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At densities greater than those supported by neutron degeneracy, quark matter is expected to occur. Several variations of this hypothesis have been proposed that represent quark-degenerate states. Strange matter is a degenerate gas of quarks that is often assumed to contain strange quarks in addition to the usual up and down quarks. Color superconductor materials are degenerate gases of quarks in which quarks pair up in a manner similar to Cooper pairing in electrical superconductors. The equations of state for the various proposed forms of quark-degenerate matter vary widely, and are usually also poorly defined, due to the difficulty of modelling strong force interactions.
Quark-degenerate matter may occur in the cores of neutron stars, depending on the equations of state of neutron-degenerate matter. It may also occur in hypothetical quark stars, formed by the collapse of objects above the Tolman–Oppenheimer–Volkoff mass limit for neutron-degenerate objects. Whether quark-degenerate matter forms at all in these situations depends on the equations of state of both neutron-degenerate matter and quark-degenerate matter, both of which are poorly known. Quark stars are considered to be an intermediate category between neutron stars and black holes. | 7 | Physical Chemistry |
The cinnamyl alcohol glycosides rosin, rosavin and rosarin occur in the context of rhodiola species, only in Rhodiola rosea. | 0 | Organic Chemistry |
Thiones are usually prepared from ketones using reagents that exchange S and O atoms. A common reagent is phosphorus pentasulfide and the related reagent Lawesson's reagent. Other methods uses a mixture of hydrogen chloride combined with hydrogen sulfide. Bis(trimethylsilyl)sulfide has also been employed.
Thiobenzophenone [(CH)CS] is a stable deep blue compound that dissolves readily in organic solvents. It photooxidizes in air to benzophenone and sulfur. Since its discovery, a variety of related thiones have been prepared. | 0 | Organic Chemistry |
A table with experimental single bonds for carbon to other elements is given below. Bond lengths are given in picometers. By approximation the bond distance between two different atoms is the sum of the individual covalent radii (these are given in the chemical element articles for each element). As a general trend, bond distances decrease across the row in the periodic table and increase down a group. This trend is identical to that of the atomic radius. | 4 | Stereochemistry |
Many metal-ligand combinations have been reported to catalyze hydroamination, including main group elements including alkali metals such as lithium, group 2 metals such as calcium, as well as group 3 metals such as aluminum, indium, and bismuth. In addition to these main group examples, extensive research has been conducted on the transition metals with reports of early, mid, and late metals, as well as first, second, and third row elements. Finally the lanthanides have been thoroughly investigated. Zeolites have also shown utility in hydroamination. | 0 | Organic Chemistry |
The organosilane is activated with fluoride (as some sort of salt such as TBAF or TASF) or a base to form a pentavalent silicon center which is labile enough to allow for the breaking of a C-Si bond during the transmetalation step. The general scheme to form this key intermediate is shown below. This step occurs in situ or at the same time as the catalytic cycle in the reaction.
The mechanism for the Hiyama coupling follows a catalytic cycle, including an A) oxidative addition step, in which the organic halide adds to the palladium oxidizing the metal from palladium(0) to palladium(II); a B) transmetalation step, in which the C-Si bond is broken and the second carbon fragment is bound to the palladium center; and finally C) a reductive elimination step, in which the C-C bond is formed and the palladium returns to its zero-valent state to start the cycle over again. The catalytic cycle is shown below. | 0 | Organic Chemistry |
Olfactory receptor gene ([https://senselab.med.yale.edu/ordb/ OR]) is normally expressed in human and mouse olfactory tissue with a main function as odorant receptor for the detection of odorants. Individuals with a defect in this gene have disorders of taste and smell. It has been reported that ORs is also expressed on sperms and testis with special emphasis in a manner of ectopic expression. In a study, researchers identified ectopic expression of OR genes in non-olfactory tissues in the mouse model by measuring transcript levels. Here they found relatively low OR gene expression compared to the olfactory tissue, which result indicates that the OR gene in other tissue have no extra function, but they suggest that there is a possibility that small OR subsets can have functional roles in different tissue. | 1 | Biochemistry |
A carbon source is a carbon-containing molecule that is used by an organism to synthesise biomass. Such sources may be organic or inorganic. Heterotrophs must use organic molecules as a source of both carbon and energy. In contrast, autotrophs may use inorganic materials as a source for both, such as inorganic chemical energy (chemolithotrophs) or light (photoautotrophs). The carbon cycle, which begins with an inorganic carbon source (such as carbon dioxide) and progresses through the biological carbon fixation process, includes the biological use of carbon as one of its components. | 1 | Biochemistry |
There are at least three distinct mechanisms in which pRb can repress transcription of E2F-regulated promoters. Though these mechanisms are known, it is unclear which are the most important for the control of the cell cycle.
E2Fs are a family of proteins whose binding sites are often found in the promoter regions of genes for cell proliferation or progression of the cell cycle. E2F1 to E2F5 are known to associate with proteins in the pRb-family of proteins while E2F6 and E2F7 are independent of pRb. Broadly, the E2Fs are split into activator E2Fs and repressor E2Fs though their role is more flexible than that on occasion. The activator E2Fs are E2F1, E2F2 and E2F3 while the repressor E2Fs are E2F4, E2F5 and E2F6. Activator E2Fs along with E2F4 bind exclusively to pRb. pRb is able to bind to the activation domain of the activator E2Fs which blocks their activity, repressing transcription of the genes controlled by that E2F-promoter. | 1 | Biochemistry |
A balance of magnesium is vital to the well-being of all organisms. Magnesium is a relatively abundant ion in Earth's crust and mantle and is highly bioavailable in the hydrosphere. This availability, in combination with a useful and very unusual chemistry, may have led to its utilization in evolution as an ion for signaling, enzyme activation, and catalysis. However, the unusual nature of ionic magnesium has also led to a major challenge in the use of the ion in biological systems. Biological membranes are impermeable to magnesium (and other ions), so transport proteins must facilitate the flow of magnesium, both into and out of cells and intracellular compartments. | 1 | Biochemistry |
In 2019 it was reported that ordinary graphite exhibits second sound at 120 K. This feature was both predicted theoretically and observed experimentally, and
was by far the highest temperature at which second sound has been observed. However, this second sound is observed only at the microscale, because the wave dies out exponentially with
characteristic length 1-10 microns. Therefore, presumably graphite in the right temperature regime has extraordinarily high thermal conductivity but only for the purpose of transferring heat pulses distances of order 10 microns, and for pulses of duration on the order of 10 nanoseconds. For more "normal" heat-transfer, graphite's observed thermal conductivity is less than that of, e.g., copper. The theoretical models, however, predict longer absorption lengths would be seen in isotopically pure graphite, and perhaps over a wider temperature range, e.g. even at room temperature. (As of March 2019, that experiment has not yet been tried.) | 7 | Physical Chemistry |
mTOR is implicated in the failure of a pruning mechanism of the excitatory synapses in autism spectrum disorders. | 1 | Biochemistry |
Iron–sulfur clusters occur in many biological systems, often as components of electron transfer proteins. The ferredoxin proteins are the most common Fe–S clusters in nature. They feature either 2Fe–2S or 4Fe–4S centers. They occur in all branches of life.
Fe–S clusters can be classified according to their Fe:S stoichiometry [2Fe–2S], [4Fe–3S], [3Fe–4S], and [4Fe–4S]. The [4Fe–4S] clusters occur in two forms: normal ferredoxins and high potential iron proteins (HiPIP). Both adopt cuboidal structures, but they utilize different oxidation states. They are found in all forms of life.
The relevant redox couple in all Fe–S proteins is Fe(II)/Fe(III).
Many clusters have been synthesized in the laboratory with the formula [FeS(SR)], which are known for many R substituents, and with many cations. Variations have been prepared including the incomplete cubanes [FeS(SR)]. | 7 | Physical Chemistry |
The follicle-stimulating hormone receptor or FSH receptor (FSHR) is a transmembrane receptor that interacts with the follicle-stimulating hormone (FSH) and represents a G protein-coupled receptor (GPCR). Its activation is necessary for the hormonal functioning of FSH. FSHRs are found in the ovary, testis, and uterus. | 1 | Biochemistry |
Polysulfides are compounds that have chains of sulfur atoms. This reactant has been tested on the field in treating TCE and in comparison to EHC. The use of polysulfides is a type of abiotic reduction and works best in anaerobic conditions where iron (III) is available. The benefit of using polysulfides is that they do not produce any biological waste products; however, the reaction rates are slow and they require more time to create the DVI (dual valent iron) minerals that are needed for the reduction to occur. | 2 | Environmental Chemistry |
The integrated stress response is a cellular stress response conserved in eukaryotic cells that downregulates protein synthesis and upregulates specific genes in response to internal or environmental stresses. | 1 | Biochemistry |
Histones H2A, H2B, H3 and H4 form the core of a nucleosome and thus are called core histones. Processing of core histones is done differently because typical histone mRNA lacks several features of other eukaryotic mRNAs, such as poly(A) tail and introns. Thus, such mRNAs do not undergo splicing and their 3' processing is done independent of most cleavage and polyadenylation factors. Core histone mRNAs have a special stem-loop structure at 3-prime end that is recognized by a stem–loop binding protein and a downstream sequence, called histone downstream element (HDE) that recruits U7 snRNA. Cleavage and polyadenylation specificity factor 73 cuts mRNA between stem-loop and HDE
Histone variants, such as H2A.Z or H3.3, however, have introns and are processed as normal mRNAs including splicing and polyadenylation. | 1 | Biochemistry |
Folin's reagent or sodium 1,2-naphthoquinone-4-sulfonate is a chemical reagent used as a derivatizing agent to measure levels of amines and amino acids. The reagent reacts with them in alkaline solution to produce a fluorescent material that can be easily detected.
This should not be confused with Folin-Ciocalteu reagent, that is used to detect phenolic compounds.
The Folin reagent can be used with an acidic secondary reagent to distinguish MDMA and related compounds from PMMA and related compounds. | 3 | Analytical Chemistry |
Another type of environmental contaminant can be found in the form of genetically modified organisms (GMOs), specifically when they come in contact with organic agriculture. This sort of contamination can result in the decertification of a farm. This sort of contamination can at times be difficult to control, necessitating mechanisms for compensating farmers where there has been contamination by GMOs. A Parliamentary Inquiry in Western Australia considered a range of options for compensating farmers whose farms had been contaminated by GMOs but ultimately settled on recommending no action. | 9 | Geochemistry |
* Cabaniss, Steve, Greg Madey, Patricia Maurice, Yingping Zhou, Laura Leff, Ola Olapade, Bob Wetzel, Jerry Leenheer, and Bob Wershaw, comps. Stochastic Synthesis of Natural Organic Matter. UNM, ND, KSU, UNC, USGS. 22 Apr. 2007.
* Cho, Min, Hyenmi Chung, and Jeyong Yoon. "Disinfection of Water Containing Natural Organic Matter by Using Ozone-Initiated Radical Reactions." Abstract. Applied and Environmental Microbiology Vol. 69 No.4 (2003): 2284–2291.
* Fortner, John D., Joseph B. Hughes, Jae-Hong Kim, and Hoon Hyung. "Natural Organic Matter Stabilizes Carbon Nanotubes in the Aqueous Phase." Abstract. Environmental Science & Technology Vol. 41 No. 1 (2007): 179–184.
* "Researchers Study Role of Natural Organic Matter in Environment." Science Daily 20 Dec. 2006. 22 Apr. 2007 <https://www.sciencedaily.com/releases/2006/12/061211221222.htm>.
* Senesi, Nicola, Baoshan Xing, and P.m. Huang. Biophysico-Chemical Processes Involving Natural Nonliving Organic Matter in Environmental Systems. New York: IUPAC, 2006.
* "Table 1: Surface Area, Volume, and Average Depth of Oceans and Seas." Encyclopædia Britannica.
* "Topic Snapshot: Natural Organic Material." American Water Works Association Research Foundation. 2007. 22 Apr. 2007 <https://web.archive.org/web/20070928102105/http://www.awwarf.org/research/TopicsAndProjects/topicSnapShot.aspx?Topic=Organic>.
* United States of America. United States Geological Survey. Earth's Water Distribution. 10 May 2007. <http://ga.water.usgs.gov/edu/waterdistribution.html>
* Water Sheds: Organic Matter. North Carolina State University. 1 May 2007 <http://www.water.ncsu.edu/watershedss/info/norganics.html >. | 0 | Organic Chemistry |
Many reef aquarium keepers use RO systems to make fish-friendly seawater. Ordinary tap water can contain excessive chlorine, chloramines, copper, nitrates, nitrites, phosphates, silicates, or other chemicals detrimental to marine organisms. Contaminants such as nitrogen and phosphates can lead to unwanted algae growth. An effective combination of both RO and deionization is popular among reef aquarium keepers, and is preferred above other water purification processes due to the low cost of ownership and operating costs. Where chlorine and chloramines are found in the water, carbon filtration is needed before RO, as common residential membranes do not address these compounds.
Freshwater aquarists also use RO to duplicate the soft waters found in many tropical waters. While many tropical fish can survive in treated tap water, breeding can be impossible. Many aquatic shops sell containers of RO water for this purpose. | 3 | Analytical Chemistry |
There are three types of persistent infections, latent, chronic and slow, in which the virus stays inside the host cell for prolonged periods of time. During latent infections there is minimal to no expression of infected viral genome. The genome remains within the host cell until the virus is ready for replication. Chronic infections have similar cellular effects as acute cytocidal infections but there is a limited number of progeny and viruses involved in transformation. Lastly, slow infections have a longer incubation period in which no physiological, morphological or subcellular changes may be involved. | 1 | Biochemistry |
A theory about the magnetic sense of birds assumes that a protein in the retina is changed due to the Zeeman effect. | 7 | Physical Chemistry |
Reactions of linear topology are the most common, and consist of all transformations whose transition states are acyclic, including addition, elimination, substitution, and (some types of) fragmentation reactions. By contrast, in pericyclic reactions, the atoms under chemical change form a single closed cycle, and include reactions like the Diels–Alder reaction and Cope rearrangement, among many others.
In contrast to these types of reactions, a coarctate reaction is characterized by a doubly cyclic transition state, in which at least one atom undergoes the simultaneous making and breaking of two bonds. Thus, the topology of the transition state of a coarctate reaction is a constricted cycle that meets with itself (resembling a figure eight) while the topology of pericyclic and linear reactions are a circle (or Möbius strip) and line segment, respectively. The concept was first proposed by Rainer Herges. | 0 | Organic Chemistry |
Endonucleases are enzymes that recognise and cleave nucleic acid segments and they can be used to direct DNA assembly. Of the different types of restriction enzymes, the type II restriction enzymes are the most commonly available and used because their cleavage sites are located near or in their recognition sites. Hence, endonuclease-mediated assembly methods make use of this property to define DNA parts and assembly protocols. | 1 | Biochemistry |
* Recherches sur les composés octyliques (1870).
* Application du sulfure de manganèse comme conleur plastique (1890). | 0 | Organic Chemistry |
In the limiting case of no interaction, the system is an ideal gas and the structure factor is completely featureless: , because there is no correlation between the positions and of different particles (they are independent random variables), so the off-diagonal terms in Equation () average to zero: . | 3 | Analytical Chemistry |
France 24 documentary "Nicola Spaldin: The pioneer behind multiferroics" (12 minutes) [https://www.youtube.com/watch?v=bfVKtIcl2Nk&t=10s Nicola Spaldin: The pioneer behind multiferroics]
Seminar "Electric field control of magnetism" by R. Ramesh at U Michigan (1 hour) [https://www.youtube.com/watch?v=dTpr9CEYP6M Ramamoorthy Ramesh | Electric Field Control of Magnetism]
Max Roessler prize for multiferroics at ETH Zürich (5 minutes): [https://www.youtube.com/watch?v=Nq0j6xrNcLk Nicola Spaldin, Professor of Materials Theory at ETH Zurich]
ICTP Colloquium "From materials to cosmology; Studying the early universe under the microscope" by Nicola Spaldin (1 hour) [https://www.youtube.com/watch?v=CYHB0BZQU-U From Materials to Cosmology: Studying the early universe under the microscope - ICTP COLLOQUIUM]
Tsuyoshi Kimura's research on "Toward highly functional devices using mulitferroics" (4 minutes): [https://www.youtube.com/watch?v=_KfySbeVO4M Toward highly functional devices using multi-ferroics]
"Strong correlation between electricity and magnetism in materials" by Yoshi Tokura (45 minutes): [https://www.youtube.com/watch?v=i6tcSXbEELE 4th Kyoto Prize Symposium [Materials Science and Engineering] Yoshinori Tokura, July 2, 2017]
"Breaking the wall to the next material age", Falling Walls, Berlin (15 minutes): [https://www.youtube.com/watch?v=pirXBfwni-w How Materials Science Heralds a New Class of Technologies | NICOLA SPALDIN] | 7 | Physical Chemistry |
In the field of solid state physics, the electron affinity is defined differently than in chemistry and atomic physics. For a semiconductor-vacuum interface (that is, the surface of a semiconductor), electron affinity, typically denoted by E or χ, is defined as the energy obtained by moving an electron from the vacuum just outside the semiconductor to the bottom of the conduction band just inside the semiconductor:
In an intrinsic semiconductor at absolute zero, this concept is functionally analogous to the chemistry definition of electron affinity, since an added electron will spontaneously go to the bottom of the conduction band. At nonzero temperature, and for other materials (metals, semimetals, heavily doped semiconductors), the analogy does not hold since an added electron will instead go to the Fermi level on average. In any case, the value of the electron affinity of a solid substance is very different from the chemistry and atomic physics electron affinity value for an atom of the same substance in gas phase. For example, a silicon crystal surface has electron affinity 4.05 eV, whereas an isolated silicon atom has electron affinity 1.39 eV.
The electron affinity of a surface is closely related to, but distinct from, its work function. The work function is the thermodynamic work that can be obtained by reversibly and isothermally removing an electron from the material to vacuum; this thermodynamic electron goes to the Fermi level on average, not the conduction band edge: . While the work function of a semiconductor can be changed by doping, the electron affinity ideally does not change with doping and so it is closer to being a material constant. However, like work function the electron affinity does depend on the surface termination (crystal face, surface chemistry, etc.) and is strictly a surface property.
In semiconductor physics, the primary use of the electron affinity is not actually in the analysis of semiconductor–vacuum surfaces, but rather in heuristic electron affinity rules for estimating the band bending that occurs at the interface of two materials, in particular metal–semiconductor junctions and semiconductor heterojunctions.
In certain circumstances, the electron affinity may become negative. Often negative electron affinity is desired to obtain efficient cathodes that can supply electrons to the vacuum with little energy loss. The observed electron yield as a function of various parameters such as bias voltage or illumination conditions can be used to describe these structures with band diagrams in which the electron affinity is one parameter. For one illustration of the apparent effect of surface termination on electron emission, see Figure 3 in Marchywka Effect. | 7 | Physical Chemistry |
Nitriles can be prepared by the dehydration of primary amides. Common reagents for this include phosphorus pentoxide () and thionyl chloride (). In a related dehydration, secondary amides give nitriles by the von Braun amide degradation. In this case, one C-N bond is cleaved. | 0 | Organic Chemistry |
Boronate affinity chromatography consists of using boronic acid or boronates to elute and quantify amounts of glycoproteins. Clinical adaptations have applied this type of chromatography for use in determining long term assessment of diabetic patients through analysis of their glycated hemoglobin. | 3 | Analytical Chemistry |
In the Euclidean plane, reflections and glide reflections are the only two kinds of indirect (orientation-reversing) isometries.
For example, there is an isometry consisting of the reflection on the x-axis, followed by translation of one unit parallel to it. In coordinates, it takes
This isometry maps the x-axis to itself; any other line which is parallel to the x-axis gets reflected in the x-axis, so this system of parallel lines is left invariant.
The isometry group generated by just a glide reflection is an infinite cyclic group.
Combining two equal glide reflections gives a pure translation with a translation vector that is twice that of the glide reflection, so the even powers of the glide reflection form a translation group.
In the case of glide-reflection symmetry, the symmetry group of an object contains a glide reflection, and hence the group generated by it. If that is all it contains, this type is frieze group p11g.
Example pattern with this symmetry group:
A typical example of glide reflection in everyday life would be the track of footprints left in the sand by a person walking on a beach.
Frieze group nr. 6 (glide-reflections, translations and rotations) is generated by a glide reflection and a rotation about a point on the line of reflection. It is isomorphic to a semi-direct product of Z and C.
Example pattern with this symmetry group:
For any symmetry group containing some glide-reflection symmetry, the translation vector of any glide reflection is one half of an element of the translation group. If the translation vector of a glide reflection is itself an element of the translation group, then the corresponding glide-reflection symmetry reduces to a combination of reflection symmetry and translational symmetry. | 3 | Analytical Chemistry |
A rapid antigen test (RAT), sometimes called a rapid antigen detection test (RADT), antigen rapid test (ART), or loosely just a rapid test, is a rapid diagnostic test suitable for point-of-care testing that directly detects the presence or absence of an antigen. RATs are a type of lateral flow test detecting antigens, rather than antibodies (antibody tests) or nucleic acid (nucleic acid tests). Rapid tests generally give a result in 5 to 30 minutes, require minimal training or infrastructure, and have significant cost advantages. Rapid antigen tests for the detection of SARS-CoV-2, the virus that causes COVID-19, have been commonly used during the COVID-19 pandemic.
For many years, an early and major class of RATs—the rapid strep tests for streptococci—were so often the referent when RATs or RADTs were mentioned that the two latter terms were often loosely treated as synonymous with those. Since the COVID-19 pandemic, awareness of RATs is no longer limited to health professionals and COVID-19 has become the expected referent, so more precise usage is required in other circumstances.
RATs are based on the principle of antigen-antibody interaction. They detect antigens (generally a protein on the surface of a virus). A linear chromatography substrate (a porous piece of material) bears an indicator line, onto which antibodies directed against the target antigen are fixed. Antibodies are also fixed to a visualisation marker (generally a dye, though sometimes these antibodies are modified to fluoresce), to which the sample is added. Any virus particles present will bind to these markers. This mix then travels through the substrate through capillarity. When it reaches the indicator line, virus particles are immobilised by the antibodies fixed there, along with the visualisation marker, allowing concentration and thus visual detection of significant levels of virus in a sample.
A positive result with an antigen test should generally be confirmed by RT-qPCR or some other test with higher sensitivity and specificity. | 1 | Biochemistry |
Because Grignard reagents are so sensitive to moisture and oxygen, many methods have been developed to test the quality of a batch. Typical tests involve titrations with weighable, anhydrous protic reagents, e.g. menthol in the presence of a color-indicator. The interaction of the Grignard reagent with phenanthroline or 2,2'-biquinoline causes a color change. | 0 | Organic Chemistry |
Tholins were detected in situ by the Rosetta mission to comet 67P/Churyumov–Gerasimenko. Tholins are not typically characteristic of main-belt asteroids, but have been detected on the asteroid 24 Themis. | 9 | Geochemistry |
Printing quality is highly influenced by the various treatments and methods used in creating paper and enhancing the paper surface. Consumers are most concerned with the paper-ink interactions which vary for certain types of paper due to different chemical properties of the surface. Inkjet paper is the most commercially used type of paper. Filter paper is another key type of paper whose surface chemistry affects its various forms and uses. The ability of adhesives to bond to a paper surface is also affected by the surface chemistry. | 7 | Physical Chemistry |
Measuring the composition of a cow's rumen can also indicate the quality of its feed, a process called a forage analysis.
Once the cannula is surgically placed, the cow is then allowed to graze for a certain period of time—for example, 30 to 45 minutes, in a 1960 study at the University of Nevada, Reno. Researchers will then remove some or all of the ruminated material through the cannula. Analyzing rumen this way can indicate whether particular grasses on which cows are grazing are nutritionally adequate. | 1 | Biochemistry |
Sellar and Boreman have argued that this SNR improvement can be considered as a result of freedom from needing an exit slit inside the spectrometer, since an exit slit reduces the light collected by the detector by the same factor. | 7 | Physical Chemistry |
Levomilnacipran was developed by Forest Laboratories and Pierre Fabre Group, and was approved by the Food and Drug Administration in July 2013. | 4 | Stereochemistry |
For globular proteins, interior atomic packing (arising from short-range, local interactions) of side-chains has been shown to be pivotal in the structural stabilization of the protein-fold. On the other hand, the electrostatic harmony (non-local, long-range) of the overall fold has also been shown to be essential for its stabilization. Packing anomalies include steric clashes, short contacts, holes and cavities while electrostatic disharmony refer to unbalanced partial charges in the protein core (particularly relevant for designed protein interiors). While the clash-score of [http://molprobity.biochem.duke.edu/ Molprobity] identifies steric clashes at a very high resolution, the Complementarity Plot combines packing anomalies with electrostatic imbalance of side-chains and signals for either or both. | 1 | Biochemistry |
The Irving–Williams series refers to the relative stabilities of complexes formed by transition metals. In 1953 Harry Irving and Robert Williams observed that the stability of complexes formed by divalent first-row transition metal ions generally increase across the period to a maximum stability at copper: Mn(II) < Fe(II) < Co(II) < Ni(II) < Cu(II) > Zn(II).
Specifically, the Irving–Williams series refers to the exchange of aqua (HO) ligands for any other ligand (L) within a metal complex. In other words, the Irving–Williams series is almost exclusively independent of the nature of the incoming ligand, L.
The main application of the series is to empirically suggest an order of stability within first row transition metal complexes (where the transition metal is in oxidation state II).
Another application of the Irving–Williams series is to use it as a correlation "ruler" in comparing the first stability constant for replacement of water in the aqueous ion by a ligand. | 7 | Physical Chemistry |
In reference to biochemistry, this is an important concept as far as kinetics is concerned in metalloproteins. This can allow for the rapid synthesis and degradation of substrates in biological systems. | 1 | Biochemistry |
Well-defined, molecular clusters are known, invariably containing organic ligands on their exteriors. Two examples are and . In order to generate naked gold clusters for catalytic applications, the ligands must be removed, which is typically done via a high-temperature ( or higher) calcination process, but can also be achieved chemically at low temperatures (below ), e.g. using a peroxide-assisted route. | 7 | Physical Chemistry |
Factors governing organic reactions are essentially the same as that of any chemical reaction. Factors specific to organic reactions are those that determine the stability of reactants and products such as conjugation, hyperconjugation and aromaticity and the presence and stability of reactive intermediates such as free radicals, carbocations and carbanions.
An organic compound may consist of many isomers. Selectivity in terms of regioselectivity, diastereoselectivity and enantioselectivity is therefore an important criterion for many organic reactions. The stereochemistry of pericyclic reactions is governed by the Woodward–Hoffmann rules and that of many elimination reactions by Zaitsev's rule.
Organic reactions are important in the production of pharmaceuticals. In a 2006 review, it was estimated that 20% of chemical conversions involved alkylations on nitrogen and oxygen atoms, another 20% involved placement and removal of protective groups, 11% involved formation of new carbon–carbon bond and 10% involved functional group interconversions. | 0 | Organic Chemistry |
As promoters are typically immediately adjacent to the gene in question, positions in the promoter are designated relative to the transcriptional start site, where transcription of DNA begins for a particular gene (i.e., positions upstream are negative numbers counting back from -1, for example -100 is a position 100 base pairs upstream). | 1 | Biochemistry |
In sedimentology, winnowing is the natural removal of fine material from a coarser sediment by wind or flowing water. Once a sediment has been deposited, subsequent changes in the speed or direction of wind or water flowing over it can agitate the grains in the sediment and allow the preferential removal of the finer grains. This action can improve the sorting and increase the mean grain size of a sediment after it has been deposited.
The term winnowing is from the analogous process for the agricultural separation of wheat from chaff. | 3 | Analytical Chemistry |
The Wohl degradation in carbohydrate chemistry is a chain contraction method for aldoses. The classic example is the conversion of glucose to arabinose as shown below. The reaction is named after the German chemist Alfred Wohl (1863–1939).
In one modification, d-glucose is converted to the glucose oxime by reaction with hydroxylamine and sodium methoxide. In the second step the is formed by reaction with acetic anhydride in acetic acid with sodium acetate. In this reaction step the oxime is converted into the nitrile with simultaneous conversion of all the alcohol groups to acetate groups.
In the final step sodium methoxide in methanol is added, leading to removal of all the acetate groups and ejection of the nitrile group and collapse of the second carbon from a tetrahedral structure to an aldehyde. | 0 | Organic Chemistry |
In alkaline media oxygen evolution reactions, multiple adsorbent species (O, OH, OOH, and OO) and multiple steps are involved. Steps 4 and 5 often occur in a single step, but there is evidence that suggests steps 4 and 5 occur separately at pH 11 and higher.
Where the * indicate species adsorbed to the surface of the catalyst. | 7 | Physical Chemistry |
Housekeeping genes account for majority of the active genes in the genome, and their expression is obviously vital to survival. The housekeeping gene expression levels are fine-tuned to meet the metabolic requirements in various tissues. Biochemical studies on transcription initiation of the housekeeping gene promoters have been difficult, partly due to the less-characterized promoter motifs and transcription initiation process.
Human housekeeping gene promoters are generally depleted of TATA-box, have high GC content and high incidence of CpG Islands. In Drosophila, where promoter specific CpG Islands are absent, housekeeping gene promoters contain DNA elements like DRE, E-box or DPE. Transcription start sites of housekeeping genes can span over a region of around 100 bp whereas transcription start sites of developmentally regulated genes are usually focused in a narrow region. Little is known about how the dispersed transcription initiation of housekeeping gene is established. There are transcription factors that are specifically enriched on and regulate housekeeping gene promoters. Furthermore, housekeeping promoters are regulated by housekeeping enhancers but not developmentally regulated enhancers. | 1 | Biochemistry |
DKPs have been shown to inhibit the activities of bacteria, fungi, viruses, and potentially protozoa, as well as exhibit antitumor and antiprion properties. The molecule glionitrin, for instance, proved to be very effective against methicillin-resistant Staphylococcus aureus (MRSA), in addition to four different human cancer cell lines in vitro. As antivirals, however, DPKs appear to have a poor outlook when compared to those already on the market.
Despite the great potential for diversity in this class of molecules, natural DPKs containing proline are significantly overrepresented among those known to be biologically active. There also appears to be some bias with regards to stereochemistry, as DD-stereoisomers tend to display stronger antibiotic capabilities. | 0 | Organic Chemistry |
In order to remove the C15 alcohol group, Enol 15 was converted to tosylate 16 (TsCl, pyridine) and then to mercaptoester 17 (sodium benzylmercaptide) which was then reduced to unsaturated ester 18 by Raney nickel and hydrogen. Further reduction with hydrogen / palladium on carbon afforded the saturated ester 19. Alkaline ester hydrolysis to carboxylic acid 20 was accompanied by epimerization at C14.
This particular compound was already known from strychnine degradation studies. Until now all intermediates were racemic but chirality was introduced at this particular stage via chiral resolution using quinidine.
The C20 carbon atom was then introduced by acetic anhydride to form enol acetate 21 and the free aminoketone 22 was obtained by hydrolysis with hydrochloric acid. Ring VII in intermediate 23 was closed by selenium dioxide oxidation, a process accompanied by epimerization again at C14.
The formation of 21 can be envisioned as a sequence of acylation, deprotonation, rearrangement with loss of carbon dioxide and again acylation: | 0 | Organic Chemistry |
RNA secondary structure can be determined from atomic coordinates (tertiary structure) obtained by X-ray crystallography, often deposited in the Protein Data Bank. Current methods include 3DNA/DSSR and MC-annotate. | 4 | Stereochemistry |
Nature produces massive amounts of chloromethane and bromomethane. Most concern focuses on anthropogenic sources, which are potential toxins, even carcinogens. Similarly, great interest has been shown in remediation of man made halocarbons such as those produced on large scale, such as dry cleaning fluids. Volatile halocarbons degrade photochemically because the carbon-halogen bond can be labile. Some microorganisms dehalogenate halocarbons. While this behavior is intriguing, the rates of remediation are generally very slow. | 0 | Organic Chemistry |
Conserved signature inserts and deletions (CSIs) in protein sequences provide an important category of molecular markers for understanding phylogenetic relationships. CSIs, brought about by rare genetic changes, provide useful phylogenetic markers that are generally of defined size and they are flanked on both sides by conserved regions to ensure their reliability. While indels can be arbitrary inserts or deletions, CSIs are defined as only those protein indels that are present within conserved regions of the protein.
The CSIs that are restricted to a particular clade or group of species, generally provide good phylogenetic markers of common evolutionary descent. Due to the rarity and highly specific nature of such changes, it is less likely that they could arise independently by either convergent or parallel evolution (i.e. homoplasy) and therefore are likely to represent synapomorphy. Other confounding factors such as differences in evolutionary rates at different sites or among different species also generally do not affect the interpretation of a CSI. By determining the presence or absence of CSIs in an out-group species, one can infer whether the ancestral form of the CSI was an insert or deletion and this can be used to develop a rooted phylogenetic relationship among organisms.
CSIs are discovered by looking for shared changes in a phylogenetic tree constructed from protein sequences. Most CSIs that have been identified have been found to have high predictive value upon addition of new sequences, retaining the specificity for the originally identified clades of species. They can be used to identify both known and even previously unknown species belonging to these groups in different environments. Compared to tree branching orders which can vary among methods, specific CSIs make for more concrete circumscriptions that are computationally cheaper to apply. | 1 | Biochemistry |
The study of interactomes is called interactomics. The basic unit of a protein network is the protein–protein interaction (PPI). While there are numerous methods to study PPIs, there are relatively few that have been used on a large scale to map whole interactomes.
The yeast two hybrid system (Y2H) is suited to explore the binary interactions among two proteins at a time. Affinity purification and subsequent mass spectrometry is suited to identify a protein complex. Both methods can be used in a high-throughput (HTP) fashion. Yeast two hybrid screens allow false positive interactions between proteins that are never expressed in the same time and place; affinity capture mass spectrometry does not have this drawback, and is the current gold standard. Yeast two-hybrid data better indicates non-specific tendencies towards sticky interactions rather while affinity capture mass spectrometry better indicates functional in vivo protein–protein interactions. | 1 | Biochemistry |
Formate is produced by the cleavage of pyruvate. This reaction is catalysed by the enzyme pyruvate-formate lyase (PFL), which plays an important role in regulating anaerobic fermentation in E. coli.
pyruvate + CoA → acetyl-CoA + formate | 1 | Biochemistry |
The VSMOW–SLAP scale is recommended by the USGS, IUPAC, and IAEA for measurement of deuterium and O concentrations in any substance. For O, a scale based on Vienna Pee Dee Belemnite can also be used. The physical samples, which are distributed by the IAEA and U.S. National Institute of Standards and Technology, are used to calibrate isotope-measuring equipment.
Variations in isotopic content are useful in hydrology, meteorology, and oceanography. Different parts of the ocean do have slightly different isotopic concentrations: δ O values range from –11.35‰ in water off the coast of Greenland to +1.32‰ in the north Atlantic, and δ H concentrations in deep ocean water range from roughly –1.7‰ near Antarctica to +2.2‰ in the Arctic. Variations are much larger in surface water than in deep water. | 9 | Geochemistry |
The Cells Alive System (CAS) is a line of commercial freezers manufactured by ABI Corporation, Ltd. of Chiba, Japan claimed to preserve food with greater freshness than ordinary freezing by using electromagnetic fields and mechanical vibrations to limit ice crystal formation that destroys food texture. They also are claimed to increase tissue survival without having its water replaced by cryogenically compatible fluids; whether they have any effect is unclear. The freezers have attracted attention among organ banking and transplantation surgeons, as well as the food processing industry. | 1 | Biochemistry |
Keepers are substances (typically solvents, but sometimes adsorbent solids) added in relatively small quantities during an evaporative procedure in analytical chemistry, such as concentration of an analyte-solvent mixture by rotary evaporation. The purpose of a keeper is to reduce losses of a target analyte during the procedure. Keepers typically have reduced volatility and are added to a more volatile solvent.
In the case of volatile target analytes, it is difficult to totally avoid loss of the analyte in an evaporative procedure, but the presence of a keeper solvent or solid is intended to preferentially solvate or adsorb the analyte, so that the volatility of the analyte is reduced as the evaporative procedure continues. In the case of non-volatile target analytes, the presence of the keeper solvent or solid is intended to prevent all the solvent from being evaporated off, thereby preventing the loss of analytes which might irreversibly adsorb to the container walls when completely dried, or if it is totally dried (in the case of a solid keeper), provide a surface where the analyte can be reversibly rather than irreversibly adsorbed. A solid keeper of sodium sulfate has been shown to be effective for reducing losses of polycyclic aromatic hydrocarbons (PAHs) in evaporative procedures. | 3 | Analytical Chemistry |
In industry, methanethiol is prepared by the reaction of hydrogen sulfide with methanol. This method is employed for the industrial synthesis of methanethiol:
:CHOH + HS → CHSH + HO
Such reactions are conducted in the presence of acidic catalysts. The other principal route to thiols involves the addition of hydrogen sulfide to alkenes. Such reactions are usually conducted in the presence of an acid catalyst or UV light. Halide displacement, using the suitable organic halide and sodium hydrogen sulfide has also been used.
Another method entails the alkylation of sodium hydrosulfide.
: RX + NaSH → RSH + NaX(X = Cl, Br, I)
This method is used for the production of thioglycolic acid from chloroacetic acid. | 0 | Organic Chemistry |
Calorie restriction, vitamin E, and increased glutathione appear to reduce or halt the production of lipofuscin.
The nootropic drug piracetam appears to significantly reduce accumulation of lipofuscin in the brain tissue of rats.
Other possible treatments:
*Centrophenoxine
*Acetyl-L-carnitine
*Ginkgo biloba
*Dimethylethanolamine
*Curcumin
Wet macular degeneration can be treated using selective photothermolysis where a pulsed unfocused laser predominantly heats and kills lipofuscin-rich cells, leaving untouched healthy cells to multiply and fill in the gaps. The technique is also used as a skin treatment to remove tattoos, liverspots, and in general make skin appear younger. This ability to selectively target lipofuscin has opened up research opportunities in the field of anti-aging medicine.
Soraprazan (remofuscin) has been found to remove lipofuscin from retinal pigment epithelial cells in animals. This opens up a new therapy option for the treatment of dry age-related macular degeneration and Stargardt disease, for which there is currently no treatment. The drug has now been granted orphan drug designation for the treatment of Stargardt disease by the European Medicines Agency. | 1 | Biochemistry |
A planet is in thermal equilibrium when the incident energy reaching it (typically the solar irradiance from its parent star) is equal to the infrared energy radiated away to space. | 7 | Physical Chemistry |
In 1972, scientists discovered that chlorophyll could absorb sunlight and transfer energy into electrochemical cells. This discovery eventually led to the use of photosensitizers as sunlight-harvesting materials in solar cells, mainly through the use of photosensitizer dyes. Dye Sensitized Solar cells utilize these photosensitizer dyes to absorb photons from solar light and transfer energy rich electrons to the neighboring semiconductor material to generate electric energy output. These dyes act as dopants to semiconductor surfaces which allows for the transfer of light energy from the photosensitizer to electronic energy within the semiconductor. These photosensitizers are not limited to dyes. They may take the form of any photosensitizing structure, dependent on the semiconductor material to which they are attached. | 5 | Photochemistry |
Some polymers containing sulfone groups are useful engineering plastics. They exhibit high strength and resistance to oxidation, corrosion, high temperatures, and creep under stress. For example, some are valuable as replacements for copper in domestic hot water plumbing. Precursors to such polymers are the sulfones bisphenol S and 4,4′-dichlorodiphenyl sulfone. | 0 | Organic Chemistry |
NADPH plays an important role as an antioxidant by decreasing the reactive oxygen produced during rapid cell proliferation. It has been shown that attenuation of the PPP would dampen NADPH production in cancer cells, leading to the decrease in macromolecular biosynthesis and rendering the transformed cells that are vulnerable free radical-mediated damage. In this way, the advantage conferred by PKM2 expression would be eliminated. In preclinical studies, drugs such as 6-amino-nicotinamide (6-AN), which inhibits G6P dehydrogenase, the enzyme that initiates the PPP have shown anti-tumorigenic effects in leukemia, glioblastoma and lung cancer cell lines.
Cyclosporine inhibits TOR and is used as an effective immunosuppressant. Mycophenolic acid inhibits of IMPDH and pyrimidine biosynthesis and is clinically used as immunosuppressant. Both agents also display anti-tumor effects in animal studies. Metabolites such as Alanine, Saturated lipids, Glycine, Lactate, Myo-Inositol, Nucleotides, Polyunsaturated fatty acids and Taurine are considered as the potential biomarkers in various studies. | 1 | Biochemistry |
In phosphor thermometry, the temperature dependence of the photoluminescence process is exploited to measure temperature. | 7 | Physical Chemistry |
There are two types of genes: protein coding genes and noncoding genes. Noncoding genes are an important part of non-coding DNA and they include genes for transfer RNA and ribosomal RNA. These genes were discovered in the 1960s. Prokaryotic genomes contain genes for a number of other noncoding RNAs but noncoding RNA genes are much more common in eukaryotes.
Typical classes of noncoding genes in eukaryotes include genes for small nuclear RNAs (snRNAs), small nucleolar RNAs (sno RNAs), microRNAs (miRNAs), short interfering RNAs (siRNAs), PIWI-interacting RNAs (piRNAs), and long noncoding RNAs (lncRNAs). In addition, there are a number of unique RNA genes that produce catalytic RNAs.
Noncoding genes account for only a few percent of prokaryotic genomes but they can represent a vastly higher fraction in eukaryotic genomes. In humans, the noncoding genes take up at least 6% of the genome, largely because there are hundreds of copies of ribosomal RNA genes. Protein-coding genes occupy about 38% of the genome; a fraction that is much higher than the coding region because genes contain large introns.
The total number of noncoding genes in the human genome is controversial. Some scientists think that there are only about 5,000 noncoding genes while others believe that there may be more than 100,000 (see the article on Non-coding RNA). The difference is largely due to debate over the number of lncRNA genes. | 1 | Biochemistry |
This method can be used to detect co-binding of two factors to the same genomic locus. The Dam methylase may be expressed in two halves which are fused to different proteins of interest. When both proteins bind to the same region of DNA, the Dam enzyme is reconstituted and is able to methylate the surrounding GATC sites. | 1 | Biochemistry |
Research on thyroid cancer has elucidated the theory that paracrine signaling may aid in creating tumor microenvironments. Chemokine transcription is upregulated when Ras is in the GTP-bound state. The chemokines are then released from the cell, free to bind to another nearby cell. Paracrine signaling between neighboring cells creates this positive feedback loop. Thus, the constitutive transcription of upregulated proteins form ideal environments for tumors to arise. Effectively, multiple bindings of ligands to the RTK receptors overstimulates the Ras-Raf-MAPK pathway, which overexpresses the mitogenic and invasive capacity of cells. | 1 | Biochemistry |
Hydrogel encapsulation of the QDs opens up a new range of applications, such as:
* Biosensors
:Enzymes and other bio-active molecules serve as biorecognition units while QDs serve as signalling units. By adding enzymes to the QD hydrogel network both units can be combined to form a biosensor. The enzymatic reaction that detects a particular molecule causes the fluoresce of QDs to be quenched. In this way, the location of molecules of interest can be observed.
* Cell Influence and Imaging
: Adding iron oxide nanoparticles to the QD micelles allows them to be fluorescent and magnetic. These micelles can be moved in a magnetic field to create concentration gradients that will influence a cell's processes.
* Gold Hyperthermia
:When excited by high energy radiation, such as with a laser, gold nanoparticles emit a thermal field. This phenomenon can be used as a form of hyperthermia therapy to destroy malignant cancers without damaging surrounding tissues. When combined with QDs in a hydrogel this could facilitate real-time monitoring of the tumor treatment. | 7 | Physical Chemistry |
Ehrlichs reagent or Ehrlich reagent is a reagent containing p'-dimethylaminobenzaldehyde (DMAB) and thus can act as an indicator to presumptively identify indoles and urobilinogen. Several Ehrlich tests use the reagent in a medical test; some are drug tests and others contribute to diagnosis of various diseases or adverse drug reactions. It is named after Nobel Prize winner Paul Ehrlich who used it to distinguish typhoid from simple diarrhoea.
The Ehrlich reagent works by binding to the C2 position of two indole moieties to form a resonance stabilised carbenium ion compound. | 3 | Analytical Chemistry |
A Langmuir–Taylor detector, also called surface ionization detector or hot wire detector, is a kind of ionization detector used in mass spectrometry, developed by John Taylor based on the work of Irving Langmuir and K. H. Kingdon. | 3 | Analytical Chemistry |
The lactose operon (lac operon) is an operon required for the transport and metabolism of lactose in E. coli and many other enteric bacteria. Although glucose is the preferred carbon source for most enteric bacteria, the lac operon allows for the effective digestion of lactose when glucose is not available through the activity of beta-galactosidase. Gene regulation of the lac operon was the first genetic regulatory mechanism to be understood clearly, so it has become a foremost example of prokaryotic gene regulation. It is often discussed in introductory molecular and cellular biology classes for this reason. This lactose metabolism system was used by François Jacob and Jacques Monod to determine how a biological cell knows which enzyme to synthesize. Their work on the lac operon won them the Nobel Prize in Physiology in 1965.
Most bacterial cells including E. coli lack introns in their genome. They also lack a nuclear membrane. Hence the gene regulation by lac operon occurs at the transcriptional level, by preventing conversion of DNA into mRNA.
Bacterial operons are polycistronic transcripts that are able to produce multiple proteins from one mRNA transcript. In this case, when lactose is required as a sugar source for the bacterium, the three genes of the lac operon can be expressed and their subsequent proteins translated: lacZ, lacY, and lacA. The gene product of lacZ is β-galactosidase which cleaves lactose, a disaccharide, into glucose and galactose. lacY encodes β-galactoside permease, a membrane protein which becomes embedded in the Plasma membrane to enable the cellular transport of lactose into the cell. Finally, lacA encodes β-galactoside transacetylase.
Note that the number of base pairs in diagram given above are not for scale.
It would be wasteful to produce enzymes when no lactose is available or if a preferable energy source such as glucose were available. The lac operon uses a two-part control mechanism to ensure that the cell expends energy producing the enzymes encoded by the lac operon only when necessary.
In the absence of lactose, the lac repressor, encoded by lacI, halts production of the enzymes and transport proteins encoded by the lac operon. It does so by blocking the DNA dependent RNA polymerase. This blocking/ halting is not perfect, and a minimal amount of gene expression does take place all the time. The repressor protein is always expressed, but the lac operon (enzymes and transport proteins) are repressed. (But not completely stopped)
When lactose is available but not glucose, then some lactose enters the cell using pre-existing transport protein encoded by lacY. This lactose then combines with the repressor and inactivates it, hence allowing the lac operon to be expressed. Then more β-galactoside permease is synthesized allowing even more lactose to enter and the enzymes encoded by lacZ and lacA can digest it.
However, In the presence of glucose, regardless of the presence of lactose, the operon will be repressed. This is because the catabolite activator protein (CAP), required for production of the enzymes, remains inactive, and EIIA shuts down lactose permease to prevent transport of lactose into the cell. This dual control mechanism causes the sequential utilization of glucose and lactose in two distinct growth phases, known as diauxie. | 1 | Biochemistry |
Other hypothetical gene therapies could include changes to physical appearance, metabolism, mental faculties such as memory and intelligence, and well-being (by increasing resistance to depression or relieving chronic pain, for example). | 1 | Biochemistry |
For bottom-up proteomics, the proteins can be separated by two-dimensional gel electrophoresis and analyzed by matrix-assisted laser desorption/ionization (MALDI) or electrospray ionization mass spectrometry for relative quantification or by inductively coupled plasma mass spectrometry for absolute quantification. For top-down proteomics, the undigested labeled proteins are analyzed. | 3 | Analytical Chemistry |
Red blood cell transketolase activity is reduced in deficiency of thiamine (vitamin B), and may be used in the diagnosis of Wernicke encephalopathy and other B-deficiency syndromes if the diagnosis is in doubt. Apart from the baseline enzyme activity (which may be normal even in deficiency states), acceleration of enzyme activity after the addition of thiamine pyrophosphate may be diagnostic of thiamine deficiency (0-15% normal, 15-25% deficiency, >25% severe deficiency). | 5 | Photochemistry |
Electrically detected magnetic resonance (EDMR) is a materials characterisation technique that improves upon electron spin resonance. It involves measuring the change in electrical resistance of a sample when exposed to certain microwave frequencies. It can be used to identify very small numbers (down to a few hundred atoms) of impurities in semiconductors. | 7 | Physical Chemistry |
* TGFα is upregulated in some human cancers. It is produced in macrophages, brain cells, and keratinocytes, and induces epithelial development. It belongs to the EGF family.
* TGFβ exists in three known subtypes in humans, TGFβ1, TGFβ2, and TGFβ3. These are upregulated in Marfan's syndrome and some human cancers, and play crucial roles in tissue regeneration, cell differentiation, embryonic development, and regulation of the immune system. Isoforms of transforming growth factor-beta (TGF-β1) are also thought to be involved in the pathogenesis of pre-eclampsia. They belong to the transforming growth factor beta family. TGFβ receptors are single pass serine/threonine kinase receptors. | 1 | Biochemistry |
Under steady-state conditions, the catalyst and substrate undergo reversible association followed by a relatively rapid consumption of the catalyst–substrate complex (by both forward reactions to product and reverse reactions to unbound catalyst.) The steady-state approximation holds that the concentration of the catalyst-substrate complex is not changing over time; the total concentration of this complex remains low as it is whisked away almost immediately after formation. A steady-state rate law contains all of the rate constants and species required to go from starting material to product, while the denominator consists of a sum of terms describing the relative rates of the forward and reverse reactions consuming the steady-state intermediate. For the simplest case where one substrate goes to one product through a single intermediate:
In a slightly more complex situation where two substrates bind in sequence followed by product release:
Increasingly complex systems can be described simply with the algorithm described in this reference.
In the case of the steady-state conditions described above, the catalyst resting state is the unbound form (because the substrate-bound intermediate is, by definition, only present at a minimal concentration.) | 7 | Physical Chemistry |
Many experimenters tried to immobilize the electrolyte of an electrochemical cell to make it more convenient to use. The Zamboni pile of 1812 is a high-voltage dry battery but capable of delivering only minute currents. Various experiments were made with cellulose, sawdust, spun glass, asbestos fibers, and gelatine.
In 1886, Carl Gassner obtained a German patent (No. 37,758) on a variant of the (wet) Leclanché cell, which came to be known as the dry cell because it did not have a free liquid electrolyte. Instead, the ammonium chloride was mixed with Plaster of Paris to create a paste, with a small amount of zinc chloride added in to extend the shelf life. The manganese dioxide cathode was dipped in this paste, and both were sealed in a zinc shell, which also acts as the anode. In November 1887, he obtained for the same device. A dry-battery was invented in Japan during the Meiji Era in 1887. The inventor was Sakizō Yai. However, Yai didn't have enough money to file the patent, the first patent holder of a battery in Japan was not Yai, but Takahashi Ichisaburo. Wilhelm Hellesen also invented a dry-battery in 1887 and obtained in 1890.
Unlike previous wet cells, Gassners dry cell is more solid, does not require maintenance, does not spill, and can be used in any orientation. It provides a potential of 1.5 volts. The first mass-produced model was the Columbia dry cell, first marketed by the National Carbon Company in 1896. The NCC improved Gassners model by replacing the plaster of Paris with coiled cardboard, an innovation that leaves more space for the cathode and makes the battery easier to assemble. It was the first convenient battery for the masses and made portable electrical devices practical. Gasner is a German scientist.
The zinc–carbon cell (as it came to be known) is still manufactured today. | 7 | Physical Chemistry |
In metallurgy, selective leaching, also called dealloying, demetalification, parting and selective corrosion, is a corrosion type in some solid solution alloys, when in suitable conditions a component of the alloys is preferentially leached from the initially homogenous material. The less noble metal is removed from the alloy by a microscopic-scale galvanic corrosion mechanism. The most susceptible alloys are the ones containing metals with high distance between each other in the galvanic series, e.g. copper and zinc in brass. The elements most typically undergoing selective removal are zinc, aluminium, iron, cobalt, chromium, and others. | 8 | Metallurgy |
The Eschenmoser sulfide contraction is an organic reaction first described by Albert Eschenmoser for the synthesis of 1,3-dicarbonyl compounds from a thioester. The method requires a base and a tertiary phosphine. The method is of some relevance to organic chemistry and has been notably applied in the vitamin B total synthesis.
A base abstracts the labile hydrogen atom in the thioester, a sulfide anion is formed through an episulfide intermediate which is removed by the phosphine. | 0 | Organic Chemistry |
In Denmark, modafinil is a prescription drug but not listed as a controlled substance. According to the Danish Medicines Agency, modafinil is approved for use in the treatment of narcolepsy, still, importing modafinil to Denmark is considered illegal without a valid prescription.
In Finland, modafinil is a prescription drug but not listed as a controlled substance. Finland is a member of the European Union, and it is illegal to import prescription medicine from outside the European Union unless the person has a valid prescription.
In the Republic of Moldova, modafinil is classified as a psychotropic drug (included in table III list 3 which is the list of psychotropic substances as defined by the Government) and is available by prescription. Importation of modafinil may be considered illegal and subject to severe penalties, even if you have a prescription. For example, on June 29, 2017, postal officers discovered 60 tablets of Modalert (200 mg modafinil tablets) in a parcel sent from India to a resident in Chișinău, Moldova. The prohibited substance was detected during a routine scan and was seized as illegal. The authorities were notified of the incident and the recipient was charged with criminal penalties. In the Transnistria region of Moldova, modafinil is completely prohibited, due to application of the legislation similar to that of Russia where modafinil is completely prohibited and is in the same list as narcotics. Possession or an attempt to bring modafinil to Transnistria potentially leads to imprisonment.
In Romania, modafinil is classified as a stimulant doping agent and is prohibited in sports competitions. In 2022, laws were passed making its importation or sale a felony, punishable by three to seven years in jail. Simple possession for personal use may result in a fine and confiscation.
In Sweden, modafinil is classified as a schedule IV substance, which means that it is considered to have low potential for abuse and low risk of dependence. Still, possession is illegal without prescription.
In the United Kingdom, it is not listed in Misuse of Drugs Act, so possession is not illegal, but a prescription is required. | 4 | Stereochemistry |
In crystallography, the transition temperature is the temperature at which a material changes from one crystal state (allotrope) to another. More formally, it is the temperature at which two crystalline forms of a substance can co-exist in equilibrium. For example, when rhombic sulfur is heated above 95.6 °C, it changes form into monoclinic sulfur; when cooled
below 95.6 °C, it reverts to rhombic sulfur. At 95.6 °C the two forms can co-exist. Another example is tin, which transitions from a cubic crystal below 13.2 °C to a tetragonal crystal above that temperature.
In the case of ferroelectric or ferromagnetic crystals, a transition temperature may be known as the Curie temperature. | 3 | Analytical Chemistry |
Third generation TSH assay is the current requirement for modern standards of care. At present, TSH testing in the United States is typically carried out with automated platforms using advanced forms of immunometric assay. Nonetheless, there is currently no international standard for measurement of thyroid-stimulating hormone. | 1 | Biochemistry |
Perfluorocarbon emulsions are emulsions containing either bubbles or droplets which have perfluorocarbons inside them. Some of them are commonly used in medicine as ultrasound contrast agents, and others have been studied for use as oxygen therapeutics. | 7 | Physical Chemistry |
The regulation of bio-luminescence in bacteria is achieved through the regulation of the oxidative enzyme called luciferase. It is important that bio-luminescent bacteria decrease production rates of luciferase when the population is sparse in number in order to conserve energy. Thus, bacterial bioluminescence is regulated by means of chemical communication referred to as quorum sensing. Essentially, certain signaling molecules named autoinducers with specific bacterial receptors become activated when the population density of bacteria is high enough. The activation of these receptors leads to a coordinated induction of luciferase production that ultimately yields visible luminescence. | 1 | Biochemistry |
pHT01 is a plasmid used as a cloning vector for expressing proteins in Bacillus subtilis. It is 7,956 base pairs in length. pHT01 carries Pgrac, an artificial, strong, IPTG-inducible promoter consisting of the Bacillus subtilis groE promoter, a lac operator, and the gsiB ribosome binding site. It was first found on plasmid pNDH33. The plasmid also carries replication regions from the pMTLBs72. The plasmid also carries genes to confer resistance to ampicillin and chloramphenicol.
Plasmid pHT01 is generally stable in both B. subtilis and Escherichia coli, and can be used for protein expression in these host strains. pNDH33/pHT01 have been used to produce up to 16% of total protein output in B. subtilis. Pgrac100 is an improved version of Pgrac, which can produce up to 30% of total cellular proteins in B. subtilis. | 1 | Biochemistry |
In 1977 the US Federal Drug Administration published a clinical trial guideline that excluded women of "childbearing potential" from the early phases of most clinical trials, which in practice led to their exclusion from later trial phases as well. This 1977 FDA guideline was implemented in response to a protectionist climate caused by the thalidomide tragedy. In the 1980s, a US task force on womens health concluded that a lack of womens health research (in part due to the FDA guideline) had compromised the amount and quality of information available about diseases and treatments affecting women. This led to the National Institute of Health policy that women should, when beneficial, be included in clinical trials. | 4 | Stereochemistry |
The evolution of oxygen during the light-dependent steps in photosynthesis (Hill reaction) was proposed and proven by British biochemist Robin Hill. He demonstrated that isolated chloroplasts would make oxygen (O) but not fix carbon dioxide (CO). This is evidence that the light and dark reactions occur at different sites within the cell.
Hills finding was that the origin of oxygen in photosynthesis is water (HO) not carbon dioxide (CO) as previously believed. Hills observation of chloroplasts in dark conditions and in the absence of CO, showed that the artificial electron acceptor was oxidized but not reduced, terminating the process, but without production of oxygen and sugar. This observation allowed Hill to conclude that oxygen is released during the light-dependent steps (Hill reaction) of photosynthesis.
Hill also discovered Hill reagents, artificial electron acceptors that participate in the light reaction, such as Dichlorophenolindophenol (DCPIP), a dye that changes color when reduced. These dyes permitted the finding of electron transport chains during photosynthesis.
Further studies of the Hill reaction were made in 1957 by plant physiologist Daniel I. Arnon. Arnon studied the Hill reaction using a natural electron acceptor, NADP. He demonstrated the light-independent reaction, observing the reaction under dark conditions with an abundance of carbon dioxide. He found that carbon fixation was independent of light. Arnon effectively separated the light-dependent reaction, which produces ATP, NADPH, H and oxygen, from the light-independent reaction that produces sugars. | 5 | Photochemistry |
In chemistry, peroxycarbonate (sometimes peroxocarbonate, IUPAC name: oxocarbonate or oxidocarbonate) or percarbonate is a divalent anion with formula . It is an oxocarbon anion that consists solely of carbon and oxygen. It would be the anion of a hypothetical peroxycarbonic acid HO–CO–O–OH (sometimes peroxocarbonic acid). or the real hydroperoxyformic acid, HO-O-CO-OH (a.k.a. percarbonic acid, carbonoperoxoic acid, hydroxycarbonic acid).
The peroxycarbonate anion is formed, together with peroxydicarbonate , at the negative electrode during electrolysis of molten lithium carbonate. Lithium peroxycarbonate can be produced also by combining carbon dioxide with lithium hydroxide in concentrated hydrogen peroxide HO at −10 °C.
Electrolysis of a solution of lithium carbonate at -30° to -40 °C yields a solution of the Lithium percarbonate, which can liberate iodine from potassium iodide instantaneously. The crystalline salt has not been isolated.
The peroxycarbonate anion has been proposed as an intermediate to explain the catalytic effect of CO on the oxidation of organic compounds by O.
The potassium and rubidium salts of the monovalent hydrogenperoxycarbonate anion (aka. hydroxycarbonate, biperoxycarbonate) have also been obtained. | 7 | Physical Chemistry |
The formation of raw iron ore pellets, also known as pelletizing, has the objective of producing pellets in an appropriate band of sizes and with mechanical properties high usefulness during the stresses of transference, transport, and use. For example, waste materials are ground before being heated and introduced into a press for compression. Both mechanical force and thermal processes are used to produce the correct pellet properties. From an equipment point of view there are two alternatives for industrial production of iron ore pellets: the drum and the pelletizing disk. | 8 | Metallurgy |
A drug in blood exists in two forms: bound and unbound. Depending on a specific drug's affinity for plasma proteins, a proportion of the drug may become bound to the proteins, with the remainder being unbound. If the protein binding is reversible, then a chemical equilibrium will exist between the bound and unbound states, such that:
:Protein + drug ⇌ Protein-drug complex
Notably, it is the unbound fraction which exhibits pharmacologic effects. It is also the fraction that may be metabolized and/or excreted. For example, the "fraction bound" of the anticoagulant warfarin is 97%. This means that out of the amount of warfarin in the blood, 97% is bound to plasma proteins. The remaining 3% (the fraction unbound) is the fraction that is actually active and may be excreted.
Protein binding can influence the drug's biological half-life. The bound portion may act as a reservoir or depot from which the drug is slowly released as the unbound form. Since the unbound form is being metabolized and/or excreted from the body, the bound fraction will be released in order to maintain equilibrium.
Since albumin is alkalotic, acidic and neutral drugs will primarily bind to albumin. If albumin becomes saturated, then these drugs will bind to lipoprotein. Basic drugs will bind to the acidic alpha-1 acid glycoprotein. This is significant because various medical conditions may affect the levels of albumin, alpha-1 acid glycoprotein, and lipoproteins. | 1 | Biochemistry |
The most recently completed dexpramipexole clinical trial was EXHALE-1 (AS201), a Phase II clinical trial in participants with moderate-to-severe eosinophilic asthma. Dexpramipexole demonstrated highly significant, dose dependent eosinophil lowering during the primary assessment phase and was maximal at Week 12. Dexpramipexole produced clinically relevant changes in FEV across study arms and time points and the magnitude of FEV improvement was comparable to currently approved biologics. Dexpramipexole was well tolerated in the trial, with adverse events balanced across treatment and placebo groups, no serious adverse events, and no adverse events leading to discontinuation. | 4 | Stereochemistry |
Using the specific values of in matrix , it can be shown that the fourth-rank elasticity stiffness tensor may be written in 2-index Voigt notation as the matrix
The elasticity stiffness matrix has 5 independent constants, which are related to well known engineering elastic moduli in the following way. These engineering moduli are experimentally determined.
The compliance matrix (inverse of the elastic stiffness matrix) is
where . In engineering notation,
Comparing these two forms of the compliance matrix shows us that the longitudinal Young's modulus is given by
Similarly, the transverse Young's modulus is
The inplane shear modulus is
and the Poisson's ratio for loading along the polar axis is
Here, L represents the longitudinal (polar) direction and T represents the transverse direction. | 3 | Analytical Chemistry |
Patchoulene oxide (1) could be accessed from terpene patchoulol (52) through a series of acid-catalyzed carbocation rearrangements proceeded by an elimination following Zaitzev's rule to give pathoulene (53). The driving force for the rearrangement is relief of ring strain. Epoxidation of 53 with peracetic acid gave patchoulene oxide 1. | 0 | Organic Chemistry |
Often molecules do form multilayers, that is, some are adsorbed on already adsorbed molecules, and the Langmuir isotherm is not valid. In 1938 Stephen Brunauer, Paul Emmett, and Edward Teller developed a model isotherm that takes that possibility into account. Their theory is called BET theory, after the initials in their last names. They modified Langmuir's mechanism as follows:
:A + S ⇌ AS,
:A + AS ⇌ AS,
:A + AS ⇌ AS and so on.
The derivation of the formula is more complicated than Langmuir's (see links for complete derivation). We obtain:
where x is the pressure divided by the vapor pressure for the adsorbate at that temperature (usually denoted ), v is the STP volume of adsorbed adsorbate, v is the STP volume of the amount of adsorbate required to form a monolayer, and c is the equilibrium constant K we used in Langmuir isotherm multiplied by the vapor pressure of the adsorbate. The key assumption used in deriving the BET equation that the successive heats of adsorption for all layers except the first are equal to the heat of condensation of the adsorbate.
The Langmuir isotherm is usually better for chemisorption, and the BET isotherm works better for physisorption for non-microporous surfaces. | 7 | Physical Chemistry |
The two main pressure scales used in static high-pressure experiments are X-ray diffraction of a material with a known equation of state and measuring the shift in ruby fluorescence lines. The first began with NaCl, for which the compressibility has been determined by first principles in 1968. The major pitfall of this method of measuring pressure is that the use of X-rays is required. Many experiments do not require X-rays and this presents a major inconvenience to conduct both the intended experiment and a diffraction experiment. In 1971, the NBS high pressure group was set in pursuit of a spectroscopic method for determining pressure. It was found that the wavelength of ruby fluorescence emissions change with pressure; this was easily calibrated against the NaCl scale.
Once pressure could be generated and measured it quickly became a competition for which cells can go the highest. The need for a reliable pressure scale became more important during this race. Shock-wave data for the compressibilities of Cu, Mo, Pd, and Ag were available at this time and could be used to define equations of states up to Mbar pressure. Using these scales these pressures were reported:
Both methods are continually refined and in use today. However, the ruby method is less reliable at high temperature. Well defined equations of state are needed when adjusting temperature and pressure, two parameters that affect the lattice parameters of materials. | 7 | Physical Chemistry |
Direct-EI may offer a clear advantage over ESI in several applications, but it may excel in the following cases:
*Large number of compounds of different polarities and chemical properties: EI can offer a shortcut, do-it-all solution when hard-to-detect substances are included or and when a combination of positive and negative ion detection runs are required for complete coverage of analyte detection.
*Characterization of unknowns: library matching offer an invaluable tool for compound identification.
*Detection of non chromophoric compounds that also give poor or no signal with API: for these compounds additional HPLC detectors such as evaporative light scattering detector (ELSD), refractive index (RI) or corona discharge aerosol detector (CAD) are also available but each of them has limitations which restrain obtaining a universal detection with reasonable sensitivity. EI-MS would offer a suitable solution for this type of compounds, in terms of sensitivity and universal response. GC is anyway feasible only for compounds with high to medium volatility and therefore cannot be adopted for a full characterization of mixtures of complex nature. The possibility of hyphenating EI to HPLC separation represents an ideal solution.
*Quantitative analyses in presence of matrix effects: EI-MS offers a superior performance compared to ESI or APCI when intruding interferences from complex matrices pass cleanup procedure and cause signal suppression or enhancement. | 3 | Analytical Chemistry |
When iodide is added to a solution of hexacyanoferrate(III), the following equilibrium exists:
Under strongly acidic solution, the above equilibrium lies far to the right hand side, but is reversed in almost neutral solution. This makes analysis of hexacyanoferrate(III) troublesome as the iodide and thiosulfate decomposes in strongly acidic medium. To drive the reaction to completion, an excess amount of zinc salt can be added to the reaction mixture containing potassium ions, which precipitates the hexacyanoferrate(II) ion quantitatively:
The precipitation occurs in slightly acidic medium, thus avoids the problem of decomposition of iodide and thiosulfate in strongly acidic medium, and the hexacyanoferrate(III) can be determined by iodometry as usual. | 3 | Analytical Chemistry |
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