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Depending on the nature of the substance, an elementary entity may be an atom, a molecule, an ion, an ion pair, or a subatomic particle such as a proton. For example, 10 moles of water (a chemical compound) and 10 moles of mercury (a chemical element) contain equal numbers of substance, with one atom of mercury for each molecule of water, despite the two quantities having different volumes and different masses.
The mole corresponds to a given count of entities. Usually the entities counted are chemically identical and individually distinct. For example, a solution may contain a certain number of dissolved molecules that are more or less independent of each other. However, in a solid the constituent entities are fixed and bound in a lattice arrangement, yet they may be separable without losing their chemical identity. Thus the solid is composed of a certain number of moles of such entities. In yet other cases, such as diamond, where the entire crystal is essentially a single molecule, the mole is still used to express the number of atoms bound together, rather than a count of molecules. Thus, common chemical conventions apply to the definition of the constituent entities of a substance, in other cases exact definitions may be specified.
The mass of a substance is equal to its relative atomic (or molecular) mass multiplied by the molar mass constant, which is almost exactly 1 g/mol. | 3 | Analytical Chemistry |
A major application of supramolecular chemistry is the design and understanding of catalysts and catalysis. Non-covalent interactions are extremely important in catalysis, binding reactants into conformations suitable for reaction and lowering the transition state energy of reaction. Template-directed synthesis is a special case of supramolecular catalysis. Encapsulation systems such as micelles, dendrimers, and cavitands are also used in catalysis to create microenvironments suitable for reactions (or steps in reactions) to progress that is not possible to use on a macroscopic scale. | 6 | Supramolecular Chemistry |
Anammox stands for anaerobic ammonia oxidation and the organisms responsible were relatively recently discovered, in the late 1990s. This form of metabolism occurs in members of the Planctomycetota (e.g. "Candidatus Brocadia anammoxidans") and involves the coupling of ammonia oxidation to nitrite reduction. As oxygen is not required for this process, these organisms are strict anaerobes. Amazingly, hydrazine ( – rocket fuel) is produced as an intermediate during anammox metabolism. To deal with the high toxicity of hydrazine, anammox bacteria contain a hydrazine-containing intracellular organelle called the anammoxasome, surrounded by highly compact (and unusual) ladderane lipid membrane. These lipids are unique in nature, as is the use of hydrazine as a metabolic intermediate. Anammox organisms are autotrophs although the mechanism for carbon dioxide fixation is unclear. Because of this property, these organisms could be used to remove nitrogen in industrial wastewater treatment processes. Anammox has also been shown to have widespread occurrence in anaerobic aquatic systems and has been speculated to account for approximately 50% of nitrogen gas production in the ocean. | 1 | Biochemistry |
Conditions have been developed for the transformation of pseudoephedrine amides into enantiomerically enriched carboxylic acids, alcohols, aldehydes, and ketones - after cleavage, the auxiliary can be recovered and reused.
<br /> | 4 | Stereochemistry |
Acidic, sandy, or coarse soils often contain less calcium. Uneven soil moisture and overuse of fertilizers can also cause calcium deficiency. At times, even with sufficient calcium in the soil, it can be in an insoluble form and is then unusable by the plant or it could be attributed to a "transport protein". Soils containing high phosphorus are particularly susceptible to creating insoluble forms of calcium.
Calcium and magnesium are opposed within the plant cells, and have antagonistic interactions. As a result, a homeostatic balance between Ca and Mg within the plant is necessary for optimal growth and proper development. | 1 | Biochemistry |
PNRC1 functions as a coactivator for several nuclear receptors including AR, ERα, ERRα, ERRγ, GR, SF1, PR, TR, RAR and RXR. The interaction between PNRC1 with nuclear receptors occurs through the SH3 domain of PNRC1. | 1 | Biochemistry |
The fundamental law of extinction states that the extinction process is linear in the intensity of radiation and amount of radiatively active matter, provided that the physical state is held constant. (Neither concentration or length are fundamental parameters.) There are two factors that determine the degree to which a medium containing particles will attenuate a light beam: the number of particles encountered by the light beam, and the degree to which each particle extinguishes the light.
For the case of absorption (Beer), this later quantity is called the absorptivity [], which is defined as "the property of a body that determines the fraction of incident radiation absorbed by the body". The Beer-Lambert law uses concentration and length in order to determine the number of particles the beam encounters. If we know the area of a collimated beam (directed radiation), we can get the number of particles in a distance. The number of particles encountered can be calculated from Avogadro's number, the molar concentration, the cross-sectional area of the incident beam .
There must be a large number of particles that are uniformly distributed for this relationship to hold. In practice, the beam area is thought of as a constant, and since the fraction [] has the area in both the numerator and denominator, the beam area cancels in the calculation of the absorbance. The units of the absorptivity must match the units in which the sample is described. For example, if the sample is described by mass concentration (g/L) and length (cm), then the units on the absorptivity would be [ L g cm], so that the absorbance has no units.
For the case of "extinction" (Bouguer), the sum of absorption and scatter, the terms absorption, scattering, and extinction cross-sections are often used. The fraction of light extinguished by the sample may be described by the extinction cross section (fraction extinguished per particle). the number of particles in a unit distance and the distance in those units. For example: [ (fraction extinguished / particle) (# particles / meter) (# meters / sample) = fraction extinguished / sample ] | 7 | Physical Chemistry |
Small non-coding RNA (sncRNA) are a type of RNA. which is usually defined as transcripts which are lesser than 200 base-pairs in length and not translated into proteins. This limitation distinguishes sncRNA from lncRNA. This class includes but is not limited to microRNAs (miRNAs), small interfering RNAs (siRNAs), Piwi-interacting RNAs (piRNAs), small nucleolar RNAs (snoRNAs), and other short RNAs. | 1 | Biochemistry |
Homologous paired receptors are located in the same gene cluster and are thought to have evolved through gene duplication. Sequence features such as the presence of an ITIM-like sequence in the 3' untranslated region of some activating receptors imply that the activating members of the pair likely evolved from the inhibitory members. A number of pathogens interact with the inhibitory member of a pair as a means of immune evasion or viral entry, suggesting that activating members with similar binding competencies may be an evolutionary response to this mechanism. This hypothesis is known as the "counterbalance theory" and these evolutionary dynamics represent an evolutionary arms race between pathogens and the host immune system. The evolutionary pressures on some paired-receptor families have been described as examples of the "Red Queen" effect.
Including non-paired examples, over 300 potential immune inhibitory receptors have been identified in the human genome. There are strong indications that paired receptors are rapidly and recently evolving. These genetic regions have high levels of gene polymorphism, and the gene repertoires found in the genomes of closely related lineages vary significantly. The selective pressure experienced by the host from pathogens is thought to underlie this rapid evolution.
Although paired receptors are best characterized as part of the human and mouse immune systems, they have also been studied in other organisms. The chicken (Gallus gallus domesticus) genome contains a number of examples including a very large family, the chicken Ig-like receptors (CHIR) with over 100 members. Paired receptor evolution has also been studied in Xenopus (clawed frog) species. The adaptive immune system is unique to jawed vertebrates, but an example of a paired receptor family has been identified in a jawless vertebrate, termed agnathan paired receptors resembling Ag receptors (APAR) in the hagfish. | 1 | Biochemistry |
Copper concentrates produced by mines are sold to smelters and refiners who treat the ore and refine the copper and charge for this service via treatment charges (TCs) and refining charges (RCs). The TCs are charged in US$ per tonne of concentrate treated and RCs are charged in cents per pound treated, denominated in US dollars, with benchmark prices set annually by major Japanese smelters. The customer in this case can be a smelter, who on-sells blister copper ingots to a refiner, or a smelter-refiner which is vertically integrated.
One prevalent form of copper concentrate contains gold and silver, like the one produced by Bougainville Copper Limited from the Panguna mine from the early 1970s to the late 1980s.
The typical contract for a miner is denominated against the London Metal Exchange price, minus the TC-RCs and any applicable penalties or credits. Penalties may be assessed against copper concentrates according to the level of deleterious elements such as arsenic, bismuth, lead or tungsten. Because a large portion of copper sulfide ore bodies contain silver or gold in appreciable amounts, a credit can be paid to the miner for these metals if their concentration within the concentrate is above a certain amount. Usually the refiner or smelter charges the miner a fee based on the concentration; a typical contract will specify that a credit is due for every ounce of the metal in the concentrate above a certain concentration; below that, if it is recovered, the smelter will keep the metal and sell it to defray costs.
Copper concentrate is traded either via spot contracts or under long term contracts as an intermediate product in its own right. Often the smelter sells the copper metal itself on behalf of the miner. The miner is paid the price at the time that the smelter-refiner makes the sale, not at the price on the date of delivery of the concentrate. Under a Quotational Pricing system, the price is agreed to be at a fixed date in the future, typically 90 days from time of delivery to the smelter.
A-grade copper cathode is of 99.99% copper in sheets that are 1 cm thick, and approximately 1 meter square weighing approximately 200 pounds. It is a true commodity, deliverable to and tradeable upon the metal exchanges in New York City (COMEX), London (London Metals Exchange) and Shanghai (Shanghai Futures Exchange). Often copper cathode is traded upon the exchanges indirectly via warrants, options, or swap contracts such that the majority of copper is traded upon the LME/COMEX/SFE, but delivery is achieved directly, logistically moving the physical copper, and transferring the copper sheet from the physical warehouses themselves.
The chemical specification for electrolytic grade copper is ASTM B 115-00 (a standard that specifies the purity and maximum electrical resistivity of the product). | 8 | Metallurgy |
An SADP is acquired under parallel electron illumination. In the case of convergent beam, a convergent beam electron diffraction (CBED) is achieved. The beam used in SAD is broad illuminating a wide sample area. In order to analyze only a specific sample area, the selected area aperture in the image plane is used. This is in contrast with nanodiffraction, where the site-selectivity is achieved using a beam condensed to a narrow probe. SAD is important in direct imaging for instance when orienting the sample for high resolution microscopy or setting up dark-field imaging conditions.
High-resolution electron microscope images can be transformed into an artificial diffraction pattern using Fourier transform. Then, they can be processed the same way as real diffractograms allowing to determine crystal orientation, measure interplanar angles and distances even with picometric precision.
SAD is similar to X-ray diffraction, but unique in that areas as small as several hundred nanometers in size can be examined, whereas X-ray diffraction typically samples areas much larger. | 3 | Analytical Chemistry |
In organic chemistry, the term cyanomethyl (cyanide (N≡C) + methyl (CH)) designates:
* A cyanomethyl group (N≡CCH–), a type of nitrile group
* The cyanomethyl radical (N≡CCH·)
* The cyanomethyl carbanion (N≡CCH) | 0 | Organic Chemistry |
Mitscherlich's law of isomorphism, or the law of isomorphism, is an approximate law suggesting that crystals composed of the same number of similar elements tend to demonstrate isomorphism.
Mitscherlich's law is named for German chemist Eilhard Mitscherlich, who formulated the law and published it between 1819 and 1823.
According to Ferenc Szabadváry, one of the clues that helped Berzelius determine the atomic weights of the elements was "the discovery of Mitscherlich that compounds which contain the same number of atoms and have similar structures, exhibit similar crystal forms (isomorphism)." | 3 | Analytical Chemistry |
Diazomethane is both isomeric and isoelectronic with the more stable cyanamide, but they cannot interconvert.
Many substituted derivatives of diazomethane have been prepared:
*The very stable (CF)CN (2-diazo-1,1,1,3,3,3-hexafluoropropane; b.p. 12–13 °C),
*PhCN (diazodiphenylmethane; m.p. 29–30 °C).
*(CH)SiCHN (trimethylsilyldiazomethane), which is commercially available as a solution and is as effective as CHN for methylation.
*PhC(H)N, a red liquid b.p.< 25 °C at 0.1 mm Hg. | 0 | Organic Chemistry |
Everolimus is the second novel Rapamycin analog. Compared with the parent compound rapamycin, everolimus is more selective for the mTORC1 protein complex, with little impact on the mTORC2 complex. mTORC1 inhibition by everolimus has been shown to normalize tumor blood vessels, to increase tumor-infiltrating lymphocytes, and to improve adoptive cell transfer therapy.
From March 30, 2009, to May 5, 2011, the U.S. FDA approved everolimus for the treatment of advanced renal cell carcinoma after failure of treatment with sunitinib or sorafenib, subependymal giant cell astrocytoma (SEGA) associated with tuberous sclerosis (TS), and progressive neuroendocrine tumors of pancreatic origin (PNET). In July and August 2012, two new indications were approved, for advanced hormone receptor-positive, HER2-negative breast cancer in combination with exemestane, and pediatric and adult patients with SEGA. In 2009 and 2011, it was also approved throughout the European Union for advanced breast cancer, pancreatic neuroendocrine tumours, advanced renal cell carcinoma, and SEGA in patients with tuberous sclerosis. | 1 | Biochemistry |
The state-of-the-art mechanism of today's sensor-based ore sorters is a pneumatic ejection. Here, a combination of high speed air valves and an array of nozzles perpendicular to the acceleration belt or chute allows precise application of air pulses to change the direction of flight of single particles. The nozzle pitch and diameter is adapted to the particle size. The air impulse must be precise enough to change the direction of flight of a single particle by applying the drag force to this single particle and directing it over the mechanical splitter plate. | 3 | Analytical Chemistry |
Theories of the structure of water involve three-dimensional networks of tetrahedra and chains and rings, linked via hydrogen bonding.
A polycatenated network, with rings formed from metal-templated hemispheres linked by hydrogen bonds, was reported in 2008.
In organic chemistry, hydrogen bonding is known to facilitate the formation of chain structures. 4-tricyclanol CHO, for example, shows catenated hydrogen bonding between the hydroxyl groups, leading to the formation of helical chains; crystalline isophthalic acid CHO is built up from molecules connected by hydrogen bonds, forming infinite chains.
In unusual conditions, a 1-dimensional series of hydrogen molecules confined within a single wall carbon nanotube is expected to become metallic at a relatively low pressure of 163.5 GPa. This is about 40% of the ~400 GPa thought to be required to metallize ordinary hydrogen, a pressure which is difficult to access experimentally. | 0 | Organic Chemistry |
A three-step mechanism was derived in 1987 by Peters and Forman A. Williams by assuming steady-state approximation for the hydrogen radical. Then, | 7 | Physical Chemistry |
The Kapustinskii equation calculates the lattice energy U for an ionic crystal, which is experimentally difficult to determine. It is named after Anatoli Fedorovich Kapustinskii who published the formula in 1956.
The calculated lattice energy gives a good estimation for the Born–Landé equation; the real value differs in most cases by less than 5%.
Furthermore, one is able to determine the ionic radii (or more properly, the thermochemical radius) using the Kapustinskii equation when the lattice energy is known. This is useful for rather complex ions like sulfate (SO) or phosphate (PO). | 3 | Analytical Chemistry |
Magnesium and vitamin D have a synergistic relationship in the body, meaning they work together to optimize each other's functions:
* Magnesium activates vitamin D
* Vitamin D influences magnesium absorption.
* Bone health: They play crucial roles in calcium absorption and bone metabolism.
* Muscle function: They contribute to muscle contraction and relaxation, impacting physical performance and overall well-being.
* Immune function: They support a healthy immune system and may help reduce inflammation.
Overall, maintaining adequate levels of both magnesium and vitamin D is essential for optimal health and well-being. | 1 | Biochemistry |
G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their activity is regulated by factors that control their ability to bind to and hydrolyze guanosine triphosphate (GTP) to guanosine diphosphate (GDP). When they are bound to GTP, they are on, and, when they are bound to GDP, they are off. G proteins belong to the larger group of enzymes called GTPases.
There are two classes of G proteins. The first function as monomeric small GTPases (small G-proteins), while the second function as heterotrimeric G protein complexes. The latter class of complexes is made up of alpha (G), beta (G) and gamma (G) subunits. In addition, the beta and gamma subunits can form a stable dimeric complex referred to as the beta-gamma complex
Heterotrimeric G proteins located within the cell are activated by G protein-coupled receptors (GPCRs) that span the cell membrane. Signaling molecules bind to a domain of the GPCR located outside the cell, and an intracellular GPCR domain then in turn activates a particular G protein. Some active-state GPCRs have also been shown to be "pre-coupled" with G proteins, whereas in other cases a collision coupling mechanism is thought to occur. The G protein triggers a cascade of further signaling events that finally results in a change in cell function. G protein-coupled receptors and G proteins working together transmit signals from many hormones, neurotransmitters, and other signaling factors. G proteins regulate metabolic enzymes, ion channels, transporter proteins, and other parts of the cell machinery, controlling transcription, motility, contractility, and secretion, which in turn regulate diverse systemic functions such as embryonic development, learning and memory, and homeostasis. | 1 | Biochemistry |
A southwestern blot is based on Southern blot and is used to identify and characterize DNA-binding proteins by their ability to bind to specific oligonucleotide probes. The proteins are separated by gel electrophoresis and are subsequently transferred to nitrocellulose membranes similar to other types of blotting. | 1 | Biochemistry |
Sea foam is formed under conditions that are similar to the formation of sea spray. One of the main distinctions from sea spray formation is the presence of higher concentrations of dissolved organic matter from macrophytes and phytoplankton. The dissolved organic matter in the surface water, which can be derived from the natural environment or human-made sources, provides stability to the resulting sea foam.
The physical processes that contribute to sea foam formation are breaking surface waves, bubble entrainment, a process of bubbles being incorporated or captured within a liquid such as sea water and whitecap formation. Breaking of surface waves injects air from the atmosphere into the water column, leading to bubble creation. These bubbles get transported around the top few meters of the surface ocean due to their buoyancy. The smallest bubbles entrained in the water column dissolve entirely, leading to higher ratios of dissolved gases in the surface ocean. The bubbles that do not dissolve eventually make it back to the surface. As they rise, these bubbles accumulate hydrophobic substances. Presence of dissolved organic matter stabilizes the bubbles, aggregating together as sea foam. Some studies on sea foam report that breaking of algal cells in times of heavy swells makes sea foam production more likely.
Falling rain drops on the sea surface can also contribute to sea foam formation and destruction. There have been some non-mechanistic studies demonstrating increased sea foam formation due to high rainfall events. Turbulence in the surface mixed layer can affect the concentration of dissolved organic matter and aids in the formation of nutrient-dense foam. | 9 | Geochemistry |
Specific weight can be used in civil engineering and mechanical engineering to determine the weight of a structure designed to carry certain loads while remaining intact and remaining within limits regarding deformation. | 7 | Physical Chemistry |
Aliphatic metal alkoxides decompose in water as summarized in this idealized equation:
In the transesterification process, metal alkoxides react with esters to bring about an exchange of alkyl groups between metal alkoxide and ester. With the metal alkoxide complex in focus, the result is the same as for alcoholysis, namely the replacement of alkoxide ligands, but at the same time the alkyl groups of the ester are changed, which can also be the primary goal of the reaction. Sodium methoxide in solution, for example, is commonly used for this purpose, a reaction that is used in the production of biodiesel. | 0 | Organic Chemistry |
Home pill testing equipment is illegal in the US state of Illinois where the (720 ILCS 600/) Drug Paraphernalia Control Act specifically outlaws "testing equipment intended to be used unlawfully in a private home for identifying or in analyzing the strength, effectiveness or purity of cannabis or controlled substances;" | 3 | Analytical Chemistry |
*2000: L'Oréal-UNESCO Awards for Women in Science
*2007: Order of Mapungubwe - Silver
*2013: Christophe Mérieux Prize
*2018: Harry Oppenheimer Fellowship Award | 1 | Biochemistry |
Solid-state physics is the study of rigid matter, or solids, through methods such as solid-state chemistry, quantum mechanics, crystallography, electromagnetism, and metallurgy. It is the largest branch of condensed matter physics. Solid-state physics studies how the large-scale properties of solid materials result from their atomic-scale properties. Thus, solid-state physics forms a theoretical basis of materials science. Along with solid-state chemistry, it also has direct applications in the technology of transistors and semiconductors. | 8 | Metallurgy |
Although the energy difference between coplanar anisole and its isomer is quite large, the rotation between the O–CH bond becomes favorable when the electronic properties of methoxy group on aromatic rings need to be altered to stabilize an unusual intermediate or a transition state. In the following reaction, the regioselectivity could be rationalized as the out-of-plane rotation of the O–C bond which changes the methoxy group from an in-plane donor group to an out-of-plane acceptor group.
The intermediate of the above reaction is the di-anion and the stereoelectronic effect that stabilizes this intermediate over the other one is the fact that the anionic charge at the para position could delocalize to the oxygen atom via orbital interaction: π(benzene) → σ*(O–CH). | 4 | Stereochemistry |
The functioning of a signal transduction pathway is based on extra-cellular signaling that in turn creates a response that causes other subsequent responses, hence creating a chain reaction, or cascade. During the course of signaling, the cell uses each response for accomplishing some kind of a purpose along the way. Insulin secretion mechanism is a common example of signal transduction pathway mechanism.
Insulin is produced by the pancreas in a region called Islets of Langerhans. In the islets of Langerhans, there are beta-cells, which are responsible for production and storage of insulin. Insulin is secreted as a response mechanism for counteracting the increasing excess amounts of glucose in the blood.
Glucose in the body increases after food consumption. This is primarily due to carbohydrate intake, but to a much lesser degree protein intake ([http://jcem.endojournals.org/content/89/6/3048.long])([http://genesdev.cshlp.org/content/24/24/2717.long]). Depending on the tissue type, the glucose enters the cell through facilitated diffusion or active transport. In muscle and adipose tissue, glucose enters through GLUT 4 receptors via facilitated diffusion ([http://ajpendo.physiology.org/content/299/2/E169.long]). In brain, retina, kidney, RBC, placenta and many other organs, glucose enters using GLUT 1 and GLUT 3. In the beta-cells of the pancreas and in liver cells, glucose enters through the GLUT 2 receptors
(process described below). | 1 | Biochemistry |
Raluca Ripan (27 June 1894 – 5 December 1972) was a Romanian chemist, and a titular member of the Romanian Academy. She wrote many treatises, especially in the field of analytical chemistry. | 3 | Analytical Chemistry |
Grb2 is widely expressed and is essential for multiple cellular functions. Inhibition of Grb2 function impairs developmental processes in various organisms and blocks transformation and proliferation of various cell types. It is thus not surprising that targeted gene disruption of Grb2 in mice is lethal at an early embryonic stage. Grb2 is best known for its ability to link the epidermal growth factor receptor tyrosine kinase to the activation of Ras and its downstream kinases, ERK1,2. Grb2 is composed of an SH2 domain flanked on each side by an SH3 domain. Grb2 has two closely related proteins with similar domain organizations, Gads and Grap. Gads and Grap are expressed specifically in hematopoietic cells and function in the coordination of tyrosine kinase mediated signal transduction. | 1 | Biochemistry |
In molecular biology, ribosomal s6 kinase (rsk) is a family of protein kinases involved in signal transduction. There are two subfamilies of rsk, p90, also known as MAPK-activated protein kinase-1 (MAPKAP-K1), and p70, also known as S6-H1 Kinase or simply S6 Kinase. There are three variants of p90 in humans, rsk 1-3. Rsks are serine/threonine kinases and are activated by the MAPK/ERK pathway. There are two known mammalian homologues of S6 Kinase: S6K1 and S6K2. | 1 | Biochemistry |
Promoters can be very closely located in the DNA. Such "closely spaced promoters" have been observed in the DNAs of all life forms, from humans to prokaryotes and are highly conserved. Therefore, they may provide some (presently unknown) advantages.
These pairs of promoters can be positioned in divergent, tandem, and convergent directions. They can also be regulated by transcription factors and differ in various features, such as the nucleotide distance between them, the two promoter strengths, etc.
The most important aspect of two closely spaced promoters is that they will, most likely, interfere with each other. Several studies have explored this using both analytical and stochastic models. There are also studies that measured gene expression in synthetic genes or from one to a few genes controlled by bidirectional promoters.
More recently, one study measured most genes controlled by tandem promoters in E. coli. In that study, it was measured and then modeled two main forms of interference. One is when an RNAP is on the downstream promoter, blocking the movement of RNAPs elongating from the upstream promoter. The other is when the two promoters are so close that when an RNAP sits on one of the promoters, it blocks any other RNAP from reaching the other promoter. These events are possible because the RNAP occupies several nucleotides when bound to the DNA, including in transcription start sites.
Similar events occur when the promoters are in divergent and convergent formations. The possible events also depend on the distance between them. | 1 | Biochemistry |
Per meg equals 0.001 permil or 0.0001 percent or parts per million ppm. The unit is typically used in isotope analysis by multiplying an isotope ratio in delta annotation, for example δO, by 1000000.
This annotation is typically used in studies of atmospheric trace gases, where a high precision is needed for a significant interpretation of results. | 9 | Geochemistry |
Longer stretches of DNA are entropically elastic under tension. When DNA is in solution, it undergoes continuous structural variations due to the energy available in the thermal bath of the solvent. This is due to the thermal vibration of the molecule combined with continual collisions with water molecules. For entropic reasons, more compact relaxed states are thermally accessible than stretched out states, and so DNA molecules are almost universally found in a tangled relaxed layouts. For this reason, one molecule of DNA will stretch under a force, straightening it out. Using optical tweezers, the entropic stretching behavior of DNA has been studied and analyzed from a polymer physics perspective, and it has been found that DNA behaves largely like the Kratky-Porod worm-like chain model under physiologically accessible energy scales. | 4 | Stereochemistry |
The diverse functions of peroxisomes require dynamic interactions and cooperation with many organelles involved in cellular lipid metabolism such as the endoplasmic reticulum, mitochondria, lipid droplets, and lysosomes.
Peroxisomes interact with mitochondria in several metabolic pathways, including β-oxidation of fatty acids and the metabolism of reactive oxygen species. Both organelles are in close contact with the endoplasmic reticulum and share several proteins, including organelle fission factors. Peroxisomes also interact with the endoplasmic reticulum and cooperate in the synthesis of ether lipids (plasmalogens), which are important for nerve cells (see above). In filamentous fungi, peroxisomes move on microtubules by hitchhiking, a process involving contact with rapidly moving early endosomes. Physical contact between organelles is often mediated by membrane contact sites, where membranes of two organelles are physically tethered to enable rapid transfer of small molecules, enable organelle communication and are crucial for coordination of cellular functions and hence human health. Alterations of membrane contacts have been observed in various diseases. | 1 | Biochemistry |
The most common adverse effects of levetiracetam treatment include CNS effects such as somnolence, decreased energy, headache, dizziness, mood swings and coordination difficulties. These adverse effects are most pronounced in the first month of therapy. About 4% of patients dropped out of pre-approval clinical trials due to these side effects.
About 13% of people taking levetiracetam experience adverse neuropsychiatric symptoms, which are usually mild. These include agitation, hostility, apathy, anxiety, emotional lability, and depression. Serious psychiatric adverse side effects that are reversed by drug discontinuation occur in about 1%. These include hallucinations, suicidal thoughts, or psychosis. These occurred mostly within the first month of therapy, but they could develop at any time during treatment.
Although rare, Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), which appears as a painful spreading rash with redness and blistering and/or peeling skin, have been reported in patients treated with levetiracetam. The incidence of SJS following exposure to anti-epileptics such as levetiracetam is about 1 in 3,000.
Levetiracetam should not be used in people who have previously shown hypersensitivity to levetiracetam or any of the inactive ingredients in the tablet or oral solution. Such hypersensitivity reactions include, but are not limited to, unexplained rash with redness or blistered skin, difficulty breathing, and tightness in the chest or airways.
In a study, the incidence of decreased bone mineral density of patients on levetiracetam was significantly higher than those for other epileptic medications. | 4 | Stereochemistry |
Levonorgestrel is used in emergency contraceptive pills (ECPs), both in a combined Yuzpe regimen which includes estrogen, and as a levonorgestrel-only method. The levonorgestrel-only method uses levonorgestrel 1.5 mg (as a single dose or as two 0.75 mg doses 12 hours apart) taken within three days of unprotected sex. With one study indicating that beginning as late as 120 hours (5 days) after intercourse could be effective. However, taking more than one dose of emergency contraception does not increase the chance of pregnancy not happening. Planned Parenthood asserts "Taking the morning-after pill (also known as emergency contraception) multiple times doesnt change its effectiveness, and wont cause any long-term side effects." There is no age, I.D., or prescription required to purchase emergency contraception. Plan B hit the market in 1999 where it could be bought by anyone older than 18. However, in 2013, the rules were changed so that Plan B could be purchased at any age without ID or prescription.
The primary mechanism of action of levonorgestrel as a progestogen-only emergency contraceptive pill is, according to International Federation of Gynecology and Obstetrics (FIGO), to prevent fertilization by inhibition of ovulation and thickening of cervical mucus. FIGO has stated that: "review of the evidence suggests that LNG [levonorgestreol] ECPs cannot prevent implantation of a fertilized egg. Language on implantation should not be included in LNG ECP product labeling." In November 2013, the European Medicines Agency (EMA) approved a change to the label saying it cannot prevent implantation of a fertilized egg.
Other studies still find the evidence to be unclear. While it is unlikely that emergency contraception affects implantation it is impossible to completely exclude the possibility of post-fertilization effect.
In November 2013, the EMA also approved a change to the label for HRA Pharmas NorLevo' saying: "In clinical trials, contraceptive efficacy was reduced in women weighing 75 kg [165 pounds] or more, and levonorgestrel was not effective in women who weighed more than 80 kg [176 pounds]." In November 2013 and January 2014, the FDA and the EMA said they were reviewing whether increased weight and body mass index (BMI) reduce the efficacy of emergency contraceptives.
An analysis of four WHO randomised clinical trials, published in January 2017, showed pregnancy rates of 1.25% (68/5428) in women with BMI under 25, 0.61% (7/1140) in women with BMI between 25 and 30, and 2.03% (6/295) in women with BMI over 30. These values yield an eight-fold reduction in efficacy for women with BMI over 30 compared to women with BMI under 25. However, emergency contraceptives remain effective regardless of BMI. | 4 | Stereochemistry |
Early in his career, Kai Simons pursued research in the field of medical biochemistry. Both his master's thesis and postgraduate research focused on vitamin B12 absorption. After returning from his post-doc scholarship he continued research on vitamin B12 as well as on blood plasma proteins, but soon started investigating Semliki Forest virus, focusing on its membrane and its lipid composition and their role in the virus budding and its transport, as the model for lipid and protein secretion. During this period, Simons also investigated the application of detergents in biochemistry with a special attention to their role in biological membrane research.
The virus lifecycle and how it uses components of vesicular pathways while shuttling to the cell surface, turned Simons' attention toward vesicular transport pathways and cell polarization. Applying epithelial model cells – MDCK (Madin-Darby canine kidney), he investigated lipid transport, protein sorting and their role in polarizing cells.
In these studies, he described the role of the trans-Golgi network (TGN) in protein and lipid sorting according to their destination. In his works from 1988, together with Gerit van Meer, Simons proposed the existence of lipid microdomains in cell membranes for the first time. Such microdomains differ in their composition from the surrounding membrane and have special functions. Simons coined the term lipid rafts to describe these microdomains. This concept was developed over the years to be presented more fully in 1997 in Nature journal by Simons and Ikonen. This paper became one of the most frequently cited works in the field of membrane research. Other Simons' paper, on role of lipid rafts in the signal transduction is second highest cited work and Simons is fourth highest cited scientist in the field of signal transduction. Kai Simons was also recognized by ISI Web of Knowledge, as one of the most cited scientist ever.
In subsequent years, Simons continued to work on the role of lipid rafts, and more generally lipids, in cell polarization and protein sorting. He was interested also in the role of lipids and protein sorting in neurodegenerative diseases, especially in Alzheimer's disease.
His scientific record includes more than 350 scientific articles, mostly in the field of biochemistry, molecular organization of the cell, and biochemistry and physiology of a cell membrane.
Considering his work from years 1996–2007 tracked until May 2009, Simons was 12. in the list of the most frequently cited scientists in the field cell biology with 90 articles and 16,299 citations. | 1 | Biochemistry |
Researchers in the 1960s investigating brown adipose tissue, found that in addition to producing more heat than typical of other tissues, brown adipose tissue seemed to short circuit, or uncouple, respiration coupling. Uncoupling protein 1 was discovered in 1976 by David G. Nicholls, Vibeke Bernson, and Gillian Heaton, and the discovery was published in 1978 and shown to be the protein responsible for this uncoupling effect. UCP1 was later purified for the first time in 1980 and was first cloned in 1988.
Uncoupling protein two (UCP2), a homolog of UCP1, was identified in 1997. UCP2 localizes to a wide variety of tissues, and is thought to be involved in regulating reactive oxygen species (ROS). In the past decade, three additional homologs of UCP1 have been identified, including UCP3, UCP4, and UCP5 (also known as BMCP1 or SLC25A14). | 1 | Biochemistry |
Ferromagnetic resonance was experimentally discovered by V. K. Arkadyev when he observed the absorption of UHF radiation by ferromagnetic materials in 1911. A qualitative explanation of FMR along with an explanation of the results from Arkadyev was offered up by Ya. G. Dorfman in 1923, when he suggested that the optical transitions due to Zeeman splitting could provide a way to study ferromagnetic structure.
A 1935 paper published by Lev Landau and Evgeny Lifshitz predicted the existence of ferromagnetic resonance of the Larmor precession, which was independently verified in experiments by J. H. E. Griffiths (UK) and E. K. Zavoiskij (USSR) in 1946. | 7 | Physical Chemistry |
Nesfatin-1 is a neuropeptide produced in the hypothalamus of mammals. It participates in the regulation of hunger and fat storage. Increased nesfatin-1 in the hypothalamus contributes to diminished hunger, a sense of fullness, and a potential loss of body fat and weight.
A study of metabolic effects of nesfatin-1 in rats was done in which subjects administered nesfatin-1 ate less, used more stored fat and became more active. Nesfatin-1-induced inhibition of feeding may be mediated through the inhibition of orexigenic neurons. In addition, the protein stimulated insulin secretion from the pancreatic beta cells of both rats and mice. | 1 | Biochemistry |
An electrode electrolyte interface behaves like a capacitance called electrochemical double-layer capacitance . The equivalent circuit for the redox reaction in Fig. 2 includes the double-layer capacitance as well as the charge transfer resistance . Another analog circuit commonly used to model the electrochemical double-layer is called a constant phase element.
The electrical impedance of this circuit is easily obtained remembering the impedance of a capacitance which is given by:
where is the angular frequency of a sinusoidal signal (rad/s), and .
It is obtained:
Nyquist diagram of the impedance of the circuit shown in Fig. 3 is a semicircle with a diameter and an angular frequency at the apex equal to (Fig. 3). Other representations, Bode plots, or Black plans can be used. | 7 | Physical Chemistry |
The root ar- is used in organic chemistry to form classification names for classes of organic compounds which contain a carbon skeleton and one or multiple aromatic rings. It was extracted from the word aromatic. See e.g. aryl. | 0 | Organic Chemistry |
In −1 frameshifting, the ribosome slips back one nucleotide and continues translation in the −1 frame. There are typically three elements that comprise a −1 frameshift signal: a slippery sequence, a spacer region, and an RNA secondary structure. The slippery sequence fits a X_XXY_YYH motif, where XXX is any three identical nucleotides (though some exceptions occur), YYY typically represents UUU or AAA, and H is A, C or U. Because the structure of this motif contains 2 adjacent 3-nucleotide repeats it is believed that −1 frameshifting is described by a tandem slippage model, in which the ribosomal P-site tRNA anticodon re-pairs from XXY to XXX and the A-site anticodon re-pairs from YYH to YYY simultaneously. These new pairings are identical to the 0-frame pairings except at their third positions. This difference does not significantly disfavor anticodon binding because the third nucleotide in a codon, known as the wobble position, has weaker tRNA anticodon binding specificity than the first and second nucleotides. In this model, the motif structure is explained by the fact that the first and second positions of the anticodons must be able to pair perfectly in both the 0 and −1 frames. Therefore, nucleotides 2 and 1 must be identical, and nucleotides 3 and 2 must also be identical, leading to a required sequence of 3 identical nucleotides for each tRNA that slips. | 1 | Biochemistry |
Lipofectamine or Lipofectamine 2000 is a common transfection reagent, produced and sold by Invitrogen, used in molecular and cellular biology. It is used to increase the transfection efficiency of RNA (including mRNA and siRNA) or plasmid DNA into in vitro cell cultures by lipofection. Lipofectamine contains lipid subunits that can form liposomes in an aqueous environment, which entrap the transfection payload, e.g. DNA plasmids.
Lipofectamine consists of a 3:1 mixture of DOSPA (2,3‐dioleoyloxy‐N‐ [2(sperminecarboxamido)ethyl]‐N,N‐dimethyl‐1‐propaniminium trifluoroacetate) and DOPE, which complexes with negatively charged nucleic acid molecules to allow them to overcome the electrostatic repulsion of the cell membrane. Lipofectamine's cationic lipid molecules are formulated with a neutral co-lipid (helper lipid). The DNA-containing liposomes (positively charged on their surface) can fuse with the negatively charged plasma membrane of living cells, due to the neutral co-lipid mediating fusion of the liposome with the cell membrane, allowing nucleic acid cargo molecules to cross into the cytoplasm for replication or expression.
In order for a cell to express a transgene, the nucleic acid must reach the nucleus of the cell to begin transcription. However, the transfected genetic material may never reach the nucleus in the first place, instead being disrupted somewhere along the delivery process. In dividing cells, the material may reach the nucleus by being trapped in the reassembling nuclear envelope following mitosis. But also in non-dividing cells, research has shown that Lipofectamine improves the efficiency of transfection, which suggests that it additionally helps the transfected genetic material penetrate the intact nuclear envelope.
This method of transfection was invented by Dr. Yongliang Chu. | 1 | Biochemistry |
In bionanotechnology, intrinsic properties of the clusters (for example, fluorescence) can be made available for bionanotechnological applications by linking them with biomolecules through the process of bioconjugation. The protected gold particles' stability and fluorescence makes them efficient emitters of electromagnetic radiation that can be tuned by varying the cluster size and the type of ligand used for protection. The protective shell can function (have functional groups added) in a way that selective binding (for example, as a complementary protein receptor of DNA-DNA-interaction) qualifies them for the use as biosensors. | 7 | Physical Chemistry |
The main drawback of the aperture mode is that the small aperture size reduces the signal intensity and is difficult to fabricate. Recently, researchers have focused on the apertureless mode, which utilizes SPR theory to produce stronger signals. There are two techniques supporting this mode: SERS and TERS. | 7 | Physical Chemistry |
Diglycerides, generally in a mix with monoglycerides (E471), are common food additives largely used as emulsifiers. The values given in the nutritional labels for total fat, saturated fat, and trans fat do not include those present in mono- and diglycerides. They often are included in bakery products, beverages, ice cream, peanut butter, chewing gum, shortening, whipped toppings, margarine, confections, and some snack products, such as Pringles. | 1 | Biochemistry |
β-Hydroxy β-methylbutyric acid (HMB), otherwise known as its conjugate base, , is a naturally produced substance in humans that is used as a dietary supplement and as an ingredient in certain medical foods that are intended to promote wound healing and provide nutritional support for people with muscle wasting due to cancer or HIV/AIDS. In healthy adults, supplementation with HMB has been shown to increase exercise-induced gains in muscle size, muscle strength, and lean body mass, reduce skeletal muscle damage from exercise, improve aerobic exercise performance, and expedite recovery from exercise. Medical reviews and meta-analyses indicate that HMB supplementation also helps to preserve or increase lean body mass and muscle strength in individuals experiencing age-related muscle loss. HMB produces these effects in part by stimulating the production of proteins and inhibiting the breakdown of proteins in muscle tissue. No adverse effects from long-term use as a dietary supplement in adults have been found.
HMB is sold as a dietary supplement at a cost of about per month when taking 3 grams per day. HMB is also contained in several nutritional products, including certain formulations of Ensure and Juven. HMB is also present in insignificant quantities in certain foods, such as alfalfa, asparagus, avocados, cauliflower, grapefruit, and catfish.
The effects of HMB on human skeletal muscle were first discovered by Steven L. Nissen at Iowa State University in the . HMB has not been banned by the National Collegiate Athletic Association, World Anti-Doping Agency, or any other prominent national or international athletic organization. In 2006, only about 2% of college student athletes in the United States used HMB as a dietary supplement. As of 2017, HMB has found widespread use as an ergogenic supplement among young athletes. | 1 | Biochemistry |
The advantages of this method include good separation of large molecules from the small molecules with a minimal volume of eluate, and that various solutions can be applied without interfering with the filtration process, all while preserving the biological activity of the particles to separate. The technique is generally combined with others that further separate molecules by other characteristics, such as acidity, basicity, charge, and affinity for certain compounds. With size exclusion chromatography, there are short and well-defined separation times and narrow bands, which lead to good sensitivity. There is also no sample loss because solutes do not interact with the stationary phase.
The other advantage to this experimental method is that in certain cases, it is feasible to determine the approximate molecular weight of a compound. The shape and size of the compound (eluent) determine how the compound interacts with the gel (stationary phase). To determine approximate molecular weight, the elution volumes of compounds with their corresponding molecular weights are obtained and then a plot of “K” vs “log(Mw)” is made, where and Mw is the molecular mass. This plot acts as a calibration curve, which is used to approximate the desired compound's molecular weight. The V component represents the volume at which the intermediate molecules elute such as molecules that have partial access to the beads of the column. In addition, V is the sum of the total volume between the beads and the volume within the beads. The V component represents the volume at which the larger molecules elute, which elute in the beginning. Disadvantages are, for example, that only a limited number of bands can be accommodated because the time scale of the chromatogram is short, and, in general, there must be a 10% difference in molecular mass to have a good resolution. | 1 | Biochemistry |
The synchronous 6π-electron Diels-Alder reaction is a [4 + 2]-cycloaddition (i.e. suprafacial with respect to both components), as exemplified by the reaction to the right.
Thus as the total number of antarafacial components is 0, which is even, the reaction is symmetry-allowed. This prediction agrees with experiment as the Diels-Alder reaction is a rather facile pericyclic reaction. | 7 | Physical Chemistry |
CRPF in India had tested skunk for possible usage in crowd control situations in India but the tests failed to meet the required standards. Testing the product on crowd consisting of police personnel and general public reportedly failed to convince the local police crowd control units on its effectiveness. The test subjects were found to have tolerated the smell. According to an official associated with the test, Indians possibly had higher threshold to tolerate the stench. | 1 | Biochemistry |
*[https://www.bgc-jena.mpg.de/bgp/index.php/Site/Home Biogeochemical Processes] (Susan E. Trumbore)
**[https://www.bgc-jena.mpg.de/bgp/index.php/MolecularBiogeochemistry/MolecularBiogeochemistry Molecular Biogeochemistry] (Gerd Gleixner)
**[https://www.bgc-jena.mpg.de/TEE/index.html Theoretical Ecosystem Ecology] (Carlos A. Sierra)
**[https://www.bgc-jena.mpg.de/bgi/index.php/Research/DirectorsGroup Soil Biogeochemistry] (Marion Schrumpf)
**[https://www.bgc-jena.mpg.de/bgp/index.php/PlantAllocation/PlantAllocation Plant Allocation] (Henrik Hartmann)
**[https://www.bgc-jena.mpg.de/bgp/index.php/LandscapeProcesses/LandscapeProcesses Landscape Proceesses] (Shaun Levick)
**[https://www.bgc-jena.mpg.de/bgp/index.php/EmeritusEDS/EmeritusEDS Emeritus Group] (Ernst Detlef Schulze)
**[https://www.bgc-jena.mpg.de/bgp/index.php/TanguroFlux/TanguroFlux Tanguro Flux] (Susan E. Trumbore)
*[https://www.bgc-jena.mpg.de/bgi/index.php/Main/HomePage Biogeochemical Integration] (Markus Reichstein)
**[https://www.bgc-jena.mpg.de/bgi/index.php/Research/BAIE Biosphere-Atmosphere Interactions and Experimentation] (Mirco Migliavacca)
**[https://www.bgc-jena.mpg.de/bgi/index.php/Research/GlobalModelling Terrestrial Biosphere Modelling] (Sönke Zaehle)
**[https://www.bgc-jena.mpg.de/bgi/index.php/Research/ModelDataFusion Model-Data Integration] (Nuno Carvalhais)
**[https://www.bgc-jena.mpg.de/bgi/index.php/Research/DiagnosticModelling Global Diagnostic Modelling] (Miguel D. Mahecha)
**[https://www.bgc-jena.mpg.de/bgi/index.php/Research/DiagnosticModelling Empirical Inference of the Earth System] (Martin Jung)
**[https://www.bgc-jena.mpg.de/bgi/index.php/Research/FloraIncognita Flora Incognita] (Jana Wäldchen)
**[https://www.bgc-jena.mpg.de/bgi/index.php/Research/HydroBioClim Hydrology-Biosphere-Climate Interactions] (René Orth)
*[https://www.bgc-jena.mpg.de/bgc-systems/index.php/Site/Home Biogeochemical Systems] (Martin Heiman, emeritus)
**[https://www.bgc-jena.mpg.de/bgc-systems/index.php/ARS/MissionStatement Atmospheric Remote Sensing (ARS)] (Dietrich Feist)
**[https://www.bgc-jena.mpg.de/bgc-systems/index.php/ATM/MissionStatement Airborne trace gas measurements and mesoscale modelling (ATM)] (Christoph Gerbig)
**[https://www.bgc-jena.mpg.de/bgc-systems/index.php/IDE/ResearchGroup-IDE Inverse data-driven estimation (IDE)] (Christian Rödenbeck)
**[https://www.bgc-jena.mpg.de/bgc-systems/index.php/IPAS/MissionStatement Integrating surface-atmosphere Exchange Processes Across Scales - Modeling and Monitoring (IPAS)] (Mathias Goeckede)
**[https://www.bgc-jena.mpg.de/bgc-systems/index.php/TAG/MissionStatement Tall Tower Atmospheric Gas Measurements (TAG)] (Jošt Valentin Lavrič)
**[https://www.bgc-jena.mpg.de/bgc-systems/index.php/TBM/ResearchGroup-CCDAS Carbon Cycle Data Assimilation (CCDAS)] (Sönke Zaehle)
**[https://www.bgc-jena.mpg.de/bgc-systems/index.php/SRS/MissionStatement Satellite-based remote sensing of greenhouse gases (SRS)] (Julia Marshall) | 9 | Geochemistry |
The voltage pulses produced for every gamma ray that interacts within the detector volume are then analyzed by a multichannel analyzer (MCA). In the MCA, a pulse-shaping amplifier takes the transient voltage signal and reshapes it into a Gaussian or trapezoidal shape. From this shape, the signal is then converted into a digital form, using a fast analog-to-digital converter (ADC). In new systems with a very high-sampling-rate ADC, the analog-to-digital conversion can be performed without reshaping.
Additional logic in the MCA then performs pulse-height analysis, sorting the pulses by their height into specific bins, or channels. Each channel represents a specific range of energy in the spectrum, the number of detected signals for each channel represents the spectral intensity of the radiation in this energy range. By changing the number of channels, it is possible to fine-tune the spectral resolution and sensitivity.
The MCA can send its data to a computer, which stores, displays, and further analyzes the data. A variety of software packages are available from several manufacturers, and generally include spectrum analysis tools such as energy calibration (converting bins to energies), peak area and net area calculation, and resolution calculation.
A USB sound card can serve as a cheap, consumer off-the-shelf ADC, a technique pioneered by Marek Dolleiser. Specialized computer software performs pulse-height analysis on the digitized waveform, forming a complete MCA. Sound cards have high-speed but low-resolution (up to 192 kHz) ADC chips, allowing for reasonable quality for a low-to-medium count rate. The "sound card spectrometer" has been further refined in amateur and professional circles. | 7 | Physical Chemistry |
Alkynylations, including the asymmetric variety, have been developed as metal-catalyzed reactions. Various catalytic additions of alkynes to electrophiles in water have also been developed. | 0 | Organic Chemistry |
While some isocyanides (e.g., cyclohexyl isocyanide) are toxic, others "exhibit no appreciable toxicity for mammals". Referring to ethyl isocyanide, toxicological studies in the 1960s at Bayer showed that "oral and subcutaneous doses of 500-5000 mg/kg can be tolerated by mice". | 0 | Organic Chemistry |
The Grotthuss–Draper law (also called the principle of photochemical activation) states that only that light which is absorbed by a system can bring about a photochemical change. Materials such as dyes and phosphors must be able to absorb "light" at optical frequencies. This law provides a basis for fluorescence and phosphorescence. The law was first proposed in 1817 by Theodor Grotthuss and in 1842, independently, by John William Draper.
This is considered to be one of the two basic laws of photochemistry. The second law is the Stark–Einstein law, which says that primary chemical or physical reactions occur with each photon absorbed. | 7 | Physical Chemistry |
The stability of the Mg-Mg bond needed to be dealt with. Researchers began to investigate sterically demanding guanidinates and amidinates. Their stabilizing abilities in low-oxidation state chemistry was attractive since it allowed for other low-valent main group complexes to be achieved. This research also allowed for the first stable dimer Mg(I) dimer, [{(Priso)Mg}]. Potassium reduction of heteroleptic Mg(II) iodide precursor complexes were then carried out. The ligands guanidinato and, β-diketiminato Mg(II) iodide etherate complexes can be prepared from free NH ligands and methyl magnesium iodide in diethyl ether. An example of the synthesis of the precursor synthesis can be shown below. An additional precursor synthesis is shown, needed for [{(Nacnac)Mg}], which can be explained in the section below. | 7 | Physical Chemistry |
Jupiter, like all the gas giants, has an atmospheric methane cycle. Recent studies indicate a hydrological cycle of water-ammonia vastly different to the type operating on terrestrial planets like Earth and also a cycle of hydrogen sulfide.
Significant chemical cycles exist on Jupiter's moons. Recent evidence points to Europa possessing several active cycles, most notably a water cycle. Other studies suggest an oxygen and radiation induced carbon dioxide cycle. Io and Europa, appear to have radiolytic sulphur cycles involving their lithospheres. In addition, Europa is thought to have a sulfur dioxide cycle. In addition, the Io plasma torus contributes to a sulphur cycle on Jupiter and Ganymede. Studies also imply active oxygen cycles on Ganymede and oxygen and radiolytic carbon dioxide cycles on Callisto. | 9 | Geochemistry |
In March 2015, NASA Ames scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine and thymine, have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), the most carbon-rich chemical found in the universe, may have been formed in red giants or in interstellar dust and gas clouds. | 1 | Biochemistry |
Cyclodextrins are used to make pharmaceutical solutions by capturing hydrophobic molecules as guest hosts. Because inclusion compounds of cyclodextrins with hydrophobic molecules are able to penetrate body tissues, these can be used to release biologically active compounds under specific conditions. For example, testosterone is complexed with hydroxy-propyl-beta-cyclodextrin (HPBCD), 95% absorption of testosterone was achieved in 20 minutes via the sublingual route but HPBCD was not absorbed, whereas hydrophobic testosterone is usually absorbed less than 40% via the sublingual route. | 6 | Supramolecular Chemistry |
EDTA, ethylenediaminetetraacetic acid, has four carboxyl groups and two amine groups that can act as electron pair donors, or Lewis bases. The ability of EDTA to potentially donate its six lone pairs of electrons for the formation of coordinate covalent bonds to metal cations makes EDTA a hexadentate ligand. However, in practice EDTA is usually only partially ionized, and thus forms fewer than six coordinate covalent bonds with metal cations.
Disodium EDTA is commonly used to standardize aqueous solutions of transition metal cations. Disodium EDTA (often written as NaHY) only forms four coordinate covalent bonds to metal cations at pH values ≤ 12. In this pH range, the amine groups remain protonated and thus unable to donate electrons to the formation of coordinate covalent bonds. Note that the shorthand form NaHY can be used to represent any species of EDTA, with x designating the number of acidic protons bonded to the EDTA molecule.
EDTA forms an octahedral complex with most 2+ metal cations, M, in aqueous solution. The main reason that EDTA is used so extensively in the standardization of metal cation solutions is that the formation constant for most metal cation-EDTA complexes is very high, meaning that the equilibrium for the reaction:
:M + HY → MHY + 2H
lies far to the right. Carrying out the reaction in a basic buffer solution removes H as it is formed, which also favors the formation of the EDTA-metal cation complex reaction product. For most purposes it can be considered that the formation of the metal cation-EDTA complex goes to completion, and this is chiefly why EDTA is used in titrations and standardizations of this type. | 3 | Analytical Chemistry |
Conformational equilibrium is the tendency to favor the conformation where cyclohexane is the most stable. This equilibrium depends on the interactions between the molecules in the compound and the solvent. Polarity and nonpolarity are the main factors in determining how well a solvent interacts with a compound. Cyclohexane is considered nonpolar, meaning that there is no electronegative difference between its bonds and its overall structure is symmetrical. Due to this, when cyclohexane is immersed in a polar solvent, it will have less solvent distribution, which signifies a poor interaction between the solvent and solute. This produces a limited catalytic effect. Moreover, when cyclohexane comes into contact with a nonpolar solvent, the solvent distribution is much greater, showing a strong interaction between the solvent and solute. This strong interaction yields a heighten catalytic effect. | 4 | Stereochemistry |
The shape of the semiintegral can be used as an easy method to measure the amount of ohmic drop of an electrochemical cell in cyclic voltammetry. Essentially the semiintegral of a cyclic voltammogram at a planar electrode (an electrode that obeys to the rules of planar diffusion) has the shape of a sigmoid while the original data is gauss-sigmoid convoluted. This enables the operator to optimize parameters necessary for positive feedback compensation in an easy manner. If ohmic drop distortion is present the two sigmoids for the forward and the backward scan are far away from congruence, the ohmic drop can be calculated from the deviation from congruence in these cases. In the example shown slight distortion is present, yet this does not have adverse effects on data quality. | 3 | Analytical Chemistry |
Levobupivacaine is a drug that has analgesic, motor blocking, and sensory blocking effects on the human body, whose properties are dictated by its chemical characteristics, such as pK, which has a value of 8.1. The pK of a drug can be informative information that indicates its ionisation under physiological conditions. For example, drugs with a high pK, such as that of levobupivacaine, tend to be their ionised form under physiological state, meaning that they would not easily cross the hydrophobic plasma membrane of cells. This, however, is counteracted by the high lipid solubility of levobupivacaine, which increases the ease with which it can diffuse through the phospholipid bilayer. Additionally, high-protein binding quality (97%) is characteristic of levobupivacaine, which strengthens its binding to cell surface proteins, thereby lengthening the binding, and thus action time.
The S(-)-enantiomer of levobupivacaine is a high-potency, long-acting anaesthetic with a relatively slow onset of action. Indeed, it has been found in certain studies that, as a surgical anaesthetic, it has a sensory ad motor blocking activity for over 90% of adult patients who received appropriate doses for their bodily composition, and duration of the surgery, with an onset time of 15 minutes.
More specifically, levobupivacaine achieves its effects by acting on the neuronal voltage-sensitive sodium channels, where it prevents the transmission of nerve impulses. The normal function of these sodium channels is halted temporarily, as the drug interferes with their opening, thereby inhibiting the conduction of action potentials in nerves involved in sympathetic, sensory, and motor activity. This interruption results in decreased muscle control, and overall analgesic effects which allow for levobupivacaine to act as a local anaesthetic.
Levobupivacaine varies slightly in its effects depending on the characteristics of the neuron in question. For example, in myelinated neurons, the nodes of Ranvier are targeted and more easily blocked than unmyelinated neurons, and small nerves are more easily blocked than large nerves.
When compared to the racemic bupivacaine mixture, levobupivacaine generally has been shown to have similar effects. As an anaesthetic, it is similar in nerve-blocking potency compared to its R(+)-enantiomer and racemic mixture, although its effects are affected by the route of administration and the concentration, however, they were ultimately similar among the three. Some animal studies indicate that among the three, levobupivacaine shows an increased duration of anaesthesia and/or greater potency, and there is evidence that in humans it is as potent as bupivacaine. | 4 | Stereochemistry |
Thermophysical properties - [http://twt.mpei.ac.ru/TTHB/2/R410a-eng.html Properties of refrigerant R410a] | 2 | Environmental Chemistry |
In organic chemistry, the Hammett equation describes a linear free-energy relationship relating reaction rates and equilibrium constants for many reactions involving benzoic acid derivatives with meta- and para-substituents to each other with just two parameters: a substituent constant and a reaction constant. This equation was developed and published by Louis Plack Hammett in 1937 as a follow-up to qualitative observations in his 1935 publication.
The basic idea is that for any two reactions with two aromatic reactants only differing in the type of substituent, the change in free energy of activation is proportional to the change in Gibbs free energy. This notion does not follow from elemental thermochemistry or chemical kinetics and was introduced by Hammett intuitively.
The basic equation is:
where
: = Reference constant
: = Substituent constant
: = Reaction rate constant
relating the equilibrium constant, , for a given equilibrium reaction with substituent R and the reference constant when R is a hydrogen atom to the substituent constant sigma| which depends only on the specific substituent R and the reaction rate constant ρ which depends only on the type of reaction but not on the substituent used.
The equation also holds for reaction rates k of a series of reactions with substituted benzene derivatives:
In this equation is the reference reaction rate of the unsubstituted reactant, and k that of a substituted reactant.
A plot of for a given equilibrium versus for a given reaction rate with many differently substituted reactants will give a straight line. | 7 | Physical Chemistry |
General anesthesia is required for many surgeries, but may cause lingering fatigue, sedation, and/or drowsiness after surgery that lasts for hours to days. In outpatient surgery the sedation, fatigue, and occasional dizziness is problematic. Modafinil was tested as a potential remedy to alleviate these symptoms. For example, it was expected that modafinil would help people recover quicker from general anesthesia after a short surgery, but the results were uncertain and the inconclusive studies could not reliably verify the expectation. The use of modafinil to relieve post-anesthesia sedation is investigational. | 4 | Stereochemistry |
Charles Kettering, vice president of General Motors Research Corporation, was seeking a refrigerant replacement that would be colorless, odorless, tasteless, nontoxic, and nonflammable. He assembled a team that included Thomas Midgley, Jr., Albert Leon Henne, and Robert McNary. From 1930 to 1935, they developed dichlorodifluoromethane (CClF or R12), trichlorofluoromethane (CClF or R11), chlorodifluoromethane (CHClF or R22), trichlorotrifluoroethane (CClFCClF or R113), and dichlorotetrafluoroethane (CClFCClF or R114), through Kinetic Chemicals which was a joint venture between DuPont and General Motors. | 2 | Environmental Chemistry |
Hepoxilin-epoxide hydrolase or hepoxilin hydrolase is currently best defined as an enzyme activity that converts the biologically active monohydroxy-epoxide metabolites of arachidonic acid hepoxilin A3s and hepoxilin B3s to essentially inactive trihydroxy products, the trioxilins. That is, hepoxilin A3s (8-hydroxy-11,12-oxido-5Z,9E,14Z-eicosatrienoic acid) are metabolized to trioxilin A3s (8,11,12-trihydroxy-5Z,9E,14Z-eicosatrienoic acids) and hepoxilins B3s (10-hydroxy-11,12-oxido-5Z,8Z,14Z-eicosatrienoic acids) are metabolized to trioxilin B3s (10,11,12-trihydroxy-5Z,8Z,14Z-eicosatrienoic acids). However, this activity has not been characterized at the purified protein or gene level and recent work indicate that sEH readily metabolizes an hepoxilin A3 to a trioxilin A3 and that hepoxilin-epoxide hydrolase activity is due to sEH, at least as it is detected in mouse liver. | 1 | Biochemistry |
Erosion corrosion is a degradation of material surface due to mechanical action, often by impinging liquid, abrasion by a slurry, particles suspended in fast flowing liquid or gas, bubbles or droplets, cavitation, etc. The mechanism can be described as follows:
* mechanical erosion of the material, or protective (or passive) oxide layer on its surface,
* enhanced corrosion of the material, if the corrosion rate of the material depends on the thickness of the oxide layer.
The mechanism of erosion corrosion, the materials affected by it, and the conditions when it occurs are generally different from that of flow-accelerated corrosion, although the last one is sometimes classified as a sub-type of erosion corrosion. | 8 | Metallurgy |
Amorphous polymers do not have a crystallization temperature (Tm) like semi-crystalline polymers and have only a glass transition temperature (Tg). This has a decisive influence on the behavior of shape-shape-memory polymer systems.
A crystalline copolymer system alone can result in the crosslinker-treated copolymer losing its crystallinity and becoming practically amorphous.
An amorphous polymer depends on the level of crosslinking or the degree of polymerization to exhibit this effect. In the case of poly(norbornene), which is a linear, amorphous polymer, with a content of 70 to 80% of trans bonds in commercial products, molecular mass of approximately 3x106 g mol and Tg of approximately 35 to 45°C. Because it achieves an unusually high degree of polymerization, chain entanglements can be relied upon as anchor points to achieve the thermally induced shape-memory effect. Therefore, this polymer relies solely on physical anchor points. When heated up to Tg, the material abruptly changes from a rigid state to a tapered state (softens). To achieve the effect, the shape must be changed rapidly to avoid rearrangement of the segments of the polymer chains and immediately cool the material also very rapidly below Tg. Reheating the material back to Tg will show the recovery of the original shape. | 7 | Physical Chemistry |
In 1982, a diver discovered a shipwreck off the shore of Uluburun, Turkey. The ship contained 317 copper ingots in the normal oxhide shape, 36 with only two corner protrusions, 121 shaped like buns, and five shaped like pillows. The oxhide ingots (ingots with two or four protrusions) range in weight from after being cleaned of their corrosion. These ingots were found stacked in four rows following a herringbone pattern. The smooth sides of the ingots faced downwards, and the lowest layer rested on brushwood. There are three whole tin oxhide ingots, and there are many tin ingots cut into quarters or halves, with their corner protrusion(s) still intact. Besides metal ingots, the cargo included ivory, metal jewelry, and Mycenaean, Cypriot, and Canaanite pottery. Tree-ring dating of firewood from the ship gives an approximate date of 1300 BC. More than 160 copper oxhide ingots, 62 bun ingots, and some of the tin oxhide ingots have incised marks typically on their rough sides. Some of these marks—resembling fish, oars, and boats—relate to the sea, and they were probably incised after casting, when the ingot was received or exported.
Recently Yuval Goren proposed that the ten tons of copper ingots, one ton of tin ingots, and the resin stored in the Canaanite jars aboard the ship were one complete package. The recipients of the copper, tin, and resin would have used these materials for bronze casting through the lost-wax technique. | 8 | Metallurgy |
The center researches shotgun glycomics techniques in which glycans harvested and purified from various materials such as breast milk and pig lungs. Such techniques developed by the center and other glycomics groups can further be applied to tissues to generate an overall glycome of the tissue for research into various diseases such as cancer, inflammation and autoimmune diseases. | 0 | Organic Chemistry |
# Leave out the Bravais lattice type.
# Convert all symmetry elements with translational components into their respective symmetry elements without translation symmetry. (Glide planes are converted into simple mirror planes; screw axes are converted into simple axes of rotation.)
# Axes of rotation, rotoinversion axes, and mirror planes remain unchanged. | 3 | Analytical Chemistry |
Steel which utilizes the EPS process to remove surface scale shows few differences from steel which utilizes acid pickling to remove surface scale. "Downstream" industrial processes such as galvanizing, cold reducing and painting of EPS-processed steel strip show it to be interchangeable with acid-pickled steel strip. This also holds true for common sheet metal fabrication processes, such as laser cutting, plasma cutting, stamping, welding, bending, and roll forming – no meaningful difference between steel strip using the EPS process and steel strip using acid pickling.
An area where the difference between EPS-processed steel strip and acid-pickled steel strip is apparent is visual appearance. Steel which has undergone EPS processing exhibits a more uniform, lustrous appearance, as shown in Figure 4. In the EPS process, the impact of the abrasive particles on the steel surface serves to "smooth out" minor surface imperfections such as scratches, pits, roll marks and silicone streaks.
Another area of difference between EPS-treated steel strip and acid-pickled steel strip is rust resistance. Conventional acid-pickled steel strip is frequently coated with a thin film of oil to serve as a barrier to contact with oxygen so as to prevent rusting. EPS-processed steel is inherently rust-inhibitive and, therefore, needs no oil or other coating to prevent rusting. Many "downstream" processes and steel fabrication processes must have the steel's oil coating (or other surface contaminants) removed as a precursor step of the process. Use of EPS-treated steel in these processes precludes the need for any such "oil-stripping" precursor step, thereby simplifying the process. | 8 | Metallurgy |
Based on discovery rates and existing geologic surveys, researchers estimated in 2006 that 1.6 billion metric tons of copper could be brought into use. This figure relied on the broadest possible definition of available copper as well as a lack of energy constraints and environmental concerns.
The US Geological Survey estimated that, as of 2013, there remained 3.5 billion metric tons of undiscovered copper resources worldwide in porphyry and sediment-hosted type deposits, two types which currently provide 80% of mined copper production. This was in addition to 2.1 billion metric tons of identified resources. Combined identified and estimated undiscovered copper resources were 5.6 billion metric tons, 306 times the 2013 global production of newly mined copper of 18.3 million metric tons. | 8 | Metallurgy |
* Given the ability of southwestern blotting towards studying the affinity of proteins towards binding to DNA, this information can further be used with regards to uncovering specific protein factors that bind to DNA as well. These protein factors may be involved in controlling gene expression.
* Unlike electrophoretic mobility shift and DNA foot printing, determination of molecular weight of unknown proteins that bind to DNA can occur.
* Bowen and colleagues not only experimented and demonstrated a procedure for detecting DNA-binding proteins but also procedures for RNA-binding proteins as well as histone-binding proteins.
* Results can be combined with mass spectrometry to assist in DNA-binding protein identification.
* Isoelectric point determination is possible through the use of 2D-SDS-PAGE instead of the standard one dimension. | 1 | Biochemistry |
The Queensland Acid Sulfate Soil Technical Manual: Soil Management Guidelines is highly recommended for both scientists and engineers due to its excellent discussion on risk assessment and management strategies. Management strategies discussed in the manual include: avoidance, minimisation of disturbance, neutralisation, hydraulic separation, strategic reburial / interment, and stockpiling.
The Queensland government Acid Sulfate Soils: Laboratory Methods Guidelines is recommended for a discussion on the analytical techniques. Although the National guidance constitutes the primary authority on the subject, and covers a broader range of issues, this manual provides more commentary on the analytical techniques such as SPOCAS. | 9 | Geochemistry |
Elevated levels of the hormone insulin in the blood trigger downregulation of the associated receptors. When insulin binds to its receptors on the surface of a cell, the hormone receptor complex undergoes endocytosis and is subsequently attacked by intracellular lysosomal enzymes. The internalization of the insulin molecules provides a pathway for degradation of the hormone, as well as for regulation of the number of sites that are available for binding on the cell surface. At high plasma concentrations, the number of surface receptors for insulin is gradually reduced by the accelerated rate of receptor internalization and degradation brought about by increased hormonal binding. The rate of synthesis of new receptors within the endoplasmic reticulum and their insertion in the plasma membrane do not keep pace with their rate of destruction. Over time, this self-induced loss of target cell receptors for insulin reduces the target cell's sensitivity to the elevated hormone concentration.
This process is illustrated by the insulin receptor sites on target cells, e.g. liver cells, in a person with type 2 diabetes. Due to the elevated levels of blood glucose in an individual, the β-cells (islets of Langerhans) in the pancreas must release more insulin than normal to meet the demand and return the blood to homeostatic levels. The near-constant increase in blood insulin levels results from an effort to match the increase in blood glucose, which will cause receptor sites on the liver cells to downregulate and decrease the number of receptors for insulin, increasing the subject's resistance by decreasing sensitivity to this hormone. There is also a hepatic decrease in sensitivity to insulin. This can be seen in the continuing gluconeogenesis in the liver even when blood glucose levels are elevated. This is the more common process of insulin resistance, which leads to adult-onset diabetes.
Another example can be seen in diabetes insipidus, in which the kidneys become insensitive to arginine vasopressin. | 1 | Biochemistry |
*Estimation of the size of DNA molecules following digestion with restriction enzymes, e.g., in restriction mapping of cloned DNA.
*Estimation of the DNA concentration by comparing the intensity of the nucleic acid band with the corresponding band of the size marker.
*Analysis of products of a polymerase chain reaction (PCR), e.g., in molecular genetic diagnosis or genetic fingerprinting
*Separation of DNA fragments for extraction and purification.
*Separation of restricted genomic DNA prior to Southern transfer, or of RNA prior to Northern transfer.
*Separation of proteins, for example, screening of protein abnormalities in clinical chemistry.
Agarose gels are easily cast and handled compared to other matrices and nucleic acids are not chemically altered during electrophoresis. Samples are also easily recovered. After the experiment is finished, the resulting gel can be stored in a plastic bag in a refrigerator.
Electrophoresis is performed in buffer solutions to reduce pH changes due to the electric field, which is important because the charge of DNA and RNA depends on pH, but running for too long can exhaust the buffering capacity of the solution. Further, different preparations of genetic material may not migrate consistently with each other, for morphological or other reasons. | 1 | Biochemistry |
The gel sieves the DNA by the size of the DNA molecule whereby smaller molecules travel faster. Double-stranded DNA moves at a rate that is approximately inversely proportional to the logarithm of the number of base pairs. This relationship however breaks down with very large DNA fragments and it is not possible to separate them using standard agarose gel electrophoresis. The limit of resolution depends on gel composition and field strength. and the mobility of larger circular DNA may be more strongly affected than linear DNA by the pore size of the gel. Separation of very large DNA fragments requires pulse field gel electrophoresis (PFGE). In field inversion gel electrophoresis (FIGE, a kind of PFGE), it is possible to have "band inversion" - where large molecules may move faster than small molecules. | 1 | Biochemistry |
In thermodynamics, the quantity of work done by a closed system on its surroundings is defined by factors strictly confined to the interface of the surroundings with the system and to the surroundings of the system, for example, an extended gravitational field in which the system sits, that is to say, to things external to the system.
A main concern of thermodynamics is the properties of materials. Thermodynamic work is defined for the purposes of thermodynamic calculations about bodies of material, known as thermodynamic systems. Consequently, thermodynamic work is defined in terms of quantities that describe the states of materials, which appear as the usual thermodynamic state variables, such as volume, pressure, temperature, chemical composition, and electric polarization. For example, to measure the pressure inside a system from outside it, the observer needs the system to have a wall that can move by a measurable amount in response to pressure differences between the interior of the system and the surroundings. In this sense, part of the definition of a thermodynamic system is the nature of the walls that confine it.
Several kinds of thermodynamic work are especially important. One simple example is pressure–volume work. The pressure of concern is that exerted by the surroundings on the surface of the system, and the volume of interest is the negative of the increment of volume gained by the system from the surroundings. It is usually arranged that the pressure exerted by the surroundings on the surface of the system is well defined and equal to the pressure exerted by the system on the surroundings. This arrangement for transfer of energy as work can be varied in a particular way that depends on the strictly mechanical nature of pressure–volume work. The variation consists in letting the coupling between the system and surroundings be through a rigid rod that links pistons of different areas for the system and surroundings. Then for a given amount of work transferred, the exchange of volumes involves different pressures, inversely with the piston areas, for mechanical equilibrium. This cannot be done for the transfer of energy as heat because of its non-mechanical nature.
Another important kind of work is isochoric work, i.e., work that involves no eventual overall change of volume of the system between the initial and the final states of the process. Examples are friction on the surface of the system as in Rumfords experiment; shaft work such as in Joules experiments; stirring of the system by a magnetic paddle inside it, driven by a moving magnetic field from the surroundings; and vibrational action on the system that leaves its eventual volume unchanged, but involves friction within the system. Isochoric mechanical work for a body in its own state of internal thermodynamic equilibrium is done only by the surroundings on the body, not by the body on the surroundings, so that the sign of isochoric mechanical work with the physics sign convention is always negative.
When work, for example pressure–volume work, is done on its surroundings by a closed system that cannot pass heat in or out because it is confined by an adiabatic wall, the work is said to be adiabatic for the system as well as for the surroundings. When mechanical work is done on such an adiabatically enclosed system by the surroundings, it can happen that friction in the surroundings is negligible, for example in the Joule experiment with the falling weight driving paddles that stir the system. Such work is adiabatic for the surroundings, even though it is associated with friction within the system. Such work may or may not be isochoric for the system, depending on the system and its confining walls. If it happens to be isochoric for the system (and does not eventually change other system state variables such as magnetization), it appears as a heat transfer to the system, and does not appear to be adiabatic for the system. | 7 | Physical Chemistry |
Phototrophs () are organisms that carry out photon capture to produce complex organic compounds (e.g. carbohydrates) and acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a common misconception that phototrophs are obligatorily photosynthetic. Many, but not all, phototrophs often photosynthesize: they anabolically convert carbon dioxide into organic material to be utilized structurally, functionally, or as a source for later catabolic processes (e.g. in the form of starches, sugars and fats). All phototrophs either use electron transport chains or direct proton pumping to establish an electrochemical gradient which is utilized by ATP synthase, to provide the molecular energy currency for the cell. Phototrophs can be either autotrophs or heterotrophs. If their electron and hydrogen donors are inorganic compounds (e.g., , as in some purple sulfur bacteria, or , as in some green sulfur bacteria) they can be also called lithotrophs, and so, some photoautotrophs are also called photolithoautotrophs. Examples of phototroph organisms are Rhodobacter capsulatus, Chromatium, and Chlorobium. | 5 | Photochemistry |
* AM404 – an active metabolite of paracetamol.
* AM1172
* LY-2183240
* O-2093
* OMDM-2
* UCM-707
* VDM-11
* Guineensine
*WOBE437 and RX-055 | 1 | Biochemistry |
Lignin is a complex polyphenolic macromolecule composed mainly of beta-O4-aryl linkages. After cellulose, lignin is the second most abundant biopolymer and is one of the primary structural components of most plants. It contains subunits derived from p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol and is unusual among biomolecules in that it is racemic. The lack of optical activity is due to the polymerization of lignin which occurs via free radical coupling reactions in which there is no preference for either configuration at a chiral center. | 0 | Organic Chemistry |
Michael Ramsey attended Bowling Green State University for his undergraduate studies where he obtained his Bachelor of Science in Chemistry with dual minors in Physics and Mathematics in June 1974.
He then went on to obtain his Doctor of Philosophy in Analytical chemistry from Indiana University Bloomington in January 1979. Dr. Ramsey conducted his research under the direction of Gary M. Hieftje from 1974-1979 culminating in his published dissertation "New Approaches for the Measurement of Subnanosecond Chemical Phenomena" [https://inis.iaea.org/search/searchsinglerecord.aspx?recordsFor=SingleRecord&RN=11540509]. | 3 | Analytical Chemistry |
On September 27, 2012, NASA scientists announced that the Curiosity rover found evidence for an ancient streambed suggesting a "vigorous flow" of water on Mars.
On December 3, 2012, NASA reported that Curiosity performed its first extensive soil analysis, revealing the presence of water molecules, sulfur and chlorine in the Martian soil. On December 9, 2013, NASA reported that, based on evidence from Curiosity rover studying Aeolis Palus, Gale Crater contained an ancient freshwater lake which could have been a hospitable environment for microbial life. | 9 | Geochemistry |
In medical training, thermochromic ink can be used to imitate human blood because it shares its color changing property. It is currently being tested in medical simulations involving extracorporeal membrane oxygenation (ECMO). In these procedures, a change in color of blood between a dark and light red indicates blood oxygenation and blood deoxygenation, which describes the oxygen concentration levels within a persons blood sample. Its important to accurately identify this change in order to safely and correctly operate the ECMO machines. This has led to simulation-based trainings (SBT) which allows medical students to run simulations that mimic real ECMO machines before using them in serious situations. By using thermochromic ink in these simulations, the color changing effect can be realistically copied and observed without using real human blood or other costly methods.
Artificial blood or animal blood is typically used in these simulations; however, there are some advantages in using thermochromic ink as an alternative. It can be reused for multiple simulations with minimal variance in the outcomes and it is more cost effective. There are limitations to using this as the ink does not share any other properties with blood, so its only practical use is to observe the change in color of blood. | 7 | Physical Chemistry |
Several manufacturers produce EDM machines for the specific purpose of removing broken cutting tools and fasteners from work pieces. In this application, the process is termed "metal disintegration machining" or MDM. The metal disintegration process removes only the center of the broken tool or fastener, leaving the hole intact and allowing a ruined part to be reclaimed. | 8 | Metallurgy |
Spectral lines are the result of interaction between a quantum system (usually atoms, but sometimes molecules or atomic nuclei) and a single photon. When a photon has about the right amount of energy (which is connected to its frequency) to allow a change in the energy state of the system (in the case of an atom this is usually an electron changing orbitals), the photon is absorbed. Then the energy will be spontaneously re-emitted, either as one photon at the same frequency as the original one or in a cascade, where the sum of the energies of the photons emitted will be equal to the energy of the one absorbed (assuming the system returns to its original state).
A spectral line may be observed either as an emission line or an absorption line. Which type of line is observed depends on the type of material and its temperature relative to another emission source. An absorption line is produced when photons from a hot, broad spectrum source pass through a cooler material. The intensity of light, over a narrow frequency range, is reduced due to absorption by the material and re-emission in random directions. By contrast, a bright emission line is produced when photons from a hot material are detected, perhaps in the presence of a broad spectrum from a cooler source. The intensity of light, over a narrow frequency range, is increased due to emission by the hot material.
Spectral lines are highly atom-specific, and can be used to identify the chemical composition of any medium. Several elements, including helium, thallium, and caesium, were discovered by spectroscopic means. Spectral lines also depend on the temperature and density of the material, so they are widely used to determine the physical conditions of stars and other celestial bodies that cannot be analyzed by other means.
Depending on the material and its physical conditions, the energy of the involved photons can vary widely, with the spectral lines observed across the electromagnetic spectrum, from radio waves to gamma rays. | 7 | Physical Chemistry |
The "conventional recycle process" for recovering and reusing the reactants has largely been supplanted by a stripping process, developed in the early 1960s by Stamicarbon in The Netherlands, that operates at or near the full pressure of the reaction vessel. It reduces the complexity of the multi-stage recycle scheme, and it reduces the amount of water recycled in the carbamate solution, which has an adverse effect on the equilibrium in the urea conversion reaction and thus on overall plant efficiency. Effectively all new urea plants use the stripper, and many total recycle urea plants have converted to a stripping process.
In the conventional recycle processes, carbamate decomposition is promoted by reducing the overall pressure, which reduces the partial pressure of both ammonia and carbon dioxide, allowing these gasses to be separated from the urea product solution. The stripping process achieves a similar effect without lowering the overall pressure, by suppressing the partial pressure of just one of the reactants in order to promote carbamate decomposition. Instead of feeding carbon dioxide gas directly to the urea synthesis reactor with the ammonia, as in the conventional process, the stripping process first routes the carbon dioxide through the stripper. The stripper is a carbamate decomposer that provides a large amount of gas-liquid contact. This flushes out free ammonia, reducing its partial pressure over the liquid surface and carrying it directly to a carbamate condenser (also under full system pressure). From there, reconstituted ammonium carbamate liquor is passed to the urea production reactor. That eliminates the medium-pressure stage of the conventional recycle process. | 0 | Organic Chemistry |
The 5' UTR of eukaryotes is more complex than prokaryotes. It contains a Kozak consensus sequence (ACCAUGG). This sequence contains the initiation codon. The initiation codon is the start site of translation into protein. | 1 | Biochemistry |
Another popular method for decomplexation involves oxidation of a low valent complex. Oxidants include air, dioxirane, ceric ammonium nitrate (CAN), and halogens. Oxidants are selected to avoid reaction with the released organic ligand. Illustrative is the use of ferric chloride to release alkynes from Co(CR)(CO). One drawback to this method is that the organometallic center is usually destroyed. One example of oxidative decomplexation involves the CAN-induced release and trapping of cyclobutadiene from cyclobutadieneiron tricarbonyl. | 0 | Organic Chemistry |
An analysis of two infants suffering from cholelithiasis observed that a substantial amount of stercobilin was present in brown pigment gallstones. This study suggested that brown pigment gallstones could form spontaneously in infants suffering from bacterial infections of the biliary tract. | 1 | Biochemistry |
::</big>
where:
* D is the diffusion coefficient
* n is the surface concentration of protein
* Co is the bulk concentration of proteins
* t is time
A higher bulk concentration and/or higher diffusion coefficient (inversely proportional to molecular size) results in a larger number of molecules arriving at the surface. The consequential protein surface interactions result in high local concentrations of adsorbed protein, reaching concentrations of up to 1000 times higher than in the bulk solution. However, the body is much more complex, containing flow and convective diffusion, and these must be considered in the rate of protein adsorption. | 1 | Biochemistry |
Copolymerization is used to modify the properties of manufactured plastics to meet specific needs, for example to reduce crystallinity, modify glass transition temperature, control wetting properties or to improve solubility. It is a way of improving mechanical properties, in a technique known as rubber toughening. Elastomeric phases within a rigid matrix act as crack arrestors, and so increase the energy absorption when the material is impacted for example. Acrylonitrile butadiene styrene is a common example. | 7 | Physical Chemistry |
The Kidd Process development team modified its cathode plates to cope with high-corrosion environments, such as the liberator cells used to remove contaminants in refineries and some high-corrosion environments in electrowinning plants.
The design of the plate features a stainless-steel jacket that surrounds a solid-copper hanger bar, protecting it from corrosion. A corrosion-resistant resin inside the stainless steel jacket protects the conductive interior weld between the header bar and the plate. The hanger bar is then finished with high-quality sealing to prevent ingress of electrolytes into the conductive interior weld.
This corrosion resistance electrode is marketed as the HP cathode plate. | 8 | Metallurgy |
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