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In clinical trials SPINA-GT was significantly elevated in patients with Graves disease and toxic adenoma compared to normal subjects. It is also elevated in diffuse and nodular goiters, and reduced in untreated autoimmune thyroiditis. In patients with toxic adenoma it has higher specificity and positive likelihood ratio for diagnosis of thyrotoxicosis than serum concentrations of thyrotropin, free T4 or free T3. GTs specificity is also high in thyroid disorders of secondary or tertiary origin.
Calculating SPINA-GT has proved to be useful in challenging clinical situations, e.g. for differential diagnosis of subclinical hypothyroidism and elevated TSH concentration due to type 2 allostatic load (as it is typical for obesity and certain psychiatric diseases). For this purpose, its usage has been recommended in sociomedical assessment. | 1 | Biochemistry |
A pair of forward and reverse reactions may occur simultaneously with comparable speeds. For example, A and B react into products P and Q and vice versa (a, b, p, and q are the stoichiometric coefficients):
The reaction rate expression for the above reactions (assuming each one is elementary) can be written as:
where: k is the rate coefficient for the reaction that consumes A and B; k is the rate coefficient for the backwards reaction, which consumes P and Q and produces A and B.
The constants k and k are related to the equilibrium coefficient for the reaction (K) by the following relationship (set v=0 in balance): | 7 | Physical Chemistry |
Since PECT materials expand and contract upon ion-insertion it is possible to use this effect for actuation. Several different materials have been proposed for this, including: carbon fibers inserted with lithium, sodium, and potassium; lithium cobalt oxide; and vanadium oxide nanofibers inserted with lithium and sodium. Applications for PECT-based actuation range from microelectromechanical systems (MEMS), to large morphing structures.
Different materials exhibit different amounts of expansion/contraction, with a response that is dependent on the type of ion, as well as the amount of charge. For example, silicon expands by more than 300% when inserted with lithium, whereas graphite expands by around 13%. Carbon fibres expand by up to 1% when inserted with lithium, but only around 0.2% when inserted with potassium. | 7 | Physical Chemistry |
Research based on the split gene theory sheds light on other basic questions of exons and introns. The exons of eukaryotes are generally short (human exons average ~120 bases, and can be as short as 10 bases) and introns are usually long (average of ~3,000 bases, and can be several hundred thousands bases long), for example genes RBFOX1, CNTNAP2, PTPRD and DLG2. Senapathy provided a plausible answer to these questions, the only explanation to date. If eukaryotic genes originated from random DNA sequences, they have to match the lengths of ORFs from random sequences, and possibly should be around 100 bases (close to the median length of ORFs in random sequence). The genome sequences of living organisms exhibit exactly the same average lengths of 120 bases for exons, and the longest exons of 600 bases (with few exceptions), which is the same length as that of the longest random ORFs.
If split genes originated in random DNA sequences, then introns would be long for several reasons. The stop codons occur in clusters leading to numerous consecutive short ORFs: longer ORFs that could be defined as exons would be rarer. Furthermore, the best of the coding sequence parameters for functional proteins would be chosen from the long ORFs in random sequence, which may occur rarely. In addition, the combination of donor and acceptor splice junction sequences within short lengths of coding sequence segments that would define exon boundaries would occur rarely in a random sequence. These combined reasons would make introns long compared to exons. | 1 | Biochemistry |
Mutation in genes (XPB), (XPD) or (TTDA) cause trichothiodystrophy, a condition characterized by photosensitivity, ichthyosis, brittle hair and nails, intellectual impairment, decreased fertility and/or short stature. | 1 | Biochemistry |
To act as glycosyl donors, those monosaccharides should exist in a highly energetic form. This occurs as a result of a reaction between nucleoside triphosphate (NTP) and glycosyl monophosphate (phosphate at anomeric carbon). The recent discovery of the reversibility of many glycosyltransferase-catalyzed reactions calls into question the designation of sugar nucleotides as activated donors. | 0 | Organic Chemistry |
The captive bubble method is a method for measuring contact angle between a liquid and a solid, by using drop shape analysis. In this method, a bubble of air is injected beneath a solid, the surface of which is located in the liquid, instead of placing a drop on the solid as in the case of the sessile drop technique.
The method is particularly suitable for solids with high surface free energy on which liquids spread out. Hydrogels, such as those that comprise soft contact lenses, are inaccessible to the standard arrangement; so the captive bubble method is also used in such cases. A contact angle is formed on a smooth, periodically heterogeneous solid surface. Above the solid surface, a liquid drop is submerged to the solid in a fluid. The measurement of contact angles usually contributes to the measurement of the surface energy of solids in the industry. Different from other methods of measuring the contact angle, such as the sessile drop technique, the system utilized in the captive bubble method has the fluid bubble attached from below to the solid surface, such that both the liquid bubble and the solid interact with a fluid. | 7 | Physical Chemistry |
Most imides are cyclic compounds derived from dicarboxylic acids, and their names reflect the parent acid. Examples are succinimide, derived from succinic acid, and phthalimide, derived from phthalic acid. For imides derived from amines (as opposed to ammonia), the N-substituent is indicated by a prefix. For example, N-ethylsuccinimide is derived from succinic acid and ethylamine. Isoimides are isomeric with normal imides and have the formula RC(O)OC(NR′)R″. They are often intermediates that convert to the more symmetrical imides. Organic compounds called carbodiimides have the formula RN=C=NR. They are unrelated to imides. | 0 | Organic Chemistry |
During the 1990s, the lactic acid hypothesis was created to explain why people experienced burning or muscle cramps that occurred during and after intense exercise. The hypothesis proposes that a lack of oxygen in muscle cells results in a switch from cellular respiration to fermentation. Lactic acid created as a byproduct of fermentation of pyruvate from glycolysis accumulates in muscles causing a burning sensation and cramps.
Research from 2006 has suggested that acidosis isn't the main cause of muscle cramps. Instead cramps may be due to a lack of potassium in muscles, leading to contractions under high stress.
Animals, in fact, do not produce lactic acid during fermentation. Despite the common use of the term lactic acid in the literature, the byproduct of fermentation in animal cells is lactate.
Another change to the lactic acid hypothesis is that when sodium lactate is inside of the body, there is a higher period of exhaustion in the host after a period of exercise.
Lactate fermentation is important to muscle cell physiology. When muscle cells are undergoing intense activity, like sprinting, they need energy quickly. There is only enough ATP stored in muscles cells to last a few seconds of sprinting. The cells then default to fermentation, since they are in an anaerobic environment. Through lactate fermentation, muscle cells are able to regenerate NAD+ to continue glycolysis, even under strenuous activity. [5]
The vaginal environment is heavily influenced by lactic acid producing bacteria. Lactobacilli spp. that live in the vaginal canal assist in pH control. If the pH in the vagina becomes too basic, more lactic acid will be produced to lower the pH back to a more acidic level. Lactic acid producing bacteria also act as a protective barrier against possible pathogens such as bacterial vaginosis and vaginitis species, different fungi, and protozoa through the production of hydrogen peroxide, and antibacterial compounds. It is unclear if further use of lactic acid, through fermentation, in the vaginal canal is present [6] | 1 | Biochemistry |
The P element has found wide use in Drosophila research as a mutagen. The mutagenesis system typically uses an autonomous but immobile element, and a mobile nonautonomous element. Flies from subsequent generations can then be screened by phenotype or PCR. Naturally-occurring P elements contain coding sequence for the enzyme transposase and recognition sequences for transposase action. Transposase regulates and catalyzes the excision of a P element from the host DNA, cutting at the two recognition sites, and then reinserting randomly. It is the random insertion that may interfere with existing genes, or carry an additional gene, that can be used for genetic research.
To use this as a useful and controllable genetic tool, the two parts of the P element must be separated to prevent uncontrolled transposition. The normal genetic tools are DNA coding for transposase with no transposase recognition sequences so it cannot insert and a "P Plasmid". P Plasmids always contain a Drosophila reporter gene, often a red-eye marker (the product of the white gene), and transposase recognition sequences. They may contain a gene of interest, an E. coli selectable marker gene, often some kind of antibiotic resistance, an origin of replication or other associated plasmid "housekeeping" sequences. | 1 | Biochemistry |
Various cultures divide the semantic field of colors differently from the English language usage and some do not distinguish between blue and green in the same way. An example is Welsh where can mean blue or green, or Vietnamese where likewise can mean either. Conversely, in Russian and some other languages, there is no single word for blue, but rather different words for light blue (, ) and dark blue (, ).
Other color names assigned to bodies of water are sea green and ultramarine blue. Unusual oceanic colorings have given rise to the terms red tide and black tide.
The Ancient Greek poet Homer uses the epithet "wine-dark sea"; in addition, he also describes the sea as "grey". William Ewart Gladstone has suggested that this is due to the Ancient Greeks classifying colors primarily by luminosity rather than hue, while others believe Homer was color blind.
The Ancient Indian Wisdom of Veda consider life giving contributions of water a part of divine and recognize water as a primeval God Varuna; and the color of Varuna is described as blue. In the Gayatri associated with Varuna, the word "neela purusha" comes in second line which calls the water deity, the blue one. | 3 | Analytical Chemistry |
A wide variety of enantioselective additions employing chiral, non-racemic Lewis acids are known. The chiral (acyloxy)borane or "CAB" catalyst 1, titanium-BINOL system 2, and silver-BINAP system 3 provide addition products in high ee via the Lewis-acid-promoted mechanism described above. | 0 | Organic Chemistry |
Sarfati was a founder of the Wellington Christian Apologetics Society in New Zealand, and has long retained an interest in Christian apologetics and the creation–evolution controversy. His first two books, Refuting Evolution in 1999, and Refuting Evolution 2 in 2002, are intended as rebuttals to the National Academy of Sciences publication Teaching about Evolution and the Nature of Science and the PBS/Nova series Evolution, respectively. Refuting Compromise, published in 2004, is Sarfatis rebuttal of the day-age creationist teachings of Hugh Ross, who attempts to harmonise the Genesis account of creation with mainstream science regarding the age of the Earth and the possible size of the Biblical Flood, against which Sarfati defends a literal biblical timeline and a global flood. Eugenie Scott and Glenn Branch of the National Center for Science Education called Sarfatis Refuting Evolution 2' a "crude piece of propaganda".
Sarfati is a critic of geocentrism, the Myth of the flat Earth and flat Earth teaching, homosexual behaviour, and abortion except to save the life of the mother. While opposing embryonic stem cell research, he supports adult stem cell research. Sarfati also supports vaccination and rebuts anti-vaccination arguments. | 7 | Physical Chemistry |
Hydrogen cyanide is a poisonous gas that interferes with cellular respiration. Cyanide prevents the cell from producing adenosine triphosphate (ATP) by binding to one of the proteins involved in the electron transport chain. This protein, cytochrome c oxidase, contains several subunits and has ligands containing iron groups. The cyanide component of Zyklon B can bind at one of these iron groups, heme a3, forming a more stabilized compound through metal-to-ligand pi bonding. As a result of the formation of this new iron–cyanide complex, the electrons that would situate themselves on the heme a3 group can no longer do so. Instead, these electrons destabilize the compound; thus, the heme group no longer accepts them. Consequently, electron transport is halted, and cells can no longer produce the energy needed to synthesize ATP. Death occurs in a human being weighing within two minutes of inhaling 70 mg of hydrogen cyanide. | 1 | Biochemistry |
With cyclopropylketones, transition metal can coordinate to the ketone to direct oxidative addition into the proximal C-C bond. The resulting metallacyclobutane intermediate can be in equilibrium with the six-membered alkyl metal enolate depending on presence of a Lewis acid (e.g. dimethylaluminum chloride).
With the metallacyclobutane intermediate, 1,2-migratory insertion into an alkyne followed by reductive elimination yields a substituted cyclopentene product. Examples of intramolecular reactions with a tethered alkyne and intermolecular reactions with a nontethered alkyne both exist with use of a nickel or rhodium catalyst. With the six-membered alkyl metal enolate intermediate, dimerization or reaction with an added alpha-beta unsaturated ketone yields a 1,3-substituted cyclopentane product. | 0 | Organic Chemistry |
A primary amine and carbon disulfide react to give a dithiocarbamic acid:
In the presence of diimides or pyridine, these acids convert to isothiocyanates: | 0 | Organic Chemistry |
G-protein-coupled receptor oligomerisation is a widespread phenomenon. One of the best-studied examples is the metabotropic GABA receptor. This so-called constitutive receptor is formed by heterodimerization of GABAR1 and GABAR2 subunits. Expression of the GABAR1 without the GABAR2 in heterologous systems leads to retention of the subunit in the endoplasmic reticulum. Expression of the GABAR2 subunit alone, meanwhile, leads to surface expression of the subunit, although with no functional activity (i.e., the receptor does not bind agonist and cannot initiate a response following exposure to agonist). Expression of the two subunits together leads to plasma membrane expression of functional receptor. It has been shown that GABAR2 binding to GABAR1 causes masking of a retention signal of functional receptors. | 1 | Biochemistry |
For metal oxides acidity and basicity are dependent on the charge and the radius of the metal ions as well as the character of the metal oxygen bond. The bond between oxygen and the metal is influenced by the coordination of the metal cations and the oxygen anions as well as the filling of the metal d-orbitals. The surface coordination is controlled by the face that is exposed and by the surface relaxation. Structural defects can greatly contribute to the acidity or basicity as sites of high unsaturation can occur from oxygen or metal ion vacancies. | 7 | Physical Chemistry |
The die casting process forces molten metal under high pressure into mold cavities (which are machined into dies). Most die castings are made from nonferrous metals, specifically zinc, copper, and aluminium-based alloys, but ferrous metal die castings are possible. The die casting method is especially suited for applications where many small to medium-sized parts are needed with good detail, a fine surface quality and dimensional consistency. | 8 | Metallurgy |
Non-synonymous is the variant in exons that change the amino acid sequence encoded by the gene, including single base changes and non frameshift indels. It has been extremely investigated the function of non-synonymous variants on protein and many algorithms have been developed to predict the deleteriousness and pathogenesis of single nucleotide variants (SNVs). Classical bioinformatics tools, such as SIFT, Polyphen and MutationTaster, successfully predict the functional consequence of non-synonymous substitution. PopViz webserver provides a gene-centric approach to visualize the mutation damage prediction scores (CADD, SIFT, PolyPhen-2) or the population genetics (minor allele frequency) versus the amino acid positions of all coding variants of a certain human gene. PopViz is also cross-linked with UniProt database, where the protein domain information can be found, and to then identify the predicted deleterious variants fall into these protein domains on the PopViz plot. | 1 | Biochemistry |
As mentioned, Gram-negative bacteria primarily use acylated homoserine lactones (AHLs) as autoinducer molecules. The minimum quorum sensing circuit in Gram-negative bacteria consists of a protein that synthesizes an AHL and a second, different protein that detects it and causes a change in gene expression. First identified in V. fischeri, these two such proteins are LuxI and LuxR, respectively. Other Gram-negative bacteria use LuxI-like and LuxR-like proteins (homologs), suggesting a high degree of evolutionary conservation. However, among Gram-negatives, the LuxI/LuxI-type circuit has been modified in different species. Described in more detail below, these modifications reflect bacterial adaptations to grow and respond to particular niche environments. | 1 | Biochemistry |
Suppose an analyst is determining the concentration of silver in samples of waste solution in photographic film by atomic absorption spectroscopy. Using the calibration curve method, the analyst can calibrate the spectrometer with a pure silver aqueous solutions, and use the calibration graph to determine the amount of silver present in the waste samples. This method, however, assumes the pure aqueous solution of silver and a photographic waste sample have the same matrix and therefore the waste samples are free of matrix effect.
Matrix effects occur even with methods such as plasma spectrometry, which have a reputation for being relatively free from interferences. As such, analyst would use standard additions in this case.
For standard additions, equal volumes of the sample solutions are taken, and all are separately spiked with varying amounts of the analyte – 0, 1, 2, 3, 4, 5 mL, where 0 mL addition is a pure test sample solution. All solutions are then diluted to the same volume of 25 mL, by using the same solvent as the one used to prepare the spiking solutions. Each prepared solution is then analyzed using an atomic absorption spectrometer. The resulting signals and corresponding spiked silver concentrations are plotted, with concentration on the x-axis and the signal on the y-axis. A regression line is calculated through least squares analysis and the x-intercept of the line is determined by the ratio of the y-intercept and the slope of the regression line. This x-intercept represents the silver concentration of the test sample where there is no standard solution added. | 3 | Analytical Chemistry |
Type K (chromel–alumel) is the most common general-purpose thermocouple with a sensitivity of approximately 41 μV/°C. It is inexpensive, and a wide variety of probes are available in its −200 °C to +1350 °C (−330 °F to +2460 °F) range. Type K was specified at a time when metallurgy was less advanced than it is today, and consequently characteristics may vary considerably between samples. One of the constituent metals, nickel, is magnetic; a characteristic of thermocouples made with magnetic material is that they undergo a deviation in output when the material reaches its Curie point, which occurs for type K thermocouples at around 185 °C.
They operate very well in oxidizing atmospheres. If, however, a mostly reducing atmosphere (such as hydrogen with a small amount of oxygen) comes into contact with the wires, the chromium in the chromel alloy oxidizes. This reduces the emf output, and the thermocouple reads low. This phenomenon is known as green rot, due to the color of the affected alloy. Although not always distinctively green, the chromel wire will develop a mottled silvery skin and become magnetic. An easy way to check for this problem is to see whether the two wires are magnetic (normally, chromel is non-magnetic).
Hydrogen in the atmosphere is the usual cause of green rot. At high temperatures, it can diffuse through solid metals or an intact metal thermowell. Even a sheath of magnesium oxide insulating the thermocouple will not keep the hydrogen out.
Green rot does not occur in atmospheres sufficiently rich in oxygen, or oxygen-free. A sealed thermowell can be filled with inert gas, or an oxygen scavenger (e.g. a sacrificial titanium wire) can be added. Alternatively, additional oxygen can be introduced into the thermowell. Another option is using a different thermocouple type for the low-oxygen atmospheres where green rot can occur; a type N thermocouple is a suitable alternative. | 8 | Metallurgy |
Sulfide stress cracking (SSC) is a form of hydrogen embrittlement which is a cathodic cracking mechanism. It should not be confused with the term stress corrosion cracking which is an anodic cracking mechanism. Susceptible alloys, especially steels, react with hydrogen sulfide (), forming metal sulfides (MeS) and atomic hydrogen (H) as corrosion byproducts. Atomic hydrogen either combines to form H at the metal surface or diffuses into the metal matrix. Since sulfur is a hydrogen recombination poison, the amount of atomic hydrogen which recombines to form H on the surface is greatly reduced, thereby increasing the amount of diffusion of atomic hydrogen into the metal matrix. This aspect is what makes wet HS environments so severe.
Since SSC is a form of hydrogen embrittlement, it is most susceptibile to cracking at or slightly below ambient temperature.
Sulfide stress cracking has special importance in the gas and oil industry, as the materials being processed there (natural gas and crude oil) often contain considerable amounts of hydrogen sulfide. Equipment that comes in contact with HS environments can be rated for sour service with adherence to NACE MR0175/ISO 15156 for oil and gas production environments or NACE MR0103/ISO17945 for oil and gas refining environments.
"High Temperature Hydrogen Attack" (HTHA) does not rely on atomic hydrogen. At high temperature and high hydrogen partial pressure, hydrogen can diffuse into carbon steel alloys. In susceptible alloys, hydrogen combines with carbon within the alloy and forms methane. The methane molecules create a pressure buildup in the metal lattice voids, which leads to embrittlement and even cracking of the metal. | 8 | Metallurgy |
The Cornforth reagent is very toxic to aquatic life and may cause long-term damage to the environment if released in large amounts. It irritates skin and mucous membranes and may induce allergic reactions; it is carcinogenic. The maximum allowable concentration varies between 0.01 and 0.1 mg·m in air depending on the country. Because it contains hexavalent chromium, it is a suspected carcinogen, and as a strong oxidant, pyridinium dichromate promotes fires, releasing carbon monoxide, carbon dioxide and toxic metal smoke. The fire can be extinguished by water or CO. | 0 | Organic Chemistry |
Thermal physics, generally speaking, is the study of the statistical nature of physical systems from an energetic perspective. Starting with the basics of heat and temperature, thermal physics analyzes the first law of thermodynamics and second law of thermodynamics from the statistical perspective, in terms of the number of microstates corresponding to a given macrostate. In addition, the concept of entropy is studied via quantum theory.
A central topic in thermal physics is the canonical probability distribution. The electromagnetic nature of photons and phonons are studied which show that the oscillations of electromagnetic fields and of crystal lattices have much in common. Waves form a basis for both, provided one incorporates quantum theory.
Other topics studied in thermal physics include: chemical potential, the quantum nature of an ideal gas, i.e. in terms of fermions and bosons, Bose–Einstein condensation, Gibbs free energy, Helmholtz free energy, chemical equilibrium, phase equilibrium, the equipartition theorem, entropy at absolute zero, and transport processes as mean free path, viscosity, and conduction. | 7 | Physical Chemistry |
Carbon nanotubes have also been used to create surfaces similar to rice leaves. Similar to the lotus leaf, a hierarchical structure provides the hydrophobicity of rice leaf. Unlike the lotus leaf, rice leaves have an anisotropic structure. When CNT’s are made to mimic rice leaf papillae patterns, the contact angle to differ along the CNT direction or perpendicular. Sun et al. observed anisotropic dewetting of this CNT film. They then hypothesized and tested a three-dimensional anisotropic CNT array, which in fact exhibited anisotropic dewetting depending on the CNT spacing. | 7 | Physical Chemistry |
Drospirenone is an antimineralocorticoid with potassium-sparing properties, though in most cases no increase of potassium levels is to be expected. In women with mild or moderate chronic kidney disease, or in combination with chronic daily use of other potassium-sparing medications (ACE inhibitors, angiotensin II receptor antagonists, potassium-sparing diuretics, heparin, antimineralocorticoids, or nonsteroidal anti-inflammatory drugs), a potassium level should be checked after two weeks of use to test for hyperkalemia. Persistent hyperkalemia that required discontinuation occurred in 2 out of around 1,000 women (0.2%) with 4 mg/day drospirenone alone in clinical trials. | 4 | Stereochemistry |
After a neurotransmitter molecule binds to a receptor molecule, it must be removed to allow for the postsynaptic membrane to continue to relay subsequent EPSPs and/or IPSPs. This removal can happen through one or more processes:
*The neurotransmitter may diffuse away due to thermally-induced oscillations of both it and the receptor, making it available to be broken down metabolically outside the neuron or to be reabsorbed.
*Enzymes within the subsynaptic membrane may inactivate/metabolize the neurotransmitter.
*Reuptake pumps may actively pump the neurotransmitter back into the presynaptic axon terminal for reprocessing and re-release following a later action potential. | 1 | Biochemistry |
Bitumen ( , ) is an immensely viscous constituent of petroleum. Depending on its exact composition it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In the U.S., the material is commonly referred to as asphalt. Whether found in natural deposits or refined from petroleum, the substance is classed as a pitch. Prior to the 20th century the term asphaltum was in general use. The word derives from the ancient Greek ἄσφαλτος ásphaltos, which referred to natural bitumen or pitch. The largest natural deposit of bitumen in the world is the Pitch Lake of southwest Trinidad, which is estimated to contain 10 million tons.
70% of annual bitumen production is destined for road construction, its primary use. In this application bitumen is used to bind aggregate particles like gravel and forms a substance referred to as asphalt concrete, which is colloquially termed asphalt. Its other main uses lie in bituminous waterproofing products, such as roofing felt and roof sealant.
In material sciences and engineering the terms "asphalt" and "bitumen" are often used interchangeably and refer both to natural and manufactured forms of the substance, although there is regional variation as to which term is most common. Worldwide, geologists tend to favor the term "bitumen" for the naturally occurring material. For the manufactured material, which is a refined residue from the distillation process of selected crude oils, "bitumen" is the prevalent term in much of the world; however, in American English, "asphalt" is more commonly used. To help avoid confusion, the phrases "liquid asphalt", "asphalt binder", or "asphalt cement" are used in the U.S. to distinguish it from asphalt concrete. Colloquially, various forms of asphalt are sometimes referred to as "tar", as in the name of the La Brea Tar Pits.
Naturally occurring bitumen is sometimes specified by the term "crude bitumen". Its viscosity is similar to that of cold molasses while the material obtained from the fractional distillation of crude oil boiling at is sometimes referred to as "refined bitumen". The Canadian province of Alberta has most of the world's reserves of natural bitumen in the Athabasca oil sands, which cover , an area larger than England. | 7 | Physical Chemistry |
In general, ultraviolet detectors use either a solid-state device, such as one based on silicon carbide or aluminium nitride, or a gas-filled tube as the sensing element. UV detectors that are sensitive to UV in any part of the spectrum respond to irradiation by sunlight and artificial light. A burning hydrogen flame, for instance, radiates strongly in the 185- to 260-nanometer range and only very weakly in the IR region, whereas a coal fire emits very weakly in the UV band yet very strongly at IR wavelengths; thus, a fire detector that operates using both UV and IR detectors is more reliable than one with a UV detector alone. Virtually all fires emit some radiation in the UVC band, whereas the Suns radiation at this band is absorbed by the Earths atmosphere. The result is that the UV detector is "solar blind", meaning it will not cause an alarm in response to radiation from the Sun, so it can easily be used both indoors and outdoors.
UV detectors are sensitive to most fires, including hydrocarbons, metals, sulfur, hydrogen, hydrazine, and ammonia. Arc welding, electrical arcs, lightning, X-rays used in nondestructive metal testing equipment (though this is highly unlikely), and radioactive materials can produce levels that will activate a UV detection system. The presence of UV-absorbing gases and vapors will attenuate the UV radiation from a fire, adversely affecting the ability of the detector to detect flames. Likewise, the presence of an oil mist in the air or an oil film on the detector window will have the same effect. | 5 | Photochemistry |
Diazomethane is a popular methylating agent in the laboratory, but it is too hazardous (explosive gas with a high acute toxicity) to be employed on an industrial scale without special precautions. Use of diazomethane has been significantly reduced by the introduction of the safer and equivalent reagent trimethylsilyldiazomethane. | 0 | Organic Chemistry |
There are three pairs of main salivary glands and between 800 and 1,000 minor salivary glands, all of which mainly serve the digestive process, and also play an important role in the maintenance of dental health and general mouth lubrication, without which speech would be impossible. The main glands are all exocrine glands, secreting via ducts. All of these glands terminate in the mouth. The largest of these are the parotid glands—their secretion is mainly serous. The next pair are underneath the jaw, the submandibular glands, these produce both serous fluid and mucus. The serous fluid is produced by serous glands in these salivary glands which also produce lingual lipase. They produce about 70% of the oral cavity saliva. The third pair are the sublingual glands located underneath the tongue and their secretion is mainly mucous with a small percentage of saliva.
Within the oral mucosa, and also on the tongue, palates, and floor of the mouth, are the minor salivary glands; their secretions are mainly mucous and they are innervated by the facial nerve (CN7). The glands also secrete amylase a first stage in the breakdown of food acting on the carbohydrate in the food to transform the starch content into maltose. There are other serous glands on the surface of the tongue that encircle taste buds on the back part of the tongue and these also produce lingual lipase. Lipase is a digestive enzyme that catalyses the hydrolysis of lipids (fats). These glands are termed Von Ebner's glands which have also been shown to have another function in the secretion of histatins which offer an early defense (outside of the immune system) against microbes in food, when it makes contact with these glands on the tongue tissue. Sensory information can stimulate the secretion of saliva providing the necessary fluid for the tongue to work with and also to ease swallowing of the food. | 1 | Biochemistry |
Lacking the ability to form hydrogen bonds, acyl chlorides have lower boiling and melting points than similar carboxylic acids. For example, acetic acid boils at 118 °C, whereas acetyl chloride boils at 51 °C. Like most carbonyl compounds, infrared spectroscopy reveals a band near 1750 cm.
The simplest stable acyl chloride is acetyl chloride; formyl chloride is not stable at room temperature, although it can be prepared at –60 °C or below.
Acyl chlorides hydrolyze (react with water) to form the corresponding carboxylic acid and hydrochloric acid: | 0 | Organic Chemistry |
He was appointed as the Foreign Secretary of the National Academy of Sciences in 1974 and served for one term retiring in 1978. He also gave notable speeches on political issues such as the invasion of Cambodia, and various topics on Chemistry. The talks he gave sometimes had negative impacts on his life, exemplified by Nixon's withdrawal of his name for major National Science Foundation positions. In 1979 he retired from academia and joined the Allied Chemical Corporation as Executive Chairman, serving for ten years. He retired from this capacity and all others after his tenure concluded. | 7 | Physical Chemistry |
A virtually imaged phased array (VIPA) is an angular dispersive device that, like a prism or a diffraction grating, splits light into its spectral components. The device works almost independently of polarization. In contrast to prisms or regular diffraction gratings, the VIPA has a much higher angular dispersion but has a smaller free spectral range. This aspect is similar to that of an Echelle grating, since it also uses high diffraction orders. To overcome this disadvantage, the VIPA can be combined with a diffraction grating. The VIPA is a compact spectral disperser with high wavelength resolving power. | 7 | Physical Chemistry |
The name octasulfur is the most commonly used for this chemical. It is systematically named cyclo-octasulfur (which is the preferred IUPAC name) and cyclooctasulfane. It is also the final member of the thiocane heterocylic series, where every carbon atom is substituted with a sulfur atom, thus this sulfur allotrope is systematically named octathiocane as well. | 1 | Biochemistry |
Harford County, Maryland, found MTBE in wells near several of its filling stations beginning in 2004. This led the state of Maryland to make moves to ban MTBE.
In 2005, an Exxon-Mobil station in Fallston, Maryland, was found to be leaking MTBE into the local wells. The discovery resulted in the station being abruptly closed. Exxon-Mobil referred to the closure as a "business decision". Following the closure, MTBE levels in the area dropped.
In September 2004, Harford County placed a six-month moratorium on construction of filling stations. | 2 | Environmental Chemistry |
Despite the widespread interest in organocatalysis and the large number of new catalytic systems that are continuously being discovered, progress in the understanding of mechanism and catalyst design in the field of hydrogen-bond catalysis is extremely limited. Compared to a more developed field like palladium-catalyzed coupling reactions, hydrogen-bond catalysis presents many challenges that have not yet been successfully tackled.
*Turnover: While palladium-catalyzed reactions can often be effective with catalyst loading of less than 0.1 mol%, hydrogen-bond catalysts are often added in more than 10 mol%. Poor rate acceleration is a general trend that will have to be overcome in order for hydrogen-bond catalysis to be a practical synthetic strategy.
*Mechanism: In the future, further investigation of the precise steps involved in the mechanism of hydrogen-bond catalysis will be required that will enable chemists to rationally design catalytic strategies for more complex or more useful transformations. For comparison, the basic steps of palladium-catalyzed cross coupling have been systematically and thoroughly studied over the last few decades and have led to dramatic advances in catalytic scope, control and reaction design principles. For example, improved understanding of oxidative addition has led to aryl chlorides becoming practical coupling partners, while improved understanding of reductive elimination has led to the development of new reactions involving sp centers. Knowing these fundamental catalytic steps, the ability to rationally plan new reactions and cascades has been extremely useful in the field of total synthesis. In contrast, we lack a general, systematic mechanistic understanding of the steps of hydrogen-bond catalysis and how to influence them. Detailed mechanistic studies have so far been limited to individual systems, and their findings have not been of demonstrable predictive use.
*Catalyst: A related challenge is the investigation of how changes in catalyst, structural, conformational, and electronic can be used to rationally influence the reaction. The goal would be to fully understand how to use multiple co-operative interactions to best accelerate a reaction and impart selectivity. Ideally, rational catalyst design will eventually replace screening of families of catalysts and the choice of building blocks will become more systematic.
*Scope: While new reactions are constantly being discovered, most reactions have extremely narrow substrate scope and the reason for such narrow scope is often not understood. In the field of palladium catalysis, after the foundations of mechanistic understanding were established, the scope of reactions saw rapid growth. Knowing the factors that affected each step of catalysis allowed for the chemists to envision and pursue new reactions of high synthetic utility, such as C-H bond activation reactions. In the field hydrogen-bond catalysis, chemists have not yet reached a stage where new types of reactivity can be easily and systematically targeted. At this point, reaction discovery is useful, but more detailed mechanistic study is required to realize the full potential of hydrogen-bond catalysis. | 0 | Organic Chemistry |
The double-helix model of DNA structure was first published in the journal Nature by James Watson and Francis Crick in 1953, (X,Y,Z coordinates in 1954) based on the work of Rosalind Franklin and her student Raymond Gosling, who took the crucial X-ray diffraction image of DNA labeled as "Photo 51", and Maurice Wilkins, Alexander Stokes, and Herbert Wilson, and base-pairing chemical and biochemical information by Erwin Chargaff. Before this, Linus Pauling—who had already accurately characterised the conformation of protein secondary structure motifs—and his collaborator Robert Corey had posited, erroneously, that DNA would adopt a triple-stranded conformation.
The realization that the structure of DNA is that of a double-helix elucidated the mechanism of base pairing by which genetic information is stored and copied in living organisms and is widely considered one of the most important scientific discoveries of the 20th century. Crick, Wilkins, and Watson each received one-third of the 1962 Nobel Prize in Physiology or Medicine for their contributions to the discovery. | 4 | Stereochemistry |
In plants and animals, mineral absorption, also called mineral uptake is the way in which minerals enter the cellular material, typically following the same pathway as water. In plants, the entrance portal for mineral uptake is usually through the roots. Some mineral ions diffuse in-between the cells. In contrast to water, some minerals are actively taken up by plant cells. Mineral nutrient concentration in roots may be 10,000 times more than in surrounding soil. During transport throughout a plant, minerals can exit xylem and enter cells that require them. Mineral ions cross plasma membranes by a chemiosmotic mechanism. Plants absorb minerals in ionic form: nitrate (NO), phosphate (HPO) and potassium ions (K); all have difficulty crossing a charged plasma membrane.
It has long been known plants expend energy to actively take up and concentrate mineral ions. Proton pump hydrolyzes adenosine triphosphate (ATP) to transport H ions out of cell; this sets up an electrochemical gradient that causes positive ions to flow into cells. Negative ions are carried across the plasma membrane in conjunction with H ions as H ions diffuse down their concentration gradient.
In animals, minerals found in low small amounts are microminerals while the seven elements that are required in large quantity are known as macrominerals; these are Ca, P, Mg, Na, K, Cl, and S. In most cases, minerals that enter the blood pass through the epithelial cells which line the gastrointestinal mucosa of the small intestine. Minerals can diffuse through the pores of the tight junction in paracellular absorption if there is an electrochemical gradient. Through the process of solvent drag, minerals can also enter with water when solubilized by dipole-ion interactions. Furthermore, the absorption of trace elements can be enhanced by the presence of amino acids that are covalently bonded to the mineral. | 1 | Biochemistry |
SoRI-20041 is an "antagonist-like" allosteric modulator of amphetamine-induced dopamine release (in contrast to the related research chemicals SoRI-9804 and SoRI-20040, which are "agonist-like"). SoRI-20041 is believed to be the first example of a drug that separately modulates uptake versus release in the dopamine transporter (possibly showing how inward and outward transport represent distinct operational modes of DAT); it produces the same effects as SoRI-20040 and SoRI-9804 in uptake assays and binding assays, inhibiting the re-uptake of dopamine, but does not modulate d-amphetamine-induced DA release by inhibiting that as well, like agonists of the series do.
This suggests the possibility of simultaneous action and increase of indirect-agonism through the dual action of DRA and DRI efficacy existing together. This increases the inhibition of re-uptake at synaptic dopamine concentrations without interfering in the flow of release of dopamine from amphetaminergic phosphorylation at the affected transporter. This overcomes the obstacle of a compromised binding site that would be rendered unusable through the action of amphetamine. Conventional dopamine re-uptake inhibitors (such as cocaine or methylphenidate) would otherwise ineffectively target such a site on each specific transporter so affected by amphetamine, making this an example of a DRI that does not have a mutually exclusive functionality against DRA action at individual instances of DAT. | 1 | Biochemistry |
The major industrial synthesis involves the reaction of sulfur trioxide and sulfur dichloride: This synthesis can be adapted to the laboratory by heating oleum to slowly distill the sulfur trioxide into a cooled flask of sulfur dichloride.
Other methods include syntheses from:
*Phosphorus pentachloride:
*Chlorine and sulfur dichloride:
*Phosgene:
The second of the above four reactions also affords phosphorus oxychloride (phosphoryl chloride), which resembles thionyl chloride in many of its reactions. | 0 | Organic Chemistry |
3-membered rings are strained moieties in organic chemistry. When a 3-membered ring contains a heteroatom, such as in an epoxide or in a bromonium intermediate, the three atoms in the ring become polarized. It is impossible to assign (+) and (-) polarities to a 3-membered ring without having two adjacent atoms with the same polarity. Therefore, whenever a polarized 3-membered ring is opened by a nucleophile, umpolung inevitably results . For example, the opening of ethylene oxide with hydroxide leads to ethylene glycol. | 0 | Organic Chemistry |
The Mg-Mg bond for a neutral magnesium(I) dimer has shown to be significantly sigma-bonding. This arises from the s-orbital overlap of the two metals. The bonding interaction that occurs may be connected to the highest occupied molecular orbital (HOMO), giving the highest energy bond of the molecule. This can be reflected through the Wiberg Bond Index (WBI). The sigma single bond gives a WBI value of 0.9, having 90% s-character. Further theoretical investigations have proved that this does not hold for every complex. There can be notable p-orbital contribution to the Mg—Mg, with it being determined to be 55% in some complexes as the charge changes. There were also findings regarding the lowest unoccupied molecular orbital (LUMO). For example, bonding character was also discovered in nearly degenerate LUMO and LUMO+1, with a HOMO-LUMO gap of 93 kcal mol. | 7 | Physical Chemistry |
MicroRNAs, or miRNAs for short, are small (~22nt) segments of RNA which have been found to play a crucial role in gene regulation. One of the most commonly used methods for cloning and identifying miRNAs within a cell or tissue was developed in the Bartel Lab and published in a paper by Lau et al. (2001). Since then, several variant protocols have arisen, but most have the same basic format. The procedure is quite similar to SAGE: The small RNA are isolated, then linkers are added to each, and the RNA is converted to cDNA by RT-PCR. Following this, the linkers, containing internal restriction sites, are digested with the appropriate restriction enzyme and the sticky ends are ligated together into concatamers. Following concatenation, the fragments are ligated into plasmids and are used to transform bacteria to generate many copies of the plasmid containing the inserts. Those may then be sequenced to identify the miRNA present, as well as analysing expression levels of a given miRNA by counting the number of times it is present, similar to SAGE. | 1 | Biochemistry |
Using the technique of flash photolysis with the compound diazomethane,
Gerhard Herzberg and Jack Shoosmith
were the first to
produce and spectroscopically characterize the methylene molecule. In their work they obtained
the ultraviolet spectrum of gas phase methylene at around 141.5 nm. Their
analysis of the spectrum lead them to the conclusion that the ground electronic state was an
electronic triplet state and that the equilibrium structure was either linear, or else it had
a large bond angle of about 140°. It turns out that the latter is correct. The reactions of methylene were also studied around 1960, by infrared spectroscopy in frozen gas matrix isolation experiments.
Methylene can be prepared, under suitable conditions, by decomposition of compounds with a methylidene or methanediyl group, such as ketene (ethenone) (=CO), diazomethane (linear =), diazirine (cyclic [--N=N-]) and diiodomethane (I--I). The decomposition can be effected by photolysis, photosensitized reagents (such as benzophenone), or thermal decomposition.
The methylene molecule (CH) was mentioned for the first time by Donald Duck in a comic in 1944. | 0 | Organic Chemistry |
Epicillin (INN) is a penicillin antibiotic. It is not approved by the FDA for use in the United States.
It is an aminopenicillin. | 4 | Stereochemistry |
The element is named after ytterbite, a mineral first identified in 1787 by the chemist Carl Axel Arrhenius. He named the mineral after the village of Ytterby, in Sweden, where it had been discovered. When one of the chemicals in ytterbite was later found to be a previously unidentified element, the element was then named yttrium after the mineral. | 8 | Metallurgy |
EBSD is used in a wide range of applications, including materials science and engineering, geology, and biological research. In materials science and engineering, EBSD is used to study the microstructure of metals, ceramics, and polymers, and to develop models of material behaviour. In geology, EBSD is used to study the crystallographic structure of minerals and rocks. In biological research, EBSD is used to study the microstructure of biological tissues and to investigate the structure of biological materials such as bone and teeth. | 7 | Physical Chemistry |
Nitrate esters are typically prepared by condensation of nitric acid and the alcohol: For example, the simplest nitrate ester, methyl nitrate, is formed by reaction of methanol and nitric acid in the presence of sulfuric acid:
Formation of a nitrate ester is called a nitrooxylation (less commonly, nitroxylation). | 0 | Organic Chemistry |
In a gravitational field, liquids exert pressure on the sides of a container as well as on anything within the liquid itself. This pressure is transmitted in all directions and increases with depth. If a liquid is at rest in a uniform gravitational field, the pressure at depth is given by
where:
: is the pressure at the surface
: is the density of the liquid, assumed uniform with depth
: is the gravitational acceleration
For a body of water open to the air, would be the atmospheric pressure.
Static liquids in uniform gravitational fields also exhibit the phenomenon of buoyancy, where objects immersed in the liquid experience a net force due to the pressure variation with depth. The magnitude of the force is equal to the weight of the liquid displaced by the object, and the direction of the force depends on the average density of the immersed object. If the density is smaller than that of the liquid, the buoyant force points upward and the object floats, whereas if the density is larger, the buoyant force points downward and the object sinks. This is known as Archimedes' principle. | 7 | Physical Chemistry |
When referring to DNA transcription, the coding strand (or informational strand) is the DNA strand whose base sequence is identical to the base sequence of the RNA transcript produced (although with thymine replaced by uracil). It is this strand which contains codons, while the non-coding strand contains anticodons. During transcription, RNA Pol II binds to the non-coding template strand, reads the anti-codons, and transcribes their sequence to synthesize an RNA transcript with complementary bases.
By convention, the coding strand is the strand used when displaying a DNA sequence. It is presented in the 5 to 3 direction.
Wherever a gene exists on a DNA molecule, one strand is the coding strand (or sense strand), and the other is the noncoding strand (also called the antisense strand, anticoding strand, template strand or transcribed strand). | 1 | Biochemistry |
Although the applications of pharmacometabolomics to personalized medicine are largely only being realized now, the study of an individual's metabolism has been used to treat disease since the Middle Ages. Early physicians employed a primitive form of metabolomic analysis by smelling, tasting and looking at urine to diagnose disease. Obviously the measurement techniques needed to look at specific metabolites were unavailable at that time, but such technologies have evolved dramatically over the last decade to develop precise, high-throughput devices, as well as the accompanying data analysis software to analyze output. Currently, sample purification processes, such as liquid or gas chromatography, are coupled with either mass spectrometry (MS)-based or nuclear magnetic resonance (NMR)-based analytical methods to characterize the metabolite profiles of individual patients. Continually advancing informatics tools allow for the identification, quantification and classification of metabolites to determine which pathways may influence certain pharmaceutical interventions. One of the earliest studies discussing the principle and applications of pharmacometabolomics was conducted in an animal model to look at the metabolism of paracetamol and liver damage. NMR spectroscopy was used to analyze the urinary metabolic profiles of rats pre- and post-treatment with paracetamol. The analysis revealed a certain metabolic profile associated with increased liver damage following paracetamol treatment. At this point, it was eagerly anticipated that such pharmacometabolomics approaches could be applied to personalized human medicine. Since this publication in 2006, the Pharmacometabolomics Research Network led by Duke University researchers and that included partnerships between centers of excellence in metabolomics, pharmacogenomics and informatics (over sixteen academic centers funded by NIGMS) has been able to illustrate for the first time the power of the pharmacometabolomics approach in informing about treatment outcomes in large clinical studies and with use of drugs that include antidepressants, statins, antihypertensives, antiplatelet therapies and antipsychotics. Totally new concepts emerged from these studies on use of pharmacometabolomics as a tool that can bring a paradigm shift in the field of pharmacology. It illustrated how pharmacometabolomics can enable a Quantitative and Systems Pharmacology approach.
Pharmacometabolomics has been applied for the treatment of numerous human diseases, such as schizophrenia, diabetes, neural disease, depression and cancer. | 1 | Biochemistry |
He was born in Greenock, in 1872, but his family came to Edinburgh in his youth and he was then educated at Merchiston Castle School. He then studied Chemistry at Andersonian college in Glasgow under Prof William Dittmar.
He then went to Heidelberg where he gained his first doctorate (PhD) in 1896. He was greatly influenced there by Victor Meyer. Returning to Britain, he was the first Priestley scholar at the University of Birmingham. In 1904, he began lecturing in Chemistry at Glasgow University. In 1919, he became the first Gardiner chair of Organic Chemistry. | 0 | Organic Chemistry |
An olfactory receptor neuron (ORN), also called an olfactory sensory neuron (OSN), is a sensory neuron within the olfactory system. | 1 | Biochemistry |
The first recorded observation is attributed to English scholar Francis Bacon when he recorded in his 1620 Novum Organum that "It is well known that all sugar, whether candied or plain, if it be hard, will sparkle when broken or scraped in the dark." The scientist Robert Boyle also reported on some of his work on triboluminescence in 1663. In 1675. Astronomer Jean-Felix Picard observed that his barometer was glowing in the dark as he carried it. His barometer consisted of a glass tube that was partially filled with mercury. The empty space above the mercury would glow whenever the mercury slid down the glass tube.
In the late 1790s, sugar production began to produce more refined sugar crystals. These crystals were formed into a large solid cone for transport and sale. This solid sugar cone had to be broken into usable chunks using a sugar nips device. People began to notice that tiny bursts of light were visible as sugar was "nipped" in low light, an established example of triboluminescence. | 5 | Photochemistry |
Phosphatases act in opposition to kinases/phosphorylases, which add phosphate groups to proteins. The addition of a phosphate group may activate or de-activate an enzyme (e.g., kinase signalling pathways) or enable a protein-protein interaction to occur (e.g., SH2 domains ); therefore phosphatases are integral to many signal transduction pathways. Phosphate addition and removal do not necessarily correspond to enzyme activation or inhibition, and that several enzymes have separate phosphorylation sites for activating or inhibiting functional regulation. CDK, for example, can be either activated or deactivated depending on the specific amino acid residue being phosphorylated. Phosphates are important in signal transduction because they regulate the proteins to which they are attached. To reverse the regulatory effect, the phosphate is removed. This occurs on its own by hydrolysis, or is mediated by protein phosphatases.
Protein phosphorylation plays a crucial role in biological functions and controls nearly every cellular process, including metabolism, gene transcription and translation, cell-cycle progression, cytoskeletal rearrangement, protein-protein interactions, protein stability, cell movement, and apoptosis. These processes depend on the highly regulated and opposing actions of PKs and PPs, through changes in the phosphorylation of key proteins. Histone phosphorylation, along with methylation, ubiquitination, sumoylation and acetylation, also regulates access to DNA through chromatin reorganisation.
One of the major switches for neuronal activity is the activation of PKs and PPs by elevated intracellular calcium. The degree of activation of the various isoforms of PKs and PPs is controlled by their individual sensitivities to calcium. Furthermore, a wide range of specific inhibitors and targeting partners such as scaffolding, anchoring, and adaptor proteins also contribute to the control of PKs and PPs and recruit them into signalling complexes in neuronal cells. Such signalling complexes typically act to bring PKs and PPs in close proximity with target substrates and signalling molecules as well as enhance their selectivity by restricting accessibility to these substrate proteins. Phosphorylation events, therefore, are controlled not only by the balanced activity of PKs and PPs but also by their restricted localisation. Regulatory subunits and domains serve to restrict specific proteins to particular subcellular compartments and to modulate protein specificity. These regulators are essential for maintaining the coordinated action of signalling cascades, which in neuronal cells include short-term (synaptic) and long-term (nuclear) signalling. These functions are, in part, controlled by allosteric modification by secondary messengers and reversible protein phosphorylation.
It is thought that around 30% of known PPs are present in all tissues, with the rest showing some level of tissue restriction. While protein phosphorylation is a cell-wide regulatory mechanism, recent quantitative proteomics studies have shown that phosphorylation preferentially targets nuclear proteins. Many PPs that regulate nuclear events, are often enriched or exclusively present in the nucleus. In neuronal cells, PPs are present in multiple cellular compartments and play a critical role at both pre- and post-synapses, in the cytoplasm and in the nucleus where they regulate gene expression.
Phosphoprotein phosphatase is activated by the hormone insulin, which indicates that there is a high concentration of glucose in the blood. The enzyme then acts to dephosphorylate other enzymes, such as phosphorylase kinase, glycogen phosphorylase, and glycogen synthase. This leads to phosphorylase kinase and glycogen phosphorylase's becoming inactive, while glycogen synthase is activated. As a result, glycogen synthesis is increased and glycogenolysis is decreased, and the net effect is for energy to enter and be stored inside the cell. | 1 | Biochemistry |
The biosynthesis of lovastatin occurs via an iterative type I polyketide synthase (PKS) pathway. The six genes that encode enzymes that are essential for the biosynthesis of lovastatin are lovB, lovC, lovA, lovD, lovG, and lovF . The synthesis of dihydromonacolin L requires a total of 9-malonyl Coa . It proceeds in the PKS pathway until it reaches (E) a hexaketide, where it undergoes a Diels-Alder cycloaddition to form the fused rings. After cyclization it continues through the PKS pathway until it reaches (I) a nonaketide, which then undergoes release from LovB through the thioesterase encoded by LovG. Dihydromonacolin L, (J), then undergoes oxidation and dehydration via a cytochrome P450 oxygenase encoded by LovA to obtain monacolin J, (L).
The MT domain from lovB is active in the conversion of (B) to (C) when it transfers a methyl group from S-adenosyl-L-methionine (SAM) to the tetraketide (C) . Owing to the fact that LovB contains an inactive ER domain, LovC is required at specific steps to obtain fully reduced products. The domain organization of LovB, LovC, LovG and LovF is shown in Figure 2. The inactive ER domain of lovB is shown with an oval and where LovC acts in trans to LovB is shown with a red box.
In a parallel pathway, the diketide side chain of lovastatin is synthesized by another highly reducing type I polyketide synthase enzyme encoded by LovF . Lastly, the side chain, 2-methylbutyrate (M) is covalently attached to C-8 hydroxy group of monacolin J (L) by a transesterase encoded by LovD to form lovastatin. | 0 | Organic Chemistry |
Svante Arrhenius (1889) equation is often used to characterize the effect of temperature on the rates of chemical reactions. The Arrhenius formula gave a simple and powerful law, which in a vast generality of cases describes the dependence on absolute temperature of the rate constant as following,
where is the absolute temperature, is the gas constant and the factor varies only slightly with temperature. The meaning attached to the energy of activation is as the minimum energy, which molecules need have to overcome the threshold to reaction. Therefore, the year 1889 can be considered as the birth date of reactive dynamics as the study of the motion of atoms and molecules in a reactive event. Eq. (1) was motivated by the 1884 discovery by vant Hoff of the exponential dependence from the temperature of the equilibrium constants for most reactions: Eq.(1), when used for both a reaction and its inverse, agrees with vant Hoff's equation interpreting chemical equilibrium as dynamical at the microscopic level. In case of a single rate-limited thermally activated process, an Arrhenius plot gives a straight line, from which the activation energy and the pre-exponential factor can both be determined.
However, advances in experimental and theoretical methods have revealed the existence of deviation from Arrhenius behavior (Fig.1).
To overcome this problem, Aquilanti and Mundim proposed (2010) a generalized Arrhenius law based on algebraic deformation of the usual exponential function. Starting from the Euler exponential definition given by,
defining the deformed exponential function as,
Identifying the deformation parameter as a continuous generalization of . At the limit the d-exponential function, , coincides with the usual exponential according to the well-known limit due to Euler, that is,
This definition was first used in thermodynamics and statistical mechanics by Landau. In the most recent scientific literature, there is a variety of deformed algebras with applications in different areas of science. Considering the d-exponential function, we introduce the deformed reaction rate coefficient, , in the following way,
and at the limit the usual Arrhenius reaction law is recovered (Figs.1 and 1a). is pre-exponential factor. Taking the logarithm of , Eq.(5), we obtain the following expression for the non-Arrhenius plot,
The logarithm of the reaction rate coefficient against reciprocal temperature shows a curvature, rather than the straight-line behavior described by the usual Arrhenius law (Figs.1 and 1a).
In Tolman’s definition the barrier or activation energy is a phenomenological quantity defined in terms of the slope of an Arrhenius law; it is usually assumed to be independent of absolute temperature (T), requires only local equilibrium and in general is given by
where is constant and is the ideal gas constant.
To generalize Tolman´s definition, in the case chemical reactions, we assume that the barrier or activation energy is a function of the temperature given by the following differential equation,
or → (8)
where (constant) at limit and the usual activation energy law is recovered as a constant. Noticeably, on the contrary of the usual Arrhenius case, the barrier or activation energy is temperature dependent and has different concavities depending on the value of the d parameter (see Figs.1 and 1a). Thus, a positive convexity means that decreases with increasing temperature. This general result is explained by a new Tolman-like interpretation of the activation energy through Eq.(8).
In the recent literature, it is possible to find different applications to verify the applicability of this new chemical reaction formalism | 7 | Physical Chemistry |
Pyridine crystallizes in an orthorhombic crystal system with space group Pna2 and lattice parameters a = 1752 pm, b = 897 pm, c = 1135 pm, and 16 formula units per unit cell (measured at 153 K). For comparison, crystalline benzene is also orthorhombic, with space group Pbca, a = 729.2 pm, b = 947.1 pm, c = 674.2 pm (at 78 K), but the number of molecules per cell is only 4. This difference is partly related to the lower symmetry of the individual pyridine molecule (C vs D for benzene). A trihydrate (pyridine·3HO) is known; it also crystallizes in an orthorhombic system in the space group Pbca, lattice parameters a = 1244 pm, b = 1783 pm, c = 679 pm and eight formula units per unit cell (measured at 223 K). | 0 | Organic Chemistry |
NADK phosphorylates NAD at the 2’ position of the ribose ring that carries the adenine moiety. It is highly selective for its substrates, NAD and ATP, and does not tolerate modifications either to the phosphoryl acceptor, NAD, or the pyridine moiety of the phosphoryl donor, ATP. NADK also uses metal ions to coordinate the ATP in the active site. In vitro studies with various divalent metal ions have shown that zinc and manganese are preferred over magnesium, while copper and nickel are not accepted by the enzyme at all. A proposed mechanism involves the 2' alcohol oxygen acting as a nucleophile to attack the gamma-phosphoryl of ATP, releasing ADP. | 1 | Biochemistry |
At birth, infants don't develop enough ability to conjugate bilirubin. Up to 8% to 11% neonates will develop hyperbilirubinemia in the first week of their lives. | 1 | Biochemistry |
The rusting of iron is an electrochemical process that begins with the transfer of electrons from iron to oxygen. The iron is the reducing agent (gives up electrons) while the oxygen is the oxidizing agent (gains electrons). The rate of corrosion is affected by water and accelerated by electrolytes, as illustrated by the effects of road salt on the corrosion of automobiles. The key reaction is the reduction of oxygen:
:O + 4 + 2 → 4
Because it forms hydroxide ions, this process is strongly affected by the presence of acid. Likewise, the corrosion of most metals by oxygen is accelerated at low pH. Providing the electrons for the above reaction is the oxidation of iron that may be described as follows:
:Fe → Fe + 2
The following redox reaction also occurs in the presence of water and is crucial to the formation of rust:
:4 Fe + O → 4 Fe + 2 O
In addition, the following multistep acid–base reactions affect the course of rust formation:
:Fe + 2 HO ⇌ Fe(OH) + 2
:Fe + 3 HO ⇌ Fe(OH) + 3
as do the following dehydration equilibria:
:Fe(OH) ⇌ FeO +
:Fe(OH) ⇌ FeO(OH) +
:2 FeO(OH) ⇌ FeO +
From the above equations, it is also seen that the corrosion products are dictated by the availability of water and oxygen. With limited dissolved oxygen, iron(II)-containing materials are favoured, including FeO and black lodestone or magnetite (FeO). High oxygen concentrations favour ferric materials with the nominal formulae Fe(OH)O. The nature of rust changes with time, reflecting the slow rates of the reactions of solids.
Furthermore, these complex processes are affected by the presence of other ions, such as Ca, which serve as electrolytes which accelerate rust formation, or combine with the hydroxides and oxides of iron to precipitate a variety of Ca, Fe, O, OH species.
The onset of rusting can also be detected in the laboratory with the use of ferroxyl indicator solution. The solution detects both Fe ions and hydroxyl ions. Formation of Fe ions and hydroxyl ions are indicated by blue and pink patches respectively. | 8 | Metallurgy |
Main article smFRET.
In single-molecule fluorescence resonance energy transfer, the molecule is labeled in (at least) two places. A laser beam is focused on the molecule exciting the first probe. When this probe relaxes and emits a photon, it has a chance of exciting the other probe. The efficiency of the absorption of the photon emitted from the first probe in the second probe depends on the distance between these probes. Since the distance changes with time, this experiment probes the internal dynamics of the molecule. | 7 | Physical Chemistry |
In terms of structure, GPCRs are characterized by an extracellular N-terminus, followed by seven transmembrane (7-TM) α-helices (TM-1 to TM-7) connected by three intracellular (IL-1 to IL-3) and three extracellular loops (EL-1 to EL-3), and finally an intracellular C-terminus. The GPCR arranges itself into a tertiary structure resembling a barrel, with the seven transmembrane helices forming a cavity within the plasma membrane that serves a ligand-binding domain that is often covered by EL-2. Ligands may also bind elsewhere, however, as is the case for bulkier ligands (e.g., proteins or large peptides), which instead interact with the extracellular loops, or, as illustrated by the class C metabotropic glutamate receptors (mGluRs), the N-terminal tail. The class C GPCRs are distinguished by their large N-terminal tail, which also contains a ligand-binding domain. Upon glutamate-binding to an mGluR, the N-terminal tail undergoes a conformational change that leads to its interaction with the residues of the extracellular loops and TM domains. The eventual effect of all three types of agonist-induced activation is a change in the relative orientations of the TM helices (likened to a twisting motion) leading to a wider intracellular surface and "revelation" of residues of the intracellular helices and TM domains crucial to signal transduction function (i.e., G-protein coupling). Inverse agonists and antagonists may also bind to a number of different sites, but the eventual effect must be prevention of this TM helix reorientation.
The structure of the N- and C-terminal tails of GPCRs may also serve important functions beyond ligand-binding. For example, The C-terminus of M muscarinic receptors is sufficient, and the six-amino-acid polybasic (KKKRRK) domain in the C-terminus is necessary for its preassembly with G proteins. In particular, the C-terminus often contains serine (Ser) or threonine (Thr) residues that, when phosphorylated, increase the affinity of the intracellular surface for the binding of scaffolding proteins called β-arrestins (β-arr). Once bound, β-arrestins both sterically prevent G-protein coupling and may recruit other proteins, leading to the creation of signaling complexes involved in extracellular-signal regulated kinase (ERK) pathway activation or receptor endocytosis (internalization). As the phosphorylation of these Ser and Thr residues often occurs as a result of GPCR activation, the β-arr-mediated G-protein-decoupling and internalization of GPCRs are important mechanisms of desensitization. In addition, internalized "mega-complexes" consisting of a single GPCR, β-arr(in the tail conformation), and heterotrimeric G protein exist and may account for protein signaling from endosomes.
A final common structural theme among GPCRs is palmitoylation of one or more sites of the C-terminal tail or the intracellular loops. Palmitoylation is the covalent modification of cysteine (Cys) residues via addition of hydrophobic acyl groups, and has the effect of targeting the receptor to cholesterol- and sphingolipid-rich microdomains of the plasma membrane called lipid rafts. As many of the downstream transducer and effector molecules of GPCRs (including those involved in negative feedback pathways) are also targeted to lipid rafts, this has the effect of facilitating rapid receptor signaling.
GPCRs respond to extracellular signals mediated by a huge diversity of agonists, ranging from proteins to biogenic amines to protons, but all transduce this signal via a mechanism of G-protein coupling. This is made possible by a guanine-nucleotide exchange factor (GEF) domain primarily formed by a combination of IL-2 and IL-3 along with adjacent residues of the associated TM helices. | 1 | Biochemistry |
Application of electric pulses of sufficient strength to the cell causes an increase in the trans-membrane potential difference, which provokes the membrane destabilization. Cell membrane permeability is increased and otherwise nonpermeant molecules enter the cell.
Although the mechanisms of gene electrotransfer are not yet fully understood, it was shown that the introduction of DNA only occurs in the part of the membrane facing the cathode and that several steps are needed for successful transfection: electrophoretic migration of DNA towards the cell, DNA insertion into the membrane, translocation across the membrane, migration of DNA towards the nucleus, transfer of DNA across the nuclear envelope and finally gene expression. There are a number of factors that can influence the efficiency of gene electrotransfer, such as: temperature, parameters of electric pulses, DNA concentration, electroporation buffer used, cell size and the ability of cells to express transfected genes. In in vivo gene electrotransfer, DNA diffusion through extracellular matrix, properties of tissue and overall tissue conductivity are also crucial. | 1 | Biochemistry |
Oximes can be synthesized by condensation of an aldehyde or a ketone with hydroxylamine. The condensation of aldehydes with hydroxylamine gives aldoximes, and ketoximes are produced from ketones and hydroxylamine. In general, oximes exist as colorless crystals or as thick liquids and are poorly soluble in water. Therefore, oxime formation can be used for the identification of ketone or aldehyde functional groups.
Oximes can also be obtained from reaction of nitrites such as isoamyl nitrite with compounds containing an acidic hydrogen atom. Examples are the reaction of ethyl acetoacetate and sodium nitrite in acetic acid, the reaction of methyl ethyl ketone with ethyl nitrite in hydrochloric acid. and a similar reaction with propiophenone, the reaction of phenacyl chloride, the reaction of malononitrile with sodium nitrite in acetic acid
A conceptually related reaction is the Japp–Klingemann reaction. | 0 | Organic Chemistry |
Nitrosation is a process of converting organic compounds into nitroso derivatives, i.e., compounds containing the R-NO functionality. | 0 | Organic Chemistry |
Methods for the synthesis of aromatic, organofluorine, heterocyclic and heteroatomic compounds. Study of properties and formation of organic, hybrid and polymer materials. Study of pharmacological properties and mechanisms of action of biologically active agents of natural and synthetic origin etc. | 0 | Organic Chemistry |
Glyceroneogenesis is a metabolic pathway which synthesizes glycerol 3-phosphate (used to form triglycerides) from precursors other than glucose. Usually, glycerol 3-phosphate is generated from glucose by glycolysis, in the liquid of the cells cytoplasm (the cytosol'). Glyceroneogenesis is used when the concentrations of glucose in the cytosol are low, and typically uses pyruvate as the precursor, but can also use alanine, glutamine, or any substances from the TCA cycle. The main regulator enzyme for this pathway is an enzyme called phosphoenolpyruvate carboxykinase (PEPC-K), which catalyzes the decarboxylation of oxaloacetate to phosphoenolpyruvate. Glyceroneogenesis is observed mainly in adipose tissue, and in the liver. A significant biochemical pathway regulates cytosolic lipid levels. Intense suppression of glyceroneogenesis may lead to metabolic disorders such as type 2 diabetes. | 1 | Biochemistry |
In electrochemistry, Faraday efficiency (also called faradaic efficiency, faradaic yield, coulombic efficiency or current efficiency) describes the efficiency with which charge (electrons) is transferred in a system facilitating an electrochemical reaction. The word "Faraday" in this term has two interrelated aspects: first, the historic unit for charge is the faraday (F), but has since been replaced by the coulomb (C); and secondly, the related Faradays constant () correlates charge with moles of matter and electrons (amount of substance). This phenomenon was originally understood through Michael Faradays work and expressed in his laws of electrolysis. | 7 | Physical Chemistry |
When a substance reacts simultaneously to give two different products, a parallel or competitive reaction is said to take place. | 7 | Physical Chemistry |
There are two common methods in which to construct a DNA molecular-weight size marker. One such method employs the technique of partial ligation. DNA ligation is the process by which linear DNA pieces are connected to each other via covalent bonds; more specifically, these bonds are phosphodiester bonds. Here, a 100bp duplex DNA piece is partially ligated. The consequence of this is that dimers of 200bp, trimers of 300bp, tetramers of 400bp, pentamers of 500bp, etc. will form. Additionally, a portion of the 100bp dsDNA will remain. As a result, a DNA "ladder" composed of DNA pieces of known molecular mass is created on the gel.
The second method employs the use of restriction enzymes and a recognized DNA sequence. The DNA is digested by a particular restriction enzyme, resulting in DNA pieces of varying molecular masses. One of the advantages of this method is that more marker can readily be created simply by digesting more of the known DNA. On the other hand, the size of the DNA pieces are based on the sites where the restriction enzyme cuts. This makes it more difficult to control the size of the fragments in the marker.
More recently, another method for constructing DNA molecular-weight size markers is being employed by laboratories. This strategy involves the use of Polymerase Chain Reaction (PCR). This is achieved one or two ways: 1) a DNA target is amplified at the same time via primer sets, or 2) different DNA targets are amplified independently via particular primers. | 1 | Biochemistry |
Today, a muffle furnace is often a front-loading box-type oven or kiln for high-temperature applications such as fusing glass, creating enamel coatings, ceramics and soldering and brazing articles. They are also used in many research facilities, for example by chemists in order to determine what proportion of a sample is non-combustible and non-volatile (i.e., ash). Some models incorporate programmable digital controllers, allowing automatic execution of ramping, soaking, and sintering steps. Also, advances in materials for heating elements, such as molybdenum disilicide, can now produce working temperatures up to , which facilitate more sophisticated metallurgical applications. The heat source may be gas or oil burners, but more often they are now electric.
The term muffle furnace may also be used to describe another oven constructed on many of the same principles as the box-type kiln mentioned above, but takes the form of a long, wide, and thin hollow tube used in roll-to-roll manufacturing processes.
Both of the above-mentioned furnaces are usually heated to desired temperatures by conduction, convection, or blackbody radiation from electrical resistance heater elements. Therefore, there is (usually) no combustion involved in the temperature control of the system, which allows for much greater control of temperature uniformity and assures isolation of the material being heated from the byproducts of fuel combustion. | 8 | Metallurgy |
In monometallic complexes, aldehydes and ketones can bind to metals in either of two modes, η-O-bonded and η-C,O-bonded. These bonding modes are sometimes referred to sigma- and pi-bonded. These forms may sometimes interconvert.
The sigma bonding mode is more common for higher valence, Lewis-acidic metal centers (e.g., Zn). The pi-bonded mode is observed for low valence, electron-rich metal centers (e.g., Fe(0) and Os(0)).
For the purpose of electron-counting, O-bonded ligands count as 2-electron "L ligands": they are Lewis bases. η-C,O ligands are described as analogues of alkene ligands, i.e. the Dewar-Chatt-Duncanson model.
η-C,O ketones and aldehydes can function as bridging ligands, utilizing a lone pair of electrons on oxygen. One such complex is , which features a ring. | 0 | Organic Chemistry |
The development of VR started in 1957, after the Soviet Union obtained information about detection of high level of toxicity in phosphorylthiocholines (the same year Lars-Erik Tammelin published his first articles on fluorophosphorylcholines and phosphorylthiocholines in Acta Chemica Scandinavica) by a team from the Soviet Union's Scientific Research Institute No. 42 (NII-42). Sergei Zotovich Ivin, Leonid Soborovsky, and Iya Danilovna Shilakova jointly developed this analogue of VX. They completed their work in 1963 and were later awarded the Lenin Prize for their achievement. A binary weapon comprising two less toxic precursors which mixed during flight to form Substance 33 was later developed by a team led by Nikolai Kuznetsov.
In 1972 the Soviets opened Cheboksary Khimprom, a manufacturing plant for VR in Novocheboksarsk. All facilities in USSR produced 15,557 tons of VR according to their declaration to the Organisation for the Prohibition of Chemical Weapons (OPCW), although most if not all of this has now been destroyed under disarmament treaties. | 1 | Biochemistry |
Fucosylation is the process of adding fucose sugar units to a molecule. It is a type of glycosylation.
It is important clinically, and high levels of fucosylation have been reported in cancer. In cancer and inflammation there are significant changes in the expression of fucosylated molecules. Therefore, antibodies and lectins that are able to recognize cancer associated fucosylated oligosaccharides have been used as tumor markers in oncology.
It is performed by fucosyltransferase enzymes.
Fucosylation has been observed in vertebrates, invertebrates, plants, bacteria, and fungi. It has a role in cellular adhesion and immune regulation. Fucosylation inhibition applications are being explored for a range of clinical application including some associated with sickle cell disease, rheumatoid arthritis, tumor inhibition, and chemotherapy improvements. Recent studies on melanoma patient specimens indicated that melanoma fucosylation and fucosylated HLA-DRB1 are associated with anti-programmed cell death protein 1 (PD1) responder status, pointing to the potential use of melanoma fucosylation as a method for immunotherapy patient stratification. Moreover, it has been reported that fucosylation is an important regulator of anti-tumor immunity and -fucose can be used as a potent tool for increasing immunotherapy efficacy in melanoma.
Fucosylation can help with immune response when a foreign pathogen is introduced in the body. Rapid fucosylation can occur in the epithelial lining of the small intestine as a protective mechanism to support the body’s symbiotic gut bacteria. This may regulate the bacterial genes responsible for quorum sensing or virulence, thus resulting in an increased tolerance of the infection. | 0 | Organic Chemistry |
A set of structure utilities has been included for various applications such as: the transformation of unit cells ([http://www.cryst.ehu.es/cryst/celltran.html CELLTRAN]) or complete structures ([http://www.cryst.ehu.es/cryst/transtru.html TRANSTRU]); strain tensor calculation ([http://www.cryst.ehu.es/cryst/strain.html STRAIN]); assignment of Wyckoff Positions ([http://www.cryst.ehu.es/cryst/wpassign.html WPASSIGN]); equivalent descriptions of a given structure ([http://www.cryst.ehu.es/cryst/equivstru.html EQUIVSTRU]); comparison of different structures with support for the affine normalizers of monoclinic space groups. [http://www.cryst.ehu.es/cryst/rel.html STRUCTURE RELATIONS] calculates the possible transformation matrices for a given pair of group-subgroup related structures. | 3 | Analytical Chemistry |
Any protein that can be split into two parts and reconstituted non-covalently to form a functional protein may be used in a PCA. The two fragments however have low affinity for each other and must be brought together by other interacting proteins fused to them (often called "bait" and "prey" since the bait protein can be used to identify a prey protein, see figure). The protein that produces a detectable readout is called "reporter". Usually enzymes which confer resistance to nutrient deprivation or antibiotics, such as dihydrofolate reductase or beta-lactamase respectively, or proteins that give colorimetric or fluorescent signals are used as reporters. When fluorescent proteins are reconstituted the PCA is called Bimolecular fluorescence complementation assay. The following proteins have been used in split protein PCAs:
*Beta-lactamase
*Dihydrofolate reductase (DHFR)
*Focal adhesion kinase (FAK)
*Gal4, a yeast transcription factor (as in the classical yeast two-hybrid system)
*GFP (split-GFP), e.g. EGFP (enhanced green fluorescent protein)
*Horseradish peroxidase
*Infrared fluorescent protein IFP1.4, an engineered chromophore-binding domain (CBD) of a bacteriophytochrome from Deinococcus radiodurans
*LacZ (beta-galactosidase)
*Luciferase, including ReBiL (recombinase enhanced bimolecular luciferase) and Gaussia princeps luciferase. Commercial products using luciferase include NanoLuc and NanoBIT. A modification has also been developed for lipid droplet-associated interactions.
*TEV (Tobacco etch virus protease)
*Ubiquitin | 1 | Biochemistry |
In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence of chemical reactions catalyzed by enzymes. In most cases of a metabolic pathway, the product of one enzyme acts as the substrate for the next. However, side products are considered waste and removed from the cell.
Different metabolic pathways function in the position within a eukaryotic cell and the significance of the pathway in the given compartment of the cell. For instance, the electron transport chain and oxidative phosphorylation all take place in the mitochondrial membrane. In contrast, glycolysis, pentose phosphate pathway, and fatty acid biosynthesis all occur in the cytosol of a cell.
There are two types of metabolic pathways that are characterized by their ability to either synthesize molecules with the utilization of energy (anabolic pathway), or break down complex molecules and release energy in the process (catabolic pathway).
The two pathways complement each other in that the energy released from one is used up by the other. The degradative process of a catabolic pathway provides the energy required to conduct the biosynthesis of an anabolic pathway. In addition to the two distinct metabolic pathways is the amphibolic pathway, which can be either catabolic or anabolic based on the need for or the availability of energy.
Pathways are required for the maintenance of homeostasis within an organism and the flux of metabolites through a pathway is regulated depending on the needs of the cell and the availability of the substrate. The end product of a pathway may be used immediately, initiate another metabolic pathway or be stored for later use. The metabolism of a cell consists of an elaborate network of interconnected pathways that enable the synthesis and breakdown of molecules (anabolism and catabolism). | 1 | Biochemistry |
The ore concentrate is first introduced into an IsaMill. This comminution step places a high degree of strain on the mineral lattice and causes an increase in the number of grain boundary fractures and lattice defects of several orders of magnitude. The increase in the number of defects within the mineral lattice "activates" the mineral, facilitating leaching. The rate of leaching is also enhanced, due to the increase in the mineral surface area.
The oxidative leaching stage is carried out in agitated tanks operating at atmospheric pressure. Oxygen is introduced to the leach slurry to assist the oxidation. Leaching is autothermal, not requiring any external heat. Temperature is controlled by the rate of addition of oxygen, and by the leach slurry density. | 8 | Metallurgy |
The STAT3-Ser/Hes3 signaling axis is a specific type of intracellular signaling pathway that regulates several fundamental properties of cells. | 1 | Biochemistry |
Both agriculture and sewage treatment produce inputs into rivers with very high concentrations of bacteria and viruses including a wide range of pathogenic organisms. Even in areas with little human activity significant levels of bacteria and viruses can be detected originating from fish and aquatic mammals and from animals grazing near rivers such as deer. Upland waters draining areas frequented by sheep, goats or deer may also harbour a variety of opportunistic human parasites such as liver fluke. Consequently, there are very few rivers from which the water is safe to drink without some form of sterilisation or disinfection. In rivers used for contact recreation such as swimming, safe levels of bacteria and viruses can be established based on risk assessment.
Under certain conditions bacteria can colonise freshwaters occasionally making large rafts of filamentous mats known as sewage fungus – usually Sphaerotilus natans. The presence of such organisms is almost always an indicator of extreme organic pollution and would be expected to be matched with low dissolved oxygen concentrations and high BOD values.
E. coli bacteria have been commonly found in recreational waters and their presence is used to indicate the presence of recent fecal contamination, but E. coli presence may not be indicative of human waste. E. coli are found in all warm-blooded animals. E. coli have also been found in fish and turtles. Enterobacteria may also persist in the environment in mud, sediments, sand and soil for considerable lengths of time. | 2 | Environmental Chemistry |
Zero-order ultrasensitivity takes place under saturating conditions. For example, consider an enzymatic step with a kinase, phosphatase, and substrate. Steady state levels of the phosphorylated substrate have an ultrasensitive response when there is enough substrate to saturate all available kinases and phosphatases. Under these conditions, small changes in the ratio of kinase to phosphatase activity can dramatically change the number of phosphorylated substrate (For a graph illustrating this behavior, see ). This enhancement in sensitivity of steady state phosphorylated substrate to Km, or the ratio of kinase to phosphatase activity, is termed zero-order to distinguish it from the first order behavior described by Michaelis-Menten dynamics, wherein the steady state concentration responds in a more gradual fashion than the switch-like behavior exhibited in ultrasensitivity.
Using the notation from Goldbeter & Koshland, let W be a certain substrate protein and let W be a covalently modified version of W. The conversion of W to W is catalyzed by some enzyme and the reverse conversion of W' to W is catalyzed by a second enzyme according to following equations:
The concentrations of all necessary components (such as ATP) are assumed to be constant and represented in the kinetic constants.
Using the chemical equations above, the reaction rate equations for each component are:
The total concentration of each component is given by:
The zero order mechanism assumes that the or . In other words, the system is in a Michaelis-Menten steady state, which means, to a good approximation, and are constant.
From these kinetic expressions one can solve for at steady state defining and
where and
When the is plotted against the molar ratio and it can be seen that the W to W conversion occurs over a much smaller change in the ratio than it would under first order (non-saturating) conditions, which is the telltale sign of ultrasensitivity. | 1 | Biochemistry |
Dimethylallyl pyrophosphate (DMAPP; or alternatively, dimethylallyl diphosphate (DMADP); also isoprenyl pyrophosphate) is an isoprenoid precursor. It is a product of both the mevalonate pathway and the MEP pathway of isoprenoid precursor biosynthesis. It is an isomer of isopentenyl pyrophosphate (IPP) and exists in virtually all life forms. The enzyme isopentenyl pyrophosphate isomerase catalyzes isomerization between DMAPP and IPP.
In the mevalonate pathway DMAPP is synthesised from mevalonic acid. In contrast, DMAPP is synthesised from HMBPP in the MEP pathway.
At present, it is believed that there is crossover between the two pathways in organisms
that use both pathways to create terpenes and terpenoids, such as in plants, and that DMAPP is the crossover product. | 1 | Biochemistry |
The alternative flatworm mitochondrial code (translation table 14) is a genetic code found in the mitochondria of Platyhelminthes and Nematodes. | 1 | Biochemistry |
Although there are many other molecular display technologies, such as phage display, bacterial display, yeast display, and ribosome display, mRNA display technology has many advantages over the others. The first three biological display libraries listed have polypeptides or proteins expressed on the respective microorganism’s surface and the accompanying coding information for each polypeptide or protein is retrievable from the microorganism’s genome. However, the library size for these three in vivo display systems is limited by the transformation efficiency of each organism. For example, the library size for phage and bacterial display is limited to 1-10 × 10^9 different members. The library size for yeast display is even smaller. Moreover, these cell-based display system only allow the screening and enrichment of peptides/proteins containing natural amino acids. In contrast, mRNA display and ribosome display are in vitro selection methods. They allow a library size as large as 10^15 different members. The large library size increases the probability to select very rare sequences, and also improves the diversity of the selected sequences. In addition, in vitro selection methods remove unwanted selection pressure, such as poor protein expression, and rapid protein degradation, which may reduce the diversity of the selected sequences. Finally, in vitro selection methods allow the application of in vitro mutagenesis and recombination techniques throughout the selection process.
Although both ribosome display and mRNA display are in vitro selection methods, mRNA display has some advantage over the ribosome display technology. mRNA display utilizes covalent mRNA-polypeptide complexes linked through puromycin; whereas, ribosome display utilizes stalled, noncovalent ribosome-mRNA-polypeptide complexes. For ribosome display, selection stringency is limited to keep ribosome-mRNA-polypeptide in a complex because of the noncovalent ribosome-mRNA-polypeptide complexes. This may cause difficulties in reducing background binding during the selection cycle. Also, the polypeptides under selection in a ribosome display system are attached to an enormous rRNA-protein complex, a ribosome, which has a molecular weight of more than 2,000,000 Da. There might be some unpredictable interaction between the selection target and the ribosome, and this may lead to a loss of potential binders during the selection cycle. In contrast, the puromycin DNA spacer linker used in mRNA display technology is much smaller comparing to a ribosome. This linker may have less chance to interact with an immobilized selection target. Thus, mRNA display technology is more likely to give less biased results. | 1 | Biochemistry |
Values for log K typically range between -3 (very hydrophilic) and +10 (extremely lipophilic/hydrophobic).
The values listed here are sorted by the partition coefficient. Acetamide is hydrophilic, and 2,2′,4,4′,5-Pentachlorobiphenyl is lipophilic. | 7 | Physical Chemistry |
Current research interests in the Naim laboratory focus on the molecular mechanisms underlying protein trafficking, particularly polarized protein sorting in epithelial cells, in health and disease. | 1 | Biochemistry |
New DNA is made during this phase by enzymes which synthesize DNA in the 5’ to 3’ direction. DNA polymerase is essential for both the leading strand which is made as a continuous strand and lagging strand which is made in small pieces in DNA Synthesis. This process happens for extension of the newly synthesized fragment and expulsion of the RNA and DNA segment. Synthesis occurs in 3 phases with two different polymerases, DNA polymerase α-primase and DNA polymerase δ. This process starts with polymerase α-primase displacing from the RNA and DNA primer by the clamp loader replication Effect, this Effect leads the sliding clamp onto the DNA. After this, DNA polymerase δ begins to go into its holoenzyme form which then synthesis begins. The synthesis process will continue until the 5’end of the previous Okazaki fragment has arrived. Once arrived, Okazaki fragment processing proceeds to join the newly synthesized fragment to the lagging strand. Last function of DNA polymerase δ is to serve as a supplement to FEN1/RAD27 5’ Flap Endonuclease activity. The rad27-p allele is lethal in most combinations but was viable with the rad27-p polymerase and exo1. Both rad27-p polymerase and exo1 portray strong synergistic increases in CAN 1 duplication mutations. The only reason this mutation is viable is due to the double-strand break repair genes RAD50, RAD51 and RAD52. The RAD27/FEN1 creates nicks between adjacent Okazaki fragments by minimizing the amount of strand-expulsion in the lagging strand. | 1 | Biochemistry |
Palmitoylcarnitine has demonstrated potential as a diagnostic marker in newborns for the medical condition of primary carnitine deficiency.
Levels of palmitoylcarnitine (palcar) demonstrated significant correlation with dihydrotestosterone (DHT) and its effects in prostate cancer models, suggesting a similar role between the two molecules. | 1 | Biochemistry |
In atomic, molecular, and optical physics, above-threshold ionization (ATI) is a multi-photon effect where an atom is ionized with more than the energetically required number of photons. It was first observed in 1979 by Pierre Agostini and colleagues in xenon gas. | 7 | Physical Chemistry |
The three ketone bodies, each synthesized from acetyl-CoA molecules, are:
* Acetoacetate, which can be converted by the liver into β-hydroxybutyrate, or spontaneously turn into acetone. Most acetoacetate is reduced to beta-hydroxybutyrate, which serves to additionally ferry reducing electrons to the tissues, especially the brain, where they are stripped back off and used for metabolism.
* Acetone, which is generated through the decarboxylation of acetoacetate, either spontaneously or through the enzyme acetoacetate decarboxylase. It can then be further metabolized either by CYP2E1 into hydroxyacetone (acetol) and then via propylene glycol to pyruvate, lactate and acetate (usable for energy) and propionaldehyde, or via methylglyoxal to pyruvate and lactate.
* β-hydroxybutyrate (not technically a ketone according to IUPAC nomenclature) is generated through the action of the enzyme D-β-hydroxybutyrate dehydrogenase on acetoacetate. Upon entering the tissues, beta-hydroxybutyrate is converted by D-β-hydroxybutyrate dehydrogenase back to acetoacetate along with a proton and a molecule of NADH, the latter of which goes on to power the electron transport chain and other redox reactions. β-Hydroxybutyrate is the most abundant of the ketone bodies, followed by acetoacetate and finally acetone.
β-Hydroxybutyrate and acetoacetate can pass through membranes easily, and are therefore a source of energy for the brain, which cannot directly metabolize fatty acids. The brain receives 60-70% of its required energy from ketone bodies when blood glucose levels are low. These bodies are transported into the brain by monocarboxylate transporters 1 and 2. Therefore, ketone bodies are a way to move energy from the liver to other cells. The liver does not have the critical enzyme, succinyl CoA transferase, to process ketone bodies, and therefore cannot undergo ketolysis. The result is that the liver only produces ketone bodies, but does not use a significant amount of them. | 1 | Biochemistry |
Pacific West Coast Inorganic Lectureship, USA and Canada, 1985; Gold Medal "S. Cannizzaro", Italian Chemical Society, 1988; Doctorate "Honoris Causa", University of Fribourg (CH), 1989; Accademia dei Lincei Award in Chemistry, Italy, 1992; Ziegler-Natta Lecturer, Gesellschaft Deutscher Chemiker, Germany, 1994; Italgas European Prize for Research and Innovation, 1994; Centenary Lecturer, The Royal Chemical Society (U.K.), 1995; Porter Medal for Photochemistry, 2000; Prix Franco-Italien de la Société Française de Chimie, 2002; Grande Ufficiale dell’Ordine al Merito della Repubblica Italiana, 2006; Quilico Gold Metal, Organic Division, Italian Chemical Society, 2008; Honor Professor, East China University of Science and Technology of Shanghai, 2009; Blaise Pascal Medal, European Academy of Sciences, 2009; Rotary Club Galileo International Prize for scientific research, 2011; Nature Award for Mentoring in Science, 2013; Archiginnasio d’oro, Città di Bologna, 2016; Grand Prix de la Maison de la Chimie (France) 2016; Leonardo da Vinci Award, European Academy of Sciences, 2017; Nicholas J. Turro Award, Inter-American Photochemical Society, 2018; Cavaliere di Gran Croce della Repubblica Italiana per meriti scientifici, 2019; Primo Levi Award, Gesellschaft Deutscher Chemiker and Società Chimica Italiana, 2019; UNESCO-Russia Mendeleev Prize, 2021. | 5 | Photochemistry |
Battery leakage is the escape of chemicals, such as electrolytes, within an electric battery due to generation of pathways to the outside environment caused by factory or design defects, excessive gas generation, or physical damage to the battery. The leakage of battery chemical often causes destructive corrosion to the associated equipment and may pose a health hazard. | 8 | Metallurgy |
*Lecturer, 1952–53; assistant professor, 195658, Department of Chemistry, Dhaka University
*Professor, Department of Chemistry and Applied Chemistry, Rajshahi University, 195890
*Nuffield Fellow, Cambridge University, U.K. 196062
*Dean, Faculty of Science, Rajshahi University, 1972
*Commonwealth Senior Fellow, Cambridge University, U.K. 197374
*Member, University Grants Commission (UGC), 197476
*Vice Chancellor, University of Dhaka, 197683
*Fellow of Bangladesh Academy of Sciences, 1979
*Asia Foundation Fellowship, 1984
*President, Bangladesh Chemical Society, 198486
*Senior Advisor in Basic Sciences, UNESCO, New Delhi, 198590
*University of Asia Pacific, Dhaka, 199596
*President, The Rajshahi University Teachers Association
*Provost, Abdul Latif Hall, Rajshahi University
*Senior Researcher, American Association for the Advancement of Science Washington D.C. | 7 | Physical Chemistry |
Isothiocyanate and its linkage isomer thiocyanate are ligands in coordination chemistry. Thiocyanate is a more common ligand. | 0 | Organic Chemistry |
Concentration of rNTPs within the cell is 10 to 10 times higher than the concentration of dNTP. Thus, during DNA replication the higher concentration of rNTP poses a problem as it can be erroneously incorporated into the developing DNA strand by DNA polymerases. The usage of RNA primers during DNA replication is an example of a correct incorporation of rNTPs during the process. Although, overly long RNA primers can decrease the effectiveness of T7 DNA polymerase in incorporating dNTP into the growing strand and weaken the binding between T7 and the template DNA strand. Essentially as the RNA primer grows, these rNMP residues inhibit RNA synthesis, decrease dNTP incorporation efficiency, decrease affinity between the helicase, DNA polymerase and template DNA strand overall decreases productivity of the DNA-protein complex. rNMPs are rNTPs without a pyrophosphate group attached, 2 P. However, DNA polymerases have a method to prevent rNTP incorporation centered around the major distinguishing feature between ribose and deoxyribose sugar bases, that feature being the absence of a 2-OH on the deoxyribose. The use of a steric gate residue present on the DNA polymerase prevents incorporation of rNTP by creating a steric clash between an active site amino acid residue on the DNA polymerase and the 2-OH on the sugar base of the rNTP. This steric clash is absent when incorporating dNTP since the sugar base on dNTPs have a 2-H instead of a 2-OH. Specifically the amino acid tyrosine positioned at residue 416 in DNA polymerase serves as the steric residue gate to prevent rNTP incorporation while in RNA polymerase the presence of a stabilizing electrostatic interaction between the 2-OH on the ribose allows for correct incorporation into a growing RNA strand as opposed to dNTP incorporation. The results obtained from using changes in the free energy of the transition state of T7 DNA polymerase and RNA polymerase when binding to either dNTP or rNTP substrates support the above method of discriminating between rNTP and dNTP during their respective biological procedures. The presence of correct water binding during dNTP or rNTP incorporation is also necessary. However, a specific human DNA polymerase known as DNA polymerase η incorporates rNTPs into the developing DNA strand at points in which the template strand has lesions or is damaged. DNA polymerase η ensures that the rNTP being incorporated is complementary to the DNA residue of the template strand based on Watson and Crick base pairing rules. It overcomes the steric interference with the steric gate residue via propeller twist of to allow enough space for the 2-OH. Incorporation of the appropriate rNTP into the developing DNA strand allows for corrections to be done on segments of the DNA that are damaged or have lesions. | 1 | Biochemistry |
The use of iron isotopes may also have applications when studying potential evidence for life on other planets. The ability of microbes to utilize iron in their metabolisms makes it possible for organisms to survive in anoxic, iron-rich environments, such as Mars. Thus, the continual improvement of knowledge regarding the biological fractionations of iron observed on Earth can have applications when studying extraterrestrial samples in the future. While this field of research is still developing, this could provide evidence regarding whether a sample was generated as a result of biologic or abiologic processes depending on the isotopic fractionation. For example, it has been hypothesized that magnetite crystals found in Martian meteorites may have formed biologically as a result of their striking similarity to magnetite crystals produced by magnetotactic bacteria on Earth. Iron isotopes could be used to study the origin of the proposed "magnetofossils" and other rock formations on Mars. | 9 | Geochemistry |
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