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In almost all Fe–S proteins, the Fe centers are tetrahedral and the terminal ligands are thiolato sulfur centers from cysteinyl residues. The sulfide groups are either two- or three-coordinated. Three distinct kinds of Fe–S clusters with these features are most common. | 7 | Physical Chemistry |
Multidisciplinary observations are still needed in the deep water column to properly understand the biological pump:
* Physics: stratification affects particle sinking; understanding the origin of the particles and the residence time of the DIC from particle remineralization in the deep ocean requires measurement of advection and mixing.
* Biogeochemistry: export/mixing down of particulate and dissolved organic matter from the surface layer determines labile organic matter arriving at the seafloor, which is either respired by seafloor biota or stored for longer times in the sediment.
* Biology and ecosystems: zooplankton and microorganisms break down and remineralize sinking particles in the water column. Exported organic matter feeds all water column and benthic biota (zooplankton, benthic invertebrates, microbes) sustaining their biomass, density, and biodiversity. | 9 | Geochemistry |
The extensive dark areas on the trailing hemisphere of Saturn's moon Rhea are thought to be deposited tholins. | 9 | Geochemistry |
The graphs below show the behaviour of fractional derivatives calculated by different algorithms for ferrocene in acetonitrile at 100mV/s, the reference electrode is 0.1M Ag/Ag in acetonitrile (+0.04V vs. Fc). | 3 | Analytical Chemistry |
Eutrophication can be a natural process and occurs naturally through the gradual accumulation of sediment and nutrients. Naturally, eutrophication is usually caused by the natural accumulation of nutrients from dissolved phosphate minerals and dead plant matter in water.
Natural eutrophication has been well-characterized in lakes. Paleolimnologists now recognise that climate change, geology, and other external influences are also critical in regulating the natural productivity of lakes. A few artificial lakes also demonstrate the reverse process (meiotrophication), becoming less nutrient rich with time as nutrient poor inputs slowly elute the nutrient richer water mass of the lake. This process may be seen in artificial lakes and reservoirs which tend to be highly eutrophic on first filling but may become more oligotrophic with time. The main difference between natural and anthropogenic eutrophication is that the natural process is very slow, occurring on geological time scales. | 2 | Environmental Chemistry |
Histatins are histidine-rich (cationic) antimicrobial proteins found in saliva. Histatin's involvement in antimicrobial activities makes histatin part of the innate immune system.
Histatin was first discovered (isolated) in 1988, with functions that's responsible in keeping homeostasis inside the oral cavity, helping in the formation of pellicles, and assist in bonding of metal ions.
__TOC__ | 1 | Biochemistry |
In coordination chemistry, the bite angle is the angle on a central atom between two bonds to a bidentate ligand. This ligand–metal–ligand geometric parameter is used to classify chelating ligands, including those in organometallic complexes. It is most often discussed in terms of catalysis, as changes in bite angle can affect not just the activity and selectivity of a catalytic reaction but even allow alternative reaction pathways to become accessible.
Although the parameter can be applied generally to any chelating ligand, it is commonly applied to describe diphosphine ligands, as they can adopt a wide range of bite angles. | 0 | Organic Chemistry |
The reagent removes pairs of H atoms from organic molecules. The stoichiometry of its action is illustrated by the conversion of tetralin to naphthalene:
:2 CCl(CN)O + CH → 2 CCl(CN)(OH) + CH
The resulting hydroquinone is poorly soluble in typical reaction solvents (dioxane, benzene, alkanes), which facilitates workup.
Solutions of DDQ in benzene are red, due to the formation of a charge-transfer complex. | 0 | Organic Chemistry |
In photochemistry, photohydrogen is hydrogen produced with the help of artificial or natural light. This is how the leaf of a tree splits water molecules into protons (hydrogen ions), electrons (to make carbohydrates) and oxygen (released into the air as a waste product). Photohydrogen may also be produced by the photodissociation of water by ultraviolet light.
Photohydrogen is sometimes discussed in the context of obtaining renewable energy from sunlight, by using microscopic organisms such as bacteria or algae. These organisms create hydrogen with the help of hydrogenase enzymes which convert protons derived from the water splitting reaction into hydrogen gas which can then be collected and used as a biofuel. | 5 | Photochemistry |
Today, most trichloroethylene is produced from ethylene. First, ethylene is chlorinated over a ferric chloride catalyst to produce 1,2-dichloroethane:
:CH=CH + Cl → ClCHCHCl
When heated to around 400 °C with additional chlorine, 1,2-dichloroethane is converted to trichloroethylene:
:ClCHCHCl + 2 Cl → ClCH=CCl + 3 HCl
This reaction can be catalyzed by a variety of substances. The most commonly used catalyst is a mixture of potassium chloride and aluminum chloride. However, various forms of porous carbon can also be used. This reaction produces tetrachloroethylene as a byproduct and depending on the amount of chlorine fed to the reaction, tetrachloroethylene can even be the major product. Typically, trichloroethylene and tetrachloroethylene are collected together and then separated by distillation.
Prior to the early 1970s, however, most trichloroethylene was produced in a two-step process from acetylene. First, acetylene was treated with chlorine using a ferric chloride catalyst at 90 °C to produce 1,1,2,2-tetrachloroethane according to the chemical equation:
:HC≡CH + 2 Cl → ClCHCHCl
The 1,1,2,2-tetrachloroethane is then dehydrochlorinated to give trichloroethylene. This can be accomplished either with an aqueous solution of calcium hydroxide:
:2 ClCHCHCl + Ca(OH) → 2 ClCH=CCl + CaCl + 2 HO
or in the vapor phase by heating it to 300–500 °C on a barium chloride or calcium chloride catalyst:
:ClCHCHCl → ClCH=CCl + HCl
Common impurities in reagent and technical grade TCE are methyl chloroform, carbon tetrachloride, ethylene dichloride, tetrachloroethanes, benzene and phenol. However, these compounds are present in very small amounts and do not possess any risk. | 2 | Environmental Chemistry |
Meta-analyses of intervention and observational trials for various types of cancer report mixed results. Supplementation with β-carotene did not appear to decrease the risk of cancer overall, nor specific cancers including: pancreatic, colorectal, prostate, breast, melanoma, or skin cancer generally. High-dose β-carotene supplementation unexpectedly resulted in a higher incidence of lung cancer and of total mortality in people who were cigarette smokers.
For dietary retinol, no effects were observed for high dietary intake and breast cancer survival, risk of liver cancer, risk of bladder cancer or risk of colorectal cancer, although the last review did report lower risk for higher beta-carotene consumption. In contrast, an inverse association was reported between retinol intake and relative risk of esophageal cancer, gastric cancer, ovarian cancer, pancreatic cancer, lung cancer, melanoma, and cervical cancer. For lung cancer, an inverse association was also seen for beta-carotene intake, separate from the retinol results. When high dietary intake was compared to low dietary intake, the decreases in relative risk were in the range of 15 to 20%. For gastric cancer, a meta-analysis of prevention trials reported a 29% decrease in relative risk from retinol supplementation at 1500 μg/day. | 1 | Biochemistry |
Karrer was married to Helena Froelich in 1914 and had three sons, one of whom died in infancy. He died on 18 June 1971, at the age of 82 in Zürich. His wife died in 1972. | 0 | Organic Chemistry |
The higher heating value is experimentally determined in a bomb calorimeter. The combustion of a stoichiometric mixture of fuel and oxidizer (e.g. two moles of hydrogen and one mole of oxygen) in a steel container at is initiated by an ignition device and the reactions allowed to complete. When hydrogen and oxygen react during combustion, water vapor is produced. The vessel and its contents are then cooled to the original 25 °C and the higher heating value is determined as the heat released between identical initial and final temperatures.
When the lower heating value (LHV) is determined, cooling is stopped at 150 °C and the reaction heat is only partially recovered. The limit of 150 °C is based on acid gas dew-point.
Note: Higher heating value (HHV) is calculated with the product of water being in liquid form while lower heating value (LHV) is calculated with the product of water being in vapor form. | 7 | Physical Chemistry |
Observations have shown that fluxes of ballast minerals (calcium carbonate, opal, and lithogenic material) and organic carbon fluxes are closely correlated in the bathypelagic zones of the ocean. A large fraction of particulate organic matter occurs in the form of marine snow aggregates (>0.5 mm) composed of phytoplankton, detritus, inorganic mineral grains, and fecal pellets in the ocean. Formation and sinking of these aggregates drive the biological carbon pump via export and sedimentation of organic matter from the surface mixed layer to the deep ocean and sediments. The fraction of organic matter that leaves the upper mixed layer of the ocean is, among other factors, determined by the sinking velocity and microbial remineralisation rate of these aggregates. Recent observations have shown that the fluxes of ballast minerals (calcium carbonate, opal, and lithogenic material) and the organic carbon fluxes are closely correlated in the bathypelagic zones of the ocean. This has led to the hypothesis that organic carbon export is determined by the presence of ballast minerals within settling aggregates.
Mineral ballasting is associated with about 60% of the flux of particulate organic carbon (POC) in the high-latitude North Atlantic, and with about 40% of the flux in the Southern Ocean. Strong correlations exist also in the deep ocean between the presence of ballast minerals and the flux of POC. This suggests ballast minerals enhance POC flux by increasing the sink rate of ballasted aggregates. Ballast minerals could additionally provide aggregated organic matter some protection from degradation.
It has been proposed that organic carbon is better preserved in sinking particles due to increased aggregate density and sinking velocity when ballast minerals are present and/or via protection of the organic matter due to quantitative association to ballast minerals. In 2002, Klaas and Archer observed that about 83% of the global particulate organic carbon (POC) fluxes were associated with carbonate, and suggested carbonate was a more efficient ballast mineral as compared to opal and terrigenous material. They hypothesized that the higher density of calcium carbonate compared to that of opal and the higher abundance of calcium carbonate relative to terrigenous material might be the reason for the efficient ballasting by calcium carbonate. However, the direct effects of ballast minerals on sinking velocity and degradation rates in sinking aggregates are still unclear.
A 2008 study demonstrated copepod fecal pellets produced on a diet of diatoms or coccolithophorids show higher sinking velocities as compared to pellets produced on a nanoflagellate diet. Carbon-specific respiration rates in pellets, however, were similar and independent of mineral content. These results suggest differences in mineral composition do not lead to differential protection of POC against microbial degradation, but the enhanced sinking velocities may result in up to 10-fold higher carbon preservation in pellets containing biogenic minerals as compared to that of pellets without biogenic minerals
Minerals seem to enhance the flocculation of phytoplankton aggregates and may even act as a catalyst in aggregate formation. However, it has also been shown that incorporation of minerals can cause aggregates to fragment into smaller and denser aggregates. This can potentially lower the sinking velocity of the aggregated organic material due to the reduced aggregate sizes, and, thus, lower the total export of organic matter. Conversely, if the incorporation of minerals increases the aggregate density, its size-specific sinking velocity may also increase, which could potentially increase the carbon export. Therefore, there is still a need for better quantitative investigations of how the interactions between minerals and organic aggregates affect the degradation and sinking velocity of the aggregates and, hence, carbon sequestration in the ocean. | 9 | Geochemistry |
Changes in animal populations, whether increases or decreases, can indicate pollution. For example, if pollution causes depletion of a plant, animal species that depend on that plant will experience population decline. Conversely, overpopulation may be opportunistic growth of a species in response to loss of other species in an ecosystem. On the other hand, stress-induced sub-lethal effects can be manifested in animal physiology, morphology, and behaviour of individuals long before responses are expressed and observed at the population level. Such sub-lethal responses can be very useful as "early warning signals" to predict how populations will further respond.
Pollution and other stress agents can be monitored by measuring any of several variables in animals: the concentration of toxins in animal tissues; the rate at which deformities arise in animal populations; behaviour in the field or in the laboratory; and by assessing changes in individual physiology. | 2 | Environmental Chemistry |
The primary role of CTCF is thought to be in regulating the 3D structure of chromatin. CTCF binds together strands of DNA, thus forming chromatin loops, and anchors DNA to cellular structures like the nuclear lamina. It also defines the boundaries between active and heterochromatic DNA.
Since the 3D structure of DNA influences the regulation of genes, CTCF's activity influences the expression of genes. CTCF is thought to be a primary part of the activity of insulators, sequences that block the interaction between enhancers and promoters. CTCF binding has also been both shown to promote and repress gene expression. It is unknown whether CTCF affects gene expression solely through its looping activity, or if it has some other, unknown, activity. In a recent study, it has been shown that, in addition to demarcating TADs, CTCF mediates promoter–enhancer loops, often located in promoter-proximal regions, to facilitate the promoter–enhancer interactions within one TAD. This is in line with the concept that a subpopulation of CTCF associates with the RNA polymerase II (Pol II) protein complex to activate transcription. It is likely that CTCF helps to bridge the transcription factor-bound enhancers to transcription start site-proximal regulatory elements and to initiate transcription by interacting with Pol II, thus supporting a role of CTCF in facilitating contacts between transcription regulatory sequences. This model has been demonstrated by the previous work on the beta-globin locus. | 1 | Biochemistry |
As far back as 1974, DNA sequence similarity was recognized as a valuable tool for determining relationships among taxa. Structural genes in general are more highly conserved due to functional constraint, and so can prove useful in examinations of more disparate taxa. Original analyses enriched samples for structural genes via hybridization to mRNA.
More recent phylogenetic approaches focused on structural genes of known function, conserved to varying degrees. rRNA sequences frequent targets, as they are conserved in all species. Microbiology has specifically targeted the 16S gene to determine species level differences. In higher-order taxa, COI is now considered the “barcode of life,” and is applied for most biological identification. | 1 | Biochemistry |
Some microorganisms utilize selenium in formate dehydrogenase. Formate is produced in large amounts in the hepatic (liver cells) mitochondria of embryonic cells and in cancer cells by the folate cycle.
Formate is reversibly oxidized by the enzyme formate dehydrogenase:
:HCO → CO + H + 2 e | 1 | Biochemistry |
Cerium in coal is typically weakly negative, meaning that it is present at slightly lower concentrations than the other rare-earth elements. Cerium anomalies in coal are influenced by the sediment source region. Coal mined from mafic regions dominated by basalts, such as the location of the Xinde Mine in China, does not have a Ce-anomaly. In contrast, coal mined in felsic rock regions, such as Guxu Coalfield in China, does have weakly negative Ce-anomalies. Negative Ce-anomalies can also be attributed to the weathering and oxidation of the coal-mining region. During oxidation, Ce precipitates out as CeO, leaving less Ce in the coal. | 9 | Geochemistry |
Antonella Buccianti (born 1960) is an Italian statistician and earth scientist, known for her work on the statistics of compositional data and its applications in geochemistry and geostatistics. She is an associate professor in the department of earth sciences at the University of Florence. | 9 | Geochemistry |
To capture genomic regions of interest using in-solution capture, a pool of custom oligonucleotides (probes) is synthesized and hybridized in solution to a fragmented genomic DNA sample. The probes (labeled with beads) selectively hybridize to the genomic regions of interest after which the beads (now including the DNA fragments of interest) can be pulled down and washed to clear excess material. The beads are then removed and the genomic fragments can be sequenced allowing for selective DNA sequencing of genomic regions (e.g., exons) of interest.
This method was developed to improve on the hybridization capture target-enrichment method. In solution capture (as opposed to hybrid capture) there is an excess of probes to target regions of interest over the amount of template required. The optimal target size is about 3.5 megabases and yields excellent sequence coverage of the target regions. The preferred method is dependent on several factors including: number of base pairs in the region of interest, demands for reads on target, equipment in house, etc. | 1 | Biochemistry |
The history of the mole is intertwined with that of units of molecular mass, and the Avogadro constant.
The first table of standard atomic weight was published by John Dalton (1766–1844) in 1805, based on a system in which the relative atomic mass of hydrogen was defined as 1. These relative atomic masses were based on the stoichiometric proportions of chemical reaction and compounds, a fact that greatly aided their acceptance: It was not necessary for a chemist to subscribe to atomic theory (an unproven hypothesis at the time) to make practical use of the tables. This would lead to some confusion between atomic masses (promoted by proponents of atomic theory) and equivalent weights (promoted by its opponents and which sometimes differed from relative atomic masses by an integer factor), which would last throughout much of the nineteenth century.
Jöns Jacob Berzelius (1779–1848) was instrumental in the determination of relative atomic masses to ever-increasing accuracy. He was also the first chemist to use oxygen as the standard to which other masses were referred. Oxygen is a useful standard, as, unlike hydrogen, it forms compounds with most other elements, especially metals. However, he chose to fix the atomic mass of oxygen as 100, which did not catch on.
Charles Frédéric Gerhardt (1816–56), Henri Victor Regnault (1810–78) and Stanislao Cannizzaro (1826–1910) expanded on Berzelius' works, resolving many of the problems of unknown stoichiometry of compounds, and the use of atomic masses attracted a large consensus by the time of the Karlsruhe Congress (1860). The convention had reverted to defining the atomic mass of hydrogen as 1, although at the level of precision of measurements at that time – relative uncertainties of around 1% – this was numerically equivalent to the later standard of oxygen = 16. However the chemical convenience of having oxygen as the primary atomic mass standard became ever more evident with advances in analytical chemistry and the need for ever more accurate atomic mass determinations.
The name mole is an 1897 translation of the German unit Mol, coined by the chemist Wilhelm Ostwald in 1894 from the German word Molekül (molecule). The related concept of equivalent mass had been in use at least a century earlier. | 3 | Analytical Chemistry |
In dielectric spectroscopy, large frequency dependent contributions to the dielectric response, especially at low frequencies, may come from build-ups of charge. This Maxwell–Wagner–Sillars polarization (or often just Maxwell-Wagner polarization), occurs either at inner dielectric boundary layers on a mesoscopic scale, or at the external electrode-sample interface on a macroscopic scale. In both cases this leads to a separation of charges (such as through a depletion layer). The charges are often separated over a considerable distance (relative to the atomic and molecular sizes), and the contribution to dielectric loss can therefore be orders of magnitude larger than the dielectric response due to molecular fluctuations. | 7 | Physical Chemistry |
* Academician Nikolai Dmitrievich Zelinsky: Ninetieth birthday. Sat. - M., 1952.
* Zelinsky A.N. [http://www.rv.ru/content.php3?id=11132 Спаси и сохрани: К 100-летию «Противогаза Зелинского»] // Russian Bulletin - 07/03/2015.
* Zelinsky Nikolai Dmitrievich // Great Soviet Encyclopedia: [in 30 volumes] / ch. ed. A. M. Prokhorov. - 3rd ed. - M .: Soviet Encyclopedia, 1969-1978.
* Kazansky B. A., Nesmeyanov A. N., Plate A. F. Работы академика Н. Д. Зелинского и его школы в области химии углеводородов и органического катализа. / Ученые записки МГУ. Issue. 175. - M., 1956.
* Moscow University in the Great Patriotic War. - 4th, revised and supplemented. Moscow: Moscow University Press, 2020 - 1000 copies. - ISBN 978-5-19-011499-7.
* Nametkin S. S. President of the Moscow Society of Naturalists, Academician Nikolai Dmitrievich Zelinsky: On the occasion of his 80th birthday. - B. m., 1941.
* Nikolai Dmitrievich Zelinsky / USSR Academy of Sciences. — M.; L .: Publishing house of the Academy of Sciences of the USSR, 1946. - 88 p. - (Materials for the bio-bibliography of scientists of the USSR. Series of chemical sciences. Issue 1).
* Plate A.F. Nikolai Dmitrievich Zelinsky // People of Russian science: Mathematics - Mechanics - Astronomy - Physics - Chemistry. - M., 1961.
* Sysoeva E. K., Terentiev P. B. ZELINSKY Nikolai Dmitrievich // Imperial Moscow University: 1755-1917: encyclopedic dictionary / compiled by A. Yu. Andreev, D. A. Tsygankov. - M.: Russian Political Encyclopedia (ROSSPEN), 2010. - S. 254-255. — 894 p. - 2000 copies. — ISBN 978-5-8243-1429-8.
* Figurovsky N. A. Essay on the emergence and development of a coal gas mask by N. D. Zelinsky. M., 1952.
* Yuryev Yu. K., Levina R. Ya. / Sci. ed. Ioffe S.T.; Moscow Society of Naturalists. — M.: MOIP, 1953. — 120 p. - (Historical series; No. 48). - 7000 copies. | 0 | Organic Chemistry |
Peter D. Mitchell proposed the chemiosmotic hypothesis in 1961. In brief, the hypothesis was that most adenosine triphosphate (ATP) synthesis in respiring cells comes from the electrochemical gradient across the inner membranes of mitochondria by using the energy of NADH and FADH formed during the oxidative breakdown of energy-rich molecules such as glucose.
Molecules such as glucose are metabolized to produce acetyl CoA as a fairly energy-rich intermediate. The oxidation of acetyl coenzyme A (acetyl-CoA) in the mitochondrial matrix is coupled to the reduction of a carrier molecule such as nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD).
The carriers pass electrons to the electron transport chain (ETC) in the inner mitochondrial membrane, which in turn pass them to other proteins in the ETC. The energy at every redox transfer step is used to pump protons from the matrix into the intermembrane space, storing energy in the form of a transmembrane electrochemical gradient. The protons move back across the inner membrane through the enzyme ATP synthase. The flow of protons back into the matrix of the mitochondrion via ATP synthase provides enough energy for ADP to combine with inorganic phosphate to form ATP.
This was a radical proposal at the time, and was not well accepted. The prevailing view was that the energy of electron transfer was stored as a stable high potential intermediate, a chemically more conservative concept. The problem with the older paradigm is that no high energy intermediate was ever found, and the evidence for proton pumping by the complexes of the electron transfer chain grew too great to be ignored. Eventually the weight of evidence began to favor the chemiosmotic hypothesis, and in 1978 Peter D. Mitchell was awarded the Nobel Prize in Chemistry.
Chemiosmotic coupling is important for ATP production in mitochondria, chloroplasts
and many bacteria and archaea. | 1 | Biochemistry |
SDS is synthesized by treating lauryl alcohol with sulfur trioxide, oleum, or chlorosulfuric acid to produce hydrogen lauryl sulfate. Lauryl alcohol can be used in pure form or as a mixtures of fatty alcohols. When produced from these sources, "SDS" products are a mixture of various sodium alkyl sulfates with SDS being the main component. For instance, SDS is a component, along with other chain-length amphiphiles, when produced from coconut oil, and is known as sodium coco sulfate (SCS). SDS is available commercially in powder, pellet, and other forms (each differing in rates of dissolution), as well as in aqueous solutions of varying concentrations. | 1 | Biochemistry |
Resiniferatoxin has a score of 16 billion Scoville heat units, making pure resiniferatoxin about 500 to 1000 times hotter than pure capsaicin. Resiniferatoxin activates transient vanilloid receptor 1 (TRPV1) in a subpopulation of primary afferent sensory neurons involved in nociception, the transmission of physiological pain. TRPV1 is an ion channel in the plasma membrane of sensory neurons and stimulation by resiniferatoxin causes this ion channel to become permeable to cations, especially calcium. The influx of cations causes the neuron to depolarize, transmitting signals similar to those that would be transmitted if the innervated tissue were being burned or damaged. This stimulation is followed by desensitization and analgesia, in part because the nerve endings die from calcium overload. | 0 | Organic Chemistry |
Diazomethane and the safer analogue trimethylsilyldiazomethane methylate carboxylic acids, phenols, and even alcohols:
The method offers the advantage that the side products are easily removed from the product mixture. | 0 | Organic Chemistry |
These are solutions containing FSL Kode constructs where the construct will exist as a clear micellular dispersion. FSL-GB3 as a solution/gel has been used to inhibit HIV infection and to neutralise Shiga toxin. FSL blood group A as a solution has been used to neutralise circulating antibodies in a mouse model and allow incompatible blood group A (murine kodecytes) transfusion. This model experiment was used to demonstrate the potential of FSLs to neutralise circulating antibody and allow for incompatible blood transfusion or organ transplantation. | 1 | Biochemistry |
Cyclins are a group of proteins that activate kinases involved in cell division. The degradation of cyclins is the key step that governs the exit from mitosis and progress into the next cell cycle. Cyclins accumulate in the course the cell cycle, then abruptly disappear just before the anaphase of mitosis. The cyclins are removed via a ubiquitin-mediated proteolytic pathway. | 1 | Biochemistry |
A microchannel plate is a slab made from resistive material (most often glass) 0.5 to 2mm thick with a regular array of tiny tubes (microchannels) leading from one face to the other. The microchannels are typically 5-20 micrometers in diameter, parallel to each other and enter the plate at a small angle to the surface (8-13° from normal). Plates are often round disks, but can be cut to any shape from sizes 10mm up to 200mm. They may also be curved. | 7 | Physical Chemistry |
In supramolecular chemistry, molecular encapsulation is the confinement of a guest molecule inside the cavity of a supramolecular host molecule (molecular capsule, molecular container or cage compounds). Examples of supramolecular host molecule include carcerands and endohedral fullerenes. | 6 | Supramolecular Chemistry |
Bioconjugation is a chemical strategy to form a stable covalent link between two molecules, at least one of which is a biomolecule. | 1 | Biochemistry |
(p)ppGpp is created via pppGpp synthase, also known as RelA, and is converted from pppGpp to ppGpp via pppGpp phosphohydrolase. RelA is associated with about every one in two hundred ribosomes and it becomes activated when an uncharged transfer RNA (tRNA) molecule enters the A site of the ribosome, due to the shortage of amino acid required by the tRNA. If a mutant bacterium is relA it is said to be relaxed and no regulation of RNA production due to amino acid absence is seen. | 1 | Biochemistry |
Chlororespiration is a respiratory process that takes place within plants. Inside plant cells there is an organelle called the chloroplast which is surrounded by the thylakoid membrane. This membrane contains an enzyme called NAD(P)H dehydrogenase which transfers electrons in a linear chain to oxygen molecules. This electron transport chain (ETC) within the chloroplast also interacts with those in the mitochondria where respiration takes place. Photosynthesis is also a process that Chlororespiration interacts with. If photosynthesis is inhibited by environmental stressors like water deficit, increased heat, and/or increased/decreased light exposure, or even chilling stress then chlororespiration is one of the crucial ways that plants use to compensate for chemical energy synthesis. | 1 | Biochemistry |
Due to their toxicity, use of first-generation glycopeptide antibiotics is restricted to patients who are critically ill, who have a demonstrated hypersensitivity to the β-lactams, or who are infected with β-lactam-resistant species, as in the case of methicillin-resistant Staphylococcus aureus. These antibiotics are effective principally against Gram-positive cocci. First-generation examples exhibit a narrow spectrum of action, and are bactericidal only against the enterococci. Some tissues are not penetrated very well by glycopeptides, and they do not penetrate into the cerebrospinal fluid.
The second-generation glycopeptides, or "lipoglycopeptides", have better binding to Lipid II due to the lipophilic moieties, expanding the antibacterial spectrum. Telavancin also has a hydrophilic moiety attached to enhance tissue distribution and reduce nephrotoxicity. | 0 | Organic Chemistry |
Podocin is localized on the membranes of podocyte pedicels (foot-like long processes), where it oligomerizes in lipid rafts together with nephrin to form the filtration slits. | 1 | Biochemistry |
In optical spectroscopy, the detectors typically measure the intensity of the light field rather than the electric field because there are no detectors that can directly measure electromagnetic fields in the optical range. However, there are multiple techniques, such as antennas and electro-optical sampling, that can be applied to measure the time evolution of E(t) directly. For example, one can propagate a THz pulse through a semiconductor sample and measure the transmitted and reflected fields as function of time. Therefore, one collects information of semiconductor excitation dynamics completely in time domain, which is the general principle of the terahertz time-domain spectroscopy.
By using short THz pulses, a great variety of physical phenomena have already been studied. For unexcited, intrinsic semiconductors one can determine the complex permittivity or THz-absorption coefficient and refractive index, respectively. The frequency of transversal-optical phonons, to which THz photons can couple, lies for most semiconductors at several THz. Free carriers in doped semiconductors or optically excited semiconductors lead to a considerable absorption of THz photons. Since THz pulses passes through non-metallic materials, they can be used for inspection and transmission of packaged items. | 7 | Physical Chemistry |
PHBV was first manufactured in 1983 by Imperial Chemical Industries (ICI). It is commercialized under the trade name Biopol. ICI (Zeneca) sold it to Monsanto in 1996. This was then obtained by Metabolix in 2001. Biomer L is the trade name of PHBV from Biomer. | 1 | Biochemistry |
Hydrophilic membrane filtration is used in several industries to filter various liquids. These hydrophilic filters are used in the medical, industrial, and biochemical fields to filter elements such as bacteria, viruses, proteins, particulates, drugs, and other contaminants. Common hydrophilic molecules include colloids, cotton, and cellulose (which cotton consists of).
Unlike other membranes, hydrophilic membranes do not require pre-wetting: they can filter liquids in their dry state. Although most are used in low-heat filtration processes, many new hydrophilic membrane fabrics are used to filter hot liquids and fluids. | 6 | Supramolecular Chemistry |
Repellents generally work by taking advantage of an animal's natural aversion to something, and often the thing chosen is something that the animal has learned to avoid (or instinctively avoids) in its natural environment.
Chemical repellents fall into two main categories, odor and taste. The former work better in the warm season and the latter, which ward off an animal only after it eats, in the cold season. (For example, the smell of the lawn fertilizer Milorganite is claimed to make it an effective repellent.) Such repellents mimic natural substances that deter animals and/or are designed to be so irritating to a specific animal or type of animal that it will avoid the protected object or area. Contact plant-origin repellents such as pepper, peppermint, tarragon, garlic, various essential oils, and castor oil, as well as diatomaceous earth and putrescent egg solids, are examples.
Further, some repellents function by inducing fear in the target animal. Such a repellent may contain animal urine, dried blood, or hair. Some animals will avoid anything that has the odor of the urine of their predators. Tiger urine is thus very effective at keeping away animals. Coyote urine has gained currency as a deer repellent. Fox urine is used to repel rabbits, groundhogs, woodchucks, squirrels and chipmunks. Bobcat urine repels moles, mice, voles and other rodents. Wolf urine is used to repel moose. Used cat litter is also effective. Domestic dogs can be repelled by vinegar.
Other repellents are not chemical. A simple electrified or barbed-wire fence can mechanically repel livestock or predator animals. Some electrical repellent systems have been tested against sharks. High-frequency whistles are used on vehicles to drive deer away from highways, and similar devices are used to deter certain types of insects or rodents. Repellents of this kind for domestic cats and dogs include ultrasonic devices which emit a high-frequency noise that does not affect humans. These types of non-chemical repellents are controversial, both because their effectiveness varies from animal to animal and because there have been few scientific studies conducted to prove that they work. They are, however, safe and humane, as are motion-activated sprinklers and electronic pet barriers, which latter are used by pet owners to confine their own pets to designated areas.
Flashing lights are used to repel lions in Kenya.
The ideal repellent is completely specific for the target animal; that is, it drives away the animal that one wishes to repel without affecting or harming any other animals or people. One type of animal repellent may be effective for raccoons, while another animal repellent may be more effective for skunks. It can be difficult to design a repellent method that drives away only undesirable animals while having no effect on people or other creatures. | 1 | Biochemistry |
The difference in mass density between the colloidal particles of mass density and the medium of suspension of mass density , and the diameter of the particles, have an influence on the value of . As an example, consider a colloidal suspension of polyethylene particles in water, and three different values for the diameter of the particles: 0.1 μm, 1 μm and 10 μm. The volume of a colloidal particles can be calculated using the volume of a sphere .
is the mass density of polyethylene, which is approximately on average 920 kg/m and is the mass density of water, which is approximately 1000 kg/m at room temperature (293K). Therefore is -80 kg/m.
Generally, decreases with . For the 0.1 μm diameter particle, is larger than the diameter, and the particles will be able to diffuse. For the 10 μm diameter particle, is much smaller than the diameter. As is negative the particles will cream, and the substance will no longer be a colloidal suspension.
In this example, the difference is mass density is relatively small. Consider a colloid with particles much denser than polyethylene, for example silicon with a mass density of approximately 2330 kg/m. If these particles are suspended in water, will be 1330 kg/m. will decrease as increases. For example, if the particles had a diameter of 10 μm the sedimentation length would be 5.92×10 μm, one order of magnitude smaller than for polyethylene particles. Also, because the particles are more dense than water, is positive and the particles will sediment. | 1 | Biochemistry |
Fructosephosphates are sugar phosphates based upon fructose, and are common in the biochemistry of cells.
Fructosephosphates play integral roles in many metabolic pathways, particularly glycolysis, gluconeogenesis and the pentose phosphate pathway.
The major biologically active fructosephosphates are:
*Fructose 1-phosphate
*Fructose 2-phosphate
*Fructose 3-phosphate
*Fructose 6-phosphate
*Fructose 1,6-bisphosphate
*Fructose 2,6-bisphosphate | 1 | Biochemistry |
August Friedrich Horstmann (20 November 1842 – 8 October 1929) was a German physical chemist who contributed to a thermodynamic understanding of chemical reactions and equilibria. His mathematical approach published in 1873 was largely overshadowed by the independent and identical findings of Josiah Willard Gibbs made about three years later.
Horstmann was born in Mannheim where his parents Georg Friedrich and Charlotte Friederike née Köhler ran a grocery business. He went to the Lycaeum and dropped out of high school due to short-sight and worked with his father. After three years he decided to study again and went to Heidelberg in 1862 where he attended chemistry classes under Emil Erlenmeyer. In 1865 he received a doctorate and went to study in Zurich under Johannes Wislicenus and Rudolf Clausius followed in 1866 with studies at Bonn with Hans Heinrich Landolt. He examined molecular weight and specific gravity of liquids. He became an associate professor in 1870 but short sight was still a problem and few students joined him. His major work was on the application of the laws of thermodynamics to chemical equilibria.
Horstmann married Clothilde Henriette Gernandt (1844–1921) in 1873 and they had five children. He went blind in 1902. | 7 | Physical Chemistry |
Twenty of the 32 crystal classes are piezoelectric, and crystals belonging to one of these classes (point groups) display piezoelectricity. All piezoelectric classes lack inversion symmetry. Any material develops a dielectric polarization when an electric field is applied, but a substance that has such a natural charge separation even in the absence of a field is called a polar material. Whether or not a material is polar is determined solely by its crystal structure. Only 10 of the 32 point groups are polar. All polar crystals are pyroelectric, so the 10 polar crystal classes are sometimes referred to as the pyroelectric classes.
There are a few crystal structures, notably the perovskite structure, which exhibit ferroelectric behavior. This is analogous to ferromagnetism, in that, in the absence of an electric field during production, the ferroelectric crystal does not exhibit a polarization. Upon the application of an electric field of sufficient magnitude, the crystal becomes permanently polarized. This polarization can be reversed by a sufficiently large counter-charge, in the same way that a ferromagnet can be reversed. However, although they are called ferroelectrics, the effect is due to the crystal structure (not the presence of a ferrous metal). | 3 | Analytical Chemistry |
The equation for converting Photosynthetic Photon Flux Density (PPFD) to DLI, assuming constant PPFD, is below. </blockquote>whereLight-hours is the number of hours in a day active photons are delivered to the target area, measured in hours.
Note that the factor 3.6·10 is due to the conversion factors coming from μmol being converted to mol and the unit of hours (from Light-Hours) being converted to seconds. | 5 | Photochemistry |
Anti-sigma factors are small proteins that bind to sigma factors and inhibit transcriptional activity in regulating prokaryote gene expression. Anti-sigma factors have both a sigma-binding domain and a sensory/signaling domain; this allows them to respond to signals inside and outside the cell. Anti-sigma factors have been found in several bacteria, including Escherichia coli and Salmonella, and viruses such as the T4 bacteriophage. Anti-sigma factors have an antagonistic effect on sigma factors. Each sigma factor has an associated anti-sigma factor that regulates it. These anti-sigma factors are divided into cytoplasmic-bound anti-sigma factors and inner membrane-bound anti-sigma factors. The differences in these sigma factors are where in the cell they are bound. Cytoplasmic-bound anti-sigma factors include FlgM, DnaK, RssB, and HscC. Inner membrane-bound anti-sigma factors, also called extra-cytoplasmic function (ECF) anti-sigma factors, include FecR and RseA. ECF anti-sigma factors tend to be more diverse in genetic sequence than cytoplasmic-bound anti-sigma factors. These factors regulate many cellular processes, such as flagellum assembly, transport of materials, cell growth, and the cell's stress response.Sigma factors are essential proteins that start the transcription by binding with RNAP; anti-sigma factors are proteins that inhibit the activities of sigma factors affected by several mechanisms. These mechanisms include adding up the anti-sigma factor between sigma or twisting the anti-sigma factor around sigma—gene regulation, especially in bacteria, allows for adaptivity and normal cell differentiation and development. Gene regulation has many different layers of regulators. Yet, initiating transcription is crucial in controlling which genes are expressed.
Anti-sigma factors are simultaneously transcribed with their associated sigma factor. This pairing creates a negative feedback loop, maintaining proper levels of both contrasting factors as there can only be one anti-sigma factor per sigma factor that is transcribed.
Research shows anti-sigma factors have more activities than contouring sigma factors effects. Anti-sigma factors can also activate some cells while inhibiting others, meaning they have an essential role in cell function. | 1 | Biochemistry |
The main metabolic challenge for methylotrophs is the assimilation of single carbon units into biomass. Through de novo synthesis, methylotrophs must form carbon-carbon bonds between 1-Carbon () molecules. This is an energy intensive process, which facultative methylotrophs avoid by using a range of larger organic compounds. However, obligate methylotrophs must assimilate molecules. There are four distinct assimilation pathways with the common theme of generating one molecule. Bacteria use three of these pathways while Fungi use one. All four pathways incorporate 3 molecules into multi-carbon intermediates, then cleave one intermediate into a new molecule. The remaining intermediates are rearranged to regenerate the original multi-carbon intermediates. | 0 | Organic Chemistry |
Bidirectional promoters are short (<1 kbp) intergenic regions of DNA between the 5 ends of the genes in a bidirectional gene pair. A “bidirectional gene pair” refers to two adjacent genes coded on opposite strands, with their 5 ends oriented toward one another. The two genes are often functionally related, and modification of their shared promoter region allows them to be co-regulated and thus co-expressed. Bidirectional promoters are a common feature of mammalian genomes. About 11% of human genes are bidirectionally paired.
Bidirectionally paired genes in the Gene Ontology database shared at least one database-assigned functional category with their partners 47% of the time. Microarray analysis has shown bidirectionally paired genes to be co-expressed to a higher degree than random genes or neighboring unidirectional genes. Although co-expression does not necessarily indicate co-regulation, methylation of bidirectional promoter regions has been shown to downregulate both genes, and demethylation to upregulate both genes. There are exceptions to this, however. In some cases (about 11%), only one gene of a bidirectional pair is expressed. In these cases, the promoter is implicated in suppression of the non-expressed gene. The mechanism behind this could be competition for the same polymerases, or chromatin modification. Divergent transcription could shift nucleosomes to upregulate transcription of one gene, or remove bound transcription factors to downregulate transcription of one gene.
Some functional classes of genes are more likely to be bidirectionally paired than others. Genes implicated in DNA repair are five times more likely to be regulated by bidirectional promoters than by unidirectional promoters. Chaperone proteins are three times more likely, and mitochondrial genes are more than twice as likely. Many basic housekeeping and cellular metabolic genes are regulated by bidirectional promoters.
The overrepresentation of bidirectionally paired DNA repair genes associates these promoters with cancer. Forty-five percent of human somatic oncogenes seem to be regulated by bidirectional promoters – significantly more than non-cancer causing genes. Hypermethylation of the promoters between gene pairs WNT9A/CD558500, CTDSPL/BC040563, and KCNK15/BF195580 has been associated with tumors.
Certain sequence characteristics have been observed in bidirectional promoters, including a lack of TATA boxes, an abundance of CpG islands, and a symmetry around the midpoint of dominant Cs and As on one side and Gs and Ts on the other. A motif with the consensus sequence of TCTCGCGAGA, also called the CGCG element, was recently shown to drive PolII-driven bidirectional transcription in CpG islands. CCAAT boxes are common, as they are in many promoters that lack TATA boxes. In addition, the motifs NRF-1, GABPA, YY1, and ACTACAnnTCCC are represented in bidirectional promoters at significantly higher rates than in unidirectional promoters. The absence of TATA boxes in bidirectional promoters suggests that TATA boxes play a role in determining the directionality of promoters, but counterexamples of bidirectional promoters do possess TATA boxes and unidirectional promoters without them indicates that they cannot be the only factor.
Although the term "bidirectional promoter" refers specifically to promoter regions of mRNA-encoding genes, luciferase assays have shown that over half of human genes do not have a strong directional bias. Research suggests that non-coding RNAs are frequently associated with the promoter regions of mRNA-encoding genes. It has been hypothesized that the recruitment and initiation of RNA polymerase II usually begins bidirectionally, but divergent transcription is halted at a checkpoint later during elongation. Possible mechanisms behind this regulation include sequences in the promoter region, chromatin modification, and the spatial orientation of the DNA. | 1 | Biochemistry |
An excess of acid is called acidosis or acidemia, while an excess in bases is called alkalosis or alkalemia. The process that causes the imbalance is classified based on the cause of the disturbance (respiratory or metabolic) and the direction of change in pH (acidosis or alkalosis). This yields the following four basic processes: | 7 | Physical Chemistry |
A number of related compounds are known, with a similar structure but having the indole core flipped and/or replaced with related cores such as indoline, indazole, benzothiophene, or benzofuran. These similarly are primarily active as agonists at the 5-HT family of serotonin receptors, with applications in the treatment of glaucoma, cluster headaches or as anorectics. | 0 | Organic Chemistry |
Kelvin probe force microscopy (KPFM), also known as surface potential microscopy, is a noncontact variant of atomic force microscopy (AFM). By raster scanning in the x,y plane the work function of the sample can be locally mapped for correlation with sample features. When there is little or no magnification, this approach can be described as using a scanning Kelvin probe (SKP). These techniques are predominantly used to measure corrosion and coatings.
With KPFM, the work function of surfaces can be observed at atomic or molecular scales. The work function relates to many surface phenomena, including catalytic activity, reconstruction of surfaces, doping and band-bending of semiconductors, charge trapping in dielectrics and corrosion. The map of the work function produced by KPFM gives information about the composition and electronic state of the local structures on the surface of a solid. | 7 | Physical Chemistry |
*Bamfield Peter and Hutchings Michael, Chromic Phenomena; technological applications of colour chemistry, 3rd Edition, Royal Society of Chemistry, Cambridge, 2018. {EPUB }.
*Vik Michal and Periyasamy Aravin Prince, Chromic Materials; Fundamentals, Measurements and Applications, Apple Academic Press, 2018. .
*Ferrara Mariella and Murat Bengisu, Materials that Change Color: Smart Materials and Intelligent Design, Springer, 2014. | 5 | Photochemistry |
Some cyanobacteria are sold as food, notably Arthrospira platensis (Spirulina) and others (Aphanizomenon flos-aquae).
Some microalgae contain substances of high biological value, such as polyunsaturated fatty acids, amino acids, proteins, pigments, antioxidants, vitamins, and minerals. Edible blue-green algae reduce the production of pro-inflammatory cytokines by inhibiting NF-κB pathway in macrophages and splenocytes. Sulfate polysaccharides exhibit immunomodulatory, antitumor, antithrombotic, anticoagulant, anti-mutagenic, anti-inflammatory, antimicrobial, and even antiviral activity against HIV, herpes, and hepatitis. | 5 | Photochemistry |
The superfluid phase of neutron matter exists in neutron stars.
The superfluidity is described by the BCS model with a realistic nucleon-nucleon interaction potential.
By increasing the density of nuclear matter above the saturation density, quark matter is formed. It is expected that dense quark matter at low
temperatures is a color superconductor.
In the case of the SU(3) color group, a Bose–Einstein condensate of the quark Cooper pairs carries an open color. To meet the requirement of confinement,
a Bose–Einstein condensate of colorless 6-quark states is considered, or the projected BCS theory is used. | 7 | Physical Chemistry |
Organic Geochemistry is a monthly peer-reviewed scientific journal published by Elsevier covering research on all aspects of organic geochemistry. It is an official journal of the European Association of Organic Geochemists. The editors-in-chief are Steven Rowland (University of Plymouth), John Volkman (CSIRO Oceans and Atmosphere), and Cliff Walters (University of Texas at Austin). | 9 | Geochemistry |
When an initially homogenous alloy is placed in an acid that can preferentially dissolve one or more components out of the alloy, the remaining component will diffuse and organize into a unique, nano-porous microstructure. The resulting material will have ligaments, formed by the remaining material, surrounded by pores, empty space from which atoms were leached/diffused away. | 8 | Metallurgy |
Polysaccharides with unprotected vicinal diols or amino sugars (where some hydroxyl groups are replaced with amines) give a positive periodic acid-Schiff stain (PAS). The list of polysaccharides that stain with PAS is long. Although mucins of epithelial origins stain with PAS, mucins of connective tissue origin have so many acidic substitutions that they do not have enough glycol or amino-alcohol groups left to react with PAS. | 0 | Organic Chemistry |
*APOBEC1
*APOBEC3A-H, APOBEC3G - affects HIV
*Activation-induced cytidine deaminase (AICDA)
*Cytidine deaminase (CDA)
*dCMP deaminase (DCTD)
*AMP deaminase (AMPD1)
*Adenosine Deaminase acting on tRNA (ADAT)
*Adenosine Deaminase acting on dsRNA (ADAR)
**Double-stranded RNA-specific editase 1 (ADARB1)
*Adenosine Deaminase acting on mononucleotides (ADA)
*Guanine Deaminase (GDA) | 1 | Biochemistry |
The use of radioactive tracer elements in ion uptake assays allows the calculation of km, Ki and Vmax and determines the initial change in the ion content of the cells. Mg decays by the emission of a high-energy beta or gamma particle, which can be measured using a scintillation counter. However, the radioactive half-life of Mg, the most stable of the radioactive magnesium isotopes, is only 21 hours. This severely restricts the experiments involving the nuclide. Also, since 1990, no facility has routinely produced Mg, and the price per mCi is now predicted to be approximately US$30,000. The chemical nature of Mg is such that it is closely approximated by few other cations. However, Co, Mn and Ni have been used successfully to mimic the properties of Mg in some enzyme reactions, and radioactive forms of these elements have been employed successfully in cation transport studies. The difficulty of using metal ion replacement in the study of enzyme function is that the relationship between the enzyme activities with the replacement ion compared to the original is very difficult to ascertain. | 1 | Biochemistry |
The plot of the Hammett equation is typically seen as being linear, with either a positive or negative slope correlating to the value of rho. However, nonlinearity emerges in the Hammett plot when a substituent affects the rate of reaction or changes the rate-determining step or reaction mechanism of the reaction. For the reason of the former case, new sigma constants have been introduced to accommodate the deviation from linearity otherwise seen resulting from the effect of the substituent. σ+ takes into account positive charge buildup occurring in the transition state of the reaction. Therefore, an electron donating group (EDG) will accelerate the rate of the reaction by resonance stabilization and will give the following sigma plot with a negative rho value.
σ- is designated in the case where negative charge buildup in the transition state occurs, and the rate of the reaction is consequently accelerated by electron withdrawing groups (EWG). The EWG withdraws electron density by resonance and effectively stabilizes the negative charge that is generated. The corresponding plot will show a positive rho value.
In the case of a nucleophilic acyl substitution the effect of the substituent, X, of the non-leaving group can in fact accelerate the rate of the nucleophilic addition reaction when X is an EWG. This is attributed to the resonance contribution of the EWG to withdraw electron density thereby increasing the susceptibility for nucleophilic attack on the carbonyl carbon. A change in rate occurs when X is EDG, as is evidenced when comparing the rates between X = Me and X = OMe, and nonlinearity is observed in the Hammett plot.
The effect of the substituent may change the rate-determining step (rds) in the mechanism of the reaction. A certain electronic effect may accelerate a certain step so that it is no longer the rds.
A change in the mechanism of a reaction also results in nonlinearity in the Hammett plot. Typically, the model used for measuring the changes in rate in this instance is that of the SN2 reaction. However, it has been observed that in some cases of an SN2 reaction that an EWG does not accelerate the reaction as would be expected and that the rate varies with the substituent. In fact, the sign of the charge and degree to which it develops will be affected by the substituent in the case of the benzylic system.
For example, the substituent may determine the mechanism to be an SN1 type reaction over a SN2 type reaction, in which case the resulting Hammett plot will indicate a rate acceleration due to an EDG, thus elucidating the mechanism of the reaction.
Another deviation from the regular Hammett equation is explained by the charge of nucleophile. Despite nonlinearity in benzylic SN2 reactions, electron withdrawing groups could either accelerate or retard the reaction. If the nucleophile is negatively charged (e.g. cyanide) the electron withdrawing group will increase the rate due to stabilization of the extra charge which is put on the carbon in the transition state. On the other hand, if the nucleophile is not charged (e.g. triphenylphosphine), electron withdrawing group is going to slow down the reaction by decreasing the electron density in the anti bonding orbital of leaving group in the transition state. | 7 | Physical Chemistry |
Photogeochemical reactions are described by the same principles used to describe photochemical reactions in general, and may be classified similarly:
# Photosynthesis: in the most general sense, photosynthesis refers to any light-activated reaction for which the change in free energy (ΔG) is positive for the reaction itself (without considering the presence of a catalyst or light). The products have higher energy than the reactants, and therefore the reaction is thermodynamically unfavorable, except through the action of light in conjunction with a catalyst. Examples of photosynthetic reactions include the splitting of water to form H and O, the reaction of CO and water to form O and reduced carbon compounds such as methanol and methane, and the reaction of N with water to yield NH and O.
# Photocatalysis: this refers to reactions that are accelerated by the presence of a catalyst (the light itself is not the catalyst as may be erroneously implied). The overall reaction has a negative change in free energy, and is therefore thermodynamically favored. Examples of photocatalytic reactions include the reaction of organic compounds with O to form CO and water, and the reaction of organic compounds with water to give H and CO.
# Uncatalyzed photoreactions: photoinduced or photoactivated reactions proceed via the action of light alone. For example, photodegradation of organic compounds often proceeds without a catalyst if the reactants themselves absorb light. | 5 | Photochemistry |
Increase in the number of dislocations is a quantification of work hardening. Plastic deformation occurs as a consequence of work being done on a material; energy is added to the material. In addition, the energy is almost always applied fast enough and in large enough magnitude to not only move existing dislocations, but also to produce a great number of new dislocations by jarring or working the material sufficiently enough. New dislocations are generated in proximity to a Frank–Read source.
Yield strength is increased in a cold-worked material. Using lattice strain fields, it can be shown that an environment filled with dislocations will hinder the movement of any one dislocation. Because dislocation motion is hindered, plastic deformation cannot occur at normal stresses. Upon application of stresses just beyond the yield strength of the non-cold-worked material, a cold-worked material will continue to deform using the only mechanism available: elastic deformation, the regular scheme of stretching or compressing of electrical bonds (without dislocation motion) continues to occur, and the modulus of elasticity is unchanged. Eventually the stress is great enough to overcome the strain-field interactions and plastic deformation resumes.
However, ductility of a work-hardened material is decreased. Ductility is the extent to which a material can undergo plastic deformation, that is, it is how far a material can be plastically deformed before fracture. A cold-worked material is, in effect, a normal (brittle) material that has already been extended through part of its allowed plastic deformation. If dislocation motion and plastic deformation have been hindered enough by dislocation accumulation, and stretching of electronic bonds and elastic deformation have reached their limit, a third mode of deformation occurs: fracture. | 8 | Metallurgy |
Inverse agonists differ from regular agonists in that they effect receptors to which a regular agonist binds such that the bound receptors demonstrate reduced activity compared to when they are normally inactive. In other words, inverse antagonists limit the efficacy of the bound receptor in some way. This is noted to be beneficial in instances wherein expression of receptors or up-regulated receptor sensitivity could be detrimental, thus making suppression of response the best recourse. A handful of examples of inverse agonist use in therapy include β-blockers, antihistamines, ACP-103 to treat Parkinson's disease, hemopressin, drugs to treat obesity, and more besides. | 1 | Biochemistry |
The Catskill-Delaware Water Ultraviolet Disinfection Facility is a ultraviolet (UV) water disinfection plant built in Westchester County, New York to disinfect water for the New York City water supply system. The compound is the largest ultraviolet germicidal irradiation plant in the world.
The UV facility treats water delivered by two of the citys aqueduct systems, the Catskill Aqueduct and the Delaware Aqueduct, via the Kensico Reservoir. (The citys third supply system, the New Croton Aqueduct, has a separate treatment plant.)
The plant has 56 energy-efficient UV reactors, and cost the city $1.6 billion. Mayor Michael Bloomberg created research groups between 2004-2006 to decide the best and most cost-effective ways to modernize the citys water filtration process, as a secondary stage following the existing chlorination and fluoridation facilities. The UV technology effectively controls microorganisms such as giardia and cryptosporidium' which are resistant to chlorine treatment. The city staff determined that the cheapest alternatives to a UV system would cost over $3 billion. In response to this finding, Bloomberg decided to set up a public competitive contract auction. Ontario based Trojan Technologies won the contract.
The facility treats of water per day. The new facility was originally set to be in operation by the end of 2012. The facility opened on October 8, 2013. | 5 | Photochemistry |
The Gateway cloning method, invented and commercialized by Invitrogen since the late 1990s, is the cloning method of the integration and excision recombination reactions that take place when bacteriophage lambda infects bacteria. This technology provides a fast and highly efficient way to transport DNA sequences into multi-vector systems for functional analysis and protein expression using Gateway att sites, and two proprietary enzyme mixes called BP Clonase and LR Clonase. In vivo, these recombination reactions are facilitated by the recombination of attachment sites from the lambda/phage chromosome (attP) and the bacteria (attB). As a result of recombination between the attP and attB sites, the phage integrates into the bacterial genome flanked by two new recombination sites (attLeft and attRight). The removal of the phage from the bacterial chromosome and the regeneration of attP and attB sites can both result from the attL and attR sites recombining under specific circumstances.
DNA sequences to be cloned are added to modified versions of these special Gateway Att sites. Two enzyme reactions take place, BP Clonase and LR Clonase. The BP Clonase occurs between the attB sites surrounding the insert and the attP sites of the donor vector. This reaction is catalyzed by the BP Clonase enzyme mixture and produces the entry clone containing the DNA of interest flanked by attL domains. As a byproduct of the reaction, the ccdB gene is cut from the donor vector. The LR Clonase occurs between the attL regions of the generated entry clone and the attR regions of the target vector and is catalyzed by the LR Clonase enzyme mix. As a result, an expression clone with DNA of interest flanked by attB regions is produced. As in the BP reaction, a DNA sequence containing the ccdB gene is cut from the target vector.
Large archives of Gateway Entry clones, containing the vast majority of human, mouse and rat ORFs (open reading frames) have been cloned from human cDNA libraries or chemically synthesized to support the research community using NIH (National Institutes of Health) funding (e.g., Mammalian Gene Collection, http://mgc.nci.nih.gov/). The availability of these gene cassettes in a standard Gateway cloning plasmid helps researchers quickly transfer these cassettes into plasmids that facilitate the analysis of gene function. Gateway cloning does take more time for initial set-up, and is more expensive than traditional restriction enzyme and ligase-based cloning methods, but it saves time, and offers simpler and highly efficient cloning for down-stream applications.
The technology has been widely adopted by the life science research community especially for applications that require the transfer of thousands of DNA fragments into one type of plasmid (e.g., one containing a CMV promoter for protein expression in mammalian cells), or for the transfer of one DNA fragment into many different types of plasmids (e.g., for bacterial, insect and mammalian protein expression). | 1 | Biochemistry |
The English word antagonist in pharmaceutical terms comes from the Greek ἀνταγωνιστής – antagonistēs, "opponent, competitor, villain, enemy, rival", which is derived from anti- ("against") and agonizesthai ("to contend for a prize"). Antagonists were discovered in the 20th century by American biologist Bailey Edgren. | 1 | Biochemistry |
Avogadros law (sometimes referred to as Avogadros hypothesis or Avogadros principle) or Avogadro-Ampères hypothesis is an experimental gas law relating the volume of a gas to the amount of substance of gas present. The law is a specific case of the ideal gas law. A modern statement is:
The law is named after Amedeo Avogadro who, in 1812, hypothesized that two given samples of an ideal gas, of the same volume and at the same temperature and pressure, contain the same number of molecules. As an example, equal volumes of gaseous hydrogen and nitrogen contain the same number of molecules when they are at the same temperature and pressure, and observe ideal gas behavior. In practice, real gases show small deviations from the ideal behavior and the law holds only approximately, but is still a useful approximation for scientists. | 7 | Physical Chemistry |
A group of researchers at Georgia Tech made dye-sensitized solar cells with a higher effective surface area by wrapping the cells around a quartz optical fiber. The researchers removed the cladding from optical fibers, grew zinc oxide nanowires along the surface, treated them with dye molecules, surrounded the fibers by an electrolyte and a metal film that carries electrons off the fiber. The cells are six times more efficient than a zinc oxide cell with the same surface area. Photons bounce inside the fiber as they travel, so there are more chances to interact with the solar cell and produce more current. These devices only collect light at the tips, but future fiber cells could be made to absorb light along the entire length of the fiber, which would require a coating that is conductive as well as transparent. Max Shtein of the University of Michigan said a sun-tracking system would not be necessary for such cells, and would work on cloudy days when light is diffuse. | 5 | Photochemistry |
The 25 year record of ocean carbon measurements at Station ALOHA document that the partial pressure of (p) in the mixed layer is increasing at a rate slightly greater than the trend observed in the atmosphere. This has been accompanied by progressive decreases in seawater pH. Although the effect of anthropogenic is evidenced by long-term decreases in seawater pH throughout the upper 600 m, the rate of acidification at Station ALOHA varies with depth. For example, in the upper mesopelagic waters (~160–310 m) pH is decreasing at nearly twice the rate observed in the surface waters. Such depth-dependent differences in acidification are due to a combination of regional differences in time-varying climate signatures, mixing, and changes in biological activity. | 9 | Geochemistry |
M2-PK, as measured in feces, is a potential tumor marker for colorectal cancer. When measured in feces with a cutoff value of 4 U/ml, its sensitivity has been estimated to be 85% (with a 95% confidence interval of 65 to 96%) for colon cancer and 56% (confidence interval 41–74%) for rectal cancer. Its specificity is 95%.
The M2-PK test is not dependent on occult blood (ELISA method), so it can detect bleeding or non-bleeding bowel cancer and also polyps with high sensitivity and high specificity with no false negative, but false positives may occur.
Most people are more willing to accept non-invasive preventive medical check-ups. Therefore, the measurement of tumor M2-PK in stool samples, with follow-up by colonoscopy to clarify the tumor M2-PK positive results, may prove to be an advance in the early detection of colorectal carcinomas. The CE marked M2-PK Test is available in form of an ELISA test for quantitative results or as point of care test to receive results within minutes.
Tumor M2-PK is also useful to diagnose lung cancer and better than SCC and NSE tumor markers. With renal cell carcinoma (RCC), the M2PK test has sensitivity of 66.7 percent for metastatic RCC and 27.5 percent for nonmetastatic RCC, but M2PK test cannot detect transitional cell carcinoma of the bladder, prostate cancer and benign prostatic hyperplasia. | 1 | Biochemistry |
Unlike crystalline materials which exhibit strong Bragg diffraction, the diffraction patterns of amorphous materials are characterized by broad and diffuse peaks. As a result, detailed analysis and complementary techniques are required to extract real space structural information from the diffraction patterns of amorphous materials. It is useful to obtain diffraction data from both X-ray and neutron sources as they have different scattering properties and provide complementary data. Pair distribution function analysis can be performed on diffraction data to determine the probability of finding a pair of atoms separated by a certain distance. Another type of analysis that is done with diffraction data of amorphous materials is radial distribution function analysis, which measures the number of atoms found at varying radial distances away from an arbitrary reference atom. From these techniques, the local order of an amorphous material can be elucidated. | 7 | Physical Chemistry |
Reductions with metal alkoxyaluminium hydrides are chemical reactions that involve either the net hydrogenation of an unsaturated compound or the replacement of a reducible functional group with hydrogen by metal alkoxyaluminium hydride reagents. | 0 | Organic Chemistry |
After the exhaustion of the glycogen reserve, and for the next 2–3 days, fatty acids are the principal metabolic fuel. At first, the brain continues to use glucose, because if a non-brain tissue is using fatty acids as its metabolic fuel, the use of glucose in the same tissue is switched off. Thus, when fatty acids are being broken down for energy, all of the remaining glucose is made available for use by the brain.
After 2 or 3 days of fasting, the liver begins to synthesize ketone bodies from precursors obtained from fatty acid breakdown. The brain uses these ketone bodies as fuel, thus cutting its requirement for glucose. After fasting for 3 days, the brain gets 30% of its energy from ketone bodies. After 4 days, this goes up to 75%.
Thus, the production of ketone bodies cuts the brain's glucose requirement from 80 g per day to about 30 g per day. Of the remaining 30 g requirement, 20 g per day can be produced by the liver from glycerol (itself a product of fat breakdown). This still leaves a deficit of about 10 g of glucose per day that must come from some other source. This deficit is supplied via gluconeogenesis from amino acids from proteolysis of body proteins.
After several days of fasting, all cells in the body begin to break down protein. This releases amino acids into the bloodstream, which can be converted into glucose by the liver. Since much of the human body's muscle mass is protein, this phenomenon is responsible for the wasting away of muscle mass seen in starvation.
However, the body can selectively decide which cells break down protein and which do not. About 2–3 g of protein must be broken down to synthesize 1 g of glucose; about 20–30 g of protein is broken down each day to make 10 g of glucose to keep the brain alive. However, to conserve protein, this number may decrease the longer the fasting.
Starvation ensues when the fat reserves are completely exhausted and protein is the only fuel source available to the body. Thus, after periods of starvation, the loss of body protein affects the function of important organs, and death results, even if there are still fat reserves left unused. (In a leaner person, the fat reserves are depleted earlier, the protein depletion occurs sooner, and therefore death occurs sooner.)
The ultimate cause of death is, in general, cardiac arrhythmia or cardiac arrest brought on by tissue degradation and electrolyte imbalances.
In the very obese, it has been shown that proteins can be depleted first. Accordingly, death from starvation is predicted to occur before fat reserves are used up. | 1 | Biochemistry |
High-gradient magnetic separator is to separate magnetic and non-magnetic particles (concentrate and tails) from the feed slurry. This feed comes from intermediate thickener underflow pump through Linear Screen & Passive Matrix. Tailings go to tailing thickener & product goes to throw launder through vacuum tanks. | 3 | Analytical Chemistry |
Functional null mutations in this gene cause Carney complex (CNC), an autosomal dominant multiple neoplasia syndrome. This gene can fuse to the RET protooncogene by gene rearrangement and form the thyroid tumor-specific chimeric oncogene known as PTC2.
Mutation of PRKAR1A leads to the Carney complex, associating multiple endocrine tumors. | 1 | Biochemistry |
Williams was born in Tonypandy, Wales, the son of a coal miner. In 1944, he won a scholarship to study at the University of Bristol, where he earned a bachelors degree in 1948 and later a Master of Science in physics. In working to earn his masters degree, he studied stereo micro-radiography at the University of Chicago, under the direction of Cyril Stanley Smith. Around the same time, he also took up a position as a metallurgist with the Revere Copper Company in Rome, New York.
In 1960, Williams earned his doctorate from the University of Toronto. | 8 | Metallurgy |
The Sonogashira reaction is a cross-coupling reaction used in organic synthesis to form carbon–carbon bonds. It employs a palladium catalyst as well as copper co-catalyst to form a carbon–carbon bond between a terminal alkyne and an aryl or vinyl halide.
:* </span>: aryl or vinyl
:* </span>: arbitrary
:* X: I, Br, Cl or OTf
The Sonogashira cross-coupling reaction has been employed in a wide variety of areas, due to its usefulness in the formation of carbon–carbon bonds. The reaction can be carried out under mild conditions, such as at room temperature, in aqueous media, and with a mild base, which has allowed for the use of the Sonogashira cross-coupling reaction in the synthesis of complex molecules. Its applications include pharmaceuticals, natural products, organic materials, and nanomaterials. Specific examples include its use in the synthesis of tazarotene, which is a treatment for psoriasis and acne, and in the preparation of SIB-1508Y, also known as Altinicline, a nicotinic receptor agonist. | 0 | Organic Chemistry |
In benzene the two cyclohexatriene Kekulé structures, first proposed by Kekulé, are taken together as contributing structures to represent the total structure. In the hybrid structure on the right, the dashed hexagon replaces three double bonds, and represents six electrons in a set of three molecular orbitals of π symmetry, with a nodal plane in the plane of the molecule.
In furan a lone pair of the oxygen atom interacts with the π orbitals of the carbon atoms. The curved arrows depict the permutation of delocalized π electrons, which results in different contributors. | 7 | Physical Chemistry |
Often parents of children with a developmental disability want to know more about their childs conditions before choosing to have another child. These concerns can be addressed by analysis of the parents and childs DNA. In cases where the childs developmental disability is not understood, the cause of it can potentially be determined using FISH and cytogenetic techniques. Examples of diseases that are diagnosed using FISH include Prader-Willi syndrome, Angelman syndrome, 22q13 deletion syndrome, chronic myelogenous leukemia, acute lymphoblastic leukemia, Cri-du-chat, Velocardiofacial syndrome, and Down syndrome. FISH on sperm cells is indicated for men with an abnormal somatic or meiotic karyotype as well as those with oligozoospermia, since approximately 50% of oligozoospermic men have an increased rate of sperm chromosome abnormalities. The analysis of chromosomes 21, X, and Y is enough to identify oligozoospermic individuals at risk.
In medicine, FISH can be used to form a diagnosis, to evaluate prognosis, or to evaluate remission of a disease, such as cancer. Treatment can then be specifically tailored. A traditional exam involving metaphase chromosome analysis is often unable to identify features that distinguish one disease from another, due to subtle chromosomal features; FISH can elucidate these differences. FISH can also be used to detect diseased cells more easily than standard Cytogenetic methods, which require dividing cells and requires labor and time-intensive manual preparation and analysis of the slides by a technologist. FISH, on the other hand, does not require living cells and can be quantified automatically, a computer counts the fluorescent dots present. However, a trained technologist is required to distinguish subtle differences in banding patterns on bent and twisted metaphase chromosomes. FISH can be incorporated into Lab-on-a-chip microfluidic device. This technology is still in a developmental stage but, like other lab on a chip methods, it may lead to more portable diagnostic techniques. | 1 | Biochemistry |
A scene featuring a volcano in the film Fair Wind to Java (1953) was shot at Mono Lake.
Most of the film High Plains Drifter (1973) by Clint Eastwood was shot on the southern shores of Mono Lake in the 1970s. An entire town was built here for the film, and later removed when shooting was complete. | 2 | Environmental Chemistry |
Because the molecule d-biotin has a much higher affinity to Strep-Tactin than Strep-tag, it can effectively compete for the binding site. Therefore, a MHC multimer based on the interaction of Strep-tag with Strep-Tactin is easily disrupted in the presence of relatively low concentrations of d-biotin. Without the Strep-Tactin backbone, the single MHC-Strep-tag fusion proteins spontaneously detach from the TCR of the T cell, because of weak binding affinities (monomeric MHC-epitope complexes cannot provide stable binding, see above). | 1 | Biochemistry |
Stream metabolism, often referred to as aquatic ecosystem metabolism in both freshwater (lakes, rivers, wetlands, streams, reservoirs) and marine ecosystems, includes gross primary productivity (GPP) and ecosystem respiration (ER) and can be expressed as net ecosystem production (NEP = GPP - ER). Analogous to metabolism within an individual organism, stream metabolism represents how energy is created (primary production) and used (respiration) within an aquatic ecosystem. In heterotrophic ecosystems, GPP:ER is <1 (ecosystem using more energy than it is creating); in autotrophic ecosystems it is >1 (ecosystem creating more energy than it is using).[https://doi.org/10.4319/lo.1956.1.2.0102] Most streams are heterotrophic.[https://doi.org/10.1016/B978-0-12-813047-6.00012-7] A heterotrophic ecosystem often means that allochthonous (coming from outside the ecosystem) inputs of organic matter, such as leaves or debris fuel ecosystem respiration rates, resulting in respiration greater than production within the ecosystem. However, autochthonous (coming from within the ecosystem) pathways also remain important to metabolism in heterotrophic ecosystems. In an autotrophic ecosystem, conversely, primary production (by algae, macrophytes) exceeds respiration, meaning that ecosystem is producing more organic carbon than it is respiring.
Stream metabolism can be influenced by a variety of factors, including physical characteristics of the stream (slope, width, depth, and speed/volume of flow), biotic characteristics of the stream (abundance and diversity of organisms ranging from bacteria to fish), light and nutrient availability to fuel primary production, organic matter to fuel respiration, water chemistry and temperature, and natural or human-caused disturbance, such as dams, removal of riparian vegetation, nutrient pollution, wildfire or flooding.
Measuring stream metabolic state is important to understand how disturbance may change the available primary productivity, and whether and how that increase or decrease in NEP influences foodweb dynamics, allochthonous/autochthonous pathways, and trophic interactions. Metabolism (encompassing both ER and GPP) must be measured rather than primary productivity alone, because simply measuring primary productivity does not indicate excess production available for higher trophic levels. One commonly used method for determining metabolic state in an aquatic system is daily changes in oxygen concentration, from which GPP, ER, and net daily metabolism can be estimated.
Disturbances can affect trophic relationships in a variety of ways, such as simplifying foodwebs, causing trophic cascades, and shifting carbon sources and major pathways of energy flow (Power et al. 1985, Power et al. 2008). Part of understanding how disturbance will impact trophic dynamics lies in understanding disturbance impacts to stream metabolism (Holtgrieve et al. 2010). For example, in Alaska streams, disturbance of the benthos by spawning salmon caused distinct changes in stream metabolism; autotrophic streams became net heterotrophic during the spawning run, then reverted to autotrophy after the spawning season (Holtgrieve and Schindler 2011). There is evidence that this seasonal disturbance impacts trophic dynamics of benthic invertebrates and in turn their vertebrate predators (Holtgrieve and Schindler 2011, Moore and Schindler 2008). Wildfire disturbance may have similar metabolic and trophic impacts in streams. | 1 | Biochemistry |
Initiation factor IF3 is a small protein of 21 kDa containing two compact α/β domains (IF3C and IF3N) connected by a flexible lysine-rich linker. Most IF3 functions are mediated by the IF3C domain, while IF3N regulates 30S subunit binding. Bacterial initiation factor 3 (infC) is not universally found in all bacterial species but in E. coli it is required for the 30S subunit to bind to the initiation site in mRNA. IF3 is required by the small subunit to form initiation complexes, but has to be released to allow the 50S subunit to bind. IF3 attaches to the platform side of the 30S subunit, close to helices 23, 24, 25, 26 and 45 of 16S rRNA, as well as ribosomal proteins S7, S11, and S12. The IF3C domain interacts with the 30S subunit via its conserved basic residues R99, R116, R147 and R168 . A major function of IF3 is inspecting codon-anticodon pairing at the P-site during start codon selection. It accelerates the dissociation of non-canonical initiation complexes containing mismatched or incorrect tRNAs. IF3 also inspects the initiator tRNA, rejecting elongator tRNAs and it also promotes the dissociation of the 70S ribosome into subunits, providing a pool of free 30S subunits for initiation. Another key role of IF3 is repositioning mRNA on the 30S subunit from a standby site to the P-site decoding site for start codon selection. IF3 works cooperatively with IF1 and IF2 during initiation and modulates IF2 binding and enhances the fidelity of start codon selection. | 1 | Biochemistry |
Conferences are normally scheduled for May or June in Europe, North America or Asia. However, most conferences are held in Europe because the majority of the current membership resides in Europe. Conferences start with an informal reception on Sunday evening followed by two and a half days of technical sessions. Ample time is allowed for technical discussion, and various social events are scheduled in association with the conference. Typical topics include machinery and press tools, new processes, new materials, experimental methods for evaluating formability and studying press operations, springback, constitutive equations, plasticity criteria, and friction and wear with attention to interface behavior as characterized by topography and surface chemistry, lubrication, speed, and temperature. | 8 | Metallurgy |
The core RNA polymerase (consisting of 2 alpha (α), 1 beta (β), 1 beta-prime (β'), and 1 omega (ω) subunits) binds a sigma factor to form a complex called the RNA polymerase holoenzyme. It was previously believed that the RNA polymerase holoenzyme initiates transcription, while the core RNA polymerase alone synthesizes RNA. Thus, the accepted view was that sigma factor must dissociate upon transition from transcription initiation to transcription elongation (this transition is called "promoter escape"). This view was based on analysis of purified complexes of RNA polymerase stalled at initiation and at elongation. Finally, structural models of RNA polymerase complexes predicted that, as the growing RNA product becomes longer than ~15 nucleotides, sigma must be "pushed out" of the holoenzyme, since there is a steric clash between RNA and a sigma domain. However, σ can remain attached in complex with the core RNA polymerase in early elongation and sometimes throughout elongation. Indeed, the phenomenon of promoter-proximal pausing indicates that sigma plays roles during early elongation. All studies are consistent with the assumption that promoter escape reduces the lifetime of the sigma-core interaction from very long at initiation (too long to be measured in a typical biochemical experiment) to a shorter, measurable lifetime upon transition to elongation. | 1 | Biochemistry |
Proteins and other molecules are constantly in competition with one another over binding sites on a surface. The Vroman Effect, developed by Leo Vroman, postulates that small and abundant molecules will be the first to coat a surface. However, over time, molecules with higher affinity for that particular surface will replace them. This is often seen in materials that contact the blood where fibrinogen will bind to the surface first and over time will be replaced by kininogen. | 1 | Biochemistry |
The ability for a mechanical bond to reduce reactivity and hence prevent unwanted reactions has been exploited in a number of areas. One of the earliest applications was in the protection of organic dyes from environmental degradation. | 6 | Supramolecular Chemistry |
Examples of siderophores produced by various bacteria and fungi:
Hydroxamate siderophores
Catecholate siderophores
Mixed ligands
Amino carboxylate ligands
A comprehensive list of siderophore structures (over 250) is presented in Appendix 1 in reference. | 1 | Biochemistry |
* [http://www.piercenet.com/method/desalting-gel-filtration#gelfiltration Animation of desalting using gel filtration chromatography] | 3 | Analytical Chemistry |
The Jaffe reaction is a colorimetric method used in clinical chemistry to determine creatinine levels in blood and urine. In 1886, Max Jaffe (1841–1911) wrote about its basic principles in the paper Über den Niederschlag, welchen Pikrinsäure in normalem Harn erzeugt und über eine neue Reaction des Kreatinins in which he described the properties of creatinine and picric acid in an alkaline solution. The color change that occurred was directly proportional to the concentration of creatinine, however he also noted that several other organic compounds induced similar reactions. In the early 20th century, Otto Folin adapted Jaffe's research into a clinical procedure. The Jaffe reaction, despite its nonspecificity for creatinine, is still widely employed as the method of choice for creatinine testing due to its speed, adaptability in automated analysis, and cost-effectiveness, and is the oldest methodology continued to be used in the medical laboratory. It is this nonspecificity that has motivated the development of new reference methods for creatinine analysis into the 21st century. | 1 | Biochemistry |
Joshi et al. (2006) propose the Koenigs-Knorr reaction in the stereoselective synthesis of alkyl D-glucopyranosides via glycosylation, with the exception of using lithium carbonate which is less expensive and toxic than the conventional method of using silver or mercury salts. D-glucose is first protected by forming the peracetate by addition of acetic anhydride in acetic acid, and then addition of hydrogen bromide which brominates at the 5-position. On addition of the alcohol ROH and lithium carbonate, the OR replaces the bromine and on deprotecting the acetylated hydroxyls the product is synthesized in relatively high purity. It was suggested by Joshi et al. (2001) that lithium acts as the nucleophile that attacks the carbon at the 5-position and through a transition state the alcohol is substituted for the bromine group. Advantages of this method as well as its stereoselectivity and low cost of the lithium salt include that it can be done at room temperature and its yield compares relatively well with the conventional Koenigs-Knorr method. | 0 | Organic Chemistry |
*1991 National Science Foundation Faculty Award for Women Scientists
*1994 Alexander von Humboldt Foundation Max Planck Research Award
*1996 American Physical Society Fellow
*2005 American Physical Society Herbert P. Broida Prize
*2006 National Science Foundation CAREER Award
*2007 University of Southern California Remarkable Women Award
*2010 University of Southern California Provost's Mentoring Award
*2012 American Association for the Advancement of Science Fellow | 7 | Physical Chemistry |
Besides setups in multi-purpose facilities, the first dedicated end-station has been built at the PETRA-III storage ring, where this technique is routinely applied. | 7 | Physical Chemistry |
The ability to control the electrode potential for electro-switchable biosurfaces facilitates several different applications. One example is the field of molecular electronics, for instance the investigation of DNA-mediated charge transfer.
Another application is the analysis of molecular interactions. To that end, the DNA strand is labeled with a fluorescent dye. Excited fluorescent dyes can transfer energy to metal. Consequently, the fluorescence is quenched in proximity to the metal electrode. To measure interactions, a ligand is additionally attached at the head of the DNA molecule and the interacting analyte is flushed across the biosensor. Two different measurement modes can be performed with the biosensor, a static mode and a dynamic mode. In static mode, the potential applied to the electrode is fixed, keeping the DNA molecule in an upright position. Binding of the analyte to the ligand will change the local environment of the fluorescent dye and thereby quench its fluorescence. The static mode can also be used to measure the activity of enzymes like polymerases that influence the structure of the DNA molecule. In dynamic mode, the potential applied to the electrode is oscillating, thus the DNA molecule switches between the upright and the horizontal position. Binding of an analyte will change the size of the attached complex. Consequently, the hydrodynamic friction will change and the DNA molecule will move through the buffer with a different speed. This speed change can be used to investigate size changes or conformational changes induced by the binding of the analyte. The application of electro-switchable biosurfaces as a sensor for molecular interactions is also known as switchSENSE technology. It belongs to the category of microfluidic surface-bound methods to measure molecular interactions.
A similar application in this category is surface plasmon resonance (SPR), where a thin gold film on top of a glass slide is the sensor surface. In SPR, the gold film can additionally be modified with SAM or other specific layers. One difference to electro-switchable biosurfaces is that no potential is applied to the SPR surface. In contrast to surface-bound methods, there are also in-solution methods to measure molecule interactions, for example isothermal titration calorimetry (ITC).
The electric potential cannot only be used to control the movement of the DNA strands, but also to control the release of the molecules into solution. This has possible applications in the field of gene therapy since it might enable the delivery of genetic material to specific locations. | 1 | Biochemistry |
Iron technology was further advanced by several inventions in medieval Islam, during the Islamic Golden Age. These included a variety of water-powered and wind-powered industrial mills for metal production, including geared gristmills and forges. By the 11th century, every province throughout the Muslim world had these industrial mills in operation, from Islamic Spain and North Africa in the west to the Middle East and Central Asia in the east. There are also 10th-century references to cast iron, as well as archeological evidence of blast furnaces being used in the Ayyubid and Mamluk empires from the 11th century, thus suggesting a diffusion of Chinese metal technology to the Islamic world.
Geared gristmills were invented by Muslim engineers, and were used for crushing metallic ores before extraction. Gristmills in the Islamic world were often made from both watermills and windmills. In order to adapt water wheels for gristmilling purposes, cams were used for raising and releasing trip hammers. The first forge driven by a hydropowered water mill rather than manual labour was invented in the 12th century Islamic Spain.
One of the most famous steels produced in the medieval Near East was Damascus steel used for swordmaking, and mostly produced in Damascus, Syria, in the period from 900 to 1750. This was produced using the crucible steel method, based on the earlier Indian wootz steel. This process was adopted in the Middle East using locally produced steels. The exact process remains unknown, but it allowed carbides to precipitate out as micro particles arranged in sheets or bands within the body of a blade. Carbides are far harder than the surrounding low carbon steel, so swordsmiths could produce an edge that cut hard materials with the precipitated carbides, while the bands of softer steel let the sword as a whole remain tough and flexible. A team of researchers based at the Technical University of Dresden that uses X-rays and electron microscopy to examine Damascus steel discovered the presence of cementite nanowires and carbon nanotubes. Peter Paufler, a member of the Dresden team, says that these nanostructures give Damascus steel its distinctive properties and are a result of the forging process. | 8 | Metallurgy |
The concentration of ATP must be kept above equilibrium level so that the rates of ATP-dependent biochemical reactions meet metabolic demands. A decrease in ATP will result in a decreased saturation of enzymes that use ATP as substrate, and thus a decreased reaction rate. The concentration of ATP is also kept higher than that of AMP, and a decrease in the ATP/AMP ratio triggers AMPK to activate cellular processes that will return ATP and AMP concentrations to steady state.
In one step of the glycolysis pathway catalyzed by PFK-1, the equilibrium constant of reaction is approximately 1000, but the steady state concentration of products (fructose-1,6-bisphosphate and ADP) over reactants (fructose-6-phosphate and ATP) is only 0.1, indicating that the ratio of ATP to AMP remains in a steady state significantly above equilibrium concentration. Regulation of PFK-1 maintains ATP levels above equilibrium.
In the cytoplasm of hepatocytes, the steady state ratio of NADP to NADPH is approximately 0.1 while that of NAD to NADH is approximately 1000, favoring NADPH as the main reducing agent and NAD as the main oxidizing agent in chemical reactions. | 7 | Physical Chemistry |
Large molecules that have one end with polar groups attached and another end with nonpolar groups are described as amphiphiles or amphiphilic molecules. They are good surfactants and can aid in the formation of stable emulsions, or blends, of water and fats. Surfactants reduce the interfacial tension between oil and water by adsorbing at the liquid–liquid interface. | 7 | Physical Chemistry |
Phasor analysis is commonly used for fluorescence-lifetime imaging microscopy (FLIM) data analysis and has been adapted for pump–probe imaging data analysis. Signals are decomposed into their real and imaginary parts of the Fourier transform at a given frequency. By plotting the real and imaginary parts against one another, the distribution of different chromophores with distinct lifetimes can be mapped. In melanoma studies, this approach has again shown to be able to distinguish between the different forms of melanin. One of the main advantages of phasor analysis is that it provides an intuitive qualitative, graphical view of the content It has also been combined with PCA for quantitative analysis. | 7 | Physical Chemistry |
In poorly-managed soils, particularly on sloped ground, erosion and transport of soil sediment rich in POM can contaminate water bodies. Because POM provides a source of energy and nutrients, rapid build-up of organic matter in water can result in eutrophication. Suspended organic materials can also serve as a potential vector for the pollution of water with fecal bacteria, toxic metals or organic compounds. | 9 | Geochemistry |
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