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5β-coprostanol is formed by the conversion of cholesterol to coprostanol in the gut of most higher animals by intestinal bacteria. It is generally accepted that the metabolism of cholesterol to coprostanol by gut bacteria proceeds in an indirect manner via ketone intermediates, rather than direct reduction of the Δ double bond. be seen in the figure proposed by Grimalt et al., (1990).
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There are a small number of animals, however, that have been shown not to produce 5β-coprostanol and these can be seen in the table. | 2 | Environmental Chemistry |
MicroRNAs (miRNAs) are small RNAs that typically are partially complementary to sequences in metazoan messenger RNAs. Binding of a miRNA to a message can repress translation of that message and accelerate poly(A) tail removal, thereby hastening mRNA degradation. The mechanism of action of miRNAs is the subject of active research. | 1 | Biochemistry |
The carbylamine reaction (also known as the Hoffmann isocyanide synthesis) is the synthesis of an isocyanide by the reaction of a primary amine, chloroform, and base. The conversion involves the intermediacy of dichlorocarbene.
Illustrative is the synthesis of tert-butyl isocyanide from tert-butylamine in the presence of catalytic amount of the phase transfer catalyst benzyltriethylammonium chloride.
:MeCNH + CHCl + 3 NaOH → MeCNC + 3 NaCl + 3 HO
Similar reactions have been reported for aniline. It is used to prepare secondary amines. | 0 | Organic Chemistry |
The boundary between one grain and its neighbour (grain boundary) is a defect in the crystal structure and so it is associated with a certain amount of energy. As a result, there is a thermodynamic driving force for the total area of boundary to be reduced. If the grain size increases, accompanied by a reduction in the actual number of grains per volume, then the total area of grain boundary will be reduced.
In the classic theory, the local velocity of a grain boundary at any point is proportional to the local curvature of the grain boundary, i.e.:
where is the velocity of grain boundary, is grain boundary mobility (generally depends on orientation of two grains), is the grain boundary energy and is the sum of the two principal surface curvatures. For example, shrinkage velocity of a spherical grain embedded inside another grain is
where is radius of the sphere. This driving pressure is very similar in nature to the Laplace pressure that occurs in foams.
In comparison to phase transformations the energy available to drive grain growth is very low and so it tends to occur at much slower rates and is easily slowed by the presence of second phase particles or solute atoms in the structure.
Recently, in contrast to the classic linear relation between grain boundary velocity and curvature, grain boundary velocity and curvature are observed to be not correlated in Ni polycrystals, which conflicting results has been revealed and be theoretically interpreted by a general model of grain boundary (GB) migration in the previous literature. According to the general GB migration model, the classical linear relation can only be used in a specical case. | 8 | Metallurgy |
In common usage the terms "ring" and "ring system" are frequently interchanged, with the appropriate definition depending upon context. Typically a "ring" denotes a simple ring, unless otherwise qualified, as in terms like "polycyclic ring", "fused ring", "spiro ring" and "indole ring", where clearly a polycyclic ring system is intended. Likewise, a "ring system" typically denotes a polycyclic ring system, except in terms like "monocyclic ring system" or "pyridine ring system". To reduce ambiguity, IUPAC's recommendations on organic nomenclature avoid the use of the term "ring" by using phrases such as "monocyclic parent" and "polycyclic ring system". | 4 | Stereochemistry |
Asymmetrical trichlorotrifluoroethane, also called 1,1,1-Trichloro-2,2,2-trifluoroethane or CFC-113a is a chlorofluorocarbon (CFC). It has the formula . | 2 | Environmental Chemistry |
Composition of isometries mixes kinds in assorted ways. We can think of the identity as either two mirrors or none; either way, it has no effect in composition. And two reflections give either a translation or a rotation, or the identity (which is both, in a trivial way). Reflection composed with either of these could cancel down to a single reflection; otherwise it gives the only available three-mirror isometry, a glide reflection. A pair of translations always reduces to a single translation; so the challenging cases involve rotations. We know a rotation composed with either a rotation or a translation must produce an even isometry. Composition with translation produces another rotation (by the same amount, with shifted fixed point), but composition with rotation can yield either translation or rotation. It is often said that composition of two rotations produces a rotation, and Euler proved a theorem to that effect in 3D; however, this is only true for rotations sharing a fixed point. | 3 | Analytical Chemistry |
*1960–61 – Fulbright–Smith–Mundt Fellowship
*1962–63 – Harrison Fellowship at University of Pennsylvania
*1986 – Guggenheim Fellowship
*2000 – Sir Edward Frankland Prize Lectureship
*2009 – Invited Lectureship, 4th Mitsui International Catalysis Symposium (MICS-4), Kisarazu, Japan
*2010 – Order of Culture
*2010 – Person of Cultural Merit
*2011 – Sagamore of the Wabash
*2011 – Order of the Griffin, Purdue University
*2011 – Fellow, American Academy of Arts & Sciences
*2011 – Honorary doctor of science, University of Pennsylvania.
*2012 – Honorary Fellow of Royal Society of Chemistry (RSC)
*2014 – Foreign Associate of the National Academy of Sciences | 0 | Organic Chemistry |
Liu et al. synthesized a HILIC/RP stationary phase which could show RPLC or HILIC retention by adjusting the organic phase in mobile phase. | 3 | Analytical Chemistry |
García Mancheño earned her bachelor's degree in 2001 from the Faculty of Sciences of the Autonomous University of Madrid in Madrid, Spain. She continued at the Autonomous University of Madrid to earn her Ph.D. in 2005 under the mentorship of Juan Carlos Carretero. She continued her training in organic chemistry as a postdoctoral researcher in the lab of Carsten Bolm at RWTH Aachen University in Aachen, Germany. She completed her habilitation at University of Münster mentored by Frank Glorius, and then worked in a temporary professorship at the University of Göttingen in the city of Göttingen, Germany before acquiring her first permanent faculty position. She was an assistant professor of organic chemistry at the University of Regensburg in Bavaria, Germany from 2013-2017. In 2017, García Mancheño became a professor of organic chemistry at the University of Münster, in Münster, North Rhine-Westphalia, Germany, where she also completed her habilitation. | 0 | Organic Chemistry |
Questions about certain areas of forensic science, such as fingerprint evidence and the assumptions behind these disciplines have been brought to light in some publications including the New York Post. The article stated that "No one has proved even the basic assumption: That everyone's fingerprint is unique." The article also stated that "Now such assumptions are being questioned—and with it may come a radical change in how forensic science is used by police departments and prosecutors." Law professor Jessica Gabel said on NOVA that forensic science "lacks the rigors, the standards, the quality controls and procedures that we find, usually, in science".
The National Institute of Standards and Technology has reviewed the scientific foundations of bite-mark analysis used in forensic science. Bite mark analysis is a forensic science technique that analyzes the marks on the victim's skin compared to the suspects teeth. NIST reviewed the findings of the National Academies of Sciences, Engineering, and Medicine 2009 study. The National Academics of Sciences, Engineering, and Medicine conducted research to address the issues of reliability, accuracy, and reliability of bitemark analysis, where they concluded that there is a lack of sufficient scientific foundation to support the data. Yet the technique is still legal to use in court as evidence. NIST funded a 2019 meeting that consisted of dentists, lawyers, researchers and others to address the gaps in this field.
In the US, on 25 June 2009, the Supreme Court issued a 5-to-4 decision in Melendez-Diaz v. Massachusetts stating that crime laboratory reports may not be used against criminal defendants at trial unless the analysts responsible for creating them give testimony and subject themselves to cross-examination. The Supreme Court cited the National Academies of Sciences report Strengthening Forensic Science in the United States in their decision. Writing for the majority, Justice Antonin Scalia referred to the National Research Council report in his assertion that "Forensic evidence is not uniquely immune from the risk of manipulation."
In the US, another area of forensic science that has come under question in recent years is the lack of laws requiring the accreditation of forensic labs. Some states require accreditation, but some states do not. Because of this, many labs have been caught performing very poor work resulting in false convictions or acquittals. For example, it was discovered after an audit of the Houston Police Department in 2002 that the lab had fabricated evidence which led George Rodriguez being convicted of raping a fourteen-year-old girl. The former director of the lab, when asked, said that the total number of cases that could have been contaminated by improper work could be in the range of 5,000 to 10,000.
The Innocence Project database of DNA exonerations shows that many wrongful convictions contained forensic science errors. According to the Innocence project and the US Department of Justice, forensic science has contributed to about 39 percent to 46 percent of wrongful convictions. As indicated by the National Academy of Sciences report Strengthening Forensic Sciences in the United States, part of the problem is that many traditional forensic sciences have never been empirically validated; and part of the problem is that all examiners are subject to forensic confirmation biases and should be shielded from contextual information not relevant to the judgment they make.
Many studies have discovered a difference in rape-related injuries reporting based on race, with white victims reporting a higher frequency of injuries than black victims. However, since current forensic examination techniques may not be sensitive to all injuries across a range of skin colors, more research needs to be conducted to understand if this trend is due to skin confounding healthcare providers when examining injuries or if darker skin extends a protective element. In clinical practice, for patients with darker skin, one study recommends that attention must be paid to the thighs, labia majora, posterior fourchette and fossa navicularis, so that no rape-related injuries are missed upon close examination. | 3 | Analytical Chemistry |
Seminaphtharhodafluor or SNARF is a fluorescent dye that changes color with pH.
It can be used to construct optical biosensors that use enzymes that change pH.
The absorption peak of the derivative carboxy-SNARF at pH 6.0 is at wavelength (515 and) 550 nm, while that at pH 9.0 is at 575 nm.
The emission peak of carboxy-SNARF at pH 6.0 is at wavelength 585 nm, while that at pH 9.0 is at 640 nm.
SNARF-1 can serve as a substrate for the MRP1 (multidrug resistance-associated protein-1) drug transporter, to measure the activity of the MRP1 transporter. For this purpose, an acetomethoxyester group is added to SNARF-1. Cellular esterases cleave off SNARF-1, and its transport out of the cells can be measured by following the loss of fluorescence from the cells. | 1 | Biochemistry |
Via hydrogenation, benzene and its derivatives convert to cyclohexane and derivatives. This reaction is achieved by the use of high pressures of hydrogen in the presence of heterogeneous catalysts, such as finely divided nickel. Whereas alkenes can be hydrogenated near room temperatures, benzene and related compounds are more reluctant substrates, requiring temperatures >100 °C. This reaction is practiced on a large scale industrially. In the absence of the catalyst, benzene is impervious to hydrogen. Hydrogenation cannot be stopped to give cyclohexene or cyclohexadienes as these are superior substrates. Birch reduction, a non catalytic process, however selectively hydrogenates benzene to the diene. | 2 | Environmental Chemistry |
The glycocalyx (: glycocalyces or glycocalyxes), also known as the pericellular matrix and sometime cell coat, is a glycoprotein and glycolipid covering that surrounds the cell membranes of bacteria, epithelial cells, and other cells. It was described in a review article in 1970.
Animal epithelial cells have a fuzz-like coating on the external surface of their plasma membranes. This viscous coating is the glycocalyx that consists of several carbohydrate moieties of membrane glycolipids and glycoproteins, which serve as backbone molecules for support. Generally, the carbohydrate portion of the glycolipids found on the surface of plasma membranes helps these molecules contribute to cell–cell recognition, communication, and intercellular adhesion.
The glycocalyx is a type of identifier that the body uses to distinguish between its own healthy cells and transplanted tissues, diseased cells, or invading organisms. Included in the glycocalyx are cell-adhesion molecules that enable cells to adhere to each other and guide the movement of cells during embryonic development. The glycocalyx plays a major role in regulation of endothelial vascular tissue, including the modulation of red blood cell volume in capillaries.
The term was initially applied to the polysaccharide matrix coating epithelial cells, but its functions have been discovered to go well beyond that. | 1 | Biochemistry |
Compounds that have a monocyclic, planar conjugated system containing (4n + 2) π-electrons for whole numbers n are aromatic and exhibit an unusual stability. The classic example benzene has a system of six π electrons, which, together with the planar ring of C–C σ bonds containing 12 electrons and radial C–H σ bonds containing six electrons, forms the thermodynamically and kinetically stable benzene ring, the common core of the benzenoid aromatic compounds. For benzene itself, there are two equivalent conjugated contributing Lewis structures (the so-called Kekulé structures) that predominate. The true electronic structure is therefore a quantum-mechanical combination (resonance hybrid) of these contributors, which results in the experimentally observed C–C bonds which are intermediate between single and double bonds and of equal strength and length. In the molecular orbital picture, the six p atomic orbitals of benzene combine to give six molecular orbitals. Three of these orbitals, which lie at lower energies than the isolated p orbital and are therefore net bonding in character (one molecular orbital is strongly bonding, while the other two are equal in energy but bonding to a lesser extent) are occupied by six electrons, while three destabilized orbitals of overall antibonding character remain unoccupied. The result is strong thermodynamic and kinetic aromatic stabilization. Both models describe rings of π electron density above and below the framework of C–C σ bonds. | 7 | Physical Chemistry |
The effect of changing the temperature in the equilibrium can be made clear by 1) incorporating heat as either a reactant or a product, and 2) assuming that an increase in temperature increases the heat content of a system. When the reaction is exothermic (ΔH is negative and energy is released), heat is included as a product, and when the reaction is endothermic (ΔH is positive and energy is consumed), heat is included as a reactant. Hence, whether increasing or decreasing the temperature would favor the forward or the reverse reaction can be determined by applying the same principle as with concentration changes.
Take, for example, the reversible reaction of nitrogen gas with hydrogen gas to form ammonia:
:N(g) + 3 H(g) ⇌ 2 NH(g) ΔH = −92 kJ mol
Because this reaction is exothermic, it produces heat:
:N(g) + 3 H(g) ⇌ 2 NH(g) + heat
If the temperature were increased, the heat content of the system would increase, so the system would consume some of that heat by shifting the equilibrium to the left, thereby producing less ammonia. More ammonia would be produced if the reaction were run at a lower temperature, but a lower temperature also lowers the rate of the process, so, in practice (the Haber process) the temperature is set at a compromise value that allows ammonia to be made at a reasonable rate with an equilibrium concentration that is not too unfavorable.
In exothermic reactions, an increase in temperature decreases the equilibrium constant, K, whereas in endothermic reactions, an increase in temperature increases K.
Le Chateliers principle applied to changes in concentration or pressure can be understood by giving K a constant value. The effect of temperature on equilibria, however, involves a change in the equilibrium constant. The dependence of K on temperature is determined by the sign of ΔH. The theoretical basis of this dependence is given by the Van t Hoff equation. | 7 | Physical Chemistry |
Some gourmets believe sea salt tastes better and has a better texture than ordinary table salt. In applications that retain sea salt's coarser texture, it can provide a different mouthfeel, and may change flavor due to its different rate of dissolution. The mineral content also affects the taste. The colors and variety of flavors are due to local clays and algae found in the waters the salt is harvested from. For example, some boutique salts from Korea and France are pinkish gray and some from India are black. Black and red salts from Hawaii may even have powdered black lava and baked red clay added in. Some sea salt contains sulfates. It may be difficult to distinguish sea salt from other salts, such as pink Himalayan salt, Maras salt from the ancient Inca hot springs, or rock salt (halite) .
Black lava salt is a marketing term for sea salt harvested from various places around the world that has been blended and colored with activated charcoal. The salt is used as a decorative condiment to be shown at the table. | 9 | Geochemistry |
A variation of the Washoe process was developed in the Reese River mining district around Austin, Nevada. The Washoe process was found not to work well for ores with arsenic or antimony sulfides, or with galena or sphalerite. In 1869, Carl A. Stetefeldt of Reno found that roasting the ore with salt converted the silver sulfides to silver chlorides, which could then be recovered in amalgamation pans. The process was introduced in the Reese River District in 1879, with great success.
Other silver-mining districts using the Reese River process included Georgetown, Colorado, Caribou, Colorado, and Silver Cliff, Colorado. | 8 | Metallurgy |
Xylomannan is an antifreeze molecule, found in the freeze-tolerant Alaskan beetle Upis ceramboides. Unlike antifreeze proteins, xylomannan is not a protein. Instead, it is a combination of a sugar (saccharide) and a fatty acid that is found in cell membranes. As such is expected to work in a different manner than AFPs. It is believed to work by incorporating itself directly into the cell membrane and preventing the freezing of water molecules within the cell.
Xylomannan is also found in the red seaweed Nothogenia fastigiata (Scinaiaceae family). Fraction F6 of a sulphated xylomannan from Nothogenia fastigiata was found to inhibit replication of a variety of viruses, including Herpes simplex virus types 1 and 2 (HSV-1, HSV-2), Human cytomegalovirus (HCMV, HHV-5), Respiratory syncytial virus (RSV), Influenzavirus A, Influenzavirus B, Junin and Tacaribe virus, Simian immunodeficiency virus, and (weakly) Human immunodeficiency virus types 1 and 2. | 1 | Biochemistry |
Chemoenzymatic glycorandomization was inspired by the early pathway engineering work of Hutchinson and coworkers that suggested natural product glycosyltransferases were capable of utilizing non-native sugar nucleotide donors. The initial platform for chemoenzymatic glycorandomization was based upon a set of two highly permissive sugar activation enzymes (a sugar anomeric kinase and sugar-1-phosphate nucleotidyltransferase) to afford sugar nucleotide libraries as donors for these promiscuous glycosyltransferases where the permissivity of the corresponding sugar kinase and nucleotidyltransferase was expanded by enzyme engineering and directed evolution. The first application of this three enzyme (kinase, nucleotidyltransferase and glycosyltransferase) strategy enabled the product of a set of >30 differentially glycosylated vancomycins, some members of which were further diversified chemoselectively by virtue of the installation of sugars bearing chemoselective handles. This enzymatic platform has been further advanced through glycosyltransferase evolution and capitalizing upon the discovery of the reversibility of glycosyltransferase-catalyzed reactions first discovered in the context of calicheamicin biosynthesis. | 0 | Organic Chemistry |
Channels differ with respect to the ion they let pass (for example, Na, K, Cl), the ways in which they may be regulated, the number of subunits of which they are composed and other aspects of structure. Channels belonging to the largest class, which includes the voltage-gated channels that underlie the nerve impulse, consists of four or sometimes five subunits with six transmembrane helices each. On activation, these helices move about and open the pore. Two of these six helices are separated by a loop that lines the pore and is the primary determinant of ion selectivity and conductance in this channel class and some others. The existence and mechanism for ion selectivity was first postulated in the late 1960s by Bertil Hille and Clay Armstrong. The idea of the ionic selectivity for potassium channels was that the carbonyl oxygens of the protein backbones of the "selectivity filter" (named by Bertil Hille) could efficiently replace the water molecules that normally shield potassium ions, but that sodium ions were smaller and cannot be completely dehydrated to allow such shielding, and therefore could not pass through. This mechanism was finally confirmed when the first structure of an ion channel was elucidated. A bacterial potassium channel KcsA, consisting of just the selectivity filter, "P" loop, and two transmembrane helices was used as a model to study the permeability and the selectivity of ion channels in the Mackinnon lab. The determination of the molecular structure of KcsA by Roderick MacKinnon using X-ray crystallography won a share of the 2003 Nobel Prize in Chemistry.
Because of their small size and the difficulty of crystallizing integral membrane proteins for X-ray analysis, it is only very recently that scientists have been able to directly examine what channels "look like." Particularly in cases where the crystallography required removing channels from their membranes with detergent, many researchers regard images that have been obtained as tentative. An example is the long-awaited crystal structure of a voltage-gated potassium channel, which was reported in May 2003. One inevitable ambiguity about these structures relates to the strong evidence that channels change conformation as they operate (they open and close, for example), such that the structure in the crystal could represent any one of these operational states. Most of what researchers have deduced about channel operation so far they have established through electrophysiology, biochemistry, gene sequence comparison and mutagenesis.
Channels can have single (CLICs) to multiple transmembrane (K channels, P2X receptors, Na channels) domains which span plasma membrane to form pores. Pore can determine the selectivity of the channel. Gate can be formed either inside or outside the pore region. | 1 | Biochemistry |
The first step in the formation of biofilms is adhesion. The initial bacterial adhesion to surfaces involves the adhesin–receptor interactions. Certain polysaccharides, lipids and proteins in the matrix function as the adhesive agents. EPS also promotes cell–cell cohesion (including interspecies recognition) to facilitate microbial aggregation and biofilm formation. In general, the EPS-based matrix mediates biofilm assembly as follows. First, the EPS formation takes place at the site of adhesion, it will be either produced on bacterial surfaces or secreted on the surface of attachment, and form an initial polymeric matrix promoting microbial colonization and cell clustering. Next, continuous production of EPS further expands the matrix in 3 dimensions while forming a core of bacterial cells. The bacterial core provides a supporting framework, and facilitates the development of 3D clusters and aggregation of microcolonies. Studies on P. aeruginosa, B. subtilis, V. cholerae, and S. mutans suggested that the transition from initial cell clustering to microcolony appears to be conserved among different biofilm-forming model organisms. As an example, S. mutans produces an exoenzymes, called glucosyltransferases (Gtfs), which synthesize glucans in situ using host diet sugars as substrates. Gtfs even bind to the bacteria that do not synthesize Gtfs, and therefore, facilitate interspecies and interkingdom coadhesion. | 1 | Biochemistry |
As algal blooms grow, they deplete the oxygen in the water and block sunlight from reaching fish and plants. Such blooms can last from a few days to many months. With less light, plants beneath the bloom can die and fish can starve. Furthermore, the dense population of a bloom reduces oxygen saturation during the night by respiration. And when the algae eventually die off, the microbes which decompose the dead algae use up even more oxygen, which in turn causes more fish to die or leave the area. When oxygen continues to be depleted by blooms it can lead to hypoxic dead zones, where neither fish nor plants are able to survive. These dead zones in the case of the Chesapeake Bay, where they are a normal occurrence, are also suspected of being a major source of methane.
Scientists have found that HABs were a prominent feature of previous mass extinction events, including the End-Permian Extinction. | 3 | Analytical Chemistry |
TNP refers to the chemical compound 2,4,6-trinitrophenol, also known as Picric acid. It is a primary constituent of many unexploded landmines, and is a cousin to TNT, but less stable. It is recognized as an environmental contaminant and is toxic to many organisms. It is still commonly used in the manufacturing of fireworks, explosives, and rocket fuels, as well as in leather, pharmaceutical, and dye industries.
ATP is an essential mediator of life. It is used to overcome unfavorable energy barriers to initiate and fuel chemical reactions. It is also used to drive biological machinery and regulate a number of processes via protein-phosphorylation. However, the proteins that bind ATP for both regulation and enzymatic reactions are very diverse—many yet undiscovered—and for many proteins their relationship to ATP in terms of number of binding sites, binding constants, and dissociation constants remain unclear. | 7 | Physical Chemistry |
Bacterial anaerobic corrosion is the bacterially-induced oxidation of metals. Corrosion of metals typically alters the metal to a form that is more stable. Thus, bacterial anaerobic corrosion typically occurs in conditions favorable to the corrosion of the underlying substrate. In humid, anoxic conditions the corrosion of metals occurs as a result of a redox reaction. This redox reaction generates molecular hydrogen from local hydrogen ions. Conversely, anaerobic corrosion occurs spontaneously. Anaerobic corrosion primarily occurs on metallic substrates but may also occur on concrete. | 8 | Metallurgy |
According to the researchers' mass spectrometry, hemolithin is largely composed of glycine and hydroxyglycine amino acids. The researchers noted that the protein was related to "very high extraterrestrial" ratios of Deuterium/Hydrogen (D/H); such high D/H ratios are not found anywhere on Earth, but are "consistent with long-period comets" and suggest, as reported, "that the protein was formed in the proto-solar disc or perhaps even earlier, in interstellar molecular clouds that existed long before the Sun’s birth".
A natural development of hemolithin may have started with glycine forming first, and then later linking with other glycine molecules into polymer chains, and later still, combining with iron and oxygen atoms. The iron and oxygen atoms reside at the end of the newly found molecule. The researchers speculate that the iron oxide grouping formed at the end of the molecule may be able to absorb photons, thereby enabling the molecule to split water (HO) into hydrogen and oxygen and, as a result, produce a source of energy that might be useful to the development of life.
Exobiologist and chemist Jeffrey Bada expressed concerns about the possible protein discovery commenting, "The main problem is the occurrence of hydroxyglycine, which, to my knowledge, has never before been reported in meteorites or in prebiotic experiments. Nor is it found in any proteins. ... Thus, this amino acid is a strange one to find in a meteorite, and I am highly suspicious of the results." Likewise, Lee Cronin of the University of Glasgow stated, "The structure makes no sense." | 9 | Geochemistry |
Many ketones are cyclic. The simplest class have the formula , where n varies from 2 for cyclopropanone () to the tens. Larger derivatives exist. Cyclohexanone (), a symmetrical cyclic ketone, is an important intermediate in the production of nylon. Isophorone, derived from acetone, is an unsaturated, asymmetrical ketone that is the precursor to other polymers. Muscone, 3-methylpentadecanone, is an animal pheromone. Another cyclic ketone is cyclobutanone, having the formula . | 0 | Organic Chemistry |
Hydrolysis is one of the primary reactions to occur in diboryl porphyrin complexes. In this reaction, RBOBR(por) reacts with water to exchange a B-OH bond for a B-R bond, liberating the R group.
Hydrolysis products are important intermediates in the synthesis of the B-O-B(por) compounds from BX(por) compounds. In fact, simply performing column chromatography on (BF)(por) on silica gives the partial hydrolysis product BOF(por).
DFT computations show that hydrolysis, as in the scheme shown here, is energetically favorable (breaking of a relatively weak B-C bond, formation of a strong B-O bond, formation of benzene). However, only one of the two phenyl groups is observed to undergo hydrolysis. This suggests thermodynamic favorability is not the only factor at play. Rather, as Belcher et al. suggest, there is a significant steric component to this reaction. The boron in the porphyrin ring plane undergoes substitution, while the out-of-plane boron retains its phenyl bond. | 5 | Photochemistry |
Mucolipin-1 also known as TRPML1 (transient receptor potential cation channel, mucolipin subfamily, member 1) is a protein that in humans is encoded by the MCOLN1 gene. It is a member of the small family of the TRPML channels, a subgroup of the large protein family of TRP ion channels.
TRPML1 is a 65 kDa protein associated with mucolipidosis type IV. Its predicted structure includes six transmembrane domains, a transient receptor potential (TRP) cation-channel domain, and an internal channel pore. TRPML1 is believed to channel iron ions across the endosome/lysosome membrane into the cell and so its malfunction causes cellular iron deficiency. It is important in lysosome function and plays a part in processes such as vesicular trafficking, exocytosis and autophagy. | 1 | Biochemistry |
The term "plastic scintillator" typically refers to a scintillating material in which the primary fluorescent emitter, called a fluor, is suspended in the base, a solid polymer matrix. While this combination is typically accomplished through the dissolution of the fluor prior to bulk polymerization, the fluor is sometimes associated with the polymer directly, either covalently or through coordination, as is the case with many Li6 plastic scintillators. Polyethylene naphthalate has been found to exhibit scintillation by itself without any additives and is expected to replace existing plastic scintillators due to higher performance and lower price. The advantages of plastic scintillators include fairly high light output and a relatively quick signal, with a decay time of 2–4 nanoseconds, but perhaps the biggest advantage of plastic scintillators is their ability to be shaped, through the use of molds or other means, into almost any desired form with what is often a high degree of durability. Plastic scintillators are known to show light output saturation when the energy density is large (Birks' Law). | 5 | Photochemistry |
Flow injection analysis (FIA) is an approach to chemical analysis. It is accomplished by injecting a plug of sample into a flowing carrier stream. The principle is similar to that of Segmented Flow Analysis (SFA) but no air is injected into the sample or reagent streams.. | 3 | Analytical Chemistry |
Hepatitis B infection can be successfully controlled through the use of a recombinant subunit hepatitis B vaccine, which contains a form of the hepatitis B virus surface antigen that is produced in yeast cells. The development of the recombinant subunit vaccine was an important and necessary development because hepatitis B virus, unlike other common viruses such as polio virus, cannot be grown in vitro. | 1 | Biochemistry |
Reverse osmosis is a more economical way to concentrate liquids (such as fruit juices) than conventional heat-treatment. Concentration of orange and tomato juice has advantages including a lower operating cost and the ability to avoid heat-treatment, which makes it suitable for heat-sensitive substances such as protein and enzymes.
RO is used in the dairy industry to produce whey protein powders and concentrate milk. The whey (liquid remaining after cheese manufacture) is concentrated with RO from 6% solids to 10–20% solids before ultrafiltration processing. The retentate can then be used to make whey powders, including whey protein isolate. Additionally, the permeate, which contains lactose, is concentrated by RO from 5% solids to 18–total solids to reduce crystallization and drying costs.
Although RO was once avoided in the wine industry, it is now widespread. An estimated 60 RO machines were in use in Bordeaux, France, in 2002. Known users include many of elite firms, such as Château Léoville-Las Cases. | 3 | Analytical Chemistry |
The ability to produce chemical state information, i.e. the local bonding environment of an atomic species in question from the topmost few nanometers of the sample makes XPS a unique and valuable tool for understanding the chemistry of the surface. The local bonding environment is affected by the formal oxidation state, the identity of its nearest-neighbor atoms, and its bonding hybridization to the nearest-neighbor or next-nearest-neighbor atoms. For example, while the nominal binding energy of the C electron is 284.6 eV, subtle but reproducible shifts in the actual binding energy, the so-called chemical shift (analogous to NMR spectroscopy), provide the chemical state information.
Chemical-state analysis is widely used for carbon. It reveals the presence or absence of the chemical states of carbon, in approximate order of increasing binding energy, as: carbide (-C), silane (-Si-CH), methylene/methyl/hydrocarbon (-CH-CH-, CH-CH-, and -CH=CH-), amine (-CH-NH), alcohol (-C-OH), ketone (-C=O), organic ester (-COOR), carbonate (-CO), monofluoro-hydrocarbon (-CFH-CH-), difluoro-hydrocarbon (-CF-CH-), and trifluorocarbon (-CH-CF), to name but a few.
Chemical state analysis of the surface of a silicon wafer reveals chemical shifts due to different formal oxidation states, such as: n-doped silicon and p-doped silicon (metallic silicon), silicon suboxide (SiO), silicon monoxide (SiO), SiO, and silicon dioxide (SiO). An example of this is seen in the figure "High-resolution spectrum of an oxidized silicon wafer in the energy range of the Si 2p signal". | 7 | Physical Chemistry |
Scanning electron microscopy is a useful tool to employ before any of the above analyses that may result in loss of the original material since it can be used to check for daughter minerals or vapor bubbles and help determine the best technique that should be chosen for melt inclusion analysis. | 9 | Geochemistry |
Ribosomal RNA (rRNA) is essential to the makeup of ribosomes and peptide transfer during translation processes. Ribosomal RNA modifications are made throughout ribosome synthesis, and often occur during and/or after translation. Modifications primarily play a role in the structure of the rRNA in order to protect translational efficiency. Chemical modification in rRNA consists of methylation of ribose sugars, isomerization of uridines, and methylation and acetylation of individual bases. | 1 | Biochemistry |
Zn isotope ratios vary between individual blood components, bones and the different organs in humans, though in general, δZn values fall within a narrow range. In the blood of healthy individuals, the Zn isotopic composition of erythrocytes is typically ~0.3‰ lighter than that of serum, and no significant differences in erythrocyte or serum δZn values exist between men and women. For example, in the blood of 49 healthy blood donors, the average erythrocyte δZn value was +0.44 ± 0.33‰, while that of serum was +0.17 ± 0.26‰. In a separate study on 29 donors, a similar average δZn value of +0.29 ± 0.27‰ was obtained for the patients' serum. Additionally, in a small sample set of volunteers, whole blood δZn values were ~+0.15‰ higher for vegetarians than for omnivores, suggesting diet plays an important role in driving Zn isotope compositions in the human body. | 9 | Geochemistry |
*1st degree order of the Great Patriotic War
*State Prize of the Republic of Azerbaijan (1980)
*Y. Mammadaliyev medal (1995)
*Shohrat Order (2005)
* "OGS" golden medal and diploma (2006)
*Honorary title of Honored Scientist (2009)
*Y. Mammadaliyev prize (2014)
*Sharaf Order (2014) | 0 | Organic Chemistry |
Its physiological function is unknown. It is a member of the C1Q domain proteins which have important signalling roles in inflammation and in adaptive immunity. | 1 | Biochemistry |
Langerin consists of a relatively short intracellular domain and an extracellular domain which consists of a neck-region and a carbohydrate recognition domain (CRD). The intracellular part contains a proline-rich domain (PRD). The neck region consists of alpha-helixes and mediates a formation of langerin homotrimers via a coiled-coil interaction. The homotrimers formation increases avidity and specificity of the antigen.
The CRD of langerin is similar to CRDs of other C-type lectins. It contains an EPN motif – a Glu-Pro-Asn rich region. The CRD is divided into two lobes by 2 anti-parallel beta-sheets. The upper lobe creates the primary Ca2+ dependent carbohydrates binding site. In contrast to other lectins, for instance, DC-SIGN / DC-SIGNR and MBP, langerin has only one binding site for Ca2+. In the upper lobe, there have been discovered two other binding sites by a crystallization method. These sites are not dependent on Ca2+ and their relation to the primary binding site is not completely understood. All the binding sites are flanked by positively charged amino acids (K299 and K313) which enable binding of negatively charged sulphated carbohydrates. These amino acids are not present in DC-SIGN. | 1 | Biochemistry |
A free concentration [A] or activity {A} of a species A is measured by means of an ion selective electrode such as the glass electrode. If the electrode is calibrated using activity standards it is assumed that the Nernst equation applies in the form
where is the standard electrode potential. When buffer solutions of known pH are used for calibration the meter reading will be a pH.
At 298 K, 1 pH unit is approximately equal to 59 mV.
When the electrode is calibrated with solutions of known concentration, by means of a strong acid–strong base titration, for example, a modified Nernst equation is assumed.
where is an empirical slope factor. A solution of known hydrogen ion concentration may be prepared by standardization of a strong acid against borax. Constant-boiling hydrochloric acid may also be used as a primary standard for hydrogen ion concentration. | 7 | Physical Chemistry |
The technology has been automated, leading to a dramatic increase in the efficiency of amplification. Now, a single cycle results in a 2500-fold increase in sensitivity of detection over western blotting, whereas 2 and 7 consecutive cycles result in 6 million and 3 billion-fold increases in sensitivity of detection over western blotting, a technique widely used in BSE surveillance in several countries. | 1 | Biochemistry |
Adderall is a 3.1:1 mixture of dextro- to levo- amphetamine base equivalent pharmaceutical that contains equal amounts (by weight) of four salts: dextroamphetamine sulfate, amphetamine sulfate, dextroamphetamine saccharate and amphetamine (D,L)-aspartate monohydrate. This result is a 76% dextroamphetamine to 24% levoamphetamine, or to ratio. | 4 | Stereochemistry |
Isofalcarintriol (IUPAC name (3S,8R,9R,E)-heptadeca-10-en-4,6-diyne-3,8,9-triol) is a polyacetylene contained in the root of carrots (Daucus carota). | 1 | Biochemistry |
Lipids have been drawing considerable attention as a substrate for biodiesel production owing to its sustainability, non-toxicity and energy efficient properties. However, due to cost reasons, attention must be focused on the non-edible sources of lipids, in particular oleaginous microorganisms. Such microbes have the ability to assimilate the carbon sources from a medium and convert the carbon into lipid storage materials. The lipids accumulated by these oleaginous cells can then be transesterified to form biodiesel. | 0 | Organic Chemistry |
Yu is the recipient of numerous awards and honors for his work in organic chemistry reaction development, including a MacArthur Fellowship (also known as a "Genius Grant") in 2016. He was elected a member of the American Academy of Arts and Sciences in 2019, a fellow of the American Association for the Advancement of Science and the Royal Society of Chemistry in 2012. In 2013, he received the Raymond and Beverly Sackler Prize in the Physical Sciences.
Yu received the Pedler Award from the Royal Society of Chemistry in 2016, and the Elias J. Corey Award for Outstanding Original Contribution in Organic Synthesis by a Young Investigator from the American Chemical Society. In 2012, he was awarded the Mukaiyama Award from the Japanese Society of Organic Synthesis, the ACS Cope Scholar Award, and the Bristol-Myers Squibb Award. His honors also include the Novartis Early Career Award in Organic Chemistry (2011), Eli Lilly Grantee Award (2008), Amgen Young Investigator's Award (2008), and Sloan Research Fellowship (2008). | 0 | Organic Chemistry |
Monatomic ions are formed by the gain or loss of electrons to the valence shell (the outer-most electron shell) in an atom. The inner shells of an atom are filled with electrons that are tightly bound to the positively charged atomic nucleus, and so do not participate in this kind of chemical interaction. The process of gaining or losing electrons from a neutral atom or molecule is called ionization.
Atoms can be ionized by bombardment with radiation, but the more usual process of ionization encountered in chemistry is the transfer of electrons between atoms or molecules. This transfer is usually driven by the attaining of stable ("closed shell") electronic configurations. Atoms will gain or lose electrons depending on which action takes the least energy.
For example, a sodium atom, Na, has a single electron in its valence shell, surrounding 2 stable, filled inner shells of 2 and 8 electrons. Since these filled shells are very stable, a sodium atom tends to lose its extra electron and attain this stable configuration, becoming a sodium cation in the process
On the other hand, a chlorine atom, Cl, has 7 electrons in its valence shell, which is one short of the stable, filled shell with 8 electrons. Thus, a chlorine atom tends to gain an extra electron and attain a stable 8-electron configuration, becoming a chloride anion in the process:
This driving force is what causes sodium and chlorine to undergo a chemical reaction, wherein the "extra" electron is transferred from sodium to chlorine, forming sodium cations and chloride anions. Being oppositely charged, these cations and anions form ionic bonds and combine to form sodium chloride, NaCl, more commonly known as table salt. | 7 | Physical Chemistry |
According to the structure and function study on the antifreeze protein from Pseudopleuronectes americanus, the antifreeze mechanism of the type-I AFP molecule was shown to be due to the binding to an ice nucleation structure in a zipper-like fashion through hydrogen bonding of the hydroxyl groups of its four Thr residues to the oxygens along the direction in ice lattice, subsequently stopping or retarding the growth of ice pyramidal planes so as to depress the freeze point.
The above mechanism can be used to elucidate the structure-function relationship of other antifreeze proteins with the following two common features:
# recurrence of a Thr residue (or any other polar amino acid residue whose side-chain can form a hydrogen bond with water) in an 11-amino-acid period along the sequence concerned, and
# a high percentage of an Ala residue component therein. | 1 | Biochemistry |
The total synthesis of quinine, a naturally-occurring antimalarial drug, was developed over a 150-year period. The development of synthetic quinine is considered a milestone in organic chemistry although it has never been produced industrially as a substitute for natural occurring quinine. The subject has also been attended with some controversy: Gilbert Stork published the first stereoselective total synthesis of quinine in 2001, meanwhile shedding doubt on the earlier claim by Robert Burns Woodward and William Doering in 1944, claiming that the final steps required to convert their last synthetic intermediate, quinotoxine, into quinine would not have worked had Woodward and Doering attempted to perform the experiment. A 2001 editorial published in Chemical & Engineering News sided with Stork, but the controversy was eventually laid to rest once and for all when Williams and coworkers successfully repeated Woodward's proposed conversion of quinotoxine to quinine in 2007. | 0 | Organic Chemistry |
From the equivalent circuit it is evident that the current produced by the solar cell is equal to that produced by the current source, minus that which flows through the diode, minus that which flows through the shunt resistor:
where
*I, output current (ampere)
*I, photogenerated current (ampere)
*I, diode current (ampere)
*I, shunt current (ampere).
The current through these elements is governed by the voltage across them:
where
*V, voltage across both diode and resistor R (volt)
*V, voltage across the output terminals (volt)
*I, output current (ampere)
*R, series resistance (Ω).
By the Shockley diode equation, the current diverted through the diode is:
where
*I, reverse saturation current (ampere)
*n, diode ideality factor (1 for an ideal diode)
*q, elementary charge
*k, Boltzmann constant
*T, absolute temperature
* the thermal voltage. At 25 °C, volt.
By Ohm's law, the current diverted through the shunt resistor is:
where
*R, shunt resistance (Ω).
Substituting these into the first equation produces the characteristic equation of a solar cell, which relates solar cell parameters to the output current and voltage:
An alternative derivation produces an equation similar in appearance, but with V on the left-hand side. The two alternatives are identities; that is, they yield precisely the same results.
Since the parameters I, n, R, and R cannot be measured directly, the most common application of the characteristic equation is nonlinear regression to extract the values of these parameters on the basis of their combined effect on solar cell behavior. An online simulator to extract the circuit parameters can be found at SolarDesign.
When R is not zero, the above equation does not give the current I directly, but it can then be solved using the Lambert W function:
When an external load is used with the cell, its resistance can simply be added to R and V set to zero in order to find the current.
When R is infinite there is a solution for V for any less than :
Otherwise one can solve for V using the Lambert W function:
However, when R is large it's better to solve the original equation numerically.
The general form of the solution is a curve with I decreasing as V increases (see graphs lower down). The slope at small or negative V (where the W function is near zero) approaches , whereas the slope at high V approaches . | 7 | Physical Chemistry |
Efficiency, temperature resistance and cost are the three major factors for choosing a TPV emitter. Efficiency is determined by energy absorbed relative to incoming radiation. High temperature operation is crucial because efficiency increases with operating temperature. As emitter temperature increases, black-body radiation shifts to shorter wavelengths, allowing for more efficient absorption by photovoltaic cells. | 7 | Physical Chemistry |
From 1992 to 1993, Marrow was appointed as postdoctoral research associate in the Department of Materials, University of Oxford, and a junior research fellow at Linacre College, Oxford, but moved with an Engineering and Physical Sciences Research Council (EPSRC) postdoctoral research fellowship to the School of Metallurgy and Materials, University of Birmingham. In 2001, he joined the Manchester Materials Science Centre, University of Manchester, as senior lecturer in physical metallurgy, where he became assistant director of Materials Performance Centre in 2002 and the director in 2009.
Marrow moved to the University of Oxford to become Oxford Martin School co-director of the school programme in Nuclear and Energy Materials from 2010 to 2015, Professor in Energy Materials, Department of Materials, Oxford University, and Fellow of Mansfield College, Oxford. , Marrow is the Associate Head of Department of Materials (Teaching).
Marrow is a council member of the UK Forum for Engineering Structural Integrity (FESI), UK representative for the European Energy Research Alliance Joint Programme on Nuclear Materials, member (ex-chair) of the OECD-NEA Expert Group on Innovative Structural Materials, independent advisor to the UK Office of Nuclear Regulation on materials/structural integrity, and UK representative on Graphite for BEIS to the Generation IV International Forum. Marrow is the co-director of the Nuclear Research Centre (NRC), which is a joint venture between the University of Bristol and the University of Oxford to train new nuclear scientists and engineers. | 8 | Metallurgy |
The sodium fusion extract is made alkaline by adding NaOH. To this mixture, freshly prepared FeSO solution is added and boiled for sometimes and then cooled. A few drops of FeCl are added and Prussian blue (bluish green) color forms due to formation of ferric ferrocyanide along with NaCl. This shows the presence of nitrogen in the organic compound.<blockquote><chem>6CN- +Fe^2+ -> [Fe(CN)6]^4-
<blockquote><chem>{3[Fe(CN)6]}^{4-} +4Fe^3+ ->[\ce{xH2O}]Fe4[Fe(CN)6]3\cdot xH2O | 3 | Analytical Chemistry |
Researchers from Baltic Nest Institute published in one of PNAS issues reports that the dead zones in the Baltic Sea have grown from approximately 5,000 km to more than 60,000 km in recent years.
Some of the causes behind the elevated increase of dead zones can be attributed to the use of fertilizers, large animal farms, the burning of fossil fuels, and effluents from municipal wastewater treatment plants.
With its massive size, the Baltic Sea is best analyzed in sub-areas rather than as a whole. In a paper published in 2004, researchers specifically divided the Baltic Sea into 9 sub-areas, each having its own specific characteristics. The 9 sub-areas are discerned as follows: Gulf of Bothnia, Archipelago region, Gulf of Finland, Gulf of Riga, Gulf of Gdansk, Swedish East-coast, Central Baltic, Belt Sea region, and Kattegat. Each sub-area has responded differently to nutrient additions and eutrophication; however, there are a few general patterns and measures for the Baltic Sea as a whole. As the researchers Rönnberg and Bonsdorff state,
"Irrespective of the area-specific effects of the increased loads of nutrients to the Baltic Sea, the sources are more or less similar in the whole region. The extent and the severity of the discharges may differ, however. As is seen in e.g. HELCOM (1996) and Rönnberg (2001), the major sources in the input of nutrients are derived from agriculture, industry, municipal sewage and transports. Nitrogen emissions in form of atmospheric depositions are also important, as well as local point sources, such as aquaculture and leakage from forestry."
In general, each area of the Baltic Sea is experiencing similar anthropogenic effects. As Rönnberg and Bonsdorff state, "Eutrophication is a serious problem in the Baltic Sea area." However, when it comes to implementation of water revival programs, each area likely will need to be handled on a local level. | 9 | Geochemistry |
The corrosive effect of polluted, acidic city air on limestone and marble was noted in the 17th century by John Evelyn, who remarked upon the poor condition of the Arundel marbles.
Since the Industrial Revolution, emissions of sulfur dioxide and nitrogen oxides into the atmosphere have increased. In 1852, Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester, England. Smith coined the term "acid rain" in 1872.
In the late 1960s, scientists began widely observing and studying the phenomenon. At first, the main focus in this research lay on local effects of acid rain. Waldemar Christofer Brøgger was the first to acknowledge long-distance transportation of pollutants crossing borders from the United Kingdom to Norway – a problem systematically studied by Brynjulf Ottar in the 1970s. Ottars work was strongly influenced by Swedish soil scientist Svante Odén, who had drawn widespread attention to Europes acid rain problem in popular newspapers and wrote a landmark paper on the subject in 1968. | 2 | Environmental Chemistry |
The RNA world hypothesis describes an early Earth with self-replicating and catalytic RNA but no DNA or proteins. Many researchers concur that an RNA world must have preceded the DNA-based life that now dominates. However, RNA-based life may not have been the first to exist. Another model echoes Darwin's "warm little pond" with cycles of wetting and drying.
RNA is central to the translation process. Small RNAs can catalyze all the chemical groups and information transfers required for life. RNA both expresses and maintains genetic information in modern organisms; and the chemical components of RNA are easily synthesized under the conditions that approximated the early Earth, which were very different from those that prevail today. The structure of the ribosome has been called the "smoking gun", with a central core of RNA and no amino acid side chains within 18 Å of the active site that catalyzes peptide bond formation.
The concept of the RNA world was proposed in 1962 by Alexander Rich, and the term was coined by Walter Gilbert in 1986. There were initial difficulties in the explanation of the abiotic synthesis of the nucleotides cytosine and uracil. Subsequent research has shown possible routes of synthesis; for example, formamide produces all four ribonucleotides and other biological molecules when warmed in the presence of various terrestrial minerals.
RNA replicase can function as both code and catalyst for further RNA replication, i.e. it can be autocatalytic. Jack Szostak has shown that certain catalytic RNAs can join smaller RNA sequences together, creating the potential for self-replication. The RNA replication systems, which include two ribozymes that catalyze each other's synthesis, showed a doubling time of the product of about one hour, and were subject to natural selection under the experimental conditions. If such conditions were present on early Earth, then natural selection would favor the proliferation of such autocatalytic sets, to which further functionalities could be added. Self-assembly of RNA may occur spontaneously in hydrothermal vents. A preliminary form of tRNA could have assembled into such a replicator molecule.
Possible precursors to protein synthesis include the synthesis of short peptide cofactors or the self-catalysing duplication of RNA. It is likely that the ancestral ribosome was composed entirely of RNA, although some roles have since been taken over by proteins. Major remaining questions on this topic include identifying the selective force for the evolution of the ribosome and determining how the genetic code arose.
Eugene Koonin has argued that "no compelling scenarios currently exist for the origin of replication and translation, the key processes that together comprise the core of biological systems and the apparent pre-requisite of biological evolution. The RNA World concept might offer the best chance for the resolution of this conundrum but so far cannot adequately account for the emergence of an efficient RNA replicase or the translation system." | 9 | Geochemistry |
The use of modafinil as a supposed cognitive enhancer may be considered as cheating, unnatural, or risky. The University of Sussex explained that it is a prescription drug and the decision should be made by the doctor on whether to prescribe modafinil to a student. As a matter of bioethics, the US President's Council on Bioethics argued that excellence achieved through the use of drugs like modafinil is "cheap" as it obviates the need for hard work and study, and is not fully authentic because the excellence is partly attributable to the drug, not the individual. Alternately, people in environments like Wall Street trading may not view the use of modafinil as cheating, believing that if modafinil can give them an edge and they are aware of the risks involved, it should not be considered as cheating. Due to such varying views, modafinil users for narcolepsy may cope with stigma by hiding, denying, or justifying their use, or by seeking support from others who share their views or experiences. | 4 | Stereochemistry |
Many adhesion GPCRs undergo proteolytic events posttranslationally at highly conserved Cys-rich motifs known as GPCR proteolysis sites (GPS), located next to the first transmembrane region. This site is called the HL-S(T) site. Once this protein is cleaved, the pieces are expressed at the cell surface as a heterodimer. This cleavage is thought to happen from within the protein itself, through the conserved GAIN domain. This process seems to be similar to those found in other auto-proteolytic proteins such as the Ntn hydrolases and hedgehog proteins. | 1 | Biochemistry |
A decade before Michaelis and Menten, Victor Henri found that enzyme reactions could be explained by assuming a binding interaction between the enzyme and the substrate. His work was taken up by Michaelis and Menten, who investigated the kinetics of invertase, an enzyme that catalyzes the hydrolysis of sucrose into glucose and fructose. In 1913 they proposed a mathematical model of the reaction. It involves an enzyme E binding to a substrate A to form a complex EA that releases a product P regenerating the original form of the enzyme. This may be represented schematically as
where (forward rate constant), (reverse rate constant), and (catalytic rate constant) denote the rate constants, the double arrows between A (substrate) and EA (enzyme-substrate complex) represent the fact that enzyme-substrate binding is a reversible process, and the single forward arrow represents the formation of P (product).
Under certain assumptions – such as the enzyme concentration being much less than the substrate concentration – the rate of product formation is given by
in which is the initial enzyme concentration. The reaction order depends on the relative size of the two terms in the denominator. At low substrate concentration , so that the rate varies linearly with substrate concentration (first-order kinetics in ). However at higher , with , the reaction approaches independence of (zero-order kinetics in ), asymptotically approaching the limiting rate . This rate, which is never attained, refers to the hypothetical case in which all enzyme molecules are bound to substrate. , known as the turnover number or catalytic constant, normally expressed in s , is the limiting number of substrate molecules converted to product per enzyme molecule per unit of time. Further addition of substrate would not increase the rate, and the enzyme is said to be saturated.
The Michaelis constant is not affected by the concentration or purity of an enzyme. Its value depends both on the identity of the enzyme and that of the substrate, as well as conditions such as temperature and pH.
The model is used in a variety of biochemical situations other than enzyme-substrate interaction, including antigen–antibody binding, DNA–DNA hybridization, and protein–protein interaction. It can be used to characterize a generic biochemical reaction, in the same way that the Langmuir equation can be used to model generic adsorption of biomolecular species. When an empirical equation of this form is applied to microbial growth, it is sometimes called a Monod equation.
Michaelis–Menten kinetics have also been applied to a variety of topics outside of biochemical reactions, including alveolar clearance of dusts, the richness of species pools, clearance of blood alcohol, the photosynthesis-irradiance relationship, and bacterial phage infection.
The equation can also be used to describe the relationship between ion channel conductivity and ligand concentration, and also, for example, to limiting nutrients and phytoplankton growth in the global ocean. | 7 | Physical Chemistry |
Crack growth is reported to be very slow by Luxfer, a major manufacturer of aluminium high-pressure cylinders. Cracks are reported to develop over periods in the order of 8 or more years before reaching a stage where the cylinder is likely to leak, which allows timely detection by properly trained inspectors using eddy-current crack-detection equipment.
SLC cracks have been detected in cylinders produced by several manufacturers, including Luxfer, Walter Kidde, and CIG gas cylinders.
Most of the cracking has been observed in the neck and shoulder areas of cylinders, though some cracks in the cylindrical part have also been reported. | 8 | Metallurgy |
Metabolic regulation of nitrogen-containing molecules, such as amino acids, is also kept at steady state. The amino acid pool, which describes the level of amino acids in the body, is maintained at a relatively constant concentration by balancing the rate of input (i.e. from dietary protein ingestion, production of metabolic intermediates) and rate of depletion (i.e. from formation of body proteins, conversion to energy-storage molecules). Amino acid concentration in lymph node cells, for example, is kept at steady state with active transport as the primary source of entry, and diffusion as the source of efflux. | 7 | Physical Chemistry |
First discovered and named by E. Rink and H. Böhm in 1974 they were isolated in cell suspension cultures of the Papaveraceae Macleaya microcarpa.
Since then, many minor advancements have been made in this particular topic, but BBE-like enzymes, either for their lack of study, or the lack of clear indications that it might contain useful information for other scientific research, have yet to be fully worked on, and subsequently known at their full complexity. | 1 | Biochemistry |
The William F. Meggers Award has been awarded annually since 1970 by the Optical Society (originally called the Optical Society of America) for outstanding contributions to spectroscopy. It was established to honor William Frederick Meggers and his contributions to the fields of spectroscopy and metrology. | 7 | Physical Chemistry |
* Harper's Illustrated Biochemistry(Published by LANGE)
* Dinesh Puri's Medical Biochemistry(Published by ELSEVIER) | 1 | Biochemistry |
Rule-based modeling is a modeling approach that uses a set of rules that indirectly specifies a mathematical model. The rule-set can either be translated into a model such as Markov chains or differential equations, or be treated using tools that directly work on the rule-set in place of a translated model, as the latter is typically much bigger. Rule-based modeling is especially effective in cases where the rule-set is significantly simpler than the model it implies, meaning that the model is a repeated manifestation of a limited number of patterns. An important domain where this is often the case is biochemical models of living organisms. Groups of mutually corresponding substances are subject to mutually corresponding interactions.
BioNetGen is a suite of software tools used to generate mathematical models consisting of ordinary differential equations without generating the equations directly. For example below is an example rule in the BioNetGen format:
Where:
# A(a,a): Represents a model species A with two free binding sites a
# B(b): Represents a model species B with one free binding site
# A(a!1).B(b!1): Represents model species where at least one binding site of A is bound to the binding site of B
With the above line of code, BioNetGen will automatically create an ODE for each model species with the correct mass balance. Additionally, an additional species will be created because the rule above implies that two B molecules can bind to a single A molecule since there are two binding sites. Therefore, the following species will be generated:
4. A(a!1,a!2).B(b!1).B(b!2): Molecule A with both binding sites occupied by two different B molecules. | 1 | Biochemistry |
Industrial applications of alkene insertions include metal-catalyzed routes to polyethylene and polypropylene. Typically these conversions are catalyzed heterogeneously by titanium trichloride which are activated by aluminium alkyls. This technology is known as Ziegler–Natta catalysts. In these reactions, ethylene coordinates to titanium metal followed by its insertion. These steps can be repeated multiple times, potentially leading to high molecular weight polymers. | 0 | Organic Chemistry |
In crude olive oil production, the traditional system, i.e. pressing, and the three-phase system produce a press cake and a considerable amount of waste water while the two-phase system, which is mainly used in Spain, produces a paste-like waste called "alperujo" or "two-phase pomace" that has a higher water content and is more difficult to treat than traditional solid waste. The water content of the press cake, composed of crude olive cake, pomace and husk, is about 30 percent if it is produced by traditional pressing technology and about 45–50 percent using decanter centrifuges. The press cake still has some oil that is normally recovered in a separate installation. The exhausted olive cake is incinerated or used as a soil conditioner in olive groves. | 9 | Geochemistry |
Lignin is a highly crosslinked polymer that comprises the main structural material of higher plants. A hydrophobic material, it is derived from precursor monolignols. Heterogeneity arises from the diversity and degree of crosslinking between these lignols. | 7 | Physical Chemistry |
With respect to acute toxicity, simple alcohols have low acute toxicities. Doses of several milliliters are tolerated. For pentanols, hexanols, octanols, and longer alcohols, LD50 range from 2–5 g/kg (rats, oral). Ethanol is less acutely toxic. All alcohols are mild skin irritants.
The metabolism of methanol (and ethylene glycol) is affected by the presence of ethanol, which has a higher affinity for liver alcohol dehydrogenase. In this way, methanol will be excreted intact in urine. | 0 | Organic Chemistry |
The HRM methodology has also been exploited to provide a reliable analysis of the methylation status of DNA. This is of significance since changes to the methylation status of tumour suppressor genes, genes that regulate apoptosis and DNA repair, are characteristics of cancers and also have implications for responses to chemotherapy. For example, cancer patients can be more sensitive to treatment with DNA alkylating agents if the promoter of the DNA repair gene MGMT of the patient is methylated. In a study which tested the methylation status of the MGMT promoter on 19 colorectal samples, 8 samples were found to be methylated. Another study compared the predictive power of MGMT promoter methylation in 83 high grade glioma patients obtained by either MSP, pyrosequencing, and HRM. The HRM method was found to be at least equivalent to pyrosequencing in quantifying the methylation level.
Methylated DNA can be treated by bi-sulphite modification, which converts non-methylated cytosines to uracil. Therefore, PCR products resulting from a template that was originally unmethylated will have a lower melting point than those derived from a methylated template. HRM also offers the possibility of determining the proportion of methylation in a given sample, by comparing it to a standard curve which is generated by mixing different ratios of methylated and non-methylated DNA together. This can offer information regarding the degree of methylation that a tumour may have and thus give an indication of the character of the tumour and how far it deviates from what is "normal".
HRM also is practically advantageous for use in diagnostics, due to its capacity to be adapted to high throughput screening testing, and again it minimises the possibility of amplicon spread and contamination within a laboratory, owing to its closed-tube format. | 1 | Biochemistry |
The T-matrix expressed in the form of stationary value of the functional reads
where and are the initial and the final states respectively, is the interaction potential and is the retarded Greens operator for collision energy . The condition for the stationary value of the functional is that the functions and satisfy the Lippmann-Schwinger equation
and | 7 | Physical Chemistry |
In chemistry, IUPAC changed its definition of standard temperature and pressure in 1982:
* Until 1982, STP was defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 atm (101.325 kPa).
* Since 1982, STP has been defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 10 Pa (100 kPa, 1 bar).
NIST uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa). This standard is also called normal temperature and pressure (abbreviated as NTP). However, a common temperature and pressure in use by NIST for thermodynamic experiments is 298.15 K (25°C, 77°F) and 1 bar (14.5038 psi, 100 kPa). NIST also uses "15 °C (59 °F)" for the temperature compensation of refined petroleum products, despite noting that these two values are not exactly consistent with each other.
The ISO 13443 standard reference conditions for natural gas and similar fluids are and 101.325 kPa;
by contrast, the American Petroleum Institute adopts . | 7 | Physical Chemistry |
Soil tilth is naturally maintained by the interaction of plant roots with the soil biota.
Short lived tilth can be obtained through mechanical and biological manipulation. | 9 | Geochemistry |
Dixanthogen disulfides are a class of organosulfur compounds with the formula . Usually yellow solids, they are the product of the oxidation of xanthate salts. A common derivative is diethyl dixanthogen disulfide. Diisopropyl dixanthogen disulfide is commercially available. They are structurally related to thiuram disulfides. | 0 | Organic Chemistry |
* Liquid chromatography: Traditional chromatography columns were made of glass. Modern columns are mostly made of borosilicate glass, acrylic glass or stainless steel. To prevent the stationary phase from leaking out of the column interior a polymer, stainless steel or ceramic net is usually applied. Depending on the application material- and size-requirements may change.
* Gas chromatography (GC): Older columns were made of glass or metal packed with particles of a solid stationary phase. More recently, narrower diameter (capillary) columns have been made using fused silica coated on the inside with a film of the stationary phase material. GC columns are typically very long to take advantage of their low resistance to the flow of carrier gas. The materials of the column and the stationary phase must be suitable for GC operating temperatures, which may range as high as 300°C or more. | 3 | Analytical Chemistry |
A defining advantage of COFs is the exceptional porosity that results from the substitution of analogous SBUs of varying sizes. Pore sizes range from 7-23 Å and feature a diverse range of shapes and dimensionalities that remain stable during the evacuation of solvent. The rigid scaffold of the COF structure enables the material to be evacuated of solvent and retain its structure, resulting in high surface areas as seen by the Brunauer–Emmett–Teller analysis. This high surface area to volume ratio and incredible stability enables the COF structure to serve as exceptional materials for gas storage and separation. | 6 | Supramolecular Chemistry |
Carcass weight predicts what an animal's total retail product will be compared to other animals of that breed. It does not however predict percent retail value, or the actual amount of sellable meat that can be produced from the carcass.
Fat thickness determined the expected external and seam fat the animal will contain. These two factors contribute to the greatest waste in an animal and best way to reduce economic loss. Fat thickness EPDs can help producers reduce this loss, by using animals with mid range EPDs, so as not to have too little or too much fat.
Marbling EPDs are also important in the beef industry for predicting palatability in a beef carcass. They show the estimated USDA Quality grading System and marbling score an animal would receive if it were slaughtered. This EDP is different in that it is measured in units of marbling score, and not in weight gained by an animal. Higher values indicate the presence of genes that will produce more intramuscular fat. | 1 | Biochemistry |
Radical clock reactions involve a competition between a unimolecular radical reaction with a known rate constant and a bimolecular radical reaction with an unknown rate constant to produce unrearranged and rearranged products. The rearrangement of an unrearranged radical, U•, proceeds to form R• (the clock reaction) with a known rate constant (k). These radicals react with a trapping agent, AB, to form the unrearranged and rearranged products UA and RA, respectively.
The yield of the two products can be determined by gas chromatography (GC) or nuclear magnetic resonance (NMR). From the concentration of the trapping agent, the known rate constant of the radical clock, and the ratio of the products, the unknown rate constant can be indirectly established.
If a chemical equilibrium exists between U• and R•, the rearranged products are dominant. Because the unimolecular rearrangement reaction is first order and the bimolecular trapping reaction is second order (both irreversible), the unknown rate constant (k) can be determined by: | 7 | Physical Chemistry |
In this process, the dispersed phase is forced through the pores of a microporous membrane directly into the continuous phase. Emulsified droplets are formed and detached at the end of the pores with a drop-by-drop mechanism. The advantages of membrane emulsification over conventional emulsification processes are that it enables one to obtain very fine emulsions of controlled droplet sizes and narrow droplet size distributions. Successful emulsification can be carried out with much less consumption of emulsifier and energy, and because of the lowered shear stress effect, membrane emulsification allows the use of shear-sensitive ingredients, such as starch and proteins. The membrane emulsification process is generally carried out in cross-flow (continuous or batch) mode or in a stirred cell (batch).
A major limiting factor of ME was the low dispersed phase flux. In order to expand the industrial applications, the productivity of this method had to be increased. Some research has been aimed at solving this problem and others, such as membrane fouling.
High dispersed phase flux has now been shown to be possible using single-pass annular gap crossflow membranes. | 7 | Physical Chemistry |
Work performed in the Bradbury laboratory showed that nucleosomes reconstituted onto the 5S DNA positioning sequence were able to reposition themselves translationally onto adjacent sequences when incubated thermally. Later work showed that this repositioning did not require disruption of the histone octamer but was consistent with nucleosomes being able to "slide" along the DNA in cis. In 2008, it was further revealed that CTCF binding sites act as nucleosome positioning anchors so that, when used to align various genomic signals, multiple flanking nucleosomes can be readily identified. Although nucleosomes are intrinsically mobile, eukaryotes have evolved a large family of ATP-dependent chromatin remodelling enzymes to alter chromatin structure, many of which do so via nucleosome sliding. In 2012, Beena Pillai's laboratory has demonstrated that nucleosome sliding is one of the possible mechanism for large scale tissue specific expression of genes. The work shows that the transcription start site for genes expressed in a particular tissue, are nucleosome depleted while, the same set of genes in other tissue where they are not expressed, are nucleosome bound. | 1 | Biochemistry |
Detergents and surfactants are molecules that combine highly nonpolar and highly polar groups. Traditionally, soaps are the popular surfactants, being derived from fatty acids. Since the mid-20th century, the usage of sulfonic acids has surpassed soap in advanced societies. For example, an estimated 2 billion kilograms of alkylbenzenesulfonates are produced annually for diverse purposes. Lignin sulfonates, produced by sulfonation of lignin are components of drilling fluids and additives in certain kinds of concrete. | 0 | Organic Chemistry |
Hydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds. Ordinarily the reaction is conducted catalytically and usually the substrates are unsaturated organic compounds. Alkenes and alkynes give alkyl and vinyl silanes; aldehydes and ketones give silyl ethers. Hydrosilylation has been called the "most important application of platinum in homogeneous catalysis." | 7 | Physical Chemistry |
NAPCO was the first company which was able to progress to registration of final 14001 certification. This was primarily due to the increased costs of surveillance audits and an absence of market incentives to promote this certificate as the gold standard within the Australian beef industry. A ‘cluster approach’ was utilised by the company when working towards certification; this meant that the entire company qualified for certification, rather than each individual worker. The effect of the ‘cluster approach’ was to reduce the substantive cost involved in certification and the subsequent surveillance audits that would have to be implemented; this meant that cost was able to be reduced by approximately 50%. This approach also provided a means by which workload and ideas between producers could be collectively distributed. | 2 | Environmental Chemistry |
Sustainable materials are key elements of green buildings. Some benefits of sustainable materials include durability, long life, recyclability, and energy and thermal efficiency. Copper ranks highly in all of these categories.
Copper is one of natures most efficient thermal and electrical conductors, which helps to conserve energy. Because of its high thermal conductivity, it is used extensively in building heating systems, direct exchange heat pumps, and solar power and hot water equipment. Its high electrical conductivity increases the efficiency of lighting, electrical motors, fans, and appliances, making a buildings operation more cost effective with less energy and environmental impact.
Because copper has a better thermal conductivity rating than usual façade and roofing materials, it is well-suited to solar thermal façade systems. The first commercial application of a fully integrated solar thermal copper façade system was installed at the Pori Public Swimming Complex in Finland. The installation is an urban example of sustainability and carbon emissions reduction. The solar façade works in conjunction with roof collectors and is supplemented by roof-mounted photovoltaics that provide 120,000 kWh of heat, an amount of energy equivalent to that used annually by six average family houses in cold-climate Finland.
One standard in the United States Green Building Council (USGBC)'s Leadership in Energy and Environmental Design rating system (LEED) requires that newly constructed buildings include materials containing pre- and post-consumer recycled content. Most copper products used in construction (except electrical materials that require highly refined virgin copper) contain a large percentage of recycled content. See: Copper in architecture#Recycling. | 8 | Metallurgy |
The activity of calcifediol and calcitriol can be reduced by hydroxylation at position 24 by vitamin D3 24-hydroxylase, forming secalciferol and calcitetrol, respectively. | 1 | Biochemistry |
The dipeptide derived from glycine and (R-)valine is converted into a 2,5-Diketopiperazine (a cyclic dipeptide). Double O-methylation gives the bis-lactim. A proton is then abstracted from the prochiral position on glycine with n-BuLi. The next step decides the stereoselectivity of the method: One face of the carbanionic center is shielded by steric hindrance from the isopropyl residue on valine. The reaction of the anion with an alkyl iodide will form the alkylated product with a strong preference for just one enantiomer. In the final step the dipeptide is cleaved by acidic hydrolysis in two amino acid methyl esters which can be separated from each other.
With valine Schöllkopf selected the natural proteinogenic amino acid with the largest non-reactive and nonchiral residue in order to achieve the largest possible stereoselectivity, generally speaking enantiomeric excess of over 95% ee is feasible.
With the Schöllkopf method all amino acids can be synthesised when a suitable R-I reagent is available. R does not need to be an alkyl group but can also be more complicated. The method is limited to the laboratory for the synthesis of exotic amino acids. Industrial applications are not known. One disadvantage is limited atom economy. | 0 | Organic Chemistry |
Acylals in organic chemistry are a group of chemical compounds sharing a functional group with the general structure RCH(OOCR). Acylals are obtained by reaction of carbonyls with acetic anhydride or other acid anhydrides and a suitable catalyst, for instance with sulfated zirconia at low temperatures when used as protective groups for aldehydes. High temperature exposure converts the acylal back to the aldehyde. | 0 | Organic Chemistry |
Metal whiskering is a crystalline metallurgical phenomenon involving the spontaneous growth of tiny, filiform hairs from a metallic surface. The effect is primarily seen on elemental metals but also occurs with alloys.
The mechanism behind metal whisker growth is not well understood, but seems to be encouraged by compressive mechanical stresses including:
* energy gained due to electrostatic polarization of metal filaments in the electric field,
* residual stresses caused by electroplating,
* mechanically induced stresses,
* stresses induced by diffusion of different metals,
* thermally induced stresses, and
* strain gradients in materials.
Metal whiskers differ from metallic dendrites in several respects: dendrites are fern-shaped and grow across the surface of the metal, while metal whiskers are hair-like and project normal to the surface. Dendrite growth requires moisture capable of dissolving the metal into a solution of metal ions, which are then redistributed by electromigration in the presence of an electromagnetic field. While the precise mechanism for whisker formation remains unknown, it is known that whisker formation does not require either dissolution of the metal or the presence of an electromagnetic field. | 8 | Metallurgy |
Past winners of the Martin Medal are:
* Robert Kennedy (2019)
* Jean-Luc Veuthey (2018)
* Andreas Manz (2017)
* Ian Wilson & Peter Myers (2016)
* Pavel Jandera (2015)
* Nobuo Tanaka (2014)
* Günther Bonn & Frantisek Svec (2013)
* Edward S. Yeung (2012)
* Peter J. Schoenmakers (2011)
* Peter Carr (2010)
* Wolfgang F. Lindner (2009)
* Ron Majors & Johan Roeraade (2007)
* Jim Waters (2006)
* Vadim A. Davankov (2005)
* Terry Berger (2004)
* Jack Henion (2003)
* Paul R. Haddad & Werner Engewald (2002)
* John Michael Ramsey (2001)
* Klaus Mosbach & William S. Hancock (2000)
* Hans Poppe & Geoffrey Eglinton, FRS (1999)
* Albert Zlatkis (1998, awarded posthumously)
* Will Jennings & Joseph Jack Kirkland (1997)
* Milton L. Lee (1996)
* Milos Novotny & Shigeru Terabe (1995)
* Pat Sandra & Csaba Horvath (1994)
* Hans Engelhardt, Fred E. Regnier, & Klaus K. Unger (1993)
* Irving Wainer & James W. Jorgenson (1992)
* Dai E. Games, Barry L. Karger, Daniel W. Armstrong, & Dennis H. Desty (1991)
* Egil Jellum, William Pirkle, & Carl A. Cramers (1990)
* Jon Calvin Giddings, Udo. A Th Brinkman, J. F. K. Huber, Rudolf E. Kaiser, & Lloyd R. Snyder (1986)
* Ervin Kovats & John Knox (1985)
* C. E. Roland Jones & Arnaldo L. Liberti (1984)
* Gerhard Schomburg & Ralph Stock (1983)
* Edward R. Adlard, Leslie S. Ettre, Courtney S. G. Phillips, & Raymond P. W. Scott (1982)
* G. A. Peter Tuey & Georges Guiochon (1980)
* Ernst Bayer & C. E. H. Knapman (1978) | 3 | Analytical Chemistry |
The distribution half-life of drospirenone is about 1.6 to 2 hours. The apparent volume of distribution of drospirenone is approximately 4 L/kg. The plasma protein binding of drospirenone is 95 to 97%. It is bound to albumin and 3 to 5% circulates freely or unbound. Drospirenone has no affinity for sex hormone-binding globulin (SHBG) or corticosteroid-binding globulin (CBG), and hence is not bound by these plasma proteins in the circulation. | 4 | Stereochemistry |
Atoms in molecules analysis of ((Dipp)P)Ge suggests that there is a double bond between P1-Ge. Bond order can be assessed by measuring the ellipticity, a measure of anisotropic electron density, at the bond critical point. For example, butane, ethylene, and ethyne have a bond ellipticity of 0.01, 0.30, and 0.00 respectively, which correspond to a single, double, and a triple bond. A bond critical point between P1-Ge with ρ=0.091 and ellipticity 0.297 was observed in ((Dipp)P)Ge, consistent with a double bond. . This contrasts ρ=0.083 and ellipticity 0.064 at the bond critical point of P2-Ge in ((Dipp)P)Ge. Delocalization index (DI) was also used to predict the bond order of ((Dipp)P)Ge. DI values for P1-Ge and P2-Ge were determined to be 1.275 and 0.843, consistent with a P1-Ge double bond and Wiberg bond indices calculated. | 0 | Organic Chemistry |
Much of the food that we consume today is put in a wide variety of packages to ensure food quality and provide a possibility for transportation and distribution. Many of these packages are air or gas tight, making it difficult to study the gas composition without perforation. In many cases it is of great value to study the composition of gases without destroying the package.
The perhaps best example is studies of the amount of oxygen in food packages. Oxygen is naturally present in most food and food packages as it is a major component in air. However, oxygen is also one of the great causes or needs for aging of biological substances, due to its source for increase of chemical and microbiological activity. Today, methods like [Modified atmosphere] (MAP) and [Controlled atmosphere] packaging (CAP) are implemented to reduce and control the oxygen content in food packages to prolong [shelf life] and ensure safe food. To assure the effectiveness of these methods it is important to regularly measure the concentration of oxygen (and other gases) inside these packages. GASMAS provides the possibility of doing this non-intrusively, without destroying any food or packages. The two main advantages of measuring the gas-composition in packages without perforation is that no food is wasted in the controlling process and that the same package can be controlled repeatedly during an extended time period to monitor any time-dependence of the gas composition. The studies can be used to guarantee the tightness of packages but also to study food deterioration processes.
Much food itself contains free gas distributed in pores within. Examples are fruit, bread, flour, beans, cheese, etc. Also this gas can be of great value to study to monitor quality and maturity level (see e.g. and ). | 7 | Physical Chemistry |
The high functional group tolerance of the intramolecular Heck reaction allows it to be used at a very late stage in synthetic routes. In a synthesis of (±)-FR900482, IMHR establishes a tricyclic ring system in high yield without disturbing any of the sensitive functionality nearby.
Intramolecular Heck reactions have been employed for the construction of complex natural products. An example is the late-stage, macrocyclic ring closure in the total synthesis of the cytotoxic natural product (–)-Mandelalide A.
In another example a fully intramolecular tandem Heck reaction is used in a synthesis of (–)-scopadulcic acid. A 6-exo cyclization sets the quaternary center and provides a neopentyl σ-palladium intermediate, which undergoes a 5-exo reaction to provide the ring system. | 0 | Organic Chemistry |
PMCA was originally developed to, in vitro, mimic prion replication with a similar efficiency to the in vivo process, but with accelerated kinetics. PMCA is conceptually analogous to the polymerase chain reaction - in both systems a template grows at the expense of a substrate in a cyclic reaction, combining growing and multiplication of the template units. | 1 | Biochemistry |
A blacklight, also called a UV-A light, Wood's lamp, or ultraviolet light, is a lamp that emits long-wave (UV-A) ultraviolet light and very little visible light. One type of lamp has a violet filter material, either on the bulb or in a separate glass filter in the lamp housing, which blocks most visible light and allows through UV, so the lamp has a dim violet glow when operating. Blacklight lamps which have this filter have a lighting industry designation that includes the letters "BLB". This stands for "blacklight blue". A second type of lamp produces ultraviolet but does not have the filter material, so it produces more visible light and has a blue color when operating. These tubes are made for use in "bug zapper" insect traps, and are identified by the industry designation "BL". This stands for "blacklight".
Blacklight sources may be specially designed fluorescent lamps, mercury-vapor lamps, light-emitting diodes (LEDs), lasers, or incandescent lamps. In medicine, forensics, and some other scientific fields, such a light source is referred to as a Woods lamp, named after Robert Williams Wood, who invented the original Woods glass UV filters.
Although many other types of lamp emit ultraviolet light with visible light, black lights are essential when UV-A light without visible light is needed, particularly in observing fluorescence, the colored glow that many substances emit when exposed to UV. Black lights are employed for decorative and artistic lighting effects, diagnostic and therapeutic uses in medicine, the detection of substances tagged with fluorescent dyes, rock-hunting, scorpion-hunting, the detection of counterfeit money, the curing of plastic resins, attracting insects and the detection of refrigerant leaks affecting refrigerators and air conditioning systems. Strong sources of long-wave ultraviolet light are used in tanning beds. | 5 | Photochemistry |
Aldehydes (except those without an alpha carbon, or without protons on the alpha carbon, such as formaldehyde and benzaldehyde) can exist in either the keto or the enol tautomer. Keto–enol tautomerism is catalyzed by either acid or base. In neutral solution, the enol is the minority tautomer, reversing several times per second. But it becomes the dominant tautomer in strong acid or base solutions, and enolized aldehydes undergo nucleophilic attack at the α position. | 0 | Organic Chemistry |
The human genome contains about 28 million CpG sites, and roughly 60% of the CpG sites are methylated at the 5 position of the cytosine. During formation of a cancer there is an average reduction of the number of methylated cytosines of about 5% to 20%, or about 840,00 to 3.4 million demethylations of CpG sites.
DNMT1 methylates CpGs on hemi-methylated DNA during DNA replication. Thus, when a DNA strand has a methylated CpG, and the newly replicated strand during semi-conservative replication lacks a methyl group on the complementary CpG, DNMT1 is normally recruited to the hemimethylated site and adds a methyl group to cytosine in the newly synthesized CpG. However, recruitment of DNMT1 to hemimethylated CpG sites during DNA replication depends on the UHRF1 protein. If UHRF1 does not bind to a hemimethylated CpG site, then DNMT1 is not recruited and cannot methylate the newly synthesized CpG site. The arginine methyltransferase PRMT6 regulates DNA methylation by methylating the arginine at position 2 of histone 3 (H3R2me2a). (See Protein methylation#Arginine.) In the presence of H3R2me2a UHRF1 can not bind to a hemimethylated CpG site, and then DNMT1 is not recruited to the site, and the site remains hemimethylated. Upon further rounds of replication the methylated CpG is passively diluted out. PRMT6 is frequently overexpressed in many types of cancer cells. The overexpression of PRMT6 may be a source of DNA demethylation in cancer. | 1 | Biochemistry |
EDC is commercially available. It may be prepared by coupling ethyl isocyanate to N,N-dimethylpropane-1,3-diamine to give a urea, followed by dehydration: | 1 | Biochemistry |
Activity coefficients for binary mixtures are often reported at the infinite dilution of each component. Because activity coefficient models simplify at infinite dilution, such empirical values can be used to estimate interaction energies. Examples are given for water: | 7 | Physical Chemistry |
Over the almost 12 years it took the two groups to reach their goal, both Woodward and Eschenmoser periodically reported on the stage of the collaborative project in lectures, some of them appearing in print. Woodward discussed the A/B approach in lectures published in 1968, and 1971, culminating in the announcement of the "Total Synthesis of Vitamin B" in New Delhi in February 1972 published in 1973. This publication, and lectures with the same title Woodward delivered in the later part of the year 1972 are confined to the A/B approach of the synthesis and do not discuss the ETH A/D approach.
Eschenmoser had discussed the ETH contributions to the A/B approach in 1968 at the 22nd Robert A. Welch Foundation conference in Houston, as well as in his 1969 RSC Centenary Lecture "Roads to Corrins", published in 1970. He presented the ETH photochemical A/D approach to the B synthesis at the 23rd IUPAC Congress in Boston in 1971. The Zürich group announced the accomplishment of the synthesis of cobyric acid by the photochemical A/D-approach in two lectures delivered by PhD students Maag and Fuhrer at the Swiss Chemical Society Meeting in April 1972, Eschenmoser presented a lecture "Total Synthesis of Vitamin B: the Photochemical Route" for the first time as Wilson Baker Lecture at the University of Bristol, Bristol/UK on May 8, 1972.
As a joint full publication of the syntheses by the Harvard and ETH groups (announced in and expected in) had not appeared by 1977, an article describing the final version of the photochemical A/D approach already accomplished in 1972 was published 1977 in Science. This article is an extended English translation of one that had already appeared 1974 in Naturwissenschaften, based on a lecture given by Eschenmoser on January 21, 1974, at a meeting of the Zürcher Naturforschende Gesellschaft. Four decades later, in 2015, the same author finally published a series of six full papers describing the work of the ETH group on corrin synthesis. Part I of the series contains a chapter entitled "The Final Phase of the Harvard/ETH Collaboration on the Synthesis of Vitamin B", in which the contributions of the ETH group to the collaborative work on the synthesis of vitamin B between 1965 and 1972 are recorded.
The entire ETH work is documented in full experimental detail in publicly accessible Ph.D. theses, almost 1,900 pages, all in German. Contributions of the 14 postdoctoral ETH researchers involved in the cobyric acid syntheses are mostly integrated in these theses. The detailed experimental work at Harvard was documented in reports by the 77 postdoctoral researchers involved, with a total volume of more than 3,000 pages.
Representative reviews of the two approaches to the chemical synthesis of vitamin B have been published in detail by A. H. Jackson and K. M. Smith, T. Goto, R. V. Stevens, K. C. Nicolaou & E. G. Sorensen, summarized by J. Mulzer & D. Riether, and G. W. Craig, besides many other publications where these epochal syntheses are discussed. | 0 | Organic Chemistry |
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