text
stringlengths 105
4.44k
| label
int64 0
9
| label_text
stringclasses 10
values |
|---|---|---|
Vinyl- and acetylenic ethers are far less common than alkyl or aryl ethers. Vinylethers, often called enol ethers, are important intermediates in organic synthesis. Acetylenic ethers are especially rare. Di-tert-butoxyacetylene is the most common example of this rare class of compounds. | 0 | Organic Chemistry |
The Maxwell Garnett equation reads:
where is the effective dielectric constant of the medium, of the inclusions, and of the matrix; is the volume fraction of the inclusions.
The Maxwell Garnett equation is solved by:
so long as the denominator does not vanish. A simple MATLAB calculator using this formula is as follows. | 7 | Physical Chemistry |
The diagnosis of sepiapterin reductase deficiency in a patient at the age of 14 years was delayed by an earlier diagnosis of an initially unclassified form of methylmalonic aciduria at the age of 2. At that time the hypotonia and delayed development were not considered to be suggestive of a neurotransmitter defect. The clinically relevant diagnosis was only made following the onset of dystonia with diurnal variation, when the patient was a teenager. Variability in occurrence and severity of other symptoms of the condition, such as hypotonia, ataxia, tremors, spasticity, bulbar involvement, oculogyric crises, and cognitive impairment, is comparable with autosomal dominant GTPCH and tyrosine hydroxylase deficiency, which are both classified as forms of DOPA-responsive dystonia. | 1 | Biochemistry |
*Biochemical Society, London
*American Chemical Society
*Grandmaster, United Grand Masonic Lodge of Queensland | 0 | Organic Chemistry |
Due to internal attractive forces of a liquid, air bubbles within the liquids are compressed. The resulting pressure (bubble pressure) rises at a decreasing bubble radius. The bubble pressure method makes use of this bubble pressure which is higher than in the surrounding environment (water). A gas stream is pumped into a capillary that is immersed in a fluid. The resulting bubble at the end of the capillary tip continually becomes bigger in surface; thereby, the bubble radius is decreasing.
The pressure rises to a maximum level. At this point the bubble has achieved its smallest radius (the capillary radius) and begins to form a hemisphere. Beyond this point the bubble quickly increases in size and soon bursts, tearing away from the capillary, thereby allowing a new bubble to develop at the capillary tip. It is during this process that a characteristic pressure pattern develops (see picture), which is evaluated for determining the surface tension.
Because of the easy handling and the low cleaning effort of the capillary, bubble pressure tensiometers are a common alternative for monitoring the detergent concentration in cleaning or electroplating processes. | 7 | Physical Chemistry |
In May 2005 the Save Spodden Valley group claimed that it had uncovered internal MMC correspondence which identified numerous sites where asbestos fibres had been found in September 2004, predating the planning application. The document stated: "The audit undertaken was visual and no samples have been sent away for analysis. I enclose a site map where the asbestos has been located: Top section of road near hair pin bend, asbestos sheets and asbestos fibre found in tree stumps. Road leading to Healey Dell, asbestos cloth." The developers responded that they had been aware of contamination in the northern portion of the site, but their testing report submitted to the council did not include this area as there had been no intention to develop there. Instead they had confined their testing only to those areas where they intended to develop and that there had been "some misunderstanding of our intentions and the test result." | 2 | Environmental Chemistry |
Protein adsorption and protein fouling can cause major problems in the food industry (particularly the dairy industry) when proteins from food adsorb to processing surfaces, such as stainless steel or plastic (e.g. polypropylene). Protein fouling is the gathering of protein aggregates on a surface. This is most common in heating processes that create a temperature gradient between the equipment and the bulk substance being heated. In protein-fouled heating equipment, adsorbed proteins can create an insulating layer between the heater and the bulk material, reducing heating efficiency. This leads to inefficient sterilization and pasteurization. Also, proteins stuck to the heater may cause a burned taste or color in the bulk material. Additionally, in processes that employ filtration, protein aggregates that gather on the surface of the filter can block the flow of the bulk material and greatly reduce filter efficiency. | 1 | Biochemistry |
Katsonis serves on the Nature Travel Grants panel. She is an Editor of the journals Communications Chemistry and ChemPhotoChem. | 0 | Organic Chemistry |
Metallacrowns form via self-assembly, i.e. by dissolving the ligand in a solvent followed by the desired metal salt.
The first reported metallacrown was Mn(OAc)(DMF)[12-MC-4]. Metallacrowns can be prepared with a variety of metals in the ring and in a variety of ring sizes. Many metallacrowns have been prepared, including 9-MC-3, 15-MC-5, and 18-MC-6. Ring size is controlled by a number of factors, such as the geometry of the ligand chelate ring, ring metal Jahn–Teller distortion, central metal size, steric effects, and stoichiometry. Common ring metals have included V(III), Mn(III), Fe(III), Ni(II) and Cu(II). Hydroxamic acids, such as salicylhydroxamic acid, and oximes are commonly utilized in metallacrown ligands. | 6 | Supramolecular Chemistry |
Noble metals tend to be highly resistant to oxidation and other forms of corrosion, and this corrosion resistance is often considered to be a defining characteristic. Some exceptions are described below.
Copper is dissolved by nitric acid and aqueous potassium cyanide.
Ruthenium can be dissolved in aqua regia, a highly concentrated mixture of hydrochloric acid and nitric acid, only when in the presence of oxygen, while rhodium must be in a fine pulverized form. Palladium and silver are soluble in nitric acid, while silver's solubility in aqua regia is limited by the formation of silver chloride precipitate.
Rhenium reacts with oxidizing acids, and hydrogen peroxide, and is said to be tarnished by moist air. Osmium and iridium are chemically inert in ambient conditions. Platinum and gold can be dissolved in aqua regia. Mercury reacts with oxidising acids.
In 2010, US researchers discovered that an organic "aqua regia" in the form of a mixture of thionyl chloride SOCl and the organic solvent pyridine CHN achieved "high dissolution rates of noble metals under mild conditions, with the added benefit of being tunable to a specific metal" for example, gold but not palladium or platinum. | 8 | Metallurgy |
The Finnish Alcoholic Beverages Act 1 March 2018 legalized the manufacture of fermented water and wine from fruits, berries and other carbohydrate sources, without the pretense of making proper wine. | 1 | Biochemistry |
Currently, the Australian agricultural industry follows various models of Environmental Management Systems (EMS) which provides an environmental management service tool that assists the continued improvement of Australia's natural habitat. However, there is a significant financial cost involved in EMS strategies that can provide obstacles that make it difficult to maintain these initiatives. This is currently being achieved by way of a four tier approach which aims to cultivate the environment and ensure its longevity. The four tiered approach concerns an initial environmental self-assessment, secondly an environmental check-list, and then complementing the second step by following an industry standard of EMS and lastly by implementing a certified EMS that is to the ISO 14001. | 2 | Environmental Chemistry |
The curing process can be monitored by measuring changes in various parameters:
*the concentration of specific reactive resin species using spectroscopic methods such as FTIR & Raman;
*the refractive index or fluorescence of the resin (optical property);
*the internal resin strain (mechanical property) with the use of Fiber Bragg grating (FBG) sensors. | 7 | Physical Chemistry |
Mercapturic acids are condensation products formed from the coupling of cysteine with aromatic compounds. They are formed as conjugates in the liver and are excreted in the urine.
Glutathione adducts lose glutamate and glycine portions, and are acetylated to form mercapturic acids, which are excreted.
Levels of mercapturic acids in urine may be used as an indicator of exposure to, e.g., ethylene dibromide, acrylamide, and terbuthylazine. | 1 | Biochemistry |
A chiral condensate is an example of a fermionic condensate that appears in theories of massless fermions with chiral symmetry breaking, such as the theory of quarks in Quantum Chromodynamics. | 7 | Physical Chemistry |
The carbon:nutrient balance hypothesis, also known as the environmental constraint hypothesis or Carbon Nutrient Balance Model (CNBM), states that the various types of plant defenses are responses to variations in the levels of nutrients in the environment. This hypothesis predicts the Carbon/Nitrogen ratio in plants determines which secondary metabolites will be synthesized. For example, plants growing in nitrogen-poor soils will use carbon-based defenses (mostly digestibility reducers), while those growing in low-carbon environments (such as shady conditions) are more likely to produce nitrogen-based toxins. The hypothesis further predicts that plants can change their defenses in response to changes in nutrients. For example, if plants are grown in low-nitrogen conditions, then these plants will implement a defensive strategy composed of constitutive carbon-based defenses. If nutrient levels subsequently increase, by for example the addition of fertilizers, these carbon-based defenses will decrease. | 1 | Biochemistry |
An important group of SNPs are those that corresponds to missense mutations causing amino acid change on protein level. Point mutation of particular residue can have different effect on protein function (from no effect to complete disruption its function). Usually, change in amino acids with similar size and physico-chemical properties (e.g. substitution from leucine to valine) has mild effect, and opposite. Similarly, if SNP disrupts secondary structure elements (e.g. substitution to proline in alpha helix region) such mutation usually may affect whole protein structure and function. Using those simple and many other machine learning derived rules a group of programs for the prediction of SNP effect was developed:
* [http://sift-dna.org SIFT] This program provides insight into how a laboratory induced missense or nonsynonymous mutation will affect protein function based on physical properties of the amino acid and sequence homology.
* [https://gsponerlab.msl.ubc.ca/software/list/ LIST] (Local Identity and Shared Taxa) estimates the potential deleteriousness of mutations resulted from altering their protein functions. It is based on the assumption that variations observed in closely related species are more significant when assessing conservation compared to those in distantly related species.
* [https://rostlab.org/services/snap SNAP2]
* [http://www.sbg.bio.ic.ac.uk/suspect/index.html SuSPect]
* [http://genetics.bwh.harvard.edu/pph2/ PolyPhen-2]
* [http://loschmidt.chemi.muni.cz/predictsnp/ PredictSNP]
* MutationTaster: [http://www.mutationtaster.org/ official website]
* [http://www.ensembl.org/info/docs/tools/vep/index.html Variant Effect Predictor] from the Ensembl project
* [https://genomicscomputbiol.org/ojs3/GCB/article/view/48/182 SNPViz] This program provides a 3D representation of the protein affected, highlighting the amino acid change so doctors can determine pathogenicity of the mutant protein.
* [http://provean.jcvi.org/index.php PROVEAN]
* [http://phyrerisk.bc.ic.ac.uk PhyreRisk] is a database which maps variants to experimental and predicted protein structures.
* [http://www.sbg.bio.ic.ac.uk/~missense3d/ Missense3D] is a tool which provides a stereochemical report on the effect of missense variants on protein structure. | 1 | Biochemistry |
Some genes involved in critical developmental processes contain multiple enhancers of overlapping function. Secondary enhancers, or "shadow enhancers", may be found many kilobases away from the primary enhancer ("primary" usually refers to the first enhancer discovered, which is often closer to the gene it regulates). On its own, each enhancer drives nearly identical patterns of gene expression. Are the two enhancers truly redundant? Recent work has shown that multiple enhancers allow fruit flies to survive environmental perturbations, such as an increase in temperature. When raised at an elevated temperature, a single enhancer sometimes fails to drive the complete pattern of expression, whereas the presence of both enhancers permits normal gene expression. | 1 | Biochemistry |
Barbara Grzybowska-Świerkosz (born 1937), is a Polish chemist. She graduated from the Faculty of Mathematics, Physics and Chemistry of the Jagiellonian University in Kraków in 1959, and received a PhD from the Department of Chemistry at the University of Edinburgh in 1963. After completing a post-doctoral degree at the Institute of Physical Chemistry of the Polish Academy of Sciences in Warsaw in 1974, she researched and taught at that institution, where she has been a professor of chemical sciences since 1990. She has authored more than 140 publications, including articles, monographs and teaching documents.
Her scientific achievements have been recognized with multiple awards, and she has been a member or leader of professional groups including the Academy of Sciences of the Comecon Countries, the Coordinating Committee of Research on Catalysis of the Polish Academy of Sciences, EUROCAT-oxides, and the European Commission Action COST-15 "Interfacial Chemistry and Catalysis". She also served on the editorial boards of the journals Applied Catalysis (1991-1993) and the Polish Journal of Chemistry (1997-). | 7 | Physical Chemistry |
The citric acid cycle is also called the Krebs cycle or the tricarboxylic acid cycle. When oxygen is present, acetyl-CoA is produced from the pyruvate molecules created from glycolysis. Once acetyl-CoA is formed, aerobic or anaerobic respiration can occur. When oxygen is present, the mitochondria will undergo aerobic respiration which leads to the Krebs cycle. However, if oxygen is not present, fermentation of the pyruvate molecule will occur. In the presence of oxygen, when acetyl-CoA is produced, the molecule then enters the citric acid cycle (Krebs cycle) inside the mitochondrial matrix, and is oxidized to CO while at the same time reducing NAD to NADH. NADH can be used by the electron transport chain to create further ATP as part of oxidative phosphorylation. To fully oxidize the equivalent of one glucose molecule, two acetyl-CoA must be metabolized by the Krebs cycle. Two low-energy waste products, HO and CO, are created during this cycle.
The citric acid cycle is an 8-step process involving 18 different enzymes and co-enzymes. During the cycle, acetyl-CoA (2 carbons) + oxaloacetate (4 carbons) yields citrate (6 carbons), which is rearranged to a more reactive form called isocitrate (6 carbons). Isocitrate is modified to become α-ketoglutarate (5 carbons), succinyl-CoA, succinate, fumarate, malate and, finally, oxaloacetate.
The net gain from one cycle is 3 NADH and 1 FADH as hydrogen- (proton plus electron)-carrying compounds and 1 high-energy GTP, which may subsequently be used to produce ATP. Thus, the total yield from 1 glucose molecule (2 pyruvate molecules) is 6 NADH, 2 FADH, and 2 ATP. | 1 | Biochemistry |
Frank Erhart Emmanuel Germann (December 6, 1887 – February 27, 1974) was an American physicist, physical chemist, and university professor. He was a founding member of the modern chemistry department of the University of Colorado. | 7 | Physical Chemistry |
Asialoglycoprotein receptors function to catabolize galactosyl and N-acetylgalactosaminyl-containing substrates. More specifically, in most mammals, the asialoglycoprotein receptor removes glycoproteins that have had some of their sugars, particularly a terminal sialic acid, removed from the end of the protein. | 1 | Biochemistry |
The APPI interface for LC–MS was developed simultaneously by Bruins and Syage in 2000. APPI is another LC–MS ion source/ interface for the analysis of neutral compounds that cannot be ionized using ESI. This interface is similar to the APCI ion source, but instead of a corona discharge, the ionization occurs by using photons coming from a discharge lamp. In the direct-APPI mode, singly charged analyte molecular ions are formed by absorption of a photon and ejection of an electron. In the dopant-APPI mode, an easily ionizable compound (Dopant) is added to the mobile phase or the nebulizing gas to promote a reaction of charge-exchange between the dopant molecular ion and the analyte. The ionized sample is later transferred to the mass analyzer at high vacuum as it passes through small orifice skimmers. | 3 | Analytical Chemistry |
Pressure oxidation is a process for extracting gold from refractory ore.
The most common refractory ores are pyrite and arsenopyrite, which are sulfide ores that trap the gold within them. Refractory ores require pre-treatment before the gold can be adequately extracted. The pressure oxidation process is used to prepare such ores for conventional gold extraction processes such as cyanidation. It is performed in an autoclave at high pressure and temperature, where high-purity oxygen mixes with a slurry of ore.
When the original sulfide minerals are oxidized at high temperature and pressure, it completely releases the trapped gold. Pressure oxidation has a very high gold recovery rate, normally at least 10% higher than roasting.
The oxidation of the iron sulfide minerals produces sulfuric acid, soluble compounds such as ferric sulfate, and solids such as iron sulfate or jarosite. The iron-based solids produced pose an environmental challenge, as they can release acid and heavy metals to the environment. They can also make later precious metal recovery more difficult. Arsenic in the ore is converted to solid scorodite inside the autoclave, allowing it to be easily disposed of. This is an advantage over processes such as roasting where these toxic products are released as gases.
A disadvantage of pressure oxidation is that any silver in the feed material will often react to form silver jarosite inside the autoclave, making it difficult and expensive to recover the silver.
An example of a mine utilizing this technology is the Pueblo Viejo mine in the Dominican Republic. At Pueblo Viejo, the process is performed by injecting high-purity oxygen into autoclaves operating at 230 degrees C and 40 bar of pressure. The resulting chemical reactions oxides the sulfide minerals the gold is trapped within. The oxidation of pyrite is highly exothermic, allowing the autoclave to operate at this temperature without an external heat source. | 8 | Metallurgy |
Size-exclusion chromatography (SEC) separates polymer molecules and biomolecules based on differences in their molecular size (actually by a particle's Stokes radius). The separation process is based on the ability of sample molecules to permeate through the pores of gel spheres, packed inside the column, and is dependent on the relative size of analyte molecules and the respective pore size of the absorbent. The process also relies on the absence of any interactions with the packing material surface.
Two types of SEC are usually termed:
# Gel permeation chromatography (GPC)—separation of synthetic polymers (aqueous or organic soluble). GPC is a powerful technique for polymer characterization using primarily organic solvents.
# Gel filtration chromatography (GFC)—separation of water-soluble biopolymers. GFC uses primarily aqueous solvents (typically for aqueous soluble biopolymers, such as proteins, etc.).
The separation principle in SEC is based on the fully, or partially penetrating of the high molecular weight substances of the sample into the porous stationary-phase particles during their transport through column. The mobile-phase eluent is selected in such a way that it totally prevents interactions with the stationary phase's surface. Under these conditions, the smaller the size of the molecule, the more it is able to penetrate inside the pore space and the movement through the column takes longer. On the other hand, the bigger the molecular size, the higher the probability the molecule will not fully penetrate the pores of the stationary phase, and even travel around them, thus, will be eluted earlier. The molecules are separated in order of decreasing molecular weight, with the largest molecules eluting from the column first and smaller molecules eluting later. Molecules larger than the pore size do not enter the pores at all, and elute together as the first peak in the chromatogram and this is called total exclusion volume which defines the exclusion limit for a particular column. Small molecules will permeate fully through the pores of the stationary phase particles and will be eluted last, marking the end of the chromatogram, and may appear as a total penetration marker.
In biomedical sciences it is generally considered as a low resolution chromatography and thus it is often reserved for the final, "polishing" step of the purification. It is also useful for determining the tertiary structure and quaternary structure of purified proteins. SEC is used primarily for the analysis of large molecules such as proteins or polymers. SEC works also in a preparative way by trapping the smaller molecules in the pores of a particles. The larger molecules simply pass by the pores as they are too large to enter the pores. Larger molecules therefore flow through the column quicker than smaller molecules: that is, the smaller the molecule, the longer the retention time.
This technique is widely used for the molecular weight determination of polysaccharides. SEC is the official technique (suggested by European pharmacopeia) for the molecular weight comparison of different commercially available low-molecular weight heparins. | 3 | Analytical Chemistry |
Nearly all animals have more than one kind of Hb present in the RBC. Multiple Hb isoforms (see isoforms) are particularly common in ectotherms, but especially in fish that are required to cope with both fluctuating temperature and oxygen availability. Hbs isolated from the European eel can be separated into anodic and cathodic isoforms. The anodic isoforms have low oxygen affinities (high P50) and marked Bohr effects, while the cathodic lack significant pH effects and are therefore thought to confer hypoxia tolerance. Several species of African cichlids raised from early stage development under either hypoxic or normoxic conditions were contrasted in an attempt to compare Hb isoforms. They demonstrated there were Hb isoforms specific to the hypoxia-raised individuals. | 9 | Geochemistry |
SIN3B has been shown to interact with HDAC1, Zinc finger and BTB domain-containing protein 16, SUDS3 and IKZF1. | 1 | Biochemistry |
Even greater in scope than metalloboranes are metallacarboranes. These cages have carbon vertices, often CH, in addition to BH and M vertices. A well-developed class of metallacarboranes are prepared from dicarbollides, anions of the formula [CBH]. These anions function as ligands for a variety of metals, often forming sandwich complexes.
Some metalloboranes are derived by the metalation of neutral carboranes. Illustrative are the six-and seven-vertex cages prepared from closo-. Reaction of this carborane with iron carbonyl sources gives closo Fe- and Fe2-containing products, according to these idealized equations:
A further example of insertion into a closo carborane is the synthesis of the yellow-orange solid closo-1,2,3-:
A closely related reaction involves the capping of an anionic nido carborane
The last reaction is worked up with acid and air. | 7 | Physical Chemistry |
The Acree-Rosenheim reaction is a chemical test used for detecting the presence of tryptophan in proteins. A protein mixture is mixed with formaldehyde. Concentrated sulfuric acid is added to form two layers. A purple ring appears between the two layers if the test is positive for tryptophan.
The test was named after two greats in biochemistry, namely, Solomon Farley Acree (1875–1957), a distinguished American Biochemist at Johns Hopkins University, and Sigmund Otto Rosenheim (1871–1955), an Anglo-German Medical Chemist at the University of Manchester. | 3 | Analytical Chemistry |
Research in 2014, suggested that favipiravir may have efficacy against Ebola based on studies in mouse models; efficacy in humans was unaddressed.
During the 2014 West Africa Ebola virus outbreak, a French nurse who contracted Ebola while volunteering for Médecins Sans Frontières (MSF) in Liberia reportedly recovered after receiving a course of favipiravir. A clinical trial investigating the use of favipiravir against Ebola virus disease began in Guéckédou, Guinea, in December 2014. Preliminary results presented in 2016 at the Conference on Retroviruses and Opportunistic Infections (CROI), later published, showed a decrease in mortality in patients with low-to-moderate levels of virus in blood, but no effect on patients with high levels (the group at a higher risk of death). The trial design was concomitantly criticised for using only historical controls. | 4 | Stereochemistry |
The equilibrium constant for the protonation of a base, B,
: + H
is an association constant, K, which is simply related to the dissociation constant of the conjugate acid, BH.
The value of is ca. 14 at 25°C. This approximation can be used when the correct value is not known. Thus, the Henderson–Hasselbalch equation can be used, without modification, for bases. | 7 | Physical Chemistry |
Dexpramipexole is a first-in-class oral investigational medicine that lowers blood and tissue eosinophils before they can cause damage in the target organ. Dexpramipexole is being developed by [https://areteiatx.com/ Areteia Therapeutics] and has the potential to be the first oral treatment ever approved for eosinophilic asthma.
The eosinophil-targeting effects of oral dexpramipexole were discovered during its clinical development. Across five clinical trials, dexpramipexole has consistently been shown to significantly reduce blood eosinophil counts. | 4 | Stereochemistry |
In the early 1950s two groundbreaking series of papers were written independently on the relationship between grain boundaries and strength.
In 1951, while at the University of Sheffield, E. O. Hall wrote three papers which appeared in volume 64 of the Proceedings of the Physical Society. In his third paper, Hall showed that the length of slip bands or crack lengths correspond to grain sizes and thus a relationship could be established between the two. Hall concentrated on the yielding properties of mild steels.
Based on his experimental work carried out in 1946–1949, N. J. Petch of the University of Leeds, England published a paper in 1953 independent from Halls. Petchs paper concentrated more on brittle fracture. By measuring the variation in cleavage strength with respect to ferritic grain size at very low temperatures, Petch found a relationship exact to that of Hall's. Thus this important relationship is named after both Hall and Petch. | 8 | Metallurgy |
The modern approach is to carry out DNA–DNA hybridization in silico utilizes completely or partially sequenced genomes. The [http://ggdc.dsmz.de GGDC] and [https://tygs.dsmz.de/ TYGS] developed at DSMZ are the most accurate known tools for calculating DDH-analogous values. Among other algorithmic improvements, it solves the problem with paralogous sequences by carefully filtering them from the matches between the two genome sequences. The method has been used for resolving difficult taxa such as Escherichia coli, Bacillus cereus group, and Aeromonas. The Judicial Commission of International Committee on Systematics of Prokaryotes has admitted dDDH as taxonomic evidence. | 1 | Biochemistry |
The isotope was first hypothesized and subsequently imaged by Patrick Blackett in Rutherford's lab in 1925:
It was a product out of the first man-made transmutation of N and He conducted by Frederick Soddy and Ernest Rutherford in 1917–1919. Its natural abundance in Earth's atmosphere was later detected in 1929 by Giauque and Johnson in absorption spectra. | 9 | Geochemistry |
The IL-10 family is a family of interleukins.
In addition to IL-10, it includes IL-19, IL-20, IL-22, IL-24 and IL-26.
Some sources also include the interferons IL-28 and IL-29.
The IL-10 family are helical cytokines categorized based on their specific similarities and can be classified as class 2 cytokines. | 1 | Biochemistry |
* Total TBG can be increased (thereby decreasing the THBR) congenitally, or in conditions such as pregnancy (period of increased estrogen) and with the treatment of certain infections such as Hepatitis C. In the latter, reduction of inflammation of the liver results in increased protein synthesis
* Total TBG can be decreased (thereby increasing the THBR) congenitally, or in conditions such as liver failure, protein-losing conditions, or nephrotic conditions. Increased androgen levels will also decrease TBG synthesis, increasing THBR.
* THBR can be directly altered by drugs such as;
** Anticonvulsants such as phenytoin and carbamazepine
** Antinflammatory drugs such as salicylates (Aspirin) or phenylbutazone (NSAID)
** High levels of free fatty acids, commonly seen in acutely ill patients. | 1 | Biochemistry |
Various institutions have proposed different recommendations for the amount of daily intake of vitamin D. These vary according to precise definition, age, pregnancy or lactation, and the extent assumptions are made regarding skin synthesis of vitamin D.
Conversion: 1μg (microgram) = 40IU (international unit). | 1 | Biochemistry |
For the use of hormone antagonists in cancer, see hormonal therapy (oncology)
A hormone antagonist is a specific type of receptor antagonist which acts upon hormone receptors. Such pharmaceutical drugs are used in antihormone therapy. | 1 | Biochemistry |
In the TTC assay (also known as TTC test or tetrazolium test), TTC is used to differentiate between metabolically active and inactive tissues. The white compound is enzymatically reduced to red TPF (1,3,5-triphenylformazan) in living tissues due to the activity of various dehydrogenases (enzymes important in oxidation of organic compounds and thus cellular metabolism), while it remains as white TTC in areas of necrosis since these enzymes have been either denatured or degraded.
For this reason, TTC has been employed in autopsy pathology to assist post-mortem identification of myocardial infarctions. Healthy viable heart muscle will stain deep red from the cardiac lactate dehydrogenase; while areas of potential infarctions will be more pale.
Note: TTC is somewhat heat and light unstable, so avoid these environments as much as possible. | 3 | Analytical Chemistry |
Kerrigan's 2016 Agaricus of North America P45:
(Referring to Schaffers reaction) "In fact I recommend switching to the following modified test. Frank (1988) developed an alternative formulation in which aniline oil is combined with glacial acetic acid (GAA, essentially distilled vinegar) in a 50:50 solution. GAA is a much safer, less reactive acid. This single combined reagent is relatively stable over time. A single spot or line applied to the pileus (or other surface). In my experience the newer formulation works as well as Schaffers while being safer and more convenient." | 3 | Analytical Chemistry |
Water quality modeling involves water quality based data using mathematical simulation techniques. Water quality modeling helps people understand the eminence of water quality issues and models provide evidence for policy makers to make decisions in order to properly mitigate water. Water quality modeling also helps determine correlations to constituent sources and water quality along with identifying information gaps. Due to the increase in freshwater usage among people, water quality modeling is especially relevant both in a local level and global level. In order to understand and predict the changes over time in water scarcity, climate change, and the economic factor of water resources, water quality models would need sufficient data by including water bodies from both local and global levels.
A typical water quality model consists of a collection of formulations representing physical mechanisms that determine position and momentum of pollutants in a water body. Models are available for individual components of the hydrological system such as surface runoff; there also exist basin wide models addressing hydrologic transport and for ocean and estuarine applications. Often finite difference methods are used to analyze these phenomena, and, almost always, large complex computer models are required. | 9 | Geochemistry |
In crystallography, the R-factor (sometimes called residual factor or reliability factor or the R-value or R) is a measure of the agreement between the crystallographic model and the experimental X-ray diffraction data. In other words, it is a measure of how well the refined structure predicts the observed data. The value is also sometimes called the discrepancy index, as it mathematically describes the difference between the experimental observations and the ideal calculated values. It is defined by the following equation:
where F is the so-called structure factor and the sum extends over all the reflections of X-rays measured and their calculated counterparts respectively. The structure factor is closely related to the intensity of the reflection it describes:
The minimum possible value is zero, indicating perfect agreement between experimental observations and the structure factors predicted from the model. There is no theoretical maximum, but in practice, values are considerably less than one even for poor models, provided the model includes a suitable scale factor. Random experimental errors in the data contribute to even for a perfect model, and these have more leverage when the data are weak or few, such as for a low-resolution data set. Model inadequacies such as incorrect or missing parts and unmodeled disorder are the other main contributors to , making it useful to assess the progress and final result of a crystallographic model refinement. For large molecules, the R-factor usually ranges between 0.6 (when computed for a random model and against an experimental data set) and 0.2 (for example for a well refined macro-molecular model at a resolution of 2.5 Ångström). Small molecules (up to ca. 1000 atoms) usually form better-ordered crystals than large molecules, and thus it is possible to attain lower R-factors. In the Cambridge Structural Database of small-molecule structures, more than 95% of the 500,000+ crystals have an R-factor lower than 0.15, and 9.5% have an R-factor lower than 0.03.
Crystallographers also use the Free R-Factor () to assess possible overmodeling of the data. is computed according to the same formula given above, but on a small, random sample of data that are set aside for the purpose and never included in the refinement. will always be greater than because the model is not fitted to the reflections that contribute to , but the two statistics should be similar because a correct model should predict all the data with uniform accuracy. If the two statistics differ significantly then that indicates the model has been over-parameterized, so that to some extent it predicts not the ideal error-free data for the correct model, but rather the error-afflicted data actually observed.
The quantities and are similarly used to describe the internal agreement of measurements in a crystallographic data set. | 3 | Analytical Chemistry |
Deviations of the compressibility factor, Z, from unity are due to attractive and repulsive intermolecular forces. At a given temperature and pressure, repulsive forces tend to make the volume larger than for an ideal gas; when these forces dominate Z is greater than unity. When attractive forces dominate, Z is less than unity. The relative importance of attractive forces decreases as temperature increases (see effect on gases).
As seen above, the behavior of Z is qualitatively similar for all gases. Molecular nitrogen, N, is used here to further describe and understand that behavior. All data used in this section were obtained from the NIST Chemistry WebBook. It is useful to note that for N the normal boiling point of the liquid is 77.4 K and the critical point is at 126.2 K and 34.0 bar.
The figure on the right shows an overview covering a wide temperature range. At low temperature (100 K), the curve has a characteristic check-mark shape, the rising portion of the curve is very nearly directly proportional to pressure. At intermediate temperature (160 K), there is a smooth curve with a broad minimum; although the high pressure portion is again nearly linear, it is no longer directly proportional to pressure. Finally, at high temperature (400 K), Z is above unity at all pressures. For all curves, Z approaches the ideal gas value of unity at low pressure and exceeds that value at very high pressure.
To better understand these curves, a closer look at the behavior for low temperature and pressure is given in the second figure. All of the curves start out with Z equal to unity at zero pressure and Z initially decreases as pressure increases. N is a gas under these conditions, so the distance between molecules is large, but becomes smaller as pressure increases. This increases the attractive interactions between molecules, pulling the molecules closer together and causing the volume to be less than for an ideal gas at the same temperature and pressure. Higher temperature reduces the effect of the attractive interactions and the gas behaves in a more nearly ideal manner.
As the pressure increases, the gas eventually reaches the gas-liquid coexistence curve, shown by the dashed line in the figure. When that happens, the attractive interactions have become strong enough to overcome the tendency of thermal motion to cause the molecules to spread out; so the gas condenses to form a liquid. Points on the vertical portions of the curves correspond to N being partly gas and partly liquid. On the coexistence curve, there are then two possible values for Z, a larger one corresponding to the gas and a smaller value corresponding to the liquid. Once all the gas has been converted to liquid, the volume decreases only slightly with further increases in pressure; then Z is very nearly proportional to pressure.
As temperature and pressure increase along the coexistence curve, the gas becomes more like a liquid and the liquid becomes more like a gas. At the critical point, the two are the same. So for temperatures above the critical temperature (126.2 K), there is no phase transition; as pressure increases the gas gradually transforms into something more like a liquid. Just above the critical point there is a range of pressure for which Z drops quite rapidly (see the 130 K curve), but at higher temperatures the process is entirely gradual.
The final figures shows the behavior at temperatures well above the critical temperatures. The repulsive interactions are essentially unaffected by temperature, but the attractive interaction have less and less influence. Thus, at sufficiently high temperature, the repulsive interactions dominate at all pressures.
This can be seen in the graph showing the high temperature behavior. As temperature increases, the initial slope becomes less negative, the pressure at which Z is a minimum gets smaller, and the pressure at which repulsive interactions start to dominate, i.e. where Z goes from less than unity to greater than unity, gets smaller. At the Boyle temperature (327 K for N), the attractive and repulsive effects cancel each other at low pressure. Then Z remains at the ideal gas value of unity up to pressures of several tens of bar. Above the Boyle temperature, the compressibility factor is always greater than unity and increases slowly but steadily as pressure increases. | 7 | Physical Chemistry |
In organic chemistry, electronegativity is associated more with different functional groups than with individual atoms. The terms group electronegativity and substituent electronegativity are used synonymously. However, it is common to distinguish between the inductive effect and the resonance effect, which might be described as σ- and π-electronegativities, respectively. There are a number of linear free-energy relationships that have been used to quantify these effects, of which the Hammett equation is the best known. Kabachnik parameters are group electronegativities for use in organophosphorus chemistry. | 3 | Analytical Chemistry |
Peanut agglutinin (PNA) is plant lectin protein derived from the fruits of Arachis hypogaea. Peanut agglutinin may also be referred to as Arachis hypogaea lectin. Lectins recognise and bind particular sugar sequences in carbohydrates; peanut agglutinin binds the carbohydrate sequence Gal-β(1-3)-GalNAc. The name "peanut agglutinin" originates from its ability to stick together (agglutinate) cells, such as neuraminidase-treated erythrocytes, which have glycoproteins or glycolipids on their surface which include the Gal-β(1-3)-GalNAc carbohydrate sequence. | 1 | Biochemistry |
Exogenous retroviruses are infectious RNA- or DNA-containing viruses that are transmitted from one organism to another. In the Baltimore classification system, which groups viruses together based on their manner of messenger RNA synthesis, they are classified into two groups: Group VI: single-stranded RNA viruses with a DNA intermediate in their life cycle, and Group VII: double-stranded DNA viruses with an RNA intermediate in their life cycle. | 1 | Biochemistry |
Heat cramps, a type of heat illness, are muscle spasms that result from loss of large amount of salt and water through exercise. Heat cramps are associated with cramping in the abdomen, arms and calves. This can be caused by inadequate consumption of fluids or electrolytes. Heavy sweating causes heat cramps, especially when the water is replaced without also replacing salt or potassium.
Although heat cramps can be quite painful, they usually don't result in permanent damage, though they can be a symptom of heat stroke or heat exhaustion. Heat cramps can indicate a more severe problem in someone with heart disease or if they last for longer than an hour.
In order to prevent them, one may drink electrolyte solutions such as sports drinks during exercise or strenuous work or eat potassium-rich foods like bananas and apples. When heat cramps occur, the affected person should avoid strenuous work and exercise for several hours to allow for recovery. | 7 | Physical Chemistry |
Sulfuric acid contains not only molecules, but is actually an equilibrium of many other chemical species, as it is shown in the table below.
Sulfuric acid is a colorless oily liquid, and has a vapor pressure of <0.001 mmHg at 25 °C and 1 mmHg at 145.8 °C, and 98% sulfuric acid has a vapor pressure of <1 mmHg at 40 °C.
In the solid state, sulfuric acid is a molecular solid that forms monoclinic crystals with nearly trigonal lattice parameters. The structure consists of layers parallel to the (010) plane, in which each molecule is connected by hydrogen bonds to two others. Hydrates are known for n = 1, 2, 3, 4, 6.5, and 8, although most intermediate hydrates are stable against disproportionation. | 7 | Physical Chemistry |
There has been some controversy about AstraZenecas behaviour in creating, patenting, and marketing the drug. Esomeprazoles successful predecessor, omeprazole, is a mixture of two mirror-imaged molecules (esomeprazole which is the S-enantiomer, and R-omeprazole); critics said the company was trying to "evergreen" its omeprazole patent by patenting the pure esomeprazole and aggressively marketing to doctors that it is more effective than the mixture. | 4 | Stereochemistry |
In day-to-day life all of us observe that a stream of water emerging from a faucet will break up into droplets, no matter how smoothly the stream is emitted from the faucet. This is due to a phenomenon called the Plateau–Rayleigh instability, which is entirely a consequence of the effects of surface tension.
The explanation of this instability begins with the existence of tiny perturbations in the stream. These are always present, no matter how smooth the stream is. If the perturbations are resolved into sinusoidal components, we find that some components grow with time while others decay with time. Among those that grow with time, some grow at faster rates than others. Whether a component decays or grows, and how fast it grows is entirely a function of its wave number (a measure of how many peaks and troughs per centimeter) and the radii of the original cylindrical stream. | 6 | Supramolecular Chemistry |
Paramural bodies are membranous or vesicular structures located between the cell walls and cell membranes of plant and fungal cells. When these are continuous with the cell wall, they are termed lomasomes, while they are referred to as plasmalemmasomes if associated with the plasmalemma. | 1 | Biochemistry |
Coagulation or blood clotting relies on, in addition to the production of fibrin, interactions between platelets. When the endothelium or the lining of a blood vessel is damaged, connective tissue including collagen fibers is locally exposed. Initially, platelets stick to the exposed connective tissue through specific cell-surface receptors. This is followed by platelet activation and aggregation in which platelets become firmly attached and release chemicals that recruit neighboring platelets to the site of vascular injury. A meshwork of fibrin then forms around this aggregation of platelets to increase the strength of the clot. | 1 | Biochemistry |
Amperometric transducers detect change in current as a result of electrochemical oxidation or reduction. Typically, the bioreceptor molecule is immobilized on the working electrode (commonly gold, carbon, or platinum). The potential between the working electrode and the reference electrode (usually Ag/AgCl) is fixed at a value and then current is measured with respect to time. The applied potential is the driving force for the electron transfer reaction. The current produced is a direct measure of the rate of electron transfer. The current reflects the reaction occurring between the bioreceptor molecule and analyte and is limited by the mass transport rate of the analyte to the electrode. | 1 | Biochemistry |
SOD2 uses cyclic proton-coupled electron transfer reactions to convert superoxide (O) into either oxygen (O) or hydrogen peroxide (HO), depending on the oxidation state of the manganese metal and the protonation status of the active site.
Mn + O ↔ Mn + O
Mn + O + 2H ↔ Mn + HO
The protons of the active site have been directly visualized and revealed that SOD2 utilizes proton transfers between a glutamine residue and a Mn-bound solvent molecule in concert with its electron transfers. During the Mn to Mn redox reaction, Gln143 donates an amide proton to hydroxide bound to the Mn and forms an amide anion. The amide anion is stabilized by short-strong hydrogen bonds (SSHBs) with the Mn-bound solvent and the nearby Trp123 residue. For the Mn to Mn redox reaction, the proton is donated back to the glutamine to reform the neutral amide state. The fast and efficient PCET catalysis of SOD2 is explained by the use of a proton that is always present and never lost to bulk solvent. | 7 | Physical Chemistry |
Here, the aglycone is coumarin or a derivative. An example is apterin which is reported to dilate the coronary arteries as well as block calcium channels. Other coumarin glycosides are obtained from dried leaves of Psoralea corylifolia. | 0 | Organic Chemistry |
In a gridless ion source, ions are generated by a flow of electrons (no grids). The most common gridless ion source is the end-Hall ion source. Here, the discharge current and the gas flow are used to control the beam current. | 7 | Physical Chemistry |
Several strategies exist for avoiding β-hydride elimination. The most common strategy is to employ alkyl ligands that do not have any hydrogen atoms at the β position. Common substituents include methyl and neopentyl. β-Hydride elimination is also inhibited when the reaction would produce a strained alkene. This situation is illustrated by the stability of metal complexes containing norbornyl ligands, where the β-hydride elimination product would violate Bredt's rule.
Bulky alkyl ligands, such as tert-butyl or trimethylsilyl, may prohibit the hydrogen atom from approaching a coplanar configuration with respect to the metal, and the α and β atoms. If the metal center does not have empty coordination sites, for example by the complex already having an 18-electron configuration, β-hydride elimination is not possible as well.
In some cases, the coligands can impose geometries that inhibit β-hydride elimination. For the above example, the unwanted β-hydride elimination is prevented by using a diphosphine where the two phosphorus atoms are fixed apart in space. One way of doing this is to use a trans spanning ligand such as Xantphos. As these metal complexes traditionally form square planar geometries, no vacant site cis to the alkyl group can be formed. Hence the β-hydride elimination is prevented. (See trans-spanning ligand.) | 0 | Organic Chemistry |
Emanuel Gil-Av (Zimkin) (7 August 1916 – 24 March 1996) was an Israeli chemist. The main emphasis of his work constituted chiral chromatography for the analytical separation of enantiomers. | 3 | Analytical Chemistry |
The standard photovoltaic effect, as operating in standard photovoltaic cells, involves the excitation of negative charge carriers (electrons) within a semiconductor medium, and it is negative charge carriers (free electrons) which are ultimately extracted to produce power. The classification of photoelectrochemical cells which includes Grätzel cells meets this narrow definition, albeit the charge carriers are often excitonic.
The situation within a photoelectrolytic cell, on the other hand, is quite different. For example, in a water-splitting photoelectrochemical cell, the excitation, by light, of an electron in a semiconductor leaves a hole which "draws" an electron from a neighboring water molecule:
This leaves positive charge carriers (protons, that is, H+ ions) in solution, which must then bond with one other proton and combine with two electrons in order to form hydrogen gas, according to:
A photosynthetic cell is another form of photoelectrolytic cell, with the output in that case being carbohydrates instead of molecular hydrogen. | 5 | Photochemistry |
In the solar thermochemical process, water is split into hydrogen and oxygen using direct solar heat, rather than electricity, inside a high temperature solar reactor which receives highly concentrated solar flux from a solar field of heliostats that focus the highly concentrated sunlight into the reactor.
The two most promising routes are the two step cerium oxide cycle and the copper chlorine hybrid cycle. For the cerium oxide cycle the first step is to strip the CeO into CeO at more than 1400 °C. After the thermal reduction step to reduce the metal oxide, hydrogen is then produced through hydrolysis at around 800 °C. The copper chloride cycle requires a lower temperature (~500°C), which makes this process more efficient, but the cycle contains more steps and is also more complex than the cerium oxide cycle.
Because hydrogen manufacture requires continuous performance, the solar thermochemical process includes thermal energy storage. Another thermochemical method uses solar reforming of methane, a process that replicates traditional fossil fuel reforming process but substitutes solar heat.
In a November 2021 publication in Nature, Aldo Steinfeld of Swiss technological university ETH Zurich reported an artificial photosynthesis where carbon dioxide and water vapour absorbed from the air are passed over a cerium oxide catalyst heated by concentrated solar power to produce hydrogen and carbon monoxide, transformed through the Fischer-Tropsch process into complex hydrocarbons forming methanol, a liquid fuel.
Scaling could produce the of aviation fuel used in 2019 with a surface of : 0.5% of the Sahara Desert.
One author, Philipp Furler, leads specialist Synhelion, which in 2022 was building a solar fuel production facility at Jülich, west of Cologne, before another one in Spain.
Swiss airlines, part of the Lufthansa Group, should become its first customer in 2023. | 5 | Photochemistry |
The primary conditions for soil development are controlled by the chemical composition of the rock on which the soil will be. Rock types that form the base of the soil profile are often either sedimentary (carbonate or siliceous), igneous or metaigneous (metamorphosed igneous rocks) or volcanic and metavolcanic rocks. The rock type and the processes that lead to its exposure at the surface are controlled by the regional geologic setting of the specific area under study, which revolve around the underlying theory of plate tectonics, subsequent deformation, uplift, subsidence and deposition.
Metaigneous and metavolcanic rocks form the largest component of cratons and are high in silica. Igneous and volcanic rocks are also high in silica, but with non-metamorphosed rock, weathering becomes faster and the mobilization of ions is more widespread. Rocks high in silica produce silicic acid as a weathering product. There are few rock types that lead to localized enrichment of some of the biologically limiting elements like phosphorus (P) and nitrogen (N). Phosphatic shale (O) and phosphorite (> 15% PO) form in anoxic deep water basins that preserve organic material. Greenstone (metabasalt), phyllite, and schist release up to 30–50% of the nitrogen pool. Thick successions of carbonate rocks are often deposited on craton margins during sea level rise. The widespread dissolution of carbonate and evaporites leads to elevated levels of Mg, , Sr, Na, Cl and ions in aqueous solution. | 9 | Geochemistry |
According to the safety data sheet of PPA, it should not be allowed in contact with the skin or eyes as it may lead to skin, eye, and respiratory irritations or allergic reactions. In addition, as some unfunctionalized PPA are unstable at temperatures even lower than room temperature, it is important to note that PPA should be stored at temperatures below -10 °C under inert atmosphere and away from sunlight, moisture, and heat, but with proper ventilation.
Since the depolymerization of PPA is greatly studied in its applications, it is important to also note the possible safety concerns of its monomer. In addition to the abovementioned hazards of PPA, phthalaldehyde is very toxic if swallowed and for aquatic life. | 7 | Physical Chemistry |
Fugacity is closely related to the chemical potential . In a pure substance, is equal to the Gibbs energy for a mole of the substance, and
where and are the temperature and pressure, is the volume per mole and is the entropy per mole. | 7 | Physical Chemistry |
Murexide (NHCHNO, or CHNO·NH), also called ammonium purpurate or MX, is the ammonium salt of purpuric acid. It is a purple solid that is soluble in water. The compound was once used as an indicator reagent. Aqueous solutions are yellow at low pH, reddish-purple in weakly acidic solutions, and blue-purple in alkaline solutions. | 3 | Analytical Chemistry |
The world's supply of titanium metal, about 250,000 tons per year, is made from . The conversion involves the reduction of the tetrachloride with magnesium metal. This procedure is known as the Kroll process:
In the Hunter process, liquid sodium is the reducing agent instead of magnesium. | 0 | Organic Chemistry |
A more detailed knowledge of the structures of metals, and binary and ternary phases of metals and non metals shows that:
*generally at low concentrations of the small atom, the phase can be described as a solution, and this approximates to the historical description of an interstitial compound above.
*at higher concentrations of the small atom, phases with different lattice structures may be present, and these may have a range of stoichiometries.
One example is the solubility of carbon in iron. The form of pure iron stable between 910 °C and 1390 °C, γ-iron, forms a solid solution with carbon termed austenite which is also known as steel. | 8 | Metallurgy |
Polyelectrolytes that bear both cationic and anionic repeat groups are called polyampholytes. The competition between the acid-base equilibria of these groups leads to additional complications in their physical behavior. These polymers usually only dissolve when sufficient added salt screens the interactions between oppositely charged segments. In the case of amphoteric macroporous hydrogels, the action of concentrated salt solution does not lead to the dissolution of polyampholyte material due to the covalent cross-linking of macromolecules. Synthetic 3-D macroporous hydrogels shows the excellent ability to adsorb heavy-metal ions in a wide range of pH from extremely diluted aqueous solutions, which can be later used as an adsorbent for purification of salty water All proteins are polyampholytes, as some amino acids tend to be acidic, while others are basic. | 7 | Physical Chemistry |
The Imd pathway appears to have evolved in the last common ancestor of centipedes and insects. However certain lineages of insects have since lost core components of Imd signalling. The first-discovered and most famous example is the pea aphid Acyrthosiphon pisum. It is thought that plant-feeding aphids have lost Imd signalling as they bear a number of bacterial endosymbionts, including both nutritional symbionts that would be disrupted by aberrant expression of antimicrobial peptides, and defensive symbionts that cover for some of the immune deficiency caused by loss of Imd signalling. It has also been suggested that antimicrobial peptides, the downstream components of Imd signalling, may be detrimental to fitness and lost by insects with exclusively plant-feeding ecologies. | 1 | Biochemistry |
A mathematical description of vacuum Rabi oscillation begins with the Jaynes–Cummings model, which describes the interaction between a single mode of a quantized field and a two level system inside an optical cavity. The Hamiltonian for this model in the rotating wave approximation is
where is the Pauli z spin operator for the two eigenstates and of the isolated two level system separated in energy by ; and are the raising and lowering operators of the two level system; and are the creation and annihilation operators for photons of energy in the cavity mode; and
is the strength of the coupling between the dipole moment of the two level system and the cavity mode with volume and electric field polarized along .
The energy eigenvalues and eigenstates for this model are
where is the detuning, and the angle is defined as
Given the eigenstates of the system, the time evolution operator can be written down in the form
If the system starts in the state , where the atom is in the ground state of the two level system and there are photons in the cavity mode, the application of the time evolution operator yields
The probability that the two level system is in the excited state as a function of time is then
where is identified as the Rabi frequency. For the case that there is no electric field in the cavity, that is, the photon number is zero, the Rabi frequency becomes . Then, the probability that the two level system goes from its ground state to its excited state as a function of time is
For a cavity that admits a single mode perfectly resonant with the energy difference between the two energy levels, the detuning vanishes, and becomes a squared sinusoid with unit amplitude and period | 7 | Physical Chemistry |
Atoms and molecules of gas or liquid can be trapped on a solid surface in a process called adsorption. This is an exothermic process involving a release of heat, and heating the surface increases the probability that an atom will escape within a given time. At a given temperature , the residence time of an adsorbed atom is given by
where is the gas constant, is an activation energy, and is a prefactor that is correlated with the vibration times of the surface atoms (generally of the order of seconds).
In vacuum technology, the residence time of gases on the surfaces of a vacuum chamber can determine the pressure due to outgassing. If the chamber can be heated, the above equation shows that the gases can be "baked out"; but if not, then surfaces with a low residence time are needed to achieve ultra-high vacuums. | 9 | Geochemistry |
In the Semail Nappe of Oman in the United Arb Emirates, silicified serpentinite was found. The occurrence of such geological features is rather unusual. It is a pseudomorphic alteration where the protolith of serpentinite was already silicified. Due to tectonic events, basal serpentinite was fractured and groundwater permeated along the faults, forming a large-scale circulation of groundwater within the strata. Through hydrothermal dissolution, silica precipitated and crystallized around the voids of serpentinite. Therefore, silicification can only be seen along groundwater paths. The silicification of serpentinite was formed under the condition where groundwater flow and carbon dioxide concentration are low. | 9 | Geochemistry |
Just as relative entropy of "actual from ambient" measures thermodynamic availability, relative entropy of "reality from a model" is also useful even if the only clues we have about reality are some experimental measurements. In the former case relative entropy describes distance to equilibrium or (when multiplied by ambient temperature) the amount of available work, while in the latter case it tells you about surprises that reality has up its sleeve or, in other words, how much the model has yet to learn.
Although this tool for evaluating models against systems that are accessible experimentally may be applied in any field, its application to selecting a statistical model via Akaike information criterion are particularly well described in papers and a book by Burnham and Anderson. In a nutshell the relative entropy of reality from a model may be estimated, to within a constant additive term, by a function of the deviations observed between data and the model's predictions (like the mean squared deviation) . Estimates of such divergence for models that share the same additive term can in turn be used to select among models.
When trying to fit parametrized models to data there are various estimators which attempt to minimize relative entropy, such as maximum likelihood and maximum spacing estimators. | 7 | Physical Chemistry |
In Rutherford scattering, an incident particle with charge and energy scatters off a fixed particle with charge . The differential cross section is
where is the Coulomb constant. The total cross section is infinite unless a cutoff for small scattering angles is applied. This is due to the long range of the Coulomb potential. | 7 | Physical Chemistry |
Current RO membranes, thin-film composite (TFC) polyamide membranes, are being studied to find ways of improving their permeability. Through new imaging methods, researchers were able to make 3D models of membranes and examine how water flowed through them. They found that TFC membranes with areas of low flow significantly decreased water permeability. By ensuring uniformity of the membranes and allowing water to flow continuously without slowing down, membrane permeability could be improved by 30%-40%. | 3 | Analytical Chemistry |
After amplifying and then concentrating the target analyte, the samples are labeled with a fluorescent dye using an antibody for specificity and then finally loaded into a microcapillary tube. This tube is placed in a specially constructed apparatus so it is totally surrounded by optical fibers to capture all light emitted once the dye is excited using a laser. | 1 | Biochemistry |
The exo-anomeric effect is similar to the endo-anomeric effect. The difference being that the lone pair being donated is coming from the substituent at C-1. However, since the substituent can be either axial or equatorial there are two types of exo-anomeric effects, one from axial glycosides and one from equatorial glycosides as long as the donating orbital is anti-periplanar to the accepting orbital. | 0 | Organic Chemistry |
According to Arrhenius's original molecular definition, an acid is a substance that dissociates in aqueous solution, releasing the hydrogen ion (a proton):
The equilibrium constant for this dissociation reaction is known as a dissociation constant. The liberated proton combines with a water molecule to give a hydronium (or oxonium) ion (naked protons do not exist in solution), and so Arrhenius later proposed that the dissociation should be written as an acid–base reaction:
Brønsted and Lowry generalised this further to a proton exchange reaction:
The acid loses a proton, leaving a conjugate base; the proton is transferred to the base, creating a conjugate acid. For aqueous solutions of an acid HA, the base is water; the conjugate base is and the conjugate acid is the hydronium ion. The Brønsted–Lowry definition applies to other solvents, such as dimethyl sulfoxide: the solvent S acts as a base, accepting a proton and forming the conjugate acid .
In solution chemistry, it is common to use as an abbreviation for the solvated hydrogen ion, regardless of the solvent. In aqueous solution denotes a solvated hydronium ion rather than a proton.
The designation of an acid or base as "conjugate" depends on the context. The conjugate acid of a base B dissociates according to
which is the reverse of the equilibrium
The hydroxide ion , a well known base, is here acting as the conjugate base of the acid water. Acids and bases are thus regarded simply as donors and acceptors of protons respectively.
A broader definition of acid dissociation includes hydrolysis, in which protons are produced by the splitting of water molecules. For example, boric acid () produces as if it were a proton donor, but it has been confirmed by Raman spectroscopy that this is due to the hydrolysis equilibrium:
Similarly, metal ion hydrolysis causes ions such as to behave as weak acids:
According to Lewis's original definition, an acid is a substance that accepts an electron pair to form a coordinate covalent bond. | 7 | Physical Chemistry |
The use of molten CaCl is important because this molten salt can dissolve and transport the "O" ions to the anode to be discharged. The anode reaction depends on the material of the anode. Depending on the system it is possible to produce either CO or CO or a mixture at the carbon anode:
However, if an inert anode is used, such as that of high density SnO, the discharge of the O ions leads to the evolution of oxygen gas. However the use of an inert anode has disadvantages. Firstly, when the concentration of CaO is low, Cl evolution at the anode becomes more favourable. In addition, when compared to a carbon anode, more energy is required to achieve the same reduced phase at the cathode. Inert anodes suffer from stability issues. | 7 | Physical Chemistry |
Photobromination with elemental bromine proceeds analogous to photochlorination also via a radical mechanism. In the presence of oxygen, the hydrogen bromide formed is partly oxidised back to bromine, resulting in an increased yield. Because of the easier dosage of the elemental bromine and the higher selectivity of the reaction, photobromination is preferred over photochlorination at laboratory scale. For industrial applications, bromine is usually too expensive (as it is present in sea water in small quantities only and produced from oxidation with chlorine). Instead of elemental bromine, N-bromosuccinimide is also suitable as a brominating agent. The quantum yield of photobromination is usually much lower than that of photochlorination. | 5 | Photochemistry |
Etiocholanedione, also known as 5β-androstanedione or as etiocholane-3,17-dione, is a naturally occurring etiocholane (5β-androstane) steroid and an endogenous metabolite of androgens like testosterone, dihydrotestosterone, dehydroepiandrosterone (DHEA), and androstenedione. It is the C5 epimer of androstanedione (5α-androstanedione). Although devoid of androgenic activity like other 5β-reduced steroids, etiocholanedione has some biological activity of its own. The compound has been found to possess potent haematopoietic effects in a variety of models. In addition, it has been found to promote weight loss in animals and in a double-blind, placebo-controlled clinical study in humans conducted in 1993. These effects are said to be similar to those of DHEA. Unlike DHEA however, etiocholanedione cannot be metabolized further into steroid hormones like androgens and estrogens. | 1 | Biochemistry |
When a photon is the incident particle, there is an inelastic scattering process called Raman scattering. In this scattering process, the incident photon interacts with matter (gas, liquid, and solid) and the frequency of the photon is shifted towards red or blue. A red shift can be observed when part of the energy of the photon is transferred to the interacting matter, where it adds to its internal energy in a process called Stokes Raman scattering. The blue shift can be observed when internal energy of the matter is transferred to the photon; this process is called anti-Stokes Raman scattering.
Inelastic scattering is seen in the interaction between an electron and a photon. When a high-energy photon collides with a free electron (more precisely, weakly bound since a free electron cannot participate in inelastic scattering with a photon) and transfers energy, the process is called Compton scattering. Furthermore, when an electron with relativistic energy collides with an infrared or visible photon, the electron gives energy to the photon. This process is called inverse Compton scattering. | 7 | Physical Chemistry |
The metabolism of bacteria is adversely affected by silver ions at concentrations of 0.01–0.1 mg/L. Therefore, even less soluble silver compounds, such as silver chloride, also act as bactericides or germicides, but not the much less soluble silver sulfide. In the presence of atmospheric oxygen, metallic silver also has a bactericidal effect due to the formation of silver oxide, which is soluble enough to cause it. Even objects with a solid silver surface (e.g., table silver, silver coins, or silver foil) have a bactericidal effect. Silver drinking vessels were carried by military commanders on expeditions for protection against disease. It was once common to place silver foil or even silver coins on wounds for the same reason.
Silver sulfadiazine is used as an antiseptic ointment for extensive burns. An equilibrium dispersion of colloidal silver with dissolved silver ions can be used to purify drinking water at sea. Silver is incorporated into medical implants and devices such as catheters. Surfacine (silver iodide) is a relatively new antimicrobial for application to surfaces. Silver-impregnated wound dressings have proven especially useful against antibiotic-resistant bacteria. Silver nitrate is used as a hemostatic, antiseptic and astringent. At one time, many states required that the eyes of newborns be treated with a few drops of silver nitrate to guard against an infection of the eyes called gonorrheal neonatal ophthalmia, which the infants might have contracted as they passed through the birth canal. Silver ions are increasingly incorporated into many hard surfaces, such as plastics and steel, as a way to control microbial growth on items such as toilet seats, stethoscopes, and even refrigerator doors. Among the newer products being sold are plastic food containers infused with silver nanoparticles, which are intended to keep food fresher, and silver-infused athletic shirts and socks, which claim to minimize odors. | 1 | Biochemistry |
Fluorescein diacetate (FDA) hydrolysis assays can be used to measure the enzyme activity of microbes in a sample. A bright yellow-green glow is produced and is strongest when enzymatic activity is greatest. This can be quantified using a spectrofluorometer or a spectrophotometer. | 1 | Biochemistry |
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable atoms survive. The term is also used more generally to characterize any type of exponential (or, rarely, non-exponential) decay. For example, the medical sciences refer to the biological half-life of drugs and other chemicals in the human body. The converse of half-life (in exponential growth) is doubling time.
The original term, half-life period, dating to Ernest Rutherfords discovery of the principle in 1907, was shortened to half-life in the early 1950s. Rutherford applied the principle of a radioactive elements half-life in studies of age determination of rocks by measuring the decay period of radium to lead-206.
Half-life is constant over the lifetime of an exponentially decaying quantity, and it is a characteristic unit for the exponential decay equation. The accompanying table shows the reduction of a quantity as a function of the number of half-lives elapsed. | 7 | Physical Chemistry |
Integrated pest management (IPM), also known as integrated pest control (IPC) is a broad-based approach that integrates both chemical and non-chemical practices for economic control of pests. IPM aims to suppress pest populations below the economic injury level (EIL). The UN's Food and Agriculture Organization defines IPM as "the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the environment. IPM emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms." Entomologists and ecologists have urged the adoption of IPM pest control since the 1970s. IPM allows for safer pest control.
The introduction and spread of invasive species can also be managed with IPM by reducing risks while maximizing benefits and reducing costs. | 9 | Geochemistry |
Fluorination by sulfur tetrafluoride produces organofluorine compounds from oxygen-containing organic functional groups using sulfur tetrafluoride. The reaction has broad scope, and SF is an inexpensive reagent. It is however hazardous gas whose handling requires specialized apparatus. Thus, for many laboratory scale fluorinations diethylaminosulfur trifluoride ("DAST") is used instead. | 0 | Organic Chemistry |
Control coefficients measure the response of a biochemical pathway to changes in enzyme activity. The response coefficient, as originally defined by Kacser and Burns, is a measure of how external factors such as inhibitors, pharmaceutical drugs, or boundary species affect the steady-state fluxes and species concentrations. The flux response coefficient is defined by:
where is the steady-state pathway flux. Similarly, the concentration response coefficient is defined by the expression:
where in both cases is the concentration of the external factor. The response coefficient measures how sensitive a pathway is to changes in external factors other than enzyme activities.
The flux response coefficient is related to control coefficients and elasticities through the following relationship:
Likewise, the concentration response coefficient is related by the following expression:
The summation in both cases accounts for cases where a given external factor, , can act at multiple sites. For example, a given drug might act on multiple protein sites. The overall response is the sum of the individual responses.
These results show that the action of an external factor, such as a drug, has two components:
# The elasticity indicates how potent the drug is at affecting the activity of the target site itself.
# The control coefficient indicates how any perturbation at the target site will propagate to the rest of the system and thereby affect the phenotype.
When designing drugs for therapeutic action, both aspects must therefore be considered. | 1 | Biochemistry |
Luteal support is the administration of medication, generally progesterone, progestins, hCG, or GnRH agonists, and often accompanied by estradiol, to increase the success rate of implantation and early embryogenesis, thereby complementing and/or supporting the function of the corpus luteum. A Cochrane review found that hCG or progesterone given during the luteal phase may be associated with higher rates of live birth or ongoing pregnancy, but that the evidence is not conclusive. Co-treatment with GnRH agonists appears to improve outcomes, by a live birth rate RD of +16% (95% confidence interval +10 to +22%). On the other hand, growth hormone or aspirin as adjunctive medication in IVF have no evidence of overall benefit. | 1 | Biochemistry |
Cefuroxime axetil is an ester prodrug of cefuroxime which is effective when taken by mouth. It is a second-generation cephalosporin. | 4 | Stereochemistry |
The amount of strain energy in bicyclic systems is commonly the sum of the strain energy in each individual ring. This isn't always the case, as sometimes the fusion of rings induces some extra strain. | 4 | Stereochemistry |
A body of icy or rocky material in outer space may, if it can build and retain sufficient heat, develop a differentiated interior and alter its surface through volcanic or tectonic activity. The length of time through which a planetary body can maintain surface-altering activity depends on how well it retains heat, and this is governed by its surface area-to-volume ratio. For Vesta (r=263 km), the ratio is so high that astronomers were surprised to find that it did differentiate and have brief volcanic activity. The moon, Mercury and Mars have radii in the low thousands of kilometers; all three retained heat well enough to be thoroughly differentiated although after a billion years or so they became too cool to show anything more than very localized and infrequent volcanic activity. As of April 2019, however, NASA has announced the detection of a "marsquake" measured on April 6, 2019, by NASA's InSight lander. Venus and Earth (r>6,000 km) have sufficiently low surface area-to-volume ratios (roughly half that of Mars and much lower than all other known rocky bodies) so that their heat loss is minimal. | 7 | Physical Chemistry |
Plant virus transmission from generation to generation occurs in about 20% of plant viruses. When viruses are transmitted by seeds, the seed is infected in the generative cells and the virus is maintained in the germ cells and sometimes, but less often, in the seed coat. When the growth and development of plants is delayed because of situations like unfavorable weather, there is an increase in the amount of virus infections in seeds. There does not seem to be a correlation between the location of the seed on the plant and its chances of being infected. Little is known about the mechanisms involved in the transmission of plant viruses via seeds, although it is known that it is environmentally influenced and that seed transmission occurs because of a direct invasion of the embryo via the ovule or by an indirect route with an attack on the embryo mediated by infected gametes. These processes can occur concurrently or separately depending on the host plant. It is unknown how the virus is able to directly invade and cross the embryo and boundary between the parental and progeny generations in the ovule.
Many plants species can be infected through seeds including but not limited to the families Leguminosae, Solanaceae, Compositae, Rosaceae, Cucurbitaceae, Gramineae. Bean common mosaic virus is transmitted through seeds. | 1 | Biochemistry |
Red edge refers to the region of rapid change in reflectance of vegetation in the near infrared range of the electromagnetic spectrum. Chlorophyll contained in vegetation absorbs most of the light in the visible part of the spectrum but becomes almost transparent at wavelengths greater than 700 nm. The cellular structure of the vegetation then causes this infrared light to be reflected because each cell acts something like an elementary corner reflector. The change can be from 5% to 50% reflectance going from 680 nm to 730 nm. This is an advantage to plants in avoiding overheating during photosynthesis. For a more detailed explanation and a graph of the photosynthetically active radiation (PAR) spectral region, see .
The phenomenon accounts for the brightness of foliage in infrared photography and is extensively utilized in the form of so-called vegetation indices (e.g. Normalized difference vegetation index). It is used in remote sensing to monitor plant activity, and it has been suggested that it could be useful to detect light-harvesting organisms on distant planets. | 5 | Photochemistry |
S. pneumoniae is human pathogenic bacterium in which the process of genetic transformation was first described in the 1930s. In order for a bacterium to take up exogenous DNA from its surroundings, it must become competent. In S. pneumoniae, a number of complex events must occur to achieve a competent state, but it is believed that quorum sensing plays a role. Competence stimulating peptide (CSP) is a 17-amino acid peptide autoinducer required for competency and subsequent genetic transformation. CSP is produced by proteolytic cleavage of a 41-amino acid precursor peptide (ComC); is secreted by an ABC transporter (ComAB); and is detected by a sensor kinase protein (ComD) once it has reached a threshold concentration. Detection is followed by autophosphorylation of ComD, which in turn, phosphorylates ComE. ComE is a response regulator responsible for activating transcription of comX, the product of which is required to activate transcription of a number of other genes involved in the development of competence. | 1 | Biochemistry |
Ordinarily, carbon dioxide is fixed to ribulose 1,5-bisphosphate (RuBP) by the enzyme RuBisCO in mesophyll cells exposed directly to the air spaces inside the leaf. This exacerbates the transpiration problem for two reasons: first, RuBisCo has a relatively low affinity for carbon dioxide, and second, it fixes oxygen to RuBP, wasting energy and carbon in a process called photorespiration. For both of these reasons, RuBisCo needs high carbon dioxide concentrations, which means wide stomatal apertures and, as a consequence, high water loss.
Narrower stomatal apertures can be used in conjunction with an intermediary molecule with a high carbon dioxide affinity, phosphoenolpyruvate carboxylase (PEPcase). Retrieving the products of carbon fixation from PEPCase is an energy-intensive process, however. As a result, the PEPCase alternative is preferable only where water is limiting but light is plentiful, or where high temperatures increase the solubility of oxygen relative to that of carbon dioxide, magnifying RuBisCo's oxygenation problem. | 5 | Photochemistry |
Superhydrophobic surfaces can be created in a number of different ways including plasma or ion etching, crystal growth on a material surface, and nanolithography to name a few. All of these processes create nano-topographical features which imbue a surface with superhydrophobicity. The ultimate goal in developing superhydrophobic surfaces is to recreate the self-cleaning properties of the Lotus Leaf that has the inherent ability to repel all water in nature. The basis for superhydrophobic self-cleaning is the ability of these surfaces to prevent water from spreading out when in contact with the surface. This is reflected in a water contact angle nearing 180 degrees. Superhydrophobic self-cleaning surfaces also have low sliding angles which allows for water that is collected on the surface to easily be removed, commonly by gravity. While superhydrophobic surfaces are great for removing any water-based debris, these surfaces likely will not be able to clean away other types of fouling matter such as oil. | 7 | Physical Chemistry |
Resource intensity is a measure of the resources (e.g. water, energy, materials) needed for the production, processing and disposal of a unit of good or service, or for the completion of a process or activity; it is therefore a measure of the efficiency of resource use. It is often expressed as the quantity of resource embodied in unit cost e.g. litres of water per $1 spent on product. In national economic and sustainability accounting it can be calculated as units of resource expended per unit of GDP. When applied to a single person it is expressed as the resource use of that person per unit of consumption. Relatively high resource intensities indicate a high price or environmental cost of converting resource into GDP; low resource intensity indicates a lower price or environmental cost of converting resource into GDP.
Resource productivity and resource intensity are key concepts used in sustainability measurement as they measure attempts to decouple the connection between resource use and environmental degradation. Their strength is that they can be used as a metric for both economic and environmental cost. Although these concepts are two sides of the same coin, in practice they involve very different approaches and can be viewed as reflecting, on the one hand, the efficiency of resource production as outcome per unit of resource use (resource productivity) and, on the other hand, the efficiency of resource consumption as resource use per unit outcome (resource intensity). The sustainability objective is to maximize resource productivity while minimizing resource intensity. | 7 | Physical Chemistry |
Sometimes drugs are formulated in an inactive form that is designed to break down inside the body to form the active drug. These are called prodrugs. The reasons for this type of formulation may be because the drug is more stable during manufacture and storage as the prodrug form, or because the prodrug is better absorbed by the body or has superior pharmacokinetics (e.g., lisdexamphetamine). | 1 | Biochemistry |
The mold, protozoan, and coelenterate mitochondrial code and the mycoplasma/spiroplasma code (translation table 4) is the genetic code used by various organisms, in some cases with slight variations, notably the use of UGA as a tryptophan codon rather than a stop codon. | 1 | Biochemistry |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.