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Roberts is a inventor or co-inventor on over 100 issued patents. He has received the E.B. Hershberg award and induction into the MEDI Hall of Fame in 2021. He has also been involved in the commercialization of some of his research, contributing to the establishment of biotech companies such as Receptos Pharmaceuticals and BlackThorn Pharmaceuticals. He is a member of the Royal Society of Chemistry, the Royal Society of Medicine, and the Medicinal Chemistry division of the American Chemical Society. | 0 | Organic Chemistry |
The matrix is the space enclosed by the inner membrane. It contains about 2/3 of the total proteins in a mitochondrion. The matrix is important in the production of ATP with the aid of the ATP synthase contained in the inner membrane. The matrix contains a highly concentrated mixture of hundreds of enzymes, special mitochondrial ribosomes, tRNA, and several copies of the mitochondrial DNA genome. Of the enzymes, the major functions include oxidation of pyruvate and fatty acids, and the citric acid cycle. The DNA molecules are packaged into nucleoids by proteins, one of which is TFAM. | 1 | Biochemistry |
In this section, we present in rough outline a purely classical derivation of the non-extensive entropy for an ideal gas considered by Gibbs before "correct counting" (indistinguishability of particles) is accounted for. This is followed by a brief discussion of two standard methods for making the entropy extensive. Finally, we present a third method, due to R. Swendsen, for an extensive (additive) result for the entropy of two systems if they are allowed to exchange particles with each other. | 7 | Physical Chemistry |
Various factors affect the rate of glucuronidation, which in turn will affect these molecules' clearance from the body. Generally, an increased rate of glucuronidation results in a loss of potency for the target drugs or compounds. | 0 | Organic Chemistry |
A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is formed between one hybridized orbital from each of the carbon atoms. In ethane, the orbitals are sp-hybridized orbitals, but single bonds formed between carbon atoms with other hybridizations do occur (e.g. sp to sp). In fact, the carbon atoms in the single bond need not be of the same hybridization. Carbon atoms can also form double bonds in compounds called alkenes or triple bonds in compounds called alkynes. A double bond is formed with an sp-hybridized orbital and a p-orbital that is not involved in the hybridization. A triple bond is formed with an sp-hybridized orbital and two p-orbitals from each atom. The use of the p-orbitals forms a pi bond. | 0 | Organic Chemistry |
Although there are no set plans to search for biosignatures on Saturns sixth-largest moon, Enceladus, the prospects of biosignature discovery there are exciting enough to warrant several mission concepts that may be funded in the future. Similar to Jupiters moon Europa, there is much evidence for a subsurface ocean to also exist on Enceladus. Plumes of water vapor were first observed in 2005 by the Cassini mission and were later determined to contain salt as well as organic compounds. In 2014, more evidence was presented using gravimetric measurements on Enceladus to conclude that there is in fact a large reservoir of water underneath an icy surface. Mission design concepts include:
*Enceladus Life Finder (ELF)
*Enceladus Life Signatures and Habitability
* Enceladus Organic Analyzer
* Enceladus Explorer (En-Ex)
* Explorer of Enceladus and Titan (ET)
* Journey to Enceladus and Titan (JET)
* Life Investigation For Enceladus (LIFE)
* Testing the Habitability of Enceladus's Ocean (THEO)
All of these concept missions have similar science goals: To assess the habitability of Enceladus and search for biosignatures, in line with the strategic map for exploring the ocean-world Enceladus. | 2 | Environmental Chemistry |
Corona treatment is a surface modification method using a low temperature corona discharge to increase the surface energy of a material, often polymers and natural fibers. Most commonly, a thin polymer sheet is rolled through an array of high-voltage electrodes, using the plasma created to functionalize the surface. The limited penetration depth of such treatment provides vastly improved adhesion while preserving bulk mechanical properties.
Commercially, corona treatment has been used widely for improved dye adhesion before printing text and images on plastic packaging materials. The hazardous nature of remnant ozone after corona treatment stipulates careful filtration and ventilation during processing, restricting its implementation to applications with strict catalytic filtered systems. This limitation prevents widespread use within open-line manufacturing processes
Several factors influence the efficiency of the flame treatment such as air-to-gas ratio, thermal output, surface distance, and oxidation zone dwell time. Upon conception of the process, a corona treatment immediately followed film extrusions, but the development of careful transportation techniques allows treatment at an optimized location. Conversely, in-line corona treatments have been implemented into full-scale production lines such as those in the newspaper industry. These in-line solutions are developed to counteract the decrease in wetting characteristics caused by excessive solvent use. | 7 | Physical Chemistry |
One katal refers to an amount of enzyme that gives a catalysed rate of conversion of one mole per second. Because this is such a large unit for most enzymatic reactions, the nanokatal (nkat) is used in practice.
The katal is not used to express the rate of a reaction; that is expressed in units of concentration per second, as moles per liter per second. Rather, the katal is used to express catalytic activity, which is a property of the catalyst. | 3 | Analytical Chemistry |
An intense effort has been made towards the total synthesis of (+)-discodermolide in order to meet the growing interest of studying its clinical profile. More than a dozen of syntheses have been published by different research groups. After decade of work, discodermolide syntheses have become more convergent and more practical. All of the total syntheses approaches started with the construction of three major fragments of roughly equivalent complexity, each of which contains the methyl-hydroxyl-methyl triad of contiguous centers that matches the stereogenicity of discodermolide target. Here are three examples of the retrosynthetic analyses of (+)-discodermolide: | 0 | Organic Chemistry |
Rfam is a database containing information about non-coding RNA (ncRNA) families and other structured RNA elements. It is an annotated, open access database originally developed at the Wellcome Trust Sanger Institute in collaboration with Janelia Farm, and currently hosted at the European Bioinformatics Institute. Rfam is designed to be similar to the Pfam database for annotating protein families.
Unlike proteins, ncRNAs often have similar secondary structure without sharing much similarity in the primary sequence. Rfam divides ncRNAs into families based on evolution from a common ancestor. Producing multiple sequence alignments (MSA) of these families can provide insight into their structure and function, similar to the case of protein families. These MSAs become more useful with the addition of secondary structure information. Rfam researchers also contribute to Wikipedia's RNA WikiProject. | 1 | Biochemistry |
The thermodynamic entropy (at equilibrium) is a function of the state variables of the model description. It is therefore as "real" as the other variables in the model description. If the model constraints in the probability assignment are a "good" description, containing all the information needed to predict reproducible experimental results, then that includes all of the results one could predict using the formulae involving entropy from classical thermodynamics. To that extent, the MaxEnt S is as "real" as the entropy in classical thermodynamics.
Of course, in reality there is only one real state of the system. The entropy is not a direct function of that state. It is a function of the real state only through the (subjectively chosen) macroscopic model description. | 7 | Physical Chemistry |
Initiation factors are proteins that bind to the small subunit of the ribosome during the initiation of translation, a part of protein biosynthesis.
Initiation factors can interact with repressors to slow down or prevent translation. They have the ability to interact with activators to help them start or increase the rate of translation. In bacteria, they are simply called IFs (i.e.., IF1, IF2, & IF3) and in eukaryotes they are known as eIFs (i.e.., eIF1, eIF2, eIF3). Translation initiation is sometimes described as three step process which initiation factors help to carry out. First, the tRNA carrying a methionine amino acid binds to the small ribosome, then binds to the mRNA, and finally joins together with the large ribosome. The initiation factors that help with this process each have different roles and structures. | 1 | Biochemistry |
The factors affecting V̇O may be separated into supply and demand. Supply is the transport of oxygen from the lungs to the mitochondria (combining pulmonary function, cardiac output, blood volume, and capillary density of the skeletal muscle) while demand is the rate at which the mitochondria can reduce oxygen in the process of oxidative phosphorylation. Of these, the supply factors may be more limiting. However, it has also been argued that while trained subjects are probably supply limited, untrained subjects can indeed have a demand limitation.
General characteristics that affect V̇O max include age, sex, fitness and training, and altitude. V̇O max can be a poor predictor of performance in runners due to variations in running economy and fatigue resistance during prolonged exercise. The body works as a system. If one of these factors is sub-par, then the whole system's normal capacity is reduced.
The drug erythropoietin (EPO) can boost V̇O max by a significant amount in both humans and other mammals. This makes EPO attractive to athletes in endurance sports, such as professional cycling. EPO has been banned since the 1990s as an illicit performance-enhancing substance. But by 1998 it had become widespread in cycling and led to the Festina affair as well as being mentioned ubiquitously in the USADA 2012 report on the U.S. Postal Service Pro Cycling Team. Greg LeMond has suggested establishing a baseline for riders' V̇O max (and other attributes) to detect abnormal performance increases. | 1 | Biochemistry |
Because the ligaments of these materials are essentially small metallic samples, they are themselves expected to be quite ductile; although, the entire nano-porous material is often observed to be brittle in tension. Dislocation behavior is extensive within the ligaments (just as would be expected in a metal): a high density. of partial dislocations, stacking faults and twins have been observed both in simulation and in TEM. However, the morphology of the ligaments makes bulk dislocation motion very difficult; the limited size of each ligament and complex connectivity within the nano-porous structure means that a dislocation cannot freely travel long distances and thus induce large-scale plasticity. | 8 | Metallurgy |
The complex adopts a trigonal bipyramidal geometry with trans CO and hydrido ligands, resulting in pseudo-C symmetry. The Rh-P, Rh-C, and Rh-H distances are 2.32, 1.83, and 1.60 Å, respectively. This complex is one of a small number of stable pentacoordinate rhodium hydrides. | 0 | Organic Chemistry |
Mathematically, PCLake is composed of a set of coupled differential equations. With a large number of state variables (>100) and parameters (>300), the model may be characterized as relatively complex. The main biotic variables are phytoplankton and submerged aquatic vegetation, describing primary production. A simplified food web is made up of zooplankton, zoobenthos, young and adult whitefish and piscivorous fish. The main abiotic factors are transparency and the nutrients phosphorus (P), nitrogen (N) and silica (Si). At the base of the model are the water and nutrient budgets (in- and outflow). The model describes a completely mixed water body and comprises both the water column and the upper sediment layer. The overall nutrient cycles for N, P and Si are described as completely closed (except for in- and outflow and denitrification). Inputs to the model are: lake hydrology, nutrient loading, dimensions and sediment characteristics. The model calculates chlorophyll-a, transparency, cyanobacteria, vegetation cover and fish biomass, as well as the concentrations and fluxes of nutrients N, P and Si, and oxygen. Optionally, a wetland zone with marsh vegetation and water exchange with the lake can be included.
PCLake is calibrated against nutrient, transparency, chlorophyll and vegetation data on more than 40 European (but mainly Dutch) lakes, and systematic sensitivity and uncertainty analysis have been performed.
Although PCLake is primarily used for Dutch lakes, it is likely that the model is also applicable to comparable non-stratifying lakes in other regions, if parameters are adjusted or some small changes to the model are made. | 2 | Environmental Chemistry |
ANAs are found in many disorders, as well as some healthy individuals. These disorders include: systemic lupus erythematosus (SLE), rheumatoid arthritis, Sjögren syndrome, scleroderma, polymyositis, dermatomyositis, primary biliary cirrhosis, drug induced lupus, autoimmune hepatitis, multiple sclerosis, discoid lupus, thyroid disease, antiphospholipid syndrome, juvenile idiopathic arthritis, psoriatic arthritis, juvenile dermatomyositis, idiopathic thrombocytopaenic purpura, infection and cancer. These antibodies can be subdivided according to their specificity, and each subset has different propensities for specific disorders. | 1 | Biochemistry |
Enantioselective dioxirane oxidations may rely on chiral, non-racemic dioxiranes, such as Shis fructose-based dioxirane. Enantioselective oxidation of meso-diols with Shis catalyst, for instance, produces chiral α-hydroxy ketones with moderate enantioselectivity. | 0 | Organic Chemistry |
Photochromism is the phenomenon that produces a change of colour in a substance by incident radiation. In other words, Photochromism is a light-induced change of colour of a chemical substance. The spiropyrans are one of the photochromatic molecules that have raised more interest lately. These molecules consist of two heterocyclic functional groups in orthogonal planes bound by a carbon atom. Spiropyrans are one of the oldest families of photochromism. As solids, the spiropyrans do not present photochromism. It is possible in solution and in the dry state that radiation between 250 nm and 380 nm (approximately) is able to, by breaking the C-O binding, transform the spiropyrans into its colour emitting merocyanin-form. The structure of the colourless molecules, the substrate of the reaction (N), is more thermodynamically stable than the product – depending on the solvent in which it is stored. For example in NMP the equilibrium could be switched more toward the merocyanin form (solvatochromic effects). The photoisomers of the spiropyrans have a structure similar to cyanines, even though it is not symmetric about the center of the polymethine chain, and it is classified as a merocyanine (Figure 2).
Once the irradiation has stopped, the merocyanine in solution starts to discolour and to revert to its original form, the spiropyran (N).
Procedure:
* Irradiation of spiropyrans in solution with UV light of wavelength 250–380 nm breaks C-O bonds.
* Consequently, the structure of the initial molecule changes, the resulting one being merocyanine (MC). Because of the apparent conjugated system after UV illumination the extinction coefficient of the MC-form is significantly higher than the one of the closed spiropyran form.
* Unlike the initial solution, the product of the photochromism reaction is not colourless.
*Depending on substituent on the aromatic system the switching behaviour of the derivatives can change in their switching velocity and photo-fatigue resistance. | 5 | Photochemistry |
Most chemical safety legislation in the UK covers the transport of hazardous chemicals by road. Companies carrying dangerous substances must comply with the legislation. The NCEC worked with the European Chemical Industry Council (CEFIC) to develop a set of safety codes for carrying dangerous chemicals for National Intervention in Chemical Transport Emergencies Centres across Europe. | 2 | Environmental Chemistry |
Devapamil consists of two aromatic rings with methoxy substituents connected by an alkylamine chain increasing flexibility and overall potency. | 1 | Biochemistry |
Disulfides have a C-S-S-C dihedral angle approaching 90°. The S-S bond length is 2.03 Å in diphenyl disulfide, similar to that in elemental sulfur.
Two kinds of disulfides are recognized, symmetric and unsymmetric. Symmetrical disulfides are compounds of the formula . Most disulfides encountered in organo sulfur chemistry are symmetrical disulfides. Unsymmetrical disulfides (also called heterodisulfides or mixed disulfides) are compounds of the formula . Unsymmetrical disulfide are less common in organic chemistry, but many disulfides in nature are unsymmetrical. Illustrative of a symmetric disulfide is cystine. | 0 | Organic Chemistry |
In general, vitamin D is found in animal source foods, particularly fish, meat, offal, egg and dairy.
Vitamin D is found in fungi and is produced by ultraviolet irradiation of ergosterol. The vitamin D content in mushrooms and Cladina arbuscula, a lichen, increases with exposure to ultraviolet light, and is stimulated by industrial ultraviolet lamps for fortification. The United States Department of Agriculture reports D and D content combined in one value. | 1 | Biochemistry |
Boris Smirnov and Alexander Marchenko (USSR) discovered in 1975 that cobalt porphyrins are able to reduce the molecular weight of PMMA formed during radical polymerization of methacrylates. Later investigations showed that the cobalt dimethylglyoxime complexes were as effective as the porphyrin catalysts and also less oxygen sensitive. Due to their lower oxygen sensitivity these catalysts have been investigated much more thoroughly than the porphyrin catalysts and are the catalysts actually used commercially. | 7 | Physical Chemistry |
Grb2 has been shown to interact with:
* ADAM15,
* Abl gene,
* Arachidonate 5-lipoxygenase,
* B-cell linker,
* BCAR1,
* BCR gene,
* Beta-2 adrenergic receptor,
* C-Met,
* CBLB,
* CD117,
* CD22,
* CD28,
* CDKN1B,
* CRK,
* Cbl gene,
* Colony stimulating factor 1 receptor,
* DCTN1,
* DNM1,
* Dock180,
* Dystroglycan,
* EPH receptor A2,
* ETV6,
* Epidermal growth factor receptor,
* Erythropoietin receptor,
* FRS2,
* Fas ligand,
* GAB1,
* GAB2,
* Glycoprotein 130,
* Granulocyte colony-stimulating factor receptor,
* HER2/neu,
* HNRNPC,
* Huntingtin,
* INPP5D,
* IRS1,
* ITK,
* Janus kinase 1,
* Janus kinase 2,
* KHDRBS1,
* Linker of activated T cells,
* Lymphocyte cytosolic protein 2,
* MAP2,
* MAP3K1
* MAP4K1,
* MED28,
* MST1R,
* MUC1,
* Mitogen-activated protein kinase 9,
* NCKIPSD,
* NEU3,
* PDGFRB,
* PIK3R1,
* PLCG1,
* PRKAR1A,
* PTK2,
* PTPN11,
* PTPN12,
* PTPN1,
* PTPN6,
* PTPRA,
* RAPGEF1,
* RET proto-oncogene,
* SH2B1,
* SH3KBP1,
* SHC1,
* SOS1,
* Src,
* Syk,
* TNK2,
* TrkA,
* VAV1,
* VAV2,
* VAV3, and
* Wiskott-Aldrich syndrome protein. | 1 | Biochemistry |
Friedrich Kohlrausch in 1875–1879 established that to a high accuracy in dilute solutions, molar conductivity can be decomposed into contributions of the individual ions. This is known as Kohlrausch's law of independent ionic migration.
For any electrolyte AB, the limiting molar conductivity is expressed as x times the limiting molar conductivity of A and y times the limiting molar conductivity of B.
where:
: λ is the limiting molar ionic conductivity of ion i,
: ν is the number of ions i in the formula unit of the electrolyte (e.g. 2 and 1 for Na and sulfate| in NaSO).
Kohlrausch's evidence for this law was that the limiting molar conductivities of two electrolytes with two different cations and a common anion differ by an amount which is independent of the nature of the anion. For example, = for X = Cl, I and . This difference is ascribed to a difference in ionic conductivities between K and Na. Similar regularities are found for two electrolytes with a common anion and two cations. | 7 | Physical Chemistry |
Barrier activity has been linked to the disruption of specific processes in the heterochromatin formation pathway. These types of insulators modify the nucleosomal substrate in the reaction cycle that is central to heterochromatin formation. Modifications are achieved through various mechanisms including nucleosome removal, in which nucleosome-excluding elements disrupt heterochromatin from spreading and silencing (chromatin-mediated silencing). Modification can also be done through recruitment of histone acetyltransferase(s) and ATP-dependent nucleosome remodelling complexes. | 1 | Biochemistry |
Chemically, oxidative stress is associated with increased production of oxidizing species or a significant decrease in the effectiveness of antioxidant defenses, such as glutathione. The effects of oxidative stress depend upon the size of these changes, with a cell being able to overcome small perturbations and regain its original state. However, more severe oxidative stress can cause cell death, and even moderate oxidation can trigger apoptosis, while more intense stresses may cause necrosis.
Production of reactive oxygen species is a particularly destructive aspect of oxidative stress. Such species include free radicals and peroxides. Some of the less reactive of these species (such as superoxide) can be converted by oxidoreduction reactions with transition metals or other redox cycling compounds (including quinones) into more aggressive radical species that can cause extensive cellular damage. Most long-term effects are caused by damage to DNA. DNA damage induced by ionizing radiation is similar to oxidative stress, and these lesions have been implicated in aging and cancer. Biological effects of single-base damage by radiation or oxidation, such as 8-oxoguanine and thymine glycol, have been extensively studied. Recently the focus has shifted to some of the more complex lesions. Tandem DNA lesions are formed at substantial frequency by ionizing radiation and metal-catalyzed HO reactions. Under anoxic conditions, the predominant double-base lesion is a species in which C8 of guanine is linked to the 5-methyl group of an adjacent 3'-thymine (G[8,5- Me]T). Most of these oxygen-derived species are produced by normal aerobic metabolism. Normal cellular defense mechanisms destroy most of these. Repair of oxidative damages to DNA is frequent and ongoing, largely keeping up with newly induced damages. In rat urine, about 74,000 oxidative DNA adducts per cell are excreted daily. There is also a steady state level of oxidative damages in the DNA of a cell. There are about 24,000 oxidative DNA adducts per cell in young rats and 66,000 adducts per cell in old rats. Likewise, any damage to cells is constantly repaired. However, under the severe levels of oxidative stress that cause necrosis, the damage causes ATP depletion, preventing controlled apoptotic death and causing the cell to simply fall apart.
Polyunsaturated fatty acids, particularly arachidonic acid and linoleic acid, are primary targets for free radical and singlet oxygen oxidations. For example, in tissues and cells, the free radical oxidation of linoleic acid produces racemic mixtures of 13-hydroxy-9Z,11E-octadecadienoic acid, 13-hydroxy-9E,11E-octadecadienoic acid, 9-hydroxy-10E,12-E-octadecadienoic acid (9-EE-HODE), and 11-hydroxy-9Z,12-Z-octadecadienoic acid as well as 4-Hydroxynonenal while singlet oxygen attacks linoleic acid to produce (presumed but not yet proven to be racemic mixtures of) 13-hydroxy-9Z,11E-octadecadienoic acid, 9-hydroxy-10E,12-Z-octadecadienoic acid, 10-hydroxy-8E,12Z-octadecadienoic acid, and 12-hydroxy-9Z-13-E-octadecadienoic (see 13-Hydroxyoctadecadienoic acid and 9-Hydroxyoctadecadienoic acid). Similar attacks on arachidonic acid produce a far larger set of products including various isoprostanes, hydroperoxy- and hydroxy- eicosatetraenoates, and 4-hydroxyalkenals. While many of these products are used as markers of oxidative stress, the products derived from linoleic acid appear far more predominant than arachidonic acid products and therefore easier to identify and quantify in, for example, atheromatous plaques. Certain linoleic acid products have also been proposed to be markers for specific types of oxidative stress. For example, the presence of racemic 9-HODE and 9-EE-HODE mixtures reflects free radical oxidation of linoleic acid whereas the presence of racemic 10-hydroxy-8E,12Z-octadecadienoic acid and 12-hydroxy-9Z-13-E-octadecadienoic acid reflects singlet oxygen attack on linoleic acid. In addition to serving as markers, the linoleic and arachidonic acid products can contribute to tissue and/or DNA damage but also act as signals to stimulate pathways which function to combat oxidative stress.
Table adapted from. | 1 | Biochemistry |
In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms reactant and reagent are often used interchangeably, but reactant specifies a substance consumed in the course of a chemical reaction. Solvents, though involved in the reaction mechanism, are usually not called reactants. Similarly, catalysts are not consumed by the reaction, so they are not reactants. In biochemistry, especially in connection with enzyme-catalyzed reactions, the reactants are commonly called substrates. | 0 | Organic Chemistry |
The SBSP concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power:
* It is always solar noon in space and full sun.
* Collecting surfaces could receive much more intense sunlight, owing to the lack of obstructions such as atmospheric gasses, clouds, dust and other weather events. Consequently, the intensity in orbit is approximately 144% of the maximum attainable intensity on Earth's surface.
* A satellite could be illuminated over 99% of the time and be in Earth's shadow a maximum of only 72 minutes per night at the spring and fall equinoxes at local midnight. Orbiting satellites can be exposed to a consistently high degree of solar radiation, generally for 24 hours per day, whereas earth surface solar panels currently collect power for an average of 29% of the day.
* Power could be relatively quickly redirected directly to areas that need it most. A collecting satellite could possibly direct power on demand to different surface locations based on geographical baseload or peak load power needs.
* Reduced plant and wildlife interference. | 7 | Physical Chemistry |
Ylides can be formed from münchnones, which are mesoionic heterocycles, and act as cyclic azomethine ylides. | 0 | Organic Chemistry |
There are a few unusual circumstances where speleothems have been created in caves as a result of hyperalkaline leachate, with the same chemistry as occurs in [Equations to ]. This chemistry can occur when there is a source of concrete, lime, mortar or other manmade calcareous material located above a cave system and the associated hyperalkaline leachate can penetrate into the cave below. An example can be found in the Peak District – Derbyshire, England where pollution from 19th century industrial lime production has leached into the cave system below (e.g. Poole's Cavern) and created speleothems, such as stalactites and stalagmites. | 8 | Metallurgy |
In living cells, signals are processed by networks of proteins that can act as complex computational devices. These networks rely on the ability of single proteins to exist in a variety of functionally different states achieved through multiple mechanisms, including post-translational modifications, ligand binding, conformational change, or formation of new complexes. Similarly, nucleic acids can undergo a variety of transformations, including protein binding, binding of other nucleic acids, conformational change and DNA methylation.
In addition, several types of modifications can co-exist, exerting a combined influence on a biological macromolecule at any given time. Thus, a biomolecule or complex of biomolecules can often adopt a very large number of functionally distinct states. The number of states scales exponentially with the number of possible modifications, a phenomenon known as "combinatorial explosion". This is of concern for computational biologists who model or simulate such biomolecules, because it raises questions about how such large numbers of states can be represented and simulated. | 1 | Biochemistry |
An advantage is silent operation, with none of the fan noise of current resistive grid designs.
Disadvantages include:
* corrosion to the copper connection cables and to the wire rope
* lack of insulation from ground which may trip a ground detection system | 7 | Physical Chemistry |
Polypeptides, the precursors of proteins, are chains of amino acids. The two ends of a polypeptide are called the N-terminus, or amino end, and the C-terminus, or carboxyl end. For many (but not all) chloroplast proteins encoded by nuclear genes, cleavable transit peptides are added to the N-termini of the polypeptides, which are used to help direct the polypeptide to the chloroplast for import (N-terminal transit peptides are also used to direct polypeptides to plant mitochondria).
N-terminal transit sequences are also called presequences because they are located at the "front" end of a polypeptide—ribosomes synthesize polypeptides from the N-terminus to the C-terminus.
Chloroplast transit peptides exhibit huge variation in length and amino acid sequence. They can be from 20 to 150 amino acids long—an unusually long length, suggesting that transit peptides are actually collections of domains with different functions. Transit peptides tend to be positively charged, rich in hydroxylated amino acids such as serine, threonine, and proline, and poor in acidic amino acids like aspartic acid and glutamic acid. In an aqueous solution, the transit sequence forms a random coil.
Not all chloroplast proteins include a N-terminal cleavable transit peptide though. Some include the transit sequence within the functional part of the protein itself. A few have their transit sequence appended to their C-terminus instead. Most of the polypeptides that lack N-terminal targeting sequences are the ones that are sent to the outer chloroplast membrane, plus at least one sent to the inner chloroplast membrane. | 5 | Photochemistry |
Although the self-cleaning phenomenon of the lotus was possibly known in Asia long before (reference to the lotus effect is found in the Bhagavad Gita), its mechanism was explained only in the early 1970s after the introduction of the scanning electron microscope. Studies were performed with leaves of Tropaeolum and lotus (Nelumbo).. Similar to lotus effect, a recent study has revealed honeycomb-like micro-structures on the taro leaf, which makes the leaf superhydrophobic. The measured contact angle on this leaf in this study is around 148 degrees. | 7 | Physical Chemistry |
Cresol red (full name: o-cresolsulfonephthalein) is a triarylmethane dye frequently used for monitoring the pH in aquaria. | 3 | Analytical Chemistry |
Some common expressions of gas volume with defined or variable temperature, pressure and humidity inclusion are:
*ATPS: Ambient temperature (variable) and pressure (variable), saturated (humidity depends on temperature)
*ATPD: Ambient temperature (variable) and pressure (variable), dry (no humidity)
*BTPS: Body temperature (37 °C or 310 K) and pressure (generally same as ambient), saturated (47 mmHg or 6.2 kPa)
*STPD: Standard temperature (0 °C or 273 K) and pressure ( or ), dry (no humidity) | 7 | Physical Chemistry |
Electromigration decreases the reliability of integrated circuits (ICs). It can cause the eventual loss of connections or failure of a circuit. Since reliability is critically important for space travel, military purposes, anti-lock braking systems, medical equipment like Automated External Defibrillators and is even important for personal computers or home entertainment systems, the reliability of chips (ICs) is a major focus of research efforts.
Due to difficulty of testing under real conditions, Black's equation is used to predict the life span of integrated circuits.
To use Blacks equation, the component is put through high temperature operating life (HTOL) testing. The components expected life span under real conditions is extrapolated from data gathered during the testing.
Although electromigration damage ultimately results in failure of the affected IC, the first symptoms are intermittent glitches, and are quite challenging to diagnose. As some interconnects fail before others, the circuit exhibits seemingly random errors, which may be indistinguishable from other failure mechanisms (such as electrostatic discharge damage). In a laboratory setting, electromigration failure is readily imaged with an electron microscope, as interconnect erosion leaves telltale visual markers on the metal layers of the IC.
With increasing miniaturization, the probability of failure due to electromigration increases in VLSI and ULSI circuits because both the power density and the current density increase. Specifically, line widths will continue to decrease over time, as will wire cross-sectional areas. Currents are also reduced due to lower supply voltages and shrinking gate capacitances. However, as current reduction is constrained by increasing frequencies, the more marked decrease in cross-sectional areas (compared to current reduction) will give rise to increased current densities in ICs going forward.
In advanced semiconductor manufacturing processes, copper has replaced aluminium as the interconnect material of choice. Despite its greater fragility in the fabrication process, copper is preferred for its superior conductivity. It is also intrinsically less susceptible to electromigration. However, electromigration (EM) continues to be an ever-present challenge to device fabrication, and therefore the EM research for copper interconnects is ongoing (though a relatively new field).
In modern consumer electronic devices, ICs rarely fail due to electromigration effects. This is because proper semiconductor design practices incorporate the effects of electromigration into the ICs layout. Nearly all IC design houses use automated EDA tools to check and correct electromigration problems at the transistor layout-level. When operated within the manufacturers specified temperature and voltage range, a properly designed IC device is more likely to fail from other (environmental) causes, such as cumulative damage from gamma-ray bombardment.
Nevertheless, there have been documented cases of product failures due to electromigration. In the late 1980s, one line of Western Digitals desktop drives suffered widespread, predictable failure 12–18 months after field usage. Using forensic analysis of the returned bad units, engineers identified improper design-rules in a third-party suppliers IC controller. By replacing the bad component with that of a different supplier, WD was able to correct the flaw, but not before significant damage to the company's reputation.
Electromigration can be a cause of degradation in some power semiconductor devices such as low voltage power MOSFETs, in which the lateral current through the source contact metallisation (often aluminium) can reach the critical current densities during overload conditions. The degradation of the aluminium layer causes an increase in on-state resistance, and can eventually lead to complete failure. | 7 | Physical Chemistry |
SH2 domains contain about 100 amino acid residues and exhibit a central antiparallel β-sheet centered between two α-helices. Binding to phosphotyrosine-containing peptides involves a strictly-conserved Arg residue that pairs with the negatively-charged phosphate on the phosphotyrosine, and a surrounding pocket that recognizes flanking sequences on the target peptide. Compared to other signaling proteins, SH2 domains exhibit only a moderate degree of specificity for their target peptides, due to the relative weakness of the interactions with the flanking sequences.
Over 100 human proteins are known to contain SH2 domains. A variety of tyrosine-containing sequences have been found to bind SH2 domains and are conserved across a wide range of organisms, performing similar functions. Binding of a phosphotyrosine-containing protein to an SH2 domain may lead to either activation or inactivation of the SH2-containing protein, depending on the types of interactions formed between the SH2 domain and other domains of the enzyme. Mutations that disrupt the structural stability of the SH2 domain, or that affect the binding of the phosphotyrosine peptide of the target, are involved in a range of diseases including X-linked agammaglobulinemia and severe combined immunodeficiency. | 1 | Biochemistry |
In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occupied by spheres – that can be achieved by a lattice packing is
The same packing density can also be achieved by alternate stackings of the same close-packed planes of spheres, including structures that are aperiodic in the stacking direction. The Kepler conjecture states that this is the highest density that can be achieved by any arrangement of spheres, either regular or irregular. This conjecture was proven by T. C. Hales. Highest density is known only for 1, 2, 3, 8, and 24 dimensions.
Many crystal structures are based on a close-packing of a single kind of atom, or a close-packing of large ions with smaller ions filling the spaces between them. The cubic and hexagonal arrangements are very close to one another in energy, and it may be difficult to predict which form will be preferred from first principles.
__TOC__ | 3 | Analytical Chemistry |
Meibom obtained a PhD in physics at the University of Southern Denmark in 1997. He then pursued a two-and-a-half-year postdoc at the Hawaii Institute for Geophysics and Planetology where he studied the mineralogy of primitive chondrotic meteorites. In 2000, he moved to Stanford University as a research associate in the Stanford-USGS ion microprobe laboratory, department of geological and environmental sciences. In 2005, he was appointed as an associate professor at the Museum National d’Histoire Naturelle in Paris, where he was promoted to full professor in 2007. From 2006 to 2011, he served as the director of the French National NanoSIMS analytical facility. In 2012, he was named full professor at the EPFL (École Polytechnique Fédérale de Lausanne) in the School of Architecture, Civil and Environmental Engineering (ENAC). He has also been full professor ad personam at the University of Lausanne since 2014. From 2015 to 2017, he was the director of the Institute of Environmental Engineering at EPFL.
In 2019, Meibom founded the Transnational Red Sea Center (TRSC), an initiative for scientific diplomacy supported by the Swiss Federal Department of Foreign Affairs and which aims to promote scientific collaboration in a politically unstable region endowed with fundamental ecological stakes. | 9 | Geochemistry |
Several thermodynamic definitions are very useful in thermochemistry. A system is the specific portion of the universe that is being studied. Everything outside the system is considered the surroundings or environment. A system may be:
* a (completely) isolated system which can exchange neither energy nor matter with the surroundings, such as an insulated bomb calorimeter
* a thermally isolated system which can exchange mechanical work but not heat or matter, such as an insulated closed piston or balloon
* a mechanically isolated system which can exchange heat but not mechanical work or matter, such as an uninsulated bomb calorimeter
* a closed system which can exchange energy but not matter, such as an uninsulated closed piston or balloon
* an open system which it can exchange both matter and energy with the surroundings, such as a pot of boiling water | 7 | Physical Chemistry |
The final structural question of the exact geometric configuration about the first carbon at ring position 3 of ring I, the carbon bound to the hydroxyl group, has been shown to be the chiral S configuration.
Like heme B, heme A is often attached to the apoprotein through a coordinate bond between the heme iron and a conserved amino acid side-chain. In the important respiratory protein cytochrome c oxidase (CCO) this ligand 5 for the heme A at the oxygen reaction center is a histidyl group. Histidine is a common ligand for many hemeproteins including hemoglobin and myoglobin.
Heme A in the cytochrome a portion of cytochrome c oxidase, bound by two histidine residues (shown in pink)
An example of a metalloprotein that contains heme A is cytochrome c oxidase. This very complicated protein contains heme A at two different sites, each with a different function. The iron of the heme A of cytochrome a is hexacoordinated, that is bound with 6 other atoms. The iron of the heme A of cytochrome a3 is sometimes bound by 5 other atoms leaving the sixth site available to bind dioxygen (molecular oxygen). In addition, this enzyme binds 3 copper, magnesium, zinc, and several potassium and sodium ions. The two heme A groups in CCO are thought to readily exchange electrons between each other, the copper ions and the closely associated protein cytochrome c.
Both the formyl group and the isoprenoid side chain are thought to play important roles in conservation of the energy of oxygen reduction by cytochrome c oxidase. CCO is thought to be responsible for conserving the energy of dioxygen reduction by pumping protons into the inter-membrane mitochondrial space. Both the formyl and hydroxyethylfarnesyl groups of heme A are thought to play important roles in this critical process, as published by the influential group of S. Yoshikawa. | 1 | Biochemistry |
Chirality is a symmetry property, not a property of any part of the periodic table. Thus many inorganic materials, molecules, and ions are chiral. Quartz is an example from the mineral kingdom. Such noncentric materials are of interest for applications in nonlinear optics.
In the areas of coordination chemistry and organometallic chemistry, chirality is pervasive and of practical importance. A famous example is tris(bipyridine)ruthenium(II) complex in which the three bipyridine ligands adopt a chiral propeller-like arrangement. The two enantiomers of complexes such as [Ru(2,2′-bipyridine)] may be designated as Λ (capital lambda, the Greek version of "L") for a left-handed twist of the propeller described by the ligands, and Δ (capital delta, Greek "D") for a right-handed twist (pictured). Also cf. dextro- and levo- (laevo-).
Chiral ligands confer chirality to a metal complex, as illustrated by metal-amino acid complexes. If the metal exhibits catalytic properties, its combination with a chiral ligand is the basis of asymmetric catalysis. | 4 | Stereochemistry |
Scientists and engineers are able to use liquid crystals in a variety of applications because external perturbation can cause significant changes in the macroscopic properties of the liquid crystal system. Both electric and magnetic fields can be used to induce these changes. The magnitude of the fields, as well as the speed at which the molecules align are important characteristics industry deals with. Special surface treatments can be used in liquid crystal devices to force specific orientations of the director. | 7 | Physical Chemistry |
Several synthesis routes exist, the most common being the reaction between alkyl halides and alkali thiocyanate in aqueous media. Illustrative is the preparation of isopropyl thiocyanate by treatment of isopropyl bromide with sodium thiocyanate in boiling ethanol. The main complication with this route is the competing formation of alkyisothiocyanates. "SN1-type" substrates (e.g., benzyl halides) tend to give the isothiocyanate derivatives.
Some organic thiocyanates are generated by cyanation of some organosulfur compounds. Sulfenyl thiosulfates (RSSO) react with alkali metal cyanides to give thiocyanates with displacement of sulfite. This approach has been applied to allyl thiocyanate:
Sulfenyl chlorides (RSCl) also convert to thiocyanates.
Aryl thiocyanates are traditionally produced by the Sandmeyer reaction, which involves combining copper(I) thiocyanate and diazonium salts:
Some arylthiocyanates can also often be obtained by thiocyanogenation, i.e. the reaction of thiocyanogen. This reaction is favored for electron-rich aromatic substrates. | 0 | Organic Chemistry |
Compared to natural vegetation, cropland soils are depleted in soil organic carbon (SOC). When soil is converted from natural land or semi-natural land, such as forests, woodlands, grasslands, steppes, and savannas, the SOC content in the soil reduces by about 30–40%. This loss is due to the removal of plant material containing carbon, in terms of harvests. When land use changes, the carbon in the soil will either increase or decrease, and this change will continue until the soil reaches a new equilibrium. Deviations from this equilibrium can also be affected by variated climate.
The decreasing of SOC content can be counteracted by increasing the carbon input. This can be done with several strategies, e.g. leave harvest residues on the field, use manure as fertilizer, or including perennial crops in the rotation. Perennial crops have a larger below ground biomass fraction, which increases the SOC content.
Perennial crops reduce the need for tillage and thus help mitigate soil erosion, and may help increase soil organic matter. Globally, soils are estimated to contain >8,580 gigatons of organic carbon, about ten times the amount in the atmosphere and much more than in vegetation.
Researchers have found that rising temperatures can lead to population booms in soil microbes, converting stored carbon into carbon dioxide. In laboratory experiments heating soil, fungi-rich soils released less carbon dioxide than other soils.
Following carbon dioxide (CO) absorption from the atmosphere, plants deposit organic matter into the soil. This organic matter, derived from decaying plant material and root systems, is rich in carbon compounds. Microorganisms in the soil break down this organic matter, and in the process, some of the carbon becomes further stabilized in the soil as humus - a process known as humification.
On a global basis, it is estimated that soil contains about 2,500 gigatons of carbon. This is greater than 3-fold the carbon found in the atmosphere and 4-fold of that found in living plants and animals. About 70% of the global soil organic carbon in non-permafrost areas is found in the deeper soil within the upper 1 meter and stabilized by mineral-organic associations. | 5 | Photochemistry |
The fluorescent-dye DNA sequencing is a molecular biology technique that involves labeling single-strand DNA sequences of varied length with 4 fluorescent dyes (corresponding to 4 different bases used in DNA) and subsequently separating the DNA sequences by "slab gel"- or capillary-electrophoresis method (see DNA Sequencing). The electrophoresis run is monitored by a CCD on the DNA sequencer and this produces a time "trace" data (or "chromatogram") of the fluorescent "peaks" that passed the CCD point. Examining the fluorescence peaks in the trace data, we can determine the order of individual bases (nucleobase) in the DNA. Since the intensity, shape and the location of a fluorescence peak are not always consistent or unambiguous, however, sometimes it is difficult or time-consuming to determine (or "call") the correct bases for the peaks accurately if it is done manually.
Automated DNA sequencing techniques have revolutionized the field of molecular biology – generating vast amounts of DNA sequence data. However, the sequence data is produced at a significantly higher rate than can be manually processed (i.e. interpreting the trace data to produce the sequence data), thereby creating a bottleneck. To remove the bottleneck, both automated software that can speed up the processing with improved accuracy and a reliable measure of the accuracy are needed. To meet this need, many software programs have been developed. One such program is Phred. | 1 | Biochemistry |
Observations of rocks on the plains show they contain the minerals pyroxene, olivine, plagioclase, and magnetite. These rocks can be classified in different ways. The amounts and types of minerals make the rocks primitive basalts—also called picritic basalts. The rocks are similar to ancient terrestrial rocks called basaltic komatiites. Rocks of the plains also resemble the basaltic shergottites, meteorites which came from Mars. One classification system compares the amount of alkali elements to the amount of silica on a graph; in this system, Gusev plains rocks lie near the junction of basalt, picrobasalt, and tephrite. The Irvine-Barager classification calls them basalts.
Plain's rocks have been very slightly altered, probably by thin films of water because they are softer and contain veins of light colored material that may be bromine compounds, as well as coatings or rinds. It is thought that small amounts of water may have gotten into cracks inducing mineralization processes).
Coatings on the rocks may have occurred when rocks were buried and interacted with thin films of water and dust.
One sign that they were altered was that it was easier to grind these rocks compared to the same types of rocks found on Earth.
The first rock that Spirit studied was Adirondack. It turned out to be typical of the other rocks on the plains. | 9 | Geochemistry |
The deformation fields around large (over 1 μm) non-deformable particles are characterised by high dislocation densities and large orientation gradients and so are ideal sites for the development of recrystallization nuclei. This phenomenon, called particle stimulated nucleation (PSN), is notable as it provides one of the few ways to control recrystallization by controlling the particle distribution.
The size and misorientation of the deformed zone is related to the particle size and so there is a minimum particle size required to initiate nucleation. Increasing the extent of deformation will reduce the minimum particle size, leading to a PSN regime in size-deformation space.
If the efficiency of PSN is one (i.e. each particle stimulates one nuclei), then the final grain size will be simply determined by the number of particles. Occasionally the efficiency can be greater than one if multiple nuclei form at each particle but this is uncommon. The efficiency will be less than one if the particles are close to the critical size and large fractions of small particles will actually prevent recrystallization rather than initiating it (see above). | 8 | Metallurgy |
Calmodulin belongs to one of the two main groups of calcium-binding proteins, called EF hand proteins. The other group, called annexins, bind calcium and phospholipids such as lipocortin. Many other proteins bind calcium, although binding calcium may not be considered their principal function in the cell. | 1 | Biochemistry |
In 1956, two British scientists, John Barnes and Peter Magee, reported that a simple member of the large class of N-nitrosamines, dimethylnitrosamine, produced liver tumours in rats. Subsequent studies showed that approximately 90% of the 300 nitrosamines tested were carcinogenic in a wide variety of animals. | 0 | Organic Chemistry |
Erwin Nick Hiebert (May 27, 1919 – November 28, 2012) was a Canadian-American physical chemist and professor of the history of science. He was the president of the History of Science Society for a two-year term from 1973 to 1974. | 7 | Physical Chemistry |
The origin of surface stress is the difference between bonding in the bulk and at a surface. The bulk spacings set the values of the in-plane surface spacings, and consequently the in-plane distance between atoms. However, the atoms at the surface have a different bonding, so would prefer to be at a different spacing, often (but not always) closer together. If they want to be closer, then will be positive—a tensile or expansive strain will increase the surface energy.
For many metals the derivative is positive, but in other cases it is negative, for instance solid argon and some semiconductors. The sign can also strongly depend upon molecules adsorbed on the surface. If these want to be further apart that will introduce a negative component. | 7 | Physical Chemistry |
Creating a genetically modified organism (GMO) is a multi-step process. Genetic engineers must isolate the gene they wish to insert into the host organism. This gene can be taken from a cell or artificially synthesized. If the chosen gene or the donor organism's genome has been well studied it may already be accessible from a genetic library. The gene is then combined with other genetic elements, including a promoter and terminator region and a selectable marker.
A number of techniques are available for inserting the isolated gene into the host genome. Bacteria can be induced to take up foreign DNA, usually by exposed heat shock or electroporation. DNA is generally inserted into animal cells using microinjection, where it can be injected through the cells nuclear envelope directly into the nucleus, or through the use of viral vectors. In plants the DNA is often inserted using Agrobacterium'-mediated recombination, biolistics or electroporation.
As only a single cell is transformed with genetic material, the organism must be regenerated from that single cell. In plants this is accomplished through tissue culture. In animals it is necessary to ensure that the inserted DNA is present in the embryonic stem cells. Further testing using PCR, Southern hybridization, and DNA sequencing is conducted to confirm that an organism contains the new gene.
Traditionally the new genetic material was inserted randomly within the host genome. Gene targeting techniques, which creates double-stranded breaks and takes advantage on the cells natural homologous recombination repair systems, have been developed to target insertion to exact locations. Genome editing uses artificially engineered nucleases that create breaks at specific points. There are four families of engineered nucleases: meganucleases, zinc finger nucleases, transcription activator-like effector nucleases (TALENs), and the Cas9-guideRNA system (adapted from CRISPR). TALEN and CRISPR are the two most commonly used and each has its own advantages. TALENs have greater target specificity, while CRISPR is easier to design and more efficient. | 1 | Biochemistry |
The thermal bump is compatible with the existing flip-chip manufacturing infrastructure, extending the use of conventional solder bumped interconnects to provide active, integrated cooling of a flip-chipped component using the widely accepted copper pillar bumping process. The result is higher performance and efficiency within the existing semiconductor manufacturing paradigm. The thermal bump also enables power generating capabilities within copper pillar bumps for energy recycling applications.
Thermal bumps have been shown to achieve a temperature differential of 60 °C between the top and bottom headers; demonstrated power pumping capabilities exceeding 150 W/cm2; and when subjected to heat, have demonstrated the capability to generate up to 10 mW of power per bump. | 7 | Physical Chemistry |
Broadband acoustic resonance dissolution spectroscopy (BARDS) is a technique in analytical chemistry. Developed in the late 2000s, it involves the analysis of the changes in sound frequency generated when a solute dissolves in a solvent, by harnessing the hot chocolate effect.
The technique is partly based on the solubility difference of gas in pure solvents and in solutions. The dissolution of a compound in a pure solvent results in the generation of gas bubbles in the solvent, due to the lowering of gas solubility in the resulting solution, as well as the introduction of gases with the solute. The presence of these gas bubbles increases the compressibility of the solution, thereby lowering the velocity of sound in the solution. This effect can be monitored by means of the frequency change of acoustic resonances that are mechanically produced in the solvent. | 7 | Physical Chemistry |
Impure pyridine was undoubtedly prepared by early alchemists by heating animal bones and other organic matter, but the earliest documented reference is attributed to the Scottish scientist Thomas Anderson. In 1849, Anderson examined the contents of the oil obtained through high-temperature heating of animal bones. Among other substances, he separated from the oil a colorless liquid with unpleasant odor, from which he isolated pure pyridine two years later. He described it as highly soluble in water, readily soluble in concentrated acids and salts upon heating, and only slightly soluble in oils.
Owing to its flammability, Anderson named the new substance pyridine, after (pyr) meaning fire. The suffix idine was added in compliance with the chemical nomenclature, as in toluidine, to indicate a cyclic compound containing a nitrogen atom.
The chemical structure of pyridine was determined decades after its discovery. Wilhelm Körner (1869) and James Dewar (1871) suggested that, in analogy between quinoline and naphthalene, the structure of pyridine is derived from benzene by substituting one C–H unit with a nitrogen atom. The suggestion by Körner and Dewar was later confirmed in an experiment where pyridine was reduced to piperidine with sodium in ethanol. In 1876, William Ramsay combined acetylene and hydrogen cyanide into pyridine in a red-hot iron-tube furnace. This was the first synthesis of a heteroaromatic compound.
The first major synthesis of pyridine derivatives was described in 1881 by Arthur Rudolf Hantzsch. The Hantzsch pyridine synthesis typically uses a 2:1:1 mixture of a β-keto acid (often acetoacetate), an aldehyde (often formaldehyde), and ammonia or its salt as the nitrogen donor. First, a double hydrogenated pyridine is obtained, which is then oxidized to the corresponding pyridine derivative. Emil Knoevenagel showed that asymmetrically substituted pyridine derivatives can be produced with this process.
The contemporary methods of pyridine production had a low yield, and the increasing demand for the new compound urged to search for more efficient routes. A breakthrough came in 1924 when the Russian chemist Aleksei Chichibabin invented a pyridine synthesis reaction, which was based on inexpensive reagents. This method is still used for the industrial production of pyridine. | 0 | Organic Chemistry |
Though certainly not all insect pheromones have been discovered, many are known and many more are discovered every year. Some sites curate large lists of insect pheromones. Pheromones are frequently used to monitor and control lepidopteran and coleopteran species, with many available commercially. Pheromones are available for insects including:
*African bollworm
*African cotton leafworm
*Apple brown tortrix
*Apple clearwing moth
*Apple fruit moth
*Apple maggot
*Artichoke moth
*Asian beetle
*Asian corn borer moth
*Baluchistan fruit fly
*Banana weevil
*Banded elm bark beetle
*Barred fruit-tree tortrix
*Beech tortrix moth
*Beet armyworm
*Bertha armyworm
*Black cutworm
*Blueberry maggot
*Bollworm
*Bright-line brown-eye or tomato moth
*Brown oak tortrix
*Cabbage leaf roller
*Cabbage looper moth
*Cabbage moth
*Carnation tortrix
*Carob moth
*Cherry-bark moth
*Cherry fruit fly
*Citrus cutworm
*Citrus flower moth
*Citrus leafmining moth
*Citrus mealybug
*Codling moth
*Corn earworm
*Corn stalk borer
*Cucumber fruit fly
*Cucumber moth
*Currant clearwing moth
*Cutworm
*Date palm fruit stalk borer
*Diamond back moth
*Douglas-fir tussock moth
*Dubas bug
*Durra stem borer
*Eastern cherry fruit fly
*Eggplant shoot and fruit borer
*Egyptian cotton leaf worm
*Engraver beetle
*European corn borer
*European goat moth
*European pine shoot moth
*European spruce bark beetle
*Eye-spotted bud moth
*Fall armyworm
*False codling moth
*Fruit fly
*Fruit tree leaf roller
*Garden pebble
*Golden leaf roller
*Golden twin moth or groundnut semi-looper moth
*Grape moth or vine moth
*Green oak moth
*Grey tortrix
*Hants moth
*Japanese beetle
*Jasmine moth
*Large fruit tree tortrix
*Leche's twist moth
*Leek moth or onion moth
*Legume pod borer
*Leopard moth
*Lesser peach tree borer
*Longhorn date stem borer
*Marbled orchard tortrix
*Mediterranean fruit fly
*Mediterranean pine engraver beetle
*Melon fly
*Northern bark beetle
*Nun moth
*Olive fruit fly
*Olive moth
*Orange tortrix
*Oriental fruit fly
*Oriental fruit moth
*Pea moth
*Peach fruit fly
*Pear leaf blister moth
*Pear twig borer
*Pine processionary moth
*Pine sawfly
*Pink bollworm
*Plum fruit moth
*Potato moth
*Potato tuber moth
*Queensland fruit fly
*Quince moth
*Red palm weevil
*Rhinoceros beetle
*Rice stem borer
*Rose tortrix
*San Jose scale
*Sesiidae (some)
*Silver Y moth
*Six-spined spruce bark beetle
*Six-toothed bark beetle
*Spiny boll worm
*Spongy moth
*Spotted bollworm
*Spotted tentiform miner
*Straw coloured tortrix moth
*Sugar beet weevil
*Summer fruit tortrix moth
*Tobacco budworm
*Tomato leaf miner
*Tomato looper
*Turnip moth
*Variegated golden tortrix
*Winter moth
*Xyloterus bark beetle | 1 | Biochemistry |
The "upper phase" is formed by the more hydrophobic polyethylene glycol (PEG), which is of lower density than the "lower phase," consisting of the more hydrophilic and denser dextran solution.
Although PEG is inherently denser than water, it occupies the upper layer. This is believed to be due to its solvent ordering properties, which excludes excess water, creating a low density water environment. The degree of polymerization of PEG also affects the phase separation and the partitioning of molecules during extraction. | 3 | Analytical Chemistry |
NURF interacts with chromatin by binding to modified histones or interacting with various transcription factors. NURF catalyzes nucleosome sliding in either direction on DNA without any apparent modifications to the histone octamer itself. NURF is essential for the expression of homeotic genes. The ISWI ATPase specifically recognizes intact N-terminal histone tails. In Drosophila, NURF interacts with the transcription factor GAGA to remodel chromatin at the hsp70 promoter, and null mutations in the Nurf301 subunit prevent larval metamorphosis. Other NURF mutants cause the development of melanotic tumors from larval blood cells. In humans, hNURF is involved in neuronal development and has been shown to enhance neurite outgrowth in vitro. | 1 | Biochemistry |
In addition to cooling, passive daytime radiative cooling surfaces can be modified to be self-adaptive for temperature-dependent switching from cooling to heating or, in other words, for full-scale thermal regulation. This can be achieved through switching the thermal emittance of the surface from a high to low value. Applications are limited to testing and commercially available self-switching PDRCs are in research and development. | 7 | Physical Chemistry |
Treatment with organolithium reagents gives the dilithio derivative.
:CBH + 2 BuLi → LiCBH + 2 BuH
This dilithiated compound reacts with a variety of electrophiles, e.g. chlorophosphines, chlorosilanes, and sulfur. | 7 | Physical Chemistry |
Esterification is a reversible reaction. Esters undergo hydrolysis under acidic and basic conditions. Under acidic conditions, the reaction is the reverse reaction of the Fischer esterification. Under basic conditions, hydroxide acts as a nucleophile, while an alkoxide is the leaving group. This reaction, saponification, is the basis of soap making.
The alkoxide group may also be displaced by stronger nucleophiles such as ammonia or primary or secondary amines to give amides: (ammonolysis reaction)
This reaction is not usually reversible. Hydrazines and hydroxylamine can be used in place of amines. Esters can be converted to isocyanates through intermediate hydroxamic acids in the Lossen rearrangement.
Sources of carbon nucleophiles, e.g., Grignard reagents and organolithium compounds, add readily to the carbonyl. | 0 | Organic Chemistry |
The basic working principle of diffraction topography is as follows:
An incident, spatially extended beam (mostly of X-rays, or neutrons) impinges on a sample.
The beam may be either monochromatic, i.e. consist one single wavelength of X-rays or neutrons, or polychromatic, i.e. be composed of a mixture of wavelengths ("white beam" topography). Furthermore, the incident beam may be either parallel, consisting only of "rays" propagating all along nearly the same direction, or divergent/convergent, containing several more strongly different directions of propagation.
When the beam hits the crystalline sample, Bragg diffraction occurs, i.e. the incident wave is reflected by the atoms on certain lattice planes of the sample, if it hits those planes at the right Bragg angle.
Diffraction from sample can take place either in reflection geometry (Bragg case), with the beam entering and leaving through the same surface, or in transmission geometry (Laue case).
Diffraction gives rise to a diffracted beam, which will leave the sample and propagate along a direction differing from the incident direction by the scattering angle .
The cross section of the diffracted beam may or may not be identical to the one of the incident beam. In the case of strongly asymmetric reflections, the beam size (in the diffraction plane) is considerably expanded or compressed, with expansion occurring if the incidence angle is much smaller than the exit angle, and vice versa. Independently of this beam expansion, the relation of sample size to image size is given by the exit angle alone: The apparent lateral size of sample features parallel to the exit surface is downscaled in the image by the projection effect of the exit angle.
A homogeneous sample (with a regular crystal lattice) would yield a homogeneous intensity distribution in the topograph (a "flat" image with no contrast). Intensity modulations (topographic contrast) arise from irregularities in the crystal lattice, originating from various kinds of defects such as
* voids and inclusions in the crystal
* phase boundaries (regions of different crystallographic phase, polytype, ...)
* defective areas, non-crystalline (amorphous) areas / inclusions
* cracks, surface scratches
* stacking faults
* dislocations, dislocation bundles
* grain boundaries, domain walls
* growth striations
* point defects or defect clusters
* crystal deformation
* strain fields
In many cases of defects such as dislocations, topography is not directly sensitive to the defects themselves (atomic structure of the dislocation core), but predominantly to the strain field surrounding the defect region. | 3 | Analytical Chemistry |
For trisubstituted alkenes such as 1, boron is predominantly placed on the less substituted carbon. The minor product, in which the boron atom is placed on the more substituted carbon, is usually produced in less than 10%. A notable case with lower regioselectivity is styrene, and the selectivity is strongly influenced by the substituent on the para position.
Hydroboration of 1,2-disubstituted alkenes, such as a cis or trans olefin, produces generally a mixture of the two organoboranes of comparable amounts, even if the substituents are very different in terms of steric bulk. For such 1,2-disubstituted olefins, regioselectivity can be observed only when one of the two substituents is a phenyl ring. In such cases, such as trans-1-phenylpropene, the boron atom is placed on the carbon adjacent to the phenyl ring. The observations above indicate that the addition of H-B bond to olefins is under electronic control rather than steric control. | 0 | Organic Chemistry |
VMAT1 (SLC18A1) maps to a shared bipolar disorder(BPD)/schizophrenia locus, which is located on chromosome 8p21. It is thought that disruption in transport of monoamine neurotransmitters due to variation in the VMAT1 gene may be relevant to the etiology of these mental disorders. One study looked at a population of European descent, examining the genotypes of a bipolar group and a control group. The study confirmed expression of VMAT1 in the brain at a protein and mRNA level, and found a significant difference between the two groups, suggesting that, at least for people of European descent, variation in the VMAT1 gene may confer susceptibility. A second study examined a population of Japanese individuals, one group healthy and the other schizophrenic. This study resulted in mostly inconclusive findings, but some indications that variation in the VMAT1 gene would confer susceptibility to schizophrenia in Japanese women. While these studies provide some promising insight into the cause of some of the most prevalent mental disorders, it is clear that additional research will be necessary in order to gain a full understanding. | 1 | Biochemistry |
Globo H-targeting antibodies are another strategy currently being evaluated in the cancer therapeutic space. OBI Pharmas OBI-888 is a humanized IgG1 antibody that selectively binds to the Globo H antigen among other Globo series glycosphingolipids such as SSEA-3 and SSEA-4. Additionally, in vivo studies of OBI-888 in various Globo H-positive (GH) xenografts models showed promising tumor growth inhibition results. OBI-888s human Phase I/II study for the treatment of metastatic and locally advanced solid tumors is estimated to finish in December 2022.
Based on OBI-888, the first-in-class antibody-drug conjugate (ADC) 0BI-999 was additionally developed, linking OBI-888 to monomethyl auristatin E, a synthetic antineoplastic agent. The ADC is currently undergoing phase II trial in patients with advanced solid tumors, with an estimated completion date in Dec 2023. In Dec 2019 & Jan 2020, OBI-999 was granted two Orphan Drug Designations by the FDA for the treatment of pancreatic and gastric cancer. | 1 | Biochemistry |
Organic nitrites are prepared from alcohols and sodium nitrite in sulfuric acid solution. They decompose slowly on standing, the decomposition products being oxides of nitrogen, water, the alcohol, and polymerization products of the aldehyde. They are also prone to undergo homolytic cleavage to form alkyl radicals, the nitrite C–O bond being very weak (on the order of 40–50 kcal ⋅ mol). | 0 | Organic Chemistry |
In the presence of a non-competitive inhibitor, the apparent enzyme affinity is equivalent to the actual affinity. In terms of Michaelis-Menten kinetics, K = K. This can be seen as a consequence of Le Chatelier's principle because the inhibitor binds to both the enzyme and the enzyme-substrate complex equally so that the equilibrium is maintained. However, since some enzyme is always inhibited from converting the substrate to product, the effective enzyme concentration is lowered.
Mathematically, | 1 | Biochemistry |
Transcriptional repressor CTCF also known as 11-zinc finger protein or CCCTC-binding factor is a transcription factor that in humans is encoded by the CTCF gene. CTCF is involved in many cellular processes, including transcriptional regulation, insulator activity, V(D)J recombination and regulation of chromatin architecture. | 1 | Biochemistry |
The reaction is:
The reaction is an exothermic equilibrium reaction in which the gas volume is reduced. The equilibrium constant K of the reaction (see table) and obtained from:
Since the reaction is exothermic, the equilibrium of the reaction shifts at lower temperatures to the ammonia side. Furthermore, four volumetric units of the raw materials produce two volumetric units of ammonia. According to Le Chatelier's principle, higher pressure favours ammonia. High pressure is necessary to ensure sufficient surface coverage of the catalyst with nitrogen. For this reason, a ratio of nitrogen to hydrogen of 1 to 3, a pressure of 250 to 350 bar, a temperature of 450 to 550 °C and α iron are optimal.
The catalyst ferrite (α-Fe) is produced in the reactor by the reduction of magnetite with hydrogen. The catalyst has its highest efficiency at temperatures of about 400 to 500 °C. Even though the catalyst greatly lowers the activation energy for the cleavage of the triple bond of the nitrogen molecule, high temperatures are still required for an appropriate reaction rate. At the industrially used reaction temperature of 450 to 550 °C an optimum between the decomposition of ammonia into the starting materials and the effectiveness of the catalyst is achieved. The formed ammonia is continuously removed from the system. The volume fraction of ammonia in the gas mixture is about 20%.
The inert components, especially the noble gases such as argon, should not exceed a certain content in order not to reduce the partial pressure of the reactants too much. To remove the inert gas components, part of the gas is removed and the argon is separated in a gas separation plant. The extraction of pure argon from the circulating gas is carried out using the Linde process. | 7 | Physical Chemistry |
A famous example is the detection of cyclobutadiene released upon oxidation of cyclobutadieneiron tricarbonyl. When this degradation is conducted in the presence of an alkyne, the cyclobutadiene is trapped as a bicyclohexadiene. The requirement for this trapping experiment is that the oxidant (ceric ammonium nitrate) and the trapping agent be mutually compatible. | 3 | Analytical Chemistry |
One of the largest volume uses for ICP-MS is in the medical and forensic field, specifically, toxicology. A physician may order a metal assay for a number of reasons, such as suspicion of heavy metal poisoning, metabolic concerns, and even hepatological issues. Depending on the specific parameters unique to each patient's diagnostic plan, samples collected for analysis can range from whole blood, urine, plasma, serum, to even packed red blood cells. Another primary use for this instrument lies in the environmental field. Such applications include water testing for municipalities or private individuals all the way to soil, water and other material analysis for industrial purposes.
In recent years, industrial and biological monitoring has presented another major need for metal analysis via ICP-MS. Individuals working in factories where exposure to metals is likely and unavoidable, such as a battery factory, are required by their employer to have their blood or urine analyzed for metal toxicity on a regular basis. This monitoring has become a mandatory practice implemented by the U.S. Occupational Safety and Health Administration, in an effort to protect workers from their work environment and ensure proper rotation of work duties (i.e. rotating employees from a high exposure position to a low exposure position).
ICP-MS is also used widely in the geochemistry field for radiometric dating, in which it is used to analyze relative abundance of different isotopes, in particular uranium and lead. ICP-MS is more suitable for this application than the previously used thermal ionization mass spectrometry, as species with high ionization energy such as osmium and tungsten can be easily ionized. For high precision ratio work, multiple collector instruments are normally used to reduce the effect noise on the calculated ratios.
In the field of flow cytometry, a new technique uses ICP-MS to replace the traditional fluorochromes. Briefly, instead of labelling antibodies (or other biological probes) with fluorochromes, each antibody is labelled with a distinct combinations of lanthanides. When the sample of interest is analysed by ICP-MS in a specialised flow cytometer, each antibody can be identified and quantitated by virtue of a distinct ICP "footprint". In theory, hundreds of different biological probes can thus be analysed in an individual cell, at a rate of ca. 1,000 cells per second. Because elements are easily distinguished in ICP-MS, the problem of compensation in multiplex flow cytometry is effectively eliminated.
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a powerful technique for the elemental analysis of a wide variety of materials encountered in forensic casework. (LA-ICP-MS) has already successfully been applied to applications in forensics, metals, glasses, soils, car paints, bones and teeth, printing inks, trace elemental, fingerprint, and paper. Among these, forensic glass analysis stands out as an application for which this technique has great utility to provide highly.
Car hit and runs, burglaries, assaults, drive-by shootings and bombings such as these situations may cause glass fragments that could be used as evidence of association in glass transfer conditions. LA-ICP-MS is considered one of the best techniques for analysis of glass due to the short time for sample preparation and sample, small sample size of less than 250 nanograms. In addition there is no need for complex procedure and handling of dangerous materials that is used for digestion of the samples. This allows detecting major, minor and tracing elements with high level of precision and accuracy. There are set of properties that are used to measure glass sample such as physical and optical properties including color, thickness, density, refractive index (RI) and also, if necessary, elemental analysis can be conducted in order to enhance the value of an association. | 3 | Analytical Chemistry |
A rather intuitive route to cyclic isomers is the intramolecular conjugate addition to α,β–unsaturated carbonyls (intramolecular Michael addition or IMA). Competent Michael acceptors include conjugated enones, enals or nitroalkene derivatives and examples of other acceptors are sparse. Despite IMA reactions being ubiquitous in synthesis, very few examples of asymmetric IMA transformations exist.
Thiourea catalysts with pendant chiral backbones have shown to activate systems with tethered nitroalkane and ester motifs to induce asymmetric IMA. The utility of this transformation was demonstrated in the synthesis of cyclic γ– amino acid precursors (figure 1). It is proposed that activation occurs via H–bonding of both the nitronate and the ester to the thiourea catalyst and explains the interesting selectivity for the E–ester.
A functional stereodivergent organocatalyzed IMA/lactonization transformation in the synthesis of substituted dihydrofurans and tetrahydrofurans has been studied for its ability to construct important structural motifs in numerous natural products (figure 2). When ethers such as 3 are subject to (S)–(–)–tetramisole hydrochloride (4) catalyst the result is the syn–2,3–substituted THF while the complementary anti–product is easily accessible via a Cinchona alkaloid catalyst such as 7. | 0 | Organic Chemistry |
For the creation of dies for producing jewelry and badges, or blanking and piercing (through use of a pancake die) by the coinage (stamping) process, the positive master may be made from sterling silver, since (with appropriate machine settings) the master is significantly eroded and is used only once. The resultant negative die is then hardened and used in a drop hammer to produce stamped flats from cutout sheet blanks of bronze, silver, or low proof gold alloy. For badges these flats may be further shaped to a curved surface by another die. This type of EDM is usually performed submerged in an oil-based dielectric. The finished object may be further refined by hard (glass) or soft (paint) enameling, or electroplated with pure gold or nickel. Softer materials such as silver may be hand engraved as a refinement. | 8 | Metallurgy |
Unlike gases or liquids, solid materials tend to keep their shape when undergoing thermal expansion.
Thermal expansion generally decreases with increasing bond energy, which also has an effect on the melting point of solids, so high melting point materials are more likely to have lower thermal expansion. In general, liquids expand slightly more than solids. The thermal expansion of glasses is slightly higher compared to that of crystals. At the glass transition temperature, rearrangements that occur in an amorphous material lead to characteristic discontinuities of coefficient of thermal expansion and specific heat. These discontinuities allow detection of the glass transition temperature where a supercooled liquid transforms to a glass.
Absorption or desorption of water (or other solvents) can change the size of many common materials; many organic materials change size much more due to this effect than due to thermal expansion. Common plastics exposed to water can, in the long term, expand by many percent. | 7 | Physical Chemistry |
Historically, an association between the color of blood and rust occurs in the association of the planet Mars, with the Roman god of war, since the planet is an orange-red, which reminded the ancients of blood. Although the color of the planet is due to iron compounds in combination with oxygen in the Martian soil, it is a common misconception that the iron in hemoglobin and its oxides gives blood its red color. The color is actually due to the porphyrin moiety of hemoglobin to which the iron is bound, not the iron itself, although the ligation and redox state of the iron can influence the pi to pi* or n to pi* electronic transitions of the porphyrin and hence its optical characteristics.
Artist Julian Voss-Andreae created a sculpture called Heart of Steel (Hemoglobin) in 2005, based on the proteins backbone. The sculpture was made from glass and weathering steel. The intentional rusting of the initially shiny work of art mirrors hemoglobins fundamental chemical reaction of oxygen binding to iron.
Montreal artist Nicolas Baier created Lustre (Hémoglobine), a sculpture in stainless steel that shows the structure of the hemoglobin molecule. It is displayed in the atrium of McGill University Health Centre's research centre in Montreal. The sculpture measures about 10 metres × 10 metres × 10 metres. | 7 | Physical Chemistry |
Protein structure prediction is important in several fields of science, including bioinformatics, molecular biology, and medicine. Identifying natural proteins' structural configurations enables scientists to understand them better. This can lead to creating novel proteins by design, advances in treating disease, and solutions for other real-world problems such as invasive species, waste, and pollution.
The process by which living beings create the primary structure of proteins, protein biosynthesis, is reasonably well understood, as is the means by which proteins are encoded as DNA. However, determining how a given proteins primary structure becomes a functioning three-dimensional structure, how the molecule folds, is more difficult. The general process is understood, but predicting a proteins eventual, functioning structure is computationally demanding. | 1 | Biochemistry |
Polymeric materials have widespread application due to their versatile characteristics, cost-effectiveness, and highly tailored production. The science of polymer synthesis allows for excellent control over the properties of a bulk polymer sample. However, surface interactions of polymer substrates are an essential area of study in biotechnology, nanotechnology, and in all forms of coating applications. In these cases, the surface characteristics of the polymer and material, and the resulting forces between them largely determine its utility and reliability. In biomedical applications for example, the bodily response to foreign material, and thus biocompatibility, is governed by surface interactions. In addition, surface science is integral part of the formulation, manufacturing, and application of coatings.
__TOC__ | 7 | Physical Chemistry |
The and can be approximated up to nth order as
where and are two basic polynomials of order n (Refer Chandrasekhar chapter VIII equation (97)), where are the zeros of Legendre polynomials and , where are the positive, non vanishing roots of the associated characteristic equation
where are the quadrature weights given by | 7 | Physical Chemistry |
Sevoflurane, sold under the brand name Sevorane, among others, is a sweet-smelling, nonflammable, highly fluorinated methyl isopropyl ether used as an inhalational anaesthetic for induction and maintenance of general anesthesia. After desflurane, it is the volatile anesthetic with the fastest onset. While its offset may be faster than agents other than desflurane in a few circumstances, its offset is more often similar to that of the much older agent isoflurane. While sevoflurane is only half as soluble as isoflurane in blood, the tissue blood partition coefficients of isoflurane and sevoflurane are quite similar. For example, in the muscle group: isoflurane 2.62 vs. sevoflurane 2.57. In the fat group: isoflurane 52 vs. sevoflurane 50. As a result, the longer the case, the more similar will be the emergence times for sevoflurane and isoflurane.
It is on the World Health Organization's List of Essential Medicines. | 2 | Environmental Chemistry |
The photo-reduction of CO on p-type semiconductor photo-electrodes has been achieved in both aqueous and non-aqueous media. Main difference between aqueous and non-aqueous media is the solubility of CO. The solubility of CO in aqueous media at 1 atm. of CO is around ≈ 35 mM; whereas solubility of CO in methanol is around 210 mM and in acetonitrile is around 210 mM. | 5 | Photochemistry |
Biochemists are typically employed in the life sciences, where they work in the pharmaceutical or biotechnology industry in a research role. They are also employed in academic institutes, where in addition to pursuing their research they may also be involved with teaching undergraduates, training graduate students, and collaborating with post-doctoral fellows.
The U.S. Bureau of Labor Statistics (BLS) estimates that jobs in the biochemist, combined with the statistics of biophysicists, field would increase by 31% between 2004 and 2014 because of the demand in medical research and development of new drugs and products, and the preservation of the environment.
Because of a biochemists' background in both biology and chemistry, they may also be employed in the medical, industrial, governmental, and environmental fields. Slightly more than half of the biological scientists are employed by the Federal State and local governments. The field of medicine includes nutrition, genetics, biophysics, and pharmacology; industry includes beverage and food technology, toxicology, and vaccine production; while the governmental and environmental fields includes forensic science, wildlife management, marine biology, and viticulture.
The average income of a biochemist was $82,150 in 2017. The range of the salaries begin around 44,640 to 153,810, reported in 2017. The Federal Government in 2005 reported the average salaries in different fields associated with biochemistry and being a biochemist. General biological scientists in nonsupervisory, supervisory, and managerial positions earned an average salary of $69,908; microbiologists, $80,798; ecologists, $72,021; physiologists, $93,208; geneticists, $85,170; zoologists, $101,601; and botanists, $62,207. | 1 | Biochemistry |
In eukaryotes, a corepressor is a protein that binds to transcription factors. In the absence of corepressors and in the presence of coactivators, transcription factors upregulate gene expression. Coactivators and corepressors compete for the same binding sites on transcription factors. A second mechanism by which corepressors may repress transcriptional initiation when bound to transcription factor/DNA complexes is by recruiting histone deacetylases which catalyze the removal of acetyl groups from lysine residues. This increases the positive charge on histones which strengthens the electrostatic attraction between the positively charged histones and negatively charged DNA, making the DNA less accessible for transcription.
In humans several dozen to several hundred corepressors are known, depending on the level of confidence with which the characterisation of a protein as a corepressors can be made. | 1 | Biochemistry |
The presence of atmospheric oxygen has led to the formation of ozone (O) and the ozone layer within the stratosphere:
:O + O :- O
The ozone layer is extremely important to modern life as it absorbs harmful ultraviolet radiation: | 5 | Photochemistry |
An ideal, defect-free semiconductor quantum well structure is a useful model system to illustrate the fundamental processes in typical PL experiments. The discussion is based on results published in Klingshirn (2012) and Balkan (1998).
The fictive model structure for this discussion has two confined quantized electronic and two hole subbands, e, e and h, h, respectively.
The linear absorption spectrum of such a structure shows the exciton resonances of the first (e1h1) and the second quantum well subbands (e, h), as well as the absorption from the corresponding continuum states and from the barrier. | 7 | Physical Chemistry |
The interactions that lead to the assembly of the chlorophylls in chlorosomes are rather simple and the results may one day be used to build artificial photosynthetic systems that convert solar energy to electricity or biofuel. | 5 | Photochemistry |
Comprehensive metabolic panel (CMP) - 14 tests - above BMP plus total protein, albumin, alkaline phosphatase (ALP), alanine amino transferase (ALT), aspartate amino transferase (AST), bilirubin. | 1 | Biochemistry |
PEA is metabolized by the cellular enzymes fatty acid amide hydrolase (FAAH) and N-acylethanolamine acid amide hydrolase (NAAA), the latter of which has more specificity toward PEA over other fatty acid amides. | 1 | Biochemistry |
The order of modules and domains of a complete nonribosomal peptide synthetase is as follows:
* Initiation or Starting module: [F/NMT]-A-PCP-
* Elongation or Extending modules: -(C/Cy)-[NMT]-A-PCP-[E]-
* Termination or Releasing module: -(TE/R)
(Order: N-terminus to C-terminus; []: optionally; (): alternatively) | 1 | Biochemistry |
The correct name of the method is guanidinium thiocyanate-phenol-chloroform extraction. The use of TRIzol can result in DNA yields comparable to other extraction methods, and it leads to >50% bigger RNA yield. An alternative method for RNA extraction is phenol extraction and TCA/acetone precipitation. Chloroform should be exchanged with 1-bromo-3-chloropropane when using the new generation TRI Reagent.
DNA and RNA from TRIzol and TRI reagent can also be extracted using the Direct-zol Miniprep kit by Zymo Research. This method eliminates the use of Chloroform and 1-bromo-3-chloropropane completely, bypassing phase-separation and precipitation steps.
TRIzol is light-sensitive and is often stored in a dark-colored, glass container covered in foil. It is stored at room temperature.
When used, it resembles cough syrup, bright pink. The smell of the phenol is extremely strong. TRIzol works by maintaining RNA integrity during tissue homogenization, while at the same time disrupting and breaking down cells and cell components. | 1 | Biochemistry |
The (oral, mouse) is 80 mg/kg. Rats fed malachite green experience "a dose-related increase in liver DNA adducts" along with lung adenomas. Leucomalachite green causes an "increase in the number and severity of changes". As leucomalachite green is the primary metabolite of malachite green and is retained in fish muscle much longer, most human dietary intake of malachite green from eating fish would be in the leuco form. During the experiment, rats were fed up to 543 ppm of leucomalachite green, an extreme amount compared to the average 5 ppb discovered in fish. After a period of two years, an increase in lung adenomas in male rats was discovered but no incidences of liver tumors. Therefore, it could be concluded that malachite green caused carcinogenic symptoms, but a direct link between malachite green and liver tumor was not established. | 3 | Analytical Chemistry |
The following genes are part of the chemical pathway for making heme:
*ALAD: aminolevulinic acid, δ-, dehydratase (deficiency causes ala-dehydratase deficiency porphyria)
*ALAS1: aminolevulinate, δ-, synthase 1
*ALAS2: aminolevulinate, δ-, synthase 2 (deficiency causes sideroblastic/hypochromic anemia)
*CPOX: coproporphyrinogen oxidase (deficiency causes hereditary coproporphyria)
*FECH: ferrochelatase (deficiency causes erythropoietic protoporphyria)
*HMBS: hydroxymethylbilane synthase (deficiency causes acute intermittent porphyria)
*PPOX: protoporphyrinogen oxidase (deficiency causes variegate porphyria)
*UROD: uroporphyrinogen decarboxylase (deficiency causes porphyria cutanea tarda)
*UROS: uroporphyrinogen III synthase (deficiency causes congenital erythropoietic porphyria) | 1 | Biochemistry |
In molecular biology and physiology, something is GABAergic or GABAnergic if it pertains to or affects the neurotransmitter gamma-aminobutyric acid (GABA). For example, a synapse is GABAergic if it uses GABA as its neurotransmitter, and a GABAergic neuron produces GABA. A substance is GABAergic if it produces its effects via interactions with the GABA system, such as by stimulating or blocking neurotransmission.
A GABAergic or GABAnergic agent is any chemical that modifies the effects of GABA in the body or brain. Some different classes of GABAergic drugs include agonists, antagonists, modulators, reuptake inhibitors and enzymes. | 1 | Biochemistry |
The Enders SAMP/RAMP hydrazone alkylation reaction is an asymmetric carbon-carbon bond formation reaction facilitated by pyrrolidine chiral auxiliaries. It was pioneered by E. J. Corey and Dieter Enders in 1976, and was further developed by Enders and his group. This method is usually a three-step sequence. The first step is to form the hydrazone between (S)-1-amino-2-methoxymethylpyrrolidine (SAMP) or (R)-1-amino-2-methoxymethylpyrrolidine (RAMP) and a ketone or aldehyde. Afterwards, the hydrazone is deprotonated by lithium diisopropylamide (LDA) to form an azaenolate, which reacts with alkyl halides or other suitable electrophiles to give alkylated hydrazone species with the simultaneous generation of a new chiral center. Finally, the alkylated ketone or aldehyde can be regenerated by ozonolysis or hydrolysis.
This reaction is a useful technique for asymmetric α-alkylation of ketones and aldehydes, which are common synthetic intermediates for medicinally interesting natural products and other related organic compounds. These natural products include (-)-C10-demethyl arteannuin B, the structural analog of antimalarial artemisinin, the polypropionate metabolite (-)-denticulatin A and B isolated from Siphonaria denticulata, zaragozic acid A, a potent inhibitor of sterol synthesis, and epothilone A and B, which have been proven to be very effective anticancer drugs. | 0 | Organic Chemistry |
Many C-symmetric complexes are known. Some arise not from C-symmetric ligands, but from the orientation or disposition of high symmetry ligands within the coordination sphere of the metal. Notably, EDTA and triethylenetetraamine form complexes that are C-symmetric by virtue of the way the ligands wrap around the metal centers. Two isomers are possible for (indenyl)MX, C- and C-symmetric. The C-symmetric complexes are optically stable. | 4 | Stereochemistry |
Potassium humate is the potassium salt of humic acid. It is manufactured commercially by alkaline extraction of brown coal (lignite) leonardite and is used mainly as a soil conditioner. | 9 | Geochemistry |
Axiomatic thermodynamics is a mathematical discipline that aims to describe thermodynamics in terms of rigorous axioms, for example by finding a mathematically rigorous way to express the familiar laws of thermodynamics.
The first attempt at an axiomatic theory of thermodynamics was Constantin Carathéodorys 1909 work Investigations on the Foundations of Thermodynamics', which made use of Pfaffian systems and the concept of adiabatic accessibility, a notion that was introduced by Carathéodory himself. In this formulation, thermodynamic concepts such as heat, entropy, and temperature are derived from quantities that are more directly measurable. Theories that came after, differed in the sense that they made assumptions regarding thermodynamic processes with arbitrary initial and final states, as opposed to considering only neighboring states. | 7 | Physical Chemistry |
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