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Ellipsometry has a number of advantages compared to standard reflection intensity measurements:
* Ellipsometry measures at least two parameters at each wavelength of the spectrum. If generalized ellipsometry is applied up to 16 parameters can be measured at each wavelength.
* Ellipsometry measures an intensity ratio instead of pure intensities. Therefore, ellipsometry is less affected by intensity instabilities of the light source or atmospheric absorption.
* By using polarized light, normal ambient unpolarized stray light does not significantly influence the measurement, no dark box is necessary.
* No reference measurement is necessary.
Ellipsometry is especially superior to reflectivity measurements when studying anisotropic samples. | 7 | Physical Chemistry |
The popularization of NHC ligands can be traced to Arduengo, who reported the deprotonation of dimesitylimidazolium cation to give IMes. IMes is a free NHC that can be used as a ligand. Other NHCs have been isolated as the free ligands. Aside from IMes, another important NHC ligand is IPr, which features diisopropylphenyl groups in place of the mesityl groups. NHCs with saturated backbones include SIMes and SIPr. | 0 | Organic Chemistry |
TCF7L2 modulates pancreatic islet β-cell function strongly implicating its significant association with GDM risk. T alleles of rs7903146 and rs1799884 TCF7L2 polymorphisms increase susceptibility to GDM in the Chinese Han population. | 1 | Biochemistry |
As mentioned above, MAPKs typically form multi-tiered pathways, receiving input several levels above the actual MAP kinase. In contrast to the relatively simple, phosphorylation-dependent activation mechanism of MAPKs and MAP2Ks, MAP3Ks have stunningly complex regulation. Many of the better-known MAP3Ks, such as c-Raf, MEKK4 or MLK3 require multiple steps for their activation. These are typically allosterically-controlled enzymes, tightly locked into an inactive state by multiple mechanisms. The first step en route to their activation consists of relieving their autoinhibition by a smaller ligand (such as Ras for c-Raf, GADD45 for MEKK4 or Cdc42 for MLK3). This commonly (but not always) happens at the cell membrane, where most of their activators are bound (note that small G-proteins are constitutively membrane-associated due to prenylation). That step is followed by side-to-side homo- and heterodimerisation of their now accessible kinase domains. Recently determined complex structures reveal that the dimers are formed in an orientation that leaves both their substrate-binding regions free. Importantly, this dimerisation event also forces the MAP3 kinase domains to adopt a partially active conformation. Full activity is only achieved once these dimers transphosphorylate each other on their activation loops. The latter step can also be achieved or aided by auxiliary protein kinases (MAP4 kinases, members of the Ste20 family). Once a MAP3 kinase is fully active, it may phosphorylate its substrate MAP2 kinases, which in turn will phosphorylate their MAP kinase substrates. | 1 | Biochemistry |
The International Deep Drawing Research Group ([http://www.iddrg.com IDDRG]) focuses on sheet metal research in industry and academia. It was started 1957 as an organization of national groups. The original focus was on the fabrication of cups hence the name Deep Drawing Research Group. At the initial meeting the purpose was enlarged to do cooperative research on tests, materials, and processes. Such work included for example, methods for determining the strain hardening exponent n, the anisotropy-values (lankford coefficient), as well as other tests for sheet metal formability and, later, forming limit diagrams.
Starting in 1960, a schedule was established for working group meetings every year with open Congresses in every second, even numbered years. The working group meetings were closed sessions made up of delegations from the National Groups that comprised the IDDRG. The reason for these closed sessions was to allow experts to informally review critical issues related to materials, tests, and processes.
As some of the initial technical issues were resolved, the working groups became progressively more informal, and over the years became mini conferences. By 1998, it had become obvious that the former format of the IDDRG has to be changed. This evolution took time, but starting in 2003, the meeting schedule shifted to yearly Conferences with both regular papers and poster presentations that are included in conference proceedings. | 8 | Metallurgy |
Some of the most common DNA extraction methods include organic extraction, Chelex extraction, and solid phase extraction. These methods consistently yield isolated DNA, but they differ in both the quality and the quantity of DNA yielded. When selecting a DNA extraction method, there are multiple factors to consider, including cost, time, safety, and risk of contamination.
Organic extraction involves the addition of incubation in multiple different chemical solutions; including a lysis step, a phenol-chloroform extraction, an ethanol precipitation, and washing steps. Organic extraction is often used in laboratories because it is cheap, and it yields large quantities of pure DNA. Though it is easy, there are many steps involved, and it takes longer than other methods. It also involves the unfavorable use of the toxic chemicals phenol and chloroform, and there is an increased risk of contamination due to transferring the DNA between multiple tubes. Several protocols based on organic extraction of DNA were effectively developed decades ago, though improved and more practical versions of these protocols have also been developed and published in the last years.
The chelex extraction method involves adding the Chelex resin to the sample, boiling the solution, then vortexing and centrifuging it. The cellular materials bind to the Chelex beads, while the DNA is available in the supernatant. The Chelex method is much faster and simpler than organic extraction, and it only requires one tube, which decreases the risk of DNA contamination. Unfortunately, Chelex extraction does not yield as much quantity and the DNA yielded is single-stranded, which means it can only be used for PCR-based analyses and not for RFLP.
Solid phase extraction such as using a spin-column-based extraction method takes advantage of the fact that DNA binds to silica. The sample containing DNA is added to a column containing a silica gel or silica beads and chaotropic salts. The chaotropic salts disrupt the hydrogen bonding between strands and facilitate the binding of the DNA to silica by causing the nucleic acids to become hydrophobic. This exposes the phosphate residues so they are available for adsorption. The DNA binds to the silica, while the rest of the solution is washed out using ethanol to remove chaotropic salts and other unnecessary constituents. The DNA can then be rehydrated with aqueous low-salt solutions allowing for elution of the DNA from the beads.
This method yields high-quality, largely double-stranded DNA which can be used for both PCR and RFLP analysis. This procedure can be automated and has a high throughput, although lower than the phenol-chloroform method. This is a one-step method i.e. the entire procedure is completed in one tube. This lowers the risk of contamination making it very useful for the forensic extraction of DNA. Multiple solid-phase extraction commercial kits are manufactured and marketed by different companies; the only problem is that they are more expensive than organic extraction or Chelex extraction. | 1 | Biochemistry |
Evidence for the role of the endocannabinoid system in food-seeking behavior comes from a variety of cannabinoid studies. Emerging data suggests that THC acts via CB receptors in the hypothalamic nuclei to directly increase appetite. It is thought that hypothalamic neurons tonically produce endocannabinoids that work to tightly regulate hunger. The amount of endocannabinoids produced is inversely correlated with the amount of leptin in the blood. For example, mice without leptin not only become massively obese but express abnormally high levels of hypothalamic endocannabinoids as a compensatory mechanism. Similarly, when these mice were treated with an endocannabinoid inverse agonists, such as rimonabant, food intake was reduced. When the CB receptor is knocked out in mice, these animals tend to be leaner and less hungry than wild-type mice. A related study examined the effect of THC on the hedonic (pleasure) value of food and found enhanced dopamine release in the nucleus accumbens and increased pleasure-related behavior after administration of a sucrose solution. A related study found that endocannabinoids affect taste perception in taste cells. In taste cells, endocannabinoids were shown to selectively enhance the strength of neural signaling for sweet tastes, whereas leptin decreased the strength of this same response. While there is need for more research, these results suggest that cannabinoid activity in the hypothalamus and nucleus accumbens is related to appetitive, food-seeking behavior. | 1 | Biochemistry |
Fluoroalkanes are generally inert and non-toxic.
Fluoroalkanes are not ozone depleting, as they contain no chlorine or bromine atoms, and they are sometimes used as replacements for ozone-depleting chemicals.
The term fluorocarbon is used rather loosely to include any chemical containing fluorine and carbon, including chlorofluorocarbons, which are ozone depleting. Fluoroalkanes are sometimes confused with fluorosurfactants, which significantly bioaccumulate.
Perfluoroalkanes do not bioaccumulate; those used in medical procedures are rapidly excreted from the body, primarily via expiration with the rate of excretion as a function of the vapour pressure; the half-life for octafluoropropane is less than 2 minutes, compared to about a week for perfluorodecalin.
Low-boiling perfluoroalkanes are potent greenhouse gases, in part due to their very long atmospheric lifetime, and their use is covered by the Kyoto Protocol. The global warming potential (compared to that of carbon dioxide) of many gases can be found in the IPCC 5th assessment report, with an extract below for a few perfluoroalkanes.
The aluminium smelting industry has been a major source of atmospheric perfluorocarbons (tetrafluoromethane and hexafluoroethane especially), produced as by-product of the electrolysis process. However, the industry has been actively involved in reducing emissions in recent years. | 2 | Environmental Chemistry |
The outer chloroplast membrane is a semi-porous membrane that small molecules and ions can easily diffuse across. However, it is not permeable to larger proteins, so chloroplast polypeptides being synthesized in the cell cytoplasm must be transported across the outer chloroplast membrane by the TOC complex, or translocon on the outer chloroplast membrane.
The chloroplast membranes sometimes protrude out into the cytoplasm, forming a stromule, or stroma-containing tubule. Stromules are very rare in chloroplasts, and are much more common in other plastids like chromoplasts and amyloplasts in petals and roots, respectively. They may exist to increase the chloroplast's surface area for cross-membrane transport, because they are often branched and tangled with the endoplasmic reticulum. When they were first observed in 1962, some plant biologists dismissed the structures as artifactual, claiming that stromules were just oddly shaped chloroplasts with constricted regions or dividing chloroplasts. However, there is a growing body of evidence that stromules are functional, integral features of plant cell plastids, not merely artifacts. | 5 | Photochemistry |
Tramadol is metabolised in the liver via the cytochrome P450 isozyme CYP2B6, CYP2D6, and CYP3A4, being O- and N-demethylated to five different metabolites. Of these, desmetramadol (O-desmethyltramadol) is the most significant, since it has 200 times the μ-affinity of (+)-tramadol, and furthermore has an elimination half-life of 9 hours, compared with 6 hours for tramadol itself. As with codeine, in the 6% of the population who have reduced CYP2D6 activity (hence reducing metabolism), a reduced analgesic effect is seen. Those with decreased CYP2D6 activity require a dose increase of 30% to achieve the same degree of pain relief as those with a normal level of CYP2D6 activity.
Phase II hepatic metabolism renders the metabolites water-soluble, which are excreted by the kidneys. Thus, reduced doses may be used in renal and hepatic impairment.
Its volume of distribution is around 306 L after oral administration and 203 L after parenteral administration. | 4 | Stereochemistry |
It gives the ratio of the occurrence each amino acid combination in the observed data to the expected value of occurrence of the pair.
It is rounded off and used in the substitution matrix.
where is the probability of observing the pair and is the expected probability of such a pair occurring, given the background probabilities of each amino acid. | 1 | Biochemistry |
In addition to activating PKC, diacylglycerol has a number of other functions in the cell:
* a source for prostaglandins
* a precursor of the endocannabinoid 2-arachidonoylglycerol
* an activator of a subfamily of transient receptor potential canonical (TRPC) cation channels, TRPC3/6/7. | 1 | Biochemistry |
The bioluminescent bacterium A. fischeri is the first organism in which QS was observed. It lives as a mutualistic symbiont in the photophore (or light-producing organ) of the Hawaiian bobtail squid. When A. fischeri cells are free-living (or planktonic), the autoinducer is at low concentration, and, thus, cells do not show luminescence. However, when the population reaches the threshold in the photophore (about cells/ml), transcription of luciferase is induced, leading to bioluminescence.
In A. fischeri bioluminescence is regulated by AHLs (N-acyl-homoserine lactones) which is a product of the LuxI gene whose transcription is regulated by the LuxR activator. LuxR works only when AHLs binds to the LuxR. | 1 | Biochemistry |
Removal of a proton from an aliphatic –OH group is difficult to achieve in aqueous solution because the energy required for this process is rather large. Thus, ionization of aliphatic –OH groups occurs in aqueous solution only in special circumstances. One such circumstance is found with compounds containing the HN–C–C–OH substructure. For example, compounds containing the 2-aminoethanol substructure can form metal–chelate complexes with the deprotonated form, HN–C–C–O. The chelate effect supplies the extra energy needed to break the O–H bond.
An important example occurs with the molecule tris. This molecule should be used with caution as a buffering agent as it will form chelate complexes with ions such as Fe and Cu. | 7 | Physical Chemistry |
Liquid water and ice, for example, form a frigorific mixture at 0 °C or 32 °F. This mixture was once used to define 0 °C. That temperature is now defined as the triple point of Water with well-defined isotope ratios. A mixture of ammonium chloride, water, and ice form a frigorific mixture at about −17.8 °C or 0 °F. This mixture was once used to define 0 °F. | 7 | Physical Chemistry |
In the following section XH stands for any hydrogen compound, e.g. CH- and NH-compounds.
* Thermal dissociation: gaseous hydrogen molecules are being dissociated at temperatures above 3000 K e.g. in a plasma. At temperatures above 3500 K H und O are dissociated.
* electron impact dissociation:
The density of radicals scales with the electron density and higher gas and electron temperatures (thermal dissociation and electron impact).
* ion impact dissociation: <br />
* dissociative electron attachment:
This process generates negative ions as well as neutral particles. The collision electron is captured by collision excitation. The energy difference between the ground state and the excited state dissociates the molecule. The electron-induced dissociation of water depends on the electron temperature, which influences the ratio of the OH density (n_OH) to the electron density (n_e) significantly. The maximum OH density is reached in the early afterglow when the electron temperature (T_e) is low.
* Photoionisation:<br> High-energy photons dissociate molecules
* Solvated electrons:<br> Reducing agent in liquid | 7 | Physical Chemistry |
As far back as 1905, marine researchers attempted to develop an equation to be used as the standard in establishing the relationship between solar irradiance and photosynthetic production. Several groups had relative success, but in 1976 a comparison study conducted by Alan Jassby and Trevor Platt, researchers at the Bedford Institute of Oceanography in Dartmouth, Nova Scotia, reached a conclusion that solidified the way in which a PI curve is developed. After evaluating the eight most-used equations, Jassby and Platt argued that the PI curve can be best approximated by a hyperbolic tangent function, at least until photoinhibition is reached. | 5 | Photochemistry |
Only recently also other extraction applications have been investigated, e.g. the large scale recovery of apolar organics on offshore oil platforms using the so-called Macro-Porous Polymer Extraction (MPPE) Technology. In such an application, where the SIR particles are contained in a packed bed, flow rates from 0.5 m h upward without maximum flow restrictions can apparently be treated cost competitive to air stripping/activated carbon, steam stripping and bio treatment systems, according to the technology developer. Additional investigations, mostly done in an academic environment, include polar organics like amino-alcohols, organic acids, amino acids, flavonoids, and aldehydes on a bench-scale or pilot-scale. Also, the application of SIRs for the separation of more polar solutes, such as for instance ethers and phenols, has been investigated in the group of A.B. de Haan. | 3 | Analytical Chemistry |
MIM signed the first ISASMELT licence agreement with Agip Australia Proprietary Limited ("Agip") in July 1990. Agip, a subsidiary of the Italian oil company ENI, was developing the Radio Hill nickel-copper deposit near Karratha in Western Australia. MIM and representatives of Agip conducted a series of trials in which 4 tonnes of Radio Hill concentrate was smelted in the 250 kg/h test rig at Mount Isa.
The Agip ISASMELT plant was designed to treat 7.5 t/h of the Radio Hill concentrate and produce 1.5 t/h of granulated matte with a combined nickel and copper content of 45% for sale., It was the same size as the copper ISASMELT demonstration plant (2.3 m internal diameter) and had a 5.5 Nm3/s blower to provide the lance air. Commissioning of the plant began in September 1991; however, the Radio Hill mine and smelter complex were forced to close by low nickel prices after less than six months, before commissioning was completed. The ISASMELT furnace achieved its design capacity within three months. Subsequent owners of the mine focussed on mining and mineral processing only, and the ISASMELT plant has been dismantled. | 8 | Metallurgy |
Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. | 9 | Geochemistry |
Neutral methylene complexes undergo different chemical reactions depending on the pi character of the coordinate bond to the carbon centre. A weak contribution, such as in diazomethane, yields mainly substitution reactions, whereas a strong contribution, such as in ethenone, yields mainly addition reactions. Upon treatment with a standard base, complexes with a weak contribution convert to a metal methoxide. With strong acids (e.g., fluorosulfuric acid), they can be protonated to give . Oxidation of these complexes yields formaldehyde, and reduction yields methane.
Free methylene undergoes the typical chemical reactions of a carbene. Addition reactions are very fast and exothermic.
When the methylene molecule is in its state of lowest energy, the unpaired valence electrons are in separate atomic orbitals with independent spins, a configuration known as triplet state.
Methylene may gain an electron yielding a monovalent anion methanidyl (), which can be obtained as the trimethylammonium (()) salt by the reaction of phenyl sodium () with trimethylammonium bromide (()). The ion has bent geometry, with a H-C-H angle of about 103°. | 0 | Organic Chemistry |
In contrast to photoautotrophs, photoheterotrophs are organisms that depend solely on light for their energy and principally on organic compounds for their carbon. Photoheterotrophs produce ATP through photophosphorylation but use environmentally obtained organic compounds to build structures and other bio-molecules. | 5 | Photochemistry |
Neuroepithelial cells (NEC) are thought to be neuron-like chemoreceptor cells because they rely on membrane potential changes for the release of neurotransmitters and signal transmission onto nearby cells. Once NEC of the zebrafish gills come in contact with either environmental or aortic hypoxia, an outward K "leak" channel is inhibited. It remains unclear how these K channels are inhibited by a shortage of oxygen because there are yet to be any known direct binding sites for "a lack of oxygen", only whole cell and ion channel responses to hypoxia. K "leak" channels are two-pore-domain ion channels that are open at the resting membrane potential of the cell and play a major role in setting the equilibrium resting membrane potential of the cell. Once this "leak" channel is closed, the K is no longer able to freely flow out of the cell, and the membrane potential of the NEC increases; the cell becomes depolarized. This depolarization causes voltage-gated Ca channels to open, and for extracellular Ca to flow down its concentration gradient into the cell causing the intracellular Ca concentration to greatly increase. Once the Ca is inside the cell, it binds to the vesicle release machinery and facilitates binding of the t-snare complex on the vesicle to the s-snare complex on the NEC cell membrane which initiates the release of neurotransmitters into the synaptic cleft. | 9 | Geochemistry |
Adverse effects of drospirenone alone occurring in more than 1% of women may include unscheduled menstrual bleeding (breakthrough or intracyclic) (40.3–64.4%), acne (3.8%), metrorrhagia (2.8%), headache (2.7%), breast pain (2.2%), weight gain (1.9%), dysmenorrhea (1.9%), nausea (1.8%), vaginal hemorrhage (1.7%), decreased libido (1.3%), breast tenderness (1.2%), and irregular menstruation (1.2%). | 4 | Stereochemistry |
Deprotonation of methylcyclopentadiene gives the aromatic methylcyclopentadienyl anion. This ion is useful as a ligand for organometallic complexes. Relative to the corresponding cyclopentadienyl (Cp) complexes, complexes of Cp′ exhibit enhanced solubility in organic solvents.
Cp′ can be used to probe the structure of organometallic complexes. For example, Cp′Fe(PPh)(CO)I has four different signals in the H NMR spectrum for the ring hydrogens and five different signals in the C NMR spectrum for the ring carbons. There is therefore no symmetry within the ring even accounting for rotation around the ring–metal axis, but instead there is a diastereotopic relationship as a result of being part of a chiral complex. The achiral precursor complex Cp′Fe(CO)I has only two signals for those hydrogens and three for those carbons, indicating a symmetric structure. | 0 | Organic Chemistry |
The PECT effect is also present in typical ion-insertion-based battery electrodes (e.g. Li-ion). The electrodes expand and contract when inserted with ions, which is one of the issues that leads to battery ageing and capacity loss over time. The PECT effect in battery electrodes could be an issue in situations where battery electrodes are mechanically stressed (e.g. in structural batteries), causing a change in electrical potential when the stress-state changes.
It has been proposed that the PECT effect in Li-ion batteries could be exploited to measure battery health., and to harvest mechanical energy. | 7 | Physical Chemistry |
The proopiomelanocortin gene (POMC) is expressed in the hypothalamus, in the pituitary gland. It yields a range of biologically active peptides and hormones and undergoes tissue-specific posttranslational processing to yield a range of biologically active peptides producing adrenocorticotropic hormone (ACTH), b-endorphin, and a-, b- and c-melanocyte-stimulating hormone (MSH). These peptides then interact with different melanocortin receptors (MCRs) and are involved in a wide range of processes including the regulation of body weight (MC3R and MC4R), adrenal steroidogenesis (MC2R) and hair pigmentation (MC1R). Published in the British Associations of Dermatologists in 2012, Lack of red hair phenotype in a North-African obese child homozygous for a novel POMC null mutation showed nonsense-mediated decay RNA evaluation in a hair pigment chemical analysis. They found that inactivating the POMC gene mutation results in obesity, adrenal insufficiency, and red hair. This has been seen in both in humans and mice. In this experiment they described a 3-year-old boy from Rome, Italy. He was a source of focus because he had Addison's disease and early onset obesity. They collected his DNA and amplified it using PCR. Sequencing analysis revealed a homozygous single substitution determining a stop codon. This caused an aberrant protein and the corresponding amino acid sequence indicated the exact position of the homozygous nucleotide. The substitution was localized in exon 3 and nonsense mutation at codon 68. The results from this experiment strongly suggest that the absence of red hair in non-European patients with early onset obesity and hormone deficiency does not exclude the occurrence of POMC mutations. By sequencing the patients DNA they found that this novel mutation has a collection of symptoms because of a malfunctioning nonsense-mediated mRNA decay surveillance pathway. | 1 | Biochemistry |
The first examples of insulators in vertebrates was seen in the chicken β-globin locus, cHS4. cHS4 marks the border between the active euchromatin in the β-globin locus and the upstream heterochromatin region that is highly condensed and inactive. The cHS4 insulator acts as both a barrier to chromatin-mediated silencing via heterochromatin spreading, and blocks interactions between enhancers and promoters. A distinguishing characteristic of cHS4 is that it has a repetitive heterochromatic region on its 5' end.
The human β-globin locus homologue of cHS4 is HS5. Different from the chicken β-globin locus, the human β-globin locus has an open chromatin structure and is not flanked by a 5 heterochromatic region. HS5 is thought to be a genetic insulator in vivo' as it has both enhancer-blocking activity and transgene barrier activities.
CTCF was first characterized for its role in regulating β-globin gene expression. At this locus, CTCF functions as an insulator-binding protein forming a chromosomal boundary. CTCF is present in both the chicken β-globin locus and human β-globin locus. Within cHS4 of the chicken β-globin locus, CTCF binds to a region (FII) that is responsible for enhancer blocking activity. | 1 | Biochemistry |
RNAP was discovered independently by Charles Loe, Audrey Stevens, and Jerard Hurwitz in 1960. By this time, one half of the 1959 Nobel Prize in Medicine had been awarded to Severo Ochoa for the discovery of what was believed to be RNAP, but instead turned out to be polynucleotide phosphorylase. | 1 | Biochemistry |
StochSim is a particle-based stochastic simulator used mainly to model chemical reactions and other molecular transitions. The algorithm used in StochSim is different from the more widely known Gillespie stochastic algorithm in that it operates on individual entities, not entity pools, making it particle-based rather than population-based.
In StochSim, each molecular species can be equipped with a number of binary state flags representing a particular modification. Reactions can be made dependent on a set of state flags set to particular values. In addition, the outcome of a reaction can include a state flag being changed. Moreover, entities can be arranged in geometric arrays (for instance, for holoenzymes consisting of several subunits), and reactions can be "neighbor-sensitive", i.e. the probability of a reaction for a given entity is affected by the value of a state flag on a neighboring entity. These properties make StochSim ideally suited to modeling multi-state molecules arranged in holoenzymes or complexes of specified size. Indeed, StochSim has been used to model clusters of bacterial chemotactic receptors, and CaMKII holoenzymes.
An extension to StochSim includes a particle-based simulator DYNSTOC, which uses a StochSim-like algorithm to simulate models specified in the BioNetGen language (BNGL), and improves the handling of molecules within macromolecular complexes.
Another particle-based stochastic simulator that can read BNGL input files is RuleMonkey. Its simulation algorithm differs from the algorithms underlying both StochSim and DYNSTOC in that the simulation time step is variable.
The Network-Free Stochastic Simulator (NFSim) differs from those described above by allowing for the definition of reaction rates as arbitrary mathematical or conditional expressions and thereby facilitates selective coarse-graining of models. RuleMonkey and NFsim implement distinct but related simulation algorithms. A detailed review and comparison of both tools is given by Yang and Hlavacek.
It is easy to imagine a biological system where some components are complex multi-state molecules, whereas others have few possible states (or even just one) and exist in large numbers. A hybrid approach has been proposed to model such systems: Within the Hybrid Particle/Population (HPP) framework, the user can specify a rule-based model, but can designate some species to be treated as populations (rather than particles) in the subsequent simulation. This method combines the computational advantages of particle-based modeling for multi-state systems with relatively low molecule numbers and of population-based modeling for systems with high molecule numbers and a small number of possible states. Specification of HPP models is supported by BioNetGen, and simulations can be performed with NFSim. | 1 | Biochemistry |
Step 1: We take layer 1 as x, and layer 2 as y. By our assumptions in this case, { }.
Step 2: We take the result from step 1 as the value for new x [ x is old x+y; (-x) is old y+x ], and the value for layer 3 as new y.
<math>T_{x+y} = \frac {T_x T_y}{1-R_{(-x)} R_y} = \frac {(0.912)(0.96)}{1-(0.0361)(0.04)} =0.877 = T_{123}
Dahm has shown that for this special case, the total amount of light absorbed by the interior of the sheet (considering surface remission) is the same as that absorbed in a single trip (independent of surface remission). This is borne out by the calculations.
The decadic absorbance () of the sheet is given by: | 7 | Physical Chemistry |
The prestigious Paul Karrer Gold Medal and lecture was established in his honour in 1959 by a group of leading companies such as CIBA AG, J.R. Geigy, F. Hoffmann-La Roche & Co. AG, Sandoz AG, Société des Produits Nestlé AG and Dr. A. Wander AG. It is awarded annually or biannually to an outstanding chemist who delivers a lecture at the University of Zurich.
The Paul Karrer Lecture Foundation is based at the Chemistry Institute of the University of Zurich at Rämistrasse 71, in Zürich. | 0 | Organic Chemistry |
Direct reduction processes were developed to overcome the difficulties of conventional blast furnaces. DRI plants need not be part of an integrated steel plant, as is characteristic of blast furnaces. The initial capital investment and operating costs of direct reduction plants are lower than integrated steel plants and are more suitable for developing countries where supplies of high grade coking coal are limited, but where steel scrap is generally available for recycling. Many other countries use variants of the process.
Factors that help make DRI economical:
* Direct-reduced iron has about the same iron content as pig iron, typically 90–94% total iron (depending on the quality of the raw ore) so it is an excellent feedstock for the electric furnaces used by mini mills, allowing them to use lower grades of scrap for the rest of the charge or to produce higher grades of steel.
* Hot-briquetted iron (HBI) is a compacted form of DRI designed for ease of shipping, handling, and storage.
* Hot direct reduced iron (HDRI) is DRI that is transported hot, directly from the reduction furnace, into an electric arc furnace, thereby saving energy.
* The direct reduction process uses pelletized iron ore or natural "lump" ore. One exception is the fluidized bed process which requires sized iron ore particles.
* The direct reduction process can use natural gas contaminated with inert gases, avoiding the need to remove these gases for other use. However, any inert gas contamination of the reducing gas lowers the effect (quality) of that gas stream and the thermal efficiency of the process. The use of natural gas also produces greenhouse gases.
* Supplies of powdered ore and raw natural gas are both available in areas such as Northern Australia, avoiding transport costs for the gas. In most cases the DRI plant is located near a natural gas source as it is more cost effective to ship the ore rather than the gas.
* To eliminate fossil fuel use in iron and steel making, renewable hydrogen gas can be used in place of syngas to produce DRI and eliminate production of greenhouse gases. | 8 | Metallurgy |
According to their material safety data sheets, CFCs and HCFCs are colorless, volatile, non-toxic liquids and gases with a faintly sweet ethereal odor. Overexposure at concentrations of 11% or more may cause dizziness, loss of concentration, central nervous system depression or cardiac arrhythmia. Vapors displace air and can cause asphyxiation in confined spaces. Dermal absorption of chlorofluorocarbons is possible, but low. Where the pulmonary uptake of inhaled chlorofluorocarbons occurs quickly with peak blood concentrations occurring in as little as 15 seconds with steady concentrations evening out after 20 minutes. Absorption of orally ingested chlorofluorocarbons is 35 to 48 times lower compared to inhalation. Although non-flammable, their combustion products include hydrofluoric acid and related species.
Normal occupational exposure is rated at 0.07% and does not pose any serious health risks. | 2 | Environmental Chemistry |
An enantiomer can be named by the direction in which it rotates the plane of polarized light. Clockwise rotation of the light traveling toward the viewer is labeled (+) enantiomer. Its mirror-image is labeled (−). The (+) and (−) isomers have been also termed d- and l- (for dextrorotatory and levorotatory); but, naming with d- and l- is easy to confuse with - and - labeling and is therefore discouraged by IUPAC. | 4 | Stereochemistry |
The working principle of molography is illustrated in Figure 1. Molography is based on diffraction of laser light at a special 2D nanopattern of molecular binding sites on the surface of a sensor chip, termed mologram. A mologram is a coherent assembly of binding sites on a chip that form the blueprint of molecular hologram. The hologram has the shape of a focusing diffractive lens and is illuminated by an evanescent wave. Evanescent waves occur when light is totally internally reflected at an interface of two dielectrics. Biomolecules that bind to the mologram diffract laser light into a diffraction-limited focal spot in three dimensional space, the focal point of the mologram. The intensity of the focused light correlates quadratically with the amount of bound molecules on the mologram and therefore also the number of biomolecular interactions that take place.
In complex biological samples, the concentration of off-target molecules is usually significantly higher than the target molecules. Therefore, even in the absence of recognition elements the off-target molecules readily adsorb to the surface of the sensor. However, this a random process and the off-target molecules do not bind to the ordered binding sites of the mologram. Thus, scattering of off-target molecules is uniform in all spatial directions and therefore off-target molecules hardly contribute to the measured light intensity in the narrow solid angle of the focal spot. In essence, focal molography forms a high-frequency spatial affinity lock-in that only measures the Fourier component of the refractive index distribution that corresponds to the binding modulation of the mologram. Since the environmental noise (temperature gradients, buffer changes and nonspecific binding of off-target molecules) is inversely proportional to the spatial frequency and therefore situated mostly at "long" spatial periods most of the noise can be rejected. This property makes molography extremely robust and renders temperature stabilization or sensor equilibration obsolete. | 1 | Biochemistry |
The diagram above depicts a reaction between m-cresol and methanol where a c-alkylation product is produced. The c-alkylation reaction means that instead of replacing the hydrogen atom on the -OH group, the methyl group (from the methanol) replaces the hydrogen on a carbon in the benzene ring. The products of this c-alkylation can be in either a para- or ortho- orientation on the molecule, as seen in the diagram, and water, which is not shown. Isomers of the dimethylphenol (DMP) compound are the products of the para- and ortho-c-alkylation. Dimethylphenol (DMP) compound is listed as an aquatic hazard by characteristic, and is toxic with long lasting effects. | 7 | Physical Chemistry |
Enol esters are formed from ketenes with enolisable carbonyl compounds. The following example shows the reaction of ethenone with acetone to form a propen-2-yl acetate: | 0 | Organic Chemistry |
The Societys wholly owned publishing subsidiary, Portland Press, publishes books, a magazine, The Biochemist', and several print and online academic journals:
*Biochemical Journal
*Biochemical Society Symposium (online only)
*Biochemical Society Transactions
*Cell Signalling Biology
*Clinical Science
*Essays in Biochemistry
*Bioscience Reports
The Societys flagship publication, the Biochemical Journal', celebrated its centenary in 2006 with the launch of a free online archive back to its first issue in 1906. | 1 | Biochemistry |
Cleavage forms parallel to crystallographic planes:
*Basal, pinacoidal, or planar cleavage occurs when there is only cleavage plane. Talc has basal cleavage. Mica (like muscovite or biotite) also has basal cleavage; this is why mica can be peeled into thin sheets.
*Prismatic cleavage occurs when there are cleavage planes in a crystal that intersect at 90 degrees. Spodumene exhibits prismatic cleavage.
*Non-Prismatic cleavage occurs when there are cleavage planes in a crystal that do not intersect at 90 degrees (two non-perpendicular directions of cleavage, e.g 60 & 120 degrees).
*Cubic cleavage occurs when there are cleavage planes intersecting at 90 degrees. Halite (or salt) has cubic cleavage, and therefore, when halite crystals are broken, they will form more cubes.
*Rhombohedral cleavage occurs when there are cleavage planes intersecting at angles that are not 90 degrees. Calcite has rhombohedral cleavage.
*Octahedral cleavage occurs when there are cleavage planes in a crystal. Fluorite exhibits perfect octahedral cleavage. Octahedral cleavage is common for semiconductors. Diamond also has octahedral cleavage.
*Dodecahedral cleavage occurs when there are cleavage planes in a crystal. Sphalerite has dodecahedral cleavage. | 3 | Analytical Chemistry |
Nuclear DNA is normally wrapped tightly around histones, making it hard or impossible for the transcription machinery to access the DNA. This association is due primarily to the electrostatic attraction between the DNA and histones as the DNA phosphate backbone is negatively charged and histones are rich in lysine residues, which are positively charged. The tight DNA-histone association prevents the transcription of DNA into RNA.
Many coactivators have histone acetyltransferase (HAT) activity meaning that they can acetylate specific lysine residues on the N-terminal tails of histones. In this method, an activator binds to an enhancer site and recruits a HAT complex that then acetylates nucleosomal promoter-bound histones by neutralizing the positively charged lysine residues. This charge neutralization causes the histones to have a weaker bond to the negatively charged DNA, which relaxes the chromatin structure, allowing other transcription factors or transcription machinery to bind to the promoter (transcription initiation). Acetylation by HAT complexes may also help keep chromatin open throughout the process of elongation, increasing the speed of transcription.
Acetylation of the N-terminal histone tail is one of the most common protein modifications found in eukaryotes, with about 85% of all human proteins being acetylated. Acetylation is crucial for synthesis, stability, function, regulation and localization of proteins and RNA transcripts.
HATs function similarly to N-terminal acetyltransferases (NATs) but their acetylation is reversible unlike in NATs. HAT mediated histone acetylation is reversed using histone deacetylase (HDAC), which catalyzes the hydrolysis of lysine residues, removing the acetyl group from the histones. This causes the chromatin to close back up from their relaxed state, making it difficult for the transcription machinery to bind to the promoter, thus repressing gene expression.
Examples of coactivators that display HAT activity include CARM1, CBP and EP300. | 1 | Biochemistry |
In 1994, Donald and Kevin Dahm began using numerical techniques to calculate remission and transmission from samples of varying numbers of plane parallel layers from absorption and remission fractions for a single layer. Their plan was to "start with a simple model, treat the problem numerically rather than analytically, then look for analytical functions that describe the numerical results. Assuming success with that, the model would be made more complex, allowing more complex analytical expressions to be derived, eventually, leading to an understanding of diffuse reflection at a level that appropriately approximated particulate samples." They were able to show the fraction of incident light remitted, , and transmitted, , by a sample composed of layers, each absorbing a fraction and remitting a fraction of the light incident upon it, could be quantified by an Absorption/Remission function (symbolized and called the ART function), which is constant for a sample composed of any number of identical layers. | 7 | Physical Chemistry |
Ptaquiloside is a norsesquiterpene glucoside produced by bracken ferns (majorly Pteridium aquilinum) during metabolism. It is identified to be the main carcinogen of the ferns and to be responsible for their biological effects, such as haemorrhagic disease and bright blindness in livestock and oesophageal, gastric cancer in humans. Ptaquiloside has an unstable chemical structure and acts as a DNA alkylating agent under physiological conditions. It was first isolated and characterized by Yamada and co-workers in 1983.
The pure form ptaquiloside is a colorless amorphous compound. It is readily soluble in water and fairly soluble in ethyl acetate. Except in the plants, ptaquiloside has been detected in the milk and meat of affected livestock, as well as in the underground water and dry soil around bracken fern vegetation. The prevalence of ptaquiloside in daily sources along with its carcinogenic effects make it an increasing biological hazard in modern days. | 0 | Organic Chemistry |
Valence is defined by the IUPAC as:
:The maximum number of univalent atoms (originally hydrogen or chlorine atoms) that may combine with an atom of the element under consideration, or with a fragment, or for which an atom of this element can be substituted.
An alternative modern description is:
: The number of hydrogen atoms that can combine with an element in a binary hydride or twice the number of oxygen atoms combining with an element in its oxide or oxides.
This definition differs from the IUPAC definition as an element can be said to have more than one valence. | 3 | Analytical Chemistry |
Let be an orientation-preserving rigid motion of R. The set of these transformations is a subgroup of Euclidean motions known as the special Euclidean group SE(3). These rigid motions are defined by transformations of x in R given by
consisting of a three-dimensional rotation A followed by a translation by the vector d.
A three-dimensional rotation A has a unique axis that defines a line L. Let the unit vector along this line be S so that the translation vector d can be resolved into a sum of two vectors, one parallel and one perpendicular to the axis L, that is,
In this case, the rigid motion takes the form
Now, the orientation preserving rigid motion D* = A(x) + d transforms all the points of R so that they remain in planes perpendicular to L. For a rigid motion of this type there is a unique point c in the plane P perpendicular to L through 0, such that
The point C can be calculated as
because d does not have a component in the direction of the axis of A.
A rigid motion D* with a fixed point must be a rotation of around the axis L through the point c. Therefore, the rigid motion
consists of a rotation about the line L followed by a translation by the vector d in the direction of the line L.
Conclusion: every rigid motion of R is the result of a rotation of R about a line L followed by a translation in the direction of the line. The combination of a rotation about a line and translation along the line is called a screw motion. | 3 | Analytical Chemistry |
The energy of Rydberg states can be refined by including a correction called the quantum defect in the Rydberg formula. The "quantum defect" correction is associated with the presence of a distributed ionic core. Even for many electronically excited molecular systems, the ionic core interaction with an excited electron can take on the general aspects of the interaction between the proton and the electron in the hydrogen atom. The spectroscopic assignment of these states follows the Rydberg formula and they are called Rydberg states of molecules. | 7 | Physical Chemistry |
This molecular logic gate illustrated demonstrates the advancement from redox-fluorescent switches to multi-input logic gates with an electrochemical switch. This two-input AND logic gate incorporates a tertiary amine proton receptor and a tetrathiafulvalene redox donor. These groups, when attached to anthracene, can simultaneously process information concerning acid concentration and oxidizing ability of the solution. | 6 | Supramolecular Chemistry |
In the early years of the twentieth century, the vapor absorption cycle using water-ammonia systems or LiBr-water was popular and widely used. After the development of the vapor compression cycle, the vapor absorption cycle lost much of its importance because of its low coefficient of performance (about one fifth of that of the vapor compression cycle). Today, the vapor absorption cycle is used mainly where fuel for heating is available but electricity is not, such as in recreational vehicles that carry LP gas. It is also used in industrial environments where plentiful waste heat overcomes its inefficiency.
The absorption cycle is similar to the compression cycle, except for the method of raising the pressure of the refrigerant vapor. In the absorption system, the compressor is replaced by an absorber which dissolves the refrigerant in a suitable liquid, a liquid pump which raises the pressure and a generator which, on heat addition, drives off the refrigerant vapor from the high-pressure liquid. Some work is needed by the liquid pump but, for a given quantity of refrigerant, it is much smaller than needed by the compressor in the vapor compression cycle. In an absorption refrigerator, a suitable combination of refrigerant and absorbent is used. The most common combinations are ammonia (refrigerant) with water (absorbent), and water (refrigerant) with lithium bromide (absorbent). | 7 | Physical Chemistry |
Though polysaccharides are also biopolymers, it is not so common to talk of sequencing a polysaccharide, for several reasons. Although many polysaccharides are linear, many have branches. Many different units (individual monosaccharides) can be used, and bonded in different ways. However, the main theoretical reason is that whereas the other polymers listed here are primarily generated in a template-dependent manner by one processive enzyme, each individual join in a polysaccharide may be formed by a different enzyme. In many cases the assembly is not uniquely specified; depending on which enzyme acts, one of several different units may be incorporated. This can lead to a family of similar molecules being formed. This is particularly true for plant polysaccharides. Methods for the structure determination of oligosaccharides and polysaccharides include NMR spectroscopy and methylation analysis. | 1 | Biochemistry |
As listed by ECS:
* 2023 Fred Roozeboom
* 2021 Hiroshi Iwai
* 2019 David J. Lockwood
* 2015 Yue Kuo
* 2005 Dennis Hess
* 1999 Isamu Akasaki
* 1995 Wayne L. Worrell
* 1993 Bruce E. Deal
* 1987 Alfred Y. Cho
* 1985 Jerry M. Woodall
* 1983 Nick Holonyak, Jr.
* 1981 Gerald L. Pearson
* 1979 Morton B. Panish
* 1977 Robert N. Hall
* 1973 William G. Pfann | 7 | Physical Chemistry |
Boyles law was perhaps the first expression of an equation of state. In 1662 Robert Boyle performed a series of experiments employing a J-shaped glass tube, which was sealed on one end. Mercury was added to the tube, trapping a fixed quantity of air in the short, sealed end of the tube. Then the volume of gas was carefully measured as additional mercury was added to the tube. The pressure of the gas could be determined by the difference between the mercury level in the short end of the tube and that in the long, open end. The image of Boyles equipment shows some of the exotic tools used by Boyle during his study of gases.
Through these experiments, Boyle noted that the pressure exerted by a gas held at a constant temperature varies inversely with the volume of the gas. For example, if the volume is halved, the pressure is doubled; and if the volume is doubled, the pressure is halved. Given the inverse relationship between pressure and volume, the product of pressure (P) and volume (V) is a constant (k) for a given mass of confined gas as long as the temperature is constant. Stated as a formula, thus is:
Because the before and after volumes and pressures of the fixed amount of gas, where the before and after temperatures are the same both equal the constant k, they can be related by the equation: | 7 | Physical Chemistry |
It can also be used with highly specific meanings in specialised contexts. In the description of protein structure, in particular in the Protein Data Bank file format, a heteroatom record (HETATM) describes an atom as belonging to a small molecule cofactor rather than being part of a biopolymer chain. | 0 | Organic Chemistry |
Alkenes are named for their parent alkane chain with the suffix "-ene" and a numerical root indicating the position of the carbon with the lower number for each double bond in the chain: is but-1-ene.
Multiple double bonds take the form -diene, -triene, etc., with the size prefix of the chain taking an extra "a": is buta-1,3-diene. Simple cis and trans isomers may be indicated with a prefixed cis- or trans-: cis-but-2-ene, trans-but-2-ene. However, cis- and trans- are relative descriptors. It is IUPAC convention to describe all alkenes using absolute descriptors of Z- (same side) and E- (opposite) with the Cahn–Ingold–Prelog priority rules (see alse E–Z notation). | 0 | Organic Chemistry |
Statins are a class of drugs used to treat cardiovascular disease by lowering lipid levels, specifically LDL-C levels. Statins have shown to reduce new cardiovascular events by 30-40%. However, complications may still arise even after taking the drug and some patients are statin-intolerant. Lipoprotein apheresis therapy is another nonsurgical treatment for reducing LDL-C concentrations.
PCSK9 inhibitors are a new drug that can replace statins and lipoprotein apheresis therapy. For patients that are statin-intolerant, PCSK9 inhibitors can provide a therapeutic alternative. | 1 | Biochemistry |
He is a member of American Academy of Arts and Sciences, National Academy of Sciences, American Philosophical Society, European Molecular Biology Organization, American Crystallographic Association and American Association for the Advancement of Science. | 1 | Biochemistry |
The electronic transitions in organic compounds and some other compounds can be determined by ultraviolet–visible spectroscopy, provided that transitions in the ultraviolet (UV) or visible range of the electromagnetic spectrum exist for the compound. Electrons occupying a HOMO (highest-occupied molecular orbital) of a sigma bond (σ) can get excited to the LUMO (lowest-unoccupied molecular orbital) of that bond. This process is denoted as a transition. Likewise, promotion of an electron from a pi-bonding orbital (π) to an antibonding pi orbital (π*) is denoted as a transition. Auxochromes with free electron pairs (denoted as "n") have their own transitions, as do aromatic pi bond transitions. Sections of molecules which can undergo such detectable electron transitions can be referred to as chromophores, since such transitions absorb electromagnetic radiation (light), which may be hypothetically perceived as color somewhere in the electromagnetic spectrum. The following molecular electronic transitions exist:
In addition to these assignments, electronic transitions also have so-called bands associated with them. The following bands are defined (by A. Burawoy in 1930):
*The R-band ();
*The K-band ();
*The B-band (from benzoic);
*The E-band (from ethylenic).
For example, the absorption spectrum for ethane shows a transition at 135 nm and that of water a transition at 167 nm with an extinction coefficient of 7,000. Benzene has three transitions; two E-bands at 180 and 200 nm and one B-band at 255 nm with extinction coefficients respectively 60,000, 8,000 and 215. These absorptions are not narrow bands but are generally broad because the electronic transitions are superimposed on the other molecular energy states. | 7 | Physical Chemistry |
Mutation studies in prokaryotes and eukaryotes show that ractopamine is not mutagenic. However, the results of several in vitro studies, including chromosome aberration tests in human lymphocytes, are positive. The positive genotoxic results are explained with limited evidence to be due to a secondary auto-oxidative mechanism from ractopamine-catechol-producing reactive intermediates. | 4 | Stereochemistry |
Nitrate was also used as a film stock through nitrocellulose. Due to its high combustibility, the studios swapped to acetate safety film in 1950. | 0 | Organic Chemistry |
Singlet and triplet carbenes exhibit divergent reactivity.
Triplet carbenes are diradicals, and participate in stepwise radical additions. Triplet carbene addition necessarily involves (at least one) intermediate with two unpaired electrons.
Singlet carbenes can (and do) react as electrophiles, nucleophiles, or ambiphiles. Their reactions are typically concerted and often cheletropic. Singlet carbenes are typically electrophilic, unless they have a filled p orbital, in which case they can react as Lewis bases. The Bamford-Stevens reaction gives carbenes in aprotic solvents and carbenium ions in protic ones.
The different mechanisms imply that singlet carbene additions are stereospecific but triplet carbene additions stereoselective. Methylene from diazomethane photolysis reacts with either cis- or trans-2-butene to give a single diastereomer of 1,2-dimethylcyclopropane: cis from cis and trans from trans. Thus methylene is a singlet carbene; if it were triplet, the product would not depend on the starting alkene geometry. | 0 | Organic Chemistry |
Mulder was born in Utrecht and earned a medical degree from Utrecht University.
He became a reader of chemistry in Rotterdam and in 1840 he was appointed professor at Utrecht University. | 0 | Organic Chemistry |
Glycoside hydrolases (or glycosidases), are enzymes that break glycosidic bonds. Glycoside hydrolases typically can act either on α- or on β-glycosidic bonds, but not on both. This specificity allows researchers to obtain glycosides in high epimeric excess, one example being Wen-Ya Lus conversion of D-Glucose to Ethyl β-D-glucopyranoside using naturally-derived glucosidase. It is worth noting that Wen-Ya Lu utilized glucosidase in a reverse manner opposite to the enzymes biological functionality: | 0 | Organic Chemistry |
Flies lacking in FICD (CG9523) have been described as blind. Initially, this defect was attributed to a role for FICD on the cell surface of capitate projections - a putative site of neurotransmitter recycling however a later study implicated FICD-mediated AMPylation of BiP Thr366 in the visual problem | 1 | Biochemistry |
Vacuum ceramic filters are to be found in the following industries:
* paper making
* metallurgy
* water treatment
* chemical
* ore beneficiation process in mining (iron, gold, nickel, copper and quartz).
The process is used during a large continuous process of separating free filtering suspensions where washing is not required. Basically the filter works to separates solid-liquid mixtures by removing the water from mineral concentrates and moulding the feed slurries into pellets. This is accomplished by capillary action under low vacuum pressure. The pelletizing of the slurries is done by adding some solid matter to the sewage sludge so that water can be easily removed from the mixture. Eventually, the final cake products contain very little moisture and can be deposited as sewage. This process is commonly followed by bleaching and heating the cake. The end product of this filtration is a dry cake and filtrate containing no solid product. | 3 | Analytical Chemistry |
Tholins were detected on the dwarf planet Ceres by the Dawn mission. Most of the planet's surface is extremely rich in carbon, with approximately 20% carbon by mass in its near surface. The carbon content is more than five times higher than in carbonaceous chondrite meteorites analyzed on Earth. | 9 | Geochemistry |
In chemistry, the mass concentration (or ) is defined as the mass of a constituent divided by the volume of the mixture .
For a pure chemical the mass concentration equals its density (mass divided by volume); thus the mass concentration of a component in a mixture can be called the density of a component in a mixture. This explains the usage of (the lower case Greek letter rho), the symbol most often used for density. | 3 | Analytical Chemistry |
Notable people with mitochondrial disease include:
* Mattie Stepanek, a poet, peace advocate, and motivational speaker who had dysautonomic mitochondrial myopathy, and who died at age 13.
* Rocco Baldelli, a coach and former center fielder in Major League Baseball who had to retire from active play at age 29 due to mitochondrial channelopathy.
* Charlie Gard, a British boy who had mitochondrial DNA depletion syndrome; decisions about his care were taken to various law courts.
* Charles Darwin, a nineteenth century naturalist who suffered from a disabling illness, is speculated to have MELAS syndrome. | 1 | Biochemistry |
Dealuminification is a corresponding process for aluminum alloys. Similar effects for different metals are decarburization (removal of carbon from the surface of alloy), decobaltification, denickelification, etc. The prototypical system for dealloying to create nano-porous metals is the np-Au system, which is created by selectively leaching Ag out of an Au-Ag homogenous alloy. | 8 | Metallurgy |
Garnet-Garnet reaction can be used to estimate the redox state of transition zone.
A recent study showed that the oxygen fugacity of transition referred from Garnet-Garnet reaction is -0.26 to +3 relative to the Fe-FeO (IW, iron- wütstite) oxygen buffer. | 9 | Geochemistry |
The Dukhin number () is a dimensionless quantity that characterizes the contribution of the surface conductivity to various electrokinetic and electroacoustic effects, as well as to electrical conductivity and permittivity of fluid heterogeneous systems. The number was named after Stanislav and Andrei Dukhin. | 7 | Physical Chemistry |
Pentamethyltantalum was reported by Richard Schrock in 1974.
Salts of [Ta(CH)] are prepared by alkylation of TaF using methyl lithium:
:TaF + 6 LiCH → Li[Ta(CH)] + 5 LiF | 0 | Organic Chemistry |
Leslie Hicks is an American associate professor of analytical chemistry at the University of North Carolina at Chapel Hill. Her work primarily focuses on the study of proteomics and protein post-translational modifications using mass spectrometry, and identifying biologically active peptides in plants. | 3 | Analytical Chemistry |
* Photosynthesis, a process whereby carbon dioxide and water are transformed into a number of organic molecules in plant cells.
* Nitrogen fixation from the soil into organic molecules by symbiotic bacteria which live in the roots of certain plants, such as Leguminosae.
* Magnesium supplements orotate, oxide, sulfate, citrate, and glycerate are all structurally similar. However, oxide and sulfate are not water-soluble and do not enter the bloodstream, while orotate and glycerate have normal exiguous liver conversion. Chlorophyll sources or magnesium citrate are highly bioassimilable.
* The absorption of nutrients into the body after digestion in the intestine and its transformation in biological tissues and fluids. | 1 | Biochemistry |
In 2011, a record outbreak of blooming microcystis occurred in Lake Erie, in part related to the wettest spring on record, and expanded lake bottom dead zones, reduced fish populations, fouled beaches, and damaged the local tourism industry, which generates more than $10 billion in revenue annually.
In August 2014, the City of Toledo, Ohio detected unsafe levels of microcystin in its water supply due to harmful algal blooms in Lake Erie, the shallowest of the Great Lakes. The city issued an advisory to approximately 500,000 people that the water was not safe for drinking or cooking. An Ohio state task force found that Lake Erie received more phosphorus than any other Great Lake, both from crop land, due to the farming practices, and from urban water-treatment centres. | 2 | Environmental Chemistry |
An acid is classified as "strong" when the concentration of its undissociated species is too low to be measured. Any aqueous acid with a pK value of less than 0 is almost completely deprotonated and is considered a strong acid. All such acids transfer their protons to water and form the solvent cation species (HO in aqueous solution) so that they all have essentially the same acidity, a phenomenon known as solvent leveling. They are said to be fully dissociated in aqueous solution because the amount of undissociated acid, in equilibrium with the dissociation products, is below the detection limit. = −1.4) behaves as a strong acid. When the ratio of water molecules to acid molecules in a solution of an acid is too small to fully solvate the dissociation products, dissociation is not complete, for example, with extremely concentrated solutions of sulfuric acid and hydrochloric acid.}}.
--> Likewise, any aqueous base with an association constant pK less than about 0, corresponding to pK greater than about 14, is leveled to OH and is considered a strong base.
Nitric acid, with a pK value of around −1.7, behaves as a strong acid in aqueous solutions with a pH greater than 1. At lower pH values it behaves as a weak acid.
pK values for strong acids have been estimated by theoretical means. For example, the pK value of aqueous HCl has been estimated as −9.3. | 7 | Physical Chemistry |
Hydroxylamine (also known as hydroxyammonia) is an inorganic compound with the chemical formula . The compound is in a form of a white hygroscopic crystals. Hydroxylamine is almost always provided and used as an aqueous solution. It is consumed almost exclusively to produce Nylon-6. The oxidation of Ammonia| to hydroxylamine is a step in biological nitrification. | 0 | Organic Chemistry |
Pyruvate carboxylase deficiency is an inherited metabolic disorder where anaplerosis is greatly reduced. Other anaplerotic substrates such as the odd-carbon-containing triglyceride triheptanoin can be used to treat this disorder. | 1 | Biochemistry |
Cassies law, or the Cassie equation, describes the effective contact angle θ for a liquid on a chemically heterogeneous surface, i.e. the surface of a composite material consisting of different chemistries, that is non uniform throughout. Contact angles are important as they quantify a surfaces wettability, the nature of solid-fluid intermolecular interactions. Cassies law is reserved for when a liquid completely covers both smooth and rough' heterogeneous surfaces.
More of a rule than a law, the formula found in literature for two materials is;
where and are the contact angles for components 1 with fractional surface area , and 2 with fractional surface area in the composite material respectively. If there exist more than two materials then the equation is scaled to the general form of;
, with . | 7 | Physical Chemistry |
Carbene radicals are a special class of organometallic carbenes. The carbene radical can be formed by one-electron reduction of Fischer-type carbenes using an external reducing agent, or directly upon carbene formation at an open-shell transition metal complex (in particular low-spin cobalt(II) complexes) using diazo compounds and related carbene precursors.
Cobalt(III)-carbene radicals have found catalytic applications in cyclopropanation reactions, as well as in a variety of other catalytic radical-type ring-closing reactions.
Theoretical calculations and EPR studies confirmed their radical-type behaviour and explained the bonding interactions underlying the stability of the carbene radical.
Stable carbene radicals of other metals are known, but the catalytically relevant cobalt(III)-carbene radicals have thus far only been synthesized as long-lived reactive intermediates. | 0 | Organic Chemistry |
Growth factor receptor-bound protein 2, also known as Grb2, is an adaptor protein involved in signal transduction/cell communication. In humans, the GRB2 protein is encoded by the GRB2 gene.
The protein encoded by this gene binds receptors such as the epidermal growth factor receptor and contains one SH2 domain and two SH3 domains. Its two SH3 domains direct complex formation with proline-rich regions of other proteins, and its SH2 domain binds tyrosine phosphorylated sequences. This gene is similar to the sem-5 gene of Caenorhabditis elegans, which is involved in the signal transduction pathway. Two alternatively spliced transcript variants encoding different isoforms have been found for this gene. | 1 | Biochemistry |
Type B (70%Pt/30%Rh–94%Pt/6%Rh, by weight) thermocouples are suited for use at up to 1800 °C. Type-B thermocouples produce the same output at 0 °C and 42 °C, limiting their use below about 50 °C. The emf function has a minimum around 21 °C, meaning that cold-junction compensation is easily performed, since the compensation voltage is essentially a constant for a reference at typical room temperatures. | 8 | Metallurgy |
Crystallography is a technique that characterizes the chemical structure of materials at the atomic level by analyzing the diffraction patterns of electromagnetic radiation or particles that have been deflected by atoms in the material. X-rays are most commonly used. From the raw data, the relative placement of atoms in space may be determined. | 3 | Analytical Chemistry |
Hydrothermal H may have played a major role in pre-biotic chemistry. Production of H by serpentinization supported formation of the reactants proposed in the iron-sulfur world origin of life hypothesis. The subsequent evolution of hydrogenotrophic methanogenesis is hypothesized as one of the earliest metabolisms on Earth.
Serpentinization can occur on any planetary body with chondritic composition. The discovery of H on other ocean worlds, such as Enceladus, suggests that similar processes are ongoing elsewhere in the Solar System, and potentially in other planetary systems as well. | 1 | Biochemistry |
The product is manufactured by hydrogenation of methylene diphenyl diisocyanate. It may also be manufactured by phosgenation of 4,4-Diaminodicyclohexylmethane. | 0 | Organic Chemistry |
The surface energy is measured in units of joules per square meter, which is equivalent in the case of liquids to surface tension, measured in newtons per meter. The overall surface tension/energy of a liquid can be acquired through various methods using a tensiometer or using the pendant drop method and maximum bubble pressure method.
The interface tension at the interface of the probe liquid and the solid surface can additionally be viewed as being the result of different types of intermolecular forces. As such, surface energies can be subdivided according to the various interactions that cause them, such as the surface energy due to dispersive (e.g. van der Waals forces) and other interactions (e.g. hydrogen bonding, polar interactions, acid–base interactions, etc.). It is often useful for the sessile drop technique to use liquids that are known to be incapable of some of those interactions (see table 1). For example, the surface tension of all straight alkanes is said to be entirely dispersive, and all of the other components are zero. This is algebraically useful, as it eliminates a variable in certain cases and makes these liquids essential testing materials.
The overall surface energy, both for a solid and a liquid, is assumed traditionally to simply be the sum of the components considered. For example, the equation describing the subdivision of surface energy into the contributions of dispersive interactions and polar interactions would be
where σ is the total surface energy of the solid, σ and σ are respectively the dispersive and polar components of the solid surface energy,
σ is the total surface tension/surface energy of the liquid, and
σ and σ are respectively the dispersive and polar components of the surface tension.
In addition to the tensiometer and pendant drop techniques, the sessile drop technique can be used in some cases to separate the known total surface energy of a liquid into its components. This is done by reversing the above idea with the introduction of a reference solid surface that is assumed to be incapable of polar interactions, such as polytetrafluoroethylene (PTFE). | 7 | Physical Chemistry |
* Orbifold signature:
* Coxeter notation (rectangular): [((∞,2),(∞,2))]
* Coxeter notation (square): [4,4]
* Lattice: rectangular
* Point group: D
* The group pgg contains two rotation centres of order two (180°), and glide reflections in two perpendicular directions. The centres of rotation are not located on the glide reflection axes. There are no reflections.
;Examples of group pgg | 3 | Analytical Chemistry |
PHLPP1 and 2 also dephosphorylate the hydrophobic motifs of two classes of the protein kinase C (PKC) family: the conventional PKCs and the novel PKCs. (The third class of PKCs, known as the atypicals, have a phospho-mimetic at the hydrophobic motif, rendering them insensitive to PHLPP.)
The PKC family of kinases consists of 10 isoforms, whose sensitivity to various second messengers is dictated by their domain structure. The conventional PKCs can be activated by calcium and diacylglycerol, two important mediators of G protein-coupled receptor signaling. The novel PKCs are activated by diacylglycerol but not calcium, while the atypical PKCs are activated by neither.
The PKC family, like Akt, plays roles in cell survival and motility. Most PKC isoforms are anti-apoptotic, although PKCδ (a novel PKC isoform) is pro-apoptotic in some systems.
Although PKC possesses the same phosphorylation sites as Akt, its regulation is quite different. PKC is constitutively phosphorylated, and its acute activity is regulated by binding of the enzyme to membranes. Dephosphorylation of PKC at the hydrophobic motif by PHLPP allows PKC to be dephosphorylated at two other sites (the activation loop and the turn motif). This in turn renders PKC sensitive to degradation. Thus, prolonged increases in PHLPP expression or activity inhibit PKC phosphorylation and stability, decreasing the total levels of PKC over time. | 1 | Biochemistry |
A photocyte is a cell that specializes in catalyzing enzymes to produce light (bioluminescence). Photocytes typically occur in select layers of epithelial tissue, functioning singly or in a group, or as part of a larger apparatus (a photophore). They contain special structures termed as photocyte granules. These specialized cells are found in a range of multicellular animals including ctenophora, coelenterates (cnidaria), annelids, arthropoda (including insects) and fishes. Although some fungi are bioluminescent, they do not have such specialized cells. | 1 | Biochemistry |
Vitamin D was discovered in 1922 following on from previous research. American researchers Elmer McCollum and Marguerite Davis in 1914 discovered a substance in cod liver oil which later was called "vitamin A". British doctor Edward Mellanby noticed dogs that were fed cod liver oil did not develop rickets and concluded vitamin A, or a closely associated factor, could prevent the disease. In 1922, Elmer McCollum tested modified cod liver oil in which the vitamin A had been destroyed. The modified oil cured the sick dogs, so McCollum concluded the factor in cod liver oil which cured rickets was distinct from vitamin A. He called it vitamin D because he thought it was the fourth vitamin to be named. It was not initially realized that vitamin D can be synthesized by humans (in the skin) through exposure to UV light, and therefore is technically not a vitamin, but rather can be considered to be a hormone.
In 1925, it was established that when 7-dehydrocholesterol is irradiated with light, a form of a fat-soluble substance is produced (now known as D). Alfred Fabian Hess stated: "Light equals vitamin D." Adolf Windaus, at the University of Göttingen in Germany, received the Nobel Prize in Chemistry in 1928 for his work on the constitution of sterols and their connection with vitamins. In 1929, a group at NIMR in Hampstead, London, were working on the structure of vitamin D, which was still unknown, as well as the structure of steroids. A meeting took place with J.B.S. Haldane, J.D. Bernal, and Dorothy Crowfoot to discuss possible structures, which contributed to bringing a team together. X-ray crystallography demonstrated the sterol molecules were flat, not as proposed by the German team led by Windaus. In 1932, Otto Rosenheim and Harold King published a paper putting forward structures for sterols and bile acids which found immediate acceptance. The informal academic collaboration between the team members Robert Benedict Bourdillon, Otto Rosenheim, Harold King, and Kenneth Callow was very productive and led to the isolation and characterization of vitamin D. At this time, the policy of the Medical Research Council was not to patent discoveries, believing the results of medical research should be open to everybody. In the 1930s, Windaus clarified further the chemical structure of vitamin D.
In 1923, American biochemist Harry Steenbock at the University of Wisconsin demonstrated that irradiation by ultraviolet light increased the vitamin D content of foods and other organic materials. After irradiating rodent food, Steenbock discovered the rodents were cured of rickets. Using of his own money, Steenbock patented his invention. His irradiation technique was used for foodstuffs, most notably for milk. By the expiration of his patent in 1945, rickets had been all but eliminated in the US.
In 1969, a specific binding protein for vitamin D called the vitamin D receptor was identified. Shortly thereafter, the conversion of vitamin D to calcifediol and then to calcitriol, the biologically active form, was confirmed. The photosynthesis of vitamin D in skin via previtamin D and its subsequent metabolism was described in 1980. | 1 | Biochemistry |
El-Sayed was born in Zifta, Egypt and spent his early life in Cairo. He earned his B.Sc. in chemistry from Ain Shams University Faculty of Science, Cairo in 1953. El-Sayed earned his doctoral degree in chemistry from Florida State University working with Michael Kasha, the last student of the legendary G. N. Lewis. While attending graduate school he met and married Janice Jones, his wife of 48 years. He spent time as a post-doctoral researcher at Harvard University, Yale University and the California Institute of Technology before joining the faculty of the University of California at Los Angeles in 1961. In 1994, he retired from UCLA and accepted the position of Julius Brown Chair and Regents Professor of Chemistry and Biochemistry at the Georgia Institute of Technology. He led the [http://www.ldl.gatech.edu/ Laser Dynamics Lab] there until his full retirement in 2020.
El-Sayed is a former editor-in-chief of the Journal of Physical Chemistry (1980–2004). | 1 | Biochemistry |
Bromocresol green (BCG) is a dye of the triphenylmethane family (triarylmethane dyes). It belongs to a class of dyes called sulfonephthaleins. It is used as a pH indicator in applications such as growth mediums for microorganisms and titrations. In clinical practise, it is commonly used as a diagnostic technique. The most common use of bromocresol green is to measure serum albumin concentration within mammalian blood samples in possible cases of kidney failure and liver disease. In chemistry, bromocresol green is used in Thin-layer chromatography staining solutions to visualize acidic compounds. | 3 | Analytical Chemistry |
The concentration of naturally produced HMB has been measured in several human body fluids using nuclear magnetic resonance spectroscopy, liquid chromatography–mass spectrometry, and gas chromatography–mass spectrometry methods. In the blood plasma and cerebrospinal fluid (CSF) of healthy adults, the average molar concentration of HMB has been measured at 4.0 micromolar (μM). The average concentration of HMB in the intramuscular fluid of healthy men of ages has been measured at 7.0 μM. In the urine of healthy individuals of any age, the excreted urinary concentration of HMB has been measured in a range of micromoles per millimole (μmol/mmol) of creatinine. In the breast milk of healthy lactating women, HMB and have been measured in ranges of μg/L and mg/L. In comparison, HMB has been detected and measured in the milk of healthy cows at a concentration of μg/L. This concentration is far too low to be an adequate dietary source of HMB for obtaining pharmacologically active concentrations of the compound in blood plasma.
In a study where participants consumed 2.42 grams of pure while fasting, the average plasma HMB concentration increased from a basal level of 5.1 to 408 μM after 30 minutes. At 150 minutes post-ingestion, the average plasma HMB concentration among participants was 275 μM.
Abnormal HMB concentrations in urine and blood plasma have been noted in several disease states where it may serve as a diagnostic biomarker, particularly in the case of metabolic disorders. The following table lists some of these disorders along with the associated HMB concentrations detected in urine or blood plasma. | 1 | Biochemistry |
PbSnSe/PbSrSe quantum well materials, which can be grown by MBE on silicon substrates, have been proposed for low cost TPV device fabrication. These IV-VI semiconductor materials can have bandgaps between 0.3 and 0.6 eV. Their symmetric band structure and lack of valence band degeneracy result in low Auger recombination rates, typically more than an order of magnitude smaller than those of comparable bandgap III-V semiconductor materials. | 7 | Physical Chemistry |
Choi researched jasmonates, which are believed to participate in signal transduction processes between external stresses, such as wounding, pathogenic attack, or cell response by activating the defense genes. He discovered a new enzyme, (EC2.1.1.141) jasmonate carboxyl methyltransferase (JMT), which catalyzes the methylation of jasmonate to MeJA. The overexpression of the JMT gene confers resistance to pathogens. He is currently working to understand the molecular function of MeJA, JMT, and its effector genes. Furthermore, the genetic engineering of crops by application of those genes and knowledge is under investigation.
The major research activity is the discovery of a novel enzyme and its genes encoding jasmonic acid carboxyl methyltransferase, which is involved in stress response and signal transduction in plant. Other achievements are the development of drought tolerant transgenic rice and transferred technology to Mahyco, India and the development of yield-enhanced transgenic rice and transferred technologies to BASF Plant Science in Germany. | 1 | Biochemistry |
Since warming of Earth means less ice on the ground on average, it would cause lower albedo and more sunlight absorbed, hence further increasing Earth's temperature.
As a rough estimate, we note that the average temperature on most of Earth are between -20 and +30 Celsius degree, a good guess will be that 2% of its surface are between -1 and 0 °C, and thus an equivalent area of its surface will be changed from ice-covered (or snow-covered) to either ocean or forest.
For comparison, in the northern hemisphere, the arctic sea ice has shrunk between 1979 and 2015 by 1.43x10 m at maxima and 2.52x10 m at minima, for an average of almost 2x10 m, which is 0.4% of Earth's total surface of 510x10 m. At this time the global temperature rose by ~0.6 °C. The areas of inland glaciers combined (not including the antarctice ice sheet), the antarctic sea ice, and the arctic sea ice are all comparable, so one may expect the change in ice of the arctic sea ice is roughly a third of the total change, giving 1.2% of the Earth surface turned from ice to ocean or bare ground per 0.6 °C, or equivalently 2% per 1 °C. The antarctic ice cap size oscillates, and it is hard to predict its future course, with factors such as relative thermal insulated and constraints due to the Antarctic Circumpolar Current probably playing a part.
As the difference in albedo between ice and e.g. ocean is around 2/3, this means that due to a 1 °C rise, the albedo will drop by 2%*2/3 = 4/3%. However this will mainly happen in northern and southern latitudes, around 60 degrees off the equator, and so the effective area is actually 2% * cos(60) = 1%, and the global albedo drop would be 2/3%.
Since a change in radiation of 1.3% causes a direct change of 1 degree Celsius (without feedback), as calculated above, and this causes another change of 2/3% in radiation due to positive feedback, whice is half the original change, this means the total factor caused by this feedback mechanism would be:
Thus, this feedback would double the effect of the change in radiation, causing a change of ~ 2 K in the global temperature, which is indeed the commonly accepted short-term value. For long-term value, including further feedback mechanisms, ~3K is considered more probable. | 2 | Environmental Chemistry |
The uses that have been derived from Vectorette PCR are many and have been useful to the science of biology. For example, it gives rise to methods that can help during the outbreaks of diseases by making it easier to subtype pathogens that are similar or closely related. It can also be used to help diagnose certain diseases. Earlier in this page it was noted that Vectorette PCR can give rise to multiple functions that can be performed on novel DNA sequences located near a sequence that is already known. These functions like isolating DNA, amplifying it, and analyzing it are behind the uses for Vectorette PCR. These uses are things like genome walking, DNA sequencing for the termini of Yeast Artificial Chromosomes (YAC) and cosmid inserts, being able to map introns and promoters in genomic DNA and regions with mutations, facilitating the sequencing of clones of a large size, and filling in the gaps that arise during the mapping of genomes.
An intron is a DNA sequence that is flanked by exons and therefore located in between them. It is the region that gets cut out while exons are expressed, and so introns do not affect the code of amino acids. Gene expression can be affected by only a number of intronic sequences. Vectorette PCR has been found to be beneficial when it comes to the characterization of these intronic sequences when they are found to be next to known sequences.
cDNA or complementary DNA is a DNA sequence which is complementary to the RNA that is the template when synthesizing DNA during the reverse transcriptase process. Vectorette PCR that utilizes the primers that originate from cDNA gives rise to a method that is capable of acquiring intron sequences which are located adjacent to exons and aiding in the development of the structure of genes. It is able to achieve this when initializing the process with a sequence of cDNA and a clone of a genome.
Vectorette PCR also gives the user an advantage than if he/she were using other existing technologies. The user will be able to carry out tasks like gene manipulation that is cell-free, Vectorette PCR with minimal material to start with, and performing Vectorette PCR with DNA that needs not be of high purity. These advantages allow the user to save time and resources while increasing the range of DNA that can be targeted. | 1 | Biochemistry |
In organic chemistry, phosphinites are organophosphorus compounds with the formula . They are used as ligands in homogeneous catalysis and coordination chemistry. | 0 | Organic Chemistry |
On January 15, 2013, the Regulation (EU) No. 98/2013 of the European Parliament and of the Council on the marketing and use of explosives precursors was adopted.
The Regulation harmonises rules across Europe on the making available, introduction, possession and use, of certain substances or mixtures that could be misused for the illicit manufacture of explosives. | 1 | Biochemistry |
Generally, the role of the arginine finger in catalysis is to function in transition state stabilization to allow water to perform a nucleophilic attack to cleave off a number of phosphate groups. However, there are exceptions, and arginine fingers can assist in other roles. Additionally, arginine fingers may be attached to different subunits or other proteins in a multiprotein complex. Arginine fingers sometimes interact with guanidinium during their role in catalysis. | 1 | Biochemistry |
The photovoltaic effect was experimentally demonstrated first by French physicist Edmond Becquerel. In 1839, at age 19, he built the worlds first photovoltaic cell in his fathers laboratory. Willoughby Smith first described the "Effect of Light on Selenium during the passage of an Electric Current" in a 20 February 1873 issue of Nature. In 1883 Charles Fritts built the first solid state photovoltaic cell by coating the semiconductor selenium with a thin layer of gold to form the junctions; the device was only around 1% efficient. Other milestones include:
* 1888 – Russian physicist Aleksandr Stoletov built the first cell based on the outer photoelectric effect discovered by Heinrich Hertz in 1887.
* 1904 – Julius Elster, together with Hans Friedrich Geitel, devised the first practical photoelectric cell.
* 1905 – Albert Einstein proposed a new quantum theory of light and explained the photoelectric effect in a landmark paper, for which he received the Nobel Prize in Physics in 1921.
* 1941 – Vadim Lashkaryov discovered p-n-junctions in CuO and AgS protocells.
* 1946 – Russell Ohl patented the modern junction semiconductor solar cell, while working on the series of advances that would lead to the transistor.
* 1948 - Introduction to the World of Semiconductors states Kurt Lehovec may have been the first to explain the photo-voltaic effect in the peer reviewed journal Physical Review.
* 1954 – The first practical photovoltaic cell was publicly demonstrated at Bell Laboratories. The inventors were Calvin Souther Fuller, Daryl Chapin and Gerald Pearson.
* 1958 – Solar cells gained prominence with their incorporation onto the Vanguard I satellite. | 7 | Physical Chemistry |
Geranylgeranylation is a form of prenylation, which is a post-translational modification of proteins that involves the attachment of one or two 20-carbon lipophilic geranylgeranyl isoprene units from geranylgeranyl diphosphate to one or two cysteine residue(s) at the C-terminus of specific proteins. Prenylation (including geranylgeranylation) is thought to function, at least in part, as a membrane anchor for proteins.
The process of geranylgeranylation can be catalyzed by either geranylgeranyl transferase I (GGTase I) or Rab GGTase (also GGTase II). GGTase I catalyzes the addition of one geranylgeranyl group onto the C-terminal consensus sequence CAAL (somewhat similar to farnesyltransferase reactions), where C=cysteine, A=any aliphatic amino acid, and L=leucine. Rab GGTase adds a total of two geranylgeranyl groups onto two cysteine residues at the C-terminal consensus sequence CXC or XXCC. The source of the geranylgeranyl group is geranylgeranyl diphosphate, which is synthesized by GGPS1 within the isoprenoid biosynthetic pathway.
An example of this can be seen in the lipid anchoring of the Rho GTPase family of signaling molecules and the gamma subunit of heterotrimeric G proteins. | 1 | Biochemistry |
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