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Most of the well-recognized phototrophs are autotrophic, also known as photoautotrophs, and can fix carbon. They can be contrasted with chemotrophs that obtain their energy by the oxidation of electron donors in their environments. Photoautotrophs are capable of synthesizing their own food from inorganic substances using light as an energy source. Green plants and photosynthetic bacteria are photoautotrophs. Photoautotrophic organisms are sometimes referred to as holophytic.
Oxygenic photosynthetic organisms use chlorophyll for light-energy capture and oxidize water, "splitting" it into molecular oxygen. | 0 | Theoretical and Fundamental Chemistry |
Radioactivity was discovered in 1896 by scientists Henri Becquerel and Marie Skłodowska-Curie, while working with phosphorescent materials. These materials glow in the dark after exposure to light, and Becquerel suspected that the glow produced in cathode ray tubes by X-rays might be associated with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent salts on it. All results were negative until he used uranium salts. The uranium salts caused a blackening of the plate in spite of the plate being wrapped in black paper. These radiations were given the name "Becquerel Rays".
It soon became clear that the blackening of the plate had nothing to do with phosphorescence, as the blackening was also produced by non-phosphorescent salts of uranium and by metallic uranium. It became clear from these experiments that there was a form of invisible radiation that could pass through paper and was causing the plate to react as if exposed to light.
At first, it seemed as though the new radiation was similar to the then recently discovered X-rays. Further research by Becquerel, Ernest Rutherford, Paul Villard, Pierre Curie, Marie Curie, and others showed that this form of radioactivity was significantly more complicated. Rutherford was the first to realize that all such elements decay in accordance with the same mathematical exponential formula. Rutherford and his student Frederick Soddy were the first to realize that many decay processes resulted in the transmutation of one element to another. Subsequently, the radioactive displacement law of Fajans and Soddy was formulated to describe the products of alpha and beta decay.
The early researchers also discovered that many other chemical elements, besides uranium, have radioactive isotopes. A systematic search for the total radioactivity in uranium ores also guided Pierre and Marie Curie to isolate two new elements: polonium and radium. Except for the radioactivity of radium, the chemical similarity of radium to barium made these two elements difficult to distinguish.
Marie and Pierre Curies study of radioactivity is an important factor in science and medicine. After their research on Becquerels rays led them to the discovery of both radium and polonium, they coined the term "radioactivity" to define the emission of ionizing radiation by some heavy elements. (Later the term was generalized to all elements.) Their research on the penetrating rays in uranium and the discovery of radium launched an era of using radium for the treatment of cancer. Their exploration of radium could be seen as the first peaceful use of nuclear energy and the start of modern nuclear medicine. | 0 | Theoretical and Fundamental Chemistry |
is a common Lewis-acid catalyst for Friedel-Crafts reactions, both acylations and alkylations. Important products are detergents and ethylbenzene. These types of reactions are the major use for aluminium chloride, for example, in the preparation of anthraquinone (used in the dyestuffs industry) from benzene and phosgene. In the general Friedel-Crafts reaction, an acyl chloride or alkyl halide reacts with an aromatic system as shown:
The alkylation reaction is more widely used than the acylation reaction, although its practice is more technically demanding. For both reactions, the aluminium chloride, as well as other materials and the equipment, should be dry, although a trace of moisture is necessary for the reaction to proceed. Detailed procedures are available for alkylation and acylation of arenes.
A general problem with the Friedel-Crafts reaction is that the aluminium chloride catalyst sometimes is required in full stoichiometric quantities, because it complexes strongly with the products. This complication sometimes generates a large amount of corrosive waste. For these and similar reasons, the use of aluminium chloride has often been displaced by zeolites.
Aluminium chloride can also be used to introduce aldehyde groups onto aromatic rings, for example via the Gattermann-Koch reaction which uses carbon monoxide, hydrogen chloride and a copper(I) chloride co-catalyst. | 0 | Theoretical and Fundamental Chemistry |
The use of antioxidants to prevent some diseases is controversial. In a high-risk group like smokers, high doses of beta carotene increased the rate of lung cancer since high doses of beta-carotene in conjunction of high oxygen tension due to smoking results in a pro-oxidant effect and an antioxidant effect when oxygen tension is not high. In less high-risk groups, the use of vitamin E appears to reduce the risk of heart disease. However, while consumption of food rich in vitamin E may reduce the risk of coronary heart disease in middle-aged to older men and women, using vitamin E supplements also appear to result in an increase in total mortality, heart failure, and hemorrhagic stroke. The American Heart Association therefore recommends the consumption of food rich in antioxidant vitamins and other nutrients, but does not recommend the use of vitamin E supplements to prevent cardiovascular disease. In other diseases, such as Alzheimers, the evidence on vitamin E supplementation is also mixed. Since dietary sources contain a wider range of carotenoids and vitamin E tocopherols and tocotrienols from whole foods, ex post facto epidemiological studies can have differing conclusions than artificial experiments using isolated compounds. AstraZenecas radical scavenging nitrone drug NXY-059 shows some efficacy in the treatment of stroke.
Oxidative stress (as formulated in Denham Harmans free-radical theory of aging) is also thought to contribute to the aging process. While there is good evidence to support this idea in model organisms such as Drosophila melanogaster and Caenorhabditis elegans, recent evidence from Michael Ristows laboratory suggests that oxidative stress may also promote life expectancy of Caenorhabditis elegans by inducing a secondary response to initially increased levels of reactive oxygen species. The situation in mammals is even less clear. Recent epidemiological findings support the process of mitohormesis, but a 2007 meta-analysis finds that in studies with a low risk of bias (randomization, blinding, follow-up), some popular antioxidant supplements (vitamin A, beta carotene, and vitamin E) may increase mortality risk (although studies more prone to bias reported the reverse).
The USDA removed the table showing the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods Release 2 (2010) table due to the lack of evidence that the antioxidant level present in a food translated into a related antioxidant effect in the body. | 1 | Applied and Interdisciplinary Chemistry |
Pulsed SILAC (pSILAC) is a variation of the SILAC method where the labelled amino acids are added to the growth medium for only a short period of time. This allows monitoring differences in de novo protein production rather than raw concentration. | 1 | Applied and Interdisciplinary Chemistry |
The Mountain Pass deposit is in a 1.4 billion-year-old Precambrian carbonatite intruded into gneiss. It contains 8% to 12% rare-earth oxides, mostly contained in the mineral bastnäsite. Gangue minerals include calcite, barite, and dolomite. It is regarded as a world-class rare-earth mineral deposit. The metals that can be extracted from it include: cerium, lanthanum, neodymium, and europium.
At 1 July 2020, Proven and Probable Reserves, using a 3.83% total rare-earth oxide (REO) cutoff grade, were 18.9 million tonnes of ore containing 1.36 million tonnes of REO at an average grade of 7.06% REO. | 1 | Applied and Interdisciplinary Chemistry |
Occupational exposure to PFASs occurs in numerous industries due to the widespread use of the chemicals in products and as an element of industrial process streams. PFASs are used in more than 200 different ways in industries as diverse as electronics and equipment manufacturing, plastic and rubber production, food and textile production, and building and construction. Occupational exposure to PFASs can occur at fluorochemical facilities that produce them and other manufacturing facilities that use them for industrial processing like the chrome plating industry. Workers who handle PFAS-containing products can also be exposed during their work, such as people who install PFAS-containing carpets and leather furniture with PFAS coatings, professional ski-waxers using PFAS-based waxes, and fire-fighters using PFAS-containing foam and wear flame-resistant protective gear made with PFASs. | 0 | Theoretical and Fundamental Chemistry |
A coin assayer is often assigned to each mint or assay office to determine and assure that all coins produced at the mint have the correct content or purity of each metal specified, usually by law, to be contained in them. This was particularly important when gold and silver coins were produced for circulation and used in daily commerce. Few nations, however, persist in minting silver or gold coins for general circulation. For example, the U.S. discontinued the use of gold in coinage in 1933. The U.S. was one of the last nations to discontinue the use of silver in circulating coins after its 1970 A.D. half dollar coin, although the amount of silver used in smaller denomination coins was ended after 1964. Even with the half dollar, the amount of silver used in the coins was reduced from 90% in 1964 and earlier to 40% between 1965 and 1970. Copper, nickel, cupro-nickel and brass alloys now predominate in coin making. Notwithstanding, several national mints, including the Perth Mint in Australia, the Austrian Mint, the British Royal Mint, the Royal Canadian Mint, the South African Mint, and the U.S. Mint continue to produce precious metal bullion coins for collectors and investors. The precious metal purity and content of these coins is guaranteed by the respective mint or government, and, therefore, the assay of the raw materials and finished coins is an important quality control.
In the UK, the Trial of the Pyx is a ceremonial procedure for ensuring that newly minted coins conform to required standards. | 1 | Applied and Interdisciplinary Chemistry |
Xenin promotes beta-cell survival and xenin has been evaluated in animal models of obesity and diabetes where it has demonstrated an antidiabetic potential. In humans, co-administration of xenin-25 and gastric inhibitory polypeptide (GIP) reduces postprandial glycemia by delaying gastric emptying. | 1 | Applied and Interdisciplinary Chemistry |
Practical applications of the respiratory quotient can be found in severe cases of chronic obstructive pulmonary disease, in which patients spend a significant amount of energy on respiratory effort. By increasing the proportion of fats in the diet, the respiratory quotient is driven down, causing a relative decrease in the amount of CO produced. This reduces the respiratory burden to eliminate CO, thereby reducing the amount of energy spent on respirations.
Respiratory Quotient can be used as an indicator of over or underfeeding. Underfeeding, which forces the body to utilize fat stores, will lower the respiratory quotient, while overfeeding, which causes lipogenesis, will increase it. Underfeeding is marked by a respiratory quotient below 0.85, while a respiratory quotient greater than 1.0 indicates overfeeding. This is particularly important in patients with compromised respiratory systems, as an increased respiratory quotient significantly corresponds to increased respiratory rate and decreased tidal volume, placing compromised patients at a significant risk.
Because of its role in metabolism, respiratory quotient can be used in analysis of liver function and diagnosis of liver disease. In patients with liver cirrhosis, non-protein respiratory quotient (npRQ) values act as good indicators in the prediction of overall survival rate. Patients having a npRQ < 0.85 show considerably lower survival rates as compared to patients with a npRQ > 0.85. A decrease in npRQ corresponds to a decrease in glycogen storage by the liver. Similar research indicates that non-alcoholic fatty liver diseases are also accompanied by a low respiratory quotient value, and the non protein respiratory quotient value was a good indication of disease severity.
Recently the respiratory quotient is also used from aquatic scientists to illuminate its environmental applications. Experimental studies with natural bacterioplankton using different single substrates suggested that RQ is linked to the elemental composition of the respired compounds. By this way, it is demonstrated that bacterioplankton RQ is not only a practical aspect of Bacterioplankton Respiration determination, but also a major ecosystem state variable that provides unique information about aquatic ecosystem functioning. Based on the stoichiometry of the different metabolized substrates, the scientists can predict that dissolved oxygen (O) and carbon dioxide (CO) in aquatic ecosystems should covary inversely due to the processing of photosynthesis and respiration. Using this quotient we could shed light on the metabolic behavior and the simultaneous roles of chemical and physical forcing that shape the biogeochemistry of aquatic ecosystems. | 1 | Applied and Interdisciplinary Chemistry |
Many human tumors occur because of dysregulation of mTOR signaling, and can confer higher susceptibility to inhibitors of mTOR. Deregulations of multiple elements of the mTOR pathway, like PI3K amplification/mutation, PTEN loss of function, AKT overexpression, and S6K1, 4EBP1, and eIF4E overexpression have been related to many types of cancers. Therefore, mTOR is an interesting therapeutic target for treating multiple cancers, both the mTOR inhibitors themselves or in combination with inhibitors of other pathways.
Upstream, PI3K/AKT signalling is deregulated through a variety of mechanisms, including overexpression or activation of growth factor receptors, such as HER-2 (human epidermal growth factor receptor 2) and IGFR (insulin-like growth factor receptor), mutations in PI3K and mutations/amplifications of AKT. Tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a negative regulator of PI3K signaling. In many cancers the PTEN expression is decreased and may be downregulated through several mechanisms, including mutations, loss of heterozygosity, methylation, and protein instability.
Downstream, the mTOR effectors S6 kinase 1 (S6K1), eukaryotic initiation factor 4E-binding protein 1 (4EBP1) and eukaryotic initiation factor 4E (eIF4E) are related to cellular transformation. S6K1 is a key regulator of cell growth and also phosphorylates other important targets. Both eIF4E and S6K1 are included in cellular transformation and their overexpression has been linked to poor cancer prognosis. | 1 | Applied and Interdisciplinary Chemistry |
Reduction of hydroxylamine by e(aq) has also been suggested to produce the amino radical in the following reaction.
The reactivity of the amino radical in this reaction is expected to be pH dependent and should occur in the region of pH 3–7. | 0 | Theoretical and Fundamental Chemistry |
Aluminium hydroxide finds use as a fire retardant filler for polymer applications. It is selected for these applications because it is colorless (like most polymers), inexpensive, and has good fire retardant properties. Magnesium hydroxide and mixtures of huntite and hydromagnesite are used similarly. It decomposes at about , absorbing a considerable amount of heat in the process and giving off water vapour.
In addition to behaving as a fire retardant, it is very effective as a smoke suppressant in a wide range of polymers, most especially in polyesters, acrylics, ethylene vinyl acetate, epoxies, polyvinyl chloride (PVC) and rubber.
Aluminium hydroxide is used as filler in some artificial stone compound material, often in acrylic resin. | 0 | Theoretical and Fundamental Chemistry |
Insulin is synthesized and secreted in the beta cells of the islets of Langerhans. Once insulin is synthesized, the beta cells are ready to release it in two different phases. As for the first phase, insulin release is triggered rapidly when the blood glucose level is increased. The second phase is a slow release of newly formed vesicles that are triggered regardless of the blood sugar level.
Glucose enters the beta cells and goes through glycolysis to form ATP that eventually causes depolarization of the beta cell membrane (as explained in Insulin secretion section of this article). The depolarization process causes voltage-controlled calcium channels (Ca2+) opening, allowing the calcium to flow into the cells. An increased calcium level activates phospholipase C, which cleaves the membrane phospholipid phosphatidylinositol 4,5-bisphosphate into Inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 binds to receptor proteins in the membrane of the endoplasmic reticulum (ER). This releases (Ca2+) from the ER via IP3 gated channels, and raises the cell concentration of calcium even more. The influx of Ca2+ ions causes the secretion of insulin stored in vesicles through the cell membrane. The process of insulin secretion is an example of a trigger mechanism in a signal transduction pathway because insulin is secreted after glucose enters the beta cell and that triggers several other processes in a chain reaction. | 1 | Applied and Interdisciplinary Chemistry |
Glycoproteins have distinct Oligosaccharide structures which have significant effects on many of their properties, affecting critical functions such as antigenicity, solubility, and resistance to proteases. Glycoproteins are relevant as cell-surface receptors, cell-adhesion molecules, immunoglobulins, and tumor antigens. | 0 | Theoretical and Fundamental Chemistry |
In all organisms, two steps are required to read the information encoded in a genes DNA and produce the protein it specifies. First, the genes DNA is transcribed to messenger RNA (mRNA). Second, that mRNA is translated to protein. RNA-coding genes must still go through the first step, but are not translated into protein. The process of producing a biologically functional molecule of either RNA or protein is called gene expression, and the resulting molecule is called a gene product. | 1 | Applied and Interdisciplinary Chemistry |
The Salters School of Chemistry is a branch of Christs Hospital that teaches mainly chemistry to all Christs Hospital pupils. It was founded by Samuel Porter and the Worshipful Company of Salters (one of the livery company that sponsors children to study at CH) in 1993. It is currently Christs Hospitals Chemistry Department. | 1 | Applied and Interdisciplinary Chemistry |
Flucloxacillin, also known as floxacillin, is an antibiotic used to treat skin infections, external ear infections, infections of leg ulcers, diabetic foot infections, and infection of bone. It may be used together with other medications to treat pneumonia, and endocarditis. It may also be used prior to surgery to prevent Staphylococcus infections. It is not effective against methicillin-resistant Staphylococcus aureus (MRSA). It is taken by mouth or given by injection into a vein or muscle.
Common side effects include an upset stomach. Other side effects may include muscle or joint pains, shortness of breath, and liver problems. It appears to be safe during pregnancy and breastfeeding. It should not be used in those who are allergic to penicillin. It is a narrow-spectrum beta-lactam antibiotic of the penicillin class. It is similar in effect to cloxacillin and dicloxacillin, being active against penicillinase forming bacteria.
Flucloxacillin was patented in 1961. It is not commonly used in the United States or Canada as of 2011. | 0 | Theoretical and Fundamental Chemistry |
A continuous cooling transformation (CCT) phase diagram is often used when heat treating steel. These diagrams are used to represent which types of phase changes will occur in a material as it is cooled at different rates. These diagrams are often more useful than time-temperature-transformation diagrams because it is more convenient to cool materials at a certain rate (temperature-variable cooling), than to cool quickly and hold at a certain temperature (isothermal cooling). | 1 | Applied and Interdisciplinary Chemistry |
The uranium is then stripped from the DEHPA/kerosene solution with hydrochloric acid, hydrofluoric acid, or carbonate solutions. Sodium carbonate solutions effectively strip uranium from the organic layer, but the sodium salt of DEHPA is somewhat soluble in water, which can lead to loss of the extractant. | 0 | Theoretical and Fundamental Chemistry |
The screw axis is noted by a number, n, where the angle of rotation is . The degree of translation is then added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. For example, 2 is a 180° (twofold) rotation followed by a translation of of the lattice vector. 3 is a 120° (threefold) rotation followed by a translation of of the lattice vector.
The possible screw axes are: 2, 3, 3, 4, 4, 4, 6, 6, 6, 6, and 6.
There are 4 enantiomorphic pairs of axes: (3 – 3), (4 – 4), (6 – 6), and (6 – 6). This enantiomorphism results in 11 pairs of enantiomorphic space groups, namely | 0 | Theoretical and Fundamental Chemistry |
The Flory–Fox equation serves the purpose of providing a model for how glass transition temperature changes over a given molecular weight range. Another method to modify the glass transition temperature is to add a small amount of low molecular weight diluent, commonly known as a plasticizer, to the polymer. The presence of a low molecular weight additive increases the free volume of the system and subsequently lowers T , thus allowing for rubbery properties at lower temperatures. This effect is described by the Fox equation:
Where w and w are weight fractions of components 1 and 2, respectively. In general, the accuracy of the Fox equation is very good and it is commonly also applied to predict the glass transition temperature in (miscible) polymer blends and statistical copolymers. | 0 | Theoretical and Fundamental Chemistry |
Born in Ararat, Victoria, Sarfati moved with his family to New Zealand as a child, where he became a dual Australian and New Zealand citizen. He attended Wellington College in New Zealand, later graduating from Victoria University of Wellington with a BSc (Hons.) in chemistry, and a PhD in the same subject for a thesis entitled "A Spectroscopic Study of some Chalcogenide Ring and Cage Molecules". He co-authored a paper on high-temperature superconductors that was published in Nature in 1987 ("Letters to Nature"), and from 1988 to 1995, had five papers on spectroscopy of condensed matter samples published in other peer-reviewed scientific journals. In 1996, he returned to Brisbane, Australia to work for the Creation Science Foundation, then Answers in Genesis, then its current name Creation Ministries International. In 2010, he moved to the American office of that ministry. | 0 | Theoretical and Fundamental Chemistry |
Photosystem II light-harvesting proteins are the intrinsic transmembrane proteins CP43 (PsbC) and CP47 (PsbB) occurring in the reaction centre of photosystem II (PSII). These polypeptides bind to chlorophyll a and β-Carotene and pass the excitation energy on to the reaction centre.
This family also includes the iron-stress induced chlorophyll-binding protein CP43, encoded by the IsiA gene, which evolved in cyanobacteria from a PSII protein to cope with light limitations and stress conditions. Under iron-deficient growth conditions, CP43 associates with photosystem I (PSI) to form a complex that consists of a ring of 18 or more CP43 molecules around a PSI trimer, which significantly increases the light-harvesting system of PSI. The IsiA' protein can also provide photoprotection for PSII.
Plants, algae and some bacteria use two photosystems, PSI with P700 and PSII with P680. Using light energy, PSII acts first to channel an electron through a series of acceptors that drive a proton pump to generate adenosine triphosphate (ATP), before passing the electron on to PSI. Once the electron reaches PSI, it has used most of its energy in producing ATP, but a second photon of light captured by P700 provides the required energy to channel the electron to ferredoxin, generating reducing power in the form of NADPH. The ATP and NADPH produced by PSII and PSI, respectively, are used in the light-independent reactions for the formation of organic compounds. This process is non-cyclic, because the electron from PSII is lost and is only replenished through the oxidation of water. Hence, there is a constant flow of electrons and associated hydrogen atoms from water for the formation of organic compounds. It is this stripping of hydrogens from water that produces the oxygen we breathe.
IsiA has an inverse relationship with the iron stress repressed RNA (IsrR). IsrR is an antisense RNA that acts as a reversible switch that responds to changes in environmental conditions to modulate the expression of IsiA. | 0 | Theoretical and Fundamental Chemistry |
Manufacturers of bulk tape provided extremely detailed technical descriptions of their product, with numerous charts and dozens of numeric parameters. From the end user viewpoint, the most important electromagnetic properties of the tape are:
* Maximum output levels, usually specified in dB relative to the nominal zero reference level of or the Dolby level of . Often incorrectly called recording levels, these are always expressed in terms of the tapes output', thus taking its sensitivity out of the equation. Performance at low and middle, and at treble frequencies was traditionally characterized by two related but different parameters:
**Maximum output level (MOL) is relevant at low and middle frequencies. It is usually specified at 315Hz (MOL) or 400Hz (MOL), and its value marks the point when the third harmonic coefficient reaches 3%. Further magnetization of the tape is technically possible, but at the cost of unacceptable compression and distortion. For all types of tape, MOL reaches a maximum in the 125800Hz area, while dropping off below and above . The maximum output of Type I tape at is 35dB lower than MOL, while in Type IV tapes it is 67dB lower. As a result, ferric tapes handle bass-heavy music with apparent ease compared to expensive metal tapes. Double-layer Type III (IEC III, ferrichrome or ferrochrome) tape formulations were supposed to allow bass frequencies to be recorded deeper into the ferric layer, while keeping the high frequencies in the upper chromium oxide layer.
** At treble frequencies the playback head cannot reliably reproduce harmonics of the recorded signal. This makes distortion measurements impossible; instead of MOL, high-frequency performance is characterized by saturation output level (SOL), usually specified at (SOL). Once the tape reaches saturation point, any further increase in recording flux actually decreases output to below SOL.
* Noise level, usually understood as bias noise (hiss) of a tape recorded with zero input signal, replayed without noise reduction, A-weighted and referred to the same level as MOL and SOL. The difference between bias noise and the noise of virgin tape is an indicator of tape uniformity. Another important but rarely quantified type of noise is modulation noise, which appears only in the presence of a recorded signal, and which cannot be reduced by Dolby or dbx noise reduction systems.
* Dynamic range, or signal-to-noise ratio, was usually understood as the ratio between MOL and A-weighted bias noise level. High fidelity audio requires a dynamic range of at least 6065dB; the best cassettes tapes reached this threshold in the 1980s, at least partially eliminating the need for the use of noise reduction systems. Dynamic range is the most important property of the tape. The higher the dynamic range of music, the more demanding it is of tape quality; alternatively, heavily compressed music sources can do well even with basic, inexpensive tapes.
* Sensitivity of the tape, referred to that of an IEC reference tape and expressed in dB, was usually measured at and .
* Stability of playback in time. Low-quality or damaged cassette tape is notoriously prone to signal dropouts, which are absolutely unacceptable in high fidelity audio. For high quality tapes, playback stability is sometimes lumped together with modulation noise and wow and flutter into an integral smoothness parameter.
Frequency range, per se, is usually unimportant. At low recording levels (−20 dB referred to nominal level) all quality tapes can reliably reproduce frequencies from to , which is sufficient for high fidelity audio. However, at high recording levels the treble output is further limited by saturation. At the Dolby recording level the upper frequency limit shrinks to a value between for a typical chromium dioxide tape, and for metal tapes; for chromium dioxide tapes, this is partially offset by lower hiss levels. In practice, the extent of the high-level frequency range is not as important as the smoothness of the midrange and treble frequency response. | 0 | Theoretical and Fundamental Chemistry |
In a zeta-potential titration, the Zeta potential is the indicator. Measurement of the zeta potential can be performed using microelectrophoresis, or electrophoretic light scattering, or electroacoustic phenomena. The last method makes possible to perform titrations in concentrated systems, with no dilution. | 0 | Theoretical and Fundamental Chemistry |
At present the IPF employs about 480 people. Scientists (chemists, physicists, biologists) and engineers work closely together. About 100 guest scientists from all over the world come every year for some weeks or months to work at the IPF. The institute supports young researchers, e.g. in establishing independent research groups.
The annual budget of about 26 Million Euro is supplied in equal parts by the Federal Republic of Germany and the German federal states. In addition to institutional funding the IPF Dresden raises project resources of about 10 Million Euro per year. | 1 | Applied and Interdisciplinary Chemistry |
The zilch is often described in terms of the zilch tensor, . The latter can be expressed using the dual electromagnetic tensor as
The zilch tensor is symmetric under the exchange of its first two indices, and , while it is also traceless with respect to any two indices, as well as divergence-free with respect to any index.
The conservation law means that the following ten quantities are time-independent:
:These are the ten zilches (or just the zilch) discovered by Lipkin. In fact, only nine zilches are independent.
:The time-independent quantity is known as the 00-zilch and is equal to the aforementioned optical chirality
:In general, the time-independent quantity is known as the -zilch (the indices run from 0 to 3) and it is clear that there are ten such quantities (nine independent).
It was later demonstrated that Lipkin's zilch is part of an infinite number of zilch-like conserved quantities, a general property of free fields. | 0 | Theoretical and Fundamental Chemistry |
The Gibbsian ensemble idealizes the notion of repeating an experiment again and again on different systems, not again and again on the same system. So long-term time averages and the ergodic hypothesis, despite the intense interest in them in the first part of the twentieth century, strictly speaking are not relevant to the probability assignment for the state one might find the system in.
However, this changes if there is additional knowledge that the system is being prepared in a particular way some time before the measurement. One must then consider whether this gives further information which is still relevant at the time of measurement. The question of how rapidly mixing different properties of the system are then becomes very much of interest. Information about some degrees of freedom of the combined system may become unusable very quickly; information about other properties of the system may go on being relevant for a considerable time.
If nothing else, the medium and long-run time correlation properties of the system are interesting subjects for experimentation in themselves. Failure to accurately predict them is a good indicator that relevant macroscopically determinable physics may be missing from the model. | 0 | Theoretical and Fundamental Chemistry |
The precursor to RREMS was the Radioactive Incident Monitoring Network (RIMNET), established in 1988 as a response to the Chernobyl disaster in 1986. RIMNET was managed by the Met Office and Department for Environment, Food and Rural Affairs.
RIMNET data was collected at a central computer based in a DEFRA building in central London alongside a backup computer at a secret location in the UK. | 0 | Theoretical and Fundamental Chemistry |
Jander was born in Altdöbern, Oberspreewald-Lausitz. Jander studied in Technical University of Munich, and at University of Berlin where he received his Ph.D for work with Arthur Rosenheim in 1917. He joined Richard Zsigmondy at the University of Göttingen. He became professor in 1925 and after a two-year period being a temporary director of the Kaiser Wilhelm Institute for Physical Chemistry and Elektrochemistry from 1933 till 1935 he became professor for inorganic chemistry at the University of Greifswald. In 1951 he changed to the Technical University of Berlin. Jander died in Berlin in 1961. | 0 | Theoretical and Fundamental Chemistry |
Chelation therapy is a form of medical treatment in which a chelating ligand is used to selectively remove a metal from the body. When the metal exists as a divalent ion, such as with lead, Pb or mercury, Hg selectivity against calcium, Ca and magnesium, Mg, is essential in order that the treatment does not remove essential metals.
Selectivity is determined by various factors. In the case of iron overload, which may occur in individuals with β-thalessemia who have received blood transfusions, the target metal ion is in the +3 oxidation state and so forms stronger complexes than the divalent ions. It also forms stronger complexes with oxygen-donor ligands than with nitrogen-donor ligands. deferoxamine, a naturally occurring siderophore produced by the actinobacter Streptomyces pilosus and was used initially as a chelation therapy agent. Synthetic siderophores such as deferiprone and deferasirox have been developed, using the known structure of deferoxamine as a starting point. Chelation occurs with the two oxygen atoms.
Wilson's disease is caused by a defect in copper metabolism which results in accumulation of copper metal in various organs of the body. The target ion in this case is divalent, Cu. This ion is classified as borderline in the scheme of Ahrland, Chatt and Davies. This means that it forms roughly equally strong complexes with ligands whose donor atoms are N, O or F as with ligands whose donor atoms are P, S or Cl. Penicillamine, which contains nitrogen and sulphur donor atoms, is used as this type of ligand binds more strongly to copper ions than to calcium and magnesium ions.
Treatment of poisoning by heavy metals such as lead and mercury is more problematical, because the ligands used do not have high specificity relative to calcium. For example, EDTA may be administered as a calcium salt to reduce the removal of calcium from bone together with the heavy metal. Factors determining selectivity for lead against zinc, cadmium and calcium have been reviewed, | 0 | Theoretical and Fundamental Chemistry |
In 1958, research for project SUNSHINE was brought to Belgium. Scientists started doing tests that were slightly different than those done previously in the United States and Europe by analyzing soils in agricultural regions instead of human bones. They headed in two main directions: environmental surveys and experimental research in natural and in controlled conditions. Their goal was to see the effect of Strontium-90 in the soils as well as to see how it transferred to the grass and grazing animals such as cows and sheep, the animals from which humans consume milk and meat. Researchers also looked for direct influences of strontium-90 by observing how well the contaminated grass and crops grew.
In a 1957 article, Dr. Whitlock, director of Health Education in the National Dairy Council, Chicago, Illinois, discussed the impact of strontium-90 in the cow milk consumed by humans, concluding that the effects of Sr-90 would not be detectably harmful to the general populace of the US. "From the foregoing information, it would seem we have a long way to go before the presence of Strontium-90 in milk and other foods can catch up with the amounts of radioactivity to which we have long been exposed through natural resources." Specifically referring to the natural radioactivity one is exposed to from potassium-40." | 0 | Theoretical and Fundamental Chemistry |
A combination of different types of constructed wetlands is possible to use the specific advantages of each system. | 1 | Applied and Interdisciplinary Chemistry |
* The reaction 2 H + O → 2 HO provides an example of chain branching. The propagation is a sequence of two steps whose net effect is to replace an H atom by another H atom plus two OH radicals. This leads to an explosion under certain conditions of temperature and pressure.
** H• + O → •OH + •O•
** •O• + H → •OH + H•
* In chain-growth polymerization, the propagation step corresponds to the elongation of the growing polymer chain. Chain transfer corresponds to transfer of the activity from this growing chain, whose growth is terminated, to another molecule which may be a second growing polymer chain. For polymerization, the kinetic chain length defined above may differ from the degree of polymerization of the product macromolecule.
* Polymerase chain reaction, a technique used in molecular biology to amplify (make many copies of) a piece of DNA by in vitro enzymatic replication using a DNA polymerase. | 0 | Theoretical and Fundamental Chemistry |
The precursor to acetic acid is the thioester acetyl CoA. The key aspects of the acetogenic pathway are several reactions that include the reduction of carbon dioxide () to carbon monoxide (CO) and the attachment of CO to a methyl group (–CH). The first process is catalyzed by enzymes called carbon monoxide dehydrogenase. The coupling of the methyl group (provided by methylcobalamin) and CO is catalyzed by acetyl-CoA synthase.
The global reduction reaction of into acetic acid by is the following:
: ΔG° = −95 kJ/mol
while the conversion of one mole of glucose into 3 moles of acetic acid corresponds to a more exothermic reaction:
: ΔG° = −310.9 kJ/mol
However, the energy released by mole of acetic acid produced by each reaction is about the same: −95 kJ/mol for the reduction of by , and more for the conversion of glucose into acetic acid (−104 kJ/mol). | 1 | Applied and Interdisciplinary Chemistry |
* Loading: The first amino acid is activated with ATP as a mixed acyl-phosphoric acid anhydride with AMP by the A-domain and loaded onto the serine-attached 4-phospho-pantethine (4PP) sidechain of the PCP-domain catalyzed by the PCP-domain (thiolation).
* Some A domains require interaction with MbtH-like proteins for their activity.
* Sometimes the amino group of the bound amino acid is formylated by an F-domain or methylated by an NMT-domain. | 1 | Applied and Interdisciplinary Chemistry |
Regulation of CYP7A1 occurs at several levels including synthesis. Bile acids, steroid hormones, inflammatory cytokines, insulin, and growth factors inhibit CYP7A1 transcription through the 5′-upstream region of the promoter. The average life of this enzyme is between two and three hours. Activity can be regulated by phosphorylation-dephosphorylation.
CYP7A1 is upregulated by the nuclear receptor LXR (liver X receptor) when cholesterol (to be specific, oxysterol) levels are high. The effect of this upregulation is to increase the production of bile acids and reduce the level of cholesterol in hepatocytes.
It is downregulated by sterol regulatory element-binding proteins (SREBP) when plasma cholesterol levels are low.
Bile acids provide feedback inhibition of CYP7A1 by at least two different pathways, both involving the farnesoid X receptor, FXR. In the liver, bile acids bound to FXR induce small heterodimer partner, SHP which binds to LRH-1 and so inhibits the transcription of the enzyme. In the intestine, bile acids/FXR stimulate production of FGF15/19 (depending on species), which then acts as a hormone in the liver via FGFR4. | 1 | Applied and Interdisciplinary Chemistry |
A Nanocoulombmeter in combination with a Faraday cup can be used
to detect and measure the beams emitted from ion guns. | 0 | Theoretical and Fundamental Chemistry |
In mathematics and physics, a soliton is a nonlinear, self-reinforcing, localized wave packet that is strongly stable, in that it preserves its shape while propagating freely, at constant velocity, and recovers it even after collisions with other such localized wave packets. Its remarkable stability can be traced to a balanced cancellation of nonlinear and dispersive effects in the medium. (Dispersive effects are a property of certain systems where the speed of a wave depends on its frequency.) Solitons were subsequently found to provide stable solutions of a wide class of weakly nonlinear dispersive partial differential equations describing physical systems.
The soliton phenomenon was first described in 1834 by John Scott Russell (1808–1882) who observed a solitary wave in the Union Canal in Scotland. He reproduced the phenomenon in a wave tank and named it the "Wave of Translation". The term soliton was coined by Zabusky and Kruskal to describe localized, strongly stable propagating solutions to the Korteweg–de Vries equation, which models waves of the type seen by Russell. The name was meant to characterize the solitary nature of the waves, with the on suffix recalling the usage for particles such as electrons, baryons or hadrons, reflecting their observed particle-like behaviour. | 1 | Applied and Interdisciplinary Chemistry |
There is a need for new methods of C radiosynthesis because current methods are largely limited to methylation. The Vasdev lab has co-developed new techniques of CO fixation that are suitable for human use with diverse precursors synthesized by labeling at the carbonyl group (rather than the common methyl group). This methodology can label C-carbamates for imaging the enzyme FAAH ([C]CURB) or C-oxazolidinones for imaging MAO-B (C-SL25.1188), both of which they have translated for human use. They have also synthesized C-ureas and a C-carboxylic acid (C-Bexarotene). | 0 | Theoretical and Fundamental Chemistry |
The green fluorescent protein (GFP) is a protein that exhibits green fluorescence when exposed to light in the blue to ultraviolet range. The label GFP traditionally refers to the protein first isolated from the jellyfish Aequorea victoria and is sometimes called avGFP. However, GFPs have been found in other organisms including corals, sea anemones, zoanithids, copepods and lancelets.
The GFP from A. victoria has a major excitation peak at a wavelength of 395 nm and a minor one at 475 nm. Its emission peak is at 509 nm, which is in the lower green portion of the visible spectrum. The fluorescence quantum yield (QY) of GFP is 0.79. The GFP from the sea pansy (Renilla reniformis) has a single major excitation peak at 498 nm. GFP makes for an excellent tool in many forms of biology due to its ability to form an internal chromophore without requiring any accessory cofactors, gene products, or enzymes / substrates other than molecular oxygen.
In cell and molecular biology, the GFP gene is frequently used as a reporter of expression. It has been used in modified forms to make biosensors, and many animals have been created that express GFP, which demonstrates a proof of concept that a gene can be expressed throughout a given organism, in selected organs, or in cells of interest. GFP can be introduced into animals or other species through transgenic techniques, and maintained in their genome and that of their offspring. To date, GFP has been expressed in many species, including bacteria, yeasts, fungi, fish and mammals, including in human cells. Scientists Roger Y. Tsien, Osamu Shimomura, and Martin Chalfie were awarded the 2008 Nobel Prize in Chemistry on 10 October 2008 for their discovery and development of the green fluorescent protein.
Most commercially available genes for GFP and similar fluorescent proteins are around 730 base-pairs long. The natural protein has 238 amino acids. Its molecular mass is 27 kD. Therefore, fusing the GFP gene to the gene of a protein of interest can significantly increase the proteins size and molecular mass, and can impair the proteins natural function or change its location or trajectory of transport within the cell. | 1 | Applied and Interdisciplinary Chemistry |
The Van 't Hoff relation is particularly useful for the determination of the micellization enthalpy of surfactants from the temperature dependence of the critical micelle concentration (CMC):
However, the relation loses its validity when the aggregation number is also temperature-dependent, and the following relation should be used instead:
with and being the free energies of the surfactant in a micelle with aggregation number and respectively. This effect is particularly relevant for nonionic ethoxylated surfactants or polyoxypropylene–polyoxyethylene block copolymers (Poloxamers, Pluronics, Synperonics). The extended equation can be exploited for the extraction of aggregation numbers of self-assembled micelles from differential scanning calorimetric thermograms. | 0 | Theoretical and Fundamental Chemistry |
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.
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.) | 1 | Applied and Interdisciplinary Chemistry |
In fluid dynamics, Beltrami flows are flows in which the vorticity vector and the velocity vector are parallel to each other. In other words, Beltrami flow is a flow in which the Lamb vector is zero. It is named after the Italian mathematician Eugenio Beltrami due to his derivation of the Beltrami vector field, while initial developments in fluid dynamics were done by the Russian scientist Ippolit S. Gromeka in 1881. | 1 | Applied and Interdisciplinary Chemistry |
NAIL-MS (short for nucleic acid isotope labeling coupled mass spectrometry) is a technique based on mass spectrometry used for the investigation of nucleic acids and its modifications. It enables a variety of experiment designs to study the underlying mechanism of RNA biology in vivo. For example, the dynamic behaviour of nucleic acids in living cells, especially of RNA modifications, can be followed in more detail. | 0 | Theoretical and Fundamental Chemistry |
DNA damage appears to be the primary underlying cause of cancer. If accurate DNA repair is deficient, DNA damages tend to accumulate. Unrepaired DNA damage can increase mutational errors during DNA replication due to error-prone translesion synthesis. DNA damage can also increase epigenetic alterations due to errors during DNA repair. Such mutations and epigenetic alterations can give rise to cancer (see malignant neoplasms). Investigation of epigenetic down- or upregulation of repaired DNA genes as possibly central to progression of cancer has been regularly undertaken since 2000.
As described in Regulation of transcription in cancer, epigenetic downregulation of the DNA repair gene MGMT occurs in 93% of bladder cancers, 88% of stomach cancers, 74% of thyroid cancers, 40–90% of colorectal cancers and 50% of brain cancers. Similarly, epigenetic downregulation of LIG4 occurs in 82% of colorectal cancers and epigenetic downregulation of NEIL1 occurs in 62% of head and neck cancers and in 42% of non-small-cell lung cancers.
Epigenetic upregulation of the DNA repair genes PARP1 and FEN1 occurs in numerous cancers (see Regulation of transcription in cancer). PARP1 and FEN1 are essential genes in the error-prone and mutagenic DNA repair pathway microhomology-mediated end joining. If this pathway is upregulated, the excess mutations it causes can lead to cancer. PARP1 is over-expressed in tyrosine kinase-activated leukemias, in neuroblastoma, in testicular and other germ cell tumors, and in Ewing's sarcoma. FEN1 is upregulated in the majority of cancers of the breast, prostate, stomach, neuroblastomas, pancreas, and lung. | 1 | Applied and Interdisciplinary Chemistry |
The ECPM is a hub for scientific research. Five laboratories associated with the CNRS form the ECPM's research federation. The fields of research are varied: materials, catalysis, polymers, organic synthesis, analysis of biomolecules. The laboratories collaborate with industries and major European research organizations as part of European agreements. A 1000m² hall with a cleanroom further the exchanges with industry.
Associated Laboratories
- The SYBIO Laboratory (Synthèse Organique et Molécules Bioactives)
- Laboratoire de Chimie Bioorganique et Médicale
- The Nierengarten group
- Laboratoire de Synthèse et Catalyse Asymétrique (SynCat)
- Laboratoire de Chimie organométallique | 1 | Applied and Interdisciplinary Chemistry |
The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in which self-replicating RNA molecules proliferated before the evolution of DNA and proteins. The term also refers to the hypothesis that posits the existence of this stage.
Alexander Rich first proposed the concept of the RNA world in 1962, and Walter Gilbert coined the term in 1986. Alternative chemical paths to life have been proposed, and RNA-based life may not have been the first life to exist. Even so, the evidence for an RNA world is strong enough that the hypothesis has gained wide acceptance. The concurrent formation of all four RNA building blocks further strengthened the hypothesis. Regardless of its plausibility in a prebiotic scenario, the RNA world can serve as a model system for studying the origin of life.
* Like DNA, RNA can store and replicate genetic information.
* Like protein enzymes, RNA enzymes (ribozymes) can catalyze (start or accelerate) chemical reactions that are critical for life.
One of the most critical components of cells, the ribosome, is composed primarily of RNA. Ribonucleotide moieties in many coenzymes, such as acetyl-CoA, NADH, FADH, and F420, may be surviving remnants of covalently bound coenzymes in an RNA world.
Although RNA is fragile, some ancient RNAs may have evolved the ability to methylate other RNAs to protect them.
If the RNA world existed, it was probably followed by an age characterized by the evolution of ribonucleoproteins (RNP world), which in turn ushered in the era of DNA and longer proteins. DNA has greater stability and durability than RNA; this may explain why it became the predominant information storage molecule. Protein enzymes may have come to replace RNA-based ribozymes as biocatalysts because their greater abundance and diversity of monomers makes them more versatile. As some cofactors contain both nucleotide and amino-acid characteristics, it may be that amino acids, peptides and finally proteins initially were cofactors for ribozymes. | 0 | Theoretical and Fundamental Chemistry |
Freshwaters are surprisingly difficult to sample because they are rarely homogeneous and their quality varies during the day and during the year. In addition the most representative sampling locations are often at a distance from the shore or bank increasing the logistic complexity. | 1 | Applied and Interdisciplinary Chemistry |
Estimates in 2023 found that the current carbon dioxide concentration in the atmosphere may be the highest it has been in the last 14 million years. However the IPCC Sixth Assessment Report estimated similar levels 3 to 3.3 million years ago in the mid-Pliocene warm period. This period can be a proxy for likely climate outcomes with current levels of .
Carbon dioxide is believed to have played an important effect in regulating Earths temperature throughout its 4.54 billion year history. Early in the Earths life, scientists have found evidence of liquid water indicating a warm world even though the Suns output is believed to have only been 70% of what it is today. Higher carbon dioxide concentrations in the early Earths atmosphere might help explain this faint young sun paradox. When Earth first formed, Earth's atmosphere may have contained more greenhouse gases and concentrations may have been higher, with estimated partial pressure as large as , because there was no bacterial photosynthesis to reduce the gas to carbon compounds and oxygen. Methane, a very active greenhouse gas, may have been more prevalent as well.
Carbon dioxide concentrations have shown several cycles of variation from about 180 parts per million during the deep glaciations of the Holocene and Pleistocene to 280 parts per million during the interglacial periods. Carbon dioxide concentrations have varied widely over the Earths history. It is believed to have been present in Earths first atmosphere, shortly after Earth's formation. The second atmosphere, consisting largely of nitrogen and was produced by outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge asteroids. A major part of carbon dioxide emissions were soon dissolved in water and incorporated in carbonate sediments.
The production of free oxygen by cyanobacterial photosynthesis eventually led to the oxygen catastrophe that ended Earths second atmosphere and brought about the Earths third atmosphere (the modern atmosphere) 2.4 billion years ago. Carbon dioxide concentrations dropped from 4,000 parts per million during the Cambrian period about 500 million years ago to as low as 180 parts per million 20,000 years ago . | 1 | Applied and Interdisciplinary Chemistry |
The following equation can be used to correct a measured pollutant concentration in an emitted gas (containing a measured CO content) to an equivalent pollutant concentration in an emitted gas containing a specified reference amount of CO:
Thus, a measured particulates concentration of 0.1 grain per dscf in a gas that has 8 volume % CO is<br>
0.1 × ( 12 ÷ 8 ) = 0.15 grain per dscf when corrected to a gas having a specified reference CO content of 12 volume %.
Notes:
* Although ppmv and grains per dscf have been used in the above examples, concentrations such as ppbv (i.e., parts per billion by volume), volume percent, grams per dscm and many others may also be used.
* 1 percent by volume = 10,000 ppmv (i.e., parts per million by volume).
* Care must be taken with the concentrations expressed as ppbv to differentiate between the British billion which is 10 and the USA billion which is 10. | 1 | Applied and Interdisciplinary Chemistry |
A typical run-around coil system comprises two or more multi-row finned tube coils connected to each other by a pumped pipework circuit. The pipework is charged with a heat exchange fluid, normally water, which picks up heat from the exhaust air coil and gives up heat to the supply air coil before returning again. Thus heat from the exhaust air stream is transferred through the pipework coil to the circulating fluid, and then from the fluid through the pipework coil to the supply air stream.
The use of this system is generally limited to situations where the air streams are separated and no other type of device can be utilised since the heat recovery efficiency is lower than other forms of air-to-air heat recovery. Gross efficiencies are usually in the range of 40 to 50%, but more significantly seasonal efficiencies of this system can be very low, due to the extra electrical energy used by the pumped fluid circuit.
The fluid circuit containing the circulating pump also contains an expansion vessel, to accommodate changes in fluid pressure. In addition, there is a fill device to ensure the system remains charged. There are also controls to bypass and shut down the system when not required, and other safety devices. Pipework runs should be as short as possible, and should be sized for low velocities to minimize frictional losses, hence reducing pump energy consumption. It is possible to recover some of this energy in the form of heat given off by the motor if a glandless pump is used, where a water jacket surrounds the motor stator, thus picking up some of its heat.
The pumped fluid will have to be protected from freezing, and is normally treated with a glycol based anti-freeze. This also reduces the specific heat capacity of the fluid and increases the viscosity, increasing pump power consumption, further reducing the seasonal efficiency of the device. For example, a 20% glycol mixture will provide protection down to , but will increase system resistance by 15%.
For the finned tube coil design, there is a performance maximum corresponding to an eight- or ten-row coil, above this the fan and pump motor energy consumption increases substantially and seasonal efficiency starts to decrease. The main cause of increased energy consumption lies with the fan, for the same face velocity, fewer coil rows will decrease air pressure drop and increase water pressure drop. The total energy consumption will usually be less than that for a greater number of coil rows with higher air pressure drops and lower water pressure drops. | 0 | Theoretical and Fundamental Chemistry |
In the United States in 1964, the Federal Trade Commission proscribed the use of the word leakproof or the phrase "guaranteed leakproof" in advertisements for or on the packages of dry-cell batteries, as they had determined that no manufacturer had yet developed a battery that was truly impervious to leaking. The FTC repealed this ban in 1997. | 1 | Applied and Interdisciplinary Chemistry |
Zinc chloride is a common reagent in the laboratory useful Lewis acid in organic chemistry.
Molten zinc chloride catalyses the conversion of methanol to hexamethylbenzene:
Other examples include catalyzing (A) the Fischer indole synthesis, and also (B) Friedel-Crafts acylation reactions involving activated aromatic rings
Related to the latter is the classical preparation of the dye fluorescein from phthalic anhydride and resorcinol, which involves a Friedel-Crafts acylation. This transformation has in fact been accomplished using even the hydrated sample shown in the picture above.
Zinc chloride also activates benzylic and allylic halides towards substitution by weak nucleophiles such as alkenes:
In similar fashion, promotes selective sodium cyanoborohydride| reduction of tertiary, allylic or benzylic halides to the corresponding hydrocarbons.
Zinc chloride is also a useful starting reagent for the synthesis of many organozinc reagents, such as those used in the palladium catalyzed Negishi coupling with aryl halides or vinyl halides. In such cases the organozinc compound is usually prepared by transmetallation from an organolithium or a Grignard reagent, for example:
Zinc enolates, prepared from alkali metal enolates and , provide control of stereochemistry in aldol condensation reactions due to chelation on to the zinc. In the example shown below, the threo product was favored over the erythro by a factor of 5:1 when in DME/ether was used. The chelate is more stable when the bulky phenyl group is pseudo-equatorial rather than pseudo-axial, i.e., threo rather than erythro. | 0 | Theoretical and Fundamental Chemistry |
One of the major differences between p-block-element-centered porphyrins and transition-metal-centered porphyrins is the far smaller size of the interstitial atom, especially in the case of the first-row p-block. Other than protons, the next smallest atom known to bind to the central N pocket is lithium. The first two isolated lithium porphyrin complexes each reported a 2:1 metal to base ratio, and XRD suggested both lithium atoms reside out of the porphyrin plane.
Boron has a covalent radius of 85 pm, significantly smaller than lithium's 133 pm. This suggests the porphyrin pocket is more likely to accommodate two boron atoms rather than one. Indeed, each boron porphyrin synthesized thus far has adopted a ratio of 2:1, with a range of orientations relative to the N plane. The boron atoms can exist in the same plane as the porphyrin (both with and without additional out-of-plane B-X bonds), or out of N plane in either a cisoid or transoid geometry.
This coordination motif is interesting because it introduces both boron and porphyrin to geometries they do not regularly adopt. Porphyrin readily binds to transition metals, which are capable of octahedral or square planar geometries. Boron, without available d-orbitals, typically adopts a trigonal planar or tetrahedral local bonding environment. Diboryl porphyrins, on the other hand, find boron in a pseudo-tetrahedral local environment and introduce a tetragonal distortion to the porphyrin, as can be seen in the DFT image above.
Corroles are distinct from porphyrins in that they contain one less methine to bridge between pyrrole units, creating a lower-symmetry compound and a smaller N pocket. For boron chemistry, this slightly smaller core allows for the possibility of binding to a single boron, whereas the porphyrin pocket has thus far always bound two. For such monoboryl corroles, DFT studies have suggested the boron preferentially binds to the dipyrromethene (A) site shown here, in which stability is attained by maximizing both BX—HN hydrogen bonding and BH—HN dihydrogen bonding, in addition to minimizing steric crowding.
The Brothers group has shown the stereochemical implications of comparing diboryl porphyrin with diboryl corrole: porphyrin prefers transoid orientation of the diboryl unit, whereas corrole prefers the cisoid orientation.<nowiki/> | 0 | Theoretical and Fundamental Chemistry |
Particularly for older samples, it may be useful to enrich the amount of in the sample before testing. This can be done with a thermal diffusion column. The process takes about a month and requires a sample about ten times as large as would be needed otherwise, but it allows more precise measurement of the / ratio in old material and extends the maximum age that can be reliably reported.
Once contamination has been removed, samples must be converted to a form suitable for the measuring technology to be used. Where gas is required, is widely used. For samples to be used in liquid scintillation counters, the carbon must be in liquid form; the sample is typically converted to benzene. For accelerator mass spectrometry, solid graphite targets are the most common, although gaseous can also be used.
The quantity of material needed for testing depends on the sample type and the technology being used. There are two types of testing technology: detectors that record radioactivity, known as beta counters, and accelerator mass spectrometers. For beta counters, a sample weighing at least is typically required. Accelerator mass spectrometry is much more sensitive, and samples containing as little as 0.5 milligrams of carbon can be used. | 0 | Theoretical and Fundamental Chemistry |
The virion is a flexible filament (worm-like chain) about 6 nm in diameter and 900 nm long. Several thousand copies of a small (50 amino-acid residues) elongated alpha-helical major coat protein subunit (the product of gene 8, or p8) in an overlapping shingle-like array form a hollow cylinder enclosing the circular single-stranded DNA genome. Each p8 subunit has a collection of basic residues near the C-terminus of the elongated protein and acidic residues near the N-terminus; these two regions are separated by about 20 hydrophobic (non-polar) residues. The shingle-like arrangement places the acidic residues of p8 near the outside surface of the cylinder, where they cause the virus particle to be negatively-charged; non-polar regions near non-polar regions of neighbouring p8 subunits, where non-polar interactions contribute to a notable physical stability of the virus particle; and basic residues near the centre of the cylinder, where they interact with the negatively-charged DNA phosphates at the core of the virion. Longer (or shorter) DNA molecules can be packaged, since more (or fewer) p8 subunits can be added during assembly as required to protect the DNA, making the phage useful for genetic studies. (This effect should not be confused with polyphage, which can package several separate and distinct DNA molecules). About 5 copies each of four minor proteins cap the two ends of the virion.
The molecular structure of the virion capsid (the assembly of p8 subunit proteins) has been determined by X-ray fiber diffraction, and structural models have been deposited in the Protein Data Bank. In particular, the series of fd and Pf1 virion structures deposited in the PDB over decades illustrate the improvements in methods for fiber diffraction data collection and computational analysis. Structures of the p3 capsid protein and the p5 replication/assembly protein have also been determined from X-ray crystallography and deposited in the PDB. | 1 | Applied and Interdisciplinary Chemistry |
Mud cake (also mudcake) is the layer of particulates from drill mud coating (caking) the inside of a borehole after the suspension medium has seeped through a porous geological formation. Similar to filter cake.
Mud cake provides a physical barrier to prevent further penetration and loss of drilling fluid, as well a later loss of produced fluids, into a permeable formation. | 1 | Applied and Interdisciplinary Chemistry |
Q-vectors are used in atmospheric dynamics to understand physical processes such as vertical motion and frontogenesis. Q-vectors are not physical quantities that can be measured in the atmosphere but are derived from the quasi-geostrophic equations and can be used in the previous diagnostic situations. On meteorological charts, Q-vectors point toward upward motion and away from downward motion. Q-vectors are an alternative to the omega equation for diagnosing vertical motion in the quasi-geostrophic equations. | 1 | Applied and Interdisciplinary Chemistry |
Metabolism and homeostasis of fatty acid synthase is transcriptionally regulated by Upstream Stimulatory Factors (USF1 and USF2) and sterol regulatory element binding protein-1c (SREBP-1c) in response to feeding/insulin in living animals.
Although liver X receptors (LXRs) modulate the expression of sterol regulatory element binding protein-1c (SREBP-1c) in feeding, regulation of FAS by SREBP-1c is USF-dependent.
Acylphloroglucinols isolated from the fern Dryopteris crassirhizoma show a fatty acid synthase inhibitory activity. | 1 | Applied and Interdisciplinary Chemistry |
Mercury(I) oxide, also known as mercurous oxide, is an inorganic metal oxide with the chemical formula HgO.
It is a brown/black powder, insoluble in water but soluble in nitric acid. With hydrochloric acid, it reacts to form calomel, HgCl. Mercury(I) oxide is toxic but without taste or smell. It is chemically unstable and converts to mercury(II) oxide and mercury metal. | 0 | Theoretical and Fundamental Chemistry |
On 20 October 1818, Davy was created a baronet; this was the first such honour conferred on a man of science in Britain. It was followed a year later with the presidency of the Royal Society. The Society was in transition from a club for gentlemen interested in natural philosophy, connected with the political and social elite, to an academy representing increasingly specialised sciences. The previous president, Joseph Banks, had held the post for over 40 years and had presided autocratically over what David Philip Miller calls the "Banksian Learned Empire", in which natural history was prominent. Banks had groomed Davies Gilbert to succeed him and preserve the status quo, but Gilbert declined to stand. Fellows who thought royal patronage was important proposed Prince Leopold of Saxe-Coburg (later Leopold I of Belgium), who also withdrew, as did the Whig Edward St Maur, 11th Duke of Somerset. Davy was the outstanding scientist but some fellows did not approve of his popularising work at the Royal Institution.
Elections took place on St Andrews Day and Davy was elected on 30 November 1820. Although he was unopposed, other candidates had received initial backing. These candidates embodied the factional difficulties that beset Davys presidency and which eventually defeated him. The strongest alternative had been William Hyde Wollaston, who was supported by the "Cambridge Network" of outstanding mathematicians such as Charles Babbage and John Herschel, who tried to block Davy. They were aware that Davy supported some modernisation, but thought that he would not sufficiently encourage aspiring young mathematicians, astronomers and geologists, who were beginning to form specialist societies. Davy was only 41, and reformers were fearful of another long presidency.
In his early years Davy was optimistic about reconciling the reformers and the Banksians. In his first speech as president he declared, "I trust that, with these new societies, we shall always preserve the most amicable relations ... I am sure there is no desire in [the Royal Society] to exert anything like patriarchal authority in relation to these institutions". | 1 | Applied and Interdisciplinary Chemistry |
Aluminium chloride is manufactured on a large scale by the exothermic reaction of aluminium metal with chlorine or hydrogen chloride at temperatures between .
Aluminium chloride may be formed via a single displacement reaction between copper(II) chloride and aluminium.
In the US in 1993, approximately 21,000 tons were produced, not counting the amounts consumed in the production of aluminium.
Hydrated aluminium trichloride is prepared by dissolving aluminium oxides in hydrochloric acid. Metallic aluminium also readily dissolves in hydrochloric acid ─ releasing hydrogen gas and generating considerable heat. Heating this solid does not produce anhydrous aluminium trichloride, the hexahydrate decomposes to aluminium hydroxide when heated:
Aluminium also forms a lower chloride, aluminium(I) chloride (AlCl), but this is very unstable and only known in the vapour phase. | 0 | Theoretical and Fundamental Chemistry |
Functional magnetic resonance spectroscopy of the brain (fMRS) uses magnetic resonance imaging (MRI) to study brain metabolism during brain activation. The data generated by fMRS usually shows spectra of resonances, instead of a brain image, as with MRI. The area under peaks in the spectrum represents relative concentrations of metabolites.
fMRS is based on the same principles as in vivo magnetic resonance spectroscopy (MRS). However, while conventional MRS records a single spectrum of metabolites from a region of interest, a key interest of fMRS is to detect multiple spectra and study metabolite concentration dynamics during brain function. Therefore, it is sometimes referred to as dynamic MRS, event-related MRS or time-resolved MRS. A novel variant of fMRS is functional diffusion-weighted spectroscopy (fDWS) which measures diffusion properties of brain metabolites upon brain activation.
Unlike in vivo MRS which is intensively used in clinical settings, fMRS is used primarily as a research tool, both in a clinical context, for example, to study metabolite dynamics in patients with epilepsy, migraine and dyslexia, and to study healthy brains. fMRS can be used to study metabolism dynamics also in other parts of the body, for example, in muscles and heart; however, brain studies have been far more popular.
The main goals of fMRS studies are to contribute to the understanding of energy metabolism in the brain, and to test and improve data acquisition and quantification techniques to ensure and enhance validity and reliability of fMRS studies. | 0 | Theoretical and Fundamental Chemistry |
In Italy a shortage of coal led the steel industry to specialize in the use of hydro-electrical energy, exploiting ideas pioneered by Ernesto Stassano from 1898 (Stassano furnace). Despite periods of innovation (1907–14), growth (1915–18), and consolidation (1918–22), early expectations were only partly realized. Steel output in the 1920s and 1930s averaged about 2.1 million metric tons. Per capita consumption was much lower than the average of Western Europe. Electrical processes were an important substitute, yet did not improve competitiveness or reduce prices. Instead, they reinforced the dualism of the sector and initiated a vicious circle that prevented market expansion. Italy modernized its industry in the 1950s and 1960s and it grew rapidly, becoming second only to West Germany in the 1970s. Strong labour unions kept employment levels high. Troubles multiplied after 1980, however, as foreign competition became stiffer. In 1980 the largest producer Nuova Italsider [now dubbed Ilva (company) lost 746 billion lira in its inefficient operations. In the 1990s the Italian steel industry, then mostly state-owned, was largely privatised. Today the country is the world's seventh-largest steel exporter. | 1 | Applied and Interdisciplinary Chemistry |
Crystal structures of the resting or ground states of AR1 (3.4 Å resolution), AR2 (1.8 Å resolution) and AR3 (1.07 and 1.3 Å) have been deposited in the Protein Data Bank. Proteins possess seven transmembrane α-helices and a two-stranded extracellular-facing β-sheet. Retinal is covalently bonded via Schiff base to a lysine residue on helix G. The conserved DLLxDGR sequence, close to the extracellular-facing N-terminus of both proteins, forms a tightly curved omega loop that has been implicated in bacterioruberin binding. The cleavage of the first 6 amino acids and the conversion of Gln7 to a pyroglutamate (PCA) residue was also observed in AR3, as previously reported for bacteriorhodopsin. | 0 | Theoretical and Fundamental Chemistry |
David Auerbach has described an effect that he observed in samples in glass beakers placed into a liquid cooling bath. In all cases the water supercooled, reaching a temperature of typically before spontaneously freezing. Considerable random variation was observed in the time required for spontaneous freezing to start and in some cases this resulted in the water which started off hotter (partially) freezing first.
In 2016, Burridge and Linden defined the criterion as the time to reach , carried out experiments, and reviewed published work to date. They noted that the large difference originally claimed had not been replicated, and that studies showing a small effect could be influenced by variations in the positioning of thermometers: "We conclude, somewhat sadly, that there is no evidence to support meaningful observations of the Mpemba effect."
In controlled experiments, the effect can entirely be explained by undercooling and the time of freezing was determined by what container was used. Experimental results confirming the Mpemba effect have been criticized for being flawed, not accounting for dissolved solids and gasses, and other confounding factors.
Philip Ball, a reviewer for Physics World wrote: "Even if the Mpemba effect is real — if hot water can sometimes freeze more quickly than cold — it is not clear whether the explanation would be trivial or illuminating." Ball wrote that investigations of the phenomenon need to control a large number of initial parameters (including type and initial temperature of the water, dissolved gas and other impurities, and size, shape and material of the container, and temperature of the refrigerator) and need to settle on a particular method of establishing the time of freezing, all of which might affect the presence or absence of the Mpemba effect. The required vast multidimensional array of experiments might explain why the effect is not yet understood.
New Scientist recommends starting the experiment with containers at , respectively, to maximize the effect. In a related study, it was found that freezer temperature also affects the probability of observing the Mpemba phenomenon as well as container temperature does. | 0 | Theoretical and Fundamental Chemistry |
Light scattering spectroscopy has been applied for detection of precancer in many organs including esophagus, colon, urinary bladder, oral cavity, cervix, pancreatic cyst, stomach, skin, and bile duct. | 0 | Theoretical and Fundamental Chemistry |
In 1996, Waters was awarded the Massey Medal of Massey University, in recognition of services to the university and to science. In the 2006 New Year Honours, she was appointed an Officer of the New Zealand Order of Merit, for services to chemistry.
Waters was elected a Fellow of the Royal Society of New Zealand in 1999, and is also a Fellow of the New Zealand Institute of Chemistry. | 0 | Theoretical and Fundamental Chemistry |
The term sewage treatment plant (STP) (or sewage treatment works) is nowadays often replaced with the term wastewater treatment plant (WWTP). Strictly speaking, the latter is a broader term that can also refer to industrial wastewater treatment.
The terms water recycling center or water reclamation plants are also in use as synonyms. | 1 | Applied and Interdisciplinary Chemistry |
The CFIIm complex is responsible for transcription termination and triggering the disassembly of the elongation complex. It is composed of only two proteins:
*PCF11
*CLP1 | 1 | Applied and Interdisciplinary Chemistry |
Isoserine is a non-proteinogenic α-hydroxy-β-amino acid, and an isomer of serine. Non-proteinogenic amino acids do not form proteins, and are not part of the genetic code of any known organism. Isoserine has only been produced synthetically.
The first documented synthesis of isoserine in a laboratory setting was by Miyazawa et al., who published their results in 1976. | 1 | Applied and Interdisciplinary Chemistry |
After amplification with PCR, samples are loaded into a gel (either agarose or polyacrylamide) for gel electrophoresis. The differing sizes created through random amplification will separate along the gel in a repeatable manner depending on the sample source. This creates a distinct DNA fingerprint.
Unlike traditional PCR analysis, RAPD does not require any specific knowledge of the DNA sequence of the target organism: the identical 10-mer primers will or will not amplify a segment of DNA, depending on positions that are complementary to the primers sequence. For example, no fragment is produced if primers annealed too far apart or 3 ends of the primers are not facing each other. Therefore, if a mutation has occurred in the template DNA at the site that was previously complementary to the primer, a PCR product will not be produced, resulting in a different pattern of amplified DNA segments on the gel. | 1 | Applied and Interdisciplinary Chemistry |
Hybridization is one way to determine the sequence of a DNA strand from detecting the changes in the length of a hairpin. When a probe hybridizes to an open hairpin, complete refolding of the hairpin is stalled, and the position of the hybridized probe can be inferred. Thus the sequence of a DNA fragment of interest can be inferred from overlapping the positions of probes sets, which are allowed to hybridize one by one. | 1 | Applied and Interdisciplinary Chemistry |
At room temperature, taurates are usually pasty masses, which dissolve well in water and react then neutral to slightly alkaline (pH 7–8). Their toxicity is low (the LD, rat, oral is 7800 mg·kg for cocoyl tauride). They are easily biodegradable, they are not prone to bioaccumulation, but they are harmful to aquatic organisms (like all surfactants). Due to their amide bond, taurates are stable in a much wider pH range (about 2–10) than the corresponding esters, as for example isethionates. They are very mild surfactants with good foaming ability and high foam stability, even in the presence of fats and oils. Taurates retain their good washing properties even in hard water or seawater. Taurates are suitable in concentrations of about 2% as co-surfactants because of their good compatibility with all nonionic and anionic surfactants. | 0 | Theoretical and Fundamental Chemistry |
* CUORE (Cryogenic Underground Observatory for Rare Events) experiment:
** The CUORE experiment consists of an array of 988 ultra-cold TeO crystals (for a total mass of 206 kg of ) used as bolometers to detect the emitted beta particles and as the source of the decay. CUORE is located underground at the Laboratori Nazionali del Gran Sasso, and it began its first physics data run in 2017. CUORE published in 2020 results from the search for neutrinoless double-beta decay in with a total exposure of 372.5 kg⋅yr, finding no evidence for 0νββ decay and setting a 90% CI Bayesian lower limit of years and in April 2022 a new limit was set on years at the same confidence level. The experiment is steadily taking data, and it is expected to finalize its physics program by 2024.
* KamLAND-Zen (Kamioka Liquid Scintillator Antineutrino Detector-Zen) experiment:
** The KamLAND-Zen experiment commenced using 13 tons of xenon as a source (enriched with about 320 kg of ), contained in a nylon balloon that is surrounded by a liquid scintillator outer balloon of 13 m diameter. Starting in 2011, KamLAND-Zen Phase I started taking data, eventually leading to set a limit on the lifetime for neutrinoless double beta decay of years (90% C.L.). This limit could be improved by combining with Phase II data (data-taking started in December 2013) to years (90% C.L.). For Phase II, the collaboration especially managed to reduce the decay of , which disturbed the measurements in the region of interest for 0νββ decay of . In August 2016, KamLAND-Zen 800 was completed containing 800 kg of , reporting a limit of years (90% C.L.). In 2023 the limit was improved limit of years (90% C.L.). | 0 | Theoretical and Fundamental Chemistry |
The grandson of Eastern European Jewish immigrants, Braterman was born and raised in London. He received his Master of Arts and DPhil degrees from Balliol College, Oxford. In 1985 he received a DSc degree.
After postdoctoral research at University College London (adviser Robert Williams), and University of California at Los Angeles (advisers Herbert D. Kaesz and Mostafa El-Sayed), he worked in the chemistry departments of the University of Glasgow, where he rose to the rank of reader, and the University of North Texas as professor and chair, and later as Regents Professor, with several periods as visiting investigator at Scripps Institution of Oceanography at the University of California San Diego, and Sandia National Laboratories.
Braterman's work has been supported by the Robert A. Welch Foundation, the National Science Foundation, and NASA’s exobiology and astrobiology programs, for which he also served as an adviser.
In 2007, he returned to Glasgow where he is now an Honorary Senior Research Fellow. | 0 | Theoretical and Fundamental Chemistry |
De-AMPylation is the reverse reaction in which the AMP molecule is detached from the amino acid side of a chain protein.
There are three known mechanisms for this reaction.
The bacterial GS-ATase (GlnE) encodes a bipartite protein with separate N-terminal AMPylation and C-terminal de-AMPylation domains whose activity is regulated by P and associated posttranslational modifications. De-AMPylation of its substrate AMPylated glutamine synthetase proceeds by a phosphorolytic reaction between the adenyl-tyrosine of GS and orthophosphate, leading to the formation of ADP and unmodified glutamine synthetase.
SidD, a protein introduced in the host cell by the pathogenic bacteria Legionella pneumophila, de-AMPylates Rab1 a host protein AMPylated by a different Legionella pneumophila enzyme, the AMPylase SidM. Whilst the benefit to the pathogen of introducing these two antagonistic effectors in the host remains unclear, the biochemical reaction carried out by SidD involves the use of a phosphatase-like domain to catalyse the hydrolytic removal of the AMP from tyrosine 77 of the host's Rab1.
In animal cells the removal of AMP from threonine 518 of BiP/Grp78 is catalysed by the same enzyme, FICD, that AMPylates BiP. Unlike the bacterial GS-ATase, FICD carries out both reactions with same catalytic domain. | 1 | Applied and Interdisciplinary Chemistry |
The IUPAC 1961 definition of the unified atomic mass unit, with that name and symbol "u", was adopted by the International Bureau for Weights and Measures (BIPM) in 1971 as a non-SI unit accepted for use with the SI. | 0 | Theoretical and Fundamental Chemistry |
In biochemistry, a metabolite is an intermediate or end product of metabolism.
The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, catalytic activity of their own (usually as a cofactor to an enzyme), defense, and interactions with other organisms (e.g. pigments, odorants, and pheromones).
A primary metabolite is directly involved in normal "growth", development, and reproduction. Ethylene exemplifies a primary metabolite produced large-scale by industrial microbiology.
A secondary metabolite is not directly involved in those processes, but usually has an important ecological function. Examples include antibiotics and pigments such as resins and terpenes etc.
Some antibiotics use primary metabolites as precursors, such as actinomycin, which is created from the primary metabolite tryptophan. Some sugars are metabolites, such as fructose or glucose, which are both present in the metabolic pathways.
Examples of primary metabolites produced by industrial microbiology include:
The metabolome forms a large network of metabolic reactions, where outputs from one enzymatic chemical reaction are inputs to other chemical reactions.
Metabolites from chemical compounds, whether inherent or pharmaceutical, form as part of the natural biochemical process of degrading and eliminating the compounds.
The rate of degradation of a compound is an important determinant of the duration and intensity of its action. Understanding how pharmaceutical compounds are metabolized and the potential side effects of their metabolites is an important part of drug discovery. | 1 | Applied and Interdisciplinary Chemistry |
A transmetallation involves a ligand transfer to one another such as this:
M is not limited to any main group and/or transition metal. R can be limited to almost any phosphine, aryl, alkyl, halogen, hydrogen and/or carbene.
In this case organoberyllium can form reactions such as: | 0 | Theoretical and Fundamental Chemistry |
A disc, also known as a valve member, is a movable obstruction inside the stationary body that adjustably restricts flow through the valve. Although traditionally disc-shaped, discs come in various shapes. Depending on the type of valve, a disc can move linearly inside a valve, or rotate on the stem (as in a butterfly valve), or rotate on a hinge or trunnion (as in a check valve). A ball is a round valve member with one or more paths between ports passing through it. By rotating the ball, flow can be directed between different ports. Ball valves use spherical rotors with a cylindrical hole drilled as a fluid passage. Plug valves use cylindrical or conically tapered rotors called plugs. Other round shapes for rotors are possible as well in rotor valves, as long as the rotor can be turned inside the valve body. However, not all round or spherical discs are rotors; for example, a ball check valve uses the ball to block reverse flow, but is not a rotor because operating the valve does not involve rotation of the ball. | 1 | Applied and Interdisciplinary Chemistry |
Rotational spectroscopy has primarily been used to investigate fundamental aspects of molecular physics. It is a uniquely precise tool for the determination of molecular structure in gas-phase molecules. It can be used to establish barriers to internal rotation such as that associated with the rotation of the group relative to the group in chlorotoluene (). When fine or hyperfine structure can be observed, the technique also provides information on the electronic structures of molecules. Much of current understanding of the nature of weak molecular interactions such as van der Waals, hydrogen and halogen bonds has been established through rotational spectroscopy. In connection with radio astronomy, the technique has a key role in exploration of the chemical composition of the interstellar medium. Microwave transitions are measured in the laboratory and matched
to emissions from the interstellar medium using a radio telescope. was the first stable polyatomic molecule to be identified in the interstellar medium. The measurement of chlorine monoxide is important for atmospheric chemistry. Current projects in astrochemistry involve both laboratory microwave spectroscopy and observations made using modern radiotelescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA). | 0 | Theoretical and Fundamental Chemistry |
When bonded side-on to a single metal atom, an alkyne serves as a dihapto usually two-electron donor. For early metal complexes, e.g., CpTi(CR), strong π-backbonding into one of the π* antibonding orbitals of the alkyne is indicated. This complex is described as a metallacyclopropene derivative of Ti(IV). For late transition metal complexes, e.g., Pt(PPh)(MeCPh), the π-backbonding is less prominent, and the complex is assigned oxidation state 0.
In some complexes, the alkyne is classified as a four-electron donor. In these cases, both pairs of pi-electrons donate to the metal. This kind of bonding was first implicated in complexes of the type W(CO)(RC). | 0 | Theoretical and Fundamental Chemistry |
With the invention of hollow casting bronze became the most important medium of monumental sculpture, largely because of its strength and lightness, which admitted poses that would not be possible in stone. But the value of the metal in later ages has involved the destruction of nearly all such statues. The few complete figures that survive, and a somewhat more numerous series of detached heads and portrait-busts, attest the excellence of ancient work in this material. The earliest statuettes are chiselled, wrought and welded; next in time come solid castings, but larger figures were composed of hammered sections, like domestic utensils, each part worked separately in repoussé and the whole assembled with rivets (σφυρήλατα). Very little of this flimsy fabric is extant, but chance has preserved one bust entire, in the Polledrara Tomb at Vulci. This belongs to the early 6th century BC, the age of repoussé work.
The process was soon superseded in such subjects by hollow casting, but beaten reliefs, the household craft from which Greek bronze work sprang, persisted in some special and highly perfected forms, as handle-plates on certain vases, emblemata on mirror-cases, and particularly as ornaments of armour, where light weight was required. The Siris bronzes in the British Museum are shoulder-pieces from a 4th-century cuirass. Casting was done by the cire perdue process in clay moulds, but a great deal of labour was spent on finishing. The casts are very finely chased, and most large pieces contain patches, inserted to make good the flaws. Heads and limbs of statues were cast separately and adjusted to the bodies: besides the evidence of literature and of the actual bronzes, there is an illustration of a dismembered statue in the making on a painted vase in Berlin.
Pliny and other ancient writers have much to say in regard to various alloys of bronze — Corinthian, Delian, Aeginetan, Syracusan — in regard to their composition and uses and particularly to their colour effects, but their statements have not been confirmed by modern analyses and are sometimes manifestly false. Corinthian bronze is said to have been first produced by accident in the Roman burning of the city (146 BC) when streams of molten copper, gold and silver mingled. Similar tales are told by Plutarch and Pliny about the artists' control of colour: Silanion made a pale-faced Jocasta by mixing silver with his bronze, Aristonidas made Athamas blush with an alloy of iron. There is good evidence that Greek and Roman bronzes were not artificially patinated, though many were gilt or silvered. Plutarch admires the blue colour of some very ancient statues at Delphi, and wonders how it was produced; Pliny mentions a bitumen wash, but this was doubtless a protective lacquer; and a 4th-century inscription from Chios records the regulations made there for keeping a public statue clean and bright. | 1 | Applied and Interdisciplinary Chemistry |
Resazurin is prepared by acid-catalyzed condensation between resorcinol and 4-nitrosoresorcinol followed by oxidation of the intermediate with manganese(IV) oxide:
Treatment of the crude reaction product with excess sodium carbonate yields the sodium salt of resazurin, which is typically the commercial form of the dye. Running the condensation step in alcohols is possible but results in lower yields of the product; in pure water or acetic acid, the reaction does not proceed satisfactorily. | 0 | Theoretical and Fundamental Chemistry |
The Chinese compound combines the common word outside; exterior; external with cinnabar; vermillion; elixir; alchemy. The antonym of is meaning inside; inner; internal, and the term external elixir/alchemy was coined in connection with the complementary term internal elixir/alchemy.
The sinologist and expert on Chinese alchemy Fabrizio Pregadio lists four generally accepted meanings of : "The color cinnabar, scarlet, or light scarlet", "The mineral cinnabar, defined as a red stone formed by the combination of quicksilver and sulphur", "Sincerity (corresponding to )", and "An essence obtained by the refining of a medicinal substance; a refined medicinal substance, the so-called medicine of the seekers of immortality for avoiding aging and death; a term often used for matters concerning the immortal". Pregadio concludes that the semantic field of the word dan evolves from a root-meaning of "essence", and its connotations include "the reality, principle, or true nature of an entity or its essential part, and by extension, the cognate notions of oneness, authenticity, sincerity, lack of artifice, simplicity, and concentration."
The date for the earliest use of the term is unclear. It occurs in Du Guangtings 901 (Explications Expanding on the Sages [Commentaries] on the Daodejing), which is quoted in the 978 Taiping guangji. Liu Xiyues 988 (Master Taixuan Langrans Poems on Advancing in the Dao) has the earliest mention of both the terms and .'
(Way of the Golden Elixir) was a classical name for alchemy, and (with art; skill; technique; method) is the Modern Standard Chinese term. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, a pentagonal bipyramid is a molecular geometry with one atom at the centre with seven ligands at the corners of a pentagonal bipyramid. A perfect pentagonal bipyramid belongs to the molecular point group D.
The pentagonal bipyramid is a case where bond angles surrounding an atom are not identical (see also trigonal bipyramidal molecular geometry). This is one of the three common shapes for heptacoordinate transition metal complexes, along with the capped octahedron and the capped trigonal prism.
Pentagonal bipyramids are claimed to be promising coordination geometries for lanthanide-based single-molecule magnets, since (a) they present no extradiagonal crystal field terms, therefore minimising spin mixing, and (b) all of their diagonal terms are in first approximation protected from low-energy vibrations, minimising vibronic coupling. | 0 | Theoretical and Fundamental Chemistry |
Atomic Homefront is a 2017 documentary film about the effects of radioactive waste stored in West Lake Landfill in St. Louis County, Missouri, by Rebecca Cammisa and co-produced by James Freydberg and Larissa Bills. | 0 | Theoretical and Fundamental Chemistry |
In 2017, Russia banned imports of beef from New Zealand after finding ractopamine in New Zealand beef. Ractopamine is not registered for use in cattle in New Zealand. | 0 | Theoretical and Fundamental Chemistry |
In the surroundings of a thermodynamic system, external to it, all the various mechanical and non-mechanical macroscopic forms of work can be converted into each other with no limitation in principle due to the laws of thermodynamics, so that the energy conversion efficiency can approach 100% in some cases; such conversion is required to be frictionless, and consequently adiabatic. In particular, in principle, all macroscopic forms of work can be converted into the mechanical work of lifting a weight, which was the original form of thermodynamic work considered by Carnot and Joule (see History section above). Some authors have considered this equivalence to the lifting of a weight as a defining characteristic of work. For example, with the apparatus of Joule's experiment in which, through pulleys, a weight descending in the surroundings drives the stirring of a thermodynamic system, the descent of the weight can be diverted by a re-arrangement of pulleys, so that it lifts another weight in the surroundings, instead of stirring the thermodynamic system.
Such conversion may be idealized as nearly frictionless, though it occurs relatively quickly. It usually comes about through devices that are not simple thermodynamic systems (a simple thermodynamic system is a homogeneous body of material substances). For example, the descent of the weight in Joules stirring experiment reduces the weights total energy. It is described as loss of gravitational potential energy by the weight, due to change of its macroscopic position in the gravity field, in contrast to, for example, loss of the weight's internal energy due to changes in its entropy, volume, and chemical composition. Though it occurs relatively rapidly, because the energy remains nearly fully available as work in one way or another, such diversion of work in the surroundings may be idealized as nearly reversible, or nearly perfectly efficient.
In contrast, the conversion of heat into work in a heat engine can never exceed the Carnot efficiency, as a consequence of the second law of thermodynamics. Such energy conversion, through work done relatively rapidly, in a practical heat engine, by a thermodynamic system on its surroundings, cannot be idealized, not even nearly, as reversible.
Thermodynamic work done by a thermodynamic system on its surroundings is defined so as to comply with this principle. Historically, thermodynamics was about how a thermodynamic system could do work on its surroundings. | 0 | Theoretical and Fundamental Chemistry |
Another drug delivery system that has shown potential for chemotactic applicability is protocells. In general, protocells are artificial cells that mimic living cells but cannot reproduce and have genetic mutations like living cells do. Moreover, protocells combine the advantages of liposomes with that of mesoporous silica nanoparticles. These advantages include but are not limited to stability, large capacity for various cargos, low toxicity, immunogenicity, and the ability to circulate the blood for long periods. Thus, researchers aim to create a tunable chemotactic protocell that can move towards or away from a chemical signal. In fact, researchers have devised a way to use the enzymes catalase, urease, and ATPase to move the protocell closer or further away from the reactant, giving them direction and movement control of these protocells. Overall, the development of chemotactic controlled protocols holds great promise for the targeted delivery of drugs to specific areas of the body, potentially increasing treatment efficacy while minimizing side effects. However, more research is needed to fully understand the capabilities and limitations of protocells as drug delivery systems and optimize their design and functionality for specific applications. | 1 | Applied and Interdisciplinary Chemistry |
It is the standardized method to deal with durability, also known as deem-to-satisfy approach, and provided by current european regulation EN 206. It is required that the designer identifies the environmental exposure conditions and the expected degradation process, assessing the correct exposure class. Once this is defined, design code gives standard prescriptions for w/c ratio, the cement content, and the thickness of the concrete cover.
This approach represents an improvement step for the durability design of reinforced concrete structures, it is suitable for the design of ordinary structures designed with traditional materials (Portland cement, carbon steel rebar) and with an expected service life of 50 years. Nevertheless, it is considered not completely exhaustive in some cases. The simple prescriptions do not allow to optimize the design for different parts of the structures with different local exposure conditions. Furthermore, they do not allow to consider the effects on service life of special measures such as the use of additional protections. | 1 | Applied and Interdisciplinary Chemistry |
Large scale use of chloromethane is for the production of dimethyldichlorosilane and related organosilicon compounds. These compounds arise via the direct process. The relevant reactions are (Me = CH):
:x MeCl + Si → MeSiCl, MeSiCl, MeSiCl, MeSiCl, ...
Dimethyldichlorosilane (MeSiCl) is of particular value as a precursor to silicones, but trimethylsilyl chloride (MeSiCl) and methyltrichlorosilane (MeSiCl) are also valuable.
Smaller quantities are used as a solvent in the manufacture of butyl rubber and in petroleum refining.
Chloromethane is employed as a methylating and chlorinating agent, e.g. the production of methylcellulose. It is also used in a variety of other fields: as an extractant for greases, oils, and resins, as a propellant and blowing agent in polystyrene foam production, as a local anesthetic, as an intermediate in drug manufacturing, as a catalyst carrier in low-temperature polymerization, as a fluid for thermometric and thermostatic equipment, and as a herbicide. | 1 | Applied and Interdisciplinary Chemistry |
The determination of solubility is fraught with difficulties. First and foremost is the difficulty in establishing that the system is in equilibrium at the chosen temperature. This is because both precipitation and dissolution reactions may be extremely slow. If the process is very slow solvent evaporation may be an issue. Supersaturation may occur. With very insoluble substances, the concentrations in solution are very low and difficult to determine. The methods used fall broadly into two categories, static and dynamic. | 0 | Theoretical and Fundamental Chemistry |
A chloridometer is a measuring instrument used to determine the concentration of chloride ions (Cl) in a solution. It uses a process known as coulometric titration or amperostatic coulometry, the accepted electrochemistry reference method to determine the concentration of chloride in biological fluids, including blood serum, blood plasma, urine, sweat, and cerebrospinal fluid. The coulometry process generates silver ions, which react with the chloride to form silver chloride (AgCl).
The first chloridometer was designed by a team led by Ernest Cotlove in 1958.
Other methods to determine chloride concentration include photometric titration and isotope dilution mass spectrometry. | 0 | Theoretical and Fundamental Chemistry |
The CBP of this type, also known as parG is composed of:
* N-terminal NTPase binding domain
* Ribon-Helix-Helix (RHH) domain
For this type, the parS site is called parC. | 1 | Applied and Interdisciplinary Chemistry |
In molecular spectroscopy, a Jablonski diagram is a diagram that illustrates the electronic states and often the vibrational levels of a molecule, and also the transitions between them. The states are arranged vertically by energy and grouped horizontally by spin multiplicity. Nonradiative transitions are indicated by squiggly arrows and radiative transitions by straight arrows. The vibrational ground states of each electronic state are indicated with thick lines, the higher vibrational states with thinner lines.
The diagram is named after the Polish physicist Aleksander Jabłoński who first proposed it in 1933. | 0 | Theoretical and Fundamental Chemistry |
Ethene and oxygen are passed co-currently in a reaction tower at about 130 °C and 400 kPa. The catalyst is an aqueous solution of PdCl and CuCl. The acetaldehyde is purified by extractive distillation followed by fractional distillation. Extractive distillation with water removes the lights ends having lower boiling points than acetaldehyde (chloromethane, chloroethane, and carbon dioxide) at the top, while water and higher-boiling byproducts, such as acetic acid, crotonaldehyde or chlorinated acetaldehydes, are withdrawn together with acetaldehyde at the bottom.
Due to the corrosive nature of catalyst, the reactor is lined with acid-proof ceramic material and the tubing is made of titanium. | 0 | Theoretical and Fundamental Chemistry |
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