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Applications of quorum quenching that have been exploited by humans include the use of AHL-degrading bacteria in aquacultures to limit the spread of diseases in aquatic populations of fish, mollusks and crustaceans. This technique has also been translated to agriculture, to restrict the spread of pathogenic bacteria that use quorum sensing in plants. Anti-biofouling is another process that exploits quorum quenching bacteria to mediate the dissociation of unwanted biofilms aggregating on wet surfaces, such as medical devices, transportation infrastructure and water systems. Quorum quenching is recently studied for the control of fouling and emerging contaminants in electro membrane bioreactors (eMBRs) for the advanced treatment of wastewater. Extracts of several traditional medicinal herbs display quorum quenching acivity, and have potential antibacterial applications. | 1 | Biochemistry |
Rwanda and Burundi, former Belgian colonies in Central Africa, are RHT but are considering switching to LHT like neighbouring members of the East African Community (EAC). A survey in 2009 found that 54% of Rwandans favoured the switch. Reasons cited were the perceived lower costs of RHD vehicles, easier maintenance and the political benefit of harmonising traffic regulations with other EAC countries. The survey indicated that RHD cars were 16% to 49% cheaper than their LHD counterparts. In 2014, an internal report by consultants to the Ministry of Infrastructure recommended a switch to LHT. In 2015, the ban on RHD vehicles was lifted; RHD trucks from neighbouring countries cost $1,000 less than LHD models imported from Europe. | 4 | Stereochemistry |
Based on the simplifying assumption that the signal can be attributed to temperature change alone, with the effects of salinity and ice volume change ignored, Epstein et al. (1953) estimated that
a increase of 0.22‰ is equivalent to a cooling of 1 °C (or 1.8 °F).
More precisely, Epstein et al. (1953) give a quadratic extrapolation for the temperature, as
where T is the temperature in °C (based on a least-squares fit for a range of temperature values between 9 °C and 29 °C, with a standard deviation of ±0.6 °C, and δ is δO for a calcium carbonate sample). | 9 | Geochemistry |
Persistent stimulation at the neuronal synapse can lead to markedly different outcomes for the post-synaptic neuron. Extended weak signaling can result in long-term depression (LTD), in which activation of the post-synaptic neuron requires a stronger signal than before LTD was initiated. In contrast, long-term potentiation (LTP) occurs when the post-synaptic neuron is subjected to a strong stimulus, and this results in strengthening of the neural synapse (i.e., less neurotransmitter signal is required for activation).
In the CA1 region of the hippocampus, the decision between LTD and LTP is mediated solely by the level of intracellular at the post-synaptic dendritic spine. Low levels of (resulting from low-level stimulation) activates the protein phosphatase calcineurin, which induces LTD. Higher levels of results in activation of /calmodulin-dependent protein kinase II (CaMKII), which leads to LTP. The difference in Ca concentration required for a cell to undergo LTP is only marginally higher than for LTD, and because neurons show bistability (either LTP or LTD) following persistent stimulation, this suggests that one or more components of the system respond in a switch-like, or ultrasensitive manner. Bradshaw et al. demonstrated that CaMKII (the LTP inducer) responds to intracellular calcium levels in an ultrasensitive manner, with <10% activity at 1.0 uM and ~90% activity at 1.5 uM, resulting in a Hill coefficient of ~8. Further experiments showed that this ultrasenstivity was mediated by cooperative binding of CaMKII by two molecules of calmodulin (CaM), and autophosphorylation of activated CaMKII leading to a positive feedback loop.
In this way, intracellular calcium can induce a graded, non-ultrasensitive activation of calcineurin at low levels, leading to LTD, whereas the ultrasensitive activation of CaMKII results in a threshold intracellular calcium level that generates a positive feedback loop that amplifies the signal and leads to the opposite cellular outcome: LTP. Thus, binding of a single substrate to multiple enzymes with different sensitivities facilitates a bistable decision for the cell to undergo LTD or LTP. | 1 | Biochemistry |
In general terms, chemotaxis is a biological process where living entities, such as cells or organisms, detect, maneuver, and react in response to a chemical signal in their environment. Such a phenomenon is critical for many biological processes, including but not limited to wound healing, detection of food, and avoidance of many toxins. Chemotaxis also plays an essential role in serval diseases, such as tumor metastasis, the recruitment of T-lymphocytes during inflammation, and HIV-1 entry into T cells. At the core of chemotaxis are specialized sensory cells called chemoreceptors. These cells allow an organism to detect chemical molecules within its environment and respond accordingly. Such chemical molecules are either known as chemoattractants or chemorepellents, which play a crucial role in attracting or repelling the organism towards or away from the source of the chemical signal, respectively. Thus, with this natural process of chemotaxis in mind, researchers have sought to apply the same phenomenon to targeted drug delivery, a medical technique aimed at delivering drugs to a specific cell, tissue, or organ within the body while minimizing its disruptive effects on healthy tissue. By using both chemotaxes to help guide the drug delivery process, researchers aim to reduce toxicity by avoiding healthy tissues, improve drug efficacy by focusing only on the intended site, and decrease drug dosage by delivering the directly rather than throughout the whole body. | 1 | Biochemistry |
Being a widely available reagent, TsCl has been heavily examined from the perspective of reactivity. It is used in dehydrations to make nitriles, isocyanides and diimides. In an unusual reaction focusing on the sulfur center, zinc reduces TsCl to the sulfinate, CHCHSONa. | 0 | Organic Chemistry |
An example of a repressor protein is the methionine repressor MetJ. MetJ interacts with DNA bases via a ribbon-helix-helix (RHH) motif. MetJ is a homodimer consisting of two monomers, which each provides a beta ribbon and an alpha helix. Together, the beta ribbons of each monomer come together to form an antiparallel beta-sheet which binds to the DNA operator ("Met box") in its major groove. Once bound, the MetJ dimer interacts with another MetJ dimer bound to the complementary strand of the operator via its alpha helices. AdoMet binds to a pocket in MetJ that does not overlap the site of DNA binding.
The Met box has the DNA sequence AGACGTCT, a palindrome (it shows dyad symmetry) allowing the same sequence to be recognized on either strand of the DNA. The junction between C and G in the middle of the Met box contains a pyrimidine-purine step that becomes positively supercoiled forming a kink in the phosphodiester backbone. This is how the protein checks for the recognition site as it allows the DNA duplex to follow the shape of the protein. In other words, recognition happens through indirect readout of the structural parameters of the DNA, rather than via specific base sequence recognition.
Each MetJ dimer contains two binding sites for the cofactor S-Adenosyl methionine (SAM) which is a product in the biosynthesis of methionine. When SAM is present, it binds to the MetJ protein, increasing its affinity for its cognate operator site, which halts transcription of genes involved in methionine synthesis. When SAM concentration becomes low, the repressor dissociates from the operator site, allowing more methionine to be produced. | 1 | Biochemistry |
Common synthetic polymers have main chains composed of carbon, i.e. C-C-C-C.... Examples include polyolefins such as polyethylene ((CHCH)) and many substituted derivative ((CHCH(R))) such as polystyrene (R = CH), polypropylene (R = CH), and acrylates (R = COR').
Other major classes of organic polymers are polyesters and polyamides. They have respectively -C(O)-O- and -C(O)-NH- groups in their backbones in addition to chains of carbon. Major commercial products are polyethyleneterephthalate ("PET"), ((CHCOCHOC(O))) and nylon-6 ((NH(CH)C(O))). | 0 | Organic Chemistry |
When a molecule absorbs a photon, the photon energy is converted and increases the molecule's internal energy level. Likewise, when an excited molecule releases energy, it can do so in the form of a photon. Depending on the energy of the photon, this could correspond to a change in vibrational, electronic, or rotational energy levels. The changes between these levels are called "transitions" and are plotted on the Jablonski diagram.
Radiative transitions involve either the absorption or emission of a photon. As mentioned above, these transitions are denoted with solid arrows with their tails at the initial energy level and their tips at the final energy level.
Nonradiative transitions arise through several different mechanisms, all differently labeled in the diagram. Relaxation of the excited state to its lowest vibrational level is called vibrational relaxation. This process involves the dissipation of energy from the molecule to its surroundings, and thus it cannot occur for isolated molecules.
A second type of nonradiative transition is internal conversion (IC), which occurs when a vibrational state of an electronically excited state can couple to a vibrational state of a lower electronic state. The molecule could then subsequently relax further through vibrational relaxation.
A third type is intersystem crossing (ISC); this is a transition to a state with a different spin multiplicity. In molecules with large spin-orbit coupling, intersystem crossing is much more important than in molecules that exhibit only small spin-orbit coupling. ISC can be followed by phosphorescence. | 7 | Physical Chemistry |
Phytoreoviruses are non-turreted reoviruses that are major agricultural pathogens, particularly in Asia. One member of this family, Rice Dwarf Virus (RDV), has been extensively studied by electron cryomicroscopy and x-ray crystallography. From these analyses, atomic models of the capsid proteins and a plausible model for capsid assembly have been derived. While the structural proteins of RDV share no sequence similarity to other proteins, their folds and the overall capsid structure are similar to those of other Reoviridae. | 1 | Biochemistry |
The common names for aldehydes do not strictly follow official guidelines, such as those recommended by IUPAC, but these rules are useful. IUPAC prescribes the following nomenclature for aldehydes:
# Acyclic aliphatic aldehydes are named as derivatives of the longest carbon chain containing the aldehyde group. Thus, HCHO is named as a derivative of methane, and is named as a derivative of butane. The name is formed by changing the suffix -e of the parent alkane to -al, so that HCHO is named methanal, and is named butanal.
# In other cases, such as when a group is attached to a ring, the suffix -carbaldehyde may be used. Thus, is known as cyclohexanecarbaldehyde. If the presence of another functional group demands the use of a suffix, the aldehyde group is named with the prefix formyl-. This prefix is preferred to methanoyl-.
# If the compound is a natural product or a carboxylic acid, the prefix oxo- may be used to indicate which carbon atom is part of the aldehyde group; for example, is named 2-oxoethanoic acid.
# If replacing the aldehyde group with a carboxyl group () would yield a carboxylic acid with a trivial name, the aldehyde may be named by replacing the suffix -ic acid or -oic acid in this trivial name by -aldehyde. | 0 | Organic Chemistry |
The transfer of acylated amines is more difficult than that of unsubstituted amines, although, unlike amine transfer by oxaziridines, there are no alternative methods that directly transfer acylated amines. Acylamine transfer has primarily been performed using amines and hydrazines as nucleophiles. Very few transfers of acylated nitrogens to carbon nucleophiles have been successfully performed, although some do exist in the literature. | 0 | Organic Chemistry |
With metals in group 4 or 5 a so-called edge-capped octahedral clusters are more common. Twelve halides are located along the edge of the octahedron and six are terminal. Examples of this structure type are tungsten(III) chloride, TaCl(HO), NbF, and NbF.
Many of the early metal clusters can only be prepared when they incorporate interstitial atoms. One example is ZrCCl. | 7 | Physical Chemistry |
Thioesters have general structure R−C(O)−S−R. They are related to regular esters (R−C(O)−O−R) but are more susceptible to hydrolysis and related reactions. Thioesters formed from coenzyme A are prominent in biochemistry, especially in fatty acid synthesis. | 9 | Geochemistry |
Ninhydrin (2,2-dihydroxyindane-1,3-dione) is an organic compound with the formula CH(CO)C(OH). It is used to detect ammonia and amines. Upon reaction with these amines, ninhydrin gets converted into deep blue or purple derivatives, which are called Ruhemann's purple. Ninhydrin is most commonly used to detect fingerprints in forensic cases, as the terminal amines of lysine residues in peptides and proteins sloughed off in fingerprints react with ninhydrin.
Ninhydrin is a white solid that is soluble in ethanol and acetone. Ninhydrin can be considered as the hydrate of indane-1,2,3-trione. | 0 | Organic Chemistry |
This enzyme belongs to the family of transferases, to be specific, those glycosyltransferases that transfer hexoses (hexosyltransferases). The systematic name of this enzyme class is 1,4-alpha-D-glucan:1,4-alpha-D-glucan 6-alpha-D-(1,4-alpha-D-glucano)-transferase. Other names in common use include branching enzyme, amylo-(1,4→1,6)-transglycosylase, Q-enzyme, alpha-glucan-branching glycosyltransferase, amylose isomerase, enzymatic branching factor, branching glycosyltransferase, enzyme Q, glucosan transglycosylase, 1,4-alpha-glucan branching enzyme 1, plant branching enzyme, alpha-1,4-glucan:alpha-1,4-glucan-6-glycosyltransferase, and starch branching enzyme. This enzyme participates in starch and sucrose metabolism. | 1 | Biochemistry |
The first swords known so far date to ca. the 33rd to 31st centuries BCE, during the Early Bronze Age, and have been founds at Arslantepe by Marcella Frangipane of Sapienza University of Rome. A cache of nine swords and daggers was found; they are cast from an arsenic–copper alloy. Analysis of two swords showed a copper/arsenic composition of 96%/3.15% and 93%/2.65%. Two daggers tested at copper/arsenic 96%/3.99% and 97%/3.06% with a third at copper/silver composition of 50%/35% with a trace of arsenic. Among them, three swords were beautifully inlaid with silver. These objects were found in the "hall of weapons" in the area of the palace.
These weapons have a total length of 45 to 60 cm which suggests their description as either short swords or long daggers.
These discoveries were made back in the 1980s. They belong to the local phase VI A. Also, 12 spearheads were found. These objects were dated to the period VI A (3400-3200 BC). Phase VI A at Arslantepe ended in destruction—the city was burned.
Kfar Monash Hoard was found in 1962 in Israel. Among the many copper objects in it, "Egyptian type" copper axes were found. These axes were made using copper-arsenic-nickel (CuAsNi) alloy that probably originated in Arslantepe area. Objects from Arslantepe using such polymetallic ores are mainly ascribed to Level VIA (3400–3000 BCE), dating to the Uruk period.
The next Phases or periods were VI B1 and VI B2. This is the time to which the other big discovery at Arslantepe belongs. This is the rich “Royal Tomb” where high quality pottery, and a large number of refined metal objects, made with several kinds of copper based alloys, were found. A sword was also found in the tomb. This tomb is also known as the tomb of "Signor Arslantepe", as he was called by archaeologists. He was about 40 years old, and the tomb is radiocarbon dated to 3085–2900 Cal. BC.
This “Royal Tomb” dates to the beginning of period VI B2, or perhaps even earlier to period VI B1. There’s a considerable similarity between these two groups of objects in the “hall of weapons”, and in the “Royal Tomb”, and the times of manufacture of some of them must have been pretty close together. | 8 | Metallurgy |
* Honorary Member of the Academy of Sciences of the Armenian SSR
* Honorary Member of Academy of Sciences of the Tajik SSR
* Honorary member of Academy of Sciences of the Turkmen SSR
* Honorary Member of Bulgarian Academy of Sciences (1952)
* Honorary Member of Hungarian Academy of Sciences (1953)
* Honorary Member of the Romanian Academy of Sciences (1957)
* Honorary Member of New York Academy of Sciences USA (1958)
* Honorary Member of American Academy of Arts and Sciences in Boston (1960)
* Honorary Member of the London Chemical Society
* Honorary Member of the Chemical Industry Society of Great Britain
* Honorary Member of the Polish Chemical Society
* Honorary Member of National Institute of Sciences of India
* Honorary Member of the Royal Society of Edinburgh
* Full member of German Academy of Naturalists "Leopoldina" (1959)
* Full member of International Academy of Astronautics (1966)
* Member of the Polish Academy of Sciences (1954)
* Full member of Czechoslovak Academy of Sciences (1957)
* Foreign Member Royal Society of London (1961)
* Foreign member GDR Academy of Sciences (1950)
* Member of the European Society of Cultural Workers
* Doctor "honoris causa" University of Paris (1964)
* Doctor "honoris causa" University of Bordeaux (1966)
* Doctor "honoris causa" University of Jena
* Doctor "honoris causa" University of Calcutta
* Doctor Iasi Polytechnic Institute
* Member of World Peace Council (1950) | 0 | Organic Chemistry |
Eutrophication, an influx of nutrients (phosphate/nitrate), often a byproduct of agricultural run-off and sewage discharge, can result in large but short-lived algae blooms. Upon a bloom's conclusion, the dead algae sink to the bottom and are broken down until all oxygen is expended. Such a case is the Gulf of Mexico where a seasonal dead zone occurs, which can be disturbed by weather patterns such as hurricanes and tropical convection. Sewage discharge, specifically that of nutrient concentrated "sludge", can be especially damaging to ecosystem diversity. Species sensitive to anoxic conditions are replaced by fewer hardier species, reducing the overall variability of the affected area.
Gradual environmental changes through eutrophication or global warming can cause major oxic-anoxic regime shifts. Based on model studies this can occur abruptly, with a transition between an oxic state dominated by cyanobacteria, and an anoxic state with sulfate-reducing bacteria and phototrophic sulfur bacteria. | 9 | Geochemistry |
Alkoxyaluminium and closely related hydride reagents reduce a wide variety of functional groups, often with good selectivity. This section, organized by functional group, covers the most common or synthetically useful methods for alkoxyaluminium hydride reduction of organic compounds.
Many selective reductions of carbonyl compounds can be effected by taking advantage of the unique reactivity profiles of metal alkoxylaluminium hydrides. For instance, lithium tri-tert-butoxy)aluminium hydride (LTBA) reduces aldehydes and ketones selectively in the presence of esters, with which it reacts extremely slowly.
α,β-Unsaturated ketones may be reduced selectively in a 1,2 or 1,4 sense by a judicious choice of reducing agent. Use of relatively unhindered lithium trimethoxyaluminium hydride results in nearly quantitative direct addition to the carbonyl group (Eq. ()). On the other hand, use of the bulky reagent LTBA leads to a high yield of the conjugate addition product (Eq. ()).
Ether cleavage is difficult to accomplish with most hydride reagents. However, debenzylation of benzyl aryl ethers may be accomplished with SMEAH. This protocol is a useful alternative to methods requiring acid or hydrogenolysis (e.g., Pd/C and hydrogen gas).
Epoxides are generally attacked by alkoxyaluminium hydrides at the less substituted position. A nearby hydroxyl group may facilitate intramolecular delivery of the hydride reagent, allowing for selective opening of 1,2-disubstituted epoxides at the position closer to the hydroxyl group. The configuration at the untouched epoxide carbon is preserved.
Unsaturated carbonyl compounds may be reduced either to saturated or unsaturated alcohols by alkoxyaluminium hydride reagents. Addition of an unsaturated aldehyde to a solution of Red-Al afforded the saturated alcohol; inverse addition yielded the unsaturated alcohol product.
Alkenes undergo hydroalumination in the presence of some alkoxyaluminium hydrides. In a related application, NaAlH(OCHCHOCH) (sodium bis(methoxyethoxy) aluminium dihydride, SMEAH or Red-Al) reacts with zirconocene dichloride to afford zirconocene chloride hydride (Schwartz's reagent). Alkenes undergo hydrozirconation in the presence of this reagent, affording functionalized products after quenching with an electrophile.
Functional groups containing heteroatoms other than oxygen may also be reduced to the corresponding hydrocarbons in the presence of an alkoxyaluminium hydride reagent. Primary alkyl halides undergo reduction to the corresponding alkanes in the presence of NaAlH(OH)(OCHCHOCH). Secondary halides are less reactive, but afford alkanes in reasonable yield.
Sulfoxides are reduced to the corresponding sulfides in good yield in the presence of SMEAH.
Imines are reduced by metal alkoxyaluminium hydrides to the corresponding amines. In the example below, use of the exo amine forms with high diastereoselectivity. The selectivity of hydride reduction in this case is higher than that of catalytic hydrogenation. | 0 | Organic Chemistry |
Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which increases the substance's temperature to the melting point. At the melting point, the ordering of ions or molecules in the solid breaks down to a less ordered state, and the solid melts to become a liquid.
Substances in the molten state generally have reduced viscosity as the temperature increases. An exception to this principle is elemental sulfur, whose viscosity increases in the range of 160 °C to 180 °C due to polymerization.
Some organic compounds melt through mesophases, states of partial order between solid and liquid. | 7 | Physical Chemistry |
Pteropods and brittle stars both form the base of the Arctic food webs and are both seriously damaged from acidification. Pteropods shells dissolve with increasing acidification and the brittle stars lose muscle mass when re-growing appendages. For pteropods to create shells they require aragonite which is produced through carbonate ions and dissolved calcium and strontium. Pteropods are severely affected because increasing acidification levels have steadily decreased the amount of water supersaturated with carbonate. The degradation of organic matter in Arctic waters has amplified ocean acidification; some Arctic waters are already undersaturated with respect to aragonite.
The brittle star's eggs die within a few days when exposed to expected conditions resulting from Arctic acidification. Similarly, when exposed in experiments to pH reduced by 0.2 to 0.4, larvae of a temperate brittle star, a relative of the common sea star, fewer than 0.1 percent survived more than eight days. | 9 | Geochemistry |
Ampicillin has been used extensively to treat bacterial infections since 1961. Until the introduction of ampicillin by the British company Beecham, penicillin therapies had only been effective against gram-positive organisms such as staphylococci and streptococci. Ampicillin (originally branded as "Penbritin") also demonstrated activity against gram-negative organisms such as H. influenzae, coliforms, and Proteus spp. | 4 | Stereochemistry |
U. R. Ghatak was born on 26 February 1931 at Brahmanbaria, a town of historic importance in the undivided Bengal of British India (presently in Bangladesh) to Hem Ranjan Ghatak-Soudamini Devi couple as one among their seven children. He did his schooling locally and after passing matriculation examination in 1947, he completed his intermediate studies in Agartala in 1949. His graduate studies (BSc hons) were at Asutosh College in chemistry and secured his master's degree from Rajabazar Science College in 1953, winning Motilal Mullick Medal and University Gold Medal for standing first in the examination. Subsequently, he enrolled for doctoral studies at Indian Association for the Cultivation of Science (IACS) and studied under the guidance of P. C. Dutta, a synthetic organic chemist, and obtained a PhD from Rajabazar Science College, Calcutta University in 1957. He stayed with IACS for two more years before moving to the US for his post-doctoral studies at three centres viz. University of Maine, the University of California, Berkeley and St. John’s University. He returned to India to IACS in 1963 to resume his career there and worked there till his official retirement from service in 1996; in between, he served as the head of the department of organic chemistry (1977–89) and as the director (1989–96). Later, he was associated with the Indian Institute of Chemical Biology as an INSA Senior Scientist.
Ghatak was married to Anindita and the couple lived in Kolkata. It was here he died, succumbing a massive heart attack, on 18 June 2005, at the age of 76, survived by his wife. | 4 | Stereochemistry |
Fuel made from microalgae could potentially have a low carbon footprint and is an active area of research, although no large-scale production system has been commercialized to date. Microalgae are aquatic unicellular organisms. Although they, unlike most plants, have extremely simple cell structures, they are still photoautotrophic, able to use solar energy to convert carbon dioxide into carbohydrates and fats via photosynthesis. These compounds can serve as raw materials for biofuels like bioethanol or biodiesel. Therefore, even though combusting microalgae-based fuel for energy would still produce emissions like any other fuel, it could be close to carbon-neutral if they, as a whole, consumed as much carbon dioxide as is emitted during combustion.
The advantages of microalgae are their higher CO-fixation efficiency compared to most plants and their ability to thrive in a wide variety of aquatic habitats. Their main disadvantage is their high cost. It has been argued that their unique and highly variable chemical compositions may make it attractive for specific applications.
Microalgae also can be used as livestock feed due to their proteins. Even more, some species of microalgae produce valuable compounds such as pigments and pharmaceuticals. | 0 | Organic Chemistry |
The bond angles in aziridine are approximately 60°, considerably less than the normal hydrocarbon bond angle of 109.5°, which results in angle strain as in the comparable cyclopropane and ethylene oxide molecules. A banana bond model explains bonding in such compounds. Aziridine is less basic than acyclic aliphatic amines, with a pKa of 7.9 for the conjugate acid, due to increased s character of the nitrogen free electron pair. Angle strain in aziridine also increases the barrier to nitrogen inversion. This barrier height permits the isolation of separate invertomers, for example the cis and trans invertomers of N-chloro-2-methylaziridine. | 0 | Organic Chemistry |
Because alkynes have two π bonds, alkynes can form stable complexes in which they bridge two metal centers. The alkyne donates a total of four electrons, with two electrons donated to each of the metals. And example of a complex with this bonding scheme is η-diphenylacetylene-(hexacarbonyl)dicobalt(0). | 0 | Organic Chemistry |
Polyols may be classified according to their chemistry. Some of these chemistries are polyether, polyester, polycarbonate and also acrylic polyols. Polyether polyols may be further subdivided and classified as polyethylene oxide or polyethylene glycol (PEG), polypropylene glycol (PPG) and Polytetrahydrofuran or PTMEG. These have 2, 3 and 4 carbons respectively per oxygen atom in the repeat unit. Polycaprolactone polyols are also commercially available. There is also an increasing trend to use biobased (and hence renewable) polyols. | 7 | Physical Chemistry |
Polyfluorene is a polymer with formula , consisting of fluorene units linked in a linear chain — specifically, at carbon atoms 2 and 7 in the standard fluorene numbering. It can also be described as a chain of benzene rings linked in para positions (a polyparaphenylene) with an extra methylene bridge connecting every pair of rings.
The two benzene rings in each unit make polyfluorene an aromatic hydrocarbon, specifically conjugated polymer, and give it notable optical and electrical properties, such as efficient photoluminescence.
When spoken about as a class, polyfluorenes are derivatives of this polymer, obtained by replacing some of the hydrogen atoms by other chemical groups, and/or by substituting other monomers for some fluorene units. These polymers are being investigated for possible use in light-emitting diodes, field-effect transistors, plastic solar cells, and other organic electronic applications. They stand out among other luminescent conjugated polymers because the wavelength of their light output can be tuned through the entire visible spectrum by appropriate choice of the substituents. | 7 | Physical Chemistry |
Fluorenylmethyloxycarbonyl chloride (Fmoc-Cl) is a chloroformate ester. It is used to introduce the fluorenylmethyloxycarbonyl protecting group as the Fmoc carbamate. | 0 | Organic Chemistry |
The rate for the hydrolysis of cobalt(III) ammine (-containing) halide complexes are deceptive, appearing to be associative but proceeding by a pathway that is dissociative in character. The hydrolysis of follows second order kinetics: the rate increases linearly with concentration of hydroxide as well as the starting complex. Studies show, however, that in the hydroxide deprotonates one ligand to give the conjugate base of the starting complex, i.e., . In this monocation, the chloride spontaneously dissociates from this conjugate base of the starting complex. This pathway is called the Sn1CB mechanism. | 0 | Organic Chemistry |
WECs are sub-surface white cracks networks within local microstructural changes that are characterised by a changed microstructure known as white etching area (WEA). The term "white etching" refers to the white appearance of the altered microstructure of a polished and etched steel sample in the affected areas. The WEA is formed by amorphisation (phase transformation) of the martensitic microstructure due to friction at the crack faces during over-rolling, and these areas appear white under an optical microscope due to their low-etching response to the etchant. The microstructure of WECs consists of ultra-fine, nano-crystalline, carbide-free ferrite, or ferrite with a very fine distribution of carbide particles that exhibits a high degree of crystallographic misorientation.
WEC propagation is mostly transgranular and does not follow a certain cleavage plane.
Researchers observed three distinct types of microstructural alterations near the generated cracks: uniform white etching areas (WEAs), thin elongated regions of dark etching areas (DEA), and mixed regions comprising both light and dark etching areas with some misshaped carbides. During repeated stress cycles, the position of the crack constantly shifts, leaving behind an area of intense plastic deformation composed of ferritic, martensite, austenite (due to austenitization) and carbides. nano-grains, i.e., WEAs. The microscopic displacement of the crack plane in a single stress cycle accumulates to form micron-sized WEAs during repeated stress cycles. After the initial development of a fatigue crack around inclusions, the faces of the crack rub against each other during cycles of compressive stress. This results in the creation of WEAs through localised intense plastic deformation. It also causes partial bonding of the opposing crack faces and material transfer between them. Consequently, the WEC reopens at a slightly different location compared to its previous position during the release of stress.
Furthermore, it has been acknowledged that WEA is one of the phases that arise from different processes and is generally observed as a result of a phase transformation in rolling contact fatigue. WEA is harder than the matrix and . Additionally, WECs are caused by stresses higher than anticipated and occur due to bearing rolling contact fatigue as well as accelerated rolling contact fatigue.
WECs in bearings are accompanied with a white etching matter (WEM). WEM forms asymmetrically along WECs. There is no significant microstructural differences between the untransformed material adjacent to cracking and the parent material although WEM exhibits variable carbon content and increased hardness compared to the parent material. A study in 2019 suggests that WEM may initiate ahead of the crack, challenging the conventional crack-rubbing mechanism. | 8 | Metallurgy |
Substituted derivatives of porphine are called porphyrins. Many porphyrins are found in nature with the dominant example being protoporphyrin IX. Many synthetic porphyrins are also known, including octaethylporphyrin and tetraphenylporphyrin. | 1 | Biochemistry |
* 1993 RACI Polymer Division Citation
* 1999 Applied Research Award and Don Rivett Medal of RACI
* 2002 Euro-Asia Promotion and Cultural Foundation (Romanian Branch)Diploma of Excellence
* 2003 Corresponding Member of the Romanian Academy of Scientists
* 2014 SRB Excellence Award of the Romanian Society for Biomaterials
* 2014 Emeritus Member of Politehnica Foundation, Timișoara, Romania | 0 | Organic Chemistry |
As mentioned previously, Pseudomonas aeruginosa has the ability to metabolise a variety of substrates including n-alkanes, hexadecane and oils. Uptake of these hydrophobic substrates is speculated to rely on the production of rhamnolipids. It is thought that rhamnolipids either cause the Pseudomonas aeruginosa cell surface to become hydrophobic, promoting an interaction between the substrate and the cell, or secreted rhamnolipids emulsify the substrate and allow it to be taken up by the Pseudomonas aeruginosa cell. There is evidence that rhamnolipids are highly adsorbent to the Pseudomonas aeruginosa cell surface, causing it to become hydrophobic. It has also been shown that production of rhamnolipids promotes uptake of hexadecane by overcoming the inhibitory effect of the hydrophilic interactions caused by LPS. Production of rhamnolipids is observed on hydrophobic substrates but equally high yields are achievable on other carbon sources such as sugars. Furthermore, although mono-rhamnolipids have been shown to interact with the Pseudomonas aeruginosa cell membrane and cause it to become hydrophobic, di-rhamnolipids do not interact well with the cell membrane because the polar head group is too large to penetrate the LPS layer. Therefore, although Rhamnolipids may play a part in interaction of Pseudomonas aeruginosa with hydrophobic carbon sources, they are likely to have additional functions. | 0 | Organic Chemistry |
A number of companies have commercialized mercury detection via CVAFS and produced transportable analysers capable of measuring mercury in ambient air. These devices can measure levels in the low parts per quadrillion range (10). | 7 | Physical Chemistry |
Biodegradation of any plastic is a process that happens at solid/liquid interface whereby the enzymes in the liquid phase depolymerize the solid phase. Certain types of bioplastics as well as conventional plastics containing additives are able to biodegrade. Bioplastics are able to biodegrade in different environments hence they are more acceptable than conventional plastics. Biodegradability of bioplastics occurs under various environmental conditions including soil, aquatic environments and compost. Both the structure and composition of biopolymer or bio-composite have an effect on the biodegradation process, hence changing the composition and structure might increase biodegradability. Soil and compost as environment conditions are more efficient in biodegradation due to their high microbial diversity. Composting not only biodegrades bioplastics efficiently but it also significantly reduces the emission of greenhouse gases. Biodegradability of bioplastics in compost environments can be upgraded by adding more soluble sugar and increasing temperature. Soil environments on the other hand have high diversity of microorganisms making it easier for biodegradation of bioplastics to occur. However, bioplastics in soil environments need higher temperatures and a longer time to biodegrade. Some bioplastics biodegrade more efficiently in water bodies and marine systems; however, this causes danger to marine ecosystems and freshwater. Hence it is accurate to conclude that biodegradation of bioplastics in water bodies which leads to the death of aquatic organisms and unhealthy water can be noted as one of the negative environmental impacts of bioplastics. | 7 | Physical Chemistry |
Often the surroundings of a thermodynamic system may also be regarded as another thermodynamic system. In this view, one may consider the system and its surroundings as two systems in mutual contact, with long-range forces also linking them. The enclosure of the system is the surface of contiguity or boundary between the two systems. In the thermodynamic formalism, that surface is regarded as having specific properties of permeability. For example, the surface of contiguity may be supposed to be permeable only to heat, allowing energy to transfer only as heat. Then the two systems are said to be in thermal equilibrium when the long-range forces are unchanging in time and the transfer of energy as heat between them has slowed and eventually stopped permanently; this is an example of a contact equilibrium. Other kinds of contact equilibrium are defined by other kinds of specific permeability. When two systems are in contact equilibrium with respect to a particular kind of permeability, they have common values of the intensive variable that belongs to that particular kind of permeability. Examples of such intensive variables are temperature, pressure, chemical potential.
A contact equilibrium may be regarded also as an exchange equilibrium. There is a zero balance of rate of transfer of some quantity between the two systems in contact equilibrium. For example, for a wall permeable only to heat, the rates of diffusion of internal energy as heat between the two systems are equal and opposite. An adiabatic wall between the two systems is permeable only to energy transferred as work; at mechanical equilibrium the rates of transfer of energy as work between them are equal and opposite. If the wall is a simple wall, then the rates of transfer of volume across it are also equal and opposite; and the pressures on either side of it are equal. If the adiabatic wall is more complicated, with a sort of leverage, having an area-ratio, then the pressures of the two systems in exchange equilibrium are in the inverse ratio of the volume exchange ratio; this keeps the zero balance of rates of transfer as work.
A radiative exchange can occur between two otherwise separate systems. Radiative exchange equilibrium prevails when the two systems have the same temperature. | 7 | Physical Chemistry |
Ge joined the University of Wisconsin–Madison as an assistant scientist, where she oversaw the mass spectrometry programme. She became an Associate Professor in 2015, and full Professor in 2019.
Ge develops high-resolution mass spectrometry proteomics to better understand cardiac disease. To image the very large proteins of human heart tissue, Ge combines fourier-transform ion cyclotron resonance (FT–ICR) mass spectrometry with electron-capture dissociation. She has worked to create a top-down disease proteomic platform that allows for the separation, detection and characterisation of the biomarkers of heart damage.
Nanoproteomics, a technique developed by Ge and co-workers, makes use of nanoparticles and high resolution mass spectrometry to capture and characterise cardiac troponins, including troponin I. Being able to test for and characterise troponin I would help with the early detection and diagnosis of heart disease. The peptide-functionalised superparamagnetic nanoparticles are combined with top-down mass spectrometry to identify the molecular fingerprints of troponins. Rather than just detecting cardiac troponins, which is possible using ELISA-based antibody testing, this higher level of characterisation will allow Ge to identify various forms of modified troponins, allowing a personalised understanding of cardiac disease.
Ge served on the board of the Top-Down Proteomics Consortium, on the editorial board of the Journal of Muscle Research and Cell Motility, as treasurer for the American Society for Mass Spectrometry (2016-2018).
[https://scholar.google.com/citations?user=Ymgpd5QAAAAJ&hl=en&oi=sra Ying Ge] publications indexed by Google Scholar. | 1 | Biochemistry |
NCAs are typically prepared by phosgenation of amino acids:
They were first synthesized by Hermann Leuchs by heating an N-ethoxycarbonyl or N-methoxycarbonyl amino acid chloride in a vacuum at 50-70 °C:
A moisture-tolerant route to unprotected NCAs employs epoxides as scavengers of hydrogen chloride.
This synthesis of NCAs is sometimes called the . The relatively high temperatures necessary for this cyclization results in the decomposition of several NCAs. Of several improvements, one notable procedure involves treating an unprotected amino acid with phosgene or its trimer. | 0 | Organic Chemistry |
The following forces play an important role in the interaction of colloid particles:
*Excluded volume repulsion: This refers to the impossibility of any overlap between hard particles.
*Electrostatic interaction: Colloidal particles often carry an electrical charge and therefore attract or repel each other. The charge of both the continuous and the dispersed phase, as well as the mobility of the phases are factors affecting this interaction.
*van der Waals forces: This is due to interaction between two dipoles that are either permanent or induced. Even if the particles do not have a permanent dipole, fluctuations of the electron density gives rise to a temporary dipole in a particle. This temporary dipole induces a dipole in particles nearby. The temporary dipole and the induced dipoles are then attracted to each other. This is known as van der Waals force, and is always present (unless the refractive indexes of the dispersed and continuous phases are matched), is short-range, and is attractive.
*Steric forces between polymer-covered surfaces or in solutions containing non-adsorbing polymer can modulate interparticle forces, producing an additional steric repulsive force (which is predominantly entropic in origin) or an attractive depletion force between them. | 7 | Physical Chemistry |
The Koenigs–Knorr reaction in organic chemistry is the substitution reaction of a glycosyl halide with an alcohol to give a glycoside. It is one of the oldest glycosylation reactions. It is named after Wilhelm Koenigs (1851–1906), a student of von Baeyer and fellow student with Hermann Emil Fischer, and Edward Knorr, a student of Koenigs.
In its original form, Koenigs and Knorr treated acetobromoglucose with alcohols in the presence of silver carbonate. Shortly afterwards Fischer and Armstrong reported very similar findings.
In the above example, the stereochemical outcome is determined by the presence of the neighboring group at C2 that lends anchimeric assistance, resulting in the formation of a 1,2-trans stereochemical arrangement. Esters (e.g. acetyl, benzoyl, pivalyl) generally provide good anchimeric assistance, whereas ethers (e.g. benzyl, methyl etc.) do not, leading to mixtures of stereoisomers. | 0 | Organic Chemistry |
The CFL phase has several remarkable properties.
* It breaks chiral symmetry.
* It is a superfluid.
* It is an electromagnetic insulator, in which there is a "rotated" photon, containing a small admixture of one of the gluons.
* It has the same symmetries as sufficiently dense hyperonic matter.
There are several variants of the CFL phase, representing distortions of the pairing structure in response to external stresses such as a difference between the mass of the strange quark and the mass of the up and down quarks. | 7 | Physical Chemistry |
Many, if not all, retinalophototrophs are photoheterotrophs: although sufficient ATP is produced by light, they cannot subsist on light and inorganic substances alone because they cannot produce needed organic materials from only . This category includes retinalophototrophs that perform anaplerotic fixation, such as a flavobacterium that can use pyruvate and CO to make malate. This ability does, however, help "stretch" limited supplies of carbon. | 5 | Photochemistry |
In EPR spectroscopy, g-strain refers to broadening of g-values owing to small sample inhomogeneity owing to slight variations in the orientation of the paramagnetic centers. The phenomenon is indicated by broadening of the g-values that depends on the frequency of the spectrometer, such as X- or Q-band. If the line width were determined only by hyperfine coupling (which are field-independent), then the line widths would also be field independent, but they often are not. In iron-sulfur proteins, some other metalloproteins, as well as some solids, g-strain can be substantial. | 7 | Physical Chemistry |
Natural water reservoirs in Texas have been threatened by anthropogenic activities due to large petroleum refineries and oil wells (i.e. emission and wastewater discharge), massive agricultural activities (i.e. pesticide release) and mining extractions (i.e. toxic wastewater) as well as natural phenomena involving frequent HAB events. For the first time in 1985, the state of Texas documented the presence of the P. parvum (golden alga) bloom along the Pecos River. This phenomenon has affected 33 reservoirs in Texas along major river systems, including the Brazos, Canadian, Rio Grande, Colorado, and Red River, and has resulted in the death of more than 27 million fish and caused tens of millions of dollars in damage. | 3 | Analytical Chemistry |
The van der Waals forces arise from interaction between uncharged atoms or molecules, leading not only to such phenomena as the cohesion of condensed phases and physical absorption of gases, but also to a universal force of attraction between macroscopic bodies. | 6 | Supramolecular Chemistry |
The Condylostoma nuclear code (translation table 28) is a genetic code used by the nuclear genome of the heterotrich ciliate Condylostoma magnum. This code, along with translation tables 27 and 31, is remarkable in that every one of the 64 possible codons can be a sense codon. Experimetnal evidence suggests that translation termination relies on context, specifically proximity to the poly(A) tail. Near such a tail, PABP could help terminate the protein by recruiting eRF1 and eRF3 to prevent the cognate tRNA from binding. | 1 | Biochemistry |
The raw material was bar iron, or (from the introduction of mild steel in the late 19th century), a bar of steel. This was drawn into a flat bar (known as a tin bar) at the ironworks or steel works where it was made. The cross-section of the bar needed to be accurate in size as this would be the cross-section of the pack of plates made from it. The bar was cut to the correct length (being the width of the plates) and heated. It was then passed four or five times through the rolls of the rolling mill, to produce a thick plate about 30 inches long. Between each pass the plate is passed over (or round) the rolls, and the gap between the rolls is narrowed by means of a screw.
This was then rolled until it had doubled in length. The plate was then folded in half (doubled) using a doubling shear, which was like a table where one half of the surface folds over on top of the other. It is then put into a furnace to be heated until it is well soaked. This is repeated until there is a pack of 8 or 16 plates. The pack is then allowed to cool. When cool, the pack was sheared (using powered shears) and the plates separated by openers (usually women). Defective plates were discarded, and the rest passed to the pickling department.
In the pickling department, the plates were immersed in baths of acid (to remove scale, i.e., oxide), then in water (washing them). After inspection they were placed in an annealing furnace, where they were heated for 10–14 hours. This was known as black pickling and black annealing. After being removed they were allowed to cool for up to 48 hours. The plates were then rolled cold through highly polished rolls to remove any unevenness and give them a polished surface. They were then annealed again at a lower temperature and pickled again, this being known as white annealing and white pickling. They were then washed and stored in slightly acid water (where they would not rust) awaiting tinning.
The tinning set consisted of two pots with molten tin (with flux on top) and a grease pot. The flux dries the plate and prepares it for the tin to adhere. The second tin pot (called the wash pot) had tin at a lower temperature. This is followed by the grease pot (containing an oil), removing the excess tin. Then follow cleaning and polishing processes. Finally, the tinplates were packed in boxes of 112 sheets ready for sale. Single plates were 14 inches by 20 inches; doubles twice that. A box weighed approximately a hundredweight.
What is described here is the process as employed during the 20th century. The process grew somewhat in complexity with the passage of time, as gradually it was found that the inclusion of additional procedures improved quality. The practice of hot rolling and then cold rolling evidently goes back to the early days, as the Knight family's tinplate works had (from its foundation in about 1740) two rolling mills, one at Bringewood (west of Ludlow) which made blackplate, and the other the tin mill at Mitton (now part of Stourport), evidently for the later stages. | 8 | Metallurgy |
Transesterification, which involves changing one ester into another one, is widely practiced:
Like the hydrolysation, transesterification is catalysed by acids and bases. The reaction is widely used for degrading triglycerides, e.g. in the production of fatty acid esters and alcohols. Poly(ethylene terephthalate) is produced by the transesterification of dimethyl terephthalate and ethylene glycol:
A subset of transesterification is the alcoholysis of diketene. This reaction affords 2-ketoesters. | 0 | Organic Chemistry |
There have been reports of off-label uses of pseudoephedrine for its stimulant properties. Long-distance truck drivers and athletes, for example, have reportedly used pseudoephedrine as a stimulant to increase their state of alertness/awareness.
A study has also found that pseudoephedrine can reduce milk production in breastfeeding women. | 4 | Stereochemistry |
Electrochemical impedance spectroscopy (EIS) involves measuring resistive and capacitive changes caused by a biorecognition event. Typically, a small amplitude sinusoidal electrical stimulus is applied, causing current to flow through the biosensor. The frequency is varied over a range to obtain the impedance spectrum. The resistive and capacitive components of impedance are determined from in phase and out of phase current responses. Typically, a conventional three-electrode system is made specific to the analyte by immobilizing a biorecognition element to the surface. A voltage is applied and the current is measured. The interfacial impedance between the electrode and solution changes as a result of the analyte binding. An impedance analyzer can be used to control and apply the stimulus as well as measure the impedance changes. | 1 | Biochemistry |
In this process molten metal is poured in the mold and allowed to solidify while the mold is rotating. Metal is poured into the center of the mold at its axis of rotation. Due to inertial force, the liquid metal is thrown out toward the periphery.
Centrifugal casting is both gravity and pressure independent since it creates its own force feed using a temporary sand mold held in a spinning chamber. Lead time varies with the application. Semi- and true-centrifugal processing permit 30–50 pieces/hr-mold to be produced, with a practical limit for batch processing of approximately 9000 kg total mass with a typical per-item limit of 2.3–4.5 kg.
Industrially, the centrifugal casting of railway wheels was an early application of the method developed by the German industrial company Krupp and this capability enabled the rapid growth of the enterprise.
Small art pieces such as jewelry are often cast by this method using the lost wax process, as the forces enable the rather viscous liquid metals to flow through very small passages and into fine details such as leaves and petals. This effect is similar to the benefits from vacuum casting, also applied to jewelry casting. | 8 | Metallurgy |
The serotonin created by the brain comprises around 10% of total body serotonin. The majority (80-90%) is found in the gastrointestinal (GI) tract. It travels around the brain along the medial forebrain bundle and acts on serotonin receptors. In the peripheral nervous system (such as in the gut wall) serotonin regulates vascular tone. | 1 | Biochemistry |
PDE inhibitors have been identified as new potential therapeutics in areas such as pulmonary arterial hypertension, coronary heart disease, dementia, depression, asthma, COPD, protozoal infections (including malaria) and schizophrenia.
PDE also are important in seizure incidence. For example, PDE compromised the antiepileptic activity of adenosine. In addition, using of a PDE inhibitor (pentoxifylline) in pentylenetetrazole-induced seizure indicated the antiepileptic effect by increasing the time latency to seizure incidence and decreasing the seizure duration in vivo.
Cilostazol (Pletal) inhibits PDE3. This inhibition allows red blood cells to be more able to bend. This is useful in conditions such as intermittent claudication, as the cells can maneuver through constricted veins and arteries more easily.
Dipyridamole inhibits PDE-3 and PDE-5. This leads to intraplatelet accumulation of cAMP and/or cGMP, inhibiting platelet aggregation.
Zaprinast inhibits the growth of asexual blood-stage malaria parasites (Plasmodium falciparum) in vitro with an ED value of 35 μM, and inhibits PfPDE1, a P. falciparum cGMP-specific phosphodiesterase, with an IC value of 3.8 μM.
Xanthines such as caffeine and theobromine are cAMP-phosphodiesterase inhibitors. However, the inhibitory effect of xanthines on phosphodiesterases are only seen at dosages higher than what people normally consume.
Sildenafil, Tadalafil and Vardenafil are PDE-5 inhibitors and are widely used in the treatment of erectile dysfunction. | 1 | Biochemistry |
Glide reflections, denoted by G, where c is a point in the plane, v is a unit vector in R, and w is non-null a vector perpendicular to v are a combination of a reflection in the line described by c and v, followed by a translation along w. That is,
or in other words,
(It is also true that
that is, we obtain the same result if we do the translation and the reflection in the opposite order.)
Alternatively we multiply by an orthogonal matrix with determinant −1 (corresponding to a reflection in a line through the origin), followed by a translation. This is a glide reflection, except in the special case that the translation is perpendicular to the line of reflection, in which case the combination is itself just a reflection in a parallel line.
The identity isometry, defined by I(p) = p for all points p is a special case of a translation, and also a special case of a rotation. It is the only isometry which belongs to more than one of the types described above.
In all cases we multiply the position vector by an orthogonal matrix and add a vector; if the determinant is 1 we have a rotation, a translation, or the identity, and if it is −1 we have a glide reflection or a reflection.
A "random" isometry, like taking a sheet of paper from a table and randomly laying it back, "almost surely" is a rotation or a glide reflection (they have three degrees of freedom). This applies regardless of the details of the probability distribution, as long as θ and the direction of the added vector are independent and uniformly distributed and the length of the added vector has a continuous distribution. A pure translation and a pure reflection are special cases with only two degrees of freedom, while the identity is even more special, with no degrees of freedom. | 3 | Analytical Chemistry |
There are a number of problems that can be encountered during the casting process. The main types are: gas porosity, shrinkage defects, mold material defects, pouring metal defects, and metallurgical defects. | 8 | Metallurgy |
* Food chemistry
* Food physics and Rheology
* Biophysical chemistry
* Physical chemistry
** Spectroscopy-applied
** Intermolecular forces
** Nanotechnology and nanostructures
* Chemical physics
** Molecular dynamics
** Surface chemistry and Van der Waals forces
** Chemical reactions and Reaction chemistry
* Quantum chemistry
** Quantum genetics
** Molecular models of DNA and Molecular modelling of proteins and viruses
* Bioorganic chemistry
* Polymer chemistry
* Biochemistry and Biological chemistry
** Enzymology
** Protein–protein interactions
** Biomembranes
* Complex system biology
** Integrative biology
** Mathematical biophysics
** Systems biology
** Genomics, Proteomics, Interactomics, Structural bioinformatics and Cheminformatics
* Food technology, Food engineering, Food safety and Food biotechnology
** Agricultural biotechnology
****Immobilized cells and enzymes
****Microencapsulation of food additives and vitamins, etc.
* Chemical engineering
* Plant biology and Crop sciences
* Animal sciences | 7 | Physical Chemistry |
An isocyanide (also called isonitrile or carbylamine) is an organic compound with the functional group –. It is the isomer of the related nitrile (–C≡N), hence the prefix is isocyano. The organic fragment is connected to the isocyanide group through the nitrogen atom, not via the carbon. They are used as building blocks for the synthesis of other compounds. | 0 | Organic Chemistry |
The main precursors of glyceroneogenesis are pyruvate, lactate, glutamine, and alanine. Glyceroneogenesis is also known as the branched pathway of gluconeogenesis because its first few steps are the same.
When pyruvate or lactate is used as the precursor for glycerol 3-phosphate, glyceroneogenesis follows the same pathway as gluconeogenesis until it generates dihydroxyacetone phosphate. Lactate catalyzed by lactate dehydrogenase will form pyruvate at the expense of NAD+. By using one ATP and bicarbonate, pyruvate will be converted to oxaloacetate, catalysed by pyruvate carboxylase. The PEPC-K enzyme will catalyze oxaloacetate to generate phosphoenolpyruvate. This phosphorylation and decarboxylation of oxaloacetate is a significant step in glyceroneogenesis, since it regulates the entire pathway. After the production of phosphoenolpyruvate, gluconeogenesis will continue until dihydroxyacetone phosphate is generated, which produces 2-phosphoglycerate, 3-phosphoglycerate, 1,3-bisphosphoglycerate and glyceraldehyde 3-phosphate as intermediates. When dihydroxyacetone phosphate is produced, glyceroneogenesis will branch off from gluconeogenesis. With the expense of NADH, dihydroxyacetone phosphate will convert to glycerol 3-phosphate, which is the final product of glyceroneogenesis. In addition, triglyceride can be generated by re-esterifying 3 fatty acid chains on glycerol 3-phosphate. Instead of producing fructose 1,6- bisphosphate as gluconeogenesis does, glyceroneogenesis converts dihydroxyacetone phosphate to glycerol 3-phosphate.
Alanine can also be used as a precursor of glyceroneogenesis because alanine can be degraded to pyruvate. Alanine will degrade to pyruvate by transferring its amino group to 2-oxoglutarate with an enzyme called alanine aminotransferase. Alanine aminotransferase cleaves off the amino group from alanine and binds it to 2-oxoglutarate, generating pyruvate from alanine, and glutamate from 2-oxoglutarate. Pyruvate generated from alanine will enter glyceroneogenesis and generate glycerol 3-phosphate.
Glutamate can also enter glyceroneogenesis. Since the key reaction of glyceroneogenesis is the decarboxylation and phosphorylation of oxaloacetate to phosphoenolpyruvate, in theory any biochemical pathway which generates oxaloacetate is related to glyceroneogenesis. For example, glutamate can generate oxaloacetate in 2 steps. Firstly, glutamate can be converted to 2-oxoglutarate with the expense of NAD+ and HO with the help of glutamate dehydrogenase. Secondly, 2-oxoglutarate can enter the tricarboxylic acid cycle to generate oxaloacetate. Therefore, theoretically any metabolites in the TCA cycle or any metabolites generating the metabolites of the TCA cycle can be used as a precursor of glyceroneogenesis, but glutamate is the only precursor confirmed. | 1 | Biochemistry |
Research in photocatalysis again paused until 1964, when V.N. Filimonov investigated isopropanol photooxidation from ZnO and ; while in 1965 Kato and Mashio, Doerffler and Hauffe, and Ikekawa et al. (1965) explored oxidation/photooxidation of and organic solvents from ZnO radiance. In 1970, Formenti et al. and Tanaka and Blyholde observed the oxidation of various alkenes and the photocatalytic decay of NO, respectively.
A breakthrough occurred in 1972, when Akira Fujishima and Kenichi Honda discovered that electrochemical photolysis of water occurred when a electrode irradiated with ultraviolet light was electrically connected to a platinum electrode. As the ultraviolet light was absorbed by the electrode, electrons flowed from the anode to the platinum cathode where hydrogen gas was produced. This was one of the first instances of hydrogen production from a clean and cost-effective source, as the majority of hydrogen production comes from natural gas reforming and gasification. Fujishimas and Hondas findings led to other advances. In 1977, Nozik discovered that the incorporation of a noble metal in the electrochemical photolysis process, such as platinum and gold, among others, could increase photoactivity, and that an external potential was not required. Wagner and Somorjai (1980) and Sakata and Kawai (1981) delineated hydrogen production on the surface of strontium titanate (SrTiO) via photogeneration, and the generation of hydrogen and methane from the illumination of and PtO in ethanol, respectively.
For many decades photocatalysis had not been developed for commercial purposes. However, in 2023 multiple patents were granted to a U.S. company, (Pure-Light Technologies, Inc.) that has developed various formulas and processes that allow for widespread commercialization for VOC reduction and germicidal action. Chu et al. (2017) assessed the future of electrochemical photolysis of water, discussing its major challenge of developing a cost-effective, energy-efficient photoelectrochemical (PEC) tandem cell, which would, “mimic natural photosynthesis". | 5 | Photochemistry |
A telluroketone is an analog of a ketone in which the oxygen atom has been replaced by a tellurium atom. This change makes the functional group less stable, requiring greater steric and electronic stabilization. | 0 | Organic Chemistry |
The addition of hydrogen and an amino group (NR) using reagents other than the amine HNR is known as a "formal hydroamination" reaction. Although the advantages of atom economy and/or ready available of the nitrogen source are diminished as a result, the greater thermodynamic driving force, as well as ability to tune the aminating reagent are potentially useful. In place of the amine, hydroxylamine esters and nitroarenes have been reported as nitrogen sources. | 0 | Organic Chemistry |
There are three types of viral infections that can be considered under the topic of viral transformation. These are cytocidal, persistent, and transforming infections. Cytocidal infections can cause fusion of adjacent cells, disruption of transport pathways including ions and other cell signals, disruption of DNA, RNA and protein synthesis, and nearly always leads to cell death. Persistent infections involve viral material that lays dormant within a cell until activated by some stimulus. This type of infection usually causes few obvious changes within the cell but can lead to long chronic diseases. Transforming infections are also referred to as malignant transformation. This infection causes a host cell to become malignant and can be either cytocidal (usually in the case of RNA viruses) or persistent (usually in the case of DNA viruses). Cells with transforming infections undergo immortalization and inherit the genetic material to produce tumors. Since the term cytocidal, or cytolytic, refers to cell death, these three infections are not mutually exclusive. Many transforming infections by DNA tumor viruses are also cytocidal.
Table 1: Cellular effects of viral infections
Rounding of the cell<br/>
Fusion with adjacent cells<br/>
Appearance of inclusion bodies
Inhibit DNA, RNA, and protein synthesis<br/>
Interfere with sub-cellular interactions
Insufficient movement of ions<br/>
Formation of secondary messengers<br/>
Activation of cellular cascades
| Persistent ||
Fusion with adjacent cells<br/>
Appearance of inclusion bodies<br/>
Budding
Immune responses limit viral spread<br/>
Antigen-antibody complexes can incorporate <br/>viral antigens causing inflammation
Rare until stimulated
| Transforming ||
Unlimited cell replication
Inactivates tumor suppressor proteins<br/>
Impairs cell cycle regulation
Unlimited cell replication | 1 | Biochemistry |
In chemistry, a polyoxometalate (abbreviated POM) is a polyatomic ion, usually an anion, that consists of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional frameworks. The metal atoms are usually group 6 (Mo, W) or less commonly group 5 (V, Nb, Ta) and group 7 (Tc , Re) transition metals in their high oxidation states. Polyoxometalates are often colorless, orange or red diamagnetic anions. Two broad families are recognized, isopolymetalates, composed of only one kind of metal and oxide, and heteropolymetalates, composed of one or more metals, oxide, and eventually a main group oxyanion (phosphate, silicate, etc.). Many exceptions to these general statements exist. | 7 | Physical Chemistry |
Sialic acid containing glycoproteins (sialoglycoproteins) bind selectin in humans and other organisms. Metastatic cancer cells often express a high density of sialic acid-rich glycoproteins. This overexpression of sialic acid on surfaces creates a negative charge on cell membranes. This creates repulsion between cells (cell opposition) and helps these late-stage cancer cells enter the blood stream. Recent experiments have demonstrated the presence of sialic acid in the cancer-secreted extracellular matrix.
Sialic acid-rich oligosaccharides on the glycoconjugates (glycolipids, glycoproteins, proteoglycans) found on surface membranes help keep water at the surface of cells. The sialic acid-rich regions contribute to creating a negative charge on the cells' surfaces. Since water is a polar molecule with partial positive charges on both hydrogen atoms, it is attracted to cell surfaces and membranes. This also contributes to cellular fluid uptake.
Sialic acid residues are present in the mucin glycoproteins of mucus.
Sialic acid can "hide" mannose antigens on the surface of host cells or bacteria from mannose-binding lectin. This prevents activation of complement.
Sialic acid in the form of polysialic acid is an unusual posttranslational modification that occurs on the neural cell adhesion molecules (NCAMs). In the synapse, the strong negative charge of the polysialic acid prevents NCAM cross-linking of cells.
Administration of estrogen to castrated mice leads to a dose-dependent reduction of the sialic acid content of the vagina. Conversely, the sialic acid content of mouse vagina is a measure of the potency of the estrogen. Reference substances are estradiol for subcutaneous application and ethinylestradiol for oral administration. | 0 | Organic Chemistry |
Iron–sulfur clusters are molecular ensembles of iron and sulfide. They are most often discussed in the context of the biological role for iron–sulfur proteins, which are pervasive. Many Fe–S clusters are known in the area of organometallic chemistry and as precursors to synthetic analogues of the biological clusters (see Figure). It is believed that the last universal common ancestor had many iron-sulfur clusters. | 7 | Physical Chemistry |
The Spodden Valley asbestos controversy arose in May 2004 when approximately of land in Spodden Valley in Rochdale, England, formerly used by Turner Brothers Asbestos Company (later known as Turner & Newall), and the site of the worlds largest asbestos textile factory, was sold to MMC Estates, a property developer. The developer subsequently submitted a planning application to Rochdale Metropolitan Borough Council in December 2004 to build an "urban village" consisting of 650 homes, a childrens daycare centre and a business park on the site. The planning application summary claimed: "of particular note is the absence of any asbestos contamination". However, asbestos containing materials were abundantly visible on the ground, and local residents claimed that there were numerous asbestos dumping sites across the area, and that the woodland there had been heavily contaminated with asbestos dust. Site clearance work had begun as early as May 2004, prior to the submission of the application, including tree felling and soil disturbance, and some waste had been removed on flatbed trailers and open trucks. In September 2005 MMC admitted that the woods were significantly contaminated with asbestos.
A campaign group, Save Spodden Valley, was formed to oppose the development, claiming disturbance of the site in a contaminated state posed too great a risk to public health. Greater Manchester Association of Trade Unions Councils said: "The planners must do their public duty and deem the site permanently unsafe for urban development and formulate a plan to seal all possible sources of asbestos dust as an urgent priority."
The initial planning application was placed on hold in 2005, and Richard Butler, Principal Planning Officer for Rochdale Borough Council said in October 2008: "The application has not yet been determined and is suspended whilst the applicants and their consultants, together with our own contamination experts, assess a number of issues, the most important being the asbestos risk and the remediation required as part of the redevelopment." In December 2009, despite no decontamination work having been carried out, the council earmarked the site for 568 houses, based on a housing density of 30 dwellings per hectare, in a draft allocation of future brownfield land targets. In January 2010, however, the council deleted references to the redevelopment of the site. Rochdale parliamentary candidate Simon Danczuk warned that the council believe a housing development on the site is an inevitability and iterated that they are "sleepwalking into a catastrophic mistake." MMC have stated that "there is no viable alternative to development led remediation of the site." A National Health and Safety Commissioner who was formerly a Health and Safety Manager at the factory has said that the felling of trees and disturbing of soil on the site is "sheer madness... With the potential amount of asbestos on that site, no development should be built on this land." Hilda Palmer of the Greater Manchester Hazards Centre has said: "Asbestos is a carcinogen and it causes lung diseases. When asbestos gets into the air and can be inhaled by people it can cause those diseases 10, 20, 50 years down the line. So if there is any development on that site there is a potential for serious lung diseases, cancers and death from that development." Spokesman Jason Addy of Save Spodden Valley, stated: "The key issue is contamination. Asbestos from this site has killed far too many people already."
The planning application was finally officially rejected by Rochdale Council in January 2011. MMC Estates put the land back up for sale in August 2011. As of December 2018, the land was owned by Renshaw Properties, a company registered in the British Virgin Islands. | 2 | Environmental Chemistry |
A core suite of environmental variables was selected at the start of the program that is expected to display detectable change on time scales of several days to one decade. Since 1988, the interdisciplinary station work has included physical, chemical, biological and sedimentological observations and rate measurements. The initial phase of the HOT program (October 1988 – February 1991) was entirely supported by research vessels, with the exception of the availability of existing satellite and ocean buoy sea surface data. In February 1991, an array of inverted echosounders (IES) was deployed around Station ALOHA and in June 1992, a sequencing sediment trap mooring was deployed a few km north of it. In 1993, the IES network was replaced with two strategically positioned instruments: one at Station ALOHA and the other at the coastal station Kaena. A physical-biogeochemical mooring (known as HALE-ALOHA) was deployed from January 1997 to June 2000 for high frequency atmospheric and oceanic observations.
HOT relies on the University-National Oceanographic Laboratory System research vessel Kilo Moana operated by the University of Hawaii for most of the near-monthly sampling expeditions. When at Station ALOHA, a variety of sampling strategies is used to capture the range of physical and biogeochemical dynamics natural to the NPSG ecosystem. These strategies include high resolution conductivity-temperature-depth (CTD) profiles, biogeochemical analyses of discrete water samples, in situ vertically profiling bio-optical instrumentation, free-drifting arrays for determinations of primary production and particle fluxes, deep ocean sediment traps, and oblique plankton net tows.
The suite of core measurements conducted by HOT has remained largely unchanged over the program’s lifetime. On each HOT cruise, samples are collected from the surface ocean to near the sea bed (~4,800 m), with the most intensive sampling occurring in the upper 1,000 m. HOT utilizes a “burst” vertical profiling strategy where physical and biogeochemical properties are measured at 3 hour intervals over a 36-hour period, covering 3 semi-diurnal tidal cycles and 1 inertial period (~31 hours). This approach captures variability in ocean dynamics due to internal tides around Station ALOHA. It is designed to assess variability on time scales of a few hours to a few years. High frequency variability (less than 6 hours) and variability on time scales of between 3–60 days are not adequately sampled at the present time. | 9 | Geochemistry |
A study published in 2016, by researchers from the University of South Florida, Canada and the Netherlands, used GRACE satellite data to estimate freshwater flux from Greenland. They concluded that freshwater runoff is accelerating, and could eventually cause a disruption of AMOC in the future, which would affect Europe and North America.
Another study published in 2016, found further evidence for a considerable impact from sea level rise for the U.S. East Coast. The study confirms earlier research findings which identified the region as a hotspot for rising seas, with a potential to divert 3–4 times higher than the global average sea level rise rate. The researchers attribute the possible increase to an ocean circulation mechanism called deep water formation, which is reduced due to AMOC slow down, leading to more warmer water pockets below the surface. Additionally, the study noted: "Our results suggest that higher carbon emission rates also contribute to increased [sea level rise] in this region compared to the global average". | 9 | Geochemistry |
Transketolase (abbreviated as TK) is an enzyme that, in humans, is encoded by the TKT gene. It participates in both the pentose phosphate pathway in all organisms and the Calvin cycle of photosynthesis. Transketolase catalyzes two important reactions, which operate in opposite directions in these two pathways. In the first reaction of the non-oxidative pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose (D-xylulose-5-P), then transfers this fragment to a 5-carbon aldose (D-ribose-5-P) to form a 7-carbon ketose (sedoheptulose-7-P). The abstraction of two carbons from D-xylulose-5-P yields the 3-carbon aldose glyceraldehyde-3-P. In the Calvin cycle, transketolase catalyzes the reverse reaction, the conversion of sedoheptulose-7-P and glyceraldehyde-3-P to pentoses, the aldose D-ribose-5-P and the ketose D-xylulose-5-P.
The second reaction catalyzed by transketolase in the pentose phosphate pathway involves the same thiamine diphosphate-mediated transfer of a 2-carbon fragment from D-xylulose-5-P to the aldose erythrose-4-phosphate, affording fructose 6-phosphate and glyceraldehyde-3-P. Again, in the Calvin cycle exactly the same reaction occurs, but in the opposite direction. Moreover, in the Calvin cycle this is the first reaction catalyzed by transketolase, rather than the second.
In mammals, transketolase connects the pentose phosphate pathway to glycolysis, feeding excess sugar phosphates into the main carbohydrate metabolic pathways. Its presence is necessary for the production of NADPH, especially in tissues actively engaged in biosyntheses, such as fatty acid synthesis by the liver and mammary glands, and for steroid synthesis by the liver and adrenal glands. Thiamine diphosphate is an essential cofactor, along with calcium.
Transketolase is abundantly expressed in the mammalian cornea by the stromal keratocytes and epithelial cells and is reputed to be one of the corneal crystallins. | 5 | Photochemistry |
The Phillips catalyst, or the Phillips supported chromium catalyst, is the catalyst used to produce approximately half of the world's polyethylene. A heterogeneous catalyst, it consists of a chromium oxide supported on silica gel. Polyethylene, the most-produced synthetic polymer, is produced industrially by the polymerization of ethylene:
:n CH → (CH)
Although exergonic (i.e., thermodynamically favorable), the reaction requires catalysts. Three main catalysts are employed commercially: the Phillips catalyst, Ziegler–Natta catalysts (based on titanium trichloride), and, for specialty polymers, metallocene-based catalysts. | 7 | Physical Chemistry |
Coined by Herbert J. Webber, the term clone derives from the Ancient Greek word (), twig, which is the process whereby a new plant is created from a twig. In botany, the term lusus was used. In horticulture, the spelling clon was used until the early twentieth century; the final e came into use to indicate the vowel is a "long o" instead of a "short o". Since the term entered the popular lexicon in a more general context, the spelling clone has been used exclusively. | 1 | Biochemistry |
The Henderson limit is the X-ray dose (energy per unit mass) a cryo-cooled crystal can absorb before the diffraction pattern decays to half of its original intensity. Its value is defined as 2 × 10 Gy (J/kg). | 1 | Biochemistry |
Some alcohols are reduced to alkanes when treated with hydrosilanes in the presence of a strong Lewis acid. Brønsted acids may also be used. Tertiary alcohols undergo facile reduction using boron trifluoride etherate as the Lewis acid. Primary alcohols require an excess of the silane, a stronger Lewis acid, and long reaction times.
Skeletal rearrangements are sometimes induced. Another side reaction is nucleophilic attack of the conjugate base on the intermediate carbocation. In organosilane reductions of substrates bearing prostereogenic groups, diastereoselectivity is often high. Reduction of either diastereomer of 2-phenyl-2-norbornanol leads exclusively to the endo diastereomer of 2-phenylnorbornane. None of the exo diastereomer was observed.
Allylic alcohols may be deoxygenated in the presence of tertiary alcohols when ethereal lithium perchlorate is employed as a source of Li.
Reductions of alkyl halides and triflates gives poorer yields in general than reductions of alcohols. A Lewis or Bronsted acid is required. | 0 | Organic Chemistry |
Like some other ethers, dioxane combines with atmospheric oxygen upon prolonged exposure to air to form potentially explosive peroxides. Distillation of these mixtures is dangerous. Storage over metallic sodium could limit the risk of peroxide accumulation. | 6 | Supramolecular Chemistry |
Giuseppe Resnati (born 26 August 1955) is an Italian chemist with interests in supramolecular chemistry and fluorine chemistry. He has a particular focus on self-assembly processes driven by halogen bonds and chalcogen bonds. | 0 | Organic Chemistry |
Purely decorative work is rare among Minoan bronzes, and is comparatively poor in quality. There are several statuettes, very completely modelled but roughly cast; they are solid and unchased, with blurred details. Well known are a figure of a praying or dancing woman from the Troad, now at Berlin, and another from Hagia Triada; praying men from Tylissos and Psychro, another in the British Museum, a flute-player at Leyden, and an ambitious group of a man turning a somersault over a charging bull, known as the Minoan Bull-leaper. This last was perhaps a weight; there are smaller Mycenaean weights in the forms of animals, filled with lead, from Rhodes and Cyprus. Among the latest Mycenaean bronzes found in Cyprus are several tripod-stands of simple openwork construction, a type that has also been found with transitional material in Crete and in Early Iron Age (Geometric) contexts on the Greek mainland. Some more elaborate pieces, cast in designs of ships and men and animals, belong to a group of bronzes found in the Idaean cave in Crete, most of which are Asiatic works of the 9th or 8th centuries BC. The openwork tripods may have had the same origin. They are probably not Greek. | 8 | Metallurgy |
The presence of chlorides to the steel surface, above a certain critical amount, can locally break the protective thin film of oxides on the steel surface, even if concrete is still alkaline, causing a very localized and aggressive form of corrosion known as pitting. Current regulations forbid the use of chloride contaminated raw materials, therefore one factor influencing the initiation time is chloride penetration rate from the environment. This is a complex task, because chloride solutions penetrate in concrete through the combination of several transport phenomena, such as diffusion, capillary effect and hydrostatic pressure. Chloride binding is another phenomenon affecting the kinetic of chloride penetration. Part of the total chloride ions can be absorbed or can chemically react with some constituents of the cement paste, leading to a reduction of chlorides in the pore solution (free chlorides that are steel able to penetrate in concrete). The ability of a concrete to chloride binding is related to the cement type, being higher for blended cements containing silica fume, fly ash or furnace slag.
Being the modelling of chloride penetration in concrete particularly complex, a simplified correlation is generally adopted, which was firstly proposed by Collepardi in 1972
Where is the chloride concentration at the exposed surface, x is the chloride penetration depth, D is the chloride diffusion coefficient, and t is time.
This equation is a solution of Fick's II law of diffusion in the hypothesis that chloride initial content is zero, that is constant in time on the whole surface, and D is constant in time and through the concrete cover. With and D known, the equation can be used to evaluate the temporal evolution of the chloride concentration profile in the concrete cover and evaluate the initiation time as the moment in which critical chloride threshold () is reached at the depth of steel rebar.
However, there are many critical issues related to the practical use of this model. For existing reinforced concrete structures in chloride-bearing environment and D can be identified calculating the best-fit curve for measured chloride concertation profiles. From concrete samples retrieved on field is therefore possible to define the values of C and D for residual service life evaluation.
On the other hand, for new structures it is more complicated to define and D. These parameters depend on the exposure conditions, the properties of concrete such as porosity (and therefore w/c ratio and curing process) and type of cement used. Furthermore, for the evaluation of long-term behaviour of structure, a critical issue is related to the fact that and D can not be considered constant in time, and that the transport penetration of chlorides can be considered as pure diffusion only for submerged structures.
A further issue is the assessment of . There are various influencing factors, such as are the potential of steel rebar and the pH of the solution included in concrete pores. Moreover, pitting corrosion initiation is a phenomenon with a stochastic nature, therefore also can be defined only on statistical basis. | 8 | Metallurgy |
In chemistry, control coefficients are used to describe how much influence (i.e., control) a given reaction step has on the steady-state flux or species concentration level. In practice, this can be accomplished by changing the expression level of a given enzyme and measuring the resulting changes in flux and metabolite levels. Control coefficients form a central component of metabolic control analysis.
There are two primary control coefficients:
* Flux Control Coefficients
* Concentration Control Coefficients.
The simplest way to look at control coefficients is as the scaled derivatives of the steady-state change in an observable with respect to a change in enzyme activity. For example, the flux control coefficients can be written as:
while the concentration control coefficients can be written as:
Control coefficients can have any value that includes negative and positive values. A negative value indicates that the observable in question decreases as a result of the change in enzyme activity.
In theory, other observables, such as growth rate, or even combinations of observables, can be defined using a control coefficient. But flux and concentration control coefficients are by far the most commonly used.
The approximation in terms of percentages makes control coefficients easier to measure and more intuitively understandable.
Control coefficients are useful because they tell us how much influence each enzyme or protein has in a biochemical reaction network.
It is important to note that control coefficients are not fixed values but will change depending on the state of the pathway or organism. If an organism shifts to a new nutritional source, then the control coefficients in the pathway will change. | 1 | Biochemistry |
A useful novel radiolabelled compound is one that is suitable either for medical imaging of certain body parts such as brain or tumors (injecting low doses of radioactivity) or for treating tumors (requiring injection of high doses of radioactivity). In both cases, the compound needs to accumulate in the target organ and any surplus compound present needs to clear the body rapidly. In medical diagnostic imaging, this then produces a clear diagnostic image (high image contrast), and in radiotherapy leads to an attack of the target (e.g. tumor) while minimizing side effects to non-target organs. Additional factors need to be evaluated in the development of a new diagnostic or therapeutic compound, including safety for humans. From an efficacy point of view, the biodistribution is an important aspect which can be measured by dissection or by imaging. | 1 | Biochemistry |
HeSE has been used to construct empirical helium-surface scattering potentials through the measurement of selective adsorption resonances (bound state resonances) on the clean LiF(001) surface and the hydrogenated Si(111) surface. | 7 | Physical Chemistry |
The expansion of gold mining in the Rand of South Africa began to slow down in the 1880s, as the new deposits being found tended to contain pyritic ore. The gold could not be extracted from this compound with any of the then available chemical processes or technologies.
In 1887, John Stewart MacArthur, working in collaboration with brothers Robert and William Forrest for the Tennant Company in Glasgow, Scotland, developed the MacArthur–Forrest process for the extraction of gold from gold ores. Several patents were issued in the same year. By suspending the crushed ore in a cyanide solution, a separation of up to 96 percent pure gold was achieved.
The process was first used on the Rand in 1890 and, despite operational imperfections, led to a boom of investment as larger gold mines were opened up.
By 1891, Nebraska pharmacist Gilbert S. Peyton had refined the process at his Mercur Mine in Utah, "the first mining plant in the United States to make a commercial success of the cyanide process on gold ores." In 1896, Bodländer confirmed that oxygen was necessary for the process, something that had been doubted by MacArthur, and discovered that hydrogen peroxide was formed as an intermediate.
Around 1900, the American metallurgist Charles Washington Merrill (1869–1956) and his engineer Thomas Bennett Crowe improved the treatment of the cyanide leachate, by using vacuum and zinc dust. Their process is the Merrill–Crowe process. | 8 | Metallurgy |
Because of the link between chlorophyll content and nitrogen content in leaves, chlorophyll fluorometers can be used to detect nitrogen deficiency in plants, by several methods.
Based on several years of research and experimentation, polyphenols can be the indicators of nitrogen status of a plant. For instance, when a plant is under optimal conditions, it favours its primary metabolism and synthesises the proteins (nitrogen molecules) containing chlorophyll, and few flavonols (carbon-based secondary compounds). On the other hand, in case of lack of nitrogen, we will observe an increased production of flavonols by the plant.
The NBI (Nitrogen Balance Index) by Force-A, allows the assessment of nitrogen conditions of a culture by calculating the ratio between Chlorophyll and Flavonols (related to Nitrogen/Carbon allocation) . | 5 | Photochemistry |
Mesoscopic methods operate on length and time scales between the particle and continuum levels. For this reason, they combine elements of particle-based dynamics and continuum hydrodynamics.
An example is the lattice Boltzmann method, which models a fluid as a collection of fictitious particles that exist on a lattice. The particles evolve in time through streaming (straight-line motion) and collisions. Conceptually, it is based on the Boltzmann equation for dilute gases, where the dynamics of a molecule consists of free motion interrupted by discrete binary collisions, but it is also applied to liquids. Despite the analogy with individual molecular trajectories, it is a coarse-grained description that typically operates on length and time scales larger than those of true molecular dynamics (hence the notion of "fictitious" particles).
Other methods that combine elements of continuum and particle-level dynamics include smoothed-particle hydrodynamics, dissipative particle dynamics, and multiparticle collision dynamics. | 7 | Physical Chemistry |
Production of QGP in the laboratory is achieved by colliding heavy atomic nuclei (called heavy ions as in an accelerator atoms are ionized) at relativistic energy in which matter is heated well above the Hagedorn temperature T = 150 MeV per particle, which amounts to a temperature exceeding 1.66×10 K. This can be accomplished by colliding two large nuclei at high energy (note that is not the energy of the colliding beam). Lead and gold nuclei have been used for such collisions at CERN SPS and BNL RHIC, respectively. The nuclei are accelerated to ultrarelativistic speeds (contracting their length) and directed towards each other, creating a "fireball", in the rare event of a collision. Hydrodynamic simulation predicts this fireball will expand under its own pressure, and cool while expanding. By carefully studying the spherical and elliptic flow, experimentalists put the theory to test. | 7 | Physical Chemistry |
Perfluorocarbons dissolve relatively high volumes of gases. The high solubility of gases is attributed to the weak intermolecular interactions in these fluorocarbon fluids.
The table shows values for the mole fraction, , of nitrogen dissolved, calculated from the Blood–gas partition coefficient, at 298.15 K (25 °C), 0.101325 MPa. | 2 | Environmental Chemistry |
Halons are usually defined as hydrocarbons where the hydrogen atoms have been replaced by bromine, along with other halogens. They are referred to by a system of code numbers similar to (but simpler than) the system used for freons. The first digit specifies the number of carbon atoms in the molecule, the second is the number of fluorine atoms, the third is the chlorine atoms, and the fourth is the number of bromine atoms. If the number includes a fifth digit, the fifth number indicates the number of iodine atoms (though iodine in halon is rare). Any bonds not taken up by halogen atoms are then allocated to hydrogen atoms.
For example, consider Halon 1211. This halon has number 1211 in its name, which tells it has 1 carbon atom, 2 fluorine atoms, 1 chlorine atom, and 1 bromine atom. A single carbon only has four bonds, all of which are taken by the halogen atoms, so there is no hydrogen. Thus its formula is , hence its IUPAC name is bromochlorodifluoromethane. | 2 | Environmental Chemistry |
It was long assumed that the midbody was simply a structural part of cytokinesis, and was totally degraded with the completion of mitosis. However, it is now understood that post-abscission, the midbody is converted into an endosome-like signalling molecule, and can be internalised by nearby cells.
This endosome is marked by MKLP1, and can persist for up to 48 hours once internalised into another cell. It is coated in Actin, which is slowly degraded by the internalising cell. | 1 | Biochemistry |
Level P vectors are similar to level M constructs except that the BpiI sites are replaced by BsaI sites and the BsaI sites are replaced by BpiI sites. Several level M constructs with compatible fusion sites can be subcloned into a level P vector in one step. Theoretically, as many as 36 genes can be assembled in one construct using 6 parallel level M reactions (each required for assembly of 6 genes per level M construct) followed by one final level P reaction. In practice, fewer genes are usually assembled as most cloning projects do not require so many genes.
The structure of level M and P vectors is designed in a such as way that genes cloned in level P constructs can be further assembled in level M vectors. Repeated cloning in level M and P vectors forms a loop that can be repeated indefinitely to assemble progressively large constructs. | 1 | Biochemistry |
In 2021, the globally tilled soil volume was estimated at 1840 km/yr. This value exceeds by two orders of magnitude the global total of all engineering earthworks. For comparison globally, the natural process of soil bioturbation by plant roots and earthworms, was estimated at 960 km/yr.
Mechanical soil cultivation practices, including primary tillage (mold-board or chisel plowing) followed by secondary tillage (disking, harrowing, etc.), break up and aerate soil. Mechanical traffic and intensive tilling methods have a negative impact on soil aggregates, friability, soil porosity, and soil-bulk density. When soils become degraded and compacted, such tillage practices are often deemed necessary. The tilth created by tillage, however, tends to be unstable, because the aggregation is obtained through the physical manipulation of the soil, which is short lived, especially after years of intensive tillage. The compaction of soil aggregates can also decrease soil biota due to the low levels of oxygen in the top-soil. The resulting high soil-bulk density results in lower water infiltration from rainfall or conventional irrigation (surface, sprinkler, center-pivot); in turn, the series of processes will naturally erode and dissolve small soil particles and organic matter. The consequences from these processes cyclically require more tilling and intervention, thus tillage practices have the capability to disrupt biological mechanisms that stabilize soil structure, the soil carbon sponge and tilth quality. | 9 | Geochemistry |
SH2 domains, and other binding domains, have been used in protein engineering to create protein assemblies. Protein assemblies are formed when several proteins bind to one another to create a larger structure (called a supramolecular assembly). Using molecular biology techniques, fusion proteins of specific enzymes and SH2 domains have been created, which can bind to each other to form protein assemblies.
Since SH2 domains require phosphorylation in order for binding to occur, the use of kinase and phosphatase enzymes gives researchers control over whether protein assemblies will form or not. High affinity engineered SH2 domains have been developed and utilized for protein assembly applications.
The goal of most protein assembly formation is to increase the efficiency of metabolic pathways via enzymatic co-localization. Other applications of SH2 domain mediated protein assemblies have been in the formation of high density fractal-like structures, which have extensive molecular trapping properties. | 1 | Biochemistry |
# Excitatory synapse: Enhances the probability of depolarization in postsynaptic neurons and the initiation of an action potential.
# Inhibitory Synapse: Diminishes the probability of depolarization in postsynaptic neurons and the initiation of an action potential.
An influx of Na+ driven by excitatory neurotransmitters opens cation channels, depolarizing the postsynaptic membrane toward the action potential threshold. In contrast, inhibitory neurotransmitters cause the postsynaptic membrane to become less depolarized by opening either Cl- or K+ channels, reducing firing. Depending on their release location, the receptors they bind to, and the ionic circumstances they encounter, various transmitters can be either excitatory or inhibitory. For instance, acetylcholine can either excite or inhibit depending on the type of receptors it binds to. For example, glutamate serves as an excitatory neurotransmitter, in contrast to GABA, which acts as an inhibitory neurotransmitter. Additionally, dopaminergic is a neurotransmitter that exerts dual effects, displaying both excitatory and inhibitory impacts through binding to distinct receptors.
The membrane potential prevents Cl- from entering the cell, even when its concentration is much higher outside than inside. The resting potential for Cl- in many neurons is quite negative, nearly equal to the resting potential. Opening Cl- channels tends to buffer the membrane potential, but this effect is countered when the membrane starts to depolarize, allowing more negatively charged Cl- ions to enter the cell. Consequently, it becomes more difficult to depolarize the membrane and excite the cell when Cl- channels are open. Similar effects result from the opening of K+ channels. The significance of inhibitory neurotransmitters is evident from the effects of toxins that impede their activity. For instance, strychnine binds to glycine receptors, blocking the action of glycine and leading to muscle spasms, convulsions, and death. | 1 | Biochemistry |
Trommel screens have a rotating drum on a shallow angle with screen panels around the diameter of the drum. The feed material always sits at the bottom of the drum and, as the drum rotates, always comes into contact with clean screen. The oversize travels to the end of the drum as it does not pass through the screen, while the undersize passes through the screen into a launder below. | 8 | Metallurgy |
Plastocyanin is an electron carrier that transfers the electron from cytochrome b6f to the P700 cofactor of PSI in its ionized state P700. | 5 | Photochemistry |
Dentin bonding refers to process of bonding a resin to conditioned dentin, where mineral component is replaced with resin monomers to form a biocomposite comprising dentin collagen and cured resin. The adhesive-dentin interface forms a tight and permanent bond between dentin and composite resins.
It can be accomplished by either etch-and-rinse (total etch) or self-etch adhesives. In etch-and rinse, acid will dissolve the minerals to a certain depth and leaves the highly porous dentinal collagen network suspended in water. Then, the collagen network is infiltrated with resin monomers. After chemical polymerization of these monomers happen, activated by light cure, it will result in a polymer-collagen biocomposite, commonly known as the hybrid layer:
The mechanism of action is explained below:
a) Application of acid to dentin will result in partial/total removal of smear layer and demineralization of the dentin.
b) Acid will demineralize the intertubular and peritubular dentin, and then open the dentinal tubules while exposing the collagen fibres, hence increasing the microporosity of intertubular dentin.
c) Dentin will be demineralized by up to approximately 7.5 µmeter, depending on the type of acid used, time of application and concentration.
d) Primer system is designed to increase critical surface tension of dentin, which gets decreased after etching of acid.
e) Bonding mechanism is when:
# When primer and bonding resin are applied to etched dentin, they penetrate the intertubular dentin, forming hybrid layer.
# They also penetrate and polymerize in open dentinal tubules, forming resin tags.
Moist bonding technique has been shown repeatedly to enhance bond strengths of etch-and-rinse adhesives because water preserves the porosity of collagen network for monomer interdiffusion. | 7 | Physical Chemistry |
Sigma B was the first anti-sigma factor identified in a bacterium. It is found in Bacillus subtilis and other similar bacteria. Sigma B is a stress response factor that plays a role in survival and against destruction that could be caused by other organisms such as mammals. General stress responses that are controlled by Sigma B are stimulated by things like temperature, salt concentration, energy depletion, etc. Once activated, Sigma B binds to the RNAP and recognizes a promoter, causing inhibition of the stimuli. Because Sigma B orthologs are conserved in various gram-positive bacteria, this anti-sigma factor plays an essential role in the evolution of different bacteria and their ability to respond to stressing factors. Scientist have found that the anti- sigma factor, Sigma B controls more than 150 genes that are influential in stress response. | 1 | Biochemistry |
DNA adenine methyltransferase identification, often abbreviated DamID, is a molecular biology protocol used to map the binding sites of DNA- and chromatin-binding proteins in eukaryotes. DamID identifies binding sites by expressing the proposed DNA-binding protein as a fusion protein with DNA methyltransferase. Binding of the protein of interest to DNA localizes the methyltransferase in the region of the binding site. Adenine methylation does not occur naturally in eukaryotes and therefore adenine methylation in any region can be concluded to have been caused by the fusion protein, implying the region is located near a binding site. DamID is an alternate method to ChIP-on-chip or ChIP-seq. | 1 | Biochemistry |
Many scientific endeavors are dependent upon accurate quantification of drugs and endogenous substances in biological samples; the focus of bioanalysis in the pharmaceutical industry is to provide a quantitative measure of the active drug and/or its metabolite(s) for the purpose of pharmacokinetics, toxicokinetics, bioequivalence and exposure–response (pharmacokinetics/pharmacodynamics studies). Bioanalysis also applies to drugs used for illicit purposes, forensic investigations, anti-doping testing in sports, and environmental concerns.
Bioanalysis was traditionally thought of in terms of measuring small molecule drugs. However, the past twenty years has seen an increase in biopharmaceuticals (e.g. proteins and peptides), which have been developed to address many of the same diseases as small molecules. These larger biomolecules have presented their own unique challenges to quantification. | 3 | Analytical Chemistry |
A catalyst's function is to increase the speed of the electron transfer (redox) reaction. Plastocyanin is believed to work less like an enzyme where enzymes decrease the transition energy needed to transfer the electron. Plastocyanin works more on the principles of entatic states where it increases the energy of the reactants, decreasing the amount of energy needed for the redox reaction to occur. Another way to rephrase the function of plastocyanin is that it can facilitate the electron transfer reaction by providing a small reorganization energy, which has been measured to about .
To study the properties of the redox reaction of plastocyanin, methods such as quantum mechanics / molecular mechanics (QM/MM) molecular dynamics simulations. This method was used to determine that plastocyanin has an entatic strain energy of about .
Four-coordinate copper complexes often exhibit square planar geometry, however plastocyanin has a trigonally distorted tetrahedral geometry. This distorted geometry is less stable than ideal tetrahedral geometry due to its lower ligand field stabilization as a result of the trigonal distortion. This unusual geometry is induced by the rigid “pre-organized” conformation of the ligand donors by the protein, which is an entatic state. Plastocyanin performs electron transfer with the redox between Cu(I) and Cu(II), and it was first theorized that its entatic state was a result of the protein imposing an undistorted tetrahedral geometry preferred by ordinary Cu(I) complexes onto the oxidized Cu(II) site. However, a highly distorted tetrahedral geometry is induced upon the oxidized Cu(II) site instead of a perfectly symmetric tetrahedral geometry. A feature of the entatic state is a protein environment that is capable of preventing ligand dissociation even at a high enough temperature to break the metal-ligand bond. In the case of plastocyanin, it has been experimentally determined through absorption spectroscopy that there is a long and weak Cu(I)-S bond that should dissociate at physiological temperature due to increased entropy. However, this bond does not dissociate due to the constraints of the protein environment dominating over the entropic forces.
In ordinary copper complexes involved in Cu(I)/Cu(II) redox coupling without a constraining protein environment, their ligand geometry changes significantly, and typically corresponds to the presence of a Jahn-Teller distorting force. However, the Jahn-Teller distorting force is not present in plastocyanin due to a large splitting of the d and d orbitals (See Blue Copper Protein Entatic State). Additionally, the structure of plastocyanin exhibits a long Cu(I)-S bond (2.9Å) with decreased electron donation strength. This bond also shortens the Cu(I)-S bond (2.1Å), increasing its electron donating strength. Overall, plastocyanin exhibits a lower reorganization energy due to the entatic state of the protein ligand enforcing the same distorted tetrahedral geometry in both the Cu(II) and Cu(I) oxidation states, enabling it to perform electron transfer at a faster rate. The reorganization energy of blue copper proteins such as plastocyanin from 0.7 to 1.2 eV (68-116 kJ/mol) compared to 2.4 eV (232 kJ/mol) in an ordinary copper complex such as [Cu(phen)]. | 5 | Photochemistry |
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