomers are consumed in different pathways at equal rates. PKR experiments can be stereodivergent, regiodivergent, or structurally divergent. One of the most highly efficient PKR's reported to date was accomplished by Yoshito Kishi in 1998; CBS reduction of a racemic steroidal ketone resulted in stereoselective reduction, producing two diastereomers of >99% ee, as shown below.
PKR have also been accomplished with the use of enzyme catalysts. Using the fungus Mortierella isabellina NRRL 1757, reduction of racemic β-ketonitriles affords two diastereomers, which can be separated and re-oxidized to give highly enantiopure β-ketonitriles.
Highly synthetically useful parallel kinetic resolutions have truly yet to be discovered, however. A number of procedures have been discovered that give acceptable ees and yields, but there are very few examples which give highly selective parallel kinetic resolution and not simply somewhat selective reactions. For example, Fus parallel kinetic resolution of 4-alkynals yields very enantioenriched cyclobutanone in low yield and slightly enantioenriched cyclopentenone, as shown below.
In theory, parallel kinetic resolution can give the highest ee's of products, since only one enantiomer gives each desired product. For example, for two complementary reactions both with s=49, 100% conversion would give products in 50% yield and 96% ee. These same values would require s=200 for a simple kinetic resolution. As such, the promise of PKR continues to attract much attention. The Kishi CBS reduction remains one of the few examples to fulfill this promise. | 0 | Theoretical and Fundamental Chemistry |
The underlying mechanisms that enable bioactive glasses to act as materials for bone repair have been investigated since the first work of Hench et al. at the University of Florida. Early attention was paid to changes in the bioactive glass surface. Five inorganic reaction stages are commonly thought to occur when a bioactive glass is immersed in a physiological environment:
# Ion exchange in which modifier cations (mostly Na) in the glass exchange with hydronium ions in the external solution.
# Hydrolysis in which Si-O-Si bridges are broken, forming Si-OH silanol groups, and the glass network is disrupted.
# Condensation of silanols in which the disrupted glass network changes its morphology to form a gel-like surface layer, depleted in sodium and calcium ions.
# Precipitation in which an amorphous calcium phosphate layer is deposited on the gel.
# Mineralization in which the calcium phosphate layer gradually transforms into crystalline hydroxyapatite, that mimics the mineral phase naturally contained with vertebrate bones.
Later, it was discovered that the morphology of the gel surface layer was a key component in determining the bioactive response. This was supported by studies on bioactive glasses derived from sol-gel processing. Such glasses could contain significantly higher concentrations of SiO than traditional melt-derived bioactive glasses and still maintain bioactivity (i.e., the ability to form a mineralized hydroxyapatite layer on the surface). The inherent porosity of the sol-gel-derived material was cited as a possible explanation for why bioactivity was retained, and often enhanced with respect to the melt-derived glass.
Subsequent advances in DNA microarray technology enabled an entirely new perspective on the mechanisms of bioactivity in bioactive glasses. Previously, it was known that a complex interplay existed between bioactive glasses and the molecular biology of the implant host, but the available tools did not provide a sufficient quantity of information to develop a holistic picture. Using DNA microarrays, researchers are now able to identify entire classes of genes that are regulated by the dissolution products of bioactive glasses, resulting in the so-called "genetic theory" of bioactive glasses. The first microarray studies on bioactive glasses demonstrated that genes associated with osteoblast growth and differentiation, maintenance of extracellular matrix, and promotion of cell-cell and cell-matrix adhesion were up-regulated by conditioned cell culture media containing the dissolution products of bioactive glass. | 0 | Theoretical and Fundamental Chemistry |
Examples of Fano resonances can be found in atomic physics, nuclear physics, condensed matter physics, electrical circuits, microwave engineering, nonlinear optics, nanophotonics, magnetic metamaterials, and in mechanical waves.
Fano can be observed with photoelectron spectroscopy and Raman spectroscopy. The phenomenon can be also observed at visible frequencies using simple glass microspheres, which may allow enhancing the magnetic field of light (which is typically small) by a few orders of magnitude. | 0 | Theoretical and Fundamental Chemistry |
Bose–Einstein condensation also applies to quasiparticles in solids. Magnons, excitons, and polaritons have integer spin which means they are bosons that can form condensates.
Magnons, electron spin waves, can be controlled by a magnetic field. Densities from the limit of a dilute gas to a strongly interacting Bose liquid are possible. Magnetic ordering is the analog of superfluidity. In 1999 condensation was demonstrated in antiferromagnetic , at temperatures as great as 14 K. The high transition temperature (relative to atomic gases) is due to the magnons' small mass (near that of an electron) and greater achievable density. In 2006, condensation in a ferromagnetic yttrium-iron-garnet thin film was seen even at room temperature, with optical pumping.
Excitons, electron-hole pairs, were predicted to condense at low temperature and high density by Boer et al., in 1961. Bilayer system experiments first demonstrated condensation in 2003, by Hall voltage disappearance. Fast optical exciton creation was used to form condensates in sub-kelvin in 2005 on.
Polariton condensation was first detected for exciton-polaritons in a quantum well microcavity kept at 5 K. | 0 | Theoretical and Fundamental Chemistry |
The use of organometallic structures led by π–metal bonding plays an enormous role in the catalysis of organic reactions. The Stille reaction is a widely known and important reaction in organic synthesis. π interactions with the Pd catalyst in this reaction are almost necessary in pushing this reaction to completion (alkyl groups transfer is rather slow).
Other widely known reactions based on π–metal catalysis interactions are:
*Heck reaction
*Hiyama coupling
*Kumada coupling
*Negishi coupling
*Petasis reaction
*Sonogashira coupling
*Suzuki reaction.
π–metal interactions can also be involved directly with the function of ligands on the catalyst. Chemistry involving nickel catalysis of Suzuki reactions was greatly affected by pyrazoles and pyrazolates acting as coplanar ligand. The π interactions tied multiple pyrazoles and pyrazolates together around the nickel metal to cause reaction results.
Another π metal interaction directly involved with catalysis involves π stacking. Ferrocene is the standard example where the metal (iron) is trapped in between two cyclopentadienyl ligands. These interactions are commonly referred to as sandwich compounds.
Specific research
Due to reasons explained earlier in the article, the bonding between a nucleophilic olefin and an electrophilic palladium(II) leaves olefin susceptible to nucleophilic attack. This is true if the olefin is coordinated around Pd as the corner of a square planar complex or as the side of a cationic 18-electron Pd complex. In both cases electron donating groups on the olefin stabilize the complex, but anionic electron donors actually destabilized the complex in the case of the 18-electron Pd complex. The authors of this research proposed that when the olefin π bond is aligned on the side of the square planar Pd complex, the π* backfilling of electron density from Pd to olefin is enhanced because the more electron withdrawing orbital of the π complex can overlap better with the electron donating orbital of Pd. | 0 | Theoretical and Fundamental Chemistry |
Antibody is famous for its high affinity and selectivity, so it is the good way to detect AMPylated proteins. Recently, ɑ- AMP antibodies is used to directly detect and isolate AMPylated proteins (especially AMPylated tyrosine and AMPylated threonine) from cells and cell lysates. AMPylation is a post-translational modification, so it will modify protein properties by giving the polar character of AMP and hydrophobicity. Thus, instead of using antibodies that detect a whole peptide sequence, raising AMP antibodies directly targeted to specific amino acids are preferred. | 1 | Applied and Interdisciplinary Chemistry |
Anti-Ro/SSA antibodies are found in 40–90% of patients with systematic lupus erythematosus (SLE). The antibodies can be detected years before symptoms of SLE surface, making them an effective diagnostic tool.
In patients with SLE, high levels of Anti-Ro/SSA are correlated with elevated levels of IFN-α. The presence of Anti-Ro/SSA antibodies also correlates with symptoms of photosensitivity, cutaneous vasculitis, and hematological disorders.
In individuals with cutaneous lupus erythematosus (CLE), a subcategory of lupus erythematosus, elevated levels of Ro52 are found regardless of expression of Anti-Ro autoantibodies. | 1 | Applied and Interdisciplinary Chemistry |
*NAS Award in Chemical Sciences
*Saul Winstein Endowed Chair in Organic Chemistry
*National Medal of Science, 1993
*International Academy of Science, Munich, member
*Glenn T. Seaborg Medal, 1989
*Golden Plate Award of the American Academy of Achievement, 1988
*ACS Southern California Tolman Award, 1984
*ACS Chicago Section Willard Gibbs Award, 1985
*ACS Cope Award for Distinguished Achievement in Organic Chemistry, 1974
*American Academy of Arts and Sciences, member, 1967
*American Chemical Society Award for Creative Work in Synthetic Organic Chemistry, 1965
*National Academy of Sciences, member, 1961
*1987 Nobel Prize in Chemistry | 0 | Theoretical and Fundamental Chemistry |
Besides pzc, iep, and cip, there are also numerous other terms used in the literature, usually expressed as initialisms, with identical or (confusingly) near-identical meaning: zero point of charge (zpc), point of zero net charge (pznc), point of zero net proton charge (pznpc), pristine point of zero charge (ppzc), point of zero salt effect (pzse), zero point of titration (zpt) of colloidal dispersion, and isoelectric point of the solid (ieps) and point of zero surface tension (pzst or pzs). | 0 | Theoretical and Fundamental Chemistry |
The phenomenon was first noticed in 1983 in hoop-wound fibre-reinforced aluminium alloy cylinders, which burst in use in the USA. The alloy was 6351 with a relatively high lead content (400 ppm), but even after the lead content was lowered, the problem recurred, and subsequently the problem was detected in monolithic aluminium cylinders. The first incidence of an SLC crack in the cylindrical part of a cylinder was reported in 1999. | 1 | Applied and Interdisciplinary Chemistry |
Initially, More O’Ferrall introduced this type of analysis to discuss the continuity between concerted and step-wise β-elimination reaction mechanisms. The model also provided a framework within which to explain the effects of substituents and reaction conditions on the mechanism. The appropriate lower energy species were placed at the corners of the two dimensional plot (Figure 2). These were the reactants (top left), the products (bottom right) and the intermediates of the two possible stepwise reactions: the carbocation for E1 (bottom left) and the carbanion for E1cB (top-right). Thus, the horizontal axes represent the extent of deprotonation (C-H bond distance) and the vertical axes represent the extent of leaving group departure (C-LG distance). By applying the Hammond and anti-Hammond effects, he predicted the effects of various changes in the reactants or reaction conditions. For example, the effects of introducing a better leaving group on a substrate that initially eliminates via an E2 mechanism are illustrated in Figure 2. A better leaving group increases the energy of the reactants and of the carbanion intermediate. Thus, the transition state moves towards the reactants and away from the carbanion intermediate.
The model does not predict any change in leaving group departure at the transition state. Instead the extent of deprotonation is expected to decrease. This can be explained by the fact that a better leaving group needs less assistance from a developing neighbouring negative charge in order to depart. The true change predicts more carbocation character at the transition state and a mechanism that is more E1-like. These observations can be correlated with Hammett ρ-values. Poor leaving groups correlate with large positive ρ-values. Gradually increasing the leaving group ability decreases the ρ-value until it becomes large and negative, indicating the development of positive charge in the transition state. | 0 | Theoretical and Fundamental Chemistry |
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