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The primary application of proton-exchange membranes is in PEM fuel cells. These fuel cells have a wide variety of commercial and military applications including in the aerospace, automotive, and energy industries.
Early PEM fuel cell applications were focused within the aerospace industry. The then-higher capacity of fuel cells compared to batteries made them ideal as NASA's Project Gemini began to target longer duration space missions than had previously been attempted.
, the automotive industry as well as personal and public power generation are the largest markets for proton-exchange membrane fuel cells. PEM fuel cells are popular in automotive applications due to their relatively low operating temperature and their ability to start up quickly even in below-freezing conditions. As of March 2019 there were 6,558 fuel cell vehicles on the road in the United States, with the Toyota Mirai being the most popular model. PEM fuel cells have seen successful implementation in other forms of heavy machinery as well, with Ballard Power Systems supplying forklifts based on the technology. The primary challenge facing automotive PEM technology is the safe and efficient storage of hydrogen, currently an area of high research activity.
Polymer electrolyte membrane electrolysis is a technique by which proton-exchange membranes are used to decompose water into hydrogen and oxygen gas. The proton-exchange membrane allows for the separation of produced hydrogen from oxygen, allowing either product to be exploited as needed. This process has been used variously to generate hydrogen fuel and oxygen for life-support systems in vessels such as US and Royal Navy submarines. A recent example is the construction of a 20 MW Air Liquide PEM electrolyzer plant in Québec. Similar PEM-based devices are available for the industrial production of ozone. | 0 | Theoretical and Fundamental Chemistry |
# J.P. Thomas, A. Oladipo and M. Fallavier; 1988;B32: 354–359.
# J.P. Thomas, A. Oladipo and M. Fallavier; 1988; "Secondary Ion Emission Induced in Insulators: Analytical Applications"605-611.
# J.P. Thomas, A. Oladipo and M. Fallavier; 1989; "Collective Effects in the Desorption Process Induced by Hn+ Clusters near the Bohr's Velocity";
# J.P. Thomas, A. Oladipo and M. Fallavier; 1989; "Surface Profiling of Insulating Layers using Desorption Induced by Monatomic or Cluster Ions of Beam Diameter in the 5–10µm Range";
# A. Oladipo, M. Fallavier and J.P. Thomas; 1991; "Secondary Ion Emission from Cesium Salts under Megaelectronvolt Ion Bombardment: Comparative Study and Beam Secondary Effects";.
# B. Nsouli, P. Rumeau, H. Allali, B. Chabert, O. Debre, A. A. Oladipo, J. P. Soulier and J. P. Thomas; 1995; "Plasma Desorption Time-of-flight Mass Spectrometric Elucidation of the Mechanisms of Adhesion Enhancement between Plasma-treated PEEK-Carbon Composite and an Epoxyamine Adhesive";
# H. Allali, O. Debre, B. Lagrange, B. Nsouli, A. A. Oladipo and J. P. Thomas; 1995; "Spontaneous Desorption : A Controlled Phenomenon for Surface Analysis Application? Part I : New evidence for a sputtering process induced by a well localized field enhanced desorption";
# C. A Adesanmi, I. A. Tubosun, F. A. Balogun, and A. A. Oladipo; 1997; "Advantages of Combined IENAA and Ko-factor Technique in the Determination of U and Th Concentrations in Exploration Rock Samples";
# H. Allali, M. Ben Embarek, O. Debre, B. Nsouli, A. Oladipo, A. Roche and J. P. Thomas: 1997; "An HSF-SIMS Investigation of the Prephosphatation Contribution to the Phosphatation Process of Silicon Steel Surface"; Rapid Comm. Mass Spectr. 11 1377–1382.
# C. A. Adesanmi, F. A. Balogun, M. K. Fasasi, I. A. Tubosun, A. A. Oladipo; 2001; A semi- empirical formula for HPGe detector efficiency calibration; | 0 | Theoretical and Fundamental Chemistry |
Conformational proofreading or conformational selection is a general mechanism of molecular recognition systems, suggested by Yonatan Savir and Tsvi Tlusty, in which introducing an energetic barrier - such as a structural mismatch between a molecular recognizer and its target - enhances the recognition specificity and quality. Conformational proofreading does not require the consumption of energy and may therefore be used in any molecular recognition system. Conformational proofreading is especially useful in scenarios where the recognizer has to select the appropriate target among many similar competitors. Proteins evolve the capacity for conformational proofreading through fine-tuning their geometry, flexibility and chemical interactions with the target. | 1 | Applied and Interdisciplinary Chemistry |
Several natural ingredients are certified by the United States Environmental Protection Agency as insect repellents, namely catnip oil, oil of lemon eucalyptus (OLE) (and its active ingredient p-Menthane-3,8-diol), oil of citronella, and 2-Undecanone, which is usually produced synthetically but has also been isolated from many plant sources.
Many other studies have also investigated the potential of natural compounds from plants as insect repellents. Moreover, there are many preparations from naturally occurring sources that have been used as a repellent to certain insects. Some of these act as insecticides while others are only repellent. Below is a list of some natural products with repellent activity:
* Achillea alpina (mosquitos)
* alpha-terpinene (mosquitos)
* Andrographis paniculata extracts (mosquito)
* Basil
** Sweet basil (Ocimum basilicum)
* Breadfruit (Insect repellent, including mosquitoes)
* Callicarpa americana (beautyberry)
* Camphor (mosquitoes)
* Carvacrol (mosquitos)
* Castor oil (Ricinus communis) (mosquitos)
* Catnip oil (Nepeta species) (nepetalactone against mosquitos)
* Cedar oil (mosquitos, moths)
* Celery extract (Apium graveolens) (mosquitos) In clinical testing an extract of celery was demonstrated to be at least equally effective to 25% DEET, although the commercial availability of such an extract is not known.
* Cinnamon (leaf oil kills mosquito larvae)
* Citronella oil (repels mosquitos) (contains insect repelling substances, such as citronellol and geraniol)
* Clove oil (mosquitos)
* D-Limonene (ticks, fleas, flies, mosquitoes, and other insects) (widely used in insect repellents for pets)
* Eucalyptus oil (70%+ eucalyptol), (cineol is a synonym), mosquitos, flies, dust mites In the U.S., eucalyptus oil was first registered in 1948 as an insecticide and miticide.
* Fennel oil (Foeniculum vulgare) (mosquitos)
* Garlic (Allium sativum) (Mosquito, rice weevil, wheat flour beetle)
* Geranium oil (also known as Pelargonium graveolens)
* Hinokitiol (ticks, mosquitos, larvae)
* Lavender (ineffective alone, but measurable effect in certain repellent mixtures)
* Lemon eucalyptus (Corymbia citriodora) essential oil and its active ingredient p-menthane-3,8-diol (PMD)
* Lemongrass oil (Cymbopogon species) (mosquitos)
** East-Indian lemon grass (Cymbopogon flexuosus)
* Linalool (ticks, fleas, mites, mosquitoes, spiders, cockroach)
* Marjoram (spider mites Tetranychus urticae and Eutetranychus orientalis)
* Mint (menthol is active chemical.) (Mentha sp.)
* Neem oil (Azadirachta indica) (Repels or kills mosquitos, their larvae and a plethora of other insects including those in agriculture)
* Nootkatone (ticks, mosquitoes and other insects)
* Oleic acid, repels bees and ants by simulating the "smell of death" produced by their decomposing corpses.
* Pennyroyal (Mentha pulegium) (mosquitos, fleas,) but very toxic to pets
* Peppermint (Mentha x piperita) (mosquitos)
* Pyrethrum (from Chrysanthemum species, particularly C. cinerariifolium and C. coccineum)
* Rosemary (Rosmarinus officinalis) (mosquitos)
* Spanish Flag (Lantana camara) (against Tea Mosquito Bug, Helopeltis theivora)
* Tea tree oil from the leaves of Melaleuca alternifolia
* Thyme (Thymus species) (mosquitos)
* Yellow nightshade (Solanum villosum), berry juice (against Stegomyia aegypti mosquitos) | 1 | Applied and Interdisciplinary Chemistry |
In his 2016 Handbook of Synthetic Organic Chemistry, Michael Pirrung wrote that yield is one of the primary factors synthetic chemists must consider in evaluating a synthetic method or a particular transformation in "multistep syntheses." He wrote that a yield based on recovered starting material (BRSM) or (BORSM) does not provide the theoretical yield or the "100% of the amount of product calculated", that is necessary in order to take the next step in the multistep systhesis.
Purification steps always lower the yield, through losses incurred during the transfer of material between reaction vessels and purification apparatus or imperfect separation of the product from impurities, which may necessitate the discarding of fractions deemed insufficiently pure. The yield of the product measured after purification (typically to >95% spectroscopic purity, or to sufficient purity to pass combustion analysis) is called the isolated yield of the reaction. | 0 | Theoretical and Fundamental Chemistry |
An enhancer near the gene GADD45g has been described that may regulate brain growth in chimpanzees and other mammals, but not in humans. The GADD45G regulator in mice and chimps is active in regions of the brain where cells that form the cortex, ventral forebrain, and thalamus are located and may suppress further neurogenesis. Loss of the GADD45G enhancer in humans may contribute to an increase of certain neuronal populations and to forebrain expansion in humans. | 1 | Applied and Interdisciplinary Chemistry |
Another approach of preparing carbenes has relied on the desulfurisation of thioureas with potassium in THF. A contributing factor to the success of this reaction is that the byproduct, potassium sulfide, is insoluble in the solvent. The elevated temperatures suggest that this method is not suitable for the preparation of unstable dimerising carbenes. A single example of the deoxygenation of a urea with a fluorene derived carbene to give the tetramethyldiaminocarbene and fluorenone has also been reported:
The desulfurisation of thioureas with molten potassium to give imidazol-2-ylidenes or diaminocarbenes has not been widely used. The method was used to prepare dihydroimidazole carbenes. | 0 | Theoretical and Fundamental Chemistry |
E-AB biosensors as basis for controlled drug delivery. Feedback-controlled drug delivery for continuous drug administration with dosage levels based on integrating E-AB signal calculations into a drug administering medical device. E-AB biosensors do not require reagents, are inexpensive compared to antibody detection methods, can be used in blood or other fluids with high abundance of non-target molecules, and they are reusable. These are all factors that make E-AB biosensors a promising method for feedback-controlled drug delivery dependent on integrated calculations of computer programming. | 0 | Theoretical and Fundamental Chemistry |
The condition to get a partially ideal solution on mixing is that the volume of the resulting mixture V to equal double the volume V of each solution mixed in equal volumes due to the additivity of volumes. The resulting volume can be found from the mass balance equation involving densities of the mixed and resulting solutions and equalising it to 2:
implies
Of course for real solutions inequalities appear instead of the last equality. | 0 | Theoretical and Fundamental Chemistry |
Optical tweezers (originally called single-beam gradient force trap) are scientific instruments that use a highly focused laser beam to hold and move microscopic and sub-microscopic objects like atoms, nanoparticles and droplets, in a manner similar to tweezers. If the object is held in air or vacuum without additional support, it can be called optical levitation.
The laser light provides an attractive or repulsive force (typically on the order of piconewtons), depending on the relative refractive index between particle and surrounding medium. Levitation is possible if the force of the light counters the force of gravity. The trapped particles are usually micron-sized, or even smaller. Dielectric and absorbing particles can be trapped, too.
Optical tweezers are used in biology and medicine (for example to grab and hold a single bacterium, a cell like a sperm cell or a blood cell, or a molecule like DNA), nanoengineering and nanochemistry (to study and build materials from single molecules), quantum optics and quantum optomechanics (to study the interaction of single particles with light). The development of optical tweezing by Arthur Ashkin was lauded with the 2018 Nobel Prize in Physics. | 1 | Applied and Interdisciplinary Chemistry |
Glucuronidation consists of transfer of the glucuronic acid component of uridine diphosphate glucuronic acid to a substrate by any of several types of UDP-glucuronosyltransferase.
UDP-glucuronic acid (glucuronic acid linked via a glycosidic bond to uridine diphosphate) is an intermediate in the process and is formed in the liver. One example is the N-glucuronidation of an aromatic amine, 4-aminobiphenyl, by UGT1A4 or UGT1A9 from human, rat, or mouse liver.
The substances resulting from glucuronidation are known as glucuronides (or glucuronosides) and are typically much more water-soluble than the non-glucuronic acid-containing substances from which they were originally synthesised. The human body uses glucuronidation to make a large variety of substances more water-soluble, and, in this way, allow for their subsequent elimination from the body through urine or feces (via bile from the liver). Hormones are glucuronidated to allow for easier transport around the body. Pharmacologists have linked drugs to glucuronic acid to allow for more effective delivery of a broad range of potential therapeutics. Sometimes toxic substances are also less toxic after glucuronidation.
The conjugation of xenobiotic molecules with hydrophilic molecular species such as glucuronic acid is known as phase II metabolism. | 0 | Theoretical and Fundamental Chemistry |
BMT is the first company registered in European Feed Materials Register for the production and sale of laboratory-grown meat for pet food; specifically cat and dog food. BMT claims to be the only entity in the world that can produce and sell this product for the pet food market. By 2024, BMT plans to make several metric tons per day of laboratory-grown meat meant for pet food. | 1 | Applied and Interdisciplinary Chemistry |
Progesterone binds extensively to plasma proteins, including albumin (50–54%) and transcortin (43–48%). It has similar affinity for albumin relative to the PR. | 0 | Theoretical and Fundamental Chemistry |
*2002 Jean Jeener. Contribution: Multi-dimensional Fourier NMR spectroscopy.
*2004 Erwin L. Hahn. Contribution: Spin echo phenomena and experiments.
*2005 Nicolaas Bloembergen. Contribution: Nuclear magnetic relaxation.
*2006 John S. Waugh. Contribution: Average Hamiltonian theory.
*2007 Alfred G. Redfield. Contribution: Relaxation Theory.
*2008 Alexander Pines. Contribution: Cross-polarization method for NMR in solids.
*2009 Albert W. Overhauser. Contribution: Nuclear Overhauser effect (NOE).
*2010 Martin Karplus. Contribution: Karplus equation.
*2011 Gareth A. Morris. Contribution: INEPT pulse sequence.
*2012 Ray Freeman and Weston A. Anderson. Contribution: Double resonance.
*2013 Lucio Frydman. Contribution: Ultrafast NMR.
*2014 Ad Bax. Contribution: Homonuclear broad band decoupled absorption spectra.
*2015 Malcolm Levitt. Contribution: Composite pulses. | 0 | Theoretical and Fundamental Chemistry |
Pliny reports the use of sarcocolla in creating paints and as a medicine.
Dioscorides and Galenus mention its power of healing wounds.
The 8th century philosopher Al-Kindi used sarcocolla as a component of many recipes in his medical formulary Akrabadhin, among others for leprosy.
The most detailed description is given by the 13th century botanist and pharmacologist Ibn al-Baytar on the basis of Greek and Arabic sources as well as his own observations. The resin consumes the festering flesh of putrescent abscesses, assists the ripening of tumours, carries away mucus and yellow gall, and is a remedy for inflammations of the eye, for agglutinating eyelids and for excessive secretion of the eye. Taken internally, the resin is a strong purgative, but causes also the hair to fall out. The best sarcocolla consists of crushed, white seeds, mixed with walnut oil. Measured out in different ways, it can be mingled with other drugs (sagapenum, myrobalanum, aloes, bdellium, etc.). When taken neat, the resin can be lethal; therefore, the dose should not be more than 2¼ dirhams. Ibn al-Baytar, however, maintains that he saw in Egypt women partaking, immediately after a bath, of up to 4 ounces of anzarūt, together with the pulp of the yellow melon, hoping to increase thus their corpulence.
According to the c. 13th-century ("Book of Fires") of Marcus Graecus, sarcocolla was an ingredient of Greek Fire.
The 16th-century surgeon Brunus of Calabria recommended a plaster for skull fractures consisting of sarcocolla, bitter vetch meal, dragon's blood, and myrrh. | 1 | Applied and Interdisciplinary Chemistry |
The PI3K/AKT pathway has a natural inhibitor called Phosphatase and tensin homolog (PTEN) whose function is to limit proliferation in cells, helping to prevent cancer. Knocking out PTEN has been shown to increase the mass of the brain because of the unregulated proliferation that occurs.
PTEN works by dephosphorylating PIP3 to PIP2 which limits AKTs ability to bind to the membrane, decreasing its activity. PTEN deficiencies can be compensated downstream to rescue differentiation or quiescence. Knocking out PTEN is not as serious as knocking out FOXO for this reason. | 1 | Applied and Interdisciplinary Chemistry |
In 2009, Larhlimi and Bockmayr presented a new approach called "minimal metabolic behaviors" for the analysis of metabolic networks. Like elementary modes or extreme pathways, these are uniquely determined by the network, and yield a complete description of the flux cone. However, the new description is much more compact. In contrast with elementary modes and extreme pathways, which use an inner description based on generating vectors of the flux cone, MMBs are using an outer description of the flux cone. This approach is based on sets of non-negativity constraints. These can be identified with irreversible reactions, and thus have a direct biochemical interpretation. One can characterize a metabolic network by MMBs and the reversible metabolic space. | 1 | Applied and Interdisciplinary Chemistry |
Air cylinders are available in a variety of sizes and can typically range from a small air cylinder, which might be used for picking up a small transistor or other electronic component, to diameter air cylinders which would impart enough force to lift a car. Some pneumatic cylinders reach in diameter, and are used in place of hydraulic cylinders for special circumstances where leaking hydraulic oil could impose an extreme hazard. | 1 | Applied and Interdisciplinary Chemistry |
Ion-exchange membranes are traditionally used in electrodialysis or diffusion dialysis by means of an electrical potential or concentration gradient, respectively, to selectively transport cationic and anionic species. When applied in an electrodialysis desalination process, anion- and cation-exchange membranes are typically arranged in an alternating pattern between two electrodes (an anode and a cathode) within the electrodialysis stack. A galvanic potential is supplied as a voltage generated at the electrodes.
A typical industrial electrodialysis stack consists of two chambers: a product-water chamber and a concentrate-reject chamber. During stack operation, salts are transferred from the product to the concentrate. As a result, the reject stream is concentrated up while the product stream is desalted.
Exemplary applications of ion-exchange membranes utilized in electrodialysis and EDR include seawater desalination, industrial wastewater treatment of highly scaling waters, food and beverage production, and other industrial wastewaters. | 0 | Theoretical and Fundamental Chemistry |
Antibubbles are a common but widely unrecognized phenomenon, in part because of their resemblance to air bubbles, and in part because of their typically transient, or short-lived, nature. With certain (soapy) solutions, they can be made to last much longer.
Antibubbles can be created by allowing a tap to drip into a container of water to which a drop or two of soap has been added. They have all been produced aided by an ultrasound contrast agent. Being inherently unstable, they are difficult to form.
The soap reduces the water's surface tension and allows the skin of air surrounding the droplet to remain in place for more than just a fraction of a second. As antibubbles can be easily created at home, they have attracted attention from popular science magazines.
Just as soap bubbles, with air inside and air outside, have negative buoyancy and tend to sink towards the ground, so antibubbles, with water inside and air outside have positive buoyancy and tend to rise towards the water surface. But again, just as soap bubbles can be filled with a lighter gas to give them positive buoyancy, so antibubbles can be filled with a heavier liquid to give them negative buoyancy. Using a drinking straw to drop droplets of sugar solution onto soapy water will produce antibubbles that sink.
Antibubbles usually pop when they touch the bottom or the side of the vessel containing the liquid. This can be prevented by tipping a few teaspoons of sugar into the soapy water and giving it some time to dissolve (but without stirring it). This will produce a denser layer of sugary water at the bottom of the container. Antibubbles made from sugar solution will then sink through the water and rest on top of the denser layer at the bottom. Antibubbles made this way can last for several minutes.
The layers of an antibubble are water, which it is submerged in, air, and the water trapped in the air. | 1 | Applied and Interdisciplinary Chemistry |
Butyrate has been shown to be a critical mediator of the colonic inflammatory response. It is responsible for about 70% of energy from the colonocytes, being a critical SCFA in colon homeostasis. Butyrate possesses both preventive and therapeutic potential to counteract inflammation-mediated ulcerative colitis (UC) and colorectal cancer. It produces different effects in healthy and cancerous cells: this is known as the "butyrate paradox". In particular, butyrate inhibits colonic tumor cells and stimulates proliferation of healthy colonic epithelial cells. The explanation why butyrate is an energy source for normal colonocytes and induces apoptosis in colon cancer cells, is the Warburg effect in cancer cells, which leads to butyrate not being properly metabolized. This phenomenon leads to the accumulation of butyrate in the nucleus, acting as a histone deacetylase (HDAC) inhibitor. One mechanism underlying butyrate function in suppression of colonic inflammation is inhibition of the IFN-γ/STAT1 signalling pathways. It has been shown that butyrate inhibits activity of HDAC1 that is bound to the Fas gene promoter in T cells, resulting in hyperacetylation of the Fas promoter and upregulation of Fas receptor on the T cell surface. It is thus suggested that butyrate enhances apoptosis of T cells in the colonic tissue and thereby eliminates the source of inflammation (IFN-γ production). Butyrate inhibits angiogenesis by inactivating Sp1 transcription factor activity and downregulating vascular endothelial growth factor gene expression.
In summary, the production of volatile fatty acids such as butyrate from fermentable fibers may contribute to the role of dietary fiber in colon cancer. Short-chain fatty acids, which include butyric acid, are produced by beneficial colonic bacteria (probiotics) that feed on, or ferment prebiotics, which are plant products that contain dietary fiber. These short-chain fatty acids benefit the colonocytes by increasing energy production, and may protect against colon cancer by inhibiting cell proliferation.
Conversely, some researchers have sought to eliminate butyrate and consider it a potential cancer driver. Studies in mice indicate it drives transformation of MSH2-deficient colon epithelial cells. | 1 | Applied and Interdisciplinary Chemistry |
In June 2010, it was revealed that a phase II study of armodafinil as an adjunctive therapy in adults with schizophrenia had failed to meet the primary endpoints, and the clinical program was subsequently terminated. However, a study published later that year showed that patients with schizophrenia treated with armodafinil showed fewer of the negative symptoms of schizophrenia. | 0 | Theoretical and Fundamental Chemistry |
Unlike stationary normal shockwaves, moving normal shockwaves are more commonly available in physical situations. For example, a blunt object entering into the atmosphere faces a shock that comes through the medium of a non-moving gas. The fundamental problem that comes through moving normal shockwaves is the moment of a normal shockwave through motionless gas. The viewpoint of the moving shockwaves characterizes it as a moving or non-moving shock wave. The example of an object entering into the atmosphere depicts an object traveling in the opposite direction of the shockwave resulting in a moving shockwave, but if the object was launching into space, riding on top of the shockwave, it would appear to be a stationary shockwave. The relations and comparisons along with speed and shock ratios of moving and stationary shockwaves can be calculated through extensive formulas. | 1 | Applied and Interdisciplinary Chemistry |
* Birch, Alan. Economic History of the British Iron and Steel Industry (Routledge, 2013).
* Burn, D. L. “Recent Trends in the History of the Steel Industry.” Economic History Review, 17#2 1947, pp. 95–102. [https://www.jstor.org/stable/2590552 online].
* Burn, Duncan. The Steel Industry, 1939–1959: A Study in Competition and Planning (1961)
* Burn, Duncan. The Economic History of Steelmaking, 1867–1939: A Study in Competition. Cambridge University Press, 1961
* Carr, J. C. and W. Taplin; History of the British Steel Industry Harvard University Press, 1962
* Tweedale, Geoffrey. Steel City: Entrepreneurship, Strategy, and Technology in Sheffield, 1743–1993. (Oxford U.P. 1995)
* Vaizy, John. The history of British steel (1974), well illustrated
* Warren, Kenneth. British Iron and Sheet Steel Industry since 1840 (1970) Economic geography. | 1 | Applied and Interdisciplinary Chemistry |
The fluorescence quantum yield is defined as the ratio of the number of photons emitted to the number of photons absorbed.
Fluorescence quantum yield is measured on a scale from 0 to 1.0, but is often represented as a percentage. A quantum yield of 1.0 (100%) describes a process where each photon absorbed results in a photon emitted. Substances with the largest quantum yields, such as rhodamines, display the brightest emissions; however, compounds with quantum yields of 0.10 are still considered quite fluorescent.
Quantum yield is defined by the fraction of excited state fluorophores that decay through fluorescence:
where
* is the fluorescence quantum yield,
* is the rate constant for radiative relaxation (fluorescence),
* is the rate constant for all non-radiative relaxation processes.
Non-radiative processes are excited state decay mechanisms other than photon emission, which include: Förster resonance energy transfer, internal conversion, external conversion, and intersystem crossing. Thus, the fluorescence quantum yield is affected if the rate of any non-radiative pathway changes. The quantum yield can be close to unity if the non-radiative decay rate is much smaller than the rate of radiative decay, that is .
Fluorescence quantum yields are measured by comparison to a standard of known quantum yield. The quinine salt quinine sulfate in a sulfuric acid solution was regarded as the most common fluorescence standard, however, a recent study revealed that the fluorescence quantum yield of this solution is strongly affected by the temperature, and should no longer be used as the standard solution. The quinine in 0.1M perchloric acid ( 0.60) shows no temperature dependence up to 45 °C, therefore it can be considered as a reliable standard solution.
Experimentally, relative fluorescence quantum yields can be determined by measuring fluorescence of a fluorophore of known quantum yield with the same experimental parameters (excitation wavelength, slit widths, photomultiplier voltage etc.) as the substance in question. The quantum yield is then calculated by:
where
* is the quantum yield,
* is the area under the emission peak (on a wavelength scale),
* is absorbance (also called "optical density") at the excitation wavelength,
* is the refractive index of the solvent.
The subscript denotes the respective values of the reference substance. The determination of fluorescence quantum yields in scattering media requires additional considerations and corrections. | 0 | Theoretical and Fundamental Chemistry |
Ali Musa oglu Guliyev (31 May 1912, Yelizavetpol – 29 January 1989, Baku) was a Soviet and Azerbaijani scientist. | 0 | Theoretical and Fundamental Chemistry |
Odours may be a kind of male "ornament" selected for by female choice. They meet the criteria for such ornaments that Charles Darwin set out in The Descent of Man, and Selection in Relation to Sex. After many years of study the importance of such chemical communication is becoming clear.
Males usually compete for scarce females, which make adaptive choices based on male traits. The choice can benefit the female directly and/or genetically. In tiger moths (Utetheisa ornatrix), females choose the males that produce the most pheromone; an honest signal of the amount of protective alkaloids the male has, as well as an indicator of the size of female offspring (females fertilised by such males lay more eggs). Male cockroaches form dominance hierarchies based on pheromone "badges", while females use the same pheromone for male choice.
In most species, pheromones are released by the non-limiting sex. Some female moths signal, but this is cheap and low risk; it means the male has to fly to her, taking a high risk. This mirrors communication with other sensory modalities, e.g. male frogs croak; male birds are usually colourful. Male long-range pheromone signals may be associated with patchy resources for the female. In some species, both sexes signal. Males can sometimes attract other males instead, the sex pheromone acting as an aggregation pheromone. | 1 | Applied and Interdisciplinary Chemistry |
Conjugated polymers, such as polyfluorene, can be designed and synthesized with different properties for a wide variety of applications. The color of the molecules can be designed through synthetic control over the electron donating or withdrawing character of the substituents on fluorene or the comonomers in polyfluorene.
Solubility of the polymers are important because solution state processing is very common. Since conjugated polymers, with their planar structure, tend to aggregate, bulky side chains are added (to the 9 position of fluorene) to increase the solubility of the polymer. | 0 | Theoretical and Fundamental Chemistry |
Secreted abundant heat soluble (SAHS) proteins are similar to fatty acid-binding proteins, notably in their structure with an antiparallel beta-barrel and internal fatty acid binding pocket. SAHS proteins are often secreted into media and associated with special extracellular structures. Dried tardigrades have an abundance of secretory cells which are not found in hydrated individuals. The mechanism behind SAHS proteins has not yet been determined, but the presence of secretory cells only during desiccation suggests they are used to protect cells during periods of dehydration. | 1 | Applied and Interdisciplinary Chemistry |
Nanocomposite hydrogels are tough, and can withstand stretching, bending, knotting, crushing, and other modifications. | 0 | Theoretical and Fundamental Chemistry |
*Invention of the multiple-effect evaporator for processing sugar by Norbert Rillieux in 1846
*Discovery of Vitamin C by Albert Szent-Györgyi between 1930 and 1936
*Noyes Laboratory at the University of Illinois at Urbana Champaign, named for chemist William A. Noyes and opened in 1902
*Development of occupational medicine by Alice Hamilton at Hull House between 1897 and 1935
*Research on the quality and stability of frozen foods conducted at the USDA-ARS Western Regional Research Center between 1948 and 1965 | 1 | Applied and Interdisciplinary Chemistry |
Diethylzinc (CH)Zn, or DEZ, is a highly pyrophoric and reactive organozinc compound consisting of a zinc center bound to two ethyl groups. This colourless liquid is an important reagent in organic chemistry. It is available commercially as a solution in hexanes, heptane, or toluene, or as a pure liquid. | 0 | Theoretical and Fundamental Chemistry |
Version 1.0 of Rfam was launched in 2003 and contained 25 ncRNA families and annotated about 50 000 ncRNA genes. In 2005, version 6.1 was released and contained 379 families annotating over 280 000 genes. In August 2012, version 11.0 contained 2208 RNA families, while the current version (14.9, released in November 2022) annotates 4108 families. | 1 | Applied and Interdisciplinary Chemistry |
Copy number variation was initially thought to occupy an extremely small and negligible portion of the genome through cytogenetic observations. Copy number variations were generally associated only with small tandem repeats or specific genetic disorders, therefore, copy number variations were initially only examined in terms of specific loci. However, technological developments led to an increasing number of highly accurate ways of identifying and studying copy number variations. Copy number variations were originally studied by cytogenetic techniques, which are techniques that allow one to observe the physical structure of the chromosome. One of these techniques is fluorescent in situ hybridization (FISH) which involves inserting fluorescent probes that require a high degree of complementarity in the genome for binding. Comparative genomic hybridization was also commonly used to detect copy number variations by fluorophore visualization and then comparing the length of the chromosomes. One major drawback of these early techniques is that the genomic resolution is relatively low and only large repeats such as whole gene repeats can be detected.
Recent advances in genomics technologies gave rise to many important methods that are of extremely high genomic resolution and as a result, an increasing number of copy number variations in the genome have been reported. Initially these advances involved using bacterial artificial chromosome (BAC) array with around 1 megabase of intervals throughout the entire gene, BACs can also detect copy number variations in rearrangement hotspots allowing for the detection of 119 novel copy number variations. High throughput genomic sequencing has revolutionized the field of human genomics and in silico studies have been performed to detect copy number variations in the genome. Reference sequences have been compared to other sequences of interest using fosmids by strictly controlling the fosmid clones to be 40kb. Sequencing end reads would provide adequate information to align the reference sequence to the sequence of interest, and any misalignments are easily noticeable thus concluded to be copy number variations within that region of the clone. This type of detection technique offers a high genomic resolution and precise location of the repeat in the genome, and it can also detect other types of structural variation such as inversions.
In addition, another way of detecting copy number variation is using single nucleotide polymorphisms (SNPs). Due to the abundance of the human SNP data, the direction of detecting copy number variation has changed to utilize these SNPs. Relying on the fact that human recombination is relatively rare and that many recombination events occur in specific regions of the genome known as recombination hotspots, linkage disequilibrium can be used to identify copy number variations. Efforts have been made in associating copy number variations with specific haplotype SNPs by analyzing the linkage disequilibrium, using these associations, one is able to recognize copy number variations in the genome using SNPs as markers. Next-generation sequencing techniques including short and long read sequencing are nowadays increasingly used and have begun to replace array-based techniques to detect copy number variations. In contrast to array-based techniques, sequencing-based detection methods readily identify other classes of structural variation such as inversions and translocations. | 1 | Applied and Interdisciplinary Chemistry |
In environmental terms, the residence time definition is adapted to fit with ground water, the atmosphere, glaciers, lakes, streams, and oceans. More specifically it is the time during which water remains within an aquifer, lake, river, or other water body before continuing around the hydrological cycle. The time involved may vary from days for shallow gravel aquifers to millions of years for deep aquifers with very low values for hydraulic conductivity. Residence times of water in rivers are a few days, while in large lakes residence time ranges up to several decades. Residence times of continental ice sheets is hundreds of thousands of years, of small glaciers a few decades.
Ground water residence time applications are useful for determining the amount of time it will take for a pollutant to reach and contaminate a ground water drinking water source and at what concentration it will arrive. This can also work to the opposite effect to determine how long until a ground water source becomes uncontaminated via inflow, outflow, and volume. The residence time of lakes and streams is important as well to determine the concentration of pollutants in a lake and how this may affect the local population and marine life.
Hydrology, the study of water, discusses the water budget in terms of residence time. The amount of time that water spends in each different stage of life (glacier, atmosphere, ocean, lake, stream, river), is used to show the relation of all of the water on the earth and how it relates in its different forms. | 0 | Theoretical and Fundamental Chemistry |
Contrary to the abundance of theoretical and experimental work on the MPI of rare gas atoms, the amount of research on the prediction of the rate of MPI of neutral molecules was scarce until recently. Walsh et al. have measured the MPI rate of some diatomic molecules interacting with a CO laser. They found that these molecules are tunnel-ionized as if they were structureless atoms with an ionization potential equivalent to that of the molecular ground state. A. Talebpour et al. were able to quantitatively fit the ionization yield of diatomic molecules interacting with a Ti:sapphire laser pulse. The conclusion of the work was that the MPI rate of a diatomic molecule can be predicted from the PPT model by assuming that the electron tunnels through a barrier given by instead of barrier which is used in the calculation of the MPI rate of atoms. The importance of this finding is in its practicality; the only parameter needed for predicting the MPI rate of a diatomic molecule is a single parameter, . Using the semi-empirical model for the MPI rate of unsaturated hydrocarbons is feasible. This simplistic view ignores the ionization dependence on orientation of molecular axis with respect to polarization of the electric field of the laser, which is determined by the symmetries of the molecular orbitals. This dependence can be used to follow molecular dynamics using strong field multiphoton ionization. | 0 | Theoretical and Fundamental Chemistry |
Biopanning is an affinity selection technique which selects for peptides that bind to a given target. All peptide sequences obtained from biopanning using combinatorial peptide libraries have been stored in a special freely available database named [http://i.uestc.edu.cn/bdb BDB]. This technique is often used for the selection of antibodies too.
Biopanning involves 4 major steps for peptide selection. The first step is to have phage display libraries prepared. This involves inserting foreign desired gene segments into a region of the bacteriophage genome, so that the peptide product will be displayed on the surface of the bacteriophage virion. The most often used are genes pIII or pVIII of bacteriophage M13.
The next step is the capturing step. It involves conjugating the phage library to the desired target. This procedure is termed panning. It utilizes the binding interactions so that only specific peptides presented by bacteriophage are bound to the target. For example, selecting antibody presented by bacteriophage with coated antigen in microtiter plates.
The washing step comes after the capturing step to wash away the unbound phages from solid surface. Only the bound phages with strong affinity are kept. The final step involves the elution step where the bound phages are eluted through changing of pH or other environment conditions.
The end result is the peptides produced by bacteriophage are specific. The resulting filamentous phages can infect gram-negative bacteria once again to produce phage libraries. The cycle can occur many times resulting with strong affinity binding peptides to the target. | 1 | Applied and Interdisciplinary Chemistry |
At the start of the 20th century, scientists had become interested in the stability of colloids, both the dispersions of solid particles and the solutions of polymeric molecules. It was known that salts and temperature could often be used to cause flocculation of a colloid. The German chemist F.W. Tiebackx reported in 1911 that flocculation could also be induced in certain polymer solutions by mixing them together. In particular, he reported the observation of opalescence (a turbid mixture) when equal volumes of acidified 0.5% “washed” gelatine solution, and 2% gum arabic solution were mixed. Tiebackx did not further analyse the nature of the flocs, but it is likely that this was an example of complex coacervation.
Dutch chemist H. G. Bungenberg-de Jong reported in his PhD thesis (Utrecht, 1921) two types of flocculation in agar solutions: one that leads to a suspensoid state, and one that leads to an emulsoid state. He observed the emulsoid state under the microscope and described small particles that merged into larger particles (Thesis, p. 82), most likely a description of coalescing coacervate droplets. Several years later, in 1929, Bungenberg-de Jong published a seminal paper with his PhD advisor, H. R. Kruyt, entitled “Coacervation. Partial miscibility in colloid systems”. In their paper, they give many more examples of colloid systems that flocculate into an emulsoid state, either by varying the temperature, by adding salts, co-solvents or by mixing together two oppositely charged polymer colloids, and illustrate their observations with the first microscope pictures of coacervate droplets. They term this phenomenon coacervation, derived from the prefix co and the Latin word acervus (heap), which relates to the dense liquid droplets. Coacervation is thus loosely translated as ‘to come together in a heap’. Since then, Bungenberg-de Jong and his research group in Leiden published a range of papers on coacervates, including results on self-coacervation, salt effects, interfacial tension, multiphase coacervates and surfactant-based coacervates.
In the meantime, Russian chemist Alexander Oparin, published a pioneering work in which he laid out his protocell theory on the origin of life. In his initial protocell model, Oparin took inspiration from Graham's description of colloids from 1861 as substances that usually give cloudy solutions and cannot pass through membranes. Oparin linked these properties to the protoplasm, and reasoned that precipitates of colloids form as clots or lumps of mucus or jelly, some of which have structural features that resemble the protoplasm. According to Oparin, protocells could therefore have formed by precipitation of colloids. In his later work, Oparin became more specific about his protocell model. He described the work of Bungenberg-de Jong on coacervates in his book from 1938, and postulated that the first protocells were coacervates.
Other researchers followed, and in the 1930s and 1940s various examples of coacervation were reported, by Bungenberg-de Jong, Oparin, Koets, Bank, Langmuir and others. In the 1950s and 1960s, focus shifted to a theoretical description of the phenomenon of (complex) coacervation. Voorn and Overbeek developed the first mean-field theory to describe coacervation. They estimated the total free energy of mixing as a sum of mixing entropy terms and mean-field electrostatic interactions in a Debye-Hückel approximation. Veis and Aranyi suggested to extend this model with an electrostatic aggregation step in which charge-paired symmetrical soluble aggregates are formed, followed by phase separation into liquid droplets.
In the decades after that, until about 2000, the scientific interest in coacervates had faded. Oparin's theory on the role of coacervates in the origin of life had been replaced by interest in the RNA world hypothesis. Renewed interest in coacervates originated as scientists recognized the relevance and versatility of the interactions that underlie complex coacervation in the natural fabrication of biological materials and in their self-assembly.
Since 2009, coacervates have become linked to membraneless organelles and there has been a renewed interest in coacervates as protocells. | 0 | Theoretical and Fundamental Chemistry |
Boyle's law states that:
The concept can be represented with these formulae:
*, meaning "Volume is inversely proportional to Pressure", or
*, meaning "Pressure is inversely proportional to Volume", or
*, or
where is the pressure, is the volume of a gas, and is the constant in this equation (and is not the same as the proportionality constants in the other equations). | 0 | Theoretical and Fundamental Chemistry |
In a cascade mediated by a GPCR known as β adrenoceptor, activated by catecholamines (notably norepinephrine), PKA gets activated and phosphorylates numerous targets, namely: L-type calcium channels, phospholamban, troponin I, myosin binding protein C, and potassium channels. This increases inotropy as well as lusitropy, increasing contraction force as well as enabling the muscles to relax faster. | 1 | Applied and Interdisciplinary Chemistry |
* TGFα is upregulated in some human cancers. It is produced in macrophages, brain cells, and keratinocytes, and induces epithelial development. It belongs to the EGF family.
* TGFβ exists in three known subtypes in humans, TGFβ1, TGFβ2, and TGFβ3. These are upregulated in Marfan's syndrome and some human cancers, and play crucial roles in tissue regeneration, cell differentiation, embryonic development, and regulation of the immune system. Isoforms of transforming growth factor-beta (TGF-β1) are also thought to be involved in the pathogenesis of pre-eclampsia. They belong to the transforming growth factor beta family. TGFβ receptors are single pass serine/threonine kinase receptors. | 1 | Applied and Interdisciplinary Chemistry |
Zirconia exists in the monoclinic, tetragonal or cubic crystal system depending on the temperature. The surface acidity and basicity of the oxide depends on the crystal structure and surface orientation. The surfaces of zirconia have hydroxyl groups, which can act as Brønsted acids or bases, and coordination-unsaturated ZrO acid base pairs which contribute to its overall acid–base properties. Adsorption studies have shown that monoclinic zirconia is more basic than tetragonal, as it forms stronger bonds with CO. Adsorption of CO shows that the tetragonal phase has more acidic Lewis acid sites than the monoclinic phase, but that it has a lower concentration of Lewis acid sites. | 0 | Theoretical and Fundamental Chemistry |
Pittacal was the first synthetic dyestuff to be produced commercially. It was accidentally discovered in 1832 by German chemist Carl Ludwig Reichenbach, who is also recognized as being the discoverer of kerosene, phenol, eupion, paraffin wax and creosote.
According to history, Reichenbach applied creosote to the wooden posts of his home, in order to drive away dogs who urinated on them. The strategy was ineffective, however, and he noted that the dogs urine reacted with creosote to form an intense dark blue deposit. He named the new substance píttacal (from Greek words tar and beautiful). He later succeeded in producing pure pittacal by treating beechwood tar with barium oxide and using alumina as a mordant to the dyes fabrics. Although sold commercially as a dyestuff, it did not fare well.
Eupittone (derived from eu- + pittacal + -one) is a yellow crystalline substance resembling aurin, and obtained by the oxidation of pittacal. It is also called also eupittonic acid or eupitton. | 1 | Applied and Interdisciplinary Chemistry |
The molecular mechanisms of CB-mediated changes to the membrane voltage have also been studied in detail. Cannabinoids reduce calcium influx by blocking the activity of voltage-dependent N-, P/Q- and L-type calcium channels. In addition to acting on calcium channels, activation of Gi/o and Gs, the two most commonly coupled G-proteins to cannabinoid receptors, has been shown to modulate potassium channel activity. Recent studies have found that CB activation specifically facilitates potassium ion flux through GIRKs, a family of potassium channels. Immunohistochemistry experiments demonstrated that CB is co-localized with GIRK and Kv1.4 potassium channels, suggesting that these two may interact in physiological contexts.
In the central nervous system, CB receptors influence neuronal excitability, reducing the incoming synaptic input.
This mechanism, known as presynaptic inhibition, occurs when a postsynaptic neuron releases endocannabinoids in retrograde transmission, which then bind to cannabinoid receptors on the presynaptic terminal. CB receptors then reduce the amount of neurotransmitter released, so that subsequent excitation in the presynaptic neuron results in diminished effects on the postsynaptic neuron. It is likely that presynaptic inhibition uses many of the same ion channel mechanisms listed above, although recent evidence has shown that CB receptors can also regulate neurotransmitter release by a non-ion channel mechanism, i.e., through Gi/o-mediated inhibition of adenylyl cyclase and protein kinase A.
Direct effects of CB receptors on membrane excitability have been reported, and strongly impact the firing of cortical neurons.
A series of behavioral experiments demonstrated that NMDAR, an ionotropic glutamate receptor, and the metabotropic glutamate receptors (mGluRs) work in concert with CB to induce analgesia in mice, although the mechanism underlying this effect is unclear. | 1 | Applied and Interdisciplinary Chemistry |
The ATP synthase isolated from bovine (Bos taurus) heart mitochondria is, in terms of biochemistry and structure, the best-characterized ATP synthase. Beef heart is used as a source for the enzyme because of the high concentration of mitochondria in cardiac muscle. Their genes have close homology to human ATP synthases.
Human genes that encode components of ATP synthases:
* ATP5A1
* ATP5B
* ATP5C1, ATP5D, ATP5E, ATP5F1, ATP5G1, ATP5G2, ATP5G3, ATP5H, ATP5I, ATP5J, ATP5J2, ATP5L, ATP5O
* MT-ATP6, MT-ATP8 | 0 | Theoretical and Fundamental Chemistry |
In 2021, SLR14 was reported to prevent infection in the lower respiratory tract and severe disease in an interferon type I (IFN-I)–dependent manner in mice. Immunodeficient mice with chronic SARS-CoV-2 infection experienced near-sterilizing innate immunity with no help from the adaptive immune system. | 1 | Applied and Interdisciplinary Chemistry |
Agarose gels are made from the natural polysaccharide polymers extracted from seaweed.
Agarose gels are easily cast and handled compared to other matrices because the gel setting is a physical rather than chemical change. Samples are also easily recovered. After the experiment is finished, the resulting gel can be stored in a plastic bag in a refrigerator.
Agarose gels do not have a uniform pore size, but are optimal for electrophoresis of proteins that are larger than 200 kDa. Agarose gel electrophoresis can also be used for the separation of DNA fragments ranging from 50 base pair to several megabases (millions of bases), the largest of which require specialized apparatus. The distance between DNA bands of different lengths is influenced by the percent agarose in the gel, with higher percentages requiring longer run times, sometimes days. Instead high percentage agarose gels should be run with a pulsed field electrophoresis (PFE), or field inversion electrophoresis.
"Most agarose gels are made with between 0.7% (good separation or resolution of large 5–10kb DNA fragments) and 2% (good resolution for small 0.2–1kb fragments) agarose dissolved in electrophoresis buffer. Up to 3% can be used for separating very tiny fragments but a vertical polyacrylamide gel is more appropriate in this case. Low percentage gels are very weak and may break when you try to lift them. High percentage gels are often brittle and do not set evenly. 1% gels are common for many applications." | 1 | Applied and Interdisciplinary Chemistry |
Glass-ceramic from the LAS-System is a mechanically strong material and can sustain repeated and quick temperature changes, and its smooth glass-like surface is easy to clean, therefore it is often used as a cooktop surface.
The material has a very low heat conduction coefficient, which means that it stays cool outside the cooking area. It can be made nearly transparent (15–20% loss in a typical cooktop) for radiation in the infrared wavelengths. In the visible range glass-ceramics can be transparent, translucent or opaque and even colored by coloring agents.
However, glass-ceramic is not totally unbreakable. Because it is still a brittle material as glass and ceramics are, it can be broken - in particular it is less robust than traditional cooktops made of steel or cast iron. There have been instances where users reported damage to their cooktops when the surface was struck with a hard or blunt object (such as a can falling from above or other heavy items).
, there are two major types of electrical stoves with cooktops made of glass-ceramic:
* A radiant heating stove uses coils or infrared halogen lamps as the heating elements. The surface of the glass-ceramic cooktop above the burner heats up, but the adjacent surface remains cool because of the low heat conduction coefficient of the material.
* An induction stove heats a metal pot's bottom directly through electromagnetic induction.
This technology is not entirely new, as glass-ceramic ranges were first introduced in the 1970s using Corningware tops instead of the more durable material used today. These first generation smoothtops were problematic and could only be used with flat-bottomed cookware as the heating was primarily conductive rather than radiative.
Compared to conventional kitchen stoves, glass-ceramic cooktops are relatively simple to clean, due to their flat surface. However, glass-ceramic cooktops can be scratched very easily, so care must be taken not to slide the cooking pans over the surface. If food with a high sugar content (such as jam) spills, it should never be allowed to dry on the surface, otherwise damage will occur.
For best results and maximum heat transfer, all cookware should be flat-bottomed and matched to the same size as the burner zone. | 0 | Theoretical and Fundamental Chemistry |
Open-celled metal foam, also called metal sponge, can be used in heat exchangers (compact electronics cooling, cryogen tanks, PCM heat exchangers), energy absorption, flow diffusion, scrubbers, flame arrestors, and lightweight optics. The high cost of the material generally limits its use to advanced technology, aerospace, and manufacturing.
Fine-scale open-cell foams, with cells smaller than can be seen unaided, are used as high-temperature filters in the chemical industry.
Metal foams are used in compact heat exchangers to increase heat transfer at the cost of reduced pressure. However, their use permits substantial reduction in physical size and fabrication costs. Most models of these materials use idealized and periodic structures or averaged macroscopic properties.
Metal sponge has very large surface area per unit weight and catalysts are often formed into metal sponge, such as palladium black, platinum sponge, and spongy nickel. Metals such as osmium and palladium hydride are metaphorically called "metal sponges", but this term is in reference to their property of binding to hydrogen, rather than the physical structure. | 0 | Theoretical and Fundamental Chemistry |
Photoelectrochemical oxidation (PECO) is the process by which light enables a semiconductor to promote a catalytic oxidation reaction. While a photoelectrochemical cell typically involves both a semiconductor (electrode) and a metal (counter-electrode), at sufficiently small scales, pure semiconductor particles can behave as microscopic photoelectrochemical cells. PECO has applications in the detoxification of air and water, hydrogen production, and other applications. | 0 | Theoretical and Fundamental Chemistry |
The stereotypic inflammatory response provoked by toll-like receptor activation has prompted speculation that endogenous activators of toll-like receptors might participate in autoimmune diseases. TLRs have been suspected of binding to host molecules including fibrinogen (involved in blood clotting), heat shock proteins (HSPs), HMGB1, extracellular matrix components and self DNA (it is normally degraded by nucleases, but under inflammatory and autoimmune conditions it can form a complex with endogenous proteins, become resistant to these nucleases and gain access to endosomal TLRs as TLR7 or TLR9). These endogenous ligands are usually produced as a result of non-physiological cell death. | 1 | Applied and Interdisciplinary Chemistry |
In autoimmunity the immune system wrongly recognizes certain native molecules in the body as foreign (self-antigen), and mounts an immune response against them. Since these native molecules, as normal parts of the body, will naturally always exist in the body, the attacks against them can get stronger over time (akin to secondary immune response). Moreover, many organisms exhibit molecular mimicry, which involves showing those antigens on their surface that are antigenically similar to the host proteins. This has two possible consequences: first, either the organism will be spared as a self antigen; or secondly, that the antibodies produced against it will also bind to the mimicked native proteins. The antibodies will attack the self-antigens and the tissues harboring them by activating various mechanisms like the complement activation and antibody-dependent cell-mediated cytotoxicity. Hence, wider the range of antibody-specificities, greater the chance that one or the other will react against self-antigens (native molecules of the body). | 1 | Applied and Interdisciplinary Chemistry |
In Japan, pesticide residues are regulated by the Food Safety Act.
Pesticide tolerances are set by the Ministry of Health, Labour and Welfare through the Drug and Food Safety Committee. Unlisted residue amounts are restricted to 0.01ppm. | 1 | Applied and Interdisciplinary Chemistry |
Ligands of the sigma-2 receptor are exogenous and internalized by endocytosis, and can act as either agonists or antagonists. They can typically be classified into four groups, which are structurally related. It is not entirely understood how binding to the sigma-2 receptor occurs. Proposed models commonly include one small and one bulky hydrophobic pocket, electrostatic hydrogen interactions, and less commonly a third hydrophobic pocket.
A study of the four groups has revealed that a basic nitrogen and at least one hydrophobic moiety is needed to bind a sigma-2 receptor. In addition, there are molecular characteristics that increase the selectivity for sigma-2 receptors, which include bulky hydrophobic regions, nitrogen-carboxylic interaction, and additional basic nitrogens.
Since its discovery in 1990, the sigma-2 receptor has been considered an orphan receptor; however, in 2021 20S-hydroxycholesterol was identified as the putative endogenous ligand. | 1 | Applied and Interdisciplinary Chemistry |
Hydroxybenzotriazole (abbreviated HOBt) is an organic compound that is a derivative of benzotriazole. It is a white crystalline powder, which as a commercial product contains some water (~11.7% wt as the HOBt monohydrate crystal). Anhydrous HOBt is explosive.
It is mainly used to suppress the racemization of single-enantiomer chiral molecules and to improve the efficiency of peptide synthesis. | 1 | Applied and Interdisciplinary Chemistry |
All influenza A virus strains need sialic acid to connect with cells. There are different forms of sialic acids which have different affinity with influenza A virus variety. This diversity is an important fact that determines which species can be infected. When a certain influenza A virus is recognized by a sialic acid receptor the cell tends to endocytose the virus so the cell becomes infected. | 0 | Theoretical and Fundamental Chemistry |
Pseudoephedrine was on the International Olympic Committees (IOC) banned substances list until 2004, when the World Anti-Doping Agency (WADA) list replaced the IOC list. Although WADA initially only monitored' pseudoephedrine, it went back onto the "banned" list on 1 January 2010.
Pseudoephedrine is excreted through urine, and concentration in urine of this drug shows a large inter-individual spread; that is, the same dose can give a vast difference in urine concentration for different individuals. Pseudoephedrine is approved to be taken up to 240 mg per day. In seven healthy male subjects this dose yielded a urine concentration range of 62.8 to 294.4 microgram per milliliter (µg/mL) with mean ± standard deviation 149 ± 72 µg/mL. Thus, normal dosage of 240 mg pseudoephedrine per day can result in urine concentration levels exceeding the limit of 150 µg/mL set by WADA for about half of all users. Furthermore, hydration status does not affect urinary concentration of pseudoephedrine.
Canadian rower Silken Laumann was stripped of her 1995 Pan American Games team gold medal after testing positive for pseudoephedrine.
In February 2000, Elena Berezhnaya and Anton Sikharulidze won gold at the 2000 European Figure Skating Championships but were stripped of their medals after Berezhnaya tested positive. This resulted in a three-month disqualification from the date of the test, and the medal being stripped. She stated that she had taken cold medication approved by a doctor but had failed to inform the ISU as required. The pair missed the World Championships that year as a result of the disqualification.
Romanian gymnast Andreea Răducan was stripped of her gold medal at the 2000 Summer Olympic Games after testing positive. She took two pills given to her by the team coach for a cold. Although she was stripped of the overall gold medal, she kept her other medals, and, unlike in most other doping cases, was not banned from competing again; only the team doctor was banned for a number of years. Ion Țiriac, the president of the Romanian Olympic Committee, resigned over the scandal.
In the 2010 Winter Olympic Games, the IOC issued a reprimand against the Slovak ice hockey player Lubomir Visnovsky for usage of pseudoephedrine.
In the 2014 Winter Olympic Games Team Sweden and Washington Capitals ice hockey player Nicklas Bäckström was prevented from playing in the final for usage of pseudoephedrine. Bäckström claimed he was using it as allergy medication. In March 2014, the IOC Disciplinary Commission decided that Bäckström would be awarded the silver medal. In January 2015 Bäckström, the IOC, WADA and the IIHF agreed to a settlement in which he accepted a reprimand but was cleared of attempting to enhance his performance. | 0 | Theoretical and Fundamental Chemistry |
In molecular biology, a guanine tetrad (also known as a G-tetrad or G-quartet) is a structure composed of four guanine bases in a square planar array. They most prominently contribute to the structure of G-quadruplexes, where their hydrogen bonding stabilizes the structure. Usually, there are at least two guanine tetrads in a G-quadruplex, and they often feature Hoogsteen-style hydrogen bonding.
Guanine tetrads are formed by sequences rich in guanine, such as GGGGC. They may also play a role in the dimerization of non-endogenous RNAs to facilitate the replication of some viruses. Guanine tetrads dimerize through their 5' ends since it is more energetically favorable.
They can be stabilized by central cations, such as lithium, sodium, potassium, rubidium, or caesium. However, they still form a variety of different structures. Guanine tetrads are not always stable, but the sugar-phosphate backbone of DNA can assist in stability of the guanine tetrads themselves. Guanine tetrads are more stable when stacked, as intermolecular forces between each layers help stabilize them.
Guanine tetrads can also influence recombination, replication, and transcription. For instance, guanine tetrads are found in the promoter region of the Myc family of oncogenes. They also function in immunoglobulin class switching and may play a role in the genome of HIV. Guanine tetrads appear frequently in the telomeric regions of DNA. | 1 | Applied and Interdisciplinary Chemistry |
In Australia, Chartered Membership (MRACI CChem) is for:
* Individuals who have been awarded with an Australian degree in chemistry or a chemistry-related discipline consisting of a minimum of three years academic study and have completed three years relevant experience working in a chemistry field.
* Individuals who do not hold a chemistry degree but have a minimum of six years relevant experience working in a chemistry field. | 1 | Applied and Interdisciplinary Chemistry |
It is sometime useful to look at the percent resonance (%r), because r is dependent on the reaction and is the same for all substituents.
One can predict the difference in data comparing two substituents using %r:
The most dominant effect is clear when looking at the ratio of R to F. For example, a tungsten complex was shown to alkylate allyl carbonates A and B. The ratio of products A1 and B1 can be attributed to the para substituent, X (Fig. 3). Using Swain–Lupton parameters (σ = 0.2F + 0.8R) a ρ value of -2.5 was found to be the slope.
This is in agreement with the proposed mechanism (a positive charge forms on the benzylic carbon and is stabilized by resonance; R dominates by a ratio of 0.8/0.2). | 0 | Theoretical and Fundamental Chemistry |
Historically, some of the first chemistry offices were located in the main building of Saint Petersburg State University called Twelve Collegia. The remainder of these is the Mendeleev museum located on the first floor of the central part of this enormous building. In the 20th century, the Department of Chemistry was headquartered at 41/43 Sredniy prospekt on Vasilievsky Island, about one mile west of Twelve Collegia. In the 1980s, most of the laboratories were relocated to a more spacious building in the newly constructed campus in the suburb of Peterhof. | 1 | Applied and Interdisciplinary Chemistry |
Anandamide (ANA), also known as N-arachidonoylethanolamine (AEA), an N-acylethanolamine (NAE), is a fatty acid neurotransmitter. Anandamide was the first endocannabinoid to be discovered: it participates in the bodys endocannabinoid system by binding to cannabinoid receptors, the same receptors that the psychoactive compound THC in cannabis acts on. Anandamide is found in nearly all tissues in a wide range of animals. Anandamide has also been found in plants, including small amounts in chocolate. The name anandamide is taken from the Sanskrit word ananda', which means "joy, bliss, delight", plus amide.
Anandamide is derived from the non-oxidative metabolism of arachidonic acid, an essential omega-6 fatty acid. It is synthesized from N-arachidonoyl phosphatidylethanolamine by multiple pathways. It is degraded primarily by the fatty acid amide hydrolase (FAAH) enzyme, which converts anandamide into ethanolamine and arachidonic acid. As such, inhibitors of FAAH lead to elevated anandamide levels and are being pursued for therapeutic use.
Anandamide is also being explored for its role in diabetic neuropathy/neuropathy, as cannabinoids as well as exogenous or endogenous anandamide, demonstrate broad-spectrum antinociceptive properties in a model of painful diabetic neuropathy, mediated through peripheral activation of both cannabinoid receptors, i.e. CB1 and CB2, beside involvement of transient receptor vanilloid type-1 (TRPV1) channels in the pain modulation, as endovanilloid signalling modulates local pain, as well as in reduction of inflammation associated with renal injury. | 1 | Applied and Interdisciplinary Chemistry |
*Bamfield Peter and Hutchings Michael, Chromic Phenomena; technological applications of colour chemistry, 3rd Edition, Royal Society of Chemistry, Cambridge, 2018. {EPUB }.
*Vik Michal and Periyasamy Aravin Prince, Chromic Materials; Fundamentals, Measurements and Applications, Apple Academic Press, 2018. .
*Ferrara Mariella and Murat Bengisu, Materials that Change Color: Smart Materials and Intelligent Design, Springer, 2014. | 0 | Theoretical and Fundamental Chemistry |
The reaction involves the addition of and cyanide () to the substrate. Usually the substrate is an alkene and the product is a nitrile.
The reaction proceeds via the oxidative addition of HCN to a low-valent metal complex to give a hydrido cyanide complex. Subsequent binding of the alkene gives the intermediate , which then undergoes migratory insertion to give an alkylmetal cyanide. The cycle is completed by the reductive elimination of the nitrile.
Lewis acids, such as triphenylboron (), induce reductive elimination of the nitrile product, increasing rates.
In the case of nickel-based systems, catalyst deactivation involves formation of dicyanonickel(II) species, which are unreactive toward alkenes. The dicyanide arises via two pathways (L = phosphite): | 0 | Theoretical and Fundamental Chemistry |
Chemical shielding is a local property of each nuclear site in a molecule or compound, and is proportional to the applied external magnetic field. The external magnetic field induces currents of the electrons in molecular orbitals. These induced currents create local magnetic fields that lead to characteristic changes in resonance frequency. These changes can be predicted from molecular structure using empirical rules or quantum-chemical calculations.
In general, the chemical shielding is anisotropic because of the anisotropic distribution of molecular orbitals around the nuclear sites. Under sufficiently fast magic angle spinning, or under the effect of molecular tumbling in solution-state NMR, the anisotropic dependence of the chemical shielding is time-averaged to zero, leaving only the isotropic chemical shift. | 0 | Theoretical and Fundamental Chemistry |
Electrons leave the cathode with an energy of about 1 eV, which is not enough to ionize or excite atoms, leaving a thin dark layer next to the cathode. | 0 | Theoretical and Fundamental Chemistry |
In his work at the University of Giessen, Kröhnke observed condensation of α-pyridinium methyl ketone salts 1 with α,β-unsaturated carbonyl compounds 2 via a Michael reaction when treated with ammonium acetate to give 2,4,6-trisubstituted pyridines in high yields under mild reaction conditions. The proposed intermediates, 1, 5-dicarbonyl compound 3, have not been isolated. Since its discovery, the Kröhnke synthesis has enjoyed broad applicability to the preparation of di-,tri- and tetrapyridine derivatives, demonstrating a number of advantages over related reactions such as the Hantzsch pyridine synthesis. | 0 | Theoretical and Fundamental Chemistry |
*3.A.1 ABC transporters including BtuCD, molybdate uptake transporter, Cystic fibrosis transmembrane conductance regulator and others
*3.A.2 The H- or Na-translocating F-type ATPase, V-type ATPase and A-type ATPase superfamily
*3.A.3 The P-type ATPase Superfamily
*3.A.4 The Arsenite-Antimonite efflux family
*3.A.5 General secretory pathway (Sec) translocon (preprotein translocase SecY)
*3.A.6 The Type III (Virulence-related) Secretory Pathway (IIISP) Family
*3.A.7 The Type IV (Conjugal DNA-Protein Transfer or VirB) Secretory Pathway (IVSP) Family
*3.A.8 The Mitochondrial Protein Translocase (MPT) Family
*3.A.9 The Chloroplast Envelope Protein Translocase (CEPT or Tic-Toc) Family
*3.A.10 H, Na-translocating Pyrophosphatase family
*3.A.11 The Bacterial Competence-related DNA Transformation Transporter (DNA-T) Family
*3.A.12 The Septal DNA Translocator (S-DNA-T) Family
*3.A.13 The Filamentous Phage Exporter (FPhE) Family
*3.A.14 The Fimbrilin/Protein Exporter (FPE) Family
*3.A.15 The Outer Membrane Protein Secreting Main Terminal Branch (MTB) Family
*3.A.16 The Endoplasmic Reticular Retrotranslocon (ER-RT) Family
*3.A.17 The Phage T7 Injectisome (T7 Injectisome) Family
*3.A.18 The Nuclear mRNA Exporter (mRNA-E) Family
*3.A.19 The TMS Recognition/Insertion Complex (TRC) Family
*3.A.20 The Peroxisomal Protein Importer (PPI) Family
*3.A.21 The C-terminal Tail-Anchored Membrane Protein Biogenesis/ Insertion Complex (TAMP-B) Family
*3.A.22 The Transcription-coupled TREX/TAP Nuclear mRNA Export Complex (TREX) Family
*3.A.23 The Type VI Symbiosis/Virulence Secretory Pathway (VISP) Family
*3.A.24 Type VII or ESX Protein Secretion System (T7SS) Family
*3.A.25 The Symbiont-specific ERAD-like Machinery (SELMA) Family
*3.A.26 The Plasmodium Translocon of Exported proteins (PTEX) Family | 1 | Applied and Interdisciplinary Chemistry |
The enzyme responsible for apoptotic DNA fragmentation is the Caspase-Activated DNase (CAD). CAD is normally inhibited by another protein, the Inhibitor of Caspase Activated DNase (ICAD). During apoptosis, the apoptotic effector caspase, caspase-3, cleaves ICAD and thus causes CAD to become activated.
CAD cleaves DNA at internucleosomal linker sites between nucleosomes, protein-containing structures that occur in chromatin at ~180-bp intervals. This is because the DNA is normally tightly wrapped around histones, the core proteins of the nucleosomes. The linker sites are the only parts of the DNA strand that are exposed and thus accessible to CAD.
Degradation of nuclear DNA into nucleosomal units is one of the hallmarks of apoptotic cell death. It occurs in response to various apoptotic stimuli in a wide variety of cell types. Molecular characterization of this process identified a specific DNase (CAD, caspase-activated DNase) that cleaves chromosomal DNA in a caspase-dependent manner. CAD is synthesized with the help of ICAD (inhibitor of CAD), which works as a specific chaperone for CAD and is found complexed with ICAD in proliferating cells. When cells are induced to undergo apoptosis, caspase 3 cleaves ICAD to dissociate the CAD:ICAD complex, allowing CAD to cleave chromosomal DNA. Cells that lack ICAD or that express caspase-resistant mutant ICAD thus do not show DNA fragmentation during apoptosis, although they do exhibit some other features of apoptosis and die.
Even though much work has been performed on the analysis of apoptotic events, little information is available to link the timing of morphological features at the cell surface and in the nucleus to the biochemical degradation of DNA in the same cells. Apoptosis can be initiated by a myriad of different mechanisms in different cell types, and the kinetics of these events vary widely, from only a few minutes to several days depending on the cell system. The presence or absence of particular apoptotic event(s), including DNA fragmentation, depends on the "time window" at which the kinetic process of apoptosis is being investigated. Often this may complicate identification of apoptotic cells if cell populations are analyzed only at a single time point e.g. after induction of apoptosis. | 1 | Applied and Interdisciplinary Chemistry |
Superconductor material classes include chemical elements (e.g. mercury or lead), alloys (such as niobium–titanium, germanium–niobium, and niobium nitride), ceramics (YBCO and magnesium diboride), superconducting pnictides (like fluorine-doped LaOFeAs) or organic superconductors (fullerenes and carbon nanotubes; though perhaps these examples should be included among the chemical elements, as they are composed entirely of carbon). | 0 | Theoretical and Fundamental Chemistry |
A runoff footprint is the total surface runoff that a site produces over the course of a year. According to the United States Environmental Protection Agency (EPA) stormwater is "rainwater and melted snow that runs off streets, lawns, and other sites". Urbanized areas with high concentrations of impervious surfaces like buildings, roads, and driveways produce large volumes of runoff which can lead to flooding, sewer overflows, and poor water quality. Since soil in urban areas can be compacted and have a low infiltration rate, the surface runoff estimated in a runoff footprint is not just from impervious surfaces, but also pervious areas including yards. The total runoff is a measure of the site’s contribution to stormwater issues in an area, especially in urban areas with sewer overflows. Completing a runoff footprint for a site allows a property owner to understand what areas on his or her site are producing the most runoff and what scenarios of stormwater green solutions like rain barrels and rain gardens are most effective in mitigating this runoff and its costs to the community. | 1 | Applied and Interdisciplinary Chemistry |
In the Gattermann reaction, benzenediazonium chloride is warmed with copper powder and HCl or HBr to produce chlorobenzene and bromobenzene respectively. It is named after the German chemist Ludwig Gattermann. | 0 | Theoretical and Fundamental Chemistry |
In flame tests, ions are excited thermally. These excited states then relax to the ground state with emission of a photon. The energy of the excited state(s) and associated emitted photon is characteristic of the element. The nature of the excited and ground states depends only on the element. Ordinarily, there are no bonds to be broken, and molecular orbital theory is not applicable. The emission spectrum observed in flame test is also the basis of flame emission spectroscopy, atomic emission spectroscopy, and flame photometry. | 1 | Applied and Interdisciplinary Chemistry |
The dalton or unified atomic mass unit (symbols: Da or u) is a non-SI unit of mass defined as of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. The atomic mass constant, denoted m, is defined identically, giving .
This unit is commonly used in physics and chemistry to express the mass of atomic-scale objects, such as atoms, molecules, and elementary particles, both for discrete instances and multiple types of ensemble averages. For example, an atom of helium-4 has a mass of . This is an intrinsic property of the isotope and all helium-4 atoms have the same mass. Acetylsalicylic acid (aspirin), , has an average mass of about . However, there are no acetylsalicylic acid molecules with this mass. The two most common masses of individual acetylsalicylic acid molecules are , having the most common isotopes, and , in which one carbon is carbon-13.
The molecular masses of proteins, nucleic acids, and other large polymers are often expressed with the units kilo<nowiki/>dalton (kDa) and mega<nowiki/>dalton (MDa). Titin, one of the largest known proteins, has a molecular mass of between 3 and 3.7 megadaltons. The DNA of chromosome 1 in the human genome has about 249 million base pairs, each with an average mass of about , or total.
The mole is a unit of amount of substance used in chemistry and physics, which defines the mass of one mole of a substance in grams as numerically equal to the average mass of one of its particles in daltons. That is, the molar mass of a chemical compound is meant to be numerically equal to its average molecular mass. For example, the average mass of one molecule of water is about 18.0153 daltons, and one mole of water is about 18.0153 grams. A protein whose molecule has an average mass of would have a molar mass of . However, while this equality can be assumed for practical purposes, it is only approximate, because of the 2019 redefinition of the mole.
In general, the mass in daltons of an atom is numerically close but not exactly equal to the number of nucleons in its nucleus. It follows that the molar mass of a compound (grams per mole) is numerically close to the average number of nucleons contained in each molecule. By definition, the mass of an atom of carbon-12 is 12 daltons, which corresponds with the number of nucleons that it has (6 protons and 6 neutrons). However, the mass of an atomic-scale object is affected by the binding energy of the nucleons in its atomic nuclei, as well as the mass and binding energy of its electrons. Therefore, this equality holds only for the carbon-12 atom in the stated conditions, and will vary for other substances. For example, the mass of an unbound atom of the common hydrogen isotope (hydrogen-1, protium) is ,
the mass of a proton is , the mass of a free neutron is and the mass of a hydrogen-2 (deuterium) atom is . In general, the difference (absolute mass excess) is less than 0.1%; exceptions include hydrogen-1 (about 0.8%), helium-3 (0.5%), lithium-6 (0.25%) and beryllium (0.14%).
The dalton differs from the unit of mass in the atomic units systems, which is the electron rest mass (m). | 0 | Theoretical and Fundamental Chemistry |
In 1802, William Hyde Wollaston built a spectrometer, improving on Newtons model, that included a lens to focus the Suns spectrum on a screen. Upon use, Wollaston realized that the colors were not spread uniformly, but instead had missing patches of colors, which appeared as dark bands in the suns spectrum. At the time, Wollaston believed these lines to be natural boundaries between the colors, but this hypothesis was later ruled out in 1815 by Fraunhofers work.
Joseph von Fraunhofer made a significant experimental leap forward by replacing a prism with a diffraction grating as the source of wavelength dispersion. Fraunhofer built off the theories of light interference developed by Thomas Young, François Arago and Augustin-Jean Fresnel. He conducted his own experiments to demonstrate the effect of passing light through a single rectangular slit, two slits, and so forth, eventually developing a means of closely spacing thousands of slits to form a diffraction grating. The interference achieved by a diffraction grating both improves the spectral resolution over a prism and allows for the dispersed wavelengths to be quantified. Fraunhofer's establishment of a quantified wavelength scale paved the way for matching spectra observed in multiple laboratories, from multiple sources (flames and the sun) and with different instruments. Fraunhofer made and published systematic observations of the solar spectrum, and the dark bands he observed and specified the wavelengths of are still known as Fraunhofer lines.
Throughout the early 1800s, a number of scientists pushed the techniques and understanding of spectroscopy forward. In the 1820s, both John Herschel and William H. F. Talbot made systematic observations of salts using flame spectroscopy. | 0 | Theoretical and Fundamental Chemistry |
The Brazilian Journal of Chemical Engineering publishes papers, reporting basic and applied research and innovation in the field of chemical engineering and related areas. It was first published by the Associação Brasileira de Engenharia Química, São Paulo, in 1983 as the Revista Brasileira de Engenharia, Caderno de Engenharia Química. With vol. 11 (1994), it continued as the Brazilian Journal of Chemical Engineering.
It continues the Revista Brasileira de Engenharia, Caderno de Engenharia Química from 1994 on.
Fulltext of the journal is available via SciElo starting from vol. 14 (1997) to vol. 36 (2019).
From January 2020 on, the journal is published by Springer. | 1 | Applied and Interdisciplinary Chemistry |
Exome sequencing is only able to identify those variants found in the coding region of genes which affect protein function. It is not able to identify the structural and non-coding variants associated with the disease, which can be found using other methods such as whole genome sequencing. There remains 99% of the human genome that is not covered using exome sequencing, and exome sequencing allows sequencing of portions of the genome over at least 20 times as many samples compared to whole genome sequencing. For translation of identified rare variants into the clinic, sample size and the ability to interpret the results to provide a clinical diagnosis indicates that with the current knowledge in genetics, there are reports of exome sequencing being used for assisting diagnosis. The cost of exome sequencing is typically lower than whole genome sequencing. | 1 | Applied and Interdisciplinary Chemistry |
The term pharmacogenomics is often used interchangeably with pharmacogenetics. Although both terms relate to drug response based on genetic influences, there are differences between the two. Pharmacogenetics is limited to monogenic phenotypes (i.e., single gene-drug interactions). Pharmacogenomics refers to polygenic drug response phenotypes and encompasses transcriptomics, proteomics, and metabolomics. | 1 | Applied and Interdisciplinary Chemistry |
Magnetometers are also used to detect archaeological sites, shipwrecks, and other buried or submerged objects. Fluxgate gradiometers are popular due to their compact configuration and relatively low cost. Gradiometers enhance shallow features and negate the need for a base station. Caesium and Overhauser magnetometers are also very effective when used as gradiometers or as single-sensor systems with base stations.
The TV program Time Team popularised geophys, including magnetic techniques used in archaeological work to detect fire hearths, walls of baked bricks and magnetic stones such as basalt and granite. Walking tracks and roadways can sometimes be mapped with differential compaction in magnetic soils or with disturbances in clays, such as on the Great Hungarian Plain. Ploughed fields behave as sources of magnetic noise in such surveys. | 0 | Theoretical and Fundamental Chemistry |
Pressure oxidation is a process for extracting gold from refractory ore.
The most common refractory ores are pyrite and arsenopyrite, which are sulfide ores that trap the gold within them. Refractory ores require pre-treatment before the gold can be adequately extracted. The pressure oxidation process is used to prepare such ores for conventional gold extraction processes such as cyanidation. It is performed in an autoclave at high pressure and temperature, where high-purity oxygen mixes with a slurry of ore.
When the original sulfide minerals are oxidized at high temperature and pressure, it completely releases the trapped gold. Pressure oxidation has a very high gold recovery rate, normally at least 10% higher than roasting.
The oxidation of the iron sulfide minerals produces sulfuric acid, soluble compounds such as ferric sulfate, and solids such as iron sulfate or jarosite. The iron-based solids produced pose an environmental challenge, as they can release acid and heavy metals to the environment. They can also make later precious metal recovery more difficult. Arsenic in the ore is converted to solid scorodite inside the autoclave, allowing it to be easily disposed of. This is an advantage over processes such as roasting where these toxic products are released as gases.
A disadvantage of pressure oxidation is that any silver in the feed material will often react to form silver jarosite inside the autoclave, making it difficult and expensive to recover the silver.
An example of a mine utilizing this technology is the Pueblo Viejo mine in the Dominican Republic. At Pueblo Viejo, the process is performed by injecting high-purity oxygen into autoclaves operating at 230 degrees C and 40 bar of pressure. The resulting chemical reactions oxides the sulfide minerals the gold is trapped within. The oxidation of pyrite is highly exothermic, allowing the autoclave to operate at this temperature without an external heat source. | 1 | Applied and Interdisciplinary Chemistry |
Generally, ingested insoluble actinide compounds such as high-fired uranium dioxide and mixed oxide (MOX) fuel will pass through the digestive system with little effect since they cannot dissolve and be absorbed by the body. Inhaled actinide compounds, however, will be more damaging as they remain in the lungs and irradiate the lung tissue. Ingested Low-fired oxides and soluble salts such as nitrate can be absorbed into the blood stream. If they are inhaled then it is possible for the solid to dissolve and leave the lungs. Hence the dose to the lungs will be lower for the soluble form.
Radon and radium are not actinides—they are both radioactive daughters from the decay of uranium. Aspects of their biology and environmental behaviour is discussed at radium in the environment.
In India, a large amount of thorium ore can be found in the form of monazite in placer deposits of the Western and Eastern coastal dune sands, particularly in the Tamil Nadu coastal areas. The residents of this area are exposed to a naturally occurring radiation dose ten times higher than the worldwide average.
Thorium has been linked to liver cancer. In the past thoria (thorium dioxide) was used as a contrast agent for medical X-ray radiography but its use has been discontinued. It was sold under the name Thorotrast.
Uranium is about as abundant as arsenic or molybdenum. Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as lignite, and monazite sands in uranium-rich ores (it is recovered commercially from these sources).
Seawater contains about 3.3 parts per billion of uranium by weight as uranium(VI) forms soluble carbonate complexes. The extraction of uranium from seawater has been considered as a means of obtaining the element. Because of the very low specific activity of uranium the chemical effects of it upon living things can often outweigh the effects of its radioactivity.
Plutonium, like other actinides, readily forms a plutonium dioxide (plutonyl) core (PuO). In the environment, this plutonyl core readily complexes with carbonate as well as other oxygen moieties (OH, , , and ) to form charged complexes which can be readily mobile with low affinities to soil. | 0 | Theoretical and Fundamental Chemistry |
Most domains have a very broad substrate specificity and usually only the A-domain determines which amino acid is incorporated in a module. Ten amino acids that control substrate specificity and can be considered the codons of nonribosomal peptide synthesis have been identified, and rational protein design has yielded methodologies to computationally switch the specificities of A-domains. The condensation C-domain is also believed to have substrate specificity, especially if located behind an epimerase E-domain-containing module where it functions as a filter for the epimerized isomer. Computational methods, such as SANDPUMA and NRPSpredictor2, have been developed to predict substrate specificity from DNA or protein sequence data. | 1 | Applied and Interdisciplinary Chemistry |
A number of technologies remove greenhouse gases emissions from the atmosphere. Most widely analyzed are those that remove carbon dioxide from the atmosphere, either to geologic formations such as bio-energy with carbon capture and storage and carbon dioxide air capture, or to the soil as in the case with biochar. Many long-term climate scenario models require large-scale human-made negative emissions to avoid serious climate change.
Negative emissions approaches are also being studied for atmospheric methane, called atmospheric methane removal. | 1 | Applied and Interdisciplinary Chemistry |
The cell cycle is a four-stage process that a cell goes through as it develops and divides. It includes Gap 1 (G1), synthesis (S), Gap 2 (G2), and mitosis (M).The cell either restarts the cycle from G1 or leaves the cycle through G0 after completing the cycle. The cell can progress from G0 through terminal differentiation.
The interphase refers to the phases of the cell cycle that occur between one mitosis and the next, and includes G1, S, and G2. | 1 | Applied and Interdisciplinary Chemistry |
Formazine (formazin) is a heterocyclic polymer produced by reaction of hexamethylenetetramine with hydrazine sulfate.
The hexamethylenetetramine tetrahedral cage-like structure, similar to adamantane, serves as molecular building block to form a tridimensional polymeric network.
Formazine is very poorly soluble in water and when directly synthesized in aqueous solution, by simply mixing its two highly soluble precursors, it forms small size colloidal particles. These organic colloids are responsible of the light scattering of the formazine suspensions in all the directions. Optical properties of colloidal suspensions depend on the suspended particles size and size distribution. Because formazine is a stable synthetic material with uniform particle size it is commonly used as a standard to calibrate turbidimeters and to control the reproducibility of their measurements. Formazin use was first proposed by Kingsbury et al. (1926) for the rapid standardization of turbidity measurements of albumin in urine. The unit is called Formazin Turbidity Unit (FTU). A suspension of 1.25 mg/L hydrazine sulfate and 12.5 mg/L hexamethylenetetramine in water has a turbidity of one FTU.
In the United States environmental monitoring the turbidity standard unit is called Nephelometric Turbidity Units (NTU), while the international standard unit is called Formazin Nephelometric Unit (FNU). The most generally applicable unit is Formazin Turbidity Unit (FTU), although different measurement methods can give quite different values as reported in FTU. | 0 | Theoretical and Fundamental Chemistry |
In addition to different B cells reacting to different epitopes on the same antigen, B cells belonging to different clones may also be able to react to the same epitope. An epitope that can be attacked by many different B cells is said to be highly immunogenic. In these cases, the binding affinities for respective epitope-paratope pairs vary, with some B cell clones producing antibodies that bind strongly to the epitope, and others producing antibodies that bind weakly. | 1 | Applied and Interdisciplinary Chemistry |
Acetylides are sometimes intermediates in coupling reactions. Examples include Sonogashira coupling, Cadiot-Chodkiewicz coupling, Glaser coupling and Eglinton coupling. | 0 | Theoretical and Fundamental Chemistry |
In 1850, T. J. Mulvany was probably the first investigator to use mathematical modeling in a stream hydrology context, although there was no chemistry involved. By 1892 M.E. Imbeau had conceived an event model to relate runoff to peak rainfall, again still with no chemistry. Robert E. Horton’s seminal work on surface runoff along with his coupling of quantitative treatment of erosion laid the groundwork for modern chemical transport hydrology. | 1 | Applied and Interdisciplinary Chemistry |
River engineering is a discipline of civil engineering which studies human intervention in the course, characteristics, or flow of a river with the intention of producing some defined benefit. People have intervened in the natural course and behaviour of rivers since before recorded history—to manage the water resources, to protect against flooding, or to make passage along or across rivers easier. Since the Yuan Dynasty and Ancient Roman times, rivers have been used as a source of hydropower. From the late 20th century, the practice of river engineering has responded to environmental concerns broader than immediate human benefit. Some river engineering projects have focused exclusively on the restoration or protection of natural characteristics and habitats.
Hydromodification encompasses the systematic response to alterations to riverine and non-riverine water bodies such as coastal waters (estuaries and bays) and lakes. The U.S. Environmental Protection Agency (EPA) has defined hydromodification as the "alteration of the hydrologic characteristics of coastal and non-coastal waters, which in turn could cause degradation of water resources." River engineering has often resulted in unintended systematic responses, such as reduced habitat for fish and wildlife, and alterations of water temperature and sediment transport patterns.
Beginning in the late 20th century, the river engineering discipline has been more focused on repairing hydromodified degradations and accounting for potential systematic response to planned alterations by considering fluvial geomorphology. Fluvial geomorphology is the study of how rivers change their form over time. Fluvial geomorphology is the cumulation of a number of sciences including open channel hydraulics, sediment transport, hydrology, physical geology, and riparian ecology. River engineering practitioners attempt to understand fluvial geomorphology, implement a physical alteration, and maintain public safety. | 1 | Applied and Interdisciplinary Chemistry |
Polyacrylamide gel electrophoresis (PAGE) is used for separating proteins ranging in size from 5 to 2,000 kDa due to the uniform pore size provided by the polyacrylamide gel. Pore size is controlled by modulating the concentrations of acrylamide and bis-acrylamide powder used in creating a gel. Care must be used when creating this type of gel, as acrylamide is a potent neurotoxin in its liquid and powdered forms.
Traditional DNA sequencing techniques such as Maxam-Gilbert or Sanger methods used polyacrylamide gels to separate DNA fragments differing by a single base-pair in length so the sequence could be read. Most modern DNA separation methods now use agarose gels, except for particularly small DNA fragments. It is currently most often used in the field of immunology and protein analysis, often used to separate different proteins or isoforms of the same protein into separate bands. These can be transferred onto a nitrocellulose or PVDF membrane to be probed with antibodies and corresponding markers, such as in a western blot.
Typically resolving gels are made in 6%, 8%, 10%, 12% or 15%. Stacking gel (5%) is poured on top of the resolving gel and a gel comb (which forms the wells and defines the lanes where proteins, sample buffer, and ladders will be placed) is inserted. The percentage chosen depends on the size of the protein that one wishes to identify or probe in the sample. The smaller the known weight, the higher the percentage that should be used. Changes in the buffer system of the gel can help to further resolve proteins of very small sizes. | 1 | Applied and Interdisciplinary Chemistry |
Amoxicillin is used to treat odontogenic infections, infections of the tongue, lips, and other oral tissues. It may be prescribed following a tooth extraction, particularly in those with compromised immune systems. | 0 | Theoretical and Fundamental Chemistry |
The protons in the lumen come from three primary sources.
*Photolysis by photosystem II oxidises water to oxygen, protons and electrons in the lumen.
*The transfer of electrons from photosystem II to plastoquinone during non-cyclic electron transport consumes two protons from the stroma. These are released in the lumen when the reduced plastoquinol is oxidized by the cytochrome b6f protein complex on the lumen side of the thylakoid membrane. From the plastoquinone pool, electrons pass through the cytochrome b6f complex. This integral membrane assembly resembles cytochrome bc1.
*The reduction of plastoquinone by ferredoxin during cyclic electron transport also transfers two protons from the stroma to the lumen.
The proton gradient is also caused by the consumption of protons in the stroma to make NADPH from NADP+ at the NADP reductase. | 0 | Theoretical and Fundamental Chemistry |
Phenols are susceptible to Electrophilic aromatic substitutions. Condensation with formaldehyde gives resinous materials, famously Bakelite.
Another industrial-scale electrophilic aromatic substitution is the production of bisphenol A, which is produced by the condensation with acetone. | 0 | Theoretical and Fundamental Chemistry |
In response to the environmental disasters at Love Canal and Times Beach, Missouri, Congress passed the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), commonly known as the Superfund legislation. CERCLA gave EPA primary responsibility for identifying, investigating, and cleaning up hazardous waste sites. CERCLA also authorized the establishment of ATSDR to assess the presence and nature of health hazards to communities living near Superfund sites, to help prevent or reduce harmful exposures, and to expand the knowledge base about the health effects that result from exposure to hazardous substances. ATSDR was created as an agency under the Department of Health and Human Services on April 19, 1983, and James O. Mason served as the agencys first administrator. The Hazardous and Solid Waste Amendments of 1984 to the Resource Conservation and Recovery Act (RCRA) gave ATSDR additional authority related to hazardous waste storage facilities. ATSDR was charged with conducting public health assessments at these sites when requested by EPA, states, or individuals, as well as assisting EPA to determine which substances should be regulated and the levels at which chemicals may pose a threat to human health. ATSDR was formally organized as an agency on June 11, 1985. The Superfund Amendments and Reauthorization Act of 1986 (SARA) broadened ATSDRs responsibilities in the areas of public health assessments, establishment and maintenance of toxicological databases, information dissemination, and medical education. In 2003, the position of assistant administrator was replaced with a director who is shared with NCEH. | 1 | Applied and Interdisciplinary Chemistry |
One of the ways cell apoptosis is activated is by release of cytochrome c from the mitochondria into cytosol. A study has shown that cells are able to protect themselves from apoptosis by blocking the release of cytochrome c using Bcl-x. Another way that cells can control apoptosis is by phosphorylation of Tyr48, which would turn cytochrome c into an anti-apoptotic switch. | 1 | Applied and Interdisciplinary Chemistry |
A synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. Examples include technetium-99 and promethium-146. Many of these are found in, and harvested from, spent nuclear fuel assemblies. Some must be manufactured in particle accelerators. | 0 | Theoretical and Fundamental Chemistry |
Alcohol can be converted to haloalkanes. Direct reaction with a hydrohalic acid rarely gives a pure product, instead generating ethers. However, some exceptions are known: ionic liquids suppress the formation or promote the cleavage of ethers, hydrochloric acid converts tertiary alcohols to choloroalkanes, and primary and secondary alcohols convert similarly in the presence of a Lewis acid activator, such as zinc chloride. The latter is exploited in the Lucas test.
In the laboratory, more active deoxygenating and halogenating agents combine with base to effect the conversion. In the "Darzens halogenation", thionyl chloride () with pyridine converts less reactive alcohols to chlorides. Both phosphorus pentachloride () and phosphorus trichloride () function similarly, and alcohols convert to bromoalkanes under hydrobromic acid or phosphorus tribromide (PBr). The heavier halogens do not require preformed reagents: A catalytic amount of may be used for the transformation using phosphorus and bromine; is formed in situ. Iodoalkanes may similarly be prepared using red phosphorus and iodine (equivalent to phosphorus triiodide).
One family of named reactions relies on the deoxygenating effect of triphenylphosphine. In the Appel reaction, the reagent is tetrahalomethane and triphenylphosphine; the co-products are haloform and triphenylphosphine oxide. In the Mitsunobu reaction, the reagents are any nucleophile, triphenylphosphine, and a diazodicarboxylate; the coproducts are triphenyl­phosphine oxide and a hydrazodiamide. | 0 | Theoretical and Fundamental Chemistry |
Andrew Handyside (1805–1887) was born in Edinburgh and set up works in Derby where he made ornamental items, bridges and pillar boxes, many of which survive today. | 1 | Applied and Interdisciplinary Chemistry |
* [http://bioinformatics.ai.sri.com/ptools/ Pathway Tools]: A bioinformatics software package that assists in the construction of pathway/genome databases such as EcoCyc. Developed by Peter Karp and associates at the SRI International Bioinformatics Research Group, Pathway Tools has several components. Its PathoLogic module takes an annotated genome for an organism and infers probable metabolic reactions and pathways to produce a new pathway/genome database. Its MetaFlux component can generate a quantitative metabolic model from that pathway/genome database using flux-balance analysis. Its Navigator component provides extensive query and visualization tools, such as visualization of metabolites, pathways, and the complete metabolic network.
* [http://ergo.integratedgenomics.com/ ERGO]: A subscription-based service developed by Integrated Genomics. It integrates data from every level including genomic, biochemical data, literature, and high-throughput analysis into a comprehensive user friendly network of metabolic and nonmetabolic pathways.
* [http://www.cogsys.cs.uni-tuebingen.de/software/KEGGtranslator/ KEGGtranslator]: an easy-to-use stand-alone application that can visualize and convert KEGG files (KGML formatted XML-files) into multiple output formats. Unlike other translators, KEGGtranslator supports a plethora of output formats, is able to augment the information in translated documents (e.g., MIRIAM annotations) beyond the scope of the KGML document, and amends missing components to fragmentary reactions within the pathway to allow simulations on those. KEGGtranslator converts these files to SBML, BioPAX, SIF, SBGN, SBML with qualitative modeling extension, GML, GraphML, JPG, GIF, LaTeX, etc.
* [http://modelseed.org/ ModelSEED]: An online resource for the analysis, comparison, reconstruction, and curation of genome-scale metabolic models. Users can submit genome sequences to the RAST annotation system, and the resulting annotation can be automatically piped into the ModelSEED to produce a draft metabolic model. The ModelSEED automatically constructs a network of metabolic reactions, gene-protein-reaction associations for each reaction, and a biomass composition reaction for each genome to produce a model of microbial metabolism that can be simulated using Flux Balance Analysis.
* MetaMerge: algorithm for semi-automatically reconciling a pair of existing metabolic network reconstructions into a single metabolic network model.
* [https://github.com/esaskar/CoReCo CoReCo]: algorithm for automatic reconstruction of metabolic models of related species. The first version of the software used KEGG as reaction database to link with the EC number predictions from CoReCo. Its automatic gap filling using atom map of all the reactions produce functional models ready for simulation. | 1 | Applied and Interdisciplinary Chemistry |
The pK of [HDABCO] (the protonated derivative) is 8.8, which is almost the same as ordinary alkylamines. The nucleophilicity of the amine is high because the amine centers are unhindered. It is sufficiently basic to promote a variety of coupling reactions. | 0 | Theoretical and Fundamental Chemistry |
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