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Compounds of fluorine However, if a molecule was synthesized, it would have to go through a high-energy transitional state, from which it could decay into two molecules. But since the transitional state is higher in energy than the hexatomic molecule, the energy difference would need to be added to reach the transitional state and thus allow the decay. This energy is called reaction activation barrier. (The second decay mode has an analogical position.) Thus if little energy was added (low temperatures), then the compound could exist; however, the synthesis is a serious problem (not yet solved). The carbon–fluorine chemical bond of the organofluorine compounds is the strongest bond in organic chemistry. Along with the low polarizability of the molecules, these are the most important factors contributing to the great stability of the organofluorines. The carbon–fluorine bond of the smaller molecules is formed in three principal ways: Fluorine replaces a halogen or hydrogen, or adds across a multiple bond. The direct reaction of hydrocarbons with fluorine gas can be dangerously reactive, so the temperature may need to be lowered even to −150 °C (−240 °F). "Solid fluorine carriers", compounds that can release fluorine upon heating, notably cobalt trifluoride, may be used instead, or hydrogen fluoride. After the reaction, the molecular size is not changed significantly, as the elements have very similar van der Waals radii | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine Direct fluorination becomes even less important when it comes to organohalogens or unsaturated compounds reactions, or when a prefluorocarbon is desired (then HF-based electrolysis is typically used). In contrast, the fluoropolymers are formed by polymerizing free radicals; other techniques used for hydrocarbon polymers do not work in that way with fluorine. The range of organofluorine compounds is diverse, reflecting the inherent complexity of organic chemistry. A vast number of small molecules exist with varying amounts of fluorine substitution, as well as many polymers—research into particular areas is driven by the commercial value of applications. Monofluoroalkanes (alkanes with one hydrogen replaced with fluorine) may be chemically and thermally unstable, yet are soluble in many solvents; but as more fluorines are in instead of hydrogens, the stability increases, while melting and boiling points, and solubility decrease. While the densities and viscosities are increased, the dielectric constants, surface tensions, and refractive indices fall. Partially fluorinated alkanes are the hydrofluorocarbons (HFCs). Substituting other halogens in combination with fluorine gives rise to chlorofluorocarbons (CFCs) or bromofluorocarbons (BFCs) and the like (if some hydrogen is retained, HCFCs and the like). Properties depend on the number and identity of the halogen atoms | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine In general, the boiling points are even more elevated by combination of halogen atoms because the varying size and charge of different halogens allows more intermolecular attractions. As with fluorocarbons, chlorofluorocarbons and bromofluorocarbons are not flammable: they do not have carbon–hydrogen bonds to react and released halides quench flames. When all hydrogens are replaced with fluorine to achieve perfluoroalkanes, a great difference is revealed. Such compounds are extremely stable, and only sodium in liquid ammonia attacks them at standard conditions. They are also very insoluble, with few organic solvents capable of dissolving them. However, if a perfluorocarbon contains double or triple bonds (perfluoroalkenes or -alkynes), a very reactive towards ligand accepting result, even less stable than corresponding hydrocarbons. Difluoroacetylene, which decomposes even under liquid nitrogen temperatures, is a notable example. If such a molecule is asymmetric, then the more fluorinated carbon is attacked, as it holds positive charge caused by the C–F bonds and is shielded weakly (similarly to that how unsaturated hydrocarbons attacked by HF add hydrogen to the more hydrogen-rich atom per Markovnikov's rule). Perfluorinated compounds, as opposed to perfluorocarbons, is the term used for molecules that would be perfluorocarbons—only carbon and fluorine atoms—except for having an extra functional group (even though another definition exists) | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine They share most of perfluorocarbon properties (inertness, stability, non-wettingness and insolubility in water and oils, slipperiness, etc.), but may differ because of the functional group properties, although the perfluorocarbon tail differ the group-specific properties as compared to those of hydrocarbon-tailed compounds. The perfluoroalkanesulfonic acids are also very notable for their acidity. The sulfonic acid derivative, trifluoromethanesulfonic acid, is comparable in strength to perchloric acid. These compounds lower surface energy; for this reason, they, especially perfluorooctanesulfonic acid (PFOS, formerly the active component in brand "Scotchgard") have found industrial use as surfactants (see above). If a perfluorinated compound has a fluorinated tail, but also a few non-fluorinated carbons (typically two) near the functional group, it is called a fluorotelomer (such molecules are commercially treated as perfluorinated), but such molecules are more of industrial value than chemical. The chain end may similarly be attached to different functiuonal groups (via the hydrogenized terminal carbon), such as hydroxyl resulting in fluorotelomer alcohols, sulfonate resulting in fluorotelomer sulfonates, etc. Fluoropolymers are similar in many regards with smaller molecules; adding fluorine to a polymer affects the properties in the same manner as in small molecules (increasing chemical stability, melting point, reducing flammability, solubility, etc.) | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine Each fluoropolymer has own characteristic properties, though. The simplest fluoroplastic is polytetrafluoroethylene (PTFE, DuPont brand Teflon), which is a simple linear chain polymer with the repeating structural unit:–CF–. PTFE has a backbone of carbons single bonded in a long chain, with all side bonds to fluorines. It contains no hydrogens and can be thought of as the perfluoro analog of polyethylene (structural unit: –CH–). PTFE has high chemical and thermal stability, as expected for a perfluorocarbon, much stronger than polyethylene. Its resistance to van der Waals forces makes PTFE the only known surface to which a gecko cannot stick. The compound, however, lacks an ability to transform upon melting, which is not a problem for various PTFE deratives, namely FEP (fluorinated ethylene propylene, with some fluorines replaced with the–CF group) or PFA (perfluoroalkoxy, some fluorines replaced with –OCF). They share most properties with PTFE, but there are still differences, namely maximum usage temperature (highest for the non-flexible PTFE). There are other fluoroplastics other than perfluorinated. Polyvinylidene fluoride (PVDF, structural unit: –CFCH–), is an analog of PTFE with half the fluorines. PVF (polyvinyl fluoride, structural unit: –CHCHF–) contains one one-fourth the fluorines of PTFE. Despite this, it still has many properties of more fluorinated compounds. PCTFE (polychlorotrifluoroethylene, structural unit: –CFCFCl–) is another important compound | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine It differs from PTFE by having a quarter of fluorine replaced with chlorines, yet this difference brings even greater hardness, creep resistance, and moisture persistence. Mild fluorination of polyethylene gives does not make all of the plastic lose its hydrogens for fluorine; only a thin layer (0.01 mm at maximum) is then affected. This is somewhat similar to metal passivation: the bulk properties are not affected, but the surface properties are, most notably, a greater vapor barrier. Therefore, they are a cheaper alternative to the perfluoro plastics if only surface is important. Nafion is a structurally complicated polymer. It has a PTFE-like backbone, but also contains side chains of perfluoro ether that end in sulfonic acid(–SOOH) groups. It also possesses great chemical stability, while exact properties vary with morphology. However, because of the difficult chemical structure, it is also relatively easily converted to an ionomer (shows conductivity) by adding cations like Na or by converting into the sulfonic acid rather than the given sulfonyl fluoride. The conductivity is due to that the main carbon chain separates from the side chains, thus forming polar and non-polar regions. This form is also very hydroscopic. Fluoroelastomers, like other elastomers (artificial rubbers), consist of disordered polymer chains connected in three dimensions. The main challenges in making fluorelastomers are cross-linking (reacting the unreactive polymers), as well as removing the HF formed during curing | https://en.wikipedia.org/wiki?curid=39292926 |
Compounds of fluorine There are three main families of fluoroelasters. VDF/HFP is a copolymer system of vinylidene fluoride and (at least 20%) hexafluoropropylene. TFE/propylene is another copylymer system with better chemical resistance to some solvents. TFE/PMVE (perfluoromethylvinyl ether) is a copolymer system which creates a perfluorinated fluoroelastomer. | https://en.wikipedia.org/wiki?curid=39292926 |
Lely method The or Lely process is a crystal growth technology used for producing silicon carbide crystals for the semi-conductor industry. The patent for this process was filed in the Netherlands in 1954 and in the United States in 1955 by Jan Anthony Lely of Philips Electronics. The patent was subsequently granted on 30 September 1958, and was refined by D.R. Hamilton et al. in 1960, and by V.P. Novikov and V.I. Ionov in 1968. The produces bulk silicon carbide crystals through the process of sublimation. Silicon carbide powder is loaded into a graphite crucible, which is purged with Argon gas and heated to approximately . The silicon carbide near the outer walls of the crucible sublimes and is deposited on a graphite rod near the center of the crucible, which is at a lower temperature. Several modified versions of the exist, most commonly the silicon carbide is heated from the bottom end rather than the walls of the crucible, and deposited on the lid. Other modifications include varying the temperature, temperature gradient, Argon pressure, and geometry of the system. Typically, an induction furnace is used to achieve the required temperatures of . | https://en.wikipedia.org/wiki?curid=39295868 |
Edwards equation The in organic chemistry is a two-parameter equation for correlating nucleophilic reactivity, as defined by relative rate constants, with the basicity of the nucleophile (relative to protons) and its polarizability. This equation was first developed by John O. Edwards in 1954 and later revised based on additional work in 1956. The general idea is that most nucleophiles are also good bases because the concentration of negatively charged electron density that defines a nucleophile will strongly attract positively charged protons, which is the definition of a base according to Brønsted–Lowry acid-base theory. Additionally, highly polarizable nucleophiles will have greater nucleophilic character than suggested by their basicity because their electron density can be shifted with relative ease to concentrate in one area. Prior to Edwards developing his equation, other scientists were also working to define nucleophilicity quantitatively. Brønsted and Pederson first discovered the relationship between basicity, with respect to protons, and nucleophilicity in 1924: where k is the rate constant for nitramide decomposition by a base (B) and β is a parameter of the equation | https://en.wikipedia.org/wiki?curid=39302352 |
Edwards equation Swain and Scott later tried to define a more specific and quantitative relationship by correlating nucleophilic data with a single-parameter equation derived in 1953: This equation relates the rate constant "k", of a reaction, normalized to that of a standard reaction with water as the nucleophile ("k"), to a nucleophilic constant "n" for a given nucleophile and a substrate constant "s" that depends on the sensitivity of a substrate to nucleophilic attack (defined as 1 for methyl bromide). This equation was modeled after the Hammett equation. However, both the Swain–Scott equation and the Brønsted relationship make the rather inaccurate assumption that all nucleophiles have the same reactivity with respect to a specific reaction site. There are several different categories of nucleophiles with different attacking atoms (e.g. oxygen, carbon, nitrogen) and each of these atoms has different nucleophilic characteristics. The attempts to account for this additional parameter by introducing a polarizability term. The first generation of the was where k and k are the rate constants for a nucleophile and a standard (HO). H is a measure of the basicity of the nucleophile relative to protons, as defined by the equation: where the pK is that of the conjugate acid of the nucleophile and the constant 1.74 is the correction for the pK of HO. E is the term Edwards introduced to account for the polarizability of the nucleophile | https://en.wikipedia.org/wiki?curid=39302352 |
Edwards equation It is related to the oxidation potential (E) of the reaction formula_5 (oxidative dimerization of the nucleophile) by the equation: where 2.60 is the correction for the oxidative dimerization of water, obtained from a least-squares correlation of data in Edwards’ first paper on the subject. α and β are then parameters unique to specific nucleophiles that relate the sensitivity of the substrate to the basicity and polarizability factors. However, because some β’s appeared to be negative as defined by the first generation of the Edwards equation, which theoretically should not occur, Edwards adjusted his equation. The term E was determined to have some dependence on the basicity relative to protons (H) due to some factors that affect basicity also influencing the electrochemical properties of the nucleophile. To account for this, E was redefined in terms of basicity and polarizability (given as molar refractivity, R): The values of a and b, obtained by the method of least squares, are 3.60 and 0.0624 respectively. With this new definition of E, the can be rearranged: where A= αa and B = β + αb. However, because the second generation of the equation was also the final one, the equation is sometimes written as formula_10, especially since it was republished in that form in a later paper of Edwards’, leading to confusion over which parameters are being defined | https://en.wikipedia.org/wiki?curid=39302352 |
Edwards equation A later paper by Edwards and Pearson, following research done by Jencks and Carriuolo in 1960 led to the discovery of an additional factor in nucleophilic reactivity, which Edwards and Pearson called the alpha effect, where nucleophiles with a lone pair of electrons on an atom adjacent to the nucleophilic center have enhanced reactivity. The alpha effect, basicity, and polarizability are still accepted as the main factors in determining nucleophilic reactivity. As such, the is applied in a qualitative sense much more frequently than in a quantitative one. In studying nucleophilic reactions, Edwards and Pearson noticed that for certain classes of nucleophiles most of the contribution of nucleophilic character originated from their basicity, resulting in large β values. For other nucleophiles, most of the nucleophilic character came from their high polarizability, with little contribution from basicity, resulting in large α values. This observation led Pearson to develop his hard-soft acid-base theory, which is arguably the most important contribution that the has made to current understanding of organic and inorganic chemistry. Nucleophiles, or bases, that were polarizable, with large α values, were categorized as “soft”, and nucleophiles that were non-polarizable, with large β and small α values, were categorized as “hard”. The parameters have since been used to help categorize acids and bases as hard or soft, due to the approach’s simplicity. | https://en.wikipedia.org/wiki?curid=39302352 |
Nanofluids in solar collectors Nanofluid-based direct solar collectors are solar thermal collectors where nanoparticles in a liquid medium can scatter and absorb solar radiation. They have recently received interest to efficiently distribute solar energy. Nanofluid-based solar collector have the potential to harness solar radiant energy more efficiently compared to conventional solar collectors. Nanofluids have recently found relevance in applications requiring quick and effective heat transfer such as industrial applications, cooling of microchips, microscopic fluidic applications, etc. Moreover, in contrast to conventional heat transfer (for solar thermal applications) like water, ethylene glycol, and molten salts, nanofluids are not transparent to solar radiant energy; instead, they absorb and scatter significantly the solar irradiance passing through them. Typical solar collectors use a black-surface absorber to collect the sun's heat energy which is then transferred to a fluid running in tubes embedded within. Various limitations have been discovered with these configuration and alternative concepts have been addressed. Among these, the use of nanoparticles suspended in a liquid is the subject of research. Nanoparticle materials including aluminium, copper, carbon nanotubes and carbon-nanohorns have been added to different base fluids and characterized in terms of their performance for improving heat transfer efficiency | https://en.wikipedia.org/wiki?curid=39313159 |
Nanofluids in solar collectors Dispersing trace amounts of nanoparticles into common base fluids has a significant impact on the optical as well as thermo physical properties of base fluid. This characteristic can be used to effectively capture and transport solar radiation. Enhancement of the solar irradiance absorption capacity leads to a higher heat transfer resulting in more efficient heat transfer as shown in figure 2. The efficiency of a solar thermal system is reliant on several energy conversion steps, which are in turn governed by the effectiveness of the heat transfer processes. While higher conversion efficiency of solar to thermal energy is possible, the key components that need to be improved are the solar collector. An ideal solar collector will absorb the concentrated solar radiation, convert that incident solar radiation into heat and transfer the heat to the heat transfer fluid. Higher the heat transfer to fluid, higher is the outlet temperature and higher temp lead to improved conversion efficiency in the power cycle. nanoparticles have several orders of magnitude higher heat transfer coefficient when transferring heat immediately to the surrounding fluid. This is simply due to the small size of nanoparticle. We know that thermal conductivity of solids is greater than liquids. Commonly used fluids in heat transfer applications such as water, ethylene glycol and engine oil have low thermal conductivity when compared to thermal conductivity of solids, especially metals | https://en.wikipedia.org/wiki?curid=39313159 |
Nanofluids in solar collectors So, addition of solid particles in a fluid can increase the conductivity of liquids .But we cannot add large solid particles due to main problems: Due to these drawbacks, usage of solid particles have not become practically feasible. Recent improvements in nanotechnology made it possible to introduce small solid particles with diameter smaller than 10 nm. Liquids, thus obtained have higher thermal conductivity and are known as Nanofluids. As can be clearly seen from figure 4 that carbon nanotubes have highest thermal conductivity as compared to other materials. Maxwel model Pak and Choi model Koo and Kleinstreuer model Udawattha and Narayana model where Keblinski et al. had named four main possible mechanisms for the anomalous increase in nanofluids heat transfer which are : Due to Brownian motion particles randomly move through the liquid. And hence better transport of heat. Although it was originally believed that the fluid motions resulting from Brownian motion of the nanoparticles could explain the enhancement in heat transfer properties, this hypothesis was later rejected. Liquid molecules can form a layer around the solid particles and there by enhance the local ordering of the atomic structure at the interface region.hence, the atomic structure of such liquid layer is more ordered than that of the bulk liquid. The effective volume of a cluster is considered much larger than the volume of the particles due to the lower packing fraction of the cluster | https://en.wikipedia.org/wiki?curid=39313159 |
Nanofluids in solar collectors Since, heat can be transferred rapidly within the such clusters, the volume fraction of the highly conductive phase is larger than the volume of solid, thus increasing its thermal conductivity In the last ten years, many experiments have been conducted numerically and analytically to validate the importance of nanofluids. From the table 1 it is clear that nanofluid-based collector have a higher efficiency than a conventional collector. So, it is clear that we can improve conventional collector simply by adding trace amounts of nano-particles. It has also been observed through numerical simulation that mean outlet temperature increase by increasing volume fraction of nanoparticles, length of tube and decreases by decreasing velocity. Nanofluids poses the following advantages as compared to conventional fluids which makes them suitable for use in solar collectors: The fundamental difference between the conventional and nanofluid-based collector lies in the mode of heating of the working fluid. In the former case the sunlight is absorbed by a surface, where as in the latter case the sunlight is directly absorbed by the working fluid (through radiative transfer). On reaching the receiver the solar radiations transfer energy to the nanofluid via scattering and absorption. | https://en.wikipedia.org/wiki?curid=39313159 |
Gerhard Schmidt (crystallographer) Gerhard Martin Julius Schmidt (born, 21 August 1919 in Berlin – died July 12, 1971 in Zurich, buried in Rehovot), organic chemist and chemical crystallographer, director of the Weizmann Institute of Science in the late 1950s and again in the late 1960s. Schmidt was the founder of X-ray crystallography at the Weizmann Institute and in Israel – a field in which Weizmann Institute's Professor Ada Yonath was awarded the Nobel Prize in Chemistry for 2009. Professor Gerhard Schmidt was born in Berlin in 1919 and went to high school in Munich, where his father was a professor of chemistry. Being the son of a Jewish mother, Gerhard was forced to leave Germany at the age of 16, after the Nazis came to power; he spent a year in Switzerland, then moved to England, where he finished high school in 1938. He then won a scholarship to study at the University of Oxford (Oriel College). He earned a master's degree in organic chemistry in 1942 under the guidance of Robert Robertson, and a doctorate in X-ray crystallography under Dorothy Hodgkin in 1948. Both of his supervisors were later awarded Nobel Prizes in chemistry. During his doctoral studies, Schmidt took part in structural studies of biologically important molecules, focusing on the structure of the antibacterial natural peptide Gramicidin S using the method of X-ray crystallography. During this period he supervised another student of Hodgkin, Margaret Roberts, later Margaret Thatcher. After the breakout of World War II, Schmidt was forced to interrupt his studies | https://en.wikipedia.org/wiki?curid=39313294 |
Gerhard Schmidt (crystallographer) Being an emigrant from Germany, he was deported in July 1940, together with 200 other “enemy aliens,” to a detention camp in Australia. In August 1941, he was finally cleared and returned to England. Later in life, Schmidt liked to date some of his most original ideas in chemistry to this deportation period. Schmidt arrived in Israel and joined the soon-to-be-dedicated Weizmann Institute in late 1948. He had been invited by Ernst Bergmann, then the Institute's scientific director, to set up a research group in chemical crystallography. He later gradually broadened his activities to include solid-state chemistry and crystal spectroscopy. At the Weizmann Institute, Schmidt combined scientific research with holding senior administrative positions. From 1959 to 1961, he served as chairman of the Institute's Scientific Committee and its administrative director. He was appointed head of the Department of Chemistry in 1967 and, with the establishment of the chemistry faculty in 1970, became its first dean. From 1969 to 1971, he served as the director of the Weizmann Institute. In the late 1950s, while serving as Weizmann's Administrative Director, Schmidt was among the pioneers of the German-Israeli scientific collaboration, which began with ties between the Weizmann Institute and the Max Planck Society. This initiative led to the creation of the Minerva Foundation in 1964 and paved the way for the establishment of formal relations between Israel and Germany in 1965 | https://en.wikipedia.org/wiki?curid=39313294 |
Gerhard Schmidt (crystallographer) Schmidt devoted considerable time to applied science. From 1960 to 1964, he chaired the Board of Yeda Research & Development Co., the Weizmann Institute's technology transfer arm. Outside the Weizmann Institute, Schmidt was actively involved in Israel's scientific and technological development. From 1960 to 1968, he served on the Board of Directors of the Dead Sea Works. In 1967, he became a member of the Executive Committee of the new Center for Industrial Research in Haifa. In addition, from 1967 to 1969, he chaired two committees established by Israel's National Council for Research and Development – on technical applications of photochemistry and on bromine chemistry. He founded the Israel Crystallography Society and was its first President (1958-1960), negotiating its adherence to the International Union of Crystallography. In 1963, he received the Weizmann Prize in the Exact Sciences from Tel Aviv municipality for his research on the structure and chemical behavior of crystals. The Weizmann Institute has established the annual Gerhard M. J. Schmidt Memorial Lecture held in the Schmidt Lecture Hall, and the Gerhard M.J. Schmidt Minerva Center on Supramolecular Architectures, which supports collaboration between Weizmann faculty and German scientists. Professor Schmidt is recognized as one of the founders of modern organic solid-state chemistry | https://en.wikipedia.org/wiki?curid=39313294 |
Gerhard Schmidt (crystallographer) At the Weizmann Institute, the work of his group centered around the development of X-ray crystallographic methods for the determination of molecular structures in order to understand the properties and reactivity of organic solids. In the early 1950s, Schmidt investigated the structure and chemistry of over-crowded molecules and their activity. In other studies, he discovered a correlation between the crystalline structure and the symmetry of photochemical products. This finding helped in understanding chemical reactions in organized systems. He then coined the term “topochemistry” for this kind of reaction. In his research, Schmidt sought to clarify the way by which the structure of molecules affects their packing mode in the crystal. During these studies, he revealed the occurrence of halogen-halogen interactions. Later, he coined the term “crystal engineering,” suggesting that by understanding the ways in which molecules interact, it should be possible to design packing motifs in crystals for rational planning of solid-state reactions. This approach was implemented successfully in the first “absolute” asymmetric synthesis in crystals. Schmidt's achievements stemmed from his earlier ideas recognizing the importance of combining chemistry with molecular geometry. He also suggested that an ordered arrangement of reactive units in space was the key to understanding biological processes such as photosynthesis and enzymatic activity. Jack D. Dunitz | https://en.wikipedia.org/wiki?curid=39313294 |
Gerhard Schmidt (crystallographer) Gerhard Schmidt (1919-1971) and the Road to Chemical Crystallography. In: "Solid State Photochemistry. A Collection of Papers by G. M. J. Schmidt and his Collaborators Describing a Symbiotic Relationship between X-Ray Crystallography and Synthetic Organic Photochemistry. Herausgegeben von D. Ginsburg." (edited by David Ginsburg). Monographs in Modern Chemistry, Vol. 8, pp. 255–269. VCH, Weinheim–New York, 1976. Margaret Thatcher shares her memories of Gerhard Schmidt in a 1985 speech upon the establishment of a Chair bearing her name at the Weizmann Institute G. M. J. Schmidt: Memorial Volume, Israel Journal of Chemistry (http://onlinelibrary.wiley.com/doi/10.1002/ijch.v10.2/issuetoc) Eds.: Cohen M.D., Ginsburg D., Hirshfeld F., 1972, vol. 10, issue 2, pp. 59–658. G. M. J. Schmidt et al. Solid State Photochemistry. Weinheim: Verlag Chemie, 1976. A collection of papers by Schmidt and his collaborators https://www.amazon.com/Solid-State-Photochemistry-alSchmidt/dp/B002JCCSY8/ref=sr_1_1?s=books&ie=UTF8&qid=1387293920&sr=1-1 L. Leiserowitz, "Overlapping with Jack Dunitz", Israel Journal of Chemistry, EarlyView (2016). https://dx.doi.org/10.1002/ijch.201600001 | https://en.wikipedia.org/wiki?curid=39313294 |
Gold glass or gold sandwich glass is a luxury form of glass where a decorative design in gold leaf is fused between two layers of glass. First found in Hellenistic Greece, it is especially characteristic of the Roman glass of the Late Empire in the 3rd and 4th century AD, where the gold decorated roundels of cups and other vessels were often cut out of the piece they had originally decorated and cemented to the walls of the catacombs of Rome as grave markers for the small recesses where bodies were buried. About 500 pieces of gold glass used in this way have been recovered. Complete vessels are far rarer. Many show religious imagery from Christianity, traditional Greco-Roman religion and its various cultic developments, and in a few examples Judaism. Others show portraits of their owners, and the finest are "among the most vivid portraits to survive from Early Christian times. They stare out at us with an extraordinary stern and melancholy intensity". From the 1st century AD the technique was also used for the gold colour in mosaics. Various different techniques may sometimes also be described as "gold glass". Zwischengoldglas is very similar but the two layers of glass are cemented, not fused. It mostly comes from Germany and Bohemia from the 18th and 19th centuries. Verre églomisé properly covers a single layer of glass which is gilded (or coated with other types of metal leaf) on the back, as used in 19th century shop signs and the like. One process was revived by Jean-Baptise Glomy (1711–1786), hence the name | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass Both of these processes were also used in ancient times, and the German and French languages often use their native terms for what is called "gold glass" in English. Gold ruby glass or "cranberry glass" is actually red, coloured by the addition of gold oxide. Gold-band glass is another ancient technique covered below. The manufacturing process for gold glass was difficult and required great skill. For a Late Roman glass, first a small round flat disc, typically about three to five inches across, was cut away from a blown sphere with a flattened bottom, either made of coloured or plain glass. A piece of gold leaf was then glued to this with gum arabic. The design was created by scraping away gold leaf. The main vessel, a cup or bowl, was formed by blowing and cutting, with a flat bottom the same size as the first disc. This was then heated again and carefully lowered onto the disc with the design, superimposing the flat bottom with the disc with the design so that they fused together. The complete vessel was then heated a final time to complete the fusing. Different accounts of different periods vary somewhat as to the precise sequence of stages and other details, but the process is essentially the same. The larger Hellenistic glass bowls are thought to have been formed using moulding rather than blown, as the whole bowl is doubled and the inner and outer vessels must fit together exactly | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass Some of the finer later medallions seem to have been made as such from the start, and some contain pigments other than the gold. These smoother-edged medallions exploited the medium of glass as a matrix for portrait miniatures, and it has proved to be a very effective one, outlasting all alternatives except for precious metal and engraved gems. They were probably initially made to be hung for display, or set in jewellery in smaller examples like that of Gennadios, but were also used for funerary purposes, and often use a base of blue glass. They are a few Roman examples of vessels from Cologne of a different style where several of what have been called "sidewall blobs", small gold glass medallions about 2–3 cm across, with images, are fused into the walls of a vessel. Apart from roundels with figurative images the fused sandwich technique was used to create the tesserae for gold in mosaics, and for beads and the like. tesserae, at least by Byzantine times, had a very thin top layer of glass, which was probably poured onto the lower glass with the gold leaf glued to it. Tesserae were made in blocks or "cakes" and then cut into cubes, which are relatively large in the case of gold backgrounds. Gold backgrounds were laid over earth red or yellow ochre backgrounds which enhanced their visual effect. Most colours of tesserae seem to have been made locally to the mosaic, but there is some discussion as to whether this was true for gold glass ones | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass In the 11th century the relatively new Christian centre of Kiev seems to have used gold tesserae made in Constantinople. Roman gold glass beads were made by using an inner tube or rod to which the gold leaf was stuck. A larger tube was slid over that and the beads crimped off. Easily transported and very attractive, Roman gold glass beads have been found as far outside the Empire as the Wari-Bateshwar ruins in Bangladesh, and sites in China, Korea, Thailand and Malaysia. Gold-band glass is a related Hellenistic and Roman technique, where strips of gold leaf, sandwiched between colourless glass, are used as part of the marbling effect in onyx glass. It is mostly found in small perfume bottles and the like. The most common form of vessel in late Roman examples was a bowl or drinking cup, which are thought to have been originally family gifts for weddings, anniversaries, New Year, the various religious festivals and the like, in some cases perhaps presented at birth or Christian baptism. None of the type of gold glass vessels cut down as grave-markers has survived complete, though about 500 of the cut-off bottoms are known, but since so many have inscriptions encouraging the owner to drink, they are usually referred to as "cups" or "glasses". However Roman drinking cups and glasses were often very wide and shallow, though tall straight-sided or slightly flared shapes like modern tumblers are also found | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass A mosaic in the North African ruins of Dougga shows two hefty slaves pouring wine from "amphorae" into two shallow bowls held by slaves waiting on the banquet. The two "amphorae" are inscribed with "ΠΙΕ" and "ΣΗϹΗϹ" the Greek originals of the toasting formulae "pie zeses" ("Drink, may you live", discussed below) so common on Roman glasses, and it has been suggested that the mosaic shows the shape a complete cup would have had. At what was probably a much later date, perhaps after decades of use, on the death of the owner the main vessel of undecorated glass was cut away and trimmed to leave only the gold glass roundel, which was then used in the catacombs as a grave marker. Presumably in many cases the cup had already broken in the normal course of use, and the thick bottom with the decoration had been preserved for later use in this way. Bodies were buried in the catacombs in small recesses called "loculi", stacked one above another mostly along narrow corridors hollowed out from the soft rock, and no doubt some form of marker was necessary for visitors to locate the right spot. They may also have functioned as a seal on the grave, as they were pressed into the mortar or stucco forming the final surface of the wall of the "loculus"; other classes of small decorative objects were also used in the same way. They may also have been regarded as capable of warding off evil spirits, especially in the later part of the period, when portraits of saints become most common | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass The very untidy trimming of many examples may be explained by this; an example in the Metropolitan Museum of Art is still attached to a chunk of mortar round much of its edge, showing that the mortar overlapped the edge of the glass. Rough edges would mostly have been hidden by the mortar and also provided a firmer key for the mortar to hold the glass in place (as it happens the edges of the New York piece are unusually neatly trimmed). Many pieces of gold glass had portraits of private individuals, mostly married couples, who may have included the deceased, while others had portraits of religious figures such as saints, or religious symbols. This custom was followed by Christian, Jewish (13 identifiably Jewish examples are known) and pagan Romans. The different sets of imagery, apart from the increased number of private portraits, are typical of the paintings also found in the catacombs and other Early Christian art and its Jewish equivalent from the period. As Christian art developed in the late 4th and 5th centuries, its changes are reflected in the subjects and their treatment in gold glass, before the catacombs ceased to be used and the supply of examples ends. The technique was used in Hellenistic times, and Hellenistic examples are generally both more technically ambitious than Roman ones, with wide bowls or drinking cups decorated all round their curved sides in gold glass, and executed with more artistry. The British Museum has a virtually complete bowl (broken but repaired) 19.3 cm wide and 11 | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass 4 cm high, one of two from a tomb in Canosa in Apulia dating to around 270–160 BC. It has most of the interior very finely decorated with lotus and acanthus motifs, which are more typical of gold glass in this period than designs with human figures. There are a handful of other near complete examples, and rather more fragments. These pieces are usually assigned to Alexandria in Egypt, which is often seen as the originating centre for luxury Hellenistic glass, and is mentioned as the source of over-elaborate glass by the 1st century satirist Martial and other sources; one seems to show a Nilotic landscape, though this was a popular subject elsewhere. However fragments have been found when excavating a glass factory on Rhodes. A description perhaps dating from the 270s BC (surviving in the works of the later writer Athenaeus) mentions two vessels that are "diachysa" ("with gold in it") and very likely made by this technique. mosaic tesserae begin to be used in domestic mosaics in the 1st century AD, with Rome apparently the first location. They continued to be used throughout the ancient and medieval periods into the modern day. By around 400 gold began to be used as the background colour for Christian religious mosaics, as it was throughout the Byzantine period | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass The decorated late Roman pieces are usually assumed to have been made in and around Rome, especially in the case of portraits of residents there, but also in the Rhineland around Cologne and Augusta Treverorum, modern Trier, which was a centre for other luxury glass products like cage cups. Alexandria is still thought to have been a major centre, and from linguistic analysis of the inscriptions it has been suggested that the technique, and perhaps the actual artists and craftsmen, reached Rome and Germany from there. Yet it may just be a coincidence of survival that the other large body of "middle-class" portraiture from the period is the Fayum mummy portraits from Egypt. Apart from the Rhineland finds discussed below, small numbers of cut-off vessel bases have been found in northern Italy and modern Hungary and Croatia. The Gennadios medallion in New York, illustrated above, is a fine example of an Alexandrian portrait on blue glass, using a rather more complex technique and naturalistic style than most Roman examples, including painting onto the gold to create shading, and with the Greek inscription showing local dialect features. He had perhaps been given or commissioned the piece to celebrate victory in a musical competition | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass One of the most famous Alexandrian-style portrait medallions, with an inscription in Egyptian Greek, was later mounted in an Early Medieval crux gemmata in Brescia, in the mistaken belief that it showed the pious empress and Gothic queen Galla Placida (died 450) and her children; in fact the knot in the central figure's dress may mark a devotee of Isis. The portrait in the Brescia medallion also shares clear stylistic features with the Fayum mummy portraits of Roman Egypt, in addition to a Greek inscription in the Alexandrian dialect of Egypt. This is one of a group of 14 pieces dating to the 3rd century AD, all individualized secular portraits of high quality. Yet Jás Elsner (2007) contends that the Brescia medallion, likely depicting a family from Alexandria since the inscription is in the Alexandrian dialect of Greek, has a range of possible dates ranging from the early-3rd to mid-5th century AD, before it found its way to Italy where it adorned a 7th-century Christian cross. It is thought that the tiny detail of pieces such as these can only have been achieved using lenses. Where the refined "Alexandrian" medallions, wherever they were actually produced, mostly have a simple thin gold line framing the subject, the Roman examples have a variety of heavier frames, often using two round borders, the style of which forms part of efforts to group them by workshop. The level of portraiture is rudimentary, with features, hairstyles and clothes all following stereotypical styles | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass An "Alexander plate with hunting scene" in the Cleveland Museum of Art is, if genuine, a very rare example of a complete vessel decorated with gold glass, and comes from the upper elite of Roman society. It is a shallow bowl or plate 25.7 cm (10 1/8 inches) in diameter and 4.5 cm (1 3/4 inches) high. The decorated flat roundel in the centre takes about two thirds of the whole diameter. It shows a mounted huntsman with a spear pursuing two elk, while beneath his horse a huntsman on foot with a hound on a leash confronts a wild boar. The Latin inscription "" means "Alexander fortunate man, drink, may you live, together with yours". The identity of "Alexander" has been the subject of discussion, but he is on the whole though to be an unknown aristocrat rather than Alexander the Great or the Emperor Alexander Severus (reigned 232–235). The dish is perhaps slightly later than his reign and at least during his reign he could never be addressed as merely a "man". The Greek drinking toast ZHCAIC given in Latin letters as ZESES, meaning "live!" or "may you live", is a very common part of inscriptions on gold glass, and sometimes the only inscription. It is more common than the Latin equivalent VIVAS, probably because it was considered more refined, somewhat like the modern "bon appétit" used in English. Two glasses including images of Jesus "misspell" "ZESES" as "ZESUS", managing to achieve wordplay between a drinking toast and the name of the Christian saviour | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass Such secular "blessings" are typical, and on roundels made from cups they often urge the owner to drink, even when the iconography is religious. One Jewish example has the usual array of symbols and the inscription "Drink, [so] you may live, Elares". The Wedding at Cana is a popular Christian subject, with one example inscribed "Worthy of your friends, may you live in the peace of God, drink". Another popular phrase is DIGNITAS AMICORUM or "[you are] the honour of your friends". The majority of inscriptions are made up of either names or such conventional expressions, or the two combined. An example inscribed "DIGNITAS AMICORVM PIE ZESES VIVAS" typifies the tendency to pile together the common phrases. The convivial dedications found on so many examples are paralleled by several of the far more luxurious cage cups or "diatreta". One round bottom from a larger bowl found in the catacombs is 10.8 cm across, and now in the Ashmolean Museum in Oxford. It has five abbreviated scenes from the Old and New Testaments surrounding a married couple in a roundel, with the feet of the outer figures to the centre. A large and complex bowl from Cologne was decorated all over with Christian scenes and Imperial portraits, but presumably because of its size (height 8.6, diameter 11.4 cm) no second layer of glass was fused on, so the gold has now all been lost, though the shapes of the design can be seen | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass The portraits of the sons of Constantine I allow an unusually precise probable dating to 326, his "vicennalia", or the 25th anniversary of his reign. Another complete piece is a paten from the Basilica of St. Severin, Cologne, founded in the 4th century. This is decorated with roundels containing Old Testament scenes and floral motifs. According to the "Liber Pontificalis", Pope Zephyrinus, in office from 199–217, had approved the use of glass patens, and ones in other glass techniques survive. A variant technique is only known from vessels from Cologne with what have been called "sidewall blobs", where small gold glass medallions with images are fused into the walls of a vessel; one of the few examples was found in the cemetery of St Severin. Almost all the Roman vessel bottoms have imagery of some sort, and around 240 have legible inscriptions as well. Of these, about half of the total number of gold glasses known, portraits are most common, but there are small narrative scenes, mainly Christian but a few pagan. Portraits of Christian sacred figures are on about half the full corpus. There are a small number of depictions of sports, animals, wreaths and the like, and a single example with a central image of a plant. No Imperial portraits are recorded, nor military scenes; unlike so much Roman public art the glasses concentrate on the private interests of individuals. Apart from a single near-naked Venus and some figures of erotes, sexual themes are another notable absence compared to much Roman art | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass Most glasses feature a single image occupying most of the round space within the border, but some have a number of small scenes, usually arranged in small circular frames around a central image. Most portraits are between bust and half-length. The small number of glasses with Jewish iconography are covered separately below. Either portraits or inscriptions naming private individuals are very common, though other examples have no personalizing aspect and were perhaps just bought from a dealer's stock. Portraits of married couples are at first most the common, but saints were more numerous towards the end of the period; the two are also often combined. It is not always possible to distinguish the two confidently, despite "tituli" inscriptions and a convention of using contemporary dress for owners and a conventional out of date costume for sacred figures, even recent male ones such as Pope Damasus I (r. 366–384). Damasus, exceptionally for a contemporary cleric, appears on at least four glasses, or at least it is thought he is who "DAMAS" refers to. Saints Peter and Paul together are very common, usually facing each other in profile, but sometimes with other figures. Both were martyred in Rome, and especially popular there; other local martyrs such as Agnes are depicted several times, and according to Lucy Grig "the "Roman-ness" of the saints portrayed on the Roman glasses is striking", and five popes from the 3rd and 4th centuries are probably depicted | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass Christ is shown in a number of examples, usually as clean-shaven and youthful, as well as figures such as the Good Shepherd which may symbolize him, or in some cases Orpheus or general bucolic imagery. A small Christ may stand between the heads of a married couple, blessing them. Orants perhaps representing the soul of an owner when not identified as a saint, and as in the catacombs always shown as female, appear a number of times, and female saints and the Virgin are always shown in the orant pose. Narrative scenes from the Old Testament are more common than miracles of Christ, as in the catacomb paintings, and the same "abbreviated representations" of scenes of deliverance feature: the story of Jonah, Daniel in the lions' den, the three youths in the Fiery Furnace. The most common scenes in later Christian art, centred around the liturgical calendar, are very rare. There are really only two non-Christian narrative scenes: one labour of Hercules (two more are shown in "sidewall blobs"), and one of Achilles, but a number of "portrait" figures, as with Christian sacred figures often combined with owners. There are a small number of "agonistic" or sporting scenes, with wrestlers, boxers, one gladiator, and several racing chariot teams. Several of these, like others seeming to represent victory in a musical or dramatic context, feature palms and crowns and may well have been presented to celebrate victory in these fields in some amateur or professional setting, like the Alexandrian Gennadios portrait | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass Two identical glasses featuring two boxers with a trainer, all named, suggest that the glasses may sometimes have been ordered in sets; one may speculate that this may have been common. Single examples show Athena presiding over shipbuilders, a pair of personifications of Rome and Constantinople, and female figures representing the "monetae" or mints, which are often shown on coins. A number have animals that may carry symbolic meaning, or objects such as scrolls or wreaths. The short inscriptions tend to be similar regardless of the content of the image, with names and the "convivial formulae" described above together or separately predominating. A religious implication (as may be intended in "vivas" or "zeses" for example) is relatively rarely explicitly stated. The names are in the single "cognomen" form which is hard to relate to such records as survive, but three glasses can possibly be related to known individuals who were potential owners, and one to a family (that of the poet Ausonius). These persons are rather grand, and one might think belonged to the classes buried in sarcophagi rather than "loculi"; the glasses perhaps belonged to ""amici"", clients or dependents, or had passed as gifts or legacies by the subjects | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass One glass in the British Museum is unusual in a number of respects: between a named couple is a smaller figure of Hercules, and the inscription: "ORFITVS ET CONSTANTIA IN NOMINE HERCVLlS ACERENTINO FELICES BIBATIS" or "Orfitus and Constantia, may you live/drink in happiness in the name of Hercules of Acerentia". This may well represent Memmius Vitruvius Orfitus, prefect of Rome, and his wife. Acerentia in southern Italy had a local cult of Hercules. For some historians Orfitus was "notorious as the propaganda mastermind of the 'pagan revival'" of his day. Only 13 of the more than 500 known Late Roman vessel bottoms are identifiably Jewish, but these have still been said to represent "the most appealing group of Jewish realia that have come down from antiquity". They are all presumed to have been used in the Roman catacombs as grave-markers, though as with the examples identifiable with other religions, the exact find spot and context of the great majority is unrecorded. Rather surprisingly, the only two of the 13 with full histories were found in Christian catacombs, whereas the only gold glass remains found in Jewish catacombs have no Jewish iconography, and show that "some Jews felt no qualm in using gold glasses with pagan iconographical motifs". Identifiably Jewish roundels do not feature portraits but with one exception have a fairly standard array of religious symbols | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass The most common arrangement is on two levels, with two Lions of Judah flanking a Torah ark above, and below two menarot, a shofar (rams horn), etrog, lulav and perhaps others of the four Species, scrolls and vases. Not all the tiny symbols can be confidently identified. Alternatively, the objects are all in the top tier, above a banqueting scene. The single exception to such compositions has what is thought to be a representation of the Temple of Jerusalem, perhaps representing the feat of Purim. Most scholars are confident that Jewish customers used the same workshops as those of the other religions, who presumably kept patterns for designs for all religions, or were provided with sketches. Some of the attempts to group glasses by workshop attribute Jewish glasses and those of other religions to the same workshop. Apart from the use of symbols rather than human figures, the Jewish glasses seem to have been used in very much the same way as those from other religious groups, which is also characteristic of other classes of Jewish artefacts from Rome at this time, where the Jewish community adopted many aspects of the general Roman way of life. Of the 13 known, five have inscriptions including the phrase ""pie zeses"" (see above) and two ""anima dulcis"" (literally "sweet soul", equating to "sweetheart"), both very common phrases in Christian and pagan inscriptions. The rarer phrase ""vivas cum ..."" ("live with ...") is also found on Jewish and non-Jewish glasses | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass They would seem to have been given as gifts on the same sort of occasions, and there is evidence that Roman Jews shared the general Roman custom of New Year present-giving. The technique continued to be used for mosaic tesserae, and at times for pieces that remained relatively large, for example in a small tile in New York with a pattern forming a cross, perhaps from a Syrian church of the 9th to 12th centuries. A small group of Islamic vessels are decorated with mostly simplified vegetal motifs and probably date to the 10th century from Syria; the most complete ones are decorated over a large curved area and must have been made by using a "double vessel" method. In both respects these are closer to the Hellenistic vessels than most Roman ones. From at least the 17th century the Roman glasses attracted antiquarian interest and they began to be removed from the catacombs, in a largely disorganized and unrecorded fashion; now only a "handful" remain in their original position in the catacomb walls | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass The first significant publication on them was by Filippo Buonarroti in 1716, "Osservazioni sopra alcuni frammenti di vasi antichi di vetro ornate di figure trovati nei cimiteri di Roma" ("Observations on some fragments of antique glass vases decorated with figures, found in the cemeteries of Rome"), in which he made the extraordinary, almost proto-Romantic assertion that the aesthetic crudity of early Christian art, often remarked by connoisseurs of Roman arts, had served to intensify the piety of the worshipper, an early expression of feeling for primitive art. After other studies, the Italian Jesuit Raffaele Garrucci published the first illustrated survey in 1858, with an expanded second edition in 1864. In the 19th century a number of imitations, copies and downright forgeries of Roman pieces were made, mostly in Murano off Venice, by firms such as Salviati. The first major public exhibition of these seems to have been at the Exposition Universelle of 1878 in Paris, by Italian firms. A number of museums around the world have examples of Roman vessel bottoms. The largest collection is in the Vatican Museums, with the 60 pieces of Late Antique glass in the British Museum the second largest. A research project on their collection was due to finish in 2010 (see further reading below). The Wilshere Collection in the Ashmolean is the third largest, with some 34 pieces. The Corning Museum of Glass has 18 examples and the Metropolitan Museum in New York nearly as many | https://en.wikipedia.org/wiki?curid=39320626 |
Gold glass The most recent of many catalogues since the 18th century are by C.R. Morey in 1959, with 460 Roman vessel bases, against 426 in S. Smith's thesis of 2000. The corpus continues to be expanded by occasional new finds. | https://en.wikipedia.org/wiki?curid=39320626 |
Dihydroxyflavone may refer to: | https://en.wikipedia.org/wiki?curid=39335837 |
Dualin is an explosive material based on nitroglycerin and nitrogenized cellulose using sawdust or wood pulp. is inferior to dynamite and more liable to explosion. was invented by the Prussian chemist Lieutenant Dittmar in April 1869. In December 1909, Dougherty, and A. Rioux were killed by an explosion of Dualin, and W. Brennan, F. Lavally and E. Lalonde were injured. They were working in a shaft 40 feet deep. | https://en.wikipedia.org/wiki?curid=39336973 |
Cylindrocyclophanes are a class of cyclophane, a group of aromatic hydrocarbons composed of two benzene rings attached in a unique structure. were the first cyclophanes found in nature, isolated from a species of cyanobacteria, and have proven to be an interesting group of compounds to study due to their unusual molecular structure and intriguing biological possibilities, especially its cytotoxicity to some cancer cell lines. Before the cylindrocyclophanes, the cyclophanes had all been produced synthetically. However, when a culture of the cyanobacteria "Cylindrospermum lichenforme" was being evaluated for antitumor activity, the extract was analyzed for new compounds, and a [7,7] paracyclophane was discovered. The structure of the cyclophane was determined and cylindrocyclophane A was named. A related class of compounds, the nostocyclophanes, were discovered during the same study but from another species of cyanobacteria, the "Nostoc linckia". In a later study on the cytotoxicity of cyanobacterial compounds, an additional related class of compounds was discovered, the carbamidocyclophanes, from a Vietnamese species of "Nostoc" sp. are all [7,7] paracyclophanes, differing only in the functional groups present on C-1, C-14, C-29, and C-33. There are currently 16 cylindrocyclophanes that have been identified: cylindrocyclophanes A - F, A - A, C - C, F, and A. A-F differ only in the functional groups present on C-1 (R) and C-14 (R), and the only functional groups present are hydroxyl (OH) and acetoxy (OAc) groups | https://en.wikipedia.org/wiki?curid=39339970 |
Cylindrocyclophanes A - A, C - C, F, and A also have functional groups on C-29 (R) and C-33 (R) and differ from cylindrocyclophanes A-F mainly in their halogenated functional groups. See the following table for a complete list of functional groups for the known cylindrocyclophanes: When cylindrocyclophane A was discovered, it was during an evaluation of the cyanobacteria "Cylindrospermum lichenforme" for antitumor activity. It was shown that "Cylindrospermum lichenforme" did indeed have moderate cytotoxicity again the KB and LoVo tumor cell lines, and this was attributed to cylindrocyclophane A. However, this cytotoxicity is not reserved only for tumor cells, which may limit its ability to be developed pharmaceutically. Since, as stated by Bui, et al., "cyanobacteria have been identified as one of the most promising sources of highly complex natural products" due to their biological activities, more insight has been gained into the mechanism behind the cylindrocyclophanes' cytotoxicity. A team at the University of Illinois-Chicago studied the cytotoxicity of the cylindrocyclophanes further and determined that they may act as proteasome inhibitors., specifically inhibiting the 20S proteasome. Since the function of the proteasome is to break down damaged or unnecessary proteins, it is extremely important to the cells' ability to continue to proliferate. When the proteasome does not perform its function, apoptosis can result | https://en.wikipedia.org/wiki?curid=39339970 |
Cylindrocyclophanes The team at University of Illinois-Chicago determined that cylindrocyclophanes A, A, and A displayed the greatest inhibition of the proteasome, which they attributed to the dichloromethyl functional group present at R. When the cytotoxicity of cylindrocyclophanes A, C, F were examined, A was twice as effective as C, which was attributed to its two hydroxyl functional groups compared to only one for C and none for F. When the effectiveness of the dichloromethyl and hydroxyl functional groups were examined together, it was determined that the most effective arrangement was to have the dichloromethyl and hydroxyl groups "adjacent" spatially to each other. Since the cylindrocyclophanes have such a unique structure and exciting biological possibilities due to their cytotoxicity, there have been numerous efforts to create them synthetically in the laboratory. One of the first attempts was the total synthesis of cylindrocyclophane F, which was accomplished in 20 steps with an 8.3% yield. This, along with other syntheses of cylindrocyclophanes, relies on multistep reaction mechanisms, typically employing Myers reductive coupling and Kowalski ester homologation to obtain the beginning resorcinol fragments and Danheiser benzannulation to construct the aromatic rings with multiple functional groups. After the first total synthesis of cylindrocyclophane F, total synthesis of cylindrocyclophanes A and F were accomplished using a new olefin metathesis dimerization cascade | https://en.wikipedia.org/wiki?curid=39339970 |
Cylindrocyclophanes For synthesis of cylindrocyclophane F, this reduced the number of steps to 11 and increased the yield to 22%. This process was also able to be applied to the synthesis of cylindrocyclophane A in a 16-step reaction with an 8.1% yield. Significant increase in yield was accomplished when a head-to-tail cyclodimerization was paired with a Ramberg-Bäcklund reaction, resulting in a yield of 71% for A and 74% for F. | https://en.wikipedia.org/wiki?curid=39339970 |
Silver overlay is an electroplated coating of silver on a non-conductive surface such as porcelain or glass. Most techniques used to create silver overlay involve the use of special flux which contains silver and turpentine oil. This is then painted on the glass ornament as a design. After the painting is complete, the entire ornament is fired under relatively low heat, it is then cleaned after being quenched and cooled, then it is placed in a solution of silver. A low voltage current is run through the solution and the silver binds in the design, creating a permanent fusion of the silver with the glass. A much older technique of overlay, which was commonly used in the Indian subcontinent since ancient times, involves the use of a silver sheet wrapped around the ornament and then the design beaten onto the sheet or it may be burnished. This technique renders the design silhouetted against a dark backdrop and was commonly called the Aftabi design technique. This technique of overlay predates the technique that is common today, but without the use of electroplating, it was a time consuming and tedious process, which could only be accomplished by skilled artisans. The history of who first devised the process is unknown. What is known is that from 1870 onwards, a number of patents were filed for the process. Although all patents appear after 1870, it has been suggested that the process may have been discovered earlier, and the patents claimed a short time afterwards | https://en.wikipedia.org/wiki?curid=39348113 |
Silver overlay The most well known patent holders are Frederick Shirley from the United States of America, whose patent dates to 1879, Erard and Round who were under the auspices of Stevens & Williams Ltd. whose patent is from 1889, John Sharling also of the USA, whose patent is from 1893 and Friedrich Deusch, the German inventor whose name is most associated with silver overlay today, whose patented the process in 1895 and displayed his work in 1907 at an exhibition in Bordeaux. Deusch returned to Schwäbisch Gmünd in southern Germany where, in 1912, he founded his firm Deusch & Co. Deusch continued exhibiting his wares and gained the Gold Medal at the 1913 World Exposition in Ghent, Belgium. With his presence, Schwäbisch Gmünd became the center of German silver overlay production. Schwäbisch Gmünd (about 20,000 inhabitants in that time) had a long tradition since the 16th century in the art of artists working with gold and silver. A school for applied arts existed there from an early date, which became a school for the precious metal industry in 1907. In the 1920s almost 190 firms were involved in the precious metals industry. The presence of materials, artisans, and component suppliers in on place created an ideal environment for the industry to thrive. After Deusch and Company, other firms specializing in silver overlay were founded. In particular, the firms of Friedrich Wilhelm Spahr and Alfred and Manfred Vehyl were established | https://en.wikipedia.org/wiki?curid=39348113 |
Silver overlay Parallel to the development of German silver overlay, silver overlay production was also initiated in the United States. The specific feature of German silver overlay is the degree of purity – 925 for Sterling silver or 999 for fine silver. The quality of silver used for German overlay can be seen by identifying the impressed 1000 mark (usually on the base or side of an item). The purity and thickness of the silver overlay ensures the beauty of the item is maintained without any loss to the silver even after many years of cleaning. Although other kinds of silver, such as nickel silver, can be sued for silver overlay, the effect is not as vibrant. Bohemian and Venetian Murano glass are often described as silver overlay, but the silver is so thin that it looks as though it has been painted onto the surface, producing a flat effect. Friedrich Deusch invented a way to combine silver and a non-conductive surface such as porcelain or glass with galvanization. He achieved this with a special conductive fluid (a type of flux) which was fixed permanently on the prepared form. The particular objects (such as a vase) were first roughened by engraving or using hydrofluoric acid to etch a design. This implies that a very exact covering of the surfaces had to be achieved to prevent any damage to areas which were not to be overlaid. Maybe they used a masking lacquer which could withstand the following baking in the kiln which was used to fuse the flux with the surface of the item | https://en.wikipedia.org/wiki?curid=39348113 |
Silver overlay The next step was to galvanize the item with the purest silver (1000). It was very important to monitor items being overlaid with silver – waiting too long resulted in visible dark spots and slight roughness where the cathode or anode were fixed. The cathode and anode were used to charge the item electronically and this allowed the fusion of silver to the area painted with the silver flux. The thickness of silver desired on the finished item determined how long the item needed to be left in the silver bath; this could be more than 30 hours. Finally, if the masking lacquer (discussed earlier) did not burn in the kiln, it must have been removed later (probably with chemical fluids). When colored enamels were to be used on the finished product, they had to be fired prior to the final stage of the silver overlay process. Engraving the silver was the last, and sometimes most laborious, work; it was brought to the highest level by Friedrich Wilhelm Spahr and his workers. Early items designed and produced by Friedrich Deusch are very classical, and this was followed by an abstract phase of Art Déco in its purest form. From the 1950s, it was more a concrete style with flowers and so forth. Deusch applied silver overlay to vases, plates, coffee and tea services, and other items. From the outset, the firm of Alfred Veyhl had its own style. It was mostly the combination of polychromatic painted details of birds, flowers, and similar motifs, framed with silver. The more abstract designs are rare | https://en.wikipedia.org/wiki?curid=39348113 |
Silver overlay Alfred, and later his son Manfred Veyhl, were the only ones who used a varnish to avoid silver oxidation. Alfred used more softer and rounder lines in his designs, whereas Manfred had a more angular, expressive style. A specialty for this company was that clients could choose from a certain range of porcelain forms and décors. The items were then produced exclusively in a single production run. An outstanding figure is Friedrich Wilhelm Spahr. There is evidence that he learned his skill from Friedrich Deusch (some items of both firms have very similar formal designs). He was not only an artisan but an artist in developing repeating circumferential forms in a perfect and harmonic proportion. Very often it is the pure arrangement of lines (curved or straight), or their combination, with flowers or birds. Never over-designed, but enough to divide the small surface (for example of a vase) in a self-evident and harmonious way. Like the others, not only did he design and apply the silver overlay, he also prepared the porcelain with his own enamel colors, painted the motifs and engraved the silver. Of course he did not produce all these items by himself. Spahr's factory employed about forty specialized workers. The outstanding engraved pieces show the unrivaled quality of Spahr. The early items typically have a thicker silver layer. One can also see the stroke of the brush which proves the overlay and painted surface were handcrafted | https://en.wikipedia.org/wiki?curid=39348113 |
Silver overlay Printed designs were used more often on items produced later, especially those of Manfred Vehyl. These can be recognized by studying the design: if the color is flat and full of small dots, this strongly indicates a printed design. Also, the silver work on printed color designs appears not to cover the design closely, as it should. The three companies bought and used porcelain blanks from several well known producers such as Rosenthal, Hutschenreuther, Thomas Bavaria, Krautheim & Adelberg and marketed the finished products under their own names. They also produced silver overlay glass in the same manner. A large amount of glassware came from WMF in Geislingen, which is not far from Schwäbisch Gmünd. A respectable amount of glass to be overlaid also came from Jean Beck, a famous glass designer in Munich. Until recently, it was believed that Beck created the brilliant silver designs himself and that Deusch only produced them. However, this was not the case. As with the porcelain, Deusch and others bought the delightfully stylized glass blanks, decorated them in silver overlay, and sold them under their own names. Friedrich Deusch used the impressed mark "Deusch 1000 / 1000" on the early items. This mark was punched directly into the silver. Very often one may also find a red three-digit number on the bottom of the porcelain or glass which indicates this early production. Later, it was replaced by a red stamp which shows a coffeepot and the name Deusch | https://en.wikipedia.org/wiki?curid=39348113 |
Silver overlay In addition, to these marks, the following marks may also be found: "1000 / 1000 Silber" or "1000 / 1000 Feinsilber". Later items may have the additional mark "Made in Western Germany". Alfred and Manfred Veyhl used many different marks, stamps and labels (always placed on the bottom of the item). Vehyl's work often shows the "1000/1000 silver" mark included in the body of the design. Some rare items are signed by handwritten monogram (MV for Manfred Veyhl) and the word "Handgemalt" (handpainted). Friedrich Wilhelm Spahr mostly used marks impressed directly into the silver. The very earliest and rarest of Spahr's marks began with "MSG 1000 10" ("MSG" standing for "Manufaktur Schwäbisch Gmünd"). This mark was followed by "Spahr 1000 10" (sometimes stamped in black letters on a porcelain base), later with "Spahr 1000", and finally with transparent plastic labels on the bottom printed "Spahr Feinsilberauflage 1000 / 1000". Alvin Corporation, which was later owned by the Gorham Mfg. Co. after 1928, also used special marks. They manufactures pieces of sterling silver flatware, as well as hollowware and special toilet ware. The La Pierre Manufacturing Company also sued special marks. It was established by Frank H. La Pierre in 1885, and headquartered at 18 East 14th Street, NY. It relocated its offices to Newark, NJ before its incorporation in 1895. Their special marks appear on their silver overlay item such as hollowware and novelty items | https://en.wikipedia.org/wiki?curid=39348113 |
Silver overlay The Rockwell Silver Company established in Meriden, CT around 1905 created a number designs which featured silver overlay, however they were merged with Silver City Glass Company in 1978, so even though they have done extensive work, there are no unique marks associated with the company. The Gorham Manufacturing Co. which was active from 1848 till 1865 used alion as their mark. They also used a rams head and the phrase "coin" to mark their items. These luxurious products were most often sold in important jewellery stores. Sometimes the retailer's paper labels survived the cleaning attempts of the last decades, and these labels are always a keen addition for any collector. They confirm that silver overlay porcelain and glass was sold all over Germany. Friedrich Deusch, the oldest and biggest firm, also sold internationally and even produced a large amount of silver overlay tableware for the Royal House of Saudi Arabia. Deusch is the only firm that has survived (as of 2013), although the focus of production has changed from fine art to galvanizing parts for the automobile industry. In 1976, after three generations, the Deusch family relinquished interest in the firm of Friedrich Deusch and Company Today, there is scant knowledge and interest about this firm's history. Veyhl (father and son) traveled a lot offering their newest items to different jewellery stores. Later, they opened their own shop in Plüderhausen (close to Schwäbisch Gmünd) | https://en.wikipedia.org/wiki?curid=39348113 |
Silver overlay Friedrich Wilhelm Spahr created timeless designs which can be found today all over Europe and even in the United States. These are rare, desirable and mostly exquisite. was a very exclusive luxury ware from the beginning because of the very complicated and time-consuming steps of manufacturing. items were never mass-produced and were made in limited numbers. The development of silver overlay was forged by a technical alliance between artists, artisans and advances in chemistry, physics, electronics and, ultimately, the industrialized techniques of the late 19th century. The arts movements of the day were philosophically against industrialized techniques. Yet, ironically, many delightfully decorated pieces of silver overlay porcelain and glass can be seen with superb handicraft and Art Nouveau-inspired designs. Thus, while the handicraft movement died after a single incandescent generation, their designs live on, as do the stunning works of Friedrich Deusch, Friedrich Wilhelm Spahr, and Alfred & Manfred Vehyl. | https://en.wikipedia.org/wiki?curid=39348113 |
Singlet fission is a spin-allowed process, unique to molecular photophysics, whereby one singlet excited state is converted into two triplet states. The phenomenon has been observed in molecular crystals, aggregates, disordered thin films, and covalently-linked dimers, where the chromophores are oriented such that the electronic coupling between singlet and the double triplet states is large. Being spin allowed, the process can occur very rapidly (on a picosecond or femtosecond timescale) and out-compete radiative decay (that generally occurs on a nanosecond timescale) thereby producing two triplets with very high efficiency. The process is distinct from intersystem crossing, in that singlet fission does not involve a spin flip, but is mediated by two triplets coupled into an overall singlet. It has been proposed that singlet fission in organic photovoltaic devices could improve the photoconversion efficiencies. The process of singlet fission was first introduced to describe the photophysics of anthracene in 1965. Early studies on the effect of the magnetic field on the fluorescence of crystalline tetracene solidified understanding of singlet fission in polyacenes. Acenes, Pentacene and Tetracene in particular, are a prominent candidates for singlet fission. The energy of the triplet states are smaller than or equal to half of the singlet (S) state energy, thus satisfying the requirement of S ≥ 2T. in functionalized pentacene compounds has been observed experimentally | https://en.wikipedia.org/wiki?curid=39352563 |
Singlet fission Intramolecular singlet fission in covalently linked pentacene and tetracene dimers has also been reported. The detailed mechanism of the process is unknown. Particularly, the role of charge transfer states in the singlet fission process is still debated. Typically, the mechanisms for singlet fission are classified into (a) Direct coupling between the molecules and (b) Step-wise one-electron processes involving the charge-transfer states. Intermolecular interactions and the relative orientation of the molecules within the aggregates are known to critically effect the singlet fission efficiencies. | https://en.wikipedia.org/wiki?curid=39352563 |
Fluorenylidene 9-is an aryl carbene derived from the bridging methylene group of fluorene. has the unusual property that the triplet ground state is only 1.1 kcal/mol (4.6 kJ/mol) lower in energy than the singlet state. For this reason, fluorenylidene has been studied extensively in organic chemistry. is a reactive intermediate. Reactions involving fluorenylidene proceed through either the triplet or singlet state carbene, and the products formed depend on the relative concentration of spin states in solution, as influenced by experimental conditions. The rate of intersystem crossing is determined by the temperature and concentration of specific spin-trapping agents. The ground state is believed to be a bent triplet, with two orthogonal sp hybrid orbitals singly occupied by unpaired spins. One electron occupies an orbital of sigma symmetry in the plane of the rings, while the other occupies an orbital of pi symmetry, which interacts with the pi systems of the adjacent aromatic rings (delocalization into the rings is minimal, since zero-field parameter D is high). The zero field splitting parameters predict a bond angle greater than 135°, and since the ideal bond geometry for cyclopentane carbons is about 109°, considerable ring strain causes the methylene sigma bonds to be bent. In the singlet state, the spin-paired electrons occupy the sp hybrid orbital, orthogonal to an empty p-orbital. Conversion of singlet to triplet fluorenylidene is achieved through intersystem crossing (ISC) | https://en.wikipedia.org/wiki?curid=39355292 |
Fluorenylidene can be produced by photolysis of 9-diazofluorene (DAF). Ultra-fast (300 fs) time resolved laser-flash photolysis of DAF implicates a four-step process in the formation of fluorenylidene by irradiation of 9-diazofluorene. reacts with olefins as predicted by the Skell-Woodworth rules. The stereochemistry of cycloaddition products depends on the relative rates of cyclopropanation (or other reactions) and intersystem crossing. Stabilization of specific spin states, and, by extension, increased stereospecificity can be achieved by using solvents of different polarities . Triplet fluorenylidene reacts with olefins in a stepwise fashion to produce a racemic mixture, provided that the rate of spin inversion (intersystem crossing) is not significantly faster than rates of intermediate bond rotation. Singlet fluorenylidene reacts with olefins in a concerted fashion, maintaining the stereochemistry of the reactant olefin. Triplet quenchers such as butadiene solvents can be used to increase stereospecific yields. Halogenated solvents also stabilize the singlet state. For example, dibromomethane and hexafluorobenzene deactivate the higher-energy singlet state, decelerating the rate of intersystem crossing in accordance with earlier studies of diphenylcarbene. The mechanism of singlet state deactivation is theorized to occur through halogen-lone pair complexation of empty 1Fl P-orbitals. | https://en.wikipedia.org/wiki?curid=39355292 |
Melvin Mooney Distinguished Technology Award The is a professional award conferred by the American Chemical Society, Rubber Division. Established in 1983, the award is named after Melvin Mooney, developer of the Mooney viscometer and of the Mooney-Rivlin hyperelastic law. The award consists of an engraved plaque and prize money. The medal honors individuals "who have exhibited exceptional technical competency by making significant and repeated contributions to rubber science and technology". Source: Rubber Division, American Chemical Society | https://en.wikipedia.org/wiki?curid=39355617 |
Tetrahydroxyflavone may refer to: | https://en.wikipedia.org/wiki?curid=39358105 |
Pentahydroxyflavone may refer to: | https://en.wikipedia.org/wiki?curid=39358124 |
Phase Transitions and Critical Phenomena is a 20-volume series of books, comprising review articles on phase transitions and critical phenomena, published during 1972-2001. It is "considered the most authoritative series on the topic". Volumes 1-6 were edited by Cyril Domb and Melville S. Green, and after Green's death, volumes 7-20 were edited by Domb and Joel Lebowitz. Volume 4 was never published. Volume 5 was published in two volumes, as 5A and 5B. | https://en.wikipedia.org/wiki?curid=39359065 |
Biological aspects of fluorine Fluorine may interact with biological systems in the form of fluorine-containing compounds. Though elemental fluorine (F) is very rare in everyday life, hundreds of fluorine-containing compounds occur naturally as minerals, medicines, pesticides, and materials. Naturally occurring organofluorine compounds are extremely rare, yet man-made fluoride compounds are common: for example, twenty percent of all commercialized pharmaceuticals contain fluorine, including Lipitor and Prozac. In many contexts, fluorine-containing compounds are harmless or even beneficial to living organisms; in others, they are toxic. Aside from their use in medicine, man-made fluorinated compounds have also played a role in several noteworthy environmental concerns. Chlorofluorocarbons (CFCs), once major components of numerous commercial aerosol products, have proven damaging to Earth's ozone layer and resulted in the wide-reaching Montreal Protocol; though in truth the chlorine in CFCs is the destructive actor, fluorine is an important part of these molecules because it makes them very stable and long-lived. Similarly, the stability of many organofluorine compounds has raised the issue of biopersistence. Long-lived molecules from waterproofing sprays, for example PFOA and PFOS, are found worldwide in the tissues of wildlife and humans, including newborn children. Fluorine biology is also relevant to a number of cutting-edge technologies. PFCs (perfluorocarbons) are capable of holding enough oxygen to support human liquid breathing | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Organofluorine in the form of its radioisotope F is also at the heart of a modern medical imaging technique known as positron emission tomography (PET). A PET scan produces three-dimensional colored images of parts of the body that use a lot of sugar, particularly the brain or tumors. Since the mid-20th century, it has been discerned from population studies (though incompletely understood) that fluoride reduces tooth decay. Initially, researchers hypothesized that fluoride helped by converting tooth enamel from the more acid-soluble mineral hydroxyapatite to the less acid-soluble mineral fluorapatite. However, more recent studies showed no difference in the frequency of caries (cavities) between teeth that were pre-fluoridated to different degrees. Current thinking is that fluoride prevents cavities primarily by helping teeth that are in the very early stages of tooth decay. When teeth begin to decay from the acid produced by sugar-consuming bacteria, calcium is lost ("demineralization"). However, teeth have a limited ability to recover calcium if decay is not too far advanced ("remineralization"). Fluoride appears to reduce demineralization and increase remineralization. Also, there is some evidence that fluoride interferes with the bacteria that consume sugars in the mouth and make tooth-destroying acids. In any case, it is only the fluoride that is directly present in the mouth (topical treatment) that prevents cavities; fluoride ions that are swallowed do not benefit the teeth | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Water fluoridation is the controlled addition of fluoride to a public water supply in an effort to reduce tooth decay in people who drink the water. Its use began in the 1940s, following studies of children in a region where water is naturally fluoridated. It is now used widely in public water systems in the United States and some other parts of the world, such that about two-thirds of the U.S. population is exposed to fluoridated water supplies and about 5.7% of people worldwide. Although the best available evidence shows no association with adverse effects other than fluorosis (dental and, in worse cases, skeletal), most of which is mild, water fluoridation has been contentious for ethical, safety, and efficacy reasons, and opposition to water fluoridation exists despite its widespread support by public health organizations. The benefits of water fluoridation have lessened recently, presumably because of the availability of fluoride in other forms, but are still measurable, particularly for low-income groups. Systematic reviews in 2000 and 2007 showed significant reduction of cavities in children exposed to water fluoridation. Sodium fluoride, tin difluoride, and, most commonly, sodium monofluorophosphate, are used in toothpaste. In 1955, the first fluoride toothpaste was introduced in the United States. Now, almost all toothpaste in developed countries is fluoridated. For example, 95% of European toothpaste contains fluoride | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Gels and foams are often advised for special patient groups, particularly those undergoing radiation therapy to the head (cancer patients). The patient receives a four-minute application of a high amount of fluoride. Varnishes, which can be more quickly applied, exist and perform a similar function. Fluoride is also often present in prescription and non-prescription mouthwashes and is a trace component of foods manufactured using fluoridated water supplies. Of all commercialized pharmaceutical drugs, twenty percent contain fluorine, including important drugs in many different pharmaceutical classes. Fluorine is often added to drug molecules during drug design, as even a single atom can greatly change the chemical properties of the molecule in desirable ways. Because of the considerable stability of the carbon–fluorine bond, many drugs are fluorinated to delay their metabolism, which is the chemical process in which the drugs are turned into compounds that allows them to be eliminated. This prolongs their half-lives and allows for longer times between dosing and activation. For example, an aromatic ring may prevent the metabolism of a drug, but this presents a safety problem, because some aromatic compounds are metabolized in the body into poisonous epoxides by the organism's native enzymes. Substituting a fluorine into a "para" position, however, protects the aromatic ring and prevents the epoxide from being produced | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Adding fluorine to biologically active organic compounds increases their lipophilicity (ability to dissolve in fats), because the carbon–fluorine bond is even more hydrophobic than the carbon–hydrogen bond. This effect often increases a drug's bioavailability because of increased cell membrane penetration. Although the potential of fluorine being released in a fluoride leaving group depends on its position in the molecule, organofluorides are generally very stable, since the carbon–fluorine bond is strong. Fluorines also find their uses in common mineralocorticoids, a class of drugs that increase the blood pressure. Adding a fluorine increases both its medical power and anti-inflammatory effects. Fluorine-containing fludrocortisone is one of the most common of these drugs. Dexamethasone and triamcinolone, which are among the most potent of the related synthetic corticosteroid class of drugs, contain fluorine as well. Several inhaled general anesthetic agents, including the most commonly used inhaled agents, also contain fluorine. The first fluorinated anesthetic agent, halothane, proved to be much safer (neither explosive nor flammable) and longer-lasting than those previously used. Modern fluorinated anesthetics are longer-lasting still and almost insoluble in blood, which accelerates the awakening. Examples include sevoflurane, desflurane, enflurane, and isoflurane, all hydrofluorocarbon derivatives | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Prior to the 1980s, antidepressants altered not only serotonin uptake but also the uptake of altered norepinephrine; the latter caused most of the side effects of antidepressants. The first drug to alter only the serotonin uptake was Prozac; it gave birth to the extensive selective serotonin reuptake inhibitor (SSRI) antidepressant class and is the best-selling antidepressant. Many other SSRI antidepressants are fluorinated organics, including Celexa, Luvox, and Lexapro. Fluoroquinolones are a commonly used family of broad-spectrum antibiotics. Compounds containing fluorine-18, a radioactive isotope that emits positrons, are often used in positron emission tomography (PET) scanning, because the isotope's half-life of about 110 minutes is usefully long by positron-emitter standards. One such radiopharmaceutical is 2-deoxy-2-(F)fluoro-D-glucose (generically referred to as fludeoxyglucose), commonly abbreviated as F-FDG, or simply FDG. In PET imaging, FDG can be used for assessing glucose metabolism in the brain and for imaging cancer tumors. After injection into the blood, FDG is taken up by "FDG-avid" tissues with a high need for glucose, such as the brain and most types of malignant tumors. Tomography, often assisted by a computer to form a PET/CT (CT stands for "computer tomography") machine, can then be used to diagnose or monitor treatment of cancers, especially Hodgkin's lymphoma, lung cancer, and breast cancer. Natural fluorine is monoisotopic, consisting solely of fluorine-19 | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Fluorine compounds are highly amenable to nuclear magnetic resonance (NMR), because fluorine-19 has a nuclear spin of , a high nuclear magnetic moment, and a high magnetogyric ratio. Fluorine compounds typically have a fast NMR relaxation, which enables the use of fast averaging to obtain a signal-to-noise ratio similar to hydrogen-1 NMR spectra. Fluorine-19 is commonly used in NMR study of metabolism, protein structures and conformational changes. In addition, inert fluorinated gases have the potential to be a cheap and efficient tool for imaging lung ventilation. Liquid fluorocarbons have a very high capacity for holding gas in solution. They can hold more oxygen or carbon dioxide than blood does. For that reason, they have attracted ongoing interest related to the possibility of artificial blood or of liquid breathing. Blood substitutes are the subject of research because the demand for blood transfusions grows faster than donations. In some scenarios, artificial blood may be more convenient or safe. Because fluorocarbons do not normally mix with water, they must be mixed into emulsions (small droplets of perfluorocarbon suspended in water) in order to be used as blood. One such product, Oxycyte, has been through initial clinical trials. Possible medical uses of liquid breathing (which uses pure perfluorocarbon liquid, not a water emulsion) involve assistance for premature babies or for burn victims (if normal lung function is compromised) | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Both partial and complete filling of the lungs have been considered, although only the former has undergone any significant tests in humans. Several animal tests have been performed and there have been some human partial liquid ventilation trials. One effort, by Alliance Pharmaceuticals, reached clinical trials but was abandoned because of insufficient advantage compared to other therapies. Nanocrystals represent a possible method of delivering water- or fat-soluble drugs within a perfluorochemical fluid. The use of these particles is being developed to help treat babies with damaged lungs. Perfluorocarbons are banned from sports, where they may be used to increase oxygen use for endurance athletes. One cyclist, Mauro Gianetti, was investigated after a near-fatality where PFC use was suspected. Other posited applications include deep-sea diving and space travel, applications that both require total, not partial, liquid ventilation. The 1989 film "The Abyss" depicted a fictional use of perfluorocarbon for human diving but also filmed a real rat surviving while cooled and immersed in perfluorocarbon. (See also list of fictional treatments of perfluorocarbon breathing.) An estimated 30% of agrichemical compounds contain fluorine. Most of them are used as poisons, but a few stimulate growth instead. Sodium fluoroacetate has been used as an insecticide, but it is especially effective against mammalian pests. The name "1080" refers to the catalogue number of the poison, which became its brand name | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Fluoroacetate is similar to acetate, which has a pivotal role in the Krebs cycle (a key part of cell metabolism). Fluoroacetate halts the cycle and causes cells to be deprived of energy. Several other insecticides contain sodium fluoride, which is much less toxic than fluoroacetate. Insects fed 29-fluorostigmasterol use it to produce fluoroacetates. If a fluorine is transferred to a body cell, it blocks metabolism at the position occupied. Trifluralin was widely used in the 20th century, for example, in over half of U.S. cotton field acreage in 1998.) Because of its suspected carcinogenic properties some Northern European countries banned it in 1993. As of 2015, the European Union has banned it, although Dow made a case to cancel the decision in 2011. Biologically synthesized organofluorines are few in number, although some are widely produced. The most common example is fluoroacetate, with an active poison molecule identical to commercial "1080". It is used as a defense against herbivores by at least 40 green plants in Australia, Brazil, and Africa; other biologically synthesized organofluorines include ω-fluoro fatty acids, fluoroacetone, and 2-fluorocitrate. In bacteria, the enzyme adenosyl-fluoride synthase, which makes the carbon–fluorine bond, has been isolated. The discovery was touted as possibly leading to biological routes for organofluorine synthesis | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Fluoride is considered a semi-essential element for humans: not necessary to sustain life, but contributing (within narrow limits of daily intake) to dental health and bone strength. Daily requirements for fluorine in humans vary with age and sex, ranging from 0.01 mg in infants below 6 months to 4 mg in adult males, with an upper tolerable limit of 0.7 mg in infants to 10 mg in adult males and females. Small amounts of fluoride may be beneficial for bone strength, but this is an issue only in the formulation of artificial diets. (See also fluoride deficiency.) Elemental fluorine is highly toxic. Above a concentration of 25 ppm, it causes significant irritation while attacking the eyes, airways and lungs and affecting the liver and kidneys. At a concentration of 100 ppm, human eyes and noses are seriously damaged. People can be exposed to fluorine in the workplace by breathing it in, skin contact, or eye contact. The Occupational Safety and Health Administration (OSHA) has set the legal limit (Permissible exposure limit) for fluorine exposure in the workplace as 0.1 ppm (0.2 mg/m) over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 0.1 ppm (0.2 mg/m) over an 8-hour workday. At levels of 25 ppm, fluorine is immediately dangerous to life and health. Hydrofluoric acid, the water solution of hydrogen fluoride (HF), is a contact poison | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Even though it is from a chemical perspective a relatively weak acid, it is far more dangerous than conventional strong mineral acids, such as nitric acid, sulfuric acid, or hydrochloric acid. Owing to its lesser chemical dissociation in water (remaining a neutral molecule), hydrogen fluoride penetrates tissue more quickly than typical acids. Poisoning can occur readily through the skin or eyes or when inhaled or swallowed. From 1984 to 1994, at least nine workers died in the United States from accidents with HF. Once in the blood, hydrogen fluoride reacts with calcium and magnesium, resulting in electrolyte imbalances, potentially including hypocalcemia. The consequent effect on the heart (cardiac arrhythmia) may be fatal. Formation of insoluble calcium fluoride also causes severe pain. Burns with areas larger than 160 cm, about the size of a man's hand, can cause serious systemic toxicity. Symptoms of exposure to hydrofluoric acid may not be immediately evident, with an eight-hour delay for 50% HF and up to 24 hours for lower concentrations. Hydrogen fluoride interferes with nerve function, meaning that burns may not initially be painful. If the burn has been initially noticed, then HF should be washed off with a forceful stream of water for ten to fifteen minutes to prevent its further penetration into the body. Clothing used by the person burned may also present a danger. Hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca that binds with the fluoride ions | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Skin burns can be treated with a water wash and 2.5 percent calcium gluconate gel or special rinsing solutions. Because HF is absorbed, further medical treatment is necessary. Calcium gluconate may be injected or administered intravenously. Use of calcium chloride is contraindicated and may lead to severe complications. Sometimes surgical excision of tissue or amputation is required. Soluble fluorides are moderately toxic. For sodium fluoride, the lethal dose for adults is 5–10 g, which is equivalent to 32–64 mg of elemental fluoride per kilogram of body weight. The dose that may lead to adverse health effects is about one fifth of the lethal dose. Chronic excess fluoride consumption can lead to skeletal fluorosis, a disease of the bones that affects millions in Asia and Africa. The fluoride ion is readily absorbed by the stomach and intestines. Ingested fluoride forms hydrofluoric acid in the stomach. In this form, fluoride crosses cell membranes and then binds with calcium and interferes with various enzymes. Fluoride is excreted through urine. Fluoride exposure limits are based on urine testing, which is used to determine the human body's capacity for ridding itself of fluoride. Historically, most cases of fluoride poisoning have been caused by accidental ingestion of insecticides containing inorganic fluoride. Most calls to poison control centers for possible fluoride poisoning come from the ingestion of fluoride-containing toothpaste | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine Malfunction of water fluoridation equipment has occurred several times, including an Alaskan incident that sickened nearly 300 people and killed one. Because of the strength of the carbon–fluorine bond, organofluorines endure in the environment. Perfluorinated compounds (PFCs) have attracted particular attention as persistent global contaminants. These compounds can enter the environment from their direct uses in waterproofing treatments and firefighting foams or indirectly from leaks from fluoropolymer production plants (where they are intermediates). Because of the acid group, PFCs are water-soluble in low concentrations. While there are other PFAAs, the lion's share of environmental research has been done on the two most well-known: perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). The U.S. Environmental Protection Agency classifies these materials as "emerging contaminants" based on the growing but still incomplete understanding of their environmental impact. Trace quantities of PFCs have been detected worldwide, in organisms from polar bears in the Arctic to the global human population. Both PFOS and PFOA have been detected in breast milk and the blood of newborns. A 2013 review showed widely varying amounts of PFOS and PFOA in different soils and groundwater, with no clear pattern of one chemical dominating. PFC concentrations were generally higher in areas with more human population or industrial activity, and areas with more PFOS generally also had more PFOA | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine the two chemicals have been found at different concentrations in different populations; for example, one study showed more PFOS than PFOA in Germans, while another study showed the reverse for Americans. PFCs may be starting to decrease in the biosphere: one study indicated that PFOS levels in wildlife in Minnesota were decreasing, presumably because 3M discontinued its production. In the body, PFCs bind to proteins such as serum albumin. Their tissue distribution in humans is unknown, but studies in rats suggest it is present mostly in the liver, kidney, and blood. They are not metabolized by the body but are excreted by the kidneys. Dwell time in the body varies greatly by species. Rodents have half-lives of days, while in humans they remain for years. Many animals show sex differences in the ability to rid the body of PFAAs, but without a clear pattern. Gender differences of half lives vary by animal species. The potential health impact of PFCs is unclear. Unlike chlorinated hydrocarbons, PFCs are not lipophilic (stored in fat), nor genotoxic (damaging genes). Both PFOA and PFOS in high doses cause cancer and the death of newborns in rodents. Studies on humans have not been able to prove an impact at current exposures. Bottlenose dolphins have some of the highest PFOS concentrations of any wildlife studied; one study suggests an impact on their immune systems. The biochemical causes of toxicity are also unclear and may differ by molecule, health effect, and even animal | https://en.wikipedia.org/wiki?curid=39367145 |
Biological aspects of fluorine PPAR-alpha is a protein that interacts with PFAAs and is commonly implicated in contaminant-caused rodent cancers. Less fluorinated chemicals (i.e. not perfluorinated compounds) can also be detected in the environment. Because biological systems do not metabolize fluorinated molecules easily, fluorinated pharmaceuticals like antibiotics and antidepressants can be found in treated city sewage and wastewater. Fluorine-containing agrichemicals are measurable in farmland runoff and nearby rivers. | https://en.wikipedia.org/wiki?curid=39367145 |
Phases of fluorine Fluorine forms diatomic molecules () that are gaseous at room temperature with a density about 1.3 times that of air. Though sometimes cited as yellow-green, pure fluorine gas is actually a very pale yellow. The color can only be observed in concentrated fluorine gas when looking down the axis of long tubes, as it appears transparent when observed from the side in normal tubes or if allowed to escape into the atmosphere. The element has a "pungent" characteristic odor that is noticeable in concentrations as low as 20 ppb. Fluorine condenses to a bright yellow liquid at −188 °C (−307 °F), which is near the condensation temperatures of oxygen and nitrogen. The solid state of fluorine relies on Van der Waals forces to hold molecules together, which, because of the small size of the fluorine molecules, are relatively weak. Consequently, the solid state of fluorine is more similar to that of oxygen or the noble gases than to those of the heavier halogens. Fluorine solidifies at −220 °C (−363 °F) into a cubic structure, called beta-fluorine. This phase is transparent and soft, with significant disorder of the molecules; its density is 1.70 g/cm. At −228 °C (−378 °F) fluorine undergoes a solid–solid phase transition into a monoclinic structure called alpha-fluorine. This phase is opaque and hard, with close-packed layers of molecules, and is denser at 1.97 g/cm | https://en.wikipedia.org/wiki?curid=39368969 |
Phases of fluorine The solid state phase change requires more energy than the melting point transition and can be violent, shattering samples and blowing out sample holder windows. Solid fluorine received significant study in the 1920s and 30s, but relatively less until the 1960s. The crystal structure of alpha-fluorine given, which still has some uncertainty, dates to a 1970 paper by Linus Pauling. | https://en.wikipedia.org/wiki?curid=39368969 |
Residual sodium carbonate index The residual sodium carbonate (RSC) index of irrigation water or soil water is used to indicate the alkalinity hazard for soil. The RSC index is used to find the suitability of the water for irrigation in clay soils which have a high cation exchange capacity. When dissolved sodium in comparison with dissolved calcium and magnesium is high in water, clay soil swells or undergoes dispersion which drastically reduces its infiltration capacity. In the dispersed soil structure, the plant roots are unable to spread deeper into the soil due to lack of moisture. However, high RSC index water does not enhance the osmotic pressure to impede the off take of water by the plant roots unlike high salinity water. Clay soils irrigation with high RSC index water leads to fallow alkali soils formation. RSC is expressed in meq/l units. RSC should not be higher than 1 and preferably less than +0.5 for considering the water use for irrigation. The formula for calculating RSC index is: While calculating RSC index, the water quality present at the root zone of the crop should be considered which would take into account the leaching factor in the field. Calcium present in dissolved form is also influenced by the partial pressure of dissolved CO2 at the plants root zone in the field water. Soda ash [NaCO] can be present in natural water from the weathering of basalt which is an igneous rock | https://en.wikipedia.org/wiki?curid=39374186 |
Residual sodium carbonate index Lime [Ca(OH)] can be present in natural water when rain water comes in contact with calcined minerals such as ash produced from the burning of calcareous coal or lignite in boilers. Anthropogenic use of soda ash also finally adds to the RSC of the river water. Where the river water and ground water are repeatedly used in the extensively irrigated river basins, the river water available in lower reaches is often rendered not useful in agriculture due to high RSC index or alkalinity. The salinity of water need not be high. In industrial water treatment terminology, water quality with high RSC index is synonymous with the soft water but is chemically very different from naturally soft water which has a very low ionic concentration. When calcium and magnesium salts are present in dissolved form in water, these salts precipitate on the heat transfer surfaces forming insulating hard scaling / coating which reduces the heat transfer efficiency of the heat exchangers. To avoid scaling in water cooled heat exchangers, water is treated by lime and or soda ash to remove the water hardness. The following chemical reactions take place in lime soda softening process which precipitates the calcium and magnesium salts as calcium carbonate and magnesium hydroxide which have very low solubility in water. The excess soda ash after precipitating the calcium and magnesium salts is in carbonates & bicarbonates of sodium which imparts high pH or alkalinity to soil water | https://en.wikipedia.org/wiki?curid=39374186 |
Residual sodium carbonate index The endorheic basin lakes are called soda or alkaline lakes when the water inflows contain high concentrations of NaCO. The pH of the soda lake water is generally above 9 and sometimes the salinity is close to brackish water due to depletion of pure water by solar evaporation. Soda lakes are rich with algal growth due to enhanced availability of dissolved CO in the lake water compared to fresh water or saline water lakes. Sodium carbonate and sodium hydroxide are in equilibrium with availability of dissolved carbon dioxide as given below in the chemical reaction During day time when sun light is available, Algae undergoes photosynthesis process which absorbs CO to shift the reaction towards NaOH formation and vice versa takes place during night time with the release of CO from the respiration process of Algae towards NaCO and NaHCO formation. In soda lake waters, carbonates of sodium act as catalyst for the algae growth by providing favourable higher concentration of dissolved CO during the day time. Due to fluctuation in dissolved CO, the pH and alkalinity of the water also keep varying. | https://en.wikipedia.org/wiki?curid=39374186 |
C16H20N4O2 The molecular formula CHNO (molar mass: 300.36 g/mol) may refer to: | https://en.wikipedia.org/wiki?curid=39375353 |
Fluorochemical industry The global market for chemicals from fluorine was about US$16 billion per year as of 2006. The industry was predicted to reach 2.6 million metric tons per year by 2015. The largest market is the United States. Western Europe is the second largest. Asia Pacific is the fastest growing region of production. China in particular has experienced significant growth as a fluorochemical market and is becoming a producer of them as well. Fluorite mining (the main source of fluorine) was estimated in 2003 to be a $550 million industry, extracting 4.5 million tons per year. Mined fluorite is separated into two main grades, with about equal production of each. "Acidspar" is at least 97% CaF; "metspar" is much lower purity, 60–85%. (A small amount of the intermediate, "ceramic", grade is also made.) Metspar is used almost exclusively for iron smelting. Acidspar is primarily converted to hydrofluoric acid (by reaction with sulfuric acid). The resultant HF is mostly used to produce organofluorides and synthetic cryolite. About 3 kg (6.5 lb) of metspar grade fluorite, added directly to the batch, are used for every metric ton of steel made. The fluoride ions from CaF lower the melt's temperature and viscosity (make the liquid runnier). The calcium content has a tangential benefit in removing sulfur and phosphorus, but other additives such as lime are still needed. Metspar is similarly used in cast iron production and for other iron-containing alloys | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry Fluorite of the acidspar grade is used directly as an additive to ceramics and enamels, glass fibers and clouded glass, and cement, as well as in the outer coating of welding rods. Acidspar is primarily used for making hydrofluoric acid, which is a chemical intermediate for most fluorine-containing compounds. Significant direct uses of HF include pickling (cleaning) of steel, cracking of alkanes in the petrochemical industry, and etching of glass. One third of HF (one sixth of mined fluorine) is used to make synthetic cryolite (sodium hexafluoroaluminate) and aluminium trifluoride. These compounds are used in the electrolysis of aluminium by the Hall–Héroult process. About 23 kg (51 lb) are required for every metric ton of aluminium. These compounds are also used as a flux for glass. Fluorosilicates are the next most significant inorganic fluorides formed from HF. The most common one, that of sodium, is used for water fluoridation, as an intermediate for synthetic cryolite and silicon tetrafluoride, and for treatment of effluents in laundries. MgF and, to a lesser extent, other alkaline earth difluorides are specialty optical materials. Magnesium difluoride is widely used as an antireflection coating for spectacles and optical equipment. The compound is also a component in newly devised constructions (negative index metamaterials) which are the subject of "invisibility" research. The layered structures can curve light around objects | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry Other inorganic fluorides made in large quantities include cobalt difluoride (for organofluorine synthesis), nickel difluoride (electronics), lithium fluoride (a flux), sodium fluoride (water fluoridation), potassium fluoride (flux), and ammonium fluoride (various). Sodium and potassium bifluorides are significant to the chemical industry. Making organic fluorides is the main use for hydrofluoric acid, consuming over 40% of it (over 20% of all mined fluorite). Within organofluorides, refrigerant gases are still the dominant segment, consuming about 80% of HF. Even though chlorofluorocarbons are widely banned, the replacement refrigerants are often other fluorinated molecules. Fluoropolymers are less than one quarter the size of refrigerant gases in terms of fluorine usage, but are growing faster. Fluorosurfactants are a small segment in mass but are significant economically because of very high prices. Traditionally chlorofluorocarbons (CFCs) were the predominant fluorinated organic chemical. CFCs are identified by a system of numbering that explains the amount of fluorine, chlorine, carbon and hydrogen in the molecules. The term Freon has been colloquially used for CFCs and similar halogenated molecules, though strictly speaking this is just a DuPont brand name, and many other producers exist. Brand neutral terminology is to use "R" as the prefix. Prominent CFCs included R-11 (trichlorofluoromethane), R-12 (dichlorodifluoromethane), and R-114 (1,2-dichlorotetrafluoroethane) | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry Production of CFCs grew strongly through the 1980s, primarily for refrigeration and air conditioning but also for propellants and solvents. Since the end use of these materials is banned in most countries, this industry has shrunk dramatically. By the early 21st century, production of CFCs was less than 10% of the mid-1980s peak, with remaining use primarily as an intermediate for other chemicals. The banning of CFCs initially depressed the overall demand for fluorite but 21st century production of the source mineral has recovered to 1980s levels. Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) now serve as replacements for CFC refrigerants; few were commercially manufactured before 1990. Currently more than 90% of fluorine used for organics goes into these two classes (in about equal amounts). Prominent HCFCs include R-22 (chlorodifluoromethane) and R-141b (1,1-dichloro-1-fluoroethane). The main HFC is R-134a (1,1,1,2-tetrafluoroethane). A bromofluoroalkane, "Halon" (bromotrifluoromethane) is still widely used in ship and aircraft gaseous fire suppression systems. Because Halon production has been banned since 1994, systems are dependent on the pre-ban stores and on recycling. A new type of Fluorine refrigerant, that is scoped to replace the high Global Warming Potential HFC compounds, are Hydrofluoroolefins (HFO). Fluoropolymers are less than 0.1% of all polymers produced in terms of weight. Compared to other polymers, they are more expensive and their consumption is growing at a higher rate | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry As of about 2006–2007, estimates of the global fluoropolymer production varied from over 100,000 to 180,000 metric tons per year. Yearly revenue estimates ranged from over $2.5 billion to over $3.5 billion. Polytetrafluoroethylene (PTFE) is 60–80% of the world's fluoropolymer production on a weight basis. The term Teflon is sometimes used generically for the substance, but is a Chemours Company and Dupont brand name—other PTFE producers exist and Chemours sometimes uses the Teflon brand for other materials. PTFE gets its fluorine without the need for fluorine gas: chloroform (trichloromethane) is treated with HF to make chlorodifluoromethane (R-22, an HFC); this chemical when heated makes tetrafluoroethylene (abbreviated TFE), the monomer of PTFE. The largest application for PTFE is in electrical insulation. It is an excellent dielectric and very chemically stable. It is also used extensively in the chemical process industry where corrosion resistance is needed: in coating pipes, in tubing, and gaskets. Another major use is architectural fabric (PTFE-coated fiberglass cloth used for stadium roofs and such). The major consumer application is non-stick cookware. When stretched with a jerk, a PTFE film makes a fine-pored membrane: expanded PTFE (ePTFE). The term "Gore-Tex" is sometimes used generically for this material, but that is a specific brand name. W.L. Gore & Associates is not the only producer of ePTFE and furthermore "Gore-Tex" often refers to more complicated multi-layer membranes or laminated fabrics | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry ePTFE is used in rainwear, protective apparel and liquids and gas filters. PTFE can also be formed into fibers which are used in pump packing seals and bag house filters for industries with corrosive exhausts. Other fluoropolymers tend to have similar properties to PTFE—high chemical resistance and good dielectric properties—which leads to use in the chemical process industry and electrical insulation. They are easier to work with (to form into complex shapes), but are more expensive than PTFE and have lower thermal stability. Fluorinated ethylene propylene (FEP) is the second most produced fluoropolymer. Films from two different fluoropolymers serve as glass-replacements in solar cells. Fluorinated ionomers (polymers that include charged fragments) are expensive, chemically resistant materials used as membranes in certain electrochemical cells. Nafion, developed in the 1960s, was the first example and remains the most prominent material in the class. The initial Nafion application was as a fuel cell material in spacecraft. Since then, the material has been transforming the 55 million tons per year chloralkali industry; it is replacing hazardous mercury-based cells with membrane cells that are also more energy efficient. While older technology plants continue to run, new plants typically use membrane cells. By 2002, more than a third of the global capacity for the industry was membrane-cell based | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry Recently, the fuel cell application has reemerged; significant research is being conducted and investments made related to getting proton exchange membrane (PEM) fuel cells into vehicles. Fluoroelastomers are rubber-like substances that are composed of crosslinked mixtures of fluoropolymers. Viton is a prominent example. Chemical-resistant O-rings are the primary application. Fluoroelastomers tend to be more stiff than conventional elastomers, but with superior chemical and heat resistance. Fluorinated surfactants are small organofluorine molecules, principally used in durable water repellent (DWR). Fluorosurfactants form a large market, over $1 billion per year as of 2006. Scotchgard is a prominent brand, with over $300 million revenue in 2000. Fluorosurfactants are expensive chemicals, comparable to pharmaceutical chemicals: $200–2000 per kilogram ($90–900 per pound). Fluorosurfactants make a very small part of the overall surfactant market, most of which is hydrocarbon based and much cheaper. Some potential applications (e.g. low cost paints) are unable to use fluorosurfactants because of the price impact of compounding in even small amounts of fluorosurfactant. Use in paints was only about $100 million as of 2006. DWR is a finish (very thin coating) put on fabrics that makes them lightly rain resistant, that makes water bead. First developed in the 1950s, fluorosurfactants were 90% of the DWR industry by 1990. DWR is used with garment fabrics, carpeting, and food packaging | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry DWR is applied to fabrics by "dip-squeeze-dry" (immersion in DWR-water bath, pressing water out, and then drying). For countries with available data (free-market countries), about 17,000 metric tons of fluorine are produced per year by 11 companies, all G7-resident. Fluorine is relatively inexpensive, costing about $5–8 per kilogram ($2–4 per pound) when sold as uranium hexafluoride or sulfur hexafluoride. Because of difficulties in storage and handling, the price of pure fluorine gas is much higher. Processes demanding large amounts of fluorine gas generally vertically integrate and produce the gas onsite for direct use. The largest application for elemental fluorine is the preparation of uranium hexafluoride, which is used in the production of nuclear fuels. To obtain the compound, uranium dioxide is first treated with hydrofluoric acid, to produce uranium tetrafluoride. This compound is then further fluorinated by direct exposure to fluorine gas to make the hexafluoride. Fluorine's monoisotopic natural occurrence makes it useful in uranium enrichment, because uranium hexafluoride molecules will differ in mass only because of mass differences between uranium-235 and uranium-238. These mass differences are used to separate uranium-235 and uranium-238 via diffusion and centrifugation. Up to 7,000 metric tons per year of fluorine gas are used for this application | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry As of 2013, 686,500 metric tons of UF6, containing about 470,000 metric tons of depleted uranium (the remainder being fluorine), were stored at the Paducah Gaseous Diffusion Plant, the USEC's Piketon site, Ohio and the East Tennessee Technology Park (formerly known as the K-25 Site). The second largest application for fluorine gas is sulfur hexafluoride, which is used as a dielectric medium in high voltage switching stations. SF gas has a much higher dielectric strength than air. It is extremely inert and, compared to oil-filled switchgear, has no hazardous polychlorinated biphenyls (PCBs). Sulfur hexafluoride is also used in soundproof windows, in the electronics industry, as well as niche medical and military applications. The compound can be made without using fluorine gas, but the reaction between pure sulfur and pure fluorine gas, first developed by Henri Moissan, remains the commercial practice. About 6,000 metric tons per year of fluorine gas are consumed. Several compounds made from elemental fluorine serve the electronics industry. Rhenium and tungsten hexafluorides are used for chemical vapor deposition of thin metal films onto semiconductors. Tetrafluoromethane, is used for plasma etching in semiconductor manufacturing, flat panel display production, and microelectromechanical systems fabrication. Nitrogen trifluoride is increasingly used for cleaning equipment at display manufacturing plants. Elemental fluorine, itself, is used sometimes for cleaning equipment | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry For making niche organofluorines and fluorine-containing pharmaceuticals, direct fluorination is usually too hard to control. Preparation of intermediate strength fluorinators from fluorine gas solves this problem. The halogen fluorides ClF, BrF, and IF provide gentler fluorination, with a series of strengths. They are also easier to handle. Sulfur tetrafluoride is used particularly for making fluorinated pharmaceuticals. United States and Soviet space scientists in the early 1960s studied elemental fluorine as a possible rocket propellant because of the higher specific impulse generated when fluorine replaced oxygen in combustion. The experiments failed because fluorine proved difficult to handle, and its combustion product (typically hydrogen fluoride) was extremely toxic and corrosive. Commercial producers of fluorine gas continue to use the method of electrolysis pioneered by Moissan, with some modifications in the cell design. Owing to the gas's corrosiveness, special containment materials and handling precautions are required. Chemical routes to the elemental form were published in 1986. Several thousand metric tons of elemental fluorine are produced annually by electrolysis of potassium bifluoride in hydrogen fluoride. Potassium bifluoride forms spontaneously from potassium fluoride and the hydrogen fluoride: A mixture with the approximate composition KF•2HF melts at 70 °C (158 °F) and is electrolyzed between 70 °C and 130 °C (160–265 °F) | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry Potassium bifluoride increases the electrical conductivity of the solution and provides the bifluoride anion, which releases fluorine at the anode (negative part of the cell). If HF alone is electrolyzed, hydrogen forms at the cathode (positive part of the cell) and the fluoride ions remain in solution. After electrolysis, potassium fluoride remains in solution. The modern version of the process uses steel containers as cathodes, while blocks of carbon are used as anodes. The carbon electrodes are similar to those used in the electrolysis of aluminium. An earlier version of fluorine production process, by Moissan, uses platinum group metal electrodes and carved fluorite containers. The voltage for the electrolysis is between 8 and 12 volts. Pure fluorine gas may be stored in steel cylinders where the inside surface is passivated by a metal fluoride layer that resists further attack. Passivated steel will withstand fluorine provided the temperature is kept below 200 °C (400 °F). Above that temperature, nickel is required. Regulator valves are made of nickel. Fluorine piping is generally made of nickel or Monel (nickel-copper alloy). Care must be taken to passivate all surfaces frequently and to exclude any water or greases. In the laboratory, fluorine gas can be used in glass tubing provided the pressure is low and moisture is excluded, although some sources recommend systems made of nickel, Monel, and PTFE | https://en.wikipedia.org/wiki?curid=39379160 |
Fluorochemical industry In 1986, when preparing for a conference to celebrate the 100th anniversary of the discovery of fluorine, Karl O. Christe discovered a purely chemical preparation of fluorine gas; however, he stated in his work that the basics were known 50 years before the actual reaction. The main idea is that some metal fluoride anions do not have a neutral counterpart (or those are very unstable) and their acidifying would result in chemical oxidation, rather than formation of the expected molecules. Christe lists the following reactions as a possible way: This synthetic route is a rare chemical preparation of elemental fluorine, a reaction not previously thought possible. | https://en.wikipedia.org/wiki?curid=39379160 |
George E. Davis Medal The is a medal of the IChemE given not more frequently than every three years, for achievements in chemical engineering. It is named after George E. Davis. Source: IChemE | https://en.wikipedia.org/wiki?curid=39387700 |
Modes of toxic action A mode of toxic action is a common set of physiological and behavioral signs that characterize a type of adverse biological response. A mode of action should not be confused with mechanism of action, which refer to the biochemical processes underlying a given mode of action. are important, widely used tools in ecotoxicology and aquatic toxicology because they classify toxicants or pollutants according to their type of toxic action. There are two major types of modes of toxic action: non-specific acting toxicants and specific acting toxicants. Non-specific acting toxicants are those that produce narcosis, while specific acting toxicants are those that are non-narcotic and that produce a specific action at a specific target site. result in narcosis; therefore, narcosis is a mode of toxic action. Narcosis is defined as a generalized depression in biological activity due to the presence of toxicant molecules in the organism. The target site and mechanism of toxic action through which narcosis affects organisms are still unclear, but there are hypotheses that support that it occurs through alterations in the cell membranes at specific sites of the membranes, such as the lipid layers or the proteins bound to the membranes. Even though continuous exposure to a narcotic toxicant can produce death, if the exposure to the toxicant is stopped, narcosis can be reversible | https://en.wikipedia.org/wiki?curid=39392026 |
Modes of toxic action Toxicants that at low concentrations modify or inhibit some biological process by binding at a specific site or molecule have a specific acting mode of toxic action. However, at high enough concentrations, toxicants with specific acting modes of toxic actions can produce narcosis that may or may not be reversible. Nevertheless, the specific action of the toxicant is always shown first because it requires lower concentrations. There are several specific acting modes of toxic action: The pioneer work of identifying the major categories of modes of toxic action (see description above) was conducted by investigators from the U.S. Environmental Protection Agency (EPA) at the Duluth Laboratory using fish, reason why they named the categories as "" (FATS). They proposed the FATS by assessing the behavioral and physiological responses of the fish when subjected to toxicity tests, such as locomotive activities, body color, ventilation patterns, cough rate, heart rate, and others. It has been proposed that modes of toxic action could be estimated by developing a data set of critical body residues (CBR). The CBR is the whole-body concentration of a chemical that is associated with a given adverse biological response and it is estimated using a partition coefficient and a bioconcentration factor. The whole-body residues are reasonable first approximations of the amount of chemical present at the toxic action site(s) | https://en.wikipedia.org/wiki?curid=39392026 |
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