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A pseudoknot is a nucleic acid secondary structure containing at least two stem-loop structures in which half of one stem is intercalated between the two halves of another stem. Pseudoknots fold into knot-shaped three-dimensional conformations but are not true topological knots. The base pairing in pseudoknots is not well nested; that is, base pairs occur that "overlap" one another in sequence position. This makes the presence of general pseudoknots in nucleic acid sequences impossible to predict by the standard method of dynamic programming, which uses a recursive scoring system to identify paired stems and consequently cannot detect non-nested base pairs with common algorithms. However, limited subclasses of pseudoknots can be predicted using modified dynamic programs.
Newer structure prediction techniques such as stochastic context-free grammars are also unable to consider pseudoknots.
Pseudoknots can form a variety of structures with catalytic activity and several important biological processes rely on RNA molecules that form pseudoknots. For example, the RNA component of the human telomerase contains a pseudoknot that is critical for its activity. The hepatitis delta virus ribozyme is a well known example of a catalytic RNA with a pseudoknot in its active site. Though DNA can also form pseudoknots, they are generally not present in standard physiological conditions. | 4 | Stereochemistry |
Creaming, in the laboratory sense, is the migration of the dispersed phase of an emulsion under the influence of buoyancy. The particles float upwards or sink depending on how large they are and density compared to the continuous phase as well as how viscous or how thixotropic the continuous phase might be. For as long as the particles remain separated, the process is called creaming.
Where it is important that either the form or the concentration of the emulsion should be stable, it is desirable that the continuous and the dispersed phases should have similar densities and it also is desirable that the continuous phase should be viscous or thixotropic. Thixotropy is particularly valuable in paints, sauces, and similar products, partly because it counteracts tendencies towards creaming. It also is important that the particles be as small as practicable because that reduces their tendency to migrate under the influence of buoyant forces due to Brownian motion, which keeps the particles in suspension. The electric charges on their surfaces should preferably tend to be uniform, so that the particles repel rather than attract each other.
Creaming is usually seen as undesirable because it causes difficulties in storage and handling and can be dangerous in health care settings by causing a fat embolism (fat in the blood stream) or occluding capillaries (blockage of capillaries) if an emulsion that has undergone creaming is administered intravenously. It can be useful in special cases especially where it is desirable to concentrate an emulsion. A particular example is in the separation of dairy cream, either to achieve a desired concentration of butterfat, or to make butter.
Depending on whether the dispersed particles are less dense or more dense than the continuous phase, they may move either to the top or bottom of a sample. In this it differs from flocculation (where particles clump) or emulsion breaking (where particles coalesce). Unlike flocculation and breaking, creaming of an emulsion is a relatively simple process to reverse. | 7 | Physical Chemistry |
A potentiometric sensor is a type of chemical sensor that may be used to determine the analytical concentration of some components of the analyte gas or solution. These sensors measure the electrical potential of an electrode when no current is present. | 7 | Physical Chemistry |
Adiabatic accessibility denotes a certain relation between two equilibrium states of a thermodynamic system (or of different such systems). The concept was coined by Constantin Carathéodory in 1909 ("adiabatische Erreichbarkeit") and taken up 90 years later by Elliott Lieb and J. Yngvason in their axiomatic approach to the foundations of thermodynamics. It was also used by R. Giles in his 1964 monograph. | 7 | Physical Chemistry |
* [http://www.aps.org/units/damop/ American Physical Society - Division of Atomic, Molecular & Optical Physics]
* [https://web.archive.org/web/20090927053332/http://ampd.epsdivisions.org/ European Physical Society - Atomic, Molecular & Optical Physics Division]
* [https://www.nsf.gov/funding/pgm_summ.jsp?pims_id=13622 National Science Foundation - Atomic, Molecular and Optical Physics]
* [http://cuaweb.mit.edu/ MIT-Harvard Center for Ultracold Atoms]
*[https://qfarm.stanford.edu Stanford QFARM Initiative for Quantum Science & Enginneering]
* [https://web.archive.org/web/20190101155151/http://jila.colorado.edu/research/atomic-molecular-physics/atomic-molecular-physics JILA - Atomic and Molecular Physics]
* [http://jqi.umd.edu/ Joint Quantum Institute at University of Maryland and NIST]
*[http://www.phy.ornl.gov/ ORNL Physics Division]
*[http://web.am.qub.ac.uk/ctamop/ Queen's University Belfast - Center for Theoretical, Atomic, Molecular and Optical Physics],
*[http://physics.berkeley.edu/research/atomic-molecular-and-optical-physics University of California, Berkeley - Atomic, Molecular and Optical Physics] | 7 | Physical Chemistry |
Dioxirane is highly unstable and the majority of studies of it have been computational; it has been detected during the low temperature (–196 °C) reaction of ethylene and ozone, although even at these temperatures such a mixture can be explosive. Its formation is thought to be radical in nature, preceding via a Criegee intermediate. Microwave analysis has indicated C-H, C-O and O-O bond lengths of 1.090, 1.388 and 1.516 Å respectively. The very long and weak O-O bond (c.f. hydrogen peroxide O-O = 1.47 Å) is the origin of its instability. | 0 | Organic Chemistry |
The reads from the last step are realigned to the reference genome. In this method, SSCS family pairs that have complementary tags will be grouped (family αβ and βα in Figure 2). These reads originate from two complementary strands of DNA. High confidence sequences are selected based on the perfectly matched base calls of each family. The final sequence is called the DCS. True mutations are those that match perfectly between complementary SSCSs. This step filters out remaining errors raised during the first round of PCR amplification or during sample preparation. | 1 | Biochemistry |
pH partition is the tendency for acids to accumulate in basic fluid compartments, and bases to accumulate in acidic compartments. The reason for this phenomenon is that acids become negatively electric charged in basic fluids, since they donate a proton. On the other hand, bases become positively electric charged in acid fluids, since they receive a proton. Since electric charge decrease the membrane permeability of substances, once an acid enters a basic fluid and becomes electrically charged, then it cannot escape that compartment with ease and therefore accumulates, and vice versa with bases. | 1 | Biochemistry |
N-linked glycosylation is a very prevalent form of glycosylation and is important for the folding of many eukaryotic glycoproteins and for cell–cell and cell–extracellular matrix attachment. The N-linked glycosylation process occurs in eukaryotes in the lumen of the endoplasmic reticulum and widely in archaea, but very rarely in bacteria. In addition to their function in protein folding and cellular attachment, the N-linked glycans of a protein can modulate a protein's function, in some cases acting as an on/off switch. | 0 | Organic Chemistry |
Iron salt aerosols are one proposed method of enhanced atmospheric methane oxidation which involves lofting iron-based particles into the atmosphere (e.g. from planes or ships) to enhance atmospheric chlorine radicals, a natural methane sink.
Winds over the Sahara raise dust into the troposphere and disperse it over the Atlantic. A 2023 study suggests that this has contributed to natural atmospheric methane oxidation.
Iron salt aerosols are being studied for the potential of iron(III) chloride (FeCl) to catalyze chlorine radical production. Chlorine atoms are produced by photolysis from the FeCl stemming from iron-containing airborne dust aerosol particles in the oceanic boundary layer.
:FeCl + hv → FeCl + Cl
The chlorine atoms initiate methane oxidation:
:CH + Cl → HCl + CH
The resulting methyl radical is unstable and oxidises naturally to CO and water:
:3.5O + 2CH → 2CO + 3HO | 2 | Environmental Chemistry |
A post column oxidation-reduction reactor is a chemical reactor that performs derivatization to improve the measurement of organic molecules. It is used in gas chromatography (GC), after the column, and before a flame ionization detector (FID), to make the detector response uniform for all organic molecules.
The reactor converts the carbon atoms of organic molecules in GC column effluents into methane before reaching the FID. The resulting detector response is uniform on a per-carbon basis and avoids the need for response factors and calibration standards for each molecule. It can improve the response of the FID to many molecules with poor/low response including carbon monoxide (CO), carbon dioxide (CO), hydrogen cyanide (HCN), formamide (CHNO), formaldehyde (CHO) and formic acid (CHO), because these molecules are converted to methane. | 3 | Analytical Chemistry |
In Runyon et al. 2006, the researchers demonstrate how the parasitic plant, Cuscuta pentagona (field dodder), uses VOCs to interact with various hosts and determine locations. Dodder seedlings show direct growth toward tomato plants (Lycopersicon esculentum) and, specifically, tomato plant volatile organic compounds. This was tested by growing a dodder weed seedling in a contained environment, connected to two different chambers. One chamber contained tomato VOCs while the other had artificial tomato plants. After 4 days of growth, the dodder weed seedling showed a significant growth towards the direction of the chamber with tomato VOCs. Their experiments also showed that the dodder weed seedlings could distinguish between wheat (Triticum aestivum) VOCs and tomato plant volatiles. As when one chamber was filled with each of the two different VOCs, dodder weeds grew towards tomato plants as one of the wheat VOCs is repellent. These findings show evidence that volatile organic compounds determine ecological interactions between plant species and show statistical significance that the dodder weed can distinguish between different plant species by sensing their VOCs.
Tomato plant to plant communication is further examined in Zebelo et al. 2012, which studies tomato plant response to herbivory. Upon herbivory by Spodoptera littoralis, tomato plants emit VOCs that are released into the atmosphere and induce responses in neighboring tomato plants. When the herbivory-induced VOCs bind to receptors on other nearby tomato plants, responses occur within seconds. The neighboring plants experience a rapid depolarization in cell potential and increase in cytosolic calcium. Plant receptors are most commonly found on plasma membranes as well as within the cytosol, endoplasmic reticulum, nucleus, and other cellular compartments. VOCs that bind to plant receptors often induce signal amplification by action of secondary messengers including calcium influx as seen in response to neighboring herbivory. These emitted volatiles were measured by GC-MS and the most notable were 2-hexenal and 3-hexenal acetate. It was found that depolarization increased with increasing green leaf volatile concentrations. These results indicate that tomato plants communicate with one another via airborne volatile cues, and when these VOC's are perceived by receptor plants, responses such as depolarization and calcium influx occur within seconds. | 1 | Biochemistry |
It has been proposed that oxidative stress may play a major role in determining cardiac complications in COVID-19. | 1 | Biochemistry |
Falconbridge Limited in mid-1981 commissioned a copper smelter and refinery near Timmins, Ontario, to treat concentrate from its Kidd Mine. However, at the outset, the quality of the cathode copper produced in the Kidd refinery suffered from the presence of higher than usual concentrations of lead and selenium in the copper smelter’s anodes. Kidd cathode copper was not able to meet its customers’ specifications and obtaining product certification for the London Metal Exchange (“LME”) became a key focus.
After several process improvements were instigated, it was ultimately realised that the use of copper starter sheets was preventing the Kidd refinery meeting its cathode quality targets. Test work then began on the use of permanent stainless-steel cathodes. Preliminary tests using full-scale titanium blanks showed a reduction in the lead content of the cathode copper of a factor of four and a six-fold reduction in the selenium content, compared with the use of copper starter sheets.
The focus then shifted to developing a stripping machine, to develop stainless steel cathodes incorporating the existing header bars and evaluating edge-strip technology. The company’s board of directors gave approval for the conversion of the refinery to the Kidd technology in April 1985. The conversion was completed in 1986 and the Kidd refinery became the third to install permanent cathode and automated stripping technology.
Falconbridge began marketing the technology in 1992, after many requests from other refinery operators. Thus, the Kidd Process created competition between two suppliers of permanent cathode technology. The main differences between them were the cathode header bar, edge stripping and the stripping machine technology.
In contrast to the stainless steel header bar then used in the Isa Process cathode, the Kidd Process cathode used a solid copper header bar, which was welded onto the stainless steel sheet. This gave a lower voltage drop (by 8–10 millivolts) than the Isa Process cathode.
The Isa Process technology used the waxed edge at the bottom of the cathode plate to stop the copper depositing around the plate’s bottom to form a single mass of copper running from the top of one side of the cathode plate around the bottom to the top of the other side. The copper was stripped from the cathode plates as two separate sheets. The Kidd Process technology did not use wax, as it was thought that it could exacerbate the impurity problems with which the plant had been struggling. At Kidd, the stripping approach was to remove the copper from the cathode plate as a single V-shaped cathode product, akin to a taco shell.
The Kidd Process initially used a “carousel” stripping machine, but a linear installation was subsequently developed to provide machines with lower to medium stripping capacities for electrowinning plants and smaller refineries. The linear stripping machines, first installed in 1996, were more compact, less complex and had lower installation costs than the carousel machines. | 8 | Metallurgy |
A colorimeter is a device used in colorimetry that measures the absorbance of particular wavelengths of light by a specific solution. It is commonly used to determine the concentration of a known solute in a given solution by the application of the Beer–Lambert law, which states that the concentration of a solute is proportional to the absorbance. | 7 | Physical Chemistry |
For classical silencers, the signaling pathway is relatively simple. Since repression is active, silencer elements target the assembly of GTFs, necessary for transcription of the gene. These silencer elements are mostly located upstream of the gene and can vary between short and long distances. For long-range silencers, it has been observed that the DNA will form a loop in order to bring the silencer closer to the promoter and loop out the interfering DNA. Silencers also target helicase sites in the DNA that are rich in adenine and thymine (AT) and prone to unwinding the DNA, allowing room to initiate transcription. The inhibited helicase activity leads to the inhibition of transcription. This is commonly seen in the human thyrotropin-β gene promoter. NREs can induce a bend in the promoter region to block interactions, as seen when an NRE binds to Yin-Yang 1 (YY1), and flank regulatory signals or promoter regions as well. When the silencer region is located within an intron, there can be two types of repressions. First, there can be a physical blockage of a splice site. Second, there can be a bend in the DNA that will inhibit RNA processing.
When located in the exon or the untranslated region, the silencer will mainly be classical or position-dependent. However, these silencers can carry out their activity prior to transcription. Most silencers are constitutively expressed in organisms, only allowing activation of a gene by either inhibiting the silencer or by activating an enhancer region. The best example of this is the Neuronal-Restrictive Silencer Factor (NRSF) that is produced by the REST gene. The REST gene produces NRSF in order to repress the transcription of neuronal genes that are essential for localization of neuronal tissue. When a silencer represses REST, NRSF is also inhibited, allowing for the transcription of neuronal genes. | 1 | Biochemistry |
The Vital Question is a book by the English biochemist Nick Lane about the way the evolution and origin of life on Earth was constrained by the provision of energy.
The book was well received by critics; The New York Times, for example, found it "seductive and often convincing" though the reviewer considered much of it speculative beyond the evidence provided. The Guardian wrote that the book presented hard evidence and tightly interlocking theory on a question once thought inaccessible to science, the origin of life. New Scientist found the books arguments powerful and persuasive with many testable ideas; that it was not easy to read was compensated by the "incredible, epic story" that it told. The Telegraph wrote that the book succeeded brilliantly as science writing, expanding the readers horizons with a gripping narrative. | 1 | Biochemistry |
Coenzyme A (CoA, SHCoA, CoASH) is a coenzyme, notable for its role in the synthesis and oxidation of fatty acids, and the oxidation of pyruvate in the citric acid cycle. All genomes sequenced to date encode enzymes that use coenzyme A as a substrate, and around 4% of cellular enzymes use it (or a thioester) as a substrate. In humans, CoA biosynthesis requires cysteine, pantothenate (vitamin B), and adenosine triphosphate (ATP).
In its acetyl form, coenzyme A is a highly versatile molecule, serving metabolic functions in both the anabolic and catabolic pathways. Acetyl-CoA is utilised in the post-translational regulation and allosteric regulation of pyruvate dehydrogenase and carboxylase to maintain and support the partition of pyruvate synthesis and degradation. | 1 | Biochemistry |
Much of the Martian surface is deeply covered by dust as fine as talcum powder. The global predominance of dust obscures the underlying bedrock, making spectroscopic identification of primary minerals impossible from orbit over many areas of the planet. The red/orange appearance of the dust is caused by iron(III) oxide (nanophase FeO) and the iron(III) oxide-hydroxide mineral goethite.
The Mars Exploration Rovers identified magnetite as the mineral responsible for making the dust magnetic. It probably also contains some titanium.
The global dust cover and the presence of other wind-blown sediments has made soil compositions remarkably uniform across the Martian surface. Analysis of soil samples from the Viking landers in 1976 shows that the soils consist of finely broken up basaltic rock fragments and are highly enriched in sulphur and chlorine, probably derived from volcanic gas emissions. | 9 | Geochemistry |
Since the invention of agriculture, humans have directly and gradually influenced the carbon cycle over century-long timescales by modifying the mixture of vegetation in the terrestrial biosphere. Over the past several centuries, direct and indirect human-caused land use and land cover change (LUCC) has led to the loss of biodiversity, which lowers ecosystems' resilience to environmental stresses and decreases their ability to remove carbon from the atmosphere. More directly, it often leads to the release of carbon from terrestrial ecosystems into the atmosphere.
Deforestation for agricultural purposes removes forests, which hold large amounts of carbon, and replaces them, generally with agricultural or urban areas. Both of these replacement land cover types store comparatively small amounts of carbon so that the net result of the transition is that more carbon stays in the atmosphere. However, the effects on the atmosphere and overall carbon cycle can be intentionally and/or naturally reversed with reforestation. | 5 | Photochemistry |
In August 2005 a second report commissioned by the developers, from Encia Environmental, revealed levels of asbestos fibres in two soil samples from the site at 1.3% and 2.3%, 13 and 23 times above the limit at which waste is deemed "hazardous". A level of 3% is categorised as "toxic". Regarding the developers earlier assertions that they had not intended to develop the controversial northern section, council planning officer Ken Smith claimed that the developers had been told they would have to submit a planning application for the whole of the site, which would have to show any asbestos tests and plans for removal, and not just selected portions. "They were clearly told remediation work must take place on the whole of the site," he said. "It's been quite clear it was 72 acres and not [just] part of that site." | 2 | Environmental Chemistry |
Various methods are used to prevent and protect against corrosion, such as cathodic protection, selection and injection of chemicals such as corrosion inhibitors or other ways to prevent corrosion. However, in order to see the results of these methods and how effective these measures are, corrosion monitoring should be done and, if necessary, corrosion protection methods should be modified or optimized based on the results obtained from corrosion monitoring. In many industries, preventive measures are used to protect against corrosion, but obviously without knowing the results of these measures, protection is a chance, that is, either full protection will not be done or in case of excessive protection, it will waste capital and resources. | 8 | Metallurgy |
Smolková-Keulemansová was born on 27 April 1927, in Prague, the Czech Republic (then Czechoslovakia) to a Jewish family. She had a normal childhood in Czechoslovakia as an only child to her parents Alice and Oskar. She finished primary school and had started grammar school but was taken out of school by her father after anti-Jewish laws started applying to grammar schools. She was employed at various Jewish workshops after leaving school. | 3 | Analytical Chemistry |
PSII, PSI, and cytochrome bf are found in chloroplasts. All plants and all photosynthetic algae contain chloroplasts, which produce NADPH and ATP by the mechanisms described above. In essence, the same transmembrane structures are also found in cyanobacteria.
Unlike plants and algae, cyanobacteria are prokaryotes. They do not contain chloroplasts; rather, they bear a striking resemblance to chloroplasts themselves. This suggests that organisms resembling cyanobacteria were the evolutionary precursors of chloroplasts. One imagines primitive eukaryotic cells taking up cyanobacteria as intracellular symbionts in a process known as endosymbiosis. | 5 | Photochemistry |
Cory was educated at Case Western Reserve University, earning a bachelor's degree there in 1981 and a Ph.D. in chemistry in 1987. He carried out postdoctoral research at Radboud University Nijmegen in the Netherlands and at Naval Research Laboratory in Washington, D.C. He was a Professor of Nuclear Engineering at Massachusetts Institute of Technology prior to his 2010 appointment at Waterloo. At MIT, he worked on NMR, including his work on NMR quantum computation. Together with Amr Fahmy and Timothy Havel he developed the concept of pseudo-pure states and performed the first experimental demonstrations of NMR quantum computing.
Cory's research also concerns the realization and application of quantum control in various physical systems and devices. In 2015, he and teams from University of Waterloo, National Institute of Standards and Technology and Boston University demonstrated the generation and control of orbital angular momentum of neutron beams using a fork-dislocation grating, extending the existing work in optical and electron beams to neutrons. They subsequently demonstrated the control of both the spin and orbital angular momentum degrees of freedom of neutron beams. | 7 | Physical Chemistry |
Measurements of organic matter generally measure only organic compounds or carbon, and so are only an approximation of the level of once-living or decomposed matter. Some definitions of organic matter likewise only consider "organic matter" to refer to only the carbon content, or organic compounds, and do not consider the origins or decomposition of the matter. In this sense, not all organic compounds are created by living organisms, and living organisms do not only leave behind organic material. A clam's shell, for example, while biotic, does not contain much organic carbon, so may not be considered organic matter in this sense. Conversely, urea is one of many organic compounds that can be synthesized without any biological activity.
Organic matter is heterogeneous and very complex. Generally, organic matter, in terms of weight, is:
* 45–55% carbon
* 35–45% oxygen
* 3–5% hydrogen
* 1–4% nitrogen
The molecular weights of these compounds can vary drastically, depending on if they repolymerize or not, from 200 to 20,000 amu. Up to one third of the carbon present is in aromatic compounds in which the carbon atoms form usually six-membered rings. These rings are very stable due to resonance stabilization, so they are difficult to break down. The aromatic rings are also susceptible to electrophilic and nucleophilic attack from other electron-donating or electron-accepting material, which explains the possible polymerization to create larger molecules of organic matter.
There are also reactions that occur with organic matter and other material in the soil to create compounds never seen before. Unfortunately, it is very difficult to characterize these because so little is known about natural organic matter in the first place. Research is currently being done to figure out more about these new compounds and how many of them are being formed. | 0 | Organic Chemistry |
Environment-sensitive dyes change their properties (intensity, half-life, and excitation and emission spectra) depending on the polarity (hydrophobicity and charge) of their environments. Examples include: Indole, Cascade Yellow, prodan, Dansyl, Dapoxyl, NBD, PyMPO, Pyrene and diethylaminocumarin.<br />
This change is most pronounced when electron-donating and electron-withdrawing groups are placed at opposite ends of an aromatic ring system, as this results in a large change in dipole moment when excited.
When a fluorophore is excited, it generally has a larger dipole moment (μ) than in the ground state (μ). Absorption of a photon by a fluorophore takes a few picoseconds. Before this energy is released (emission: 1–10 ns), the solvent molecules surrounding the fluorophore reorient (10–100 ps) due to the change in polarity in the excited singlet state; this process is called solvent relaxation. As a result of this relaxation, the energy of the excited state of the fluorophore is lowered (longer wavelength), hence fluorophores that have a large change in dipole moment have larger stokes shift changes in different solvents. The difference between the energy levels can be roughly determined with the Lipper-Mataga equation.
A hydrophobic dye is a dye which is insoluble in water, a property independent of solvatochromism. <br>Additionally, The term environment-sensitive in chemistry actually describes changes due to one of a variety of different environmental factors, such as pH or temperature, not just polarity; however, in biochemistry environment-sensitive fluorphore and solvatochromic fluorophore are used interchangeably: this convention is so widespread that suppliers describe them as environment-sensitive over solvatochromic. | 1 | Biochemistry |
MLST databases contain the reference allele sequences and sequence types for each organism, and also isolate epidemiological data. The websites contain interrogation and analysis software which allow users to query their allele sequences and sequence types. MLST is widely used as a tool for researchers and public healthcare workers.
The majority of MLST databases are hosted at web server currently located in Oxford University ([http://www.pubmlst.org pubmlst.org]).
The database hosted at the site hold the organism specific reference allele sequences and lists of STs for individual organisms.
To assist the gathering and formatting of the utilized sequences a simple and free plug-in for Firefox has been developed ([http://science.agrool.gr/mtrantas/?p=168 link] ). | 1 | Biochemistry |
In the early 20th century, chemists observed that various aromatic hydrocarbons in the presence of oxygen could absorb wavelength specific light to generate a peroxide species. This discovery of oxygen's reduction by a photosensitizer led to chemists studying photosensitizers as photoredox catalysts for their roles in the catalysis of pericyclic reactions and other reduction and oxidation reactions. Photosensitizers in synthetic chemistry allow for the manipulation of electronic transitions within molecules through an externally applied light source. These photosensitizers used in redox chemistry may be organic, organometallic, or nanomaterials depending on the physical and spectral properties required for the reaction. | 5 | Photochemistry |
In organic chemistry, episulfides are a class of organic compounds that contain a saturated, heterocyclic ring consisting of two carbon atoms and one sulfur atom. It is the sulfur analogue of an epoxide or aziridine. They are also known as thiiranes, olefin sulfides, thioalkylene oxides, and thiacyclopropanes. Episulfides are less common and generally less stable than epoxides. The most common derivative is ethylene sulfide (). | 0 | Organic Chemistry |
A simple and widely used model for molecular interactions is the Hill equation, which provides a way to quantify cooperative binding by describing the fraction of saturated ligand binding sites as a function of the ligand concentration. | 1 | Biochemistry |
Salts comprising these cations are typically prepared by alkylation of thiourea:
:SC(NH) + RX → [RSC(NH)]X | 0 | Organic Chemistry |
The nitrogen cycle is as important in the ocean as it is on land. While the overall cycle is similar in both cases, there are different players and modes of transfer for nitrogen in the ocean. Nitrogen enters the ocean through precipitation, runoff, or as N from the atmosphere. Nitrogen cannot be utilized by phytoplankton as N so it must undergo nitrogen fixation which is performed predominantly by cyanobacteria. Without supplies of fixed nitrogen entering the marine cycle, the fixed nitrogen would be used up in about 2000 years. Phytoplankton need nitrogen in biologically available forms for the initial synthesis of organic matter. Ammonia and urea are released into the water by excretion from plankton. Nitrogen sources are removed from the euphotic zone by the downward movement of the organic matter. This can occur from sinking of phytoplankton, vertical mixing, or sinking of waste of vertical migrators. The sinking results in ammonia being introduced at lower depths below the euphotic zone. Bacteria are able to convert ammonia to nitrite and nitrate but they are inhibited by light so this must occur below the euphotic zone. Ammonification or mineralization is performed by bacteria to convert organic nitrogen to ammonia. Nitrification can then occur to convert the ammonium to nitrite and nitrate. Nitrate can be returned to the euphotic zone by vertical mixing and upwelling where it can be taken up by phytoplankton to continue the cycle. N can be returned to the atmosphere through denitrification.
Ammonium is thought to be the preferred source of fixed nitrogen for phytoplankton because its assimilation does not involve a redox reaction and therefore requires little energy. Nitrate requires a redox reaction for assimilation but is more abundant so most phytoplankton have adapted to have the enzymes necessary to undertake this reduction (nitrate reductase). There are a few notable and well-known exceptions that include most Prochlorococcus and some Synechococcus that can only take up nitrogen as ammonium.
Phosphorus is an essential nutrient for plants and animals. Phosphorus is a limiting nutrient for aquatic organisms. Phosphorus forms parts of important life-sustaining molecules that are very common in the biosphere. Phosphorus does enter the atmosphere in very small amounts when the dust is dissolved in rainwater and seaspray but remains mostly on land and in rock and soil minerals. Eighty per cent of the mined phosphorus is used to make fertilizers. Phosphates from fertilizers, sewage and detergents can cause pollution in lakes and streams. Over-enrichment of phosphate in both fresh and inshore marine waters can lead to massive algae blooms which, when they die and decay leads to eutrophication of freshwaters only. Recent research suggests that the predominant pollutant responsible for algal blooms in saltwater estuaries and coastal marine habitats is nitrogen.
Phosphorus occurs most abundantly in nature as part of the orthophosphate ion (PO), consisting of a P atom and 4 oxygen atoms. On land most phosphorus is found in rocks and minerals. Phosphorus-rich deposits have generally formed in the ocean or from guano, and over time, geologic processes bring ocean sediments to land. Weathering of rocks and minerals release phosphorus in a soluble form where it is taken up by plants, and it is transformed into organic compounds. The plants may then be consumed by herbivores and the phosphorus is either incorporated into their tissues or excreted. After death, the animal or plant decays, and phosphorus is returned to the soil where a large part of the phosphorus is transformed into insoluble compounds. Runoff may carry a small part of the phosphorus back to the ocean. | 9 | Geochemistry |
Poisons derived from Acokanthera plants are known to have been used in Africa as far back as the 3rd century BC when Theophrastus reported a toxic substance that the Ethiopians would smear on their arrows. The poisons derived from this genus of plants were used throughout eastern Africa, typically as arrow poisons for hunting and warfare. Acokanthera schimperi, in particular, exhibits a very large amount of ouabain, which the Kenyans, Tanzanians, Rwandans, Ethiopians, and Somalis would use as an arrow poison.
The poison was extracted from the branches and leaves of the plant by boiling them over a fire. Arrows would then be dipped into the concentrated black tar-like juice that formed. Often, certain magical additives were also mixed in with the ouabain extract in order to make the poison work according to the hunters wishes. In Kenya, the Giriama and Langulu poison makers would add an elephant shrew to the poison mixture in order to facilitate the pursuit of their prey. They had observed that an elephant shrew would always run straight ahead or follow a direct path and thought that these properties would be transferred to the poison. A poisonous arrow made with this shrew was thought to cause the hunted animal to behave like the shrew and run in a straight path. In Rwanda members of the Nyambo tribe, also known poison arrow makers, harvest the Aconkathera' plants according to how many dead insects are found under it - more dead insects under a shrub indicating a higher potency of poison.
Although ouabain was used as an arrow poison primarily for hunting, it was also used during battle. One example of this occurred during a battle against the Portuguese, who had stormed Mombasa in 1505. Portuguese records indicated that they had suffered a great deal from the poisoned arrows. | 0 | Organic Chemistry |
3α-Etiocholanediol, or simply etiocholanediol, also known as 3α,5β-androstanediol or as etiocholane-3α,17β-diol, is a naturally occurring etiocholane (5β-androstane) steroid and an endogenous metabolite of testosterone. It is formed from 5β-dihydrotestosterone (after 5β-reduction of testosterone) and is further transformed into etiocholanolone. | 1 | Biochemistry |
COLACRO (Congreso Latinoamericano de Cromatografia) Merit Medal; Pittsburgh Analytical Chemistry Award; Eastern Analytical Symposium Award for Outstanding Achievements in the Fields of Analytical Chemistry; Tracy M. Sonneborn Award for Outstanding Research and Teaching, Indiana University; Dal Nogare Award in Chromatography; CaSSS (California Separation Science Society) Award for Excellence in Separation Science; Honorary Member of the Slovak Pharmaceutical Society; Foreign Member of the Learned Society of the Czech Republic (Czech Academy of Sciences); American Chemical Society Award in Analytical Chemistry; Jan Weber Prize and Medal, Slovak Pharmaceutical Society, Slovakia; Ralph N. Adams Award in Bioanalytical Chemistry. | 3 | Analytical Chemistry |
Dispersion is a process that occurs in soils that are particularly vulnerable to erosion by water. In soil layers where clays are saturated with sodium ions ("sodic soils"), soil can break down very easily into fine particles and wash away. This can lead to a variety of soil and water quality problems, including:
* large soil losses by gully erosion and tunnel erosion
* Soil structural degradation, clogging and sealing where dispersed particles settle
* Suspended soil causing turbidity in water and transporting nutrients off the land. | 9 | Geochemistry |
That is, the change in the internal energy of the substance within a volume is the negative of the amount carried out of the volume by the flow of material across the boundary plus the work done compressing the material on the boundary minus the flow of heat out through the boundary. More generally, it is possible to incorporate source terms. | 7 | Physical Chemistry |
Simple cations formed by adding a hydron to a hydride of a halogen, chalcogen or pnictogen are named by adding the suffix "-onium" to the element's root: is ammonium, is oxonium, and H2F+ is fluoronium. Ammonium was adopted instead of nitronium, which commonly refers to .
If the cationic center of the hydride is not a halogen, chalcogen or pnictogen then the suffix "-ium" is added to the name of the neutral hydride after dropping any final e. is methanium, is dioxidanium (HO-OH is dioxidane), and is diazanium ( is diazane). | 0 | Organic Chemistry |
The third most abundant trace metal in the human body.
It is found in cytochrome c oxidase, a protein necessary for the electron transport chain in mitochondria. | 9 | Geochemistry |
Small nuclear ribonucleoproteins (snRNPs) assemble in a tightly orchestrated and regulated process that involves both the cell nucleus and cytoplasm. | 1 | Biochemistry |
Cholesterol 7 alpha hydroxylase consists of 491 amino acids, which on folding forms 23 alpha helices and 26 beta sheets. | 1 | Biochemistry |
The majority of observed photogeochemical reactions involve a mineral catalyst. Many naturally occurring minerals are semiconductors that absorb some portion of solar radiation. These semiconducting minerals are frequently transition metal oxides and sulfides and include abundant, well-known minerals such as hematite (FeO), magnetite (FeO), goethite and lepidocrocite (FeOOH), and pyrolusite (MnO). Radiation of energy equal to or greater than the band gap of a semiconductor is sufficient to excite an electron from the valence band to a higher energy level in the conduction band, leaving behind an electron hole (h); the resulting electron-hole pair is called an exciton. The excited electron and hole can reduce and oxidize, respectively, species having suitable redox potentials relative to the potentials of the valence and conduction bands. Semiconducting minerals with appropriate band gaps and appropriate band energy levels can catalyze a vast array of reactions, most commonly at mineral-water or mineral-gas interfaces. | 5 | Photochemistry |
miCLIP (Methylation induced crosslinking immunoprecipitation) was used to detect NSUN2 targets, which were found to be mostly non-coding RNAs such as tRNA. An induced mutation of C271A in NSUN2 inhibits release of enzyme from RNA target. This mutation was over-expressed in the cells of interest, and the mutated NSUN2 was also tagged with the Myc epitope. The covalently linked RNA-protein complexes are isolated via immunoprecipitation for a Myc-specific antibody. These complexes are confirmed and detected by radiolabeling with phosphorus-32. The RNA is then extracted from the complex, reverse-transcribed, amplified with PCR, and sequenced using next-generation platforms.
Both miCLIP and Aza-IP, though limited by specific targeting of enzymes, can allow for the detection of low-abundance methylated RNA without deep sequencing. | 1 | Biochemistry |
Locascio was born November 21, 1961, in Cumberland, Maryland. Her father was a physicist at the Allegany Ballistics Laboratory. He fostered her interest in science. She attended Bishop Walsh High School. In 1977, she was awarded an educational development certificate. Locascio had an early interest in biology and won her school's senior science award. She graduated in 1979. | 3 | Analytical Chemistry |
Prepainted metal is used in a variety of products. It can be formed for many different applications, including those with T bends, without loss of coating quality. Major industries use prepainted metal in products such as building panels, metal roofs wall panels, garage doors, office furniture (desks, cubicle divider panels, file cabinets, and modular cabinets), home appliances (refrigerators, dishwashers, freezers, range hoods, microwave ovens, and washers and dryers), heating and air-conditioning outer panels and ductwork, commercial appliances, vending machines, foodservice equipment and cooking tins, beverage cans, and automotive panels and parts (fuel tanks, body panels, bumpers), The list continues to grow, with new industries making the switch from post-painted to prepainted processes each year.
Some high-tech, complex coatings are applied with the coil coating process. Coatings for cool metal roofing materials, smog-eating building panels, antimicrobial products, anti-corrosive metal parts, and solar panels use this process. Pretreatments and coatings can be applied with the coil coating process in very precise, thin, uniform layers, and makes some complex coatings feasible and more cost-effective.
The largest market for prepainted metal is in both commercial and residential construction. It is chosen for the quality, low cost, design flexibility, and environmentally beneficial properties. Using prepainted metal can contribute to credit toward LEED certification for sustainable design. A wide arrange of color options are available with prepainted metal, including vibrant colors for modern designs, and natural weathered finishes in rustic expressions. Prepainted metal also can be formed, almost like plastic, in fluid shapes. This flexibility allows architects to achieve unique, expressive designs using metal.
The output of the coil coating industry is a prepainted metal strip. This has numerous applications in various industries, including in:
* The construction industry for both indoor and outdoor applications;
* The automotive and transport industries;
* The production of white goods including washing machines;
* Cabinets for electronic goods;
* Office furniture;
* Lighting envelopes;
* Bakeware. | 8 | Metallurgy |
Liquid metals have several properties that are useful in sensing and actuation, particularly their electrical conductivity and ability to transmit forces (incompressibility). As freely flowing substances, liquid metals retain these bulk properties even under extreme deformation. For this reason, they have been proposed for use in soft robots and wearable healthcare devices, which must be able to operate under repeated deformation. The metal gallium is considered to be a promising candidate for these applications as it is a liquid near room temperature, has low toxicity, and evaporates slowly. | 7 | Physical Chemistry |
The difficulty of predicting stable crystal structures based on the knowledge of only the chemical composition has long been a stumbling block on the way to fully computational materials design. Now, with more powerful algorithms and high-performance computing, structures of medium complexity can be predicted using such approaches as evolutionary algorithms, random sampling, or metadynamics.
The crystal structures of simple ionic solids (e.g., NaCl or table salt) have long been rationalized in terms of Pauling's rules, first set out in 1929 by Linus Pauling, referred to by many since as the "father of the chemical bond". Pauling also considered the nature of the interatomic forces in metals, and concluded that about half of the five d-orbitals in the transition metals are involved in bonding, with the remaining nonbonding d-orbitals being responsible for the magnetic properties. Pauling was therefore able to correlate the number of d-orbitals in bond formation with the bond length, as well as with many of the physical properties of the substance. He subsequently introduced the metallic orbital, an extra orbital necessary to permit uninhibited resonance of valence bonds among various electronic structures.
In the resonating valence bond theory, the factors that determine the choice of one from among alternative crystal structures of a metal or intermetallic compound revolve around the energy of resonance of bonds among interatomic positions. It is clear that some modes of resonance would make larger contributions (be more mechanically stable than others), and that in particular a simple ratio of number of bonds to number of positions would be exceptional. The resulting principle is that a special stability is associated with the simplest ratios or "bond numbers": , , , , , etc. The choice of structure and the value of the axial ratio (which determines the relative bond lengths) are thus a result of the effort of an atom to use its valency in the formation of stable bonds with simple fractional bond numbers.
After postulating a direct correlation between electron concentration and crystal structure in beta-phase alloys, Hume-Rothery analyzed the trends in melting points, compressibilities and bond lengths as a function of group number in the periodic table in order to establish a system of valencies of the transition elements in the metallic state. This treatment thus emphasized the increasing bond strength as a function of group number. The operation of directional forces were emphasized in one article on the relation between bond hybrids and the metallic structures. The resulting correlation between electronic and crystalline structures is summarized by a single parameter, the weight of the d-electrons per hybridized metallic orbital. The "d-weight" calculates out to 0.5, 0.7 and 0.9 for the fcc, hcp and bcc structures respectively. The relationship between d-electrons and crystal structure thus becomes apparent.
In crystal structure predictions/simulations, the periodicity is usually applied, since the system is imagined as being unlimited in all directions. Starting from a triclinic structure with no further symmetry property assumed, the system may be driven to show some additional symmetry properties by applying Newton's Second Law on particles in the unit cell and a recently developed dynamical equation for the system period vectors
(lattice parameters including angles), even if the system is subject to external stress. | 3 | Analytical Chemistry |
A given substrate-liquid-vapor combination yields a continuous range of contact angle values in practice. The maximum contact angle is referred to as the advancing contact angle and the minimum contact angle is referred to as the receding contact angle. The advancing and receding contact angles are measured from dynamic experiments where droplets or liquid bridges are in movement. In contrast, the equilibrium contact angle described by the Young-Laplace equation is measured from a static state. Static measurements yield values in-between the advancing and receding contact angle depending on deposition parameters (e.g. velocity, angle, and drop size) and drop history (e.g. evaporation from time of deposition). Contact angle hysteresis is defined as although the term is also used to describe the expression . The static, advancing, or receding contact angle can be used in place of the equilibrium contact angle depending on the application. The overall effect can be seen as closely analogous to static friction, i.e., a minimal amount of work per unit distance is required to move the contact line.
The advancing contact angle can be described as a measure of the liquid-solid cohesion while the receding contact angle is a measure of liquid-solid adhesion. The advancing and receding contact angles can be measured directly using different methods and can also be calculated from other wetting measurements such as force tensiometry (aka Wilhemy-Plate method).
Advancing and receding contact angles can be measured directly from the same measurement if drops are moved linearly on a surface. For example, a drop of liquid will adopt a given contact angle when static, but when the surface is tilted the drop will initially deform so that the contact area between the drop and surface remains constant. The "downhill" side of the drop will adopt a higher contact angle while the "uphill" side of the drop will adopt a lower contact angle. As the tilt angle increases the contact angles will continue to change but the contact area between the drop and surface will remain constant. At a given surface tilt angle, the advancing and receding contact angles will be met and the drop will move on the surface. In practice, the measurement can be influenced by shear forces and momentum if the tilt velocity is high. The measurement method can also be challenging in practice for systems with high (>30 degrees) or low (<10 degrees) contact angle hysteresis.
Advancing and receding contact angle measurements can be carried out by adding and removing liquid from a drop deposited on a surface. If a sufficiently small volume of liquid is added to a drop, the contact line will still be pinned, and the contact angle will increase. Similarly, if a small amount of liquid is removed from a drop, the contact angle will decrease.
The Young's equation assumes a homogeneous surface and does not account for surface texture or outside forces such as gravity. Real surfaces are not atomically smooth or chemically homogeneous so a drop will assume contact angle hysteresis. The equilibrium contact angle () can be calculated from and as was shown theoretically by Tadmor and confirmed experimentally by Chibowski as,
where
On a surface that is rough or contaminated, there will also be contact angle hysteresis, but now the local equilibrium contact angle (the Young equation is now only locally valid) may vary from place to place on the surface. According to the Young–Dupré equation, this means that the adhesion energy varies locally – thus, the liquid has to overcome local energy barriers in order to wet the surface. One consequence of these barriers is contact angle hysteresis: the extent of wetting, and therefore the observed contact angle (averaged along the contact line), depends on whether the liquid is advancing or receding on the surface.
Because liquid advances over previously dry surface but recedes from previously wet surface, contact angle hysteresis can also arise if the solid has been altered due to its previous contact with the liquid (e.g., by a chemical reaction, or absorption). Such alterations, if slow, can also produce measurably time-dependent contact angles. | 7 | Physical Chemistry |
The MTBE controversy concerns Methyl tert-butyl ether (MTBE), a gasoline additive that replaced tetraethyllead. MTBE is an oxygenate and raises gasoline's octane number. Its use declined in the United States in response to environmental and health concerns. It has polluted groundwater due to MTBE-containing gasoline being spilled or leaked at gas stations. MTBE spreads more easily underground than other gasoline components due to its higher solubility in water. Cost estimates for removing MTBE from groundwater and contaminated soil range from $1 billion to $30 billion, including removing the compound from aquifers and municipal water supplies, and replacing leaky underground oil tanks. Who will pay for remediation is controversial. In one case, the cost to oil companies to clean up the MTBE in wells belonging to the city of Santa Monica, California is estimated to exceed $200 million.
Some U.S. states banned MTBE in gasoline. California and New York, which together accounted for 40% of U.S. MTBE consumption, banned usage of the chemical in gasoline, effective 2002 and 2004, respectively. As of 2007, 25 states had issued complete or partial bans on the use of MTBE.
The Energy Policy Act of 2005 prompted gasoline refiners to replace MTBE with ethanol. | 2 | Environmental Chemistry |
A number of organisms, instead of using inorganic compounds as terminal electron acceptors, are able to use organic compounds to accept electrons from respiration. Examples include:
* Fumarate reduction to succinate
* Trimethylamine N-oxide (TMAO) reduction to trimethylamine (TMA)
* Dimethyl sulfoxide (DMSO) reduction to Dimethyl sulfide (DMS)
* Reductive dechlorination
TMAO is a chemical commonly produced by fish, and when reduced to TMA produces a strong odor. DMSO is a common marine and freshwater chemical which is also odiferous when reduced to DMS. Reductive dechlorination is the process by which chlorinated organic compounds are reduced to form their non-chlorinated endproducts. As chlorinated organic compounds are often important (and difficult to degrade) environmental pollutants, reductive dechlorination is an important process in bioremediation. | 1 | Biochemistry |
A recently developed technique, acoustic force spectroscopy (AFS), allows the force manipulation of hundreds of single-molecules and single-cells in parallel, providing high experimental throughput. In this technique, a piezo element resonantly excites planar acoustic waves over a microfluidic chip. The generated acoustic waves are capable of exerting forces on microspheres with different density than the surrounding medium. Biomolecules, such as DNA, RNA or proteins, can be individually tethered between the microspheres and a surface and then probed by the acoustic forces exerted by the piezo sensor. With AFS devices it is possible to apply forces ranging from 0 to several hundreds of picoNewtons on hundreds of microspheres and obtain force-extension curves or histograms of rupture forces of many individual events in parallel.
This technique is mostly utilized to study DNA-bindings protein. For example, AFS was used to examine bacterial transcription with presence of antibacterial agents. Viral proteins also can be studied by AFS, for instance this technique was used to explore DNA compaction along with other single-molecule approaches.
Cells also can be manipulated by the acoustic forces directly, or by using microspheres as handles. | 7 | Physical Chemistry |
Electroanalytical methods measure the electric potential in volts and/or the electric current in amps in an electrochemical cell containing the analyte. These methods can be categorized according to which aspects of the cell are controlled and which are measured. The three main categories are potentiometry (the difference in electrode potentials is measured), coulometry (the cells current is measured over time), and voltammetry (the cells current is measured while actively altering the cell's potential). | 3 | Analytical Chemistry |
The Doppler cooling limit for electric dipole transitions is typically in the hundreds of microkelvins. In the 1980s this limit was seen as the lowest achievable temperature. It was a surprise then when sodium atoms were cooled to 43 microkelvin when their Doppler cooling limit is 240 microkelvin, the new low was explained by the addition of more atomic states in combination to laser polarization. Previous conceptions of laser cooling were decided to have been too simplistic. The major laser cooling breakthroughs in the 70s and 80s led to several improvements to preexisting technology and new discoveries with temperatures just above absolute zero. The cooling processes were utilized to make atomic clocks more accurate and to improve spectroscopic measurements, and led to the observation of a new state of matter at ultracold temperatures. The new state of matter, the Bose–Einstein condensate, was observed in 1995 by Eric Cornell, Carl Wieman, and Wolfgang Ketterle.
Laser cooling was primarily used to create ultracold atoms. For example, the experiments in quantum physics need to perform near absolute zero where unique quantum effects such as Bose–Einstein condensation can be observed. Laser cooling is also a primary tool in optical clock experiments. | 7 | Physical Chemistry |
A rotaxane () is a mechanically interlocked molecular architecture consisting of a dumbbell-shaped molecule which is threaded through a macrocycle (see graphical representation). The two components of a rotaxane are kinetically trapped since the ends of the dumbbell (often called stoppers) are larger than the internal diameter of the ring and prevent dissociation (unthreading) of the components since this would require significant distortion of the covalent bonds.
Much of the research concerning rotaxanes and other mechanically interlocked molecular architectures, such as catenanes, has been focused on their efficient synthesis or their utilization as artificial molecular machines. However, examples of rotaxane substructure have been found in naturally occurring peptides, including: cystine knot peptides, cyclotides or lasso-peptides such as microcin J25. | 6 | Supramolecular Chemistry |
Chlorine has been widely used for bleaching, as a disinfectant, and for biofouling prevention in water cooling systems. Remaining concentrations of oxidizing hypochlorous acid and hypochlorite ions may be measured as chlorine residual to estimate effectiveness of disinfection or to demonstrate safety for discharge to aquatic ecosystems. | 3 | Analytical Chemistry |
In theoretical thermodynamics, respected authors vary in their approaches to the definition of quantity of heat transferred. There are two main streams of thinking. One is from a primarily empirical viewpoint (which will here be referred to as the thermodynamic stream), to define heat transfer as occurring only by specified macroscopic mechanisms; loosely speaking, this approach is historically older. The other (which will here be referred to as the mechanical stream) is from a primarily theoretical viewpoint, to define it as a residual quantity after transfers of energy as macroscopic work, between two bodies or closed systems, have been determined for a process, so as to conform with the principle of conservation of energy or the first law of thermodynamics for closed systems; this approach grew in the twentieth century, though was partly manifest in the nineteenth. | 7 | Physical Chemistry |
In prokaryotes, the term corepressor is used to denote the activating ligand of a repressor protein. For example, the E. coli tryptophan repressor (TrpR) is only able to bind to DNA and repress transcription of the trp operon when its corepressor tryptophan is bound to it. TrpR in the absence of tryptophan is known as an aporepressor and is inactive in repressing gene transcription. Trp operon encodes enzymes responsible for the synthesis of tryptophan. Hence TrpR provides a negative feedback mechanism that regulates the biosynthesis of tryptophan.
In short tryptophan acts as a corepressor for its own biosynthesis. | 1 | Biochemistry |
Photocatalytic water splitting separates water into hydrogen and oxygen:
The most prevalently investigated material, , is inefficient. Mixtures of and nickel oxide (NiO) are more active. NiO allows a significant explоitation of the visible spectrum. One efficient photocatalyst in the UV range is based on sodium tantalite (NaTaO) doped with lanthanum and loaded with a nickel oxide cocatalyst. The surface is grooved with nanosteps from doping with lanthanum (3–15 nm range, see nanotechnology). The NiO particles are present on the edges, with the oxygen evolving from the grooves. | 5 | Photochemistry |
Potentiometric sensors measure a potential or charge accumulation of an electrochemical cell. The transducer typically comprises an ion selective electrode (ISE) and a reference electrode. The ISE features a membrane that selectively interacts with the charged ion of interest, causing the accumulation of a charge potential compared to the reference electrode. The reference electrode provides a constant half-cell potential that is unaffected by analyte concentration. A high impedance voltmeter is used to measure the electromotive force or potential between the two electrodes when zero or no significant current flows between them. The potentiometric response is governed by the Nernst equation in that the potential is proportional to the logarithm of the concentration of the analyte. | 1 | Biochemistry |
Except for tritium, which was determined by the helium gas emitted by radioactive decay, these measurements were taken using mass spectroscopy.
* Deuterium (H / H) – , about 1 in 6420 hydrogen atoms
* Tritium (H / H) – = , measured on 16 September 1976, about 1 in 5.4010 hydrogen atoms
* Oxygen-18 (O / O) – , about 1 in 499 oxygen atoms
* Oxygen-17 (O / O) – , about 1 in 2640 oxygen atoms | 9 | Geochemistry |
Helicase activities are initiated by the N-terminal arm and the Ski2 insertion domain. In yeast, the complex guides RNA molecules to the exosome complex for degradation via a fourth protein, called Ski7, which contains a GTPase-like protein. Ski7 involves the 3’ to 5’ degradation of RNA through two different pathways, 3’ poly(A) tail shortening and the binding of the Ski2, Ski3, and Ski8 tetramer and the exosome.
Degradation of the 3 mRNA overhang occurs by association with the 80s ribosome. The 3 end of the mRNA is threaded through the ribosome to Ski2, preparing it for the degradation process.
Biochemical studies also show that the Ski complex can thread RNA through the exosome complex, thereby coupling the Ski2 protein helicase function with the exoribonuclease activity, leading to degradation of the RNA strand. | 1 | Biochemistry |
Reading et al. have explored the use of a broadband QCL combined with thermal expansion measurements. Above, the inability of thermal broadband sources to achieve high spatial resolution is discussed (see history). In this case the frequency of modulation is limited by the mirror speed of the interferometer which, in turn, limits the lateral spatial resolution that can be achieved. When using a broadband QCL the resolution is limited not by the mirror speed but by the modulation frequency of the laser pulses (or other waveforms). The benefit of using a broadband source is that an image can be acquired that comprises an entire spectrum or part of a spectrum for each pixel. This is much more powerful than acquiring images bases on a single wavelength. The preliminary results of Reading et al. show that directing a broadband QCL though an interferometer can give an easily detectable response from a conventional AFM probe measuring thermal expansion. | 3 | Analytical Chemistry |
Despite its simplicity, Dulong–Petit law offers fairly good prediction for the heat capacity of many elementary solids with relatively simple crystal structure at high temperatures. This agreement is because in the classical statistical theory of Ludwig Boltzmann, the heat capacity of solids approaches a maximum of 3R per mole of atoms because full vibrational-mode degrees of freedom amount to 3 degrees of freedom per atom, each corresponding to a quadratic kinetic energy term and a quadratic potential energy term. By the equipartition theorem, the average of each quadratic term is kT, or RT per mole (see derivation below). Multiplied by 3 degrees of freedom and the two terms per degree of freedom, this amounts to 3R per mole heat capacity.
The Dulong–Petit law fails at room temperatures for light atoms bonded strongly to each other, such as in metallic beryllium and in carbon as diamond. Here, it predicts higher heat capacities than are actually found, with the difference due to higher-energy vibrational modes not being populated at room temperatures in these substances.
In the very low (cryogenic) temperature region, where the quantum mechanical nature of energy storage in all solids manifests itself with larger and larger effect, the law fails for all substances. For crystals under such conditions, the Debye model, an extension of the Einstein theory that accounts for statistical distributions in atomic vibration when there are lower amounts of energy to distribute, works well. | 3 | Analytical Chemistry |
Imidapril, sold under the brand name Tanatril among others, is an ACE inhibitor used as an antihypertensive drug and for the treatment of chronic heart failure.
It was patented in 1982 and approved for medical use in 1993. | 4 | Stereochemistry |
*R for any alkyl group or even any organyl group (Alk can be used to unambiguously indicate an alkyl group)
*Me for the methyl group
*Et for the ethyl group
*Pr, n-Pr, or Pr for the (normal) propyl group (Pr is also the symbol for the element praseodymium. However, since the propyl group is monovalent, while praseodymium is nearly always trivalent, ambiguity rarely, if ever, arises in practice.)
*i-Pr or Pr for the isopropyl group
*All for the allyl group (uncommon)
*Bu, n-Bu or Bu for the (normal) butyl group
*i-Bu or Bu (i often italicized) for the isobutyl group
*s-Bu or Bu for the secondary butyl group
*t-Bu or Bu for the tertiary butyl group
*Pn for the pentyl group (or Am for the synonymous amyl group, although Am is also the symbol for americium.)
*Np or Neo for the neopentyl group (Warning: Organometallic chemists often use Np for the related neophyl group, PhMeC–. Np is also the symbol for the element neptunium.)
*Cy or Chx for the cyclohexyl group
*Ad for the 1-adamantyl group
*Tr or Trt for the trityl group | 0 | Organic Chemistry |
A molecular shuttle in supramolecular chemistry is a special type of molecular machine capable of shuttling molecules or ions from one location to another. This field is of relevance to nanotechnology in its quest for nanoscale electronic components and also to biology where many biochemical functions are based on molecular shuttles. Academic interest also exists for synthetic molecular shuttles, the first prototype reported in 1991 based on a rotaxane.
This device is based on a molecular thread composed of an ethyleneglycol chain interrupted by two arene groups acting as so-called stations. The terminal units (or stoppers) on this wire are bulky triisopropylsilyl groups. The bead is a tetracationic cyclophane based on two bipyridine groups and two para-phenylene groups. The bead is locked to one of the stations by pi-pi interactions but since the activation energy for migration from one station to the other station is only 13 kcal/mol (54 kJ/mol) the bead shuttles between them. The stoppers prevent the bead from slipping from the thread. Chemical synthesis of this device is based on molecular self-assembly from a preformed thread and two bead fragments (32% chemical yield).
In certain molecular switches the two stations are non-degenerate. | 6 | Supramolecular Chemistry |
Kinetic isotope effect measurement at natural abundance is a simple general method for measuring kinetic isotope effects (KIE) for chemical reactions performed with materials of natural abundance. This technique for measuring KIEs overcomes many limitations of previous KIE measurement methods. KIE measurements from isotopically labeled materials require a new synthesis for each isotopically labeled material (a process often prohibitively difficult), a competition reaction, and an analysis. The KIE measurement at natural abundance avoids these issues by taking advantage of high precision quantitative techniques (nuclear magnetic resonance spectroscopy, isotope-ratio mass spectrometry) to site selectively measure kinetic fractionation of isotopes, in either product or starting material for a given chemical reaction. | 7 | Physical Chemistry |
From the medieval period, an indirect process began to replace the direct reduction in bloomeries. This used a blast furnace to make pig iron, which then had to undergo a further process to make forgeable bar iron. Processes for the second stage include fining in a finery forge. In the 13th century during the High Middle Ages the blast furnace was introduced by China who had been using it since as early as 200 b.c during the Qin dynasty. [https://www.britannica.com/summary/blast-furnace#:~:text=Blast%20furnaces%20were%20used%20in,century%2C%20replacing%20the%20bloomery%20process.] Puddling was also introduced in the Industrial Revolution.
Both processes are now obsolete, and wrought iron is now rarely made. Instead, mild steel is produced from a Bessemer converter or by other means including smelting reduction processes such as the Corex Process. | 8 | Metallurgy |
BIOPAN is a multi-user research program by the European Space Agency (ESA) designed to investigate the effect of the space environment on biological material. The experiments in BIOPAN are exposed to solar and cosmic radiation, the space vacuum and weightlessness, or a selection thereof. Optionally, the experiment temperature can be stabilized. BIOPAN hosts astrobiology, radiobiology and materials science experiments.
The BIOPAN facility is installed on the external surface of Russian Foton descent capsules protruding from the thermal blanket that envelops the satellite. | 1 | Biochemistry |
In 2006, the Australian military deemed mefloquine "a third-line drug" alternative, and over the five years from 2011 only 25 soldiers had been prescribed the drug, and only in cases of their intolerance for other alternatives. Between 2001 and 2012, 16,000 Canadian soldiers sent to Afghanistan were given the drug as a preventative measure. In 2013, the US Army banned mefloquine from use by its special forces such as the Green Berets. In autumn 2016, the UK military followed suit with their Australian peers after a parliamentary inquiry into the matter revealed that it can cause permanent side effects and brain damage.
In early December 2016, the German defence ministry removed mefloquine from the list of medications it would provide to its soldiers.
In autumn 2016, Canadian Surgeon General Brigadier General Hugh Colin MacKay told a parliamentary committee that faulty science supported the assertion that the drug has indelible noxious side effects. An expert from Health Canada named Barbara Raymond told the same committee that the evidence she had read failed to support the conclusion of indelible side effects. Canadian soldiers who took mefloquine when deployed overseas have claimed they have been left with ongoing mental health problems.
In 2020 the UK Ministry of Defence (MoD) admitted to a breach of duty regarding the use of Mefloquine. by acknowledging numerous instances of failure to assess the risks and warn of potential side effects of the drug. | 4 | Stereochemistry |
Like many chiral molecules, the two stereoisomers of glyceraldehyde will gradually rotate the polarization direction of linearly polarized light as it passes through it, even in solution. The two stereoisomers are identified with the prefixes - and -, according to the sense of rotation: -glyceraldehyde is dextrorotatory (rotates the polarization axis clockwise), while -glyceraldehyde is levorotatory (rotates it counterclockwise).
The - and - prefixes are also used with other monosaccharides, to distinguish two particular stereoisomers that are mirror-images of each other. For this purpose, one considers the chiral carbon that is furthest removed from the C=O group. Its four bonds must connect to −H, −OH, −C(OH)H, and the rest of the molecule. If the molecule can be rotated in space so that the directions of those four groups match those of the analog groups in -glyceraldehyde's C2, then the isomer receives the - prefix. Otherwise, it receives the - prefix.
In the Fischer projection, the - and - prefixes specifies the configuration at the carbon atom that is second from bottom: - if the hydroxyl is on the right side, and - if it is on the left side.
Note that the - and - prefixes do not indicate the direction of rotation of polarized light, which is a combined effect of the arrangement at all chiral centers. However, the two enantiomers will always rotate the light in opposite directions, by the same amount. See also system. | 0 | Organic Chemistry |
Pyroelectric biosensors generate an electric current as a result of a temperature change. This differential induces a polarization in the substance, producing a dipole moment in the direction of the temperature gradient. The result is a net voltage across the material. This net voltage can be calculated by the following equation.
where V = Voltage,
ω = angular frequency of the modulated incident,
P = pyroelectric coefficient,
L = film thickness,
ε = film dielectric constant,
A = area of film,
r = resistance of the film,
C = capacitance of the film,
τE = electrical time constant of the detector output. | 1 | Biochemistry |
SNP genotyping is the measurement of genetic variations of single nucleotide polymorphisms (SNPs) between members of a species. It is a form of genotyping, which is the measurement of more general genetic variation. SNPs are one of the most common types of genetic variation. An SNP is a single base pair mutation at a specific locus, usually consisting of two alleles (where the rare allele frequency is > 1%). SNPs are found to be involved in the etiology of many human diseases and are becoming of particular interest in pharmacogenetics. Because SNPs are conserved during evolution, they have been proposed as markers for use in quantitative trait loci (QTL) analysis and in association studies in place of microsatellites. The use of SNPs is being extended in the HapMap project, which aims to provide the minimal set of SNPs needed to genotype the human genome. SNPs can also provide a genetic fingerprint for use in identity testing. The increase of interest in SNPs has been reflected by the furious development of a diverse range of SNP genotyping methods. | 1 | Biochemistry |
The terms ‘sulfidic material’ and ‘sulfuric material’ were primarily coined by Prof Delvin Fanning (University of Maryland), Prof Martin Rabenhorst (University of Maryland), and Prof Rob Fitzpatrick (University of Adelaide) – and have been incorporated into the Australian Soil Classification (ASC) and World Reference Base (WRB) as diagnostic features of soil. For example, under the ASC, a Sulfuric Extratidal Hydrosol would refer to a soil that is saturated for 2-3 months of the year (i.e., a Hydrosol), located in an extratidal setting, and which contains sulfuric material. Therefore, acid sulfate soils may be described more technically as soils that contain sulfidic and/or sulfuric material.
Sulfuric material refers to soil material that has a pH of less than 4 owing to the oxidation of sulfidic material.
Sulfidic material refers to “soil materials containing detectable inorganic sulfides (≥0.01% sulfidic sulfur) that can exist as horizons or layers at least 30 mm thick or as surficial features”, and is further divided into 3 classes: hyposulfidic, hypersulfidic, and monosulfidic.
Conceptually, hyposulfidic and hypersulfidic materials are used to distinguish between sulfidic material that, respectively, would not and would experience a drop in pH to below 4 if exposed to prevailing oxidising conditions. By definition, hyposulfidic material does not convert to sulfuric material upon oxidation.
In contrast to both hyposulfidic and hypersulfidic materials, monosulfidic material contains high concentrations of detectable monosulfides (≥ 0.01% acid volatile sulfide) (e.g., greigite and mackinawite). Note that monosulfidic material has not replaced Monosulfidic Black Ooze (MBO), which is now considered a type of monosulfidic material.
The terms ‘sulfidisation’ and ‘sulfuricisation’ were coined to refer to the formation of sulfidic and sulfuric material, respectively. Although the terms have not been formally adopted in the ASC, their use is encouraged in Australia. However, the terms should not be used synonymously with other terms that also refer to the formation or transformation of sulfides (e.g., pyritization). Similarly, sulfidic material should not be used interchangeably with similar terms such as pyritic/sulfidic sediment, rock and regolith, which may be found in publications on Acid Rock systems. The broad term sulfidic geomedia could be used to refer to both sulfidic material and pyritic/sulfidic sediment, rock and regolith; but it has no formal definition in Australia and should not be used in lieu of sulfidic material. | 9 | Geochemistry |
While RPKA allows observation of rates over the course of the entire reaction, conducting only same-excess experiments does not provide sufficient information for determination of the corresponding rate constants. In order to construct enough independent relationships to solve for all of the unknown rate constants, it is necessary to examine systems with different-excess.
Consider again the simple example discussed above where the catalyst associates with substrate A, followed by reaction with B to form product P and free catalyst. Regardless of the approximation applied, multiple independent parameters (k and K in the case of pre-equilibrium; k, k, and k in the case of steady-state) are required to define the system. While one could imagine constructing multiple equations to describe the unknowns at different concentrations, when the data is obtained from a same-excess experiment [A] and [B] are not independent:
:e = [B] − [A]
Multiple experiments using different values of e are necessary to establish multiple independent equations defining the multiple independent rate constants in terms of experimental rates and concentrations. Non-linear least squares analysis may then be employed to obtain best fit values of the unknown rate constants to those equations. | 7 | Physical Chemistry |
The closest competing method to IMHR is radical cyclization. Radical cyclizations are often reductive, which can cause undesired side reactions to occur if sensitive substrates are employed. The IMHR, on the other hand, can be run under reductive conditions if desired. Unlike the IMHR, radical cyclization does not require the coupling of two sp-hybridized carbons. In some cases, the results of radical cyclization and IMHR are complementary. | 0 | Organic Chemistry |
Hexamethylenetetramine, also known as methenamine, hexamine, or its trade name Urotropin, is a heterocyclic organic compound with the formula (CH)N. This white crystalline compound is highly soluble in water and polar organic solvents. It has a cage-like structure similar to adamantane. It is useful in the synthesis of other organic compounds, including plastics, pharmaceuticals, and rubber additives. It sublimes in vacuum at 280 °C. | 0 | Organic Chemistry |
There are about 44,000 gigatonnes of carbon in the atmosphere and oceans. A gigatonne is one billion metric tonnes, equivalent to the mass of water in over 400,000 Olympic-size swimming pools. Large as this quantity is, it only amounts to a small fraction of one percent of Earth's carbon. Over 90% may reside in the core, most of the rest being in the crust and mantle.
In the photosphere of the Sun, carbon is the fourth most abundant element. The Earth likely started with a similar ratio but lost a lot of it to evaporation as it accreted. Even accounting for evaporation, however, the silicates making up the crust and mantle of the Earth have a carbon concentration that is five to ten times less than in CI chondrites, a form of meteor that is believed to represent the composition of the solar nebula before the planets formed. Some of this carbon may have ended up in the core. Depending on the model, carbon is predicted to contribute between 0.2 and 1 percent by weight in the core. Even at the lower concentration, this would account for half Earth's carbon.
Estimates of the carbon content in the upper mantle come from measurements of the chemistry of mid-ocean ridge basalts (MORBs). These must be corrected for degassing of carbon and other elements. Since the Earth formed, the upper mantle has lost 40–90% of its carbon by evaporation and transport to the core in iron compounds. The most rigorous estimate gives a carbon content of 30 parts per million (ppm). The lower mantle is expected to be much less depleted – about 350 ppm. | 9 | Geochemistry |
Nucleic acid was first discovered by Friedrich Miescher in 1869 at the University of Tübingen, Germany. He gave its first name as nuclein.
In the early 1880s Albrecht Kossel further purified the substance and discovered its highly acidic properties. He later also identified the nucleobases.
In 1889 Richard Altmann created the term nucleic acid – at that time DNA and RNA were not differentiated.
In 1938 Astbury and Bell published the first X-ray diffraction pattern of DNA.
In 1944 the Avery–MacLeod–McCarty experiment showed that DNA is the carrier of genetic information and in 1953 Watson and Crick proposed the double-helix structure of DNA.
Experimental studies of nucleic acids constitute a major part of modern biological and medical research, and form a foundation for genome and forensic science, and the biotechnology and pharmaceutical industries. | 1 | Biochemistry |
Frémy's salt was discovered in 1845 by Edmond Frémy (1814–1894). Its use in organic synthesis was popularized by Hans Teuber, such that an oxidation using this salt is called the Teuber reaction. | 0 | Organic Chemistry |
Grewe's cyclization is easier to handle in terms of the chemicals used, produces higher yields and higher purity of the product. | 4 | Stereochemistry |
A mannose sugar is added to the first tryptophan residue in the sequence W–X–X–W (W indicates tryptophan; X is any amino acid). A C-C bond is formed between the first carbon of the alpha-mannose and the second carbon of the tryptophan. However, not all the sequences that have this pattern are mannosylated. It has been established that, in fact, only two thirds are and that there is a clear preference for the second amino acid to be one of the polar ones (Ser, Ala, Gly and Thr) in order for mannosylation to occur. Recently there has been a breakthrough in the technique of predicting whether or not the sequence will have a mannosylation site that provides an accuracy of 93% opposed to the 67% accuracy if we just consider the WXXW motif.
Thrombospondins are one of the proteins most commonly modified in this way. However, there is another group of proteins that undergo C-mannosylation, type I cytokine receptors. C-mannosylation is unusual because the sugar is linked to a carbon rather than a reactive atom such as nitrogen or oxygen. In 2011, the first crystal structure of a protein containing this type of glycosylation was determined—that of human complement component 8. Currently it is established that 18% of human proteins, secreted and transmembrane undergo the process of C-mannosylation. Numerous studies have shown that this process plays an important role in the secretion of Trombospondin type 1 containing proteins which are retained in the endoplasmic reticulum if they do not undergo C-mannosylation This explains why a type of cytokine receptors, erythropoietin receptor remained in the endoplasmic reticulum if it lacked C-mannosylation sites. | 0 | Organic Chemistry |
In chemistry, the capped square antiprismatic molecular geometry describes the shape of compounds where nine atoms, groups of atoms, or ligands are arranged around a central atom, defining the vertices of a gyroelongated square pyramid. The symmetry group of the resulting object is C
The gyroelongated square pyramid is a square pyramid with a square antiprism connected to the square base. In this respect, it can be seen as a "capped" square antiprism (a square antiprism with a pyramid erected on one of the square faces).
It is very similar to the tricapped trigonal prismatic molecular geometry, and there is some dispute over the specific geometry exhibited by certain molecules.
Examples:
*[SiCo(CO)], defined by the Co framework, which encapsulates the Si atom
*[Pb(phen)(OClO)], defined by the NO framework, which encapsulates the Pb ion
*[Ge], a zintl ion
*Th(troopolonate)(HO), defined by the O framework, which encapsulates the Th ion
*Potassium nonahydridorhenate| is sometimes described as having a capped square antiprismatic geometry, although its geometry is most often described as tricapped trigonal prismatic.
*, a lanthanum(III) complex with a La–La bond. | 4 | Stereochemistry |
Endogenous antigens are generated within normal cells as a result of normal cell metabolism, or because of viral or intracellular bacterial infection. The fragments are then presented on the cell surface in the complex with MHC class I molecules. If activated cytotoxic CD8 T cells recognize them, the T cells secrete various toxins that cause the lysis or apoptosis of the infected cell. In order to keep the cytotoxic cells from killing cells just for presenting self-proteins, the cytotoxic cells (self-reactive T cells) are deleted as a result of tolerance (negative selection). Endogenous antigens include xenogenic (heterologous), autologous and idiotypic or allogenic (homologous) antigens. Sometimes antigens are part of the host itself in an autoimmune disease. | 1 | Biochemistry |
As it is the precise mixture of minerals dissolved in the water, together with water's pH and temperature, that determine the behaviour of the hardness, a single-number scale does not adequately describe hardness. However, the United States Geological Survey uses the following classification for hard and soft water:
Seawater is considered to be very hard due to various dissolved salts. Typically seawater's hardness is in the area of 6,570; ppm (6.57 grams per litre). In contrast, freshwater has a hardness in the range of 15 to 375 ppm; generally around 600 mg/L. | 3 | Analytical Chemistry |
, there are two different theories on the information processing that occurs on enhancers:
* Enhanceosomes – rely on highly cooperative, coordinated action and can be disabled by single point mutations that move or remove the binding sites of individual proteins.
* Flexible billboards – less integrative, multiple proteins independently regulate gene expression and their sum is read in by the basal transcriptional machinery. | 1 | Biochemistry |
In general, there are two different formats of genome-wide CRISPR knockout screens: arrayed and pooled. In an arrayed screen, each well contains a specific and known sgRNA targeting a specific gene. Since the sgRNA responsible for each phenotype is known based on well location, phenotypes can be identified and analysed without requiring genetic sequencing. This format allows for the measurement of more specific cellular phenotypes, perhaps by fluorescence or luminescence, and allows researchers to use more library types and delivery methods. For large-scale LOF screens, however, arrayed formats are considered low-efficiency, and expensive in terms of financial and material resources because cell populations have to be isolated and cultured individually.
In a pooled screen, cells grown in a single vessel are transduced in bulk with viral vectors collectively containing the entire sgRNA library. To ensure that the amount of cells infected by more than one sgRNA-containing particle is limited, a low multiplicity of infection (MOI) (typically 0.3-0.6) is used. Evidence so far has suggested that each sgRNA should be represented in a minimum of 200 cells. Transduced cells will be selected for, followed by positive or negative selection for the phenotype of interest, and genetic sequencing will be necessary to identify the integrated sgRNAs. | 1 | Biochemistry |
Potassium tert-butoxide catalyzes the reaction of hydrosilanes and heterocyclic compounds to give the silyl derivatives, with release of H. | 0 | Organic Chemistry |
Fretting refers to wear and sometimes corrosion damage of loaded surfaces in contact while they encounter small oscillatory movements tangential to the surface. Fretting is caused by adhesion of contact surface asperities, which are subsequently broken again by the small movement. This breaking causes wear debris to be formed.
If the debris and/or surface subsequently undergo chemical reaction, i.e., mainly oxidation, the mechanism is termed fretting corrosion. Fretting degrades the surface, leading to increased surface roughness and micropits, which reduces the fatigue strength of the components.
The amplitude of the relative sliding motion is often in the order of micrometers to millimeters, but can be as low as 3 nanometers.
Typically fretting is encountered in shrink fits, bearing seats, bolted parts, splines, and dovetail connections. | 8 | Metallurgy |
Neuropeptides are extremely ancient and highly diverse chemical messengers. Placozoans such as Trichoplax, extremely basal animals which do not possess neurons, use peptides for cell-to-cell communication in a way similar to the neuropeptides of higher animals.
Due to their modulatory and diffusive nature, neuropeptides can act on multiple time and spatial scales. Below are some examples of neuropeptide actions: | 1 | Biochemistry |
ADP-ribosylation is the addition of one or more ADP-ribose moieties to a protein. It is a reversible post-translational modification that is involved in many cellular processes, including cell signaling, DNA repair, gene regulation and apoptosis.
Improper ADP-ribosylation has been implicated in some forms of cancer. It is also the basis for the toxicity of bacterial compounds such as cholera toxin, diphtheria toxin, and others. | 1 | Biochemistry |
Positive and negative controls should be run after preparation of each lot of medium.
Positive control: Escherichia coli
Negative control: Klebsiella | 3 | Analytical Chemistry |
The third-generation of Glycoazodyes was first reported in 2015. These Glycoazodyes use an amido-ester linker. An amide group bonds the sugar to an n-alkane spacer, and the spacer is bonded to the dye through an ester group. | 0 | Organic Chemistry |
In heterogeneous electron transfer, an electron moves between a chemical species and a solid-state electrode. Theories addressing heterogeneous electron transfer have applications in electrochemistry and the design of solar cells. | 7 | Physical Chemistry |
For a transition where a single charged particle changes state from to , the transition dipole moment is
where q is the particles charge, r is its position, and the integral is over all space ( is shorthand for ). The transition dipole moment is a vector; for example its x'-component is
In other words, the transition dipole moment can be viewed as an off-diagonal matrix element of the position operator, multiplied by the particle's charge. | 5 | Photochemistry |
Arsenic can cause oxidative stress through the formation of reactive oxygen species (ROS), and reactive nitrogen species (RNS). Reactive oxygen species are produced by the enzyme NADPH oxidase, which transfers electrons from NADPH to oxygen, synthesizing a superoxide, which is a reactive free radical. This superoxide can react to form hydrogen peroxide and a reactive oxygen species. The enzyme NADPH oxidase is able to generate more reactive oxygen species in the presence of arsenic, due to the subunit p22phax, which is responsible for the electron transfer, being upregulated by arsenic. The reactive oxygen species are capable of stressing the endoplasmic reticulum, which increases the amount of the unfolded protein response signals. This leads to inflammation, cell proliferation, and eventually to cell death. Another mechanism in which reactive oxygen species cause cell death would be through the cytoskeleton rearrangement, which affects the contractile proteins.
The reactive nitrogen species arise once the reactive oxygen species destroy the mitochondria. This leads to the formation of the reactive nitrogen species, which are responsible for damaging DNA in arsenic poisoning. Mitochondrial damage is known to cause the release of reactive nitrogen species, due to the reaction between superoxides and nitric oxide (NO). Nitric oxide (NO) is a part of cell regulation, including cellular metabolism, growth, division and death. Nitric oxide (NO) reacts with reactive oxygen species to form peroxynitrite. In cases of chronic arsenic exposure, the nitric oxide levels are depleted, due to the superoxide reactions. The enzyme NO synthase (NOS) uses L-arginine to form nitric oxide, but this enzyme is inhibited by monomethylated arsenic (III) compounds. | 1 | Biochemistry |
The most important factor in influencing homoaromatic character is the addition of a single homoconjugate linkage into the parent aromatic compound. The location of the homoconjugate bond is not important as all homoaromatic species can be derived from aromatic compounds that possess symmetry and equal bond order between all carbons. The insertion of a homoconjugate linkage perturbs the π-electron density an amount δβ, which depending on the ring size, must be greater than 0 and less than 1, where 0 represents no perturbation and 1 represents total loss of aromaticity (destabilization equivalent to the open chain form). It is believed that with increasing ring size, the resonance stabilization of homoaromaticity is offset by the strain in forming the homoconjugate bridge. In fact, the maximum ring size for homoaromaticity is fairly low as a 16-membered annulene ring favours the formation of the aromatic dication over the strained bridged homocation. | 7 | Physical Chemistry |
Adhesives commonly react with oxygen at low temperatures, which leads to a slow break down of polymer chains. The breakdown of polymer chains is often undetectable until the adhesive has reached a critical point where the stability of remainder of the adhesive rapidly degrades. High temperature accelerated testing often cannot be used to estimate stability in oxygen environments since high temperatures often lead to new reaction pathways that would not typically exist at the temperature the adhesives would be used.
Moisture sensitivity accelerated tests involve either increased temperatures or increased surface area of a sample. The surface area of samples is increased by applying adhesives to a single surface rather than placing it between two surfaces and placing the sample in a water bath. | 3 | Analytical Chemistry |
These are exclusively coal-fired processes, with the reducing gases generated inside the reduction vessel. The ore is charged with coal into a closed container. This is then heated until the oxygen present in the ore combines with the carbon before being discharged, mainly in the form of CO or CO2. This production of gas by heating a solid material means that the reactor belongs to the retort category.
The principle is an ancient one: in northern China, the shortage of charcoal led to the development of processes using hard coal before the 4th century. To avoid any contact between iron and sulfur, the brittle element provided by coal, China developed a process that involved placing iron ore in batteries of elongated tubular crucibles and covering them with a mass of coal, which was then burned. This process survived into the 20th century.
More recently, other historic processes have come to the fore, such as that of Adrien Chenot, operational in the 1850s in a number of plants in France and Spain. Successive improvements by Blair, Yutes, Renton, and Verdié are not significant. Among the processes developed is the HOGANAS process, perfected in 1908. Three small units are still operational (as of 2010). Not very productive, it is limited to the production of powdered iron, but as it is slow and operates in closed retorts, it easily achieves the purities required by powder metallurgy.
Other retort processes were developed, such as KINGLOR-METOR, perfected in 1973. Two small units were built in 1978 (closed) and 1981 (probably closed). | 8 | Metallurgy |
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