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Kidd Metallurgical Site The (or Met Site) is a metallurgical facility in Timmins, Ontario, Canada. It was built in 1980 and owned and operated by Xstrata Copper, following their 2006 takeover of Falconbridge Ltd. The site employs approximately 675 hourly employees. The plant is southeast of the Kidd Mine, and houses a concentrator, copper smelter and refinery, zinc plant, cadmium plant, indium plant and a sulphuric acid plant. The Met Site was built away from the mine because of the muskeg-like terrain surrounding the mine. The Met Site processes material from the Kidd Mine and outside sources, and employs 875 people. Of the 875 employees 125 work at the concentrator, 205 in the copper operations and 275 in the zinc facilities. The remainder of the employees are support staff. Xstrata announced its plans to close the Metallurgical Site in May 2010. Only the concentrator will remain as the ore will now be shipped to Québec. The demolition of the rest of the plant started in February 2011. | https://en.wikipedia.org/wiki?curid=22367619 |
John C. Sheehan John Clark Sheehan (23 September 1915 – 21 March 1992) was an American organic chemist whose work on synthetic penicillin led to tailor-made forms of the drug. After nine years of hard work at the Massachusetts Institute of Technology (M.I.T.), he became the first to discover a practical method for synthesizing penicillin V. While achieving total synthesis, Sheehan also produced an intermediate compound, 6-aminopenicillanic acid, which turned out to be the foundation of hundreds of kinds of synthetic penicillin. Dr. Sheehan's research on synthetic penicillin paved the way for the development of customized forms of the lifesaving antibiotic that target specific bacteria. Over the four decades he worked at M.I.T., Sheehan came to hold over 30 patents, including the invention of ampicillin, a commonly used semi-synthetic penicillin that is taken orally rather than by injection. His research covered not only penicillin, but also peptides, other antibiotics, alkaloids, and steroids. He was born on September 23, 1915 in Battle Creek, Michigan to Florence and Leo C. Sheehan. His family had Irish and Yankee background, and he was raised as a Catholic and attended Catholic grade schools. His father was then a sports editor and police reporter for a local newspaper, The Battle Creek Enquirer. Leo C. Sheehan left home at the age of fifteen and found work as a reporter in San Francisco. As a skill writer, he progressed quickly with The Battle Creek Enquirer and became the managing editor | https://en.wikipedia.org/wiki?curid=22372550 |
John C. Sheehan At one point, he functioned as the ghostwriter for Frank Murphy, who was once the governor of Michigan and a Supreme Court Justice. Sheehan's mother was a genealogist who later became the Michigan registrar for the Daughters of the American Revolution. His paternal grandfather, John W. Sheehan, was a successful lawyer, while his maternal grandfather, Nathaniel Y. Green, was a bank manager who had a keen interest in science and nature. Green played a role in stimulating John C. Sheehan's interest in science by giving him a microscope with an oil-immersion lens. He also introduced Sheehan to the curator of a local museum and took his grandson to meetings where Green frequently met with others passionate about astronomy. At a young age, John Sheehan had been fascinated by science, especially explosives and rocketry. He started with a simple chemistry set and then progressed to a basement laboratory where he built models and performed experiments. A model airplane that he built with a delta wing won a competition in his self-design class. Apart from science, Sheehan was also very competitive in other activities. He was an excellent marble shooter in elementary school, representing his school in the state championships. In addition, he was the winner of a city-wide yo-yo competition, the winner of a Boy Scout election, an active member of his high school football team, as well as Battle Creek College's best tennis player. Sheehan's father had a long struggle with cancer and died at age fifty | https://en.wikipedia.org/wiki?curid=22372550 |
John C. Sheehan Sheehan had two brothers, Joseph Sheehan and David Sheehan. Joseph is a professor of psychology at the University of California and ran training programs for relieving speech defects with his wife, Vivian. David Sheehan, the youngest of the three, worked in the manufacturing industry in Battle Creek. John Sheehan married Marion Jennings shortly after receiving his Ph.D and had three children: Jr., David E. Sheehan, and Elizabeth (Betsy) S. Watkins. He had six grandchildren. John Sheehan attended Catholic grade schools, even though John and his brother Joseph were not particularly religious later in life. He studied chemistry and political science at Battle Creek College. In 1937, Sheehan graduated as the valedictorian of his class and won a scholarship for graduate studies in any subject of his choice. He decided to study organic chemistry at the University of Michigan, receiving his Master's in 1938 and his PhD in 1941. His doctorate advisor, Werner E. Bachmann, was involved in the synthesis of steroid hormones. As a post-doctoral fellow, Sheehan collaborated with Bachmann on the commercially feasible production of RDX also known as cyclonite, which turned out to give the Allies a huge advantage at sea during World War II. After the efficient completion of RDX synthesis, John Sheehan had the experience of applying organic chemistry to real-life problems. Having struggled against pneumonia and mastoiditis in his earlier years, Sheehan was eager to start working on antibiotics | https://en.wikipedia.org/wiki?curid=22372550 |
John C. Sheehan He wrote, "If my doctors had had a course of treatment as effective as that made possible by penicillin, I would probably not have lost that year." In 1941, he accepted a position at Merck & Co. in Rahway, New Jersey. He worked there until 1946 as a senior research chemist under the supervision of Dr. Max Tishler. Sheehan had good results for his work on many projects, including those on calcium pantothenate, streptomycin, and vitamin B6. However, he wanted to pursue the synthesis of penicillin, which was hard in an industrial setting driven by results given that many scientists of his time believed that it was impossible. John Sheehan's work attracted the attention of Arthur C. Cope, who was the head of the Department of Chemistry at the M.I.T. at the time. He decided to join the M.I.T. faculty as an assistant professor at a salary that was half of what he made at Merck. Within his first few years at M.I.T., John Sheehan was already recognized for his ingenuity in synthetic organic chemistry, especially for his new methods of synthesis of peptides, three new syntheses of β-lactams, first synthesis of the penicillin ring system, and his work on several other natural products. For three decades after the discovery of natural penicillin by Sir Alexander Fleming, the source of the antibiotic hardly changed. Scientists made the drug by natural fermentation of Penicillium mold | https://en.wikipedia.org/wiki?curid=22372550 |
John C. Sheehan However, during World War II, the United States government undertook a massive effort to determine the chemical structure of penicillin and to chemically synthesize it in large quantities. The scale of this project was compared to the development of the atomic bomb. This stemmed from the dire need for the antibiotic to treat soldiers on the battlefield. More than a thousand chemists working at thirty-nine laboratories were involved in the project. Despite the huge investment by the government, none proved to be successful in solving this elusive problem. As John Sheehan described in his book "The Enchanted Ring: The Untold Story of Penicillin", after the war, most other synthetic chemists abandoned attempting penicillin synthesis, and were convinced that such synthesis was impossible. For the nine years that he worked on penicillin synthesis, there were practically no competitors, leaving Sheehan on a lonely search for a way to synthesize the antibiotic. Most young academic chemists chose not to undertake projects that they perceived to be painfully slow because they wanted to impress faculty tenure committees with many experiments and publications. Even though many of his friends openly questioned his decision of getting involved with the drug, Sheehan was determined to work on the chemical synthesis of penicillin at M.I.T. Once he decided that penicillin was an important problem, and one that had a solution, Sheehan never re-evaluated his position | https://en.wikipedia.org/wiki?curid=22372550 |
John C. Sheehan He explained that one of the reasons he decided to switch from his job at Merck to M.I.T. was because "At M.I.T, I was a research committee of one. I could make the decision to spend the rest of my life on the penicillin problem; it was only my career that was on the line." At the time, it was known that the molecular weight of penicillin was around 350 g/mol, which was within the range of molecules that had already been chemically synthesized. The problem was the making the chemically unstable beta-lactam ring that was crucial to the antibiotic properties of the molecule. Beta-lactam antibiotics inhibit the formation of the peptidoglycan layer of the cell walls of Gram-positive bacteria. Most of the scientists experienced failure after failure because "the appropriate techniques and reactions for putting together the penicillin molecule simply had not yet been discovered." In the words of Sheehan, using traditional methods at the time was like "placing an anvil on top of a house of cards." After nine years of dogged work in the M.I.T. laboratories, this persistent organic chemist finally solved one of chemistry's most baffling problems at the time. In 1957, announced that his group had completed the first synthesis of penicillin V (one of the two most useful forms of the antibiotic). During the process, he had also produced an intermediate, 6-aminopenicillanic acid, which was later used as a foundation for preparing a variety of penicillins | https://en.wikipedia.org/wiki?curid=22372550 |
John C. Sheehan This allowed researchers to combat the resistance that certain bacteria had developed to particular forms of the drug. Sheehan later published his involvement in the synthesis of penicillins in "The Enchanted Ring: The Untold Story of Penicillin", which noted a complex legal skirmish over his patents on penicillin synthesis involving M.I.T. and Beecham, a British industrial research laboratory that was also working on penicillins. | https://en.wikipedia.org/wiki?curid=22372550 |
Synthetic Communications is a peer-reviewed scientific journal covering the synthesis of organic compounds. | https://en.wikipedia.org/wiki?curid=22379034 |
Organic Preparations and Procedures International is a bimonthly scientific journal focusing on organic chemists engaged in synthesis. Topics include original preparative chemistry in association with the synthesis of organic and organometallic compounds. | https://en.wikipedia.org/wiki?curid=22379335 |
Element collecting is the hobby of collecting the chemical elements. Many element collectors simply enjoy finding peculiar uses of chemical elements. Others enjoy studying the properties of the elements, possibly engaging in amateur chemistry, and some simply collect elements for no practical reason. Some element collectors invest in elements, while some amateur chemists have amassed a large collection of elements—Oliver Sacks, for example. In recent years, the hobby has gained popularity with media attention brought by element collectors like Theodore Gray. Some collectors attempt to collect very high purity samples of each element. Others prefer to find the element in everyday use. Some are averse to collecting the element as a compound or alloy, while others find this acceptable. Collectors may isolate elements in their own homes. Hydrogen, for example, can be easily isolated via the electrolysis of water. In addition to the element samples, some element collectors also collect items connected with the element, such as manufactured goods containing the element, rocks and minerals with the element as a constituent or compounds of the element. Some manufacturers also sell coins made from pure elements, and density cubes made from the pure element can also be sourced on auction sites such as eBay | https://en.wikipedia.org/wiki?curid=22379986 |
Element collecting Some commercial retailers now cater to the element collecting community, even selling large quantities in sets, since purchasing elements from large chemical companies like Sigma-Aldrich is frequently prohibited or uneconomical for individuals. There are a number of specialist element providers which retail to the public over the web, sell individual element samples in addition to full and partial element sets. Many also sell elements through auction sites, such as eBay. Established specialist providers include Nova Elements, RGB Elements, Smart Elements, SMT Metalle Wimmer, PEGUYS, Metallium, Collect the Periodic Table, Luciteria and Onyxmet. presents many challenges: some elements, such as mercury, thallium, and arsenic are toxic and so are difficult to find or their sale is restricted. Others are extremely rare in commercial use, such as scandium, lutetium, and thulium, and are therefore hard to source or are comparatively expensive. Some, such as caesium and fluorine, are too reactive and have restrictions on their shipping; others, such as gallium, react corrosively and very fast with aluminium (e.g., as structural material in aircraft). Some, such as phosphorus and iodine, are controlled due to use in clandestine chemistry. Others, like radon and astatine, are radioactive and have half-lives too short for practical collection in addition to their radioactive hazards | https://en.wikipedia.org/wiki?curid=22379986 |
Element collecting Usually only the stable elements from hydrogen to bismuth (except the radioactive technetium and promethium) are collected, with the exceptions of the extremely long-lived thorium and uranium. It is possible to source other radioactive elements, such as radium (usually in the form of radium sulfate as part of luminescent paint on antique watch hands), americium (in the form of radioactive buttons containing 0.29 micrograms of americium extracted from older smoke detectors), and technetium. | https://en.wikipedia.org/wiki?curid=22379986 |
Chevron CRUSH is an experimental "in situ" shale oil extraction technology to convert kerogen in oil shale to shale oil. The name stands for Chevron's Technology for the Recovery and Upgrading of Oil from Shale. It is developed jointly by Chevron Corporation and the Los Alamos National Laboratory. The technology bases on the earlier "in situ" efforts. Sinclair Oil Corporation conducted an experiment using both natural and induced fractures to establish communication between wells and developing an "in situ" combustion process. Geokinetics, the Sandia National Laboratories, and the Laramie Energy Technology Center of the U.S. Department of Energy conducted field tests fracturing oil-shale formation by explosives and hydraulic fracturing technology. Equity Oil Company, Continental Oil Company and the University of Akron studied the benefit of carbon dioxide as a carrier gas to facilitate a higher yield of shale oil. Based on these works, Chevron Corporation and the Los Alamos National Laboratory started a cooperation in 2006 to improve the recovery of hydrocarbons from oil shale. In 2006, the United States Department of the Interior issued a research, development and demonstration lease for Chevron's demonstration project on public lands in Colorado’s Piceance Basin. In February 2012, Chevron notified the Bureau of Land Management and the Department of Reclamation, Mining and Safety that it intends to divest this lease. For decomposition kerogen in oil shale, the process uses heated carbon dioxide | https://en.wikipedia.org/wiki?curid=22380334 |
Chevron CRUSH The process involves drilling vertical wells into the oil shale formation and applying horizontal fractures induced by injecting carbon dioxide through drilled wells and then pressured through the formation for circulation through the fractured intervals to rubblize the production zone. For further rubblization propellants and explosives may be used. The used carbon dioxide then be routed to the gas generator to be reheated and recycled. The remaining organic matter in previously heated and depleted zones is combusted "in-situ" to generate the heated gases required to process successive intervals. These gases would then be pressured from the depleted zone into the newly fractured portion of the formation and the process would be repeated. The hydrocarbon fluids are brought up in conventional vertical oil wells. The processing area is isolated from surrounding groundwater by creating fractured areas ("pockets"), approximately wide and high within the center of the oil shale deposit. In this way, about of the confining layer would separate the process area from the water bearing layers above and below, keeping the aquifers out of the production zone. | https://en.wikipedia.org/wiki?curid=22380334 |
Cross-validation (analytical chemistry) Cross-validation is an approach by which the sets of scientific data generated using two or more methods are critically assessed. The cross-validation can be categorized as | https://en.wikipedia.org/wiki?curid=22381665 |
ExxonMobil Electrofrac is an "in situ" shale oil extraction technology proposed by ExxonMobil for converting kerogen in oil shale to shale oil. uses a series of fractures created in the oil shale formation. Preferably these fractures should be longitudinal vertical fractures created from horizontal wells and conducting electricity from the heel to the toe of each heating well. For conductivity, an electrically-conductive material such as calcined petroleum coke is injected into the wells in fractures, forming a heating element. Heating wells are placed in a parallel row with a second horizontal well intersecting them at their toe. This allows opposing electrical charges to be applied at either end. Laboratory experiments have demonstrated that electrical continuity is unaffected by kerogen conversion and that hydrocarbons are expelled from heated oil shale even under "in situ" stress. Planar heaters should be used because they require fewer wells than wellbore heaters and offer a reduced surface footprint. The shale oil is extracted by separate dedicated production wells. | https://en.wikipedia.org/wiki?curid=22381897 |
CONQUEST is a linear scaling, or O(N), density functional theory (DFT) electronic structure code. The code is designed to perform DFT calculations on very large systems containing many thousands of atoms. It can be run at different levels of precision ranging from ab initio tight binding up to full DFT with plane wave accuracy. It has been applied to the study of three-dimensional reconstructions formed by Ge on Si(001), containing over 20,000 atoms. Tests on the UK's national supercomputer HECToR in 2009 demonstrated the capability of the code to perform ground-state calculations on systems of over 1,000,000 atoms. Instead of solving for the Kohn-Sham eigenstates as normal DFT codes do, solves for the one particle density matrix, formula_1. To make the problem computationally tractable, the density matrix is written in separable form: formula_2, where formula_3 is a "support function" centred on atom "i" (with support functions on the same atom notated by formula_4) and formula_5 is the density matrix in the basis of the support functions. The ground state is found as a series of nested loops: • Minimise the energy with respect to the density matrix for fixed charge density and support functions • Find self-consistency between charge density and potential • Minimise the energy with respect to the support functions The support functions are confined within spheres of given cutoff radius and the density matrix is forced to zero beyond a given range: formula_6 | https://en.wikipedia.org/wiki?curid=22382490 |
CONQUEST These approximations give linear scaling behaviour, and as the radii are increased tend to the exact result. is jointly developed at the Department of Physics and Astronomy and London Centre for Nanotechnology, University College London in the UK and at the Computational Materials Science Centre, National Institute for Materials Science, Tsukuba, Japan. In the UK, the development team includes Dr. David Bowler, Dr. Veronika Brazdova, Prof. Mike Gillan, Dr. Andrew Horsfield, Mr. Alex Sena, Mr. Lianheng Tong, Mr. Jack Baker and Mr. Shereif Mujahed who are all members of the Thomas Young Centre; in Japan, the development team includes Dr. Tsuyoshi Miyazaki, Dr. Takahisa Ohno, Dr. Takao Ohtsuka, Dr. Milica Todorovic and Dr. Antonio Torralba. Previous developers include Ian Bush, Rathin Choudhury, Chris Goringe and Eduardo Hernandez. | https://en.wikipedia.org/wiki?curid=22382490 |
Compendium of Analytical Nomenclature The is a IUPAC nomenclature book published by the International Union of Pure and Applied Chemistry (IUPAC) containing internationally accepted definitions for terms in analytical chemistry. It has traditionally been published in an orange cover, hence its informal name, the Orange Book. The Orange Book is one of IUPAC's "Color Books" along with the "Nomenclature of Organic Chemistry" ("Blue Book"), "Nomenclature of Inorganic Chemistry" ("Red Book"), "Quantities, Units and Symbols in Physical Chemistry" ("Green Book"), and "Compendium of Chemical Terminology" ("Gold Book"). Although the book is described as the "Definitive Rules", there have been three editions published; the first in 1978 (), the second in 1987 () and the third in 1998 (). The third edition is available online. A Catalan translation has also been published (1987, ). | https://en.wikipedia.org/wiki?curid=22384158 |
Heterocycles (journal) Heterocycles is a scientific journal on the topic of heterocyclic compounds. In 2006 it was awarded the "In Memory of Professor A.N. Kost" medal by Lomonosov Moscow State University and Mendeleev Russian Chemical Society. The impact factor of this journal is 1.079 (2014). | https://en.wikipedia.org/wiki?curid=22385759 |
Current Organic Chemistry is a scientific review journal summarizing progress in the fields of asymmetric synthesis, organo-metallic chemistry, bioorganic chemistry, heterocyclic chemistry, natural product chemistry and analytical methods in organic chemistry. | https://en.wikipedia.org/wiki?curid=22385763 |
List of highly toxic gases Many gases have toxic properties, which are often assessed using the LC50 (median lethal dose) measure. In the United States, many of these gases have been assigned an NFPA 704 health rating of 4 (may be fatal) or 3 (may cause serious or permanent injury), and/or exposure limits (TLV, TWA or STEL) determined by the ACGIH professional association. Some, but by no means all, toxic gases are detectable by odor, which can serve as a warning. Among the best known toxic gases are carbon monoxide, chlorine, nitrogen dioxide and phosgene. | https://en.wikipedia.org/wiki?curid=22387613 |
Glycorandomization Glycorandomization, is a drug discovery and drug development technology platform to enable the rapid diversification of bioactive small molecules, drug leads and/or approved drugs through the attachment of sugars. Initially developed as a facile method to manipulate carbohydrate substitutions of naturally occurring glycosides to afford the corresponding differentially glycosylated natural product libraries, glycorandomization applications have expanded to include both small molecules (drug leads and approved drugs) and even macromolecules (proteins). Also referred to as 'glycodiversification', glycorandomization has led to the discovery of new glycoside analogs which display improvements in potency, selectivity and/or ADMET as compared to the parent molecule. The traditional method for attaching sugars to natural products, drugs or drug leads is by chemical glycosylation. This classical approach typically requires multiple protection/deprotection steps in addition to the key anomeric activation/coupling reaction which, depending upon the glycosyl donor/acceptor pair, can lead to a mixture of anomers. Unlike classical chemical glycosylation, glycorandomization methods are divergent ("i.e.", diverge from a common starting material, see divergent synthesis) and are not dependent upon sugar/aglycon protection/deprotection or sugar anomeric activation | https://en.wikipedia.org/wiki?curid=22387640 |
Glycorandomization Two complementary strategies to achieve glycorandomization/diversification have been developed: an enzyme-based strategy referred to as 'chemoenzymatic glycorandomization' and a chemoselective method known as 'neoglycorandomization'. Both methods start with free reducing sugars and a target aglycon to afford a library of compounds which differ solely by the sugars appended to the target natural product, drug or drug lead. Chemoenzymatic glycorandomization was inspired by the early pathway engineering work of Hutchinson and coworkers that suggested natural product glycosyltransferases were capable of utilizing non-native sugar nucleotide donors. The initial platform for chemoenzymatic glycorandomization was based upon a set of two highly permissive sugar activation enzymes (a sugar anomeric kinase and sugar-1-phosphate nucleotidyltransferase) to afford sugar nucleotide libraries as donors for these promiscuous glycosyltransferases where the permissivity of the corresponding sugar kinase and nucleotidyltransferase was expanded by enzyme engineering and directed evolution. The first application of this three enzyme (kinase, nucleotidyltransferase and glycosyltransferase) strategy enabled the product of a set of >30 differentially glycosylated vancomycins, some members of which were further diversified chemoselectively by virtue of the installation of sugars bearing chemoselective handles | https://en.wikipedia.org/wiki?curid=22387640 |
Glycorandomization This enzymatic platform has been further advanced through glycosyltransferase evolution and capitalizing upon the discovery of the reversibility of glycosyltransferase-catalyzed reactions first discovered in the context of calicheamicin biosynthesis. Neoglycorandomization is a chemoselective glycodiversification method inspired by the alkoxyamine-based ‘neoglycosylation’ reaction first described Peri and Dumy. This reaction proceeds via an oxy-iminium intermediate to ultimately provide the more thermodynamically-favored closed ring neoglycoside. The neoglycosylation reaction is compatible with a wide range of saccharide and aglycon functionality where neoglycoside anomeric stereospecificity is a thermodynamically-driven. Importantly, structural and functional studies reveal neoglycosides to serve as good mimics of their "O"-glycosidic comparators. The first neoglycorandomization proof of concept focused upon digitoxin where the rapid generation and cancer cell line cytotoxicity screening of 78 digitoxigenin neoglycosides revealed unique analogs with improved anticancer activity and reduced potential for cardiotoxicity. This platform has since been automated and used as an effective medicinal chemistry tool to modulate the properties of a range of natural products and pharmaceutical drugs. Both chemoenzymatic glycorandomization and neoglycorandomization use free reducing sugars and unprotected aglycons and are thereby a notable advance over classical glycosylation methods | https://en.wikipedia.org/wiki?curid=22387640 |
Glycorandomization A notable advantage of the enzymatic approach is the use of the corresponding genes encoding for the permissive kinases, nucleotidyltransferases and/or glycosyltransferases for in vivo synthetic biology applications to afford in vivo glycorandomization. However, it is important to note the enzymatic platform is dependent upon the permissivity of the enzymes employed. In contrast, the main hurdle to chemoselective neoglycorandomization is installation of the alkoxylamine handle. Unlike the enzymatic approach, the anomeric stereoselectivity of the chemoselective method depends upon the reducing sugar used and can, in some cases, lead to anomeric mixtures. is used in the pharmaceutical industry and academic community to alter glycosylation patterns of sugar-containing natural products or to append sugars to drugs/drug leads. It provides a fast way to investigate the effect of subtle sugar modification on the pharmacological properties of the natural products analogues, thus, affording a new approach to drug discovery. | https://en.wikipedia.org/wiki?curid=22387640 |
Glass coloring and color marking may be obtained by in several ways. Ordinary soda-lime glass appears colorless to the naked eye when it is thin, although iron oxide impurities produce a green tint which can be viewed in thick pieces or with the aid of scientific instruments. Further metals and metal oxides can be added to glass during its manufacture to change its color which can enhance its aesthetic appeal. Examples of these additives are listed below: Tin oxide with antimony and arsenic oxides produce an opaque white glass (milk glass), first used in Venice to produce an imitation porcelain. Similarly, some smoked glasses may be based on dark-colored inclusions, but with ionic coloring it is also possible to produce dark colors (see above). Glass containing two or more phases with different refractive indices shows coloring based on the Tyndall effect and explained by the Mie theory, if the dimensions of the phases are similar or larger than the wavelength of visible light. The scattered light is blue and violet as seen in the image, while the transmitted light is yellow and red. Dichroic glass has one or several coatings in the nanometer-range (for example metals, metal oxides, or nitrides) which give the glass dichroic optical properties. Also the blue appearance of some automobile windshields is caused by dichroism. | https://en.wikipedia.org/wiki?curid=22390444 |
Liquid nitrogen engine A liquid nitrogen vehicle is powered by liquid nitrogen, which is stored in a tank. Traditional nitrogen engine designs work by heating the liquid nitrogen in a heat exchanger, extracting heat from the ambient air and using the resulting pressurized gas to operate a piston or rotary motor. Vehicles propelled by liquid nitrogen have been demonstrated, but are not used commercially. One such vehicle, "Liquid Air" was demonstrated in 1902. Liquid nitrogen propulsion may also be incorporated in hybrid systems, e.g., battery electric propulsion and fuel tanks to recharge the batteries. This kind of system is called a hybrid liquid nitrogen-electric propulsion. Additionally, regenerative braking can also be used in conjunction with this system. One advantage of the liquid nitrogen vehicle is that the exhaust gas is simply nitrogen, a component of air, and thus it produces no localized air pollution in the tailpipe emissions. This does not make it completely pollution free, since energy had been required to liquify the nitrogen in the first place, but that liquification process can be remote from the vehicle operation, and could in principle be powered by a renewable energy or clean energy source. Liquid nitrogen is generated by cryogenic or reversed Stirling engine coolers that liquefy the main component of air, nitrogen (N). The cooler can be powered by electricity or through direct mechanical work from hydro or wind turbines. Liquid nitrogen is distributed and stored in insulated containers | https://en.wikipedia.org/wiki?curid=22391303 |
Liquid nitrogen engine The insulation reduces heat flow into the stored nitrogen; this is necessary because heat from the surrounding environment boils the liquid, which then transitions to a gaseous state. Reducing inflowing heat reduces the loss of liquid nitrogen in storage. The requirements of storage prevent the use of pipelines as a means of transport. Since long-distance pipelines would be costly due to the insulation requirements, it would be costly to use distant energy sources for production of liquid nitrogen. Petroleum reserves are typically a vast distance from consumption but can be transferred at ambient temperatures. Liquid nitrogen consumption is in essence production in reverse. The Stirling engine or cryogenic heat engine offers a way to power vehicles and a means to generate electricity. Liquid nitrogen can also serve as a direct coolant for refrigerators, electrical equipment and air conditioning units. The consumption of liquid nitrogen is in effect boiling and returning the nitrogen to the atmosphere. In the Dearman Engine the nitrogen is heated by combining it with the heat exchange fluid inside the cylinder of the engine. In 2008, the US Patent Office granted a patent on a liquid nitrogen powered turbine engine. The turbine flash-expands liquid nitrogen that is sprayed into the high-pressure section of the turbine, and the expanding gas is combined with incoming pressurized air to produce a high-velocity stream of gas that is ejected from the back of the turbine | https://en.wikipedia.org/wiki?curid=22391303 |
Liquid nitrogen engine The resulting gas stream can be used to drive generators or other devices. The system has not been demonstrated to power electric generators of greater than 1 kW, however higher output may be possible. Although the liquid nitrogen is colder than the ambient temperature, the liquid nitrogen engine is nevertheless an example of a heat engine. A heat engine runs by extracting thermal energy from the temperature difference between a hot and a cold reservoir; in the case of the liquid nitrogen engine, the "hot" reservoir is the air in the ambient ("room temperature") surroundings, which is used to boil the nitrogen. As such, the nitrogen engine is extracting energy from the thermal energy of the air, and the conversion efficiency with which it converts energy can be calculated from the laws of thermodynamics using Carnot efficiency equation, which applies to all heat engines. The tanks to store the liquid nitrogen must be designed to safety standards appropriate for a pressure vessel, such as ISO 11439. The storage tank may be made of: The fiber materials are considerably lighter than metals but generally more expensive. Metal tanks can withstand a large number of pressure cycles, but must be checked for corrosion periodically. Liquid nitrogen, LN2, is commonly transported in insulated tanks, up to 50 litres, at atmospheric pressure. These tanks, being non-pressurized tanks, are not subject to inspection | https://en.wikipedia.org/wiki?curid=22391303 |
Liquid nitrogen engine Very large tanks for LN2 are sometimes pressurized to less than 25 psi to aid in transferring the liquid at point of use. A vehicle propelled by liquid nitrogen, the "Liquid Air", was demonstrated in 1902. In June 2016 trials will begin in London, UK on supermarket J. Sainsbury's fleet of food delivery vehicles: using a Dearman nitrogen engine to provide power for the cooling of food cargo when the vehicle is stationary and the main engine is off. Currently delivery lorries mostly have second smaller diesel engines to power cooling when the main engine is off. Like other non-combustion energy storage technologies, a liquid nitrogen vehicle displaces the emission source from the vehicle's tail pipe to the central electrical generating plant. Where emissions-free sources are available, net production of pollutants can be reduced. Emission control measures at a central generating plant may be more effective and less costly than treating the emissions of widely dispersed vehicles. Liquid nitrogen vehicles are comparable in many ways to electric vehicles, but use liquid nitrogen to store the energy instead of batteries. Their potential advantages over other vehicles include: The principal disadvantage is the inefficient use of primary energy. Energy is used to liquefy nitrogen, which in turn provides the energy to run the motor. Any conversion of energy has losses. For liquid nitrogen cars, electrical energy is lost during the liquefaction process of nitrogen | https://en.wikipedia.org/wiki?curid=22391303 |
Liquid nitrogen engine Liquid nitrogen is not available in public refueling stations; however, there are distribution systems in place at most welding gas suppliers and liquid nitrogen is an abundant by-product of liquid oxygen production. Liquid nitrogen production is an energy-intensive process. Currently practical refrigeration plants producing a few tons/day of liquid nitrogen operate at about 50% of Carnot efficiency. Currently surplus liquid nitrogen is produced as a byproduct in the production of liquid oxygen. Any process that relies on a phase-change of a substance will have much lower energy densities than processes involving a chemical reaction in a substance, which in turn have lower energy densities than nuclear reactions. Liquid nitrogen as an energy store has a low energy density. Liquid hydrocarbon fuels, by comparison, have a high energy density. A high energy density makes the logistics of transport and storage more convenient. Convenience is an important factor in consumer acceptance. The convenient storage of petroleum fuels combined with its low cost has led to an unrivaled success. In addition, a petroleum fuel is a primary energy source, not just an energy storage and transport medium. The energy density—derived from nitrogen's isobaric heat of vaporization and specific heat in gaseous state—that can be realised from liquid nitrogen at atmospheric pressure and zero degrees Celsius ambient temperature is about 97 watt-hours per kilogram (W·h/kg) | https://en.wikipedia.org/wiki?curid=22391303 |
Liquid nitrogen engine This compares with 100–250 W·h/kg for a lithium-ion battery and 3,000 W·h/kg for a gasoline combustion engine running at 28% thermal efficiency, 30 times the density of liquid nitrogen used at the Carnot efficiency. For an isothermal expansion engine to have a range comparable to an internal combustion engine, a insulated onboard storage vessel is required. A practical volume, but a noticeable increase over the typical gasoline tank. The addition of more complex power cycles would reduce this requirement and help enable frost free operation. However, no commercially practical instances of liquid nitrogen use for vehicle propulsion exist. Unlike internal combustion engines, using a cryogenic working fluid requires heat exchangers to warm and cool the working fluid. In a humid environment, frost formation will prevent heat flow and thus represents an engineering challenge. To prevent frost build up, multiple working fluids can be used. This adds topping cycles to ensure the heat exchanger does not fall below freezing. Additional heat exchangers, weight, complexity, efficiency loss, and expense, would be required to enable frost free operation. However efficient the insulation on the nitrogen fuel tank, there will inevitably be losses by evaporation to the atmosphere. If a vehicle is stored in a poorly ventilated space, there is some risk that leaking nitrogen could reduce the oxygen concentration in the air and cause asphyxiation | https://en.wikipedia.org/wiki?curid=22391303 |
Liquid nitrogen engine Since nitrogen is a colorless and odourless gas that already makes up 78 per cent of air, such a change would be difficult to detect. Cryogenic liquids are hazardous if spilled. Liquid nitrogen can cause frostbite and can make some materials extremely brittle. As liquid N2 is colder than 90.2K, oxygen from the atmosphere can condense. Liquid oxygen can spontaneously and violently react with organic chemicals, including petroleum products like asphalt. Since the liquid to gas expansion ratio of this substance is 1:694, a tremendous amount of force can be generated if liquid nitrogen is rapidly vaporized. In an incident in 2006 at Texas A&M University, the pressure-relief devices of a tank of liquid nitrogen were sealed with brass plugs. As a result, the tank failed catastrophically, and exploded. | https://en.wikipedia.org/wiki?curid=22391303 |
Fire-safe polymers are polymers that are resistant to degradation at high temperatures. There is need for fire-resistant polymers in the construction of small, enclosed spaces such as skyscrapers, boats, and airplane cabins. In these tight spaces, ability to escape in the event of a fire is compromised, increasing fire risk. In fact, some studies report that about 20% of victims of airplane crashes are killed not by the crash itself but by ensuing fires. also find application as adhesives in aerospace materials, insulation for electronics, and in military materials such as canvas tenting. Some fire-safe polymers naturally exhibit an intrinsic resistance to decomposition, while others are synthesized by incorporating fire-resistant additives and fillers. Current research in developing fire-safe polymers is focused on modifying various properties of the polymers such as ease of ignition, rate of heat release, and the evolution of smoke and toxic gases. Standard methods for testing polymer flammability vary among countries; in the United States common fire tests include the UL 94 small-flame test, the ASTM E 84 Steiner Tunnel, and the ASTM E 622 National Institute of Standards and Technology (NIST) smoke chamber. Research on developing fire-safe polymers with more desirable properties is concentrated at the University of Massachusetts Amherst and at the Federal Aviation Administration where a long-term research program on developing fire-safe polymers was begun in 1995 | https://en.wikipedia.org/wiki?curid=22398341 |
Fire-safe polymers The Center for UMass/Industry Research on Polymers (CUMIRP) was established in 1980 in Amherst, MA as a concentrated cluster of scientists from both academia and industry for the purpose of polymer science and engineering research. Controlling the flammability of different materials has been a subject of interest since 450 B.C. when Egyptians attempted to reduce the flammability of wood by soaking it in potassium aluminum sulfate (alum). Between 450 B.C. and the early 20th century, other materials used to reduce the flammability of different materials included mixtures of alum and vinegar; clay and hair; clay and gypsum; alum, ferrous sulfate, and gypsum; and ammonium chloride, ammonium phosphate, borax, and various acids. These early attempts found application in reducing the flammability of wood for military materials, theater curtains, and other textiles, for example. Important milestones during this early work include the first patent for a mixture for controlling flammability issued to Obadiah Wyld in 1735, and the first scientific exploration of controlling flammability, which was undertaken by Joseph Louis Gay-Lussac in 1821. Research on fire-retardant polymers was bolstered by the need for new types of synthetic polymers in World War II. The combination of a halogenated paraffin and antimony oxide was found to be successful as a fire retardant for canvas tenting. Synthesis of polymers, such as polyesters, with fire retardant monomers were also developed around this time | https://en.wikipedia.org/wiki?curid=22398341 |
Fire-safe polymers Incorporating flame-resistant additives into polymers became a common and relatively cheap way to reduce the flammability of polymers, while synthesizing intrinsically fire-resistant polymers has remained a more expensive alternative, although the properties of these polymers are usually more efficient at deterring combustion. Traditional polymers decompose under heat and produce combustible products; thus, they are able to originate and easily propagate fire (as shown in Figure 1). The combustion process begins when heating a polymer yields volatile products. If these products are sufficiently concentrated, within the flammability limits, and at a temperature above the ignition temperature, then combustion proceeds. As long as the heat supplied to the polymer remains sufficient to sustain its thermal decomposition at a rate exceeding that required to feed the flame, combustion will continue. The purpose is to control heat below the critical level. To achieve this, one can create an endothermic environment, produce non-combustible products, or add chemicals that would remove fire-propagating radicals (H and OH), to name a few. These specific chemicals can be added into the polymer molecules permanently (see Intrinsically Fire-Resistant Polymers) or as additives and fillers (see Flame-Retardant Additives and Fillers). Oxygen catalyzes the pyrolysis of polymers at low concentration and initiates oxidation at high concentration. Transition concentrations are different for different polymers. (e.g | https://en.wikipedia.org/wiki?curid=22398341 |
Fire-safe polymers , polypropylene, between 5% and 15%). Additionally, polymers exhibit a structural-dependent relationship with oxygen. Some structures are intrinsically more sensitive to decomposition upon reaction with oxygen. The amount of access that oxygen has to the surface of the polymer also plays a role in polymer combustion. Oxygen is better able to interact with the polymer before a flame has actually been ignited. In most cases, results from a typical heating rate (e.g. 10℃/min for mechanical thermal degradation studies) do not differ significantly from those obtained at higher heating rates. The extent of reaction can, however, be influenced by the heating rate. For example, some reactions may not occur with a low heating rate due to evaporation of the products. Volatile products are removed more efficiently under low pressure, which means the stability of the polymer might have been compromised. Decreased pressure also slows down decomposition of high boiling products. The polymers that are most efficient at resisting combustion are those that are synthesized as intrinsically fire-resistant. However, these types of polymers can be difficult as well as costly to synthesize. Modifying different properties of the polymers can increase their intrinsic fire-resistance; increasing rigidity or stiffness, the use of polar monomers, and/or hydrogen bonding between the polymer chains can all enhance fire-resistance | https://en.wikipedia.org/wiki?curid=22398341 |
Fire-safe polymers Most intrinsically fire-resistant polymers are made by incorporation of aromatic cycles or heterocycles, which lend rigidity and stability to the polymers. Polyimides, polybenzoxazoles (PBOs), polybenzimidazoles, and polybenzthiazoles (PBTs) are examples of polymers made with aromatic heterocycles (Figure 2). Polymers made with aromatic monomers have a tendency to condense into chars upon combustion, decreasing the amount of flammable gas that is released. Syntheses of these types of polymers generally employ prepolymers which are further reacted to form the fire-resistant polymers. Ladder polymers are a subclass of polymers made with aromatic cycles or heterocycles. Ladder polymers generally have one of two types of general structures, as shown in Figure 3.One type of ladder polymer links two polymer chains with periodic covalent bonds. In another type, the ladder polymer consists of a single chain that is double-stranded. Both types of ladder polymers exhibit good resistance to decomposition from heat because the chains do not necessarily fall apart if one covalent bond is broken. However, this makes the processing of ladder polymers difficult because they are not easily melted. These difficulties are compounded because ladder polymers are often highly insoluble. Inorganic and semiorganic polymers often employ silicon-nitrogen, boron-nitrogen, and phosphorus-nitrogen monomers. The non-burning characteristics of the inorganic components of these polymers contribute to their controlled flammability | https://en.wikipedia.org/wiki?curid=22398341 |
Fire-safe polymers For example, instead of forming toxic, flammable gasses in abundance, polymers prepared with incorporation of cyclotriphosphazene rings give a high char yield upon combustion. Polysialates (polymers containing frameworks of aluminum, oxygen, and silicon) are another type of inorganic polymer that can be thermally stable up to temperatures of 1300-1400 °C. Additives are divided into two basic types depending on the interaction of the additive and polymer. Reactive flame retardants are compounds that are chemically built into the polymer. They usually contain heteroatoms. Additive flame retardants, on the other hand, are compounds that are not covalently bound to the polymer; the flame retardant and the polymer are just physically mixed together. Only a few elements are being widely used in this field: aluminum, phosphorus, nitrogen, antimony, chlorine, bromine, and in specific applications magnesium, zinc and carbon. One prominent advantage of the flame retardants (FRs) derived from these elements is that they are relatively easy to manufacture. They are used in important quantities: in 2013, the world consumption of FRs amounted to around 1.8/2.1 Mio t for 2013 with sales of 4.9/5.2 billion USD. Market studies estimate FRs demand to rise between 5/7 % pa to 2.4/2.6 Mio t until 2016/2018 with estimated sales of 6.1/7.1 billion USD | https://en.wikipedia.org/wiki?curid=22398341 |
Fire-safe polymers The most important flame retardants systems used act either in the gas phase where they remove the high energy radicals H and OH from the flame or in the solid phase, where they shield the polymer by forming a charred layer and thus protect the polymer from being attacked by oxygen and heat. Flame retardants based on bromine or chlorine, as well as a number of phosphorus compounds act chemically in the gas phase and are very efficient. Others only act in the condensed phase such as metal hydroxides (aluminum trihydrate, or ATH, magnesium hydroxide, or MDH, and boehmite), metal oxides and salts (zinc borate and zinc oxide, zinc hydroxystannate), as well as expandable graphite and some nanocomposites (see below). Phosphorus and nitrogen compounds are also effective in the condensed phase, and as they also may act in the gas phase, they are quite efficient flame retardants. Overviews of the main flame retardants families, their mode of action and applications are given in. Further handbooks on these topics are A good example for a very efficient phosphorus-based flame retardant system acting in the gas and condensed phases is aluminium diethyl phosphinate in conjunction with synergists such as melamine polyphosphate (MPP) and others. These phosphinates are mainly used to flame retard polyamides (PA) and polybutylene terephthalate (PBT) for flame retarded applications in electrical engineering/electronics (E&E) | https://en.wikipedia.org/wiki?curid=22398341 |
Fire-safe polymers Besides providing satisfactory mechanical properties and renewability, natural fibers are easier to obtain and much cheaper than man-made materials. Moreover, they are more environmentally friendly. Recent research focuses on application of different types of fire retardants during the manufacturing process as well as applications of fire retardants (especially intumescent coatings) at the finishing stage. Nanocomposites have become a hotspot in the research of fire-safe polymers because of their relatively low cost and high flexibility for multifunctional properties. Gilman and colleagues did the pioneering work by demonstrating the improvement of fire-retardancy by having nanodispersed montmorillonite clay in the polymer matrix. Later, organomodified clays, TiO nanoparticles, silica nanoparticles, layered double hydroxides, carbon nanotubes and polyhedral silsesquioxanes were proved to work as well. Recent research has suggested that combining nanoparticles with traditional fire retardants (e.g., intumescents) or with surface treatment (e.g., plasma treatment) effectively decreases flammability. Although effective at reducing flammability, flame-retardant additives and fillers have disadvantages as well. Their poor compatibility, high volatility and other deleterious effects can change properties of polymers. Besides, addition of many fire-retardants produces soot and carbon monoxide during combustion. Halogen-containing materials cause even more concerns on environmental pollution. | https://en.wikipedia.org/wiki?curid=22398341 |
Chemical glycosylation A chemical glycosylation reaction involves the coupling of a glycosyl donor, to a glycosyl acceptor forming a glycoside. If both the donor and acceptor are sugars, then the product is an oligosaccharide. The reaction requires activation with a suitable activating reagent. The reactions often result in a mixture of products due to the creation of a new stereogenic centre at the anomeric position of the glycosyl donor. The formation of a glycosidic linkage allows for the synthesis of complex polysaccharides which may play important roles in biological processes and pathogenesis and therefore having synthetic analogs of these molecules allows for further studies with respect to their biological importance. The glycosylation reaction involves the coupling of a glycosyl donor and a glycosyl acceptor via initiation using an activator under suitable reaction conditions. An activator is commonly a Lewis acid which enables the leaving group at the anomeric position to leave and results in the formation of the oxocarbenium ion. The formation of a glycosidic linkage results in the formation of a new stereogenic centre and therefore a mixture of products may be expected to result. The linkage formed may either be axial or equatorial (α or β with respect to glucose). To better understand this, the mechanism of a glycosylation reaction must be considered. The stereochemical outcome of a glycosylation reaction may in certain cases be affected by the type of protecting group employed at position 2 of the glycosyl donor | https://en.wikipedia.org/wiki?curid=22403212 |
Chemical glycosylation A participating group, typically one with a carboxyl group present, will predominantly result in the formation of a β-glycoside. Whereas a non-participating group, a group usually without a carboxyl group, will often result in an α-glycoside. Below it can be seen that having an acetyl protecting group at position 2 allows for the formation for an acetoxonium ion intermediate that blocks attack to the bottom face of the ring therefore allowing for the formation of the β-glycoside predominantly. Alternatively, the absence of a participating group at position 2, allows for either attack from the bottom or top face. Since the α-glycoside product will be favoured by the anomeric effect, the α-glycoside usually predominates. Different protecting groups on either the glycosyl donor or the glycosyl acceptor may affect the reactivity and yield of the glycosylation reaction. Typically, electron-withdrawing groups such as acetyl or benzoyl groups are found to decrease the reactivity of the donor/acceptor and are therefore termed "disarming" groups. Electron-donating groups such as the benzyl group, are found to increase the reactivity of the donor/acceptor and are therefore called "arming" groups. Glycosyl iodides were first introduced for use in glycosylation reactions in 1901 by Koenigs and Knorr although were often considered too reactive for synthetic use | https://en.wikipedia.org/wiki?curid=22403212 |
Chemical glycosylation Recently several research groups have shown these donors to have unique reactive properties and can differ from other glycosyl chlorides or bromides with respect to reaction time, efficiency, and stereochemistry. Glycosyl iodides may be made under a variety of conditions, one method of note is the reaction of a 1-"O"-acetylpyranoside with TMSI. Iodide donors may typically be activated under basic conditions to give β-glycosides with good selectivity. The use of tetraalkylammonium iodide salts such as tetrabutylammonium iodide (TBAI) allows for in-situ anomerization of the α-glycosyl halide to the β-glycosyl halide and provides the α-glycoside in good selectivity. Thioglycosides were first reported in 1909 by Fischer and since then have been explored constantly allowing for the development of numerous protocols for their preparation. The advantage of using thioglycosides is their stability under a wide range of reaction conditions allowing for protecting group manipulations. Additionally thioglycosides act as temporary protecting groups at the anomeric position allowing for thioglycosides to be useful as both glycosyl donors as well as glycosyl acceptors. Thioglycosides are usually prepared by reacting per-acetylated sugars with BF•OEt and the appropriate thiol. Thioglycosides used in glycosylation reactions as donors can be activated under a wide range of conditions, most notably using NIS/AgOTf | https://en.wikipedia.org/wiki?curid=22403212 |
Chemical glycosylation Trichloroacetimidates were first introduced and explored by Schmidt in 1980 and since then have become very popular for glycoside synthesis. The use of trichloroacetimidates provides many advantages including ease of formation, reactivity and stereochemical outcome. "O"-Glycosyl trichloroacetimidates are prepared via the addition of trichloroacetonitrile (ClCCN) under basic conditions to a free anomeric hydroxyl group. Typical activating groups for glycosylation reactions using trichloroacetimidates are BF•OEt or TMSOTf. Below are a few examples of some notable targets obtained via a series of glycosylation reactions. | https://en.wikipedia.org/wiki?curid=22403212 |
Passive binding In complexation catalysis, the term passive binding refers to any stabilizing interaction that is equally strong at the transition state level and in the reactant-catalyst complex. Having the same effect on the stability of the transition state and the reactant-catalyst complex, passive binding contributes to acceleration only if the equilibrium between the unassociated reactant and catalyst and their complex is not completely shifted to the right. It was defined by A.J. Kirby in 1996 as opposed to the dynamic binding, "i.e." the whole of interactions that are stronger at the transition state level than in the reactant-catalyst complex. | https://en.wikipedia.org/wiki?curid=22404484 |
List of chemical arms control agreements Chemical arms control is the attempt to limit the use or possession of chemical weapons through arms control agreements. These agreements are often motivated by the common belief "that these weapons ...are abominable", and by a general agreement that chemical weapons do "not accord with the feelings and principles of civilized warfare." The first chemical arms control agreement was the Strasbourg Agreement of 1675 between France and the Holy Roman Empire. This bilateral pact prohibited the use of poisoned bullets in any war between the two states. In the several centuries after that agreement, as chemistry advanced, states developed more sophisticated chemical weapons, and the primary concern in arms control shifted from poison bullets to poison gases. Thus, in the Hague Convention of 1899, a large group of states agreed "to abstain from the use of projectiles the sole objective of which is the diffusion of asphyxiating or deleterious gases". The 1907 Hague Convention and other early attempts at chemical arms control were also significant in restricting the use of chemical weapons in warfare. World War I broke out in Europe less than 20 years after the signing of the Hague Conventions. During that conflict, chemical weapons were used extensively by all sides in what still remains the largest case of chemical warfare | https://en.wikipedia.org/wiki?curid=22407921 |
List of chemical arms control agreements The use of chemical weapons in warfare was a war crime as such use was in direct violation of the 1899 Hague Declaration Concerning Asphyxiating Gases and the 1907 Hague Convention on Land Warfare, which prohibited the use of "poison or poisoned weapons" in warfare. After World War I, arms control agreements in general, and chemical arms control agreements in particular, gained renewed support. After seeing the gas attacks of the war, the general public overwhelmingly supported provisions that strongly regulated chemical weapons. In one survey of Americans, 367,000 favored banning chemical warfare while 19 supported its continuation in the future. This public opinion stimulated increased efforts for a ban on chemical weapons. These efforts led to several agreements in the years before World War II, including the Geneva Protocol. World War II was seen as a significant success for chemical arms control as none of the belligerents made significant use of chemical weapons. In the immediate aftermath of the war, arms control efforts focused primarily on nuclear weapons given their immense destructive power, and chemical disarmament was not a priority. Nonetheless, chemical warfare began to expand again with gas attacks during the Yemeni Civil War, and allegations of use during the Korean War | https://en.wikipedia.org/wiki?curid=22407921 |
List of chemical arms control agreements Along with the substantial use of chemical weapons in the Iran–Iraq War, these incidents led to a renewed interest in chemical disarmament and increased the push towards disarmament, finally culminating in the 1993 Chemical Weapons Convention, a full-scale ban on the use, production and stockpiling of weapons, which took force in 1997. | https://en.wikipedia.org/wiki?curid=22407921 |
Compacted graphite iron (CGI), also known as vermicular graphite iron (GJV, VG, JV or GGV from the ) especially in non-English speaking countries, is a metal which is gaining popularity in applications that require either greater strength, or lower weight than cast iron. R.D. Schelleng obtained a patent for the production of compacted graphite iron in 1965. The graphite in compacted graphite iron differs in structure from that in gray iron because the graphite particles are shorter and thicker. The first commercial application for compacted graphite iron was for the brake discs for high-speed rail trains. More recently compacted graphite iron has been used for diesel engine blocks. It has proven to be useful in the manufacture of V topology diesel engines where the loading on the block is very high between the cylinder banks, and for heavy goods vehicles which use diesel engines with high combustion pressures. It is also used for turbo housings and exhaust manifolds, in the latter case to reduce corrosion. | https://en.wikipedia.org/wiki?curid=22407941 |
Ferrier carbocyclization The (or Ferrier II reaction) is an organic reaction that was first reported by the carbohydrate chemist Robert J. Ferrier in 1979. It is a metal-mediated rearrangement of enol ether pyrans to cyclohexanones. Typically, this reaction is catalyzed by mercury salts, specifically mercury(II) chloride. Several reviews have been published. Ferrier proposed the following reaction mechanism: In this mechanism, the terminal olefin undergoes hydroxymercuration to produce the first intermediate, compound 2, a hemiacetal. Next, methanol is lost and the dicarbonyl compound cyclizes through an attack on the electrophilic aldehyde to form the carbocycle as the product. A downside to this reaction is that the loss of CHOH at the anomeric position (carbon-1) results in a mixture of α- and β-anomers. The reaction also works for substituted alkenes (e. g. having an -OAc group on the terminal alkene). Ferrier also reported that the final product, compound 5, could be converted into a conjugated ketone (compound 6) by reaction with acetic anhydride (AcO) and pyridine, as shown below. In 1997, Sinaÿ and co-workers reported an alternative route to the synthesis (shown below) that did not involve cleavage of the bond at the anomeric position (the glycosidic bond). In this case, the major product formed had maintained its original configuration at the anomeric position | https://en.wikipedia.org/wiki?curid=22409391 |
Ferrier carbocyclization Sinaÿ proposed this reaction went through the following transition state: Sinaÿ also discovered that titanium (IV) derivatives such as [TiCl(O"i"Pr)] worked in the same reaction as a milder version of the Lewis acid, "i"-BuAl, which goes through a similar transition state involving the retention of configuration at the anomeric center. In 1988, Adam reported a modification of the reaction that used catalytic amounts of palladium (II) salts, which brought about the same conversion of enol ethers into carbosugars in a more environmentally friendly manner. The development of the has been useful for the synthesis of numerous natural products that contain the carbocycle group. In 1991, Bender and co-workers reported a synthetic route to pure enantiomers of "myo"-inositol derivatives using this reaction. It has also been applied to the synthesis of aminocyclitols in work done by Barton and co-workers. Finally, Amano "et al." used the Ferrier conditions to synthesise complex conjugated cyclohexanones in 1998. | https://en.wikipedia.org/wiki?curid=22409391 |
Carbohydrate conformation refers to the overall three-dimensional structure adopted by a carbohydrate (saccharide) molecule as a result of the through-bond and through-space physical forces it experiences arising from its molecular structure. The physical forces that dictate the three-dimensional shapes of all molecules—here, of all monosaccharide, oligosaccharide, and polysaccharide molecules—are sometimes summarily captured by such terms as "steric interactions" and "stereoelectronic effects" (see below). Saccharide and other chemical conformations can be reasonably shown using two-dimensional structure representations that follow set conventions; these capture for a trained viewer an understanding of the three-dimensional structure via structure drawings (see organic chemistry article, and "3D Representations" section in molecular geometry article); they are also represented by stereograms on the two dimensional page, and increasingly using 3D display technologies on computer monitors. Formally and quantitatively, conformation is captured by description of a molecule's angles—for example, sets of three sequential atoms (bond angles) and four sequential atoms (torsion angles, dihedral angles), where the locations and angular directions of nonbonding electrons ("lone pair electrons") must sometimes also be taken into account | https://en.wikipedia.org/wiki?curid=22410248 |
Carbohydrate conformation Conformations adopted by saccharide molecules in response to the physical forces arising from their bonding and nonbonding electrons, modified by the molecule's interactions with its aqueous or other solvent environment, strongly influence their reactivity with and recognition by other molecules (processes which in turn can alter conformation). Chemical transformations and biological signalling mediated by conformation-dependent molecular recognition between molecules underlie all essential processes in living organisms. Pyranose and furanose forms can exist in different conformers and one can interconvert between the different conformations if an energy requirement is met. For the furanose system there are two possible conformers: twist (T) and envelope (E). In the pyranose system five conformers are possible: chair (C), boat (B), skew (S), half-chair (H) or envelope (E). In all cases there are four or more atoms that make up a plane. In order to define which atoms are above and below the plane one must orient the molecule so that the atoms are numbered clockwise when looking from the top. Atoms above the plane are prefixed as a superscript and atoms below the plane are suffixed as a subscript. If the ring oxygen is above or below the plane it must be prefixed or suffixed appropriately. The chair conformation of six-membered rings have a dihedral angle of 60° between adjacent substituents thus usually making it the most stable conformer | https://en.wikipedia.org/wiki?curid=22410248 |
Carbohydrate conformation Since there are two possible chair conformation steric and stereoelectronic effects such as the anomeric effect, 1,3-diaxial interactions, dipoles and intramolecular hydrogen bonding must be taken into consideration when looking at relative energies. Conformations with 1,3-diaxial interactions are usually disfavored due to steric congestion and can shift equilibrium to the other chair form (example: C to C). The size of the substituents greatly affects this equilibrium. However, intramolecular hydrogen bonding can be an example of a stabilizing 1,3-diaxial interaction. Dipoles also play a role in conformer stability, aligned dipoles lead to an increase in energy while opposed dipoles lead to a lowering of energy hence a stabilizing effect, this can be complicated by solvent effects. Polar solvents tend to stabilize aligned dipoles. All interaction must be taken into account when determining a preferred conformation. Conformations of five-membered rings are limited to two, envelope and twist. The envelope conformation has four atoms in a plane while the twist form only has three. In the envelope form two different scenarios can be envisioned; one where the ring oxygen is in the four atom plane and one where it is puckered above or below the plane. When the ring oxygen is not in the plane the substituents eclipse and when it is in the plane torsional strain is relieved. Conformational analysis for the twist form is similar thus leading to the two forms being very close in energy | https://en.wikipedia.org/wiki?curid=22410248 |
Carbohydrate conformation Anomers are diastereoisomers of glycosides, hemiacetals or related cyclic forms of sugars, or related molecules differing in configuration only at C-1. When the stereochemistry of the first carbon matches the stereochemistry of the last stereogenic center the sugar is the α-anomer when they are opposite the sugar is the β-anomer. Anomers can be interconverted through a process known as mutarotation. The anomeric effect more accurately called the "endo"-anomeric effect is the propensity for heteroatoms at C-1 to be oriented axially. This is counter intuitive as one would expect the equatorially anomer to be the thermodynamic product. This effect has been rationalized through dipole–dipole repulsion and n–σ* arguments. The reverse anomeric effect, proposed in 1965 by R. U. Lemieux, is the tendency for electropositive groups at the anomeric position to be oriented equatorially. Original publication reported this phenomenon with "N"-(2,3,4,6-tetra-"O"-acetyl-α--glucopyranosyl)-4-methylpyridinium bromide. However, further studies have shown the effect to be a solvation and steric issue. It is accepted that there is no generalized reverse anomeric effect. Rotation around the C-5/C-6 bond is described by the angle "ω". Three possible staggered conformations are possible:: "gauche"–"trans" ("gt"), "gauche"–"gauche" ("gg"), and "trans"–"gauche" ("tg"). The name indicates the interaction between O-5 and OH-6 first followed by the interaction between OH-6 and C-4 | https://en.wikipedia.org/wiki?curid=22410248 |
Carbohydrate conformation In addition to the factors affecting monosaccharide residues, conformational analysis of oligosaccharides and polysaccharides requires consideration additional factors. The "exo"-anomeric effect is similar to the "endo"-anomeric effect. The difference being that the lone pair being donated is coming from the substituent at C-1. However, since the substituent can be either axial or equatorial there are two types of "exo"-anomeric effects, one from axial glycosides and one from equatorial glycosides as long as the donating orbital is anti-periplanar to the accepting orbital. Three angles are described by "φ", "ψ" and "ω" (in the case of glycosidic linkages via O-6). Steric considerations and anomeric effects need to be taken into consideration when looking at preferred angles. In solution, reducing monosaccharides exist in equilibrium between their acyclic and cyclic forms with less than 1% in the acyclic form. The open chain form can close to give the pyranose and furanose with both the α- and β-anomers present for each. The equilibrium population of conformers depends on their relative energies which can be determined to a rough approximation using steric and stereoelectronic arguments. It has been shown that cations in solution can shift the equilibrium. | https://en.wikipedia.org/wiki?curid=22410248 |
Oligosaccharide nomenclature Oligosaccharides and polysaccharides are an important class of polymeric carbohydrates found in virtually all living entities. Their structural features make their nomenclature challenging and their roles in living systems make their nomenclature important. Oligosaccharides are carbohydrates that are composed of several monosaccharide residues joined through glycosidic linkage, which can be hydrolyzed by enzymes or acid to give the constituent monosaccharide units. While a strict definition of an oligosaccharide is not established, it is generally agreed that a carbohydrate consisting of two to ten monosaccharide residues with a defined structure is an oligosaccharide. Some oligosaccharides, for example maltose, sucrose, and lactose, were trivially named before their chemical constitution was determined, and these names are still used today. Trivial names, however, are not useful for most other oligosaccharides and, as such, systematic rules for the nomenclature of carbohydrates have been developed. To fully understand oligosaccharide and polysaccharide nomenclature, one must understand how monosaccharides are named. An oligosaccharide has both a reducing and a non-reducing end. The reducing end of an oligosaccharide is the monosaccharide residue with hemiacetal functionality, thereby capable of reducing the Tollens’ reagent, while the non-reducing end is the monosaccharide residue in acetal form, thus incapable of reducing the Tollens’ reagent | https://en.wikipedia.org/wiki?curid=22412019 |
Oligosaccharide nomenclature The reducing and non-reducing ends of an oligosaccharide are conventionally drawn with the reducing-end monosaccharide residue furthest to the right and the non-reducing (or terminal) end furthest to the left. Naming of oligosaccharides proceeds from left to right (from the non-reducing end to the reducing end) as glycosyl [glycosyl] glycoses or glycosyl [glycosyl] glycosides, depending on whether or not the reducing end is a free hemiacetal group. In parentheses, between the names of the monosaccharide residues, the number of the anomeric carbon atom, an arrow symbol, and the number of the carbon atom bearing the connecting oxygen of the next monosaccharide unit are listed. Appropriate symbols are used to indicate the stereochemistry of the glycosidic bonds (α or β), the configuration of the monosaccharide residue ( or), and the substitutions at oxygen atoms ("O"). Maltose and a derivative of sucrose illustrate these concepts: Maltose: α--Glucopyranosyl-(1→4)-β--glucopyranose Methyl 2,3,4-tri-"O"-benzyl-6-deoxy-6-fluoro-α--galactopyranosyl-(1→4)-2,3,6-tri-"O"-acetyl-β--glucopyranoside In the case of branched oligosaccharides, meaning that the structure contains at least one monosaccharide residue linked to more than two other monosaccharide residues, terms designating the branches should be listed in square brackets, with the longest linear chain (the parent chain) written without square brackets | https://en.wikipedia.org/wiki?curid=22412019 |
Oligosaccharide nomenclature The following example will help illustrate this concept: Allyl α--fucopyranosyl-(1→3)-[α--galactopyranosyl-(1→4)]-α--glucopyranosyl-(1→3)-α--galactopyranoside These systematic names are quite useful in that they provide information about the structure of the oligosaccharide. They do require a lot of space, however, so abbreviated forms are used when possible. In these abbreviated forms, the names of the monosaccharide units are shortened to their corresponding three-letter abbreviations, followed by "p" for pyranose or "f" for furanose ring structures, with the abbreviated aglyconic alcohol placed at the end of the name. Using this system, the previous example would have the abbreviated name α--Fuc"p"-(1→3)-[α--Gal"p"-(1→4)]-α--Glc"p"-(1→3)-α--Gal"p"OAll.Genral Formula_Cn+1(H2o)n.. Structure Formula..C12'H22'O11. Polysaccharides are considered to be polymers of monosaccharides containing ten or more monosaccharide residues. Polysaccharides have been given trivial names that reflect their origin. Two common examples are cellulose, a main component of the cell wall in plants, and starch, a name derived from the Anglo-Saxon stercan, meaning to stiffen. To name a polysaccharide composed of a single type of monosaccharide, that is a homopolysaccharide, the ending “-ose” of the monosaccharide is replaced with “-an”. For example, a glucose polymer is named glucan, a mannose polymer is named mannan, and a galactose polymer is named galactan | https://en.wikipedia.org/wiki?curid=22412019 |
Oligosaccharide nomenclature When the glycosidic linkages and configurations of the monosaccharides are known, they may be included as a prefix to the name, with the notation for glycosidic linkages preceding the symbols designating the configuration. The following example will help illustrate this concept: (1→4)-β--Glucan A heteropolysaccharide is a polymer containing more than one kind of monosaccharide residue. The parent chain contains only one type of monosaccharide and should be listed last with the ending “-an”, and the other types of monosaccharides listed in alphabetical order as “glyco-” prefixes. When there is no parent chain, all different monosaccharide residues are to be listed alphabetically as “glyco-” prefixes and the name should end with “-glycan”. The following example will help illustrate this concept: ((1→2)-α--galacto)-(1→4)-β--Glucan | https://en.wikipedia.org/wiki?curid=22412019 |
Monosaccharide nomenclature is the naming conventions of the basic unit of carbohydrate structure, monosaccharides, which may be monomers or part of a larger polymer. Monosaccharides are subunits that cannot be further hydrolysed in to simpler units. Depending on the number of carbon atom they are further classified in to trioses, tetroses, pentoses, hexoses etc., which is further classified in to aldoses and ketoses depending on the type of functional group present in them. The elementary formula of a simple monosaccharide is CHO, where the integer "n" is at least 3 and rarely greater than 7. Simple monosaccharides may be named generically according on the number of carbon atoms "n": trioses, tetroses, pentoses, hexoses, etc. Every simple monosaccharide has an acyclic (open chain) form, which can be written as <chem>H-(CH(OH))_\mathit{x}-(C=O)-(CH(OH))_\mathit{y}-H</chem>; that is, a straight chain of carbon atoms, one of which is a carbonyl group, all the others bearing a hydrogen -H and a hydroxyl -OH each, with one extra hydrogen at either end. The carbons of the chain are conventionally numbered from 1 to "n", starting from the end which is closest to the carbonyl. If the carbonyl is at the very beginning of the chain (carbon 1), the monosaccharide is said to be an aldose, otherwise it is a ketose. These names can be combined with the chain length prefix, as in aldohexose or ketopentose | https://en.wikipedia.org/wiki?curid=22414431 |
Monosaccharide nomenclature Most ketoses found in nature have the carbonyl in position 2; when that is not the case, one uses a numeric prefix to indicate the carbonyl's position. Thus for example, aldohexose means H(C=O)(CHOH)H, ketopentose means H(CHOH)(C=O)(CHOH)H, and 3-ketopentose means H(CHOH)(C=O)(CHOH)H. An alternative nomenclature uses the suffix '-ose' only for aldoses, and '-ulose' for ketoses. The position of the carbonyl (when it is not 1 or 2) is indicated by a numerical infix. For example, hexose in this nomenclature means H(C=O)(CHOH)H, pentulose means H(CHOH)(C=O)(CHOH)H, and hexa-3-ulose means H(CHOH)(C=O)(CHOH)H. Open-chain monosaccharides with same molecular graph may exist as two or more stereoisomers. The Fischer projection is a systematic way of drawing the skeletal formula of an open-chain monosaccharide so that each stereoisomer is uniquely identified. Two isomers whose molecules are mirror-images of each other are identified by prefixes '-' or '-', according to the handedness of the chiral carbon atom that is farthest from the carbonyl. In the Fischer projection, that is the second carbon from the bottom; the prefix is '-' or '-' according to whether the hydroxyl on that carbon lies to the right or left of the backbone, respectively. If the molecular graph is symmetrical (H(CHOH)(CO)(CHOH)H) and the two halves are mirror images of each other, then the molecule is identical to its mirror image, and there is no '-' form | https://en.wikipedia.org/wiki?curid=22414431 |
Monosaccharide nomenclature A distinct common name, such as "glucose" or "ribose", is traditionally assigned to each pair of mirror-image stereoisomers, and to each achiral stereoisomer. These names have standard three-letter abbreviations, such as 'Glc' for glucose and 'Rib' for ribose. Another nomenclature uses the systematic name of the molecular graph, a '-' or '-' prefix to indicate the position of the last chiral hydroxyl on the Fischer diagram (as above), and another italic prefix to indicate the positions of the remaining hydroxyls relative to the first one, read from bottom to top in the diagram, skipping the keto group if any. These prefixes are attached to the systematic name of the molecular graph. So for example, -glucose is -"gluco"-hexose, -ribose is -"ribo"-pentose, and -psicose is -"ribo"-hexulose. Note that, in this nomenclature, mirror-image isomers differ only in the "/" prefix, even though all their hydroxyls are reversed. The following tables shows the Fischer projections of selected monosaccharides (in open-chain form), with their conventional names. The table shows all aldoses with 3 to 6 carbon atoms, and a few ketoses. For chiral molecules, only the '-' form (with the next-to-last hydroxyl on the right side) is shown; the corresponding forms have mirror-image structures. Some of these monosaccharides are only synthetically prepared in the laboratory and not found in nature. For monosaccharides in their cyclic form, an infix is placed before the '-ose', '-ulose', or "'n"-ulose' suffix to specify the ring size | https://en.wikipedia.org/wiki?curid=22414431 |
Monosaccharide nomenclature The infix is "furan" for a 5-atom ring, "pyran" for 6, "septan" for 7, and so on. Ring closure creates another chiral center at the anomeric carbon (the one with the hemiacetal or acetal functionality), and therefore each open-chain stereoisomer gives rise to two distinct stereoisomers (anomers). These are identified by the prefixes 'α-' and 'β-', which denote the relative configuration of the anomeric carbon to that of the stereocenter at the other end of the carbon chain. To determine if the sugar is α or β, the structure is drawn in a Fischer projection; if the endocyclic oxygen (O5) and exocyclic oxygen (O1) are "cis", the sugar is α; if they are "trans", the sugar is β. Examples Glycosides are saccharides in which the hydroxyl -OH at the anomeric centre is replaced by an oxygen-bridged group -OR. The carbohydrate part of the molecule is called glycone, the -O- bridge is the glycosisdic oxygen, and the attached group is the aglycone. Glycosides are named by giving the aglyconic alcohol HOR, followed by the saccharide name with the '-e' ending replaced by '-ide'; as in phenol -glucopyranoside. Modification of sugar is generally done by replacing one or more –OH group with other functional groups at all positions except C-1. Since all these cases involves the removal of an –OH group, they are all deoxy sugars. Rules for Nomenclature of Modified Sugars: Examples Sugars in which –OH is protected by some modification are called protected sugars. Rules for Nomenclature for Protected Sugars: | https://en.wikipedia.org/wiki?curid=22414431 |
Intramolecular aglycon delivery is a synthetic strategy for the construction of glycans. This approach is generally used for the formation of difficult glycosidic linkages. Glycosylation reactions are very important reactions in carbohydrate chemistry, leading to the synthesis of oligosaccharides, preferably in a stereoselective manner. The stereoselectivity of these reactions has been shown to be affected by both the nature and the configuration of the protecting group at C-2 on the glycosyl donor ring. While 1,2-"trans"-glycosides (e.g. α-mannosides and β-glucosides) can be synthesised easily in the presence of a participating group (such as OAc, or NHAc) at the C-2 position in the glycosyl donor ring, 1,2-"cis"-glycosides are more difficult to prepare. 1,2-"cis"-glycosides with the α configuration (e.g. glucosides or galactosides) can often be prepared using a non-participating protecting group (such as Bn, or All) on the C-2 hydroxy group. However, 1,2-"cis"-glycosides with the β configuration are the most difficult to achieve, and present the greatest challenge in glycosylation reactions. One of the most recent approaches to prepare 1,2-"cis"-β-glycosides in a stereospecific manner is termed ‘Intramolecular Aglycon Delivery’, and various methods have been developed based on this approach. In this approach, the glycosyl acceptor is tethered onto the C-2-O-protecting group (X) in the first step | https://en.wikipedia.org/wiki?curid=22416330 |
Intramolecular aglycon delivery Upon activation of the glycosyl donor group (Y) (usually SR, OAc, or Br group) in the next step, the tethered aglycon traps the developing oxocarbenium ion at C-1, and is transferred from the same face as OH-2, forming the glycosidic bond stereospecifically. The yield of this reaction drops as the bulkiness of the alcohol increases. In this method, the glycosyl donor is protected at the C-2 position by an OAc group. The C-2-OAc protecting group is transformed into an enol ether by the Tebbe reagent (CpTi=CH), and then the glycosyl acceptor is tethered to the enol ether under acid-catalysed conditions to generate a mixed acetal. In a subsequent step, the β-mannoside is formed upon activation of the anomeric leaving group (Y), followed by work up. This method is similar to the previous method in that the glycosyl donor is protected at C-2 by an OAc group, which is converted into an enol ether by the Tebbe reagent. However, in this approach, "N"-iodosuccinimide (NIS) is used to tether the glycosyl acceptor to the enol ether, and in a second step, activation of the anomeric leaving group leads to intramolecular delivery of the aglycon to C-1 and formation of the 1,2-"cis"-glycoside product. The glycosyl donor is protected at C-2 by OAll group. The allyl group is then isomerized to a prop-1-enyl ether using a rhodium hydride generated from Wilkinson's catalyst ((PPh)RhCl) and butyllithium (BuLi). The resulting enol ether is then treated with NIS and the glycosyl acceptor to generate a mixed acetal. The 1,2-"cis" (e | https://en.wikipedia.org/wiki?curid=22416330 |
Intramolecular aglycon delivery g. β-mannosyl) product is formed in a final step through activation of the anomeric leaving group, delivery of the aglycon from the mixed acetal and finally hydrolytic work-up to remove the remains of the propenyl ether from O-2. In this method, the glycosyl donor is protected at C-2 by a "para"-methoxybenzyl (PMB) group. The glycosyl acceptor is then tethered at the benzylic position of the PMB protecting group in the presence of 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The anomeric leaving group (Y) is then activated, and the developing oxocarbenium ion is captured by the tethered aglycon alcohol (OR) to give 1,2-"cis" β-glycoside product. This is a modification of the method of oxidative tethering to a "para"-methoxybenzyl ether. The difference here is that the "para"-alkoxybenzyl group is attached to a solid support; the β-mannoside product is released into the solution phase in the last step, while the by-products remain attached to the solid phase. This makes the purification of the β-glycoside easier; it is formed as the almost exclusive product. The initial step in this method involves the formation of a silyl ether at the C-2 hydroxy group of the glycosyl donor upon addition of dimethyldichlorosilane in the presence of a strong base such as butyllithium (BuLi); then the glycosyl acceptor is added to form a mixed silaketal. Activation of the anomeric leaving group in the presence of a hindered base then leads to the β-glycoside | https://en.wikipedia.org/wiki?curid=22416330 |
Intramolecular aglycon delivery A modified silicon-tethering method involves mixing of the glycosyl donor with the glycosyl acceptor and dimethyldichlorosilane in the presence of imidazole to give the mixed silaketal in one pot. Activation of the tethered intermediate then leads to the β-glycoside product. | https://en.wikipedia.org/wiki?curid=22416330 |
C18H36O2 The molecular formula CHO may refer to: | https://en.wikipedia.org/wiki?curid=22417292 |
C10H20O The molecular formula CHO (molar mass : 156.27 g/mol) may refer to: | https://en.wikipedia.org/wiki?curid=22417345 |
Glycopeptide Glycopeptides are peptides that contain carbohydrate moieties (glycans) covalently attached to the side chains of the amino acid residues that constitute the peptide. Over the past few decades it has been recognised that glycans on cell surface (attached to membrane proteins or lipids) and those bound to proteins (glycoproteins) play a critical role in biology. For example, these constructs have been shown to play important roles in fertilization, the immune system, brain development, the endocrine system, and inflammation. The synthesis of glycopeptides provides biological probes for researchers to elucidate glycan function in nature and products that have useful therapeutic and biotechnological applications. "N"-Linked glycans derive their name from the fact that the glycan is attached to an asparagine (Asn, N) residue, and are amongst the most common linkages found in nature. Although the majority of N-linked glycans take the form GlcNAc-β-Asn other less common structural linkages such as GlcNac-α-Asn and Glc-Asn have been observed. In addition to their function in protein folding and cellular attachment, the N-liked glycans of a protein can modulate the protein's function, in some cases acting as an on-off switch. "O"-Linked glycans are formed by a linkage between an amino acid hydroxyl side chain (usually from serine or threonine) with the glycan. The majority of "O"-linked glycans take the form GlcNac-β-Ser/Thr or GalNac-α-Ser/Thr | https://en.wikipedia.org/wiki?curid=22418724 |
Glycopeptide Of the three linkages the least common and least understood are "C"-linked glycans. The C-linkage refers to the covalent attachment of mannose to a tryptophan residue. An example of a C-linked glycan is α-mannosyl tryptophan. Several methods have been reported in the literature for the synthesis of glycopeptides. Of these methods the most common strategies are listed below. Within solid phase peptide synthesis (SPPS) there exist two strategies for the synthesis of glycopeptides, linear and convergent assembly. Linear assembly relies on the synthesis of building blocks and then the use of SPPS to attach the building block together. An outline of this approach is illustrated below. Several methods exist for the synthesis of monosaccharide amino acid building block as illustrated below. Provided the monosaccharide amino acid building block is stable to peptide coupling conditions, amine deprotection conditions and resin cleavage. Linear assembly remains a popular strategy for the synthesis of glycopeptides with many examples in the literature. In the convergent assembly strategy a peptide chain and glycan residue are first synthesis separately. Then the glycan is glycosylated onto a specific residue of the peptide chain. This approach is not as popular as the linear strategy due to the poor reaction yields in the glycosylation step. Native chemical ligation (NCL) is a convergent synthetic strategy based on the linear coupling of glycopeptide fragments | https://en.wikipedia.org/wiki?curid=22418724 |
Glycopeptide This technique makes use of the chemoselective reaction between a N-terminal cysteine residue on one peptide fragment with a thio-ester on the C-terminus of the other peptide fragment as illustrated below. Unlike standard SPPS (which is limited to 50 amino acid residue) NCL allows the construction of large glycopeptides. However the strategy is limited by the fact that it requires a cysteine residue at N-terminus, an amino acid residue that is rare in nature. However this problem has partly been address by the selective desulfurization of the cysteine residue to an alanine. | https://en.wikipedia.org/wiki?curid=22418724 |
Oxygen saturation (medicine) Oxygen saturation is the fraction of oxygen-saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal arterial blood oxygen saturation levels in humans are 95–100 percent. If the level is below 90 percent, it is considered low and called hypoxemia. Arterial blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules () enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation. In medicine, oxygen saturation, commonly referred to as "sats", measures the percentage of hemoglobin binding sites in the bloodstream occupied by oxygen. At low partial pressures of oxygen, most hemoglobin is deoxygenated. At around 90% (the value varies according to the clinical context) oxygen saturation increases according to an oxygen-hemoglobin dissociation curve and approaches 100% at partial oxygen pressures of >10 kPa. A pulse oximeter relies on the light absorption characteristics of saturated hemoglobin to give an indication of oxygen saturation | https://en.wikipedia.org/wiki?curid=22419890 |
Oxygen saturation (medicine) The body maintains a stable level of oxygen saturation for the most part by chemical processes of aerobic metabolism associated with breathing. Using the respiratory system, red blood cells, specifically the hemoglobin, gather oxygen in the lungs and distribute it to the rest of the body. The needs of the body's blood oxygen may fluctuate such as during exercise when more oxygen is required or when living at higher altitudes. A blood cell is said to be "saturated" when carrying a normal amount of oxygen. Both too high and too low levels can have adverse effects on the body. An SaO (arterial oxygen saturation, as determined by an arterial blood gas test) value below 90% indicates hypoxemia (which can also be caused by anemia). Hypoxemia due to low SaO is indicated by cyanosis. Oxygen saturation can be measured in different tissues: | https://en.wikipedia.org/wiki?curid=22419890 |
Linde–Frank–Caro process The is a method for hydrogen production by removing hydrogen and carbon dioxide from water gas by condensation. The process was invented in 1909 by Adolf Frank and developed with Carl von Linde and Heinrich Caro. Water gas is compressed to 20 bar and pumped into the Linde-Frank-Caro reactor. A water column removes most of the carbon dioxide and sulfur. Tubes with caustic soda then remove the remaining carbon dioxide, sulphur, and water from the gas stream. The gas enters a chamber and is cooled to −190 °C, resulting in the condensation of most of the gas to a liquid. The remaining gas is pumped to the next vessel where the nitrogen is liquefied by cooling to −205 °C, resulting in hydrogen gas as an end product. | https://en.wikipedia.org/wiki?curid=22423074 |
Nuclear magnetic resonance spectroscopy of carbohydrates Carbohydrate NMR Spectroscopy is the application of nuclear magnetic resonance (NMR) spectroscopy to structural and conformational analysis of carbohydrates. This method allows the scientists to elucidate structure of monosaccharides, oligosaccharides, polysaccharides, glycoconjugates and other carbohydrate derivatives from synthetic and natural sources. Among structural properties that could be determined by NMR are primary structure (including stereochemistry), saccharide conformation, stoichiometry of substituents, and ratio of individual saccharides in a mixture. Modern high field NMR instruments used for carbohydrate samples, typically 500 MHz or higher, are able to run a suite of 1D, 2D, and 3D experiments to determine a structure of carbohydrate compounds. Common chemical shift ranges for nuclei within carbohydrate residues are: In the case of simple mono- and oligosaccharide molecules, all proton signals are typically separated from one another (usually at 500 MHz or better NMR instruments) and can be assigned using 1D NMR spectrum only. However, bigger molecules exhibit significant proton signal overlap, especially in the non-anomeric region (3-4 ppm). Carbon-13 NMR overcomes this disadvantage by larger range of chemical shifts and special techniques allowing to block carbon-proton spin coupling, thus making all carbon signals high and narrow singlets distinguishable from each other | https://en.wikipedia.org/wiki?curid=22423865 |
Nuclear magnetic resonance spectroscopy of carbohydrates The typical ranges of specific carbohydrate carbon chemical shifts in the unsubstituted monosaccharides are: Direct carbon-proton coupling constants are used to study the anomeric configuration of a sugar. Vicinal proton-proton coupling constants are used to study stereo orientation of protons relatively to the other protons within a sugar ring, thus identifying a monosaccharide. Vicinal heteronuclear H-C-O-C coupling constants are used to study torsional angles along glycosidic bond between sugars or along exocyclic fragments, thus revealing a molecular conformation. Sugar rings are relatively rigid molecular fragments, thus vicinal proton-proton couplings are characteristic: NOEs are sensitive to interatomic distances, allowing their usage as a conformational probe, or proof of a glycoside bond formation. It's a common practice to compare calculated to experimental proton-proton NOEs in oligosaccharides to confirm a theoretical conformational map. Calculation of NOEs implies an optimization of molecular geometry. Relaxivities, nuclear relaxation rates, line shape and other parameters were reported useful in structural studies of carbohydrates. The following is a list of structural features that can be elucidated by NMR: Widely known methods of structural investigation, such as mass-spectrometry and X-ray analysis are only limitedly applicable to carbohydrates. Such structural studies, such as sequence determination or identification of new monosaccharides, benefit the most from the NMR spectroscopy | https://en.wikipedia.org/wiki?curid=22423865 |
Nuclear magnetic resonance spectroscopy of carbohydrates Absolute configuration and polymerization degree are not always determinable using NMR only, so the process of structural elucidation may require additional methods. Although monomeric composition can be solved by NMR, chromatographic and mass-spectroscopic methods provide this information sometimes easier. The other structural features listed above can be determined solely by the NMR spectroscopic methods. The limitation of the NMR structural studies of carbohydrates is that structure elucidation can hardly be automatized and require a human expert to derive a structure from NMR spectra. Complex glycans possess a multitude of overlapping signals, especially in a proton spectrum. Therefore, it is advantageous to utilize 2D experiments for the assignment of signals. The table and figures below list most widespread NMR techniques used in carbohydrate studies. NMR spectroscopic research includes the following steps: Multiple chemical shift databases and related services have been created to aid structural elucidation of and expert analysis of their NMR spectra. Of them, several informatics tools are dedicated solely to carbohydrates: Several approaches to simulate NMR observables of carbohydrates has been reviewed | https://en.wikipedia.org/wiki?curid=22423865 |
Nuclear magnetic resonance spectroscopy of carbohydrates They include: Growing computational power allows usage of thorough quantum-mechanical calculations at high theory levels and large basis sets for refining the molecular geometry of carbohydrates and subsequent prediction of NMR observables using GIAO and other methods with or without solvent effect account. Among combinations of theory level and a basis set reported as sufficient for NMR predictions were B3LYP/6-311G++(2d,2p) and PBE/PBE (see review). It was shown for saccharides that carbohydrate-optimized empirical schemes provide significantly better accuracy (0.0-0.5 ppm per C resonance) than quantum chemical methods (above 2.0 ppm per resonance) reported as best for NMR simulations, and work thousands times faster. However, these methods can predict only chemical shifts and perform poor for non-carbohydrate parts of molecules. As a representative example, see figure on the right. | https://en.wikipedia.org/wiki?curid=22423865 |
Protein–carbohydrate interaction Carbohydrate–protein interactions are the intermolecular and intramolecular interactions between protein and carbohydrate moieties. These interactions form the basis of specific recognition of carbohydrates by lectins. Carbohydrates are important biopolymers and have a variety of functions. Often carbohydrates serve a function as a recognition element. That is, they are specifically recognized by other biomolecules. Proteins which bind carbohydrate structures are known as lectins. Compared to the study of protein–protein and protein–DNA interaction, it is relatively recent that scientists get to know the protein–carbohydrate binding. Many of these interactions involved carbohydrates found at the cell surface, as part of a membrane glycoprotein or glycolipid. These interactions can play a role in cellular adhesion and other cellular recognition events. Intramolecular carbohydrate–protein interactions refer to interactions between glycan and polypeptide moieties in glycoproteins or the glycosylated proteins. Generally, there are two types of protein carbohydrate binding important in biological processes: Lectin and antibody. Lectin is a kind of protein that can bind to carbohydrate with their carbohydrate recognition domains (CRDs). We could use different CRD to classify them. Ca is required to activate the binding. Ca binds to the protein and carbohydrate by non covalent bond. Mannose-binding protein (MBP) contains the C-type CRD. Two types mannose-6-phosphate can recognize phosphorylated saccharide | https://en.wikipedia.org/wiki?curid=22423972 |
Protein–carbohydrate interaction One is cation-dependent and the other does not require cation to activate. I-type lectin named from the immunoglobulin-like domain. Sialoadhesin is one of the I-type lectin, which binds specifically to sialic acid. Most antibodies have the similar structure except the hypervariable region which is called the antigen binding site. This region is constituted by the combination of various amino acids. When the antigen is a kind of carbohydrate (Polysaccharide), the binding could be regarded as a protein-carbohydrate interaction. Protein–carbohydrate interactions play an important role in biological function. Just like other organic molecule study, X-ray crystallography is a very useful tool to know the detail information on the interaction between carbohydrate and protein. By using titration, NOESY(Nuclear Overhauser Effect SpectroscopY), CIDNP experiments, the specificity and affinity of binding, association constants and equilibrium thermodynamic parameters of carbohydrate–protein binding can be studied. In many cases, the conformation information is required, however, sometimes it is not able to get directly from the experiments. So the knowledge-based model building approach is used. Fluorescence spectrometry is a useful tool and has its advantages: no procedure for separation and plenty of ways to get fluorophore source: there are some of amino acids and ligands that have fluorophore after they are activated | https://en.wikipedia.org/wiki?curid=22423972 |
Protein–carbohydrate interaction Dual polarisation interferometry is a label free analytical technique for measuring interactions and associated conformational changes. Recently, studies by using metal nanoparticle probes to detect the carbohydrate–protein interactions were reported. Use of gold and silver nanoparticle probes in resonant light scattering (RLS) gives particular high sensitivity. Zhenxin Wang and coworker the same principle applied this method to detect the interaction between carbohydrate and protein. As Lectin can strongly bind to specific carbohydrate, scientists develop several lectin-based carbohydrate biosensors. Designed lectin contains specific groups can be detected by analytical method. | https://en.wikipedia.org/wiki?curid=22423972 |
Armed and disarmed saccharides The armed/disarmed approach to glycosylation is an effective way to prevent sugar molecules from self-glycosylation when synthesizing disaccharides. This approach was first recognized when acetylated sugars only acted as glycosyl acceptors when reacted with benzylated sugars. The acetylated sugars were termed “disarmed” while the benzylated sugars were termed “armed”. The selectivity in the reaction is due to the stronger electron withdrawing power of the esters compared to the ethers. A stronger electron withdrawing substituent leads to a greater destabilization of the oxocarbenium ion. This slows this reaction pathway, and allows for disaccharide formation to occur with the benzylated sugar. Other effective electron withdrawing groups that have shown selectivity are halogens and azido groups, while deoxygenation has been proven an effective tool in “arming” sugars. Disarming sugars can also be accomplished by adding 1,3-dioxane and 1,3-dioxolane protecting groups onto sugars. These protecting groups “lock” the sugars into a rigid chair conformation. When the sugar forms the necessary oxocarbenium ion, it flattens at the anomeric position. This change in configuration is a high-energy transformation when cyclic protecting groups are present, and leads to the sugar being “disarmed”. These groups can be easily removed following glycosylation, effectively “arming” the sugar, and allowing for control of the glycosylation | https://en.wikipedia.org/wiki?curid=22424123 |
Armed and disarmed saccharides Further work has shown that the effect of 1,3-dioxanes and 1,3-dioxolanes on disarming sugars can be attributed to the electronics of the systems as well as torsional strain. When a 1,3-dioxane is formed between O-4 and O-6, the oxygens adapt an anti-periplanar geometry with O-5. This orientation allows for hyperconjugation of O-5 to O-4 and O-6, removing electron density from O-5. The loss of electron density at O-5 results in a destabilization of the oxocarbenium ion, slowing its formation, and “disarming” the sugar. Experiments were conducted by altering the configuration of the O-6 and examining the rate of hydrolysis of these compounds. The gauche-gauche orientation seen in the second example has a higher rate of hydrolysis due to its longer bond length. The hydrogen at C-5 is able to hyperconjugate with O-6, effectively lengthening the bond. This increase in bond length decreases the inductive electron withdrawing ability of O-6, causing a higher rate of hydrolysis than the other two conformations. The effect of anti-periplanar orientation is also visible in comparing glucopyranose and galactopyranose hydrolysis. Glucopyranose has an anti-perplanar orientation between O-4 and O-5, while galactopyranose does not and shows the appropriate increase in reactivity. The advantage of “arming” and “disarming” glycosyl donors lies in their synthetic use. By disarming the glycosyl, a selective coupling can be achieved. The disarmed portion of the disaccharide can then be armed through selective deprotection | https://en.wikipedia.org/wiki?curid=22424123 |
Armed and disarmed saccharides The disaccharide can then be coupled to a disarmed sugar. This process can be repeated as many times as necessary to achieve an efficient synthesis of a desired oligosaccharide with minimal loss of material to undesired coupling. This can be especially useful in “one-pot” synthetic methods. In these methods, multiple sugars are added to the reaction mixture. One of the sugars is armed as the glycosyl donor, and reacts quickly with a glycosyl acceptor. The non-reducing sugar then acts as a glycosyl acceptor as a protecting group that is easily lost in solution reveals a free hydroxyl group. This reacts with a donor that was disarmed, forming the oxocarbenium ion at a slower rate, producing the desired trisaccharide. | https://en.wikipedia.org/wiki?curid=22424123 |
Reverse northern blot The reverse northern blot is a method by which gene expression patterns may be analyzed by comparing isolated RNA molecules from a tester sample to samples in a control cDNA library. It is a variant of the northern blot in which the nucleic acid immobilized on a membrane is a collection of isolated DNA fragments rather than RNA, and the probe is RNA extracted from a tissue and radioactively labelled. A reverse northern blot can be used to profile expression levels of particular sets of RNA sequences in a tissue or to determine presence of a particular RNA sequence in a sample. Although DNA Microarrays and newer next-generation techniques have generally supplanted reverse northern blotting, it is still utilized today and provides a relatively cheap and easy means of defining expression of large sets of genes. In order to prepare the reverse northern membrane, cDNA sequences for transcripts of interest are immobilized on nylon membranes, which can be accomplished by use of dot blots or bidirectional agarose gel blotting and UV fixation of the DNA to the membranes. In many cases, cDNA probes may be preferred over RNA probes in order to mitigate problems of RNA degradation by RNAses or tissue metabolites. Prepared reverse northern blot membranes are pre-hybridized in Denhardt's solution with SSC buffer and labeled cDNA probes are denatured at 100 °C and added to the pre-hybridization solution. The membrane is incubated with the probes for at least 15 hours at 65 °C, then washed and exposed | https://en.wikipedia.org/wiki?curid=22435839 |
Reverse northern blot Reverse Northern blot, much like the northern blot upon which it is based, is used to determine levels of gene expression in particular tissues. In comparison to the Northern blot, the reverse northern blot is able to probe a large number of transcripts at once with less specificity with regard to probes than is required for Northern blot. Often this will involve the use of suppression subtractive hybridization (SSH) libraries or differential display to isolate differentially expressed transcripts and create bacterial clones containing inserts for these sequences. These will serve as the targets hybridized to the membrane and will be probed by sample RNA. Expression levels can be quantified by increase or decrease in fluorescent or radioactive signal over a control treatment. Bands or dots which appear darker and larger signify transcripts which are over-expressed in a sample of interest and lighter dots indicate that a transcript is down-regulated versus a control sample. Due to a tendency to generate high numbers of false positives caused by band contamination with heterogeneous sequences, differential display hits will need to be confirmed by an alternative method for determining differential expression. While northern blot or q-PCR are often used to confirm results, both techniques have drawbacks. Northern blot is limited by its ability to only probe with one mRNA at a time, while q-PCR requires transcripts to be long enough to generate primers for the sequence and probes can be costly | https://en.wikipedia.org/wiki?curid=22435839 |
Reverse northern blot Therefore, reverse northern has been used as one means of confirming hits from DD-PCR, or sequences with altered expression levels. In this case, the membrane will be coated with amplified DD-PCR products which have been cloned into vectors, sequenced, and reamplified. DNA microarrays operate by similar procedures to those used in the reverse northern blot, consisting of many DNA probes hybridized to a solid glass, plastic or silicon substrate which is probed with labeled RNA or cDNA. This allows for significantly expanded gene expression profiling. Arrays may be purchased from commercial suppliers tailored to research needs e.g. cancer, cell cycle, or toxicology microarrays, or may be generated for custom targets. Fluorescent or radioactive signals generated by hybridization of isolated sample cDNA probes will be proportional to the transcript's abundance in the tissue being studied. | https://en.wikipedia.org/wiki?curid=22435839 |
Transgenic hydra Cnidarians such as Hydra have become attractive model organisms to study the evolution of immunity. However, despite long-term efforts, stably transgenic animals could not be generated, severely limiting the functional analysis of genes. For analytical purposes, therefore, an important technical breakthrough in the field was the development of a transgenic procedure for generation of stably transgenic lines by embryo microinjection. Hydra polyps are small and transparent which makes it possible to trace single cells in vivo. In addition, transgenic Hydra provide a ready system for generating gain-of-function phenotypes. With the use of transgenes producing dominant-negative versions of proteins, one should be able to obtain loss-of-function phenotypes as well. Current technology allows generation of reporter constructs using promoters of various Hydra genes fused to fluorescent proteins. Since transgenic Hydra lines have become an important tool to dissect molecular mechanisms of development, a “Hydra Transgenic Facility” has been established at the Christian-Albrechts-University of Kiel (Germany). | https://en.wikipedia.org/wiki?curid=22438135 |
Hawaii Ocean Time-series The (HOT) program is a long-term oceanographic study based at the University of Hawaii at Manoa. In 2015, the American Society for Microbiology designated the HOT Program's field site Station ALOHA (A Long-Term Oligotrophic Habitat Assessment; ()) a "Milestone in Microbiology", for playing "a key role in defining the discipline of microbial oceanography and educating the public about the vital role of marine microbes in global ecosystems." Scientists working on the (HOT) program have been making repeated observations of the hydrography, chemistry and biology of the water column at a station north of Oahu, Hawaii since October 1988. The objective of this research is to provide a comprehensive description of the ocean at a site representative of the North Pacific Subtropical Gyre. Cruises are made approximately once per month to the deep-water Station ALOHA located 100 km north of Oahu, Hawaii. Measurements of the thermohaline structure, water column chemistry, currents, optical properties, primary production, plankton community structure, and rates of particle export are made on each cruise. The HOT program also uses autonomous underwater vehicles, including floats and gliders, to collect data at Station ALOHA between cruises. HOT was founded to understand the processes controlling the fluxes of carbon and associated bioelements in the ocean and to document changes in the physical structure of the water column | https://en.wikipedia.org/wiki?curid=22442208 |
Hawaii Ocean Time-series To achieve this, the HOT program has several specific goals: The dissolved inorganic carbon data set that has been accumulated over the course of the HOT program shows the increase of carbon dioxide in the surface waters of the Pacific and subsequent acidification of the ocean. The data collected by these cruises are available online. The 200th cruise of the HOT program was in 2008. HOT recently celebrated its 25th year in operation, with the 250th research cruise occurring in March 2013. Station ALOHA is a deep water (~4,800 m) location approximately 100 km north of the Hawaiian Island of Oahu. Thus, the region is far enough from land to be free of coastal ocean dynamics and terrestrial inputs, but close enough to a major port (Honolulu) to make relatively short duration (less than five days) near-monthly cruises logistically and financially feasible. Sampling at this site occurs within a 10 km radius around the center of the station. Each HOT cruise begins with a stop at a coastal station south of the island of Oahu, approximately 10 km off Kahe Point (21° 20.6'N, 158° 16.4'W) in 1500 m of water. Station Kahe (termed Station 1) is used to test equipment and train new personnel before departing for Station ALOHA. Since August 2004, Station ALOHA has also been home to a surface mooring outfitted for meteorological and upper ocean measurements; this mooring, named WHOTS (also termed Station 50), is a collaborative project between Woods Hole Oceanographic Institution and HOT | https://en.wikipedia.org/wiki?curid=22442208 |
Hawaii Ocean Time-series WHOTS provides long-term, high-quality air-sea fluxes as a coordinated part of HOT, contributing to the program’s goals of observing heat, fresh water and chemical fluxes. In 2011, the ALOHA Cabled Observatory (ACO) became operational. This instrumented fiber optic cabled observatory provides power and communications to the seabed (4728 m). The ACO is currently configured with an array of thermistors, current meters, conductivity sensors, two hydrophones, and a video camera. A core suite of environmental variables was selected at the start of the program that is expected to display detectable change on time scales of several days to one decade. Since 1988, the interdisciplinary station work has included physical, chemical, biological and sedimentological observations and rate measurements. The initial phase of the HOT program (October 1988 – February 1991) was entirely supported by research vessels, with the exception of the availability of existing satellite and ocean buoy sea surface data. In February 1991, an array of inverted echosounders (IES) was deployed around Station ALOHA and in June 1992, a sequencing sediment trap mooring was deployed a few km north of it. In 1993, the IES network was replaced with two strategically positioned instruments: one at Station ALOHA and the other at the coastal station Kaena. A physical-biogeochemical mooring (known as HALE-ALOHA) was deployed from January 1997 to June 2000 for high frequency atmospheric and oceanic observations | https://en.wikipedia.org/wiki?curid=22442208 |
Hawaii Ocean Time-series HOT relies on the University-National Oceanographic Laboratory System research vessel Kilo Moana operated by the University of Hawaii for most of the near-monthly sampling expeditions. When at Station ALOHA, a variety of sampling strategies is used to capture the range of physical and biogeochemical dynamics natural to the NPSG ecosystem. These strategies include high resolution conductivity-temperature-depth (CTD) profiles, biogeochemical analyses of discrete water samples, "in situ" vertically profiling bio-optical instrumentation, free-drifting arrays for determinations of primary production and particle fluxes, deep ocean sediment traps, and oblique plankton net tows. The suite of core measurements conducted by HOT has remained largely unchanged over the program’s lifetime. On each HOT cruise, samples are collected from the surface ocean to near the sea bed (~4,800 m), with the most intensive sampling occurring in the upper 1,000 m. HOT utilizes a “burst” vertical profiling strategy where physical and biogeochemical properties are measured at 3 hour intervals over a 36-hour period, covering 3 semi-diurnal tidal cycles and 1 inertial period (~31 hours). This approach captures variability in ocean dynamics due to internal tides around Station ALOHA. It is designed to assess variability on time scales of a few hours to a few years. High frequency variability (less than 6 hours) and variability on time scales of between 3–60 days are not adequately sampled at the present time | https://en.wikipedia.org/wiki?curid=22442208 |
Hawaii Ocean Time-series The 25 year record of ocean carbon measurements at Station ALOHA document that the partial pressure of ("p") in the mixed layer is increasing at a rate slightly greater than the trend observed in the atmosphere. This has been accompanied by progressive decreases in seawater pH. Although the effect of anthropogenic is evidenced by long-term decreases in seawater pH throughout the upper 600 m, the rate of acidification at Station ALOHA varies with depth. For example, in the upper mesopelagic waters (~160–310 m) pH is decreasing at nearly twice the rate observed in the surface waters. Such depth-dependent differences in acidification are due to a combination of regional differences in time-varying climate signatures, mixing, and changes in biological activity. | https://en.wikipedia.org/wiki?curid=22442208 |
Hydroxybutanal may refer to: | https://en.wikipedia.org/wiki?curid=22452377 |
Hydroxyethyl methyl cellulose is a gelling and thickening agent derived from cellulose. | https://en.wikipedia.org/wiki?curid=22457321 |
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