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The advent of synchrotron X-ray sources has been beneficial to X-ray topography techniques. Several of the properties of synchrotron radiation are advantageous also for topography applications: The high collimation (more precisely the small angular source size) allows to reach higher geometrical resolution in topographs, even at larger sample-to-detector distances. The continuous wavelength spectrum facilitates white-beam topography. The high beam intensities available at synchrotrons make it possible to investigate small sample volumes, to work at weaker reflections or further off Bragg-conditions (weak beam conditions), and to achieve shorter exposure times. Finally, the discrete time structure of synchrotron radiation permits topographists to use stroboscopic methods to efficiently visualize time-dependent, periodically recurrent structures (such as acoustic waves on crystal surfaces). | 3 | Analytical Chemistry |
Mycobacterium tuberculosis, the causative agent of tuberculosis, expresses at least six different forms of epoxide hydrolase (forms A-F). The structure of epoxide hydrolase B reveals that the enzyme is a monomer and contains an alpha/beta hydrolase fold. In addition to providing insights into the enzyme mechanism, this hydrolase currently serves as a platform for rational drug design of potent inhibitors. In particular, urea based inhibitors have been developed. These inhibitors directly target the catalytic cavity. It is hypothesized that the structure of epoxide hydrolase B may allow for drug design to inhibit all other Mycobacterium tuberculosis hydrolases as long as they contain similar alpha/beta folds. The structure of hydrolase B contains a cap domain, which is hypothesized to regulate the active site of the hydrolase. Furthermore, Asp104, His333, and Asp302 form the catalytic triad of the protein and is critical to function of the protein. At present, other structures of Mycobacterium tuberculosis hydrolase have not been solved. Model studies on pharmacological susceptibility of these epoxide hydrolases continue. | 1 | Biochemistry |
Aldehydes () take the suffix "-al". If other functional groups are present, the chain is numbered such that the aldehyde carbon is in the "1" position, unless functional groups of higher precedence are present.
If a prefix form is required, "oxo-" is used (as for ketones), with the position number indicating the end of a chain: is 3-oxopropanoic acid. If the carbon in the carbonyl group cannot be included in the attached chain (for instance in the case of cyclic aldehydes), the prefix "formyl-" or the suffix "-carbaldehyde" is used: is cyclohexanecarbaldehyde. If an aldehyde is attached to a benzene and is the main functional group, the suffix becomes benzaldehyde. | 0 | Organic Chemistry |
Dynamic light scattering (DLS) is a technique in physics that can be used to determine the size distribution profile of small particles in suspension or polymers in solution. In the scope of DLS, temporal fluctuations are usually analyzed using the intensity or photon autocorrelation function (also known as photon correlation spectroscopy – PCS or quasi-elastic light scattering – QELS). In the time domain analysis, the autocorrelation function (ACF) usually decays starting from zero delay time, and faster dynamics due to smaller particles lead to faster decorrelation of scattered intensity trace. It has been shown that the intensity ACF is the Fourier transform of the power spectrum, and therefore the DLS measurements can be equally well performed in the spectral domain. DLS can also be used to probe the behavior of complex fluids such as concentrated polymer solutions. | 7 | Physical Chemistry |
The 600 or so subscribing members formed Industry Committees representing each of the main metal interests which discussed and agreed the topics for technical work to be done and a Council that controlled overall finances. Initially there was an annual government grant towards the work but this was changed to support funding for individual projects. When topics for research were agreed and funded by the industry they were then submitted to the government for approval of matching support funding but after the 1960s policy dictated that this became more and more difficult to obtain. The BNF also took on some contracts wholly sponsored by organisations which included some government departments. Individual technical enquiries from members were answered on a free and confidential basis. | 8 | Metallurgy |
Proxenin is the precursor to xenin. It is a 35-amino acid polypeptide. Like xenin, its amino acid sequence exactly matches the N-terminus of coatomer subunit alpha. | 1 | Biochemistry |
In spectrophotometric assays, you follow the course of the reaction by measuring a change in how much light the assay solution absorbs. If this light is in the visible region you can actually see a change in the color of the assay, and these are called colorimetric assays. The MTT assay, a redox assay using a tetrazolium dye as substrate is an example of a colorimetric assay.
UV light is often used, since the common coenzymes NADH and NADPH absorb UV light in their reduced forms, but do not in their oxidized forms. An oxidoreductase using NADH as a substrate could therefore be assayed by following the decrease in UV absorbance at a wavelength of 340 nm as it consumes the coenzyme.
Direct versus coupled assays
Even when the enzyme reaction does not result in a change in the absorbance of light, it can still be possible to use a spectrophotometric assay for the enzyme by using a coupled assay. Here, the product of one reaction is used as the substrate of another, easily detectable reaction. For example, figure 1 shows the coupled assay for the enzyme hexokinase, which can be assayed by coupling its production of glucose-6-phosphate to NADPH production, using glucose-6-phosphate dehydrogenase. | 1 | Biochemistry |
The Public Affairs Office works with the PAAC to advocate for increased research budgets for the major governmental funding agencies, primarily the National Institutes of Health and the National Science Foundation. ASBMB has developed a set of recommendations for pre-medical course requirements consistent with the new Medical College Admission Test. Advocacy efforts also focus on protecting the conditions that promote a successful research environment. In addition, the office works to maintain a healthy relationship between ASBMB members, government officials, and the public in order to foster awareness of the importance of science to everyday life.
As part of their advocacy efforts, ASBMB organizes Capitol Hill Day, an annual event that allows graduate students and trainees to meet their congressional representatives in Washington, D.C. | 1 | Biochemistry |
The single cell gel electrophoresis assay (SCGE, also known as comet assay) is an uncomplicated and sensitive technique for the detection of DNA damage at the level of the individual eukaryotic cell. It was first developed by Östling & Johansson in 1984 and later modified by Singh et al. in 1988. It has since increased in popularity as a standard technique for evaluation of DNA damage/repair, biomonitoring and genotoxicity testing. It involves the encapsulation of cells in a low-melting-point agarose suspension, lysis of the cells in neutral or alkaline (pH>13) conditions, and electrophoresis of the suspended lysed cells. The term "comet" refers to the pattern of DNA migration through the electrophoresis gel, which often resembles a comet.
The comet assay (single-cell gel electrophoresis) is a simple method for measuring deoxyribonucleic acid (DNA) strand breaks in eukaryotic cells. Cells embedded in agarose on a microscope slide are lysed with detergent and high salt to form nucleoids containing supercoiled loops of DNA linked to the nuclear matrix. Electrophoresis at high pH results in structures resembling comets, observed by fluorescence microscopy; the intensity of the comet tail relative to the head reflects the number of DNA breaks. The likely basis for this is that loops containing a break lose their supercoiling and become free to extend toward the anode. This is followed by visual analysis with staining of DNA and calculating fluorescence to determine the extent of DNA damage. This can be performed by manual scoring or automatically by imaging software. | 1 | Biochemistry |
Liquation requires that the silver-rich copper first be melted with approximately three times its weight in lead; as silver has a greater affinity with lead, most of the silver would end up within this rather than the copper. If the copper is assayed and found to contain too little silver for liquation to be financially viable (around 0.31% is the minimum required,) it is melted and allowed to settle so that much of the silver sinks towards the bottom. The ‘tops’ are then drawn off and used to produce copper while the silver-rich ‘bottoms’ are used in the liquation process. The copper-lead alloy created can be tapped off and cast into large plano-convex ingots known as ‘liquation cakes’. As the metals cool and solidify the copper and the silver-containing lead separate as they are immiscible with each other.
The ratio of lead to copper in these cakes is an important factor for the process to work efficiently. Agricola recommended 3 parts copper to 8–12 parts lead. The copper must be assayed to accurately determine how much silver it contains; for copper rich in silver the top end of this ratio was used to make sure the maximum amount of silver possible would end up within the lead. However, there also needs to be enough copper to allow the cakes to keep their shape once most of the lead has drained away; too much copper and it would trap some of the lead within and the process would be very inefficient.
The size of these cakes remained consistent from when Agricola wrote of them in 1556 to the 19th century when the process became obsolete. They were usually thick, about in diameter and weighed from . This consistency is not without reason as the size of the cakes is very important to the smooth running of the liquation process. If the cakes are too small, the product would not be worth the time and costs spent on the process, if they are too large then the copper would begin to melt before the maximum amount of lead has drained away.
The cakes are heated in a liquation furnace, usually four or five at once, to a temperature above the melting point of lead (327°C), but below that of copper (1084 °C), so that the silver-rich lead melts and flows away. As the melting point of lead is so low a high-temperature furnace is not required and it can be fuelled with wood. It is important that this takes place in a reducing atmosphere, i.e. one with little oxygen, to avoid the lead oxidising; the cakes are therefore well covered by charcoal and little air is allowed into the furnace. It is impossible to stop some of the lead oxidising, however, and this drops down and forms spiky projections known as ‘liquation thorns’ in the channel underneath the hearth.
The older and relatively simple method of cupellation can then be used to separate the silver from the lead. If the lead is assayed and found not to contain enough silver to make the cupellation process worthwhile it is reused in liquation cakes until it has sufficient silver.
The ‘exhausted liquation cakes’ which still contain some lead and silver are ‘dried’ in a special furnace which is heated to a higher temperature under oxidising conditions. This is essentially just another stage of liquation and most of the remaining lead is expelled and oxidised to form liquation thorns, though some remains as lead metal. The copper can then be refined to remove other impurities and produce copper metal.
Waste products can be reused to produce new liquation cakes to try to minimise loss of metals, especially silver. The waste products are mostly in the form of liquation thorns from the liquation and the drying process but there are also some slags produced. | 8 | Metallurgy |
During the early Eocene, the continental configuration was such that the Arctic sea was almost entirely cut off from the wider oceans. This meant that mixing — provided today by deep water currents such as the Gulf Stream — did not occur, leading to a stratified water column resembling today's Black Sea.
High temperatures and winds led to high evaporation, increasing the density of the ocean, and — through an increase in rainfall — high discharge from rivers which fed the basin. This low-density freshwater formed a nepheloid layer, floating on the surface of the dense sea.
Even a few centimetres of fresh water would be enough to allow colonization by Azolla; further, this river water would be rich in minerals such as phosphorus, which it would accumulate from mud and rocks it interacted with as it crossed the continents. To further aid the growth of the plant, concentrations of carbon (in the form of carbon dioxide) in the atmosphere are known to have been high at this time.
Blooms alone are not enough to have any geological impact; to permanently draw down CO and cause climate change, the carbon must be sequestered by the plants being buried and the remains rendered inaccessible to decomposing organisms. The anoxic bottom of the Arctic basin, a result of the stratified water column, permitted just this; the anoxic environment inhibits the activity of decomposing organisms and allows the plants to sit unrotted until they are buried by sediment. | 2 | Environmental Chemistry |
Some applications of the diffusion dialysis are explained below.
*Strong aqueous caustic soda solutions can be purified of hemicellulose by diffusion dialysis. This is specific to the largely-obsolete viscose process. The first step in that process is to treat almost-pure cellulose (cotton linters or dissolving pulp) with strong (17-20% w/w) solutions of sodium hydroxide (caustic soda) in water. One effect of that step is to dissolve the hemicelluloses (low-MW polymers). In some circumstances, it is desirable to remove as much hemicellulose as possible out of the process, and that can be done using dialysis.
* Acids can be recovered from aqueous solutions using anion-exchange membranes. That process is an alternative treatment of industrial wastewater. It is used for the recovery of mixed acid (HF+ HNO), the recovery and concentration of Zn and Cu, in HSO+ CuSO and HSO+ ZnSO and the recovery of HSO from waste sulphuric acid solutions containing Fe and Ni ions, which are produced at the diamond manufacturing process.
* Alkali waste can be recovered using diffusion dialysis because of its low energy cost. The NaOH base can be recovered from the aluminium etching solution applying a technique develop by Astom Corporation of Japan.
* De-alcoholisation of beer is another application of the diffusion dialysis. Taking into account that a concentration gradient is applied for this technique, the alcohol and other small molecule compounds transfer across the membrane from higher concentrations to lower, which is water. It is used for this application for the low operation conditions and the possibility to remove alcohol to 0.5%. | 1 | Biochemistry |
Rubber bands have been used in at least one publicized home experiment to allow for global testing of ozone pollution. Titled GORP, for Global Ozone Rubber Participant, users can see the effects of ozone pollution near their own homes or places of employment. Rubber bands were chosen due to their availability and low cost. In the experiment, two rubber bands are used to each suspend two small water bottles. One is suspended outdoors, protected from the sun and rain, and one indoors. A data recording sheet is placed behind the setup and taped to a wall. The user then marks the changes in the height of the water bottles as the natural rubber degrades from ozone pollution. Since both water bottles are nearly the same mass, the force on each rubber band is similar, and the spring constant of each rubber band is compared via ratio of the water bottle relative extensions on the rubber bands. Typically, the home experimenter sees relatively little damage to the indoor control compared to the outdoor setup. After a week or two, the home experimenters seal both rubber bands into a small plastic bag and mail them, along with their data sheets to the GORP researchers. Researchers examine loss of elasticity versus data and location. The GORP study was originally implemented during the SARS-CoV-2 pandemic as a means to test for reduced ozone pollution during the quarantine. | 7 | Physical Chemistry |
2-Methoxypropene is an ether with the chemical formula CHO. It is a reagent used in organic synthesis to introduce a protecting group for alcohols, and the conversion diols to the acetonide group.
2-Methoxypropene can be prepared by the elimination of methanol from dimethoxypropane, or by the addition of methanol to propyne or allene. | 0 | Organic Chemistry |
The working gristmill grinds wheat and corn into flour, which is available for sale during the twice-yearly shows. During the summer months, the museum grows sorghum cane, which is made into molasses for the fall show. | 8 | Metallurgy |
On the faculty of Indiana University, Bloomington, since 1971. 1978 – Professor of Chemistry. 1980 – Visiting Scientist, Department of Immunogenetics, Max Planck Institute for Biology, Tübingen, Germany. 1988 – James H. Rudy Professor of Chemistry. 1999 – Distinguished Professor of Chemistry. 1999 – Director of the Institute for Pheromone Research. 2000–2015 – Lilly Chemistry Alumni Chair. 2004 – Adjunct Professor of Medicine, Indiana University School of Medicine. 2004–2009 – Director of the National Center for Glycomics and Glycoproteomics. 2010 – Director of the Novotny Glycoscience Laboratory. 2011 – Distinguished Professor Emeritus of Chemistry. | 3 | Analytical Chemistry |
Podocin is a protein component of the filtration slits of podocytes. Glomerular capillary endothelial cells, the glomerular basement membrane and the filtration slits function as the filtration barrier of the kidney glomerulus.
Mutations in the podocin gene NPHS2 can cause nephrotic syndrome, such as focal segmental glomerulosclerosis (FSGS) or minimal change disease (MCD). Symptoms may develop in the first few months of life (congenital nephrotic syndrome) or later in childhood. | 1 | Biochemistry |
In 1972 he joined the chemistry faculty at Colorado State University as an assistant professor. He moved to the University of Washington in 1974 where he stayed until his retirement in 1999. He became a full professor in 1979 and an endowed professor of analytical chemistry in 1991. The chemistry departments newsletter, Chem Letter, reported that ten companies contributed to the endowment and that it was the first endowed professorship at the university "established through a consortium of industrial and state resources." Former graduate student David Duewer summarized Kowalskis accomplishments in the Journal of Chemometrics: "32 PhD and three MS students, over 230 research publications, editorials, chapters, and reports (32 in this journal) with 144 coauthors, more than 230 invited lectures, four patents, more than 50 quarters of undergrad and graduate sections spread over 18 courses, more than $22m in grants, and – not least – founder of this journal." | 3 | Analytical Chemistry |
Acid-base extraction is efficient at separating compounds with a large difference in solubility between their charged and their uncharged form. Therefore, this procedure will not work for:
* Zwitterions with acidic and basic functional groups in the same molecule.
** For instance, glycine is soluble in water at most pH values and is therefore difficult to be extracted into organic media.
* Lipophilic compounds.
** Compounds such as tetrabutylammonium salts or fatty acids do not easily dissolve in the aqueous phase in their charged form.
* Basic amines.
** Amines like ammonia, methylamine, or triethanolamine are miscible or significantly soluble in water at most pH and cannot be extracted into organic media.
* Hydrophilic inorganic acids.
** Acids like acetic acid are indefinitely miscible in water and have limited solubility in organic solvents. | 7 | Physical Chemistry |
Spin echo small angle neutron scattering (SESANS) measures structures from around 20 to 2000 nm in size. The information is presented as a real-space (similar to g(r)) as opposed to a reciprocal space (q(r)) mapping. This can simplify the interpretation for some systems.
SESANS is useful for studying processes that occur over relatively long time scales, as data collection is often slow, but large length scales. Aggregation of colloids, block copolymer micelles, Stöber silica particles being a prime examples.
The technique offers some advantages over SANS but there are fewer SESANS instruments available than SANS instruments. Facilities for SESANS exist at TUDelft (Netherlands) and Rutherford Appleton Laboratory (UK). | 3 | Analytical Chemistry |
Superfluidity is the characteristic property of a fluid with zero viscosity which therefore flows without any loss of kinetic energy. When stirred, a superfluid forms vortices that continue to rotate indefinitely. Superfluidity occurs in two isotopes of helium (helium-3 and helium-4) when they are liquefied by cooling to cryogenic temperatures. It is also a property of various other exotic states of matter theorized to exist in astrophysics, high-energy physics, and theories of quantum gravity. The theory of superfluidity was developed by Soviet theoretical physicists Lev Landau and Isaak Khalatnikov.
Superfluidity often co-occurs with Bose–Einstein condensation, but neither phenomenon is directly related to the other; not all Bose–Einstein condensates can be regarded as superfluids, and not all superfluids are Bose–Einstein condensates. Superfluids have some potential practical uses, such as dissolving substances in a quantum solvent. | 7 | Physical Chemistry |
The second step of nitrification is the oxidation of nitrite into nitrate. This process is sometimes known as nitratation. Nitrite oxidation is conducted by nitrite-oxidizing bacteria (NOB) from the taxa Nitrospirota, Nitrospinota, Pseudomonadota and Chloroflexota. NOB are typically present in soil, geothermal springs, freshwater and marine ecosystems. | 1 | Biochemistry |
Neutron spectroscopy is a spectroscopic method of measuring atomic and magnetic motions by measuring the kinetic energy of emitted neutrons. The measured neutrons may be emitted directly (for example, by nuclear reactions), or they may scatter off cold matter before reaching the detector. Inelastic neutron scattering observes the change in the energy of the neutron as it scatters from a sample and can be used to probe a wide variety of different physical phenomena such as the motions of atoms (diffusional or hopping), the rotational modes of molecules, sound modes and molecular vibrations, recoil in quantum fluids, magnetic and quantum excitations or even electronic transitions.
Since its discovery, neutron spectroscopy has become useful in medicine as it has been applied to radiation protection and radiation therapy.
It is also used in nuclear fusion experiments, where the neutron spectrum can be used to infer the plasma temperature, density, and composition, in addition to the total fusion power.
Although neutron spectroscopy is currently capable of operating on many orders of neutron energy, much research focuses on expanding these capabilities to higher energies. In 2001, US researchers were able to measure neutrons with energies up to 100 gigaelectronvolts | 7 | Physical Chemistry |
Cannon started her academic career in 1974 at Stockholm University, where she held various positions, including a research associate at the Wenner-Grenn Institute from 1974 to 1980. Subsequently, she served as an associate professor from 1980 to 1983 and then as a professor of physiology from 1983 to 2013. Since 2013, she has held the title of emeritus professor at Stockholm University.
Cannon's involvement with the Royal Swedish Academy of Sciences included a tenure as vice president from 2003 to 2008 and subsequently as president from 2012 to 2015. Furthermore, she played an important role in the Nobel Foundation, serving as a member of the Trustees from 2006 to 2011 and taking on the role of chairman from 2008 to 2011. | 1 | Biochemistry |
Metal cluster compounds are a molecular ion or neutral compound composed of three or more metals and featuring significant metal-metal interactions. | 7 | Physical Chemistry |
Many plants produce chemical compounds for defence against herbivores. The major classes of pharmacologically active phytochemicals are described below, with examples of medicinal plants that contain them. Human settlements are often surrounded by weeds containing phytochemicals, such as nettle, dandelion and chickweed.
Many phytochemicals, including curcumin, epigallocatechin gallate, genistein, and resveratrol are pan-assay interference compounds and are not useful in drug discovery. | 1 | Biochemistry |
Square prismatic geometry (D) is much less common compared to the square antiprism. An example of a molecular species with square prismatic geometry (a slightly flattened cube) is octafluoroprotactinate(V), [PaF], as found in its sodium salt, NaPaF. While local cubic 8-coordination is common in ionic lattices (e.g., Ca in CaF), and some 8-coordinate actinide complexes are approximately cubic, there are no reported examples of rigorously cubic 8-coordinate molecular species. A number of other rare geometries for 8-coordination are also known. | 4 | Stereochemistry |
CellCognition (Version 1.0.1) was first released in December 2009 by scientists from the Gerlich Lab and the Buhmann group at the Swiss Federal Institute of Technology Zürich and the Ellenberg Lab at the European Molecular Biology Laboratory Heidelberg. The latest release is 1.6.1 and the software is developed and maintained by the Gerlich Lab at the Institute of Molecular Biotechnology. | 1 | Biochemistry |
The side-chain of the nucleophilic residue performs covalent catalysis on the substrate. The lone pair of electrons present on the oxygen or sulfur attacks the electropositive carbonyl carbon. The 20 naturally occurring biological amino acids do not contain any sufficiently nucleophilic functional groups for many difficult catalytic reactions. Embedding the nucleophile in a triad increases its reactivity for efficient catalysis. The most commonly used nucleophiles are the hydroxyl (OH) of serine and the thiol/thiolate ion (SH/S) of cysteine. Alternatively, threonine proteases use the secondary hydroxyl of threonine, however due to steric hindrance of the side chains extra methyl group such proteases use their N'-terminal amide as the base, rather than a separate amino acid.
Use of oxygen or sulfur as the nucleophilic atom causes minor differences in catalysis. Compared to oxygen, sulfurs extra d orbital makes it larger (by 0.4 Å) and softer, allows it to form longer bonds (d and d by 1.3-fold), and gives it a lower pK (by 5 units). Serine is therefore more dependent than cysteine on optimal orientation of the acid-base triad members to reduce its pK in order to achieve concerted deprotonation with catalysis. The low pK' of cysteine works to its disadvantage in the resolution of the first tetrahedral intermediate as unproductive reversal of the original nucleophilic attack is the more favourable breakdown product. The triad base is therefore preferentially oriented to protonate the leaving group amide to ensure that it is ejected to leave the enzyme sulfur covalently bound to the substrate N-terminus. Finally, resolution of the acyl-enzyme (to release the substrate C-terminus) requires serine to be re-protonated whereas cysteine can leave as S. Sterically, the sulfur of cysteine also forms longer bonds and has a bulkier van der Waals radius and if mutated to serine can be trapped in unproductive orientations in the active site.
Very rarely, the selenium atom of the uncommon amino acid selenocysteine is used as a nucleophile. The deprotonated Se state is strongly favoured when in a catalytic triad. | 1 | Biochemistry |
Experimental work on precious metals is limited by the cost of experimentation and by the well-understood technical processes involved. Gold and silver are produced in a similar manner to copper with the additional process of cupellation. Platinum is mostly an issue in South America and is typically left out from experimental archaeometallurgy because of its traditional use as a powdered metal as an additive to produce alloys. | 8 | Metallurgy |
The enzyme Phosphoribosylaminoimidazole carboxylase, or AIR carboxylase () is involved in nucleotide biosynthesis and in particular in purine biosynthesis. It catalyzes the conversion of 5-phosphoribosyl-5-aminoimidazole ("AIR") into 5-phosphoribosyl-4-carboxy-5-aminoimidazole ("CAIR") as described in the reaction:
:5-aminoimidazole ribonucleotide + CO 5'-phosphoribosyl-4-carboxy-5-aminoimidazole + 2 H | 1 | Biochemistry |
The chemical reaction catalyzed by firefly luciferase takes place in two steps:
* luciferin + ATP → luciferyl adenylate + PP
* luciferyl adenylate + O → oxyluciferin + AMP + light
Light is produced because the reaction forms oxyluciferin in an electronically excited state. The reaction releases a photon of light as oxyluciferin goes back to the ground state.
Luciferyl adenylate can additionally participate in a side reaction with O to form hydrogen peroxide and dehydroluciferyl-AMP. About 20% of the luciferyl adenylate intermediate is oxidized in this pathway.
Firefly luciferase generates light from luciferin in a multistep process. First, D-luciferin is adenylated by MgATP to form luciferyl adenylate and pyrophosphate. After activation by ATP, luciferyl adenylate is oxidized by molecular oxygen to form a dioxetanone ring. A decarboxylation reaction forms an excited state of oxyluciferin, which tautomerizes between the keto-enol form. The reaction finally emits light as oxyluciferin returns to the ground state. | 1 | Biochemistry |
Consider a system composed of water that contains an organic electrolyte RNaz and an inorganic electrolyte NaCl that both dissociate completely such that:
The Gibbs Adsorption equation in terms of the relative surface excess becomes:
The Relation Between Surface Tension and The Surface Excess Concentration becomes:
where is the coefficient of the Gibbs adsorption. Values of are calculated using the Double layer (interfacial) models of Helmholtz, Gouy, and Stern.
Substances can have different effects on surface tension as shown :
* No effect, for example sugar
* Increase of surface tension, inorganic salts
* Decrease surface tension progressively, alcohols
* Decrease surface tension and, once a minimum is reached, no more effect: surfactants
Therefore, the Gibbs isotherm predicts that inorganic salts have negative surface concentrations. However, this view has been challenged extensively in recent years due to a combination of more precise interfacially sensitive experiments and theoretical models, both of which predict an increase in surface propensity of the halides with increasing size and polarizability. As such, surface tension is not a reliable method for determining the relative propensity of ions toward the air-water interface.
A method for determining surface concentrations is needed in order to prove the validity of the model: two different techniques are normally used: ellipsometry and following the decay of C present in the surfactant molecules. | 7 | Physical Chemistry |
Carbamoyl chlorides are prepared by the reaction of an amine with phosgene:
:2 RNH + COCl → RNCOCl + [RNH]Cl
They also arise by the addition of hydrogen chloride to isocyanates:
:RNCO + HCl → RNHCOCl
In this way, carbamoyl chlorides can be prepared with N-H functionality. | 0 | Organic Chemistry |
Recent studies have reported the ability of drug-resistant cancer cells to acquire mitogenic signals from previously neglected autocrine loops, causing tumor recurrence.
For example, despite widespread expression of epidermal growth factor receptors (EGFRs) and EGF family ligands in non-small-cell lung cancer (NSCLC), EGFR-specific tyrosine kinase inhibitors such as gefitinib have shown limited therapeutic success. This resistance is proposed to be because autocrine growth signaling pathways distinct from EGFR are active in NSCLC cells. Gene expression profiling revealed the prevalence of specific fibroblast growth factors (FGFs) and FGF receptors in NSCLC cell lines, and found that FGF2, FGF9 and their receptors encompass a growth factor autocrine loop that is active in a subset of gefitinib-resistant NSCLC cell lines.
In breast cancer, the acquisition of tamoxifen resistance is another major therapeutic problem. It has been shown that phosphorylation of STAT3 and RANTES expression are increased in response to tamoxifen in human breast cancer cells. In a recent study, one group showed that STAT3 and RANTES contribute to the maintenance of drug resistance by upregulating anti-apoptotic signals and inhibiting caspase cleavage. These mechanisms of STAT3-RANTES autocrine signaling suggest a novel strategy for management of patients with tamoxifen-resistant tumors. | 1 | Biochemistry |
A. Cellular T cell response
The first evidence of survivin-specific CTL recognition and killing was shown in an assay wherein cytotoxic T cells (CTLs) induced lysis of B cells transfected to present survivin peptides on its surface. The naive CD8+ T cells were primed with dendritic cells and could therefore recognize the specific peptides of survivin presented on the surface Major Histocompatibility Complex I (MHC I) molecules of the B cells.
B. Humoral antibody response
Taking blood samples from cancer patients, scientists have found antibodies that are specific for survivin. These antibodies were absent in the blood samples of healthy normal patients. Therefore, this shows that survivin is able to elicit a full humoral immune response. This may prove useful, as one could measure the level of survivin-specific antibodies in the patient's blood as a monitor of tumour progression. In acquiring the humoral response to tumour antigens such as survivin, CD4+ T cells are activated to induce B cells to produce antibodies directed against the particular antigens.
The isolation of the antibodies specific for survivin peptides is useful, as one can look at the structure and sequence of the epitope binding groove of the antibody and, therefore, deduce possible epitopes that may fit in that particular antibody groove. Therefore, one can determine the particular peptide portion of the survivin protein that is bound most efficiently and most commonly by humoral antibodies generated against survivin. This will lead to the production of more specific survivin vaccines that contain a specific portion of the survivin protein that is known to elicit a good immune response, generate immune memory, and allow for protection from tumour development. | 1 | Biochemistry |
The electrocalciothermic reduction mechanism may be represented by the following sequence of reactions, where "M" represents a metal to be reduced (typically titanium).
When this reaction takes place on its own, it is referred to as the "calciothermic reduction" (or, more generally, an example of metallothermic reduction). For example, if the cathode was primarily made from TiO then calciothermic reduction would appear as:
Whilst the cathode reaction can be written as above it is in fact a gradual removal of oxygen from the oxide. For example, it has been shown that TiO does not simply reduce to Ti. It, in fact, reduces through the lower oxides (TiO, TiO, TiO etc.) to Ti.
The calcium oxide produced is then electrolyzed:
: (2a)
: (2b)
and
: (2c)
Reaction (2b) describes the production of Ca metal from Ca ions within the salt, at the cathode. The Ca would then proceed to reduce the cathode.
The net result of reactions (1) and (2) is simply the reduction of the oxide into metal plus oxygen: | 7 | Physical Chemistry |
In printing, organic pigments are mainly used in the inks, so the shifting or bleaching of the color of a printing product due to the presence of UV light is usually just a matter of time. The use of organic pigments is justified primarily by their inexpensive cost compared to inorganic pigments. The particle size of the inorganic pigments is often larger than that of organic pigments, thus inorganic pigments are often not suitable to be used in offset printing.
In screen printing, the particle size of the pigment is not the limiting factor. Thus it is the preferred printing method for printing jobs requiring extreme lightfastness. The thickness of the ink layer affects the lightfastness by the amount of pigment laid on the substrate. The ink layer printed by screen printing is thicker than that printed by offset printing. In other words, it contains more pigment per area. This leads to better lightfastness even though the printing ink used in both methods would be based on the same pigment.
When mixing printing inks, the ink with the weaker lightfastness defines the lightfastness of the whole mixed color. The fading of one of the pigments leads to a tone shift towards the component with better lightfastness. If it is required that there will be something visible from the printing, even though its dominant pigment would fade, then a small amount of pigment with excellent lightfastness can be mixed with it. | 5 | Photochemistry |
9-Fluorenylidene is an aryl carbene derived from the bridging methylene group of fluorene. Fluorenylidene has the unusual property that the triplet ground state is only 1.1 kcal/mol (4.6 kJ/mol) lower in energy than the singlet state. For this reason, fluorenylidene has been studied extensively in organic chemistry.
Fluorenylidene is a reactive intermediate. Reactions involving fluorenylidene proceed through either the triplet or singlet state carbene, and the products formed depend on the relative concentration of spin states in solution, as influenced by experimental conditions. The rate of intersystem crossing is determined by the temperature and concentration of specific spin-trapping agents. | 0 | Organic Chemistry |
A recent study based on molecular simulations and compliance constants describes molecular recognition as a phenomenon of organisation. Even for small molecules like carbohydrates, the recognition process can not be predicted or designed even assuming that each individual hydrogen bond's strength is exactly known. However, as Mobley et al. concluded, the accurate prediction of the molecular recognition events needs to go beyond the static snapshot of a single frame between the guest and the host. Entropies are key contributors to binding thermodynamics and need to be accounted for in order to predict more accurately the recognition process. Entropies are rarely observable in single bound structures (static snapshot). In proteins, highly-specific recognition can be achieved by evolutionary fine-tuning of chemical interactions, conformational changes, and entropy contributions. | 6 | Supramolecular Chemistry |
Polycyclic aromatic hydrocarbons or graphenes—including fullerenes, carbon nanotubes, and graphite—have a hexagonal structure that is often described as chicken wire-like. | 4 | Stereochemistry |
Chromatin relaxation is one of the earliest cellular responses to DNA damage. Several experiments have been performed on the recruitment kinetics of proteins involved in the response to DNA damage. The relaxation appears to be initiated by PARP1, whose accumulation at DNA damage is half complete by 1.6 seconds after DNA damage occurs. This is quickly followed by accumulation of chromatin remodeler Alc1, which has an ADP-ribose–binding domain, allowing it to be quickly attracted to the product of PARP1. The maximum recruitment of Alc1 occurs within 10 seconds of DNA damage. About half of the maximum chromatin relaxation, presumably due to action of Alc1, occurs by 10 seconds. PARP1 action at the site of a double-strand break allows recruitment of the two DNA repair enzymes MRE11 and NBS1. Half maximum recruitment of these two DNA repair enzymes takes 13 seconds for MRE11 and 28 seconds for NBS1.
Another process of chromatin relaxation, after formation of a DNA double-strand break, employs γH2AX, the phosphorylated form of the H2AX protein. The histone variant H2AX constitutes about 10% of the H2A histones in human chromatin. γH2AX (phosphorylated on serine 139 of H2AX) was detected at 20 seconds after irradiation of cells (with DNA double-strand break formation), and half maximum accumulation of γH2AX occurred in one minute. The extent of chromatin with phosphorylated γH2AX is about two million base pairs at the site of a DNA double-strand break.
γH2AX does not, by itself, cause chromatin decondensation, but within seconds of irradiation the protein "Mediator of the DNA damage checkpoint 1" (MDC1) specifically attaches to γH2AX. This is accompanied by simultaneous accumulation of RNF8 protein and the DNA repair protein NBS1 which bind to MDC1 as MDC1 attaches to γH2AX. RNF8 mediates extensive chromatin decondensation, through its subsequent interaction with CHD4 protein, a component of the nucleosome remodeling and deacetylase complex NuRD. CHD4 accumulation at the site of the double-strand break is rapid, with half-maximum accumulation occurring by 40 seconds after irradiation.
The fast initial chromatin relaxation upon DNA damage (with rapid initiation of DNA repair) is followed by a slow recondensation, with chromatin recovering a compaction state close to its pre-damage level in ~ 20 min. | 1 | Biochemistry |
Localized spins are frustrated if there exist competing exchange interactions that can not all be satisfied at the same time, leading to a large degeneracy of the system's ground state. A triangle of Ising spins (meaning that the only possible orientation of the spins are either "up" or "down"), which interact antiferromagnetically, is a simple example for frustration. In the ground state, two of the spins can be antiparallel but the third one cannot. This leads to an increase of possible orientations (six in this case) of the spins in the ground state, enhancing fluctuations and thus suppressing magnetic ordering.
A recent research work used this concept in analyzing brain networks and surprisingly indicated frustrated interactions in the brain corresponding to flexible neural interactions. This observation highlights the generalization of the frustration phenomenon and proposes its investigation in biological systems. | 7 | Physical Chemistry |
The same procedure as used in acidic medium can be applied, for example, to balance the complete combustion of propane:
:Unbalanced reaction: CH + O → CO + HO
:Reduction: 4 H + O + 4 e → 2 HO
:Oxidation: 6 HO + CH → 3 CO + 20 e + 20 H
By multiplying the stoichiometric coefficients so the numbers of electrons in both half reaction match:
:20 H + 5 O + 20 e → 10 HO
:6 HO + CH → 3 CO + 20 e + 20 H
the balanced equation is obtained:
:CH + 5 O → 3 CO + 4 HO | 7 | Physical Chemistry |
It is synthesised by the deprotonation of 2,2,6,6-tetramethylpiperidine with n-butyllithium at −78 °C. Recent reports show that this reaction can also be performed 0 °C. The compound is stable in a THF/ethylbenzene solvent mixture and is commercially available as such. | 0 | Organic Chemistry |
Tinplate consists of sheets of steel coated with a thin layer of tin to impede rusting. Before the advent of cheap milled steel, the backing metal was wrought iron. While once more widely used, the primary use of tinplate now is the manufacture of tin cans.
Tinplate is made by rolling the steel (or formerly iron) in a rolling mill, removing any mill scale by pickling it in acid and then coating it with a thin layer of tin. Plates were once produced individually (or in small groups) in what became known as a pack mill. In the late 1920s pack mills began to be replaced by strip mills which produced larger quantities more economically.
Formerly, tinplate was used for tin ceiling, and holloware (cheap pots and pans), also known as tinware. The people who made tinware (metal spinning) were tinplate workers.
For many purposes, tinplate has been replaced by galvanised (zinc-coated or tinned) vessels, though not for cooking as zinc is poisonous. The zinc layer prevents the iron from rusting through sacrificial protection with the zinc oxidizing instead of the iron, whereas tin will only protect the iron if the tin-surface remains unbroken. | 8 | Metallurgy |
Glycosylation increases diversity in the proteome, because almost every aspect of glycosylation can be modified, including:
*Glycosidic bond—the site of glycan linkage
*Glycan composition—the types of sugars that are linked to a given protein
*Glycan structure—can be unbranched or branched chains of sugars
*Glycan length—can be short- or long-chain oligosaccharides | 0 | Organic Chemistry |
A compound containing the epoxide functional group can be called an epoxy, epoxide, oxirane, and ethoxyline. Simple epoxides are often referred to as oxides. Thus, the epoxide of ethylene (CH) is ethylene oxide (CHO). Many compounds have trivial names; for instance, ethylene oxide is called "oxirane". Some names emphasize the presence of the epoxide functional group, as in the compound 1,2-epoxyheptane, which can also be called 1,2-heptene oxide.
A polymer formed from epoxide precursors is called an epoxy, but such materials do not contain epoxide groups (or contain only a few residual epoxy groups that remain unreacted in the formation of the resin). | 0 | Organic Chemistry |
In polar solvents such as acetonitrile, PhPCl adopts an ionic phosphonium salt structure, [PhPCl]Cl, whereas in non-polar solvents like diethyl ether it exists as a non-solvated trigonal bipyramidal molecule. Two [PhPCl] species can also adopt an unusual dinuclear ionic structure—both interacting with a Cl via long Cl–Cl contacts. | 0 | Organic Chemistry |
Some carboxylases, particularly RuBisCO, preferentially bind the lighter carbon stable isotope carbon-12 over the heavier carbon-13. This is known as carbon isotope discrimination and results in carbon-12 to carbon-13 ratios in the plant that are higher than in the free air. Measurement of this ratio is important in the evaluation of water use efficiency in plants, and also in assessing the possible or likely sources of carbon in global carbon cycle studies. | 5 | Photochemistry |
TPCK is an irreversible inhibitor of chymotrypsin. Also inhibits some cysteine proteases such as caspase, papain, bromelain or ficin. It does not inhibit trypsin or zymogens.
TPCK is observed covalently bound in the active site of Caspase 3 in the crystal structure of the complex solved in 2010. The chloromethyl group reacts with the active site cysteine to form a covalent bond with the loss of the chlorine.
TPCK is chosen for the chemical labelling of active histidine in enzyme analysis. The phenylalanine moiety is bound to the enzyme because of specificity for aromatic amino acid residues at the active site (as in chymotrypsin, in which it binds to the Histidine-57 residue in the active site). | 1 | Biochemistry |
Ancient slag is difficult to date. It has no organic material with which to perform radiocarbon dating. There are no cultural artifacts like pottery shards in the slag with which to date it. Direct physical dating of slag through thermoluminescence dating could be a good method to solve this problem. Thermoluminescence dating is possible if the slag contains crystal elements such as quartz or feldspar. However, the complex composition of slag can make this technique difficult unless the crystal elements can be isolated. | 8 | Metallurgy |
Non-exclusives, "standard" or "catalogue products" constitute the second most important outlet for fine chemicals after custom manufacturing. API-for-Generics are the most important sub-category. Because of patent expiries, over 60 of the top 200 drugs alone, representing aggregated sales of over $150 billion, have fallen into the public domain within the past decade. This, along with government-backed incentives, are causing global sales of generics to rapidly increase.
Asian companies currently dominate the API-for-Generics business. They have multiple advantages of their low cost basis, their large home markets, and significant previous manufacturing experience compared to western manufacturers in producing for their domestic and other non-regulated markets. | 0 | Organic Chemistry |
An interesting feature of these phases is that both polar and nonpolar compounds can be retained over some range of mobile phase composition (organic/aqueous). The retention mechanism of polar compounds has recently been shown to be the result of the formation of a hydroxide layer on the surface of the silica hydride. Thus positively charged analytes are attracted to the negatively charged surface and other polar analytes are likely to be retained through displacement of hydroxide or other charged species on the surface. This property distinguishes it from a pure HILIC (hydrophilic interaction chromatography) columns where separation by polar differences is obtained through partitioning into a water-rich layer on the surface, or a pure RP stationary phase on which separation by nonpolar differences in solutes is obtained with very limited secondary mechanisms operating.
Another important feature of the hydride-based phases is that for many analyses it is usually not necessary to use a high pH mobile phase to analyze polar compounds such as bases. The aqueous component of the mobile phase usually contains from 0.1 to 0.5% formic or acetic acid, which is compatible with detector techniques that include mass spectral analysis. | 3 | Analytical Chemistry |
Grapes and tamarinds have the highest levels of tartaric acid concentration. Other fruits with tartaric acid are bananas, avocados, prickly pear fruit, apples, cherries, papayas, peaches, pears, pineapples, strawberries, mangoes and citrus fruits.
Trace amounts of tartaric acid have been found in cranberries and other berries.
Tartaric acid is also present in the leaves and pods of Pelargonium plants and beans. | 4 | Stereochemistry |
It is effective as one part of a multi-drug regimen for treatment of stomach infections of Helicobacter pylori. It is typically combined with a proton-pump inhibitor (such as omeprazole) and a macrolide antibiotic (such as clarithromycin); other drug combinations are also effective. | 4 | Stereochemistry |
There are five major reactions classed as anaplerotic, and it is estimated that the production of oxaloacetate from pyruvate has the most physiologic importance.
The malate is created by PEP carboxylase and malate dehydrogenase in the cytosol. Malate, in the mitochondrial matrix, can be used to make pyruvate (catalyzed by malic enzyme) or oxaloacetic acid, both of which can enter the citric acid cycle.
Glutamine can also be used to produce oxaloacetate during anaplerotic reactions in various cell types through "glutaminolysis", which is also seen in many c-Myc transformed cells. Anaplerotic enzymes mediate an alternative pathway to insulin secretion by aiding the production of cytosolic signal molecules. Pancreatic β-cells which regulate blood glucose level by secreting insulin,contain high a mounts of pyruvate carboxylase. A decrease in insulin secretion and anaplerotic activity has been found in β-cells that do not have hypoxia-inducible factor-1 beta | 1 | Biochemistry |
Iminium derivatives are common in biology. Pyridoxal phosphate reacts with amino acids to give iminium derivatives. Many iminium salts are encountered in synthetic organic chemistry. | 0 | Organic Chemistry |
Surfactant behavior is highly dependent on the hydrophilic-lipophilic balance (HLB) value. The HLB is a coding scale from 0 to 20 for non-ionic surfactants, and takes into account the chemical structure of the surfactant molecule. A zero value corresponds to the most lipophilic and a value of 20 is the most hydrophilic for a non-ionic surfactant. In general, compounds with an HLB between one and four will not mix with water. Compounds with an HLB value above 13 will form a clear solution in water. Oil dispersants usually have HLB values from 8–18. | 2 | Environmental Chemistry |
Drospirenone binds with high affinity to the progesterone receptor (PR) and mineralocorticoid receptor (MR), with lower affinity to the androgen receptor (AR), and with very low affinity to the glucocorticoid receptor (GR). It is an agonist of the PR and an antagonist of the MR and AR, and hence is a progestogen, antimineralocorticoid, and antiandrogen. Drospirenone has no estrogenic activity and no appreciable glucocorticoid or antiglucocorticoid activity. | 4 | Stereochemistry |
dimesitylborane is a dimer (CHMe)BH). It reacts only slowly with simple terminal alkenes. On the other hand, alkynes undergo monohydroboration with MesBH easily to produce alkenylboranes. | 0 | Organic Chemistry |
Overall measurements from OCO-3 will help quantify sources and sinks of carbon dioxide from terrestrial ecosystems, the oceans, and from anthropogenic sources. Due to the ISS orbit, measurements will be made at latitudes less than 52°. Data from OCO-3 are expected to significantly improve understanding of global emissions from human activities, for example, using measurements over cities. Near simultaneous observations from other instruments onboard the International Space Station such as ECOSTRESS (measuring plant temperatures) and Global Ecosystem Dynamics Investigation lidar (measuring forest structure) may be combined with OCO-3 observations to help improve the understanding of the terrestrial ecosystem. Similar to OCO-2, OCO-3 will also measure Solar Induced Fluorescence which is a process that occurs during plant photosynthesis. | 2 | Environmental Chemistry |
If the steady state approximation is applied, then the derivative of the concentration of the intermediate is set to zero. This reduces the second differential equation to an algebraic equation which is much easier to solve.
Therefore, so that
Since the concentration of the reaction intermediate B changes with the same time constant as [A] and is not in a steady state in that sense. | 7 | Physical Chemistry |
3 kinds of ground state or static electrical influences predominate:
* Resonance (mesomeric) effect
* Inductive effect: electrical influence of a group which is transmitted primarily by polarization of the bonding electrons from one atom to the next
* Direct electrostatic (field) effect: electrical influence of a polar or dipolar substituent which is transmitted primarily to the reactive group through space (including solvent, if any) according to the laws of classical electrostatics
The latter two influences are often treated together as a composite effect, but are treated here separately. Westheimer demonstrated that the electrical effects of π-substituted dipolar groups on the acidities of benzoic and phenylacetic acids can be quantitatively correlated, by assuming only direct electrostatic action of the substituent on the ionizable proton of the carboxyl group. Westheimer's treatment worked well except for those acids with substituents that have unshared electron pairs such as –OH and –OCH3, as these substituents interact strongly with the benzene ring.
Roberts and Moreland studied the reactivities of 4-substituted bicyclo[2.2.2]octane-1-carboxylic acids and esters. In such a molecule, transmission of electrical effects of substituents through the ring by resonance is not possible. Hence, this hints on the role of the π-electrons in the transmission of substituent effects through aromatic systems.
Reactivity of 4-substituted bicyclo[2.2.2]octane-1-carboxylic acids and esters were measured in 3 different processes, each of which had been previously used with the benzoic acid derivatives. A plot of log(k) against log(K) showed a linear relationship. Such linear relationships correspond to linear free energy relationships, which strongly imply that the effect of the substituents are exerted through changes of potential energy and that the steric and entropy terms remain almost constant through the series. The linear relationship fit well in the Hammett Equation. For the 4-substituted bicyclo[2.2.2.]octane-1-carboxylic acid derivatives, the substituent and reaction constants are designated σ’ and ρ’. | 7 | Physical Chemistry |
The Voigt profile (named after Woldemar Voigt) is a probability distribution given by a convolution of a Cauchy-Lorentz distribution and a Gaussian distribution. It is often used in analyzing data from spectroscopy or diffraction. | 7 | Physical Chemistry |
The Gibson assembly method is a relatively straightforward DNA assembly method, requiring only a few additional reagents: the 5 T5 exonuclease, Phusion DNA polymerase, and Taq DNA ligase. The DNA fragments to be assembled are synthesised to have overlapping 5 and 3' ends in the order that they are to be assembled in. These reagents are mixed together with the DNA fragments to be assembled at 50 °C and the following reactions occur:
# The T5 exonuclease chews back DNA from the 5 end of each fragment, exposing 3 overhangs on each DNA fragment.
# The complementary overhangs on adjacent DNA fragments anneal via complementary base pairing.
# The Phusion DNA polymerase fills in any gaps where the fragments anneal.
# Taq DNA ligase repairs the nicks on both DNA strands.
Because the T5 exonuclease is heat labile, it is inactivated at 50 °C after the initial chew back step. The product is thus stable, and the fragments assembled in the desired order. This one-pot protocol can assemble up to 5 different fragments accurately, while several commercial providers have kits to accurately assemble up to 15 different fragments in a two-step reaction. However, while the Gibson assembly protocol is fast and uses relatively few reagents, it requires bespoke DNA synthesis as each fragment has to be designed to contain overlapping sequences with the adjacent fragments and amplified via PCR. This reliance on PCR may also affect the fidelity of the reaction when long fragments, fragments with high GC content or repeat sequences are used. | 1 | Biochemistry |
Lipid signaling, broadly defined, refers to any biological cell signaling event involving a lipid messenger that binds a protein target, such as a receptor, kinase or phosphatase, which in turn mediate the effects of these lipids on specific cellular responses. Lipid signaling is thought to be qualitatively different from other classical signaling paradigms (such as monoamine neurotransmission) because lipids can freely diffuse through membranes (see osmosis). One consequence of this is that lipid messengers cannot be stored in vesicles prior to release and so are often biosynthesized "on demand" at their intended site of action. As such, many lipid signaling molecules cannot circulate freely in solution but, rather, exist bound to special carrier proteins in serum. | 1 | Biochemistry |
The enzyme is present in organisms capable of oxygenic photosynthesis, which includes plants, algae, and cyanobacteria. Plastid terminal oxidase and alternative oxidase are thought to have originated from a common ancestral di-iron carboxylate protein. Oxygen reductase activity was likely an ancient mechanism to scavenge oxygen in the early transition from an anaerobic to aerobic world. The plastid oxidase first evolved in ancient cyanobacteria and the alternative oxidase in Pseudomonadota before eukaryotic evolution and endosymbiosis events. Through endosymbiosis, the plastid oxidase was vertically inherited by eukaryotes that evolved into plants and algae. Sequenced genomes of various plant and algae species shows that the amino acid sequence is more than 25% conserved, which is a significant amount of conservation for an oxidase. This sequence conservation further supports the theory that both the alternative and plastid oxidases evolved before endosymbiosis and did not significantly change through eukaryote evolution.
There also exist PTOX cyanophages that contain copies of the gene for the plastid oxidase. They are known to act as viral vectors for movement of the gene between cyanobacterial species. Some evidence suggests that the phages may use the oxidase to influence photosynthetic electron flow to produce more ATP and less NADPH because viral synthesis utilizes more ATP. | 5 | Photochemistry |
Lower bainite forms between 250 and 400 °C and takes a more plate-like form than upper bainite. There are not nearly as many low angle boundaries between laths in lower bainite. In lower bainite, the habit plane in ferrite will also shift from <111> towards <110> as transformation temperature decreases. In lower bainite, cementite nucleates on the interface between ferrite and austenite. | 8 | Metallurgy |
Many vertebrate axons are surrounded by a myelin sheath, allowing rapid and efficient saltatory ("jumping") propagation of action potentials. The contacts between neurons and glial cells display a very high level of spatial and temporal organization in myelinated fibers. The myelinating glial cells - oligodendrocytes in the central nervous system (CNS), and Schwann cells in the peripheral nervous system (PNS) - are wrapped around the axon, leaving the axolemma relatively uncovered at the regularly spaced nodes of Ranvier.
The internodal glial membranes are fused to form compact myelin, whereas the cytoplasm-filled paranodal loops of myelinating cells are spirally wrapped around the axon at both sides of the nodes. This organization demands a tight developmental control and the formation of a variety of specialized zones of contact between different areas of the myelinating cell membrane. Each node of Ranvier is flanked by paranodal regions where helicoidally wrapped glial loops are attached to the axonal membrane by a septate-like junction.
The segment between nodes of Ranvier is termed as the internode, and its outermost part that is in contact with paranodes is referred to as the juxtaparanodal region. The nodes are encapsulated by microvilli stemming from the outer aspect of the Schwann cell membrane in the PNS, or by perinodal extensions from astrocytes in the CNS. | 1 | Biochemistry |
Pyruvate is converted into acetyl-coenzyme A (acetyl-CoA) by the enzyme pyruvate dehydrogenase. This acetyl-CoA is then converted into acetate in E. coli, whilst producing ATP by substrate-level phosphorylation. Acetate formation requires two enzymes: phosphate acetyltransferase and acetate kinase.
acetyl-CoA + phosphate → acetyl-phosphate + CoA
acetyl-phosphate + ADP → acetate + ATP | 1 | Biochemistry |
A solid sphere or ball is a three-dimensional object, being the solid figure bounded by a sphere. (In geometry, the term sphere properly refers only to the surface, so a sphere thus lacks volume in this context.)
For an ordinary three-dimensional ball, the SA:V can be calculated using the standard equations for the surface and volume, which are, respectively, and . For the unit case in which r = 1 the SA:V is thus 3. For the general case, SA:V equals 3/r, in an inverse relationship with the radius - if the radius is doubled, the SA:V halves (see figure). | 7 | Physical Chemistry |
Campo de Cartagena is a natural region (comarca) located in the Region of Murcia, in Spain. For administrative purposes, it is also known as Comarca del Campo de Cartagena or Comarca de Cartagena. It is located in the southeast of the Iberian Peninsula, forming a plain which extends from the Sierra de Carrascoy to the Mediterranean. The capital city is Cartagena, the most important Naval Base of the Spanish Navy in the Mediterranean Sea.
The comarca contains 393,598 inhabitants (2019) in an area of 1,481.8 km, making up the metropolitan area of Cartagena, a center for tourism, culture, industry and nature, with more than 18,500 protected hectares, among places like the Calblanque, Monte de las Cenizas y Peña del Águila Natural Park; the Sierra de la Muela, Cabo Tiñoso and Roldán Natural Park; Salinas y Arenales de San Pedro del Pinatar or Islas e Islotes del Litoral Mediterráneo (Islands and Islets of the Mediterranean Shore), among others. Beside those places, it must be added much of the marine environment, highlighting the Mar Menor, the Marine Reserve of Cabo de Palos e Islas Hormigas, and the Cape Tiñoso surroundings. | 2 | Environmental Chemistry |
The advantages of EDXRD are (1) it uses a fixed scattering angle, (2) it works directly in reciprocal space, (3) fast collection time, and (4) parallel data collection. The fixed scattering angle geometry makes EDXRD especially suitable for in situ studies in special environments (e.g. under very low or high temperatures and pressures). When the EDXRD method is used, only one entrance and one exit window are needed. The fixed scattering angle also allows for measurement of the diffraction vector directly. This allows for high-accuracy measurement of lattice parameters. It allows for rapid structure analysis and the ability to study materials that are unstable and only exist for short periods of time. Because the whole spectrum of diffracted radiation is obtained simultaneously, it enables parallel data collection studies where structural changes can be determined over time. | 3 | Analytical Chemistry |
Electric resistance corrosion probes are used in different types for different applications of online corrosion monitoring. The corrosion rate of these probes can be measured online or transferred to the control system by using corrosion handheld or fixed data loggers or by corrosion transmitters.
The general type of ER probes element are as below:
* flush type
* cylindrical
* spiral loop
* wire loop
* tube loop
ER probes can be provided by adapter in order to connect to data logger or transmitters. The length of probes is dependent on the mounting and monitoring position. | 8 | Metallurgy |
Surfactant leaching is a method of water and soil decontamination, e.g., for oil recovery in petroleum industry. It involves mixing of contaminated water or soil with surfactants with the subsequent leaching of emulsified contaminants. In oil recovery, most common surfactant types are ethoxylated alcohols, ethoxylated nonylphenols, sulphates, sulphonates, and biosurfactants. | 2 | Environmental Chemistry |
In melt spinning, the alloy or metal is first melted in a crucible. Then, an inert gas, usually argon, is used to jet the molten material out of a nozzle located on the underside of the crucible. The resulting stream of liquid is directed onto the outer circumferential surface of a rotating wheel or drum which is cooled internally. The drums outer surface is located extremely close to the nozzle but does not touch it. Generally, the velocity of the drums surface must be between 10 m/s and 60 m/s in order to avoid the formation of globules (droplets) or breaking the ribbon respectively. Once the stream contacts the drums surface, a small puddle of melt (molten material) is formed. Due to the low viscosity of the melt, the shear forces generated by the relative movement of the drums surface underneath the melt only extend a few microns into the puddle. In other words, only a small amount of the puddle is affected by the friction from the rotation of the drum. Consequently, as the drum spins, most of the melt puddle remains held between the nozzle and the drum by surface tension. However, the melt on the very bottom of the puddle, which is in direct contact with the drum, rapidly solidifies into a thin ribbon. The solidified ribbon is carried away from under the nozzle on the drums surface for up to 10° of rotation before centrifugal force from the drums rotation ejects it.
This process occurs continuously, so as solidified material is removed from underneath the puddle of melt, more liquid material is added to the puddle from the nozzle. | 8 | Metallurgy |
The transition between the ground and the excited state is based on the Franck–Condon principle, that the electronic transition is very fast compared with the motion in the lattice. The energy transitions can then be symbolized by vertical arrows between the ground and excited state, that is, there is no motion along the configurational coordinates during the transition. Figure 2 is an energy diagram for interpreting absorption and emission with and without phonons in terms of the configurational coordinate . The energy transitions originate at the lowest phonon energy level of the electronic states. As represented in the figure, the largest wavefunction overlap (and therefore largest transition probability) occurs when the photon energy is equal to the energy difference between the two electronic states () plus three quanta of lattice mode vibrational energy (). This three-phonon transition is mirrored in emission when the excited state quickly decays to its zero-point lattice vibration level by means of a radiationless process, and from there to the ground state via photon emission. The zero-phonon transition is depicted as having a lower wavefunction overlap and therefore a lower transition probability.
In addition to the Franck-Condon assumption, three other approximations are commonly assumed and are implicit in the figures. The first is that each lattice vibrational mode is well described by a quantum harmonic oscillator. This approximation is implied in the parabolic shape of the potential wells of Figure 2, and in the equal energy spacing between phonon energy levels. The second approximation is that only the lowest (zero-point) lattice vibration is excited. This is called the low temperature approximation and means that electronic transitions do not originate from any of the higher phonon levels. The third approximation is that the interaction between the chromophore and the lattice is the same in both the ground and the excited state. Specifically, the harmonic oscillator potential is equal in both states. This approximation, called linear coupling, is represented in Figure 2 by two equally shaped parabolic potentials and by equally spaced phonon energy levels in both the ground and excited states.
The strength of the zero-phonon transition arises in the superposition of all of the lattice modes. Each lattice mode has a characteristic vibrational frequency which leads to an energy difference between phonons . When the transition probabilities for all the modes are summed, the zero-phonon transitions always add at the electronic origin (), while the transitions with phonons contribute at a distribution of energies. Figure 3 illustrates the superposition of transition probabilities of several lattice modes. The phonon transition contributions from all lattice modes constitute the phonon sideband.
The frequency separation between the maxima of the absorption and fluorescence phonon sidebands is the phonon contribution to the Stokes’ shift. | 7 | Physical Chemistry |
Levetiracetam has been studied in the past for treating symptoms of neurobiological conditions such as Tourette syndrome, and anxiety disorder. However, its most serious adverse effects are behavioral, and its benefit-risk ratio in these conditions is not well understood.
Levetiracetam is being tested as a drug to reduce hyperactivity in the hippocampus in Alzheimer's disease.
Additionally, Levetiracetam has been experimentally shown to reduce Levodopa-induced dyskinesia, a type of movement disorder, or dyskinesia associated with the use of Levodopa, a medication used to treat Parkinson's disease.
Of the ten medications evaluated in a 2023 systematic review of the literature, levetiracetam was found to be the only medication with sufficient evidence showing that it may cause seizure freedom in some infants. Further, adverse effects from levetiracetam were rarely severe enough for the medication to be discontinued in this age group. Because available research included only 2 published studies reporting seizure freedom rates, however, the strength of the evidence was judged to be low. | 4 | Stereochemistry |
In electrochemistry, partial current is defined as the electric current associated with (anodic or cathodic) half of the electrode reaction.
Depending on the electrode half-reaction, one can distinguish two types of partial current:
* cathodic partial current I (called also cathodic current): is the flow of electrons from the electrode surface to a species in solution;
* anodic partial current I (called also anodic current): is the flow of electrons into the electrode from a species in solution.
The cathodic and anodic partial currents are defined by IUPAC.
The partial current densities (i and i) are the ratios of partial currents respect to the electrode areas (A and A):
:i = I/A
:i = I/A
The sum of the cathodic partial current density i (positive) and the anodic partial current density i (negative) gives the net current density i:
:i = i + i
In the case of the cathodic partial current density being equal to the anodic partial current density (for example, in a corrosion process), the net current density on the electrode is zero:
:i = i + i = 0
When more than one reaction occur on an electrode simultaneously, then the total electrode current can be expressed as:
where the index refers to the particular reactions. | 7 | Physical Chemistry |
*1985: Pittsburgh Analytical Chemistry Award
*1988: Malcolm E. Pruitt Award from the Council for Chemical Research
*1989: Theophilus Redwood Endowed Lectureship from the Royal Society of Chemistry
*1991: Endowed Professor of Analytical Chemistry, University of Washington
*1993: Torbern Bergman Medal from the Swedish Chemical Society’s analytical division | 3 | Analytical Chemistry |
These compounds are related to SO. They have planar C–N=S=N–C cores with bent C–N=S and N=S=N geometries, and various combinations of E and Z isomers are observed for the two N=S bonds.
Sulfur diimides are electrophilic. They undergo Diels–Alder reactions with dienes. Organolithium reagents attack at the sulfur to give the corresponding nitrogen anion:
:RLi + S(NR) → RS(NR)(NRLi)
The triimido analogues of sulfite can be generated by treating the sulfur diimides with a metal amide:
::4 LiNHBu-t + 2 S(NBu-t) → 2 LiS(NBu-t) + 2 t-BuNH | 0 | Organic Chemistry |
Jeehiun Katherine Lee is an organic chemist and a professor in the department of chemistry at Rutgers University. She currently runs a research lab on the New Brunswick campus.
Although she is an organic chemist by training, she has expanded her research field to biological chemistry, using mass spectrometry, computer modeling and other methods to characterize reactivity and catalysis. | 0 | Organic Chemistry |
Atalla was the chairman of A4 System, as of 2003.
He lived in Atherton, California. Atalla died on December 30, 2009, in Atherton. | 7 | Physical Chemistry |
Total triiodothyronine (Total T) is rarely measured, having been largely superseded by free T3 tests. Total T3 is generally elevated in hyperthyroidism and decreased in hypothyroidism.
Reference ranges depend on the method of analysis. Results should always be interpreted using the range from the laboratory that performed the test. Example values are: | 1 | Biochemistry |
Combustibility is a measure of how easily a substance bursts into flame, through fire or combustion. This is an important property to consider when a substance is used for construction or is being stored. It is also important in processes that produce combustible substances as a by-product. Special precautions are usually required for substances that are easily combustible. These measures may include installation of fire sprinklers or storage remote from possible sources of ignition.
Substances with low combustibility may be selected for construction where the fire risk must be reduced, such as apartment buildings, houses, or offices. If combustible resources are used there is greater chance of fire accidents and deaths. Fire resistant substances are preferred for building materials and furnishings. | 7 | Physical Chemistry |
Most spectrophotometers are used in the UV and visible regions of the spectrum, and some of these instruments also operate into the near-infrared region as well. The concentration of a protein can be estimated by measuring the OD at 280 nm due to the presence of tryptophan, tyrosine and phenylalanine. This method is not very accurate since the composition of proteins varies greatly and proteins with none of these amino acids do not have maximum absorption at 280 nm. Nucleic acid contamination can also interfere. This method requires a spectrophotometer capable of measuring in the UV region with quartz cuvettes.
Ultraviolet-visible (UV-vis) spectroscopy involves energy levels that excite electronic transitions. Absorption of UV-vis light excites molecules that are in ground-states to their excited-states.
Visible region 400–700 nm spectrophotometry is used extensively in colorimetry science. It is a known fact that it operates best at the range of 0.2–0.8 O.D. Ink manufacturers, printing companies, textiles vendors, and many more, need the data provided through colorimetry. They take readings in the region of every 5–20 nanometers along the visible region, and produce a spectral reflectance curve or a data stream for alternative presentations. These curves can be used to test a new batch of colorant to check if it makes a match to specifications, e.g., ISO printing standards.
Traditional visible region spectrophotometers cannot detect if a colorant or the base material has fluorescence. This can make it difficult to manage color issues if for example one or more of the printing inks is fluorescent. Where a colorant contains fluorescence, a bi-spectral fluorescent spectrophotometer is used. There are two major setups for visual spectrum spectrophotometers, d/8 (spherical) and 0/45. The names are due to the geometry of the light source, observer and interior of the measurement chamber. Scientists use this instrument to measure the amount of compounds in a sample. If the compound is more concentrated more light will be absorbed by the sample; within small ranges, the Beer–Lambert law holds and the absorbance between samples vary with concentration linearly. In the case of printing measurements two alternative settings are commonly used- without/with uv filter to control better the effect of uv brighteners within the paper stock.
Samples are usually prepared in cuvettes; depending on the region of interest, they may be constructed of glass, plastic (visible spectrum region of interest), or quartz (Far UV spectrum region of interest). Some applications require small volume measurements which can be performed with micro-volume platforms. | 7 | Physical Chemistry |
The great leonopteryx (Toruk in Navi, meaning last shadow) is the apex airborne predator native to Pandora. It is scientifically known as Leonopteryx rex, meaning "king lion-wing". The fierce beauty and nobility of the leonopteryx gave the species a place central to Navi lore and culture. The leonopteryx is scarlet with black stripes and a midnight blue crest on top of the head and on the lower jaw. It is celebrated in dance and song; elaborate totems symbolize both the fear and respect accorded to the creature. The leonopteryx is considered crucial to the Navi sense of destiny and interconnectedness. Prior to the events of the film, it had only been tamed five times, and Neytiri tells Jake that the riders (Toruk Makto) brought peace among the Pandoran tribes. This makes Jake the sixth Toruk Makto. He manages to capture one by jumping on it from above from his banshee but releases it after the battle with the humans has ended. The great leonopteryx and the banshee were designed with bright colors. Page based the colors on Earths birds, poison dart frogs, and monarch butterflies, though he altered the patterns so that their inspirations would not be so conspicuous to moviegoers. The skull and crest shapes appear to be derived from pterosaurs from the genus Tapejara. | 1 | Biochemistry |
Body farms subject donated cadavers to various environmental conditions to study the process of human decomposition. These include The University of Tennessees Forensic Anthropologic Facility, Western Carolina Universities Osteology Research Station (FOREST), Texas State Universitys Forensic Anthropology Research Facility (FARF), Sam Houston State Universitys Southeast Texas Applied Forensic Science Facility (STAFS), Southern Illinois Universitys Complex for Forensic Anthropology Research, and Colorado Mesa University's Forensic Investigation Research Station. The Australian Facility for Taphonomic Experimental Research, near Sydney, is the first body farm located outside of the United States In the United Kingdom there are several facilities which, instead of using human remains or cadavers, use dead pigs to study the decomposition process. Pigs are less likely to have infectious diseases than human cadavers, and are more readily available without any concern for ethical issues, but a human body farm is still highly sought after for further research. Each body farm is unique in its environmental make-up, giving researchers a broader knowledge, and allowing research into how different environmental factors can affect the rate of decomposition significantly such as humidity, sun exposure, rain or snow, altitude level and more. | 1 | Biochemistry |
The substitution of CO ligands can be induced thermally or photochemically by donor ligands. The range of ligands is large, and includes phosphines, cyanide (CN), nitrogen donors, and even ethers, especially chelating ones. Alkenes, especially dienes, are effective ligands that afford synthetically useful derivatives. Substitution of 18-electron complexes generally follows a dissociative mechanism, involving 16-electron intermediates.
Substitution proceeds via a dissociative mechanism:
:M(CO) → M(CO) + CO
:M(CO) + L → M(CO)L
The dissociation energy is for nickel tetracarbonyl and for chromium hexacarbonyl.
Substitution in 17-electron complexes, which are rare, proceeds via associative mechanisms with a 19-electron intermediates.
:M(CO) + L → M(CO)L
:M(CO)L → M(CO)L + CO
The rate of substitution in 18-electron complexes is sometimes catalysed by catalytic amounts of oxidants, via electron transfer. | 0 | Organic Chemistry |
Henry's law solubility constant for a gas 2 in a mixture M of two solvents 1 and 3 depends on the individual constants for each solvent, and according to:
Where , are the molar ratios of each solvent in the mixture and a is the interaction parameter of the solvents from Wohl expansion of the excess chemical potential of the ternary mixtures.
A similar relationship can be found for the volatility constant , by remembering that and that, both being positive real numbers, , thus:
For a water-ethanol mixture, the interaction parameter a has values around for ethanol concentrations (volume/volume) between 5% and 25%. | 7 | Physical Chemistry |
A flow battery, or redox flow battery (after reduction–oxidation), is a type of electrochemical cell where chemical energy is provided by two chemical components dissolved in liquids that are pumped through the system on separate sides and in opposite direction of a membrane. Ion transfer inside the cell (accompanied by flow of electric current through an external circuit) occurs through the membrane while both liquids circulate in their own respective space. Cell voltage is chemically determined by the Nernst equation and ranges, in practical applications, from 1.0 to 2.43 volts. The energy capacity is a function of the electrolyte volume and the power is a function of the surface area of the electrodes.
Various types of flow batteries have been demonstrated, including inorganic flow batteries and organic flow batteries. Under each category, flow battery design can be further classified into full flow batteries, semi-flow batteries, and membraneless flow batteries. The fundamental difference between conventional and flow batteries is that energy is stored in the electrode material in conventional batteries, while in flow batteries it is stored in the electrolyte. Patent Classifications for Flow Batteries have not been fully developed as of 2021. Cooperative Patent Classification considers RFBs as a subclass of regenerative fuel cell (H01M8/18), even though it is more appropriate to consider fuel cells as a subclass of flow batteries.
A flow battery may be used like a fuel cell (where new charged negolyte (a.k.a. reducer or fuel) and charged posolyte (a.k.a. oxidant) are added to the system) or like a rechargeable battery (where an electric power source drives regeneration of the reducer and oxidant). While flow batteries have certain technical advantages over conventional rechargeable batteries with solid electroactive materials, such as independent scaling of power (determined by the size of the stack) and of energy (determined by the size of the tanks), long cycle and calendar life, and potentially lower total cost of ownership, all flow batteries suffer from low cycle energy efficiency (50–80%). This inferior energy efficiency stems from the need to operate flow batteries at high (>= 100 mA/cm2) current densities to reduce the effect of the internal crossover (through the membrane/separator inside each cell) and to reduce the cost of power (size of stacks). Also, most flow batteries (Zn-Cl2, Zn-Br2 and H2-LiBrO3 are exceptions) have lower specific energy (heavier weight) compared to lithium-ion batteries. The heavier weight results mostly from the need to use a solvent (usually-water) to keep the redox active species in the liquid phase. | 7 | Physical Chemistry |
The process of creating fish emulsion begins with whole fish, or with carcass products of fish, such as bones, scales, and skin, which are left after a fish has been processed. The fish and carcass products are then ground into a slurry. After the oils and fish meal are removed from the slurry, the slurry is officially a fish emulsion. Most emulsions are then strained to remove any remaining solids, and sulfuric acid is often added to increase the acidity and prevent the growth of microbes. | 9 | Geochemistry |
In the treatment of epilepsy, drugs such as vigabatrin that target both GABA transporters and the GABA metabolizing enzyme GABA-transaminase have been marketed, providing proof of principle for the neurotransmitter cycling systems as pharmacological targets. However, with regard to glutamate transport and metabolism, no such drugs have been developed, because glutamatergic synapses are abundant, and the neurotransmitter glutamate is an important metabolite in metabolism, making interference capable of adverse effects. So far, most of the drug development directed at the glutamatergic system seems to have been focused on ionotropic glutamate receptors as pharmacological targets, although G-protein coupled receptors have been attracting increased attention over the years. | 1 | Biochemistry |
Continuing and expanding the tradition of the University of Athens within the subject, starting from Zervas of Bergmann-Zervas carbobenzoxy method fame, Photaki initially worked on further refinement of suitable protecting groups for oligopeptide synthesis. She investigated with Zervas new types of protection such as N-protection with benzyl phosphate esters (N-phosphamide derivatives), S-protection using trityl, benzhydryl or benzoyl groups (as part of the greater effort for the synthesis of asymmetric cysteine-containing peptides), N-protection using the o-nitrophenylsulfenyl (NPS) group discovered in their Athens laboratory, or S-protection using the p-methoxycarbobenzoxy group (a modification of the Z group).
With the above methodologies she embarked on the synthesis of complex polypeptides, especially fragments of enzyme active sites and peptide hormones. Some notable achievements in papers Photaki co-authored include the first synthesis of the 20-membered insulin intra-chain ring or –following her research under du Vigneaud– several previously inaccessible oxytocin analogues (e.g. 4-deamido-oxytocin) and a novel oxytocin synthesis via a different route than the du Vigneaud synthesis.
In later years she also examined the preparation of biologically active atypical peptides such as N-arginine or lanthionine-containing peptides. | 0 | Organic Chemistry |
Plakophilin are proteins of the cytoskeleton. They are involved in regulating the adhesive activity of cadherin.
The three types of plakophilin proteins found in humans are PKP1, PKP2, and PKP3; all exhibiting dual localization in the nucleus as well as desmosomes.
Genes include:
* PKP1
* PKP2
* PKP3 | 1 | Biochemistry |
Chromatographic response function, often abbreviated to CRF, is a coefficient which measures the quality of the separation in the result of a chromatography.
The CRF concept have been created during the development of separation optimization, to compare the quality of many simulated or real chromatographic separations. Many CRFs have been proposed and discussed.
In high performance liquid chromatography the CRF is calculated from various parameters of the peaks of solutes (like width, retention time, symmetry etc.) are considered into the calculation. In TLC the CRFs are based on the placement of the spots, measured as RF values. | 3 | Analytical Chemistry |
Microstructure generation is also known as stochastic microstructure reconstruction.
Computer-simulated microstructures are generated to replicate the microstructural features of actual microstructures. Such microstructures are referred to as synthetic microstructures. Synthetic microstructures are used to investigate what microstructural feature is important for a given property. To ensure statistical equivalence between generated and actual microstructures, microstructures are modified after generation to match the statistics of an actual microstructure. Such procedure enables generation of theoretically infinite number of computer simulated microstructures that are statistically the same (have the same statistics) but stochastically different (have different configurations). | 8 | Metallurgy |
The Schikorr reaction can be viewed as two distinct processes:
* the anaerobic oxidation of two Fe(II) (Fe) into Fe(III) (Fe) by the protons of water. The reduction of two water protons is accompanied by the production of molecular hydrogen (H), and;
* the loss of two water molecules from the iron(II) and iron(III) hydroxides giving rise to its dehydration and to the formation of a thermodynamically more stable phase iron(II,III) oxide.
The global reaction can thus be decomposed in half redox reactions as follows:
:2 (Fe → Fe + e) (oxidation of 2 iron(II) ions)
:2 (HO + e → ½ H + OH) (reduction of 2 water protons)
to give:
:2 Fe + 2 HO → 2 Fe + H + 2 OH
Adding to this reaction one intact iron(II) ion for each two oxidized iron(II) ions leads to:
:3 Fe + 2 HO → Fe + 2 Fe + H + 2 OH
Electroneutrality requires the iron cations on both sides of the equation to be counterbalanced by 6 hydroxyl anions (OH):
:3 Fe + 6 OH + 2 HO → Fe + 2 Fe + H + 8 OH
:3 Fe(OH) + 2 HO → Fe(OH) + 2 Fe(OH) + H
For completing the main reaction, two companion reactions have still to be taken into account:
The autoprotolysis of the hydroxyl anions; a proton exchange between two OH, like in a classical acid–base reaction:
:OH + OH → O + HO
:acid 1 + base 2 → base 1 + acid 2, or also,
:2 OH → O + HO
it is then possible to reorganize the global reaction as:
:3 Fe(OH) + 2 HO → (FeO + HO) + (FeO + 3 HO) + H
:3 Fe(OH) + 2 HO → FeO + FeO + 4 HO + H
:3 Fe(OH) → FeO + FeO + 2 HO + H
Considering then the formation reaction of iron(II,III) oxide:
it is possible to write the balanced global reaction:
:3 Fe(OH) → (FeO·FeO) + 2 HO + H
in its final form, known as the Schikorr reaction:
:3 Fe(OH) → FeO + 2 HO + H | 8 | Metallurgy |
eRNAs are transcribed from DNA sequences upstream and downstream of extragenic enhancer regions. Previously, several model enhancers have demonstrated the capability to directly recruit RNA Pol II and general transcription factors and form the pre-initiation complex (PIC) prior to the transcription start site at the promoter of genes. In certain cell types, activated enhancers have demonstrated the ability to both recruit RNA Pol II and also provide a template for active transcription of their local sequences.
Depending on the directionality of transcription, enhancer regions generate two different types of non-coding transcripts, 1D-eRNAs and 2D-eRNAs. The nature of the pre-initiation complex and specific transcription factors recruited to the enhancer may control the type of eRNAs generated. After transcription, the majority of eRNAs remain in the nucleus. In general, eRNAs are very unstable and actively degraded by the nuclear exosome. Not all enhancers are transcribed, with non-transcribed enhancers greatly outnumbering the transcribed ones in the order of magnitude of dozens of thousands in every given cell type. | 1 | Biochemistry |
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