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Protodeboronation is a chemical reaction involving the protonolysis of a boronic acid (or other organoborane compound) in which a carbon-boron bond is broken and replaced with a carbon-hydrogen bond. Protodeboronation is a well-known undesired side reaction, and frequently associated with metal-catalysed coupling reactions that utilise boronic acids (see Suzuki reaction). For a given boronic acid, the propensity to undergo protodeboronation is highly variable and dependent on various factors, such as the reaction conditions employed and the organic substituent of the boronic acid: | 0 | Organic Chemistry |
A stink bomb, sometimes called a stinkpot, is a device designed to create an unpleasant smell. They range in effectiveness from being used as simple pranks to military grade malodorants or riot control chemical agents. | 1 | Biochemistry |
Cohen et al. found that of a pair of co-expressed genes only one promoter has an Upstream Activating Sequence (UAS) associated with that expression pattern. They suggested that UASs can activate genes that are not in immediate adjacency to them. This explanation could explain the co-expression of small clusters, but many clusters contain to many genes to be regulated by a single UAS.
Chromatin changes are a plausible explanation for the co-regulation seen in clusters. Chromatin consists of the DNA strand and histones that are attached to the DNA. Regions were chromatin is very tightly packed are called heterochromatin. Heterochromatin consists very often of remains of viral genomes, transposons and other junk DNA. Because of tight packing the DNA is almost unreachable for the transcript machinery, covering deleterious DNA with proteins is the way in which the cell can protect itself. Chromatin which consists of functional genes is often an open structure were the DNA is accessible. However, most of the genes are not needed to be expressed all the time.
DNA with genes that aren't needed can be covered with histones. When a gene must be expressed special proteins can alter the chemical that are attached to the histones (histone modifications) that cause the histones to open the structure. When the chromatin of one gene is opened, the chromatin of the adjacent genes is also until this modification meets a boundary element. In that way genes is close proximity are expressed on the same time. So, genes are clustered in “expression hubs”. In comparison with this model Gilbert et al. (2004) showed that RIDGEs are mostly present in open chromatin structures.
However Johnidis et al. (2005) have shown that genes in the same cluster can be very differently expressed. How eukaryotic gene regulation, and associated chromatin changes, precisely works is still very unclear and there is no consensus about it. In order to get a clear picture about the mechanism of gene clusters first the workings chromatin and gene regulation needs to be illuminated.
Furthermore, most papers that identified clusters of co-regulated genes focused on transcription levels whereas few focused on clusters regulated by the same transcription-factors. Johnides et al. discovered strange phenomena when they did. | 1 | Biochemistry |
The iron pillar of Delhi is a structure high with a diameter that was constructed by Chandragupta II (reigned c. 375–415 CE), and now stands in the Qutub complex at Mehrauli in Delhi, India. The metals used in its construction have a rust-resistant composition. The pillar weighs more than six tonnes and is thought to have been erected elsewhere, perhaps outside the Udayagiri Caves, and moved to its present location by Anangpal Tomar in the 11th century. | 8 | Metallurgy |
Red mud is composed of a mixture of solid and metallic oxides. The red colour arises from iron oxides, which can comprise up to 60% of the mass. The mud is highly basic with a pH ranging from 10 to 13. In addition to iron, the other dominant components include silica, unleached residual aluminium compounds, and titanium oxide.
The main constituents of the residue after the extraction of the aluminium component are insoluble metallic oxides. The percentage of these oxides produced by a particular alumina refinery will depend on the quality and nature of the bauxite ore and the extraction conditions. The table below shows the composition ranges for common chemical constituents, but the values vary widely:
Mineralogically expressed the components present are:
In general, the composition of the residue reflects that of the non-aluminium components, with the exception of part of the silicon component: crystalline silica (quartz) will not react but some of the silica present, often termed, reactive silica, will react under the extraction conditions and form sodium aluminium silicate as well as other related compounds. | 2 | Environmental Chemistry |
The cyanohydrins are a special class of nitriles. Classically they result from the addition of alkali metal cyanides to aldehydes in the cyanohydrin reaction. Because of the polarity of the organic carbonyl, this reaction requires no catalyst, unlike the hydrocyanation of alkenes. O-Silyl cyanohydrins are generated by the addition trimethylsilyl cyanide in the presence of a catalyst (silylcyanation). Cyanohydrins are also prepared by transcyanohydrin reactions starting, for example, with acetone cyanohydrin as a source of HCN. | 0 | Organic Chemistry |
Geological samples, such as drill cores, can be rapidly mapped for nearly all minerals of commercial interest with hyperspectral imaging. Fusion of SWIR and LWIR spectral imaging is standard for the detection of minerals in the feldspar, silica, calcite, garnet, and olivine groups, as these minerals have their most distinctive and strongest spectral signature in the LWIR regions.
Hyperspectral remote sensing of minerals is well developed. Many minerals can be identified from airborne images, and their relation to the presence of valuable minerals, such as gold and diamonds, is well understood. Currently, progress is towards understanding the relationship between oil and gas leakages from pipelines and natural wells, and their effects on the vegetation and the spectral signatures. Recent work includes the PhD dissertations of Werff and Noomen. | 7 | Physical Chemistry |
* Iodine heptafluoride (IF) with 7 bonding groups
* Rhenium heptafluoride (ReF)
* Peroxo chromium(IV) complexes, e.g. [Cr(O)(NH)] where the peroxo groups occupy four of the planar positions.
* and | 4 | Stereochemistry |
Founded as the American Institute of Mining Engineers (AIME), the institute had a membership at the beginning of 1915 of over 5,000, made up of honorary, elected, and associate members. The annual meeting of the institute was held in February, with other meetings during the year as authorized by the council. The institute published three volumes of Transactions annually and a monthly Bulletin which appeared on the first of each month. The headquarters of the institute was in the Engineering Building in New York City.
Following creation of the Petroleum Division in 1922, the Iron and Steel Division in 1928 and the Institute of Metals Division in 1933 the name of the society was changed in 1957 to the American Institute of Mining, Metallurgical and Petroleum Engineers. Three of the current member societies were then created from the divisions, increasing to four in 1974 when the Iron and Steel Society (ISS) was formed. In 2004 ISS merged with the Association of Iron and Steel Engineers (AISE) to form the Association for Iron and Steel Technology (AIST) whilst remaining a member society of AIME. | 8 | Metallurgy |
Strong light causes the reduction of the plastoquinone pool, which leads to protonation and double reduction (and double protonation) of the Q electron acceptor of Photosystem II. The protonated and double-reduced forms of Q do not function in electron transport. Furthermore, charge recombination reactions in inhibited Photosystem II are expected to lead to the triplet state of the primary donor (P) more probably than same reactions in active PSII. Triplet P may react with oxygen to produce harmful singlet oxygen. | 5 | Photochemistry |
A reduced form of phenolphthalein, phenolphthalin, which is colorless, is used in a test to identify substances thought to contain blood, commonly known as the Kastle–Meyer test. A dry sample is collected with a swab or filter paper. A few drops of alcohol, then a few drops of phenolphthalin, and finally a few drops of hydrogen peroxide are dripped onto the sample. If the sample contains hemoglobin, it will turn pink immediately upon addition of the peroxide, because of the generation of phenolphthalein. A positive test indicates the sample contains hemoglobin and, therefore, is likely blood. A false positive can result from the presence of substances with catalytic activity similar to hemoglobin. This test is not destructive to the sample; it can be kept and used in further tests. This test has the same reaction with blood from any animal whose blood contains hemoglobin, including almost all vertebrates; further testing would be required to determine whether it originated from a human. | 3 | Analytical Chemistry |
The study of TOR originated in the 1960s with an expedition to Easter Island (known by the island inhabitants as Rapa Nui), with the goal of identifying natural products from plants and soil with possible therapeutic potential. In 1972, Suren Sehgal identified a small molecule, from a soil bacterium Streptomyces hygroscopicus, that he purified and initially reported to possess potent antifungal activity. He appropriately named it rapamycin, noting its original source and activity. However, early testing revealed that rapamycin also had potent immunosuppressive and cytostatic anti-cancer activity. Rapamycin did not initially receive significant interest from the pharmaceutical industry until the 1980s, when Wyeth-Ayerst supported Sehgals efforts to further investigate rapamycins effect on the immune system. This eventually led to its FDA approval as an immunosuppressant following kidney transplantation. However, prior to its FDA approval, how rapamycin worked remained completely unknown. | 1 | Biochemistry |
On long timescales, atmospheric concentration is determined by the balance among geochemical processes including organic carbon burial in sediments, silicate rock weathering, and volcanic degassing. The net effect of slight imbalances in the carbon cycle over tens to hundreds of millions of years has been to reduce atmospheric . On a timescale of billions of years, such downward trend appears bound to continue indefinitely as occasional massive historical releases of buried carbon due to volcanism will become less frequent (as earth mantle cooling and progressive exhaustion of internal radioactive heat proceed further). The rates of these processes are extremely slow; hence they are of no relevance to the atmospheric concentration over the next hundreds or thousands of years. | 2 | Environmental Chemistry |
Escitalopram, similarly to other SSRIs, may increase bleed risk with NSAIDs (ibuprofen, naproxen, mefenamic acid), antiplatelet drugs, anticoagulants, omega-3 fatty acids, vitamin E, and garlic supplements due to escitaloprams inhibitory effects on platelet aggregation via blocking serotonin transporters on platelets. Escitalopram inhibits CYP2D6, and hence may increase plasma levels of a number of CYP2D6 substrates such as aripiprazole, risperidone, tramadol, codeine, etc. As escitalopram is only a weak inhibitor of CYP2D6, analgesia from tramadol may not be affected. Escitalopram should be taken with caution when using St. Johns wort, ginseng, dextromethorphan (DXM), linezolid, tramadol, and other serotonergic drugs due to the risk of serotonin syndrome. Exposure to escitalopram is increased moderately, by about 50%, when it is taken with omeprazole. The authors of this study suggested that this increase is unlikely to be of clinical concern.
Bupropion has been found to significantly increase citalopram plasma concentration and systemic exposure; the interaction with escitalopram had not been studied, but some monographs warned of the potential interaction.
Escitalopram can also prolong the QT interval, and hence it is not recommended in patients that are concurrently on other medications that also have the ability to prolong the QT interval. These drugs include antiarrhythmics, antipsychotics, tricyclic antidepressants, some antihistamines (astemizole, mizolastine), macrolide and fluoroquinolone antibiotics, some 5-HT receptor antagonists (except palonosetron), and some antiretrovirals (ritonavir, saquinavir, lopinavir). As an SSRI, escitalopram should not be given concurrently with MAOIs. | 4 | Stereochemistry |
Rydberg ionization spectroscopy is a spectroscopy technique in which multiple photons are absorbed by an atom causing the removal of an electron to form an ion. | 7 | Physical Chemistry |
Visual phototransduction is the sensory transduction process of the visual system by which light is detected by photoreceptor cells (rods and cones) in the vertebrate retina. A photon is absorbed by a retinal chromophore (each bound to an opsin), which initiates a signal cascade through several intermediate cells, then through the retinal ganglion cells (RGCs) comprising the optic nerve. | 1 | Biochemistry |
In biochemistry, a metabolon is a temporary structural-functional complex formed between sequential enzymes of a metabolic pathway, held together both by non-covalent interactions and by structural elements of the cell, such as integral membrane proteins and proteins of the cytoskeleton.
The formation of metabolons allows the intermediate product from one enzyme to be passed (channelling) directly into the active site of the next consecutive enzyme of the metabolic pathway. The citric acid cycle is an example of a metabolon that facilitates substrate channeling. Another example is the dhurrin synthesis pathway in sorghum, in which the enzymes assemble as a metabolon in lipid membranes. During the functioning of metabolons, the amount of water needed to hydrate the enzymes is reduced and enzyme activity is increased. | 1 | Biochemistry |
The molybdovanadate reagent is a solution containing both the molybdate and vanadate ions. It is commonly used in the determination of phosphate ion content. The reagent used is ammonium molybdovanadate with the addition of 70% perchloric acid (sulfuric acid is also known to be used). It is used for purposes such as the analysis of wine, canned fruits and other fruit-based products such as jams and syrups. | 3 | Analytical Chemistry |
When molten, the salt sodium chloride can be electrolyzed to yield metallic sodium and gaseous chlorine. Industrially this process takes place in a special cell named Downs cell. The cell is connected to an electrical power supply, allowing electrons to migrate from the power supply to the electrolytic cell.
Reactions that take place in a Downs cell are the following:
:Anode (oxidation): 2 Cl → Cl + 2 e
:Cathode (reduction): 2 Na + 2 e → 2 Na
:Overall reaction: 2 Na + 2 Cl → 2 Na + Cl
This process can yield large amounts of metallic sodium and gaseous chlorine, and is widely used in mineral dressing and metallurgy industries.
The emf for this process is approximately −4 V indicating a (very) non-spontaneous process. In order for this reaction to occur the power supply should provide at least a potential difference of 4 V. However, larger voltages must be used for this reaction to occur at a high rate. | 7 | Physical Chemistry |
Cryoneurolysis, also referred to as cryoanalgesia, is a medical procedure that temporarily blocks nerve conduction along peripheral nerve pathways. The procedure, which inserts a small probe to freeze the target nerve, can facilitate complete regeneration of the structure and function of the affected nerve. Cryoneurolysis has been used to treat a variety of painful conditions. | 1 | Biochemistry |
In electrochemistry, cell notation or cell representation is a shorthand method of expressing a reaction in an electrochemical cell.
In cell notation, the two half-cells are described by writing the formula of each individual chemical species involved in the redox reaction across the cell, with all other common ions and inert substances being ignored. Each species is separated by a vertical bar, with the species in each half-cell grouped together, and the two half-cells separated by two bars or slashes representing a salt bridge (which generally contains an electrolyte solution such as potassium nitrate or sodium chloride that is left unwritten). It is common practice to represent the anode to the left of the double bar and the cathode to the right, and to put aqueous species closest to the double bar.
Cell notation may be used to represent other information that is not essential to the reaction but still useful to include. For example, the electrode's species may be marked by a degree symbol. The standard abbreviations for the phases of each species are often included as subscripts, in a manner similar to the notation in chemical equations. Sometimes, the initial concentrations of dissolved species may be written to the right in parentheses (see example below).
Some examples of this notation are:
This means that the left electrode (anode) is made of zinc, while the other one (right, cathode) is composed of a silver wire covered by a silver chloride layer which is not soluble. Both of the electrodes are immersed into aqueous media where zinc and chloride ions are present.
This cell is very famous: the Daniell cell. If the electrodes are connected, a spontaneous reaction takes place. Zinc is oxidized, and copper ions are reduced.
Sometimes the state of each species into the cell is written. For example, in the zinc cell (shown above), we can write that zinc, silver and silver chloride are solids, while zinc cation and chloride anion are in aqueous medium. So, the new notation will be:
It is possible to express the ion concentration too. For example, in the Galvanic cell:
In this case, all ions (sulfate, zinc and copper) are in a concentration equal to 1 mol/L. | 7 | Physical Chemistry |
During extraction of the oil from oil sand, tailings consisting of water, silt, clays and other solvents are also created. This solid will become mature fine tailings by gravity. Foght et al (1985) estimated that there are 10 anaerobic heterotrophs and 10 sulfate-reducing prokaryotes per milliliter in the tailings pond, based on conventional most probable number methods. Foght set up an experiment with two tailings ponds and an analysis of the archaea, bacteria, and the gas released from tailings ponds showed that those were methanogens. As the depth increased, the moles of CH released actually decreased.
Siddique (2006, 2007) states that methanogens in the tailings pond live and reproduce by anaerobic degradation, which will lower the molecular weight from naphtha to aliphatic, aromatic hydrocarbons, carbon dioxide and methane. Those archaea and bacteria can degrade the naphtha, which was considered as waste during the procedure of refining oil. Both of those degraded products are useful. Aliphatic, aromatic hydrocarbons and methane can be used as fuel in the humans' daily lives. In other words, these methanogens improve the coefficient of utilization. Moreover, these methanogens change the structure of the tailings pond and help the pore water efflux to be reused for processing oil sands. Because the archaea and bacteria metabolize and release bubbles within the tailings, the pore water can go through the soil easily. Since they accelerate the densification of mature fine tailings, the tailings ponds are enabled to settle the solids more quickly so that the tailings can be reclaimed earlier. Moreover, the water released from the tailings can be used in the procedure of refining oil. Reducing the demand of water can also protect the environment from drought. | 8 | Metallurgy |
Plant breeders emphasize selection and development of disease-resistant plant lines. Plant diseases can also be partially controlled by use of pesticides and by cultivation practices such as crop rotation, tillage, planting density, disease-free seeds and cleaning of equipment, but plant varieties with inherent (genetically determined) disease resistance are generally preferred. Breeding for disease resistance began when plants were first domesticated. Breeding efforts continue because pathogen populations are under selection pressure and evolve increased virulence, pathogens move (or are moved) to new areas, changing cultivation practices or climate favor some pathogens and can reduce resistance efficacy, and plant breeding for other traits can disrupt prior resistance. A plant line with acceptable resistance against one pathogen may lack resistance against others.
Breeding for resistance typically includes:
* Identification of plants that may be less desirable in other ways, but which carry a useful disease resistance trait, including wild plant lines that often express enhanced resistance.
* Crossing of a desirable but disease-susceptible variety to a plant that is a source of resistance.
* Growth of breeding candidates in a disease-conducive setting, possibly including pathogen inoculation. Attention must be paid to the specific pathogen isolates, to address variability within a single pathogen species.
* Selection of disease-resistant individuals that retain other desirable traits such as yield, quality and including other disease resistance traits.
Resistance is termed durable if it continues to be effective over multiple years of widespread use as pathogen populations evolve. "Vertical resistance" is specific to certain races or strains of a pathogen species, is often controlled by single R genes and can be less durable. Horizontal or broad-spectrum resistance against an entire pathogen species is often only incompletely effective, but more durable, and is often controlled by many genes that segregate in breeding populations. Durability of resistance is important even when future improved varieties are expected to be on the way: The average time from human recognition of a new fungal disease threat to the release of a resistant crop for that pathogen is at least twelve years.
Crops such as potato, apple, banana and sugarcane are often propagated by vegetative reproduction to preserve highly desirable plant varieties, because for these species, outcrossing seriously disrupts the preferred traits. See also asexual propagation. Vegetatively propagated crops may be among the best targets for resistance improvement by the biotechnology method of plant transformation to manage genes that affect disease resistance.
Scientific breeding for disease resistance originated with Sir Rowland Biffen, who identified a single recessive gene for resistance to wheat yellow rust. Nearly every crop was then bred to include disease resistance (R) genes, many by introgression from compatible wild relatives. | 1 | Biochemistry |
Given that direct reduction is a chemical exchange between gas and solid, the fluidization of ore by reducing gases is an attractive line of research. However, the changing nature of the constituents, combined with the high temperature and the difficulty of controlling the fluidization phenomenon, make its adoption singularly difficult.
Many processes have been developed on this principle. Some have been technical failures, such as the HIB (a single plant commissioned in 1972, converted to the Midrex in 1981) or economic failures, such as the FIOR process (a single plant commissioned in 1976, mothballed since 2001, the forerunner of FINMET).
Developed in 1991 from the FIOR process, the FINMET process seems more mature, but its expansion has not materialized (two plants were built, and only one was in operation as of 2014). The CIRCORED process, also recent, is similarly stagnant (just one plant built, commissioned in 1999, mothballed in 2012), despite its adaptability to coal (CIRCOFER process, no industrial production). | 8 | Metallurgy |
Each article at WikiPathways is dedicated to a particular pathway. Many types of molecular pathways are covered, including metabolic, signaling, regulatory, etc. and the supported species include human, mouse, zebrafish, fruit fly, C. elegans, yeast, rice and arabidopsis, as well as bacteria and plant species. Using a search feature, one can locate a particular pathway by name, by the genes and proteins it contains, or by the text displayed in its description. The pathway collection can also be browsed with combinations of species names and ontology-based categories.
In addition to the pathway diagram, each pathway page also includes a description, bibliography, pathway version history and list of component genes and proteins with linkouts to public resources. For individual pathway nodes, users can access a list of other pathways with that node. Pathway changes can be monitored by displaying previous revisions or by viewing differences between specific revisions. Using the pathway history one can also revert to a previous revision of a pathway.
Pathways can also be tagged with ontology terms from three major BioPortal ontologies (Pathway, Disease and Cell Type).
The pathway content at WikiPathways is freely available for download in several data and image formats. WikiPathways is completely open access and open source. All content is available under [http://www.wikipathways.org/index.php/WikiPathways:License_Terms Creative Commons 0]. All source code for WikiPathways and the PathVisio editor is available under the [http://www.apache.org/licenses/ Apache License, Version 2.0]. | 1 | Biochemistry |
Although the substrate scope of PLE is broad, enantioselectivity varies as a function of the structure of the substrate. This section describes substrates that are hydrolyzed by PLE with the highest enantioselectivity, as well as sensitive substrates that may be hydrolyzed to achiral carboxylic acids in high yield without side reactions.
Glutarates were the first substrates to be hydrolyzed with PLE in high enantioselectivity. Although yields are moderate, enantioselectivity is extremely high.
3-Alkyl glutarates with small alkyl substituents are hydrolyzed to the (R)-monoester; however, when a large alkyl substituent is present, the (S)-monoester forms. This switch in enantioselectivity is accurately predicted by the active site model given above.
An opposite trend is observed in desymmetrizing hydrolyses of 2-methyl malonates, which afford the (S) enantiomer when the other substituent on C-2 is small, and the (R) enantiomer when the other C-2 substituent is large.
A number of meso diesters other than the substrates described above may be hydrolyzed by PLE with high enantioselectivity. Cyclic meso diesters tend to be hydrolyzed more selectively than acyclic diesters. The predominant enantiomer of product depends on ring size.
7-Oxabicyclo[2.2.1]heptane-2,3-dicarboxylates are an interesting class of diesters that are hydrolyzed by PLE with high enantioselectivity. These substrates have been used for the enantioselective construction of biologically relevant sugars (see Synthetic Applications below).
Racemic mixtures of all of the substrates described above, as well as additional chiral diesters (such as the epoxy ester in equation (8)), may be resolved using PLE for kinetic resolution. A significant disadvantage of kinetic resolution is a maximum yield of hydrolyzed product of 50%. However, if rapid racemization is occurring alongside hydrolysis (an example of dynamic kinetic resolution), a maximum yield of 100% is possible.
Esterase enzymes may also be used for hydrolysis of base-sensitive monoesters. PLE has been applied to the synthesis of prostaglandins for the selective hydrolysis of the ester without destruction of the β-hydroxy ketone moiety. | 0 | Organic Chemistry |
The modest acidity of carbons adjacent to the sulfonyl group has made sulfones useful for organic synthesis. Upon removal of the sulfonyl group with desulfonylation or reductive elimination, the net result is the formation of a carbon-carbon bond single or double bond between two unfunctionalized carbons, a ubiquitous motif in synthetic targets. In a synthesis of (–)-anthoplalone, Julia olefination was used to establish the (E)-alkene in the target.
Reductive desulfonylation is employed when the establishment of a carbon-carbon single bond is the goal. In a synthesis of (+)-chatancin, alkylation of an α-sulfonyl carbanion followed by desulfonylation established a key allylic carbon-carbon bond. | 0 | Organic Chemistry |
The surface tension (γ) of a material is directly related to its intramolecular and intermolecular forces. The stronger the force, the greater the surface tension. This can be modeled by an equation:
Where ΔU is the energy of vaporization, N is the Avogadro constant, and a is the surface area per molecule. This equation also implies that the energy of vaporization affects surface tension. It is known that the stronger the force, the higher the energy of vaporization. Surface tension can then be used to calculate surface energy (u). An equation describing this property is:
Where T is temperature and the system is at constant pressure and area. Specifically for hydrogels, the free surface energy can be predicted using the Flory–Huggins free energy function for the hydrogels.
For hydrogels, surface tension plays a role in several additional characteristics including swelling ratio and stabilization. | 7 | Physical Chemistry |
If the forces that bind A and B together are weak, ie for all r except very small r, . The reaction rate 9 simplifies even further to
This equation is true for a very large proportion of industrially relevant reactions in solution. | 7 | Physical Chemistry |
A dearomatization reaction is an organic reaction in which the reactants are arenes and the products permanently lose their aromaticity. It is of some importance in synthetic organic chemistry for the organic synthesis of new building blocks and in total synthesis. Types of carbocyclic arene dearomization include hydrogenative (Birch reduction), alkylative, photochemical, thermal, oxidative, transition metal-assisted and enzymatic. | 0 | Organic Chemistry |
The three-dimensional protein structure of OCP (in the OCP form) was solved in 2003, before its photoprotective role had been defined. The 35 kDa protein contains two structural domains: an all-α-helical N-terminal domain (NTD) consisting of two interleaved 4-helix bundles, and a mixed α/β C-terminal domain (CTD). The two domains are connected by an extended linker. In OCP, the carotenoid spans both domains, which are tightly associated in this form of protein. In 2013 Kerfeld and co-workers showed that the NTD is the effector (quencher) domain of the protein while the CTD plays a regulatory role. | 5 | Photochemistry |
With hexagonal and rhombohedral lattice systems, it is possible to use the Bravais–Miller system, which uses four indices (h k i ℓ) that obey the constraint
: h + k + i = 0.
Here h, k and ℓ are identical to the corresponding Miller indices, and i is a redundant index.
This four-index scheme for labeling planes in a hexagonal lattice makes permutation symmetries apparent. For example, the similarity between (110) ≡ (110) and (10) ≡ (110) is more obvious when the redundant index is shown.
In the figure at right, the (001) plane has a 3-fold symmetry: it remains unchanged by a rotation of 1/3 (2/3 rad, 120°). The [100], [010] and the [0] directions are really similar. If S is the intercept of the plane with the [0] axis, then
: i = 1/S.
There are also ad hoc schemes (e.g. in the transmission electron microscopy literature) for indexing hexagonal lattice vectors (rather than reciprocal lattice vectors or planes) with four indices. However they don't operate by similarly adding a redundant index to the regular three-index set.
For example, the reciprocal lattice vector (hkℓ) as suggested above can be written in terms of reciprocal lattice vectors as . For hexagonal crystals this may be expressed in terms of direct-lattice basis-vectors a, a and a as
Hence zone indices of the direction perpendicular to plane (hkℓ) are, in suitably normalized triplet form, simply . When four indices are used for the zone normal to plane (hkℓ), however, the literature often uses instead. Thus as you can see, four-index zone indices in square or angle brackets sometimes mix a single direct-lattice index on the right with reciprocal-lattice indices (normally in round or curly brackets) on the left.
And, note that for hexagonal interplanar distances, they take the form | 3 | Analytical Chemistry |
In the 1980s, Lehn observed that Co(I) species were produced in solutions containing CoCl, 2,2'-bipyridine (bpy), a tertiary amine, and a Ru(bpy)Cl photosensitizer. The high affinity of CO to cobalt centers led both him and Ziessel to study cobalt centers as electrocatalysts for reduction. In 1982, they reported CO and H as products from the irradiation of a solution containing 700ml of CO, Ru(bpy) and Co(bpy).
Since the work of Lehn and Ziessel, several catalysts have been paired with the Ru(bpy) photosensitizer.
When paired with methylviologen, cobalt, and nickel-based catalysts, carbon monoxide and hydrogen gas are observed as products.
Paired with rhenium catalysts, carbon monoxide is observed as the major product, and with ruthenium catalysts formic acid is observed. Some product selection is attainable through tuning of the reaction environment. Other photosensitizers have also been employed as catalysts. They include FeTPP (TPP=5,10,15,20-tetraphenyl-21H,23H-porphine) and CoTPP, both of which produce CO while the latter produces formate also. Non-metal photocatalysts include pyridine and N-heterocyclic carbenes.
In August 2022, it was developed a photocatalyst based on lead–sulfur (Pb–S) bonds, with promising results. | 5 | Photochemistry |
Common effects (1–10% incidence) include:
* Abnormal dreams
* Anisocoria
* Anorgasmia
* Anxiety
* Arthralgia (joint pain)
* Constipation
* Decreased or increased appetite
* Diarrhea
* Dilated pupils
* Dizziness
* Dry mouth
* Excessive sweating
* Fatigue
* Impotence (erectile dysfunction)
* Libido changes
* Myalgia (muscular aches and pains)
* Paraesthesia (abnormal skin sensation)
* Pyrexia (fever)
* Restlessness
* Sinusitis (nasal congestion)
* Tremor
* Vomiting
* Yawning | 4 | Stereochemistry |
The previous discussion focused on single aerosol particles. In contrast, aerosol dynamics explains the evolution of complete aerosol populations. The concentrations of particles will change over time as a result of many processes. External processes that move particles outside a volume of gas under study include diffusion, gravitational settling, and electric charges and other external forces that cause particle migration. A second set of processes internal to a given volume of gas include particle formation (nucleation), evaporation, chemical reaction, and coagulation.
A differential equation called the Aerosol General Dynamic Equation (GDE) characterizes the evolution of the number density of particles in an aerosol due to these processes.
Change in time = Convective transport + brownian diffusion + gas-particle interactions + coagulation + migration by external forces
Where:
: is number density of particles of size category
: is the particle velocity
: is the particle Stokes-Einstein diffusivity
: is the particle velocity associated with an external force | 7 | Physical Chemistry |
The body's acid–base balance is tightly regulated. Several buffering agents exist which reversibly bind hydrogen ions and impede any change in pH. Extracellular buffers include bicarbonate and ammonia, while proteins and phosphate act as intracellular buffers. The bicarbonate buffering system is especially key, as carbon dioxide (CO) can be shifted through carbonic acid (HCO) to hydrogen ions and bicarbonate (HCO) as shown below.
Acid–base imbalances that overcome the buffer system can be compensated in the short term by changing the rate of ventilation. This alters the concentration of carbon dioxide in the blood, shifting the above reaction according to Le Chateliers principle, which in turn alters the pH. For instance, if the blood pH drops too low (acidemia), the body will compensate by increasing breathing, expelling CO, and shifting the reaction above to the right such that fewer hydrogen ions are free–thus the pH will rise back to normal. For alkalemia', the opposite occurs.
The kidneys are slower to compensate, but renal physiology has several powerful mechanisms to control pH by the excretion of excess acid or base. In responses to acidosis, tubular cells reabsorb more bicarbonate from the tubular fluid, collecting duct cells secrete more hydrogen and generate more bicarbonate, and ammoniagenesis leads to increased formation of the NH buffer. In responses to alkalosis, the kidney may excrete more bicarbonate by decreasing hydrogen ion secretion from the tubular epithelial cells, and lowering rates of glutamine metabolism and ammonia excretion. | 7 | Physical Chemistry |
Until 1980, laser-heated crystal growth used only two laser beams focused over the source material. This condition generated a high radial thermal gradient in the molten zone, making the process unstable. Increasing the number of beams to four did not solve the problem, although it improved the growth process.
An improvement to the laser-heated crystal growth technique was made by Fejer et al., who incorporated a special optical component known as a reflaxicon, consisting of an inner cone surrounded by a larger coaxial cone section, both with reflecting surfaces. This optical element converts the cylindrical laser beam into a larger diameter hollow cylinder surface. This optical component allows radial distribution of the laser energy over the molten zone, reducing radial thermal gradients. The axial temperature gradient in this technique can go as high as 10000 °C/cm, which is very high when compared to traditional crystal growth techniques (10–100 °C/cm). | 3 | Analytical Chemistry |
RNAs are a type of large biological molecules, whose individual building blocks are called nucleotides. The name poly(A) tail (for polyadenylic acid tail) reflects the way RNA nucleotides are abbreviated, with a letter for the base the nucleotide contains (A for adenine, C for cytosine, G for guanine and U for uracil). RNAs are produced (transcribed) from a DNA template. By convention, RNA sequences are written in a 5′ to 3′ direction. The 5′ end is the part of the RNA molecule that is transcribed first, and the 3′ end is transcribed last. The 3′ end is also where the poly(A) tail is found on polyadenylated RNAs.
Messenger RNA (mRNA) is RNA that has a coding region that acts as a template for protein synthesis (translation). The rest of the mRNA, the untranslated regions, tune how active the mRNA is. There are also many RNAs that are not translated, called non-coding RNAs. Like the untranslated regions, many of these non-coding RNAs have regulatory roles. | 1 | Biochemistry |
NAPCO began developing composite cow breeds in 1982 when they created the Alexandria composite by breeding Braham Bulls and Shorthorn cow herds. The Alexandria composite is a species of cow that is specific to the NAPCO. The composite was developed at NAPCOs Alexandria station in the Northern Territory. The Alexandria station possess a land mass of 1,641,416 hectares which are home to some 80,000 of the companys cattle. It exhibits features such as a stronger carcass yield, reduced fat cover, improved temperament and environmental adaptation, as well as improved fertility. The Barkalay Tableland in Australias Northern Rangeland industry is home to 3,000 Alexandria composites. In 1995 NAPCO also developed the Kynuna composite which is a product of the remaining Shorthorn Herd that were bread with Braham Bulls to produce the Alexandria composite. The Boomarra station in Queensland is the breeding headquarters for the companys Kynuna composite. It is currently in possession of 10,000 individual cows which NAPCO distributes amongst its other properties. The development of the Kynuna composite also utilised Tuli and Red Angus cows, breeding them with Shorthorn species. The composites are closely monitored according to three particular traits; reproductive rates, pasture and feedlot growth. The company also partakes in a carcass assessment which draws upon data extracted from analysing feedlot trials and the specie's overall climate durability. Female Kynunas are culled if they fall out of sync with regular times for calving, and therefore are without calves for an extended period of time. Bulls are also closely monitored, with particular attention given to testicle size, physical structure, feet composition and growth which is based on a predominantly grass based diet. | 2 | Environmental Chemistry |
An alternative approach for applying the Hellmann–Feynman theorem is to promote a fixed or discrete parameter which appears in a Hamiltonian to be a continuous variable solely for the mathematical purpose of taking a derivative. Possible parameters are physical constants or discrete quantum numbers. As an example, the radial Schrödinger equation for a hydrogen-like atom is
which depends upon the discrete azimuthal quantum number . Promoting to be a continuous parameter allows for the derivative of the Hamiltonian to be taken:
The Hellmann–Feynman theorem then allows for the determination of the expectation value of for hydrogen-like atoms:
In order to compute the energy derivative, the way depends on has to be known. These quantum numbers are usually independent, but here the solutions must be varied so as to keep the number of nodes in the wavefunction fixed. The number of nodes is , so . | 6 | Supramolecular Chemistry |
The intracellular life of plant viruses in hosts is still understudied especially the earliest stages of infection. Many membranous structures which viruses induce plant cells to produce are motile, often being used to traffic new virions within the producing cell and into their neighbors. Viruses also induce various changes to plants own intracellular membranes. The work of Perera et al. 2012 in mosquito virus infection and various others studying yeast models of plant viruses find this to be due to changes in homeostasis of the lipids that compose their' intracellular membranes, including increasing synthesis. These comparable lipid alterations inform our expectations and research directions for the lesser understood area of plant viruses. | 1 | Biochemistry |
Oxyhydrogen is a mixture of hydrogen (H) and oxygen (O) gases. This gaseous mixture is used for torches to process refractory materials and was the first
gaseous mixture used for welding. Theoretically, a ratio of 2:1 hydrogen:oxygen is enough to achieve maximum efficiency; in practice a ratio 4:1 or 5:1 is needed to avoid an oxidizing flame.
This mixture may also be referred to as (Scandinavian and German ; ), although some authors define knallgas to be a generic term for the mixture of fuel with the precise amount of oxygen required for complete combustion, thus 2:1 oxyhydrogen would be called "hydrogen-knallgas".
"Brown's gas" and HHO are terms for oxyhydrogen originating in pseudoscience, although is preferred due to meaning . | 7 | Physical Chemistry |
Carboxylic acids are readily identified as such by infrared spectroscopy. They exhibit a sharp band associated with vibration of the C=O carbonyl bond (ν) between 1680 and 1725 cm. A characteristic ν band appears as a broad peak in the 2500 to 3000 cm region. By H NMR spectrometry, the hydroxyl hydrogen appears in the 10–13 ppm region, although it is often either broadened or not observed owing to exchange with traces of water. | 0 | Organic Chemistry |
The efficiency of conversion of ingested food to unit of body substance (ECI, also termed "growth efficiency") is an index measure of food fuel efficiency in animals. The ECI is a rough scale of how much of the food ingested is converted into growth in the animal's mass. It can be used to compare the growth efficiency as measured by the weight gain of different animals from consuming a given quantity of food relative to its size.
The ECI effectively represents efficiencies of both digestion (approximate digestibility or AD) and metabolic efficiency, or how well digested food is converted to mass (efficiency of conversion of digested food or ECD). The formula for the efficiency of food fuel is thus:
These concepts are also very closely related to the feed conversion ratio (FCR) and feed efficiency. | 1 | Biochemistry |
RNA polymerase II (RNAP II and Pol II) is a multiprotein complex that transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. It is one of the three RNAP enzymes found in the nucleus of eukaryotic cells. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to upstream gene promoters and begin transcription. | 1 | Biochemistry |
Over the past two decades faradaic impedance has emerged as the basis for an important technique in a form of spectral analysis applicable to a wide variety of materials. This technique depends on the capacitive component of faradaic impedance. Whereas the resistive component is independent of frequency and can be measured with DC, the impedance of the capacitive component is infinite at DC (zero admittance) and decreases inversely with frequency of an applied AC signal. Varying this frequency while monitoring the faradaic impedance provides a method of spectral analysis of the composition of the materials at the electrode-electrolyte interface, in particular their electric dipole moment in the role of dielectric of a capacitor. The technique yields insights into battery design, the performance of novel fuel cell designs, biomolecular interactions, etc. | 7 | Physical Chemistry |
In chemistry, a nitrene or imene () is the nitrogen analogue of a carbene. The nitrogen atom is uncharged and univalent, so it has only 6 electrons in its valence level—two covalent bonded and four non-bonded electrons. It is therefore considered an electrophile due to the unsatisfied octet. A nitrene is a reactive intermediate and is involved in many chemical reactions. The simplest nitrene, HN, is called imidogen, and that term is sometimes used as a synonym for the nitrene class. | 0 | Organic Chemistry |
A transcritical cycle is a closed thermodynamic cycle where the working fluid goes through both subcritical and supercritical states. In particular, for power cycles the working fluid is kept in the liquid region during the compression phase and in vapour and/or supercritical conditions during the expansion phase. The ultrasupercritical steam Rankine cycle represents a widespread transcritical cycle in the electricity generation field from fossil fuels, where water is used as working fluid. Other typical applications of transcritical cycles to the purpose of power generation are represented by organic Rankine cycles, which are especially suitable to exploit low temperature heat sources, such as geothermal energy, heat recovery applications or waste to energy plants. With respect to subcritical cycles, the transcritical cycle exploits by definition higher pressure ratios, a feature that ultimately yields higher efficiencies for the majority of the working fluids. Considering then also supercritical cycles as a valid alternative to the transcritical ones, the latter cycles are capable of achieving higher specific works due to the limited relative importance of the work of compression work. This evidences the extreme potential of transcritical cycles to the purpose of producing the most power (measurable in terms of the cycle specific work) with the least expenditure (measurable in terms of spent energy to compress the working fluid).
While in single level supercritical cycles both pressure levels are above the critical pressure of the working fluid, in transcritical cycles one pressure level is above the critical pressure and the other is below. In the refrigeration field carbon dioxide, CO, is increasingly considered of interest as refrigerant. | 7 | Physical Chemistry |
TaqMan probe-based assays are widely used in quantitative PCR in research and medical laboratories:
*Gene expression assays
*Pharmacogenomics
*Human Leukocyte Antigen (HLA) genotyping
*Determination of viral load in clinical specimens (HIV, Hepatitis)
*Bacterial Identification assays
*DNA quantification
*SNP genotyping
*Verification of microarray results | 1 | Biochemistry |
The optical absorption spectrum of pyridine in hexane consists of bands at the wavelengths of 195, 251, and 270 nm. With respective extinction coefficients (ε) of 7500, 2000, and 450 L·mol·cm, these bands are assigned to π → π*, π → π*, and n → π* transitions.
The H nuclear magnetic resonance (NMR) spectrum shows signals for α-(δ 8.5), γ-(δ7.5) and β-protons (δ7). By contrast, the proton signal for benzene is found at δ7.27. The larger chemical shifts of the α- and γ-protons in comparison to benzene result from the lower electron density in the α- and γ-positions, which can be derived from the resonance structures. The situation is rather similar for the C NMR spectra of pyridine and benzene: pyridine shows a triplet at δ(α-C) = 150 ppm, δ(β-C) = 124 ppm and δ(γ-C) = 136 ppm, whereas benzene has a single line at 129 ppm. All shifts are quoted for the solvent-free substances. Pyridine is conventionally detected by the gas chromatography and mass spectrometry methods. | 0 | Organic Chemistry |
Other challenges of the cyanosulfidic prebiotic synthesis approach is that the reductant, sulfide, has low solubility in water except in alkaline conditions and the main catalyst, copper, has a relatively low abundance in Earth’s crust. To address these problems, an alternative scheme for prebiotic systems chemistry called cyanosulfitic prebiotic synthesis has been proposed. These set of reactions relies on sulfite instead of sulfide, and ferrocyanide to catalyze reactions when exposed to ultraviolet light. The products of these reactions rely on similar chemistry to cyanofidic mechanisms such as reductive homologation and produce similar products such as amino acid precursors as well as sugars and hydroxy acids. Both sulfite (from sulfur dioxide released by volcanos) and ferrous iron (FeII) are hypothesized to have been present in high quantities on the early Earth, suggesting that this is potentially a much for feasible set of reactions. | 9 | Geochemistry |
Many compounds exhibit polymorphism. It has been claimed that "every compound has different polymorphic forms, and that, in general, the number of forms known for a given compound is proportional to the time and money spent in research on that compound." | 3 | Analytical Chemistry |
Considering a quasi-spherical shell subject to thermal undulations according to Langevin dynamics, one can express the time-averaged mean square amplitudes of the fluctuation modes as
where where and index the fluctuation mode corresponding to spherical harmonics <math>Y^m_n(\theta,\phi)
is the reduced membrane tension, is the spontaneous curvature and is the bending modulus, as defined by the Helfrich hamiltonian. | 7 | Physical Chemistry |
In 2020, the gas-diffusion electrocrystallization process was presented as a great EU-funded innovation by the Innovation Radar of the European Commission, for its application on the secondary recovery of platinum group metals. | 7 | Physical Chemistry |
Also known as heated persulfate, the method utilizes the same free radical formation as UV persulfate oxidation except uses heat to magnify the oxidizing power of persulfate. Chemical oxidation of carbon with a strong oxidizer, such as persulfate, is highly efficient, and unlike UV, is not susceptible to lower recoveries caused by turbidity in samples. The analysis of system blanks, necessary in all chemical procedures, is especially necessary with heated persulfate TOC methods because the method is so sensitive that reagents cannot be prepared with carbon contents low enough to not be detected. Persulfate methods are used in the analysis of wastewater, drinking water, and pharmaceutical waters. When used in conjunction with sensitive NDIR detectors heated persulfate TOC instruments readily measure TOC at single digit parts per billion (ppb) up to hundreds of parts per million (ppm) depending on sample volumes. | 3 | Analytical Chemistry |
Possibly the most common use of affinity chromatography is for the purification of recombinant proteins. Proteins with a known affinity are protein tagged in order to aid their purification. The protein may have been genetically modified so as to allow it to be selected for affinity binding; this is known as a fusion protein. Protein tags include hexahistidine (His), glutathione-S-transferase (GST), maltose binding protein (MBP), and the Colicin E7 variant CL7 tag. Histidine tags have an affinity for nickel, cobalt, zinc, copper and iron ions which have been immobilized by forming coordinate covalent bonds with a chelator incorporated in the stationary phase. For elution, an excess amount of a compound able to act as a metal ion ligand, such as imidazole, is used. GST has an affinity for glutathione which is commercially available immobilized as glutathione agarose. During elution, excess glutathione is used to displace the tagged protein. CL7 has an affinity and specificity for Immunity Protein 7 (Im7) which is commercially available immobilized as Im7 agarose resin. For elution, an active and site-specific protease is applied to the Im7 resin to release the tag-free protein. | 3 | Analytical Chemistry |
Due to differential uptake in plants as well as marine carbonates of C, it is possible to use these isotopic signatures in earth science. Biological processes preferentially take up the lower mass isotope through kinetic fractionation. In aqueous geochemistry, by analyzing the δC value of carbonaceous material found in surface and ground waters, the source of the water can be identified. This is because atmospheric, carbonate, and plant derived δC values all differ. In biology, the ratio of carbon-13 and carbon-12 isotopes in plant tissues is different depending on the type of plant photosynthesis and this can be used, for example, to determine which types of plants were consumed by animals. Greater carbon-13 concentrations indicate stomatal limitations, which can provide information on plant behaviour during drought. Tree ring analysis of carbon isotopes can be used to retrospectively understand forest photosynthesis and how it is impacted by drought.
In geology, the C/C ratio is used to identify the layer in sedimentary rock created at the time of the Permian extinction 252 Mya when the ratio changed abruptly by 1%. More information about usage of C/C ratio in science can be found in the article about isotopic signatures.
Carbon-13 has a non-zero spin quantum number of ½, and hence allows the structure of carbon-containing substances to be investigated using carbon-13 nuclear magnetic resonance.
The carbon-13 urea breath test is a safe and highly accurate diagnostic tool to detect the presence of Helicobacter pylori infection in the stomach. The urea breath test utilizing carbon-13 is preferred to carbon-14 for certain vulnerable populations due to its non-radioactive nature. | 9 | Geochemistry |
Copurification procedures, such as co-immunoprecipitation, are commonly used to analyze interactions between proteins. Copurification is one method used to map the interactome of living organisms. | 3 | Analytical Chemistry |
Nighttime wind power is considered the most economical form of electrical power with which to synthesize fuel, because the load curve for electricity peaks sharply during the warmest hours of the day, but wind tends to blow slightly more at night than during the day. Therefore, the price of nighttime wind power is often much less expensive than any alternative. Off-peak wind power prices in high wind penetration areas of the U.S. averaged 1.64 cents per kilowatt-hour in 2009, but only 0.71 cents/kWh during the least expensive six hours of the day. Typically, wholesale electricity costs 2 to 5 cents/kWh during the day. Commercial fuel synthesis companies suggest they can produce gasoline for less than petroleum fuels when oil costs more than $55 per barrel.
In 2010, a team of process chemists led by Heather Willauer of the U.S. Navy, estimates that 100 megawatts of electricity can produce of jet fuel per day and shipboard production from nuclear power would cost about . While that was about twice the petroleum fuel cost in 2010, it is expected to be much less than the market price in less than five years if recent trends continue. Moreover, since the delivery of fuel to a carrier battle group costs about , shipboard production is already much less expensive.
Willauer said seawater is the "best option" for a source of synthetic jet fuel. By April 2014, Willauer's team had not yet made fuel to the standard required by military jets, but they were able in September 2013 to use the fuel to fly a radio-controlled model airplane powered by a common two-stroke internal combustion engine. Because the process requires a large input of electrical energy, a plausible first step of implementation would be for American nuclear-powered aircraft carriers (the Nimitz-class and the Gerald R. Ford-class) to manufacture their own jet fuel. The U.S. Navy is expected to deploy the technology some time in the 2020s.
In 2023, a study published by the NATO Energy Security Centre of Excellence, concluded that e-fuels offer one of the most promising decarbonization pathways for military mobility across the land, sea and air domains. | 0 | Organic Chemistry |
*ERH is adaptable to all soil types and sedimentary bedrock. ERH is also effective in both the vadose and saturated zones. Certain lithologies can limit traditional methods of remediation by preventing a reliable removal/destruction pathway for the contamination of concern. Because electricity can and does travel through any lithology that contains some water, ERH can be effective in any soil type. By forming buoyant steam bubbles during the heating process, ERH creates a carrier gas that transports the contamination of concern up and out of any soil type. ERH is not capable of desiccating the subsurface. In order for the subsurface to conduct electricity, there must be water present in the subsurface. Conductivity will cease before the subsurface is desiccated.
*ERH is commonly applied under active buildings or manufacturing facilities. Electrodes can be installed above grade within a fenced area or below grade to allow for unrestricted surface access to the treatment area.
*Although principally used for contaminant source areas, ERH can be used to achieve low remedial goals such as maximum contaminant levels, MCLs, for drinking water.
*After ERH treatment, elevated subsurface temperatures will slowly cool over a period of months or years and return to ambient. This period with elevated temperatures is an important part of the remediation process. The elevated temperatures will enhance Bioremediation, hydrolysis and iron reductive dehalogenation. | 2 | Environmental Chemistry |
Various geologic data suggest that Lake Chichoj stretches above of a body of gypsum well exposed on outcrops farther west. There, gypsum dissolution is responsible for repeated mountain flank collapses in the valley of Los Chorros. The lake occupies at least three coalescing dolines likely formed by dissolution of gypsum at depth. The dolines are probably only a few tens of thousands of years old, and the marshlands that surround the lake are likely covering similar, sediment-filled dolines. They are therefore susceptible to resumption of ground subsidence, if gypsum keeps dissolving at depth. The new phase of subsidence could either be slow and continuous, or pulsed, and possibly fast, even instantaneous. It is even possible that the marshes are actively subsiding, since no monitoring of subsidence has ever been undertaken. Subsidence might also be occurring under the combined effect of slow sediment compaction and oxidation/decomposition of the organic matter trapped in the sediments. The accommodation space created by the subsidence would be filled by mineral and organic sediments over the marshlands. | 2 | Environmental Chemistry |
The only oceanic anoxic event documented from the Jurassic took place during the early Toarcian (~183 Ma). Since no DSDP (Deep Sea Drilling Project) or ODP (Ocean Drilling Program) cores have recovered black shales of this age—there being little or no Toarcian ocean crust remaining—the samples of black shale primarily come from outcrops on land. These outcrops, together with material from some commercial oil wells, are found on all major continents and this event seems similar in kind to the two major Cretaceous examples. | 9 | Geochemistry |
In imaging spectroscopy (also hyperspectral imaging or spectral imaging) each pixel of an image acquires many bands of light intensity data from the spectrum, instead of just the three bands of the RGB color model. More precisely, it is the simultaneous acquisition of spatially coregistered images in many spectrally contiguous bands.
Some spectral images contain only a few image planes of a spectral data cube, while others are better thought of as full spectra at every location in the image. For example, solar physicists use the spectroheliograph to make images of the Sun built up by scanning the slit of a spectrograph, to study the behavior of surface features on the Sun; such a spectroheliogram may have a spectral resolution of over 100,000 () and be used to measure local motion (via the Doppler shift) and even the magnetic field (via the Zeeman splitting or Hanle effect) at each location in the image plane. The multispectral images collected by the Opportunity rover, in contrast, have only four wavelength bands and hence are only a little more than 3-color images.
One application is spectral geophysical imaging, which allows quantitative and qualitative characterization of the surface and of the atmosphere, using radiometric measurements. These measurements can then be used for unambiguous direct and indirect identification of surface materials and atmospheric trace gases, the measurement of their relative concentrations, subsequently the assignment of the proportional contribution of mixed pixel signals (e.g., the spectral unmixing problem), the derivation of their spatial distribution (mapping problem), and finally their study over time (multi-temporal analysis). The Moon Mineralogy Mapper on Chandrayaan-1 was a geophysical imaging spectrometer. | 7 | Physical Chemistry |
The pH of the extracellular fluid, including the blood plasma, is normally tightly regulated between 7.32 and 7.42 by the chemical buffers, the respiratory system, and the renal system. The normal pH in the fetus differs from that in the adult. In the fetus, the pH in the umbilical vein pH is normally 7.25 to 7.45 and that in the umbilical artery is normally 7.18 to 7.38.
Aqueous buffer solutions will react with strong acids or strong bases by absorbing excess ions, or ions, replacing the strong acids and bases with weak acids and weak bases. This has the effect of damping the effect of pH changes, or reducing the pH change that would otherwise have occurred. But buffers cannot correct abnormal pH levels in a solution, be that solution in a test tube or in the extracellular fluid. Buffers typically consist of a pair of compounds in solution, one of which is a weak acid and the other a weak base. The most abundant buffer in the ECF consists of a solution of carbonic acid (HCO), and the bicarbonate () salt of, usually, sodium (Na). Thus, when there is an excess of ions in the solution carbonic acid partially neutralizes them by forming HO and bicarbonate () ions. Similarly an excess of H ions is partially neutralized by the bicarbonate component of the buffer solution to form carbonic acid (HCO), which, because it is a weak acid, remains largely in the undissociated form, releasing far fewer H ions into the solution than the original strong acid would have done.
The pH of a buffer solution depends solely on the ratio of the molar concentrations of the weak acid to the weak base. The higher the concentration of the weak acid in the solution (compared to the weak base) the lower the resulting pH of the solution. Similarly, if the weak base predominates the higher the resulting pH.
This principle is exploited to regulate the pH of the extracellular fluids (rather than just buffering the pH). For the carbonic acid-bicarbonate buffer, a molar ratio of weak acid to weak base of 1:20 produces a pH of 7.4; and vice versa—when the pH of the extracellular fluids is 7.4 then the ratio of carbonic acid to bicarbonate ions in that fluid is 1:20. | 7 | Physical Chemistry |
Sulfonic acids can be converted to esters. This class of organic compounds has the general formula R−SO−OR. Sulfonic esters such as methyl triflate are considered good alkylating agents in organic synthesis. Such sulfonate esters are often prepared by alcoholysis of the sulfonyl chlorides:
:RSOCl + R′OH → RSOOR′ + HCl | 0 | Organic Chemistry |
Several, so-called mTOR/PI3K dual inhibitors (TPdIs), have been developed and are in early-stage preclinical trials and show promising results. Their development has been benefited from previous studies with PI3K-selective inhibitors. The activity of these small molecules from rapalog activity differs in the way by blocking both mTORC1-dependent phospholylation of S6K1 and mTORC2-dependent phosphorylation of AKT Ser473 residue.
Dual mTOR/PI3K inhibitors include dactolisib, voxtalisib, BGT226, SF1126, PKI-587 and many more. For example, Novartis has developed the compound NVPBE235 that was reported to inhibit tumor growth in various preclinical models. It enhances antitumor activity of some other drugs such as vincristine. Dactolisib seems to inhibit effectively both wild-type and mutant form of PI3KCA, which suggests its use towards wide types of tumors. Studies have shown superior antiproliferative activity to rapalogs and in vivo models have confirmed these potent antineoplastic effects of dual mTOR/PI3K inhibitors. These inhibitors target isoforms of PI3K (p110α, β and γ) along with ATP-binding sites of mTORC1 and mTORC2 by blocking PI3K/AKT signaling, even in cancer types with mutations in this pathway. | 1 | Biochemistry |
Nanocrystalline metals can be produced by rapid solidification from the liquid using a process such as melt spinning. This often produces an amorphous metal, which can be transformed into an nanocrystalline metal by annealing above the crystallization temperature. | 8 | Metallurgy |
The goal of the TB Structural Genomics Consortium is to determine the structures of potential drug targets in Mycobacterium tuberculosis, the bacterium that causes tuberculosis. The development of novel drug therapies against tuberculosis are particularly important given the growing problem of multi-drug-resistant tuberculosis.
The fully sequenced genome of M. tuberculosis has allowed scientists to clone many of these protein targets into expression vectors for purification and structure determination by X-ray crystallography. Studies have identified a number of target proteins for structure determination, including extracellular proteins that may be involved in pathogenesis, iron-regulatory proteins, current drug targets, and proteins predicted to have novel folds. So far, structures have been determined for 708 of the proteins encoded by M. tuberculosis. | 1 | Biochemistry |
It has been studies that a type of cerein 8A is very effective in inhibiting the effects of the pathogenic bacteria Salmonella enterica subsp. enterica that causes diarrhea, stomach aches, and fever. In clinical research, it was discovered that cerein 8A in combination with combination with sodium lactate killed Salmonella enterica in a dose-dependent fashion. Cerein 8A was also found to inhibit growth of Listeria monocytogenes, a pathogenic bacteria commonly found in dairy products such as milk. | 1 | Biochemistry |
Severyn Marcel Sternhell (30 May 1930 – 18 November 2022) was a Polish-born Australian academic and organic chemist. He was professor of Chemistry at the University of Sydney and a Fellow of the Australian Academy of Science. His research focused on the induction of chirality into mesophases, aspects of steric hindrance and the mechanochemistry of organic compounds. | 0 | Organic Chemistry |
It has been suggested that the size of an organism's interactome correlates better than genome size with the biological complexity of the organism. Although protein–protein interaction maps containing several thousand binary interactions are now available for several species, none of them is presently complete and the size of interactomes is still a matter of debate. | 1 | Biochemistry |
All the structural genes of an operon are turned ON or OFF together, due to a single promoter and operator upstream to them, but sometimes more control over the gene expression is needed. To achieve this aspect, some bacterial genes are located near together, but there is a specific promoter for each of them; this is called gene clustering. Usually these genes encode proteins which will work together in the same pathway, such as a metabolic pathway. Gene clustering helps a prokaryotic cell to produce metabolic enzymes in a correct order.
In one study, it has been posited that in the Asgard (archaea), ribosomal protein coding genes occur in clusters that are less conserved in their organization than in other Archaea; the closer an Asgard (archaea) is to the eukaryotes, the more dispersed is the arrangement of the ribosomal protein coding genes. | 1 | Biochemistry |
Calcium sulfate (its α- and β-hemihydrates) is a well known biocompatible material that is widely used as a bone graft substitute in dentistry or as its binder. | 1 | Biochemistry |
The mole ratio is defined as the amount of a constituent divided by the total amount of all other constituents in a mixture:
If is much smaller than , the mole ratio is almost identical to the mole fraction.
The SI unit is mol/mol. However, the deprecated parts-per notation is often used to describe small mole ratios. | 3 | Analytical Chemistry |
When forming any sphere-packing lattice, the first fact to notice is that whenever two spheres touch a straight line may be drawn from the center of one sphere to the center of the other intersecting the point of contact. The distance between the centers along the shortest path namely that straight line will therefore be r + r where r is the radius of the first sphere and r is the radius of the second. In close packing all of the spheres share a common radius, r. Therefore, two centers would simply have a distance 2r. | 3 | Analytical Chemistry |
The Tyndall effect is light scattering by particles in a colloid such as a very fine suspension (a sol). Also known as Tyndall scattering, it is similar to Rayleigh scattering, in that the intensity of the scattered light is inversely proportional to the fourth power of the wavelength, so blue light is scattered much more strongly than red light. An example in everyday life is the blue colour sometimes seen in the smoke emitted by motorcycles, in particular two-stroke machines where the burnt engine oil provides these particles. The same effect can also be observed with tobacco smoke whose fine particles also preferentially scatter blue light.
Under the Tyndall effect, the longer wavelengths are transmitted more, while the shorter wavelengths are more diffusely reflected via scattering. The Tyndall effect is seen when light-scattering particulate matter is dispersed in an otherwise light-transmitting medium, where the diameter of an individual particle is in the range of roughly 40 to 900 nm, i.e. somewhat below or near the wavelengths of visible light (400–750 nm).
It is particularly applicable to colloidal mixtures; for example, the Tyndall effect is used in nephelometers to determine the size and density of particles in aerosols and other colloidal matter. Investigation of the phenomenon led directly to the invention of the ultramicroscope and turbidimetry.
It is named after the 19th-century physicist John Tyndall, who first studied the phenomenon extensively. | 7 | Physical Chemistry |
Ballentine has shown that by measuring noble gas isotopes, he can identify and quantify the processes controlling the origin, migration, and interaction of subsurface water, hydrocarbons, and fluids.
He has applied noble gas tools and principles to understand how natural gas fields form inside Earth, the role of groundwater in forming hydrocarbon reservoirs, and the origins of different gases on the planet. Ballentine also has developed quantitative techniques to understand how carbon dioxide behaves in the subsurface, including its role in the crustal carbon cycle, and how carbon-rich fluids have supported subsurface life over geological timescales. | 9 | Geochemistry |
Optical depth measures the attenuation of the transmitted radiant power in a material. Attenuation can be caused by absorption, but also reflection, scattering, and other physical processes. Optical depth of a material is approximately equal to its attenuation when both the absorbance is much less than 1 and the emittance of that material (not to be confused with radiant exitance or emissivity) is much less than the optical depth:
where
*Φ is the radiant power transmitted by that material;
*Φ is the radiant power attenuated by that material;
*Φ is the radiant power received by that material;
*Φ is the radiant power emitted by that material;
*T = Φ/Φ is the transmittance of that material;
*ATT = Φ/Φ is the attenuation of that material;
*E = Φ/Φ is the emittance of that material,
and according to the Beer–Lambert law,
so: | 7 | Physical Chemistry |
Although water quality is usually sampled and analyzed at laboratories, since the late 20th century there has been increasing public interest in the quality of drinking water provided by municipal systems. Many water utilities have developed systems to collect real-time data about source water quality. In the early 21st century, a variety of sensors and remote monitoring systems have been deployed for measuring water pH, turbidity, dissolved oxygen and other parameters. Some remote sensing systems have also been developed for monitoring ambient water quality in riverine, estuarine and coastal water bodies.
The following is a list of indicators often measured by situational category:
* Alkalinity
* Color of water
* pH
* Taste and odor (geosmin, 2-Methylisoborneol (MIB), etc.)
* Dissolved metals and salts (sodium, chloride, potassium, calcium, manganese, magnesium)
* Microorganisms such as fecal coliform bacteria (Escherichia coli), Cryptosporidium, and Giardia lamblia; see Bacteriological water analysis
* Dissolved metals and metalloids (lead, mercury, arsenic, etc.)
* Dissolved organics: colored dissolved organic matter (CDOM), dissolved organic carbon (DOC)
* Radon
* Heavy metals
* Pharmaceuticals
* Hormone analogs | 3 | Analytical Chemistry |
While most iron is oxidized as a result of interaction with atmospheric oxygen or oxygenated waters, oxidation by bacteria is an active process in anoxic environments and in oxygenated, low pH (Fe values between 2 and 3‰ were measured. However, a Rayleigh trend with a fractionation factor of α ~ 1.0022 was observed, which is smaller than the fractionation factor in the abiotic control experiments (α ~ 1.0034), which has been inferred to reflect a biological isotope effect. Using iron isotopes, an improvement in the understanding of the metabolic processes controlling iron oxidation and energy production in these organisms can be developed.
Photoautrophic bacteria, which oxidize Fe(II) under anaerobic conditions, have also been studied. The Thiodictyon bacteria precipitate poorly crystalline hydrous ferric oxide when they oxidize iron. The precipitate was enriched in the Fe relative to Fe(II), with a δFe value of +1.5 ± 0.2‰. | 9 | Geochemistry |
Clay minerals are common weathering products (including weathering of feldspar) and low-temperature hydrothermal alteration products. Clay minerals are very common in soils, in fine-grained sedimentary rocks such as shale, mudstone, and siltstone and in fine-grained metamorphic slate and phyllite.
Given the requirement of water, clay minerals are relatively rare in the Solar System, though they occur extensively on Earth where water has interacted with other minerals and organic matter. Clay minerals have been detected at several locations on Mars, including Echus Chasma, Mawrth Vallis, the Memnonia quadrangle and the Elysium quadrangle. Spectrography has confirmed their presence on celestial bodies including the dwarf planet Ceres, asteroid 101955 Bennu, and comet Tempel 1, as well as Jupiter's moon Europa. | 9 | Geochemistry |
The length of the multiple conjugated double bonds determines their color and photophysics. After absorbing a photon, the carotenoid transfers its excited electron to chlorophyll for use in photosynthesis. Upon absorption of light, carotenoids transfer excitation energy to and from chlorophyll. The singlet-singlet energy transfer is a lower energy state transfer and is used during photosynthesis. The triplet-triplet transfer is a higher energy state and is essential in photoprotection. Light produces damaging species during photosynthesis, with the most damaging being reactive oxygen species (ROS). As these high energy ROS are produced in the chlorophyll the energy is transferred to the carotenoid’s polyene tail and undergoes a series of reactions in which electrons are moved between the carotenoid bonds in order to find the most balanced (lowest energy) state for the carotenoid.
Carotenoids defend plants against singlet oxygen, by both energy transfer and by chemical reactions. They also protect plants by quenching triplet chlorophyll. By protecting lipids from free-radical damage, which generate charged lipid peroxides and other oxidised derivatives, carotenoids support crystalline architecture and hydrophobicity of lipoproteins and cellular lipid structures, hence oxygen solubility and its diffusion therein. | 5 | Photochemistry |
For several compounds containing both a nitrene group and a free radical group an ESR high-spin quartet has been recorded (matrix, cryogenic temperatures). One of these has an amine oxide radical group incorporated, another system has a carbon radical group.
In this system one of the nitrogen unpaired electrons is delocalized in the aromatic ring making the compound a σ–σ–π triradical. A carbene nitrogen radical (imidyl radical) resonance structure makes a contribution to the total electronic picture.
In 2019, an authentic triplet nitrene was isolated by Betley and Lancaster, stabilized by coordination to a copper center in a bulky ligand. | 0 | Organic Chemistry |
Enhancers as sites of extragenic transcription were initially discovered in genome-wide studies that identified enhancers as common regions of RNA polymerase II (RNA pol II) binding and non-coding RNA transcription. The level of RNA pol II–enhancer interaction and RNA transcript formation were found to be highly variable among these initial studies. Using explicit chromatin signature peaks, a significant proportion (~70%) of extragenic RNA Pol II transcription start sites were found to overlap enhancer sites in murine macrophages. Out of 12,000 neuronal enhancers in the mouse genome, almost 25% of the sites were found to bind RNA Pol II and generate transcripts. In parallel studies, 4,588 high confidence extragenic RNA Pol II binding sites were identified in murine macrophages stimulated with the inflammatory mediater lipopolysaccharide to induce transcription. These eRNAs, unlike messenger RNAs (mRNAs), lacked modification by polyadenylation, were generally short and non-coding, and were bidirectionally transcribed. Later studies revealed the transcription of another type of eRNAs, generated through unidirectional transcription, that were longer and contained a poly A tail. Furthermore, eRNA levels were correlated with mRNA levels of nearby genes, suggesting the potential regulatory and functional role of these non-coding enhancer RNA molecules. | 1 | Biochemistry |
Oxygen cycle refers to the movement of oxygen through the atmosphere (air), biosphere (plants and animals) and the lithosphere (the Earth’s crust). The oxygen cycle demonstrates how free oxygen is made available in each of these regions, as well as how it is used. The oxygen cycle is the biogeochemical cycle of oxygen atoms between different oxidation states in ions, oxides, and molecules through redox reactions within and between the spheres/reservoirs of the planet Earth. The word oxygen in the literature typically refers to the most common oxygen allotrope, elemental/diatomic oxygen (O), as it is a common product or reactant of many biogeochemical redox reactions within the cycle. Processes within the oxygen cycle are considered to be biological or geological and are evaluated as either a source (O production) or sink (O consumption).
Oxygen is one of the most common elements on Earth and represents a large portion of each main reservoir. By far the largest reservoir of Earths oxygen is within the silicate and oxide minerals of the crust and mantle (99.5% by weight). The Earths atmosphere, hydrosphere, and biosphere together hold less than 0.05% of the Earth's total mass of oxygen. Besides O, additional oxygen atoms are present in various forms spread throughout the surface reservoirs in the molecules of biomass, HO, CO, HNO, NO, NO, CO, HO, O, SO, HSO, MgO, CaO, Al2O3, SiO, and PO. | 5 | Photochemistry |
Tramadol can have pharmacodynamic, pharmacokinetic, and pharmacogenetic interactions.
Tramadol is metabolized by CYP2D6 enzymes which contribute to the metabolism of approximately 25% of all medications. Any medications with the ability to inhibit or induce these enzymes may interact with tramadol. These include common antiarrhythmics, antiemetics, antidepressants (sertraline, paroxetine, and fluoxetine in particular), antipsychotics, analgesics, and tamoxifen.
Due to tramadols serotonergic effects, tramadol has the potential to contribute to the development of an acute or chronic hyper-serotonin state called serotonin syndrome when used concurrently with other pro-serotonergic medications such as antidepressants (SSRIs, SNRIs, tricyclics, MAOIs), antipsychotics, triptans, cold medications containing dextromethorphan, and some herbal products such as St. Johns wort.
Concurrent use of 5-HT3 antagonists such as ondansetron, dolasetron, and palonosetron may reduce the effectiveness of both drugs.
Tramadol also acts as an opioid agonist and thus can increase the risk for side effects when used with other opioid and opioid-containing analgesics (such as morphine, pethidine, tapentadol, oxycodone, fentanyl, and Tylenol 3).
Tramadol increases the risk for seizures by lowering the seizure threshold. Using other medications that lower seizure threshold - such as antipsychotic medications, bupropion (an anti-depressant and smoking cessation drug), and amphetamines - can further increases this risk. | 4 | Stereochemistry |
Palladacycles with ring-sizes range from 3 to 10 have been synthesized and characterized, whereas only 5-/6-membered ones are commonly used. Palladacycles of 3-/4-/>6-membered ring-sizes are usually unstable due to their ring strains. | 0 | Organic Chemistry |
These proteins were originally characterized by their capacity to induce oncogenic transformation in a specific cell culture system, rat kidney fibroblasts. Application of the transforming growth factors to normal rat kidney fibroblasts induces the cultured cells to proliferate and overgrow, no longer subject to the normal inhibition caused by contact between cells. | 1 | Biochemistry |
Cannulation requires installing a flanged rubber cylinder in the side of a cow, behind its 13th rib. The cylinder typically is fitted with a plastic, rubber, or metal cap to keep the rumen anaerobic.
The rubber cannula is surgically implanted while the cow is standing and awake, with local anesthetic. The cow is made to fast and refrain from drinking water for 24 hours in advance of the surgery. Then the veterinarian excises a small piece of the cow's skin, makes an incision through the rumen, and stitches the open sides of the rumen to the edges of skin, to prevent the contents of the rumen from leaking into the rest of the abdominal cavity. Finally, the inner flange of the cannula is pushed inside the rumen and capped. | 1 | Biochemistry |
Because of the sensitivity of the electrodes to contaminants, cleanliness of the probes is essential for accuracy and precision. Probes are generally kept moist when not in use with a medium appropriate for the particular probe, which is typically an aqueous solution available from probe manufacturers. Probe manufacturers provide instructions for cleaning and maintaining their probe designs. For illustration, one maker of laboratory-grade pH gives cleaning instructions for specific contaminants: general cleaning (15-minute soak in a solution of bleach and detergent), salt (hydrochloric acid solution followed by sodium hydroxide and water), grease (detergent or methanol), clogged reference junction (KCl solution), protein deposits (pepsin and HCl, 1% solution), and air bubbles. | 7 | Physical Chemistry |
* Spray painting
* High velocity oxygen fuel (HVOF)
* Plasma spraying
* Thermal spraying
* Kinetic metallization (KM)
* Plasma transferred wire arc thermal spraying
* The common forms of Powder coating | 8 | Metallurgy |
Potassium tetraiodomercurate(II) is an inorganic compound with the chemical formula . It consists of potassium cations and tetraiodomercurate(II) anions. It is the active agent in Nessler's reagent, used for detection of ammonia. | 3 | Analytical Chemistry |
Hypervalent molecules were first formally defined by Jeremy I. Musher in 1969 as molecules having central atoms of group 15–18 in any valence other than the lowest (i.e. 3, 2, 1, 0 for Groups 15, 16, 17, 18 respectively, based on the octet rule).
Several specific classes of hypervalent molecules exist:
* Hypervalent iodine compounds are useful reagents in organic chemistry (e.g. Dess–Martin periodinane)
* Tetra-, penta- and hexavalent phosphorus, silicon, and sulfur compounds (e.g. PCl, PF, SF, sulfuranes and persulfuranes)
* Noble gas compounds (ex. xenon tetrafluoride, XeF)
* Halogen polyfluorides (ex. chlorine pentafluoride, ClF) | 4 | Stereochemistry |
Hydroperoxides are intermediates or reagents in major commercial processes. In the cumene process, acetone and phenol are produced by decomposition of cumene hydroperoxide (Me = methyl): | 0 | Organic Chemistry |
Amino acid replacement is a change from one amino acid to a different amino acid in a protein due to point mutation in the corresponding DNA sequence. It is caused by nonsynonymous missense mutation which changes the codon sequence to code other amino acid instead of the original. | 1 | Biochemistry |
Eigen et al. and Woese proposed that the genomes of early protocells were composed of single-stranded RNA, and that individual genes corresponded to separate RNA segments, rather than being linked end-to-end as in present-day DNA genomes. A protocell that was haploid (one copy of each RNA gene) would be vulnerable to damage, since a single lesion in any RNA segment would be potentially lethal to the protocell (e.g., by blocking replication or inhibiting the function of an essential gene).
Vulnerability to damage could be reduced by maintaining two or more copies of each RNA segment in each protocell, i.e., by maintaining diploidy or polyploidy. Genome redundancy would allow a damaged RNA segment to be replaced by an additional replication of its homolog. However, for such a simple organism, the proportion of available resources tied up in the genetic material would be a large fraction of the total resource budget. Under limited resource conditions, the protocell reproductive rate would likely be inversely related to ploidy number. The protocell's fitness would be reduced by the costs of redundancy. Consequently, coping with damaged RNA genes while minimizing the costs of redundancy would likely have been a fundamental problem for early protocells.
A cost-benefit analysis was carried out in which the costs of maintaining redundancy were balanced against the costs of genome damage. This analysis led to the conclusion that, under a wide range of circumstances, the selected strategy would be for each protocell to be haploid, but to periodically fuse with another haploid protocell to form a transient diploid. The retention of the haploid state maximizes the growth rate. The periodic fusions permit mutual reactivation of otherwise lethally damaged protocells. If at least one damage-free copy of each RNA gene is present in the transient diploid, viable progeny can be formed. For two, rather than one, viable daughter cells to be produced would require an extra replication of the intact RNA gene homologous to any RNA gene that had been damaged prior to the division of the fused protocell. The cycle of haploid reproduction, with occasional fusion to a transient diploid state, followed by splitting to the haploid state, can be considered to be the sexual cycle in its most primitive form. In the absence of this sexual cycle, haploid protocells with damage in an essential RNA gene would simply die.
This model for the early sexual cycle is hypothetical, but it is very similar to the known sexual behavior of the segmented RNA viruses, which are among the simplest organisms known. Influenza virus, whose genome consists of 8 physically separated single-stranded RNA segments, is an example of this type of virus. In segmented RNA viruses, "mating" can occur when a host cell is infected by at least two virus particles. If these viruses each contain an RNA segment with a lethal damage, multiple infection can lead to reactivation providing that at least one undamaged copy of each virus gene is present in the infected cell. This phenomenon is known as "multiplicity reactivation". Multiplicity reactivation has been reported to occur in influenza virus infections after induction of RNA damage by UV-irradiation, and ionizing radiation. | 9 | Geochemistry |
For zero-order reactions, the reaction rate is independent of the concentration of a reactant, so that changing its concentration has no effect on the rate of the reaction. Thus, the concentration changes linearly with time. This may occur when there is a bottleneck which limits the number of reactant molecules that can react at the same time, for example if the reaction requires contact with an enzyme or a catalytic surface.
Many enzyme-catalyzed reactions are zero order, provided that the reactant concentration is much greater than the enzyme concentration which controls the rate, so that the enzyme is saturated. For example, the biological oxidation of ethanol to acetaldehyde by the enzyme liver alcohol dehydrogenase (LADH) is zero order in ethanol.
Similarly reactions with heterogeneous catalysis can be zero order if the catalytic surface is saturated. For example, the decomposition of phosphine () on a hot tungsten surface at high pressure is zero order in phosphine, which decomposes at a constant rate.
In homogeneous catalysis zero order behavior can come about from reversible inhibition. For example, ring-opening metathesis polymerization using third-generation Grubbs catalyst exhibits zero order behavior in catalyst due to the reversible inhibition that occurs between pyridine and the ruthenium center. | 7 | Physical Chemistry |
The Prix Michel-Sarrazin is awarded annually in the Canadian province of Quebec by the Club de Recherches Clinique du Québec to a celebrated Québécois scientist who, by their dynamism and productivity, have contributed in an important way to the advancement of research biomedical. It is named in honour of Michel Sarrazin (1659–1734) who was the first Canadian scientist. | 1 | Biochemistry |
The portmanteau word "pheromone" was coined by Peter Karlson and Martin Lüscher in 1959, based on the Greek φέρω phérō (I carry) and ὁρμων hórmōn (stimulating). Pheromones are also sometimes classified as ecto-hormones. They were researched earlier by various scientists, including Jean-Henri Fabre, Joseph A. Lintner, Adolf Butenandt, and ethologist Karl von Frisch who called them various names, like for instance "alarm substances". These chemical messengers are transported outside of the body and affect neurocircuits, including the autonomous nervous system with hormone or cytokine mediated physiological changes, inflammatory signaling, immune system changes and/or behavioral change in the recipient. They proposed the term to describe chemical signals from conspecifics that elicit innate behaviors soon after the German biochemist Adolf Butenandt had characterized the first such chemical, bombykol, a chemically well-characterized pheromone released by the female silkworm to attract mates. | 1 | Biochemistry |
There have been proposals for automation to make rapid prediction of BOD so it could be used for on-line process monitoring and control. For example, the use of a computerised machine learning method to make rapid inferences about BOD using easy to measure water quality parameters. Ones such as flow rate, chemical oxygen demand, ammonia, nitrogen, pH and suspended solids can be obtained directly and reliably using on-line hardware sensors. In a test of this idea, measurements of these values along with BOD which had been made over three years was used to train and test a model for prediction. The technique could allow for some missing data. It indicated that this approach was possible but needed sufficient historic data to be available. | 3 | Analytical Chemistry |
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